BEARINGS

and their

LUBRICATION

BEARINGS

and their

LUBRICATION

VACUUM OIL COMPANY

New York

USA

Copyright, 1920, by

‘VACUUM O I L COMPAN’

NEW YORK, U. S. A.

BEARINGS

and their LUBRICATION

INTRODUCTION

AS long as machinery has been in existence, there have been bearings to lubricate. The problem of bearing lubrication is, therefore, the oldest of all lubricating problems.
Until comparatively recent years bearings were crudely designed and low-speed conditions prevailed.

The lubricants employed were vegetable oils, such as olive, rapeseed and castor oils; animal fats and oils, such as tallow and lard oil, sperm and whale oil.

The enormous industrial development that has taken place in the last half century has brought into existence engines and machinery of all kinds embodying greater efficiency in operation. There are today a variety of bearings operating under higher speeds, higher pressures and higher temperatures than have been known at any previous time in the world’s history.

Lubricating oils have, of necessity, undergone a similar great development, made possible only by the discovery and use of mineral lubricating oils manufactured from a variety of petroleum crudes found in many parts of the world.

The important factors in bearing lubrication become apparent when the subject is divided into its fundamentals.

Therefore, we treat, in successive chapters- the construction of bearings; the conditions under which they operate; the various systems by which oil is applied; the principles of lubrication ; the treatment of frictiona l heat; the manufacture, physical properties and selection of oils; the properties and use of grease ; typical bearing troubles with their remedies; and the atta inment of true economy in bearing lubrication by the use of the correct high-grade lubricants in the right way.

CONSTRUCTION

A bearing is a support for a revolving shaft or the like. The bearing is usually composed of the following parts: the brasses-bearing pieces or steps (usually made of brass or of cast iron surfaced with anti-friction metal commonly known as babbitt) which surround the journal or bearing surface of the shaft; the block, pedestal or frame supporting and enclosing the brasses; and the keep or cap which secures the whole together by means of bolts or studs.

BEARING TYPES

There are five main types of bearings, as

follows Solid bearings,
Two-part bearings,
Four-part bearings,
Thrust bearings,
Ball and roller bearings.

SOLID BEARINGS

In all solid bearings, the shaft or bearing can only be removed from endways, and the bearings cannot be adjusted when worn. To provide for ready examination or adjustment the two-part or four-part Fig. 1- spindles used in textile mills.bearings are built up around the shaft.
Solid Bearings (Fig. 1) are used to support the vertical high-speed ring
Solid Bearings or bushings are all ring spindle ways small in size. They are bearings used for loose pulleys and small shafts, and in a variety of machinery, such as cranes, and hoisting machinery. They are also used as piston-pin bearings in the great majority of internal combustion engines.

5

BEARINGS and their LUBRICATION

A bushing or sleeve (A- Fig. 2) is frequently provideJ so that when the bushing is worn it can be replaced .

Two-PART BEARINGS

(Figs. 3, 4 and 5)

The majority of bearings are of this type. In the two-part bearings made in halves, usually of cast iron surfaced with babbitt metal.

Fig 2 Solid bearings and bushing

Fig. 3 illustrates a two-part bearing for the crank pin of connecting rod end. A and B are the bearing brasses shown in two parts.

Fig 3 Connecting rod and bearing

Fig. 4 illustrates a two-part bearing used for larger journals. Between the top and the bottom halves are placed liners, thin strips of metal. When the bearing wears, one or more of these strips may be removed, so as to bring the two bearing brasses closer together around the shaft.

Fig 4 Large two-part journal bearing

Fig. 5 illustrates a two-part bearing used for small and medium size line shafting. These bearings are usually lined with babbitt metal but are sometimes made of brass.

The two-part bearing is not suitable where the pressure on the journal is directed against the joint of two bearing halves. Large, bearings operating under such conditions are, therefore, frequently designed as four-part bearings.

FOUR-PART BEARINGS
(Frontispiece)

These bearings are used principally as main bearings in large horizontal steam

engines and gas engines.

The brasses are built up in four parts.

Side wear is taken up by turning vertical adjusting screws (A) thus moving the vertical wedge (B) which pushes the bearing brasses closer around the shaft. Vertical wear is taken up in a similar manner by adjustment of screw © which moves the horizontal wedge

Fig 5 Shaft hanger

THRUST BEARINGS

Thrust bearings are designed to counteract pressure in the direction of the shaft and so keep the shaft in its correct position while supporting the load in vertical units or acting against the thrust forces in horizontal units.
Thrust bearings are extensively used in hydro-electric units, steam turbines, for ship propulsion, for centrifugal pumps, etc.

Fig. 6 illustrates the principle of a plain foot-step bearing designed to support the vertical shaft of a steam turbine.

It consists of a housing (F) holding in position in the guide bearing (G) which, in turn, holds holds in position the vertical shaft (A) supported at the bottom by foot-step (H).

The footstep (H) may be adjusted in position by means of support and adjusting screws (D and C).

Oil is forced at high pressure between the footstep (H) and the bottom of the vertical shaft (A) through drilled passageways (J). The entire weight of the vertical shaft (A) is thus borne by the thin lubricating oil film. After lubricating the foot-step bearing, the oil passes upward around the shaft (A) supplying lubrication to the guide bearing (G). The oil then overflows and leaves the bearing through passage (K) in the housing (F).
In order to prevent condensed steam from the turbine from running down the shaft and mixing with the oil, a collar (L) is provided, which throws the water into a chamber (M) from which it is drained through passages (O) in the housing (F).

6

BEARINGS and their LUBRICATION

Fig. 7 illustrates the principle of a plain thrust bearing. On the shaft (A) are collars (B) which are of the part shaft (A). These collars revolve in recesses forming part of the thrust block casing © lined with babbitt metal (D).

Fig. 8 illustrates a vertical thrust bearing used in water wheel installation. The bearing consists of a flat annular plate (B) fixed to the top of the vertical shaft (A).

Fig 6 Vertical foot step bearing

The bottom face of the plate (B) is immersed in a bath of oil contained within the circular casing (E) and is supported in position by a number of shoes © mounted on fixed pivots (D). The oil which adheres to the bottom of the revolving plate (B) is drawn in and forms a wedge between the plate (B) and supporting shoes © due to the tilting action of the shoes.

Other types of vertical thrust bearings are made which support in a similar manner rotating parts of hydro-electric installations.

Fig. 9 illustrates a part sectional view of a hydro-electric installation supported in the manner described.

BALL AND ROLLER BEARINGS
(Figs. 10 and 11)

Ball and roller bearings operate in a different principle then do other bearings. This consists in the substitution of rolling friction for sliding friction. The contact between the balls or rollers and the revolving surfaces is point contact in ball bearings and line contact in roller bearings. Whereas ordinary bearings have large surface contact.

Ball bearings consist of a row or rows of balls help in position by a suitable retainer

Fig 7 Ring oiled thrust bearing

Between an inner and outer raceway. Roller bearings consist of a set of rollers held in position by a cage between an inner and outer raceway.

The balls or rollers and raceways are usually made of high-grade steel, machined accurately, hardened, and ground. If slightly out of line or worn, internal stresses are set up with greatly increased friction, and with ultimate breakage of balls or rollers. Ball bearings are being adopted on numerous types of mechanical equipment.

Fig 8 Vertical thrust bearing

Ball bearings are being adopted on numerous types of mechanical equipment.

They are most commonly used as automobile bearings and are also

7

BEARINGS and their LUBRICATION

Being used on motors, machine tools, transmissions and other classes of machinery.

Fig. 10 illustrates a ball bearing consisting of raceways (A and B) between which the balls © revolve, being held in a position by suitable cages or retainers (D) which travel around with the balls ©.

Roller bearings are widely used in automobiles. They have also been adopted for transmission bearings of various classes of railway equipment and heavy-duty bearings of machinery.

 

Fig 10 Ball bearing shaft hanger

Fig. 11 illustrates a roller bearing, consisting of raceways (A and B) bearing housing (E) and rollers © held in position by a suitable cage (D).

Both ball and roller bearings may be adapted to either vertical or horizontal positions. Ball bearings may or may not be of self-alligning construction, as described under the heading “Operating Conditions.”

The frictional resistance at starting, of machinery equipped with plain bearings, is several times as great as the resistance after a few revolutions when the oil film has been formed in the bearings. The friction at the starting machinery equipped with ball and roller bearings is very little greater than the friction during operation.

Due to the substitution of rolling for sliding friction, ball and roller bearings when properly lubricated will run with much less friction than plain bearings and they may be considered among the highest types of bearings. The main function of a lubricant on ball and roller bearings is to keep the highly polished surfaces clean and bright and free

From corrosion. The lubricant also reduces to a minimum the slight amount of friction present. It also acts as a deadener of the noise of the motion of the balls are rollers.

BEARING MATERIAL

The shafts and journals are usually made of iron or steel. The material of which the bearing surfaces are made is brass, anti-friction metal, or, in some cases, cast iron.

The bearing surfaces are always made of a metal softer than the steel in the revolving journal so that as wear occurs it will be chiefly in the bearing, which can be more easily replaces.

Brass has been used for a long time as bearing surface material gives excellent service if the bearing surfaces are well scraped together with the journal. Otherwise, the bearing will easily heat up, because of excessive pressure on the decreased bearing surface.

BABBITT METALS

These are combinations of hard metal, such as antimony, mixed in varying, proportions with lead and tin, forming babbitt or white metal (anti-friction metal).

When the bearings are lined with suitable babbitt metal, the journal easily beds itself clown and distributes its weight uniformly over the entire bearing surface. Lining the bearings with anti-friction metal is a practice rapidly gaining favor, for, when wear takes place, the anti-friction metal lining can be easily replaced.

CAST-IRON BEARINGS
Caste-iron bearings are generally used for small and medium-sized shafting; the bearings are long and the bearing pressures are low.

WORKMANSHIP
Workmanship refers to the attention which has been given to:
The finish of the bearing surfaces.
The clearance between the journal and the bearing.
The alignment of the erected bearing.

 

8

BEARINGS and their LUBRICATION

FINISH OF BEARING SURFACES

The rubbing surfaces are never exactly true and smooth.
If a new shaft is put into new bearings without oil, it will, when revolving, touch the bearing surfaces only on certain high spots, distributed more or less evenly over the surface.

For this reason the brasses are scraped. In this process the surface of the shaft is made as smooth as possible and the high spots of the bearing surfaces are scraped down until finally the shaft bears uniformly on the whole of the bearing area.

CLEARANCE

The diameter of the shaft is always slightly smaller than the diameter of the bearings.The difference between the two diameters is called the bearing clearance. The clearance should average about 1-1000 of an inch per 1-inch diameter of the shaft-rather less than this for large bearings.

ALIGNMENT

When machinery and shafting are erected,
It is very important that the various bearings be truly and accurately fitted. If the horizontal shafting is supported by a number of bearings, and some bearings are placed too high and others too low, or not in line, stresses will be set up in the shafts and bearings, which will produce high bearing temperatures.

Having described the principal types of bearings and commented upon the design, material and workmanship, we will now analyze the factors influencing their operating conditions.

———————-

OPERATING CONDITIONS

Correct lubrication of bearing is dependent upon the following important factors:
Size of bearing (diameter of shaft)
Speed of shaft (revolutions per minute)
Bearing pressure (pounds per square inch)
Bearing temperature (operating temperature in degrees Fahrenheit)
Mechanical conditions (good or bad).

 

SIZE OF BEARINGS

Bearings are made in all sizes and may be divided into:

Small sized bearings – up to 1 inch shaft diameter.
Medium sized bearings – 1 to 3 inches shaft diameter.
Large sized bearings – greater than 3 inches shaft diameter.

The surface of the shaft or journals is never perfectly smooth nor round, but it will possess a roughness, invisible except through a magnifying glass. The imperfections are greates in the larger journals.

SPEED OF SHAFT

The shaft may revolve at:
Low speed – below 50 r.p.m.
Medium speed – from 50 to 300 r.p.m.
High speed – over 300 r.p.m.

BEARING PRESSURES

The pressures to which bearings are subjected may be moderate or excessive.

Moderate Pressures
Moderate pressures are those well within the capacity of the design of the bearing with reference to its service requirements.

Excessive Pressures
Excessive pressures on bearings are due to excessive weight, pull or thrust.
Excessive weight conditions exist when more weight is put on the bearing than that for which it was designed.
The excessive pull is usually due to very great belt tension.
Excessive thrust is due to abnormal duty or to faulty mechanical adjustments.
Excessive pressures will usually be manifested in their effect on the oil distribution, resulting in higher temperatures. Special consideration must be given to the selection and application of the oil to meet these extreme conditions.

BEARING TEMPERATURES

The temperatures of bearing in service are termed moderate or extreme.

 

9

BEARINGS and their LUBRICATION

Moderate Temperatures
Moderate temperatures may be considered those not higher than 140 degrees F.

Extreme Temperatures
Extremely high temperatures (in excess of 140 degrees F.) are due to deficient radiation, internal friction or the effect of high surrounding temperatures.
Extreme surrounding temperatures may be due to induced heat or climatic conditions. High temperatures resulting from internal friction may be caused by one of the following conditions:

The mechanical conditions may be wrong;
An improperly selected oil may be in use;
An insufficient quantity of oil reaches the part to be lubricated.

These last three factors are due to negligence. Temperatures of bearings, operating at greater than 140 degrees F. demand investigation.

Deficient radiation, resulting in temperatures higher than 140 degrees, may exist in bearings lubricated by means of the oil bath, the circulation or the splash system. SPecial oils must be selected for this extreme condition or provision must be made for reducing such oil temperature by means of a cooling apparatus or increasing the volume of oil in the system.

NOTE. – In explanation of the first part of the foregoing paragraph it must be remembered that at high temperatures a heavier bodied oil will give the same service as a lighter bodied oil at a lower temperature. For example: A heavier bodied oil is acceptable for the circulation system of a turbine whose normal oil temperature maybe 170 degrees, whereas if operating at 140 degrees maximum a lightier bodied oil is most suitable.

Bearing temperatures higher than 170 degrees F. indicate serious service conditions requiring close engineering attention. These extreme conditions may be satisfactorily met with an automatic oiling system is in service the conditions should be corrected.

Extreme temperature conditions, due to induced heat, may be unavoidable and are more or less tolerable according to the reliability of the lubrication system and the engineering

Attention. The heavier bodied oils are usually employed under these extreme temperature conditions.

Extreme temperatures due to climatic conditions may be temporary and the heavier bodied oils should be selected for use during the period of high temperatures, i. E., summer temperatures.

Extremely low temperatures make it necessary to employ an oil of low cold test, otherwise the oil will congeal and will not flow to the bearing surfaces.

MECHANICAL CONDITIONS

Bearing in time get out of alignment and are subject to wear.

It is important that the bearings should be kept in good alignment and repair by renewing bushings, brasses or babbitt linings, adjusting bearing for wear, etc.

When trouble or irregularity in operation occurs the cause should be traced at once and the condition rectified, instead of being allowed to continue until it becomes serious.

Good Mechanical Conditions
By this term should be understood bearings of good design, suitable to conditions of operation, journals and bearing surfaces of good material, well finished and with suitable bearing clearance; bearing in good alignment and not appreciably worn.

Under good mechanical conditions, lighter bodied oils, regularly applied, may be used which will insure efficient lubrication of the bearings.

Bad Mechanical Conditions

By this term should be understood bearings are crudely designed, or of good design but allowed to get out of order; bearings made of poor or unsuitable material; bearing surfaces rough or worn; bearing out of alignment.
Bearing under bad mechanical conditions, irregularly oiled or subject to an inefficient oiling system necessitate the use of oils heavy in body.

Having described the influencing conditions under which bearings operate, let us now describe the different methods by which oil is applied.

 

10

BEARINGS and their LUBRICATION

OILING SYSTEMS

The various systems by which oil is applied to bearings may be divided as follows:

FOR lNDIVIDUAL BEARINGS

Hand Oiling
Drop Feed Oiling
Ring or Chain Oiling

FOR GROUP BEARINGS

Splash System
Circulation System

SPECIAL METHODS OF LUBRICATION

Oil Bath
Mechanical Force Feed Lubricator

OIL SYSTEMS FOR INDIVIDUAL BEARINGS HAND OILING

This is the oldest method employed for lubricating bearings. It is the least efficient and the most wasteful of all oiling methods.

Hand oiling is employed for the lubrication of low-speed shafting and low-speed bearings in a variety of machines, such as machine tools, cranes, etc.

It is largely employed for oiling small parts of valve motions, valve spindles, etc., of steam engines, internal combustion engines and other power producers.

Fig 12 Spring bottom oiler

Hand oiling is also employed on various types of machines exposed to heavy vibration . or rough usage where a lubricating ~ device would be shaken off or broken. ~ Fig. 2 illustrates a bearing designed F’ 15 for hand oiling.

Fig 15 Oil hole cover

In the bearing is an oil hole (B) usuhole ally in the top part.

The oil is applied by an oil can (Figs. 12, 13 and 14) by which it is possible to deliver one or more drops of oil.

The oil runs down the hole (B- Fig. 2), is spread by the revolving shaft over the bearing surfaces and gradually works its way toward and out through the ends of the bearings (A). After each oiling, the oil film in the bearing gradually becomes thinner and finally

the bearing runs practically without lubrication until such time as it is oiled afresh.

The lubrication is thus gradually reduced to a state of inefficiency, dependent upon the body of the oil in use, the length of the time between oilings, and the operating conditions.

In order to prevent the entrance of dust or flying matter, which would tend to choke up the oil hole or, if it entered the bearing, would cause trouble, the entrance to the oil hole may be fitted with a cap (Fig. 15). By lifting or turning the outer cover (A) an oil hole (B) in the cup ff is disclosed, through which the oil is introduced.

Fig 16 Small oil cup

Fig. 16 Another method (Fig. 16) is 1 ~;nail to have a little cup fitted into 0 1 cup the oil hole and provided with a felt pad, into which the oil is poured. This method insures more uniform feeding of the oil.

Fig 13 Long spout oiler

Fig. 13- Long spout oiler In some cases the oil is not applied through an oil hole, but simply to the end of the bearing. The guides or bearings (A and B) of mule sp indles (Fig. 17) are oiled frequent intervals.

Fig 14 Pump oil can

DROP- FEED

By the drop-feed oiling system, we ref er to any automatic appliance which feeds a moderate and more or less regular supply of oil to the bearing. One oiler is fitted to the center of small bearings and two or more, suitably spaced, for larger bearings (Fig. 4), providing at least one oil delivery into the bearing for every eight inches Fig. 17-Mule of bearing length.
There are three types of lubricating devices operating on the drop-feed system, as follows:

Siphon oiler
Bottle oiler
Sight-feed drop oiler

Fig 17 Mule spindles

11

BEARINGS and their LUBRICATION

Siphon or Wick-Feed Oiler (Fig. 18)
When, in the early days of engineering, hand oiling proved inadequate for lubricating heavy-duty bearings, the wick-feed oiler was the first improvement introduced.

Wick-feed oilers are employed for the lubrication of main bearings of arine steam engines and other prime movers, as well I as for the lubrication of medium-size bearings of shafting and a variety of machines of all kinds.

Siphon or Wick-Feed Oiler (Fig. 18)

The wick-feed oiler (Fig. 18) consists of a container (A) in which oil is filled to a certain level; the siphon oil tube (B) projects above the oil level; the wick (C) is introduced into the oil tube, this end being at a lower level than the end immersed in the oil in the container.

The wick (C) consists usually of one strand or more of wool en yarn, preferably of loose texture, which feeds more than yarn of tight twist and close texture.

The higher the oil level in the container or the thinner the oil, or the deeper the wick is introduced into the oil tube, or the greater the number of strands, the greater will be the oil feed.

When so many strands are used that they choke the oil tube, a point is reached where the addition of more strands will reduce the oil feed because of the greater resistance in passing through the tight wicking.

If the oil level is filled above the top of the oil tube, the surplus oil runs to waste.

The oil tube (B) should project below the dividing line between the housing (D) and the bearing brass (E) as otherwise the oil coming down the oil tube might find its way in between the parts and thus run to waste. The container should always be fitted with a lid or cover (F) so as to prevent the entrance of dust, dirt and water into the oil.

Siphon wicks in time get choked with impurities and become inoperative. They should, therefore be renewed at suitable intervals.

Where machines or engines are running intermittently, the wicks should be lifted out of the oil tube and left in the oil containers

every time the machinery stops; otherwise, they will continue feeding and waste the oil. Oil should be added to the container at frequent intervals so as to keep the oil level as constant as possible.

The Bottle Oiler (Fig. 19)
This device has been developed primarily for the lubrication of light and medium-size shafting bearings operating at low to moderately high speed and under conditions which make a small constant feed desirable.

Its use is spreading gradually for the lubrication of plain bearings of machines.

The glass bottle (A) has a brass holder (D ) fitted with a C brass tube (C). .

The Bottle Oiler (Fig. 19)

A steel spindle (B) fits loosely Fig. ~&ttlc inside the brass tube (C), its lower end resting on the shaft in the bearing. The shaft, when revolving, gives the spindle a very slight up and down motion, which has the effect of drawing a small supply of oil from the glass bottle. The oil flows down the spindle and finally reaches the bearing surface.

The bottle oiler is automatic in action, starting and stopping with the motion of the shaft.

If the bearing gets warm, the spindle will heat up; the oil surrounding the spindle will become thinner and more oil will be fed.

If it is found that the amount of oil supplied through the bottle oiler is insufficient, the feed can be increased by using a thinner spindle.

Bottle oilers should not be used on machinery exposed to rough usage, as the glass bottles are easily broken.

The Sight-Feed Drop Oiler (Fig. 20)
This is extensively used on modem engines and machines of all kinds. The sight-feed oiler can easily be adjusted to feed one drop of oi I per minute or more. The sight-feed oiler has a glass container (A) so that the level of the oil can be observed. Oil is poured in through the filling hole (B).

12

BEARINGS and their LUBRICATION

The end of the adjusting needle or valve spindle (E) is guided into a conical hole in the bottom of the central sleeve (F). By turning the milled collar (C) the needle can be raised or lowered so as to give a greater or smaller feed. If the top (D) of the adjusting needle (E) is turned to its horizontal position as shown, the needle (E) drops by spring tension and shuts off the oil supply; when it is again raised, the feed will be the same as previously adjusted.

Fig 20 Drop feed oiler

The oil drops passing to the bearing may be observed through the sight hole (G).

Some advantages of the sight-feed drop oiler are: the feed can be quickly adjusted; quickly started and stopped; and the oil level, as well as the oil feed, is clearly visible.

Sight-feed drop oilers have the same disadvantages as the siphon oiler as regards variation of the oil feed, i. e., the feed will vary with the oil level in the container and also with the influence of temperature on the body of the oil.

In addition, when sight-feed drop oilers are adjusted to feed a very small quantity of oil, grit and dirt may easily choke the oil outlet from the container and stop the feed altogether. Sight-feed drop oilers may be arranged with multiple feeds as illustrated by Fig. 21. In this oiler there are six oil feeds controlled by six different needle valves, the oil dropping through the six sight feeds (A) into oil tubes (8) which guide the oil to the different bearings. Multiple feed oilers, like the one illustrated, may be arranged to use siphons for the different oil tubes, the combination being a wick oiler with sight feeds. When feeding oil to the crank pins of horizontal steam engines and other prime movers, the so-called crank-pin oiler (Fig. 22) is often employed. The crank (A) is attached to the end of the main shaft (H ) which is supported by the main bearing. To the crank pin (B) is fitted the rightangled oil tube (C), having a hollow enlargement (D) at its end, which is placed central- that is, in line with the axis of the main shaft (H).

Oil flows from the sight-feed drop oiler (E), usually fixed to the railing or on a standard, through tube (F) and drops into the enlargement (D ) of tube (C). By centrifugal force the oil is thrown through the tube (C) and enters the crank pin (B) through a drilled hole, finally reaching the crank-pin bearing surface through a radial hole.

Fig 21 Multiple feed drop oiler

RING OR CHAIN OILING

This type of oiling system is largely employed on high-speed shafting bearings and on practically all electric motors, electric generators and small steam turbines.

Ring-oiled main bearings are often used on gas engines and oil engines, as well as many stationary steam engines.

Ring oiling is used for medium as well as large-size bearings, but not for small highspeed bearings, as the C oil rings would fail to revolve F on the shaft D __ due to its small size and high speed. The bearing housing (A) (Figs. 23 and 24) forms an oil reservoir in which the oil is maintained at a certain level, preferably indicated by an oil gauge. The rings will not touch the oil if the oil level be allowed to fall too low and the bearings will receive no lubrication. On the shaft (C) are usually suspended one or two rings or chains (B) which dip into the oil.

13

BEARINGS and their LUBRICATION

When the rings revolve with the motion of the shaft (C), they carry oil to the top of the shaft, from which point it runs into the oil-distributing channel and bearings.

Sometimes instead of revolving rings or chains, there is a collar (B) (Fig. 25) fixed to the shaft (C). This collar (B) dips into the oil and carries it above the shaft, whence the oiI is guided into the oil channel (D ) which bearing.

Fig 23 Section of a ring oiled bearing

The oil leaves the ends (E) of the bearing and drops back into the oil reservoir. It is thus kept in constant circulation.

There is very little oil waste in a welldesigned ring-oiled bearing.

Leakage sometimes will occur through the side of the bearing, between the top and bottom parts. This can be overcome by inserting a thin lead wire (F) (Fig. 25), which, when the bearing is put together, will be pressed flat and seal the bearing.

It is important that the Fig. 25-Seccion of collar oiled bearing oil reservoir be deep and contain a large quantity of oil. so that impurities which may enter the bearing will separate and fall into the bottom and not be kept in circulation. In large bearings, cooling of the oil by the introduction of a cold-water coil in the reservoir may be found desirable or even necessary under severe conditions.

Fig 25 Section of collar oiled bearing

OILING SYSTEMS FOR GROUP BEARINGS
SPLASH OILING (Fig. 26)

This system is employed for lubricating a number of bearings in an enclosed casing and is frequently found in small enclosed vertical or horizontal steam engines, air compressors, gas engines, oil engines, and automobile and motorcycle engines.

The enclosed crank chamber (M) is filled with oil to a certain level. Means should be provided to maintain this level as constant as possible by providing an automatic overflow (L).

In some small steam engines, motorcycle engines and certain types of automobile engines, the crank disk (B) or the fly-wheel revolving inside the crank chamber (M) is arranged so that it dips into the oil. The oil is picked up by the revolving rim and thrown off by centrifugal force. Oil wells or pockets (N) cast on the inside of the casing collect the oil and lead it through various channels, tubes, or troughs, to parts to be lubricated.

When engines are not equipped with a crank disk (B), dippers are fixed to the crank- pin bearings (E). These dippers dip into the oil when the engine is in operation and produce inside the crank chamber a spray or mist of thousands of tiny drops of oil, which constantly reach the moving parts.

The main hearings and eccentrics, crankpin (E), crosshead pin (0) and

Fig 24 Small turbine with ring oiled main bearings

crosshead guides (C) are lubricated direct by means of the oil spray, or indirectly by oil troughs (N) which catch the oil and guide it by means or oil pipes into the bearing.

14

BEARINGS and their LUBRICATION

CIRCULATION SYSTEM

There are two main systems embodying the oil circulation principle, viz:

Non-pressure oil circulation system,
Pressure oil circulation system.

Non-Pressure Oil Circulation System

This system does not deliver oil to bearings under direct pressure.

A non-pressure circulation oiling system is employed for automatically lubricating main bearings, crank pins, crossheads, crosshead guides, etc., comprising most of the external moving parts in medium or large size steam engines, gas engines and Diesel engines; also for some steam turbines, groups of large shafting bearings, etc.

In the lubrication of the steam engine shown (Fig. 27) oil flows by gravity from the supply tank (A) through the d istributing pipes (B). Sight-feed glasses (C) a re located in each pipe line, through which the oil is fed by regulated adjustment to the bearings.

Having done its work, the oil drains back from the various parts through ret urn oil pipe (H) to the sump tank (E). The oil pump (D) driven by the engine draws the oil from the sump tank (E) and delivers it, either through an oil cooler or direct through pipe (F) into the gravity supply tank (A). If more oil is delivered to the top tank (A) than is required for the bearings, the surplus oil returns through an overflow pipe into the sump tank (E).

Pressure Oil Circulation System (Fig. 28)

Oil is delivered under pressure as directly as possible to the various bearing surfaces requiring lubrication.

This system is largely employed for lubricating steam turbines, the enclosed type of steam engines, Diesel engines, oil engines and automobile engines, etc.

Fig. 28 illustrates the principle of the pressure oil circulation system as usually employed on a steam turbine.

From the lower portion of the governor spindle (H6) is driven the oil pump (T4) which takes oil from the oil tank (TJ) and delivers it at from 3 to 20 pounds pressure per square inch, through the oil cooler (T6), directly to the bearings (F2) through oil supply pipe (TI).

A relief valve (T 12) in a by-pass controls the oil pressure in the line.

It is a good practice to have inserted in the return oil pipe (T2) sight feeds in which the actual flo\\’ of oil from each bearing is shown ; frequently, test cocks (T9) a re fitted in the bearing top, which, when open, will show whether the bearing is being adequately supplied with oil.

Fig 27 Non pressure or gravity circulation system

SPECIAL METHODS OF LUBRICATION OIL BATH

This system is only employed for vertical bearings, such as the light-weight, high-speed spindles employed in textile mills, or the footsteps of heavy vertical shafts of gyratory crushers and hydro-electric units.

 

15

BEARINGS and their LUBRICATION

Fig. 29 illustrates the Oil Bath System, as employed on ring spindles.

The bolster case (A) holds in position the bolster (D) and acts as an oil reservoir.

The spindle (C) is free to revolve in the bolster (D).

Spindles are hand-oiled through the oil way (B) in the bolster case (A).

By the centrifugal force of the revolving spindle, oil is drawn into the bolster (D) through the drilled holes (E) and is constantly lifted to the top of the bearing, whence it overflows and drains back into the lower part of the bolster.

Thus a constant circulation of oiI is produced and the spindle bearing is kept flooded with oil.

Fig 29 Section ring spindle

A certain amount of oil is wasted in leakage and must be made up at suitable intervals. A small amount of oil should be added every four or six weeks through the oil hole.

MECHANICAL FORCE FEED LUBRICATOR (Fig. 30)

Either single feed or multiple feed mechanically operated lubricators are occasionally employed for feeding oil to important bearings. The advantages are, that being operated

by lever (0), actuated from some moving part of the engine, the mechanically operated lubricator starts and stops with the engine. it feeds the oil more uniformly and regularly and, therefore, with less waste than sightfeed oilers or wick oilers; also, because of the pressure, a much heavier oil can be fed if required.

The oil is taken from the container (E ) by a mechanically operated pump (A). It is fed through the feed pipe (B), fitted with a check valve at the pump and at its extreme end in order that the pipe shall always be filled with oil.

As soon as the engine starts, the lubricator operates and the oil is immediately delivered under pressure from the end of the oil pipe.

A Bullseye sight-feed arrangement (C) is either fitted in the lubricator itself, one sight feed for each oil feed, or at the extreme end of the oil pipe. ln this latter case the oil drops from the check valve through a sight feed directly into the bearing.

Whatever the oiling system employed, it is important that a regular routine be instituted for maintaining it at its highest efficiency.

Bearings that are hand-oiled should be oiled at frequent intervals to insure the presence of an oil film at all times.

The oil containers in wick-feed oilers, bottle oilers, sight-feed oilers and mechanically

Fig 28 Pressure within the bearings circulation system

16

BEARINGS and their LUBRICATION

operated lubricators should be filled at regular intervals. A system should be inaugurated for starting and stopping the oilers as required.

Lubricators should never be allowed to run empty or to get choked with dirt.

OIL DISTRIBUTION

A revolving shaft will draw the oil into the bearing because of the tendency of the oil to adhere and cling to the shaft. The heavier in body the oil. the greater will be this clinging action provided the shaft speed is moderate.

Fig 30 Single feed mechanically operated lubricator

When shafting operates at low speed, the oil used should be heavy in body. At higher speeds, an oil lighter in body may be used, and for very high speeds, oils very light in body must be used.

Oil grooves should be cut shallow and the edges rounded off as in Fig. 31 to permit oil to be drawn between the bearing surface and the revolving shaft. Sharp edges will scrape the oil from the surface of the journal.

To assist in spreading the oil over the full bearing surface, an oil groove (B) (Fig. 32) is sometimes cut in the surface of the top bearing. The edges of the bottom bearings should always be chamfered or filed away, as shown at (A) (Fig. 33), forming an oil groove parallel to the shaft to facilitate the drawing in of the oil between the revolving shaft and the bottom bearing brass.

Fig 31 Oil groove edges rounded

In a large bearing subjected to heavy pressures, with the shaft revolving at very slow speed, the tendency to form a wedge-shaped film of oil is not present and the oil grooves (0-Fig. 33) properly cut in the bottom of the brass will assist materially in distributing the oil from the chamfered edge (A) to the surface 17 area, subjected to the highest bearing pressures, thus providing adequate lubrication.

Fig 32 Oil distributing groove

Oil grooves should never be cut to the ends of the bearing brasses, otherwise the oil will escape from the bearing, resulting in the necessity of using a greater quantity of oil to prevent overheating of the bearing.

Grooves (B) (Fig. 34) cut in the bearing surface start from the place of oil entry (C) in the top bearing brass running from there at a diverging angle to the direction of rotation of the shaft. Where the shaft may rotate in either direction the oi I grooves should be cut in both directions.

Fig 33 Brass chamfered at edge

Under normal conditions of service it is undesirable to employ grooving on Fig. 33-Brass chamfered at bottom brasses, be- edge cause the surfaces of bearings made irregular by oil grooves tend to interfere with the formation of the wedgeshaped oil film between the revolving shaft and the supporting bearing.

 

17

BEARINGS and their LUBRICATION

In ring-oiled bearings, as well as in plain bearings, where the oil is supplied to the top of the shaft, oil grooves in the bearing permit the oil to flow to the chamfered edge of the bearing brass, where it is distributed over the entire surface of the revolving shaft.

Fig 34 Radial method of grooving

Oil grooves are not needed where the oil is forced under pressure to the bearing; but chamfered edges of the bearing brasses must be used under all circumstances.

In the bearing (Fig. 35) lubricated by a forced feed oiling system, an annular oil passage (B) is cut in each bearing lining, in communication with the radia l hole in the crank shaft or crank pin, thus insuring a constant flow of oil to the surface of the shaft by means of the oil ways at the chamfered edges (A) of the bearing ·brass.

LUBRICATION

Friction is defined as the resistance to motion or tendency to motion, existing between surfaces in contact. Friction is, therefore, an influence retarding motion. The effect of friction is wear and heat and is greatest between dry surfaces. The introduction of a fluid medium, between surfaces, will reduce both heat and wear. Fluid friction is the resistance co motion of the molecules of a Auid. The object of bearing lubrication is:

First, to form an oil film between the rubbing surfaces and thus replace metallic friction with fluid friction.

Second, by the selection of the correct oil to keep the fluid friction in the oil film itself as low as possible under the operating conditions.

No Lubrication
If a journal should revolve in its bearing without lubrication, metallic contact would cause abrasion of the metal. This would produce excessive friction and wear and would manifest itself in the development of great heat.

Totally unlubricated bearings could operate but a very short time before the frictional heat developed would be so great as to destroy the bearing surfaces.

Insufficient Lubrication
When an insufficient quantity of a lubricating medium is introduced between metallic rubbing surf aces, the lubricant will adhere to both journal and bearing and thus will replace only part of the metallic friction with fluid friction. There will, therefore, be less abrasion, less friction, less heat and less wear.

Fig 35 Bearing with annular groove

The majority of bearings are insufficiently lubricated, i. e., the metallic rubbing surfaces a re never kept continuously and completely apart, so that more or less wear occurs, and the loss in friction is higher than it should be.

18

BEARINGS and their LUBRICATION

Imperfect Lubrication
The application of a sufficient quantity of any oil between the rubbing surfaces may form a complete oil film and eliminate metal to metal wear. Such bearings may be said to be completely lubricated, but the fluid friction may, however, be high and, therefore, not constitute correct lubrication.
In the foregoing we have referred only to the quantity of oil used in lubricating a bearing.

Correct Lubrication
Correct lubrication can only result from the use of the particula r high-grade oil selected to suit the oiling system and the operating conditions. The oil will maintain a complete lubricating oil film, eliminate wear, and at the same time reduce the fluid friction to the lowest possible degree.
Correct lubrication insures the minimum cost of frictional losses, repairs and renewals of parts and guarantees continuous operation.

FRICTIONAL HEAT

The frictional heat developed between a revolving journal and its bearing penetrates both the journal and bearing. Where bearings are neither water-cooled nor lubricated by a circulation oiling system, the whole of the heat developed must leave the bearing or journal by radiation into the surrounding atmosphere. Bearings, therefore, assume a temperature higher than the surrounding room temperature ; and the greater the friction, the greater will be the difference in temperature between any part of the bearing and the room temperature.

This difference is termed the frictional rise in temperature, or simply the f rictional temperature, and forms a true guide to the quality of the oil in service. The frictional temperature remains constant for all room temperatures, i. e., if the bearing temperature is 86 degrees F. and the room temperature is 70 degrees F., the frictional temperature is 16 degrees F. If the room temperature rises to 74 degrees F., it will be found that the bearing temperature will rise to 90 degrees F. The friction developed is practically the same, and the bearing temperature must,

therefore, be correspondingly higher, in order to radiate the same amount of heat.

When heavy-duty bearings operate under high-speed conditions, the heat developed may become so great that it cannot be radiated from the bearing surfaces with sufficient rapidity. Under such conditions it becomes desirable or necessary to introduce a circulation oiling system.

The flow of oil through the bearings not only provides a lubricating oil film. but also carries off a large portion of the heat developed. This heat, carried away with the oil, is radiated into the atmosphere from the oil tanks, oil pipes, etc. If necessary, it can be removed by cooling water in the oil circulation system.

In the lubrication of steam turbines, which operate at very high speeds and where, in addition to the frictional heat, heat from the steam-heated parts must be reckoned with, it becomes necessary to supply the bearings with a great flow of oil to carry off the heat from the bearings and permit them to operate at safe temperatures. The heat is transferred from the oil to the water coils in an oil cooler.

Small circulation svstems are usually equipped with coolers.· By means of this apparatus the heat in the oil is given up or radiated to circulating water of lower temperature.

The apparatus usually consists of a tank in which are located a set of pipes or coils.

The passage of the oil through the pipes and the water through the tank is so arranged that greatest absorption of heat by the water is secured. This mechanical means of lowering the temperature of the oil is equivalent to the normal radiation of heat from a system containing a large volume of oil.

Fig. 36 illustrates an oil cooler. The container (A) is usually a cylindrical shell to which are bolted on each end heads or covers, making an enclosed container. Pipes or coils (B) are fixed in position, usually by means of headers or fixed partitions (C). The oil pipes constitute the passage for the oil through the cooler. The space in the container constitutes the passageway through which the cooling water is carried. The water thus completely surrounds the oil pipes or coils. By this means the temperature of the oil is radiated

19

BEARINGS and their LUBRICATION

through the walls of the pipes to the water surrounding them. The oil is introduced by means of pipe (1) and after passing through the cooling pipes or coils (B) is discharged from pipe (2). Similarly the water

Fig 36 Oil cooler for a circulating system of lubrication

is introduced by means of pipe (3) and is discharged through pipe (4). The water at its lowest temperature thus comes in contact with the oil just before it leaves the cooler. Maximum cooling is obtained through the adoption of baffles or plates, which insure the maximum circulation of water around the oil tubes.

———

In the foregoing pages we have discussed the construction and operation of bearings, the system by which the oil is supplied and the principles of lubrication and friction.

BEARING OILS

We are now in a position to analyze the lubricating oil. The subject is divided into the following heads: physical properties of oils; the selection of the correct oil; oil quality.

PHYSICAL TESTS

It is impossible, from the physical properties of lubricating oils, to draw definite conclusions as to their lubricating values. Nevertheless, during manufacture, certain scientific tests are essential. These tests are not aimed to determine the efficiency of the

oil; they are simply checks to make certain that the oil is running uniform- that every lot manufactured is up to the proven standard.

Following are outlined a number of the tests used for this purpose and most frequently quoted by chemists, i. e.: Gravity, cold test, flash and fire test, viscosity, loss by evaporation, and compounding.

Gravity
Density or specific gravity of an oil is the scientific determination as its weight as compared with the weight of the same quantity of water at 60 degrees F.

For measuring liquids lighter than water in this country the reading of the Baume hydrometer is largely employed instead of the specific gravity hydrometer. Baume gravity readings of oil are all greater than ten, corresponding to specific gravity readings of less than one. The greater the Baume gravity reading, the lighter the specific gravity reading.

In the test a hydrometer Fig. 37 (a weighted glass bulb with graduated stem) is dropped into a tube of oil. The hydrometer fl_oats in a_ v_er- ””’11JII t1cal pos1t1on Fig. 37-Hydrometer cesl at a certain depth, depending upon the density of the oil. The gravity is deter- mined by the depth to which the hydrometer sinks, as shown by the markings on the stem, with the oil at 60 degrees F. The gravities of different oils vary widely and in such an inconsistent manner that it is

 

20

BEARINGS and their LUBRICATION

hopeless to try to draw any conclusions from this test as to their lubricating value. This test is simply used to determine the uniformity in weight of the oil.

Cold Test
The cold test of oil is to determine the low temperature at which the oil ceases to flow. The test manipulation is subject to error, unless great care is taken. A bottle of oil is placed in a freezing mixture, and by frequent inspection of a thermometer fitted through the cork of the bottle the temperature at which the oil congeals is noted.

Pour Test
The pour test of an oil is likewise a low temperature reading determined by first freezing a partly filled bottle of oil; then upon removing it from the freezing mixture, notation is made of the temperature at which the oil will flow from one end of the bottle to the other.

Flashpoint
The flash test indicates the lowest temperature at which the vapor from an oil will ignite momentarily but not continue to burn when an open flame or lighted t aper is brought near its surface. Heat is applied to the oil placed in a cup and its temperature is slowly raised to the vaporization point. (Fig. 38.)

Fire Test
The fire test indicates that temperature at which the oil vapor continues to burn after the test flame is removed. As operating temperatures of bearings sel-

 

Fig 38 Flash and fire test

dom exceed 120 degrees F. to 140 degrees F. and only in rare instances go as high as 180 degrees F. to 200 degrees F., and as the flashpoint of the lightest bearing oil is over 300 degrees F., the flash and fire tests are not factors of importance.

Viscosity
Viscosity is a comparativemeasurement of oils as to their ability to form and maintain an oil film. The instruments, in commercial use, for measuring viscosity differ so much in princi pie and t ype that the readings from one type are not comparable with those of any other type. Therefore, the viscosity readings of an oil must be accompanied by the name of the instrument used and the oil temperature at which the viscosity test was made.

The Saybolt Universal Viscosimeter (Fig. 39) is the instrument in general use in this country, while the Engler and Redwood viscosimeters are used in Continental Europe.

The Saybolt Universal viscosimeter determines viscosity as the time in seconds required for a known quantity of oil, at a definite temperature to flow through an orifice of known dimensions.

In this test the oil is put in a tube surrounded by water, which is kept at the test temperature. When the oil reaches the predetermined temperature, a plug in the bottom of the tube is withdrawn. This opens a small standardized tube. The oil is then allowed to flow out of this opening into a glass receptacle of known capacity.

Viscosities of bearing oils are generally taken at 104 degrees F., which represents approximately the temperature of the oil in use in the majority of bearings, and at 140 degrees F., which represents approximately the oil temperatures in enclosed type steam engines.

 

21

BEARINGS and their LUBRICATION

The viscosity of an oil is always lower at higher temperature. The decrease in viscosity, due to increase in temperature, varies in lubricating oils made from different crudes.

Obviously it is important that the viscosity of an oil should vary as little as possible with variations in room temperature or bearing temperature. Great variation in viscosity necessitates increased oil feed when supplied through drop-feed oilers. It also means that an oil heavier in body must be used, as the oil in service must provide an oil film throughout the entire range of temperature existing in the bearings.

Oils that vary the least in viscosity with variations of temperature will feed more uniformly through the lubricating appliances than oils which vary considerably. They can, therefore, be used more economically.

It is also possible to select from such oils one the body of which more closely suits the bearing conditions than is possible with those oils the viscosity of which varies rapidly.

Loss by Evaporation
The laboratory test performed by heating a sample of oil to a certain temperature for a certain time to observe the percentage of evaporation is of no value in determining the lubricating value of a bearing oil.

The laboratory test is carried out under much higher temperatures and over a different period of time than is encountered in actual service.

Compounding
Experience has proved that under certain conditions a compounded oil- that is, a mineral oil to which has been added a certain amount of good quality fixed oil (animal or vegetableoil)- is more suitable than a straight mineral oil.
Compounded oils possess more “sticktion·· than straight mineral oils of the same vis- cosity.

They have the property of combining and emulsifying with water, so that their use is desirable where water gains access to the bearings. Water will wash away a straight mineral oi l, but will combine with a compounded oil and form a lathery emulsion, which, particularly in the case of marine steam engines, is desirable.

If, in a bearing lubricated with a compounded oil, where water is present, the lather escaping from the bearing loses its milky appearance, it is a sign of heating.

Some spindle and loom oils and so-called stainless oils used in textile mills are compounded. Due to careless handling of the machinery or shafting, oil may drop on and stain the goods during the manufacturing process. The compounding of the oil permits such stains to be washed out.

Textiles and fabrics, whether cotton, silk. wool or worsted, etc., undergo a scouring process more or less severe. In this scouring process the oil stains must be removed.

The longer the goods are stored before scouring, the less severe the scouring process, or the higher the quality of the goods manufactured, the greater must be the percentage of the right quality of compound in the oil, in order to insure its complete removal during scouring.

With goods, such as plain calico, which are afterwards scoured, washed and bleached, the question of oil stains is seldom important and pure mineral oils are frequently used. With goods which are not scoured, such as lace curtains, white goods, etc., oil stains are most objectionable. Any oil on the goods will in time produce a dark stain which will become darker and darker, the longer the goods are stored.

It takes a longer period of time for the stains of light-colored oils to show up, so that for work of this kind oils nearly colorless a re frequently used, either straight mineral or compounded.

The disadvantages in employing compounded oils for bearing lubrication are that unless they are very carefully manufactured and compounded with the right kind and amount of fixed oil, the oils will become rancid and poisonous; sticky and gummy deposits will develop in the bearings and trouble of various kinds will result.

SELECTION OF AN OIL
As mentioned under “Operating Conditions,” the oil must be selected to suit the conditions of size, speed, pressure, temperature and mechanical conditions.

22

BEARINGS and their LUBRICATION

Oils Light in Body
Light-bodied, quick-acting oils must be selected where the bearings a re small, where the shaft speed is high, where the bearing pressure or temperature is low and where the mechanical conditions are good.

Oils Heavy in Body
Heavy-bodied oils possessing great “sticktion” must be employed where bearings are large, where t he shaft speed is low, where the bearing pressure or temperature is high and where the mechanical conditions are not good.
The oil must also be selected to suit the oiling system employed.

Oil for Hand Oiling
Hand-oiled bearings a re ra rely completely lubricated. They are usually only partly lubricated and demand the use of heavier bodied oils than would be required with a more efficient oiling system. A great deal of oil is wasted by this method.

Oil for Drop-Feed
Oiling In drop-feed oiled bearings less oil is wasted than in hand-oiled bearings and, owing to the better regulation of the feed of a medium or heavy bodied oil, the oil film in the bearings is kept more nearly uniform and complete. The lubrication is, therefore, more efficient, i . e., there is less friction and less wear.

Oil for Ring Oiling
By the ring oiling system t he bearing surfaces, when operating, are constantly flooded with oil, so that the lubrication becomes as efficient as possible with the grade of oil in use.

Oil for Splash
Oiling For splash oiling systems oil should be light in body so as to splash easily to all parts, yet sufficiently heavy in body to produce complete lubrication. [ t is important to maintain a correct oil level as constantly as possible.

If the oil level is too low, too little oil spray will be formed and some of the parts will be ··starved.” Inefficient lubrication will result.
If the oil level is too high, too much oil spray will be formed. This always results in waste of oil. The oil spray will escape from t he bearings or from t he air vent usually provided in the crank chamber.

Excessive oil spray in the case of automobile engines, motor cycles and other industrial internal combustion engines is posit ively detrimental, producing excessive deposit on the hot pistons.

In vertical enclosed type steam engines, excessive oil spray means that too much oil passes the pistons and finds its way through the engine with the exhaust steam. This a lways means waste and frequently results in trouble where it is important that the exhaust steam should be as free from oil as possible.

Oil for Circulation

As the oil in a circula tion system is forced in large quantities to the bearings, the oil is given every assistance to produce complete and correct lubrication. The oil, however, must be of such a character as to maintain its nature, despite a continuous circulation and exposure to the “breaking down .. influence of high pressure and high temperature ; the oxidizing influence of the air and impurities, and the emulsifying influence of water. The oil must also be of such a character as to separate quickly from water and impurities, so that sludge or deposits developed may be easily removed from the oil in circulation. In the oil circulation system a continuous and large supply of oil is delivered to the bearings. The frictional heat of the bearings is carried away by the oil so rapidly that it becomes possible to operate engines employing this system at the highest speeds, and yet maintain a great margin of safety in operation. To minimize the formation of deposits and other impurities from the oil when splash oiling or oil circulation systems are employed, it is good practice, depend ing on the size of the oiling system and severity of service, to draw off a certain amount of oil from the system each day for treatment, in a heated separating

 

23

BEARINGS and their LUBRICATION

tank and afterward in a suitable filter. The purified oil should be returned to the system, mixed with a little fresh oil, at the same time that a corresponding quantity of oil is removed for treatment.

This practice is always desirable, particularly when the quantity of oil in use is small. In this way the vitality of the oil is kept at as high a standard as possible, and the life of the oil is greatly prolonged.

Occasionally, in very large plants, the separation and filtration apparatus are constructed as a part of the oil circulation system, so that either the whole of the oil in circulation or a certain percentage of it constantly passes through the treating apparatus.

Circulation oils a re specially treated to withstand the breaking down effect of continued use under severe conditions of service. The oils best adapted to use in splash oiling, ring oiling or oil bath system possess similar characteristics.

Where hand oiling or drop-feed oiling systems are employed, the oil, after having once passed through the bearings, is frequently run to waste and not used over again. In such cases the slight alteration which takes place in the oil passing through the bearing is of little importance.

In other cases the oil, after having once passed through the bearings, is collected and filtered for the purpose of using it again, either on the same bearings or for less impor- tant work. For such purposes the oil must possess to a great degree the same characteristics as circulation oils, particularly if it is used over and over again, on important bearings with only a slight loss of oil.

Assuming that the oil is applied by a suitable oiling system and a complete oil film is formed, an oil too heavy in body will always produce unnecessary high fluid friction. It is not unusual to find that a number of bearings in a plant are using an oil far too heavy because a few other bearings, operating under bad mechanical conditions, demand its use.

Better economy would be secured by using the heavy oil on the few troublesome bearings. The greatest economy would be brought about by correcting the mechanical condi

tions so that the correct high-grade oil could be used throughout.

A large number of bearings of modern machinery, such as the bearings of enclosed high-speed steam engines, automobile engines and other types of enclosed hjgh-speed internal combustion engines, steam turbines, ring oiled shafting bearings, etc., employ oiling systems by which the bearings are constantly supplied with a liberal amount of oil and complete lubrication is obtained, but oils too heavy in body are used.

An oil too light in body, notwithstanding a liberal feed , will be unable to form and maintain a complete oil film. Excessive metallic friction and wear will result.

An oil too heavy in body will not spread rapidly, resulting frequently in an incom- plete oil film with resultant heating and wear.

When the correct high-grade oil is introduced it will bring about a reduction in bearing temperatures, evidenced by a reduction in the temperature of the oil in circulation.

From the foregoing it will be understood that, speaking generally, oils relatively heavy in body must be selected where hand oiling or drop-feed oiling systems are employed. Oils relatively light in body may be selected where a more efficient oiling system is employed, such as ring oiling, splash oiling, oil circulation or oil bath.

OIL QUALITY

Low-grade Oils

Low-grade oils a re ordinarily oils improperly manufactured. They lack uniformity, have high internal fluid friction and many of them vary in viscosity under slight variation in temperature.

For the protection of their machinery, operators are compelled to use such oils extravagantly to insure a constant adequate oil supply to a ll parts of the bearing surfaces.

When using low-grade oils, applied by hand oiling or drop-feed oiling, it is impossible altogether to prevent wear, notwithstanding a liberal oil feed. When using low-grade oils in ring oiling, splash oiling, oil circulation or oil bath systems, the oil breaks down under the continuous service, and exposure to the effects of air, high temperature, water and impurities.

 

24

BEARINGS and their LUBRICATION

The oil has a comparatively short life, and develops troublesome deposits which accumulate in dangerous places, and choke up oil pipes, oil channels and grooves. The bearings are thus deprived of full lubrication.

Low-grade oils compounded with unsuitable fixed oils will oxidize quickly and develop gummy or sticky deposits. The development of such deposits means that bearing friction is slowly but surely on the increase and in time acute troubles may occur.

Unsuitable oils, when used in ball or roller bearings, will cause corrosion of the balls and rollers, or may oxidize and gum, thus forming a base for dirt, deposit and trouble.

High-grade Oils

High-grade oils are manufactured from specially selected crudes, carefully refined and treated with the ultimate object of giving each oil definite and uniformly maintained characteristics.

High-grade oils have low internal fluid friction and vary considerably less in viscosity under slight variations in temperature than low-grade oils. Because of this fact highgrade oils can be used much more economically than low-grade oils.

The correct high-grade oil, applied by hand oiling or drop-feed oiling, will largely reduce or entirely prevent wear, even with a scantier oil feed than is possible with an ordinary oil. When using the correct high-grade oil, applied by ring oiling, splash oiling, oil circulation or oil bath systems, the oil will have a much longer life than ordinary oil. It will not develop deposits during use, and will separate easily and quickly from water and impurities which may enter the system.

When comparing the results from the use of an ordinary oil with those of a high-grade oil, both of the same viscosity, experience proves that the high-grade oil will possess greater “sticktion” and endurance and will sustain greater bearing pressures.

Therefore, a high-grade oil which possesses a lower viscosity than an ordinary oil can be used for a given set of operating conditions and yet will maintain a complete lubricating film and safeguard against wear.
The introduction of the correct high-grade oil, therefore, always means less wear and lower

friction losses with corresponding savings in power and fuel and actual lower cost of lubrication.

LUBRICATING GREASES

In cup greases, the difference in melting point between the soft grease (No. 1 consistency) and a hard grease (No. 5 consistency) is comparatively small, i. e., 12 degrees to 15 degrees F.

Soft, light bodied greases contain more lubricating oil than heavier bodied greases. In other words, a grease of soft consistency contains more oil per pound than a hard or more dense grease.

The soft grease begins to lubricate almost the instant it is applied to the bearing, whereas a hard or more dense grease does not begin to lubricate until the bearing temperature becomes sufficiently high to soften the grease.

The efficiency of a grease depends upon the following:
First: The quality of the fat employed in the manufacture of the body and the quality of the oil incorporated in the finished grease. Second: T he selection of the correct density or consistency to suit the type of bearing and method of application.

Third: The purity of the grease (absence of dirt, improperly manufactured body, and foreign substances sometimes used as a cheapener).

Quality

The quality of the grease depends first upon the selection of high-grade fats and lubricating oils; and second, upon the care employed in the manufacturing processes to make a grease which will meet specific operating conditions.

For minimum and high speed work with no excessive bearing pressure a grease of soft density containing light bodied lubricating oil should be chosen.

For medium and slow speed work with fairly heavy bearing pressure a medium to hard density grease containing heavier bodied oils should be chosen.

Consistency

The type and character of the feeding devices determine, to a large extent, the consistency of the grease which should be used.

 

25

BEARINGS and their LUBRICATION

If the grease is fed through an automatic spring grease cup it should be of soft consistency No. I or No. 2. These same consistencies are recommended when used for high speed ball and roller bearings.

For hand compression grease cups consistencies, No. 2, No. 3 and No. 4 may be employed. Care should be taken to see that in all instances the grease is of a density that will feed easily and without waste.

A grease of 1 o. 4 or No. 5 consistency may be selected for use on open bearings where the grease rests directly on the rotating shaft. This condition is usually found only in slO\\’ speeds.

Purity
The purity of a grease is particularly important.
In the manufacture of greases, impurities in t he raw materials produce insoluble lumps and foreign substances that must be removed. This is done in a modern plant by up-to-date mechanical devices designed for this particular work.

The old time method, which is practised by many manufacturers today, is to pulverize or grind the lumps and impurities between closely ntted rolls. This merely crushes them so that their appearance is not readily discernible, but it does not remove them.

It is obvious that for high speed conditions and other exacting service, finely pulverized impurities or particles of improperly manufactured body will cause very serious trouble. ii’ If the fat employed in the manufacture of the grease body is of the proper character and body properly made, it should feed to a bearing readily under pressure without any residue remaining in the grease cups.

Grease is practically indispensable for the lubrication of certain bearings under certain conditions, for instance:

In dusty and dirty surroundings, e. g., flour and cement mills, collieries, industrial plants, bakeries, etc., grease entirely fills the bearing cavities and clearance spaces, collecting and forming a fillet around the shaft at the bearing ends. This seals the bearing and prevents dust and dirt and other abrasive material from entering the bearings.

Semi-fluid and soft density greases are sometimes used for ball and roller bearings. The bearing is completely filled with the grease, so that a fillet is formed at either end, which prevents the entrance of dust and abrasive materials. Grease is always recommended in bearings of this type that are running at very high speeds, as it is not thrown out of the bearing as is the case with oil.

ln rolling mills where hot sheets are rolled the necks of the rolls attain a temperature so high that oil cannot be used as a lubricant. Special neck greases are manufactured to take care of such conditions.
There are various kinds of roll neck greases made to take care of both hot and cold conditions, also where a large volume of water is used to keep down the heat.

A number of other high melting point greases are used on bearings exposed to high temperatures, such as steam-heated bearings on drying cylinders in paper mills, hot journals and bearings supporting the rotary kilns in cement mills, etc.

Greases should always be used for the lubrication of bearings located in inaccessible places when ordinary means for applying oil are not practicable. Such bearings are usually fitted with grease cups and the grease forced by pressure through long pipes into the bearings.

BEARING TROUBLES

When bearing trouble occurs, it is usually indicated by increased heat in the affected bearing. It will be instructive to analyze a number of the causes leading to heated bearings.

When the barrels of oil have been delivered by the manufacturer, it is important that they be stored under cover. They should never be left in the open, exposed to sun and rain. Rain water, particularly if the barrels are stood on end, will find its way through the staves and gradually dissolve the inside lining of the barrels, causing it to spread throughout the oil. When using such oil, the presence of the lining material will cause excessive heat in the bearings.

When opening a barrel, the bung should be started by striking the staves with a mallet.

26

BEARINGS and their LUBRICATION

If an auger be used, fine chips of wood and d irt from the outside of the barrel may easily find their way through the opening into the oil.

The oil should, therefore, always be poured through a strainer into the oil cans. If this is not done, the small chips of wooJ anJ other impurities may work into the bearings and cause excessive heating.

Dirty oil cans are responsible for man~ hot bearings and they should, therefore, be kept scrupulously clean. The cans should be closed at the top or provided with covers. so as to prevent as fa r as possible Lhe entrance of dirt.

An oil can should never be used for more than one grade of oil, and, in order to prevent mistakes, the name of the oil should be plainly marked on the can.

When the oil is drawn directly out of the barrels for use, the overflow runs onto the floor or into “save alls” which are not always clean. There is always the danger that some of this oil, including the dirt, will be used for lubrication. [t is good practice to heep the oil in cabinets, preferably locked, so that the oil will not be tampered with by unauthorized persons. Oil waste may thus be minimized.

Wrong Oil
Numerous hot bearings have been caused by the use of the wrong oil. I f. say, a spindle oil is used instead of an engine oil, heating will result because the oil is too light in body to provide lubrication. If a very heavy oil is used in place of spindle oil, heating will result because the oil is too heavy to spread over the bearing surfaces, owing to the high speed at which the spindles operate. The fluid friction, also, will be excessive.

In some cases, oils like linseed oil or turpentine have been used by mistake ; in other cases, the use of badly filtered oil or waste oil instead of fresh oil has caused great trouble. When hand oiling is employed, bearings will overheat if the application of oil is not sufficiently frequent or regular.

When drop-feed oiling is employed, many hot bearings can be traced to empty lubricators, particularly when the oil containers are of small capacity. Sometimes bearings heat up because the oil congeals in the lubricator or in the feed pipes and fails to reach the bearings.

Parts of the lubricator, or the oil-feeJ pipes from the lubricator to the bearings, may become choked with deposits which may cause su1ficient reduction in the oil feed to produce hearing heat. Fine sawdust in sawmills, or wood-working shops, flour dust in flour mills, lint in cotton mills, etc .. have been responsible for such trouble.

Cotton waste, still largely used for cleaning down engines and machinery, should never be used for this purpose, as fine fluffy matter from the waste get into the lubricators and oil. causing trouble. Muslin or silk cloths are much to be preferreJ, as they are free from fluffy matter and can readily be cleaned.
Another source of trouble is the escape of oil between the bearing housing and the bearing brass. With a liberal oil feed. the bearing will give no trouble, but when even a small reduction in the oil feed is attempted the bearing will heat up, as only the surplus oil has been reaching the bearing itself.

Too Few Oil Inlets
Very long bearings sometimes give trouble if they have too few oil inlets. For instance, a bearing more than 12 inches long with only one drop-feed oil inlet at the center is always liable to be a trouble maker.
Some bearings are hard to lubricate because the shaft pressure is upward instead of downward. This makes it diffkult for the oil to spread. unless it is introduced at the bottom of the bearing and there is provision made to prevent its too free escape.

In some ring-oiled bearings water of condensation from steam or a very moist atmosphere enters and accumulates in the bottom of the bearings. The water gradually lifts the oil out of the bearing, until finally the oil rings revolve in water and heating occurs.

In ring-oiled bearings, deposits formed by the oil itself or by impurities entering the bearing may cause the oil rings to stick , so that with their failure to revolve, the oil supply fails and the bearing heats up.

Bearings lubricated by the splash oiling system may heat if the oil level is too low to provide adequate oil spray, or if the oil has become emulsified by the presence of water of condensation and cylinder oil from leaking glands.

27

BEARINGS and their LUBRICATION

Water, either from the engine itself, such as condensed steam from leaking piston-rod glands, or from leaking cooling-water coils, etc., sometimes finds its way into the bearings and displaces the oil. The bearings commence to heat as soon as the oil film is destroyed by the water.

Where the entrance of water cannot well be avoided, the system of daily treatment of the oil will always effect an improvement.

In circulation oiling systems the oil capacity should be large enough to permit cooling of the oil and thorough separation from impurities. Bearings may heat, due to deposits choking the oil inlet pipes.

Deposits may be due to unsuitable or improperly manufactured oil, or to the mixing of water and oil, or two different oils. If, for example, a heavily compounded oil gets into mineral oil in circulation, a large portion of the compound will separate in the form of a sludge.

If the oil has been a long time in circulation and has become very dark in color and considerably weakened in vitality, the addition of a large quantity of fresh oil will cause a dark-colored deposit to be thrown down.

Oil-distributing grooves or oil grooves in the bearings may be choked up for various reasons already given and thus cause trouble by preventing the proper distribution of the oil.

Speeding-Up
Speeding-up of machinery in order to increase the production may cause heating. Obviously, high speed will produce greater friction and may demand the selection of a quicker acting or higher quality oil to give good results.

lf the load on an engine is increased, it is not unusual to find that some of the bearings are unable to stand the increased strain, and therefore heat.
Excessive strains in the bearings may also be produced by the settling of building foundations, which throws the bearings out of alignment.
Excessive vibration may produce similar results.

Light load on a steam engine may cause heating of the crank-pin bearing, for when there is an insufficient quantity of steam in the cylinder to properly cushion the movement of the heavy piston, the crank pin is subjected to excessive pounding.

Eccentric straps may heat as a result of poor internal lubrication, which increases the resist ance to be overcome in moving the steam or exhaust valves.
Driving bells and ropes must be shortened after they become slack. If they are shortened too much, they produce excessive pressure on the bearings supporting the pulleys over which the belts or ropes run.

Excessive moisture in the atmosphere causes cotton belts or ropes to shrink.
In textile mills, where a number of the high-speed spindles are operated by cotton tapes and bands, the shrinkage of the cotton, due to excessive moisture, puts excessive pressure on the spindle bearings and causes slippage, or reduction in spindle speed, and heating.

Increased temperature will thin the oil, so that it may not be able to withstand high bearing pressures.

Excessive Load
Excessive load on an electric motor or an unbalanced construction or imperfect adjustment will cause high temperature in the motor. The extra heat thus conducted into the bearings may cause the oil film to break down, a condition indicated by excessive heating.

With many classes of rough machinery, it is still common p ractice to replace bearings without any attention to scraping them in with the shafts. In fact, the bearings are allowed to “run themselves in.” Considerable heat develops and a liberal feed of heavybodied oil is necessary during the first few days. Needless to say, this is a crude and undesirable practice.

Whenever a bearing has been excessively hot, the bearing brasses warp, and the edges of the brass close against and nip the shaft. It is necessary in such a case to file away these corners of the brass and chamfer the edges so as to facilitate the entrance of the oil.

 

28

BEARINGS and their LUBRICATION

Cracked bearing brasses allow the oil to leak away. The oil film is destroyed, and even with a liberal oil feed the bearing will be “sensitive” and inclined to heat.

Too soft white metal frequently leads to heated bearings. It yields too readily to pressure and slowly flows out of the bearing, so that the bearing surface constantly changes and never assumes a good working skin.

Too hard bearing metal not properly fitted frequently results in heating, because the bearing pressures are not uniformly distributed over the surfaces.

The re-babbitting of a bearing should be done in one pouring. If done in two pourings, the white metal already in the bearing will have partly solidified and will not melt properly together with the second pouring. The result will be that, in operation, cracks will develop and the white metal will break loose. This will also occur when the white metal has been poured too cold, in which case it will not adhere closely to the shell.

After re-babbitting a bearing, it should be scraped to a correct fit, the bearing edges should be rounded off and all necessary oil holes and distributing grooves properly made. Failure in these matters will cause heating of the bearing.

If appreciable wear takes place, the edges of the oil grooves become sharp and act as oil scrapers rather than oil distributors. The edges must be kept well rounded and the oil grooves should, therefore, occasionally be examined, particularly if trouble has occurred.

Replacement of Bearings
When worn bearing brasses have been replaced, the bearings sometimes heat because the new brasses have not been properly fitted and scraped together.
If the bearing clearance is too small, through too close adjustment, heating will occur, as there is insufficient room for the oil to spread and form a satisfactory film.

If the adjustment of a bearing is too loose, the oil will escape from the bearing too freely. In the case of bearings such as crank-pin bearings, which are subjected to intermittent heavy pressures, the oil will be unable to provide a sufficient cushion to prevent metallic contact. Pounding or knocking of the bearing will result in consequent heating and wear.

When starting up after a stoppage, say, over Sunday, the power necessary to drive the mill or works is always considerably higher than normal. All of the bearings have cooled down and the oil throughout is cold and sluggish. As the oil heats up and the various driving belts and ropes become more flexible, the load gradually decreases to normal.

Wl hen engines and machinery have been shut down/or a longer period, very special attention should be given to the lubricators and lubrication of all parts before commencing opera- tion. Driving belts and ropes are stiff after the long standstill, and it must not be expected that the plant can be quickly run up to speed without trouble.

Excessive deflection in a shaft, due to various causes, will result in overheating of the nearest supporting bearings. The shaft will bear more heavily on one side of the bearing and the heat will develop and spread from that point.

Introduction of New Oil
29 Where oils of vegetable or animal character or heavily compounded oils have been in use and where the new oil introduced is straight mineral, or nearly so, the change-over should take place gradually. Vegetable and animal oils always leave a sticky varnish or rubber- like coating a ll over bearing surfaces and in the oil pipes. If the change is made quickly, heating is bound to occur and sometimes even seizure of the bearing surfaces. This is because the coating is loosened by the new oil in lumps or flakes which prevent the formation of a proper oil film.

The best practice in the introduction of a straight mineral oil after a compounded or animal oil has been used is to introduce the mineral oil gradually in the following manner: for the first two weeks a mixture of 75% of the former oil and 25% of the mineral oil; in the succeeding two weeks a mixture of 50% of each of the oils; the following two weeks a mixture of 25% of the oil formerly in use and 75% of the mineral oil. By this process the gummy coating is gradually loosened, worked out of the bearing, and mineral oil may be subsequently used without any danger of overheating.

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BEARINGS and their LUBRICATION

Nearly always when introducing a new oil, which is appreciably different in character from the oil previously used, some bearings will heat up. This may be due to the better quality of the new oil dissolving deposits produced by the old oil. The tleposits when loosened too quickly cause trouble, acting in the same way as grit or dirt. lt takes time for the bearing surfaces to adapt themselves to the new oil.

The use of a grease containing dirt (which is not visible as in oil) and graphite tends to choke oil pipes and oil grooves and is often responsible for heated bearings.

COOLING HEATED BEARINGS

When small bearings heat up, they are usually easy to cool down, as the total amount of heat present in the beanngs is relatively small. Usually a liberal supply of the oil in use is all that is required. If the bearing is heated to such an extent that it has been distorted or the white metal has started to flow, it must be dismantled and put in thorough working order.

When large bearings heat up, the case is very different. Large bearings may absorb and contain a grea t deal of heat. When once a large journal starts to heat and expand, there is relatively so little clearance that the oil film is easily squeezed out and the bearings may seize.

The first thing to do when a large bearing heats up is to increase the bearing clearance by slacking back the bearing brasses.

If the bearing has not seized, but is extremely hot, it is usually sufficient to feed the bearing with a liberal supply of steam cylinder oil (which possesses superior lubricating properties under high temperatures) until the bearing cools, when the normal practice of oiling the bearing can be gradually resumed.

If the bearing has commenced to sei::e, a little graphite, sulphur, white lead, or like ingredients, mixed with cylinder oil, may be used to advantage.

Castor oil or rapeseed oil is occasionally employed for cooling bearings, but their use

should be avoided, because where a ctrculation system is emploved they mix with the engine oil and afterward develop deposits. Once a bearing has become accustomed to the use of such oils it is not always a simple matter to bring about a change back co the original conditions.

In case a “hot bearing” develops, seizure of the overheated shaft may take place if water is applied direct to the bearing, on account of sudden shrinkage; if its use is necessary it should, therefore. be applied to the haft near the bearing.

TRUE ECONOMY

In judging the value of a lubricatillf4 oil. it must be borne in mind that oils are u eJ to reduce friction and wear ; that high-grade oils reduce friction and wear to a far greater degree than ordinary oils and that high-grade oils can be used most economicallv. Therefore, the price per gallon of an oil should not be considered primarily.

Where the class of machinery in use is rough or in bad repair, where wasteful and inefficient oiling systems are employed. and particularly where the care and attention given to the plant is indifferent or bad, it is not always possible to justify the uses of highgrade lubricating oils; and under these conditions the use of ordinary or intermediate grade oils is justified.

High-grade oils correctly selected to suit the operating conditions and intelligently used will outlast ordinary oils. Experience has proved time and again that the actual cost of high-grade oi ls over a period of time is less than the cost of ordinary oils.

Even where the actual cost of high-grade oils is higher than that of ordinary oils, the saving in power brought about by the reduction in friction, and the saving in wear brought about through superior lubricating properties, will amount. over a period of time, to many times the difference there maybe in the cost of the oils.

There are many plants in which it is declared that there is no lubrication trouble. Granting this, it is still a far-cry from this “no-trouble” state to perfection in operation. Only by analysis of actual conditions.

 

30

BEARINGS and their LUBRICATION

careful grouping of various parts of the machinery, and the use of specially selected high-grade oils which will give maximum lubrication service, can perfect results be secured and maintained.

In some plants there are a large number of high-speed bearings (as in textile mills), highspeed shafting, high-speed machinery and machine tools. The power consumed in overcoming friction in such plants constitutes a large percentage of the total consumption of power- sometimes more than 50%. The introduction of the correct, high-grade oils specially selected to suit the various groups of machines will effect an appreciable reduction in power, and also minimize the cost of renewals and repairs.

There are many t ypes of modern highspeed machines, such as steam turbines, highspeed steam engines, and internal combus-

tion engines of all kinds, where the continuous service conditions demand the use of the highest quality oil obtainable, almost regardless of its cost, and where smooth and safe operation and low frictional losses count many times more than the cost of the oil itself.

1 n plants where the engines or machines are chiefly of the large heavy-duty type, operating under severe conditions, such as large steam engines, large gas engines and heavy shafting and machinery, the introduction and intelligent use of the correct, heavy-bodied, high-grade oils specially selected to suit the various groups of operating conditions will result in great economy. They will assist materially in preventing breakdowns and bearing troubles of all kinds, thus reducing the cost of renewals and repairs to a minimum.

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