Shape errors affect bearing load capacity

Shape errors affect bearing load capacity The influence of surface shape errors on load capacity of reeled bimetallic bearings has been studied at the Institute of Mechanics and Machine Design of the Technical University of Gdansk*. It has been suggested that

Bush inner surface shape errors affect bearing load capacity. These errors are difficult to detect using simple measuring instruments but their effects, especially in the hydrodynamic conditions, can be considerable.

Lubricant

! LubrlCOnt Rodtol force opphed to test bearing

Fig 1 Bearing test system

270° ~ \

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a

Cross section

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The bushes to be tested were taken from normal production at a Gdansk bearing plant. They were finished by fine boring with a diamond tool either in production in special housings or after being forced into the test housings. Bushes produced by the two methods will be referred to, for brevity, as Type A and Type B respectively. The inner surfaces of the bush housings were hardened and accurately finished: errors in cylindricity of the surface were less than 2/am. The shaft of the test machine was made from steel 20H, carburised, hardened to 60 Rockwell C, and finished to 0.16~m cla.

90° 180°

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I

Tests performed Reeled bimetallic bushes, 55 mm long, with a nominal internal diameter of 40mm and a total thickness of 2mm, were inserted into solid housings with an internal diameter of 44mm and an external diameter of 100mm. The bush linings, made of four different alloys (Table 1), were 0.4mm thick.

-I

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the errors, after forcing bushes into machine casings, are the result of inner surface machining inaccuracies, such as conicity and barrelling, and outer surface errors.

/

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180°

Cross section TF

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Tests were performed in the PGII 1L machineI (Fig 1). The bearings were lubricated with Hydrol 40 oil at a pressure of 2 x l0 s N/rr~ and an inlet temperature of 20°C. Prior to each test, bush shape was measured at 3 parallel cross sections perpendicular to the bush axis (Fig 2).

LCross section TIT

Fig 2 Typical surface shape errors in reeled bimetallic bearings (a) finished in production, and (b) finished after forcing into the housing e4 E 4444

43,

4000F /

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4120

4022

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4189

4414

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3590 x /" ~x

3590

3000p

Type B "" 3394

X Type A ~2747

x~2658

~ 200 do a

014 0~6 0'8 I~0 IL2 1~4 L/d roho

0'10 0 '15 OO5 Beormg cleoronce,lO-3m

b

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c

d

50O' ~000 ~ 1500 ' 3'000 Rolotlonol speed n, m m

Fig 3 Effect on load capacity o f (a) shape errors (b) changing the bearing material (c) bearing clearance, and (d) 1/d ratio; each o f the experimental points plotted is the mean o f six repetitions

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TRIBOLOGY international December 1977

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Table 1Compositions of the bush lining alloys

occurred: the transition was observed as a violent increase in frictional torque.

Alloy

In this way, the affect of preparation method, and by implication outer surface shape errors, on load capacity of bushes was studied. In addition, the effects of varying bearing clearance and l / d ratio were examined.

Sn MB01 MB10 MB11 MB12

Composition, % Cu Sb Pb

89 4 10

3 70 74 80

8 30 22 10

Results Tasting for load capacity At rotational speeds of 500, 1000, 1500 and 3000 rpm, the load on the bearing was 'increased incrementally. The load capacity was taken as the load at which transition from hydrodynamic to boundary lubrication

Shape errors for Type A bushes were greater than for Type B, and the load capacity lower. Load capacity for Type A decreased rapidly when rotational speed exceeded 1000 rpm: this can be attributed to oil flow perturbations due to the shape errors,

The data from the further tests (Fig 3) shows that shape errors have a greater effect on load capacity than changes of 1/d ratio and clearance, within the range tested. The effect is comparable with the effect of changing bearing material. Technical University of Gdansk, Institute of Mechanics and Machine Design, Majakouskiego 11/12, 80-23 Gdansk, Poland

References l.

Neyman A. and Olszewski O. Stand

for examination of lateral slide of bearings additionally loaded by a moment of a vector perpendicular to the journal axis. Zagadniea Tarcta Zuzycia i Smarowama 10(1971) 141150 (m Polish)

Gold medal award

Saving energy

The 1977 Tribology Gold Medal has been awarded to Professor Barwell, head of the Department o f Mechanical Engineering at the University College of Swansea. The award has been made in recognition of his contribution to the advancement of tribology, particularly in its application to rail transport.

In December 1976 the American Society of Mechanical Engineers Research Committee on Lubrication began work on a research and development plan for the Energy Research and Development Administration aimed at achieving energy conservation through tribology. Earlier, ERDA had asked ASME for such assistance: they recognised the potential but wanted help delineating a specific plan.

In its citation, the Awards Committee says: " I t is difficult to think of an aspect of tribology to which he has not made a significant contribution, but apart from his own technical contributions to the field, which gained him many medals, honours, and awards, there are three ways in which his achievements have been exceptional". The citation describes these as: encouraging and attracting others to work in this field; his contribution to international co-operation in tribology; and the application of tribology to problems of rail vehicles such as braking systems, adhesion between tyre and track, and wear and dynamic motion of pantographs and conductor wire. The medal will be presented to Professor Barwell by Professor Sir Hugh Ford on 25th January, 1978 at the London Headquarters of the Institution of Mechanical Engineers.

Silver and bronze The 1977 Tribology Silver Medal has been awarded to Mr. Douglas Scott,

Professor Barwell has been awarded the 1977 Tribology Gold Medal

Head of Metallurgy at the National Engineering Laboratory for the past 17 years. It is being given for his work on the application of advanced metallurgical techniques to industrial tribology, in particular his major contribution to particle tribology and its application to machinery condition monitoring. The Bronze Medal has been awarded to Mr. D. A. Ellingham, until recently Senior Engineer at Centralube, London, for his theoretical and practical contributions in the field of industrial lubrication systems design.

An early step in developing the plan was a workshop held in Washington DC in February 1977. The workshop assessed the potential impact of tribological advances on energy conservation. From these discussions, the plan was developed: at the time of going to press the workplan was being reviewed for publication by ASME, and it was anticipated that it would be presented to a US Government official at the ASME Winter Annual Meeting in Atlanta on November 29th. It is anticipated that the workplan will be a 'living' document, modified with changing needs and opportunities. ERDA hopes to fund contractual and industry--cost--shared R and D activities described in the document. An advisory group will continue to guide and evaluate the activities, as it has the preparation of the workplan. ASME, United Engineering Center 345 E. 47th Street, New York NYI0017, USA

TRIBOLOGY international December 1977 301

anti-wear, ep, anti-foam, and antioxidation additives. According to the manufacturers, in contact with an open flame the water phase turns to steam, smothering the flame. 6155 carries the approval of the US Department of Interior Mining Enforcement and Safety Administration and Factory Mutual Research Corporation. Lubrication Engineers (UK) Ltd, 10 Station Road, Pangbourne, Berkshire RG8 7AN, UK, or Lubrication Engineers Inc, 3851 Airport Freeway, PO Box 7128, Fort Worth, Texas 76111, USA

High volume, high pressure multiple piston pump provides time controlled lubrication of processing, drilling, and excavation equipment

High volume grease pump Sufficient grease " t o lubricate an entire multiple bearing system" can be delivered within 60s by a recently announced multiple piston pump. The manufacturers describe the system as especially suited for ball mills, screens, crushers, blast-hole drills, draglines, and power shovels. The Lincoln St Louis Model 1854 pump is a self-contained unit with a 751b grease reservoir. Up to 2~lbs per minute of NLGI Grade 1 grease can be delivered at an operating pressure of 2500 psi. A one horse-power motor running at 1750 rpm drives six plungers: output from each piston is checked and combined into a single outlet. The timer permits lubrication intervals of 33 mins to 3 hours. Lincoln St Louis, Division of McNeil Corporation, 4010 Goodfellow Boulevard, St Louis, Missouri 63120, USA

Fire resistant hydraulics Combination of " . . . the wear reduction qualities of petroleum hydraulic oil with the safety of a fire resistant fluid" is the claim made for the latest addition to the range of fire resistant hydraulic fluids available. It was developed for use in equipment where flames, sparks, hot metal surfaces, and other potential sources of ignition exist. Monolec 6155 is an emulsion of paraffin base oil in water: it contains

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Film lubricants Flourocarbon and silicone lubricants are non-toxic and non-staining. They are claimed to be particularly suitable for the food and textile industries. Following their apparent success with spray versions, Rocol have introduced IFL and SL fluid lubricants. IFL is a flourocarbon telemer suspension in a solvent and SL a silicon oil in a solvent. Rocol Ltd, Swillington, Leeds LS26 8BS, UK

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at high temperature

E / M Lubricants have announced a high temperature bonded solid film lubricant. Everlube 860 contains molybdenum disulphide and graphite combined in a modified silicone resin. Everlube 860 is designed for continuous operation at temperatures beyond the range of conventional solid film lubricants. Maximum effectiveness is shown in the 500°F (260°C) range: however, it has prevented galling and seizing as high as 1500°F (800°C approx). The product can be applied by spray, dip, or brush techniques and requires an oven cure for one hour at 500°C. E / M Lubricants Inc, PO Box 2200, Highway 52 NW, West Lafayette, Indiana 47906, USA

Cold treatment Sub-zero processing of metals is widely practised in the heat treatment industry to transform retained austenite. BOC have extended the benefits of cryogenic processing by the introduction of a process for fully heat-treated tools which can he performed by the user.

TRIBOLOGY international December 1977

The Cryotough process is used to extend the wear life of heat treated alloy steel components by up to 600°70, but " . . . 300070 is more common". Prolonged exposure to liquid nitrogen transforms retained austenite to martensite, increasing the strength of the material. The amount of austenite present depends on the original heat treatment. The martensite formed in the process is super-saturated with carbon: hence there is a tendency to form additional fine carbides, improving wear life. BOC state that the results of cryotoughening are "variable". They quote, however, the following "typical increases in tool life": 600070 for drills and dies 30007o for gear cutters 20007o for milling cutters 100°70 for hacksaw blades 25007o for paper cutting knives BOC also note that the process has not been tried for tools used in impact conditions " . . . but there is no reason why this should not be effective". Nor has it been tried in lower alloy steels, where it is anticipated that improvements will be less marked. BOC Ltd, Great West House, PO Box 39, Great West Road, Brentford, Middlesex TW8 9DQ, UK

Changes in Lloyd's rules Lloyd's have announced availability of their rules for 1978, which will become effective on January I st. The rules embody both technical changes and changes in format. Some of the changes in technical rules are of tribological interest. The rules for main propulsion shafting have been amended leading to some reduction in allowable shaft diameters, in particular some propellor shafts, and lengths of bush bearings. Also, manufacturing requirements for gearing have been expanded. The change of format results in the bound volume being replaced with a loose-leaf A4 style. The rules are organised in seven basic parts with 61 individual chapters. Annual publication will cease and be replaced by a system of issuing amended sections to subscribers in January and June of each year. Lloyds Register of Shipping, 71 Fenchurch Street, London EC3M 4BS, UK

Lubricating complex machines Some complex machines need different lubricants for different parts. Typical examples are open gear trains and high temperature bearings. Bielomatik have introduced a lubrication pump for this type of application. The pump is designed to operate from a hydraulic input either from a primary lubrication system or direct from the machine. When employed in conjunction with a primary lubrication system, the pump is used to feed oil or semi-fluid grease to points requiring a different lubricant from the primary system. The pump consists of two basic components: a reservoir for the lubricant containing a spring-loaded piston and a block of pump elements. The reservoir is loaded via a greasegun nipple at its base, and the spring behind the piston is chosen to suit the

Lubrication p u m p f o r oil or greases characteristics of the lubricant used. This reservoir has a transparent polycarbonate dome giving a visual indication of lubricant level. The pump elements themselves consist of a brass body, a steel delivery plunger, and control springs. Pre-set delivery volume of the unit is 110mm 3 per impulse per pump element (up to four): the pumps can operate every 5s if required (3s in the case of oil). The reservoir holds 50cmL

Ultrasonic thickness gauge which could be used to monitor wear application as "monitoring wear of smooth surfaces". Baugh and Weedon have announced a Mark 2 version of their PAl040 thickness gauge to allow use of their DT7 probe for measuring sheet down to 0.25mm. Accuracy is claimed to be better than _+1°7o over the entire range up to 250mm. Measurements require access to only one surface of the component: the major application area envisaged is in manufacturing industries. The system can, however, be used to measure the wear of flat surfaces in situations where the surface becomes smoother. One possible application is machine tool slideways, where there is adequate access. Baugh and Weedon Ltd, Widemarsh Street, Hereford HR4 9EZ, UK

Die cooling increases life Many methods have been proposed to control temperature in steel wire drawing: the aim is to improve drawing speed and mechanical pro-

Bielomatik London Limited, Cotswold Street, London SE27 0DP, UK

Ultrasonic wear measurement Use of ultrasonic gauges for measuring thickness of sheet metal is nothing new. The manufacturers of a recent addition to the range of gauges available, however, quote one possible

t. !

Cooling process f o r wire drawing giving increased die life at higher drawing speeds

perties of the product. Kobe Steel have developed a cooling system which is claimed to allow wire to be drawn twice as fast as on a conventional machine and prolong die life by approximately 1.5 times. Kobe's system cools the rear portion of the die, including the back relief portion next to the bearing which has the highest temperature in the die, and the emerging wire. The increase in die life is attributed to reduced internal die temperatures: for example, one analysis shows a reduction of 110°C. Kobe recently announced the first overseas licence for the cooling process, to a UK firm Marshall Richards Barco Ltd. Kobe Steel Ltd, Kobe, Japan

Remote lubrication Hard-to-reach lubrication fittings can present a major maintenance problem. Hidden or guarded fittings can lead to production down-time and higher maintenance costs. Lincoln St. Louis have announced a range of remote lubrication fittings. The system of junction blocks, bulkhead connectors, and hose assemblies can extend lubrication fittings beyond sheet metal plates or guards. It is claimed to enable easier, quicker, and safer lubrication, to ensure that all elements are lubricated, and enable bearings to be safely lubricated while the machine is in motion. Lincoln St Louis, Division of McNeil Corporation, 4010 Goodfellow Boulevard, St Louis, Mo 63120, USA

TRIBOLOGYinternational December 1977 303

Inspecting cylinder bores

9 - 11 May, 1978, London, UK

In this issue of Tribology International, W. Bailey describes the laser scanning system for cylinder bores developed by the Cranfield Unit of Precision Engineering in collaboration with SKF. Sira Institute Ltd, in collaboration with Girling Ltd, have developed a similar system.

Maintenance

78

In the Sira system, a probe is inserted in the cylinder and rotated at high speed, projecting a spot of laser light onto the surface. Light reflected from the surface is picked up by the probe and passed to a photodetector. Simultaneously with the rotation of the probe, the cylinder is moved linearly along its axis at constant speed: hence the entire surface is scanned. The photodetector output is processed to give information about surface features such as cracks, scratches, and holes.

Each of the three days of the conference will have a different theme:

In 1968 it was estimated that the direct cost of engineering maintenance was £1,100m in the UK, and that consequential lost production reached a similar figure. The 4th European Maintenance Congress aims to help the maintenance manager cut costs.

Girling have tested the prototype system on automotive cylinders with varying surface roughness and surface characteristics. They were able to detect scratches, turning and tool withdrawal marks, and surface corrosion. The present system has a resolution of 100/am, but Sira suggest that it could

Conveyor idler bearings

Conveyor idler bearings operate in an environment heavily contaminated with rock dust and finely divided coal dust: many mines are wet. Ingress of abrasive slurries can cause hydrogen embrittlement and can lead to seizure. Fafnir, RHP and SKF have all developed bearings with nylon cages and increased tolerances to reduce the risk of seizure. All three are broadly

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Further information from Maintenance '78, Marks Hill, Tilford, Farnham, Surrey GU10 2A J, UK

readily be adapted to give a resolution as good as 25/am. They also suggest that the system could be used to inspect brake and engine cylinders, hydraulic systems, bearing surfaces, machine tools, and weaponry. Sira Institute Ltd, South Hill, Chislehurst, Kent BR7 5EH, UK

was achieved by increased ball size, a flexible nylon cage, and changes to track c o n f o r m i t y . . . "

Conveyor idler bearings in coal mining operations often work in wet, aggressive environments. It is estimated that 15 million conveyor idler bearings are currently used underground: bearings running near to seizure will run hot, introducing a risk of explosion. The risk of fire and explosion can be reduced by reducing the risk of seizure and by attempting to reduce the consequences. As reported in the October issue of Tribology International, the National Coal Board is investigating fire resistance greases: three manufacturers have developed conveyor idler bearings with increased seizure resistance.

'The Key Role of Maintenance in Future Industrial Efficiency', 'The Way Ahead through Maintenance Techniques', and 'International Maintenance Co-operation in Practice'. The sessions of most specific interest to tribologists are probably those on condition monitoring and on 'The maintenance/design interface'.

C o n v e y o r idler s h o w i n g S K F ' s 415705 bearing

similar in design, although Fafnir quote minor differences from SKF in cage design and RHP emphasise the metallurgical techniques used to obviate hydrogen embrittlement problems. SKF's bearing, designated 415705, is a single row deep groove bearing with metric boundary dimensions 25x52x 12mm. They state that: "The seize resistant property of the bearing

TRIBOLOGY international December 1977

In addition to the seize resistance SKF quote a number of other advantages. They state that: the larger ball size gives a 60% increase in load capacity, compared with their EE9 bearings; the bearing has approximately 50%0 greater tolerance to misalignment; and, when working in a hostile environment, the bearing has a lower frictional moment than its predecessor, giving a power saving of as much as 18%. The bearing has a 10-fold increase in service life compared with the previous bearing when exposed, without sealing or lubrication, to the free entry of. coal slurry and stone dust. Its greater capacity also gives an increase in fatigue life under normal lubrication conditions. SKF also estimate that use of the bearing may increase belt life by 15-20070; although several years service experience will be needed to verify this estimate.

SKF (UK) Ltd, Luton, Bedfordshire, UK. RHP, PO Box 7, Chelmsford CMI IPU, UK. Fafnir Bearing Company Ltd, Upper Villiers Street, Wolverhampton, Staffordshire, UK