Zollern BHW Criteria of Judgement

C R I T E R I A O F J U D G E M E N T

ZOLLERN BHW – your partner for plain bearings

Criteria of Judgementfor main and connecting-rod plain

bearings in medium-speedinternal combustion engines

in material combinationsteel/lead bronze/nickel dam/

electroplated layersteel/aluminium alloy

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We wish to support the work of our customers with thisinformation brochure which is based upon our years ofexperience. It is a non-binding general indication anddoes not free from a check on the applicability of theplain bearings by a specialist.

The following information is to assist the experiencedservice engineer in judging the reusability of engineplain bearings with normal wear behaviour.

In case of abnormal wear behaviour or in case ofserious plain bearing damages it is absolutelynecessary to consult the engine manufacturer, ifnecessary in cooperation with a plain bearing specialist.

To prevent abnormal wear behaviour the followinginstructions should be strictly observed.

Lubricating Oil careWith the use of heavy fuels containing corrosivesubstances, corrosive wear, as opposed to normalwear, may appear more frequently.

The following factors are of importance:

1. Fuel quality, in which the sulphur content plays an important part.

2. Maintenance of the lubricating oil in the circuit, in which the maintenance of the lubricating oil filter, the oil separation and the oil analysis at intervals are most important.

3. The water content in the lubricating oil.

4. Observance of the lubricating oil temperature before inlet into the engine, as specified by the engine manufacturer.

The regular maintenance of lubricating oil, carried outcarefully according to the guidelines given by theengine manufacturers, is essential for the reliability ofthe engine plain bearings. In general the following itemshave to be observed:

1. Separation temperature 90°–95°C at a load of approximately 20% of nominal load of the separator.

2. If the oil becomes increasingly dirty, indicated by more frequent cleaning intervals of the automatic filter, the cause must be traced.

3. Regular checks of all filter elements for faultless condition. All the sieve elements must be free of any kind of damages. The often held opinion that damage to an individual sieve is harmless is not correct, as the sieve elements are working parallel.

4. Filter cleaning must be done carefully in order to avoid dirty oil getting into the clean oil side while taking out the filter elements. By all means the oil content in the filter housing must be drained off before taking out the filter elements according to the manufacturer’s instruction.

5. The installation of an additional safety sieve filter in the oil circuit just before the oil enters the engine has proven to be useful in helping to avoid damages in case of failures of the main filters. Please ask engine manufacturers for advice.


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Tips for InstallationWhile refitting used bearings or fitting new bearingshells, the respective bearing temperature should bechecked by touch against the neighbouring bearingwhich has remained in place.

This check should be carried out after about 30 minutes of idling and again after about 5 hours ofoperation.

A comparative measurement with an electrical contactthermometer is safer. The temperature difference between the individual bearings should not exceed 5°C.

While fitting bearings, the instructions of the enginemanufacturer must be observed.Extreme cleanliness is very essential.

As experience shows a considerable amount of bearingdamages are the result of faulty and careless fitting ofthe bearings to the engine.

The criteria of judgement refer to trimetal plain bearingsmade from steel/lead bronze materials. These guidelines can also be applied to trimetal plainbearings made from steel/aluminium materials.

The latter have a considerably thicker intermediatenickel layer between the electroplated running layer andthe aluminium alloy. Due to the extreme hardness of thenickel layer extra caution is advised.

for main and connecting-rod plain bearings in medium-speed internal combustion engines

Material: Steel/lead bronze/nickel dam/electroplated layer

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Cast coated trimetal plain bearings of the materialcombination steel/lead bronze/nickel dam/electroplatedlayer have proved well effective for main andconnecting rod bearings of medium-speed internalcombustion engines from low up to high degrees ofbearing load.

In particular the material specifications steel C10 (orcomparable)/cast coated lead bronze G-CuPb22Sn/nickel dam with electroplated running layers are applied.

PbSn10Cu2 for normal demands corresponding to Z-BHW 40

SnSb7 for increased demands on corrosion resistance corresponding to Z-BHW 87

PbSn14Cu8 for increased demands on corrosion resistance combined with increased demands on fatigue resistance corresponding to Z-BHW XX

Sketch showing bearing design:

Trimetal bearings made from steel/lead bronze/nickeldam/electroplated running layer are protected againstcorrosive attacks during transport and storage by anoverall Sn-flash or an overall PbSn-flash. This flashmust not be removed, when assembling the bearing orwhen putting it into service.

Electroplated running layerPbSnCu resp. SnSb

Nickel damNi

Lead bronze interlayerG-CuPb22Sn

Steel back


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Evaluation criteria for bearing shellsShape and degree of exposure of nickel dam is anessential criterion for the assessment of the conditionof wear.

It is often very difficult to differentiate between theharder nickel dam and the softer electroplated runninglayer. The so-called “knife test” may be useful, notwithstanding whether the nickel dam is exposed.

Take a small sharp knife and try to scrape off carefully,by very light pressure, a tiny chip of about 3 mmlength.

If no chip comes off, then the nickel dam is exposed.This method requires some experience.

Generally speaking, the larger the exposed nickel damarea the greater the risk.Exposed nickel dam or lead bronze areas showingalready at 5.000–10.000 hours of operation indicateabnormal operating conditions mainly due to:

a) insufficient filtration of the lubricating oil (scoring by foreign particles)

b) corrosive attacks on the electroplated running layer (large areas of wear)

Both phenomena may appear simultaneously, (Fig. Nos. 7+8).

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Figure 1

Figure 2

Figure 3

Both the bearing shells show a faultless and non-objectionable “running picture”.The contact reflection of the shaft is well marked in the center area.The electroplated running layer is completely preserved.There are no signs of corrosive attack.The foreign body score, as visible in Fig. 2, has no significant influence on the operational reliability of thebearing; the shells can be re-used.

A) Dark area: remains of electroplated running layer.This “running picture” shows a normal state of wear.There is no corrosive attack.The few scores caused by foreign particles are of no consequence.The electroplated running layer is only preserved in about 70% of the contact area of the shell.The bearing shell is only conditionally fit for use because of its limited running-in properties.


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Figure 4

Figure 5

Figure 6

The “running picture” shows normalwear after about 39.000 hours.The bearing shell must be replaced.The following zones are visible:

A) Bearing metal exposed by wear (normal process)B) Nickel dam zone normally wornC) Diffusion zone. Darker colouring due to tin migrationD) No sign of wear on electroplated running layer

In this state of wear the bearing shell may be further used. The following zones are visible:A) Nickel dam visible in a small areaB) Bearing metal lead bronze locally exposed by edge wearC) Electroplated running layer is dark due to tin migration. Slight corrosive attack in the diffusion zone of the

shell on Fig. 5.D) No sign of wear on electroplated running layer.

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Figure 7

Figure 8

The electroplated running layer is almost completely worn out by corrosion and mechanical wear. Large areas of the nickel dam are visible. The nickel dam does not show any transitional phase in the wear pattern ofthe bearing shell, as in Fig. 4 and 6:The shell must be replaced because it has no “running-in” capability.

This picture also shows a large area where the electroplated running layer is worn out by corrosion andmechanical wear. The nickel dam is exposed.This shell must also be replaced because it has no “running-in” capability.

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Material: Steel/aluminium alloy without a third layer

Roll-bonded bimetal plain bearings of the materialcombination steel/aluminium alloy have proved welleffective for the main and connecting rod bearings ofmedium-speed internal combustion engines from lowup to medium degrees of bearing load.

In particular the material specification steel C10/aluminium alloy AlSn20 corresponding to Z-BHW 74 is applied.

Sketch showingbearing design:

The high-grade aluminium bonding layer, shown in thebasic sketch, is necessary to obtain a safe compoundof steel and aluminium alloy.

Bimetal bearings made from steel/aluminium alloy areall around protected against corrosive attacks duringtransport and storage by a special slushing oil, whichhas to be removed by appropriate means beforeassembling the bearing shell.

Aluminium layerAlSn20

Aluminium bonding layerAl99,7

Steel back

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Evaluation criteria for bearing shellsJudging the wear degree of a bimetal bearing shell withnormal wear behaviour visually is impossible.Contrary to trimetal bearings from steel/leadbronze/nickel dam/electroplated running layer bimetalbearings from steel/aluminium alloy include no visualindicators, which allow to judge the wear degree withthe aid of the running layer colouring when knowing thethickness of the layers in new state.

Due to this fact the wear rate of a bimetal bearing hasto be detected by either measuring the total wallthickness or by measuring the actual bearing runningclearance and comparison of these values with those innew state.

The bearing shell has to be replaced, if the wear limitsgiven by the engine manufacturer are reached or havebeen exceeded already, or if these wear limits may bereached or may have been exceeded by the time of thenext bearing inspection. The engine manufacturer’sinstructions have to be strictly observed.

The following illustrations are to support you in judgingabnormal wear behaviour. It is well experienced that inmost cases abnormal wear is caused by filtering thelubricating oil insufficiently.

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Figure 1

The contact reflection is developed uniformly, covering the whole bearing width.It is well experienced that the dirt score no. ➀ , caused by a foreign particle within the lubricating oil, has noconsiderable effect on the further operating reliability of the plain bearing.This bearing shell may be reused.

➀


Figure 2

Figure 3

The contact reflection is developed uniformly, covering the whole bearing width.This bearing shell may be reused.

Detail ofFigure No. 2

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Figure 4

Figure 5

The contact reflection is developed uniformly, covering the whole bearing width.The radially extended scores are caused by minute solid matter particles included in the lubricating oil.In case the depth of these scores is neither measurable nor tangible, the bearing shell may be re-used.In case the depth of these scores reaches or exceeds the dimension of the lubricating film thickness, the bearing shell has to be replaced.

Detail ofFigure No. 4


Figure 6

Figure 7

The contact reflection shows highly loaded areas at the bearing edges with traces of corrosion within therunning layer made from an aluminium alloy.This bearing shell is not reusable.The cause of this plain bearing damage has to be determined and eliminated.

The contact reflection shows a large damaged area with different degrees of seizure.This bearing shell is not reusable.The cause of this plain bearing damage has to be determined and eliminated.

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Figure 8

Figure 9

This bearing shell shows cracked-off bearing metal due to fatigue of the aluminium alloy running layer.Some pieces of cracked-off bearing metal are still visible in the fatigue area. The surface structure at thebottom of the cracked-off area indicates good bonding of the aluminium alloy to the steel-back.This bearing shell is not reusable.

This bearing shell shows cracked-off bearing metal due to fatigue of the aluminium alloy running layer. The surface structure at the bottom of the cracked-off area indicates good bonding of the aluminium alloyto the steel back. This bearing shell is not reusable.

This brochure provides an introduction to some of our products. lt does not include any instructions or directions for use of our products in specific applications, nor is it intended to representthat our products are appropriate for any specific use or application. Prior to using any of our products, proper investigation, including application-specific tests, should be conducted by thepotential purchaser/user. Our products are subject to constant technical alterations and developments, and thus the statements contained in this brochure are always subject to modification without prior or subsequentnotice.Only provisions, specifications, drawings, data and statements expressly set forth in contracts between ZOLLERN BHW Gleitlager GmbH + Co. KG and our customers shall be binding onZOLLERN BHW Gleitlager GmbH + Co. KGAll rights reserved. © ZOLLERN BHW Gleitlager GmbH + Co. KG 2001 TKB 0401 1.0 E-7

We supply:Plain Bearings for large-sized Diesel engines, compressors and other industrial applications made of compound bearing metals.

Thin-Walled Plain Bearing Shells Bushings

ZOLLERN BHW Gleitlager GmbH + Co. KG

Alte Leipziger Straße 117–118D-38124 BraunschweigPhone +49-531-26 05-0Fax +49-531-26 [email protected]

Thick-Walled Journal- and Thrust Plain Bearings Tilting Pad Journal- and Thrust Plain BearingsPads for Tilting Pad Journal- and Thrust Bearings

Diameter ranges of plain bearings made by ZOLLERN BHW Gleitlager GmbH + Co. KG

Plain Bearings Outside Diameter for Materials in mm:Type Steel/Lead Bronze Steel/Babbitt Steel/AluminiumBearing shells 80– 800 80–1600 80–800Bushings 80– 800 80–1600 –Thrust washers 100– 800 100–1600 100–500Tilting pad thrust bearings 70–1600 70–1600 –Tilting pad journal bearings 50– 5001) 50– 5001) –Thrust pads for tilting pad bearings 20– 6002) 20– 6002) –Repair work – 150–1600 –Housing plain bearings – 90– 3001) –

1) Shaft diameter 2) Edge length

We supply also: Machine elements made of compound materials steel/lead bronze or steel/babbitt:spherical shells, planetary wheel pinscastings of CuPbSn-, CuSn- and CuCr-alloys

Zollern BHW Criteria of Judgement

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