Zollern BHW Criteria of Judgement

CRITERIA OF JUDGEMENT

Criteria of Judgement for main and connecting-rod plain bearings in medium-speed internal combustion engines in material combination steel/lead bronze/nickel dam/ electroplated layer steel/aluminium alloy

ZOLLERN BHW – your partner for plain bearings

We wish to support the work of our customers with this information brochure which is based upon our years of experience. It is a non-binding general indication and does not free from a check on the applicability of the plain bearings by a specialist.

The regular maintenance of lubricating oil, carried out carefully according to the guidelines given by the engine manufacturers, is essential for the reliability of the engine plain bearings. In general the following items have to be observed:

The following information is to assist the experienced service engineer in judging the reusability of engine plain bearings with normal wear behaviour.

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

In case of abnormal wear behaviour or in case of serious plain bearing damages it is absolutely necessary to consult the engine manufacturer, if necessary in cooperation with a plain bearing specialist.

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

To prevent abnormal wear behaviour the following instructions should be strictly observed.

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.

Lubricating Oil care With the use of heavy fuels containing corrosive substances, corrosive wear, as opposed to normal wear, 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.

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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.

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

Tips for Installation While refitting used bearings or fitting new bearing shells, the respective bearing temperature should be checked by touch against the neighbouring bearing which has remained in place. This check should be carried out after about 30 minutes of idling and again after about 5 hours of operation. A comparative measurement with an electrical contact thermometer is safer. The temperature difference between the individual bearings should not exceed 5 °C. While fitting bearings, the instructions of the engine manufacturer must be observed. Extreme cleanliness is very essential. As experience shows a considerable amount of bearing damages are the result of faulty and careless fitting of the bearings to the engine. The criteria of judgement refer to trimetal plain bearings made from steel/lead bronze materials. These guidelines can also be applied to trimetal plain bearings made from steel/aluminium materials. The latter have a considerably thicker intermediate nickel layer between the electroplated running layer and the aluminium alloy. Due to the extreme hardness of the nickel layer extra caution is advised.

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Material: Steel/lead bronze/nickel dam/electroplated layer Cast coated trimetal plain bearings of the material combination steel/lead bronze/nickel dam/electroplated layer have proved well effective for main and connecting rod bearings of medium-speed internal combustion engines from low up to high degrees of bearing load. In particular the material specifications steel C10 (or comparable)/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: Electroplated running layer PbSnCu resp. SnSb Nickel dam Ni Lead bronze interlayer G-CuPb22Sn Steel back

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

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CRITERIA OF JUDGEMENT for main and connecting-rod plain bearings in medium-speed internal combustion engines Material: Steel/lead bronze/nickel dam/electroplated layer

Evaluation criteria for bearing shells Shape and degree of exposure of nickel dam is an essential criterion for the assessment of the condition of wear. It is often very difficult to differentiate between the harder nickel dam and the softer electroplated running layer. 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 mm length. If no chip comes off, then the nickel dam is exposed. This method requires some experience. Generally speaking, the larger the exposed nickel dam area the greater the risk. Exposed nickel dam or lead bronze areas showing already at 5.000 –10.000 hours of operation indicate abnormal 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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Material: Steel/lead bronze/nickel dam/electroplated layer

Figure 1

Figure 2

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 the bearing; the shells can be re-used.

Figure 3

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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CRITERIA OF JUDGEMENT for main and connecting-rod plain bearings in medium-speed internal combustion engines Material: Steel/lead bronze/nickel dam/electroplated layer

Figure 4

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

A) B) C) D)

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

Figure 5

Figure 6

In this state of wear the bearing shell may be further used. The following zones are visible: A) Nickel dam visible in a small area B) Bearing metal lead bronze locally exposed by edge wear C) 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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Material: Steel/lead bronze/nickel dam/electroplated layer

Figure 7

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 of the bearing shell, as in Fig. 4 and 6: The shell must be replaced because it has no “running-in” capability.

Figure 8

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

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CRITERIA OF JUDGEMENT for main and connecting-rod plain bearings in medium-speed internal combustion engines Material: Steel/aluminium alloy without a third layer Roll-bonded bimetal plain bearings of the material combination steel/aluminium alloy have proved well effective for the main and connecting rod bearings of medium-speed internal combustion engines from low up to medium degrees of bearing load. In particular the material specification steel C10/aluminium alloy AlSn20 corresponding to Z-BHW 74 is applied.

Sketch showing bearing design:

Aluminium layer AlSn20 Aluminium bonding layer Al 99,7 Steel back

The high-grade aluminium bonding layer, shown in the basic sketch, is necessary to obtain a safe compound of steel and aluminium alloy. Bimetal bearings made from steel/aluminium alloy are all around protected against corrosive attacks during transport and storage by a special slushing oil, which has to be removed by appropriate means before assembling the bearing shell.

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Material: Steel/aluminium alloy without a third layer

Evaluation criteria for bearing shells Judging the wear degree of a bimetal bearing shell with normal wear behaviour visually is impossible. Contrary to trimetal bearings from steel/lead bronze/nickel dam/electroplated running layer bimetal bearings from steel/aluminium alloy include no visual indicators, which allow to judge the wear degree with the aid of the running layer colouring when knowing the thickness of the layers in new state. Due to this fact the wear rate of a bimetal bearing has to be detected by either measuring the total wall thickness or by measuring the actual bearing running clearance and comparison of these values with those in new state. The bearing shell has to be replaced, if the wear limits given by the engine manufacturer are reached or have been exceeded already, or if these wear limits may be reached or may have been exceeded by the time of the next bearing inspection. The engine manufacturer’s instructions have to be strictly observed. The following illustrations are to support you in judging abnormal wear behaviour. It is well experienced that in most cases abnormal wear is caused by filtering the lubricating oil insufficiently.

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CRITERIA OF JUDGEMENT for main and connecting-rod plain bearings in medium-speed internal combustion engines Material: Steel/aluminium alloy without a third layer

Figure 1

➀

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 no considerable effect on the further operating reliability of the plain bearing. This bearing shell may be reused.

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Material: Steel/aluminium alloy without a third layer

Figure 2

Figure 3 Detail of Figure No. 2

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

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CRITERIA OF JUDGEMENT for main and connecting-rod plain bearings in medium-speed internal combustion engines Material: Steel/aluminium alloy without a third layer

Figure 4

Figure 5 Detail of Figure No. 4

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.

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Material: Steel/aluminium alloy without a third layer

Figure 6

The contact reflection shows highly loaded areas at the bearing edges with traces of corrosion within the running 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.

Figure 7

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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CRITERIA OF JUDGEMENT for main and connecting-rod plain bearings in medium-speed internal combustion engines Material: Steel/aluminium alloy without a third layer

Figure 8

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 the bottom of the cracked-off area indicates good bonding of the aluminium alloy to the steel-back. This bearing shell is not reusable.

Figure 9

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 alloy to the steel back. This bearing shell is not reusable.

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ZOLLERN BHW Gleitlager GmbH + Co. KG Alte Leipziger Straße 117–118 D-38124 Braunschweig Phone +49-531-26 05-0 Fax +49-531-26 05-300 [email protected] www.zollern-bhw.com

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

Thick-Walled Journal- and Thrust Plain Bearings

Tilting Pad Journal- and Thrust Plain Bearings Pads for Tilting Pad Journal- and Thrust Bearings

Diameter ranges of plain bearings made by ZOLLERN BHW Gleitlager GmbH + Co. KG Plain Bearings Type Bearing shells Bushings Thrust washers Tilting pad thrust bearings Tilting pad journal bearings Thrust pads for tilting pad bearings Repair work Housing plain bearings 1)

Shaft diameter

2)

Steel/Lead Bronze 80– 800 80– 800 100– 800 70–1600 50– 5001) 20– 6002) – –

Outside Diameter for Materials in mm: Steel/Babbitt Steel/Aluminium 80–1600 80–800 80–1600 – 100–1600 100–500 70–1600 – 50– 5001) – 20– 6002) – 150–1600 – 90– 3001) –

Edge length

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

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 represent that 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 the potential 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 subsequent notice. 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 on ZOLLERN BHW Gleitlager GmbH + Co. KG All rights reserved. © ZOLLERN BHW Gleitlager GmbH + Co. KG 2001 TKB 0401 1.0 E-7