On November 8, 2010, Jimin industry and Trade Co., Ltd. accepted the sale of imported Miba bearing pads by a customer in Weifang, and several serious accidents occurred, such as serious bearing pad strain, rolling pad and bearing pad delamination. Since the customer did not provide all the damaged parts, we can only organize relevant technicians to analyze the cause of the accident according to the damaged bearing bush provided by the customer of WD615 bearing:
Several problems can be clearly seen from the above figure:
1) The bearing bush has bilateral side load, and obvious wear marks can be seen near the fillet of the journal;
2) The surface (middle) of the bearing bush at the oil hole of the crankshaft connecting rod is seriously strained, and the coating of the bearing bush is torn after bonding in some parts;
3) There are traces of fretting corrosion (insufficient interference) in varying degrees on the back of the bearing bush.
To sum up, the main possible factors for serious strain of single cylinder bearing bush of this engine are:
For this engine, if the crankshaft with unqualified journal size and the chamfer machining deviation of crankshaft journal lubricating oil passage are replaced, if the relevant detailed measurement of connecting rod and crankshaft connecting rod journal is not made during the replacement of bearing bush, the bearing bush has poor oil film formation and local overload during operation due to the large deformation of connecting rod and crankshaft, Such accidents will occur! It should be noted that detailed cleaning and data measurement must be carried out, especially in the process of matching new tiles with old engines.
Generally, the rolling of bearing bush occurs when there is no shortage of oil, but because there is a certain out of tolerance in the fitting clearance of bearing bush, some journal surfaces are instantaneously bonded with the bearing bush after rapid wear, resulting in diffusive adhesion. Later, the bearing bush has been locked due to the overload in the project of bearing bush positioning groove working under the condition of insufficient interference of bearing bush, If the vehicle is not stopped in time, the steel back is exposed after all the coating surfaces of the bearing bush are stripped, resulting in full wear. This phenomenon is commonly known as rolling bush.
From the macroscopic trace on the back of the bearing bush, the high temperature phenomenon occurred in the middle of the bearing bush, because detailed maintenance parameters and instructions were not provided. In many similar accidents, the main reasons were due to improper fit clearance of the bearing bush and improper preload of connecting rod bol
In this accident, several phenomena occurred in the bearing bush. One is that the bearing bush has bilateral side load and middle wear; One is the insufficient interference on the back of the bearing bush and the falling off of the alloy layer of the bearing bush (commonly known as peeling). One of the main influencing factors of the falling off of the alloy layer is that the peak pressure of the oil film increases after the matching gap is damaged, resulting in the falling off of the alloy layer after fatigue overload, early damage and even bad accidents such as Bush burning.
Engine maintenance is a comprehensive technical measurement process. Failure to do any step may cause early failure of parts. Among the three accidents, the typical one is the unqualified maintenance process, which is not carefully cleaned and measured; Blindly think that as long as it is installed, it can work normally, which is a big taboo in maintenance! In the above three accidents, from a macro point of view, ordinary maintenance workers may only see the bearing bush damage, which actually contains a lot of hidden dangers!
Is it time for Chinese maintenance mode to be supervised?
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