tailieunhanh - Lubrication and Reliability Handbook 2010 Part 13

Tham khảo tài liệu 'lubrication and reliability handbook 2010 part 13', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | B22 Repair of plain bearings c Ultrasonic test This requires specialised equipment. A probe is held against the lined surface of the bearing and the echo pattern resulting from ultrasonic vibration of the probe is obser ved on a cathode ray tube. If the bond is satisfactory the echo occurs from the back of the shell or housing and its position is noted on the . If the bond is imperfect . discontinuous the echo occurs at the interface between lining and backing and the different position on the . is clearly observable. This is a very searching method on linings of appropriate thickness and will detect small local areas of poor bonding. However training of the operator in the use of the equipment and advice regarding suitable bearing sizes and lining thicknesses must be obtained from the equipment manufacturers. This method of test which is applicable to steel backed bearings is described in ISO 4386-1 BS 7585 Pt 1 . It is not very suitable for cast iron backed bearings because the cast iron dissipates the signal rather than reflecting it. For this material it is better to use a gamma ray source calibrated by the use of step wedges. d Galvanometer method An electric current is passed through the lining by probes pressed against the lining bore and the resistance between intermediate probes is measured on an ohmmeter. Discontinuities at the bond line cause a change of resistance. Again specialised equipment and operator training and advice are required but the method is searching and rapid within the scope laid down by the equipment manufacturers. 6 LOCAL REPAIR BY PATCHING OR SPRAYING In the case of large bearings localised repair of small areas of whitemetal which have cracked or broken out may be carried out by patching using stick whitemetal and a blowpipe or by spraying whitemetal into the cavity and remelting with a blowpipe. In both cases great care must be taken to avoid disruption of the bond in the vicinity of the affected area while ensuring .

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