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Troubleshooting the "Seizing" Fault Between the Pump Plunger and Cylinder Block of an Excavator

2013-07-16 540 0人评论
     An HE-280 excavator, after overhaul and replacement of the hydraulic pump's cylinder block and plungers, had a hydraulic pump that would not work and emitted abnormal noise. Upon disassembly and inspection, the plungers were found stuck to the cylinder block in a "seized" condition. Metallographic analysis of the cylinder block and plungers confirmed that residual austenite had transformed into martensite, and the lower the temperature, the greater the amount of transformation. In cold seasons, the residual transformation is completed within a very short time, causing the plungers to "seize" due to their instantaneous volume increase. To address this, a special measuring tool can be used to measure the fit clearance between the hydraulic pump's cylinder block and plungers at room temperature; the cylinder block and plungers are separately subjected to cold treatment, i.e., placed at -50 to -60°C, and removed after 30 min; the plungers are ground on a grinding machine to the fit dimensions at room temperature; the plunger surfaces are laser-quenched; and the plunger surfaces are further polished with a special metal polishing paste. After reassembly, the fault was eliminated.
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