柱塞是(图1)拖拉机燃油泵中主要零件之一。在磨削该零件头部　8毫米的外圆及　15.5毫米凸肩端面时,其裂纹常发生在柱塞凸肩的凹槽部分(图2)。由于裂纹而使工件的报废率有时达60%左右(用磁力探伤器检查)。柱塞凸肩处在比较复杂及不利的条件下工作,如果零件有裂纹,在受反复载荷作 The plunger is one of the main components of a tractor fuel pump (Figure 1). Cracks often occur in the groove portion of the shoulder of the plunger (Figure 2) when grinding the 8 mm OD and 15.5 mm shoulder faces of the head of the part. Due to cracks and the workpiece rejection rate sometimes up to 60% (with a magnetic flaw detector inspection). Plunger shoulder in the more complex and unfavorable conditions, if the parts are cracked, under repeated load