| 摘要 |
PURPOSE:To prevent contact area and contact pressure from being changed because of wear of an earth pad by decreasing the cross section area of the earth pad than the cross section area of an edge of a spindle, adopting a type of material of the earth pad subject to wear than that of the spindle and using a coil spring having a smaller spring constant than that of a plate spring. CONSTITUTION:The press contact part of the earth pad 8 wears as time is elapsed by the turning of the spindle 3. Since the cross section of the earth pad 8 is formed smaller than the cross section area of the edge of the spindle 3, the contact area is unchanged even when being subject to wear. Since the type of material of the earth pad 8 is selected to be worn easily more than that of the spindle 3, the spindle 3 hardly wears and only the earth pad 8 wears practically and the change in the contact state due to the degree of wear is less. Since the spring constant of the coil spring 10 is small, the change in the pressure of the earth pad 8 onto the edge of the spindle 3 due to the wear of the earth pad 8 is less. |
