| 摘要 |
<p>The machine includes two pairs of clamps, each pair being used to hold one workpiece, e.g. a rail by jaws fed with electric welding current. During the initial flash, one pair of jaws can be moved towards the other by a pair of hydraulic jacks. The jacks are fed with hydraulic fluid at a controlled pressure by at least one distributor and a flowmeter ensuring a linear variation in the flow of the hydraulic fluid to the jacks. The linear variation in fluid flow is achieved by using an auxiliary hydraulic cylinder provided with adjustable non- return valves on both sides of its piston. The two rails being welded together can be moved towards each other at a sufficiently low speed, e.g. 0.5mm/second, at the start of welding, and can then be moved at an increased speed, e.g. 1mm/second, to produce a constant distance during the flash.</p> |
