| 摘要 |
<p>A contact tube guides and supplies current to the wire electrode in an arc welding machine. The tube is preferably copper, with a central bore through which the wire passes. The end of the tube facing the arc, and part at least of the sides, is covered by a protective sheath. This sheath is thermally and electrically insulating, and molten metal splashed from the weld pool does not adhere to it. The sheath is preformed from fibreglass based material, coated with a silicone based binder, and held in place by silicone glue. Protecting the outer end of the contact tube greatly reduces problems due to the build-up of splashed weld metal. This can interrupt the regular advance of the welding wire, and restrict the flow of a surrounding gas shield. Sec. arcs can also be set up between built-up metal and the part being welded. Preventing these means that contact tubes have to be changed less frequently, giving a useful cost saving.</p> |
