Welding; a practical treatise on the applications of electric, gas, and thermit welding to manufacturing and repair work by Cravens George W

Author:Cravens, George W
Language: eng
Format: epub
Tags: Welding
Publisher: Chicago, American technical society
Published: 1921-03-25T05:00:00+00:00

WELDING

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heads, cause heating. There is no danger of a shock from the welding circuit because of the low voltage, but the line, or primary side of the machine, should be avoided, if possible, or handled with proper precaution.

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• Heating of Parts. If the machine has been properly installed, there should be no trouble so long as the cooling water flows through the welding dies, Fig. 53, ami everything is kept clean and all connections tight. The only moving parts on most contact welders are the clamps and jaws, Fig. 54, and these are easily watched; the transformer is so simple it should never get out of order except in cases of accident. The switches should be

enclosed to prevent accidental contact, and ordinarily they are automatic and out of reach.

ELECTRO-PERCUSSIVE PROCESS

Development of Method. The development of electro-percussive or percussion welding began in 1905 while L. W. Chubb, of the Westinghouse Electric & Manufacturing Company, was experimenting with electrolytic condensers. He found that wires of aluminum or copper could be attached to plates of these and other metals if subjected to the action of the discharge from the condensers at the instant of contact. Joints formed in this way were not strong mechanically, so further experiments resulted in the development of the device shown in Fig. 55, which looks very much like a miniature pile driver. Action. The action also is very much like that of a pile driver. The apparatus consists of a stationary base and terminal clamp, uprights to guide a moving terminal block and an upper or moving clamp which drops down to perform the operation. One of the wires or parts to be welded is clamped Tie- 55. Portable Percussion in the lower terminal and the other part in the upper terminal. Suitable electrical connections are made, and the upper clamp drops down and brings the two parts into contact and allows the condenser to discharge through them, thereby fusing the metals instantly and welding them.

This is the only type of butt welder which uses direct current, and for even small wires the current may be several hundred amperes momentarily. Satisfactory operation depends upon the capacity of the condenser, velocity and force of impact when bringing parts together, voltage used, resistance and inductance inserted in the circuit. All these factors may easily be varied to suit the job in hand. Although a relatively large current is developed during the discharge, the duration of the impact is for

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