Document Ne7GXJbRG4Xv3KrxDvZ00qOjE

WELDING AND CUTTING \ er are loose, or if ground connections are poor If a holder of the correct size for the electrode cannot be used, an extra holder should be provided so that one can cool while the other is in use Dipping hot elec trode holders tn water should be prohibited. On light or medium heavy work, where light, extremely flexible cables are used, holders may be attached directly to the work lead running to the machine On heavier work, welders generally prefer a short length, which is more flexible than the mam work lead Properly insulated cables of weight and flexibility which will not incon venience the welder are available. Machine welding Arc welding may also be done automati cally or semiautomabcally to increase the speed of welding and provide more uniform weld quality Machine weldmg is especially efficient for long welds or where a high rate or production is involved and the work can be figged The rate of electrode feed and arc length are controlled by mechanical or electrical means If speed of travel or feed of the work is controlled manually, the operation is semi automatic If the work is fed or the arc traverses the work automatically, the opera tion is automabc Insulabon of current-carrying parts, ca bles, etc, applies to machine weldmg as well as to manual weldmg Mechanical power-transmission apparatus, such as gears, shaftings, couplings, and clutches, and other moving parts to which operators may be exposed should be guard ed (see Chapter 22, "Principles of Guard ing and Transmission Guards") Protection against electric shock Although open-circuit voltages on stand ard arc-welding units are not high com pared to those of other processes, they can not be neglected as a potential hazard Nor mally, the work setup is such that the work is grounded, and unless care is exercised, the welder or operator can easily become grounded The voltage between the electrode holder and the ground, during the "off" arc or "no load" penod, is the open circuit voltage. Unless the welder or operator is properly instructed and uses the equipment provided for his proteebon, he can become exposed to this voltage while changing electrodes, setting up work, or changing working posibon. The danger is particularly great in hot weather when he is sweaty He should develop the habit of keeping his body insulated from both the work and the metal electrode and holder He should never permit the bare metal part of an elec trode, the electrode insulabon, or any metal part of the electrode holder to touch either his bare skm or any wet covering on his body. Consistent use of well-insulated electrode holders and cables, dry clothing on the hands and body, and insulabon from ground will be helpful m preventing contact Some specific precaubons for prevenbon of electric shock are 1 In confined places, cover or arrange ca bles to prevent contact with falling sparks 2 Never change electrodes with bare hands or wet gloves, or when standing on wet floors or grounded surfaces 3 Ground the frames of weldmg units, portable or stationary, in accordance with the National Electncal Code With a small weldmg unit, a primary cable con taining an extra conductor, one end of which is attached to the frame of the welding unit, can be used By means of the proper polarized plug, this ground connecbon can be earned back to the permanently grounded connecbon in the receptacle of the power supply 4 Arrange receptacles of power cables for portable weldmg umts so that it is im possible to remove the plug without opening the power supply switch, or use plugs and receptacles which have been approved to break full load circuits of the unit 5 If a cable (either work lead or electrode lead) becomes worn, exposing bare con ductors, cover the exposed portion with rubber, plasbc, or friction tape equivalent to the cable covering 6. Keep welding cables dry and free of grease and od to prevent premature breakdown of the insulabon 7. Suspend cables on substanbal overhead supports if the cables must be run some 29-18