I want arc welding Experiment (theory, operation, fig,precaution)
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INTRODUCTION
The electric arc welder remains one of our most useful and timesaving pieces of shop equipment. Almost every farm, ranch, and Vocational Agriculture shop is equipped with one or more welders which are used for fabrication, repair, and/or educational programs. Most of these welders are typically AC/DC, 240 volt transformer types using electricity as the energy source. Portable welders are of the diesel/gasoline engine powered type. Properly installed and used the arc welder is very safe, but if used improperly the operator can be exposed to a number of hazards including toxic fumes, dusts, burns, fires, explosions, electric shock, radiation, noise, and heat stress. Any of these hazards can cause injury or death. By following suggestions and guidelines in this pamphlet the risks can be greatly minimized.
SELECTING THE ARC WELDER
When purchasing an arc welder you can be assured of design safety if the unit complies with National Electric Manufacturers Association (NEMA) standards or the safety standards for arc welders as determined by the Underwriters Laboratories (UL). Be sure that the welder you purchase carries the seal of approval of one of these organizations.
INSTALLING THE ARC WELDER
Prior to installing the arc welder you should determine if your present electrical system is adequate to handle the increased load required by the welder. Your local power supplier or a qualified electrician can assist you in determining this. It is very important for your safety to install the welder in compliance with State of Arizona, Occupational Safety and Health Administration (AOSHA) regulations and the National Electric Code (NEC) by a qualified electrician. Failure to do so could cause fire, a ground fault, or equipment failure. The following rules are not a complete list but are especially important guidelines which should be adhered to:
The frame or case of the welder shall be properly grounded.
A safety-type disconnecting switch or controller shall be located near the machine (See Figure 1).
The welder or welders shall be protected by a properly sized fuse or circuit breaker on an independent circuit.
VENTILATION
The welder should be located in an area with adequate ventilation. In general, when welding is being done on metals not considered hazardous, a ventilation system that will move a minimum of 2000 cubic feet per minute (CFM) of air per welder is satisfactory. However, many materials are considered very hazardous and should be welded only in adequately ventilated areas to prevent the accumulation of toxic materials or to eliminate possible oxygen deficiency not only to the operator but to others in the immediate vicinity. Such ventilation should be supplied by an exhaust system located as close to the work as possible (See Figure 2). When welding or cutting metals with hazardous coatings such as galvanized metal the operator should use a supplied-air type respirator or a respirator specially designed to filter the specific metal fume. Materials included in the very hazardous category are welding rod fluxes, coverings, or other materials containing fluorine compounds, zinc, lead, beryllium, admium, and mercury. Some cleaning and degreasing compounds as well as the metals they were cleaned with are also hazardous. Always follow the manufacturers precautions before welding or cutting in the presence of these materials.
FIRE PREVENTION
The arc welder is capable of producing temperatures in excess of 10,000 degrees F.,therefore it is important that the workplace be made firesafe. This can be accomplished by using metal sheets or fire resistant curtains as fire barriers. The floor should be concrete or another fire resistant material. Cracks in the floor should be filled to prevent sparks and hot metal from entering. When work cannot be moved to a firesafe area then the area should be made safe by removing or protecting combustibles from ignition sources. In certain welding situations it may be necessary to ask someone to watch for fires that could go undetected until the welder has finished the job.
Suitable fire extinguishing equipment such as buckets of sand or a dry chemical extinguisher of the ABC type should be readily available. The extinguisher should be large enough for the situation with a 10# size adequate for most farm and school shops.