Aside from protecting your investment in welding equipment, perhaps the best argument for a program of ongoing and thorough maintenance is operator safety. This article covers the most common safety issues to be aware of, but does not cover all of them. Always read and follow the safety information in the operator's manual or contact the manufacturing company when in doubt.
There are three key areas that a conscientious maintenance program should focus on:
1. The power source and primary power line grounding the equipmentWelders must be concerned at all times about the possibility of electrical shock. Wet working conditions must be avoided, because water is an excellent conductor and electricity will always follow the path of least resistance. Even a person's perspiration can lower the body's resistance to electrical shock. Standing on a dry rubber mat or, when welding outdoors, standing on a dry board is always advisable. Poor connections and bare spots on cables further increase the possibility of electrical shock, and therefore, daily inspection of these items is also recommended.
Aside from these more obvious shock hazards, equipment operators should routinely inspect for proper ground connections. A proper ground connection is always necessary because it provides a safety connection from a welding machine frame to the earth. Connections typically used for grounding an engine-driven welding machine include a cable connected from a ground stud on the welding machine to a metal stake placed in the ground.
The workpiece being welded and the frame or chassis of all electrically powered machines must be connected to a good electrical ground. This can be accomplished by connecting it to a properly grounded building frame or other appropriate ground. Chains, wire ropes, cranes, hoists and elevators must never be used as grounding connectors.
The work lead is not the grounding lead. The work lead connects the work terminal on the power source to the workpiece. A separate lead is required to ground the workpiece or power source.
When arc welding equipment is properly grounded according to the National Electrical Code, and to ANSI Z49.1 "Safety in Welding and Cutting" standards, a voltage may safely exist between the electrode and any conducting object. Examples of conducting objects include buildings, power tools, work benches, welding power source cases and workpieces. Never touch the electrode and any metal object unless the welding power source is off.
When installing a welding system, connect the frames of each unit such as welding power source, control, work table and water circulator to the building ground. Conductors must be adequate to carry ground currents safely. Equipment made electrically hot by stray current may deliver a powerful shock. Never ground to an electrical conduit, or to a pipe carrying any gas or flammable liquid such as oil or fuel.
For a three-phase connection, check phase requirements of equipment before installing. If only three-phase power is available, connect single-phase equipment to only two wires of the three-phase line. Do not connect the equipment ground lead to the third (live) wire, or the equipment will become electrically hot.
Also, before welding, check the ground for continuity. Make sure conductors are touching bare metal of equipment frames at connections.
If a line cord with a ground lead is provided with the equipment for connection to a switchbox, connect the ground lead to the grounded switchbox. If a three-prong plug is added for connection to a grounded mating receptacle, the ground lead must be connected to the ground prong only. If the line cord comes with a three-prong plug, connect to a grounded mating receptacle. Never remove the ground prong from a plug, or use a plug with a broken ground prong.
Electrical "hardware"Poor electrical weld circuit connections can yield any number of problems, including excessive resistance in the weld circuit resulting in arc wanders, or an arc that won't start or is difficult to start.
The following items require routine inspection:
- Power sources - Approximately every six months, disconnect the power to the unit and blow out or vacuum the inside of the machine. In heavy service conditions, cleaning monthly may be necessary.
- Wire feeders - Periodically inspect the electrode wire drive rolls. If dirty, remove the drive rolls and clean with a wire brush. If the drive rolls are deformed, replace them. Drive rolls should be changed, adjusted or cleaned only when the wire feeder is shut off. In addition, check the inlet and outlet guides and replace if they are deformed from wire wear. Remember that when power is applied to a wire feeder, fingers should be kept away from the drive roll area.
- The gun and liner assembly - Guns/torches should be kept in good working order and serviced at regular intervals by qualified technicians. A gun or torch must be used only with the gases for which they are designed. Shielding gas pressures should be those recommended for the weld process used. MIG gun liners should be cleaned periodically.
- Electrode holders - Fully insulated electrode holders should be used. Do not use holders with protruding screws.
- Connectors - Fully insulated lock-type connectors should be used to join welding cable lengths.
- Cables - Frequently inspect cables for wear, cracks and damage. Immediately replace those with excessively worn or damaged insulation to avoid the possibility of lethal shock from bared cable. Also, keep cable dry, free of oil and grease, and protected from hot metal and sparks.
- Terminals and Other Exposed Parts - Terminals and other exposed parts of electrical units should have insulating covers secured before operation.
- Electrodes - Welding power sources for use with MIG and TIG welding normally are equipped with devices that permit on/off control of the welding power output. If so, the electrode becomes electrically hot when the power source switch is ON and the welding gun switch is closed. Never touch the electrode wire or any conducting object in contact with the electrode circuit, unless the welding power source is off. Welding power sources used for shielded metal arc welding (SMAW or stick welding) may not be equipped with welding power output on/off control devices. With such equipment, the electrode is electrically hot when the power switch is turned ON. Never touch the electrode unless the welding power source is off.
- Electrical safety devices - Safety devices, such as interlocks and circuit breakers, should not be disconnected or shunted out. Before installation, inspection or service of equipment, shut off all power (or lock or "red-tag" switches) and remove line fuses to prevent power from being turned on accidentally. Disconnect all cables from the welding power source, and disconnect all 115 volt line-cord plugs.
2. The gas cylinder and distribution system (shielding gas system) cylindersCylinders should be securely fastened at all times. Chains are usually used to secure a cylinder to a wall or cylinder cart. When moving or storing a cylinder, a threaded protector cap must be fastened to the top of the cylinder. This protects the valve system should it be bumped or dropped.
Cylinders should not be stored or used in a horizontal position. This is because some cylinders contain a liquid, which would leak out or be forced out if the cylinder was laid in a flat position. Also, welding guns and other cables should not be hung on or near cylinders. A gun could cause an arc against the cylinder wall or valve assembly, possibly resulting in a weakened cylinder or even a rupture.
RegulatorsThe following symptoms indicate a faulty regulator:
o Leaks - if gas leaks externally.
o Excessive creep - if delivery pressure continues to rise with the downstream valve closed.
o Faulty gauge - if gauge pointer does not move off the stop pin when pressurized, nor returns to the stop pin after pressure release.
Do not attempt to repair a faulty regulator. It should be sent to the manufacturer's designated repair center, where special techniques and tools are used by trained personnel.
HosesUse only ferrules or clamps designed for the hose, never ordinary wire or other substitutes, as a binding to connect hoses to fittings. Avoid long runs to prevent kinks and abuse. Suspend hose off ground to keep it from being run over, stepped on or otherwise damaged. Coil up excess hose to prevent kinks and tangles. Examine hose regularly for leaks, wear and loose connections. Immerse pressured hose in water to check for leaks, (bubbles will indicate leaks.) Repair a leaky or worn hose by cutting out damaged area and splicing. Do NOT use tape.
3.Ongoing procedure controls/recommended practices cooling of equipmentAll welding operators should be well-acquainted with the duty cycle of the particular piece of equipment they are using. A machine's duty cycle is based on the number of minutes out of a 10-minute time period an arc welding machine can be operated at its rated output. An example would be 60% duty cycle at 300 amps. This would mean that at 300 amps, the welding machine can be used for six minutes and then must be allowed to cool with the fan motor running for four minutes. (Note: Some foreign welding machines are based on a five-minute cycle.)
Electrode oxidation during cooling can result in excessive electrode consumption. This can be prevented by keeping shielding gas flowing 10-15 seconds after arc stoppage.
Preparation of shielding gas hosesThe welding operator should purge the gas hoses to expel all air and moisture condensation from lines before welding. Porosity in the weld bead and poor bead color can result from entrapped gas impurities in the line. Condensation or loose fittings in the gun or TIG torch can also cause porosity in the weld bead, as can a defective gas hose or loose hose connection. These should be inspected regularly.
Proper safety procedures or "operator maintenance"
- Arc rays and eye protection - Arc rays produce intense visible and invisible (ultraviolet and infrared) rays that can burn eyes and skin. Any exposed skin can be burned quickly by these rays. Welding helmets should be fitted with a proper filter shade to protect the operator's face and eyes when welding or watching, and approved safety glasses with side shields should also be worn. Screens or barriers to protect others from flash and glare should be installed where appropriate and maintained.
- Clothing - Gloves and clothing should be flame-resistant. Clothing made from a dark-colored, tightly woven material is best suited for welding. Gauntlet-type leather gloves should be worn to protect the hands and wrists. Shirt collars and shirt cuffs should be buttoned, and open front pockets are not advisable as they may catch sparks.
Also, operators should never store matches or lighters in their pockets.
Pants cuffs are not recommended, as they will also catch sparks. Tennis shoes do not qualify as adequate foot protection. High-top leather shoes or boots are absolutely necessary.
- Environment - The area surrounding the welder will be subjected to light, heat, smoke, sparks and fumes. Permanent booths or portable partitions can be used to contain light rays in one area. The heat and sparks given off are capable of setting flammable materials on fire. Therefore, welding should not be done in areas containing flammable gases, vapors, liquids or dusty locations where explosions are a possibility. Metals with plating, coatings or paint that come near the region of the arc may give off smoke and fumes during welding. These fumes may pose a health hazard to the lungs, therefore an exhaust hood or booth should be used to remove fumes from the area. When welding in confined spaces, such as inside tanks, large containers or even compartments of a ship, toxic fumes may gather. Also, in an enclosed room, breathable oxygen can be replaced by shielding gases used for welding or purging. Care must be taken to ensure enough clean air for breathing. In many companies, it is routine to provide welders with air masks or self-contained breathing equipment.
For more information on welder maintenance or for the Miller distributor/service center nearest you, call 1-800-4-A-MILLER (800-426-4553) or visit Miller's website at www.Miller Welds.com.)