How does Peak current and Base current affect the properties of weldments?

The current levels are only two of the parameters determining weld quality. To understand parameters function, the period can be broken down into several parts:

1. Ramp up rate increase stiffens the arc, reducing the arc column size and increasing the propelling force throwing molten drops detached from the electrode,
2. Overshoot, an instantaneous current increase above the peak current level, necessary to overcome the influence of inductance, variable with cable length,
3. Peak current level directly controls penetration: the higher the peak current, the deeper the penetration,
4. Peak Time or Peak Duration influences the width of the bead shape,
5. Tail-out drop time, speed of change and shape controls energy addition to the molten droplet, directly influencing puddle fluidity and penetration,
6. Sudden current drop down to background level, reduces the tendency for fine droplet spatter,
7. Background Current, the low-level current needed to maintain the arc,
8. Frequency or Repetition Rate shapes the weld bead by narrowing the arc cone with increased frequency.

Choosing a welding kit

When employers select work equipment, the Provision and Use of Work Equipment Regulations 1998 require them to consider the risks posed to the health and safety of people using that equipment. This includes ergonomic risks.

When selecting a welding set, consider the effect poor equipment handling might have:

■personal suffering caused by injuries;
■the financial burden of sickness absence;
■reduced productivity;
■increased insurance premiums; and
■the welder being unable to return to this type of work, which would affect their potential future earnings.

Reducing injuries caused by handling welding equipment will benefit everybody.
Here are some ergonomic design features to look for when deciding between welding sets with the same power output:
■Does the set have to be carried? Consider controlled pushing or pulling of the load instead of lifting and carrying.
■How easily can the load be grasped?

Health and Safety Executive
■Are the handles suitable?
■Can the load be held close to the body (avoid sharp corners, jagged edges, rough surfaces etc)?
■Is it well balanced?

Other considerations include:
■handle orientation;
■ease of pushing/pulling;
■axle types;
■size of wheels;
■wear and maintenance of wheels/tyres;
■effect of torch, wire feed, hoses, gas bottles etc on the handling characteristics of the welding set.

The checklist in this leaflet will help you select the right welding set.

Cutting Machine Conditions

1. Cutting and welding are done by authorized personnel in designated cutting and welding areas to the greatest extend practical.
2. Adequate ventilation is provided for all cutting and welding work.
3. Torches, regulators, pressure reducing valves, and manifolds are Underwriters Laboratory listed or Factory Mutual approved.
4. Oxygen fuel gas systems (e.g., oxygen/acetylene welders) are equipped with listed and/or approved backflow valves and pressure relief devices.
5. Eye protection and protective clothing are worn by all cutters and welders, helpers, and fire watches, as appropriate. Workers adjacent to arc welding areas are protected from the rays by screens or shields.
6. When cutting and welding are done outside of designated areas, the following actions are performed.
7. Permit is completed for each shift.
8. continuous fire watch is maintained, when designated by permit, by trained employees (see employee training, Fire Watch). A fire is attacked only when obviously within the capability of the portable extinguisher.
9. A member of supervision (i.e., craft supervisor) inspects the job site at lest once before the start of each job and at least once every 24 hours until the completion of the job.

1. A craft supervisor determines the best location (s) for the fire watch and verifies that automatic fire protection is in service, that precautions taken are adequate, and that information on the Permit is correct.
2. Combustible materials, equipment, or building surfaces within 20 feet of the work or below the work must be either covered with fire-resistant welding blankets, moved, or wetted down. Openings in ducts, tanks, or other confined spaces within 20 feet of the work are also covered or plugged. Fire-resistant welding blankets are used for electric arc operations instead of wetting the work down.
3. Cutting or welding is prohibited in the following situations.
4. In sprinklered areas while sprinkler protection is out of service.
5. In explosive atmospheres of gases, vapors, or dusts or where explosive atmospheres could develop from residues or accumulations in confined spaces (see item 8).
6. On metal walls, ceilings, or roofs built of combustible sandwich type panel construction or having combustible covering.
7. Confined spaces such as tanks are tested to ensure that the atmosphere is not in excess of 10% of the lower flammable limit prior to cutting or welding in or on the tank. Tests are repeated as conditions warrant, once each shift as a minimum. Mechanical ventilation is continuous when cutting or welding in or on a confined space.
8. When cutting or welding must be done on small tanks, piping, or containers that cannot be entered, they are cleaned, purged, and tested prior to starting the work. For work on combustible liquid or gas piping or tanks, intermittent testing is done during the work and a Job Safety Analysis is provided with the assistance of Fire Protection Engineering.