By: Jeff Moureau, Rental Operations Manager, Miller Electric Mfg. Co.

Almost every contractor or construction company rents welding or cutting equipment. Perhaps a fast-track job suddenly demands more arcs than you own, your existing equipment is down, or maybe you want to "taste" a new product before purchasing. Whatever the situation, selecting the right machine for the task helps you complete jobs more profitably and faster. However, changing technology means that yesterday’s machine might not make sense today. While not a complete list, the following questions and guidelines can help ensure you make the best choice.

Is primary power available? If primary power is available, renting an electric arc welder is the lowest cost option. However, greenfield construction sites, quarries, mines, highways, equipment yards, etc. frequently do not have electricity. For these applications, select an engine-driven welding generator ("engine drives," "diesel welders" or "gas welders"). These self-contained power sources create their own welding output and auxiliary power.

Be sure to ask if the job requires an engine drive with a lot of auxiliary power. Some engine drives can provide a wide variety of auxiliary power options – 3,000 to 20,000 watts, 120 and/or 240 VAC, single- or three-phase power – while other models have limited output or only DC capabilities. Most hand tools and lights only require a few thousand watts. Pumps, especially larger ones, may require 8,000 watts or more.

Also, note, that an engine drive with at least 8,000 watts lets you run a plasma cutter off its auxiliary power, while an engine drive with at least 12,000 watts lets you power a 400 amp welder. This is a very economical way of putting two arcs on a single site or creating a welding/cutting fabrication shop in the field.

What welding processes does the job require? Stick or TIG welding steel requires a Constant Current (CC), DC output machine; CC machines are also used for Air Carbon Arc gouging. Any type of MIG or wire welding (solid wire, flux cored, metal cored) is best done with a Constant Voltage (CV) DC output machine.

Most of the all-position, self-shielded flux cored wires used for structural welding, as well as wires used for other critical work like pipe or pressure vessel welding, run best with a CV welder and a dedicated wire feed system. These wires are very voltage sensitive and porosity can occur in the weld bead if the incorrect voltage is used. While wire welding has been done in the past with CC machines, that trend is declining rapidly because CC welders don’t provide real voltage control, where as CV welders do.

Note: To wire weld in the field, use "suitcase" style portable feeders. Their tough plastic or metal case fully encloses the spool of wire and internal components, shielding them from dust and other contaminants.

How much amperage does the job require? Heavy-duty construction applications (structural steel, hard facing) may demand running large diameter electrodes (e.g., 1/4 in. Stick rods, 1/16 or 5/64 in. flux cored wire) and gouging with big carbons (e.g., 3/8 in.). For larger electrodes, most contractors favor a welder that offers a top output of 350 to 600 amps at a high duty cycle* rating.

Lighter-duty construction (fabricating components, mechanical contracting work) applications can often use smaller diameter electrodes (perhaps Stick rods ² 3/32 in., .030 to .045 in. wires , tungstens ² 1/8 in.) that require less power. Generally speaking, a welder with roughly a 40 to 300 amp output suffices for these jobs.

To judge a plasma cutter’s capacity, use these guidelines: a 25 amp machine cuts 3/8 in steel; a 55 amp machine cuts steel up to 7/8 in; an 80 to 100 amp unit cuts 1-1/4 in. steel. Performance varies greatly between models, especially with respect to travel speed (how fast you can cut a given thickness) and quality of the cut. Ask to test the unit before renting it.

* Duty cycle is the number of minutes out of a 10 minute period a machine can operate at a given output with excess heat build-up. A rating of "500 amps at 60 percent duty cycle" means that the machine can create a 500 amp output for six continuous minutes and then needs to cool for the remaining four minutes. Duty cycle ratings typically do not reflect a machine’s maximum output.

How reliable is the welder? Downtime kills profitability. For jobs in remote locations, reliability becomes even more critical. All modern MIG and multiple process machines use circuit boards to control the arc. In this case, look for welders with a design that protects or totally encloses the circuitry, shielding it from dust, salt, etc. Machines with these features, including some inverter-based welders and plasma cutters, have a track record of proven reliability in harsh, rugged conditions.

If you only need a Stick/TIG output, you might want to consider the simplest machine possible: an engine drive or electric welder without circuitry. On engine drives, also look for one with a case that totally encloses the engine to protect it from external contaminants.

Are the operators familiar with the equipment? Chances are, no matter which welder you rent, some of the operators may never have seen that model before. Considering that you don’t want downtime because someone put a switch in the wrong position, it makes sense to rent welders with the simplest operator interface possible. If an operator can’t set the machine, it’s too complicated.

Do you want a lot of arcs in one area? If yes, consider multi-arc welders. They reduce job site clutter and costs for transportation, maintenance and fuel. Most importantly, multi-arc welders greatly reduce the cost per arc. For example, a rental company might charge about $14.25/hr. for the industry’s standard eight-arc system. Compare this to the cost for renting a single-arc, 250 amp electric welder, which is about $5.75/hr. (Examples provided are for New England region. Note that rental costs can vary between regions.)

Multi-arc options include: "dual operator" engine drives that power two independently-controlled arcs from a single diesel engine; "inverter racks" that house four or six inverter machines (Stick/TIG/MIG welders or plasma cutters); and heavy-duty systems that power six or eight welding arcs from a single main transformer. All electric arc systems provide independently-controlled arcs and use a single primary power connection. Most systems permit paralleling arcs for increased output when required (typically for gouging).

Do you need portability? If you don’t have to move the welding machine, a traditional electric arc welder can make sense. But if you need to move the machine a lot, and especially if you will be moving between sites with different types of power (i.e., 230 or 460 VAC), renting an inverter-based welder makes better sense. Inverters can provide up to 600 amps of welding output, yet only weigh 75 to 125 lb., so you can easily move them. They are so small that a rack holding six inverters still fits into a freight elevator. Also, inverters accept 230 or 460 VAC power (you might hear this referred to as "Auto-Linking") without ever needing to remove the machine’s cover and relink the jumpers. You’ll never wait for an electrician to wire power again.

How far away will operators be from the welding machine? If operators work on scaffolding or inside a tank, rent a remote control so the operator can fine tune the amperage without returning to the welder’s front panel. A remote control invariably contributes to better quality welds and operator satisfaction.

Will excessive engine noise be an issue? If you need to lower noise in urban areas or reduce noise-related stress on operators, "quiet" engine drives are available. An engine drive that produces 75 dB at 23 ft. (7 m) is considered quiet. Note that sounds levels rise exponentially: a 3 dB increase makes an engine drive 30 percent louder, while a 6 dB increase means the machine is 50 percent louder.

To "quietize" engine drives, some manufacturers completely enclose the engine and/or have sound-deadening material surrounding the engine. Engines that operate at 1800 RPM are usually quiet, as are some of the new-generation diesel engines (e.g., Deutz F3L 1011 and Perkins 104.22).

How easy is the machine to maintain? Can you easily check fluid levels and access filters? Is the fuel capacity/running time adequate for the shift length? Do you need tools to drain the oil? Can you drain the oil without worrying about a spill)

As with any job, work with the site’s welding supervisor to determine equipment needs before renting a welder. In addition, don’t let too much "tradition" influence your decision. While the traditional types of welders are still available (and for very good reasons), the choice of welding products has expanded greatly in just the last five years. Renting is an excellent way to try new products. Chances are, you’ll be pleasantly surprised how today’s generation of welding and plasma cutting machines improves productivity, lowers cost-per-arc and offers improved operator appeal.