Induction Heating Cuts Preheat Time, Provides Localized/Uniform Heat Treatment and Documents the Process for Swartfager Welding, Inc.

Swartfager Welding, Inc. puts weld quality above all other factors

Swartfager Welding, Inc. – experts in rail and marine fabrication, as well as other heavy welding and fabrication applications – puts weld quality above all else. That dedication has led to consistent growth and the skills to address the toughest weld requirements its customers have.

Part of that dedication is ensuring that each weld meets strict requirements for preheating, interpass temperature control and stress relieving. Heating the part with a rosebud torch takes too long for many fabricators. It also creates the possibility of uneven heating and includes the added costs of propane (or other heating fuels). Taking the part or assembly to an oven large enough to handle it takes too much time and is generally inconvenient. As such, Swartfager Welding has turned to induction heating for many of its preheating, interpass temperature control and stress relieving applications.

With the Miller ProHeat™ 35 induction heating system, Swartfager Welding achieves faster time-to-temperature and maintains required interpass temperatures throughout the welding process. They also conduct controlled stress relieving and document the entire process through the addition of an optional digital recorder – occasionally required by some customers and qualifying agencies as proof of procedure compliance.

“Right now, we’re using it on the assembly joints for some Cor-Ten material,” says Dustin Swartfager, engineer, Swartfager Welding. “The only other option would be to truck it almost three hours to an oven big enough for the part. Right now, we can stress relieve all of the components that go into it and then isolate the joints that put the assembly together, and we do it all fixtured so that we know we have no shrinkage.”

The benefits of induction heating

An induction heating system creates heat electromagnetically in the part rather than by surface heating like open flame or resistance heating methods. Heat is induced in the part by placing it in an alternating magnetic field created by liquid- or air-cooled induction heating cables. Operators wrap the induction cables around the part, or on the part. The cables do not heat up themselves, but create eddy currents inside the part, which generates heat. The process is safer, faster and easier to use than other methods. Induction also typically provides more uniform heating throughout the part.

“You can control your ramp speed, you’re not relying on somebody to use a melt stick or an infrared thermometer,” says Swartfager. “You put your sensors on, tell it what your allowable ramp-to is, how long you want to maintain it and how long you want it to cool down, and push start.”

Induction heating systems are better at maintaining temperatures throughout the welding process, ensuring that temperatures don’t drop outside of minimum and maximum.

“If you’re doing an elevated interpass temperature, it will actually work along while you’re welding or while you’re applying weld and cut back heat so that your interpass doesn’t go over the prescribed limit,” says Swartfager. “It will pick right back up when you let off the trigger. You can monitor three or four locations and it will control the ramping or slow the rate of ramp long enough to allow the heat sink that you’re dealing with to all come up together. It will keep within 15 to 20 degrees, and that’s a big deal. If you were to have a hot and cold side to a casting and then go to work on it, your end result wouldn’t be very good. And it definitely allows us to maintain everything the way it should be. It’s done by the book.”

The ability to maintain the workpiece at required temperatures also provides a considerable productivity advantage over other methods.

“It’s great because you don’t have to stop in the middle of the work you’re doing to heat it back up.”

Improved speed and safety

One of the greater benefits of induction is the speed with which it brings a part to temperature. This can be a major improvement to productivity on larger/thicker components where maintaining temperatures can be a long/slow process using a torch. It also provides completely uniform heating, eliminating cold spots throughout the piece.

“If you’re just wrapping something as simple as a pipe with coils, you can get your preheat temperature there in minutes compared to half an hour with a flame. It’s consistent. You’re not going to find hot and cold spots as you work around applying the weld.”

Induction heating also provides a number of other benefits. The induction cables don’t actually heat up themselves, making them safer than the open flame of a rosebud torch or resistance heating solution. It also cuts down on the need and expense for heating fuels.

Documenting quality

But as Swartfager continues to focus on quality, the ability to document the entire heating cycle gives themselves and their customers peace of mind that each they complete each weld right and to specifications.

“Buying propane is an expense,” says Swartfager, “but there’s a general problem with using propane or a flame in an open environment to produce something that is accepted by the industry for heat treatment, normalization or stress relieving. Flame is only as good as the guy running it and your infrared thermometer. The ProHeat is documented. It logs its entire cycle. You can print it. It’s hard, finite, usable data that you can fight with if you ever have somebody question your ability. It is as close as you can get to a controlled and documented oven as there is. You’re creating the same thing without traveling, without breaking the part down, without transporting it through your shop. You can do everything you need to accomplish in one set-up, in one place.”