Induction Heating Improves Safety, Cuts Preheat Time and Provides Uniform Heating in Structural Steel Reinforcement and Construction at Lambeau Field
Induction heating system provides more consistent heating while improving productivity and reducing exposure to open flames and volatile gases; reduces consumable costs associated with gas purchase.
Reader’s note: This is the fourth in a series of articles detailing the expansion of Lambeau Field in Green Bay, Wis. — home to the Green Bay Packers of the National Football League. Miller and Hobart Brothers have been named as the Official Welding Equipment Provider for the Lambeau Field Expansion by the Green Bay Packers. Through a partnership with Miron Construction Co., Inc. — the Official Provider of Construction Services for the Green Bay Packers and Lambeau Field — Miller and Hobart Brothers have worked to bring the latest in welding technology to the site. Stay tuned to MillerWelds.com/Lambeau for more articles, photos and videos from the project.
For the first article in the series on converting to Flux Cored welding, click here.
For the second article in the series on portable fume extraction equipment, click here.
For the third article in the series on dual operator engine-driven welder/generators, click here.
In this article, we’ll specifically look at the use of induction heating in structural steel welding applications. Miron Construction used the ProHeat™ 35 induction heating system from Miller throughout the project as a faster and more efficient way of bringing the steel columns to temperature – and keeping them there – than using a propane-fueled torch. Overall benefits of the process compared to heating with a torch are:
- Faster time-to-temperature
- Consistent heating throughout the entire part
- Easier to apply/wrap heat
- Lower consumable costs by reducing/eliminating gas expenses
- Reduces total weld cycle times – improving productivity
- Improved safety for employees (no open flames or hot heating elements)
Steel Reinforcements Call for Extensive Welding
Miron Construction began work on reinforcing existing steel structures at Lambeau Field in September 2011. Work ramped up in January as the regular season ended and crews were able to remove the old scoreboards. The North End Zone construction revolved around the addition of a massive elevator shaft for six new elevators, the new party deck that sits on top the stadium roof, and the new Mitsubishi Diamond Vision Video Board.
The work in the South End Zone is even more extensive: to support the structures for the new video board and the new seating, an additional bay was added to the existing bowl and seven new levels were built on top of the existing three levels. This is where the majority of the added seating will be, as well as indoor shops and concessions. It also required major reinforcement of the existing steel columns.
This reinforcement included extending base plates and adding plating and bar stock to the existing columns. Large three-inch plate steel caps were also added to the very top of each column to act as a base for the new steel structure to be built on top of it. In order to do this and meet structural requirements, the new plate steel as well as the existing column (16 inches by 16 inches) had to be brought to and maintained at a temperature of 150 degrees during the welding process. Preheating helps prevent rapid cooling of the weld metal, relieves stresses and drives out hydrogen, which can lead to cracking and embrittlement. This is historically done in the construction industry using propane-fueled torches (aka rosebuds, weed burners, etc.). This method of heating, however, poses problems, including:
- Inconsistent heating throughout the steel. The large size of the columns combined with the cold weather when much of this work was performed makes it difficult to evenly maintain temperatures
- Purchasing, storage and handling of volatile heating fuel
- Safety dangers associated with using a high-temperature open flame
- Constant starts and stops during the welding process to bring the column back up to temperature using a heating torch.
With the ProHeat 35 induction heating system, Miron Construction was able to bring each column or cap plate to temperature, leave the induction heating coils in place, and make the complete weld without stopping (except to switch out Stick electrodes). This saves a substantial amount of time and provides uniform heating throughout the weld area.
“The induction heating system has actually been great for plating the columns and welding on the side,” explains Jake Wirkuty, an ironworker with Miron Construction Co., Inc. “It saves a lot of time on the preheat set-up. Instead of welding three inches, preheating and then welding three inches, it’s been excellent just to slap the coil on the side of the column. We have an eight-foot setup which, with two guys, one on each side of the column welding and keeping that temp up, it saves probably half the time or more of preheating.”
The Benefits of Induction Heating
With an induction heating system, heat is created electromagnetically in the material rather than by surface heating, as is done with an open flame. Heat is induced by placing the steel in an alternating magnetic field created by liquid-cooled induction heating cables. In this application, Miron Construction rigged an eight-foot long strip of plywood with the induction heating cables so that it could be quickly and easily placed along each 2.5-inch thick reinforcement plate. The induction cables do not heat up themselves, but create eddy currents that generate heat throughout the plate and column. Two welders then work down the side of the each column plate.
“What we ended up doing with the coils for the unit was taking an eight-foot sheet of plywood, cutting it down to the size of our column plate, and zip tying our coils to it and just clamping the plywood to the edge of the column,” say Wirkuty. “And then, when that side is done and heated, you just unclamp it and move to the other side. It makes it very easy to get around.”
The process is safer, faster and easier to use than other heating methods and typically provides more uniform heating throughout the part. The part comes to temperature within minutes and is kept at that temperature until the welding process is completed and the system is turned off or ramped down. Unlike heating with a torch, where the uniformity of heat is at the mercy of a number of factors, including ambient temperature, operator technique and the size of the column, induction heating heats the piece evenly throughout. As much of the work was done in the dead of winter in northern Wisconsin, the ability to reach and maintain that temperature was important.
“It’s been very important to have an even heating system,” says Wirkuty. “That way our welds, if you’re welding on the plate and trying to heat the column at the same time, with a weed burner or torch it seems like it’s very hard to keep that heat consistent. With this heat induction unit, that heat flows right through the plate evenly and it heats the column evenly.”
In addition to uniform heating throughout, induction heating also creates its heat without an exposed heating element, making it considerably safer than using a propane torch. There is no open flame to burn anyone or catch anything on fire, and the coils remain cool to the touch even during the heating process. It also reduces the need to handle potentially volatile heating gases, which improves overall safety and helps lower that consumable cost.
“It will be a lot easier because you don’t have to switch out the fuel so often,” says Wirkuty, “and storing them you have to set up your own site and cages with the right signage and everything else. This (system), you can just roll in. You don’t have to worry about any of that.”
The unit plugs into most standard 480 V 3-phase receptacles found on site or on generators, making it extremely versatile regardless of what type of site you are on.
“Being electric, just hooking it up into the building, you don’t have to run a giant generator,” says Wirkuty. “You can just hook it up and go.”
While quality and safety are paramount, productivity is also an obvious factor. With this being a high-profile project with strict deadlines to meet, any process that increases productivity is going to be given serious consideration. As Wirkuty previously stated, induction heating allows the welders to bring the part to temperature in less than half the time of heating with a torch, and eliminates the need to stop welding to re-heat the part — reducing total welding cycle times. When factoring in all of the benefits, Wirkuty knows it’s a viable and much more efficient technology for this application that will help lower total weld cycle costs.
“I think over the long run, the machine would actually pay for itself between the cost of acetylene and oxygen or propane heating it,” says Wirkuty. “And the productivity of it jumps way up.”
Miron Construction affixed the induction coils to long flat boards to help heat wide sections of the beam.
The ProHeat 35 helps bring the steel to temperature faster and safer than flame heating, and also helps ensure uniform heating throughout the column.
An ironworker with Miron Construction welds on a structural column reinforcement at Lambeau Field.