Welding controls bring process under control
October 10, 2006
When Hastings Irrigation Pipe Co., a manufacturer of aluminum pipe, needed to replace its decades-old welding power supplies, it looked for units that could weld a variety of thicknesses at fast welding speeds. What it found were power supplies that allowed the company to run its mills faster and save money in several ways.
Hastings Irrigation Pipe Co., Hastings, Neb., blazed a trail in the late 1940s by manufacturing irrigation pipe out of a material that was not used commonly at that time: aluminum. Five decades later Hastings and that unusual material are both field-tested and proven for manufacturing irrigation and industrial piping.
The company's present product offering is pipe from 2 inches to 12 in. in diameter and 0.051 in. to 0.083 in. in wall thickness. Its nine tube mills use gas tungsten arc welding (GTAW) at 462 amps to weld the pipe. A mixture of argon (62 percent) and helium (38 percent) protects the weld puddle.
Hastings' previous power supplies, which had been in service since the 1970s, were becoming less reliable as the years wore on. In the company's quest to replace them, it looked for machines capable of 500 to 600 amps at 100 percent duty cycle. Also, the company looked for versatility—the ability to optimize the welding parameters for each particular tube wall thickness. Versatility was a crucial factor for another reason. Hastings, like many tubemakers, seeks new opportunities in new markets, so it has to be able to respond to unforeseen demands from existing and future customers.
Finally, it wanted machines that would run more productively and efficiently than its old machines, thereby saving the company money.
|Before it becomes finished pipe, the aluminum strip is measured, trimmed, cleaned, and formed.|
Hastings tried a number of stop-gap machines until it settled on Miller Electric's Dynasty® 700 GTAW inverter-based machines.
The new machines allow welders to control the arc in a variety of ways: by adjusting output frequency, extending the balance control, and independently controlling the current in each AC half-cycle. The ability to control these welding parameters led to several cost reductions.
"With the new welders," said Ken Shafer, superintendent at Hastings, "we can vary our frequency and get a more stable weld. It holds the tungsten better and you get a better start." The weld frequency is adjustable from 20 Hz to 400 Hz. In addition, the new machines allow fine-tuning the electrode negative (EN) portion of the AC cycle from 30 to 99 percent (also known as balance control).
On a mill that makes 5-in.-dia. pipe with a 0.078-in. wall thickness from 3004 aluminum, Hastings sets the EN portion of the AC cycle at 62 percent and the output frequency at 60 Hz. Increasing the EN portion of the cycle has provided distinct benefits in this application: a narrower weld bead, a reduced etch zone for improved cosmetics, and increased travel speeds.
"We're currently running around 21 feet per minute where it previously ran at 19 feet per minute," Shafer said.
An independent AC amperage control allows operators to set the EN and electrode positive (EP) amperages independently. This allows operators to direct more or less energy into the workpiece as well as take heat off the tungsten. Independently increasing EN while maintaining or reducing EP permits the use of a smaller-diameter tungsten to direct heat to the weld more precisely. In the past the company used a specialized electrode diameter (5/16 in.) that had to be specially ordered and cost more than off-the-shelf electrodes.
"We were using 5/16-inch electrodes on this particular mill and now we're down to 1/4 inch," said Shafer. "We look at this in dollar figures. A 1/4-inch electrode is a standard tungsten ... and it costs me $26. The 5/16-inch electrode was something special I had to order and it cost me $46."
In addition to the obvious cost difference between the two electrodes, the EN cycle adjustment extends electrode life by taking heat off of it. Shafer said that his mill workers typically redress the tungsten once each day, compared with several times per day with the old equipment.
Independently increasing EN amperage while maintaining or reducing EP amperage also allows the operator to reduce the amount of costly helium in the argon/helium shielding gas mixture.
"We're probably running 15 cubic feet [of helium per hour] right now where we used to run up to 20 or 25, but we have not eliminated it yet—we still use it to help with weld penetration," Shafer said.
Integrating the new machines into Hastings' tube mill required some work. The biggest change was running three-phase power to the tube mills instead of the single-phase power they used previously. Three-phase power ensures a constant flow of current to the inverter, which helps the machine run smoothly and drastically decreases its amperage draw. Hooked into a 240-volt, three-phase circuit, the new machines pull 67 amps at 100 percent duty cycle versus 142 amps with the old machines. Based on a mill running 2,000 hours per year, this reduction saves approximately $2,300 annually.
|While line speed and efficiency are important, nothing is as critical as strong welds. Hastings Irrigation Pipe Co. uses a vertical press to perform an expansion test on sections of aluminum pipe.|
Additional savings have come in the form of Hastings' water bill. By matching its Weldcraft WP27 welding torch with a Coolmate™ 4 water coolant system, Hastings has been able to recycle and conserve water instead of just cycling it through and dumping it down the drain. The system provides a constant flow of coolant to keep the pump primed and to reduce algae buildup.
"Between the electrical and water savings," said Shafer, "we expect payback on these machines in a year and a half."
"Our tube is better because of the people that run the mills," said Shafer. "It's the people we have working for us. But technology is part of it. This [tube mill] really is an old technology. These mills have been here for years. The people that run them and the type of welding equipment we use help a lot."
The company also plans to purchase additional Dynasty 700s for its plant in Madera, Calif. Having several mills at several locations means welding parameters vary, leading to the possibility of an improper weld. The result is costly scrap. The Dynasty 700 has taken the guesswork out of the process for Hastings by providing a program memory feature that stores four independent programs and includes a function called "last procedure recall." When switching to a different pipe product, the operator simply pulls the program up on the machine and starts welding.
This feature and the ability to lock in programs help ensure consistency.
"It's just human nature to tinker," said Shafer. "What's good about these machines is that you can lock your programs in. We make sure to set the program how we want it and then lock it in, and that ensures quality and consistency."
As Hastings continues to expand its piping business to new niches and industrial applications, it hasn't lost sight of the product that helped build the company's strong foundation: aluminum irrigation pipe. Despite the influx of PVC pipe used in that industry, Hastings' customers keep coming back for the quality of product and service they get from the company.