When stainless steel grinding dust caused reliability problems with traditional TIG machines, Miller inverters provided relief.
Field installers say that the Maxstar 140's Lift-Arc feature - unique among ultra-lightweight inverters - helps prevent tungsten inclusions in the weld bead.
Welding a single joint is easy, designing, fabricating and installing an integrated automated process flow system - an intricate network of piping, tanks, pumps, valves and other specialized stainless , steel equipment - is a bit more complex. However, A&B Process Systems Corp., Stratford, Wisconsin, a leading provider of stainless steel Turnkey Design and Build lProcess Flow Systems, always rises to the challenge. Producers in the food, beverage, pharmaceutical, chemical and paper industries rely on A&B systems for their existence.
To create these masterpieces, A&B now relies on the Maxstar® 300 DX and Maxstar® 140 inverter-based DC TIG/Stick welding units from Miller Electric. The Maxstar power sources improve reliability, slash primary power draw and increase weld quality, and the 10-lb. Maxstar 140 also offers portability for field work. A&B and its 172 associates shine as one of America's most sought-after companies in the industry. Its premier offering, the Design & Build System, can comprise thousands of feet of pipe and hundreds of system components to process anything from aspirin to baby formula to wood pulp. The company also specializes in Integrated CIP (clean-in-place) piping systems and modular skidded systems.
Using stainless steel ranging from 20 ga. to 5/16 in., A&B fabricates nearly all system components itself, including vessels that hold up to 65,000 gal.
"We found that constructing components and custom ASME vessels in-house allows us to better control cost, quality and delivery dates," says Charles R. Treankler, Marketing Coordinator for A&B. "We aren't subject to other vendor's timelines and workmanship, so we can respond to the needs of our customers more effectively."
Working with Stainless
Fabricating stainless steel equipment presents its own set of challenges. A liquid processor tank, such as A&B's VacuShear® Liqui-Processor, is a complex vessel. This unit (the first top-mounted, high-shear, vacuum vessel for mixing dry ingredients into liquids), requires numerous TIG welds for inlet and outlet ports. The end result should be a weld that seamlessly blends the main tank and its attachments together; no cracks, ripples or arc marks are permitted, in accordance with industry standards.
The smooth, shiny appearance of the weld and workpiece is paid for in hours of grinding and polishing the weld to its finished size. Unfortunately "grinding and polishing puts a lot of metal dust into the air," says A&B Maintenance Supervisor George "Diddy" Mess. "Our old TIG machines had a fan that ran continuously and sucked in this dust-laden air. The metal particles built up, eventually bridging contact points. This frequently caused the circuit boards and high frequency controls to blow out."
Mess had heard from his welding supply distributor that Miller's Wind Tunnel Technology™ and Fan-On-Demand™ feature could improve reliability, so he called Interstate Sales Representative Larry Wetzel.
Inverters Improve Reliability
"Welding unit reliability on the plant floor was the biggest issue," says Wetzel. "A&B needed a power source designed to withstand airborne contaminants (see sidebar above). They also needed a unit with positive arc starts and good tail-off at the end of the weld (crater control) to avoid marking the stainless, as well as pulsing capabilities. The Maxstar 300 DX fit the bill perfectly."
Wetzel demonstrated the 89-lb. Maxstar 300 DX inverter and left several of the units at A&B for operators to test.
"The guys loved them; there were absolutely no problems," Wetzel says. "A&B cut us a purchase order for six inverters and traded out four competitive conventional square wave machines that had reliability problems."
Dewy Rotar, A&B Supervisor, Plant #1, also likes the inverters. "We are breaking ground on our fourth fabrication plant and we want to run 460V, three-phase primary power for economic reasons," says Rotar. "The Miller inverters will let us do that. This will give us big power savings, not to mention savings on bus costs." Using 460V/three-phase power, the Maxstar 300 DX draws a mere 0.14 amps at idle and just 16.2 amps at rated output. A&B's old TIG units drew 5 amps at idle and 37 amps at rated output.
|Fig. 1 - The Maxstar's Wind Tunnel Technology.
Along with the Maxstar 300 DX inverters, A&B purchased 16 Maxstar 140 DC Stick/TIG inverters to simplify work for its field installation crew (this crew, a total of 52 sanitary installers, works in a variety of environments installing stainless steel process piping).
"Previously, we would use a small competitive inverter that ran on 115V input power for pipe-to-pipe welding, which doesn't require much amperage," says Mark Linzmeier, Job Supervisor. "But because those little machines didn't have enough power for heavier weldments, such as hangers, we also had to bring a 250 amp machine like Miller's Dialarc®. Obviously, those are bigger machines and they're more difficult to move around."
With its 5 to 140 amperage range (100 percent duty cycle at 100 amps, 230V input), the Maxstar 140 has enough power for any TIG or Stick weld A&B's installers need to make. "It weighs only 10 lb. If we need a man in the field immediately," says Linzmeier, "we can just throw it in a gangbox and go. If someone has to fly to a job site, they can take it as a carry-on and put it into an overhead compartment."
"The reports from the field installers have been excellent," continues Linzmeier. "They are in love with that little welding unit. It has been doing a super job in a variety of settings, from 100 ft. up in the air to down in the basement. The Maxstar 140s are always the first units out of the gangbox."
Linzmeier says the installers especially appreciate that the little inverter also has the Auto-Link® feature (accepting either 115V or 230V primary power without manual re-linking). "We never know for sure what type of power the job site has," he states, "but every plant has 115V or 230V. All our installers have to do is plug the Maxstar 140 into a wall, set their amperage and go."
Wetzel adds that the Maxstar 140 also features Miller's Lift-Arc™ TIG arc starting feature.
"With Lift-Arc, operators simply touch the tungsten to the workpiece, lift and the arc starts automatically. Since there is no scratching involved," he says, "there is no tungsten inclusion in the bead. This lets the operator precisely direct the arc when starting, thus helping avoid arc marks. Mechanical contractors have been looking for an ultra-lightweight inverter with features such as Lift-Arc and Auto-Link for years."
Arc Control for Quality
Making a good TIG weld on stainless, explains Rotar, requires good arc control at all stages of the weld. Unfortunately, A&B's previous conventional square wave welding units sometimes left arc marks ("peg tracks") on the workpiece during arc start and tail-off. Tight corners were especially susceptible. Polishing away arc marks wastes time, so A&B wanted a TIG welder with a better arc.
"We purchased our old TIG units three years ago, and they were state-of-the-art at the time," says Rotar. Now, A&B operators state that inverters like the Maxstar 300 DX offer much better control. Using the touch pads on its front panel, operators program the entire weld sequence, triggering the start and end of the sequence with a microswitch on their torch.
"I like the fact that I can program a gentler up-slope to start," says A&B Welding Operator Tony Rennock. "It starts out cold and then gets hot. My previous unit started out hot right away. A more gradual start gives me time to figure out where I am on the weldment."
Jason Stack, who is welding the bottom head on a food grade balance tank made from 12 Ga. stainless steel, explains his weld sequence: "I've set my gas pre-flow at 0.5 seconds, my initial amperage at 20 and the initial slope is 0.3 seconds. Next I program pulsing parameters, setting my peak amperage for 103 amps, background current at 50 percent of peak level and the amount of time spent at peak amperage at 50 percent."
To provide good crater control, prevent discoloration and eliminate the problem with peg tracks, Stack "programs a three-second final slope to keep the argon on the weld, so it doesn't turn black. And I set the final amperage at 20 to avoid a sharp tail-off that could lead to a pin hole in the weld. That's unsanitary and harder to grind."
Stack created this pulsing program to remove heat from the weldment. This gives him better control of the puddle as he welds from the bottom to the top of the tank, and it also helps prevent warping and discoloration. Stack constantly feeds a 316L stainless filler rod into the joint, rocking the TIG torch in rhythm with the weld pulses. He focuses the arc right on the bead during peak amperage and moves uphill about every sixth pulse.
Stack notes that the touch pad controls, which are arranged to follow the weld sequence, didn't take much time for him to learn. Plant Supervisor Rotar agrees, noting that "all the guys picked it right up. They like trying new things, especially tools that make the job easier. Because the Maxstar 300 DX's arc starts and tail-offs don't create peg tracks, it means we can keep the polish line on the weld bead to perhaps 1/4 to 1 in., instead of 2 or 3 in."
With its high-quality people, services and products - plus new technology like the Maxstar - A&B expects continued success with its plan to penetrate new markets.