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Friday | 07 March, 2014 | 11:01 am

Separating the good from the bad

By Tom Klemens

Above: The incoming hopper provides a steady feed to the Ward Pro unit. Water from the waste hopper is returned to the waterjet tank.

Reclamation system minimizes new abrasive needs and keeps costs down

February 2014 - Southwestern Virginia isn’t known as a hotbed of industrial activity. But for more than four decades, ABB in Bland County, Va., has been a primary source for large dry-type electrical transformers. The company produces these high-end devices for customers such as hospitals, subway systems and offshore oil rigs that require an alternative to standard oil-filled transformers. “With the dry-type transformers you don’t have to worry about them catching on fire or oil contamination of the surrounding area,” says Brin Conner, ABB’s sourcing specialist at the Bland facility. Although higher priced than standard transformers, their popularity has grown over the years as safety and environmental concerns have increased. “We just had our 40th anniversary and we’ve manufactured 50,000 transformers out of this facility,” Conner says.

Although the basic transformers are put together much as they were 40 years ago, new design and production methods allow manufacturers to customize transformer case sizes and shapes to accommodate space limitations. These factors often accompany their use in basements and underground vaults, for example.

One important manufacturing change came 11 years ago when the facility got its first waterjet. ABB uses a Jet Edge cutting table primarily to cut sheets and blocks of Haysite, an epoxy-impregnated fiberglass that is tough and strongly dielectric.

“Most of our transformers are three-phase, so you have three coils per transformer,” Conner says. Sheets of Haysite between the coils prevent electrical arcing from one coil to the other. It also is used to position and separate the various transformer components.

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“We cut Haysite blocks into a range of sizes,” says Jeff Pauley, who oversees operation of the waterjet and has worked at the Bland facility for 37 years. “Some are set under the coils, which can be huge, to hold them up off of the transformer leg and insulate them from the steel.”

The operation has used Haysite since before Pauley arrived, he says, “and before the waterjet, cutting the material was completely different. We usually used saws and drills to do what the waterjet does now. The waterjet opened up a whole new world for ABB.”

“The waterjet was brought in to replace the saws for greater productivity,” Conner says. “But after we saw its capabilities, it gave engineering a great amount of flexibility. The engineering capabilities are endless.”

Embracing custom production

Transformer production at ABB in Bland is the epitome of high-mix, low-volume manufacturing. “I would say less than 1 percent of our units would be considered standard,” Conner says. “Everything is special made, for the customer.” Fortunately, that approach plays to the strong suit of waterjet cutting technology.

ABB begins with sheets of Haysite, 4 feet by 8 feet for thicknesses up to 3⁄8 inch and 4 feet square for 1⁄2-inch to 3-inch-thick material. SigmaNest converts the engineers’ DXF files into the NC code for the machine, Conner says. It also optimizes the yield from each sheet.

Additionally, Pauley can generate and incorporate his own drawings through SigmaNest for custom cuts as required. For example, although most of the steel for the transformer cases and support structure is cut on laser cutters, the waterjet works well for making miscellaneous cuts. “If something was already formed on a brake and needed a hole put in it, they can bring it to me,” Pauley says. “Where you couldn’t do it on a laser, like adding holes on a preformed panel, you can on the waterjet.”

Waterjet cutting is used frequently in other industries to cut softer materials using a fine, high-pressure stream of water alone. “But once you get into composites, wood and metals, you have to start using abrasive,” says Benjie Massara, marketing manager for WardJet.

ABB uses garnet abrasive with a specific grain size range and quality for its waterjet cutting. “The garnet is the cutting tool, not the water,” says Conner. “Each time the garnet cuts the material, it becomes smaller, sometimes exploding or breaking into smaller pieces. Eventually the particle size is so small that it falls through the mesh screen and exits with the debris.” However, until it gets that small, garnet separated from the cuttings and other debris continues to cut effectively.

One limitation, Massara says, is cutting with very high pressure because it speeds abrasive degradation to a point that makes recycling much less effective. “At 90,000 psi, the force is too strong and the abrasive particles are pulverized, making them non-recyclable,” he says. The choices: reduce the cutting pressure or buy new abrasive.

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Although the company had been recycling abrasive all along, in 2013 it replaced its original system with a Ward Pro system from WardJet. The Tallmadge, Ohio-based company has had its patented namesake system—the waterjet abrasive recycling dispenser—on the market for more than 10 years. However, recent improvements to the system have increased its efficiency, reduced maintenance requirements and extended the life of consumables, making it much more economical for low-volume abrasive users.

“Before, the real hurdle for smaller sized businesses was the cost of consumables,” says Massara. The top screen, which wears more based on the amount of time the system is operating rather than by the volume of material being processed, is not cheap to replace and it often had a service life of 100 hours or less. “But making some modifications last year increased that. We’re now seeing around 600 hours on that screen, which drops the per-hour costs way down. That makes it feasible for a smaller company that’s not doing 70,000 pounds of abrasives a month.” 

The stand-alone Ward Pro system can be operated on an as-needed basis and need not be directly adjacent to the waterjet. The ABB installation uses two hopper tanks, one to supply the actual recycling unit and the other to return liquid to the waterjet tank.

“Debris from the waterjet tank is pumped into the back hopper, and from there into a Ward Pro unit,” Conner says. “Reusable garnet and debris are separated via a vibrating bowl and mesh screen. Small particles fall through the screen and go to the waste hopper. The reusable garnet exits the vibrating bowl and goes into the dryer.”

The dry garnet is added to the waterjet as needed. Meanwhile, scrap and waste material accumulate in the front hopper, from which a closed-loop system returns water to the waterjet tank. 

The Ward Pro’s reclamation rate averages about 2 pounds per minute of garnet that is dried and ready to use, according to WardJet production manager Tim Ghrist. “But we have recently done a redesign on our nozzle, which is kind of the heart of the unit. And that is pushing the average output toward 2 1⁄2 pounds per minute.” 

The nozzle is located at the bottom of the hopper, into which the mixture of cuttings and abrasive first comes from the waterjet. It’s the nozzle that agitates the waste material and provides a steady feed to the Ward Pro unit.

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A key technology

“The waterjet is a very handy item,” says Pauley. “I don’t think you could replace it at this point.”

Although new garnet must be added periodically to replenish the worn down abrasive particles, the Ward Pro typically reclaims more than 50 percent of the abrasive being used.  

“We use as much reclaimed garnet as we can,” Pauley says. That sounds like a pretty good plan, and an opportunity as well. MM

 

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