The reality of waterjet abrasive recycling

It’s not a widespread practice, but that could be changing

Because shipping spent waterjet abrasive off to the landfill usually is easy, not too much thought is given to attempting to recycle it. However, in today’s manufacturing world, all aspects of the operation are scrutinized for possible cost savings. That includes looking at abrasive recycling.

Figure 1
A small abrasive hopper feeds abrasive garnet from Barton International to the waterjet cutting head.

If you failed to notice the waterjet abrasive recycling market, even if you are in the waterjet cutting business, you shouldn’t feel ashamed. That’s because there’s not much of a market.

Even as waterjet cutting has grown over the past several years, beyond the hotbed areas where aerospace manufacturing is large, the recycling market for the garnet abrasive used in the cutting process has not really matured. Many shops simply collect the spent garnet from the bottom of their tanks and deliver it to landfills. As long as the fabricator is not cutting a toxic material, such as lead, many municipalities’ landfills don’t have much problem accepting the brown slurry that comes from the tanks.

This reality is not the result of inactivity. People have marketed waterjet recycling equipment over the years, and some shops have put that technology to use. The equipment separates useful abrasive from spent abrasive using screening technology, dries the useful abrasive, and feeds it into a container for reuse in a waterjet.

The manufacturing market, however, has not widely embraced the recycling equipment. Capital equipment cost may be a reason, along with the expense associated with running it and assigning an operator to it. Also, the yield may not be considered large enough, especially considering the price and availability of almandine garnet, the abrasive of choice for most fabricators that do waterjet cutting.

“Virgin garnet is widely available and relatively low-cost,” said R. Randolph Rapple, president, Barton International, a garnet supplier. “There is no shortage of garnet abrasives in the world. No one running a waterjet should be worried about their next order of abrasives [see Figure 1].”

While commodity supplies aren’t keeping manufacturers awake at night, they are becoming more sophisticated in how they look at total operational costs. The days of scrutinizing only the labor costs associated with a task are over. Today manufacturers look at total costs—the costs connected to something from the time it arrives at a facility to the day it is consumed or leaves the facility.

When it comes to waterjet cutting abrasive, manufacturers are taking a closer look at disposal costs. There is cost associated with collecting it, transporting it to a landfill, and then disposing it, which varies depending on where a manufacturing facility is located. If a shop could recycle it and be able to reclaim a third of the spent abrasive for reuse in the waterjet, the company’s managers might take recycling it more seriously.

That reality of recycling waterjet abrasive might be coming to fruition.

A Look at the Abrasive

Before discussing recycling any further, it might help to focus on the abrasive itself. Almandine garnet is the waterjet abrasive of choice for manufacturers. It is hard enough to accommodate fast cutting, but not so hard that it shortens the life of the waterjet nozzle. It is dense enough to pack a punch on the metal workpiece, but not so dense that it can’t be accelerated to maximum velocity in the water stream. It also breaks down at just the right rate, meaning that the abrasive doesn’t break down into fines too quickly and doesn’t lose its sharp edges as it is being transported to the cutting head.

As with any mineral that is mined, garnet needs to be processed to meet specifications that work for the fabricator’s waterjet operation. This is where high-purity materials are separated from low-purity materials, which contain impurities that might affect a machine’s ability to cut well.

Figure 2
The hard rock garnet abrasive has sharper edges (left) than alluvial garnet abrasive, which has more rounded edges and is considered a general-purpose abrasive for most waterjet cutting applications. Photo courtesy of Barton International.

Garnet abrasive for waterjet applications is available in two basic forms (see Figure 2), according to Barton’s Rapple. Hard rock abrasive is angular and has very sharp edges. Alluvial abrasive has more rounded edges and is generally considered a more general-purpose product. The hard rock abrasive is the choice for those fabricators that need an aggressive and fast cutting action and when specifications require a higher-quality surface finish than an alluvial abrasive can deliver.

Rapple said that fabricators who employ abrasive recycling technology in their own shops are better off using the hard rock product because more of the abrasive is likely to maintain its shape after use when compared to the lower-cost alluvial abrasive. That translates into a higher yield of potential abrasive that can be reused after collection from the tank, drying, separation, and bagging.

Making Recycling Work

Troy Cain knows a thing or two about waterjet abrasive. In fact, he knows quite a bit about recycling the stuff. He has spent the last four years as the owner of Garnet Recyclers of Washington cleaning out waterjet tanks in the Seattle area and trying to perfect the recipe for recycling used waterjet abrasive.

“It’s a real learning curve. Over the years, more companies have come to us wanting to work with us and recycle abrasive rather than put it into the landfill,” Cain said.

If recycling is going to work, it’ll be in the Puget Sound area, which is home to the world’s largest aerospace manufacturers. There are plenty of waterjet tables in operation, and Cain and his two partners, Joey Hollenbeck and Josh White, are servicing quite a few of the shops. They are extracting about 600 to 700 tons of abrasive from waterjet tanks on a monthly basis.

It’s a big job. Industrial vacuum trucks are used to suck out the water and garnet from the waterjet tanks. Cain said as much as 500 gallons of water could be contained in the slurry in the truck’s tank when it’s delivered back to his facility. The brownish mixture is dropped into an indoor pond where the settling occurs.

The water that pools during the settling process is pumped out, and a “dewatering” process begins, Cain said. This is the beginning of the drying process that can take several days.

“Drying and screening is tough,” he said.

After four years of recycling the material and slowly building a network that is using his recycled abrasive, Cain admits more work needs to be done. He said he thinks he can deliver a quality garnet abrasive in the 80-mesh size that most waterjet cutters seem to want, but new drying and separation equipment might make the job easier for him. Cain, a former Marine, is energized to keep moving forward with the business after some tough years.

“I think it’s the Marine Corps thing in me that kept me driving forward. There were a couple of times when I just wanted to quit and throw in the towel because it didn’t seem you could do anything with this stuff,” he said.

Where Is Abrasive Recycling Heading?

The acceptance of abrasive recycling has been slow, but some tangible momentum is evident:

  • Cain said that he is building a profitable business model in northwest Washington and expects other companies to seek out his services. After learning what works after four years in business, he thinks the model can translate to another geographic location that has a lot of waterjet cutting activity. High capital equipment expense is associated with such a startup, Cain added, but that is not necessarily an impediment to running a profitable endeavor.
  • Hypertherm, a technology developer known for its plasma cutting products and the acquirer of the AccuStream waterjet products company in 2013, announced at the 2015 FABTECH® tradeshow that it was launching its EcoSift™ waterjet abrasive recycling unit. Attempts to connect with Hypertherm management to discuss the new product development were not successful, but the company appears committed to putting a new spin on recycling equipment that has been on the market for the last several years.

Rapple reported that Barton is currently investigating potentially accepting used waterjet abrasive and recycling it at their own facility.

This obviously is not a quick shift in the market, but change is afoot. Interest in recycling might grow with the continued adoption of waterjet cutting technology.

“A waterjet offers a shop a certain level of versatility and capability that no other machine tool that they own can,” Rapple said. “You can cut a variety of materials. You can cut stacked material. It has no heat-affected zone. It is very easy to run, and it’s relatively easy to maintain. You can produce net parts. You can cut thick materials. There are plenty of reasons that waterjets make sense for fabricators.”

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