Deep in the Adirondacks, a stone’s throw from Gore Mountain and about a half a day’s drive due north from New York City (traffic permitting), sits one of the largest garnet deposits in the world. It’s not the only such place – Australia has vast reserves of alluvial garnet, as does India – but the mine skirting the West Canada Lake Wilderness lays claim to the hardest garnet anywhere. This is the heart of Barton Abrasives.
The original Barton Mine began operation more than 130 years ago. It shares a rich history with the surrounding area (see sidebar on page 16) and today, Barton International provides garnet abrasives for use in waterjet cutting, blasting and surface preparation, grinding and other abrasive applications.
Company president Randy Rapple has worked there since 1983 and is an expert on the use and selection of abrasives. Modern Abrasives and Deburring had an opportunity recently for a little one-on-one with the Adirondack native, a discussion that proved to be quite relevant to those who operate abrasive waterjet machines for a living.
MAD: Manufacturing gets more competitive every year. What advice can you give to waterjet shops that might be looking for a lower cost alternative to garnet abrasives?
Rapple: Well, it’s called an abrasive waterjet machine, not a garnet waterjet machine, so shops are free to use whatever they like. But for a number of very good reasons, including cost and effectiveness, roughly 97 percent of waterjets use garnet. Yes, there are a few machines that use other minerals, and we even sell some of these minerals, but it’s a very small percentage of the industry. As far as we’re concerned, garnet remains the best choice for abrasive waterjet cutting.
MAD: Are there different kinds of garnet available, and if so, what are the options?
Rapple: There is so-called “hard rock” garnet (which we refer to as Adirondack, as our garnet is different than others in the market) and alluvial garnet. The difference between the two is that hard rock must be mined – you have to drill and blast to get at it, then crush it to the desired consistency.
Alluvial garnet comes from riverbed or beach sand, where Mother Nature has done most of the hard work for you. Hard rock garnet is more expensive to produce but yields a higher quality, higher performance abrasive. Alluvial is less aggressive and as a rule, it doesn’t last as long or cut as fast, whereas Adirondack garnet is sharp as well as friable and continuously sharpens itself during waterjet operation.
MAD: So, you’re saying shops should use Adirondack garnet in all cases?
Rapple: Not necessarily. If I opened up a shop tomorrow and started cutting 1/4-in. aluminum and didn’t care all that much about surface finish or whether there was a burr on the exit side of the cut, I would use alluvial garnet. But, if I was cutting difficult material, such as titanium, Inconel or high-speed steel or very thick material or composites or glass, I would definitely use Adirondack garnet.
MAD: Alluvial garnet is much less expensive, in some cases half the price. How can someone justify spending that much more for hard garnet?
Rapple: That’s exactly why the majority of shops use alluvial garnet. And frankly, it’s a good product. We sell a lot of it, much more than we do Adirondack. But to me, it’s a little like using a high-speed steel tool bit versus a carbide one. Not everyone does the math, but if they did, they would understand the value that comes with high-performance cutting media.
They say they measure the performance of their production floor equipment, and some actually do a good job there, but in most cases the operator, supervisor or plant manager says, “Well, the harder garnet cuts faster but it’s not that much faster, so let’s just buy the less expensive stuff.”
MAD: Performance aside, most in the industry agree that garnet accounts for the majority of waterjet operating costs. How can you justify doubling that expense?
Rapple: The “operating costs” include only the consumables – abrasives and parts specifically. It doesn’t include labor, management and facility expenses. Don’t get me wrong, some shops know exactly what it costs per hour to operate a waterjet machine, but that’s pretty atypical.
To really understand the impact garnet selection has on profitability, you obviously have to know how much time it takes to cut a given part and the cost of the abrasive consumed, but there’s also the time spent deburring and finishing parts afterward. There’s the direct labor and the water and the electricity, the machine depreciation and maintenance, the cost of the building along with heating and cooling it, management and indirect labor expenses, consumables such as spare parts and nozzles – add it all together, divide by your cutting speed, and you’ve arrived at the shop’s unit cost of cutting.
That’s the figure you’re trying to reduce. For those shops that actually go through the complete exercise, the higher cost of Adirondack garnet is easily justified.
MAD: What other opportunities do you see for shops to reduce operating costs and improve part quality?
Rapple: Again, if I were managing a waterjet machine, I would spend more time evaluating different grades. I don’t necessarily mean alluvial vs. hard rock (although that’s certainly part of it), but rather the many grit sizes that are available.
I’d install different hoppers and test the impact a coarser grade has on thicker material, for example, or how a fine grit can improve edge quality without sacrificing speed. Some of our customers are having very good results using 120 grit, a relatively fine grade, for cutting thick materials with ultra-high-pressure pumps.
The important thing is to work with your abrasives supplier to evaluate different grades, but be smart about it; don’t just simply look at abrasive cost and cutting speed. If you do that, you’ll never make the right decision. But if you set it up right, changeover should only be a few minutes, and the benefits can be pretty amazing.