WATER CAN AFFECT YOUR WATERJET’S CUTTING CAPABILITY

For a waterjet, water quality and temperature have a direct impact on operating cost, overall life and productivity.

If water quality is low or the temperature is high, a waterjet owner can experience reduced life in virtually any part of the pump that comes into contact with the water. This can include high-pressure seals, plungers, high-pressure lines, orifice assemblies and other critical parts, notes Sean Schramm, global product manager for Flow waterjet company.

John Petras, service manager for OMAX Corp., adds that although well over 90 percent of the water that comes from a city’s water supply in the U.S. and Canada can be used without any conditioning, it’s the other small percentage that can cause problems for the machine.

“Almost every company has decent enough water to run their waterjet without conditioning it. Requiring a solution for conditioning water is the exception and not the rule,” Petras adds.

Water, water everywhere, but can it be used?

Water is a very complicated subject, mentions Petras. “We have a libral range of water specifications we like for our waterjets – where it can’t be too pure or too impure. Otherwise, you’re going to get detrimental affects to your pump, nozzle and perhaps the material you’re cutting as well, no matter whose waterjet you’re using.”

If the water is too pure, like deionized water, it can be quite aggressive, where it will actually leach out minerals from the stainless-steel plumbing in the waterjet and try to put them into solution, says Petras. This could cause premature plumbing failures for the waterjet system.

Dissolved solids

Impure water isn’t good either. Impure water means several things. Either it has high concentrations of solids or suspended solids or both. Dissolved solids refer to the chemistry of the water, what’s in solution. For example, deionized water literally has zero dissolved solids.

“Our sweet spot for dissolved solids is anywhere from 25 to 50 parts per million (ppm). This is very pure water, but it isn’t deionized. It’s very clean water, but not super clean,” says Petras.

“Under pressure, dissolved solids, especially calcium and magnesium, can be precipitated through the orifice that we use in the nozzle, causing a very poor stream and a bad cut. So if you don’t use a water softener, for instance, and you have a high amount of calcium, it can affect your waterjet’s working stream. If your stream does get clogged at the nozzle, you can use an inexpensive ultrasonic cleaner to clean it,” says Petras.

Petras adds that there are a number of different conditioning systems to treat dissolved solids and clean the water, such as reverse osmosis (RO), a water softener or a calcite filter that treats a low pH in the water. Having a water test done is very important to select the proper water treatment system.

For example, if the water’s pH is low, the acidic properties of the water will enter and expand the micro-fissures in the stainless steel tubing. While the result is the same as using deionized water – shortened tubing life – the reasons and treatment methods are different. Adding a calcite filter to buffer the pH is a common remedy in this scenario.

“Suspended solids, on the other hand, can be controlled easily with a properly sized filter media in a filtration system,” remarks Petras.

Suspended solids

You can see suspended solids in water making it look dirty. They are typically organic items such as algae, moss and bacteria that cause slime. These will typically clog filters, but can be effectively removed using a proper filter.

If suspended solids aren’t filtered, they can get into a waterjet pump’s seals and nozzle, causing a poor working stream under high pressure, along with a shortened pump life.

Water quality is very important when you accelerate it to Mach two,” says Bradley Schwartz, Pacific regional manager for Jet Edge. “At this speed, any particulate in the water becomes an abrasive within the pump. If you’re in an area that has a lot of particulate matters in water such as iron, it becomes a problem for the waterjet.”

Schramm says that Flow recommends using a municipal water source or well as a water supply. Process water, boiler condensate and untreated water are typically not acceptable.

“Be sure that the water-flow rate is capable of producing 1.5 times the pump-flow rate. So, if your pump produces one gallon a minute, make sure that your water source is capable of producing one and a half gallons per minute,” he remarks.

Flow includes a water-quality test kit with its pre-installation package to test the levels of hardness, iron, manganese, magnesium, silica, chlorine, PH, alkalinity and bacteria in the water to be used. If these levels are outside of the recommended range for the type of pump being used, Flow may recommend installing water treatment equipment (a water softener, for example). Schramm mentions that they don’t recommend using an RO or deionization system to remove solids from the water, because they both remove minerals and metals from the water.

Figure 1. Experimental set-up abrasive waterjet cutting process

Making stable water, filters and coolers

Waterjet companies also note that water changes throughout the year as it picks up algae in the summer, silt from high rainfall and changes temperature during the seasons.

Another byproduct of a pump’s pressure is heat, which is a deterrent to long pump life. When water is pressurized to 40,000 psi or higher, the water warms up quickly. As water temperatures go up, pump life can go down.

“Usually, water conditioning for a waterjet comes down to environmental factors depending on the region,” notes Schwartz. “If there’s a problem with the water, we offer a closed-loop water-conditioning system along with chillers to keep it at a constant temperature. About 60 percent of the waterjets that I sell have this equipment with it.”

Schwartz adds that water quality and temperature “definitely affect the operating costs of the waterjet. So in the summer you get more silt in the water, and you’ll have a higher water temperature. This can give you problems with filtration, and then you have issues with seal longevity for the pump.

“Typically we like filtered water at a 50-ppm TDS filtration level and water temperature at 60 to 70 degrees. When water meets these conditions, we can get seal longevity out to 1,000 hours for the pump seals,” Schwartz adds.

“Temperature is also important,” says Petras. “Cold water is far better than hot water for pump seal longevity. We also have a 70 degrees water specification for our pumps. This temperature is very common to get right out of the tap. For companies that can’t maintain this cooler temperature, we offer a chiller system.”

Petras mentions that OMAX offers various solutions to address water quality and extend component life. “In addition to RO systems to clean water, we offer a closed-loop filtration system for companies that can’t dump water down the drain or choose not to for environmental reasons. We have two different styles of pH neutralizers for water. One is for moderate water problems while the other is for severe ones,” says Petras.

Schwartz adds that Jet Edge has machines that are placed in facilities that don’t have a drain. “In these cases, you have to continually use the water over and over, so it should be filtered. We offer a three-stage system: two stage pre-filtration then final filtration using deionization. This is a variable deionization system, so we like to set it at 50 ppm. Actually, anything less than 100 ppm is fine. But in different parts of the world you can have 500 ppm when you test the water. In these cases you should have a very good filtration level for your waterjet system.”

Flow provides absolute rated filters to remove suspended solids that can damage seals, plungers and orifice assemblies, says Schramm. The filters included with the pump are 1 and 0.45 micron. These fine filters can clog quickly if the supply water contains too many solids.

“To extend the service life of the pump filters, a waterjet user should consider installing a pre-filter system. Depending on the water quality, installing a 50 micron and 5 micron pre-filter will extend the life of the critical pump filters,” he remarks.

Once the water is used for cutting, you have a couple choices says Schramm. You can either dispose of it or use a closed-loop system to reuse it.

“Most of our customers dispose of the water, because they’re cutting neutral materials such as aluminum, glass and steel with a natural garnet sand. If the water is disposed, we recommend using a weir tank and filtration system to remove suspended solids from the water and keep them out of the sewer system.

“If you’re cutting lead, beryllium copper, or other potentially harmful material, then a closed-loop system is required. If using a closed-loop system, ensure that the water is being chilled and that you’re using a good filtration system before the water is again used by the pump,” remarks Schramm.

Schwartz adds, “Whenever I sell a waterjet system, I always give buyers complete information on filtration systems, because this is very important for many of them. I let them make the determination on how good their water supply is.

“Some communities do demand that the water meets a certain filtered level before they will allow it down the community drain. If this is the case, then we offer our closed-loop filtration system.”

When a customer purchases a waterjet, Schwartz says his company can test the water for them as a service, or they can have a local lab do it. If a lab does it, he can take the analysis and offer them a recommendation.

Petras concludes that in reality, waterjet users companies can run with poor marginal quality water. But by doing this, they won’t get the optimum life out of their waterjet components. The best way to improve machine performance is to invest in a water quality analysis, then implement the appropriate water conditioning system for the waterjet’s specific needs.

Jet Edge Waterjet Systems / Flow / OMAX Corp.

Article from: http://www.fsmdirect.com/cutting/waterjet-cutting/164-water-can-affect-your-waterjet-s-cutting-capability

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