Waterjet Cutting Tech Tips

More is not always better

Have you been overfeeding your machine?

How many times have you heard the saying ‘more is better’? For some things, that can certainly be true. But when it comes to the amount of garnet abrasives used in your waterjet cutting operations, it can cause an opposite effect.

As you may or may not know, waterjet cutting machines are very technically advanced, and their performance can be affected by a variety of factors. The amount of garnet used for example, is one of those. If you are of that mindset of the more, the better, you may notice a reduction in speed, cut quality and overall efficiency.

What happens when you overfeed your waterjet machine?

So, how do you know if you are overfeeding your machine? One example is the garnet can tend to chug or come out sporadically or intermittently. Therefore, you need to set the right amount of garnet for mixing with the high-pressure water and flow perfectly through the mixing tube onto the material that it is cutting.

The way garnet flows and is introduced into the cutting head by a vacuum-like suction, caused by the high-pressure water flow is called the “Venturi effect”. The stream of water pushes through the high-pressure tubing to the cutting head and through another tube, garnet is fed and mixed with the high-pressure water in the cutting head.
The two elements then combine to go through the orifice first and finally through the nozzle or mixing tube. It is the combination of both garnet and the high-pressure water that gives it the ability to cut through hard materials such as stainless steel, carbon steel, aluminium and other specialty metals.

Getting the feed amount right

The way to measure the amount of garnet to be fed to the cutting head is through an Abrasive Regulator (AR). This unit is typically mounted on the rail of the waterjet machine, above the cutting head. Above the AR is a mini hopper, which feeds the garnet to the AR by gravity. It will usually have several settings that determine how much garnet goes to the cutting head.

Most waterjet OEMs will have a guide for standard abrasive feed amounts. While these are suggested starting points, they are not necessarily the best or most efficient. For example, for a particular setup, it might suggest a setting of 0.54kg (1.2 lbs.) of garnet per minute. To see if that is the best setting, try reducing the amount of garnet fed via the AR. Go down to 0.49 kg (1.1 lbs.) per minute, and if you are still achieving the same cut finish and edge quality, then drop down to 0.45kg (1 lb.) per minute. Continue to adjust the settings until you see a noticeable or unacceptable difference in the cut quality that you are trying to achieve.

Remember, in many cases, you can reduce the amount of garnet abrasives used for your waterjet cutting operations and still achieve a similar or many a time, a better cut. When you cut faster and use less garnet, you are reducing your overall costs and becoming more productive at the same time. Which in this case, 'more is certainly better'.



TGEMRittle  By Matt Rittle, GMA Americas