Abrasive for Abrasive Waterjet Cutting 

Surface Finish

The edge produced by abrasive waterjet cutting is sandblasted. This is because the garnet sand particles are removing the material rather than the water. A larger mesh size (a.k.a., grit size) will produce a slightly rougher surface than a smaller grit size. An 80-mesh abrasive will produce approximately 125 Ra surface finish on steel as long as the cut speed is 40% or less of the maximum cut speed. It’s important to note that surface finish and cut quality/edge quality are two different variables in waterjet cutting, so be mindful to not confuse the two.

Cut Speed

Generally speaking, the larger the abrasive particle, the faster the cut speed. Very fine abrasives are typically used to cut slower for special cutting when a very smooth edge or very small-sized mixing tube is needed.

Oversized Particles

The abrasive particle distribution must be such that the largest grain is no larger than 1/3 of the mixing tube ID (internal diameter). If you are using a 0.030” tube, the largest particle must be smaller than 0.010” or the mixing tube will likely clog over time as 3 grains try to exit the mixing tube at the same time.

Foreign Debris

Debris in the garnet delivery system is usually caused by carelessly cutting the bag of garnet open, or by not using a trash screen atop the garnet storage hopper.

Dust

Very small particles like dust increase static electricity and can cause a rough abrasive flow to the head. Dust-free abrasives ensure a smooth flow.

Keep your abrasives clean and dry to prevent moisture, oversized particles, debris, and dust from interfering with your flow.

Cost

Cost is reflected by not only the cost of the garnet but the cut speed and overall time to cut your part (slowing in corners versus linear areas). When possible, cut with the largest abrasive that is recommended with that mixing tube, and evaluate cutting speed along with garnet cost. Some abrasives may cost more but are tougher and more angular, thereby producing higher-speed cutting.

Mines across the world naturally produce garnets of a certain size. For example, if a mine naturally produced mostly 36 mesh, then the abrasive must be ground to obtain 50, 80, etc. Different abrasive suppliers have varying costs per mesh size. All garnet abrasives will cut differently, as well, as some garnets fracture more easily or are more rounded.

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