Posted By: Peter Yordanov | Posted On: May 9, 2022
Selecting the Right Abrasive for Your Waterjet
What is Waterjet Cutting and where is it Used?
Waterjet cutting is the process of CNC (computer-controlled cutting) for a wide variety of materials using a very high-pressure stream of water (30,000psi to 90,000psi), sometimes mixed with an abrasive substance to cut harder, denser materials such as metal. This is more suitable when the material is sensitive to heat in a traditional cutter like plastics and aluminum as it allows for cutting the material without any heat-affected zones; i.e., warping and changing the intrinsic properties of the item. Accuracy is also an advantage with abrasive cutting as intricate parts and complex shapes can be cut with incredibly sharp corners, furthermore, the cutters can be as thin as a human hair or thicker, up to an mm in thickness, allowing for a range of applications. Occasionally, the problem of taper arises but this goes to a maximum of only 1 degree and can be eliminated by slowing the water speed or tilting the material.
There is minimal wastage as the water jet machines loop the water and abrasive to be used multiple times. Additionally, the pressure of water can be controlled and the abrasive addition switched off to allow for cutting multiple different materials without needing a part changing or nozzle head replacement, contributing to the versatility of abrasive cutting.
When choosing an abrasive to use in your water jet cutting machine, a happy medium is needed between something sharp enough to effectively boost the performance without being so abrasive that the nozzle on the machine wears out too quickly as this would drastically increase the costs and also reduce the accuracy. Almandine Garnet is a naturally occurring, red-colored mineral that fulfills all the needs of abrasive cutting, some of which are discussed below;
Hardness: Mohs scale is a method of mineral hardness ranking on a scale of 1 to 10 with 10 being the hardest. For reference, diamond has a mineral hardness of 10 on this scale, Almandine Garnet lies between 7 and 8, giving it the optimal hardness for water jet cutting.
Sharpness: This mineral has 12, sharp sides, and its mineral properties make it so that it cracks into smaller, similar sharp pieces. This means that it does not wear out to be dull even after multiple uses. On the topic of sharpness, garnet is typically, either quarried to obtain more razor-edged grains or collected from river beds, called alluvial garnet. This kind has rounded edges due to water flow, eroding the sides. Alluvial garnet isn’t as sharp as the mined quality however; many manufacturers believe that the difference is too minute to pay the extra price for quarried garnet.
Density: The density of garnet is 4 (4 times as dense as water), it makes for a more efficient cut as, if the abrasive is too light, it won’t pick up enough pressure to cut through hard materials while one that is too heavy won’t pick up the necessary speed. Garnet density is perfect in this regard for the most efficient cut.
Qualities of Garnet
There is a wide price range with garnet, depending on its quality. We already discussed that alluvial garnet is cheaper than the mined variety however, there are a few more ways to classify it within different price tags;
Size: The size of the grain of garnet varies from coarse (50 mesh) all the way to very fine (230 mesh). The finer the garnet, the higher is its grade. Fine garnet gives a neater cut finish whereas the low-grade one is better for denser materials as it is heavier and carries higher force.
Purity: Non-garnet products (super fines) are often present in the garnet which have to be screened out, the purer the abrasive, the more efficient the cutting process, however, the purity comes with a higher price tag as well.
Particle Size Consistency: Very large and very small granules tend to clog up the nozzle and can become a nightmare for the operators of the machinery, double sifted garnet ensures quality as the variance in sizing is narrower due to the removal of very fine particles in the first sift and very large granules in the second. It also ensures a precision cut.
Garnet Recycling: Increasingly, operators are concerned about the disposal of abrasive after it is used; manufacturers providing recycling are preferred over ones that aren’t. Since garnet cracks into finer, sharp pieces, it is still usable however, the grade is now different. Check with your supplier to see if the garnet purchased is recyclable, if it is, the supplier will reclassify it for resale.
Depending on your budget and use for the abrasive, you should have a clearer idea with this simplified guide on all the different types available. While there are definitely a few other options for abrasives such as olivine for cutting softer materials such as aluminum, garnet is the most abundantly available one with reliable results.
Southern Fabricating Machinery Sales is your one stop shop for waterjets and waterjet cutting systems. Together with our partners like Peter Yordanov and Techni Waterjet we can provide you with the right solution for your waterjet needs. Shop now for waterjet machines by clicking the link below.