Water is a natural resource with great erosive power, capable of penetrating mountains and shaping hard cliffs and granite on its way downstream. Water pipes spray water outdoors in a powerful manner, and the force of the water increases significantly if the pressure is increased. The same principle applies to waterjet cutters: water passes through a narrow hole at extremely high pressure, ensuring that the water stream has strong cutting force to cut into the substrate. Mixing water with hard abrasives such as red garnet increases the cutting force exponentially, allowing for extremely precise cutting of almost any type of material, from cardboard and rubber to ceramics, steel, titanium, stone and quartz.
Almost all abrasives have been tested to determine their effectiveness with waterjet cutters. The ultimate conclusion is that the best abrasive is red garnet, as it has a unique set of characteristics such as hardness, density, friability and particle shape that maximize the cutting performance of waterjet cutters.
Hardness. Waterjet cutting requires an optimal balance between cutting force and wear on the cutter parts. Softer abrasives can extend the life of the nozzle, but will reduce the cutting speed. Although overly hard abrasives can increase the cutting speed, they will corrode the nozzle too quickly, causing the equipment to not work properly and increase the repair cost of machine parts. The hardness of red garnet is about Mohs 8, which effectively balances the need for fast cutting while also providing a reasonable life for the equipment.
Density. The cutting force of a water jet cutting machine depends on two factors: the weight of the abrasive multiplied by the speed. The ideal abrasive weight should enable the water to accelerate to the maximum speed, thus providing the best cutting speed. Abrasives that are too light cannot cut the material, while materials that are too heavy cannot be accelerated to the maximum speed, thus reducing the cutting speed. Red garnet is almost four times heavier than water, and this value is in the optimal range for cutting and acceleration.
Fragility. The fragility of the abrasive is critical in water jet cutting machines. Abrasives that are too friable will break into small pieces when passing through the equipment nozzle, spraying on the surface of the workpiece like dust, and cannot be cut. Abrasives that are too hard will not break up in the nozzle and will simply round off at the corners, spraying onto the workpiece as blunt particles that cannot cut. Red garnet is semi-brittle, causing it to break into angular particles with sharp edges as it passes through the nozzle, providing a superior cutting speed than any other abrasive.
Particle shape. Abrasives come in a variety of shapes, from perfect spheres (such as steel shot or glass beads) to needles (such as silicon carbide particles). However, research has found that angular shapes with multiple sharp edges, like red garnet, are best suited for high-speed cutting.
Red garnet is a natural rock found in the almandine mining area. It is a highly chemically stable material that will not contaminate other surfaces on contact. Red garnet requires a special refining process to achieve a specific purity and uniform particle size distribution for use in water jet cutting machines.
