Silver Coated RVG Diamond Delivers First Choice For Tungsten Carbide Grinding With Straight Oil Cooling

The increased acceptance of oil as a coolant when grinding tungsten carbide parts favors the use of Diamond Innovations Silver Coated RVG* diamond. There are three specific benefits that silver brings to superabrasives grinding: lubricity; capability of forming a spiked coating; and heat dissipation.

Compared to uncoated crystals, the surface texture of the coated diamond is rougher and the surface area is larger. This enhances the ability of the crystal to anchor itself firmly in the bond. Diamond Innovations is able to produce a highly spiked silver coating formation. The coating spikes mechanically retain the crystal longer in the bond and prolong grinding wheel life.

The most important characteristic is the ability of silver to conduct heat. Silver has a coefficient of thermal conductivity (458W per Kelvin per meter) that is well above other metals commonly used for coating diamond, such as nickel (58.6W/K/m) and copper (350 - 370W/K/m). Silver allows for the rapid transfer of heat from the small area where the heat is generated - the crystal/workpiece interface - to the large area of contact between the silver coating and the bond.

In grinding applications involving straight oil coolants, the majority of lubrication comes from the oil. However, microscopic amounts of silver coating melt or are sheared off the crystal surface. This silver is deposited on the wheel surface, reducing friction between the wheel and the workpiece. Consequently, the heat-generated damage to the wheel and workpiece surfaces is limited to a great extent.

Silver coated RVG diamond is recommended for aggressive grinding of tungsten carbide when straight oil coolant is utilized. Among the applications are fluting drills endmills and other rotating tools where tight tolerances and superior surface finish are required.

Aggressive Feed Rates and Slow Wheel Speed - A Winning Combination

The properties of silver coating allow the grinding machine to be run at more aggressive feed rates,
increasing the overall process productivity. Slower wheel speeds are beneficial for the overall process performance when straight oil coolants are applied. G-ratios for applications with silver coated diamond have determined that dramatically better wheel life was achieved at 20m/s than for applications run at higher wheel speeds. The higher wheel speed of 30m/s requires significantly more power and can result in unwanted levels of heat, causing workpiece expansion and/or cracking, as well as loss of tolerance control. Doubling the wheel speed from 20 m/sec to 40 m/sec results in nearly a sevenfold reduction in wheel life. Optimum wheel speed is 20 m/s or less.

Diamond Innovations is the inventor and the world's leading supplier of manufactured diamond, cubic boron nitride (CBN), and polycrystalline products used in the metalworking, stone, concrete, petroleum, glass, woodworking, electronics and mining industries.

Source: Diamond Innovations