2017-11-10

What Are the Common Causes of Wear on the Grinding Wheels?

In the grinding process, with the extension of grinding times, the cutting capacity of the coated grinding wheel decreased, the result was that various grinding defects occurred until the grinding processing could not carry out any more. At this point, it was necessary to repair the coated grinding wheel, and restored to normal grinding state. So, what are the common causes of wear on the wheels?

1. Oxidation wear

Common abrasives are oxides, carbides and nitrides. For the carbide and nitride abrasives, the oxidation will occur at high temperatures, resulting in gradual abrasive consumption.

2. Abrasion wear

When the abrasive serious worn, abrasive particles in the top surface becoming plane, and the coated grinding disc surface is looked flat. If cutting edge wear enlarges, that causing serious surface friction, it is sure that the wheel cutting edge will difficult to cut into the workpiece surface. However, the coated grinding wheel is of high hardness, the abrasive particles are not crushing and falling off in time. If you continue to use it, its grinding power and grinding heat may significantly increase, as well as causing obvious vibration and noise, which can not effectively cut the material, at this time, the wheel must be trimmed.

Abrasion wear generally occurs in the cases that abrasive particles hardness is too low, the coated  grinding wheel is of high hardness, abrasive grain size is too small, and the workpiece material has very large tensile strength. This is the most common reason for the end of wheel life when machining normal steels under normal grinding conditions.

3. Diffusion wear

When the abrasive particles and the material being contacted at high temperatures, the elements of the diamond wheel interdiffuse and weaken abrasive particles surface layer, finally cause the diffusion wear. The mutual diffusion between the two materials is closely related to the chemical composition of the material. Because the ability of carbon in diamond abrasive to dissolve in iron is greater than the ability of elements in boron nitride to dissolve in iron, therefore, the diamond grinding wheel should not grind steels.

4. Plastic damage

Under the high temperature in grinding, abrasive particles will be worn due to plastic deformation. Plastic damage mainly depends on the hot hardness of the workpiece. The abrasive grinding wheel plastic wear occurs if the hot hardness on the rake face of abrasive grain is greater than where in the abrasive contact area.

5. Thermal stress damage

If abrasive particle surface instantly rose to high temperature in grinding, the abrasive grinding wheel again through quenching effect of the grinding fluid, the alternation frequency of hot and cold is the same as the coated grinding wheel rotating speed, which formed in great alternating thermal stress on abrasive particle surface, causing surface cracked and broken.

Thermal stress damage depends mainly on the thermal conductivity of abrasive, linear expansion coefficient and the performance of grinding fluid. The smaller the thermal conductivity, the lower the linear expansion coefficient. The larger the coefficient of linear expansion, the better the grinding fluid cooling performance, the greater the thermal stress, the easier it is to make the abrasive by thermal shock cracked and broken.  A variety of abrasives with thermal conductivities from high to low are diamond, cubic boron nitride, silicon carbide, corundum.

These are some of the main causes of wheel wear. Due to the diffences of the abrasives, the workpiece materials and grinding conditions, the main reason for coated grinding wheel wear will be distinct. Therefore, the reasonable choice of grinding wheel and grinding wheel dressing accuracy will greatly affect the workpiece profile accuracy. Therefore, the grinding wheel needs timely dressing.