In the grinding process when grinding hard metal, should be used in a softer wheel. Because when the wheel is easy blunt, in order to timely self-grind, you should use a softer wheel. On the contrary, when grinding a material slightly soft, slow sand passivation, should choose a hard grinding wheel, in order to maintain grinding performance. But in grinding very soft materials, such as metals, due to chip clogging wheel easily, it should be used a softer wheel.When coarse grinding, grinding force and sand, easy self-grind, it is optional medium hardness of the wheel; high speed grinding wheel from poor grind, grinding wheel hardness than the average level of 1 to 2 hours.Molding grinding wheel in order to maintain the correct shape, should choose a harder wheel; machining a discontinuous surface, due to the impact of sand easy to fall off, you can choose a harder wheel.Poor thermal conductivity, easy to burn the workpiece, such as high-speed steel cutting tools, bearings and other applications softer wheel. Hollow and thin-walled parts, difficult to heat and easy to burn, use a softer wheel.When the grinding machine stiffness, with a softer wheel with the wheel hard and has low stiffness vibration. Large grinding area, you should choose a softer wheel.