Correct use of polishing machine: the key to operation: try to get the maximum polishing rate in order to remove the damage layer generated during polishing as soon as possible. At the same time, the polishing damage layer should not affect the final observed tissue, that is, it will not cause false tissue. The former requires the use of coarser abrasives to ensure a higher polishing rate to remove the polished damage layer, but the polishing damage layer is also deeper;
The latter requires the use of the finest material, so that the polishing damage layer is shallower, but the polishing rate is low. The best way to solve this contradiction is to divide the polishing into two stages. The purpose of rough polishing is to remove the polished damage layer. This stage should have the maximum polishing rate. The surface damage caused by rough polishing is a secondary consideration, but it should be as small as possible; the second is fine polishing (or final polishing). Its purpose is to remove surface damage caused by rough polishing and minimize polishing damage.
When polishing with a polishing machine, the grinding surface of the sample and the polishing disk should be absolutely parallel and lightly pressed on the polishing disk evenly. Take care to prevent the sample from flying out and creating new wear marks due to excessive pressure. At the same time, the sample should be rotated and moved back and forth along the radius of the turntable to avoid local abrasion of the polishing fabric too fast. In the polishing process, the micro-powder suspension should be continuously added to keep the polishing fabric at a certain humidity.
Too much humidity will weaken the effect of polishing wear marks, causing the hard phase in the sample to appear embossed and non-metallic inclusions in steel and graphite phase in cast iron to produce "tailing"; when humidity is too low, friction and heat will cause the sample When the temperature rises, the lubrication effect is reduced, the grinding surface loses its luster, and even black spots appear, and the light alloy will damage the surface.
In order to achieve the purpose of rough polishing, the rotating speed of the turntable is required to be low, preferably not more than 500r/min; the polishing time should be longer than the time required to remove the scratches, because the deformed layer must be removed. After rough polishing, the grinding surface is smooth, but dull and dull. There are even and fine wear marks under the microscope, which need to be eliminated by fine polishing.
During fine polishing, the speed of the turntable can be appropriately increased, and the polishing time is appropriate to throw away the damaged layer of rough polishing. After fine polishing, the polished surface is bright as a mirror, and no scratches can be seen under the bright field of the microscope, but the wear marks can still be seen under the phase contrast illumination.