Causes And Solutions Of Overpolishing

The tools used for polishing are generally whetstone strips, wool wheels, abrasive sandpaper, etc., and the operation method is usually mainly manual. For some workpieces with high surface quality requirements, special abrasive tools can be used for ultra-fine grinding and polishing. Ultra-fine polishing is pressing the special abrasive tool tightly on the surface of the workpiece to be processed in the polishing liquid containing abrasives and performing a high-speed rotating motion. The surface roughness of this grinding can reach 0.008μm.

 

During the polishing process, the problem of excessive polishing may occur, that is, the polishing time is too long, which will lead to the deterioration of the surface quality of the abrasive tool, which mostly occurs in mechanical polishing. Specifically, there are two different manifestations of excessive polishing, namely "orange peel" and "pitting corrosion". Let's take a look at what causes the two and how to eliminate them.

Causes of "Orange Peel"

The so-called "orange peel" refers to the high roughness and irregularity of the polished surface. The causes of "orange peel" include excessive polishing pressure, excessive polishing time, overheating of the mold surface, and excessive carburization of the workpiece. For example, suppose a polishing wheel is used for polishing, but the polishing time is improperly controlled. In that case, the heat generated by the polishing wheel will easily cause an "orange peel" phenomenon on the surface of the workpiece.

Different types of materials have different degrees of difficulty in producing "orange peel". Materials with higher hardness can withstand relatively greater polishing pressure and are less likely to produce "orange peel"; Workpieces are more likely to be over-polished, resulting in "orange peel".

Measures to eliminate "orange peel"

In actual operation, there are some wrong practices. When many people find that the surface quality is not good, they will choose to improve the surface quality by increasing the polishing pressure and prolonging the polishing time. In fact, this approach not only does not improve the surface quality, but it is counterproductive.

The correct way to remove the "orange peel" should be to remove the defective surface first and then use an abrasive tool with a slightly coarser grain size than the previous grit number to polish with a smaller polishing force. First, stress relieves the workpiece at a temperature lower than the tempering temperature of 25 degrees Celsius, then grind it with the finest abrasive tools until a satisfactory effect is achieved, and finally polish it with a lighter force.

 

Causes of "pitting"

The so-called "pitting corrosion" is the appearance of point-shaped micro-pits on the surface of the polished workpiece. This is because some non-metallic impurities, usually hard and brittle oxides, are mixed in the metal workpiece. If the polishing pressure is too high or the polishing time is too long, these impurities will be pulled from the surface of the steel to form micro pits. Especially when the purity of the steel is not enough, the content of hard impurities is high; if the surface is rusted or the black leather has not been cleaned, "pitting corrosion" is more likely to occur.

 

 

Measures to Eliminate "Pitting"

First of all, regrind the surface of the workpiece. The grain size of the abrasive used is slightly coarser than that used before, and the grinding force must be small. Then, use a soft and sharpened oil stone for the final step of grinding, and then proceed to the polishing process after satisfactory results are achieved. When polishing, the softest polishing tools should be avoided if the grit size is less than 1 mm. The intensity of the running light should be as small as possible, and the time should be as short as possible.