Post-processing method of wear-resistant coating and points to pay attention to

       Grinding is the only practical finishing method for wear-resistant coatings. Since the bonding between the coating particles mainly relies on mechanical mosaic bonding and contains certain pores, from the point of view of grinding, the heat transfer is relatively slow, and the conventional grinding method of dense materials is not suitable for the grinding of coating materials. Machining. If the grinding pressure is too high or the grinding speed is too fast, the particles on the surface of the coating may be transferred or moved, which may cause the particles inside the coating to fall off, or even cause the entire coating to peel off from the substrate. Factors that determine the grinding process method include: coating type, workpiece shape, required surface roughness and tolerances, etc.



Generally speaking, the finer the spray powder, the lower the coating porosity, the more uniform the coating, and the better the surface roughness after grinding.



Factors such as coating type, hardness, workpiece size and shape, grinding amount, surface roughness requirements, and grinding machine type should be considered when selecting a grinding wheel. Generally follow the following principles:



1) Use the sharpest grinding wheel as possible, which has a fast cutting speed and is not easy to overheat. The sharpness of the grinding wheel is related to the type and particle size of the abrasive used in the grinding wheel. For grinding wheels with wear-resistant coatings, the commonly used abrasive grains are silicon carbide and diamond. This is because the silicon carbide abrasive grains will present a new sharp cutting edge after being broken during grinding, while the diamond abrasive grains have good durability and can cleanly grind various hard wear-resistant coatings. When the abrasive grain size is smaller, it not only has a smaller surface area, but also has a sharper cutting edge, which is easier to sink into the coating than coarse abrasive grains, thereby obtaining a lower surface roughness. Generally speaking, the grit size of abrasive particles used for rough grinding of wear-resistant coating is 125~150 mesh, and the grit size for fine grinding is 380~400 mesh.



2) The internal structure of the selected grinding wheel and its hardness level should be able to provide the effect of free grinding. The internal structure of the grinding wheel refers to the spacing between the various abrasive grains inside the grinding wheel. Grinding wheels with a porous structure provide better grinding results because the gaps between the particles can provide more space for chip storage. The hardness of the grinding wheel will also affect the grinding effect of the wear-resistant coating. The harder grinding wheel has a longer service life than the soft grinding wheel. When the grinding stress is small, the contact area is large and the grinding speed is high, a softer grinding wheel is recommended; when the grinding stress is large, the surface roughness requirements are low, the contact area is small and the grinding wheel is narrow, Harder grinding wheels are recommended.



3) Select the most suitable type of grinding wheel bond. There are two commonly used grinding wheel binders, namely ceramic binders and resin binders. Grinding wheels with vitrified binder can withstand high grinding speed and precise fit tolerance, and are not affected by water, acid, oil and temperature changes, but the grinding machine speed is required to be less than the safe operating speed of the grinding wheel, generally less than 33m /s. Resin-bonded wheels, on the other hand, can be used for higher grinding speeds and produce lower surface roughness.



During the grinding process, the condition of the grinding surface of the grinding wheel will change. After a period of use, the sand grains on the grinding wheel surface are not worn away, so that the height of the abrasive grains is equal to the height of the binder, or the grinding wheel surface is ground. Filled with material, both of which will weaken the wear ability of the grinding wheel, resulting in more friction (polishing) than grinding. At this time, the grinding wheel should be dressed or replaced with a new grinding wheel. When a diamond tool is used to dress the grinding wheel, the traverse speed of the tool through the surface of the grinding wheel affects the final cutting action of the grinding wheel. The rapid traverse can open the grinding wheel surface and make the abrasive grains sharp again, thereby improving the grinding ability of the grinding wheel; on the contrary, when When the traverse is slow, the grinding wheel surface will be closed, the abrasive grains will be passivated and the grinding wheel will be hardened. The slow dressing method is not recommended for thermal spray wear-resistant coatings. Therefore, when grinding wear-resistant coatings with diamond grinding wheels, it is very important to keep the grinding wheel sharp, which is beneficial to obtain a lower surface roughness.



Wet grinding is generally recommended for the grinding of wear-resistant coatings, but dry grinding can also be used if appropriate protective measures are used. However, the advantages of wet grinding are far greater than those of dry grinding. In wet grinding, a harder wheel can be used without increasing the incidence of skin blasting or thermal cracking, minimizing the detachment of surface particles, and the resulting surface roughness is better, and the wheel will not be packed as quickly , the number of trimmings required will be less. In addition, wet grinding also helps to flush away abrasive residue. The filtration and appropriate concentration of the grinding fluid also have an effect on the surface roughness.



In conclusion, a wear-resistant coating surface with good roughness can be obtained as long as careful operation is performed during the grinding process. Below are some factors to consider when determining a wear-resistant coating grinding process.



1) Use a softer, free-grinding wheel, which greatly reduces the chance of buffing and abrasive breakout.



2) Keep the grinding wheel surface clean and sharp.



3) Use the correct grinding wheel dressing process.



4) Use a coarse-grained grinding wheel as far as possible for rough grinding, and a fine-grained grinding wheel for fine grinding. Trying to achieve a good surface finish with a coarse grinding wheel may result in abrasive pullout, contamination, or scorching.



5) Use light grinding. Wear-resistant coatings are usually thin, and excessive grinding pressure may cause surface delamination or surface particle release.



6) Non-spark grinding should be used for the last grinding process, otherwise the surface of the grinding wheel will be passivated or glazed.



7) Keep the coating under pressure at all times, and cut down to the substrate by spraying to minimize delamination and particle release.



8) Optimization of grinding process. The change of grinding parameters has a great influence on the grinding speed and roughness, and the surface roughness of the wear-resistant coating depends to a large extent on the selected grinding process. When there is a problem with a given grinding wheel, adjustments should be made to the grinding wheel speed, feed rate, workpiece speed and process.