Machining characteristics of spray coating

       The thermal spray coating is formed by the accumulation of self-fluxing alloy powder through high-temperature flame molten plastic particles at high speed. Due to this unique formation method, the spray coating has the following characteristics:



 (1) The combination of the spray coating and the part matrix is basically a mechanical combination, and the combination strength is low, generally only 20-30MPa. If the cutting force is too large during processing, the coating may fall off. Therefore, this is an important feature that should first be paid attention to.



  (2) The substrate hardness of the coating is medium, which is equivalent to the hardness of general quenched and tempered steel, but a large number of hard points such as Cr, C: and WC are dispersed in the coating substrate, and its microhardness is as high as 10480MP. 1607OMPa. These hard points cause severe abrasive wear on the cutting tool, making the sharp edge blunt quickly.



  (3) Because the sandblasting machine coating is porous and has a certain porosity, and because the coating contains more nickel and chromium elements, the thermal conductivity of the coating is very low, and the cutting heat is difficult to be transmitted from the workpiece and chips. Heat is mostly concentrated on the tip of the tool, and the thermal effect during cutting aggravates the wear of the tool edge.



  (4) The tensile strength of the coating is reduced, which is similar to that of gray cast iron.



  It can be seen from the above processing characteristics that the tool is easy to cut into the coating, but it is quickly blunt. The bonding strength of the coating is low. The automatic sandblasting machine requires that the cutting edge be kept sharp during cutting. The hardness of the hard spots in the coating is high, and the low thermal conductivity makes the cutting edge dull quickly. This pair of contradictory characteristics is that the coating is difficult to process main reason.