The thermal spray coating is a self-fluxing alloy powder which is formed by accumulating molten particles of a high-temperature flame at a high speed. Due to this unique formation method, the sprayed layer has the following characteristics:
(1) The combination of the sprayed layer and the part base is basically a mechanical bond, and the joint strength is low, generally only 20^-30 MPa. If the cutting force is too large during processing, the coating may fall off, so this is an important characteristic that should first be noticed.
(2) The hardness of the base of the coating is medium, which is equivalent to the hardness of the general quenched and tempered steel, but a large number of hard spots such as Cr, C: and WC are dispersed in the coating matrix, and the microhardness is as high as 10480 MP. 1607OMPa. These hard spots cause severe abrasive wear on the blade, which makes the blade quickly become dull.
(3) Because the coating of the sandblasting machine is porous, it has a certain porosity, and because the coating contains more nickel-chromium elements, the thermal conductivity of the coating is very low, and the cutting heat is difficult to be transmitted from the workpiece and the chips. The heat is concentrated on the tip of the tool, and the thermal effect during cutting exacerbates the blade wear.
(4) The tensile strength of the coating is lowered, which is similar to the strength of gray cast iron.
From the above processing characteristics, the tool is easy to cut into the coating, but it is quickly blunt. The bonding strength of the coating is low. The automatic blasting machine requires the sharp edge of the blade to be cut during cutting. The hardness of the hard spot in the coating is high, and the low thermal conductivity makes the blade blunt quickly. This contradiction is that the coating is difficult to process. main reason.