Thermal Spray Coating’s Characteristics

       

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

(1) The bonding between the spraying layer
and the part matrix basically belongs to mechanical bonding, and the bonding
strength is low, generally only 20 ^ - 30MPa. If the cutting force is too large
during machining, the coating may fall off. Therefore, this is an important
characteristic that should be paid attention to first.

(2) The matrix hardness of the coating is
medium, which is equivalent to that of 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 its microhardness is as high as 10480mp. 1607OMPa。 These hard spots cause serious abrasive wear on the cutting tool,
making the sharp edge blunt quickly.

(3) Because the coating of sand blasting
machine 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, the cutting heat is difficult to be transmitted from the workpiece
and chip, and the heat is mostly concentrated on the tool tip. The thermal
effect during cutting aggravates the wear of the tool edge.

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

From the above processing characteristics,
it can be seen 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 sand blasting
machine requires to keep the blade sharp during cutting. The hardness of the
hard points in the coating is high and the thermal conductivity is low, which
makes the blade blunt quickly. This contradictory characteristic is the main
reason why the coating is difficult to process.

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