Tungsten Carbide Cobalt Chromium Spraying for Valves of Petroleum Pipeline

As a wear-resistant and corrosion-resistant coating, thermal sprayed WC-Co-Cr coating has been widely used in aerospace, metallurgy, machinery and other fields because of its high hardness and good toughness.

Compared with the electroplated hard chrome layer, the thermal spray WC/Co coating has obvious advantages in wear resistance, corrosion resistance, fatigue resistance, etc., and the preparation speed is fast, the environmental pollution is small, and the performance of the thermal spray depends on the heat. The process of preparing a thermal spray powder of an ultra-high pressure seal coating by spraying the powder material, comprising the following steps:

A.Nanocrystalline tungsten carbide with a mass percentage of 25.8 38.7% and a particle size of 0.05 0.2 micron was prepared. The prepared mass percentage was 47.3 60.2% and the particle size was 2.0 5.0 micron.

B.Mixture

According to the technological requirements, nanocrystalline tungsten carbide, medium-sized tungsten carbide and 4% chromium powder were added to the ball mill, and then deionized water and 2.0% polyvinyl alcohol were added to the ball mill. The milling time is 22 28 hours, the antioxidant with mass percentage of 0.3% and titanium carbide with grain growth inhibitor of 0.6 0.8% must be added to the mixture.

C.Granulation

An open centrifugal spray drying tower was used for drying and granulating, and spherical mixture was obtained. The rotational speed of centrifugal spray drying plate was 11 000 to 12 000 revolutions per minute.

D.Sintering
The mixture was loaded into a three-layer graphite vessel and sintered continuously in a molybdenum wire furnace in a hydrogen-protected atmosphere. The pushing speed of the vessel was 11_13 minutes/vessel. The sintering temperature was 950 ℃ in the first zone and 1250 ℃ in the second zone.

E.Fragmentation classification

After sintering, the products were broken by mechanical method, and the final thermal sprayed powder was obtained by sieving or air flow classification according to the particle size distribution range. The particle size was 5_30 micron and the bulk density was 5.5_6.2 g/cm³.

The synthesized WC_10Co₄Cr thermal spraying powder has excellent toughness index and good hardness and strength. It can fully meet the requirements of valve sealing surface. It is suitable for preparing valve sealing surface coating in high-speed air fuel spraying equipment.

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