Nano Tungsten Carbide Powder for Shield Cutting Tools

At present, China's major cities are booming in the construction of rail transit projects. Because of its unparalleled advantages, shield method has been widely used in the construction of rail transit tunnels.

In view of the problems of poor wear resistance and impact resistance of shield cutting tools in the existing technology, some enterprises adopt a manufacturing process of plasma arc surfacing tungsten carbide cutting ring for shield cutting tools. A layer of hardfacing layer is deposited on both sides of the outer edge of the cutter ring by plasma arc surfacing to improve the wear resistance, high temperature resistance, corrosion resistance or impact resistance of the cutter

Step 1: mixing: 55% - 60wt% ammonium metatungstate aqueous solution and nano carbon black powder are mixed and stirred evenly to form a fluid shape, and are added into the mold to form a precursor;

Step 2: deep freezing: quickly transfer the precursor into deep freezing space for rapid deep freezing; the temperature is - 150 ~ - 160 ℃, and the time is 200 ~ 240 min;
Step 3: freeze-drying: quickly transfer the frozen precursor into the vacuum freeze-drying bin for freeze-drying;

Step 4: carbonization: close the cold well of the vacuum freeze-drying chamber, raise the temperature to 900-1200 ℃ for carbonization reduction reaction to prepare nano tungsten carbide block;

Step 5: smash the nano tungsten carbide powder block with a grinder to the nano WC powder.

After freeze-drying, the precursor block is just a microporous honeycomb block formed after water molecules sublimation, the small and uniform volume change of tungsten source and carbon source location will not change, the carbon source with fixed location and its surrounding location will react with the tungsten source with fixed location, and the location is equipotential, and finally generate uniform tungsten carbide, which is also a nanometer scale tungsten carbide block; because of the block after freeze-drying. The uniformity of microporous pores makes it easy to produce nano-sized WC with uniform particle size. Moreover, the heat absorption of microporous nano-sized WC in the plasma arc surfacing process is relatively uniform, which can rapidly melt and combine with the outer edge of the cutter ring. The strength of the combination is improved, and the dilution rate of the surfacing can be further reduced. The dilution rate can be controlled at less than 5%.

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