Nanometer 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.

Some companies use a shield cutting tools to weld a tungsten carbide cutter ring with a plasma arc. It is welded with a layer of hard-wearing surfacing layer by plasma arc surfacing on both sides of the outer edge of the cutter ring to improve the wear resistance, high temperature resistance, corrosion resistance or impact resistance of the tool. The production process of grade tungsten carbide powder is:

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

The lyophilized precursor block is only a microporous honeycomb block formed by sublimation of water molecules. The position of the tungsten source and carbon source with small and uniform volume change does not change, and the fixed carbon source and its surrounding location are also relatively fixed. The tungsten source reacts and is positionally homogenized to finally form uniform tungsten carbide, and is also a nano-sized tungsten carbide block; due to the uniformity of the microporous pores of the block after lyophilization, it is relatively easy to achieve uniform particle size. The purpose of nano-scale tungsten carbide; moreover, the microporous nano-scale tungsten carbide has a relatively uniform heat absorption in the plasma arc surfacing process, and can be rapidly melted and combined with the outer edge of the cutter ring, and the strength of the combination is improved. Correspondingly, the dilution ratio of the weld overlay is further reduced, and the dilution rate can be controlled to be less than 5%.

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