Tungsten carbide rods have been widely used in various fields due to their special corrosion resistance, high hardness, excellent fracture toughness and compressive strength. With the development of science and technology, molding technology has developed from isostatic cool pressing and mould pressing to more modern and economic extrusion process.

 

Extrusion process can be used to form a uniform length and unlimited length of tungsten carbide bar. The extrusion process has great influence on the quality of cemented carbide bar, which needs to be controlled reasonably. Among them, the mould and the binder are two important content controls.

 

1, Mould

In the extrusion process of powder mixture, there is the problem of forming and densification. If the die is not designed properly, it will cause the density of the extrusion piece to be too low and uneven, which will lead to the subsequent sintering deformation. So, the compression ratio must be chosen correctly when designing mould.

 

For tungsten carbide bars, the compression ratio (K) is usually controlled below 95%, and the extrusion nozzle taper angle at 45^。 to 75^。. When the cone angle is too small, the feed will easily flow into the shaping zone, but the center density of the blank will decrease accordingly. If the cone angle is too large, the extrusion pressure will be too large, which will lead to the transverse delamination of the blank.

 

 

2, Binder

The binder plays an important role in strengthening the flow and maintaining the shape of the cemented carbide bar during extrusion. It can be said that the binder is the core of the extrusion forming technology of cemented carbide rods. It is usually composed of the components of the bonding skeleton, the plasticizing component and a small number of additive additives acting as lubricating agents.

 

Requirements of binder can be summarized as: good wetting with powder, strong adhesion, no chemical reaction with powder, certain strength and toughness. The binder must meet the forming process of powder liquidity requirements under the premise, fully consider the degreasing process effect on extrusion performance, the performance of selection of forming agent and removing formula and forming agent and final product combination.

 

It is necessary to strictly control the amount of binder, when the amount of added is too low, the bar forming will be difficult, and there will be fracture phenomenon. When the addition amount is too high, it is easy to squeeze, but the deformation of the product is large, and it brings difficulty to subsequent degreasing.