Factors Affecting Elastic Aftereffect in Cemented Carbide Pressing

The factors affecting the elastic aftereffect during the hard alloy pressing process are as follows:

① The influence of the composition of the mixture: the powder with high hardness has a large elastic after-effect when pressed, and the elastic after-effect value increases as the hardness of the powder increases. The elastic aftereffect value of WC-Co cemented carbide mixture is generally lower than that of WC-TiC-Co cemented carbide mixture. The elastic aftereffect value of the high-cobalt cemented carbide mixture is lower than that of the low-cobalt mixture, and the high content of powder oxides and impurities will also increase the elastic aftereffect value.

② The influence of the physical properties of the powder: the powder has a fine particle size, the roughness of the particles is reduced, and the bonding strength between the particles is reduced, which will increase the elastic aftereffect of the compact. When the pellets of the mixture are too dry and hardened, the elastic aftereffect will also increase.

③ Influence of suppression pressure and suppression speed: As the suppression pressure or suppression speed increases, the elastic aftereffect value increases. At the same time, the elastic aftereffect is also related to the diameter of the compact. The larger the diameter, the greater the elastic aftereffect. Because the pressing speed is too fast, the gas in the compact will not overflow in time, and the elastic aftereffect will increase.

④ Influence of forming agent: The green compact strength of rubber, PEG, etc. used as forming agent is higher than that of paraffin wax forming agent, and the elastic after-effect is low. When the amount of forming agent is insufficient, the strength of the green compact will be reduced, and the elastic after-effect will be reduced. The value increases. All the factors that increase the bonding strength (green compact strength) between powder particles will cause the elastic aftereffect to decrease. All factors that increase the contact stress between powder particles will lead to an increase in the elastic aftereffect.

The ratio of the powder filling height to the green compact height in the cavity is called the compression ratio. The main factor that affects the compression ratio is the packing density of the powder. Normally, the compression ratio of the cemented carbide mixture is in the range of 2.5~4.0, the spray material is generally 3.5~4.0, and the mechanical granulation is 2.5~3.0.

Appears along the edge of the pressure block, and is at a certain angle to the pressure surface, forming a neat interface called delamination. If the cobalt content of the mixture is low, the carbide hardness is high, the powder or granules are finer, the forming agent is too small or unevenly distributed, the mixture is too wet or too dry, the pressing pressure is too large, and the unit weight is too large. Layered. Improving the strength of the briquettes, reducing the internal stress and elastic aftereffect of the briquettes are effective methods to solve the delamination.