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Deformation and Improvement of Vacuum Sintered Cemented Carbide
Vacuum sintering is currently a widely used product sintering process. Using a vacuum sintering furnace can achieve higher alloy density, and the production cost is relatively low. However, in actual production, the sintered products in the vacuum furnace often have bending deformation. Seriously affect production efficiency.
Causes of product deformation in vacuum sintering furnace
1.Uneven carbon distribution
Usually, the bending deformation of cemented carbide sintered body occurs in its cooling and solidification stage. When the sintered body is cooled, its solidification always starts from the part with low carbon content. If the carbon content of a part is low, this point solidifies first, and the gaps generated by shrinkage during solidification are supplemented by other points, so the same sintered body always protrudes at the part with low carbon content, while the place with high carbon content is concave . Therefore, the uneven carbon distribution of the green compact in the vacuum sintering furnace will lead to bending deformation of the product.
2.Uneven temperature distribution
There is always a temperature gradient in vacuum sintering. The heat transfer mode in the vacuum sintering furnace is mainly radiation and conduction. The strength and speed of heat transfer and the temperature gradient formed on the product, the distance from the heat source, the size and shape of the heated product It is related to the loading method. For example, cobalt tends to flow in the direction of high temperature after heating and melting, that is, the part with high temperature of the product, the cobalt content increases, and the gradient of cobalt distribution is formed to cause product deformation.
3.Uneven density of cemented carbide
Due to the limitation of the pressing method, the density distribution of the green compact in the vacuum sintering furnace is uneven. In the actual shrinkage process, the place with poor density shrinks less, while the place with high density shrinks more, resulting in product deformation.
Improvement Measures to Prevent Product Deformation in Vacuum Sintering Furnace
1.Improve the carbon atmosphere in the vacuum sintering furnace
Pay attention to the way of entering the furnace, place the product as evenly as possible in the vacuum sintering furnace, avoid the situation where the volatilization of the molding agent is hindered, and the time for removing the molding agent can be appropriately extended; for larger green compacts, use other carriers to speed up the volatilization of the molding agent. , so that the difference between the internal and external carbon content is reduced; the leakage rate of the vacuum furnace is strictly controlled, and the detection before the furnace is opened, and the detection after the program is completed, that is, the form of low-temperature and high-temperature double-layer detection, to avoid sintering in the case of leakage; for boats, it must be Carry out high-temperature calcination to remove impurities, use neutral paint as much as possible for paint, and generally do not use methods that may increase carbon such as coated paper.
2.Control the temperature in the vacuum furnace
For large products, the temperature should be around 1200°C as much as possible. Use slow heating and timely heat preservation to reduce the temperature difference, so that the temperature in the vacuum sintering furnace is basically the same, reduce the temperature difference between the inside and outside of the product, and weaken the temperature gradient. For high-quality products, a graphite sleeve can be used to cover the sintering, or the waste alloy can be used to surround the sintering to achieve the same temperature, thereby reducing the bending deformation of the product.
3.Control the uniform density of hard alloy pressing
When the pressing density has been determined, during vacuum sintering, force should be applied to the parts with poor density to make up for the defects of pressing density. When contracted, it is subjected to the frictional resistance of the boat, reducing the contracted size of the bottom so that it remains consistent with the upper part.
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