The refractory brick forming template has a large working surface. It is subjected to the extrusion, scraping and grinding of the hard particles of refractory materials on a 200t press, and its service conditions are relatively harsh. Therefore, the working surface of the mold is required to have high hardness, high wear resistance, sufficient strength and appropriate toughness. In foreign countries, high-alloy cold-worked die steel is used to make templates. After heat treatment, the surface hardness is high, the wear resistance is good, but the brittleness is large, the mold is easy to crack during installation and the cost is high. Many domestic refractory factories have tried high-chromium cast iron, high-carbon chromium-molybdenum wear-resistant alloy and cemented carbide, etc., or carried out boronizing surface strengthening of carbon steel molds, or composite treatment of carburizing and boronitriding, but The service life is still average, and the template suffers the most severe wear and failure earlier. Generally, about 2,000 to 4,000 refractory bricks are stamped for each set of molds, which will fail.
There are many forms of template failure. In addition to failure due to improper operation and installation, the following failure modes are more common.
(1) The service surface of the formwork is uniformly worn everywhere. When the brick forming part of the lower part of the formwork wears a lot, the size of the brickwork is out of tolerance, or the brickwork is difficult to demold, the formwork will fail. This type of failure is a normal failure.
(2) At the bottom of the template, the brick molding part, the wear of the board surface is not synchronized, resulting in pits of different sizes and different shapes on the surface. Bricks are hindered when demolding, and the surface of the bricks appears wrinkles and cracks after demolding. This type of failure is more common.
(3) A pit is formed on the surface of the template first, and then the pit is continuously expanded along the length of the surface under the scraping action of the hard particles to grind one or more grooves of different depths and different widths, causing the template to be scrapped. This failure form is also more common.
Template failure reason
Using a wire cutting machine to cut the finished template horizontally to make a sample for metallographic analysis and hardness testing.
The main reasons for the failure of steel formwork are as follows.
(1) The carburized layer of the template is shallow and the carbon concentration is not high. The sample taken from the template was protected and annealed with a high-temperature anti-oxidation and decarburization coating. The depth of the carburized layer was measured by metallographic method, and the carbon content of the surface layer was roughly estimated. The depth of the seepage layer is only 1.4 ~ 2.0mm. Microstructure observation shows that the carbon content of the surface layer is not high, and only a small amount of discontinuous secondary cementite network appears on the top surface of the template. The carbon content of the surface layer is estimated to be about 0.8%~0.9%. The infiltration layer of the template is shallow, and the depth of the hardened layer after quenching is also shallow. Due to the low carbon concentration of the surface layer and no secondary carbides in the quenched state, the wear resistance of the template will not be too high.
(2) The carburized layer of the template is shallow, the transition zone is narrow, and the hardness of the inner layer is low. The hardness measurement shows that the hardness decreases rapidly from the surface of the template to the core, and the hardness gradient is very large. The hardness of some parts 1.5mm from the surface has dropped below HRC30. Once the surface layer is worn, the wear resistance of the template will drop sharply.
(3) The hardness of the template is extremely uneven, and there are many soft spots. The hardness of the high hardness area is up to HRC62, and the hardness of the soft spot area is less than HRC35. The area with high hardness has better wear resistance and is not easy to wear, while the soft spot area has poor wear resistance and is easy to wear and sink, that is, the asynchrony of wear everywhere causes premature pits in the template.
The above are the main reasons leading to premature failure of the template. This is caused by improper selection of template materials and some problems in the heat treatment process.
Our company has a mature technical solution for the wear-resistant coating of refractory brick molds, and has been verified by many customers. The use of heat treatment and spraying tungsten carbide technology can increase the service life of the mold by more than 3 times. Generally, each set of molds can be approximately Punching 10,000 to 20,000 refractory bricks.
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