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Analysis of Causes of Excessive Carbon Content in Lost Foam Casting Production and Solutions!

来源: 编辑 浏览次数:636 Release date: 2019-10-15 source: editor views: 636
01
The choice of pattern materials for castings was unreasonable. Among the choices of white mold material for castings, one is that the carbon content is high; the other is that the density of the white mold is too high. As a result, the carbon content of the casting pattern during the thermal decomposition during the casting process is high, and the liquid and mist free carbon content of the casting is high during the casting filling process, which increases the carburizing probability of the steel casting.
02
Choose foam with low carbon content or pre-fired beads to make castings. At present, the domestically produced polystyrene foam EPS has a carbon content of 92%; the styrene methyl methacrylate copolymer resin STMMAC has a carbon content of 69.6%; the expandable polymethyl methacrylate EPMMA has a carbon content of 60.0 %; The use of EPS to make casting molds will increase the carbon content of molten steel by 0.1% to 0.3% during the casting process. When using EPMMA or STMMA materials to make casting molds, the castings are caused by the mold material during the casting process. The amount of carbon added is less than 0.05%.
03
Select the appropriate foam density to make the casting pattern. When ensuring the technical requirements of the mold production temperature and other defects caused by the quality of the foam during casting casting, the smaller the foam density and the smaller the foam, the better the reduction of carburizing and carbon deposition in the casting.
04
Improve the quality of castings. When the casting pattern can be made as a whole, the combined production should not be used, and the bonding surface of the casting pattern should be minimized. When bonding the patterns, it is necessary to ensure that the bonding surface of the pattern is smooth and flat, to minimize the amount of adhesive for bonding, and to reduce the amount of thermal decomposition products of the adhesive, which reduces the carbon content of the thermal decomposition products.
05
Use adhesives with low or no carbon content. That is to say, the special adhesive for negative pressure casting bonding should be used for the combined bonding of the pattern, and the low-quality ordinary adhesive with high carbon content is not used for bonding. In addition, in the combination of the patterns, when the bonding temperature and the bonding strength of the glue are ensured, the amount of the adhesive should be reduced as much as possible, thereby reducing the thermal decomposition products of the adhesive.
06
Select and determine a reasonable gating system. For the casting process design of the casting, it is necessary to make the casting have the effect of accelerating the gasification of the foam during the pouring process, and to minimize and stagger the contact and reaction time between the liquid phase and the solid phase in the thermal decomposition product, thereby reducing or avoiding Carburizing of the casting occurs.
07
Select and determine the appropriate casting temperature and speed for the casting. Because of the same casting process, the actual casting temperature is completely different when the molten steel is poured at the same temperature for casting. If the pouring temperature is increased and the pouring speed is also increased, it will cause the thermal decomposition of the casting pattern to accelerate and not be easily gasified, and the amount of the thermally decomposed products in the liquid phase will increase. After being squeezed out of the gap, the thermal decomposition products are often squeezed between the coating layer of the pattern and the molten metal, or the cold and dead angles of the molten steel flow, which causes the contact surface to increase, the carbon concentration to increase, and the carburizing amount to increase. At the same time, special attention should be paid to the fact that if the casting process molding is unreasonable, the molten steel pouring temperature is too high and the pouring speed is too fast, it will cause gas production and reverse spray production accidents.
08
Add flame retardants to the pattern to prevent cracking and combustion at high temperature, so that it does not produce carbon products or less solid products. Such as adding flame retardants 0.5% to 3% chlorinated paraffin, triphosphate, pentabromodiphenyl ether, antimony trioxide and so on. At the same time, 0.2 %% to 0.5% of dibenzoyl peroxide, dilauroyl peroxide, etc. are added to accelerate the transformation of the flame retardant-containing pattern into gas, thereby reducing the occurrence of carburizing conditions and conditions during the casting process. .
09
An anti-carburizing material can be added during the brushing of the pattern coating layer. Add some anti-carburization catalysts in the preparation process of the sample coating, such as alkali metal salt and limestone powder, to configure the sample to be able to decompose a sufficient amount of CO and CO2 gas in the coating layer after casting to absorb carbon, thereby preventing the casting from seeping. Carbon; or adding an oxidant to the coating to promote the thermal decomposition of the C, H2 gas into a neutral gas, thereby reducing the thermal decomposition of C and H into the casting, causing carbon increase or hydrogen embrittlement.
According to the analysis and summary of various reasons that may cause the excessive carbon content in the production of low-carbon steel castings by lost foam production, the technical parameter design of the production process of low-carbon steel castings produced by lost foam was modified and adjusted to create a Reasonable and reliable low-carbon steel casting casting technical conditions set the system's production operation mode, thereby ensuring the technical requirements for the production of qualified low-carbon steel castings using lost foam. When adjusting the technical parameters of the production operation control process for the production of low-carbon steel castings from lost foam production, special attention should be paid to the following points:
01
With intermediate frequency smelting, it is necessary to strictly control the calculation of the ingredients of the smelted carbon steel and the operations of actual ingredients, material selection and feeding. The calculation of the ingredients is the key to ensure that the molten steel with qualified composition and the minimum gas and inclusions are cast to produce high-quality steel castings. The accuracy of the ingredients, selection and input is the fundamental guarantee for the quality of the cast products. Therefore, a strict classification system must be implemented for the returned steel scrap. In particular, it is necessary to pick out alloy steel waste and waste with unclear material, and ensure that the composition of the smelting ingredients meets the requirements of the casting process technical parameters.
02
Choose foam with low carbon content or pre-fired beads to make castings. At present, the domestically produced polystyrene foam EPS has a carbon content of 92%; the styrene methyl methacrylate copolymer resin STMMAC has a carbon content of 69.6%; the expandable polymethyl methacrylate EPMMA has a carbon content of 60.0 %; The use of EPS to make casting molds will increase the carbon content of molten steel by 0.1% to 0.3% during the casting process. When using EPMMA or STMMA materials to make casting molds, the castings are caused by the mold material during the casting process. The amount of carbon added is less than 0.05%.
03
Select the appropriate foam density to make the casting pattern. When ensuring the technical requirements of the mold production temperature and other defects caused by the quality of the foam during casting casting, the smaller the foam density and the smaller the foam, the better the reduction of carburizing and carbon deposition in the casting.
04
Improve the quality of castings. When the casting pattern can be made as a whole, the combined production should not be used, and the bonding surface of the casting pattern should be minimized. When bonding the patterns, it is necessary to ensure that the bonding surface of the pattern is smooth and flat, to minimize the amount of adhesive for bonding, and to reduce the amount of thermal decomposition products of the adhesive, which reduces the carbon content of the thermal decomposition products.
05
Use adhesives with low or no carbon content. That is to say, the special adhesive for negative pressure casting bonding should be used for the combined bonding of the pattern, and the low-quality ordinary adhesive with high carbon content is not used for bonding. In addition, in the combination of the patterns, when the bonding temperature and the bonding strength of the glue are ensured, the amount of the adhesive should be reduced as much as possible, thereby reducing the thermal decomposition products of the adhesive.
06
Select and determine a reasonable gating system. For the casting process design of the casting, it is necessary to make the casting have the effect of accelerating the gasification of the foam during the pouring process, and to minimize and stagger the contact and reaction time between the liquid phase and the solid phase in the thermal decomposition product, thereby reducing or avoiding Carburizing of the casting occurs.
07
Select and determine the appropriate casting temperature and speed for the casting. Because of the same casting process, the actual casting temperature is completely different when the molten steel is poured at the same temperature for casting. If the pouring temperature is increased and the pouring speed is also increased, it will cause the thermal decomposition of the casting pattern to accelerate and not be easily gasified, and the amount of the thermally decomposed products in the liquid phase will increase. After being squeezed out of the gap, the thermal decomposition products are often squeezed between the coating layer of the pattern and the molten metal, or the cold and dead angles of the molten steel flow, which causes the contact surface to increase, the carbon concentration to increase, and the carburizing amount to increase. At the same time, special attention should be paid to the fact that if the casting process molding is unreasonable, the molten steel pouring temperature is too high and the pouring speed is too fast, it will cause gas production and reverse spray production accidents.
08
Add flame retardants to the pattern to prevent cracking and combustion at high temperature, so that it does not produce carbon products or less solid products. Such as adding flame retardants 0.5% to 3% chlorinated paraffin, triphosphate, pentabromodiphenyl ether, antimony trioxide and so on. At the same time, 0.2 %% to 0.5% of dibenzoyl peroxide, dilauroyl peroxide, etc. are added to accelerate the transformation of the flame retardant-containing pattern into gas, thereby reducing the occurrence of carburizing conditions and conditions during the casting process. .
09
An anti-carburizing material can be added during the brushing of the pattern coating layer. Add some anti-carburization catalysts in the preparation process of the sample coating, such as alkali metal salt and limestone powder, to configure the sample to be able to decompose a sufficient amount of CO and CO2 gas in the coating layer after casting to absorb carbon, thereby preventing the casting from seeping. Carbon; or adding an oxidant to the coating to promote the thermal decomposition of the C, H2 gas into a neutral gas, thereby reducing the thermal decomposition of C and H into the casting, causing carbon increase or hydrogen embrittlement.
According to the analysis and summary of various reasons that may cause the excessive carbon content in the production of low-carbon steel castings by lost foam production, the technical parameter design of the production process of low-carbon steel castings produced by lost foam was modified and adjusted to create a Reasonable and reliable low-carbon steel casting casting technical conditions set the system's production operation mode, thereby ensuring the technical requirements for the production of qualified low-carbon steel castings using lost foam. When adjusting the technical parameters of the production operation control process for the production of low-carbon steel castings from lost foam production, special attention should be paid to the following points:
01
With intermediate frequency smelting, it is necessary to strictly control the calculation of the ingredients of the smelted carbon steel and the operations of actual ingredients, material selection and feeding. The calculation of the ingredients is the key to ensure that the molten steel with qualified composition and the minimum gas and inclusions are cast to produce high-quality steel castings. The accuracy of the ingredients, selection and input is the fundamental guarantee for the quality of the cast products. Therefore, a strict classification system must be implemented for the returned steel scrap. In particular, it is necessary to pick out alloy steel waste and waste with unclear material, and ensure that the composition of the smelting ingredients meets the requirements of the casting process technical parameters.
02
Choose foam with low carbon content or pre-fired beads to make castings. At present, the domestically produced polystyrene foam EPS has a carbon content of 92%; the styrene methyl methacrylate copolymer resin STMMAC has a carbon content of 69.6%; the expandable polymethyl methacrylate EPMMA has a carbon content of 60.0 %; The use of EPS to make casting molds will increase the carbon content of molten steel by 0.1% to 0.3% during the casting process. When using EPMMA or STMMA materials to make casting molds, the castings are caused by the mold material during the casting process. The amount of carbon added is less than 0.05%.
03
Select the appropriate foam density to make the casting pattern. When ensuring the technical requirements of the mold production temperature and other defects caused by the quality of the foam during casting casting, the smaller the foam density and the smaller the foam, the better the reduction of carburizing and carbon deposition in the casting.
04
Improve the quality of castings. When the casting pattern can be made as a whole, the combined production should not be used, and the bonding surface of the casting pattern should be minimized. When bonding the patterns, it is necessary to ensure that the bonding surface of the pattern is smooth and flat, to minimize the amount of adhesive for bonding, and to reduce the amount of thermal decomposition products of the adhesive, which reduces the carbon content of the thermal decomposition products.
05
Use adhesives with low or no carbon content. That is to say, the special adhesive for negative pressure casting bonding should be used for the combined bonding of the pattern, and the low-quality ordinary adhesive with high carbon content is not used for bonding. In addition, in the combination of the patterns, when the bonding temperature and the bonding strength of the glue are ensured, the amount of the adhesive should be reduced as much as possible, thereby reducing the thermal decomposition products of the adhesive.
06
Select and determine a reasonable gating system. For the casting process design of the casting, it is necessary to make the casting have the effect of accelerating the gasification of the foam during the pouring process, and to minimize and stagger the contact and reaction time between the liquid phase and the solid phase in the thermal decomposition product, thereby reducing or avoiding Carburizing of the casting occurs.
07
Select and determine the appropriate casting temperature and speed for the casting. Because of the same casting process, the actual casting temperature is completely different when the molten steel is poured at the same temperature for casting. If the pouring temperature is increased and the pouring speed is also increased, it will cause the thermal decomposition of the casting pattern to accelerate and not be easily gasified, and the amount of the thermally decomposed products in the liquid phase will increase. After being squeezed out of the gap, the thermal decomposition products are often squeezed between the coating layer of the pattern and the molten metal, or the cold and dead angles of the molten steel flowing, which causes the contact surface to increase, the carbon concentration to increase, and the amount of carburizing. At the same time, special attention should be paid to the fact that if the casting process molding is unreasonable, the molten steel pouring temperature is too high and the pouring speed is too fast, it will cause gas production and reverse spray production accidents.
08
Add flame retardants to the pattern to prevent cracking and combustion at high temperature, so that it does not produce carbon products or less solid products. Such as adding flame retardants 0.5% to 3% chlorinated paraffin, triphosphate, pentabromodiphenyl ether, antimony trioxide and so on. At the same time, 0.2 %% to 0.5% of dibenzoyl peroxide, dilauroyl peroxide, etc. are added to accelerate the transformation of the flame retardant-containing pattern into gas, thereby reducing the occurrence of carburizing conditions and conditions during the casting process. .
09
An anti-carburizing material can be added during the brushing of the pattern coating layer. Add some anti-carburization catalysts in the preparation process of the sample coating, such as alkali metal salt and limestone powder, to configure the sample to be able to decompose a sufficient amount of CO and CO2 gas in the coating layer after casting to absorb carbon, thereby preventing the casting from seeping Carbon; or adding an oxidant to the coating to promote the thermal decomposition of the C, H2 gas into a neutral gas, thereby reducing the thermal decomposition of C and H into the casting, causing carbon increase or hydrogen embrittlement.
10
Strictly control the quality of recycling sand. Ensure that the production and use of molding sand meet the requirements of process and technical parameters, especially the content of dust in the molding sand must be strictly controlled to prevent the permeability of the casting sand box from being reduced by the dust, resulting in the thermal decomposition products of the casting pattern not being discharged out of the casting cavity in time, and Increasing the chance of carbon increase in castings.
11
When casting low-carbon steel castings, the vacuum degree of the pouring sand box should be increased. The molding sand box should adopt the structure of vacuuming the wall of the box. During the pouring, the vacuum of the wall of the box can accelerate the escape of the thermal decomposition products to the outside of the cavity, thereby reducing the concentration and contact time of the thermal decomposition products of the pattern, reducing or avoiding casting steel. Carburization and carbon deposition of parts. When the size of the molding sand is 20 mesh to 40 mesh, the casting steel casting is preferably 0.03 MPa to 0.06 MPa. If the negative pressure is too large, sand sticking and other defects will occur.
12
For the casting of low-carbon steel castings, bottom casting should be used as far as possible to make the filling flow of the molten steel smooth, and the thermal decomposition products of the pattern can smoothly enter the slag collecting cavity or riser, thereby reducing and reducing the thermal decomposition of the pattern. The contact reaction time between the liquid and solid phases in the product reduces and eliminates the chance of carbon addition. The pouring of low-carbon steel castings using the rain-type pouring system will increase the working conditions and conditions of increasing carburization, carburizing, and carbon deposition of the castings, which will cause serious defects in the castings and should not be used.

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