Sand casting
2023-09-15 12:12:36
In order to ensure the quality of the casting, the core used in sand casting is generally a dry core. According to different binders used in the core, the core is divided into clay sand core, oil sand core and resin sand core.
The molds used for sand casting are generally composed of an outer sand type and a core. In order to improve the surface quality of the casting, a layer of paint is often applied to the sand and core surfaces. The main components of the coating are powdery materials and binders with high refractoriness, high chemical stability, and a carrier (water or other solvent) and various additives for easy application.
Raw materials and process sand
The basic raw materials for making sand are foundry sand and sand binder. The most common foundry sand is siliceous sand. Zinc sand, chromite ore, corundum sand and other special sands are used when the high temperature performance of silica sand cannot meet the requirements. In order to make the sand mold and the core have a certain strength, when the liquid metal is conveyed, combined and poured, it is not deformed or damaged. Generally, a sand binder is added in the casting, and the loose sand is bonded to form sand. The most widely used molding sand binder is clay, and various drying oils or semi-drying oils, water-soluble silicates or phosphates, and various synthetic resins can be used as the molding sand binder. The external sand type used in sand casting is divided into three types: clay wet sand type, clay dry sand type and chemical hardening sand type.
Clay wet sand type
The soil and the right amount of water are the main binders of the molding sand. After being made into a sand mold, the water is directly combined and poured in a wet state. Wet casting has a long history and is widely used. The strength of the wet sand depends on the clay slurry in which the clay and water are mixed in a certain ratio. Once the sand is mixed, it has a certain strength. After the sand is made into a sand mold, it can meet the requirements of the combination and casting. Therefore, the amount of clay and moisture in the molding sand are important process factors.
The sand and core sand are cast into a molding material, and the liquid metal is filled with a mold under gravity to produce a casting method. Steel, iron and most non-ferrous alloy castings can be obtained by sand casting. Since the molding materials used for sand casting are cheap and easy to obtain, the molds are easy to manufacture, and can be adapted to single-piece production, batch production and mass production of castings. For a long time, it has been the basic process in casting production.
The mold used for casting is generally composed of an outer sand type and a core. In order to improve the surface quality of the casting, a layer of paint is often applied to the sand and core surfaces. The main components of the coating are powdery materials and binders with high refractoriness, high chemical stability, and a carrier (water or other solvent) and various additives for easy application.
The basic raw materials for making sand are foundry sand and sand binder. The most common foundry sand is siliceous sand. Zinc sand, chromite ore, corundum sand and other special sands are used when the high temperature performance of silica sand cannot meet the requirements. In order to make the sand mold and the core have a certain strength, when the liquid metal is conveyed, combined and poured, it is not deformed or damaged. Generally, a sand binder is added in the casting, and the loose sand is bonded to form sand. The most widely used molding sand binder is clay, and various drying oils or semi-drying oils, water-soluble silicates or phosphates, and various synthetic resins can be used as the molding sand binder. The external sand type used in sand casting is divided into three types: clay wet sand type, clay dry sand type and chemical hardening sand type.
The wet sand type uses clay and an appropriate amount of water as the main binder of the molding sand, and is formed into a sand type and directly combined and poured in a wet state. Wet casting has a long history and is widely used. The strength of the wet sand depends on the clay slurry in which the clay and water are mixed in a certain ratio. Once the sand is mixed, it has a certain strength. After the sand is made into a sand mold, it can meet the requirements of the combination and casting. Therefore, the amount of clay and moisture in the molding sand are important process factors.
The advantages of wet sand casting are: 1 clay is rich in resources and cheap. 2 The used clay wet sand can be recycled and reused after proper sand treatment. 3 The cycle for manufacturing the mold is short and the work efficiency is high. 4 Mixed sand can be used for a long time. 5 sand type tamping can still withstand a small amount of deformation without damage, which is very beneficial for drafting and lower core. Disadvantages are: 1 When the sand is mixed, the viscous clay slurry is coated on the surface of the sand, and it is necessary to use a high-power sand mixing device with a bismuth effect, otherwise it is impossible to obtain a good quality sand. 2Because the sand is well mixed, it has a relatively high strength. The molding sand is not easy to flow during the molding, and it is difficult to compact. The manual molding is both laborious and requires a certain skill. When the machine is used, the equipment is complicated and huge. 3 The rigidity of the mold is not high, and the dimensional accuracy of the casting is poor. 4 castings are prone to defects such as sand washing, sand inclusion, and porosity. At the beginning of the 20th century, the foundry industry began to use sand-mixed sand mixers to improve the quality of clay wet sand. The new high-power sand mixer can achieve high efficiency and high quality in the sand mixing work. The appearance of the shock compaction molding machine, which is mainly based on earthquakes, has significantly improved the compactness and uniformity of the mold. With the improvement of the dimensional accuracy and surface quality requirements of castings, a high-pressure molding machine based on compaction has emerged. The use of a high-pressure molding machine to produce a clay wet sand type not only improves the dimensional accuracy of the casting, but also improves the surface quality, and simplifies the operation of the compact mold and shortens the cycle, thereby realizing high speed and automation of the entire molding and forming process. A new molding machine for gas shock and pressure, using the thixotropy of clay slurry, can be applied to a very tight mold by instantaneously applying a pressure of 0.5 MPa. These advances are important conditions for clay wet sand casting to meet the requirements of modern industry. This traditional process has therefore been used to produce a large number of high quality castings.
The wet moisture of the molding sand used for the clay seed type is slightly higher than that of the wet type. After the sand mold is prepared, the surface of the cavity should be coated with refractory paint, and then dried in an oven. After it is cooled, it can be combined and poured. It takes a long time to dry the clay sand type, which consumes a large amount of fuel, and the sand type is easily deformed during the drying process, which affects the accuracy of the casting. Clay dry sand types are commonly used in the manufacture of steel castings and larger cast iron parts. Since the chemical hardening sand has been widely used, the dry sand type has been eliminated.
The type of sand used for this sand type of chemically hardened sand is called chemically hardened sand. The binder is generally a substance which can undergo molecular polymerization under the action of a hardener to form a three-dimensional structure, and various synthetic resins and water glass are commonly used. There are basically three ways of chemical hardening.
Hard: Both binder and hardener are added during sand mixing. After the sand or core is made, the binder reacts under the action of the hardener to cause the sand or core to harden by itself. The self-hardening method is mainly used for styling, but it is also used to manufacture larger cores or to produce cores with a small batch size.
Fog hardening: Add binder and other auxiliary additives during sand mixing without first adding hardener. After molding or core making, a gaseous hardener is blown in or blown into the gaseous carrier to atomize the liquid hardener, which is dispersed in the sand or core, resulting in sand hardening. Aerosol hardening is mainly used for core making and sometimes for small sand types.
Hardening: Adding a binder during sand mixing and a latent hardener that does not work at room temperature. After the sand or core is formed, it is heated, at which time the latent hardener reacts with certain components of the binder to form an effective hardener that hardens the binder, thereby hardening the sand or core. The heat hardening method is mainly used for core making in addition to the small shell sand type.
The characteristics of the hardened sand casting process are as follows: (1) The strength of the chemically hardened sand type is much higher than that of the clay sand type, and after the sand type is formed, it is released after being hardened to have a relatively high strength, and no modification is required. Therefore, the mold can accurately reflect the size and contour shape of the pattern, and is not easily deformed in the subsequent process. The resulting casting has a high dimensional accuracy. 2 Because the viscosity of the binder and hardener used are not high, it is easy to mix with the sand. The structure of the sand mixing equipment is light, low in power and high in productivity, and the sand processing work can be simplified. 3 The mixed molding sand has good fluidity before hardening, and the molding sand is easy to compact during molding, so there is no need for a large and complicated molding machine. 4 When using chemically hardened sand, the molding materials such as wood, plastic and metal can be selected according to the production requirements. 5 The content of binder in chemically hardened sand is much lower than that of clay sand, and there is no powdery auxiliary material. For example, the original sand with the same grain size is used, and the gap between sand grains is much larger than that of clay sand. In order to avoid metal penetration between the sand during casting, the sand or core surface should be coated with a good quality coating. 6 Chemical hardened sand with water glass as binder has low cost and no odor in working environment. However, after casting the metal in this mold, the sand is not easily broken; the used old sand cannot be directly recycled, and must be regenerated, and the regeneration of the water glass sand is more difficult. 7 Chemical hardened sand with resin as binder has higher cost, but after casting, the casting is easy to separate from the molding sand, the workload of casting cleaning is reduced, and most of the used sand can be recycled and reused.
In order to ensure the quality of the casting, the core used in sand casting is generally a dry core. According to different binders used in the core, the core is divided into clay sand core, oil sand core and resin sand core.
The core made of the core sand of the oil sand core with dry oil or semi-dry oil as the binder is widely used. The viscosity of the oil is low, and the mixed core sand has good fluidity and is easy to compact when the core is made. However, the strength of the newly formed core is very low, and it is generally carried out by using a contoured core plate, and then baked in an oven at 200 to 300 ° C for several hours, and the oil is oxidized by air to harden it. The disadvantage of this core making method is that the core is easily deformed during demolding, handling and baking, resulting in reduced dimensional accuracy of the casting; long baking time and high energy consumption.
Various cores made of resin sand for resin sand core. After the core is hardened in the core box, it can be taken out to ensure the correct shape and size of the core. Depending on the hardening method, the manufacture of resin sand cores is generally divided into two methods: hot core box core making and cold core box core making. 1 hot core box method core: appeared in the late 1950s. A furan resin is usually used as a core sand binder, and a latent hardener such as ammonium chloride is also added. When the core is made, the core box is kept at 200 to 300 ° C, and after the core sand is injected into the core box, ammonium chloride reacts with free formaldehyde in the resin to form an acid at a relatively high temperature, so that the core is hardened quickly. It takes about 10 to 100 seconds to establish the release strength. The core is made by the hot core box method, and the core has a relatively high dimensional accuracy, but the process device is complicated and expensive, consumes a lot of energy, emits irritating gas, and the working conditions of the workers are also poor. 2 cold core box method core: appeared in the late 60s. A urethane resin was used as the core sand binder. When the core is formed by this method, the core box is not heated, and the core is blown into the amine vapor for a few seconds to harden the core. This method is superior to the hot box method in terms of energy, environment, and production efficiency. In the mid-1970s, the furan resin cold box method of blowing sulfur dioxide hardened appeared. The hardening mechanism is completely different from the urethane cold box method, but the process characteristics, such as fast hardening and high core strength, are roughly the same as the urethane cold box method.
Advantages The advantages of clay wet sand casting are: 1 clay is rich in resources and cheap. 2 The used clay wet sand can be recycled and reused after proper sand treatment. 3 The cycle for manufacturing the mold is short and the work efficiency is high. 4 Mixed sand can be used for a long time. 5 sand type tamping can still withstand a small amount of deformation without damage, which is very beneficial for drafting and lower core. Disadvantages are: 1 When the sand is mixed, the viscous clay slurry is coated on the surface of the sand, and it is necessary to use a high-power sand mixing device with a bismuth effect, otherwise it is impossible to obtain a good quality sand. 2Because the sand is well mixed, it has a relatively high strength. The molding sand is not easy to flow during the molding, and it is difficult to compact. The manual molding is both laborious and requires a certain skill. When the machine is used, the equipment is complicated and huge. 3 The rigidity of the mold is not high, and the dimensional accuracy of the casting is poor. 4 castings are prone to defects such as sand washing, sand inclusion, and porosity.
Improved type At the beginning of the 20th century, the foundry industry began to use sand-mixed sand mixers to improve the quality of clay wet sand. The new high-power sand mixer can achieve high efficiency and high quality in the sand mixing work. The appearance of the shock compaction molding machine, which is mainly based on earthquakes, has significantly improved the compactness and uniformity of the mold. With the improvement of the dimensional accuracy and surface quality requirements of castings, a high-pressure molding machine based on compaction has emerged. The use of a high-pressure molding machine to produce a clay wet sand type not only improves the dimensional accuracy of the casting, but also improves the surface quality, and simplifies the operation of the compact mold and shortens the cycle, thereby realizing high speed and automation of the entire molding and forming process. A new molding machine for gas shock and pressure, using the thixotropy of clay slurry, can be applied to a very tight mold by instantaneously applying a pressure of 0.5 MPa. These advances are important conditions for clay wet sand casting to meet the requirements of modern industry. This traditional process has therefore been used to produce a large number of high quality castings.
Clay dry sand type
The wet moisture of the molding sand used for the sand type is slightly higher than that of the wet sand. After the sand mold is prepared, the surface of the cavity should be coated with refractory paint, and then dried in an oven. After it is cooled, it can be combined and poured. It takes a long time to dry the clay sand type, which consumes a large amount of fuel, and the sand type is easily deformed during the drying process, which affects the accuracy of the casting. Clay dry sand types are commonly used in the manufacture of steel castings and larger cast iron parts. Since the chemical hardening sand has been widely used, the dry sand type has been eliminated.
Chemically hardened sand
The molding sand used in this sand type is called chemically hardened sand. The binder is generally a substance which can undergo molecular polymerization under the action of a hardener to form a three-dimensional structure, and various synthetic resins and water glass are commonly used. There are basically three ways of chemical hardening.
Self-hardening: both binder and hardener are added during sand mixing. After the sand or core is made, the binder reacts under the action of the hardener to cause the sand or core to harden by itself. The self-hardening method is mainly used for styling, but it is also used to manufacture larger cores or to produce cores with a small batch size.
Aerosol hardening: Add binder and other auxiliary additives during sand mixing without first adding hardener. After molding or core making, a gaseous hardener is blown in or blown into the gaseous carrier to atomize the liquid hardener, which is dispersed in the sand or core, resulting in sand hardening. Aerosol hardening is mainly used for core making and sometimes for small sand types.
Heat hardening: Adding a binder during sand mixing and a latent hardener that does not work at normal temperature. After the sand or core is formed, it is heated, at which time the latent hardener reacts with certain components of the binder to form an effective hardener that hardens the binder, thereby hardening the sand or core. The heat hardening method is mainly used for core making in addition to the small shell sand type.
Characteristics of chemical hardening sand casting process The characteristics of chemical hardening sand casting process are as follows: (1) The strength of the chemically hardened sand type is much higher than that of the clay sand type, and after being made into a sand type, it is released after hardening to a relatively high strength, and no modification is required. . Therefore, the mold can accurately reflect the size and contour shape of the pattern, and is not easily deformed in the subsequent process. The resulting casting has a high dimensional accuracy. 2 Because the viscosity of the binder and hardener used are not high, it is easy to mix with the sand. The structure of the sand mixing equipment is light, low in power and high in productivity, and the sand processing work can be simplified. 3 The mixed molding sand has good fluidity before hardening, and the molding sand is easy to compact during molding, so there is no need for a large and complicated molding machine. 4 When using chemically hardened sand, the molding materials such as wood, plastic and metal can be selected according to the production requirements. 5 The content of binder in chemically hardened sand is much lower than that of clay sand, and there is no powdery auxiliary material. For example, the original sand with the same grain size is used, and the gap between sand grains is much larger than that of clay sand. In order to avoid metal penetration between the sand during casting, the sand or core surface should be coated with a good quality coating. 6 Chemical hardened sand with water glass as binder has low cost and no odor in working environment. However, after casting the metal in this mold, the sand is not easily broken; the used old sand cannot be directly recycled, and must be regenerated, and the regeneration of the water glass sand is more difficult. 7 Chemical hardened sand with resin as binder has higher cost, but after casting, the casting is easy to separate from the molding sand, the workload of casting cleaning is reduced, and most of the used sand can be recycled and reused.
Core
In order to ensure the quality of the casting, the core used in sand casting is generally a dry core. According to different binders used in the core, the core is divided into clay sand core, oil sand core and resin sand core.
Clay sand core
A simple core made of clay sand.
Oil sand core
The core made of core sand with dry oil or semi-drying oil as binder has a wide application. The viscosity of the oil is low, and the mixed core sand has good fluidity and is easy to compact when the core is made. However, the strength of the newly formed core is very low, and it is generally carried out by using a contoured core plate, and then baked in an oven at 200 to 300 ° C for several hours, and the oil is oxidized by air to harden it. The disadvantage of this core making method is that the core is easily deformed during demolding, handling and baking, resulting in reduced dimensional accuracy of the casting; long baking time and high energy consumption. Various cores made of resin sand for resin sand core. After the core is hardened in the core box, it can be taken out to ensure the correct shape and size of the core. Depending on the hardening method, the manufacture of resin sand cores is generally divided into two methods: hot core box core making and cold core box core making. 1 hot core box method core: appeared in the late 1950s. A furan resin is usually used as a core sand binder, and a latent hardener such as ammonium chloride is also added. When the core is made, the core box is kept at 200 to 300 ° C, and after the core sand is injected into the core box, ammonium chloride reacts with free formaldehyde in the resin to form an acid at a relatively high temperature, so that the core is hardened quickly. It takes about 10 to 100 seconds to establish the release strength. The core is made by the hot core box method, and the core has a relatively high dimensional accuracy, but the process device is complicated and expensive, consumes a lot of energy, emits irritating gas, and the working conditions of the workers are also poor. 2 cold core box method core: appeared in the late 60s. A urethane resin was used as the core sand binder. When the core is formed by this method, the core box is not heated, and the core is blown into the amine vapor for a few seconds to harden the core. This method is superior to the hot box method in terms of energy, environment, and production efficiency. In the mid-1970s, the furan resin cold box method of blowing sulfur dioxide hardened appeared. The hardening mechanism is completely different from the urethane cold box method, but the process characteristics, such as fast hardening and high core strength, are roughly the same as the urethane cold box method.
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The molds used for sand casting are generally composed of an outer sand type and a core. In order to improve the surface quality of the casting, a layer of paint is often applied to the sand and core surfaces. The main components of the coating are powdery materials and binders with high refractoriness, high chemical stability, and a carrier (water or other solvent) and various additives for easy application.
Raw materials and process sand
The basic raw materials for making sand are foundry sand and sand binder. The most common foundry sand is siliceous sand. Zinc sand, chromite ore, corundum sand and other special sands are used when the high temperature performance of silica sand cannot meet the requirements. In order to make the sand mold and the core have a certain strength, when the liquid metal is conveyed, combined and poured, it is not deformed or damaged. Generally, a sand binder is added in the casting, and the loose sand is bonded to form sand. The most widely used molding sand binder is clay, and various drying oils or semi-drying oils, water-soluble silicates or phosphates, and various synthetic resins can be used as the molding sand binder. The external sand type used in sand casting is divided into three types: clay wet sand type, clay dry sand type and chemical hardening sand type.
Clay wet sand type
The soil and the right amount of water are the main binders of the molding sand. After being made into a sand mold, the water is directly combined and poured in a wet state. Wet casting has a long history and is widely used. The strength of the wet sand depends on the clay slurry in which the clay and water are mixed in a certain ratio. Once the sand is mixed, it has a certain strength. After the sand is made into a sand mold, it can meet the requirements of the combination and casting. Therefore, the amount of clay and moisture in the molding sand are important process factors.
The sand and core sand are cast into a molding material, and the liquid metal is filled with a mold under gravity to produce a casting method. Steel, iron and most non-ferrous alloy castings can be obtained by sand casting. Since the molding materials used for sand casting are cheap and easy to obtain, the molds are easy to manufacture, and can be adapted to single-piece production, batch production and mass production of castings. For a long time, it has been the basic process in casting production.
The mold used for casting is generally composed of an outer sand type and a core. In order to improve the surface quality of the casting, a layer of paint is often applied to the sand and core surfaces. The main components of the coating are powdery materials and binders with high refractoriness, high chemical stability, and a carrier (water or other solvent) and various additives for easy application.
The basic raw materials for making sand are foundry sand and sand binder. The most common foundry sand is siliceous sand. Zinc sand, chromite ore, corundum sand and other special sands are used when the high temperature performance of silica sand cannot meet the requirements. In order to make the sand mold and the core have a certain strength, when the liquid metal is conveyed, combined and poured, it is not deformed or damaged. Generally, a sand binder is added in the casting, and the loose sand is bonded to form sand. The most widely used molding sand binder is clay, and various drying oils or semi-drying oils, water-soluble silicates or phosphates, and various synthetic resins can be used as the molding sand binder. The external sand type used in sand casting is divided into three types: clay wet sand type, clay dry sand type and chemical hardening sand type.
The wet sand type uses clay and an appropriate amount of water as the main binder of the molding sand, and is formed into a sand type and directly combined and poured in a wet state. Wet casting has a long history and is widely used. The strength of the wet sand depends on the clay slurry in which the clay and water are mixed in a certain ratio. Once the sand is mixed, it has a certain strength. After the sand is made into a sand mold, it can meet the requirements of the combination and casting. Therefore, the amount of clay and moisture in the molding sand are important process factors.
The advantages of wet sand casting are: 1 clay is rich in resources and cheap. 2 The used clay wet sand can be recycled and reused after proper sand treatment. 3 The cycle for manufacturing the mold is short and the work efficiency is high. 4 Mixed sand can be used for a long time. 5 sand type tamping can still withstand a small amount of deformation without damage, which is very beneficial for drafting and lower core. Disadvantages are: 1 When the sand is mixed, the viscous clay slurry is coated on the surface of the sand, and it is necessary to use a high-power sand mixing device with a bismuth effect, otherwise it is impossible to obtain a good quality sand. 2Because the sand is well mixed, it has a relatively high strength. The molding sand is not easy to flow during the molding, and it is difficult to compact. The manual molding is both laborious and requires a certain skill. When the machine is used, the equipment is complicated and huge. 3 The rigidity of the mold is not high, and the dimensional accuracy of the casting is poor. 4 castings are prone to defects such as sand washing, sand inclusion, and porosity. At the beginning of the 20th century, the foundry industry began to use sand-mixed sand mixers to improve the quality of clay wet sand. The new high-power sand mixer can achieve high efficiency and high quality in the sand mixing work. The appearance of the shock compaction molding machine, which is mainly based on earthquakes, has significantly improved the compactness and uniformity of the mold. With the improvement of the dimensional accuracy and surface quality requirements of castings, a high-pressure molding machine based on compaction has emerged. The use of a high-pressure molding machine to produce a clay wet sand type not only improves the dimensional accuracy of the casting, but also improves the surface quality, and simplifies the operation of the compact mold and shortens the cycle, thereby realizing high speed and automation of the entire molding and forming process. A new molding machine for gas shock and pressure, using the thixotropy of clay slurry, can be applied to a very tight mold by instantaneously applying a pressure of 0.5 MPa. These advances are important conditions for clay wet sand casting to meet the requirements of modern industry. This traditional process has therefore been used to produce a large number of high quality castings.
The wet moisture of the molding sand used for the clay seed type is slightly higher than that of the wet type. After the sand mold is prepared, the surface of the cavity should be coated with refractory paint, and then dried in an oven. After it is cooled, it can be combined and poured. It takes a long time to dry the clay sand type, which consumes a large amount of fuel, and the sand type is easily deformed during the drying process, which affects the accuracy of the casting. Clay dry sand types are commonly used in the manufacture of steel castings and larger cast iron parts. Since the chemical hardening sand has been widely used, the dry sand type has been eliminated.
The type of sand used for this sand type of chemically hardened sand is called chemically hardened sand. The binder is generally a substance which can undergo molecular polymerization under the action of a hardener to form a three-dimensional structure, and various synthetic resins and water glass are commonly used. There are basically three ways of chemical hardening.
Hard: Both binder and hardener are added during sand mixing. After the sand or core is made, the binder reacts under the action of the hardener to cause the sand or core to harden by itself. The self-hardening method is mainly used for styling, but it is also used to manufacture larger cores or to produce cores with a small batch size.
Fog hardening: Add binder and other auxiliary additives during sand mixing without first adding hardener. After molding or core making, a gaseous hardener is blown in or blown into the gaseous carrier to atomize the liquid hardener, which is dispersed in the sand or core, resulting in sand hardening. Aerosol hardening is mainly used for core making and sometimes for small sand types.
Hardening: Adding a binder during sand mixing and a latent hardener that does not work at room temperature. After the sand or core is formed, it is heated, at which time the latent hardener reacts with certain components of the binder to form an effective hardener that hardens the binder, thereby hardening the sand or core. The heat hardening method is mainly used for core making in addition to the small shell sand type.
The characteristics of the hardened sand casting process are as follows: (1) The strength of the chemically hardened sand type is much higher than that of the clay sand type, and after the sand type is formed, it is released after being hardened to have a relatively high strength, and no modification is required. Therefore, the mold can accurately reflect the size and contour shape of the pattern, and is not easily deformed in the subsequent process. The resulting casting has a high dimensional accuracy. 2 Because the viscosity of the binder and hardener used are not high, it is easy to mix with the sand. The structure of the sand mixing equipment is light, low in power and high in productivity, and the sand processing work can be simplified. 3 The mixed molding sand has good fluidity before hardening, and the molding sand is easy to compact during molding, so there is no need for a large and complicated molding machine. 4 When using chemically hardened sand, the molding materials such as wood, plastic and metal can be selected according to the production requirements. 5 The content of binder in chemically hardened sand is much lower than that of clay sand, and there is no powdery auxiliary material. For example, the original sand with the same grain size is used, and the gap between sand grains is much larger than that of clay sand. In order to avoid metal penetration between the sand during casting, the sand or core surface should be coated with a good quality coating. 6 Chemical hardened sand with water glass as binder has low cost and no odor in working environment. However, after casting the metal in this mold, the sand is not easily broken; the used old sand cannot be directly recycled, and must be regenerated, and the regeneration of the water glass sand is more difficult. 7 Chemical hardened sand with resin as binder has higher cost, but after casting, the casting is easy to separate from the molding sand, the workload of casting cleaning is reduced, and most of the used sand can be recycled and reused.
In order to ensure the quality of the casting, the core used in sand casting is generally a dry core. According to different binders used in the core, the core is divided into clay sand core, oil sand core and resin sand core.
The core made of the core sand of the oil sand core with dry oil or semi-dry oil as the binder is widely used. The viscosity of the oil is low, and the mixed core sand has good fluidity and is easy to compact when the core is made. However, the strength of the newly formed core is very low, and it is generally carried out by using a contoured core plate, and then baked in an oven at 200 to 300 ° C for several hours, and the oil is oxidized by air to harden it. The disadvantage of this core making method is that the core is easily deformed during demolding, handling and baking, resulting in reduced dimensional accuracy of the casting; long baking time and high energy consumption.
Various cores made of resin sand for resin sand core. After the core is hardened in the core box, it can be taken out to ensure the correct shape and size of the core. Depending on the hardening method, the manufacture of resin sand cores is generally divided into two methods: hot core box core making and cold core box core making. 1 hot core box method core: appeared in the late 1950s. A furan resin is usually used as a core sand binder, and a latent hardener such as ammonium chloride is also added. When the core is made, the core box is kept at 200 to 300 ° C, and after the core sand is injected into the core box, ammonium chloride reacts with free formaldehyde in the resin to form an acid at a relatively high temperature, so that the core is hardened quickly. It takes about 10 to 100 seconds to establish the release strength. The core is made by the hot core box method, and the core has a relatively high dimensional accuracy, but the process device is complicated and expensive, consumes a lot of energy, emits irritating gas, and the working conditions of the workers are also poor. 2 cold core box method core: appeared in the late 60s. A urethane resin was used as the core sand binder. When the core is formed by this method, the core box is not heated, and the core is blown into the amine vapor for a few seconds to harden the core. This method is superior to the hot box method in terms of energy, environment, and production efficiency. In the mid-1970s, the furan resin cold box method of blowing sulfur dioxide hardened appeared. The hardening mechanism is completely different from the urethane cold box method, but the process characteristics, such as fast hardening and high core strength, are roughly the same as the urethane cold box method.
Advantages The advantages of clay wet sand casting are: 1 clay is rich in resources and cheap. 2 The used clay wet sand can be recycled and reused after proper sand treatment. 3 The cycle for manufacturing the mold is short and the work efficiency is high. 4 Mixed sand can be used for a long time. 5 sand type tamping can still withstand a small amount of deformation without damage, which is very beneficial for drafting and lower core. Disadvantages are: 1 When the sand is mixed, the viscous clay slurry is coated on the surface of the sand, and it is necessary to use a high-power sand mixing device with a bismuth effect, otherwise it is impossible to obtain a good quality sand. 2Because the sand is well mixed, it has a relatively high strength. The molding sand is not easy to flow during the molding, and it is difficult to compact. The manual molding is both laborious and requires a certain skill. When the machine is used, the equipment is complicated and huge. 3 The rigidity of the mold is not high, and the dimensional accuracy of the casting is poor. 4 castings are prone to defects such as sand washing, sand inclusion, and porosity.
Improved type At the beginning of the 20th century, the foundry industry began to use sand-mixed sand mixers to improve the quality of clay wet sand. The new high-power sand mixer can achieve high efficiency and high quality in the sand mixing work. The appearance of the shock compaction molding machine, which is mainly based on earthquakes, has significantly improved the compactness and uniformity of the mold. With the improvement of the dimensional accuracy and surface quality requirements of castings, a high-pressure molding machine based on compaction has emerged. The use of a high-pressure molding machine to produce a clay wet sand type not only improves the dimensional accuracy of the casting, but also improves the surface quality, and simplifies the operation of the compact mold and shortens the cycle, thereby realizing high speed and automation of the entire molding and forming process. A new molding machine for gas shock and pressure, using the thixotropy of clay slurry, can be applied to a very tight mold by instantaneously applying a pressure of 0.5 MPa. These advances are important conditions for clay wet sand casting to meet the requirements of modern industry. This traditional process has therefore been used to produce a large number of high quality castings.
Clay dry sand type
The wet moisture of the molding sand used for the sand type is slightly higher than that of the wet sand. After the sand mold is prepared, the surface of the cavity should be coated with refractory paint, and then dried in an oven. After it is cooled, it can be combined and poured. It takes a long time to dry the clay sand type, which consumes a large amount of fuel, and the sand type is easily deformed during the drying process, which affects the accuracy of the casting. Clay dry sand types are commonly used in the manufacture of steel castings and larger cast iron parts. Since the chemical hardening sand has been widely used, the dry sand type has been eliminated.
Chemically hardened sand
The molding sand used in this sand type is called chemically hardened sand. The binder is generally a substance which can undergo molecular polymerization under the action of a hardener to form a three-dimensional structure, and various synthetic resins and water glass are commonly used. There are basically three ways of chemical hardening.
Self-hardening: both binder and hardener are added during sand mixing. After the sand or core is made, the binder reacts under the action of the hardener to cause the sand or core to harden by itself. The self-hardening method is mainly used for styling, but it is also used to manufacture larger cores or to produce cores with a small batch size.
Aerosol hardening: Add binder and other auxiliary additives during sand mixing without first adding hardener. After molding or core making, a gaseous hardener is blown in or blown into the gaseous carrier to atomize the liquid hardener, which is dispersed in the sand or core, resulting in sand hardening. Aerosol hardening is mainly used for core making and sometimes for small sand types.
Heat hardening: Adding a binder during sand mixing and a latent hardener that does not work at normal temperature. After the sand or core is formed, it is heated, at which time the latent hardener reacts with certain components of the binder to form an effective hardener that hardens the binder, thereby hardening the sand or core. The heat hardening method is mainly used for core making in addition to the small shell sand type.
Characteristics of chemical hardening sand casting process The characteristics of chemical hardening sand casting process are as follows: (1) The strength of the chemically hardened sand type is much higher than that of the clay sand type, and after being made into a sand type, it is released after hardening to a relatively high strength, and no modification is required. . Therefore, the mold can accurately reflect the size and contour shape of the pattern, and is not easily deformed in the subsequent process. The resulting casting has a high dimensional accuracy. 2 Because the viscosity of the binder and hardener used are not high, it is easy to mix with the sand. The structure of the sand mixing equipment is light, low in power and high in productivity, and the sand processing work can be simplified. 3 The mixed molding sand has good fluidity before hardening, and the molding sand is easy to compact during molding, so there is no need for a large and complicated molding machine. 4 When using chemically hardened sand, the molding materials such as wood, plastic and metal can be selected according to the production requirements. 5 The content of binder in chemically hardened sand is much lower than that of clay sand, and there is no powdery auxiliary material. For example, the original sand with the same grain size is used, and the gap between sand grains is much larger than that of clay sand. In order to avoid metal penetration between the sand during casting, the sand or core surface should be coated with a good quality coating. 6 Chemical hardened sand with water glass as binder has low cost and no odor in working environment. However, after casting the metal in this mold, the sand is not easily broken; the used old sand cannot be directly recycled, and must be regenerated, and the regeneration of the water glass sand is more difficult. 7 Chemical hardened sand with resin as binder has higher cost, but after casting, the casting is easy to separate from the molding sand, the workload of casting cleaning is reduced, and most of the used sand can be recycled and reused.
Core
In order to ensure the quality of the casting, the core used in sand casting is generally a dry core. According to different binders used in the core, the core is divided into clay sand core, oil sand core and resin sand core.
Clay sand core
A simple core made of clay sand.
Oil sand core
The core made of core sand with dry oil or semi-drying oil as binder has a wide application. The viscosity of the oil is low, and the mixed core sand has good fluidity and is easy to compact when the core is made. However, the strength of the newly formed core is very low, and it is generally carried out by using a contoured core plate, and then baked in an oven at 200 to 300 ° C for several hours, and the oil is oxidized by air to harden it. The disadvantage of this core making method is that the core is easily deformed during demolding, handling and baking, resulting in reduced dimensional accuracy of the casting; long baking time and high energy consumption. Various cores made of resin sand for resin sand core. After the core is hardened in the core box, it can be taken out to ensure the correct shape and size of the core. Depending on the hardening method, the manufacture of resin sand cores is generally divided into two methods: hot core box core making and cold core box core making. 1 hot core box method core: appeared in the late 1950s. A furan resin is usually used as a core sand binder, and a latent hardener such as ammonium chloride is also added. When the core is made, the core box is kept at 200 to 300 ° C, and after the core sand is injected into the core box, ammonium chloride reacts with free formaldehyde in the resin to form an acid at a relatively high temperature, so that the core is hardened quickly. It takes about 10 to 100 seconds to establish the release strength. The core is made by the hot core box method, and the core has a relatively high dimensional accuracy, but the process device is complicated and expensive, consumes a lot of energy, emits irritating gas, and the working conditions of the workers are also poor. 2 cold core box method core: appeared in the late 60s. A urethane resin was used as the core sand binder. When the core is formed by this method, the core box is not heated, and the core is blown into the amine vapor for a few seconds to harden the core. This method is superior to the hot box method in terms of energy, environment, and production efficiency. In the mid-1970s, the furan resin cold box method of blowing sulfur dioxide hardened appeared. The hardening mechanism is completely different from the urethane cold box method, but the process characteristics, such as fast hardening and high core strength, are roughly the same as the urethane cold box method.
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