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Key points of coated sand casting process:
Coated sand casting has a long history in the casting field, and the output of castings is also quite large; however, there are many problems when using coated sand casting to produce precision steel castings: sand sticking (scarring), cold shut, and pores. How to solve these problems
It remains for us to explore further.
1. Knowledge and understanding of coated sand (coated sand belongs to organic binder type and core sand)
(1) Characteristics of coated sand: It has appropriate strength properties; good fluidity, the produced sand molds and sand cores have clear outlines and dense structures, and can produce complex sand cores; the surface quality of the sand molds (cores) is good and the surface is rough Degree can be reached
Ra=6.3～12.5μm, the dimensional accuracy can reach CT7～CT9 level; the disintegration is good, and the casting is easy to clean.
(2) Scope of application: Coated sand can be used to make both casting molds and sand cores. Coated sand molds or cores can be used in conjunction with each other and other sand molds (cores); it can not only be used for metal mold gravity Casting or low pressure casting,
It can also be used for iron mold sand-coated casting and thermal centrifugal casting; it can be used not only for the production of cast iron and non-ferrous alloy castings, but also for the production of steel castings.
2. Preparation of coated sand
1. Coated sand composition
The factor should not be greater than 1.3; the acid consumption value should not be less than 5ml.
(2) Phenolic resin is commonly used as binder.
(3) The curing agent usually uses methenamine; the lubricant usually uses calcium stearate, which functions to prevent the coated sand from clumping and increase fluidity. The main function of additives is to improve the performance of coated sand.
(4) Basic ingredient ratio of coated sand (mass fraction, %) Description: Original sand 100% scrub sand, phenolic resin 1.0~3.0% of the original sand weight, urotropine (aqueous solution 2) 10~15% of the resin Heavy, calcium stearate 5~
7 accounts for the weight of the resin, and 0.1~0.5 of the additives accounts for the weight of the original sand. 1:2) 10~15 accounts for the weight of the resin, 5~7 of the calcium stearate accounts for the weight of the resin, and 0.1~0.5 of the additives accounts for the weight of the original sand.
2. Coated sand production process
There are three main preparation processes for coated sand: cold coating, warm coating, and hot coating. At present, the production of coated sand almost all uses the hot coating method. The thermal coating process is to first heat the raw sand to a certain temperature, and then separate it with the tree.
It is made by mixing fat, methenamine aqueous solution and calcium stearate, cooling, crushing and screening. Due to differences in formulations, the mixing process is different. At present, there are many types of coated sand production lines in China. The semi-automatic production line with manual feeding is about
There are 2,000 to 2,300 lines, and there are nearly 50 fully automatic production lines controlled by computers, which effectively improves production efficiency and product stability. For example, the automated visual production line of xx Casting Co., Ltd. has a feeding time control accurate to 0.1
Seconds, the heating temperature control is accurate to 1/10°C, and the sand mixing status can be observed at all times through video, and the production efficiency reaches 6 tons/hour.
3. Main product types of coated sand
(1) Ordinary coated sand Ordinary coated sand is traditional coated sand. Its composition is usually composed of quartz sand, thermoplastic phenolic resin, urotropine and calcium stearate. No relevant additives are added. The amount of resin added Usually at a certain
It has relatively high strength requirements and does not have the characteristics of high temperature resistance, low expansion, and low gas generation. It is suitable for the production of castings with low requirements.
(2) Characteristics of high-strength and low-gas-generating coated sand: high strength, low expansion, low gas generation, slow gas generation, and antioxidant. Introduction: High-strength and low-gas-generating coated sand is an updated product of ordinary coated sand. By adding the relevant feature
"Additive" and the adoption of a new preparation process, the amount of resin is greatly reduced, its strength is more than 30% higher than that of ordinary coated sand, the amount of gas generation is significantly reduced, and the gas generation rate can be delayed, which can better meet the needs of casting production. .This type of coated sand
Mainly suitable for the production of iron castings, small and medium-sized steel castings and alloy steel castings. Currently, there are three series of this type of coated sand: GD-1 high-strength, low-gas-emitting coated sand; GD-2 high-strength, low-expansion, low-gas-emission coated sand; GD-3 high-strength, low-expansion, low-gas-emitting coated sand
Gas-generating antioxidant coating.
(4) Easily collapsible coated sand has good strength and excellent low-temperature collapsibility, and is suitable for the production of non-ferrous metal castings.
(5) Other special requirements for coated sand. In order to meet the needs of different products, a series of special coated sands have been developed, such as: coated sand for centrifugal casting, chilled coated sand, wet coated sand, anti-sticking sand, anti-sticking sand, etc. Veined, anti-orange peel coated sand
wait.
3. Main process of coated sand core making
The heating temperature is 200-300℃, the curing time is 30-150s, and the sand injection pressure is 0.15-0.60MPa. For sand cores with simple shapes and coated sand with good fluidity, lower sand injection pressure can be selected. For thin sand cores, lower heating temperatures can be selected.
When the heat temperature is low, the curing time can be appropriately extended. The resin used in coated sand is phenolic resin. Advantages of the core making process: suitable strength properties; good fluidity; good surface quality of the sand core (Ra=6.3-12.5μm); sand core resistance
It has strong hygroscopicity; good dispersibility, and the castings are easy to clean.
1. Casting (mold) temperature
The mold temperature is one of the main factors affecting the thickness and strength of the shell. It is generally controlled between 220 and 260°C, and is selected according to the following principles:
(1) Ensure sufficient heat required for softening and curing of the resin on the coated sand;
(2) Ensure that the required shell thickness is formed and the surface of the shell (core) is not scorched;
(3) Minimize the crusting and hardening time to improve productivity.
4. Problems and solutions in the application of coated sand
There are many types of core-making methods, which can generally be divided into two categories: thermosetting methods and cold-setting methods. Coated sand core making belongs to the thermosetting method category. Any core making method has its own advantages and disadvantages, which mainly depend on
Which core making method to use depends on comprehensive factors such as product quality requirements, complexity, production batch size, production cost, product price, etc. Sand cores with high requirements on the surface quality of the inner cavity of castings, high dimensional accuracy requirements and complex shapes are used.
Coated sand core making is very effective. For example: the intake and exhaust passage sand cores, water passage sand cores, and oil passage sand cores of the car engine cylinder head, the water passage sand cores and oil passage sand cores of the cylinder block, the shell core sand cores of the intake manifold and the exhaust manifold, hydraulic valve flow
Sand core, automobile turbocharger air passage sand core, etc. However, there are still some problems that are often encountered in the use of coated sand. Here I will only briefly talk about my experience at work.
1. Method for determining the strength and gas generation amount of coated sand
Under the premise that the quality of raw sand and resin are certain, the key factor affecting the strength of coated sand is mainly the amount of phenolic resin added. Adding more phenolic resin will increase the strength, but the amount of gas will also increase, and the disintegrability will decrease.
Low. Therefore, in production applications, the strength of coated sand must be controlled to reduce gas generation and improve disintegration. A balance point must be found when setting strength standards. This balance point is to ensure the surface quality of the sand core and not
Strength without deformation and core breakage. In this way, the surface quality and dimensional accuracy of the castings can be ensured, the gas generation volume can be reduced, the pore defects of the castings can be reduced, and the sand production performance of the sand core can be improved. Sand core storage and transportation process
Work station equipment and sand core trolleys can be used, and a 10mm~15mm thick sponge can be laid on them, which can reduce the loss rate of the sand core.
2. Storage period of coated sand core
Any sand core will absorb moisture, especially in southern areas where the air relative humidity is high. The storage period of the sand core must be stipulated in the process documents, and the lean production first-in-first-out production method should be used to reduce the storage amount and storage cycle of the sand core.
Expect. Each enterprise should determine the storage period of sand cores based on its own factory conditions and local climate conditions.
3. Control the supply quality of coated sand
When the coated sand enters the factory, it must be accompanied by the supplier''s quality assurance information, and the company will inspect it according to sampling standards. It can only be put into storage after passing the inspection. If the enterprise fails to pass the sampling test, the quality assurance and technical department will make a decision.
Make concessions or return goods to the supplier.
It remains for us to explore further.
1. Knowledge and understanding of coated sand (coated sand belongs to organic binder type and core sand)
(1) Characteristics of coated sand: It has appropriate strength properties; good fluidity, the produced sand molds and sand cores have clear outlines and dense structures, and can produce complex sand cores; the surface quality of the sand molds (cores) is good and the surface is rough Degree can be reached
Ra=6.3～12.5μm, the dimensional accuracy can reach CT7～CT9 level; the disintegration is good, and the casting is easy to clean.
(2) Scope of application: Coated sand can be used to make both casting molds and sand cores. Coated sand molds or cores can be used in conjunction with each other and other sand molds (cores); it can not only be used for metal mold gravity Casting or low pressure casting,
It can also be used for iron mold sand-coated casting and thermal centrifugal casting; it can be used not only for the production of cast iron and non-ferrous alloy castings, but also for the production of steel castings.
2. Preparation of coated sand
1. Coated sand composition
The factor should not be greater than 1.3; the acid consumption value should not be less than 5ml.
(2) Phenolic resin is commonly used as binder.
(3) The curing agent usually uses methenamine; the lubricant usually uses calcium stearate, which functions to prevent the coated sand from clumping and increase fluidity. The main function of additives is to improve the performance of coated sand.
(4) Basic ingredient ratio of coated sand (mass fraction, %) Description: Original sand 100% scrub sand, phenolic resin 1.0~3.0% of the original sand weight, urotropine (aqueous solution 2) 10~15% of the resin Heavy, calcium stearate 5~
7 accounts for the weight of the resin, and 0.1~0.5 of the additives accounts for the weight of the original sand. 1:2) 10~15 accounts for the weight of the resin, 5~7 of the calcium stearate accounts for the weight of the resin, and 0.1~0.5 of the additives accounts for the weight of the original sand.
2. Coated sand production process
There are three main preparation processes for coated sand: cold coating, warm coating, and hot coating. At present, the production of coated sand almost all uses the hot coating method. The thermal coating process is to first heat the raw sand to a certain temperature, and then separate it with the tree.
It is made by mixing fat, methenamine aqueous solution and calcium stearate, cooling, crushing and screening. Due to differences in formulations, the mixing process is different. At present, there are many types of coated sand production lines in China. The semi-automatic production line with manual feeding is about
There are 2,000 to 2,300 lines, and there are nearly 50 fully automatic production lines controlled by computers, which effectively improves production efficiency and product stability. For example, the automated visual production line of xx Casting Co., Ltd. has a feeding time control accurate to 0.1
Seconds, the heating temperature control is accurate to 1/10°C, and the sand mixing status can be observed at all times through video, and the production efficiency reaches 6 tons/hour.
3. Main product types of coated sand
(1) Ordinary coated sand Ordinary coated sand is traditional coated sand. Its composition is usually composed of quartz sand, thermoplastic phenolic resin, urotropine and calcium stearate. No relevant additives are added. The amount of resin added Usually at a certain
It has relatively high strength requirements and does not have the characteristics of high temperature resistance, low expansion, and low gas generation. It is suitable for the production of castings with low requirements.
(2) Characteristics of high-strength and low-gas-generating coated sand: high strength, low expansion, low gas generation, slow gas generation, and antioxidant. Introduction: High-strength and low-gas-generating coated sand is an updated product of ordinary coated sand. By adding the relevant feature
"Additive" and the adoption of a new preparation process, the amount of resin is greatly reduced, its strength is more than 30% higher than that of ordinary coated sand, the amount of gas generation is significantly reduced, and the gas generation rate can be delayed, which can better meet the needs of casting production. .This type of coated sand
Mainly suitable for the production of iron castings, small and medium-sized steel castings and alloy steel castings. Currently, there are three series of this type of coated sand: GD-1 high-strength, low-gas-emitting coated sand; GD-2 high-strength, low-expansion, low-gas-emission coated sand; GD-3 high-strength, low-expansion, low-gas-emitting coated sand
Gas-generating antioxidant coating.
(4) Easily collapsible coated sand has good strength and excellent low-temperature collapsibility, and is suitable for the production of non-ferrous metal castings.
(5) Other special requirements for coated sand. In order to meet the needs of different products, a series of special coated sands have been developed, such as: coated sand for centrifugal casting, chilled coated sand, wet coated sand, anti-sticking sand, anti-sticking sand, etc. Veined, anti-orange peel coated sand
wait.
3. Main process of coated sand core making
The heating temperature is 200-300℃, the curing time is 30-150s, and the sand injection pressure is 0.15-0.60MPa. For sand cores with simple shapes and coated sand with good fluidity, lower sand injection pressure can be selected. For thin sand cores, lower heating temperatures can be selected.
When the heat temperature is low, the curing time can be appropriately extended. The resin used in coated sand is phenolic resin. Advantages of the core making process: suitable strength properties; good fluidity; good surface quality of the sand core (Ra=6.3-12.5μm); sand core resistance
It has strong hygroscopicity; good dispersibility, and the castings are easy to clean.
1. Casting (mold) temperature
The mold temperature is one of the main factors affecting the thickness and strength of the shell. It is generally controlled between 220 and 260°C, and is selected according to the following principles:
(1) Ensure sufficient heat required for softening and curing of the resin on the coated sand;
(2) Ensure that the required shell thickness is formed and the surface of the shell (core) is not scorched;
(3) Minimize the crusting and hardening time to improve productivity.
4. Problems and solutions in the application of coated sand
There are many types of core-making methods, which can generally be divided into two categories: thermosetting methods and cold-setting methods. Coated sand core making belongs to the thermosetting method category. Any core making method has its own advantages and disadvantages, which mainly depend on
Which core making method to use depends on comprehensive factors such as product quality requirements, complexity, production batch size, production cost, product price, etc. Sand cores with high requirements on the surface quality of the inner cavity of castings, high dimensional accuracy requirements and complex shapes are used.
Coated sand core making is very effective. For example: the intake and exhaust passage sand cores, water passage sand cores, and oil passage sand cores of the car engine cylinder head, the water passage sand cores and oil passage sand cores of the cylinder block, the shell core sand cores of the intake manifold and the exhaust manifold, hydraulic valve flow
Sand core, automobile turbocharger air passage sand core, etc. However, there are still some problems that are often encountered in the use of coated sand. Here I will only briefly talk about my experience at work.
1. Method for determining the strength and gas generation amount of coated sand
Under the premise that the quality of raw sand and resin are certain, the key factor affecting the strength of coated sand is mainly the amount of phenolic resin added. Adding more phenolic resin will increase the strength, but the amount of gas will also increase, and the disintegrability will decrease.
Low. Therefore, in production applications, the strength of coated sand must be controlled to reduce gas generation and improve disintegration. A balance point must be found when setting strength standards. This balance point is to ensure the surface quality of the sand core and not
Strength without deformation and core breakage. In this way, the surface quality and dimensional accuracy of the castings can be ensured, the gas generation volume can be reduced, the pore defects of the castings can be reduced, and the sand production performance of the sand core can be improved. Sand core storage and transportation process
Work station equipment and sand core trolleys can be used, and a 10mm~15mm thick sponge can be laid on them, which can reduce the loss rate of the sand core.
2. Storage period of coated sand core
Any sand core will absorb moisture, especially in southern areas where the air relative humidity is high. The storage period of the sand core must be stipulated in the process documents, and the lean production first-in-first-out production method should be used to reduce the storage amount and storage cycle of the sand core.
Expect. Each enterprise should determine the storage period of sand cores based on its own factory conditions and local climate conditions.
3. Control the supply quality of coated sand
When the coated sand enters the factory, it must be accompanied by the supplier''s quality assurance information, and the company will inspect it according to sampling standards. It can only be put into storage after passing the inspection. If the enterprise fails to pass the sampling test, the quality assurance and technical department will make a decision.
Make concessions or return goods to the supplier.
