Talking about the key points of production of casting ingot mould

The casting method of the ingot mold is all sand static casting, the difference is the choice of sand material, the skin is basically all water glass sand casting, the core difference is larger, there are three common choices of sand, water glass sand casting, resin sand casting, clay sand casting, such as simply considering the product quality, the preferred resin sand or clay sand modeling, However, at present, the overall profit margin of the foundry industry is compressed, and the cost pressure is large, resulting in the gradual increase of manufacturers using water glass sand.

1. Ingot mold process flow

Sand mixing → molding → brushing → drying → box closing → pouring → unpacking → finishing → Heat treatment. In the production process, from sand mixing to casting link has a certain impact on the surface quality of the ingot mold, especially in the water glass sand molding production, there is a little bad grasp, which is easy to cause the inner wall of the ingot mold heavy skin or other defects.

2. Main process control points

2.1 Sand mixing

Material selection: Quartz sand particle size must be moderate, generally consider choosing 30-70 mesh, the percentage of each mesh area should be uniform, it is strictly prohibited to prevent high mesh or low mesh sand concentration; The modulus of water glass should be different according to the season, especially in the northern region, the modulus of water glass should be moderately increased in winter.

Sand mixing standard: In the sand mixing process, the amount of water glass added is moderately adjusted according to the mesh number of sand, generally controlled at 8%-10%, and moderately adjusted according to the particle size, shape and other factors of the sand.

2.2 Modeling

In the process design of ingot mold casting, the exhaust method is a primary consideration, mainly because of the large gas output during the process of water glass sand casting, such as unreasonable process design, easy to cause defects such as pores. Due to the small diameter of the bottom eye of the ingot mold, the lower exhaust method is adopted, and the core molding process is increased from the original three parts to four parts. From the inside to the outside, there is a skeleton (welded pipe with a release hole is used, and the diameter changes accordingly according to the size of the core), followed by flammable materials such as straw curtains, straw ropes, and newspapers, loose materials that can be moved again (broken bricks, broken tiles, etc.), and final sand (water glass sand). See Figure 1 for details.

After the molding of sand is completed, the kiln is tested by a portable hardness tester after mold drawing, and the water glass sand is generally required to reach more than 85, otherwise it is easy to produce sand sticking phenomenon, especially the mechanical sand sticking defect is prominent. Mechanical sand is a metal liquid infiltrated into the sand mold or sand core grain gap, sintered with sand and adhered to the surface of the casting.

2.3 Brushing

The core coating is the most widely used graphite coating, which is composed of three parts: powdered graphite (45%), flake graphite (45%), binder (10%), appropriately adjusted according to the actual situation, powder graphite mainly acts on the adhesion with sand, flake graphite mainly acts on the control of refractoriness and prevent the adhesion of sand defects, and binder acts on the adhesion strength of paint and sand.

The thickness of the coating is controlled at 3mm-5mm, too thin is easy to cause sand defects, and it is easy to crack after drying, resulting in steel penetration defects or scarring defects during pouring. In order to improve the work efficiency, the paint is generally used in brush coating, and the concentration is controlled at 80-90 degrees; Special sharp corners and corners are best coated with paint paste to improve the strength and thickness of the paint, and prevent the sudden change in the flow direction of the hot metal caused by paint erosion.

2.4 Drying

Water glass sand modeling, compared with clay sand modeling, water content is less, while considering the cost problem, generally using waste heat baking, for large tonnage ingot mold into the kiln baking.

The high temperature area of the drying curve must be controlled below 200 ° C, otherwise it is easy to have sand cracks, which will increase the later repair workload, and it is easy to form a scar defect or a combination of lines in this position, resulting in the difficulty of mold release of the ingot.

2.5 Carton and pouring

The ingot mold closing process has no special requirements, the only attention to the lock box, the press box to focus on inspection, because the ingot mold shape belongs to the regular geometry, you can choose the appropriate sand box, easy to cause buoyancy greater than gravity, so the lock box, the press link pay more attention.

The casting principle is generally low temperature and fast casting, but the inner wall of the ingot mold belongs to the non-processing use surface, in the case of ensuring non-sticky sand, consider moderately increasing the temperature to increase the fluidity of hot metal and improve the finish of the inner surface.

2.6 Unpacking and finishing

When unpacking with temperature, it is best not to pump water, which is easy to increase the sand cleaning workload; Do not let go of any small defects when finishing, otherwise the defects will be amplified during use.

2.7 Heat Treatment

The heat treatment of the ingot mold is stress-relieving annealing to eliminate the casting stress, reduce the probability of cracks in the process of use, and extend the service life of the ingot mold.

3. Conclusion

The production process of the ingot mold determines the quality of the ingot mold, and the quality of the ingot mold determines the surface quality of the ingot mold. The working surface of the ingot mold is not processed, resulting in higher requirements for the production process and operation of the ingot mold, and the details must be strictly closed in order to finally produce qualified products.