Characteristics Of Chemical Hardening Sand Casting Process
Sand casting is the most commonly used casting process in the foundry industry today. It is suitable for all kinds of materials. Both ferroalloy and non-ferrous alloy castings can be cast by sand. It can produce castings from dozens of grams to dozens of tons and larger. The disadvantage of sand casting is that it can only produce castings with a relatively simple structure. The biggest advantage of sand casting is: low production cost. However, the surface finish, the metallography of the casting, and the internal density are relatively low. In terms of styling, it can be made by hand or machine. Manual molding is suitable for single-piece, small batch and large-scale castings with complex shapes that are difficult to use with molding machines. Machine modeling can greatly improve the surface accuracy and dimensional accuracy, but the investment is relatively large.
Features of sand casting:
- The strength of chemically hardened sand mold is much higher than that of clay sand mold, and after the sand mold is made, it will be released after hardening to have a relatively high strength, and it does not need to be repaired. Therefore, the mold can more accurately reflect the size and contour shape of the pattern, and it is not easy to deform in the subsequent process. The obtained castings have high dimensional accuracy.
- Because the viscosity of the binder and hardener used is not high, it is easy to mix with the sand grains. The sand mixing equipment has a light structure, low power and high productivity, and the sand processing part can be simplified.
- The mixed molding sand has good fluidity before hardening, and the molding sand is easy to pound during molding, so there is no need for a large and complicated molding machine.
- When modeling with chemically hardened sand, you can choose the pattern material according to the production requirements, such as wood, plastic and metal.
- The content of binder in chemically hardened sand is much lower than that in clay sand, and there are no powdered auxiliary materials. If raw sand with the same particle size is used, the gap between sand particles is much larger than that in clay sand. In order to prevent the metal from penetrating between the sand grains during casting, the surface of the sand mold or core should be coated with high-quality paint.
- The chemical hardening sand with water glass as the binder has low cost and no smell in the working environment. However, the molding sand is not easy to collapse after the metal is poured into the mold; the used sand cannot be directly recycled and must be recycled, and the regeneration of sodium silicate sand is more difficult.
- The cost of chemically hardened sand using resin as a binder is relatively high, but the casting is easy to separate from the sand after pouring, the workload of cleaning the casting is reduced, and most of the used sand can be recycled and reused.
The basic feature of the wet casting method is that the sand mold (core) does not need to be dried, and there is no hardening process.Its advantages:
- The production flexibility is large, the productivity is high, the production cycle is short, it is easy to organize flow production, and it is easy to realize the mechanization and automation of the production process; the material cost is low;
- Save drying equipment, fuel, electricity and workshop production area;
- Extend the service life of the sand box, etc. However, the use of wet casting can also easily cause some casting defects, such as: sand inclusion, scarring, rat tail, sticky sand, pores, blisters, bulging sand, etc.
- With the development of casting science and technology, the understanding of the principle of interaction between metal and mold has become more profound;
- It is more effective to control the quality of molding sand;
Coupled with modern sand processing equipment, the quality of molding sand is guaranteed to a certain extent;
Dry sand is a kind of sand with clay and bentonite as binder.
Sand molds (cores) made of dry sand need to be dried, so the wet strength can be slightly lower, and the water content can be slightly higher to achieve higher dry strength.
The dry type mainly depends on the coating to ensure the surface quality of the castings, and the chemical composition and refractoriness of the raw sand are not very demanding. The surface of the sand mold can be painted with water-based paint, or raw sand with a coarser grain size can be used. The sand can have higher air permeability, and it is not easy to produce defects such as sand washing, sand sticking, and pores.
Dry type is mainly used for pouring medium and large castings. The quality of molding sand and sand molds are relatively easy to control, but the dimensional accuracy of castings is poor. The sand molds require special drying equipment and the production cycle is long. Therefore, in many aspects, dry molds are gradually being replaced by self-setting sand molds.
The main characteristics of surface-drying sand are the use of coarse sand, activated bentonite and the addition of wood chips. The performance and preparation of surface dry sand basically meet the requirements of both green sand and dry sand.
The surface dry sand mold does not require special drying equipment, the production cycle is relatively short, and the sand cleaning is relatively easy, but it has strict requirements on the performance of the molding sand and the process operation. Surface dry sand molds are mainly used for pouring medium-sized castings, the larger ones weighing more than ten tons.