Introduce of Green sand processing plant

The clay sand casting process, resin sand casting process and sodium silicate sand casting process are generally referred to as the three major sand casting processes. Among the three major sand casting processes, the castings produced by the clay sand casting process exceed the sum of the castings produced by the resin sand casting process and the water glass sand casting process, and become the most commonly used sand casting process.


The clay sand casting process is a casting process method using clay sand as the modeling material. Molding sand is made by mixing sand, clay, water and additional materials in a certain proportion. Sand is a refractory aggregate, clay (bentonite) is a binder, and it combines with water to play a binding role. Additional materials are used to improve some casting process properties of molding sand.


According to whether to bake the mold, the clay sand casting process is divided into clay sand dry mold casting process, clay sand surface dry mold casting process and clay sand wet mold casting process. The molding sand used is dry molding sand, surface dry molding sand and wet molding sand respectively .


The clay sand dry casting process generally uses raw sand with a coarse particle size, and uses coatings to ensure the improvement of the surface quality of the casting. The molding sand has high air permeability and high strength after drying. Casting defects, mainly used for pouring medium and large castings. The sand mold used in the clay sand dry mold casting process needs to be dried by special drying equipment. The production cycle is long, the energy consumption is large, the working environment is harsh, and the dimensional accuracy of the casting is low. With the wide application of resin sand and water glass sand casting processes, clay sand Sand dry casting process has been rarely used in foundry production.


The moulding sand used in the dry mould casting process on the clay sand surface needs to bake the mould cavity surface before pouring to obtain a mould with a certain thickness of the cavity surface (15-20mm) dry layer. The properties and preparation of surface dry sand meet the requirements of both wet sand and dry sand. The particle size of the original sand is relatively coarse. Quartz feldspar sands of 12/30, 20/40 and 30/50 are commonly used. Activated bentonite is used as a binder. Adding wood chips, the air permeability and wet strength of the molding sand are high, and the surface of the casting mold needs to be painted to improve the anti-sticking ability. Compared with the clay sand dry casting process, the surface dry sand does not need to be dried in the kiln, which can reduce the fuel and power consumption, the production cycle is short, the falling sand performance of the casting is improved, the sand cleaning is easier, and the working environment is better. However, the requirements for molding sand performance and process operation are improved. Clay sand surface dry casting process is mainly used for casting medium and large castings, and the largest castings can reach more than ten tons. Due to the application of resin sand and water glass sand casting processes, their applications tend to decrease gradually, and only a few companies are using them.


Compared with the clay sand wet casting process and the clay sand dry casting process and the clay sand surface dry casting process, the sand mold can be directly poured and qualified castings can be produced without drying. The drying cost is shortened, the production cycle is shortened, the production organization is convenient, the mechanization and automation of casting production are easy to realize, and the casting mold has good falling sand, less dust during the working process, the environment is improved, and the surface accuracy and dimensional accuracy of the casting are accurate. High, less cleaning work, lower production costs. Compared with the clay sand dry casting process and the clay sand surface dry casting process, the clay sand wet casting process also has some shortcomings, mainly in the low strength of the mold, the poor fluidity of the molding sand, the moisture content, and the large amount of gas. Castings are prone to casting defects such as blisters, pores, and sand inclusions. Strict quality control of molding sand and management of casting production process can effectively solve the problems in clay sand wet casting process.


The main components of wet clay sand are sand, clay (bentonite), pulverized coal and water, and a small number of additives such as heavy oil, residual oil or starch. The raw sand is the refractory aggregate of wet clay sand, mainly quartz sand or quartz feldspar sand, and the particle size is mostly 50/100, 70/140 or 100/200. Sand, castings with larger quality and size should use raw sand with coarser grain size to ensure a smooth surface of the castings. In order to improve the wet strength of the molding sand and enhance the ability to resist sand inclusion, sticking sand and veining defects, the original sand of two particle sizes can also be mixed for use. Bentonite is mostly a binder for wet sand, and combines with moisture to play a bonding role. Bentonite has adhesion and plasticity after being wetted by water, so it has good reusability. However, if bentonite loses crystal water after being baked at high temperature, it will not be able to restore its adhesive properties when it encounters water. Then there is the adhesive, which is called mud. Coal powder is an indispensable additional material for the production of sand casting iron castings. It has the functions of preventing sand sticking on the surface of castings, inhibiting the occurrence of expansion defects, reducing porosity defects, and improving the surface quality of castings.


Effect of pulverized coal in clay green sand (cast iron)


Adding pulverized coal to the clay green sand has four main functions in the casting forming process: after the molten iron is injected into the sand mold, the pulverized coal in the molding sand is thermally decomposed, and the released reducing gas can prevent iron in the cavity. Liquid oxidation prevents the formation of FeO on the surface of the casting, which plays a very important role in preventing sand sticking defects;


After the molten iron fills the mold cavity, the atmosphere in the mold is a reducing atmosphere. Under this condition, the hydrocarbon gas precipitated by the coal powder will condense on the surface of the mold to form a bright carbon film, which can prevent sand sticking and make the casting contour. Clear; near the metal-mold interface, when the pulverized coal in the molding sand is heated and undergoes a coking reaction, it first softens and shrinks in volume, and then expands. The softening temperature of pulverized coal is roughly the same as the phase change expansion temperature of quartz, which can accommodate the expansion of sand particles. Therefore, expansion defects such as sand inclusion and rat tail can be prevented on the casting, and the dimensional stability of the casting can be improved;


The volume expansion occurs when the pulverized coal is coking, which can fill the gaps between the sand particles on the surface layer of the casting mold, making it difficult for the molten iron and the produced fusible silicate to penetrate, thereby improving the surface quality of the casting. At the same time, the proper air permeability can still be maintained at a certain distance from the surface of the mold