Based on the difference of molding process, the production process of coupler steel castings mainly includes wet molding clay sand process, sodium silicate sand process, resin sand process, etc. In terms of casting size, the hook body and hook tongue belong to small and medium-sized steel castings. In the existing casting process schemes of various small and medium-sized steel castings at home and abroad, the production processes adopted in different regions and countries are quite different due to various reasons such as technical development history, production habits and raw materials. North America and Japan mainly use wet molding clay sand and resin sand mold, Europe and Russia mainly use sodium silicate sand and resin sand mold, China mostly uses sodium silicate sand mold, and a small amount uses wet molding clay sand and resin sand mold. Different processes have their own characteristics, and they all have examples of successful application.
Wet molding clay sand technology. Wet clay sand is composed of raw sand, bentonite, starch additives and water. One of the important characteristics of wet clay sand is its repeated use. There are certain risks and quality control problems in the production of railway steel castings with wet clay sand, including:
1) The quality of some raw materials such as raw sand and bentonite is not very ideal;
2) Molding sand quality control is complex;
3) Compared with sodium silicate sand, it has high moisture content, low strength and low fire resistance. When molten steel is poured into the mold, the moisture in the molding sand vaporizes and the sand mold is heated and cracked, which is easy to wash out the low-strength sand mold and cause a series of defects;
4) Compared with resin sand, wet mold clay sand has better high-temperature concession, but there is still a gap compared with sodium silicate sand, and the crack tendency of castings is still large. However, the use of wet clay sand also has great advantages, which are mainly reflected in high production efficiency, low cost, short production cycle and easy to realize mechanized and automatic production.
Sodium silicate sand process. The process mainly includes water glass CO2 hardening process and ester hardening water glass sand process. Their advantages lie in the high-temperature fire resistance of the mold, the internal quality of the casting and the good crack resistance tendency. In CO2 hardening process, the mold has the advantages of increased thermal strength during initial temperature rise and good concession during casting solidification, but there are serious deficiencies such as poor collapsibility. When CO2 sodium silicate sand process is used to produce steel castings, it is not allowed to remove sand in water bath (easy to produce cracks), and CO2 sodium silicate sand cannot be removed by dry method, which becomes a CO2 sodium silicate sand worker
It is a difficult problem in the production of steel castings. Ester hardened sodium silicate sand process has good collapsibility, so dry sand removal can be adopted, and the mold has good concession during solidification, but this process has low mold strength and high requirements for the quality of sodium silicate.
Furan resin sand process. The process has the advantages of high dimensional accuracy of castings and good collapsibility of molds. When used in steel casting production, there are some disadvantages as follows:
1) Resin sand has poor concession during casting solidification. If sulfur infiltration occurs, it is easy to lead to hot crack and surface microcrack;
2) The binder and curing agent are expensive and the casting cost is high;
3) Binder, curing agent and other accessories contain a certain amount of gases harmful to human body, and toxic and harmful substances such as SO2 and formaldehyde are released during production, which has a certain impact on the health of workers and the environment of the plant. Therefore, the production of steel castings by this process is limited.