Different sand molding processes are suitable for different castings

The no-bake resin sand process refers to the general name of the molding process in which molding sand can harden by itself and obtain the required strength of pouring at room temperature. Based on statistics of the shipment volume of no-bake resin sand processing equipment and the actual development of downstream casting companies, China Bestech company concluded that no-bake resin sand that has developed rapidly in recent years mainly includes: furan resin self-hardening sand and alkali phenolic resin Hardening self-setting sand, urea resin self-setting sand (Pep-set self-setting sand), fat-hardening modified water glass self-setting sand. These self-setting sands have their own advantages and disadvantages, and should be used according to the different production and product characteristics of each enterprise.
Furan resin self-setting sand: This is the most widely used, most widely used, and most mature self-setting sand. It has relatively low casting cost, high utilization rate of old sand, and simple regeneration of old sand. It is the preferred self-setting sand process for technological transformation. .
Furan resin sand is extremely widely used in castings such as gray iron, ductile iron, cast steel, and non-ferrous metals. However, because furan resin sand has poor high temperature retreatability, the resin contains high N, and the curing agent contains S, some steel castings with uneven wall thickness are prone to thermal cracking, and thick steel castings are easy to cause N porosity, and some high Nodular iron parts of grades are easy to cause spheroidization and recession, and some low-carbon steel castings are also easy to cause carbon increase. Enough attention should be paid to the selection of process and resin types. This process is generally used in the production of single-piece cast iron in small batches.
 
2 Alkali phenolic resin hardening resin self-hardening sand: It is developed to overcome some shortcomings of furan resin self-hardening sand. It is called α-set process abroad. Because it does not contain N at all, and the curing agent does not contain S, it will not produce N pores and pinhole defects when used in cast steel and alloy steel castings. Since only part of the resin cross-linking reaction occurs in the alkali phenolic resin sand at room temperature, there is a re-hardening process when the cast metal is heated. Therefore, the high temperature dimensional stability of this resin sand is good, and the dimensional accuracy of the castings is high. It is more and more widely used in the production of alloy steel parts and large steel castings. However, the strength of alkali phenolic resin sand at room temperature is relatively low, the amount of resin added is relatively large, and the casting cost is relatively high. The hardening agent of alkali phenolic resin sand is organic grease, and the hardening time can only be adjusted by the type of grease, not the amount of addition. In addition, phenolic resin has a high viscosity and a short storage period, so attention should be paid during use.
 
3 Phenolic urethane resin self-hardening sand (Pep-set process): The Pep-set process has developed rapidly in the past two years. It combines furan resin and alkali phenolic resin and characteristics, and further improves process adaptability. It has superior The hardening characteristics also have good high temperature retreat. The hardening time can be adjusted within 0.5~15 minutes, the production efficiency is high, and the molding line is used for mass production. Through the adjustment of the proportions of the three binder components, a long enough usable time can be ensured. Once the curing starts, the pouring strength can be quickly reached, with good pouring performance and working time/mold ejection time ratio. Due to its good high temperature retreat, it can produce thin-walled complex parts without worrying about casting cracks. It is not only suitable for castings, steel castings, but also widely used in the production of non-ferrous alloy castings. It overcomes the performance defects of furan resin sand and has strong process adaptability. At the same time, the requirements for coatings are relatively low. Generally, iron castings can be produced with smooth surface without coating with some additives. The requirements for the regeneration equipment and the recovery rate are basically the same as those of the previous two processes, and the sand mixing equipment needs to add a set of liquid material system and the flow control requires high accuracy. Pep-set process is generally used for the production of thin-walled complex castings (cast iron, cast steel, cast aluminum), and is also suitable for automated molding line operations. It also has certain adaptability to the nature of multi-material and small-batch production.