In the casting process, curing agents are key auxiliary materials that determine the hardening speed of resin sand and the quality of castings. Selecting the appropriate curing agent for different types of resin sand not only improves production efficiency but also effectively enhances the surface quality and dimensional accuracy of castings.
As the casting industry places increasing demands on environmental protection, efficiency, and casting quality, the selection and matching of resin sand curing agents have gained growing attention. Currently, the mainstream casting curing agents are mainly classified into the following categories, each corresponding to different resin systems and application scenarios.
I. Curing agents for furan resin sand: organic acids dominate, inorganic acids gradually recede
The commonly used curing agents for furan resin no-bake sand are organic acids, such as benzenesulfonic acid, p-toluenesulfonic acid, and xylenesulfonic acid. These curing agents have low viscosity and are easy to mix with sand. The cured sand mold exhibits good collapsibility and excellent reclamation performance, and is widely used in the production of steel castings, iron castings, and non-ferrous alloy castings.
In contrast, inorganic acid curing agents are rarely used today due to their strong hygroscopicity, difficulty in sand reclamation, and tendency to cause gas holes and sand adhesion defects in castings.
II. Curing agents for alkaline phenolic resin: organic esters enable high-performance casting
Alkaline phenolic resin is usually paired with organic ester curing agents, such as glycerol acetate and ethylene glycol acetate. Under alkaline conditions, organic esters react with the phenolic resin, gradually curing the resin sand. This type of curing agent offers adjustable curing speed and stable casting quality. Moreover, the resin sand exhibits good thermoplasticity and secondary hardening characteristics at high temperatures, making it particularly suitable for producing alloy steel, carbon steel, high manganese steel, ductile iron, and other castings.
III. Curing agents for phenolic urethane resin: tertiary amine catalysis, preferred for cold box process
Phenolic urethane resin mostly uses tertiary amine curing agents (e.g., triethylamine), which catalyze the crosslinking reaction of the resin at room temperature to achieve rapid curing. This system is commonly used in the cold box process, featuring fast hardening speed, high core strength, and good release properties, making it suitable for high-volume, high-precision casting production.
IV. Curing agent for coated sand: hexamethylenetetramine ensures heat-curing performance
The curing of thermoplastic phenolic resin coated sand relies on hexamethylenetetramine (urotropine). Upon heating, hexamethylenetetramine decomposes and releases formaldehyde, which undergoes a crosslinking reaction with the hydroxymethyl groups in the resin, rapidly curing the coated sand. The cured cores from this system exhibit good strength and collapsibility, and are widely used in the manufacture of castings with complex internal cavities.
The rational selection of casting curing agents directly affects the hardening behavior of resin sand, the efficiency of sand reclamation, and the final casting quality. Enterprises should scientifically match the type and dosage of curing agents according to their resin type, casting material, and process conditions, in order to achieve efficient, green, and stable casting production.
