Introduction to resin sand casting process

The concept of self-hardening furan resin sand

The name of self-hardening furan resin sand comes from the English word Furan No-Bake process, which means that furan resin is used as a binder and a catalyst is added to mix the molding sand. The sand mold can be self-cured at room temperature without baking or passing hardening gas. It is usually referred to as “cold-hardening resin sand” or even “resin sand.” The following introduces two basic concepts.

1.The structure of furan resin

The ring composed of carbon atoms and other element atoms (such as O, S, N, etc.) is called a heterocycle, and the non-carbon atoms that make up the heterocycle are called heteroatoms. Organic compounds containing heterocycles are called heterocyclic compounds. The so-called “furan” is a five-membered heterocyclic organic compound containing one oxygen atom. It is a general term for the basic structure of a family of compounds. In the furan system, the heterocycle without substituents is called “furan,” and its derivatives are named according to the parent. Furan itself has no use in the industry, but its derivatives, furfural and furfuryl alcohol, are important raw materials in the industry. They are the most important furan derivatives. The scientific name of furfural is a-furan formaldehyde, and the scientific name of furfuryl alcohol is furfuryl alcohol. Their molecular structures are as follows: Resins containing furfuryl alcohol are called furan resins. Furan resins used as casting binders are generally condensed from furfuryl alcohol (FA) with urea, formaldehyde or phenol, such as urea-formaldehyde furan resin (UF/FA), phenol-formaldehyde furan resin (PF/FA), phenol-urea-formaldehyde furan resin (UPF-FA^P formaldehyde-furfuryl alcohol resin (F/FA), etc.

2. The hardening mechanism of furan resin can be cured by heating, passing hardening gas or adding acid catalyst according to the different compositions of furan resin

Acid-catalyzed (i.e., “self-hardening”) furan resin generally has a furfuryl alcohol content of more than 50%. Its hardening mechanism is very complex and has not been fully understood yet, but the basic resinification reaction includes the dehydration condensation between the first alcohol group of furfuryl alcohol and the fifth hydrogen of the furan ring, in addition to the cleavage of the furan ring to generate levulinic acid, the dehydration of the first alcohol group to generate ether and aldehyde, etc.

3.Self-hardening furan resin sand has the following advantages:

1)The casting surface is smooth, the edges and corners are clear, and the dimensional accuracy is high. This is because resin sand molding can eliminate many factors that cause mold (core) deformation, such as ：

• The sand has good fluidity and does not need to be compacted by a tamping machine, which reduces the damage and deformation of the mold (core box)
• The sand mold (core) is de-molded after solidification, which reduces the deformation caused by loose molds before demolding and damage to the sand mold (core) during demolding;
• No need to repair the mold, which reduces the deformation caused by repairing the mold;
• No baking is required, which reduces the deformation of the mold (core) caused by baking;
• The mold has high strength and good surface stability, so the core head gap is small, and the parting negative number is small, which reduces the damage and deformation of the mold during core placement and mold matching and ensures the mold matching accuracy;
• The mold (core) has high hardness and good thermal stability, which can effectively resist mold wall retreat and migration during pouring, reducing the thermal shock of the mold. Deformation (such as bulging sand, etc.);
• The sand has good disintegration properties and is easy to clean and polish, thus reducing the damage to the shape accuracy of the casting during the sand removal, shoveling and finishing process.
  Since the factors that affect the deformation and damage of the mold and casting are eliminated to the greatest extent in each process, the surface quality and geometric dimensional accuracy of resin sand castings can be improved by 1-2 levels compared with clay baking sand, reaching CT7-9 level accuracy and 1-2mm/600mm flatness, and the surface roughness is greatly improved.

2)High molding efficiency, improved productivity and site utilization, and shortened production cycle. The reasons are as follows:

• The molding sand has good fluidity and does not require a tamping machine to compact it, saving a lot of tamping work
• The mold strength is high, which saves the work of repairing the mold after demolding;
• After the alcohol-based paint on the mold (core) is dried, the drying process can be omitted, saving labor time and space;
• After the old sand is recovered, the dry mechanical regeneration makes the sand treatment a closed system, which is easy to mechanize and can save a lot of old sand treatment, sand mixing, transportation and other auxiliary labor;
• The molding sand has good disintegration, easy sand removal, less repair work,
• Save some preparatory work before molding (core), such as core solidification. According to general statistics, after using self-hardening furan resin sand instead of clay baking sand, the production efficiency can be increased by 40-100%, and the output per unit molding area can be increased by 20-50%.

3. Reduce labor intensity, greatly improve labor conditions and working environment, especially reduce noise, silica dust, etc., and reduce environmental pollution.

4. Save energy. This is reflected in the elimination of kiln drying and hydraulic sand cleaning, the improvement of molten iron finished product rate, and the significant reduction of compressed air consumption, which has significant effects in saving water, electricity, coal (coke), etc.

5. The resin sand mold (core) has high strength (including high-temperature strength), good formability, lower gas emission than other organic casting molds, good thermal stability, and good air permeability, which can greatly reduce the defects of castings such as sand sticking, sand inclusion, sand holes, pores, shrinkage holes, cracks, etc., thereby reducing the scrap rate and manufacturing complex parts and key parts that are difficult to make with clay sand.

6. It is easy to recycle old sand, and the recycling rate can reach 90-95%. It has significant effects in saving new sand, reducing transportation, and preventing waste pollution.