The main technical parameters of furan resin sand casting raw materials

1.Furfuryl alcohol content

The furan resin with acid as a catalyst generally contains more than 50% furfuryl alcohol. The most commonly used is urea-formaldehyde furfuryl alcohol resin. As the furfuryl alcohol content increases, the room temperature strength increases, and the strength is the highest. When the FA content is 70-80%, the room temperature strength is the highest. For high-temperature performance, as the furfuryl alcohol content increases, the thermal strength of furan sand also increases accordingly. This is why high-furan resin is used for ferrous metals, while low-color furan resin is sufficient for non-ferrous metals.

2.Nitrogen content

When the nitrogen content is within a certain range, the room temperature strength of furan sand increases with the increase of nitrogen content. When the nitrogen content is less than 1%, the room temperature strength drops sharply. On the contrary, the increase in nitrogen content reduces the thermal strength. Therefore, high nitrogen resin can only be cast for non-ferrous metal parts. The increase in nitrogen content is prone to pinholes in castings. For cast steel with a wide solidification range, it is most sensitive to nitrogen pinholes, and it is hoped to use low-nitrogen or nitrogen-free resins. For cast iron parts, when old sand is reused, resins with nitrogen content less than 3.5% should also be selected. Certain nitrogen content is beneficial to reduce the brittleness of furan resin, reduce the expansion of molding sand, and reduce the generation of veins on the surface of castings. In terms of cost, urea-formaldehyde furfuryl alcohol resins are cheaper, and furfuryl alcohol is very expensive, so the higher the furfuryl alcohol content in the resin, the lower the proportion of urea-formaldehyde, and the higher the cost of the resin.

3.Free formaldehyde

When self-hardening furan resin is synthesized, the amount of formaldehyde has a great influence on the performance of furan resin. According to some information, the molar ratio of formaldehyde to urea in the resin is generally 1.5-2.5, and the molding sand strength is highest when the molar ratio is 1.8. As the proportion of formaldehyde increases, the free formaldehyde in the resin increases significantly, and the hardening speed also accelerates. However, the free formaldehyde in the resin has a strong pungent odor and is not good for human health, so the free formaldehyde content is required to be less than 0.5-1.0%. The “Sanitary Standard for Design of Sanitary Enterprises” (TJ36-79) issued by China Health stipulates that the maximum allowable concentration of harmful substance formaldehyde in workshop air is 3mg/m3.

4.Viscosity

The viscosity of the resin has a great influence on the resin consumption and the uniformity of sand mixing. If the resin viscosity is too high, the coating layer on the surface of the original sand will be thicker, and it will not be easy to be uniform when the addition amount is low. This is more important in the case of continuous mixing cage sand mixers. Generally, the viscosity of furan resin should be less than 100CPS, and the viscosity of the mixing cage should be less than 50CPS (25°C). Increasing the furfuryl alcohol content can reduce the viscosity of the resin.

5.PH value

During the reaction process of the resin, the PH value is also a factor affecting the viscosity. If the pH value is too low, the reaction will be strong, and the viscosity of the resin will increase. Therefore, the pH value should not be too small. In addition, when the pH value is low, the resin solidifies faster, but the final strength is affected to a certain extent, and the storage period of the resin will also be shortened. Generally, the pH value of furan resin is preferably 6.5-7.5.

6.Water content

The water content of self-hardening resin has certain restrictions. Excessive water content will reduce the viscosity of the resin and the curing speed of the molding sand, and also affect the final strength and permeability of the molding sand, and even affect the formation of pore defects in the casting. In addition, water will also cause the silane coupling agent added to the resin to hydrolyze and fail. Therefore, the water content of self-hardening resin is specified in the technical quality standards. Generally, high furan resin should not exceed 2%, medium furan resin should not exceed 5%, and low furan resin should not exceed 10%.