In this article we will learn how the silane coupling agent used in resin coated sand.
In casting production, many natural and synthetic resins are used as the core sand binder, the process of strength building process is very interesting. At the begging, the liquid resin with catalyst were coated in sand surface and forming a layer of resin, the resin was low viscosity and had mobility. When the mold (core) sand was compacted, the sand intended to get near each other and then the sand resin “Link Bridge” was formed. The “Link Bridge” make sands closely connected, and with the passage of time, the resin gradually became sticky and hardening, and finally formed a fastening “resin neck”, the sands were firmly bonded together and had a certain extent of strength.
The sand will not easily lead to a tight chemical bond with resin because of their polar difference in structure and properties. In the same way, nor can they penetrate and dissolve each other, mainly by intermolecular attraction at the interface. Therefore, the silane coupling agents are usually used to enhance the adhesion, that is, to enhance the bond between the resin and the sand.
Silane coupling agents are silicon-based chemicals that contain two types of reactivity inorganic and organic in the same molecule. A typical general structure is
Where OR is a hydrolyzable group, such as methoxy, ethoxy or acetoxy, and Y is an organofuctional group, such as amino, methacryloxy, epoxy, etc.
The silane coupling agent will act at an interface between the sand and resin to bond, or couple, these two dissimilar materials. Silane coupling agents that contain three inorganic reactive groups on silicon (usually methxoy, ethoxy or acetoxy) will bond well to the sand surface. The alkoxy groups on silicon hydrolyze to silanols, either through the addition of water or from residual water on the sand surface. Then the silanols coordinate with metal hydroxyl groups on the sand surface to form a tight chemical bond.