The bond is applied in two adhesive layers: the first bond has the function of fixing the abrasive grains to the backing and the second reinforces the position of the abrasive grain. The types of adhesive used are glues, Resins and Varnishes.
GLUE BOND – Animal Hide Glue
These are animal hide glues form organic colloids derived from the collagen on the flesh side of beef cattle. Their strength may be modified by the use of fillers. Bonding agent is hygroscopic – absorbs and rejects moisture quickly. Flexible type bond. Ages more quickly than Resin Bonds due to bacterial action.
RESIN BONDS
These are synthetic, heat-resistant adhesives manufactured with a urea formaldehyde base, ideal for moderate workloads, or with a phenol formaldehyde base, to withstand severe workloads in which a significant amount of heat is generated due to friction. These types of resins can also be modified with the use of fillers in order to increase their durability and sanding efficiency. Not generally affected by atmospheric changes and shelf life is a vast improvement over the glue bond products. Phenolic resin bonds produce a product not generally as flexible as animal hide glue. Urea-Formaldehyde Resin Cured at much lower temperatures than the Phenolic resins. Is not as strong nor as resistant to grinding heats penetrated as the Phenolic resin. More flexible and less costly to produce.
VARNISHES
These are synthetic adhesives constituted by phenolic resins and non-water-soluble substances, which permit the use of water or other water-containing lubricants with the coated abrasive. Generally speaking, glue adhesives and their variants are the most flexible bonds, while those based on resin are harder, heat resistant and have superior grain retention. Therefore, and according to application requirements, the following adhesive combinations are used:
GLUE: Light and intermediate grinding by hand or portable sanders. Used on products when extreme flexibility is required and no less severe abrading applications – such as hand sheets.
RESIN/GLUE: Where a heat resistant and a flexible bond is required in portable or stationary machines. This system used generally on paper backings when a resin bonded product is required. Also can be used on cloth products where a flexible product is necessary and where excessive abrading temperatures are not built up. Either high temperature cured Phenolic resins or low temperature Cured Urea-Formaldehyde resins can be used depending upon final product use.
RESIN/RESIN: For intermediate and heavy stock removal in high efficiency operations. Provides an extremely strong bond, highly resistant to abrading temperatures.
RESIN/VARNISH: For applications with water and with lubricants containing water.