Sand Paper Basics - Norton

Norton-Coated Abrasives Basics

Backing Types

Backings are the base for the abrasive minerals and, combined with the adhesive bond, support and anchor the abrasive mineral. The backings used in the manufacture of coated abrasives are:

Paper

Cloth

Cloth backings used for coated abrasives are identified by weight. Cloth backings are filled or "finished" with a variety of materials (glues or resins) to create various backing characteristics, most notably flexibility. Several cloth types are used:
cotton, polyester, polyester/nylon and polyester/cotton blends, and rayon. There are three basic weights of cloth: J-weight or "jeans" is the lightest and most flexible. X-weight or "drills" is a heavier cloth that ranges in flexibility, strength and durability and is used on the broadest range of applications. Y-weight is a heavyweight drills cloth used on heavy-duty, high stock removal operations.

Fibre

Vulcanized fibre (cotton fibres which are chemically treated and then pressed under temperature and pressure to form a very durable backing) is used exclusively as the backing for resin fibre discs.

Film

Polyester film backing comes in 3 mil. and 5 mil. thicknesses, which have high strength and surface smoothness. They are used primarily in disc and roll applications requiring consistent surface finish.

Bond Types

An adhesive bond system is required to secure the abrasive mineral to the backing. All coated abrasive products are made with a two stage bonding process, the make coat and the size coat.

The make coat is the first layer of bond applied to the backing. The make coat provides the adhesive base between the abrasive mineral and the backing. The size coat is the second coat, which is applied over the abrasive mineral and make coat to anchor the abrasive mineral and provide the desired physical strength of the finished product.

Glue, urea resin and phenolic resin are the three basic bonding agents most commonly used. There are many size coat and make coat combinations, such as glue over glue, urea over glue, and resin over resin. Glue over glue is the most flexible bond while resin over resin bond is moisture resistant, harder, less flexible, heat-resistant and has superior grain retention.

Coating Types

There are two types of abrasive coatings used in the manufacturing of coated abrasives: open coat and closed coat

(OPEN COAT 1/3 LESS GRAIN THAN CLOSED) CLOSED COAT

Open Coat

With an open coat, 50% to 75% of the surface is covered by abrasive grain. There are evenly spaced voids between particles of grain, helping reduce the effect of loading caused by wood dust or metal particles.

Closed Coat

Coated Abrasive Grit Comparison Chart