A coated abrasive consists of a mineral bonded to a backing with glue or resin. The mineral may be natural or synthetic, while the backing can be cloth or paper. An electrostatic charge is used to apply the mineral to the backing. Heat and pressure are typically involved in the process of making a coated abrasive.
Sandpaper is a common example of a coated abrasive. General purpose sanding products are available in sheets, rolls, belts, and disks. Heavy duty and lightweight disks are used for grinding and shaping metal or wood. Abrasive products are produced in a variety of shapes and sizes for a multitude of purposes.
Synthetic or natural minerals can be used to make a coated abrasive. Garnet is a natural abrasive commonly used in the woodworking trades. Natural polishing minerals include emery and crocus. Silicon carbide and aluminum oxide are among the more widely used synthetic minerals.
Mineral particles are graded according to size. The grit number designation system rates the coarseness of the product. Sizes range from 12, which is the coarsest, to the finest grade of 600. The higher numbers denote finer particles.
The backing used to produce a coated abrasive can be a single type or a combination of up to three materials. Paper is graded by weight and can be light and flexible to strong and durable. Cloth and fabrics such as cotton or polyester may be used. Fiber is often used for disk and drum sanding. A combination of these materials can be used to produce specialty abrasives.
Glues and resins are generally used to bond the mineral abrasive to its backing. Two layers of bonding agents are applied. The first layer bonds the mineral to the backing, while the second locks the process together. The most common type of coating, in which the entire surface of the backing is coated with the abrasive, is known as closed coat.
The adhesive coatings may be applied in different combinations in order to achieve different performance characteristics. Glue applied over glue results in the smoothest finishes. Resin over glue provides better heat resistance. Resin over resin produces the toughest, most heat resistant abrasive.
When applying the mineral to a cloth backing, an electromagnetic process is used. In this process, the fabric is first coated with glue or resin. An electrical field is produced giving the backing and the mineral opposite charges. The abrasive is attracted to the backing and the adhesive holds it together. The final adhesive lock is then applied.
There are many other variations of coated abrasive products available, as well as various means of production. Improved abrasives, adhesives, and backings are continually being developed. The uses for abrasive products are virtually unlimited.