Choosing The Right Grinding Wheel(5)
Coated Abrasives are used for a range of surface-treatment applications including grinding, blending, dimensioning, shaping, finishing, & polishing in an extremely wide range of markets, indeed usually anywhere where a surface has been smoothed or finished.
Markets include engineered markets such as tool manufacture, prosthesis manufacture, golf club manufacture, crystal manufacture, automotive manufacture, foundries, as well as more industrial markets including welding, woodworking, floor sanding & general maintenance.
Coated abrasives are products composed of three basic elements – A flexible or semi rigid backing, Abrasive grains & an adhesive that bonds the grains to the backing.
Abrasive types
Aluminium Oxide:Tough well adapted to grinding high tensile materials, such as carbon steel, alloy steels, tough bronze and hard woods. Wherever toughness (ability to resist fracturing) is the main consideration aluminium oxide out performs all other coated abrasive grains.
Silicon Carbide: Hardest and sharpest of the minerals used in coated abrasives. Its hardness and sharpness make it the ideal abrasive for sanding non-ferrous metals (aluminium, brass, bronze, magnesium, titanium etc.), rubber, glass, plastics, fibrous woods, enamel and other relatively soft materials. Silicon Carbide is superior to any other abrasive in its ability to penetrate and cut faster under light pressure.
Zirconia Alumina: Contains a unique self-sharpening characteristic which gives it long life on rugged stock removal operations. Zirconia alumina is well suited for heavy grinding of metals & planing of wood, because the controlled grain fracture continually produces sharp new abrading points.
Ceramic Aluminium Oxide: a long lasting tough, dense abrasive due to its micro structure. The extremely small micron sized particles break off during use, producing multiple new sharp cutting edges. As cermamic aluminium oxide products stay sharp, especially in medium & high pressure machine operations, it cuts at a higher rate than other abrasive types.
Backing Types
Whether paper, cloth, vulcanised fibre or polyester, the backing must be smooth enough for a uniform adhesive coating, strong enough to withstand grinding pressure and flexible enough to conform to contours.
Paper: The lighter the backing the greater the degree of flexibility; the heavier the backing, the greater the resistance to tearing.
Cloth: Cloth backings are more durable than paper, offering greater resistance to tearing, and can tolerate continual bending and flexing during use.
Fibre: Fibre backings are made up of multiple layers of impregnated paper which gives it very hard & strong qualities. This backing is used in resin bonded fibre discs designed for heavy duty grinding applications.
Coatings
There are two types of abrasive grain coatings:
Open – typically 75% of the backing is covered in abrasive grain that is evenly spaced which is ideal for operations where the grinding debris would "load" or clog the surface, reducing the cutting efficiency & shotening the coated abrasive life.
Closed – the backing is almost completely covered with abrasive grain. It is used where loading is not a problem & fine surface finishes are desired.