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COATED ABRASIVES

Coated abrasives exist in a great variety of kinds, forms and dimensions, as they are produced for different applications, i.e. sanding, grinding, polishing and finishing. Three things are important in coated abrasives: abrasives grains, backing, bond.

BACKINGS

Backings must be strong to resist to high speed and pressure sanding and grinding and in the meantime flexible to mould easily to surface contours. Backings can be in paper, cloth, vulcanized fibre and a combination of paper and cloth.

WEIGHT ABRASIVE PAPER

Light backings are more flexible, while heavy backings are used to have a stronger mechanical resistence. Paper weights are expressed in grams for square metre and are indicated with a letter according to the following table:

Weight	Description
A = 70 g/m2 B = 90/110 g/m2	Light and flexible, they are mainly used for wet and dry hand sanding applications.
C = 110/135 g/m2	More resistant and less flexible than the previous ones, it is used for wet and dry hand sanding applications, and for low-powered sanding machines.
D = 135/160 g/m2	This backing is used for the C-wt applications, with mid-powered portable sanders and for narrow belts on fixed sanding machines.
E = 185/225 g/m2	It is used to prevent paper from cracking, so for discs and wide belts in medium and fine grits.
F = 250/300 g/m2	It is the heaviest and the least flexible, so ideal for the strongest applications with coarse grits and for wide belts.

ABRASIVE CLOTH

Cloth backings last more than paper backings, they don’t tear easily and they support continuous bendings when operating. They can be divived into 2 main categories depending on the fibres they are made of: natural cotton, usually for dry applications, and polyester, suitable for wet applications. As for papers, they are classified by their weight:

Weight	Description
J	It is the lighest and flexible backing and it is used when surface finishing and uniformity are more important than removal. It is ideal when flexibility is requested, as for applications on contours and curved surfaces.
X	It is a good compromise between resistance and flexibility and it is used both with coarse grits and in polishing applications with fine grits.
Y	It is stronger and more resitant than the previous one, it is used for strong applications such as metal grinding with narrow belts and for wooden panels calibration with wide belts.
H	It is the most resistant backing and so it is used in applications with coarse grits for big removals.

FIBRE

Made of several layers of vulcanized cellulose, fibre backings are extremely rigid and resistant, so they are particularly indicated for discs for portable high-speed sanding tools.

COMBINATION

A heavy paper is coupled with a light cloth, it is used when resistance to tearings and crackings is needed.

ABRASIVE GRAINS

Abrasive grains are made of natural or artificial minerals, according to their characteristics of hardness, heat resistance, shape and type of fracture. All these features indicate how an abrasive grain can penetrate, cut, grind and remove material from a surface.

Aluminium oxide

it is extremely hard and resistant. It is ideal for hard metal grinding and finishing applications and for hard wood sanding applications.

Silicon carbide:

it is the hardest and cutting mineral used for coated abrasives. It is ideal for non-ferrous metal working (aluminium, brass, bronze, magnesium, titanium), for soft materials such as gum and for hard materials like glass, stone and ceramic.

Zirconium:

it can get stronger while operating, so it is long-lasting in removal applications. It is suitable for metal grinding (especially stainless steel) and wood working, because as the grains grind, they fracture to form new cutting points extending the life of the abrasive.

Ceramic aluminium oxide:

it the most technological and advanced product and its pure micro-crystal structure crumbles more regularly than zirconium. Its durability, aggressivity and regularity in cutting are highly better than any other abrasive grains.

COATING

Close:

close coated products contain lots of abrasive grains, they are suitable for very hard materials for an excellent finishing.

Open:

open coat products have spaces between the abrasive grains preventing clogging.

NO-FILL SPECIAL TREATMENTS

To avoid clogging, there is a layer of zinc stearate on the second layer of the bond. The result is that products give excellent performances in plaster woodworking and in automotive.

ANTI-STATIC PRODUCTS

While sanding non-electrical conductive materials, electrostatic charges make powder adhere to the belt. Products with antistatic treatment avoid early clogging and are specially suitable for machines that are not equipped with a good vacuum system.

BOND

G = natural glue

It is a jelly got from animal skin that can be used by itself or mixed with inert fillers. As this glue tends to get soft with the heat, it is particurarly indicated for handworking and light applications.

UF = ureic resin PF = fenolic resin

Synthetic resins are mixed with additives to give more resistance, flexibility or other chracteristics. They are highly heat resistant and long-lasting in hard removal working, but fininishing results coarser. Some products are made with both the bonds, where the lower layer is natural glue to obtain a good finishing and the upper layer is synthetic resin to be heat resistant.

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