Klingspor coated abrasives guide

What are coated abrasives?

Coated abrasives have grit anchored to a flexible backing with a bonding agent. “Sandpaper” is the everyday name for them. The family includes abrasive belts, rolls, sheets, strips and discs. They have four components, sometimes five:

1. Backing
2. Base coat
3. Grit and grain type
4. Topsize coat
5. Optional: additional coating

Bonded abrasives, by contrast, bond the grit together without a backing. The most common are cutting-off wheels and grinding discs.

Grit and grain type

The grit does the stock removal, and it comes in different grain types. When choosing a grain, two properties matter most: bond and toughness.

All Klingspor grain types are synthetic, which keeps quality consistent. Coated abrasives use four grain types:

1. Aluminium oxide
2. Silicon carbide
3. Zirconia alumina
4. Ceramic aluminium oxide

Figure: Grit classification in relation to bond, toughness and their primary applications

Figure: Grain type properties and wear behaviour

Grain type	Bond / toughness	Structure	Properties / wear properties
Aluminium oxide	hard / tough	crystalline , irregular	Wedge-shaped, block grain, even wear
Silicon carbide (SiC)	very hard / less tough	crystalline	sharp-edged, brittle, highly friable / micro-wear
Zirconia alumina	hard / very tough	crystalline, even	wedge-shaped, block, drop formed grit / micro-wear, self-sharpening
Ceramic aluminium oxide	hard / very tough	micro-crystalline	sharp-edged, pointed grit / micro-wear, self-sharpening

Grit agglomerates

There are also grit agglomerates. These are not a separate grain type. Each agglomerate is many individual aluminium oxide or SiC grits bonded with resin into one large grit.

Agglomerates give an even finish from first use to last. Dull grit breaks away and exposes new, sharp grit, so stock removal stays steady and service life is very long.

Agglomerates are only used on belts.

Grit sizes

The grit number shows the size of the grain on the abrasive. The values are set by the Federation of European Producers of Abrasives (FEPA). The lower the number, the coarser (larger) the grain and the rougher the finish.

Grit classification:

Klingspor uses the FEPA P standard, which keeps grain size uniform across the scale. That’s why Klingspor grit numbers carry a P prefix.

Available grit sizes:

Our coated abrasive product pages use this table to show which grits each product comes in. Grits not available for that product are greyed out.

Klingspor makes abrasives from grit 16 up to grit 2000, for all materials and almost any grinding, sanding or polishing finish.

Backing

The backing carries the grit and transfers the stock-removal forces to the workpiece. The main backings are:

• Paper
• Cotton cloth
• Polyester cloth

Klingspor also uses these backings for specific products or applications:

• Fibre (only for fibre discs on portable angle grinders)
• Film (only for abrasive disc FP 73 WK)
• GX-blended cloth (special cotton/polyester blend for flexible yet highly tear resistant belts)

Paper backings are low-cost and mainly used where strength matters less, such as finish grinding. Paper is graded from A (very light) to H (very heavy) by mass per unit area.

Cloth backings are much tougher than paper, so they are used where tear resistance matters, such as stock-removal grinding or profile sanding with abrasive belts. Klingspor offers everything from light, highly flexible cotton to heavy, highly tear-resistant polyester cloth for stock-removal grinding.

Fibre (vulcanised fibre) is a composite of cotton and cellulose fibres that makes a very uniform, stable backing.

Foil backings are thin polyester film, very flat and tear-resistant. They are used mainly on discs and belts for finish grinding surfaces, especially varnishes.

Figure: Paper and cloth backing classification in relation to tear resistance and flexibility

Flexing

“Flexing” is the finishing treatment freshly made abrasive rolls need before they can be converted into belts, sheets, discs and other products.

Abrasive grains are applied to a flexible backing of paper, cotton or plastic blended fabric and fixed with adhesive (bond) and a special varnish (size coat / top binding). Because the top binding is hard and brittle, the abrasive is brittle and fragile straight after manufacture and not ready to use. It has to be flexed first.

In flexing, the abrasive is pulled over a flex shaft several times at different angles. This breaks up the size coat in a controlled pattern and gives the abrasive the flexibility it needs for conversion and use.

Coating

Coated abrasives come in different grit densities. Grit density describes how closely the grit covers the backing.

There are three classes:

• close coating
• semi-open coating
• open coating

Open coating leaves large gaps between the grits, so swarf and grinding dust clear from the surface more easily. This stops early clogging on long-chipping materials such as wood. Choose the grit density by how likely the dust is to clog the gaps between grits.

Size coat

The size coat works with the base coat to anchor the grit to the backing and hold it against grinding forces. Size coats are made only from resin and give the product its typical colour (except abrasives with additional coatings).

Special coatings

Special coatings with grinding aids improve the grinding process and extend the service life of the abrasive. They are applied as an additional layer.

Stearate coating

Stearate stops the belt clogging and loading, and suits high-quality varnished surfaces. Heat from grinding can make paints, varnishes and plastics soft and sticky, so they clog and load the belt early. The dust fills the gaps between the grits and forms an extra “negative bond” that blunts the sharp grit edges. A non-stick stearate coating prevents or slows this.

Multibond

Multibond is an extra coating applied over the size coat in a separate step at the end of production. It keeps grinding cool: the coating evaporates early and carries heat away.

Multibond is mainly used on high-quality abrasives for stainless steel and high-alloy steels.

Because the temperature is much lower, far less workpiece material sticks to and “vitrifies” the grain tips. The result is measurably higher stock removal and longer service life than conventional abrasives. Multibond also prevents or greatly reduces heat-induced discolouration (heat tint), which is typical when grinding stainless steel.

Klingspor offers a wide range of coated abrasives for stainless steel, each with a multibond optimised for the application.

Source: Klingspor.de: Lowdown on Grinding

ACT – Advanced Coating Technology

Klingspor uses ACT to improve the properties of its coated abrasives. On metal, ACT gives much stronger grit adhesion, for example in aggressive belt grinding of the edges of punched parts and castings, which greatly extends belt life. On belts for wood and varnish, ACT prevents early clogging and greatly extends service life.

Antistatic

Abrasives for non-conductive materials such as wood or plastic get an antistatic treatment during production. Electrically conductive ingredients let static charge discharge safely through the abrasive and the machine.

Friction between two surfaces moves electrons from one to the other. On non-conductive materials the resulting charge cannot dissipate. Charged grinding dust then sticks to the belt, the machine or the workpiece, and dust extraction alone will not remove it. An antistatic finish prevents or minimises this. It is standard in woodworking and can also extend the service life of the abrasive.

Every abrasive in Klingspor’s wood-finishing range has an antistatic finish, marked “Antistatic” on the reverse. In the basic version the backing (paper or cloth) is antistatic. Some models also have an antistatic grinding side, with conductive substances such as graphite added to the resin bond. These give extra antistatic performance with a suitable dust-extraction system.

Source: Klingspor.de: Lowdown on Grinding