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Sanding paper
Sanding paper , also called emery paper, or, technically correct, abrasive with backing, has developed into a highly specialised and optimised product. Hereby the quality is determined by the abrasive grain material, the properties of the backing and the composition of the bonding agent (glue) which connects the abrasive grains with the backing. Additives can increase the service life in relation to special processed materials.
Abrasive material
Silicon carbide (SiC)
SiC consists of approx. 60% quartz sand and 40% oil coke. The components crystallise to SiC at 1900?2200 °C. Saw dust and common salt are added to the process to increase purity. The resulting rock crystals rocks are crushed and ground down to produce the required grain size.
Due to its hard, sharp-edged crystals SiC is particularly suited for solid and tough materials like cast iron, stone, ceramics, titanium, but also for paintwork, plastics and rubber.
Aluminium oxide, fused alumina (Al2O3)
To begin with bauxite is gained from alumina which contains aluminium oxide in relative purity. By calcifying and subsequent melting after the addition of coke and iron filings in an electric arc furnace. After the molten substance has cooled down, the upper layer contains relatively pure aluminium oxide. Depending on the aluminium oxide content you can choose between the white to pink special fused alumina (approx. 99% Al2O3), brown regular fused alumina (approx. 94?97% Al2O3) and black corundum (approx. 70?85% Al2O3). The desired grain size is obtained by crushing and grinding. Aluminium oxide is very hard and tough. It is particularly suited for processing long-chipping materials like wood or metal.
Zirconic corundum
By melting a mixture of zirkonium dioxide and aluminium oxide at a temperature of approx. 1900°C one obtains a micro-crystalline structure which, when broken and worn down during normal application, develops new sharp edges again and again (self-sharpening effect).
For this reason zirconic corundum is recommended for the processing of tough materials like corrosion and acid-proof steel (stainless steel).
Backing
The backing materials used for abrasives have different properties in relation to elasticity, flexibility and tensile strength.
Papers
Papers with very firm and tough fibres and with varying weights and strengths are used. Papers with a special water-proof impregnation are used for wet sanding.
Paper backings are the most common backing materials since they fulfil the requirements of most applications.
Fabrics
Backings which are meant to fulfil high demands on tensile strength and stability are made of technical fabrics produced on the basis of cotton, synthetic fibres or a mixture of fabrics. In special cases the addition of paper will further improve their properties.
Fabric backings are more costly to produce. For this reason they are only used
if the backing will be subjected to high mechanical stress. This is typical for belt sanders.
Vulcanised fibres
Application as a stabilising material, usually together with special papers for heavy-duty abrasives. Typical application as fibre sanding sheet together with a supporting rubber backing pad on angle grinders.
Bonding agents
The performance of the abrasive is largely determined by the bond between the abrasive grain and the backing. The bond has to keep the abrasive grains firmly on the backing and at the same time it has to be rather flexible.
Natural glue bond
Natural glues are sometimes used for the bond in cases where the demands on stability are not too high, for example in standard sanding paper and for manual sanding.
Mixed bond
Here the lower bond is made with natural glue with synthetic resin as a top bond.
Synthetic resin bond
Base bond and one or more top bonds consist of synthetic resin resulting in a very firm bond between the abrasive grain and the backing. The use of different types of resin in individual layers can produce very hard and also very flexible bonds. Application mainly for machine-operated abrasives.
Additives
Suitable additives can strongly affect the properties of abrasives. A typical example for this would be a special coating.
Special coatings
Special coatings are available on abrasives with synthetic bond. The sanding surface is hereby covered in calcium stearate. This wax-like cover largely prevents the accumulation of dust and especially paint particles on the surface of the abrasive. As a result the abrasive will not clog up which ensures a longer service life, in some cases four times longer than with uncoated abrasives.
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