Grinding may be defined as the removal of excess material involving relatively coarse grit sizes. The angle grinder is ideally suited for this job and various types of discs can be employed for this purpose and include:
- Resin bonded type 27 depressed centre reinforced grinding discs. For grinding most metals and stone based materials. These are available in 100mm, 115mm, 125mm, 150mm, 180mm and 230mm diameter. Tough, rigid and strong these are ideal for removing excess material and where surface finish is not critical. Aluminium oxide abrasive is used for mild steel grinding whilst silicon carbide abrasive is use for most stone based material including concrete. Special abrasive discs are made for grinding stainless steel (INOX), and aluminium. Type 27 grinding discs should be used at an angle of 30 degrees producing a slight bevel on the periphery. Avoid using the flat of the disc as this may result in contact between the work-piece and the retaining nut. These discs are ideally suited for heavy grinding applications, especially when used with larger diameter discs, where 24 or 30 grit are used for rapid stock removal.
More on resin bonded type 27 discs for metals.
More on resin bonded type 27 discs for stone based materials.
- Resin bonded cup stones and cones. Designed for use with angle grinders, cup stones and cones give a very high stock removal rate making them ideal for coarse and aggressive surface grinding applications. M14 thread suitable for use with angle grinders 115mm and above. Please observe maximum speed (RPM) when fitting to an angle grinder.
More on resin bonded cup stones and cones for metals and stone based materials.
- Fibre backed discs consist of a single layer of abrasive bonded to a fibre backing.(These require a suitable backing pad). This offers greater flexibility, especially on contours, over depressed centre type 27 discs. These are available in 100mm, 115mm, 125mm and 180mm diameter. As with grinding discs aluminium oxide abrasive is used on most steels and silicon carbide on stone based materials with both being able to be used on wood. Zirconia abrasive is ideal for use on stainless steel (INOX) as well as wood. Long-lasting, cool grinding and aggressive with a faster cutting rate ceramic abrasive is ideal for most metal grinding.
More on fibre backed discs for grinding metals, wood and stone based materials.
More on backing pads for use with fibre discs on angle grinders.
- Semi-flexible discs are used for surface grinding of stone based products. These are available in 115mm, 125mm and 180mm diameter and should be used with a suitable backing pad. Semi-flexible discs are composed of silicon carbide abrasive with a heavy duty fibre backing and used for grinding stone based materials including marble, granite, concrete, cast iron and fibre glass.
More on semi-flexible discs.
- Flap discs are designed for surface grinding of most metals. These are available in 100mm, 115mm and 125mm diameter in grit sizes P40, P60, P80 and P120. Aluminium oxide abrasive is used for mild steel grinding whilst the more popular and versatile zirconia aluminium oxide abrasive is ideal for grinding both steel and stainless steel (INOX). Long-lasting and aggressive with a faster cutting rate ceramic abrasive is suitable for most metal grinding. Flap discs outlast fibre discs allowing less down-time and are less aggressive than resin bonded type 27 grinding discs. A cost effective answer to grinding of most metals.
More on flap discs.
- Diamond cup grinding wheels for grinding of stone based products. These are available in 100mm, 115mm, 125mm and 180mm diameter. Suitable for surface grinding of all types of masonry materials including concrete, natural stone, floor pavement and construction-site materials. Available in single or double rim with up to a 10mm layer. Diamond abrasive should not be used for grinding metals. Care should be taken when deciding the type and size of the wheel as its maximum speed may not be suitable for smaller angle grinders.
More on diamond cup grinding wheels
- Diamond electroplated grinding wheels are used for grinding of stone based products as well as ‘in situ’ sharpening of tungsten carbide tipped tooling used on stump grinders.
More on electroplated diamond abrasive wheels
Abrasive grain size.
The grain or grit size is most important in determining a disc or wheel’s ability to achieve the required surface finish and remove stock. The size is designated by a number which increases as grain size decreases. For example 10 grit has a median size of about 2.00 mm and 60 grit 0.25mm.
Standard sizes are used in all Abtec discs as specified in the European Standards laid down by FEPA.
Coated abrasive size is preceded by the letter ‘P’.
Typical grain sizes of discs used on angle grinders:
Coarse< 16, 20, 24, 30, 36, 40, 46, 50, 60, 80, 100, 120, 150 > Fine
Type 27, 41 and 42 discs are usually resin bonded with a fabric reinforcement. Resinoid bonded discs are based on thermosetting phenolic resin. ‘Fillers’ may be added to improve the mechanical strength or to act as grinding aids on dry grinding operations. Resinoid bonds are cured by heating in ovens under carefully controlled conditions at selected temperatures between 150C and 200C.
Resinoid discs are tougher and less rigid than vitrified wheels. Their inherent toughness makes them ideally suited to heavy duty operations at high operating speeds. (80 M/S).
Vitrified wheels have a high modulus of elasticity therefore highly rigid and brittle. This bond is not suitable for use with angle grinders except under carefully controlled conditions.
Adhesive bonded discs and wheels.
Referred to as a coated abrasive, adhesive bonded discs and wheels have a backing that may be composed of paper, cloth or vulcanised fibre depending on the severity of the application. Paper backed discs are generally not used with angle grinders due to the high grinding forces imposed during grinding or sanding.
Electroplated bonded discs and wheels.
A single coat of diamond particles is plated on to a steel form where it is held in a layer of nickel. The particles stand well proud of the surface and electroplated wheels provide free machining on materials such as GRP, fibreglass, carbon fibre and ceramics.
This abrasive is commonly used in most applications involving discs used on angle grinders. It is tough, blocky abrasive and is wear resistant, although loss of sharpness may be critical when working on hard metals and stainless steel. More friable white abrasive is used in conjunction with thin (less than 2mm width) discs for reducing cutting times. Often competitively priced compared to other abrasives. Versatile can be used for grinding and sanding of most metals and wood. Often designated by the letter A or WA in the specification of the disc.
Zirconia aluminium oxide.
It has a unique self-sharpening characteristic which gives it long life on rugged stock removal operations. Ideal for use on most metals and wood its long-lasting cutting characteristics and controlled fracturing of the grain make it especially suitable for use in flap discs on stainless steel. Often designated by the letter Z or ZA in the specification of the disc.
Harder yet more friable than conventional aluminium oxide is ideal for sanding glass, non-ferrous metals (aluminium, brass, bronze, magnesium and titanium), rubber, plastics, fibrous woods, leather, enamel and many stone based materials. Silicon carbide is superior to any other abrasive in its ability to penetrate and cut faster under light pressure. Often designated by the letter C or GC in the specification of the disc.
Ceramic aluminium oxide.
Ceramic aluminium oxide is a long lasting, tough, dense abrasive due to its micro structure. The extremely small micron size particles break off during grinding, producing multiple new cutting edges. As it stays sharp, especially when used in medium and high pressure operations, it cuts at a higher rate than other abrasives. Ceramic abrasive can be used on most metals and woods.
The abrasive is the hardest of all abrasives and is ideally suited for cutting and grinding of many stone based materials. Special diamond cutting discs are also available for use on reinforced concrete. However diamond abrasive should not be used for cutting or grinding of ferrous metals as it causes extreme abrasive wear.