An angle (also angle grinder , Trennjaeger , separating witch , Schleifhexe , Feuerradl or Flex is called) a mostly electrically driven hand machine with a fast rotating circular grinding wheel . The grinding wheel is driven by an angle gear that gives the angle grinder its name. In 1954 the tool was introduced by Ackermann & Schmitt (since 1996 Flex power tools ); their brand name Flex is used as a generic name in German .
In the case of a cut-off machine with a gasoline engine, however, the cut-off wheel is driven by a V-belt due to the design. Such machines are often used in track construction to cut the rail sections, as well as the fire brigade and the THW in order to be able to work independently of the power supply. A similar tool is the twin saw .
The round tool rotates at a speed of up to 13,300 revolutions per minute (at 115 mm disc diameter, at 125 mm up to 12,200 revolutions per minute) and is therefore exposed to high centrifugal forces . The theoretical cutting speed of the discs on the circumference is usually around 80 m / s, the idle speeds of the machines built for different disc diameters (115, 125, 150, 180, 230 and 300 mm, the latter only as a cut-off grinder) differ accordingly. In order to prevent the disks from bursting, they are reinforced with fabric inserts and, thanks to a particularly elastic synthetic resin bond, have a certain flexibility compared to rigid grinding disks (grindstone) or flat grinding machines. This flexibility enables manual, freehand cutting of metal, stone and other materials without the grinding wheel breaking in the event of a slight tilt.
In many angle grinders, a speed control keeps the motor torque constant when the load on the device fluctuates. Without this function, the number of revolutions of the disc can vary and the cut becomes irregular.
Different tools are used as required. These typically fit the shaft with a standardized bore diameter or thread M14 x 1.5 :
- Clamping nut for face spanner or clamp nut for tool-free exchange
- Cutting disks made of high-grade corundum are used to cut metal , those made of silicon carbide are used to cut stone . Discs for cut-off grinding of NiRo steel are made free of iron, sulfur and chlorine (<0.1% each) in order to preserve the freedom from rust. The grain of discs for aluminum is not clogged by soft metals.
- Diamond cutting discs for cutting natural stone , concrete and ceramics (e.g. paving stones and tiles ).
- Rubbing discs made of corundum for processing metal and stone (e.g. cleaning weld seams / breaking edges).
- Serrated lock washers for grinding (surface and edge grinding) or polishing
- Sanding pad with firmly applied abrasive grain or applied abrasive ( fiber disc , similar to sandpaper ) with clamping or Velcro fastening e.g. B. for rough derusting of metal, removing thick old layers of paint, smoothing coarse wood, etc.
- Wire brushes in cup or disc shape, also in knotted versions made of HSS wire , are used for derusting and cleaning as well as for welding and soldering preparation.
- Skin discs for polishing (with reduced speed).
- Planing and carving disks for woodworking.
The most common disks typically have an outside diameter of 115 to 230 mm and a nominal inside diameter of 22 mm, with a tolerance of up to approx. 22.3 mm.
When working with angle grinders, protective goggles and flame-retardant cotton clothing should be worn. When cutting workpieces that then fall to the floor, safety shoes are useful. Angle grinders must always be held with both hands; So-called "one-hand angle grinders" do not exist (see manufacturer information, intended use). Due to the high noise level, it is necessary to wear hearing protection . Never work without the appropriate protective cover on the device; this is not only an important part in the event that the window bursts, but also prevents the window from being touched from the direction of the handles and controls of the machine.
Rough grinding with cutting discs must also be avoided at all costs - there is an increased risk of bursting because the stabilizing glass fiber fabric is only applied to the outside of these discs and would be the first to be sanded through during rough grinding. The abrasive then has nothing to counter the strong axial forces. For rough grinding, there are either serrated lock washers or thicker grinding wheels , in which stabilizing layers of fabric are also embedded in the abrasive. All discs have an expiration date, which is stated on the disc by the manufacturer and is usually three years.
As with all grinding processes, abrasion occurs when working with angle grinders . The high speed of the tool releases a lot of heat at the processing point. In metalworking, especially when grinding steel and cast iron, the glowing chips are thrown away at high speed (flying sparks). If large quantities of these glowing particles hit flammable material in a concentrated manner (this also includes unsuitable clothing for the operator), there is an acute risk of fire, if they hit glass or ceramic surfaces (e.g. tiles) there is a risk of burns. Grinding sparks can also penetrate gaps or cavities and lead to hidden smoldering fires that may only show flames after hours.
When working dry on stone and concrete, it makes sense to use a suitable extraction system due to the high level of dust. An alternative to this is wet cutting, but the angle grinder must be suitable for it in terms of its protection class .
For angle grinders used commercially, a regular safety check in accordance with the Industrial Safety Ordinance on the basis of the VDE regulations is required. According to the Occupational Safety and Health Act and the Industrial Safety Ordinance, the employer must ensure the safe use of work equipment.
Since manufacturers in the Federal Republic of Germany are obliged to confirm that electrical devices comply with EU law by means of CE marking and this can be done in accordance with the Machinery Directive or the Low Voltage Directive, angle grinders without the required restart protection are also in use and in use .
Suitable tools, in this case with restart protection, must be used for use in a company.
Special features of emergency organizations
Cutoff grinders at the fire brigade and the THW often differ from conventional cutoff grinders in the cutting discs used, which can cut a wider range of materials. While conventional cut-off machines differentiate between stone, steel and concrete discs, rescue discs are able to cut different materials. As with rescue saws , commercially available machines are used as basic devices, which are upgraded with the rescue disc. Cut-off machines with conventional stone or steel disks are also used for which, depending on the material to be cut, a corresponding cut-off wheel must be used.