The most important utensil for grinding is the grinding wheel in addition to a grinding device. It is an asymmetrical body that is clamped into the grinding wheel and caused to rotate by the current.
Grinding wheels are manufactured industrially and always consist of abrasive grain, binding agent and pores, whereby the abrasive grain varies depending on the design. Minerals, crystals or other solids such as corundum, silicon carbide, CBN or diamond are common.
If the rotating grinding wheel hits another object, it uses the frictional force to remove material – this is what we call grinding, separating and sanding. Metal, wood and glass are mostly sanded with a grinder. Other names for grinding wheels are cutting discs, grinders or abrasives.
The decisive factor for the grinding project to be successful is the fit of the grinding machine, grinding wheel and the material to be processed. If you do not know your way around and use the wrong grinding wheel, you risk damage and a poor grinding result. Worn grinding wheels or broken Velcro discs are the consequences. With the right components, craftsmen can achieve better results faster when grinding.
In this article, we give you an overview of important facts and criteria for the selection of grinding wheels for wood and metal processing.
Table of Contents
- 1. Which grinding wheel for wood and light metals?
- 2. Which grinding wheel for carbide?
- 3. Criteria for the selection of grinding wheels
- 4. Surface processing with the grinding wheel: more than just grinding
- 5. How do I change a cutting or grinding wheel?
1. Which grinding wheel for wood and light metals?
Whether in industry or handicraft: The processing of wood and metal surfaces with a grinder is widespread. Grinding is usually part of a manufacturing process for workpieces and tends to be at the end of the manufacturing process. The aim of the grinding is to produce a surface that is as flat and flawless as possible and, if necessary, to prepare it for subsequent sealing.
For most types of metal, grinding wheels and attachments with a standard alloy are suitable. Conventional grinding materials include corundum and silicon carbide.
Corundum in its pure form consists of aluminum and oxygen, but contamination from other metal oxides is also common. Depending on the level of contamination, corundum appears in a wide variety of colors. Corundum is very hard and is therefore widely used in industry, also as an abrasive. The white corundum is ideal for grinding and polishing glass or steel. The pink corundum meets the requirements for profile and shape grinding. Generally, corundum grinding wheels can be used in many ways, but are unsuitable for very hard materials.
Silicon carbide or carborundum is a chemical combination of silicon and carbon. The silicon carbide (SiC) has an even higher hardness than corundum and a very high melting point. SiC grinding wheels are therefore harder and more brittle than corundum wheels. Pure SiC is colorless, in technical contexts it is usually green or black. The black SiC abrasive grains are suitable for working with non-ferrous metals, stainless steels as well as for ceramic and mineral materials. With the higher quality green SiC, craftsmen are armed for grinding glass, porcelain, marble, precious stone, artificial stone.
2. Which grinding wheel for carbide?
When it comes to hard metals, experts distinguish between three groups: tungsten carbide-cobalt hard metals, cermets and hard metal types for steel processing. In industry, hard metals are used as cutting materials or in tools and machines for stone processing. Again, there are not many materials that are suitable for grinding hard metals. Even hard materials such as SiC or corundum do not manage to process the surface of hard metals, but heat up and are affected.
For the grinding of hard metals, craftsmen therefore also need highly hard grinding materials. Ultra-hard grinding materials consist either of cubic boron nitride or synthetically produced diamond. They have much higher degrees of hardness than corundum and silicon carbide and are particularly resistant to wear. Low processing temperatures prevent heat damage.
Tough hard steels such as HSS steel, hot and cold work steel as well as a diamond at very high temperatures can be ground with Bornitid grinding wheels. Diamond grits grind hard metal, glass, ceramics, porcelain, refractory stones, germanium, graphite, cutting ceramics, silicon, rubber, non-ferrous metals, iron carbide alloys, nickel and chrome alloys and ball bearing steel.
In the following overview table, you will find the most important features and applications of different disc variants. We have summarized the most important things about grinding discs, flap discs, fever discs or diamond grinding discs or diamond cutting discs.
|Grinding discs||Flap discs||Fiber discs||Diamond grinding discs|
|Materials to be processed:||Materials to be processed||Materials to be processed:||Materials to be processed:|
3. Criteria for the selection of grinding wheels
Before buying grinding wheels, tradesmen should answer one question first: What do I want to use the grinding wheel for? Depending on the material to be processed by the grinding wheel, a certain grit or a certain degree of hardness is necessary.
In general, hard grinding wheels are the first choice
for the first rough grinding as well as for grinding work in which a lot of material needs to be removed quickly, for example when deburring. For fine sanding and polishing, users should rather use soft grinding wheels.
3.1 What grades of hardness are there for grinding wheels?
The hardness of a grinding wheel or cutting wheel does not mean the hardness of the individual abrasive grains, but the resistance of the bond to the breaking of the abrasive grains.
|extremely soft||A to D|
|very soft||E to G|
|soft||H to K|
|medium||L to O|
|hard||P to S|
|extremely hard||T to Z|
Letters have become established in the labeling for certain abrasives:
- flexible abrasives made of corundum or silicon carbide have a ‘P’
- rigid abrasives have an ‘F’
- Bornite bears a ‘B’
- Diamond coating carries a ‘D’
3.2 What does the grain size mean for a grinding wheel?
The grit number indicates the size of the abrasive grain. Their value is decisive for the removal rate. The abrasive grain size is determined using a standardized sieve. If the grain just falls through the mesh of the sieve, the number of stitches is used as the value for the grain number.
The following applies:
The higher the grit number, the smaller and finer the grit and the finer the surface of the workpiece. Exception: With diamond cutting discs, the higher number marking stands for a coarser grit.
|Rough||P12 to P80|
|medium||P100 to P280|
|Fine||P320 to P600|
|Very fine||P800 to P2500|
All abrasives are classified into the categories “coarse”, “medium”, “fine” or “very fine” according to their grain size. From P240, the grain size is called micro-grain size, including micro-grain size.
Attention: Not all grinding wheel grits are specified according to this standardized grit classification. For their Cubitron grain, 3M, for example, chose a name without letters, instead of with a plus sign. This means: The specified value covers two areas of the conventional grain sizes. A Cubitron grinding wheel with grit number 80+, therefore, comprises grit sizes P 060 and P 080.
3.3 What binders are there for grinding wheels?
The binder on the grinding wheels keeps the abrasive grains at a certain distance from each other. Common bindings are made of glass, resin or ceramic.
|Resin and synthetic resin|
3.4 The pores
The pores between the abrasive grains and the bond act as cooling lubricant chambers, which also promote the removal of the chips during grinding. Are the pores z. B. too small with inferior grinding wheels, additional friction and higher temperature rise. This can damage the abrasive. However, larger coolant can be carried through larger pore spaces. This reduces the risk of grinding burns.
3.5 The structure
The structure denotes the distance between the individual abrasive grains. The closer the grains lie together, the denser the structure and the smaller the pores. The structure is given in numbers from 1 to 18. Small numbers indicate small grain spacings, high numbers large grain spacings.
|1 to 4||close|
|5 to 7||normal|
|8 to 11||Open|
|12 to 18||Very open|
In addition, there are plate-shaped flap discs with overlapping lamellae. At Klingspor, they are also known as abrasive mop plates. They are used for welding seams, deburring and cast cleaning and are inserted into an angle grinder without a support plate.
4. Surface processing with the grinding wheel: more than just grinding
When processing surfaces with the grinder, tradesmen distinguish between different activities. Each of these activities has its own name in the technical language. Here is an overview of the most important grinding processes:
Mechanical processing of metal often results in sharp-edged projections called burrs. Burrs affect the accuracy of fit of metal workpieces and pose a risk of injury due to their sharp edges. Deburring removes the burrs by grinding. Burrs are less common in plastic molding.
- Chamfering or deburring
Sharp edges on workpieces are removed using so-called chamfers, which reduces the risk of injury. When chamfering, the craftsman removes a little material along the edge using a grinding tool, knife or milling cutter, usually at an angle of 45 °. Edge chamfering is particularly common for workpieces made of wood.
There are many contexts in leveling, in the case of surface processing, the leveling process smoothes a surface so that a smooth surface is created. Craftsmen remove rough spots, recesses and elevations by grinding. Hand sanding is recommended for sensitive wood surfaces.
- Grouting or roughing
When grouting or roughing, coarse pieces of material are lifted out using a roughing disc. For this type of surface treatment, craftsmen use a coarse and particularly stable grinding wheel that can withstand the highest loads for some time. Grinding disks also have a limited lifespan; after three years, performance usually deteriorates. The roughing process leaves a rather rough surface and allows only a small dimensional accuracy.
- Roll grinding
mill grinders are heavy machines with particularly high material removal. Roller grinders are recommended if thickly painted or particularly rough planks are to be handed over a large area.
grinding Longitudinal grinding is a variant of external cylindrical grinding, which is probably the most frequently used grinding process in the industry. Rotationally symmetrical workpieces are processed, for example, camshafts, nozzle needles or rollers.
5. How do I change a cutting or grinding wheel?
If you have found the right grinding wheels, you will certainly have to replace them more often. Therefore we want to recommend this video to you. The video shows how cutting discs on the angle grinder are changed and what you should pay attention to: