How To Choose Grinding Wheel Correctly

How to choose grinding wheel?

Grinding wheel is also known as bonded abrasive. Grinding wheel is a bonded abrasive tool that binds ordinary abrasive into a certain shape (mostly circular, with a through hole in the middle) and has a certain strength. It usually consists of abrasives, binders and pores. These three parts are often referred to as the three elements of consolidated abrasives. According to different classifications of binders, common ones are ceramic grinding wheel, resin (binder) grinding wheel and rubber (binder) grinding wheel.

Grinding wheel is one of the widely used grinding tools. When in use, it rotates at high speed, and can rough grind, semi-fine grind, fine grind, slot and cut the outer circle, inner circle, plane and various contours of metal or non-metal workpieces. There are many grinding wheels and tools of different shapes and sizes.

1. Selection of ordinary grinding wheel

1.1 Organization of grinding wheel

The structure of grinding wheel is the proportional distribution of abrasive, binder and air hole. In short, it is the distance between abrasive particles. The distance between abrasives is very difficult to measure. The percentage of abrasives in the volume of grinding wheel, i.e. abrasive rate, is used as the standard of organization. The grinding wheel can be made of different loose organization or different density according to different grinding conditions. The abrasive particles of the grinding wheel can break quickly after being blunt, so as to expose the new edge and continue grinding.

The grinding wheel with dense structure has less pores, while the grinding wheel with loose structure has more pores. There are many pores, although the combination degree is weak, but there is a large cutting space, which can improve the cutting effect. Those with large pores and few pores are called coarse sand wheel; Those with small pores and many holes are called dense grinding wheels. In short, the grinding wheel with large pores is suitable for grinding soft and sticky materials, such as aluminum, copper, etc; On the contrary, it is suitable for grinding hard and brittle materials.

1.2 Shape of grinding wheel

The shape of grinding wheel can be divided into five types: flat shape, bevel (double bevel, single bevel), dish shape, bowl shape and cup shape. Flat grinding wheel is the most widely used, grinding plane, outer circle, slotting, etc., and can be repaired into various shapes for forming grinding according to the actual use needs. There is no need to talk too much about bevel grinding wheel. We all know that carpenters usually use single bevel grinding wheel to grind alloy saw blades.

Dish shaped and bowl shaped grinding wheels are usually used to grind various cutting tools and cutting tools, such as drill bits, milling cutters, etc. The cup-shaped grinding wheel can be used for many purposes. For example, this kind of grinding wheel is used in the machine for grinding planer. In addition, the cup-shaped grinding wheel can also be used for vertical grinding of plane, which has high efficiency and poor heat dissipation. There are also many forms of grinding wheel with handle (such as those used in electric grinding). 

The grinding wheel can be made into many shapes to meet different needs. There are three kinds of commonly used Abrasives: oxide system, carbide system and high hard abrasive system. Aluminum oxide grinding wheel and silicon carbide grinding wheel are commonly used in ships and factories. Aluminum oxide grinding wheel has low hardness (hv2000-hv2400) and high toughness. It is suitable for grinding high-speed steel turning tools. The colored one is called white corundum and the grayish brown one is called brown corundum.

The abrasive hardness of silicon carbide grinding wheel is higher than that of aluminum oxide grinding wheel (above hv2800) It is brittle and sharp, and has good thermal conductivity and conductivity. It is suitable for grinding cemented carbide. Among them, the commonly used are color and green silicon carbide grinding wheel. The green silicon carbide grinding wheel is more suitable for grinding cemented carbide turning tools.

1.3 Different types of grinding wheels selection criteria

According to different grinding materials, bonding materials and manufacturing processes, each type of grinding wheel has a certain scope of application. Improper selection will directly affect the machining accuracy, surface roughness and production efficiency. Therefore, the appropriate grinding wheel must be selected according to the specific situation. How to choose grinding wheel correctly? Summarize the commonly used grinding wheels in grinding, so that everyone can clearly choose the grinding wheel.

1.3.1 Selection of abrasives mainly depends on the workpiece material and heat treatment method.

When grinding materials with high tensile strength, choose abrasives with high toughness. When grinding materials with low hardness and high elongation, brittle Abrasives should be selected. When grinding high hardness materials, choose abrasive with higher hardness. Select the abrasive that is not easy to process for chemical reaction. The most commonly used abrasives are brown fused alumina and white fused alumina, followed by black silicon carbide and green silicon carbide, and the rest are pink corundum, single crystal corundum, microcrystalline corundum and zirconium corundum.

Brown corundum grinding wheel: brown aluminium oxide has high hardness and toughness. It is suitable for grinding metals with high tensile strength, such as carbon steel, alloy steel, malleable cast iron, hard bronze, etc. This abrasive has good grinding performance and wide adaptability. It is usually used to remove large amount of rough grinding. It is cheap and can be widely used.

White aluminum oxide grinding wheel: the hardness of white aluminium oxide is slightly higher than that of brown aluminum oxide, and the toughness is lower than that of brown aluminium oxide. During the grinding process, the abrasive particles are easy to break. Therefore, the grinding heat is small. It is suitable for manufacturing grinding wheels for grinding hardened steel, high carbon steel, high-speed steel and thin-walled parts. The cost is higher than that of brown fused aluminum oxide.

Black silicon carbide grinding wheel: black silicon carbide is fragile and sharp, and its hardness is higher than that of white corundum. It is suitable for grinding materials with low mechanical strength, such as cast iron, brass, aluminum and refractory materials. Green silicon carbide grinding wheel: green silicon carbide has higher hardness and brittleness than black silicon carbide, sharp abrasive particles and good thermal conductivity. It is suitable for grinding hard and brittle materials such as cemented carbide, optical glass and ceramics.

Pink aluminum oxide grinding wheel: suitable for grinding workpieces with high surface processing quality such as cutting tools, measuring tools, instruments and threads. It is suitable for grinding single crystal stainless steel and corundum with high hardness and high toughness. Microcrystalline corundum grinding wheel: suitable for grinding stainless steel, bearing steel and special nodular cast iron. It is used for forming grinding, cutting grinding and mirror grinding. Zirconium corundum grinding wheel: suitable for grinding austenitic stainless steel, titanium alloy and heat-resistant alloy, especially for heavy-duty grinding.

1.3.2 The choice of particle size mainly depends on the surface roughness and grinding efficiency of the workpiece to be ground.

Particle size refers to the particle size of abrasive, and its size is expressed by particle size. Take the number of holes on the length of each inch that the abrasive particles can pass through as the symbol. For example, 60 particle size refers to that the abrasive particles can just pass through a screen with 60 holes per inch of length. Therefore, the larger the number, the finer the wear particles.

The grinding wheel with small abrasive grain number shall be selected for rough grinding turning tool, and the grinding wheel with large number (i.e. fine abrasive grain) shall be selected for fine grinding turning tool. Medium soft or medium hard grinding wheel with particle size of 46-0 is commonly used on board. When grinding with coarse sand wheel, the production efficiency is high, but the workpiece surface is rough. When grinding with fine-grained grinding wheel, the workpiece surface roughness is better, but the productivity is lower.

On the premise of meeting the requirements of roughness, coarse-grained grinding wheel should be selected as far as possible to ensure high grinding efficiency. Generally, coarse sand wheel is selected for coarse grinding and fine grinding wheel is selected for fine grinding. When the contact area between the grinding wheel and the workpiece is large, the grinding wheel with coarse particle size shall be selected. For example, when grinding the same plane, the grinding of the end face of the grinding wheel is rougher than that of the periphery of the grinding wheel.

1.3.3 The choice of hardness mainly depends on the material, grinding efficiency and surface quality of the workpiece to be ground.

Hardness refers to the difficulty of abrasive particles falling off under the action of external force. In order to meet the grinding requirements of different workpiece materials, the grinding wheel is processed into different hardness grades. The hardness of grinding wheel reflects the difficulty of abrasive particles falling off the surface of grinding wheel under the action of grinding force. The grinding wheel is hard, that is, the abrasive particles on the surface are difficult to fall off; The grinding wheel is soft, indicating that the abrasive particles are easy to fall off.

The hardness of grinding wheel and the hardness of abrasive grain are two different concepts, which must be clearly distinguished. When grinding high-speed steel turning tools and cemented carbide turning tools, soft or medium soft grinding wheels should be selected. Sun drying is the hero of industrial green. In addition, the bond and organization of the grinding wheel should also be considered when selecting the grinding wheel.

Ceramic bond (code a) and medium structure grinding wheel are generally used on ships and factories. We should select the grinding wheel correctly according to the tool material. When grinding high-speed steel turning tool, soft or medium soft aluminum oxide grinding wheel with particle size of 46 to 60 shall be selected. When grinding cemented carbide turning tool, soft or medium soft silicon carbide grinding wheel with particle size of 60 to 80 shall be selected, and the two shall not be mistaken.

1.3.4 The choice of adhesive shall be considered according to the grinding method, application speed, surface treatment requirements and other conditions.

The most commonly used wheel binders are ceramic binder (V) and resin binder (b). Ceramic bond is a kind of inorganic bond, which has stable chemical properties, good heat resistance, corrosion resistance and large porosity. The grinding wheel made of the binder has high grinding efficiency and small wear, can better maintain the geometry of the grinding wheel, and has the widest application range. 

The grinding wheel is suitable for grinding ordinary carbon steel, alloy steel, stainless steel, cast iron, cemented carbide, non-ferrous metals, etc. However, the ceramic bonded grinding wheel is fragile and can not withstand severe vibration. Generally speaking, it can only be used at a speed of less than 35 meters per second.

Resin adhesive is an organic adhesive. The grinding wheel made with the binder has high strength, certain elasticity, low heat resistance, good self sharpening, simple manufacture and short processing cycle. It can produce grinding wheels with working speed higher than 50m / s and very thin grinding wheels.

Its application scope is second only to ceramic binder. It is widely used in rough grinding, rough grinding, cutting and free grinding, such as grinding steel ingots, deburring castings and so on. It can be used to manufacture high-speed and high-precision grinding wheels, heavy-duty grinding wheels, cutting grinding wheels and various grinding wheels with special requirements.

1.3.5 The selection of organization mainly considers the pressure of workpiece, grinding method and material.

Microstructure refers to the percentage of abrasive particles in the volume of grinding wheel. The classification of grinding wheel microstructure grade is based on 62% microstructure with abrasive particle volume percentage of "0". When the volume of abrasive particles decreases by 2%, the tissue increases by 1, and so on. It is divided into 15 numbers. The more numbers, the looser the organization.

A compact grinding wheel can grind a better workpiece surface. The loose organization of the grinding wheel, due to the large gap, can ensure the inclusion of grinding debris in the grinding process and avoid the blockage of the grinding wheel. Generally speaking, when rough grinding and grinding soft metal, the grinding wheel is easy to be blocked, so the wheel with loose organization should be selected.

In form grinding and precision grinding, in order to maintain the geometry of the grinding wheel and obtain better roughness, the grinding wheel with relatively tight structure should be selected. When grinding machine tool guide rails and cemented carbide tools, in order to reduce the thermal deformation of workpieces and avoid burns and cracks, loosely structured grinding wheels should be used. Grinding wheels larger than 12# are used to grind high heat sensitive materials, non-ferrous metals and non-metallic materials.

1.3.6 The selection of shape and size shall be based on grinder conditions and workpiece shape.

Common grinding wheel shapes include plane grinding wheel, single-sided concave grinding wheel, double-sided concave grinding wheel, flake grinding wheel, cylindrical grinding wheel, bowl grinding wheel, dished No. 1 grinding wheel (D1), etc. The shape and size of the grinding wheel that can be used by each grinder have a certain range. 

If possible, the outer diameter of the grinding wheel should be selected as large as possible to improve the linear speed of the grinding wheel, obtain higher productivity and workpiece surface quality, and the same effect can be obtained by increasing the width of the grinding wheel.

At present, the writing order of national standard grinding wheel is: grinding wheel code, size (outer diameter) × thickness × Pore diameter), abrasive particle, particle size, hardness, texture, binder, maximum working linear speed.

2. Storage and transportation of grinding wheel

Because the grinding wheel usually works at high speed, the rotation test (to ensure that the grinding wheel will not break at high working speed) and static balance test (to prevent the vibration of the machine tool during operation) should be carried out before use. After working for a period of time, the grinding wheel should be trimmed to restore the grinding performance and correct geometry.

The grinding wheel has low strength and is easily affected by factors such as temperature, humidity, vibration, collision, extrusion and storage time. Properly storing and transporting the grinding wheel is of great significance to prevent accidents. Therefore, the following points should be achieved:

1 The grinding wheel shall be stored on a special storage rack. 2. The handling of grinding wheel shall be reduced as much as possible to prevent cracks caused by collision and vibration. The grinding wheel is brittle. Please do not be impacted, dropped or collided.

3. When storing rubber bonded grinding wheel, pay attention not to touch oil; Resin bonded grinding wheel shall not contact alkali solution. Ceramic aluminum oxide grinding wheel should not be placed in wet or frozen places, otherwise the strength and grinding force of abrasives will be reduced. The resin and rubber bonded grinding wheel shall be sandwiched between two smooth and flat metal plates when being kept. The metal plate shall be larger than the diameter of the grinding wheel. In addition, it shall not be placed under humidity and fan for direct blowing to prevent bending and deformation. The grinding wheel cannot be stored for a long time. The resin and rubber will deteriorate after more than one year. At this time, it must be strictly inspected before use.

4. Rubber and resin bonded flake grinding wheel shall be protected from deformation during storage The storage of grinding wheel shall be subject to the instructions of the manufacturer. The expired grinding wheel cannot be used casually. 5. During the transportation of grinding wheel, it shall not be installed with metal objects and; And reduce vibration and impact. 6. Abrasives shall be stored in a dry place, and the room temperature shall not be lower than 5 ℃; When the grinding wheels are stacked, the stacking height is generally not more than 1.5m.

7. Grinding wheels shall be placed separately according to specifications, and signs shall be set at the storage place to avoid confusion and errors. The placement method shall depend on the grinding shape and size. Grinding tools with large or thick diameter shall be placed upright and slightly inclined, and grinding wheels with thin and small diameter shall be stacked horizontally, but not too high. A flat iron plate shall be placed above and below it to prevent deformation or fracture of the grinding wheel.

Precautions for use of grinding wheel:

1. The grinding wheel shall be checked before installation to see if there are cracks, and the grinding wheel shall be knocked with a wooden hammer to hear if there is abnormal dumb sound. If so, the grinding wheel cannot be used to avoid the consequences of personal injury caused by the fracture of the grinding wheel.

2. When the grinding wheel is newly installed or used every other day, it should be idled for more than one minute before use. If everything is normal, it can be used in accordance with the relevant safety regulations of grinding machinery.

3. As the grinding wheel is fragile, please do not let it be impacted, collided or fall. When storing, it shall be protected from freezing and moisture. The room shall be kept cool and ventilated, placed flat and stacked neatly. Pay attention to dust prevention, keep the unused grinding wheel clean and do not press it heavily.

4. When installing the grinding wheel, the center of the grinding wheel must be aligned and fastened with a flange. After installing the flange, check whether the outer circle of the grinding wheel is concentric with the spindle, and at least one side of the grinding wheel is perpendicular to the centerline of the spindle.

5. After installing the grinding wheel, for the sake of safety, do not install the qualified protective cover before starting the machine.

After the above steps are completed, the grinding wheel can be used.

When using, you should also pay attention to:

1. The grinding wheel speed shall not exceed the specified safe working line speed. 2. Do not use the end face working grinding wheel specially. Please do not work with the end face of the grinding wheel. 3. When the grinding wheel is processing the workpiece, please do not use the lever to push the workpiece to increase the pressure on the grinding wheel.

4. Special dressing tools shall be used for dressing the grinding wheel. Operators must wear protective glasses during trimming. 5. In grinding, the coolant shall be selected correctly; If coolant is not used, there must be a dust-proof device. 6. Customers who use grinding wheel shall be familiar with the installation and operation process of grinding wheel.