Difference Between Grinding and Polishing

Grinding and Polishing

We often talk about grinding and polishing together, because the roughness of parts after these two processes is very small. First, let's understand the difference between them. The basic process of mechanical sample preparation is to use fine grinding particles to finish the material and remove the material on the surface to achieve the desired results. There are three methods to remove materials: grinding, polishing and fine grinding. These three methods are different in introducing the surface deformation of the sample.

Grinding is the finishing of the machined surface by the relative movement between the grinding tool and the workpiece under a certain pressure by using the aluminum oxide polish abrasive particles coated or embedded in the grinding tool. Grinding can be used to process all kinds of metal and non-metallic materials. The processed surface shapes include plane, inner and outer cylindrical and conical surfaces, convex and concave spherical surfaces, threads, tooth surfaces and other profiles. The machining accuracy can reach it5 ~ it1, and the surface roughness can reach Ra0.63~0.01μm.

Polishing is a processing method that uses mechanical, chemical or electrochemical action to reduce the surface roughness of the workpiece in order to obtain a bright and flat surface. The main difference between the two is that the surface finish achieved by polishing is higher than that by grinding, and chemical or electrochemical methods can be used, while abrasive grinding basically only adopts mechanical methods, and the abrasive particle size used is coarser than that used for polishing, that is, the particle size is larger.

Brown corundum grinding and polishing abrasive is the main abrasive for workpiece grinding and polishing. It has a certain grinding effect on the burr, oxide layer and some redundant edges and corners of the workpiece surface. So what are the characteristics of brown aluminium oxide grinding and polishing abrasive? Brown fused alumina manufacturers will give you a detailed introduction. A very important reason why brown corundum abrasive can be polished is that it has good chemical stability and will not have chemical reaction due to different workpiece materials, let alone corrosion to the workpiece.

The polishing effect of brown fused alumina abrasive is also very different according to the particle size. Generally, the coarse particle size is coarse polishing, while the fine particle size like brown aluminum oxide powder is fine polishing. The particle size of brown aluminum oxide for polishing can be divided into shapes, that is, people often say brown corundum grindstone, and brown aluminum oxide grinding stone has not only many specifications, but also many types of shapes, which are mainly produced for processing different workpieces.

When using brown alumina abrasive for polishing, it is generally not the abrasive alone, but the grinding and polishing machine needs to be equipped according to the workpiece material and other reasons. Of course, as far as brown fused alumina itself is concerned, most types of polishing machines are applicable. While using the polishing machine, you can also appropriately supplement the polishing grinding fluid as an auxiliary to help brown fused aluminum oxide better treat the surface of the workpiece.

Basic principle of dry grinding and wet grinding

Dry grinding mainly refers to the cutting effect of sand particles embedded on the surface of the grinding plate. When the parts slide relatively on the grinding plate embedded with sand under the action of grinding pressure, the sand will compress the high point of the ground surface and produce elastic deformation due to the increase of internal stress. When the stress exceeds the yield point, it enters plastic deformation, and there is slip between grains. With the increase of deformation, it finally loses contact and breaks, which is the so-called abrasive chip.

The existence of grinding accessories improves the cutting conditions and promotes the improvement of grinding quality and efficiency. Of course, while cutting, there are other auxiliary functions. Such as the formation and removal of oxide film; Plastic deformation caused by sand extrusion; The hot-melt effects of friction and cutting are enhanced with the refinement of abrasive particle size.

Wet grinding, due to the continuous addition of aluminum oxide abrasive, not only new sand particles participate in grinding, but also each micro edge of sand particles changes cutting, so that each edge plays a role, and the cooling and lubrication conditions are good. With the increase of activated excipients in alumina grinding media, the chemical and electrochemical effects are also enhanced. This is the main reason for making it an efficient grinding method.

What are the abrasive materials?

Abrasive materials belong to the category of "hardware tools". Abrasive materials in abrasive materials usually include: grinding wheel, sandpaper, abrasive cloth, steel wheel, grinding stone, oilstone, grinding head, grinding plate, cutting plate, abrasive belt, grinding block, page wheel, page piece, sponge wheel, cloth wheel, hemp wheel and other abrasive tools.

Abrasives in grinding materials include: grinding paste, polishing paste, polishing wax, polishing soap, polishing oil, polishing fluid, emery, polishing sand, black corundum abrasive, brown corundum abrasive, white corundum abrasive, pink corundum abrasive, zircon corundum abrasive and other natural abrasives and artificial abrasives.

What are the main uses of abrasive materials?

Alumina polish material is a material used for polishing materials. It can be used for polishing glass, metal, stainless steel, furniture, leather, semiconductors, plastics and gemstones Jade article. Grinding and polishing of stainless steel. For example, glass polishing adopts powdery mixtures such as iron oxide red, tin dioxide, alumina, cerium oxide, barium carbonate, chalk, clay and diatomite, which can be used after being mixed with water to form a suspension.

For the abrasive industry, abrasive materials are a common topic. As early as the middle and late 19th century, abrasive tools were used by people. It can be seen that they have a long history, which also witnessed how smart human beings are, such as ceramic grinding wheels made of natural abrasives and clay. At the beginning of the 20th century, various other abrasives were produced and used one after another, which made the grinding industry achieve rapid development.

Abrasive material category

There are many kinds of abrasive materials in daily life, but up to now, there are only five kinds that are widely circulated in the market. They will show different characteristics in different environments. As long as consumers choose their own abrasive materials fundamentally, they can give full play to the functional characteristics of products.

The categories of abrasive materials mainly include cloth hemp wheel, wind cloth wheel, polishing hemp wheel, white cloth wheel and oil hemp wheel.

1: This product is made of sisal and cotton cloth by rolling; The sisal hemp is sharp and the cotton cloth sticks wax, which shows the grinding force It is suitable for deep processing and surface polishing of coarse metal products such as steel, copper and cast iron.

2: The wind cloth wheel is made of high-density pure cotton grey cloth, which is planted and cut according to the cloth texture at an angle of 45 degrees. It is made of machine stamping. It is fine and wear-resistant. There is a wavy gap between each page. When the cloth wheel rotates at high speed, the high temperature generated by grinding will be dissipated and cooled by the wave fan gap, so as to avoid burning the workpiece. It can be finely ground with white wax or green wax to achieve the super mirror effect.

3: Polishing hemp wheel is made by special method, with less wear, material saving and economy. In order to improve elasticity and polishing effect, resin processing can be added, especially for stainless steel, tin, aluminum and other products with rough surface. It is better suitable for automatic polishing machine with high operation efficiency. In order to improve cutting force, resin processing can be added to hemp wheel.

4: The white cloth wheel adopts imported high-quality cloth and domestic high-quality cloth as raw materials and implements automatic production operation. The white cloth wheel produced is not only more temperature resistant and durable than similar products, but also has a better realm in the process of removing spiral lines, brightness and finish.

5: The oil hemp wheel is made of high-quality domestic hemp and pressed by sisal cart. It is air dried after soaking in tung oil. It is hard, sharp and has strong cutting force. It is suitable for the polishing of stainless steel pipe, and it becomes a better choice because of its hardness and sharpness. It is also suitable for the polishing of stainless steel workpiece, alloy workpiece, copper workpiece, etc.

In production, due to the introduction of abrasive materials, many products are more handy in production and processing. From the essence of product performance, when the abrasive particles are blunt in the use of the abrasive tool, due to the partial fragmentation of the abrasive particles themselves or the fracture of the binder, the abrasive particles fall off from the abrasive tool locally or completely, and the abrasive on the working surface of the abrasive tool continues to appear new cutting edges or expose new sharp abrasive particles, so that the abrasive tool can maintain the cutting performance within a certain period of time.

Grinding process

Grinding is the first step of mechanical material removal. Proper grinding can remove damaged or deformed surface materials and limit the deformation of other surfaces. The purpose of grinding is to obtain a plane with the least damage, and these damages can be easily removed by polishing in the shortest time.

Fixed abrasive particles can be used to remove material, but debris of sample material will be generated. The process of using sharp abrasive particles to remove material debris can minimize the deformation of the sample and achieve the highest removal rate. Grinding can be divided into two processes:

Plane grinding (PG)

This is usually the first step in the grinding process. Regardless of the initial condition of the sample and the previous treatment, plane grinding ensures that all sample surfaces remain similar. In addition, when processing several samples in the same sample holder, special attention must be paid to ensure that these samples are at the same level or "plane" before starting the next step, i.e. fine grinding.

For plane grinding, in order to obtain high uniform material removal rate, reduce grinding time and obtain maximum flatness, it is best to select completely fixed particles with relatively large size. A suitable PG surface can provide a sample with perfect flatness, thus reducing the preparation time spent in subsequent fine grinding steps. In addition, some surfaces can retain good edges. During grinding, new grinding particles will be released to ensure a consistent material removal rate.

Fine grinding (FG)

Fine grinding can provide a surface with less deformation, and the resulting deformation can be easily removed during polishing. Due to the defects of grinding paper, an alternative fine grinding composite surface is provided to improve and promote fine grinding. High material removal rates are achieved by using particles of 15, 9 and 6µm size. This applies to hard composite grinding discs (rigid grinding discs) with surfaces made of special composite materials. This helps the continuous supply of carborundum to be embedded in the surface to complete the fine grinding operation.

Using these grinding discs, a sample surface with excellent flatness can be obtained. The use of diamond abrasives on fine grinding discs ensures consistent material removal rates for hard and soft phases. Not only does the soft phase not have tailing, but also the brittle phase does not have debris, and the sample can maintain the best flatness. The subsequent polishing steps can be completed in a very short time. During fine grinding, the abrasive is suspended on the hard surface.

Do not press abrasive particles into and fix them in the surface. The abrasive particles can move freely in all directions and collide with small particles protruding from the sample surface, resulting in deep deformation. The reason is that the freely moving abrasive particles cannot produce real "debris" on the sample surface. Therefore, during fine grinding, the removal rate (material removal within a certain period of time) is very low and the processing time is very long.

In the case of soft materials, abrasive particles are often pressed into the sample surface when they are firmly embedded. Deep deformation and embedded particles should be avoided during the preparation of material phase samples. This means that fine grinding is only applicable to the preparation of hard and brittle materials, such as ceramic and mineral samples.

Polishing

Polishing is a very complex process. There are a large number of activated substances in abrasives, and the chemical action is very active and frequent. Abrasives only play the role of destroying oxide film. At the same time, some Abrasives themselves play a chemical role. For example, the free sulfur vapor in chromium oxide plays a chemical role with the metal surface to form a thin vulcanization film with low strength, which can adsorb stearic acid and chromium oxide.

When the part slides relative to the lapping tool, the chromium oxide adsorbed on the surface of the part will destroy the high point vulcanization film, re expose the fresh metal, and form the vulcanization film again. In this way, the wave crest of the part is polished repeatedly. Because the grinding tool is made of very soft materials, sand particles often exist in the soft matrix in the polishing process. Therefore, within a certain range, the influence of abrasive particle size on the polishing effect is not very obvious.

For surface finish, the polished surface finish is higher than the ground one. In fact, polishing fluid can be said to be the subsequent process of grinding, which can realize grinding and polishing on the same plane polishing agent machine at the same time. Grinding is divided into rough grinding and fine grinding; Polishing is divided into rough polishing and fine polishing. Most of the time, we use three processes to process the surface quality of products: rough grinding, fine grinding and fine polishing.

After these three processes, the flatness, parallelism and roughness of the workpiece surface are quite high. Some customers don't have so high requirements for the accuracy of the workpiece, especially if the roughness is not so high, they only use the first two processes, or finish grinding. It depends on the quality of the customer's workpiece itself and the workpiece requirements that the customer wants to meet.

Grinding and polishing can be realized on the same plane polishing machine, but all configurations and consumables are different. Grinding requires grinding disc and grinding fluid, while polishing uses polishing fluid, polishing disc, polishing cloth wheel and other consumables. Therefore, grinding plate, liquid and other consumables are needed to realize grinding and polishing on a plane polishing machine.

Polishing process

Like grinding, polishing is used to remove the damaged material left in the previous steps. This can be achieved by using finer grinding particles. Polishing can be divided into two different processes:

Emery polishing

Emery is an abrasive that can achieve the maximum material removal rate and the best flatness. At present, no abrasive can achieve comparable results. Due to the hardness of diamond, it can easily cut all materials and phases. During polishing, a smaller chip size is expected to obtain a sample surface free of scratches and deformation. If you use more elastic cloth and smaller particles, such as 3 or 1 µ m, the chip size is almost zero. Reducing the force applied to the sample also helps to reduce the size of debris generated during polishing.

Oxidation polishing

Some materials, especially soft and malleable materials, need to use oxidation polishing to perform the final polishing to obtain the best quality. Silica gel with particle size of about 0.04 µ m and pH of about 9.8 shows excellent polishing effect. The perfect combination of chemical activity and fine and mild wear effect can create a scratch free and deformation free sample.