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Coated Abrasives and Aluminum Oxide Abrasive

1.Basic knowledge of Coated Abrasives

Coated abrasives are also a kind of artificial abrasives. They refer to abrasives that adhere abrasives to flexible substrates with adhesives, also known as flexible abrasives.

They are composed of abrasives, adhesives and substrates. Generally, corundum, silicon carbide and glass sand are used as abrasives, leather glue, bone glue, casein glue and synthetic resin glue are used as adhesives, paper, cloth, steel paper, composite matrix The non-woven fabric is made of matrix.

The manufacturing process of coated abrasive tools generally includes matrix treatment, primer coating, sand planting, re coating (coating), drying and cutting.

There are many kinds of coated abrasives, which are widely used. From the perspective of grinding application, one kind is manually used (leaf abrasive cloth, abrasive paper and some roll abrasive paper); The other is the varieties used for machining (mainly sand belt, sand plate, page wheel and sand ring).

Coated abrasives are tools that can be ground and polished by bonding abrasives to flexible materials such as cloth and paper. It is combined with grinding wheel, sand tile, oilstone, grinding head and grinding green. The coated abrasives are composed of three parts: matrix, abrasive and binder.

coated abrasive products

1.1 Matrix

The Coated Abrasive Substrates mainly includes: cloth, paper, fiber, composite matrix, non-woven fabric and other types. Before manufacturing abrasive tools, the matrix must be specially treated. The performance of the matrix is related to its own type and the treatment method.

Matrix treatment is the process of improving and improving the physical and mechanical properties of the matrix through matrix treatment agent to meet the needs of gluing, sand planting and grinding. 

General substrate treatment can be divided into non water resistant treatment and water resistant treatment. According to different grinding conditions, the substrate can also be softened, high permeability resistant, oil resistant and electrostatic treated.

Different substrates, different substrate weaving methods and manufacturing processes will determine different properties of substrates and their applications. Substrates are also an extremely important aspect of the research and development of coated abrasives.

Commonly used base materials include the following categories: paper, rubber film, cloth, vulcanized fiber, polyester fiber and composite base materials. Each base material can be divided into different strength grades according to the required flexibility, strength and material removal rate.

1.1.1 paper substrate and adhesive film substrate

Paper has been used as base material for a long time with low cost. Its surface is flat and its machined surface roughness is lower than that of cloth base material, but its strength and toughness are poor, and its load capacity is not as good as that of cloth base material. 

Adhesive film as base material is rare in China. It has been applied abroad (such as Britain) and is one of the development directions of high-precision abrasives. However, like light load paper, it is often used in light load manual polishing and wood processing due to the limitations of high transmission power and high pressure in rough processing.

With the progress of manufacturing technology, people have been able to produce high-strength heavy-duty paper. High polymers are added in the production process of heavy-duty paper to further improve its strength. In the past, three or four or more layers of paper were stacked together to obtain the required strength, while heavy-duty paper only needs one or two layers to obtain greater strength and less thermal sensitivity. 

Paper substrate is easy to obtain both in length and width, so paper substrate is more and more popular. Heavy duty paper is an important direction of substrate development. In order to improve the strength and flexibility of wet grinding of paper substrate, rubber, resin or other materials are often added or coated in the paper substrate.

1.1.2 cloth substrate

It is made of cotton or synthetic fiber, and the matrix is soaked with high polymers to increase strength. Cotton fabrics are divided into two categories: one is light load fabric with good flexibility - fine twill fabric (J), and the other is heavy load fabric - coarse twill fabric (x). 

Obviously, the coarse twill cloth has high strength and poor flexibility. It is used for grinding on refitted machine tools and also for rough machining on disc grinder or abrasive belt grinder. When the surface is complex and only needs to maintain its shape, it is more suitable to use non-woven matrix, but the grinding rate is low.

Cloth base materials are often divided into four types for selection: J-type, X-type, Y-type and S-type. Type J belongs to light load cloth with soft texture. It is used in rough grinding, forming and polishing: type X cloth base is strong and durable, which is suitable for heavy-duty grinding processing: Type Y cloth is 30% heavier than type X. This heavy-duty cloth base not only has high tensile strength, but also is more resistant to puncture, fracture, wrinkle or disassembly. Facts have proved that it is very suitable for wide abrasive belt grinding of wire and plate. S-type is cotton woven fabric, which is used in combined wide abrasive belt machine.

The application scope of cloth base material is the widest. The cotton or fiber cloth base material added with high polymer has good resistance to various coolants. In high-speed belt grinding, the reasonably selected abrasive particles must match the high-strength substrate. At this time, the cloth substrate is often considered.

1.1.3 vulcanized fiber substrate

The base material is laminated by vulcanized fiber. Vulcanized fiber is made from broken cotton cloth and then chemically treated to gelatinize cotton wadding fiber. 

It is characterized by hard texture, strong strength and good toughness, but it still maintains its flexibility and is not sensitive to coolant. The coated abrasive tool made of fiber base material made by overlapping several layers of gelatinized paper, vulcanization and grinding can be used to make grinding discs and roller polishers.

coated abrasive belts

1.1.4 polyester fiber substrate

Polyester material has many advantages: it has water resistance and can be widely used in dry grinding, lubricating oil grinding and water cooling grinding without water resistance treatment. Compared with cotton base material, it has greater tensile strength, rupture strength and shear strength. It can fully meet the requirements of rough machining. It can transfer more than 100kW power during high-speed grinding. It also has the ability to buffer and absorb periodic vibration load in time.

Polyester can also form a new composite substrate with cotton fabric or paper. After the emergence of polyester fiber, it has developed rapidly and attracted the attention of belt manufacturers all over the world. It is known as the "peak" coated abrasive tool substrate by Norton company of the United States.

1.1.5 composite substrate

This is a substrate formed by laminating two or more different substrate materials together. For example, the composite substrate of paper and cloth combines the advantages of both, and of course, it is more difficult to manufacture. It can be used in high-speed drum grinder, the composite substrate of vulcanized fiber and cloth is mainly used to make grinding discs.

The combined substrate of dennier fiber, weaving cloth and polyester additives. It not only has stability to a variety of grinding fluids, but also has high toughness and heat insensitivity. This consortium can also achieve different products from "soft to hard". The flexible composite substrate can be used when it needs to be suitable for specific shape or soft contact wheel processing, while the "hard" composite substrate is used for processing hard metal materials or using rubber contact wheels.

In addition, some factories have developed fine metal mesh as the substrate of abrasive belt, which can be used in some strong grinding with good results. These substrates can be used as cathodes in electrolytic abrasive belt grinding and mild steel belt substrate.

1.2 Abrasive

Types of abrasives abrasives are the main body of coated abrasives for grinding and polishing. Abrasives can be divided into natural abrasives and artificial abrasives. The commonly used abrasives for Coated Abrasives mainly include:

Brown fused alumina(BFA): Appearance is brown or tan, high hardness, good toughness, able to withstand great pressure, high temperature resistance, corrosion resistance, good chemical stability and other characteristics. It is widely used. White corundum (WFA): the appearance is white, the hardness is higher than that of brown corundum, the property is brittle, the toughness is lower than that of brown corundum, the abrasive is easy to break, and the sharpness is good.

Black silicon carbide (c): the main component is SiC, which is black in appearance, high hardness, brittle, and good sharpness of abrasive. Zircon corundum (ZA): grayish white or grayish brown in appearance, with good toughness and wear resistance. It is suitable for high-speed heavy load grinding and processing of difficult to grind metal materials.

The particle size and composition of abrasives meet the national standard of abrasives for coated abrasives. Different kinds of abrasives are the main factors affecting the quality and performance of coated abrasives. However, the density of abrasive per unit matrix area, that is, the density of planting sand, is also an important factor affecting the quality and performance of coated abrasives.

Selection principle of Coated Abrasives: the selection of abrasives mainly considers the properties suitable for processing workpieces. When grinding workpieces with high hardness, choose abrasives with high hardness; When grinding workpieces with high tensile strength, choose abrasive with high toughness; When grinding workpiece materials with low tensile strength, choose silicon carbide abrasive with brittleness and high strength.

1.3 Binder

The adhesive can firmly bond the abrasive with the matrix. It can be primer, compound and matrix treatment agent. As a grinding and polishing tool, the performance of coated abrasives is mainly determined by the following factors: matrix, matrix treatment, abrasive, particle size, sand planting density, binder, bonding strength, super coating, shape and size, etc.

2.Characteristics of Coated Abrasives

Compared with consolidated abrasives, coated abrasives have the following characteristics:

2.1 Coated abrasives have good softness, convenient use and wide application. They can be folded, bent, wound, torn or cut into strips, blocks and other shapes to meet the requirements of different processing.

2.2 Coated abrasives are suitable for large-area and complex surface processing. They are irreplaceable products of consolidated abrasives. For example, coated abrasives are needed for the grinding of stainless steel belt, plywood, whole leather and engine blades processed by abrasive belt.

2.3 Coated abrasives have high grinding efficiency and are not easy to burn workpieces. The efficiency of common Coated Abrasives belt grinder has been increased to 96%, and almost all work has been converted into useful work.

2.4 Coated abrasives are flexible abrasives with simple equipment, safe use and convenient operation.

3.Classification of Coated Abrasives

According to different substrates, abrasives and binders, coated abrasives can be divided into many varieties with different properties and uses. Scientific and reasonable classification method of coated abrasives is an important basis for selecting coated abrasives.

coated abrasive paper

3.1 Classification according to substrate and use method

Coated abrasives are divided into dry abrasive cloth, water-resistant abrasive cloth, dry abrasive paper and water-resistant abrasive paper.

3.2 Classification according to binder and substrate treatment

Coated abrasives are divided into four categories: Animal adhesive bonded abrasives, resin bonded abrasives, all resin bonded abrasives and water-resistant abrasives.

3.3 Classification according to abrasive material and particle size

Abrasive material represents the type and performance of abrasive, and abrasive particle size represents the size and distribution of abrasive particles. Different abrasive materials and particle sizes can be divided into different types of coated abrasives. In addition, there is a code for dry abrasive cloth and water-resistant sandpaper, which are still used in the market for different particle sizes.

3.4 Classification according to planting sand density

Planting sand density refers to the density of abrasive particles on the surface of coated abrasive tools. The planting sand density of coated abrasives is divided into dense planting sand (CL) and sparse planting sand (OP).

3.5 Classification according to product shape

Coated abrasives can be divided into page, roll, strip, disc and special-shaped products according to the shape of the product. According to the classification of binder and substrate treatment, it can be divided into four categories: Animal bonded abrasives, resin bonded abrasives, all resin bonded abrasives and water-resistant abrasives.

Animal adhesive bonded abrasives: Code g / g base and compound glue are made of animal glue. Low grade substrate treatment agent has poor heat resistance and moisture resistance, but the binder is water-soluble, cheap, simple to make and easy to use. Semi resin bonded abrasives: code named R / g, primer is animal glue, compound glue is synthetic resin binder, medium and low-grade substrate treatment agent, and its characteristics are between animal glue and all resin products.

All resin bonded and coated abrasives: code name is R / R, the base and compound glue are made of bonding resin, high-grade substrate treatment agent (water-resistant or waterproof), high bonding strength, good wear resistance and heat resistance. It is mainly used in mechanical grinding. Water resistant coated abrasives: Code WP. The base material shall be treated with water or oil resistance in advance. The primer and compound glue shall be made of synthetic resin or paint, which is suitable for use in water cooling liquid.

4.Application scope of Coated Abrasives

Coated abrasive is a kind of flexible abrasive made of abrasive, substrate and binder. Grinding with coated abrasives has elastic and efficient cold cutting grinding points, which are widely used in:

4.1 The surface of large flat plate is polished, including steel plate, plywood and leather.   

4.2 Surface sanding of mass-produced workpieces, printed circuit boards, piano boards, wooden furniture, etc. 

4.3 Continuous polishing and grinding of metal strip. (the width of the strip can be more than 1200mm, and the length is unlimited).

4.4 Form grinding and polishing of complex surface.

4.5 Outer circle grinding of metal pipes, rods and rollers with various diameters, containers with inner diameter greater than 25mm, inner circle grinding, such as air cylinder, hydraulic cylinder, oil tank, etc.

4.6 The page wheel and sand ring can replace the polishing cloth wheel to realize the automation of polishing process.

4.7 The sand pan is used for grinding welds, thorns, paint, etc. of large shells, boxes and hulls.

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