Abrasive knowledge

Abrasives are tools for grinding, grinding and polishing. Most of the abrasives are artificial abrasives made of abrasives and binders, and are also natural abrasives that are directly processed from natural mineral rock.

Abrasives are classified according to their source of raw materials, including natural abrasives and artificial abrasives. The only natural abrasive used in the machinery industry is oil stone. Artificial abrasives are distinguished by their basic shape and structural characteristics, including grinding wheels, grinding heads, whetstones, sand tiles and coated abrasives. In addition, abrasives are also conventionally classified as a type of abrasive.

In addition to being widely used in machinery manufacturing and other metal processing industries, abrasive tools are also used in grain processing, papermaking, and non-metallic materials such as ceramics, glass, stone, plastic, rubber, and wood.

The main features of abrasives include five factors: abrasive, grain size, hardness, texture, and bonding agent. Appropriate selection according to different uses can directly improve processing quality and production efficiency.

Abrasive:

Abrasives used mainly abrasive brown corundum, white corundum, black silicon carbide and green silicon carbide.

Corundum has high toughness and is suitable for grinding materials with high tensile strength such as carbon steel, alloy steel, malleable cast iron and hard bronze. White corundum has a higher hardness than brown corundum, and it has good cutting performance. It is suitable for the grinding process of hardened steel, high carbon steel, high-speed tools and other materials.

Black silicon carbide has high hardness, brittleness and sharpness. It is suitable for grinding and cutting materials with low tensile strength, such as cast iron, glass, ceramics, stone and refractory.

Green silicon carbide is higher in purity than black silicon silicon. Suitable for grinding hard and brittle materials such as carbide, optical glass, precious stones, and agate.

granularity:

The choice of particle size mainly depends on the requirements of the workpiece surface machining accuracy and production efficiency. Coarse-grained and medium-grained abrasives are suitable for roughing and semi-finishing, while fine-grained abrasives are used for finishing and superfinishing. The physical and mechanical properties to be ground are also the factors that determine the grain size. Materials with low hardness, high ductility and toughness should be processed with coarse-grained abrasive tools, while those with high hardness and brittleness should use fine-grained abrasive tools.

organization:

The organization of the abrasive tool refers to the volume ratio between the abrasive, the binder, and the pores that make up the abrasive. Abrasive less, large porosity is called loose structure, and vice versa is close organization.

The closely-arranged abrasive tools should be used for fine grinding, forming grinding, and workpieces with small machining surfaces and high surface finish requirements.

Medium-sized abrasives are widely used for the grinding of general residual workpieces.

Abrasives for loose structures are suitable for grinding of large contact surfaces such as flat surfaces and internal circles, as well as grinding of workpieces that are sensitive to expansion and soft materials.

hardness:

The strength of the abrasive on the abrasive surface that is held together by the binder. Or under the action of external forces, the degree of difficulty in shedding is called the hardness of the abrasive.

Grinding tools are abbreviated as abrasive tools. Abrasives have three series of bonded abrasives, coated abrasives and superabrasives. Each has its own characteristics, exists independently, has its own strengths, and is used in the national economy of various countries in the world. Here is a brief introduction to bonded abrasives.

1. Bonded Abrasives Bonded Abrasives are tools made of abrasives (grinding materials) and binders with a certain shape and a certain degree of grinding ability.

Example of mark for bonded abrasives:

Shape Size Abrasive Size Bonding Hardness Organization 35M/S GB/T2485

Shape Code 300×50×75 Abrasive Type Abrasive Particle Size Bonding Agent Abrasive Tooling Hardness Organization No. Maximum Working Speed ​​Abrasive Tool Specifications Where Standard No. Except for the highest working speed and standard number of grinding tool specifications, the rest are for consolidation. The characteristics of abrasive tools. Abrasives of bonded abrasives have been described in detail in (i) of this paper. The abrasive grain size refers to the size of the abrasive, and the abrasive used for bonded abrasives adopts a series of standards. These 7 features are based on the 1998 national The Abrasive Abrasives Standardization Technical Committee compiles each of the provisions of the Machinery Industry Standard published by China Press. In addition to the three characteristics of the bonding agent and the microstructure of the bonded abrasives, this article will not repeat them.

(1) Hardness:

The hardness here refers to the strength of the bonding abrasive and the abrasive under the action of the bonding abrasives under external force. The hardness of the bonding agent is determined by the sandblast hardness tester and the Rockwell hardness according to the particle size. The hardness is super soft (ultra soft 1 and super soft 2) Soft (soft 1, soft 2), soft (soft 1, soft 2), medium (medium 1, medium 2), medium hard (medium hard 1, medium hard 2, medium hard 3), hard (hard 1 , hard 2), superhard (super hard 1, superhard 2) 7 large class a total of 15 small class.

(2) Binding agent:

Bonding agent refers to the bonding material of various types of bonding agents and abrasives in bonded abrasives. Bonding abrasives usually use four major types of bonding agents: ceramics, resins, rubbers, and magnesite. The four types of binders have the largest proportion of ceramic binder abrasives. The main materials of the ceramic binder are clay, feldspar, loess, quartz stone, etc. According to different abrasives, different uses and different methods of manufacturing (casting or pressing) and other different ceramic binders. Resin binder is mainly phenolic resin, Powdery resin and liquid resin are two major categories, which are also divided into different resin binders according to different methods and different uses. Rubber binders currently use three major categories of styrene-butadiene rubber, sodium butyl rubber and liquid rubber. Different methods and different uses are divided into different kinds of rubber adhesives. The main material of the magnesite binder is composed of two materials, magnesium oxide and magnesium chloride. It is mainly used for fine-grained abrasives for fine processing.

The code for various binders is as follows:

Binders Name Binder Codes Ceramic Bonds V

Resin binder B

Rubber binder R

Rare earth binding agent Mg

(3) Organization:

The organization refers to the volume occupied by the abrasive in the bonded abrasives, expressed in weight % ratio. Usually the organization is not displayed in the abrasive marks, and when the manufacturing formula is set, the self-control is represented by Arabic numerals. That is, the smaller the number is, The more loose the organization is, the lower the abrasive ratio in the bonded abrasives is, and the larger the number is, the more tight the organization is and the more abrasive particles are occupied. Usually the organization number is 13 organization numbers from 0-12.

2. Coated Abrasives Coated Abrasives are abrasives that the adhesive adheres to a flexible substrate, also known as flexible abrasives.

Coated abrasives have nine characteristics:

Substrate Type - Substrate Treatment - Type of Abrasive - Grain Size of Abrasive -

Sand-planting density - binder type - bonding strength - shape - size sand belt coated abrasive tool See the third article of this article.

3, superhard abrasive superabrasive refers to the use of people caused by diamond or cubic boron nitride superabrasive made of abrasive, Department of Abrasives another major series.

Superhard abrasive tools have the following characteristics and marks.

Concentration binder particle size Abrasives Abrasive grain thickness Thickness of pore diameter Total thickness Diameter shape code The above features and markings are in accordance with the provisions of each standard of China Machinery Industry Standard published by China Press in 1998.

About Concentration: The same as the organization number of bonded abrasives, but it should be indicated in the logo of superabrasives. The so-called concentration refers to the number of grams of superabrasive contained in the volume of superhard abrasive per cm3, in %. Said.

The concentration code is as follows:

Code Abrasive Content (g/cm3) Concentration 25 0.22 25%

50 0.44 50%

75 0.66 75%

100 0.88 100%

150 1.32 150%

About binders: refers to the type of binder used for superhard abrasives.

The binding agent code is as follows:

Bonding agent code resin binder B

Metal Bond M

Ceramic binder V

Coated abrasives are tools that can be ground and polished by bonding an abrasive to a flexible material such as cloth or paper. Together with grinding wheels, sand tiles, oil stones, grinding heads and grinding pastes, it constitutes the six major types of abrasive tools.

Coated abrasives consists of three major components: matrix, abrasives and binders, also known as three elements. From the cross-sectional view of the coated abrasive, the structure of the coated abrasive can be clearly seen.

The matrix substrate is the carrier for the abrasive and binder, which is the dominant factor in the flexibility of the coated mill.

The substrates for coated abrasives mainly include: cloth, paper, fibers, composite substrates, and non-woven fabrics. The matrix must be specially processed before it is used to make abrasive tools. It must be specially processed, and the performance of the substrate is related to its own type. But also related to the method being processed.

The matrix treatment is to improve and improve the physical and mechanical properties of the matrix through the matrix treatment agent, and to satisfy the process of applying sand and grinding.

The general matrix treatment can be divided into non-water treatment and water treatment two categories, depending on the grinding conditions, the substrate can also be soft, resistant to high permeability treatment, oil treatment and electrostatic treatment.

Abrasives are the part that acts as a grind. Commonly used are corundum, silicon carbide, and natural corundum. The abrasive grain size and composition conform to the national standard for abrasive materials for coated abrasives.

Sand-planting density Density-planting sand density is also an important factor for the quality and performance of coated abrasives. It indicates the density of abrasives on a matrix per unit area.

The binder binder firmly binds the abrasive to the substrate, which can be a primer, a sizer, and a matrix treatment agent.

Coated abrasive tools as abrasive polishing tools, its performance is mainly determined by the following factors: matrix, matrix processing, abrasive, particle size, sand, density, binder, bond strength, super-coating and shape size.

Microhardness Nowadays, the hardness of abrasives is often expressed as microhardness. Microhardness A type of indentation hardness that reflects the ability of a measured object to withstand the intrusion of another hard object. Measuring instrument microhardness tester, which is actually equipped with a loading device with an eyepiece micrometer microscope. Before the measurement, the abrasive to be measured is made into a reflective polishing sample, placed on a microhardness tester stage, and a quadrangular pyramidal diamond indenter is pressurized by a loading device. The size of the load can be increased or decreased depending on the hardness of the tested material. After the diamond indenter was pressed into the specimen, a pit was created on the surface of the specimen. The microscope reticle is aligned with the pit and the length of the diagonal of the pit is measured with an eyepiece micrometer. Based on the applied load and the diagonal length of the pit, the microhardness value of the tested material can be calculated.

Due to the different shapes of diamond indenters used, the microhardness is divided into four Vickers microhardness Knoop microhardnesses.

The Vickers microhardness was measured using a 130° diamond quadrangular pyramid as the press head. The values ​​were calculated as follows:

HV=18.18 P

D2

Variety Vickers Microhardness/Mpa(kg/mm2)

Brown fused alumina 19 600~21 600 (2 000~2 200)

White corundum 21 600~2 600 (2 200~2 300)

Chrome corundum 21 600~22 600 (2 200~2 300)

Single Crystal Corundum 21 600~23 500 (2 200~2 400)

Microcrystalline corundum 19 600~21 600 (2 000~2 200)

Bauxite sintered corundum 16 700 (1 700)

Zirconia 14 700 (1 500)

Diamond 78 500 (8 000)

Boron carbide 49 000 (5 000)

Silicon carbide 30 400 to 3 330 (3 100 to 3 400)

Garnet 13 300 (1360)

Quartz 8 000 (820)

Type: HV-Vickers hardness, Mpa;

P-load, kg;

D-diagonal diagonal length, mm.

The Knoop hardness is pressed into a diamond cube with a corner angle of 170°30'130°. The value is calculated according to the following formula: HK=139.54·P/L2. Type: HK-Knoop hardness, Mpa; P-load, kg; L-dimple diagonal length, mm. Vickers hardness is used in various countries in Europe, and Knoop hardness is used in the United States. Megapascals (MPa) The legal unit of microhardness, whereas kg/mm2 was previously commonly used in hardness calculations. The conversion formula between them is 1kg/mm2=9.80665Mpa. The commonly used abrasive microhardness is shown in the table below.

Transportation and storage To avoid damage to the abrasive transportation and storage process, care must be taken to:

Long-distance transport should be properly packed in wooden boxes or wicker baskets, and use abrasive materials such as straw sawdust to separate abrasives to prevent impact.

Ceramic abrasives cannot be placed in damp or frozen locations. Rubber abrasives cannot be in contact with oil. Resin mills can have contact with alkalis. Otherwise, abrasive strength and grinding force will be reduced.

Abrasives should be stored in a dry place with room temperature not less than 5 degrees Celsius.

Abrasive tools should be placed separately according to specifications, and signs should be placed at the storage place to avoid confusion errors. The placement method should be determined according to the size of the grinding shape. Large or thick abrasive tools should be placed slightly inclined upright, thinner and smaller grinding wheels should be stacked flat, but should not be too high, and put a flat iron plate under it to prevent deformation or rupture of the grinding wheel.

Organic abrasives should not be stored for more than one year. Ultra-precision grinding tools should be inspected before use. After the restructuring, the grinding wheel should also be used after the re-rotation test.

Installation and installation of grinding wheel should pay attention to the following aspects:

Before the grinding wheel is installed, the safety speed must be checked. Flags with unclear or unmarked grinding wheels must undergo a turn test again.

Before installation, tap the wheel with a mallet. If there is a dumb sound, there may be cracks in the grinding wheel and it cannot be used.

The flanges on both sides of the grinding wheel must have the same shape and size. The diameter of the flange is half the diameter of the grinding wheel and the inside requires a groove. Between the end flanges of the grinding wheel, a piece of elastic paperboard or fur with a thickness of about 1 to 2 mm, an oil-resistant rubber gasket, and the gasket diameter is slightly larger than the flange outer diameter.

Tighten the flange screws symmetrically in order to distribute the clamping force evenly. However, the force should not be too large to avoid fracturing the grinding wheel.

After the grinding wheel is installed, it must be at least one static balance before it can be installed on the grinding machine.

Care should be taken in the following aspects when grinding during safe grinding:

Before driving, you must carefully check the correct position of each operation handle or button, and whether the grinder is normal or not.

Before using the new grinding wheel, idle it for 5 minutes. After confirming that the operation is normal, first trim the outer circle and both ends of the grinding wheel, then remove it together with the flange, and then perform a static balance.

During the grinding wheel operation, the operator should not stand in the direction of the turning plane of the grinding wheel.

Before grinding, it is necessary to check carefully whether the workpiece is clamped correctly, and whether the fastening is reliable. Special attention should be paid to adjusting the position of the stopper and fastening it. Take care to prevent the grinding wheel from colliding with the chuck, chuck or top seat.

Grinding, the workpiece should be under the normal operation of the grinding wheel feed again (input not too aggressive); Similarly, must be retracted to stop.

It is not possible for two people to operate a grinder at the same time.

Operators must not rely on grinders to avoid accidents.

When the workpiece is still running, measurement cannot be performed. Do not touch the grinding wheel with your hand or wipe the workpiece with cotton sand.

Operators should wear fitted overalls and masks in order to avoid inhaling dust particles. Female workers should wear work caps and wear protective glasses when dressing wheel to avoid flying debris.

Before shutting down, the liquid supply system should be cut off, and the grinding wheel should be idling for 1-2 minutes to remove the grinding wheel from the grinding liquid.