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Abrasives development and use

2019-09-20  356

Abrasives are tools used for grinding, grinding and polishing. Most of the abrasives are artificial abrasives made of abrasive plus binder, and natural abrasives directly processed from natural mineral rock.

Abrasive tools were widely used in machinery manufacturing and other metal processing industries. What's more,they are also used in the processing of food processing, paper industry and non-metallic materials, such as ceramics, glass, stone, plastics, rubber, and wood.

During the use of the abrasive tool, when the abrasive particles are blunt, the abrasive grains are partially or completely detached from the abrasive tool due to partial fragmentation of the abrasive particles or the bond breakage, and the abrasives on the working surface of the abrasive tool are constantly emerging.

The cutting edge or revealing new sharp abrasive particles, which allows the grinding tool to maintain cutting performance for a certain period of time. This self-sharpness of the abrasive tool is a prominent feature of the abrasive tool compared with the general tool.

As early as the Neolithic Age, humans began to use natural grinding stones to process tools,such as stone knives, stone axes, bones, horns and teeth. In 1872, in the United States, natural abrasives and clay were combined to be Ceramic grinding wheel.Around 1900, artificial abrasives were introduced, and various abrasive tools made of artificial abrasives were successively produced, which created conditions for the rapid development of grinding. Since then, the proportion of natural abrasives in abrasive tools has gradually decreased.

According to their raw materials, abrasives are classified  as natural abrasives and artificial abrasives. Natural abrasives commonly used in the machinery industry are just oilstone. Artificial abrasives are distinguished from their basic shapes and structural features. There are five types of grinding wheels, including grinding heads, oilstones, sand tiles (collectively referred to as consolidated abrasives) and coated abrasives. In addition, it is customary to classify abrasives as a type of abrasive.

Consolidated abrasives can be divided into ordinary abrasive bonded abrasives and superhard abrasive bonded abrasives from the abrasive used. The former uses ordinary abrasives, such as corundum and silicon carbide, and the latter is made of superabrasives, such as diamond and cubic boron nitride. In addition, there are some special varieties, such as sintered corundum abrasives.

Ordinary abrasive bonded abrasives are abrasive tools in which a fixed abrasive is consolidated into a certain shape by a bonding agent and has a certain strength. In general,it composed of abrasives, binders and pores, these three parts are often referred to as the three elements of bonded abrasives.

The abrasive plays a cutting role in the abrasive tool. Bonding agents are materials that consolidate loose abrasives into inorganic and organic abrasive tools. Inorganic binders include ceramics, rhombohedral,sodium silicate, organic resins, rubber and shellac. The most commonly used are ceramic, resin and rubber binders.

The air hole acts as a chip to chip on the wear debris during grinding,and can accommodate the coolant to help dissipate the heat.

In order to meet some special processing requirements, some fillers such as sulfur and paraffin may be impregnated in the pores to improve the performance of the abrasive tool. This filler was also known as the fourth element of the abrasive tool.

The characteristics of conventional abrasive bonded abrasives including shape, size abrasive, particle size, hardness, texture, back pile, backing, and bonding agent. Abrasive hardness refers to the difficulty of the abrasive particles falling off the surface of the abrasive under the action of external force. It reflects the strength of the abrasive particles held by the binder.

The hardness of the abrasive tool has a corresponding relationship with its dynamic elastic modulus, which is advantageous for determining the dynamic modulus of the abrasive tool by the audio method to indicate the hardness of the abrasive tool. In the grinding process, if the material of the workpiece to be ground is high in hardness,  it was used a high hardness grinding tool generally; and vice versa.

Abrasives are roughly classified into three types: compact, medium, and loose. Each class can be subdivided and is distinguished by the organization number.

If the abrasive tissue number is larger,the volume fraction of the abrasive in the abrasive tool  is smaller ,and the gap between the abrasive grains is wider, indicating that the tissue is looser. Conversely, a smaller organization number indicates a tighter organization. The abrasive material of the looser structure is not easy to passivate when it was used, and the heat is less during the grinding process, which can reduce the heat deformation and burn of the workpiece. The abrasive particles of the tighter structure are not easy t