Causes of cracks in abrasives
Abrasives are tools used for grinding, lapping and polishing. Most of the abrasives are artificial abrasives made of abrasives and binders, and there are also natural abrasives that are directly processed from natural ore rocks. In addition to being widely used in machinery manufacturing and other metal processing industries, abrasive tools are also used in the processing of non-metallic materials such as food processing and glass. In the production process, cracks are a relatively common waste factor. The following manufacturers will introduce the reasons for the cracks in abrasive tools:
The damage of general materials is caused by two points: one is that there are cracks inside the abrasive material; the other is that such cracks can expand in the material until they crack. All defects in the material, including micro-cracks, small pores and places where impurities are concentrated, and places where the arrangement is loose, can become the source and cause of cracks, which are called crack sources. Any crack is generated from the crack source under the action of external force. The source of the crack is often so small that it cannot be detected by the naked eye, but under the microscope, it can be seen that there are many tiny cracks - tiny cracks, as well as pores and impurities, which are the origin of the cracks.
There are two factors that cause abrasive tool cracks: mechanical shock and thermal shock. Mechanical shocks include: flipping, bumping and beating during molding, impact during handling, excessive pressure during processing, and excessive knife feeding; thermal shocks include: excessive heating during firing, excessive cooling rate during firing, and excessive drying rate Wait too fast.
The source of the crack is brought in by the abrasive tool during the production process. No material can be completely free of defects, but this does not mean that cracks will inevitably occur if the product has defects; It cannot deform plastically like metal. It is easy to concentrate stress on a certain part, so that this part of the defect - the source of the crack is quickly transformed into a crack. Once the internal crack is formed and reaches a certain critical size, it is very easy to expand. The internal stress immediately gathers on the crack and expands to both ends. The abrasive tool cannot absorb external force through its own shape change like metal. The energy brought in can only be absorbed by the natural way of generating new appearances. The expansion of cracks means the formation of two new appearances. In this way, the crack rapidly expands and the new surface rapidly increases until the structure of the crack or crack, so that all the applied energy is converted into the energy produced by the new surface, which is the process of crack formation.
The natural formation and expansion of cracks occur in a very short period of time, or even for a while, which can really be said to be splitting. The property of an abrasive tool that cannot withstand strong vibration and impact is called brittleness. The measure of brittleness can be expressed by the energy required to form a new surface of a unit, which is called cracking work. The greater the cracking work, the greater its toughness.
From this, we can understand that the abrasive tool is brittle and cannot withstand impact, so whether it is a semi-finished product or a finished product, it should be handled with care during the use of the abrasive tool and the processing of the product, and be careful to cause the abrasive tool to crack. Factors to avoid improper operation to expand the cracks of the abrasive tool and damage.
In the process of machining workpieces with grinding wheels, it is generally necessary to use a grinding wheel dresser to dress the grinding wheel accurately. Sometimes the shape of the workpiece to be processed is special, and the shape of the grinding wheel should also be dressed with a dresser. Different types of grinding wheels require different dressers. Generally, the corundum grinding wheel and silicon carbide grinding wheel of vitrified bond can be dressed with a diamond pen. If the hardness of the grinding wheel is relatively low and the processing requirements are not high, a hardened silicon carbide grinding wheel can also be used for dressing. If you need to dress superhard grinding wheels such as diamond grinding wheels, diamond grinding wheels, CBN grinding wheels, cubic boron nitride grinding wheels, etc., most of them can be dressed with ceramic grinding wheel blocks.
Types of Grinding Wheels Grinding wheels generally combine abrasive grains with a special process, and then perform grinding, cutting, grinding, polishing, etc. on the workpiece, so the grinding wheels can be roughly classified from the perspective of bonding agents. Electroplated diamond grinding head is a general term for small shank grinding tools, which are used in electric grinders, hanging grinders, and hand drills. There are many types, mainly ceramic grinding heads, rubber grinding heads, diamond grinding heads, abrasive cloth grinding heads, etc. Through the understanding of the grinding wheel bond, it is easier to master the use of the grinding wheel, master the performance of the grinding wheel, and maximize the role of the grinding wheel. Commonly used binders can be divided into two categories: organic binders and inorganic binders, organic binders include resin binders and rubber binders, inorganic binders include ceramic binders, diamond binders and metal binders.
1. The diameter of the grinding wheel chuck shall not be less than one third of the diameter of the grinding wheel to be installed. The diameter of the grinding wheel chuck for cutting off the grinding wheel shall not be less than a quarter of the diameter of the grinding wheel to be installed.
Grinding wheel classification There are many kinds of grinding wheels. According to the abrasive used, it can be divided into ordinary abrasive (corundum and silicon carbide, etc.) grinding wheel and natural abrasive superhard abrasive and (diamond and cubic boron nitride, etc.) grinding wheel; according to shape, it can be divided into flat grinding wheel, bevel grinding wheel, cylindrical grinding wheel, Cup-shaped grinding wheel, disc-shaped grinding wheel, etc.; according to the binder, it can be divided into ceramic grinding wheel, resin grinding wheel, rubber grinding wheel, metal grinding wheel, etc. The characteristic parameters of grinding wheel mainly include abrasive, particle size, hardness, binder, shape, size, etc. Since the grinding wheel usually works at high speed, a rotation test (to ensure that the grinding wheel will not break under the working speed) and a static balance test (to prevent the machine tool from vibrating during operation) should be carried out before use. Grinding wheels should be reconditioned to restore grinding performance and correct geometry after a period of operation.