How to avoid silicon carbide oxidation when silicon carbide grinding wheel is sintered

Cracks in the surface layer of the shell mold often appear in the production of silica sol precision casting shell, and the cracks are mainly caused by the wax expansion in the dewaxing process or the insufficient wet strength of the shell mold, so how to improve the strength of the shell mold to prevent cracks? The following technical parameters are strictly controlled, and the cracks will be reduced or disappeared.

1. Drying too fast will cause micro-cracks, and the wetting is very fine, but the cracks will expand after dewaxing.

2. The temperature and humidity control of shell making is uneven.

3. The reason for the design of the product structure, according to the design of the product, it is necessary to find a way to avoid or adjust the shell, such as deep holes.

4. Long-term placement of the paint leads to expiration and deterioration, the slurry is too thin, the coating is not good, the thixotropy is poor, etc., and the product of German Jim can be appropriately added to the German Jim precision casting coating guard germ37.

5. The powder-liquid ratio of the coating needs to be adjusted, for example, the powder-liquid ratio is too small, the sand is too small, the strength of the shell mold is not enough, and the expansion stress of the wax mold cannot be withstood when dewaxing, and the powder-liquid ratio adjuster T3 can be added.

6. After dewaxing, the degassing speed is too fast, and the shrinkage is violent, resulting in cracks in the shell mold.

7. The dewaxing furnace heats up slowly, the dewaxing time is too long, and the wax mold cracks.

8. There is too much dust in the material, and the strength of the shell mold decreases.

1.Drying too quickly can lead to microcracks, which are very fine to wet, but the cracks will propagate after dewaxing;

2.The temperature and humidity control of shell making is uneven;

3.The reason for the design of the product structure is to find a way to avoid or adjust the shell according to the design of the product, such as deep holes, etc.;

4.Long-term storage of the paint leads to expiration and deterioration, the slurry is too thin, the coating is not good, the thixotropy is poor, etc.;

5.The powder-liquid ratio of the coating needs to be adjusted, for example, the powder-liquid ratio is too small, the sand is too small, the strength of the shell mold is not enough, and the wax mold expansion stress cannot be withstood during waxing, and the powder-liquid ratio adjuster T3 can be added;

6.After dewaxing, the degassing speed is too fast, and the shrinkage is violent, resulting in shell mold cracks;

7.The dewaxing furnace heats up slowly, the waxing time is too long, and the wax mold cracks;

8.There is too much dust in the material, and the strength of the shell mold decreases.

The cost determines that it is difficult to replace reaction sintering by pressureless sintering, but the products produced by pressureless sintering have a smoother surface, higher density, and higher strength than reaction sintering.

The chemical composition is the same, it is the amount of carbon and silicon elements of the substance, the chemical formula is SiC, and pressureless sintered silicon carbide is a type of silicon carbide. The reason why the physical properties are different is because of the different crystal structures.

Reactive sintered silicon carbide has the basic properties and main characteristics of high strength, high hardness, high wear resistance, high temperature resistance, corrosion resistance, strong oxidation resistance, good thermal shock resistance, good thermal conductivity, quenching and creep resistance. It can be made into beams, rollers, quenching air ducts, thermocouple protection pipes, temperature measuring pipes, flamethrowers, wear-resistant parts, corrosion-resistant parts, seals and special-shaped structural parts.

Not very likely, because of the cost! The issue of selling price.

There are generally three reasons for cracks: 1. Too much binder, 2. Uneven powder particles, too low pressing pressure, 3.

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Silicon carbide is an abrasive. The grinding wheel is made of abrasives and binder resins, etc., and is a round consolidated abrasive with through-holes. The grinding wheel is the one with the largest amount and the most widely used abrasive tool, which rotates at high speed when used, and can be used for coarse grinding, semi-fine grinding and fine grinding of the outer circle, inner circle, plane and various profiles of metal or non-metal workpieces, as well as grooving and cutting.

There are many types of grinding wheels. Abrasives are the main raw materials for the manufacture of grinding wheels, and it is responsible for the cutting work.

The grinding wheel consists of three parts: abrasive, binder (binder), and pores

Where:

1. Abrasives:It is the main grinding part of the grinding wheel, with sharp edges and corners, that is, a very small cutting edge, to cut the workpiece, the abrasive is often a very hard material, usually a chemical compound, such as emery (chemical composition is silicon carbide), corundum (chemical composition is aluminum oxide), diamond, etc., the most common is emery grinding wheel and corundum grinding wheel.

2. Binder:According to the use of different grinding wheels, there are ceramic, resin, rubber, metal, etc., and its main function is to bond the abrasives together to form a grinding wheel with a certain shape.

3. Porosity:Porosity is also the main component of the grinding wheel, the purpose of the porosity is to reduce the binding strength of the binder, store the grinding steel scraps, when the sharp part of the small abrasive is bald, it will be peeled off due to the reduction of the binding strength caused by the porosity, revealing new sharp abrasive grains, which is conducive to further grinding processing.

In addition to being used as an abrasives, silicon carbide in light industry has a variety of non-grinding applications. The following is a description of the main uses of silicon carbide.

One. Abrasives

In the long run, foreign light industrial silicon carbide is only used as an abrasive. The process of green silicon carbide storage is a high position and a certain toughness, mostly used for grinding optical glass, cemented carbide, titanium alloy and bearing steel grinding and polishing, high-speed steel tool grinding, etc.;Black silicon carbide is mostly used for cutting and grinding materials with low tensile strength, such as non-ferrous non-metallic materials, gray cast iron workpieces, glass, ceramics, stone and refractory products. -Micronized abrasives are designed for the superfinishing of bearings (materials) and are characterized by high grinding frequency and fineness.

Two. Refractories

Silicon carbide is very resistant to thermal shock, so it is a high-quality refractory material. According to the consumption process of the product, there is no same, it can be divided into recrystallized silicon carbide, products, high-temperature hot-pressed products, and products with silicon nitride or clay as the binding agent. The main products and applications are:

High-temperature furnace components, supports. Such as: sagger, lining, etc.;It is being used as a heating furnace bottom, heat exchanger, thermocouple sleeve, etc. in the electric furnace;The iron-making blast furnace is used for tapping troughs, and the molten iron ladle is lined with iron.

or silicon carbide refractory bricks, etc.;The coking plant uses silicon carbide material to line the launder for red-hot coke, masonry the bottom of the carbonization chamber, etc.

Three. Metallurgical appliance industry

In addition to being used for furnace lining of various smelting furnaces, it is also used as a deoxidizer for steelmaking, a structural improver for cast iron, etc. The chemical elements of the separating agent black silicon carbide are required to be as follows: compared with the traditional steelmaking process of aborting and deoxidation with coke and silicon powder, the use of separating agent is the best of the steel and the advantages of a good resting environment.

The detailed quality indicators are shown in the table.

Table Quality indicators of oxygen absorbers.

Item — Standard Oxygen absorber is used.

Phosphorus content () Sulfur content ().

Four. Other areas

In the electrical industry, silicon carbide materials are also widely used as electric heating elements, high-temperature semi-superconductor materials, far-infrared panels, lightning arrester valve materials, etc.

In the chemical industry, we are using the chemical stability of silicon carbide to create various chemical management, valves, etc.

The firing process is different. Reactive sintering is the process of allowing free silicon to penetrate into silicon carbide at lower temperatures. The pressureless sintering is a silicon carbide product that naturally shrinks at 2100 degrees.

The technical parameters of sintered products are different. The bulk density, hardness, compressive strength, etc. of the reaction are different from the technical parameters of non-pressure silicon carbide products.

Product performance is different. Reactive sintered products and non-pressed products are used for different times under different pH, temperature, etc.

The product produced by non-pressure sintering has a smoother surface, higher density, and higher strength than that of reaction sintering.

Pure silicon carbide is a colorless and transparent crystal. Industrial silicon carbide is light yellow, green, blue and even black due to the different types and contents of impurities it contains, and the transparency varies with its purity. After the black silicon carbide is crushed, it will become green after re-smelting in the form of secondary products, and there is no other way except this method, but the process formula at the time of re-smelting should be strictly in accordance with the production process formula and operation of green silicon carbide, otherwise there will be black and green mixed silicon carbide.

If the same blank appears black and green at the same time, it means that the impurities are not well controlled, and there is component segregation during the sintering process.

There are four main types of diamond binders: the resin method is the most common, the economic benefit is the best, the cutting force is medium and high, and the service life is medium and high. The electroforming method adheres to the iron matrix with only one layer of abrasive, so it is suitable for processing special shapes.

The bronze method is suitable for fine grinding or shaping. The sintering method has the most cutting force and life, but it is too expensive. Please provide your needs and then decide on the binding and shape of the grinding wheel.

Xiongfeng Abrasives-027 85749161, Hanjiang Superhard Abrasives-027 84693567, Zhongyouren-027 82312227, Zhongnan Diamond Tools-027 86328061

Silicon carbide hardness is very high, higher than corundum, the general grinding wheel can not process silicon carbide at all, only synthetic diamond grinding wheel can process silicon carbide ceramics.

The purity of the raw materials used in the green silicon carbide grinding wheel material is high, and it also forms green at a high temperature of about 2200 °C in the resistance furnace, which is translucent and hexagonal crystalline, and its SiC content is higher than that of black, and its physical properties are similar to those of black silicon carbide, but the performance is slightly brittle compared with black, and it also has good thermal conductivity and semiconductor characteristics. Green silicon carbide grinding wheels are used for processing cemented carbide, glass, ceramics and non-metallic materials, as well as semiconductor materials, high-temperature silicon carbon rod heating elements, far-infrared source substrates, etc.

Green silicate carbide stone is relatively soft, used to polish the mold sand particles are easy to fall off, the loss is relatively fast, and it is not suitable for polishing the shape of the surface that requires a flat shape. However, green silicon carbide itself has a relatively high hardness and is suitable for oily cemented carbide tools.