Manufacturing process of industrial ceramics:

The production process of industrial ceramics mainly includes blank preparation before green body forming, green body forming, sintering, sintering and subsequent processing of green body.

1. Preparation before blank forming

The first is to use physical, chemical and other methods to process the powder to obtain the powder of the required specifications; then according to the composition of the porcelain material, various raw materials are weighed and batched, and after batching, they are mixed and prepared into different forms according to different forming methods. of blanks.

2. Blank forming

Forming is to make a blank into a blank with a certain shape and specification. The methods that can be used are: wet molding, grouting, compression molding, injection molding, hot die casting, isostatic pressing, plastic molding, belt molding, etc.

3. Sintering

Sintering is a process in which the formed green body is heated at a high temperature below the melting point to make the powder inside it bond, and through material migration, it leads to densification and high strength.

4. Follow-up processing

After the industrial ceramics are formed and sintered, subsequent precision machining can be performed as needed to meet the accuracy requirements of surface roughness, shape, size, etc., such as grinding, grinding and polishing, ultrasonic processing, laser processing, and even cutting.

1. Extrusion forming

The extrusion (squeezingaction) method is mainly used to manufacture various tubular products with a wall thickness of about 0.2mm (such as high-temperature furnace tubes, thermowells, capacitor ceramic tubes, etc.) and ceramic rods or shafts with regular cross-section shapes (such as round shape, square, oval, hexagonal, etc.). With the improvement of powder quality and mud plasticity, it can also be used to extrude 100-200mm long and 0.2-0.3mm thick sheet-like preforms, which are semi-dried and then punched into sheet-like products of different shapes, or used for Extruded honeycomb or sieve perforated ceramic products with 100 to 200 holes per square centimeter.

>1—piston 2—extrusion barrel 3—porcelain 4—ring 5—core 6—extrusion nozzle

Extrusion forming process. Put the vacuum refining mud into the extruder, one end of the machine can apply pressure to the mud through the piston, and the other end is equipped with a nozzle (that is, a forming die). By replacing the nozzle, various shapes of bodies can be extruded, and the nozzle can also be directly installed on the vacuum mud refining extruder to become a vacuum mud refining extruder, and its product performance is better. The extruded body can be cut into finished products of desired length after drying.

2. Knife press forming and rolling forming

Cutterblank forming is also called spinning forming, as shown in Figure 4-12, it is a method of forming using a knife and a plaster model. When forming, take a certain amount of plastic mud, put it into the rotating plaster mold, and then gradually press the knife into the mud. Due to the relative movement between the moulding knife and the rotating model, with the rotation of the model and the extrusion and scraping of the moulding knife, the blank mud is spread out along the working surface of the plaster model to form a blank. The shape of the working arc of the blade and the shape of the working surface of the model constitute the thickness of the blank. This method can be divided into negative mold method and positive mold method. When the female mold method is formed, the plaster mold is concave, the inner wall of the mold determines the shape of the green body, and the knife determines the internal shape of the green body; when the male mold method is formed, the plaster mold is convex, the shape of the inner surface of the green body is determined by the model, and the outer surface is determined by the knife Spinning decision.

Spinning forming is evolved from knife pressing. The difference between it and knife pressing is that the flat knife is changed to a rotary rolling head. When forming, the rolling head and the model containing the mud material rotate around their own axes at a certain speed and in the same direction. Rolling head - surface rotation - the surface is gradually pressed into the mud, and the mud is formed into products by the action of "rolling" and "pressing". Similar to the knife pressing method, the rolling method can be divided into two types: male die rolling forming and female die rolling forming.

3. Forming by car blank method

The turning method is to use the extruded cylindrical mud mass as a blank, which is processed and formed on a horizontal or vertical lathe. The structure of the lathe is similar to that of an ordinary lathe for metal cutting. According to the amount of water content in the mud mass, it can be divided into dry car forming and wet car forming. . Products that require high dimensional accuracy are mostly formed by dry turning, but when dry turning is formed, there is a lot of dust, low productivity and large tool loss. The advantages and disadvantages of wet turning are just the opposite of those of dry turning.

The blanking method is suitable for processing circular products with complex shapes, especially large circular products.

4. Forming by rolling die method

The rolldown method is to mix the prepared billet with a certain amount of organic binder (usually polyvinyl alcohol), and mix it evenly and place it between the two rolls of the roll die machine for processing. By adjusting the distance between the rolls, after many times of rolling, the required thickness is finally achieved. The rolled billets need to be punched into the desired billets.

During the rolling process, the billet is only rolled in the thickness and advancing direction, and the force in the width direction is small, so the billet and the binder will inevitably be aligned. During drying and sintering, the transverse shrinkage is large, deformation and cracking are easy to occur, and the properties of the green body are also anisotropic. The rolling die method is suitable for the production of flake products with a thickness of less than 1 mm, but for ultra-thin sheets with a thickness of less than 0.08 mm, it is difficult to roll by this method and the quality is not easy to control.

5. Forming by grouting

The grouting method is carried out in a plaster mold. The gypsum mold is porous and has strong water absorption, which can quickly absorb the moisture of the ceramic slurry to achieve the purpose of forming.

The grouting forming process can be regarded as two stages of suction forming and consolidation and demoulding. Due to the water absorption effect of the gypsum mold, a thin mud layer is first formed on the working surface close to the model in the stage of absorbing slurry into a green body, and then the mud layer gradually thickens to the required thickness of the green body. The driving force for forming is the capillary force of the model. At this time, the mold cannot be demolded immediately, and it needs to continue to be placed, that is, it enters the consolidation stage. The model continues to absorb water and the surface of the green body evaporates with drying shrinkage. When the moisture is reduced to a certain value, the rate of water reduction in the green body will decrease sharply. At this time, because the green body shrinks and has a certain strength, it is easier to demould. There are three basic methods of grouting forming: hollow grouting, solid grouting and hot pressing grouting. In order to strengthen the grouting process, pressure grouting, centrifugal grouting and vacuum grouting are also used in production.

The production process of industrial ceramics

Industrial ceramic parts are used in many industrial fields. Therefore, compared with other materials, industrial ceramic parts have many excellent properties and will be widely used in the industry. So, what is the production process of industrial ceramics?

Industrial ceramic forming methods include: dry pressing, grouting, extrusion, cold isostatic pressing, injection, casting, hot pressing and static pressing.

The process of manufacturing industrial ceramics is generally divided into three steps. Every link must be done well to ensure quality.

Industrial ceramics are prepared with ceramic powder.

For the production of general-purpose ceramic parts, spray-dried granulation powder is ready on the market. If you need to control the material formula yourself, you need to buy a ball mill, ball mill and spray dryer.

Once you have the raw material, you can start pressing. For sheets below 2mm, colloid molding can be considered; for ceramics larger than 2mm, molding can be considered.

Now, industrial ceramic parts are mainly used for temperature measuring instruments, protection tubes and insulating tubes of thermocouple thermometers. At the same time, in industrial resistance furnaces and experiments, it can also be used in electric furnaces, heat treatment furnaces, etc.

In addition, tempered carbon and sulfur tubes, as well as other insulating instrument components that are resistant to high temperature, acid and alkali corrosion, are all based on ceramics.

Due to the advantages of strong mechanical strength, thermal shock resistance, good thermal conductivity, insulation and high softening temperature, industrial ceramic porcelain parts are widely used in many industries.

The production process of industrial ceramics

Summary of the production process of industrial ceramics: There are many kinds of molding methods for industrial ceramics. In production, the molding method should be selected according to the shape of the industrial ceramic product, and different molding methods require different binders.

1. Selection of industrial ceramic molding methods and binders

There are many kinds of industrial ceramic molding methods. In production, the molding method should be selected according to the shape of the industrial ceramic product, and different molding methods require different binders. Common industrial ceramic molding methods, binder types and dosages are as follows:

Industrial ceramic molding method Example of binder <Amount of binder (mass %)

Industrial ceramic dry pressing method Polyvinyl butyral, etc. 1~5

Industrial ceramic casting method acrylic-based resin 1~3

Industrial ceramic extrusion method Methyl cellulose, etc. 5~15

Industrial ceramic injection method Polypropylene, etc. 10~25

Industrial ceramic isostatic pressing method Ammonium polycarboxylate, etc. 0~3

Industrial ceramic adhesives can be divided into lubricants, plasticizers, dispersants, surfactants (with dispersant and lubricating functions), etc. In order to meet the needs of molding, a combination of various organic materials is usually used. When choosing an adhesive, consider the following factors:

l) It is a necessary condition that the industrial ceramic adhesive can be wetted by the powder. Good wetting occurs when the critical surface tension or surface free energy of the powder is greater than the surface tension of the binder.

2), a good industrial ceramic adhesive is easy to be fully wetted by the powder, and has a large cohesion. When the binder is wetted by the powder, the attraction between the molecules occurs, and red bonding (one-time bonding) occurs between the binder and the powder. At the same time, in the binder molecule, due to the effects of orientation, induction and dispersion And produce cohesion (secondary bonding). Although water can also fully wet the poplar material, but water is volatile, the molecular weight is small, and the cohesion is small, so it is not a good adhesive.

According to the order of cohesion of various organic materials, industrial ceramics can be arranged as follows:

<CONH1>-CONH2>-COOH>-OH>-NO2>-COOC2H5>COOCH5>-CHO>=CO>-CH3>=CH2>-CH2

3) The molecular weight of the industrial ceramic adhesive should be moderate. For adequate wetting, it is desirable to have a small molecular weight but weak cohesion. As the molecular weight increases, the binding capacity increases. However, when the molecular weight is too large, the cohesion is too large to be easily wetted, and the green body is easily deformed. In order to help the movement of the chain segments within the molecule, a plasticizer should be appropriately added at this time to make the adhesive softer and easier to shape while it is easy to wet.

4) In order to ensure the quality of industrial ceramic products, it is also necessary to prevent impurities from being mixed with adhesives, raw materials and preparation processes, resulting in harmful defects in the products.

In the preparation of industrial ceramic raw materials, mechanical methods such as crushing and mixing are used with binders and dispersants to achieve dispersion and do not contain agglomerated particles as much as possible. The binder is affected by the type and molecular weight, the properties of the particle surface and the solubility of the solvent, etc., and is adsorbed on the surface of the raw material particles, and plays a role in preventing the powder raw material from agglomerating through the steric stabilization effect. In the molding process, the binder imparts plasticity to the raw material, has a water-retaining function, and improves the strength and construction workability of the molded body. In general, the binder should be decomposed and volatilized by heating in the degreasing process because it hinders the sintering of ceramics. Therefore, it is necessary to select organic materials that can be easily scattered and removed and that do not contain harmful inorganic salts and metal ions to ensure product quality.

2. Binder for injection molding and molding of industrial ceramics

Due to its high strength, high wear resistance, low density (lightweight), heat resistance, corrosion resistance and other excellent properties, silicon nitride is suitable for the manufacture of turbine feeder impellers, rocker burners, auxiliary combustion chambers, etc. Ceramic parts for automobiles. These parts require complex shapes, high-precision dimensions, and high reliability. Intrinsic defects (cracks, pores, foreign bodies, etc.) and surface defects are not allowed.

One of the molding technologies that meet these quality requirements is ceramic injection molding (high pressure). The process flow is as follows:

In the industrial ceramic molding process, defects such as grooves caused by the fluidity of the molding material and the temperature of the metal mold and holes caused by the molding conditions cannot be generated; in the degreasing process, it is not caused by organic materials and thermal decomposition. Speed-induced degreasing cracks. The selection of organic materials must also meet these quality requirements.

Generally speaking, the organic materials used in ceramic injection molding are composed of binders, additives, and plasticizers. The binders can be polypropylene (PP), random polypropylene (APP), polyethylene (PE), ethylene- Vinyl acetate copolymer (EVA), polystyrene (PS), acrylic resin, etc. Among them, PE has excellent formability; EVA has good compatibility with other resins, as well as good fluidity and formability; APP has the characteristics of good compatibility with other resins, rich in fluidity and degreasing; PS has good fluidity. Additives include wax paraffin, microcrystalline paraffin, modified paraffin, natural paraffin, stearic acid, compounding agents, etc. The fluidity of the molding material can be evaluated using a high-flow pour point tester and a melt indexer. When the content of the binder in the degreasing is high, the degreasing property tends to decrease, and the degreasing property is good when the paraffin wax of the auxiliary agent is large. If the organic material cannot be completely scattered in a specific temperature range, it will affect the sintering of the ceramic, so it is necessary to consider the thermal decomposition characteristics and select it.

The organic material used in the injection molding of industrial ceramics should be selected so as to optimize the fluidity of the molding material and the degreasing of the molded body.

3. Industrial ceramic extrusion molding and molding binder cordierite has excellent material properties such as heat resistance, corrosion resistance, porosity, low thermal expansion, etc., so it is widely used as a carrier for automobile exhaust gas purification catalysts. The cordierite honeycomb utilizes the orientation of the raw material particles to produce low thermal expansion of the honeycomb structure, and can be produced by extrusion molding.

According to the molecular composition of cordierite (2MgO·2Al2O3·5SiO2), talc, kaolin and alumina can be selected as raw materials. The molding clay enters the mouth cover from the supply hole in the mouth cover, and after subdividing, expands to the thin wall, and then combines, so as to obtain the quality of good extensibility and combination. In addition, as a honeycomb body after extrusion molding, in order to maintain the shape, the higher the yield value of the clay is better, that is to say, the choice of the binder should make the two properties of the fluidity and self-conservation of the clay to achieve the best change.

Industrial ceramic raw material powder, binders, additives (lubricants, surfactants, etc.) and water are mechanically kneaded, and then continuously extruded with a screw extruder or extruded with a hydraulic plunger extruder. . Generally speaking, the adhesive used in extrusion molding can show high viscous bonding properties as long as a low-concentration aqueous solution is used. Commonly used are methyl cellulose (MC), carboxymethyl cellulose (CMC), polyoxyethylene (PEO), polyvinyl alcohol (PVA), hydroxyethyl cellulose (HEC) and the like. MC dissolves well in water and gels quickly when heated. CMC is well soluble in water and has high dispersibility and stability. PVA is widely used in various moldings. Lubricants can reduce friction between powders, and surfactants can improve the wettability of raw powders and water.

Industrial ceramics lack plasticity, and the clay with expansion characteristics makes the extrusion not smooth enough, and surface defects increase. Therefore, there should be an evaluation index for the performance of the adhesive. There are methods for evaluating the plasticity of returning soil, such as applying stress such as twisting, compression, and tension, and obtaining the relationship between stress and deformation, the method of using a capillary rheometer, and the method of viscoelasticity. In this way, the self-conservation and fluidity of the clay can be evaluated. When evaluated by the viscoelastic method, it can be concluded that when the amount of the adhesive is increased to a certain extent, the self-resistance and fluidity will increase. That is, an increase in the amount of binder blended contributes to an increase in the plasticity of the raw material.

Organic materials are industrial ceramics

The main binder, the rational selection of these organic materials is the key to ensuring product quality. In production, it should be comprehensively selected according to the characteristics of the powder, the shape of the product, and the molding method.