Technical indicators of calcium carbonate and its application in plastics
Some of the main technical indicators of calcium carbonate are: mesh number, whiteness, calcium carbonate content.
Mesh number: Mesh number refers to the number of holes in a certain area of the screen. The larger the mesh number, the smaller the particle size, and the required production process will be more complicated. The larger the mesh, the stronger the activity of the filler particles, the easier it is to bond with the plastic matrix, the better the compatibility, but the worse the dispersibility. Common meshes are 400, 600, 800, 1000, 1200, 2000. Generally, fillers with large meshes need to be surface treated to improve their dispersibility.
Whiteness: Since pure calcium carbonate is white, the higher the purity of the calcium carbonate product, the whiter the product and the less variegated color. Ferrite, silicon, etc. will make the product appear yellow, dark and other variegated colors. Generally speaking, when the whiteness is higher than 90%, calcium carbonate can be used as a white dye for plastics, but many manufacturers are not satisfied with the 90% standard, and even launched products with a whiteness as high as 97%. Products with higher whiteness have higher grades, less impurities, and are not easy to damage processing equipment. When the plastic is colored, the color is purer and more stable.
Calcium carbonate content: refers to the calcium carbonate content of limestone raw materials, which can also be said to be purity.
Application of calcium carbonate in plastics
Calcium carbonate has a wide range of applications, and most plastics can be used. Adding calcium carbonate has a certain effect on improving certain properties of plastic products and expanding their application range. They can reduce resin shrinkage, improve rheological behavior, and control viscosity in plastic processing. It can also play the following roles:
- Improve the dimensional stability of plastic products
The addition of light calcium carbonate plays a skeletal role in plastic products, and has a great effect on the dimensional stability of plastic products.
- Improve the hardness and rigidity of plastic products
In plastics, especially soft polyvinyl chloride, the hardness gradually increases with the addition of calcium carbonate, and the elongation decreases with the increase in hardness. Light calcium carbonate with fine particles and high oil absorption has a large increase in hardness. Conversely, light calcium carbonate with a small particle coarse oil absorption value has a small increase in the hardness of the plastic. In soft PVC, the hardness growth rate of heavy calcium carbonate is the smallest, followed by light calcium carbonate (light calcium).
The plastic (resin) of light calcium carbonate generally does not have a reinforcing effect, and the particles of light calcium carbonate can often be infiltrated by the resin. Therefore, the normal effect of adding light calcium carbonate is to increase the rigidity of the resin, the elastic modulus and the hardness. Also increase. As the amount of addition increases, both tensile strength and extreme elongation decrease.
Different calcium carbonate, different addition amount, will have different hardness.
- Improve plastic processing performance
The addition of light calcium carbonate can change the rheological properties of plastics. Light calcium carbonate powder is often added in a relatively large amount, which will help it mix with other components and also help the processing and shaping of plastics. The addition of light calcium carbonate, especially after surface treatment of light calcium carbonate, can not only increase the hardness of the product, but also improve the surface gloss and surface smoothness of the product. The addition of light calcium carbonate can reduce the shrinkage, linear expansion coefficient, and creep properties of plastic products, creating conditions for processing and forming.
- Improve the heat resistance of plastic products
Adding light calcium carbonate to general plastic products can improve the heat resistance. For example, adding about 40% light calcium carbonate to polypropylene increases the heat resistance by about 200°C. When the filling ratio is less than or equal to 20%, the heat-resistant temperature increases by 8 to 130°C.
- Improve the astigmatism of plastics
In plastic products, some products require whitening and opacity, and some hope to extinction. The addition of light calcium carbonate can play a certain role in this regard.
Light calcium carbonate with whiteness above 90 has obvious whitening effect in plastic products. When combined with titanium dioxide and lithopone, the matting properties of plastic products have been greatly improved. In calcium plastic paper, low-density polyethylene and high-density polyethylene film, calcium carbonate can be added to achieve the effects of astigmatism and extinction, making it suitable for writing and printing. Calcium carbonate with better whiteness can also replace expensive white pigments.
- It can make the product have some special properties
The addition of light calcium carbonate to the cable material has a certain insulating effect, and the addition of light calcium carbonate can improve the electroplating performance and printing performance of some products. Fine or ultrafine light calcium carbonate is added to polyvinyl chloride (PVC), which has a certain flame retardant effect.
- Reduce the cost of plastic products
The price of ordinary light calcium carbonate and heavy calcium carbonate is far lower than the price of plastics. The addition of light calcium carbonate will reduce the cost of plastic products, so light calcium carbonate is called a filler or extender.
At this stage, adding calcium carbonate to reduce the cost of plastics is the main goal. With the improvement of the surface properties of calcium carbonate and the controllable shape and particle size, calcium carbonate will gradually become a functional filler for the purpose of strengthening or imparting functionality.
Filling the plastic with calcium carbonate is like adding a skeleton to the plastic, which improves the dimensional stability and hardness of the plastic, and can also improve the wear resistance and gloss of the plastic to a certain extent. As usual, it is used for PP, PE, PVC sheets and pipes.
Calcium carbonate is non-toxic, tasteless, and environmentally free. It is a common mineral in the natural environment. It is suitable to be added to biodegradable plastics and food packaging plastics without adversely affecting people and the environment. Studies have also shown that biodegradable plastics added with calcium carbonate degrade faster in the soil.
Light calcium carbonate has a characteristic. It is relatively oil-absorbing and easy to absorb plasticizers in plastics, resulting in poor plasticizing effect. To improve this situation, calcium carbonate can be modified.
Application of graphene after airflow classification in many fields
Graphene is a hot product nowadays. Graphene is a revolutionary material, and its application continues to expand with the deepening of related research. The good properties of graphene also determine that it has an extraordinary market value.
1. The characteristics of graphene
Graphene has good strength, flexibility, electrical conductivity, thermal conductivity and other properties. It is the material with the highest thermal conductivity so far and has very good thermal conductivity, so it is widely used in the new heating industry.
Like the conventional heating film, graphene needs to be energized to generate heat. When the electrodes at both ends of the graphene heating film are energized, the carbon molecules in the heating film generate phonons, ions and electrons in the resistance, and the generated carbon molecular groups interact with each other. Friction and collision (also known as Brownian motion) generate heat energy, and the heat energy is radiated uniformly in a planar manner by controlling the far infrared rays.
After the graphene is energized, the total conversion rate of effective electrothermal energy is more than 99%, and the special superconductivity is added to ensure the stability of the heating performance. However, it is different from the conventional metal wire heating film in that the heating is stable and safe, and the emitted infrared rays are called "light of life".
2. What aspects of graphene is used after being classified by the airflow classifier
- Flexible graphene transistor
The graphene transistor is a single-electron nanodevice. This kind of transistor has received great attention from the market since its research and development. At present, some flexible graphene transistors have been applied. The main advantage of graphene transistors is that they are easy to operate at room temperature, while having the characteristics of low voltage and high sensitivity. These characteristics make graphene transistors superior to silicon transistors, and at the same time promote the development of microchip technology. In addition, due to the inherent characteristics of graphene, this transistor has extremely high flexibility and foldability.
- Graphene sensor
A sensor is a device that senses changes in the surrounding environment (such as heat, motion, light, pressure, humidity, etc.) and provides feedback through output signals (usually light, mechanical or electrical signals). Because graphene has a large surface-to-volume ratio, unique optical properties, excellent electrical conductivity, high carrier mobility and density, and high thermal conductivity, graphene can be used as a sensor in different fields, including biosensors , Diagnostic technology, field effect transistors, DNA sensors and gas sensors.
- Graphene for lithium batteries
With the wide application of lithium batteries, the types of lithium batteries are constantly enriched. Lithium-ion batteries are considered to be one of the promising electrochemical energy storage systems, with strong application potential in the fields of civil, national defense, and aerospace. However, at this stage, lithium batteries still have certain limitations. Graphene can be integrated into the positive and negative electrodes of different battery frames to enhance battery performance and increase the charge-discharge cycle rate.
- Graphene transparent conductor
Transparent conductors are the core part of devices that require high surface resistance and high transparency, such as touch screens, light-emitting diodes, and solar cells. When used as an electrode, the device must meet the conditions of light input/output. Traditional transparent conductors are composed of highly doped semiconductor oxides, and composite materials composed of graphene, silicon, metal and carbon nanotubes can be used as transparent conductor films. Among them, the transparency of graphene-silicon film is as high as 94%, and the conductivity is 0.45S/cm. This type of composite material has excellent overall performance as a transparent conductor.
- Graphene structure composite material
Graphene and different materials form composite materials, which are used in various applications, such as aviation. Studies have shown that adding graphene to the material can greatly improve the performance of the material. For the aviation industry, a lightweight composite material can save fuel costs. Graphene-based composite materials have great potential and can be used as an important choice for the development of new materials.
- Graphene catalyst carrier
Graphene and its derivatives have rich surface properties, sheet-like morphology, high surface area and high electron mobility. Studies have proved that it is a very effective catalytic material. Graphene is a chemically inert substance. Adding functional groups can change the characteristics of graphene and is suitable as a catalytic carrier.
After being classified by the air classifier, accurate and efficient powder can be obtained, and the particle size is concentrated, so that the high-precision graphene powder can be widely used in many fields.
What is the impact of the large water content of the raw material on the pulverization process of the jet mill
Jet mills are favored by many industries. Jet mills can pulverize raw materials into powder, which can increase its added value to a large extent. The jet mill is not suitable for all materials. When the equipment crushes the materials, the nature of the feed is very strict. One of the feeding properties is the moisture content. The moisture content will change under the influence of weather. One is too large and the other is too small. These two conditions have different effects on production. The following analysis is carried out for these two situations:
- Low moisture content
The jet mill is relatively easy to crush materials with low water content. Due to the low moisture content, material blockage is not easy to occur during production, and the production process is relatively smooth. Therefore, the efficiency of the jet mill is relatively high in this case, and it is also the best state of the jet mill.
- Large moisture content
When the moisture content is large, the jet mill is prone to sticking and blocking during the crushing process, which makes the crushing process abnormal. The pulverized powder is easy to stick around the grinding roller, grinding ring and liner. At this time, it will reduce the performance of the parts and reduce the production efficiency, and this situation will also cause the phenomenon of increased wear. In addition, when the moisture content is large, if the air volume of the blower in the mill is small, the animal material cannot be blown to make it float; if the air volume of the blower is increased, the unground materials may float together, and these unqualified powders will stick. On the analysis machine, when the circulating air flows to the air duct, the material will block the air duct, the grinding cavity cannot get good ventilation and heat dissipation, and the internal temperature rises, which reduces the working efficiency of the motor, which is very unfavorable for the production of the mill.
From the above situation, it can be concluded that a small moisture content is beneficial to the production of the mill, while a large moisture content will cause a decrease in the efficiency of the jet mill and an increase in wear. Therefore, in actual production, it is necessary to add The water content of the materials in the mill must be strictly controlled.
The deep processing technology of kaolin
Kaolin is a clay mineral with kaolinite as the main component, commonly known as "china clay", including: kaolinite, perlite, dickite, and halloysite. The crystalline chemical formula of kaolinite is AI4[Si4O10](OH)8 , which is a layered silicate mineral of 1:1 type. It consists of a silicon-oxygen tetrahedral layer and an aluminum-oxygen octahedral layer. The layers are composed of hydrogen-oxygen bonds. connect.
According to its texture and plasticity, it can be divided into hard kaolin, soft kaolin, and sandy kaolin. According to its genesis, it can be divided into coal series kaolin and non-coal series kaolin.
The gangue minerals of kaolin include feldspar, quartz, titanium oxide minerals, iron minerals, and mica. The main chemical components are silicon dioxide, aluminum oxide, iron oxide, calcium oxide and magnesium oxide, organic mixtures, and loss on ignition. , Alkali metal oxides, fluid anhydride.
The firing color of kaolin is white or close to white, and the maximum whiteness is greater than 95%; the hardness of soft kaolin is 1~2, and the hardness of hard kaolin can reach 3~4; it has good molding, drying and sintering properties; easy to disperse in water , Suspended, into a stable suspension; has excellent electrical insulation properties, the resistivity is greater than 1010Ω·cm-1 at 200°C. It has good resistance to acid solubility, the cation exchange capacity (CMC) is generally 0.03-0.05mmol/g, and it has good fire resistance, with a refractoriness of 1750-1790°C.
Kaolin has good properties such as plasticity, dispersibility, fire resistance, cohesiveness and stability, and has been widely used in many fields such as agriculture, refractory materials, papermaking, ceramics, and rubber.
With the emergence and development of modification technology and nanotechnology, modified kaolin and nano kaolin have shown more excellent performance, which greatly expands and extends the application field of kaolin. About 45% of global kaolin is used in papermaking, about 16% is used in refractory materials, about 15% is used in ceramics, and glass fiber and cement preparation fields each account for about 6%.
The deep processing technology of kaolin
The kaolin product after beneficiation and purification reaches the best quality in the natural state, but still does not meet the requirements of some applications, so further processing of kaolin is required. The deep processing of kaolin includes: calcination, superfine grinding, surface modification .
- Superfine grinding
In the process of ultrafine pulverization of kaolin, the product layer fractures to produce flaky particles. Therefore, the ultrafine grinding of kaolin is also called peeling. The stripping machines used in industry are mainly high-pressure homogenizers, mixing mills, etc.
The high-pressure homogenizer uses the shearing force generated by the mutual friction generated when the slurry is sprayed under high pressure and the crushing effect generated by the sudden pressure drop after the spraying, which destroys the kaolinite crystal structure and causes the hydrogen bond between the crystal layers. Fracture, causing the kaolin layers to burst and peel off one by one.
When pulverizing kaolin ultrafinely with a stirring mill, ceramic balls, glass balls, iron stone, and corundum are used as the pulverizing medium in order to avoid secondary pollution and ensure the whiteness of the product. Since the filling rate of the crushing medium will affect the production capacity of the mill, there are many media and the peeling effect is good, but the processing capacity is low, so the optimal filling rate should be determined through experiments based on the equipment performance.
- Calcination processing
The calcination of kaolin can eliminate the structural water in kaolinite minerals, and at the same time can remove organic pollution sources and some volatile substances. It is currently one of the most effective methods for processing kaolin. It can not only improve the purity and whiteness of kaolin, but also change the properties of kaolin, so that kaolin has properties that it did not have before calcination, such as: low density, large specific surface area, good covering properties, and good wear resistance. The satin firing process and equipment of kaolin mainly include inverted flame kiln calcination, rotary kiln calcination, vortex air flow calcination, and tunnel kiln calcination.
When kaolin is used as ceramics, an inverted flame kiln is usually used for calcination. Before the kaolin enters the kiln, the moisture content of the kaolin is controlled at about 15%, so that the kaolin will not cement during the calcination process and save fuel.
At present, most of the rotary kilns used are horizontal rotary kilns. The rotary kiln uses low-heat coal as the fuel. The rotation of the rotary kiln makes the kaolin continuously tumble, and the direction of movement is opposite to the direction of the high-temperature airflow, so that the kaolin and the high-temperature flue gas are thoroughly combined. Heat exchange, continuous production is possible.
The vortex air calcination uses a conical vortex to process the selected kaolin powder. During the calcination process, a rotating upward hot air flow is formed by a vortexer, and extremely fine materials are dispersed into a cone inner reaction chamber for calcination through a sprayer. At this time, the amorphous calcined kaolin obtained can be further heated, which will cause new The crystalline and physical state of the material is higher than the calcined kaolin in the first stage, and it has better characteristics.
The products calcined in the tunnel kiln have become sintered refractory clinker. In this process, the kaolin is made into a specific shape and sent to the tunnel kiln for calcination. The sintered material is crushed, classified, and made into a standard particle size. Enter the ball mill to grind to -120 mesh and -200 mesh or send to sieve to separate out 80-120 mesh.
How to avoid the failure of the ultra-fine grinding machine?
Grinding equipment such as ultra-fine pulverizers will inevitably have various failures in use, and during the construction process, once the ultra-fine pulverizer is accidentally damaged during the grinding operation, the entire process will be caused. The process delays production. How can we avoid the failure of the superfine mill?
1. Reduce the wear of wear-resistant parts of the ultra-fine pulverizer, and the feed should not be too large during the running-in period of the ultra-fine pulverizer, so as not to affect the normal state of the parts. The solution is to carry out reasonable feeding in strict accordance with the use standards.
2. After the installation of the ultra-fine mill, there will be an empty machine for commissioning, and you can check whether the various parts are installed in place. If there is a deviation of geometric shape and matching size between the parts, it will be affected by alternating loads such as impact and vibration, as well as heat, deformation and other factors during use, which will affect the production efficiency of the ultrafine mill. Therefore, check the bolts of the ultra-fine mill at a fixed time to avoid loosening.
3. The operator of the industrial pulverizing production line must have a clear understanding of the operation and principle of the equipment, and have an understanding of the performance, structure and parts of the ultrafine mill, and troubleshoot in time to reduce downtime. In addition, the lubrication of the ultra-fine pulverizer also has certain operational requirements. To match the operation of the assembly gap, the lubricant should form a uniform oil film on the friction surface to prevent wear.
Three points should be kept in mind during the use of the superfine mill: reduce wear, avoid looseness, and operate skillfully. Paying attention to these three points will avoid many unnecessary failures.
How to reduce the energy consumption of jet mill
The advantage of the jet mill is that the material after grinding does not produce pollution. After grinding, the compressed high-speed airflow speed decreases and the volume increases. It belongs to the heat absorption process and has a cooling effect on the material. It is especially suitable for ultrafine grinding. Jet mill is to use high-speed airflow to accelerate the particle production speed, collide with each other or collide with the target to crush the material to achieve the grinding effect.
Generally speaking, there are three main ways to accelerate the grinding of solid particles by high-speed airflow:
(1) Airflow particle acceleration nozzle: After the airflow and the particles are fully mixed, the particles can obtain a high speed (almost the same as the airflow speed), but the material wears seriously on the inner wall of the nozzle and is rarely used in practical applications.
(2) The injector accelerates the particles: the high-speed (supersonic) airflow and the particles are mixed and accelerated in the mixing tube, and the particles get a higher speed, but the material wears the mixing tube seriously.
(3) Free airflow accelerates particles: The particles enter the high-speed air stream in the form of free fall. At this time, only the high-speed airflow passes through the nozzle, and the wear is small. However, since the falling speed (lateral) of the particles is very low, it is difficult to enter the center of the air stream (high-speed airflow) to obtain a high-speed airflow.
From this perspective, the efficiency of jet mill mainly depends on the relative collision speed and collision angle of particles in the fluidized bed. Therefore, only by changing the geometry and structural design of the nozzle and grinding cavity can the efficiency of jet mill be improved. To reduce the energy consumption of jet mills and improve production efficiency, we can start with improving the nozzle structure, determining the nozzle spacing, improving the shape of the grinding cavity, and determining the material level of the grinding cavity.
Several uniformly distributed auxiliary nozzles are arranged around the main nozzle to accelerate the material particles around the main nozzle to enter the central area of the main stream to obtain a larger collision velocity. A feed nozzle is arranged in the center of the main nozzle, and the fluidized particles in the fluidized bed are directly sucked into the center of the main nozzle to obtain a high collision velocity.
What is the significance of jet mill in pharmaceutical ultrafine grinding
In the pharmaceutical industry, there are many raw materials with different particle sizes. When these raw materials are processed in the next step, the different particle sizes and uneven density of the powder result in poor fluidity and easy layering. Ultra-fine grinding is the operation process of making a large solid material into an appropriate degree of fine powder. Under the combined action of various forces, the solid material generates stress. Under this stress, the material undergoes elastic deformation. When the stress exceeds a certain limit, the material will undergo plastic deformation. The crushing within the range of elastic deformation is called elastic crushing, and the crushing after plastic deformation is called primary crushing. Generally, polar crystal drugs are easily crushed, and most of them are crushed elastically. On the contrary, non-polar crystal drugs are mostly grinding, which is difficult to grind.
Jet mill can greatly reduce the particle size of solid materials and increase the surface area, which is of great significance to pharmaceutical engineering:
(1) It is helpful to increase the contact surface of solid and liquid dispersion medium, accelerate the dissolution rate of the drug, and improve the utilization rate of the drug;
(2) After the raw and auxiliary materials are micronized, the large particles are broken into fine powder, which facilitates the uniform mixing of several different solid materials, improves the uniformity of the dispersion of the main drug in the particles, and improves the dispersion of the colorant or other auxiliary materials;
(3) The improvement of drug fluidity is helpful to improve the quality of preparations, and it is also convenient to be processed into various dosage forms, which is convenient for dispensing and taking. The grinding process is a physical process, and objects exhibit different hardness and performance due to different cohesion. During grinding, the cohesion between molecules must be partially destroyed by external forces to increase the surface area of the drug, that is, the process of converting mechanical energy into surface energy. The external force used in the grinding process should be determined according to the hardness and performance of the drug.
Jet mill is a mature ultrafine grinding equipment, which is different from other ultrafine grinding equipment. The grinding principle is to use high-speed airflow to bring the animal material particles to move, so that the materials collide, collide, and rub against each other. Under the shearing action of the airflow, the material is ground into fine particles. Jet mills are widely used in ultrafine grinding of powdered medicines. The grinding process is continuous, with large capacity and high degree of automation; and the processed products have narrow particle size distribution, high purity, and particles with good activity and dispersibility.
Application of Jet Mill in the Production of Titanium Dioxide
Titanium dioxide used as a pigment has excellent optical properties and stable chemical properties. Titanium dioxide has very high requirements on particle size, particle size distribution, and purity. Generally, the particle size of titanium dioxide is based on the wavelength range of visible light, which is between 0.15m and 0.35m. And as a white basic pigment, it is very sensitive to the increase of impurities, especially iron impurities, and the increase in crushing is required to be less than 5 ppm. In addition, titanium dioxide is required to have good dispersibility in different coating systems. Therefore, the general mechanical crushing equipment is difficult to meet the requirements, so the final grinding (finished product grinding) of titanium dioxide is currently selected by jet mills at home and abroad.
According to the grinding requirements of titanium dioxide: narrow particle size distribution, less increase in inclusions, good dispersibility, etc., and material characteristics of titanium dioxide: high viscosity, poor fluidity, fine particle size and easy to adhere to the wall, etc. At present, domestic and foreign titanium dioxide manufacturers choose to have self-distribution The flat-type (also known as horizontal disc type) jet mill with high-level function is used as the final grinding equipment for titanium dioxide; and superheated steam is used as the grinding working medium. Because steam is easily available and cheap, the pressure of the steam working medium is much higher than that of compressed air and is also easy to increase, so the flow energy of steam is greater than that of compressed air. At the same time, the cleanliness of the superheated steam is higher than that of the compressed air, the viscosity is low, and there is no static electricity, and while grinding, it can eliminate the static electricity generated by the collision and friction of the material, and reduce the secondary cohesion of the powdered material. In addition, grinding under high temperature conditions can improve the application dispersibility of titanium dioxide and increase the fluidity of titanium dioxide. The use of superheated steam has low energy consumption, which is only 30% to 65% of compressed air. In addition, using a flat jet mill, organic additives can be added to organically modify the surface of the titanium dioxide while pulverizing, so as to increase the dispersibility of the titanium dioxide in different application systems.
With the rapid development of the titanium dioxide industry, the requirements for equipment are getting higher and higher. Under the premise of meeting the process conditions and quality requirements, the large-scale and systematization of equipment is particularly important. Airflow grinding is also continuously improved with the development of titanium dioxide. The production capacity of the gas powder machine has also increased from 1.2t/h to 1.5 t/h at the beginning to the current 2.5 t/h to 3.5 t/h. The production capacity of the gas powder system has also increased from a single line of 10,000 t/a to the current single line 2 Ten thousand t/a, the collection method has also been changed from the relatively backward wet collection to the advanced dry collection, which greatly improves the one-time yield and reduces waste. With energy saving and emission reduction, the higher the requirements for cost reduction, the more reasonable the configuration of the gas-powder system, and the full utilization of the waste heat of the exhaust gas. In the past, the gas and powder collection method was mainly wet collection, that is, the materials from the gas and powder machine first enter the cyclone for vapor-solid separation, and the separated materials are discharged by the star unloader at the bottom of the cyclone for cooling and packaging. The separated material enters the spray tower with the air flow for spray cooling and collection. The material collected by the spray tower is in the form of slurry, which must be settled, filtered and dried before returning to the gas powder machine. The one-time yield of this process is very low, up to 90%, the energy consumption is large, the exhaust heat cannot be used, and it has been basically eliminated. The current gas and powder collection method is mainly dry collection, that is, the material from the gas and powder machine first enters the high-temperature bag filter for vapor-solid separation. The current surface-coated high-temperature resistant filter material has a separation rate of more than 99.5%. The discharged materials are discharged through the star discharger at the lower part of the high-temperature bag filter for cooling and packaging. The separated high-temperature tail gas is discharged from the clean air chamber at the upper part of the high-temperature bag filter and enters the tail gas waste heat recovery device for waste heat utilization.
Factors affecting jet milling equipment
(1) Jet mill: As the most important equipment for jet milling, the quality of the air powder machine directly determines the quality of the product. The gas powder machine is required to have reasonable design, excellent production, high impact kinetic energy, good classification effect, wear resistance and high temperature resistance. Therefore, it is very important to choose a gas powder machine.
(2) Steam quality: The grinding working fluid of jet milling is superheated steam. If the steam quality does not meet the crushing requirements, it will seriously affect the quality of gas and powder. Generally, the requirements of the gas powder engine for steam are: the pressure is 1.6 to 2.0 MPa, and the temperature is between 290°C and 310°C. If the temperature and pressure are lower than the requirements, it will cause low impact kinetic energy, decreased grinding force, insufficient heat in the system, and materials easily damp, which will affect the grinding effect, block the system and make it unable to operate normally; if the temperature and pressure are too high, it will The equipment in the system causes damage.
(3) Process control: Airflow grinding requires stable and continuous operation. The fluctuation of steam and the fluctuation of feed volume should be controlled within a certain range, and must be adjusted slowly during adjustment, and it is strictly forbidden to increase or decrease. In addition, once the gas-powder system is normal, it should maintain continuous operation and avoid frequent startup and shutdown. Furthermore, the operating procedures should be strictly followed when starting and stopping.
(4) System monitoring: In order to ensure the normal operation of the system, necessary monitoring equipment must be installed in a reasonable position of the system to make timely adjustments according to changes in the situation.
Characteristics and applications of advanced ceramic materials- silicon carbide fiber
Advanced ceramics have excellent properties such as high temperature resistance, high strength and rigidity, relatively light weight, and corrosion resistance, but they also have an inherent Achilles heel: brittleness. The use of high-strength, high-modulus continuous ceramic fiber and matrix composite is an effective method to improve the toughness and reliability of ceramics.
At present, jet mill equipment has been used in the preparation of many advanced ceramic materials. However, fiber-reinforced ceramic matrix composites mainly refer to composites made of carbon fiber, graphite fiber, silicon carbide fiber, silicon nitride fiber, zirconia fiber, etc. to enhance magnesium oxide, silicon oxide, silicon nitride, aluminum oxide, zirconia, etc. The material has the characteristics of high high temperature compressive strength, high elastic modulus, strong oxidation resistance, and good impact resistance.
Silicon carbide fiber is a kind of ceramic fiber with high tensile strength, creep resistance, high temperature resistance, oxidation resistance and good compatibility with ceramic matrix. It is used in high-tech fields such as aerospace, aviation, weapons, shipbuilding and nuclear industry. It has broad application prospects.
The ultra-fine powder sintering method is mainly based on silicon carbide powder as raw material, adding a certain amount of binder and sintering aids (B, Al2O3, etc.), through physical mixing, dry spinning or melt spinning to make fibers The raw silk is subjected to high-temperature heat treatment to obtain silicon carbide fibers. The silicon carbide fiber prepared by this method has better high temperature resistance and creep resistance, but the fiber diameter is larger and the strength is lower, which is not conducive to industrial application.
Silicon carbide fiber has the advantages of good creep resistance, oxidation resistance, chemical corrosion resistance and compatibility with ceramic matrix. It can be used as a high-temperature structural material of fiber-reinforced ceramic matrix composites and can be widely used in aerospace and other fields.
In addition, the metal matrix composite material reinforced by silicon carbide fiber has better performance in terms of specific strength, specific stiffness, thermal expansion coefficient, thermal conductivity and wear resistance. It is used in aerospace, military weapons and equipment, sports equipment, automobiles, etc. The civil industry has a wide range of application prospects.
Application of Dolomite Powder
Dolomite is a carbonate mineral, including iron dolomite and manganese dolomite. Its crystal structure is like calcite, often in the form of rhombohedrons; bubbles will slowly appear when exposed to cold dilute hydrochloric acid; some dolomites emit orange-red light under cathode ray irradiation. Dolomite is the main mineral component of dolomite and dolomitic limestone.
Dolomite can be used in building materials, ceramics, glass and refractory materials, chemical industry, agriculture, environmental protection, energy saving and other fields. It is mainly used as a flux for alkaline refractories and blast furnace ironmaking; production of calcium magnesium phosphate fertilizer and preparation of magnesium sulfate; and ingredients for the production of glass and ceramics. It is also used as a flux in the glaze. Some ancient kilns in the north, such as Ding Kiln, often add dolomite to the glaze, and dolomite is also added to some glazes in Jingdezhen, which requires a dolomite mill. support.
Dolomite powder is pure white, insoluble in water, with a relative density of 2.5, stable chemical properties, and a slippery feel. As a plastic filler, dolomite powder can improve the hardness, fire resistance, acid and alkali resistance, electrical insulation and dimensional stability of the product. It is widely used in plastics, rubber, cables, paints, coatings, ceramics, EVA, and other industries.
1. Used in rubber, it can increase the volume of the rubber, improve the processability of the rubber, play a role of semi-reinforcement or reinforcement, and can adjust the hardness of the rubber.
2. In plastics, it can increase the volume of the plastic, reduce the cost of the product, improve the dimensional stability of the plastic and the hardness and rigidity of the plastic, improve the heat resistance of the plastic, and improve the astigmatism of the plastic.
3. Used for exterior wall insulation mortar, putty powder, ball factory lawn self-leveling mortar, epoxy floor, exterior wall latex paint, real stone paint, FRP sand pipe, plastic, rubber, paint, coating, etc.
It can be seen that the application market of dolomite has broad prospects.
Dolomite powder processing is generally divided into dolomite coarse powder processing (0-3mm), fine powder processing (20 mesh-400 mesh), and dolomite ultrafine powder deep processing (400 mesh-1250 mesh) and micro powder processing (1250 mesh) -3250 mesh) four types, select the appropriate equipment according to different processing techniques.