Production Technology and Application of Silicon Micropowder

Silicon powder is made of natural quartz (SiO2) or fused quartz (amorphous SiO2 after high temperature melting and cooling of natural quartz), which is crushed, ball milled (or vibration, jet mill), flotation, pickling purification, high-purity water treatment, etc. The micro powder processed by this technology.

Silicon powder is gray or off-white powder, non-toxic, odorless, non-polluting, resistant to temperature, acid and alkali corrosion, poor thermal conductivity, high insulation, high hardness, low swelling, and stable chemical properties. According to the production process, it can be divided into crystalline silicon powder, fused silicon powder, cristobalite silicon powder, and active silicon powder. According to the level, it can be divided into ordinary silicon powder, electrical grade silicon powder, electronic grade silicon powder, fused silicon powder, ultrafine silicon powder, and "spherical" silicon powder. According to the purpose, it can be divided into silicon powder for paint and coating, silicon powder for epoxy floor, silicon powder for rubber, silicon powder for sealant, silicon powder for electronic and electrical plastic packaging materials, and silicon powder for precision ceramics.

Production process of silicon powder

• The beneficiation and purification of silicon powder raw materials

Mineral beneficiation and purification generally involves crushing, sieving and grinding siliceous raw materials with high impurity content to fully dissociate silica and impurities. In actual production, purification is carried out according to the required quality. Either through flotation, magnetic separation to remove impurities, or through water washing and grading to remove impurities, or pickling to remove impurities, and after drying, it is used as the raw material for silicon micropowder.

• Production process of silicon powder

1. Production process of angular silicon powder

Angular silicon micropowder is an irregularly angular silicon micropowder obtained by grinding the raw material of silicon micropowder. The main production equipment of angular silicon powder includes ball mill, powder classifier, vibration mill, and dryer.

2. Production process of spherical silicon powder

Spherical silicon powder is a kind of high-strength, high-hardness, and emotional spherical particles made of high-quality raw quartz ore and processed by a unique process. The production processes of spherical silicon micropowder abroad include high-temperature melting spray method, gas flame method, hydrolysis method of silicon tetroxide, etc., and control ethyl orthosilicate in the liquid phase. The main production equipment includes a powder quantitative conveying system, a gas volume control and mixing device, a gas fuel high temperature flame spray gun, and a cooling recovery device.

3. Recovery method of silicon micropowder recovery process

Pulse jet bag dust removal, anti-adhesive big bag dust removal, and electric dust removal.

Application of silicon powder

• Application fields of general silicon powder products

Ceramics, metallurgical flux, casting and metal surface treatment, electronic component packaging, rubber, high-grade paint, anti-corrosion coatings, welding rod coating, construction mortar and high-strength concrete aggregates, high-grade refractory materials, solar photovoltaic cells, military antenna reflectors, teeth Use materials, environmental protection and oil wells to pressurize.

• Application fields of fused silica powder products

Fused silicon powder has the characteristics of high purity, excellent electrical properties, high hardness, wear resistance, stable chemical properties, and good whiteness. It is often used in plastic packaging materials for ultra-large-scale integrated circuits, epoxy castables, potting materials, and other chemical fields.

• Application fields of spherical silica powder products

Low oil absorption, mixed viscosity and friction coefficient, easy to disperse, uniform mixing, can significantly increase the fluidity of materials, commonly used in VLSI plastic packaging materials, VLSI, fine chemicals, rewritable CDs and large areas Electronic substrates, special ceramics and special rubber, aviation, aerospace engineering, etc.

With the development of the high-tech industry, silicon micro-powder has become more widely used and used more and more, which has great market demand and potential. The rapid development of the microelectronics industry has put forward higher and higher requirements for silicon micropowder. Silicon micropowder not only needs to be ultra-fine, high-purity, and low-radioactive element content, but also spheroidizes the particle shape. For the huge market demand in the future, it is necessary to improve the quality of silicon raw materials, improve the technical level of silicon powder production, and strengthen the testing and control of the production process, so as to improve the quality of silicon powder products.

Article source: China Powder Network

by ALPA Powder

Flake graphite regrind process and equipment

Among graphite products, flake graphite is the most widely used and in demand, and its value is proportional to the size and grade of the flakes. However, the traditional flake graphite grinding and floating process generally damages the graphite flakes greatly. Therefore, for flake graphite ore with different embedded particle sizes, it is of great significance to select the regrind process and equipment reasonably.

Crystalline graphite, also known as flake graphite, has a series of excellent physical and chemical properties such as electrical conductivity, thermal conductivity, high temperature resistance, plasticity, lubricity, and chemical inertness. It is widely used in metallurgy, machinery, electrical, light industry, chemical industry, textile, and national defense. It is one of the non-metallic materials indispensable for global high-tech development.

Usually large flakes refer to flake graphite of +50 mesh, +80 mesh, and +100 mesh, and flake graphite below these particle sizes is called fine flake graphite.

The size of the scale and its fixed carbon content are the most important reference indicators for judging the value of graphite flakes, and the dissociation method and degree are the most important factors that determine the yield of large scales and the fixed carbon content in concentrate products. Therefore, for the optimization of flake graphite beneficiation process, we must first start from the grinding process.

In recent years, breakthroughs have been made in grinding technology, and many new technological processes have emerged, such as: graded grinding and flotation, rapid flotation technology, stage grinding and stage separation, pre-separation, collector-free flotation, and shear flocculation. Flotation process, ultrasonic strengthening process.

Flake graphite regrind equipment

Research has found that the sorting process and sorting equipment will not physically destroy the graphite flake structure, only the large flake graphite will be damaged and lost during the regrinding process. Therefore, the most critical technology for graphite beneficiation is the reasonable selection of regrinding equipment.

The most important and core part of protecting graphite flakes is the selection of regrind equipment.

• Ball mill

The ball mill is a grinding equipment with a wide range of applications, a long history, simple operation, and low production cost in the beneficiation plant. Lattice type ball mills and overflow type ball mills are widely used.

In the graphite regrinding process, the ball mill is mainly used for one-stage grinding or two-stage regrinding. The installed power is generally 80~120kW, the medium filling rate is 30%~40%, and the single processing capacity is 10~40t/h. Etc.

• Mixing mill

The biggest difference between the stirring mill and the ball mill is that the former has a stirring device inside. The stirring mill drives the grinding medium to rotate and revolve through the rotation of the stirring device, and then generates shear, impact, and friction effects to achieve the purpose of fine grinding of the material.

The common stirring device forms of agitating mills include spiral, disc, rod and impeller. In the graphite regrinding process, there are two types of impeller and rod, which are more widely used or have broad prospects. It is a double-layer impeller type and a multi-layer impeller type, which are used in graphite regrinding processes in many areas in China.

• Rod Mixing Mill

The rod-type stirring mill is a fluidized vertical stirring mill, which uses the rotating kinetic energy of the stirring rod to produce high-energy motions of the medium and slurry mixture in the grinding chamber, thereby generating shear, friction and The squeezing force forms an ideal grinding environment for fine grinding, regrinding and scrubbing.

The installed power of the rod-type stirring mill is generally 18.5~1100kW, but the application specifications in the graphite regrinding process are generally small, generally 18.5~185 kW, the grinding medium is ceramic balls, and the processing capacity of a single device is generally 1.5~ 15 t/h.

• Disc grinder

Starting from the research on the grinding characteristics of flake graphite, the regrind equipment is a disc mill. After the graphite flakes are ground under the action of the rotating thrust of the grinding disc, the scales are dissociated under the action of the grinding force along the crystal layer.

The shortcomings such as fast wear, large maintenance workload, strict requirements on the concentration of ore pulp and small processing capacity, have led to fewer applications in the graphite industry.

• Sand mill

Grinding medium and graphite pulp move both axially and radially in the sand mill. Due to the differential speed, they perform rotational friction with each other to form a peeling force, which separates the graphite from the gangues on it, and thus separates the graphite from the gangue. Body dissociation.

The protective effect of graphite flakes is average. Moreover, the equipment has certain shortcomings. For example, due to the high stirring speed during operation, the life of the equipment cylinder is short, and the replacement frequency in production is high, which directly affects the production efficiency.

• Vibration mill

Vibration mill is a kind of high-efficiency grinding equipment. As long as the amplitude is well controlled, using it as a regrinding equipment for graphite is beneficial to the protection of Dalin tablets.

Vibration mill is a dry grinding equipment, and graphite is in the form of slurry after flotation, and it must be dried before vibrating mill regrind, so it is difficult to realize in graphite production; and vibration mill has high noise and requires high infrastructure .

In the selection of grinding media, the use of rods, columns and cylinder rods to protect large scales is better than ball media. In the selection of mills, the use of disc mills, sand mills, vibration mills, vertical mixing mills, rod mills and other regrinding equipment with a grinding and stripping effect has obvious effects on the protection of large scales.

Because of the large processing capacity of the first and second stage grinding, the ball mill can be selected as the grinding equipment, but it must be noted that the ball mill is destructive to the large flake graphite and the grinding efficiency is low. Therefore, if the economic cost allows, consider using a large-size rod-type agitating mill to replace the ball mill for one or two stages of fine grinding.

For the regrind after the second stage, due to the moderate processing capacity, impeller and rod agitating mills can be selected as regrinding equipment. This type of equipment has the advantages of low power consumption, high efficiency, low consumption of grinding media, strong applicability, stronger production capacity, safer operation, and easy implementation of conventional and optimized control, especially the rod-type stirring mill, which is suitable for large The protection of flake graphite is more effective.

Article source: China Powder Network

by ALPA Powder

Application of inorganic powder in plastics

Plastic is everywhere in life, and powder is everywhere in plastic.

Powder materials for plastics include inorganic powders and carbon-containing powders.

Inorganic powder is divided into industrial waste residue and non-mineral powder. Industrial wastes include red mud, white mud, fly ash beads (glass beads), etc.; non-mineral powders are divided into heavy calcium, talc, kaolin, wollastonite, mica powder, brucite powder, which are crushed and classified , Barite powder, etc., light calcium (including nano-calcium carbonate), aluminum hydroxide, magnesium hydroxide, precipitated barium sulfate, etc. formed by chemical reaction.

Carbon-containing powder is divided into carbon and carbon oxide powder. Carbon includes carbon black, graphite, etc.; carbon oxide powder includes wood powder, straw powder, nutshell powder, starch, etc.

The role of traditional inorganic powder in plastics

• The modification effect of calcium carbonate on plastics

Mechanical properties: improve the rigidity and hardness of plastic products, improve tensile and flexural strength, and significantly increase the modulus of elasticity; thermal properties: the coefficient of thermal expansion and shrinkage are reduced in all aspects, and the warpage and curvature of the product become smaller. The deformation temperature increases with the increase of the filler, and the radiation performance: the filler has a certain absorption capacity for radiation, which can prevent the aging of plastic products.

• The modification effect of wollastonite on plastics

It has good insulation, wear resistance, and high refractive index; it can improve impact strength, enhance fluidity, and improve tensile strength and mold shrinkage; it can significantly reduce the water absorption of the material.

• Modification effect of talcum powder on plastics

It can improve the tensile strength, impact performance, creep resistance, heat resistance, tear resistance of plastic products, improve the surface appearance of the product, reduce the shrinkage of the product, improve the barrier effect, reduce the air permeability, and increase the rigidity of the plastic product And crispness.

In addition to the above inorganic powder fillers, steel sulfate can improve the chemical resistance, heat resistance, and appearance of plastic products. Mica powder can reduce the shrinkage, warpage, curvature and specific gravity of the product, and improve the product. The mechanical properties of the product increase the surface gloss and weather resistance of the product.

Comparison of application performance of different inorganic powders in plastics

Performance comparison of different materials filled in nylon 66

Comparison of properties of polypropylene filled with different materials

Several factors affecting the application of inorganic powder in plastics

• Surface modification and activation of inorganic powder

The compatibility of inorganic powder fillers with polymers is relatively poor. If added directly, inorganic powders cannot be uniformly dispersed in the polymer, and its surface modification and activation are very important. Activation rate + fastness = modification effect.

• Moisture and volatile matter in inorganic fractions

Moisture and volatile matter will form gas due to high temperature, friction and other factors during plastic processing. After cooling, it will cause irregular cracks in plastic products, and may also cause secondary agglomeration of dried fine powder. In actual production and application, when the moisture and volatile matter are at 20.3%, it will affect the plastic processing and product quality.

• Static electricity

Inorganic powder with flaky structure is easy to rub and generate static electricity in the middle of processing, which makes small particles agglomerate and affects the dispersion effect of the product.

What are the new applications of inorganic powders

• Kaolin

Improve the tensile strength and modulus of low-plasticity plastics with a lower glass transition temperature; refer to the rigidity and strength of high products; increase the electrical insulation strength of the plastic after burning, and be used for high-voltage insulation products.

• Wood flour, bamboo flour, straw flour

Rich sources, low prices, low-carbon and environmentally friendly; heat resistance is the main bottle precondition that restricts dosage and use.

• Fly ash

The specific gravity is small, the hardness is large, and the fluidity is good; the fly ash is processed into a new material with a certain particle size and has adsorption performance, which can effectively adsorb harmful substances, odors and moisture.

• Calcium silicate

Small specific gravity, strong odor adsorption, excellent physical properties; mainly used in waste plastic processing, plates, pipes, etc.

• Electric lime

The main discharge of chemical products is solid waste; it is mainly used in plastic materials.

• Black talc, black calcite

It can partially replace carbon black.

Six major trends in the development of inorganic powders

Harmless production and application, industrial extension, miniaturization of processing and application, scientific value, diversification of application, and high-performance products.

Inorganic powder is a new functional modified material with abundant resources, low price and excellent performance. However, we should strive to abandon the traditional cognition that inorganic powder is a low-value filler material. Significant technological breakthroughs should be made in low carbon and other aspects. Inorganic powders should develop in the direction of functionalization, greening, and miniaturization, so that low-value-added filler materials will be fully transformed into high-end functional modified materials.

Article source: China Powder Network

by ALPA Powder

High-purity ultra-fine electronic grade quartz powder

In semiconductor integrated circuit packaging, packaging materials can play a role in semiconductor chip support, chip protection, chip heat dissipation, chip insulation, and interconnection of the chip with external circuits and optical paths. In electronic packaging materials, filler occupies a larger share. The high-purity ultra-fine quartz powder used as a filler for packaging materials has incomparable advantages.

Quartz powder requirements for electronic packaging

• High purity and ultrafine

Traditional application areas of quartz powder

High-purity ultra-fine quartz powder can improve the acid and heat performance, mechanical strength, dielectric properties and thermal conductivity of the packaging material; reduce the thermal expansion coefficient, water absorption rate, molding shrinkage rate and cost rate of the packaging material. High-purity ultra-fine quartz powder is widely used in the manufacture of electronic inks, optical fibers, advanced precision ceramics, precision grinding of optical devices and electronic components, etc. The most important of which is in the field of electronic packaging. Quartz powder for electronic packaging must be high-purity and ultra-fine. Generally, the purity of SiO2 is required to be above 99.99%, Fe2O3 is less than 5ppm, and the total amount of impurities is required to be less than 300ppm.

• Spheroidization

With the rapid development of the microelectronics industry, large-scale and ultra-large-scale integrated circuits have increasingly higher requirements for packing materials for packaging materials. Not only ultra-fine and high-purity, but also low radioactive element content is required, especially for particle shapes. Sphericalization requirements.

High-purity ultra-fine spherical quartz powder has the properties of low friction coefficient, low impurity, low stress, low expansion, high dielectric, high heat resistance, high humidity resistance, and high filling.

The surface area of ​​the ball is the smallest, the isotropy is good, it is uniformly mixed with the resin to form a film, the amount of resin added is small, and the fluidity is the best. The higher the quartz powder filling rate, the smaller the thermal expansion coefficient of the molding compound, and the lower the thermal conductivity, the closer the thermal expansion coefficient of monocrystalline silicon is, and the better the performance of the electronic components produced therefrom.

The plastic molding compound made of spherical powder has the smallest stress concentration and the highest strength. When the stress concentration of the angular powder molding compound is 1, the stress of the spherical powder is only 0.6. Therefore, the spherical powder molding compound has a high yield when encapsulating integrated circuit chips. It is not easy to cause mechanical damage during transportation, installation and use.

The friction coefficient of spherical powder is small, and the wear on the mold is small, so that the service life of the mold is long. Can reduce costs and improve economic efficiency.

Preparation of High Purity Superfine Electronic Grade Spherical Quartz Powder

Experts show that as long as the purity can meet the requirements, it is best to use natural crystalline quartz as the raw material, with low cost and simpler process lines. Quartz raw materials include quartzite, vein quartz, quartz sandstone, powder quartz, and quartz sand.

Natural quartz minerals contain a large number of inclusions and cracks. The use of ultrafine pulverization technology can greatly reduce the number of cracks and defects. Combined with the purification process, the content of harmful impurities can be better reduced.

Thermal crushing first can greatly improve crushing efficiency, reduce equipment failure rate, and reduce crushing costs.

The requirement for grinding media is to choose less abrasion, high hardness, and a diameter between 1~5mm.

For ultrafine quartz powder, stirring mill, vibrating mill, and jet mill are often used.

• Processing technology

Quartz powder → magnetic separation → flotation → ultra-fine grinding → pickling → deacidification cleaning → filter press dehydration → drying → breaking up → finished product

The advantages of dry production of quartz powder are obvious: low comprehensive production cost, high output, and easy control of the process. However, the dust is too large and there is a crushing limit, it is difficult to produce micron-sized quartz powder. Therefore, the wet process is generally used when producing high-purity ultra-fine spherical quartz powder powder.

• Purification process

1.  Physical purification

Water washing and grading desliming, scrubbing, magnetic separation and flotation. But in order to obtain high-purity quartz powder, the quartz powder must be chemically purified.

2. Chemical purification

Acid leaching: The principle is to use the insoluble acid, but the impurities can be dissolved in the acid, and the impurities in the quartz powder are removed by acid leaching to achieve the purpose of purification. Commonly used acids are hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid and oxalic acid.

• Sphericalization process

The research of China's high-purity ultra-fine spherical quartz powder has entered the pilot stage, and has undergone three adjustments: AC high-frequency plasma fusion method, DC plasma fusion method, and arc method formed by carbon electrodes. The key to the technology is that the heating device requires a stable temperature field, an easy-to-adjust temperature range, and a clean heat source environment that will not cause secondary pollution to the quartz powder. There is currently no report on the industrialized production system.

Other commonly used silica high-temperature fusion spraying method, gas flame method, liquid phase control ethyl orthosilicate, silicon tetroxide hydrolysis method.

Status analysis and outlook

With the further development of the electronics industry, the fourth wave of development of electronic packaging technology is bound to usher in the system-in-package, which will lead to the sudden emergence of the spherical quartz powder market.

With the advancement of science and technology, especially the development of microelectronics technology, the demand for high-purity and ultra-fine electronic grade quartz powder has doubled, and its quality requirements have become higher and higher. Actively explore and promote the progress of quartz beneficiation and purification technology, and realize the low-cost, large-scale industrial production of refined quartz, high-purity and ultra-high-purity quartz, which is important for making up for the shortage of natural crystal resources and meeting the demand for high-purity ultra-fine quartz powder for high-tech use. The practical significance of.

Article source: China Powder Network

by ALPA Powder

Ultrafine talc grinding production line

Talc is generally lump, leaf, fibrous or radial, and the color is white, off-white, and it will have various colors due to other impurities. Talc is finally applied in powder form. Therefore, fine grinding and ultra-fine grinding are necessary processing techniques for talc. Superfine talcum powder is one of the most used ultrafine powder products in the world today. It is widely used in papermaking, plastics, rubber, paints, cosmetics, ceramics, etc.

At present, the processing of ultrafine talc powder mainly adopts the dry process. Although wet grinding has been studied, it is rarely used in industry.

Jet milling process

Raw material → feeding → crushing (hammer crusher → bucket elevator → vibrating feeder) → drying (vertical dryer) → medium crushing (hammer crusher) → fine grinding (Raymond mill) → superfine grinding (the jet mills used in industry include disc jet mills, fluidized bed counter-jet jet mills, circulating tube jet mills, etc.)→finished products

Talc has a Mohs hardness of 1, which is naturally crushable and has good grindability. For the fine grinding of talc, various types of Raymond mills are generally used, mainly producing 200 mesh and 325 mesh products. However, if fine grading equipment is installed, products with 500 to 1250 meshes can also be produced.

Dry production equipment mainly includes high-speed mechanical impact mills, jet mills, centrifugal self-mills, rotary mills, vibration mills, stirring mills, and tower mills. In addition to jet mills, in order to meet the requirements of user particle size distribution, other classification equipment generally needs to be equipped with fine classification equipment. Commonly used fine classification equipment is various turbo-type air centrifugal classifiers.

High-speed mechanical impact superfine grinding process

Raw material→crushing (hammer crusher, crushing to 8mm is enough)→mechanical impact superfine grinder→turbine type fine classifier (the coarse-grained product after classification can be returned to the mill or can be used as a separate product) →Finished product

The centrifugal self-grinding and rotary mill superfine grinding process of talc is generally similar to the high-speed mechanical impact superfine grinding process.

Acceptance standard for talcum powder entering the factory

Talc powder should be stored in a dry warehouse. It can be used for paper fillers and resins, stickies adsorbents, 600 mesh talcum powder is used for newsprint systems, high-end food packaging base paper (without fluorescence), and 325 mesh talcum powder is used for DIP pulping. , Low-grade food packaging base paper (no fluorescence).

Article source: China Powder Network

by ALPA Powder

Ball mill and classifying production line of silica powder

With the ultrafine processing of non-metallic minerals, ultrafine crushing and grading technology has become one of the most important deep processing technologies, which is of great significance to the development of modern high-tech industries.

Silicon micropowder (SiO₂) is an extremely widely used inorganic non-metallic material, with acid and alkali corrosion resistance, abrasion resistance; high insulation, high thermal conductivity, high thermal stability; low expansion coefficient, low dielectric coefficient, and low thermal conductivity. It is widely used in the fields of chemicals, electronics, integrated circuits (IC), electrical appliances, plastics, coatings, advanced paints, rubber, and national defense.

According to the level, it is divided into ordinary silicon powder, electrical grade silicon powder, fused silicon powder, ultra-fine silicon powder, and spherical silicon powder; according to the purpose, it is divided into silicon powder for paint and coating, silicon powder for epoxy floor, silicon powder for rubber, and sealing Silicon powder for glue, electronic grade and electrical grade silicon powder for plastic packaging, and silicon powder for precision ceramics; according to the production process, it is divided into crystalline powder, cristobalite powder, fusion powder, and various active powders.

The preparation of crystalline powder, cristobalite powder, fusion powder and various active powders all need to go through a grinding and classification process. The grinding and classification of silicon micropowder generally adopts dry ball milling and classification.

Ball Mill and Classifying Production Line

All kinds of crushed, beneficiated, calcined or melted silicon powder raw materials → hoist → silo → electromagnetic vibrating feeder → ball mill → classifier → cyclone collector → bag dust collector

• Characteristics of ball mill classification production line

Large output, simple equipment operation, low maintenance costs, flexible selection of grinding media and liners, low pollution to high-purity processing of materials, reliable overall equipment operation, and stable product quality.

The application of silicon powder can make the product high in whiteness, good gloss and stable quality index.

• Ball mill classification production line output

In actual production, in order to maximize the benefits, the output matching of the ball mill and the classifier is very important. Proper cooperation can give full play to their own characteristics, complement each other's advantages, and are highly efficient. Poor coordination will result in functional constraints, high energy consumption and low efficiency.

The influencing factors of the output of the ball mill include the fineness of the feed, the effective diameter of the mill body after lining, the speed of the ball mill, the selection and gradation of the ball mill media, the filling amount, the effective length of the mill body, and the size of the feeding amount.

The factors affecting the output of the classifier include powder concentration, turbine classifier speed, air volume and pressure, classification efficiency, particle size distribution, and product fineness.

Therefore, the output of the two equipment should have the following relationship: the output of the classifier = the processing capacity of the classifier-the amount of coarse material after classification; the output of the ball mill = the amount of raw material feeding + the return amount of coarse material after classification; the processing capacity of the classifier = The output of the ball mill.

Market Outlook of Silicon Micropowder

With the development of the high-tech industry, the use of silicon micropowder is becoming wider and wider, and the amount used is increasing. For the huge high-end market demand in the future, it is necessary to improve the quality of silicon raw materials, improve the technical level of silicon powder production, strengthen the testing and control of the production process, and break the technical barriers as soon as possible, so as to produce various specifications that meet the quality requirements of various fields according to market demand Silicon powder to meet the needs of domestic and foreign markets.

Article source: China Powder Network

by ALPA Powder

Powder metallurgy process & application

Powder metallurgy is a process technology for preparing metal or using metal powder (or a mixture of metal powder and non-metal powder) as raw materials, forming and sintering, to produce metal materials, composite materials and various types of products.

The powder metallurgy products industry in a broad sense includes iron and stone tools, cemented carbide, magnetic materials and powder metallurgy products. The powder metallurgy products industry in the narrow sense only refers to powder metallurgy products, including powder metallurgy parts (most of them), oil-bearing bearings and metal injection molding products.

Powder metallurgy process characteristics

Compared with other processes, the material utilization rate of powder metallurgy is the highest, reaching 95%, and the energy consumption of parts is the lowest!

The density of the products is controllable, such as porous materials, high-density materials, etc.; uniform microstructure, no component segregation; near-shaped forming, raw material utilization rate>95%; less and no cutting, only 40-50% of cutting processing; material group The element is controllable, which is conducive to the preparation of composite materials; the preparation of insoluble metals, ceramic materials and nuclear materials.

The basic process of powder metallurgy

The basic process of powder metallurgy is powder making → mixing → forming → sintering → vibration grinding → secondary processing → heat treatment → surface treatment → quality inspection → finished product.

Flour milling

Flour milling is the process of making raw materials into powder. Commonly used milling methods include mechanical and physical and chemical methods.

The mechanical method does not change the chemical composition of the raw material, and prepares the powder by cutting/grinding the metal to split the material to create a new interface. The mechanical method can reduce or increase the particle size of the powder, and the metal powder will be hardened after grinding, but the shape of the powder is irregular and the powder fluidity becomes poor.

The physical and chemical method is to make liquid metal prepare powder by physical methods such as cooling and atomization; in addition, it can also be prepared by reducing metal oxides and salts with reducing agents based on chemical reactions such as reduction and dissociation. Atomization powder technology can effectively reduce the segregation of alloy components, so the obtained alloy powder composition is relatively uniform. Since the water atomization method uses higher density water as the atomization medium, the shape of the powder obtained is generally irregular.

Solid particles with a size greater than 0.001mm and less than 1mm are called powders. Generally, the shape of powder particles includes spherical, nearly spherical, polygonal, flake, dendritic, irregular, porous sponge, and butterfly shapes.

Mix

Mixing is the process of mixing various required powders in a certain proportion, and homogenizing them to make green powder. It is divided into three types: dry, semi-dry, and wet, double cone mixer, V-type mixer , Dual motion mixers are used for different requirements.

The mixing of powder is not uniform, the forming process is easy to delamination and fracture, the sintering process is easy to burst and deform, and the mechanical properties such as product hardness and density do not meet the requirements.

Forming

Forming is the process of putting a uniformly mixed mixture into a compression mold and pressing it into a parison with a certain shape, size and density under a pressure of 15-600 MPa. There are two methods of pressure forming and non-pressure forming. Pressure forming The most widely used is compression molding.

Sintering

Sintering is a key process in the powder metallurgy process, and the formed compact is sintered to obtain the required final physical and mechanical properties.

Sintering is divided into unit sintering and multi-component sintering. In addition to ordinary sintering, there are loose sintering, immersion method, and hot pressing method.

Sintering is different from metal melting, at least one element is still in the solid state during sintering. During the sintering process, the powder particles undergo a series of physical and chemical processes such as diffusion, recrystallization, fusion welding, compounding, and dissolution, and become metallurgical products with a certain porosity.

Post-processing

The treatment after sintering can adopt various methods according to different product requirements. Such as finishing, oil immersion, machining, heat treatment and electroplating, steam treatment, etc. In addition, in recent years, some new processes such as rolling and forging have also been applied to the processing of powder metallurgy materials after sintering, and have achieved ideal results.

• Impregnation

Use the capillary phenomenon of the porosity of the sintered parts to be immersed in various liquids. For lubrication purposes, it can be soaked in lubricating oil; in order to improve the strength and anti-corrosion ability, it can be soaked in copper solution; for surface protection, it can be soaked in resin or varnish.

• Steam treatment

Due to the existence of pores in powder metallurgy products, this brings difficulties to surface protection. Steam bluing treatment is very important for meters, military industry and powder metallurgy products with anti-corrosion requirements, and can improve the rust resistance and airtight gaps of powder metallurgy parts.

• Cold surface pressure

To improve the dimensional accuracy of the parts and reduce the surface roughness, shaping can be used; to increase the density of the parts, multiple pressing can be used; to change the shape of the parts, fine pressing can be used.

• Heat treatment

Due to the existence of pores, for products with porosity greater than 10%, liquid carburizing or salt bath heating shall not be used to prevent salt solution from immersing in the pores and causing internal corrosion; for products with porosity less than 10%, it can be used with general steel The same heat treatment methods, such as overall quenching, carburizing quenching, carbonitriding quenching, etc.; heat treatment can improve the strength and hardness of iron-based products.

Application of powder metallurgy

The application range of powder metallurgy products is very wide, from general machinery manufacturing to precision instruments, from hardware tools to large-scale machinery, from electronics industry to motor manufacturing, from civil industry to military industry, from general technology to cutting-edge high technology. The figure of metallurgical craftsmanship.

Powder metallurgy materials can be divided into powder metallurgy porous materials, powder metallurgy structural parts, powder metallurgy anti-friction materials, powder metallurgy tool and die materials, powder metallurgy friction materials, powder metallurgy electromagnetic materials, powder metallurgy high temperature materials, etc.

Typical application: automotive industry

Powder metallurgy valve seats, valve guides, VCTs and sprockets, etc., can have high strength, high wear resistance and excellent heat resistance. Such as intake and exhaust valve seats, gears.

Typical application: aerospace industry

Special functional materials are mainly used for auxiliary machines, instruments and airborne equipment of aircraft and engines. High-temperature and high-strength structural materials are mainly used for important structural parts of aircraft engines. Such as high-pressure turbine powder disc for engine, aviation brake pair-BY2-1587.

Typical application: electronics

Such as mute button, power button, volume plus and minus buttons, SIM card tray, 8PIN data cable socket, built-in N41 feet, built-in vibration motor rotor.

The development direction of powder metallurgy

Powder metallurgy technology is developing in the direction of high densification, high performance, integration and low cost. The details are as follows:

1. Representative iron-based alloys will develop into large-volume precision products and high-quality structural parts.

2. Manufacture a high-performance alloy with uniform microstructure, difficult to process and completely dense.

3. The enhanced densification process is used to produce special alloys that generally contain mixed phase compositions.

4. Manufacture of non-uniform materials, amorphous, microcrystalline or metastable alloys.

5. Processing unique and non-general composite parts of shape or composition.

Article source: China Powder Network

by ALPA Powder

Classifier for powder industry

Classification is based on the principle that the solid particles have different sedimentation speeds in the medium due to different particle sizes, and the particle group is divided into two or more particle size levels. Classification is an indispensable part of the crushing process, and the broad classification includes sieving.

Comparison of sieving and classification

The commonly used fluid media for classification are water (called wet classification or hydraulic classification) and air (called dry classification or wind classification). The classifier system consists of air classifier, cyclone separator, dust collector, induced draft fan, electric control cabinet, etc.

Horizontal multi-rotor classifier system layout diagram

Dry classification equipment

• Gravity Air Classifier

The classification is carried out by using the different sedimentation speed and movement trajectory of the particles in the gravity and air medium resistance. Its structure is simple, the pressure drop is small, the processing capacity is large, but the classification accuracy is poor.

Gravity air classifiers include vertical flow type gravity classifiers, horizontal flow type gravity classifiers, and special flow type gravity classifiers.

• Inertial air classifier

Inertia is an inherent property of matter and is determined by mass. During the movement, when particles are subjected to a force that changes the direction of their movement, different inertias will form different trajectories to achieve classification. Its structure is simple, there are no moving parts inside, and the classification accuracy is high, but the output is low.

Inertial air classifiers include jet-type inertial classifiers, jet-type inertial classifiers, and other types of inertial classifiers.

• Centrifugal Force Air Classifier

The classification is achieved under the combined action of air resistance, gravity and centrifugal force, with high classification accuracy and large processing capacity.

Centrifugal classifiers include free vortex type centrifugal classifiers, quasi-free vortex type centrifugal classifiers, forced vortex type centrifugal classifiers, forced vortex type centrifugal classifiers include traditional fan blade type forced vortex centrifugal classifiers, cage rotor type forced vortex centrifugal classifiers Classifiers, rotary wall forced vortex centrifugal classifiers, other types of forced vortex centrifugal classifiers.

• Combined classifier

It is a combination design of the previous models, which can often integrate multiple advantages. It is the main method of setting the classifier before a new breakthrough in classification theory has been achieved.

Wet classification equipment

Equipment that uses gravity or centrifugal force to classify materials according to the sedimentation law of particles in the fluid, such as spiral classifiers, hydrocyclones, cone classifiers and trough classifiers, etc.; control the size of the screen holes and classify materials according to the particle size The equipment, such as vibrating screen, curved screen and fine screen, etc.

The role of classification

The qualified products of grinding can be separated in time to avoid over-grinding, and at the same time, unqualified coarse sand can be separated and returned to grinding. This can well guarantee the sorting effect and effectively improve the grinding efficiency.

Application of classifier

All kinds of powders are super finely graded, remove impurities, and break up; classification of coarse particles entrained by ultra-fine powder and nano powder; classification of materials with strong viscosity, agglomeration, difficult to disperse, and poor fluidity; quartz, ceramics, refractory materials, zirconium Classification of superhard materials such as British sand and silicon carbide.

The function of the fine grading equipment is to ensure that the particle size distribution of the product meets the needs of the application, and to improve the efficiency of the ultra-fine grinding operation.

According to the classification medium, fine classifiers can be divided into dry classifiers with air as the medium (mainly rotor (turbine) airflow classifiers) and wet classifiers with water as the medium (ultrafine hydrocyclones, horizontal Type screw centrifuge, sedimentation centrifuge, etc.).

The development trend of fine classification equipment is fine particle size, high precision, high efficiency, large processing capacity, low energy consumption per unit product, and low wear.

Article source: China Powder Network

by ALPA Powder

Jet mill for titanium dioxide production line

The scientific name of titanium dioxide is titanium dioxide, the molecular formula is TiO₂, and the crystal form is anatase, rutile, and brookite. The plate-titanium type is an unstable crystal type and has no practical value in industry. The anatase type is stable under normal mixing, but will be transformed into rutile type at high temperature; rutile type is the extremely stable crystal form of titanium dioxide with compact structure.

At present, jet mills are used at home and abroad to complete the final product pulverization of titanium dioxide.

Why choose jet mill?

The jet mill can pulverize solid materials into sub-micron level, and the particle size distribution is very narrow, the pollution is small, and the pulverization process does not generate hot stars, and simple chemical reactions can be carried out in the jet mill. In comparison, the Raymond mill is not suitable for the crushing of titanium dioxide.

Know the jet mill

Jet mill, also known as fluid energy mill, is a device that uses the energy of high-speed airflow or superheated steam to make particles impact, collide, and rub each other to achieve ultrafine pulverization or deaggregation.

The compressed air/superheated steam enters the Laval nozzle, the air/steam accelerates into a supersonic airflow, and the high-speed jet moves the material at a high speed, causing the particles to collide and rub against each other and be crushed. The crushed material reaches the classification zone with the airflow. The materials with the required fineness are collected by the trap, and the materials that do not meet the requirements are returned to the crushing chamber to continue crushing.

Studies have proved that more than 80% of the particles are crushed by the impact control between the particles, and less than 20% of the particles are crushed by the impact control and friction between the particles and the wall of the crushing chamber.

Features: The product has fine particle size, narrow particle size distribution, and good particle shape dispersion; low-temperature pulverization without medium, no heat is generated during the pulverization process; the system is closed with less dust, low noise, clean and environmentally friendly production process; suitable for heat sensitivity, low melting point sugar and Crushing of volatile materials.

Which jet mill to choose?

There are five types of jet mills: counter-jet (collision) jet mills, circulating tube jet mills, fluidized bed jet mills, target jet mills, and flat jet mills.

In the production process of titanium dioxide, a flat type (also known as a horizontal disc type) jet mill is used for pulverization. Compared with other types of jet mills, it has the following advantages: the flat type (also known as the horizontal disc type) jet mill has a self-grading function, and organic additives can be added while pulverizing, which can organically modify the surface of the titanium dioxide. , It is beneficial to increase the dispersibility of titanium dioxide in different application systems.

Which grinding medium to choose?

Use superheated steam as the grinding working medium. Steam is easily available and cheap, and 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. Superheated steam has higher cleanliness than compressed air, low viscosity and no static electricity. At the same time of grinding, it can eliminate static electricity generated by collision and friction of materials, and reduce the phenomenon of secondary cohesion of powdered materials. Crushing under high temperature conditions can improve the application dispersibility of titanium dioxide and increase the fluidity of titanium dioxide. Low energy consumption, only 1/3-2/3 of compressed air.

As an important equipment for ultra-fine grinding, the jet mill plays an irreplaceable important role in the production of titanium dioxide. The development of jet grinding can basically meet the needs of titanium dioxide production, but the service life and crushing of the jet mill The effect still needs to be further improved, and the configuration and automatic control of the jet grinding system still need to be improved, and the high-efficiency jet grinding with large capacity still needs to be developed. With the development of science and technology and the application of new materials, jet mills will also play a more active role in promoting the development of the titanium dioxide industry.

Article source: China Powder Network

by ALPA Powder

About powder surface modification technology

Powder surface modification refers to the use of physical, chemical, mechanical and other methods to treat the surface or interface of powder materials, and purposefully change the chemical properties of the surface of powder materials to meet the development of modern new materials, new processes and new technologies. need. It is a new technology that integrates powder processing, material processing, material properties, chemicals, and machinery.

The purpose of powder surface modification

Improve the dispersion, stability and compatibility of the powder particles; improve the chemical stability of the powder particles, such as drug resistance, light resistance, weather resistance, etc.; change the physical properties of the powder, such as optical effects, mechanical strength, etc. ; For the purpose of environmental protection and safe production.

Method for surface modification of powder

• Physical coating

The surface modification process of the powder by using surface modifiers such as polymers or resins to physically treat the surface of the powder.

• Chemical coating

A method of modifying the surface of particles by adsorption or chemical reaction.

• Precipitation coating

Using the precipitation reaction to form one or more layers of "coating" on the surface of the particles to achieve a method of improving the surface properties of the powder.

• Mechanochemical modification

Using ultrafine pulverization and other strong mechanical action to activate the powder surface.

• High energy modification

Using ultraviolet, infrared, corona discharge and plasma irradiation methods for surface treatment.

• Other surface modification methods

graft modification, acid-base treatment, chemical weather precipitation (CVD), physical precipitation (PVD).

Process of powder surface modification

• Dry process

The process is simple, and it is suitable for various organic surface modifiers, especially non-water-soluble various surface modifiers.

• Wet process

The surface modifier is well dispersed and the surface is evenly coated. It is suitable for various water-soluble or hydrolyzable organic surface modifiers, inorganic surface modifiers, etc.

• Combining crushing and surface modification into one process

The process is simple, and the crushing efficiency is improved to a certain extent, but the temperature is not easy to control, the coating rate is not high, and the surface modifier may be damaged.

• Combine drying and surface modification into one process

The process can be simplified, but the drying temperature is generally above 200 ℃, and it is difficult to ensure a uniform and firm coating.

ALPA's powder surface modification equipment includes: Turbo mill, ULM-C series Rotor Mill, Three-roller Mill, Pin Mill, High-speed Blender.

Main factors affecting the surface modification effect of powder

• The nature of the powder raw material

Specific surface area, particle size, particle size distribution, specific surface energy, surface physical and chemical properties, agglomeration

• Surface modification process

The consideration factors are the characteristics of the surface modifier, such as water solubility, hydrolysis, boiling point or decomposition temperature, etc.; the process surface modification method of the front-stage crushing or powder preparation operation.

• Surface modifier formulation

variety, dosage and usage

• Surface modification equipment

The performance of the surface modification equipment depends on the characteristics of the selected process, not the speed of the speed or the complexity of the structure.

Application of powder surface modification technology

Organic/inorganic composite materials (plastics, rubber, etc.), paints, coatings, organic/inorganic composite materials, adsorption and catalytic materials, health and environmental protection, anti-agglomeration in the preparation of ultrafine and nanopowders.

Research direction of powder surface modification technology

• Surface modification process and equipment

Strengthen the research of surface modification process, improve technology, and update equipment to realize the monolayer adsorption of surface modifier on the particle surface, reduce the amount of modifier, stabilize product quality and facilitate operation.

• Surface modifier

On the one hand, it adopts advanced technology to reduce production costs, especially the cost of various coupling agents; on the other hand, it develops new surface modifiers with good application performance, low cost, and special properties or special functions.

• Powder surface modification "soft technology"

First, select powder materials and "design" the powder surface according to the performance requirements of the target material; secondly, use advanced calculation methods, calculation techniques and intelligent technologies to assist in the design of powder surface modification processes and modifier formulations. , In order to achieve the best application performance and application effect.

Article source: China Powder Network

by ALPA Powder