As a structural-functional integrated material, sintered metal powder porous materials have been rapidly developed in recent years due to their large specific surface area, high strength, excellent permeability, weldability and good mechanical processing performance. The characteristics and molding process of powder metallurgy porous materials are introduced. The development trend of sintered metal powder porous materials is proposed around the application of sintered metal powder porous elements in different fields such as filtration separation, pressurized fluidized transportation of pulverized coal, automotive parts, fluid flow control and sound absorption.
Powder metallurgy porous materials are made of metal or alloy powders as raw materials through pressing and high-temperature sintering. They contain a large number of connected or semi-connected pores. Their uniform pore structure, porosity and pore size distribution depend on the powder particle size, molding and sintering process. Since powder metallurgy porous materials contain a large number of uniform pores, they have many excellent properties, such as large specific surface area, excellent permeability, high strength, weldability and good mechanical processing performance. Sintered metal powder porous materials include bronze, stainless steel, nickel and nickel alloys, titanium and intermetallic compounds, etc. Its research units are mainly based in Northwest China. The representative companies are the Nonferrous Metals Research Institute, Beijing Iron and Steel Research Institute, Central South University, Guangzhou Nonferrous Metals Research Institute, Kunming University of Science and Technology, etc.; the representative companies are PALL, MOTT Company of the United States, GKN Company of Germany, and the representative companies are Western Boya Technology Co., Ltd. and Antai Technology Co., Ltd. of China. They have a large scale and good performance in the production and application of sintered metal powder porous materials.
Sintered metal powder porous materials have the characteristics of both metal and porous materials, so they are widely used in filtration separation, powder fluidization transportation, automotive parts, fluid flow control, distributors, sound absorption, battery electrodes and biomedical implant materials and equipment . Sintered metal powder metallurgy porous materials have different shapes due to differences in application fields and working conditions. It is necessary to comprehensively select suitable sintered metal powder porous materials according to working conditions and economy. Common ones are tubular, sheet, plate and various large-scale special-shaped porous elements, which have better comprehensive performance.
Combining the characteristics of sintered metal powder porous materials, multi-porous materials The production process of sintered metal powder porous components and their applications in different fields are introduced. At the same time, according to the current status in the process of research and development and application, the development trend of sintered metal powder porous materials in terms of material accuracy, flux, working condition adaptability, production and processing, equipment and system integration is proposed.
1 Sintered metal powder porous materials
1.1 Production process of sintered metal powder porous components
The production process of sintered metal powder porous materials mainly consists of powder selection, powder pressing molding, high-temperature sintering and post-processing processes. Among them, molding and sintering are the two most important production processes of sintered metal powder porous components, mainly including four process steps: powder selection, pressing molding, high-temperature sintering and post-processing.
1.1.1 Powder selection
In the production process, the pore size of sintered metal powder porous materials is controlled within the design range through powder classification, which is convenient for the preparation and production of porous materials with different porosities and pore sizes. Therefore, it is necessary to select the appropriate powder type and particle size range according to the use conditions and application requirements of sintered metal powder porous materials to obtain suitable materials. Material properties and porosity requirements. Conventional powders include copper powder, stainless steel powder, nickel powder, titanium powder, etc. Additives are generally used to improve powder molding properties. Among them, stainless steel, titanium and titanium alloys, nickel, nickel alloys and intermetallic compounds are the most widely used.
1.1.2 Pressing and molding
Metal/alloy powders are molded under a certain pressure through rolling, isostatic pressing, extrusion, molding and other pressing methods to form a blank with a specific shape. The appropriate pressing and molding process needs to be determined according to the actual working conditions and use requirements of the material.
1.1.3 High-temperature sintering
By sintering the pressed powder blank in a protective atmosphere high-temperature furnace/vacuum furnace, a series of physical and chemical processes such as diffusion, recrystallization and combination occur between the metal/alloy powder particles to form an intermediate product with certain porosity and strength.
1.1.4 Post-processing
Post-processing mainly includes machining, welding and thermal stress treatment. Machining is performed according to the final required size of the sintered metal powder porous element, welding with dense support parts and post-weld heat treatment. Finally, the sintered metal powder porous element of the required specifications is obtained through processes such as sintering and processing.
1.2 Characteristics of sintered metal powder porous materials
Metal porous materials mainly include sintered metal powder porous materials, sintered metal wire mesh porous materials, sintered metal fiber felt porous materials and foam metal materials. Metal powder porous materials are generally composed of metal/alloy powders through particle size screening, pressing and molding, high-temperature sintering, machining and heat treatment. They have the characteristics of metal materials and porous materials. They are a kind of structural-functional integrated materials with excellent mechanical properties, weldability, high temperature resistance, high pressure resistance, and corrosion resistance.
The sintered metal powder porous materials made by powder metallurgy have controllable pore size and uniform pores. They have both excellent mechanical properties of metal materials and uniform pore structure and good permeability of porous materials. Therefore, it is very important to develop the application of sintered metal powder porous materials in practical engineering. Taking sintered metal powder porous filter materials as an example, their performance and pore requirements need to be determined according to the use conditions and The performance requirements determine the application of corrosion-resistant sintered metal powder porous filter elements such as stainless steel, titanium and titanium-based alloys, nickel and nickel-based alloys, and Fe-Al-based materials.
2 Application of sintered metal powder porous materials in different fields
2.1 Application in filtration technology
Filtration technology has developed rapidly as a high-efficiency separation technology. The filtration and separation conditions in industrial production vary greatly. Traditional polymer filter elements, cloth bags and other filter elements are limited in application due to their poor strength, temperature resistance, and inability to backwash and regenerate. With the continuous innovation and improvement of production processes, some production conditions have higher pressures and temperatures, and higher requirements are placed on the strength, corrosion resistance, and precision of filter elements. Before the reaction, the solid particles contained need to be removed efficiently.
Sintered metal powder filter materials are often used in the filtration and separation process of gas-solid and liquid-solid clarification systems to achieve purification of process gas/liquid and interception or recovery of solid particles (such as catalysts, pulverized coal, metal particles, etc.). Using sintered metal powder porous materials The special pore structure can block, intercept and capture trace solid particles in the fluid, effectively filter solid particles in the gas or liquid of the clarification system, and then purify or separate the fluid. Metal powder is prepared into different forms of filter elements such as tubes, sheets, and cylinders through powder metallurgy process and applied to filtration and separation to purify the process fluid. The pore structure suitable for the working conditions is obtained by controlling the powder particle size, molding, sintering and other processes.
The common form of sintered metal powder filter element is stainless steel tube, which is mainly used in the form of filter internals in industry. The filter element is fixed by the tube sheet. The working principle is that the process fluid passes through the sintered metal powder porous filter element from the outside to the inside under the action of pressure, and the solid particles are blocked on the outer surface of the filter element. As the solid particles continue to accumulate, the thickness of the filter cake gradually increases. In order to ensure the long life of the sintered metal powder filter element, when the pressure difference between the inside and outside of the filter element reaches the maximum allowable pressure difference of the design, it is necessary to start backwashing to regenerate and restore the performance of the filter element, and its permeability can be restored. More than 90%.
Sintered metal powder filter elements such as stainless steel, titanium and titanium alloys have controllable filtration accuracy, uniform pores, high mechanical strength, good corrosion resistance, good regeneration performance and thermal shock resistance. At the same time, the filter element can be regenerated by reverse backwashing of the fluid, and is widely used in coal chemical industry, petrochemical industry, fine chemical industry and other fields, such as coal gasification raw gas filtration, process gas filtration, wastewater filtration, fly ash filtration, polysilicon chlorosilane filtration, petrochemical industry catalytic oil slurry filtration, S-Zorb device adsorbent filtration, zinc sulfate solution in zinc smelting and other filtration and separation processes, which can effectively ensure the stable and long-term operation of the filtration device. Taking the liquid-solid clarification filtration system as an example, the sintered metal powder porous filter element generally adopts a process of two filters in parallel (one open and one closed) in industrial applications. One filter is operating normally, and the other filter is backwashed offline by liquid. The process filtration system is compact and simple.
2.2 Application in pressurized fluidized transportation of pulverized coal
In coal chemical industry, petrochemical industry and other industrial production, fluidized bed technology is widely used. This technology needs to be configured with a suitable gas distributor in combination with the use location and working conditions to ensure that the gas can evenly enter the bed to complete various reactions. Taking coal gasification as an example, the gasification process, as the core of modern clean coal conversion technology, can be divided into fixed bed, fluidized bed and fluidized bed gasification technology. Among them, fluidized bed gasification technology has developed rapidly, mainly including wet gasification represented by Texaco water-coal slurry and pulverized coal dry pressurized gasification technology represented by SHELL, Aerospace (HT), and GSP. Pulverized coal dry pressurized gasification technology has been widely promoted and applied in recent years due to its wide applicability to coal types and low oxygen consumption. The main processes include coal grinding unit, pulverized coal pressurized conveying unit, pulverized coal gasification unit, synthesis gas purification unit, slag and ash/ash water treatment unit.
The pulverized coal pressurized fluidized conveying unit needs to receive the pulverized coal from the coal grinding unit. The pulverized coal is transported to the burner of the gasifier through the pulverized coal storage tank, pulverized coal discharge tank and pulverized coal feeding tank to ensure the stable coal supply of the gasifier. The particle size of the raw pulverized coal in the dry pressurized gasification of pulverized coal is small. Due to adhesion and friction, it is very easy to cause bridges and blockages between fine particles during transportation, which can easily cause the shutdown of the process production system. Therefore, it is necessary to ensure the smooth flow of powder during pressurized fluidized transportation. Through independent design of special-shaped forming molds and sintering molds and introduction of near-net forming methods and sintering technologies, Northwest Nonferrous Metals Research Institute, Western Baode Technology Co., Ltd., Beijing Iron and Steel General Institute Antai Technology Co., Ltd. and other units have developed large-scale special-shaped porous components for powder fluidized transportation such as ventilation cones, purges, flute pipes, and fluidized discs according to different usage locations and uses. The widely used pulverized coal pressurized fluidized conveying components are stainless steel sintered powder porous components, which use clean low-pressure and high-pressure N2/CO2 to sinter metal The powder fluidization conveying equipment with powder as the core internal parts loosens the powder to achieve fluidization and conveying. When the clean gas enters the ventilation cone and the wall near the purge for powder fluidization conveying, it forms a uniform air film, which prevents the direct contact between the powder and the wall, not only reducing the scouring of the equipment by the powder, but also reducing the probability of powder bridging and blockage.
The ventilation cone, pipeline aerator, and flute are composed of an outer shell and internal parts. The internal parts are made of sintered metal powder with specific precision. It has a wide adaptability to working conditions and can achieve stable operation in low pressure, high pressure or pressure alternating occasions. Taking full advantage of the excellent mechanical properties and uniform pore structure of sintered metal powder porous materials, the developed ventilation cone, pipeline aerator, flute and other powder fluidization conveying elements are applied to pulverized coal storage tanks, pulverized coal discharge tanks, and pulverized coal feeding tanks to achieve pressurization, fluidization and conveying of pulverized coal, effectively avoiding the powder in The bridging and blocking phenomena in the actual working process ensure the stability of the process production process and long-term operation. It can be widely used in the fluidization and transportation of various types of powders such as pulverized coal and fly ash.
2.3 Application in automobile parts
Powder metallurgy is a process with little or no chips, which can greatly reduce the amount of machining, save metal materials and improve production efficiency. The automobile parts made by it have the advantages of a wide variety, energy saving, material saving, environmental protection and suitability for mass production. Therefore, it has achieved rapid growth in the manufacturing industry and has been widely used in many key parts of automobiles, such as steel parts for automobile engines, steel parts for automobile transmission systems, gear cages, etc., which are all made of sintered metal powders pressed, sintered and machined at high temperatures. In order to further improve the strength of powder metallurgy automobile parts, GM of the United States, GKN of the United Kingdom, FederalMogul of France and other companies have organically combined powder metallurgy and forging technology to establish a production process. The production line has been set up and mass-produced powder forged gears and inner and outer rings of bearings for automobile automatic transmissions [23], making the mechanical properties of parts better.
According to different application occasions and usage requirements, different powder metallurgy materials are widely used in the production of automobile parts. Powder metallurgy high-strength aluminum alloy is an important lightweight material for automobiles. Due to its low density, strong energy absorption, good yield strength and tensile strength, it is also widely used in the fields of powder metallurgy aluminum-based cam bearing covers. Stainless steel powder sintered metal components have the characteristics of corrosion resistance and no cutting processing, and high-precision castings can be obtained by controlling the particle size, etc., and are widely used in the base of automobile windshield rearview mirrors. Wang Guangda et al. pressed the mixed metal and non-metal powders into shape, and sintered them under pressure in an ammonia atmosphere to obtain powder metallurgy friction material brake shoes and brake pads, which are widely used in high-speed train braking. In addition, the excellent mechanical properties, corrosion resistance and fatigue resistance of powder metallurgy stainless steel at high temperatures are fully utilized to produce ABS sensor gear ring, exhaust pipe flange and other automotive parts. China’s independently developed Ti-215Nb alloy made by powder sintering process is a new type of β titanium alloy. It is widely used in the manufacture of various high-performance internal combustion engines due to its advantages of large mechanical properties adjustment range. Powder metallurgy has low cost, high efficiency and low pollution, and has become one of the important methods for preparing titanium alloys for internal combustion engines.
2.4 Application in environmental protection and purification
With the increasing stringency of environmental protection requirements, noise, dusty exhaust gas and wastewater are recognized as the three major industrial pollution sources, especially for the export indicators such as exhaust gas and wastewater treatment. Sintered metal powder porous materials as a high-precision porous element have gradually shown their advantages in gas dust removal, wastewater purification and other processes. The dusty flue gas and other gases are sintered by metal powder porous materials. Due to the effect of the hole element, the dust at the outlet can be lower than 10mg/Nm³.
The coal-to-hydrogen department of CNOOC Huizhou Petrochemical Co., Ltd. used Fe3Al porous metal sintered powder filter elements in the coke filter of the E-Gas gasification unit. The results showed that the device filtration pressure difference was stable at about 14kPa, with excellent filtration performance, stable operation and good backwash performance. Under high temperature, high pressure and corrosion environments, Fe-Al intermetallic compounds have the advantages of high temperature resistance, good thermal shock resistance and sulfur corrosion resistance. The Fe3Al sintered metal filter tube prepared by isostatic pressing can be widely used in high-temperature dust removal and purification of high-temperature reaction dust-containing gases in petrochemical and chemical industries, high-temperature tail gas in glass industry, high-temperature flue gas dust removal in catalytic cracking, high-temperature coal gas in blast furnaces and converters in metallurgical industries, and high-temperature waste gas from boilers and incinerators. Li Song et al. investigated the application of titanium metal membrane in the two-stage sewage filtration treatment process of Gaoshangbao Joint Station in Jidong Oilfield. The results showed that after filtration and separation by titanium metal membrane, the treated The average suspended matter mass concentration of the reinjection water is 1.39 mg/L, and the average median particle size is 0.79 μm. Titanium metal membrane is suitable for deep treatment of oilfield reinjection wastewater, which can ensure the stability of the suspended matter mass concentration and particle size median index in the reinjection water. In the field of water treatment, microporous sintered metal titanium tubes, stainless steel filter tubes, etc. have significant effects in water purification. As a new type of filter material, sintered metal porous titanium material is corrosion-resistant, has good mechanical properties, and high filtration accuracy. The secondary filtration system composed of microporous titanium is also effective in water treatment and purification. In the papermaking industry, 316L stainless steel, nickel and nickel alloys, and titanium sintered metal powder porous materials are also used in pulp rinsing and sewage treatment to achieve the purpose of purification or recovery.
2.5 Application in other fields
Sintered metal powder porous materials have good high temperature resistance, strong rigidity, are not easy to pollute, and have strong recycling and regeneration. In addition, due to the sintered metal Powder porous materials contain a large number of uniform pore structures and have good noise absorption function. When sound waves flow through fine porous materials with a certain aperture, they will rub against the inner wall of the porous material to produce turbulence and other phenomena and consume a certain amount of energy. Therefore, sintered metal porous materials can use these characteristics to make various environmentally friendly sound-absorbing materials, which can be widely used in sound absorption and noise reduction in generator rooms, buildings, pipelines, vehicles, etc.
Sintered metal powder porous materials also have broad applications in other fields, such as large specific surface area and support strength can be used as solid catalysts; due to the excellent ferromagnetic properties and energy absorption effect of metal powder, it can be used as absorbing materials and sound-absorbing materials; due to light weight, high porosity, and good electromagnetic wave absorption performance, it can be used as electrode materials and shielding materials, and can be used as biomaterials, such as powder metallurgy porous titanium for orthopedics and tooth defect repair in the medical industry. In addition, sintered metal Metal powder porous materials can also be used in porous molds, casting process equipment, bearing materials, valve seat rings or valve seat rings on engine cylinder heads, light weapons industrial production, heat-resistant structures for aerospace engines, sweat cooling of thermal protection structures in the aviation field, and new energy materials.
3 Development trend of sintered metal powder porous materials
3.1 High precision, high strength, and large flux
With the increasingly stringent requirements for industrial product quality and environmental protection, higher requirements are placed on the precision of porous elements in filtration separation and powder fluidization transportation. The filtration precision is continuously improved to achieve efficient separation from small solid particles, especially the development of high-precision asymmetric powder porous materials has received widespread attention.
The development and application of high-precision, high-strength, and high-flux sintered metal powder porous elements in the field of filtration separation and pulverized coal pressurized transportation can reduce the maximum allowable pressure drop in the working conditions, ensure the export quality of process products, the isolation of powder and clean gas, and the safety during the use of working conditions. Full stability and long-term operation.
３．２ Components, equipment and system application integration
With the continuous development of engineering, the entire system needs to be fully designed to improve the system efficiency. Therefore, the development of supporting equipment and system integration applications of sintered metal powder porous components is also a new trend in the development of industries in the fields of filtration and separation. Taking the application of sintered metal powder porous materials in filtration technology as an example, according to the different working conditions and application fields of filtration and separation, appropriate filtration and separation materials should be selected, and reasonable filtration and separation process routes and systems should be designed; at the same time, high automation, continuity, low energy consumption, high efficiency, low cost and low pollution of the system are also new requirements for modern filtration and separation technology and the goals pursued by filtration and separation complete sets of systems.
３．３ Wide adaptability to working conditions
The tendency of industrial development to low-energy products has gradually expanded the application of sintered metal powder porous materials in the fields of filtration technology, powder fluidized transportation, etc., and has put forward higher requirements for the suitable operating conditions of filtration products, filtration media, fluidized transportation and other working conditions. The working conditions in different fields are complex and changeable, and strengthening the sintered metal The adaptability of metal powder porous components to harsh working conditions is of great significance. In particular, the quality control, operating conditions and application feasibility analysis of sintered metal powder porous components should be strengthened.
3.4 Product diversification and long life Develop different series of sintered metal powder porous components according to different use occasions and application purposes, and continuously optimize performance parameters and use structures. High-precision tubular porous components and different large-scale special-shaped porous components are the key development directions of sintered metal powder industrial application products. In this process, it is necessary to reduce the consumption of sintered metal powder porous components and increase the life of sintered metal powder porous components in actual use to ensure stable, continuous and long-term operation of working conditions. In addition, the backflush performance evaluation and optimization of sintered metal powder porous components and industrial tests and development of porous component cleaning and regeneration should be strengthened to promote the reuse of metal powder porous components within the design use cycle and long-life stable operation.
3.5 Production of high precision and low cost
Sintered metal powder parts have high requirements for processing size, precision, etc. Strict requirements, powder metallurgy dies, CNC presses and other molding and processing equipment can effectively control the size, density and cracks of sintered metal powder porous parts, and effectively realize the high precision and near net shape of porous components. The manufacturing process of sintered metal powder parts is relatively complex. Powder metallurgy technology is one of the future development directions to reduce production costs while improving production processes and ensuring product quality.
4 Conclusion
Sintered metal powder porous materials are a kind of functional-structural integrated materials. Their sintered porous components have been widely promoted and applied in filtration separation, pressurized fluidized transportation of pulverized coal, dust removal and environmental protection, automotive parts and other fields due to their advantages such as uniform pore structure, excellent mechanical properties and permeability. It plays an important role in promoting the development of related industries and brings huge economic and social benefits.
On the basis of the application of conventional sintered metal powder porous components, different series of improved sintered metal powder porous components and components with high precision, large flux and high strength should be developed in combination with actual industrial applications. Large and special-shaped components should be used to ensure good working condition applicability and long service life. The application of sintered metal powder porous components, equipment and system integration should be accelerated to improve the work efficiency of industrial production and stable long-term operation. At the same time, the performance evaluation of sintered metal powder porous components, industrial backflush effect optimization and industrial test development of cleaning and regeneration should be done well to ensure the reuse and long-life stable operation of metal powder porous components within the design service life. In addition, the application and development of sintered metal powder porous materials in the fields of oil-containing medium filtration technology, other powder fluidized transportation, automotive parts, sound absorbing materials, etc. should be continuously explored.
