This paper describes the source, development, application range and processing method of infiltration technology, introduces the development status and level of infiltration equipment, inorganic infiltration agent and organic resin infiltration agent, and finally explains the application effect and economic benefit of infiltration technology.

1、 Preface

Infiltration technology is a new technology developed by modern science and technology, which uses the infiltrating agent to infiltrate the porous workpiece under pressure and solidify to fill the gap.

Infiltration technology is widely used for sealing casting defects, insect prevention, corrosion prevention and flame retardancy of wood, reinforcement, corrosion prevention and sealing of powder metallurgy parts, alkali or acid corrosion prevention of cement products, moisture prevention and insulation of electrical and electronic components.

The application of modern industrial infiltration technology can be traced back to the casting plugging process in the 1930s, when the casting gap was filled with water glass circularly. 5、 In the 1960s, with the development of the automobile industry, the United States, the former West Germany, the former Soviet Union and other industrial developed countries promoted the development and application of the first generation of sodium silicate type penetrant for the sealing of pressure bearing castings, and developed from local or atmospheric pressure infiltration to vacuum pressure infiltration.

Since the 1970s, the emergence of the energy crisis has promoted the development of light-weight automobiles. Many cast iron parts have been replaced by light metals such as aluminum, magnesium, zinc and their alloys, reducing the weight of automobiles, reducing energy consumption and improving the performance of automobiles. However, light metal castings are easy to produce micropores, leading to leakage of pressure castings. At the same time, the extensive application of powder metallurgy sintered parts further saves the cost of materials and machining. The leakage problem of porous materials needs to be solved urgently, which promotes the demand for infiltration technology. At the same time, the development of chemical industry has also promoted the research and development of infiltration agents. There are many kinds of infiltration agents with wide applications and excellent performance, and polyester type second generation infiltration agents and anaerobic and thermosetting acrylate type third generation infiltration agents have been introduced successively. The infiltration method and process have been continuously improved. The development of large-scale and semi-automatic infiltration equipment has further promoted the extensive application of infiltration technology. The infiltration technology has been recognized by the military industry and cutting-edge technology departments in advanced industrial countries. The application of infiltration technology promotes the thin-wall design of many complex structures. At present, some foreign enterprises have taken infiltration technology as a design means and an indispensable production process in casting production, and advocate full infiltration treatment of castings. The high infiltration efficiency and remarkable economic effect of infiltration treatment have made people realize the value of vigorously promoting this technology in industrial production.

2、 Application scope of infiltration technology

1. Impregnation of castings

The main effect of casting infiltration is to seal and prevent leakage, so that it can be used in hydraulic system and gas system. For example, automobile and tractor gearboxes, fuel pumps, hydraulic valves, carburetors, oil cylinders, compressors and hydraulic components, enclosed aircraft instruments and their electronic instrument shields, pneumatic parts and various pneumatic instruments.

Infiltration of castings can also prevent internal corrosion and increase production. As we all know, the internal corrosion of castings often starts from the micropores. When the micropores are filled with impregnating agent, they can be cured to prevent the immersion of corrosive liquid and play a role in corrosion prevention.

In addition, casting impregnation can also prepare for surface treatment such as electroplating and painting. As the impregnating agent fills the gaps in the casting, these gaps can avoid absorbing the electroplating solution, resulting in bubbles and uneven surfaces after plating.

Infiltration can be used as a remedy for the defects such as porosity and microporosity that often exist in castings and die castings. It also promotes the thin wall and light weight of casting product design and saves material consumption.

2. Infiltration of powder metallurgy parts

Powder metallurgy materials have excellent performance, so the lining kits, valve guides, gears, cams, bearing shells, clutch friction plates, electric heating elements, heat exchangers, cutting tools, tools and dies used in automobiles and tractors, as well as some corrosion-resistant, high-temperature oxidation resistant and high-temperature resistant parts, are now widely made of powder metallurgy materials.

Powder metallurgy parts (hereinafter referred to as powder metallurgy parts) are made of metal powder (or mixture of metal and non-metallic powder) as raw materials, pressed into shape and sintered into various types of workpieces. The feature of powder metallurgy parts is that there are many pore networks (about 15% of the volume of the whole work piece) inside, including small air gaps between powder metal particles. Even for high-density powder metallurgy parts, such pores still exist. Therefore, the powder metallurgy parts cannot preserve the liquid. The infiltration treatment of powder metallurgy parts can make the internal pores completely filled by the infiltration agent to achieve permanent sealing, so that it can be used in the hydraulic system, for example, it can be used to manufacture precision oil pump coupling parts, compressor shells, etc.

In addition, if the powder metallurgy parts are subject to infiltration treatment before electroplating or other surface coating treatment, the electroplating solution and cleaning agent will not be sucked into the pores, and the workpieces with smooth surface and corrosion resistance can be obtained.

It must be pointed out that the powder metallurgy parts should be impregnated immediately after sintering, because the pores are clean at this time and are easy to be completely filled by the impregnating agent. The infiltrated powder metallurgy part can also improve its cutting performance (the tool will change from intermittent cutting to continuous cutting after the micropore is filled), which is convenient for the control of the process.

3. Infiltration of electronic devices

Infiltration of electrical components such as transformers, capacitors and motors can increase their dielectric and insulation properties. For example, the assembled components of the motor stator and housing are immersed to form a single whole, and the micropores can be sealed after infiltration, and a certain degree of strength and heat dissipation effect can be increased, which solves the problem of motor insulation performance reduction due to vibration. At the same time, the immersed motor can still maintain good insulation performance in a humid environment, and improve the reliability and service life of the motor.

4. Infiltration of non-metallic parts

Non metallic materials, such as wood (sleeper, electric pole, etc.), ceramic and fiber plastic composite materials, can be used with infiltration treatment to extend their service life and improve their water resistance. For example, the cooling system parts of a large computer are generally made of FRP reinforced plastics. Infiltration can effectively seal them, thus preventing liquid leakage through the channel of fine reinforced fibers.

It can be seen from the above that the infiltration technology has a wide range of applications in the sealing of electromechanical products and porous materials.

3、 Infiltration method

Different infiltration methods can be selected according to the nature and distribution of workpiece defects, working conditions, structural dimensions and types of impregnating agents.

At present, for the overall infiltration, the most common and effective methods are vacuum pressure infiltration, Japan's Sanjian Company and Praserram Company are all engaged in the research and development of infiltration technology, supplying infiltration equipment and series of infiltration agents to countries around the world, and providing infiltration technology services. Leaching agent of Loctite meets MIL-SCD27680 and MIL-1-17563B standards of military industry. In Japan, this technology is widely used for pressure parts in various industries, and several major automobile companies in Japan take casting infiltration as an indispensable process in engine production. For example, R.S.T Company of Japan, which provides aluminum castings for engines to dozens of automobile companies, has reduced the scrap rate of aluminum castings from 16% to 3% due to the use of infiltration technology, thus reducing the loss of factories by about 70 million yen each month. The British RONCERAY company processes about 40000 tons of castings every year by infiltration method, and the American GE company manufactures insulation motor by vacuum pressure infiltration method, which has achieved huge economic benefits. In China, infiltration technology has been applied in hundreds of factories, and considerable economic and social benefits have been achieved.

Conclusion:

⑴ The production practice of infiltration technology has proved that it has certain practical significance and broad prospects in the national economy. The technology adopts vacuum pressurization process, which is feasible, reliable and ideal. It is a new technology to solve the pressure bearing sealing of castings.

⑵ Litai infiltration equipment is a relatively complete equipment in China at present, which can meet the requirements of infiltration process. In terms of performance and functions, it has reached the domestic and international advanced level.

⑶ Organic impregnating agent Litai T90 is the latest formulation and development achievement in the world, and is widely used in the domestic market.

⑸ This technology should continue to expand its application scope and create greater economic and social benefits.