I. Introduction

The infiltration technique is to infiltrate the porous workpiece by the infiltration agent under pressure to achieve the purpose of filling the gap. The infiltration technology is a new technology developed by modern technology.

Infiltration technology is widely used in the sealing of casting defects, wood insect proof, anti-corrosion, flame retardant, powder metallurgy parts reinforcement, corrosion and sealing, anti-alkali or acid corrosion of cement products, moisture 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 water filled glass was used to fill the casting voids. In the 1950s and 1960s, with the development of the automobile industry, the industrialized countries such as the United States, the former West Germany, and the former Soviet Union promoted the development of the first generation of infiltration agent-sodium silicate type infiltration agent for the sealing of pressure-bearing castings. And application, and developed from a partial or atmospheric pressure infiltration process to a vacuum pressure infiltration process.

Since the 1970s, the emergence of the energy crisis has promoted the development of automobiles. Many cast iron parts have been replaced by light metals such as aluminum, magnesium and zinc and their alloy materials to reduce the weight of automobiles, reduce energy consumption and improve the performance of automobiles. However, light metal castings are prone to micropores, resulting in leakage of pressurized castings. At the same time, the widespread use of powder metallurgy sintered parts further saves material and machining costs. The problem of leakage of porous materials has been urgently solved, which has promoted the demand for infiltration technology. At the same time, the development of the chemical industry has promoted the research and development of infiltration agents. A wide variety of applications and a wide range of infiltration agents with excellent performance have emerged. The second generation of polyester infiltrant and anaerobic and thermosetting properties have been introduced. Acrylate type third generation infiltration agent. The infiltration method and the infiltration process have been continuously improved, and the infiltration equipment has been developed to a large scale and semi-automation, which has further promoted the wide application of the infiltration technology. The infiltration technology has been recognized by the military and cutting-edge technical departments of advanced industrial countries. The application of infiltration technology has promoted the thinning of many complex structural designs. At present, some foreign companies have used infiltration technology as a design method and an indispensable production process in the production of castings, and advocated infiltration of castings. The high infiltration efficiency and the significant economic effect of the infiltration treatment have led to the recognition of the value of this technology in industrial production.

Second, the application range of infiltration technology

1. Impregnation of castings

The main function of casting impregnation is to seal against leaks so that it can be used in hydraulic and gas systems. Examples include automotive and tractor gearboxes, fuel pumps, hydraulic valves, carburetor, cylinders, compressors and hydraulic components, closed aircraft instruments and their electronic instrument covers, pneumatic components and various pneumatic instruments.

Casting infiltration also prevents corrosion inside and increases production. It is well known that the internal corrosion of castings tends to start from the micropores. When the micropores are filled with the infiltrant, after they are cured, the infiltration of corrosive liquids can be prevented and the corrosion prevention effect can be prevented.

In addition, casting impregnation can also prepare for surface treatment such as electroplating, paint, etc. Since the infiltrant fills the voids in the casting, these voids are prevented from absorbing the plating solution, causing bubbles and a non-clean surface after plating.

Infiltration can be used as a remedial measure for defects such as looseness and micropores in castings and die-casting parts. It also promotes thinning and lighter design of casting products and saves material consumption.

2. Impregnation of powder metallurgy parts

Powder metallurgy materials have excellent properties, so bushings, valve guides, gears, cams, bushings, clutch friction plates, electric heating elements, heat exchangers, cutting tools, tooling and some corrosion-resistant, high-temperature oxidation resistance for automobiles and tractors. And high temperature resistant parts are currently widely used in the manufacture of powder metallurgy materials.

Powder metallurgy parts (hereinafter referred to as powder metallurgy parts) are made of metal powder (or a mixture of metal and non-metal powder), sintered by pressing and formed into various types of workpieces. The powder metallurgy is characterized by a large number of pore networks (about 15% of the entire workpiece volume) including small air gaps between the powder metal particles. Even if it is a high-density powder, the pores still exist. . Therefore, the powder metallurgy cannot store liquid. The impregnation treatment of the powder metallurgy can make the inner pores completely filled with the infiltrant to achieve a permanent seal, so that it can be used in a hydraulic system, for example, it can manufacture precision oil pump parts, compressor casings, etc. .

In addition, if the powder metallurgy is infiltrated prior to electroplating or other surface coating treatment, the plating solution and the cleaning agent will not be sucked into the pores to obtain a surface smooth and corrosion resistant workpiece.

It must be pointed out that the powder metallurgy should be impregnated immediately after sintering, since the pores are clean and easily filled by the infiltrant. The impregnated powder metallurgy can also improve the cutting processability (the tool will change from intermittent cutting to continuous cutting after the micropores are filled) to facilitate the control of the process.

3. Impregnation of electronic devices

Impregnation of electrical components such as transformers, capacitors and motors increases their dielectric and insulating properties. For example, the assembled assembly of the stator and the casing of the motor is impregnated to form a single unit. The micropores are sealed after impregnation, and a certain strength and heat dissipation effect are added, thereby solving the insulation performance of the motor due to vibration. At the same time, the impregnated motor can maintain good insulation performance under humid conditions, improving the reliability and service life of the motor.

4. Impregnation of non-metallic parts

Non-metallic materials, such as wood (sleepers, utility poles, etc.), ceramic and fiber-plastic composite materials, are impregnated to extend their service life and improve their water resistance. For example, the cooling system components of a mainframe computer are generally made of FRP reinforced plastic, and the impregnation allows it to be effectively sealed, thereby preventing leakage of liquid through the fine reinforcing fibers as a passage.

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.