With the rapid development of China's aerospace industry, in order to ensure the normal operation of carrier rockets. It also puts forward higher requirements for the accuracy and sensitivity of aerospace instrument components. Effectively preventing the escape, emission, dripping and leakage of aerospace instruments, preventing the leakage of internal media and the invasion of external media are the basic conditions to ensure the high precision, high sensitivity, high reliability and other performance indicators of aerospace instruments.

Aerospace instruments can have a variety of structural forms according to different use requirements. In some parts, due to the use of special materials such as aluminum alloy, stainless steel, engineering plastics and quartz glass, it is not suitable to use welding, riveting, screw connection and other connection methods, and some structural miniaturization requirements, and it is not suitable to use solid sealing rings. Sealing adhesives must be used for the bonding and installation of parts and components. Because it is the most convenient, effective and reliable to use liquid sealing adhesive for the bonding and installation of these materials and structural components.

1、 Polysulfide rubber sealant

Polysulfide rubber sealant is a kind of sealing adhesive based on liquid polysulfide rubber. Polysulfide rubber is a polysulfide vinyl resin similar to rubber. In fact, it is a substance between synthetic rubber and thermoplastic. It can be prepared by condensation reaction between dichloroethane and sodium tetrasulfide. The reaction is as follows:

nClCH2—CH2Cl + nNaS4Na —→ [CH2—CH2—S4]—2nNaCl

The molecular chain of polysulfide rubber is saturated and contains sulfur atoms, so it has good oil resistance, solvent resistance, aging resistance, impact resistance, low permeability and excellent low-temperature flexibility.

Polysulfide rubber is generally a dark amber or dark brown viscous liquid with an average molecular weight of 1000 ~ 5000. With an average molecular weight of 1000, it is mainly used as a toughening modifier for epoxy resin and phenolic resin. With an average molecular weight of 4000, it is usually used as the base material of polysulfide sealant alone. The molecular chain of liquid polysulfide rubber has an active reaction group mercaptan group, which can react with a variety of metal peroxides, organic peroxides and some oxidants. When metal peroxide curing agent is added, it can be cured into elastomer in heating, normal temperature, low temperature and oil medium. At present, lead dioxide and active manganese dioxide are the most widely used, and their reaction formulas are as follows:

HS—R—SH + PbO2 —→ (RSS)n + PbO + H20

HSR—R—SH + PbO —→ (RSPbSR) + H20

—RSPBSR— + Pb02 —→ (RSS)n + PbO + H20

Because the cured polysulfide rubber has the characteristics of oil resistance and elastomer, we use it as the sealing adhesive for the stator base assembly of the angular velocimeter. The external structure of the angular velocimeter stator base is: the material of the stator base is stainless steel, the surface is gold-plated, and it is composed of glass insulator, oil filling nozzle, resistance element, tuning screw, etc. the internal medium is silicone oil. In order to prevent the internal liquid from leaking outward, the adhesive is required to have the characteristics of silicone oil resistance, shock resistance, shock absorption, etc. it is more appropriate to use polysulfide sealant for bonding.

2、 Polyurethane sealing adhesive

Polyurethane sealant is a kind of elastic sealing adhesive based on polyurethane rubber. Polyurethane rubber is a kind of special rubber, which is actually a kind of polymer compound between general rubber and plastic.

Polyurethane elastic sealant is characterized by high surface hardness, elasticity, and excellent cold and oil resistance. Its bonding strength at low temperature is even higher than that at room temperature. If the composition and proportion of raw materials are changed, it can obtain excellent elastomers with a wide range of shore hardness of 20 ~ 80, elastic modulus of 50 ~ 6000kg/cm and tensile strength of 50 ~ 80kg / cm. At present, there is no more suitable elastomer to replace such excellent performance.

3、 Silicone rubber elastic sealant

The matrix of silicone rubber type elastic hanging sealant is high molecular weight linear polysiloxane. Its molecular primary key is composed of silicon and oxygen atoms alternately

Because the bond energy of silicon oxygen bond is much higher than that of carbon carbon bond of other polymer molecules, it has high heat resistance and cold resistance, and can maintain good elasticity in the temperature range of -65 ℃ ~ 250 ℃. In addition, it does not contain double bonds on its molecular side bonds, so it has excellent aging resistance and is very stable to UV and ozone. After ten years of atmospheric aging and three years of artificial accelerated aging, it still won't crack, brittle and peel off.

4、 Anaerobic sealing adhesive (hereinafter referred to as anaerobic adhesive)

The matrix of anaerobic adhesive is thermosetting resin, which is mostly of acrylate type at present. The outstanding performance of anaerobic adhesive is pressure resistance and vibration resistance. It is used in the joint of the hydraulic system and can withstand a high pressure of 300kg/cm2. Spring washers and other fastening seals can be saved for some joint parts that bear various external forces for a long time. And it has better fastening effect than spring washer. In addition, anaerobic adhesive also has the advantages of one component, solvent-free, room temperature curing and low viscosity.

The sealing effect of anaerobic adhesive mainly depends on its curing and crosslinking under the isolation of oxygen. At present, the substrate of anaerobic adhesive mostly belongs to acrylate type. Its matrix is mainly methacrylic acid diester or acrylic acid diester and their derivatives.

Anaerobic adhesive has been widely used in instrument industry, machinery industry and automobile industry at present, which has better solved the technical problem of three leakage (water leakage, oil leakage and air leakage) of products. It plays an important role in product decoration, quality assurance, energy conservation, cost reduction and economic efficiency improvement.

5、 Epoxy resin sealing adhesive

Liquid sealant using epoxy resin as sealant base material has been widely used in various production fields, because epoxy resin has the following unique advantages:

1. Strong adhesion: polar groups such as aliphatic hydroxyl and ether chains in the molecular structure of epoxy resin generate electromagnetic attraction between the epoxy resin and the adjacent interface. The epoxy group can react with metals containing active hydrogen to form chemical bonds, so it has good adhesion to metals, glass, plastics, ceramics and other materials.

2. Small shrinkage: it has no by-products during the curing process and will not produce bubbles. For the cured product of pure resin, its shrinkage is less than 2%, and can be reduced to about 1% after adding filler.

3. Good stability: it can be stored for a long time without deterioration

4. Good medium resistance: it can withstand general acid and alkali and organic solvents

5. Low creep: it will not deform or deform very little under long-term stress

6. Good processability: select different curing agents and add other resins, rubber and fillers to achieve modification, which can cure the epoxy resin at room temperature or low temperature, and also can cure quickly.

There are many kinds of epoxy resins, and there are no less than dozens of kinds of curing agents. As the preparation of sealing adhesive, it is generally made of low molecular weight bisphenol A epoxy resin plus toughening agent and curing agent that can cure at medium or room temperature.