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What are the applications of sealing adhesives in aerospace instruments (1)

Update:15-04-2022
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What are the applications of sealing adhesives in aeros […]

What are the applications of sealing adhesives in aerospace instruments (1)?

With the rapid development of my country's aerospace industry, in order to ensure the normal operation of the launch vehicle. Higher requirements are also placed on the precision and sensitivity of aerospace instrument components. Effectively preventing the running, running, dripping and leaking of aerospace instruments, preventing the leakage of internal media and the intrusion of external media are the most basic conditions to ensure the performance indicators of aerospace instruments such as high precision, high sensitivity and high reliability. .

According to the different requirements of use, aerospace instruments can have various structural forms. 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, screwing and other connection methods, and some Due to the requirements of miniaturization of the structure, it is not suitable to use a solid sealing ring, and a sealing adhesive must be used for the glued installation of the components. Because it is the most convenient, effective and reliable for these materials and structural parts to be glued and installed with liquid sealing adhesive.

1. Polysulfide rubber sealant

Polysulfide rubber sealant is a kind of sealing adhesive based on liquid polysulfide rubber. Polysulfide rubber is a rubber-like polysulfide vinyl resin. In fact it is somewhere between synthetic rubber and thermoplastic. It can be prepared by condensation reaction of ethylene dichloride and sodium tetrasulfide, and its 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 air permeability and excellent low temperature flexibility.

Polysulfide rubber is generally dark amber or dark brown viscous liquid with an average molecular weight between 1000 and 5000. With an average molecular weight of 1000, it is mainly used as a toughening modifier for epoxy resins and phenolic resins. The average molecular weight of 4000 is usually used alone as a base for polysulfide sealants. The molecular chain of liquid polysulfide rubber has active reactive group thiol group, which can react with various metal peroxides, organic peroxides and some oxidants. When adding a metal peroxide curing agent, it can be cured into an elastomer at high temperature, normal temperature, low temperature and oil medium. At present, the most widely used and most used are lead dioxide and active manganese dioxide, and the reaction formula is as follows:
HS—R—SH + PbO2 —→ (RSS)n + PbO + H20
HSR—R—SH + PbO —→ (RSPbSR) + H20
—RSPBSR— + Pb02 —→ (RSS)n + PbO + H20

Because cured polysulfide rubber is oil and elastomer resistant, we use it as a sealant for the angular velocimeter stator seat assembly. The external structure of the angular velocity meter stator seat is: the material of the stator seat is stainless steel, the surface is gold-plated, and the surface is composed of glass insulators, oil-filled nozzles, resistance elements, tuning screws, etc., and the internal medium is silicone oil. In order to prevent the internal liquid from leaking out, the adhesive is required to have the characteristics of resistance to silicone oil, shock resistance, shock absorption, etc. It is more appropriate to use polysulfide sealant for glue installation.

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