The most important sector for the application of adhesive bonding technology is the aerospace industry. Because the structure of the aircraft adopts the bonding process, it has obviously received a series of good effects such as reducing structural quality, improving fatigue life and simplifying the process. Therefore, many countries have adopted bonding technology as a new process for aircraft manufacturing. Synthetic adhesives were used in the aircraft manufacturing industry around the 1940s, and on almost all modern aircraft, there is almost no bonding process. Some aircraft, bonding has become the basis of the entire aircraft design. In the B-58 heavy-duty supersonic bomber, the bonded wall panels accounted for 85% of the total area of the machine, of which the honeycomb sandwich structure accounted for 90%. Each aircraft uses more than 400kg of glue, which can replace about 500,000 rivets. Each Boeing 747 jet airliner uses 2,500 m2 of film and 450 kg of sealant. Adhesives commonly used in the aviation industry are phenolic-acetal, phenolic-butyronitrile, phenolic-epoxy adhesives, and the like. The second generation of acrylate adhesives have been used extensively in aircraft manufacturing, such as aircraft luggage compartments, doors, computers, and the bonding of electronic components and audio equipment.
 




There are many special optoelectronic components on the spacecraft, which are very demanding and need to meet the requirements of various environments. High temperature resistance and low temperature resistance, so it is necessary to use polyimide, polybenzimidazole, polyquinoline, polyurethane, inorganic and other adhesives. For the sealing of the cockpit and instrument cabin in aerospace, in addition to being able to withstand high and low temperatures, it is also required to be non-volatile under ultra-vacuum and resistant to strong ion radiation, so a silicone sealant should be used.


In the aerospace industry, thousands of solar cells on artificial satellites are all fixed with adhesive. The command cabin on the Apollo spacecraft, the titanium alloy honeycomb sandwich structure of the lunar module is bonded with a high temperature resistant epoxy-phenolic adhesive. Adhesives such as polysulfide rubber, polyurethane glue and polybutadiene are used in the Apollo spacecraft Shanghai. When the satellite and the spacecraft fly over or return to the atmosphere, the surface of the high-temperature ablation material and the container are fixed, the rocket liquid fuel, the -253 ° C insulation material and the container are fixed, and the high-temperature adhesive and ultra-low temperature adhesive are necessary. An important material that is indispensable.
  
Various lightweight metal alloy materials and advanced composite materials are the main materials used in aerospace and aerospace vehicles. In addition, there are many other materials with a wide variety of products, their performances are different, and the difference is very different. The structure composed of these different materials Pieces, the connection between them often can not use the traditional connection method, but only the bonding process.
 


 
Bonding materials used in spacecraft such as rockets, missiles, and satellites, in addition to meeting the performance requirements of general industrial adhesives, need to meet their performance in launch, in orbit, and re-entry into the atmosphere. Various special environmental requirements. According to the different parts of the adhesive, the requirements are different, and there are special requirements in the following aspects:


(1) The environmental characteristics of the missile warhead when it re-enters the atmosphere are subjected to transient high enthalpy high heat flow and high stagnation pressure. According to the different range of the missile, the reentry speed of the warhead reaches ten to several tens of Mach, and the stagnation temperature reaches several thousand degrees Celsius. The adhesive used is required to have excellent ablation resistance at ultra high temperatures. When spacecraft such as satellites and manned spacecraft are in the human atmosphere, their reentry environment is characterized by high enthalpy, low heat flow, low stagnation pressure and time. Adhesives used in the corresponding parts must have superior ablation resistance and Thermal insulation properties.


(2) Satellites, spacecraft and other spacecraft operate in orbit with a range of ambient alternating temperatures of several hundred degrees Celsius (for example, spacecraft operating in geosynchronous orbits with an ambient alternating temperature of -157 to 120 °C) . Adhesives used in the relevant parts not only need to adapt to the harsh alternating temperature characteristics, but also must have high temperature resistant particles and electromagnetic wave radiation characteristics, and there are no or very few volatiles and condensable volatiles in a high vacuum environment. Released (eg volatile fraction <1%, condensable volatiles <0.1%) to avoid contamination of high precision optics and related parts on the spacecraft. For example, a cloud pattern appeared on the observation window of the Apollo spacecraft service cabin, which was caused by the condensation of volatiles released by the sealing material of the window structure.


(3) Adhesives used in liquid hydrogen and liquid oxygen engine systems must have excellent characteristics against ultra-low temperature (-253~-183 °C).






(4) There are many types of bonded materials used in spacecraft such as rocket missiles and satellites. There are many kinds of metal materials, as well as various inorganic materials, organic materials and composite materials, often bonding between different materials. Moreover, due to the special structure of the bonded part, it is required that the adhesive used and the material to be adhered have excellent matching characteristics and good process characteristics, and can be cured at room temperature or medium temperature, under various harsh environmental conditions, such as shipyard. The missile must have long-term resistance to seawater and salt spray erosion; the adhesive used in the gyro-stabilized platform system must have the characteristics of chlorofluorocarbon resistant under vacuum conditions.


(5) Composite solid rocket propellant refers to a high-energy solid propellant that is burned in a rocket engine by providing rockets with high-speed forward motion energy. It is an adhesive that bonds solid particles such as oxidant and metal fuel together. . A dense substance of a composite solid, in which the amount of the adhesive is about 10% to 20%, in addition to bonding the oxidant and the metal together to maintain a certain geometric shape, and providing a certain mechanical property to withstand the rocket in assembly, transportation, Storage, ignition, and large stresses and strains during flight are also fuels that generate gas and energy. Therefore, the adhesive used in the composite solid rocket propellant should have a low viscosity (usually several to several tens of Pa·s) in order to fully infiltrate the oxidant and the metal particles, and have good chemical compatibility with them, and can form a dense Propellant column; the reaction speed is appropriate when curing, no volatiles are generated, the heat release is small, the curing shrinkage is slight; the heat insulation layer on the inner wall of the solid rocket motor casing is tightly adhered; and the flammability and gas formation are also improved. .


As the adhesive used for this special purpose, most of them are polymer prepolymers and a curing agent is added. The adhesive used in the first composite solid rocket propellant was a polysulfide adhesive, for example, 98% (mole fraction) of dichloroethyl acetal and 2% (mole fraction) of dichloroacetone were reacted with sodium polysulfide. Polysulfide. The mechanical properties and bonding properties are good, the process is simple, but the sulfur content is large, the energy provided is not ideal, and the curing temperature is high, and the use is limited. In the 1960s, the terminal carboxylated butadiene was used, and the mechanical properties of the propellant as the adhesive were obviously improved. In order to meet the propellant requirements of large solid arrow and rocket engines, the terminal hydroxyl type adhesive was successfully developed. Such as terminal hydroxyl esters, hydroxyl terminated ethers, hydroxyl terminated ether triol polychlorides and the like.






(6) In the joint welding structure of rocket missiles and satellites, the main point is to use the post-spot welding process, which requires the curing temperature to be lower than 80 ° C, preferably room temperature, and the temperature used is -45~ 200 ° C, in order to meet the above requirements, a new type of addition molding silicone gel GH-522 was selected.


(7) During the orbital operation of the spacecraft, certain pressure must be maintained in the aircraft cabin to ensure the normal operation of various instruments. The orbital environment of the spacecraft is in a high vacuum, low temperature and large temperature difference high and low temperature alternating state, with many plug holes, aircraft cabins of various hatches, etc., requiring more sealing parts, and the area and length are not small. Simply use low-temperature resistant rubber and seal it in the usual static seal form, such as O-ring. When the temperature is lower than -67 °C, the slight leakage can not meet the working pressure requirements in the aircraft cabin, and the low temperature resistance is good. Silicone rubber is the main component, and epoxy resin modified adhesive is cured at room temperature and used in combination with the above O-ring. The sealing performance is good at the bottom temperature, even when the O-ring is damaged. Due to the action of the above-mentioned low temperature sealing adhesive, the sealing requirements of the aircraft cabin are still ensured.




[Conference recommended] 2019 China Polyurethane Adhesive Technology Development and Application Innovation Seminar
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