An Overview of the Current Development Status of Adhesives for Metals

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This post was last edited by qhyhxjl on 2015-11-27 at 16:39. Metals are a type of structural material that is used extensively in various applications, and the methods used to join them include riveting, welding, brazing, and threaded connections. Due to the excellent bonding properties of synthetic adhesives for metal materials, metal adhesives were used as early as World War II. However, because of past doubts and concerns, along with the failure to develop adhesives with high strength, heat resistance, and good durability, metal adhesives have not been widely used in industrial applications. Today, adhesives for metals are gradually gaining widespread recognition. Since metal adhesives offer more effective results for repairing defects and damages in metal components, surpassing those of conventional metal processing methods, they are widely used. Additionally, bonding does not cause structural deformation or changes in the crystal structure due to high-temperature heating like welding; it also does not lead to stress concentration and reduced strength as result of drilling and threading in riveting and threaded connections; nor does it cause electrochemical corrosion due to contact with different metals as in brazing. 〔1) Structural bonding: Structural bonding is used for bonding objects that are subject to loads and stresses over extended periods of time; it serves to create materials that form a single integrated structure. For example, thermosetting resin-rubber hybrid adhesives are used to bond composite honeycomb structures in aircraft. (2) Resistance to high and low temperatures: Generally, adhesives can withstand temperatures below 150°C. Epoxy-phenolic adhesives can be used in the temperature range of 175–260°C; polyphthalamide can remain usable for 3000 hours at 227°C and still retain its toughness at 316°C, allowing it to bond stainless steel and titanium – it is thus used in the aerospace and electronics industries. However, it is inorganic adhesives that are truly resistant to high temperatures. For example, the one-component ceramic adhesive produced by Nippon Electric Chemical Corporation can withstand temperatures of up to 1300°C after being sintered and cured at 150°C. The most widely used adhesive for extreme low temperatures is polyurethane, which maintains high strength and toughness at -196°C; when appropriate modifiers are added to it, it can be used for structural bonding. Modified epoxies can also be used for bonding in ultra-low temperature applications; for example, the nylon-modified epoxy “Epon951” has a continuous operating temperature range of -251 to 149°C, and its tensile strength after 4 hours at low temperatures is 42.7 MPa. (3) Underwater bonding: Underwater bonding is a new process with great prospects. Most underwater adhesives are two-component epoxy resins, which require curing at temperatures above 15°C and take about half a day to do so. Underwater bonding also plays a significant role; for example, it can be used to attach listening devices or other components to enemy underwater vessels and warships, in order to create adhesive-time-delayed torpedoes. It can also be utilized for emergency repairs of damaged ships. (4) Instant curing: Instant adhesives based on cyanoacrylate have seen their scope of application expand continuously since their introduction in the late 1950s. Its main advantages are a fast bonding speed (measured in seconds), high bonding strength – the pulling force that can be withstood by 6.45 cm² of bonded material is sufficient to lift a small car (hence the saying \"a drop of glue has great lifting power\"); moreover, no heating or pressure is required during curing, nor is any external catalyst needed. This has played a significant role in promoting the development of continuous production lines. (5) Liquid sealing: Certain metal adhesives are liquid at room temperature; when applied to mechanical joints, they form an elastic film that serves as a substitute for conventional gaskets. Moreover, they offer better sealing performance, which is why they are known as liquid gaskets. Liquid sealants come in rubber-type, resin-type, and oil-modified types. It is widely used for sealing and bonding irregular mating surfaces such as automotive valve covers, oil pans, rear axle covers, and transmission covers. Tomorrow’s topic is the \"Future Development Trends\" of adhesives for metals.