Development of Adhesive Technology and Overview of Its Industrial Applications in the Adhesive Industry

In addition to its advantages of simplicity, speed, efficiency, and low cost, adhesive bonding technology can also join materials or structures that cannot be connected by other methods—for instance, it enables the bonding of metals to nonmetals and overcomes challenges such as the tendency for cast iron and aluminum to crack during welding, as well as the inability of aluminum to weld with cast iron or steel. Moreover, in certain applications, adhesive bonding can effectively replace welding, riveting, threaded connections, and other mechanical joining techniques. Today, the use of adhesives has permeated every sector of the national economy, becoming an indispensable technology in industrial production. Adhesive bonding is also widely employed in high-tech fields; for example, according to reports, foreign manufacturers use between 5 and 10 kilograms of adhesive in the production of a single automobile; the bonded surface area on a Boeing aircraft reaches 2,400 square meters; and a spacecraft requires the bonding of 30,000 ceramic tiles.

         Classification of Adhesives and Development of Adhesive Technologies
         At the beginning of this century, the successful development of various synthetic resins and synthetic rubbers—particularly the production and commercialization of several representative polymers such as phenolic resin, urea-formaldehyde resin, unsaturated resin, epoxy resin, and chloroprene rubber—spurred the rapid advancement of modern adhesives and adhesive technologies. Since the 1980s, significant progress has been made in adhesive and bonding technologies, with new adhesives boasting outstanding performance continuously emerging. Moreover, thanks to unique adhesive techniques, these adhesives have demonstrated extraordinary versatility and the ability to achieve multiple objectives. As a result, their applications have become even more widespread. There are many methods for classifying adhesives, and no single classification system has yet been universally adopted. Commonly used classifications include:

         1) Classification by Chemical Composition: This is a relatively scientific classification method that divides adhesives into organic adhesives and inorganic adhesives. Organic adhesives, in turn, are further divided into synthetic adhesives and natural adhesives. Synthetic adhesives include resin-based, rubber-based, and composite types; natural adhesives encompass those derived from animals, plants, minerals, and natural rubber. Inorganic adhesives, based on their chemical composition, can be categorized into various types such as phosphates, silicates, sulfates, and borates.

         2) Classified by form: Adhesives can be divided into liquid adhesives and solid adhesives. They include solution-type, emulsion-type, paste-like, adhesive films, adhesive tapes, powders, adhesive granules, and glue sticks, among others.

         3) Classification by application: This can be divided into three major categories: structural adhesives, non-structural adhesives, and special-purpose adhesives (such as high-temperature resistant, ultra-low-temperature resistant, conductive, thermally conductive, magnetically conductive, sealing, and underwater adhesives).

         4) Classified by application method: There are adhesives such as room-temperature curing types, thermosetting types, hot-melt types, pressure-sensitive types, and rewettable types. To meet the demands of industrial and agricultural production, as well as social life, countries around the world have invested heavily in developing a wide variety of adhesive products. As a result, the field has seen rapid progress, with the emergence of adhesives boasting distinctive features such as fast curing, single-component formulations, high strength, high-temperature resistance, solvent-free properties, low viscosity, non-polluting characteristics, energy efficiency, and multi-functionality. In the area of synthetic adhesives, molecular design is employed to develop high-performance adhesives; techniques such as grafting, copolymerization, blending, and interpenetrating polymer networks (IPN) are utilized to enhance adhesive performance. Significant advances have also been made in the study of adhesive mechanisms, and new developments have occurred in adhesive application equipment and tools. For example, bonding methods combining adhesives with mechanical fastening, as well as the integration of adhesive technology with electroplating techniques, have given rise to novel composite repair technologies. Since the 1980s, China’s adhesive and bonding technology has also developed rapidly, with an increasing variety of products, growing production volumes, and greatly improved quality. The quality and performance of many Chinese adhesives have reached or even surpassed those of similar advanced products worldwide. Here, taking TianGong’s “Super Metal” repair agent as an example, we can gain insight into the development of China’s adhesives and bonding technology from one particular perspective. TianGong’s “Super Metal” repair agent is a two-component composite material composed of high-molecular polymers, metal powders, ceramic powders, fibers, and a curing agent; it is also referred to as a “high-molecular alloy.” It exhibits outstanding physical and mechanical properties, wear resistance, and corrosion resistance, and its overall performance is now comparable to that of similar foreign products. The product line includes nine series—26 different repair agents—covering general-purpose, wear-resistant, friction-reducing, corrosion-resistant, fast-curing, wet-surface repair, high-strength, and conductive types, enabling it to meet diverse bonding and repair requirements under various conditions.

         Applications and Effects of TianGong “Supermetal” Repair Agent
         1) Application in Equipment Maintenance: When equipment parts experience wear, fracture, corrosion, scratches, or breakage, or when tanks, water tanks, pipelines, and other components leak oil, water, or gas, bonding technology can generally be used for repair. For example, the TG103 steel repair compound was used to repair a 1,000-ton rapid forging press imported from Germany by Beijing Shougang Steel; the TG301 friction-reducing repair compound was employed by the Tianjin Waterway Administration to restore hydraulic cylinders of a 215 dredger imported from Japan; the TG801 high-strength structural adhesive was used to repair bearing bores in tank transmission systems; and the TG406 and TG416 corrosion-resistant repair compounds were successfully applied to repair reaction vessels in chemical equipment—all achieving excellent results and earning high praise from users. In Wuhan City, we carried out bonded repairs on core components of a second-hand 1,800-ton hydraulic press imported from Germany, including the main piston (diameter Φ879 mm, length 3,130 mm), which suffered severe wear (average unilateral wear reaching 1.5–2 mm), as well as the guide sleeve (diameter Φ875 mm, length 500 mm) and the pressure sleeve (diameter Φ876.5 mm, length 210 mm). The repair cost was only 1/20 to 1/25 of that of a new part, and the repair process took just a few days, thereby saving valuable time and enabling an earlier resumption of production. For sealing and leak-stopping in oil and gas storage tanks, chemical equipment, and for repairing cracks in aluminum alloy, cast iron housings, plastics, and fiberglass parts—areas where traditional methods such as welding, riveting, brush plating, and thermal spraying prove difficult to address—we have achieved satisfactory results using Tiangong’s “Supermetal” repair compounds. For instance, we successfully repaired cracked crankcase housings of armored vehicle engines, cracks in aluminum alloy gearboxes, and leaks in oil pipes, fuel tanks, water pipes, and radiators. We also successfully addressed severe leaks around the heating equipment near the Central Television Tower and a perforation leak in the pump pipeline of a 4GC boiler at a certain factory, using the fast-setting repair compounds TG518 and TG528 for bonding and sealing.

         2) Repairing Defective New Parts and Applying Protective Coatings to New Parts: Cast iron, cast aluminum, and cast copper parts often exhibit casting defects such as porosity and sand holes, leading to scrap rates ranging from 10% to 30%, and in some cases even up to 50%. To salvage parts with casting defects, TG101 and YG111 iron-based repair compounds can be used to mend large defects in cast iron and cast steel components. For minor porosity and sand holes, the TG102 iron-based repair compound is ideal for filling these imperfections. For defects in aluminum castings, the TG104 aluminum-based repair compound is typically employed; for copper castings, the TG105 copper-based repair compound is recommended. Many factories have adopted this adhesive repair technology, successfully reviving numerous defective castings and achieving significant economic benefits. Additionally, TG406 and TG416 corrosion-resistant repair compounds are used to pre-coat vulnerable components of hovercrafts with a protective layer, thereby safeguarding these parts and extending their service life.

         3) In conventional machining, it is often difficult to meet requirements such as the stirring magnetic ring used in graphite emulsion pumps. This ring-shaped component is composed of numerous magnetic steel segments arranged in an alternating pattern of N and S poles, achieving extremely high precision. Since the magnetic steel segments cannot be magnetized once assembled, each segment must be magnetized individually. Moreover, after magnetization and assembly, the components should not undergo excessive machining; otherwise, their magnetic properties would significantly degrade. The magnetic steel has high hardness and is challenging to machine using conventional mechanical methods. By combining mechanical machining with bonding techniques, we were able to successfully address this issue and smoothly produce stirring magnetic rings that meet the required technical specifications.

         4) Expanding the scope of repair: By combining adhesive bonding with other technologies, we can leverage the strengths of each technique while compensating for their weaknesses, thereby fully harnessing the unique advantages of various methods and broadening the range of repairs. For example, in cases of deep scratches on large hydraulic cylinder liners or pistons, we can first use the TG205 wear-resistant repair compound to fill the damage, then apply the TG918 conductive repair compound as a base coat, and finally use electro-brushing to deposit a metallic layer onto the conductive repair compound. This combination of adhesive bonding and electro-brushing enables rapid filling of scratches while preserving the original metallic appearance. When adhesive bonding is combined with mechanical reinforcement, spot welding, glass fiber cloth reinforcement, and other measures, it can be effectively used for leak-sealing operations under both temperature and pressure conditions. For instance, an aluminum alloy gearbox of a U.S.-imported combine harvester in Jiamusi was accidentally cracked. We reinforced it with steel plates and repaired it using a combination of bonding and mechanical reinforcement, achieving highly satisfactory results. Similarly, when a rolling mill roll at Wuhan Iron and Steel Company fractured, we successfully repaired it by integrating bonding, mechanical reinforcement, and spot welding techniques. The application of adhesive bonding repair technology has yielded numerous successful experiences in the maintenance of large-scale equipment and in the repair of defects in new products, bringing about substantial economic benefits and earning high praise and recognition from users. Take, for example, the severe galling at the mating surface between the shaft and bearing of a large fan at the Fangshan Cement Plant in Beijing. We disassembled the bearing on-site and repaired it within just one day, significantly reducing downtime and saving the plant from substantial economic losses. Another example is the rotor in the Roots blower of an ozone generator at the Beijing Tap Water Construction Plant, where unilateral wear had reached 1 mm, severely affecting the blower’s pressure performance. By directly applying and curing the TG205 wear-resistant repair compound, followed by mechanical machining, we managed to repair all three rotors in just two days at a cost of only several hundred yuan, achieving remarkable economic benefits. The above examples of repairs using TianGong “Supermetal” repair compounds clearly demonstrate that adhesive bonding technology offers significant advantages in industrial equipment maintenance and new product defect repair—such as time savings, labor efficiency, energy conservation, material savings, and cost reduction. With its tremendous potential for development, this technology will undoubtedly play an increasingly important role in the construction of various sectors of China’s national economy.