How to choose the correct adhesive should be considered: 1. the kinds and properties of adhesive material by many kinds of adhesive material of different properties, only the general know metal, rubber and plastic, fabric is not enough to describe the specific varieties of materials, and the best object each kind of adhesive with limitations. Therefore, the better understanding of the stickies, the more appropriate the choice of adhesives, the better the effect of bonding. The surface and density of metal and its alloy are high, and the strength is high. It is suitable to use modified phenolic resin, modified epoxy resin, polyurethane rubber and acrylic structural adhesive. Because metals are easy to be corroded, it is not possible to bond the copper and its alloys with the epoxy resin adhesive solidified by fat and Zhong Anlei (ethylenediamine, three diamine, etc.). Nor can we use high acid adhesive to stick metal. Rubber or rubber adhesive with other materials should be used as rubber adhesive or rubber modified ductile adhesive. Plastics are divided into two categories: thermoplastic and thermosetting, some of which can be bonded with solvents, hot melt adhesives and adhesives. Thermosetting plastics can only be bonded with the same adhesive as metal. Polyethylene, polypropylene, polytetrafluoroethylene and other refractory plastics, without special surface treatment, can not be bonded with general adhesives. For small sticky materials, such as glass and ceramics, no matter whether they are bonded to the sticky material (such as glass and aluminum plate) with very different linear expansion coefficients, they should be selected with good elasticity and room temperature curing adhesives. If the two surfaces are not tightly contacted or the gap is large, the adhesive with larger adhesive strength or filler should be selected instead of 502 glue and anaerobic adhesive. A large area of adhesive can not be used for quick curing at room temperature. For poor heat resistance or heat sensitive adhesive, room temperature curing adhesive should be selected. For wood, paper, fabric and other porous adherend, should use water-based or emulsion adhesive, such as emulsion, urea formaldehyde resin adhesive. If a metal or thin adhesive is bonded to a low modulus of elasticity, a good toughness adhesive should be selected to adapt to the larger denaturation and reduce the stress concentration. It must be pointed out that there are many kinds of adhesive materials, and the types of adhesives are quite a few. The formulation of adhesives is constantly changing. New materials and new adhesives are being introduced. We should grasp the basic knowledge of bonding technology, analyze it according to the actual situation, and select the appropriate adhesive. One component adhesive
2. adhesive performance considerations: various types of adhesives, different formulations, efficacy is different, including the status, application period, viscosity, curing conditions and bonding process, the bonding strength, temperature, shrinkage, coefficient of linear expansion, corrosion resistance, water resistance, oil resistance, solvent resistance and aging resistance. These are all factors must be considered when choosing adhesive. Bonding strength is the first consideration. It is an important basis for selecting adhesives, but it cannot be separated from the actual work condition. If blindly emphasized, it is also inappropriate. In addition, we should consider the curing conditions, temperature and medium resistance of the adhesive, including water, hot water, acid, alkali, gasoline, lubricating oil, fuel oil, alcohol, salt, ketone, ester, aromatics, solvent, and aging resistance. 3. should be considered objective: with the use of adhesive bonding, both connection and sealing, fixed, positioning, repairing, filling, sealing, sealing, corrosion, perfusion, varnish and meet some special requirements and other effects. In fact, in the use of adhesives, often a certain aspect of the use of the dominant position, so the specific conditions should be selected to select the adhesive. For example, for connection, will use a high adhesive strength adhesive; for sealing, it is necessary to choose a sealing adhesive; used for filling, perfusion, sealing, it is necessary to choose a high viscosity, adding more filler and room temperature curing adhesives; used for fixing and positioning, assembly and repair, it is necessary to choose a room temperature fast curing adhesive; for clear, it is necessary to choose a low viscosity, a colorless and transparent adhesive. For large area bonding or large-scale production, the curing speed of the adhesive can not be too fast, otherwise one side in the construction, one side has been solidified. For large equipment and heat sensitive components, high temperature curing adhesive can not be used. The conductive adhesives of the radio industry should be used as conductive adhesives. Because of the specific purpose and use of bonding, it is impossible to give an example. In a word, different types of adhesives should be selected according to the different purposes and uses of bonding.
4., the stress condition of the bonding part should be considered. The bonding part will be subjected to some external force when it is in use, which can be generally divided into four types: stretching, shearing, tearing, stripping and so on. The force of the adhesive must not only consider the type of the force, but also the size, direction, frequency and time of the force. The tensile, shear and compressive strength of adhesive bearing load are higher, bending resistance, impact resistance, tearing strength are low, and peeling strength is lower. The strength properties of different adhesives are also different. For example, the peel strength of neoprene adhesive is high, and the adhesive layer of epoxy adhesive will be destroyed once it is stripped. Although strength performance is an important basis for selecting adhesives, the force of the adhesive is often multifaceted, and it must be considered comprehensively. Adhesives with little stress can be selected as general adhesives. The structural adhesives should be selected for larger force, and thermosetting adhesives should be selected for long term stress to prevent creep failure. Rigid adhesives, such as epoxy adhesives, can be used for adhesive parts with low or static load. For the high frequency of the force or the impact load, we should choose the ductile adhesive, such as the phenolic - NBR adhesive or the modified epoxy adhesive. For structural bonding stress is complex, to choose the better performance of comprehensive strength and elastic body composed of a thermosetting resin adhesive, such as nitrile adhesive ring.
5., we should consider the environment of the bonding parts: the environment of the bonding parts, usually including temperature, humidity, medium, vacuum, radiation and outdoor aging. For high temperature bonding parts, high temperature resistant and heat ageing resistant adhesives, such as organic silicone adhesives, polyimide adhesives, phenolic epoxy adhesives or inorganic adhesives, should be selected. For the adhesive parts used at low temperature, to avoid the brittle cracking of the adhesive to avoid the difference between the expansion coefficient of the adhesive and the sticky material, cold resistant adhesives or ultra-low temperature adhesives, such as polyurethane adhesives or epoxy nylon adhesives, should be selected. If the bonding parts work under the condition of cold and heat change, the adhesive should have good high and low temperature performance. Silicone rubber adhesive, epoxy phenolic adhesive and polyimide adhesive should be selected. Humidity has a great influence on adhesive strength of adhesives. If moisture is too large, moisture will penetrate into the adhesive interface, resulting in a significant decrease in adhesive strength, especially in the presence of damp heat. Therefore, the adhesives that work in water or wet environment should be used as adhesives with good resistance to water and moisture and heat aging. For example, phenolic - butadiene nitrile adhesive. Although adhesives are generally resistant to some media, the kinds and degrees of different adhesives are different. The adhesive that is able to withstand all kinds of media does not exist. It is usually based on the working medium of the adhesive to choose the adhesive that can resist the medium.
6. the possibility of the process should be considered: the variety of the adhesive is different, and the bonding process is different. Some of them are cured at room temperature, some need heating and curing, others need pressure solidification, others need heating and pressing curing, others need to solidify for a long time, others only need a few seconds. The choice of adhesives should not only be based on high strength and good performance, but also consider whether the technological conditions required by the adhesives. For example, the phenolic aldehyde nitrile adhesive has better comprehensive properties, but it needs pressure 0.3 to 0.5MPa at 150 degree high temperature. If the pressure and high temperature conditions are not available, the adhesive will not be selected. In the case of automatic production line operation, fast curing adhesive is to be selected because the process is fast in the upper and lower channels. Such as hot melt adhesive. The simplest process is room temperature curing and single component adhesives, such as room temperature curing epoxy adhesive, chloroprene adhesive, anaerobic adhesive and milk white glue. For large equipment or special-shaped workpiece, room temperature curing adhesive should be selected because it is difficult to realize heating and pressure. 7. should consider whether the economic source and difficulty: the price and the source of the adhesive of the difficulty, but also the selection of adhesive can not be ignored. It's not a big problem for emergency repair, but it's important for regular production, because it involves reducing production costs. In a word, it is a complicated problem to choose the appropriate adhesive. First, we should understand the performance, use and technological conditions of the adhesive.
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