The bonding process includes preparation before bonding, joint design, adhesive preparation, coating, closing, curing and quality inspection.


1、 Preparation before bonding


The bonding strength of the adhesive to the bonded material mainly depends on the mechanical connection between the adhesive and the bonded material, the physical adsorption between the molecules, the mutual diffusion and the formation of chemical bonds. The structural state of the bonded surface has a direct influence on the strength of the bonded joint.


In the process of processing, transportation and storage, there will be oxidation, oil stain, dust and other impurities on the surface of the adhesive, which must be cleaned before bonding.


The commonly used surface cleaning methods include degreasing treatment, mechanical treatment and chemical treatment.


1. Surface degreasing treatment


Organic solvent degreasing methods include organic solvent method, alkaline solution method and surfactant method. Commonly used degreasing solvents are acetone, toluene, xylene, trichloroethylene, carbon tetrachloride, ethyl acetate, banana water, gasoline, etc. For a large number of small adhesive parts, trichloroethylene can be placed in the steam tank for about half a minute to remove grease. For large areas of adhesive surface, use the top to bottom or left to right direction cleaning. When degreasing with solvent, there should be a certain drying time to prevent the residual solvent on the bonding surface from affecting the joint strength. For the bonding surface cleaned by alkali solution, the surface must be washed with hot water and cold water after cleaning, and then dried with hot air.


After use, the surface of the adhesive is easy to absorb or deposit oil. If high temperature treatment is allowed, the adhesive can be placed in the hot air drying oven at 200 ~ 250 ℃ to make the grease ooze out. Then it can be used to wipe the cotton yarn and remove the oil with solvent. It is especially emphasized that the solvent must be away from the fire source to prevent accidents.


2. Mechanical treatment


The commonly used manual tools for mechanical treatment include wire brush, copper wire brush, scraper, sandpaper, pneumatic tools, etc.; the mechanical methods include turning, planing, grinding wheel grinding, sand blasting, etc. The mechanical method is used to treat the surface, which provides the surface with appropriate roughness, increases the effective bonding area and improves the bonding performance.


3. Chemical treatment


There are two chemical treatment methods: acid solution and alkaline solution. The chemical treated metal can form a uniform, dense and strong active layer on the surface, which can easily make the adhesive wet and expand, and can significantly improve the bonding strength. For the polymers that allow chemical treatment, such as polytetrafluoroethylene, polyethylene, polypropylene, fluororubber, etc., the surface can be changed into polar groups, the free energy of the surface is increased, the wettability is increased, and the bonding strength is greatly improved.


2、 Design of adhesive joint


1) Several stress forms of adhesive joint


In practical use, a glued joint will not only be subjected to one direction of force, but also one or several forces. In order to facilitate stress analysis, the actual stress of adhesive joint is simplified as shear force, tensile force, peeling and splitting


2. The following principles should be followed when designing adhesive joint


Manufacturing a high-quality adhesive joint is closely related to the performance of the adhesive, the reasonable bonding process and the correct bonding joint form. The following points should be considered when designing adhesive joint.


1) As far as possible, the adhesive layer of the adhesive joint shall be compressed, stretched and sheared, and the joint shall not be subject to peeling and splitting. For the inevitable peeling and splitting, the measures shown in Fig. 3 shall be adopted to reduce the peeling and splitting effect of the adhesive layer.