Cooling bonded joints

There are also polymers that can be brought to melting by heat supply. They are applied to the adherends in molten and solvent-free form. When the adhesive melt has cooled down, a bonded joint develops. Such adhesives, processed by melting and cooling down, are called hot-melt adhesives (Section 5.1). 

The second component of the internal stresses is thermal stress caused by differences of the coefficients of linear thermal expansion of the adhesive and the substrate. They appear in the coiu se of heating or cooling of the adhesive-bonded joint. The mechanism of the internal stresses occurring in adhesive-bonded joints does not generally differ from that in coatings, but because there are two sohd surfaces the magnitude of the stresses in the first case appears to be substantially greater. 

They are used for fast assembly of structures designed to be only lightly loaded. Hot melts can be in the form of blocks, rods, granules, powder and film. The adhesive is heated and applied to one surface as a melt loining is then carried out immediately after application and the adhesive cools and develops strength by its consequent solidification. The quicker the surfaces are joined, the better for the bond. Because the bond strength is reached in seconds, the need for clamps of fixtures is eliminated. These adhesives can be used for joints which may subsequendy need to be detached and/or reattached due to their thermoplastic structure. In use however the bonded joint must not be heated up to its melting temperature. 

In a further exploration of the conclusions above we used the oriented films to prepare bonded joints, with thin bondlines, and cooled with pressure. The results are shown in Fig. 6. While there are some similarities, the parallel and perpendicular (machine direction of film with respect to Rheovibron strain direction) responses are shifted from one another and not identical. These curves are reproducible in all major features. 

The amount of the applied adhesive and the final bond line thickness must be monitored because they can have a significant effect on joint strength. Curing conditions should be monitored for pressure, heat-up rate, maximum and minimum temperatures during cure, time at the required temperature, and cool-down rate. The primary concerns are to ensure the following ... 

Solder is often applied by means of a soldering iron. A soldering iron consists of a steel bar through which an electric current runs. The electric current heats the bar as it passes through it. When a small piece of solder is placed on the tip of the soldering iron, it melts. The solder is then applied to the joint between two metals. When it cools, the bond is strong. In 2007, more than 50 percent of tin consumption was for solder. 

Aluminum panels, which had a thickness of 0.61 and 1.63 mm, were etched with chromic acid. ASTM procedure D3167—76 (reapproved 1981) was followed for 135° peel tests. The adhesive film was placed between the aluminum panels and press-laminated at a temperature of 177 °C for 1 h at a pressure of approximately 5 psi (34.5 x 103 Pa). The temperature was then increased to 220 °C, and the joints were kept under pressure for another hour. The heaters in the hydraulic press were then switched off and the platens air-cooled and then water-cooled until the platen temperature was down to 100 °C. The bonded panels were cut into 12.7-mm-wide joints and tested at a rate of 20 mm/min and at a peel angle of 135°. 

Automatic Bonding Evaluation System (ABES) The ABES consists of a small press and a tiny testing machine in a single unit. It enables bonds to be formed under highly controlled conditions the joints that contain the bonds which are to be measured are pressed against heated blocks for a certain time, cooled within a few seconds, and pulled immediately thereafter in shear mode. Repetition of this procedure at different curing times and temperatures yields the points (a point for each specimen) of a near-isothermal strength development curve. 96,97... 

The thermal and dynamic mechanical behaviors of triblock copolymers with a styrene/isoprene/styrene architecture were investigated in order to understand their adhesive properties. Both copolymer free films and films bonding together two titanium alloy plates were found to have thermal and mechanical response that was strongly dependent on joint preparation. Microphase separation in the melts of these triblock materials was felt to contribute to the observed phenomena namely, the presence of residual stresses in thin films which had been cooled while under high pressure. 

C and at least 5000 psi was applied in the molding. Pressure was maintained during cooling in all cases. As the bond thickness increased the tan d behavior for joints approached that of the bulk, but was shifted to higher temperatures. Identical experiments on the 40% styrene copolymer gave essentially the same conclusions (not shown). The curves were quite reproducible. 

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