Лако-красочные материалы — производство

The time elapsed between surface pretreatment and application of the adhesive should generally be kept as short as possible, as implied earlier, because surface energies are lowered by the adsorption of atmospheric moisture and contaminants. Silicone-containing contaminants and mould-release oils should particularly be avoided. Kinloch(7) discusses some theoretical aspects of the bonding operation, and Hewlett and Shaw(60) address issues pertinent to segmental bridge construction. For general construction applications the considerations would involve (a) surface cleanliness and dryness (b) adhesive useable life (c) ambient temperature (d) adherend temperature (if different from (c)) and (e) minimising air entrapment. Note that the adherend temperature should ideally not be lower than that of the surrounding air prior to application of the adhesive (and/or primers), in order to prevent moisture condensing at the interface; local heating may be advisable, which would also assist surface wetting. Brockmann(41) reports little effect on the strength of mild steel-epoxy lap joints due to storing the shot-blasted adherends at room temperature and 60% r. h. for several days prior to adhesive application. This should not occasion surprise since a shear test is insufficiently sensitive and is inappropriate for gauging effects on adhesion. Gledhill et al. (19), on the other hand, found that the effect of bonding in a high humidity environment was reflected in reduced tensile butt-joint strengths. Fig. 3.16 also demonstrates a clear time-lapse effect on fracture energy.