Лако-красочные материалы — производство

Sometimes the problem of durability is not clearly defined and the statement that ‘the adhesive is failing’ is not particularly helpful but ‘5% of the parts fail after 6 weeks in a hot, humid country’ is far more useful information to the engineer. A similar question that might be relevant is: ‘Have the failures occurred […]

Any discolouration of the adhesive in the joint may well suggest that the assembly has been subjected to environmental attack. Excessive temperatures may burn or discolour the adhesive and water ingress can cause some adhesives to discolour or lose their hardness. Thicker bond lines are often more prone to environmental attack and joints that are […]

One of the most important requirements of an adhesive joint is the ability to retain a significant proportion of its properties under the wide variety of environmental conditions that are likely to be encountered during its service life. One of the most aggressive and hostile environments for any adhesive is the combination of high humidity […]

In most situations, if ‘substrate failure’ is achieved (Figure 10.9) then no more could be asked of the adhesive as the adhesive bond is stronger than the plastic or elastomer bonded. Sometimes, however, the adhesive will change the mechanical properties of the complete assembly, especially if the adhesive creates highly stressed regions at the periphery […]

In Figure 10.8, the adhesive has remained predominantly on the lower surface and this suggests some surface contamination or other factor impeding the adhesion to that surface. Mould-release agents are sometimes used to help release plastics from the mould tool, especially for the first batch of parts off the tool when a silicone — or […]

Cohesive failure is when the failure mode is through the adhesive bond line. Inspection of the failed adhesive will show adhesive remaining on both surfaces (Figure 10.7). Figure 10.7 Cohesive failure of the adhesive If this is the failure mode then the adhesive itself should be investigated. Thinner bond lines are often stronger (especially under […]

It is now generally recognised that adhesives stick to surfaces by one of (or a combination of) four different methods (Figure 10.6) and these methods are discussed briefly here but more detail can be found in references [2] and [4]. • Mechanical keying Perhaps the most widely used of all the adhesion theories is that […]

In the same way as excess adhesive can cause blooming, a slow cure may give a similar result. The cyanoacrylate at the periphery of the joint will search for available moisture from the surrounding air and may then cure as a white powder on the adjacent surface. A slow cure may be the result of […]

When excess adhesive has been applied, the surface-to-volume-of-adhesive ratio is too low and the moisture on the surface will be insufficient to neutralise the stabiliser in the adhesive. The cyanoacrylate vapour will escape and fuming will occur. Reduce the quantity of the adhesive by using fine-bore application nozzles and/or dispensing equipment.

Blooming occurs when cyanoacrylate molecules escape from the main body of the adhesive and react with water vapour in the surrounding air. The molecules of cyanoacrylate cure and then fall to the adjacent surface as a white powder (Figure 10.4). Even with rubber-toughened cyanoacrylates (which are often black in colour), it is the monomer which […]