Архивы рубрики ‘Practical Guide to. Adhesive Bonding of Small. Engineering Plastic and. Rubber Parts’

‘No Cure’ — Adhesive Curing Problems

Sometimes cyanoacrylates will form a white powder adjacent to the bond line. This is known as ‘blooming’ or sometimes ‘frosting’. This section explains the reason for blooming and suggests various options to eliminate it from the production line. Also included are general guidelines for troubleshooting an application.

‘No Cure’ — Differential Scanning Calorimetry (DSC)

There are more sophisticated techniques to determine the extent of cure but these do require the use of specialised (and expensive) equipment. DSC is a thermo-analytical technique [2] in which the difference in the amount of heat required to increase the temperature of the sample of suspect uncured adhesive and a fully cured reference are […]

‘No Cure’ — Disturbing Partially Cured Adhesive

Adhesives do not like to be disturbed whilst they are in the critical phase of changing from a liquid to a cured adhesive. The polymer chains will be beginning to form and if broken at an early stage the chains will not always repair and then go on to create the crucial links that make […]

‘No Cure’ — Factors Inhibiting Cure

Lack of cure could be due to a number of factors and this may well depend on the type of adhesive being used. Cyanoacrylates are very dependent on the presence of small amounts of moisture on the surface and if the relative humidity in the working area is less than 25% RH, the cyanoacrylate will […]

‘No Cure’ — Odour

The adhesive must be fully cured for an effective and durable joint to be formed. Most engineering adhesives will display an odour when in the uncured state and, once cured, the adhesive is essentially a thermoset or thermoplastic and so inert and usually without odour. One key inspection technique therefore when trying to establish the […]

‘No Cure’

Having checked for the presence of adhesive (‘no glue’), the next step is to check whether the adhesive has cured. This again should be relatively straightforward in as much as that uncured adhesive will be liquid and this should be relatively easy to check when components are separated.

‘No Glue’ — Other Factors

Has the correct grade of adhesive been used? It is not unknown for the wrong grade of adhesive to be inadvertently used on the production line and if the adhesive container is situated in a pressure pot or similar dispenser, it will be out of sight and therefore it may not be immediately obvious that […]

‘No Glue’- Destructive and Non-destructive Methods

Destructive testing usually involves uplifting samples from the production line and determining the performance of the adhesive bond by strength testing against a pre­determined standard. This may not always be possible, especially if the adhesive has extended cure times but with fast-curing adhesives (cyanoacrylates or UV-curing products) the application of force to determine the failure […]

‘No Glue’ — Air Bubbles and Voids

Small air bubbles in the joint may not affect the overall strength of the joint but can cause leaks or in some cases be an aesthetic issue. These bubbles may originate from the adhesive packaging but can also be due to shrinkage of the adhesive as it cures. Most of the acrylic-based adhesives will shrink […]

‘No Glue’ — Verifying the Adhesive Has Been Dispensed

A method sometimes used is to check the pressure-time response of the adhesive dispense valve. In a pressure-time dispensing system (see Section 8.3), the adhesive is forced under pressure through a valve so that the desired quantity is dispensed onto the component part. As the dispense valve opens and closes, the pressure-time response curve can […]