Лако-красочные материалы — производство

5.1 Introduction

The importance of quality assurance in any industry is widely acknowledged. More stringent customer expectations with regard to quality, together with the realisation that continued improvements in quality are often necessary for a company to sustain good economic performance, mean that some level of quality assurance is mandatory for all those associated with adhesive bonding operations. The use of technical specifications and quality control procedures go some way towards fulfilling the requirements of a quality system, and these measures are outlined here.

Most of the aspects relating to the selection and use of adhesives have been discussed in the first four chapters. For example, the properties of adhesive materials have been reviewed, together with the design approach appropriate to structures assembled with them. The importance of surface pretreatment and its influence on joint durability has also been covered. However adhesion science must also interface with fabrication considerations and with structural engineering. To the technical difficulties facing the production engineer in using structural adhesives must be added a number of others for the civil engineer. Primarily these are that:

(1) each project tends to be a ‘one-off’ production

(2) fabrication commonly takes place on site and so the environ­ment is not easily controlled

(3) the success of the bonding operation is very dependent on the diligence employed by the operatives and the work requires skilled supervision

(4) the bonded assembly has to last for many decades

(5) adhesive polymers have poor fire resistance

A number of general fabrication precepts applicable to civil engineering uses of adhesives have been collected in Table 5.1.

(1) trained operatives must be employed under skilled supervision

(2) surface pretreatment and cleanliness are essential for a reliable and durable joint

(3) apply adhesive to prepared surface as soon as possible after surface pretreatment

(4) safe handling precautions are essential for resin products

(5) adhesive products should be stored in accordance with their manufacturers’ recommendations

(6) thorough mixing of correctly proportioned components is essential; avoid sub-dividing manufacturers’ pre-weighed packs; proper dosing equipment is desirable

(7) mix cold-cure products in quantities of less than 10 kg to reduce the exotherm in the mixing vessel and to minimise air inclusion; encourage the dissipation of heat from the mixed components

(8) ensure sufficient usable (pot) life with reference to 7

(9) match the reactivity of the adhesive to the temperature and duration of application; note that most adhesives will not cure below 5 °С

(10) superior performance is obtained from elevated temperature curing; as a rule of thumb, the reaction rate doubles and the cure­time halves for every 8 °С rise in temperature

(11) ensure gap-filling properties

(12) employ thixotropic or pseudo-plastic materials for application to vertical surfaces

(13) devise a suitable method of adhesive application to the substrate surfaces

(14) provide jigs/temporary works/permanent mechanical fixings to hold components and to apply pressure during cure

(15) adherend temperature should preferably be higher than ambient temperature to minimise condensation of moisture at the interface before adhesive application

(16) close the joint as soon as possible after application of the adhesive, and in a manner and at a rate that minimises the inclusion of air

(17) provide for heat-curing if necessary with heating tapes, focussed infra-red heaters, etc.

(18) provide appropriate physical and mechanical tests for quality assurance

(19) protect bondline from adverse environmental effects at least while curing

(20) consider post-bonding quality assurance by appropriate methods, including NDT.