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Adhesive bonding revolutionizes car headlamp manufacture
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Adhesives in Action The benefits which can be obtained from bonding are well documented, some of the more significant being: • Stress is distributed over the complete joint length. • Capital costs can be reduced, due to savings on expensive welding equipment. • Panel reworks resulting from weld deformation can be reduced or eliminated. • There is scope for using lighter weight materials. • Dissimilar materials can be bonded. • Structures inaccessible for welding can be assembled. • Corrosion resistance is improved. • The strength of the structure is increased. Since the introduction of XB 3062 GB however, Austin Rover have continued to look critically at their specifications for structural adhesives and have recently set even higher standards. In response to this, Ciba-Geigy has already developed improved singlecomponent adhesives which are being evaluated by Austin Rover but which at present seem likely to meet these more demanding
Fig. 2 The roof panel centre section being lowered into position requirements. Unlike some European competitors, UK car manufacturers have not yet incorporated epoxy adhesives in semi-structural areas such as hem flanges on doors, bonnets and trunk lids. As the performance advantages become more
apparent however, and with the pressure to ensure increased durability, the transition will probably soon be made.
Ciba-Geigy Plastics and Additives Company, Plastics Division, Duxford, Cambridge C82 4QA, England.
Adhesive bonding revolutionizes car headlamp manufacture When designers in the motor industry first asked lamp manufacturers for one-piece rectangular headlamps, engineers were presented with the problem of fixing the lens glass onto the reflector. The conventional method with round lamps had been to roll the lip of the metal reflector over the edge of the lens glass, incorporating a rubber gasket to form a moisture seal. This, however, proved to be a difficult operation to carry out for the rectangular shape, and so it was decided to bond the lamps using an epoxy resin adhesive, effectively revolutionizing headlamp production techniques.
The introduction of metallized dough moulding compound (DMC) to replace steel for reflector production followed. With this major material change, it became clear that bonding undoubtedly offered the most simple and effective method of lamp assembly. It also became clear that adhesives must be developed to meet the highvolume production requirements, and the rigorous test specifications. Thus Ciba-Geigy developed single-part epoxy adhesives which were capable of meeting the motor industrVs test requirement for good adhesion to DMC, glass and steel over a temperature range of --40°C
to -I-80°C. The major requirement of the adhesive was that it should not release any volatiles on application, during cure, or in service, because it was feared that volatiles may cause 'fogging' on the reflector surface. Furthermore, the bonded headlamp was required to pass humidity cycling, vibration, and cold water shock tests, together with the obvious long-term road testing under various climatic and road surface conditions. The adhesive would be applied to the lamp lens using pantograph controlled dispenser heads fitted with positive 'shut-off control valves. The assembled lamp unit
INT.J.ADHESION AND ADHESIVES JANUARY 1984
29
FwJN,ip mut m P oduct
Adhesives in Action then would be cured in a tunnel oven, and subsequently pressuretested to ensure that it was sealed and securely bonded. Therefore a further requirement was that the cure temperature for the Ciba-Geigy adhesive must not exceed 120°C because some headlamp assemblies incorporate direction indicator lamps made of thermoplastic materials.
The single-part adhesives developed by Ciba-Geigy have satisfied all these demanding requirements and have been successfully used in bonded headlamps for some six or seven years. For the future, the requirement will be to continue to provide single-part adhesives which can be dispensed and cured rapidly, but
which will pass test specifiCations which are becoming progressively more demanding. What is more difficult however, is that they will need to bond well to polypropylene, polybutyl terephthalate (PBT) and glass, preferably without the need for primer or pretreatment
Ciba-Geigy Plastics and Additives Company, Plastics Division, Duxford, Cambridge CB2 4QA,
Hot-melt dispensing equipment developed for automotive applications The use of hot-melt adhesives has experienced rapid growth during recent years. Mainly associated with the packaging industry in the past, hot melts have now been developed to accommodate a variety of applications of which usage in the motor industry is no exception. The benefits obtained from using hot melts are well known. They include: • Rapid setting time (which can be varied from 0.5 seconds to 90 seconds); advantageous on assembly lines and for automated applications. • Containing no harmful solvents, they are 100% adhesive and therefore more economical in use. • They will bond to a variety of surfaces, including metals, plastics, glass, rubber, and vinyls, allowing dissimilar materials to be joined. • Easy to apply. Being single component systems they can be applied through hand-held guns or automatic dispensing equipment The latter advantage has been exploited by Nordson (UK) Limited, a company who have worked closely with a number of adhesive manufacturers to develop equipment suitable for the application of hot melts for a variety of require-
30
adhesive along both inside edges of the moulding. On the same line, a one-component urethane adhesive can be extruded from separate equipment along the centre. The two hot-melt beads, setting within one second, hold the moulding in place, while the urethane adhesive cures over a period of 24 hours to full bond strength. It is estimated that this method of application results in a 79% reduction in the cost of materials over the former method of using double-sided tape in conjunction with a urethane adhesive and produces a more reliable bond. The hot-melt beads also act as a seal, keeping the urethane adhesive confined behind the moulding. Another example of the use of hot-melt adhesives in the assembly
ments such as small or large dots of adhesive, beads, formed gaskets or coatings. In all cases, application is clean and precise with equipment capable of extruding up to 5000 deposits of adhesive per minute. Flexible heated hoses allow application temperatures of around 160°C. A situation where hot-melt adhesive and specialized application equipment have combined to provide an efficient and economical improvement over the previous method of attachment, is on the protective side-moulding on an automoile body (as indicated in Fig. 1). Application of the adhesives is indicated in Fig. 2. In practice, a Model XI unit attached to a H-20A gun with dual orifice nozzle extrudes hot-melt
/ Protective side moulding Fig. 1 Side-moulding on the body of an automobile helps to protect the finish and to compliment the body design
INT.J.ADHESION AND ADHESIVES JANUARY 1984
,.F
iiiQiIiIi IIIILiIQ
Adhesives in Action The benefits which can be obtained from bonding are well documented, some of the more significant being: • Stress is distributed over the complete joint length. • Capital costs can be reduced, due to savings on expensive welding equipment. • Panel reworks resulting from weld deformation can be reduced or eliminated. • There is scope for using lighter weight materials. • Dissimilar materials can be bonded. • Structures inaccessible for welding can be assembled. • Corrosion resistance is improved. • The strength of the structure is increased. Since the introduction of XB 3062 GB however, Austin Rover have continued to look critically at their specifications for structural adhesives and have recently set even higher standards. In response to this, Ciba-Geigy has already developed improved singlecomponent adhesives which are being evaluated by Austin Rover but which at present seem likely to meet these more demanding
Fig. 2 The roof panel centre section being lowered into position requirements. Unlike some European competitors, UK car manufacturers have not yet incorporated epoxy adhesives in semi-structural areas such as hem flanges on doors, bonnets and trunk lids. As the performance advantages become more
apparent however, and with the pressure to ensure increased durability, the transition will probably soon be made.
Ciba-Geigy Plastics and Additives Company, Plastics Division, Duxford, Cambridge C82 4QA, England.
Adhesive bonding revolutionizes car headlamp manufacture When designers in the motor industry first asked lamp manufacturers for one-piece rectangular headlamps, engineers were presented with the problem of fixing the lens glass onto the reflector. The conventional method with round lamps had been to roll the lip of the metal reflector over the edge of the lens glass, incorporating a rubber gasket to form a moisture seal. This, however, proved to be a difficult operation to carry out for the rectangular shape, and so it was decided to bond the lamps using an epoxy resin adhesive, effectively revolutionizing headlamp production techniques.
The introduction of metallized dough moulding compound (DMC) to replace steel for reflector production followed. With this major material change, it became clear that bonding undoubtedly offered the most simple and effective method of lamp assembly. It also became clear that adhesives must be developed to meet the highvolume production requirements, and the rigorous test specifications. Thus Ciba-Geigy developed single-part epoxy adhesives which were capable of meeting the motor industrVs test requirement for good adhesion to DMC, glass and steel over a temperature range of --40°C
to -I-80°C. The major requirement of the adhesive was that it should not release any volatiles on application, during cure, or in service, because it was feared that volatiles may cause 'fogging' on the reflector surface. Furthermore, the bonded headlamp was required to pass humidity cycling, vibration, and cold water shock tests, together with the obvious long-term road testing under various climatic and road surface conditions. The adhesive would be applied to the lamp lens using pantograph controlled dispenser heads fitted with positive 'shut-off control valves. The assembled lamp unit
INT.J.ADHESION AND ADHESIVES JANUARY 1984
29
FwJN,ip mut m P oduct
Adhesives in Action then would be cured in a tunnel oven, and subsequently pressuretested to ensure that it was sealed and securely bonded. Therefore a further requirement was that the cure temperature for the Ciba-Geigy adhesive must not exceed 120°C because some headlamp assemblies incorporate direction indicator lamps made of thermoplastic materials.
The single-part adhesives developed by Ciba-Geigy have satisfied all these demanding requirements and have been successfully used in bonded headlamps for some six or seven years. For the future, the requirement will be to continue to provide single-part adhesives which can be dispensed and cured rapidly, but
which will pass test specifiCations which are becoming progressively more demanding. What is more difficult however, is that they will need to bond well to polypropylene, polybutyl terephthalate (PBT) and glass, preferably without the need for primer or pretreatment
Ciba-Geigy Plastics and Additives Company, Plastics Division, Duxford, Cambridge CB2 4QA,
Hot-melt dispensing equipment developed for automotive applications The use of hot-melt adhesives has experienced rapid growth during recent years. Mainly associated with the packaging industry in the past, hot melts have now been developed to accommodate a variety of applications of which usage in the motor industry is no exception. The benefits obtained from using hot melts are well known. They include: • Rapid setting time (which can be varied from 0.5 seconds to 90 seconds); advantageous on assembly lines and for automated applications. • Containing no harmful solvents, they are 100% adhesive and therefore more economical in use. • They will bond to a variety of surfaces, including metals, plastics, glass, rubber, and vinyls, allowing dissimilar materials to be joined. • Easy to apply. Being single component systems they can be applied through hand-held guns or automatic dispensing equipment The latter advantage has been exploited by Nordson (UK) Limited, a company who have worked closely with a number of adhesive manufacturers to develop equipment suitable for the application of hot melts for a variety of require-
30
adhesive along both inside edges of the moulding. On the same line, a one-component urethane adhesive can be extruded from separate equipment along the centre. The two hot-melt beads, setting within one second, hold the moulding in place, while the urethane adhesive cures over a period of 24 hours to full bond strength. It is estimated that this method of application results in a 79% reduction in the cost of materials over the former method of using double-sided tape in conjunction with a urethane adhesive and produces a more reliable bond. The hot-melt beads also act as a seal, keeping the urethane adhesive confined behind the moulding. Another example of the use of hot-melt adhesives in the assembly
ments such as small or large dots of adhesive, beads, formed gaskets or coatings. In all cases, application is clean and precise with equipment capable of extruding up to 5000 deposits of adhesive per minute. Flexible heated hoses allow application temperatures of around 160°C. A situation where hot-melt adhesive and specialized application equipment have combined to provide an efficient and economical improvement over the previous method of attachment, is on the protective side-moulding on an automoile body (as indicated in Fig. 1). Application of the adhesives is indicated in Fig. 2. In practice, a Model XI unit attached to a H-20A gun with dual orifice nozzle extrudes hot-melt
/ Protective side moulding Fig. 1 Side-moulding on the body of an automobile helps to protect the finish and to compliment the body design
INT.J.ADHESION AND ADHESIVES JANUARY 1984