Spring 2006: Society for Adhesion and Adhesives One Day Symposium on 'Adhesives in Transport'
One Day Symposium on Adhesives in Transport, held on 6th April 2006 at the Society of the Chemical Industry, 15, Belgrave Square, London
This meeting brought together a significant number of people working in a variety of areas connected with transport. Aerospace and automobile manufacturers and researchers were the largest group, as might be expected.
The first paper, entitled: ‘Effects of Chromic Acid Anodizing on the Adhesion and Durability of Bonded Joints’, was given by Xiaoring Zhou of UMIST, Manchester.
He is known as Dr. Joe, which is easier to pronounce! His work showed that it is sometimes useful to challenge existing practices. The UK DEF STAN 03-24/4 Chromic Acid Anodizing of Aluminium and Aluminium Alloys has been in use for many years with great success but this paper showed that increasing the voltage from 40V to 60V can give a larger pore size and improved bond strength measured by the lap shear test and greater durability as measured by the wedge test. No primer was used in this work but primers are generally used with the standard process to penetrate the smaller pores produced at the lower voltage; a useful piece of work that can improve the reliability of adhesive bonding to aluminium and its alloys.
The second paper, entitled: ‘From Crash Integrity to Bonding Rear-View Mirrors: The Future of Automobile Adhesives’ was given by John Hill of Ford Motors. This paper must be of interest to all drivers as crashworthiness is an important issue. It was concluded that careful design is important because adhesives are not very strong in themselves so the design must use adhesives to make the structure do the work of absorbing the crash energy. The use of DCB (Double Cantilever Beam) tests and peel tests showed that adhesive fracture toughness and strength is also important. HSLA 350 sheet steel was used for the test work. Very tough adhesives are needed for energy absorbing structures. A wide range of adhesives is used in automobile assembly and each has to be carefully selected for its particular task. Adhesives for window installations have to be removable and replaceable on site.
This last sentence leads into Paper 3, by Steve Tellwright from Autoglass Ltd. His paper: ‘Surface Cleaning of a Laminated Glass Windscreen to Improve Adhesion’, showed how much work may be needed to ensure the reliability of an apparently simple process.
It is constantly emphasised in most meetings on adhesives that surface preparation is the most important factor and this problem confirms that finding. His very interesting paper showed how simple it is to contaminate a surface in production that causes trouble later and much effort to identify the problem. He said, “Some laminated glass windscreens used in the aftermarket windscreen replacement industry have been identified as having a thin film of silicone like residue on the ceramic ink band on the internal face of the windscreen. This residue caused significant bond quality problems.” The problem was traced to the use of a silicone de-airing hose used in the manufacturing process. No screens were completely disbonded but some had sufficient areas of no bond to cause water leakage into cars in rain. Various cleaning methods were tried including flame cleaning and a type of Scotchbrite® pad. The Scotchbrite is easier and cheaper to use but not 100% reliable. Flame cleaning is not suitable under repair conditions and further efforts will be made to find a fully acceptable solution.
The fourth paper, entitled: ‘The Radshape Experience’ and given by John Harper, was a fascinating story of the development of a good company from simple beginnings to a high technology company. John described the progress from bending household radiators to the required curvature to the bonded metal structures now produced for Morgan Cars, Gibbs Technologies, Bentley and British Aerospace Systems Ltd. This required learning about surface treatment methods, toolmaking and mechanical testing.
They are now bonding extrusions and sheet metal parts. Of particular interest was the fact that they use written procedures developed for each product to ensure that all processes are themselves correctly performed and also in the correct sequence for the assembly of each chassis or other component. This method of working is highly recommended. Visits to Radshape are welcome. Try their website [www.radshape.co.uk] if you would like to go!
The fifth paper was given by Ben Hawtin of Airbus with the title: ‘Bonding in Commercial Aircraft Structures’.
He described the bonding of the inner landing flap for the A.380, which uses the standard CAA (Chromic acid anodizing) process with BR127 primer before application of the film adhesive. PAA (Phosphoric Acid Anodizing) has been tried. Chromate free bonding primers are under development. He concludes that chromate free metal bonding is achievable. Repair work was mentioned and Airbus would like to see 120°C curing film adhesives that need only vacuum pressure and less rigorous surface treatments. The last requirement has always proved difficult to achieve. He said that viable NDI solutions were also required for inspection.
For composite bonding it was stated that specially qualified peel plies are used. Grit blast or mechanical abrasion are better methods and alternatives such as plasma, laser and corona discharge methods are being studied. The use of GLARE was mentioned and it was stated that vacuum bonding was 25% cheaper than autoclave bonding.
Paper six was given by Phil Duke of QinetiQ on the subject ‘Fuel Tank Sealants in Aerospace Applications’.
He described a vast amount of work on current sealant systems and presented data that helps the selection of the correct material for each application. Although the usual sealants have a good reputation for resisting aviation fuels they have yet to provide a good enough seal to prevent fuel leaks. Potential degradants are fuel, water, icing inhibitors and bacteria. The sealants were studied for absorption of water, icing inhibitor and various mixtures of these. Useful graphs were shown but cannot be reproduced here. Those with specific interests should contact Phil.
Sealants are also adhesives and surfaces should be cleaned and given appropriate treatments before applying sealants if durable bonds are required.
Paper 7, the final talk of the day, was given by John Bishopp of Star Adhesion with the title ‘Bonding of Friction Materials’. He too said that it was time to look again at well tried processes to see if useful improvements could be made and commented that friction materials had been bonded in the same way for many decades. John explained that bonded brake linings could be used for much longer than riveted ones as early failure around the rivet holes was normal for the older method. The absence of rivets also avoids damage to the brake shoes by rivet heads or grit in the rivet holes. Surface preparation is important but abrasion is sufficient on steel for the bonding of friction materials. The adhesive is usually applied in liquid form by spray or roller coating. Special test rigs are required to provide test back up for these processes. The main problem associated with these methods is solvents. Any improvements that could eliminate or reduce the use of solvents would be welcomed.