An appreciable proportion of the cars imported into Ireland are converted into commercial vans by replacing the side windows with metal panels and modifying the floor construction.
There was a growing practice among purchasers of such vehicles to remove the rear window panels and thus avoid the duty levied on passenger cars. The Irish tax authorities were interested in a cost effective method of window panel fixing which would satisfy statutory requirements and be resistant to tampering.
• resistance spot welding of weldbonding (resistance welding + adhesive) - danger of secondary damage;
• MIG welding (spot or continuous) danger of secondary damage;
• mechanical fastening - danger of tampering;
• structural adhesives - simple procedure required.
What Was Done
• Structural adhesives literature was reviewed, and adhesive bonding experts were consulted;
• sample bonded joints were made and subjected to peel tests;
• comparative tests were made using spot welded joints with the maximum spacing of 40 mm;
• separation tests were made to check vulnerability to tampering.
This study resulted in a standardised procedure for car to van conversion. Advice was given on joint configuration and surface preparation, the latter invariably involving the removal of paint in the immediate area of the joint.
A range of toughened adhesives (acrylics or epoxies) was recommended.
A minimum peel strength was advocated (testing in accordance with the T- peel test in ASTM DI876). The level specified was based on stress analysis of `worst case' joints encountered in the study. Toughened adhesives were found to be necessary to give the required resistance to tampering (breaking the bond resulted in serious damage to the car).
• import distributors and small engineering establishments were provided with a cost-effective and simple method for modifying vehicles in accordance with Revenue Commissioners' requirements. Local secondary damage due to welding operations was eliminated;
• tax evasion was made more difficult in the largest and fastest growing segment of the Irish motor sales market.
Structural adhesives have clear potential for use in the modification and repair of vehicles (a finding supported by the work of the Motor Insurance Repair Research Centre at Thatcham in the UK).