Connect, May/June 1999
Maersk Container Industri AS began the development production process of a new design for refrigerated 'Reefer' containers. The outer panels were of stainless steel with low carbon steel formed section longitudinal rails. Assembly was by resistance spot welding and weldbonding (spot welding plus adhesives).
This joining process was a radical departure from riveted/bolted structures and improved productivity resulted from using mechanised assembly in dedicated production cells. Other benefits included lower manufacturing costs, weight savings, increased payload and improved thermal efficiency.
Lloyd's approval to the appropriate ISO standards was given on the initial test containers. However, during early stages of production, weld quality problems appeared on the weldbonded side-wall to lower rail joints.
Maersk Container Industri AS implemented a comprehensive programme of process improvements and testing but needed an independent specialist assessment of the situation.
TWI was asked to conduct a structured review of production methods, process control and joint quality to confirm the process suitability and to make recommendations to increase quality and reliability.
A TWI specialist visited the site to examine the welding equipment and procedures. After discussions with the client, a report was written providing recommendations for further refinement of the process. Implementation provided the process control needed and confidence in the spot welding and weldbonding processes for this application.
The recommendations made by TWI enabled Maersk to improve the assembly methods and continue volume manufacture with confidence. As a result, costly modifications to the £15m dedicated plant were not needed.
To date, some 15 000 refrigerated containers have been produced. Most importantly, no failures have occurred with the new method of construction.
More information on resistance welding, email: firstname.lastname@example.org