After intensive work, the group concluded that induction heating was the best method. But the researchers were not satisfied with the induction generators then available. To start with, the generators were much too large to be of practical use in shipyards. They didn’t operate at the right frequencies. And they were also potentially dangerous. The decision was made to conduct further research — and to develop solutions suited to the specific demands of deck straightening.
The legend is born
This research had three far-reaching results: induction heating equipment designed for straightening decks, the world’s first transistorised (aircooled) induction generators, the formation in 1981 of ELVA. With a tiny workforce, but unlimited faith in the potential of induction heating, ELVA launched its very first product, the now legendary Terac thermal-straightening system. It should be noted that the original members of the research group who went on to found ELVA are still with the company, which has grown and evolved into EFD Induction.
Also still with the company is the Terac. The latest version, the Terac 25, has been developed to meet the needs of today’s commercial and technical conditions. Chief among the former is a ruthless drive to cut costs. Among the latter is the widespread use of light and thin metal sheets for ships’ hulls. These sheets are stronger than their thicker predecessors, but they are still susceptible to one of the great challenges of metal shipbuilding — weld induced distortion.
The problem is that welding the plates together induces buckles and distortions that are unsightly, can prevent correct fit, and even weaken the entire assembly. Traditionally, open gas flames have been used to straighten the distortions. But it is a slow, expensive process that requires skilled operators working in uncomfortable, often dangerous environments. It also delays the entry of other trades into the production process.
Faster, safer, easier
With traditional straightening (or ‘fairing’), an operator heats the metal plate with a gas flame. As the area cools the heated side contracts more than the un-heated, causing a bend downwards or away from the heat source. Skilled operators exploit this effect to flatten bulges in steel deck plates, and to create the flowing curves seen on modern vessels.
The trend towards lighter, thinner plates has however compounded the problem of weld-induced distortion. Flame fairing is less effective on thin sheets. In fact, it can lead to even more distortion if not done correctly. Induction heating on the other hand achieves superior results in less time. In fact, in a soon-to-be published paper, one of the largest producers of naval vessels reveals the results of a recent trial carried out on thin plate decks and bulkheads. The results show a time saving of 75 per cent in the heating process alone! More savings will be realised when the cost of sacrificial materials and rework time to remove the scars caused by the traditional process is taken into account. Moreover, samples sent to an independent laboratory showed an improvement in the metallurgical properties of the steel after heating with induction compared to flame. But the benefits don’t end there. Induction
heating is more user-friendly than gas. Then there are the health and safety benefits. Induction heating is clean, with none of the dust, fumes or radiated heat common with flame straightening. Also, the lack of any open flames greatly reduces the risk of fire, and lets other trades continue working in the vicinity of the Terac operator.
One key feature that makes the Terac ideal for fairing thin, high-strength plates is its automatic overheating protection. This is a crucial benefit, as the thin plates can become brittle if overheated. And of course, the accurate, repeatable — and most importantly, the controllable — heat delivered by the Terac brings previously impossible levels of process control and quality assurance to deck fairing.