Induction straightening of bulkhead doors
A marine door from Libra-Plast. The EFD Induction solution used to straighten weld-induced distortion is based on proven Terac technology.

Induction opens doors for Libra-Plast

EFD Induction has developed an innovative door straightening solution for Libra-Plast, one of the world’s leading manufacturers of bulkhead doors, hatches and containers for the maritime industry.

The solution is based on EFD Induction’s well known Terac deck and bulkhead induction straightening system.

The traditional method for removing weld-induced distortions in metal doors is mechanical ‘cold  bending’. The method is however costly and time consuming. Cold bending requires a highly skilled  operator, and the results achieved  are not always permanent. The process is also potentially damaging to the doors’ structural integrity. The new straightening solution exploits the same thermomechanical principles as the Terac deck straightening system. “The basic approach is the same: using induction to heat selected areas that subsequently cool and contract into the desired shapes. The technical challenge for us was to ‘miniaturize’ the Terac, as a ship’s door is a relatively small scale assembly with narrow tolerances.”

After consulting closely with Libra-Plast technicians, the EFD Induction team found that using pre-programmed energy/time cycles easily straightened weldinduced bumps in the doors. Similar heating cycles were then used to straighten the door stiffeners, and to correct distortions introduced by welding hinges to the doors. The power source for the new straightening solution is an EFD Induction mobile Minac 18/25 Twin. “It’s called ‘Twin’ because it features two independent power outputs,” explains Wells. “This means two  operators can work independently from one power source— which is a major boost to productivity.”

The induction straightening system is now in everyday use at  Libra-Plast, and has slashed the time needed to remove weld-induced distortions. The solution has also  eliminated an entire straightening procedure from the doors’ manufacturing process. “That’s correct,” says Wells. “With the previous cold bending method, an extra round of straightening was required after  welding on latchings and other  customer-specific fittings. That is no longer needed with the induction straightening system.”