Before making the flat steel double bars for the collapsible security door vertical bars the flat steel lengths have to be cleaned to remove the scale which is always on new steel. This makes for a better surface and ensures good adhesion of the final powder coat finish.
The picture at right shows the cleaning process and tools used. It is a noisy and dirty job but well worth the effort in the long run.
After the flat steel bar has been cleaned two lengths are placed in a jig and welded together with steel spacer blocks which form a double flat bar with gaps in between which house the folding trellis sections of the door. The spacer blocks add considerable rigidity to the flat steel lengths by forming an open box section. They are further strengthened when the folding trellis sections are riveted into position.