Tension Leveling

Metal coil leaves the rolling mill with uneven internal stresses. Some parts of the strip may be slightly longer than others, creating conditions known as full centre (a longer middle), wavy edge (longer edges) or camber (sideways bow). When such coil is formed into wide, flat roof panels, the trapped stresses can show up as waviness, known as oil canning.

How it works

In tension leveling, the strip is stretched under tension slightly beyond its yield point, so that shorter areas of the strip lengthen to match longer ones. When the tension is released, the strip is flatter and more uniform, with less stored stress.

For roofing, leveling done after slitting is particularly useful, because cutting a wide master coil into narrower widths can itself redistribute stresses.

Benefits

• Reduces the tendency to oil canning in flat-pan standing seam and architectural panels.
• Improves flatness for wall cladding and flashings.
• Helps roll-forming produce consistent profiles.

Limits

Tension leveling cannot fix waviness caused after forming, for example by out-of-plane decks, over-engaged seams, over-driven fasteners or restrained thermal movement. Industry guidance therefore treats it as one measure among several, alongside thicker gauges, narrower pans, stiffening ribs, low-gloss finishes and good installation practice.

Specifying it

Tension-leveled coil is usually specified for architectural standing seam panels, especially wide flat pans in dark or glossy colours where waviness would be most visible. Even with leveled coil, industry guidance notes that no single measure can ensure flat panels; combined measures give the best results.