Concern:
Metal roofs covering a large area will expand and shrink significantly due to temperature changes. The panels that make up the roof must allow for movement while also guaranteeing weather-tightness.
Securing overlapping roof panels using a sheet metal screw may cause a gap on one side (right-hand figure) , while squeezing out the sealant on the other side. Over time, this may cause the roof to leak.
Countermeasure:
The sheet metal was indented to accommodate a certain amount of sealant, and embeds in the sealant were added (making the composite) to guarantee a minimum thickness, ensuring that enough sealant will be present to guarantee performance.
A longer return leg eliminates the possibility of movement (no gap) when the screw is screwed in
Limitation:
| Triz Description | 40.1: Change from uniform to composite (multiple) materials. |
|---|---|
| Image sources | (Source: Butler manufacturing product literature; http://www.butlermfg.com/images/level3_pages/returnleglink-large.jpg visited 5/23/06). |
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