Closures - WPCPIVAny wrap around shrink sleeve requires a closure of some form. What does the closure do? It simply holds the sleeve in the shape of a tube -- in place -- around the pipe during the shrink process. If you did not use a closure of some kind, your shrink sleeve would turn into a giant mess of PE and mastic in a pile on the ground underneath your pipeline!
So what are closures? First of all - we should say there are several different types.
Standard WPCPIV Closures: These are the regular closures we use for most wrap around heat shrink sleeves. They are thin and comprised of three layers. Layer 1: radiation crosslinked polyolefin backing. Layer 2: fiber mesh to imbue that PE with added strength. Layer 3: high shear adhesive designed to stick to the sleeve backing and prevent any slippage at all from occurring as the heat shrink sleeve begins to exert force on itself during the shrink process.
Rail and Channel Closure: This is a physical closure. One end of the sleeve has a PE toe sticking out. This toe meets up with the toe on the opposite side - and then a stainless steel channel is slid into place to hold those toes together during the shrink process. This method is more often used on high expansion electrical products.
An actual Zipper: some products like our Caseal and Flangeseal use an actual zipper; sewn into the backing; in order to hold that sleeve together during the shrink process. A regular closure is then used -- but only to prevent the heat from the torch from adversely effecting that zipper.
That more or less covers it. If you are looking to buy rolls of material in order to cut the sleeves yourself - you absolutely must use closure strips as well or else you are very likely going to have some major field issues -and some major irritations in your future.