The pipe finishes heating at 11:45, if you want to skip ahead.
This is just an introduction and demonstration of a simple hot box I came up with for heating PVC pipes for flattening. It uses easy to find materials and everything needed to build one can be found at most hardware / home improvement stores.
This is one of the best heat-sources for flattening PVC as it holds the pipe at a constant temperature unlike heat guns, torches, fires, and other indirect sources of heat that can cause pipe to melt and burn due to very high temperatures. Because it uses hot air, it is less messy and easier to handle than hot water, steam, and other constant sources of heat like hot sand.
This video was filmed in my garage, which was at 45 degrees F at the time. The oven gets to temperature in around 5-10 minutes, and will heat most PVC pipes in under 6 minutes when at temperature (around 250 to 300 degrees F).
Thanks for watching and enjoy! I'll have the build along up shortly!
As a side note, here are some temperatures and stages that PVC goes through. The benefit of using a hot box like this is that the pipe cannot exceed the temperature of the air in the box, greatly diminishing the chances of overheating the pipe.
PVC pipe begins to deform at around 170 degrees F. From here to about 250 degrees F, PVC pipe can be bent and shaped but not freely formed.
From about 250 to 300 degrees F, PVC pipe can be molded, formed, and shaped freely without losing its structure. So long as a PVC pipe is not heated above this range, it will return to its former round pipe shape when re-heated.
At about 350 degrees F, PVC pipe becomes viscous. It starts to melt and loses its structure. PVC pipe heated this far, once cooled, will not return to shape when re-heated and becomes very brittle. A bow would not longer be considered safe.
PVC pipe burns at about 500 degrees F and begins carbonization. PVC pipe turns yellow, then brown, then black. This should be avoided at all costs as the pipe is not only compromised, but it is at this point the plastic starts to break apart. PVC pipe will release dangerous fumes and gas at this point.
PVC pipe will combust at around 700 degrees F. The smoke released is very dangerous and can cause severe acute and chronic health problems. Never let PVC pipe get to this point and if this ever happens, evacuate the area.