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Bertram31.com General Bulletin Board
Re: Capt Patrick
Posted By: Capt Patrick McCrary In Response To: Capt Patrick (Mitch)
Date: Wednesday, 27 April 2005, at 10:58 p.m.
Mitch,
Have never tried bending heavy PVC, but I think if I were to attempt it I'd go with a steam box technique...
Most rigid PVC has a heat distortion, (temp that it starts getting soft), range of 130° to 160° F. Direct flame or dry hot air will begin to scorch the surface at around 300° F & is both are hard to control.
A steam box built of 3/4" plywood and fed by a modified stove top pressure cooker would produce more than enough wet heat to make the PVC pliable without danger of scorching. You'll want to heat the material to about 170° and then reduce the heat to around 150°. Hold that temperature for about 3 - 5 min, allowing the material to equalize the temperature throughout. A cooking thermometer stuck into the side of the box will give you the chamber temp.
PVC holds it's heat well, so no additional heat is required once the working temperture is reached. Be careful about how much pressure you apply to the softened material as it will indent and deform very easily.
Also wear heavy cotton gloves when heat bending any plastic...
To convert a stove top pressure cooker for steam generation, remove the pressure relief valve from the top of the cooker. Refit with a 3/8" brass hose barb. Add a hose barb to the top of the steam box and connect the two with a heavy rubber hose. Drill a 1/4" hole in one corner of the box bottom to drain off collected water. Configure the box to fit around the PVC, probably top loading, and in such a way that minimal steam is lost.
Fire the pressure cooker with gas grill or propane burner... You could use electric, but they are about twice the cost of a cheap K-Mart stove top unit.
As I said, this is somewhat theoretical in relation to bending a PVC guard rail...
Let me know how you make out.
Br,
Patrick
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