If I want to fabricate the PVC pipe heater, what parameter should I consider and what temperature is probably suitable to heat and bend without damaging the PVC pipes?
PVC starts to decompose at 140oC so you want to put a safety thermostat that will prevent the temperature from going over that. You will need to get up around 100oC to get it soften enough to bend without kinking but the exact temperature will vary with the materials thickness and polymer composition.
I agree with Ron. You need to reach at least the glass transition temperature of PVC (since it is an amorphous polymer) which is ~100°C, and then it will start to exhibit "rubbery" characteristics, and start to flow. The upper bound is the temperature of the onset of degradation, which will depend on the exact formulation of the PVC compound you have.
You might want to use the kind of internal support coil that we use to bend copper pipe, and you may need to use an oil bath to get to 105 - 110°, which is where I would start.
Good advice from Ron and Trevor. You can also make simple PVC pipe bends at room temperature by using an internal support spring (if the diameter is not too large). The springs are readily available in standard sizes (16, 20, 32mm). Electricians do this all the time with electrical conduits. I would suggest hot (near boiling) water as an easy way to get close to the 100C suggested to soften the pipe if needed.
@Deon - I wrote "You might want to use the kind of internal support coil that we use to bend copper pipe" which is exactly what you describe, as "using an internal support spring". I think your proposal to use just boiling water might be a good starting point, depending upon the pipe diameter / thickness.
Quite right, Trevor, I did not know this was used for copper tubing also, but your comment about internal support reminded me of seeing an electrician bending PVC conduit over his knee without heating. Does not make the prettiest bend and it is not always easy to get the spring out without it wanting to slap one in the face, but quite effective for quick and dirty jobs.
Dear Amirul Azman
Temperatures from 99 to 135 degrees Celcius are ideal for bending this tubing. For the PVC Bend, this isn't a concern. Once the Bending is plugged into a power source, it can take up to 30 minutes to heat the tubing. With this size tubing, we've been able to achieve 90-degree sweeping bends.
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