Elib
Elib
Branch Unspecified
30 Aug 2016

Plastic bender

Hello everyone,

Introduction:

I'm currently working on a project about food growing. In order to do it I need a bench to bend plastic (acrylic) easly to make the main structure. The goal is to bend plastic and also being able to make precise curvy bends.
I have seen some DIY project that propose to heat up a wire of nichrome from a batteryy/variac and other..

Here are some examples :

- https://www.wa4dsy.com/robot/hot-wire-plastic-bender
- https://www.instructables.com/id/How-to-build-a-Plastic-Heat-Bender/
-


Project:

Here are some picture of where the project is a this moment.

Picture 1: whole structure made of agglomerated wood, aluminium beams and small other pieces.
13238857_10153781752728440_7245404869062021601_n
Picture 2: show hoz the structure is going to bend the plastic
13178927_10153781752778440_5115166659484428056_n
Picture 3: it's the area where the wire is going to stand and heat up the plastic
13226925_10153781752818440_8037609706639782567_n


Next:

I'm novice in electronics and I need to find the best and safest solution to heat up the wire.
Some possibilities:
- Use a Variac : expensive but easly customable, electricity could be dangerous
- Use a 12V battery 7mAh: less expensive but how long os the battery gonna last? Less dangerous with electricity as I would be playing with 12V
- Use a voltage variator: look also dangerous because I would be playing with hight voltage. But cheap
(https://www.befr.ebay.be/itm/REGOLATORE-DI-VELOCITA-SCR-3500W-220V-PER-MOTORI-AC-LAMPADE-DIMMER-TENSIONE-TEMP-/222057172918?hash=item33b3a38fb6%3Ag%3AkMwAAOSwMORW6-KO)


What would you do?
What nichrome would you use?

Thanks in advance for your answer, I'm gonna give you the result as soon as possible!
2 years ago
In the early 70s we had done a lot of acrylic fabrication for fairly large tanks that we needed for electroforming large objects.. Typically 10 mm thick sheets were used. There was no requirement to have bends. We used a solvent 'welding' process using Dichloromethane solvent. In this process the edges to be joined are softened using the solvent. While still soft the edges are pressed together and held under pressure for 24 hours. By this time all the solvent diffuses off leaving a perfect joint. In fact the joint would be stronger than the parent material itself because of a slight material build up at the joint.
When bending was needed and the size was not large, we used a blow torch to soften the area where the sheet was to be bent. This was not suitable for sheet thickness more than 4 mm or so.
Elib

Elib

Branch Unspecified
2 years ago
@A.V.Ramani : Thanks for your answers. Your first link is usefull but I'm currently bending with a hot air device. The problem is that it's not previce enough for me to do what I want to do next (I need a better precision). Your old technic look slow and difficult to imagine at home but I like the fact that it's possible to make "perfect" joints. Tough I have learn a new process thanks to a video related to it. Thanks you!

-> I only use 2mm or 3mm thick sheets

After some research here is the solution I suggest:
- Nichrome wire 0,5mm - 5,551ohms/meter (I use 40cm, 2,2204ohms)
- 12v 7amps power supply

0,5mm nichrome wire with 6A heat up to 760°c (https://hotwirefoamcutterinfo.com/_NiChromeData_files/1_Amperage.jpg)
U = 2,2204 * 6 = 13,3224v

So I could use this kind of power supply (12v):
https://www.amazon.fr/Bloc-daliment...ie=UTF8&qid=1463613101&sr=8-1&keywords=6a+12v

What do you think about this solution?

Some questions:
- 12v power supply while needing 13,3v what's the matter? Is it better to target 649°c with 5amp and needing 11,102v or even ?
- Do you think 760° or 649°c is enough?
Elib

Elib

Branch Unspecified
2 years ago
Do you have any proposition/advice about this last solution? I'm going to buy the material.
2 years ago
Elib
@A.V.Ramani :

-> I only use 2mm or 3mm thick sheets

After some research here is the solution I suggest:
- Nichrome wire 0,5mm - 5,551ohms/meter (I use 40cm, 2,2204ohms)
- 12v 7amps power supply

0,5mm nichrome wire with 6A heat up to 760°c (https://hotwirefoamcutterinfo.com/_NiChromeData_files/1_Amperage.jpg)
U = 2,2204 * 6 = 13,3224v

So I could use this kind of power supply (12v):
https://www.amazon.fr/Bloc-daliment...ie=UTF8&qid=1463613101&sr=8-1&keywords=6a+12v

What do you think about this solution?

Some questions:
- 12v power supply while needing 13,3v what's the matter? Is it better to target 649°c with 5amp and needing 11,102v or even ?
- Do you think 760° or 649°c is enough?
Difficult to evaluate without more details.
760 C is way too high. Acrylic can be bent at near 150 C. The problem is not the temperature but the wattage of the heat source. The wattage delivered by the wire and power supply indicated is only about 50 W. Most of it will be dissipated to the ambient.
Why not a simple step down transformer 230v to 24 volts (5 to 6amps). Choose a Ni-Cr wire of a suitable diameter so that the surface temperature is about 300 C at this wattage. The acrylic sheet should be held above the hot wire so that the area of interest gets the rising hot air.
Most probably low cost triac based voltage controllers are available locally in Belgium. A 1.5 or 2 kW version can be put on the input side of the transformer. It will be easy to control the NiCr wire wattage with this.
Since the load is resistive a simple transformer set up will be sufficient as DC is not needed.
Some info on the Triac controlled circuit can be seen here:
Light dimmer circuits

A lot of hand held torches are also in the market:
Leister Plastic Welding - Kunststoflassen!
2 years ago
A.V.Ramani
230v to 24 volts (5 to 6amps)
Sorry. The amperage is at the primary. Meaning, the transformer is rated about 1 to 1.2 kW.
A simpler option is to buy a tubular heater of required voltage and wattage similar to this:
Round Cross-Section Tubular heaters, 0.475 Inch Diameter, 304 Stainless Steel Sheath, 1 kW To 7.5 kW, 50 Watts/Square Inch

If you take care of the end connections with proper insulation you can directly run it from 230 volts grid voltage.
Elib

Elib

Branch Unspecified
2 years ago
Hello,

Just to tell you that the solution worked perfectly.

I have another bigger project (which use this one). It's about automatic plant grower. Can I present it somewhere here? I would love to hear your feedbacks and advices about it.

Thanks,
Edouard
2 years ago
Put it up here. The administration will shift it if it has to go somewhere else.

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