Sheet plastic bender

Thread Starter

robismod

Joined Sep 22, 2015
217
I have several heat grid assemblies from an old HVAC unit. Could I use 120v to heat a length of the wire (roughly 32”) to make a long bend (across the width)? It’s almost 1/4” thick and I’m using it as a windshield for a UTV. (Yes, I realize the potential hazards of the mains voltage)
Thanks for any guidance.
 

MaxHeadRoom

Joined Jul 18, 2013
28,617
What is the nature of the plastic, will it conform to bending Plexiglass for e.g.?
I have used a guide and a flame at a short distance from the glass to heat it, moving it across the panel rapidly.
.
 

Thread Starter

robismod

Joined Sep 22, 2015
217
What is the nature of the plastic, will it conform to bending Plexiglass for e.g.?
I have used a guide and a flame at a short distance from the glass to heat it, moving it across the panel rapidly.
.
I believe it’s acrylic…from Lowe’s. I’ve tried a heat gun but it’s such a wide bend I can’t seem to focus enough, long enough evenly to make it work without distorting it.
I know I can order nichrome wire but…just wondered if I can make do this one time with materials I have…
 

MrSalts

Joined Apr 2, 2020
2,767
General Purpose Acrylic (Plexiglas, Lucite, ...) is a really bad idea for a windshield. If it breaks, it will break in knife-like shards. High impact acrylic is used for motorcycle windshields (occasionally) but prices of acrylic and polycarbonate have merged closer and closer in recent years so most are now made from polycarbonate.
Secondly, any stress used to bend it into shape will cause spider cracks across the acrylic over the next days to months. 6mm is pretty thick and heavy.
Be aware that acrylic that thick will have to be heated long and low. You'll need some type of hinged jig to keep it in position as you bend it and let it cool. If you heat it too hot, acrylic can depolymerize and the monomer vapors will immediately ignite. Keep your fire extinguisher handy, that's a big piece of acrylic to burn - acrylic keeps burning after you remove the heat source.

I strongly recommend polycarbonate. If you do go this route, talk to your plastic sheet seller about hard-coated polycarbonate to protect it from scratches and the weather.

finally, when polycarbonate breaks, it generally stretches and tears instead of shatters. You need a very high speed impact or spinning blade of a table saw to cause PC to shatter (way faster than an auto/ATV accident). . Thicker sections shatter at lower and lower speeds.

Good luck.
 

Thread Starter

robismod

Joined Sep 22, 2015
217
General Purpose Acrylic (Plexiglas, Lucite, ...) is a really bad idea for a windshield. If it breaks, it will break in knife-like shards. High impact acrylic is used for motorcycle windshields (occasionally) but prices of acrylic and polycarbonate have merged closer and closer in recent years so most are now made from polycarbonate.
Secondly, any stress used to bend it into shape will cause spider cracks across the acrylic over the next days to months. 6mm is pretty thick and heavy.
Be aware that acrylic that thick will have to be heated long and low. You'll need some type of hinged jig to keep it in position as you bend it and let it cool. If you heat it too hot, acrylic can depolymerize and the monomer vapors will immediately ignite. Keep your fire extinguisher handy, that's a big piece of acrylic to burn - acrylic keeps burning after you remove the heat source.

I strongly recommend polycarbonate. If you do go this route, talk to your plastic sheet seller about hard-coated polycarbonate to protect it from scratches and the weather.

finally, when polycarbonate breaks, it generally stretches and tears instead of shatters. You need a very high speed impact or spinning blade of a table saw to cause PC to shatter (way faster than an auto/ATV accident). . Thicker sections shatter at lower and lower speeds.

Good luck.
I’m not exactly sure which material I have, but I know it was expensive…
And yes, I’ve built a hinged-table that should work quite well for the bend IF I can just get some even heat across it…
 

MisterBill2

Joined Jan 23, 2018
18,167
A hot wire is not suitable for bending thick plastic because it must be heated all the way through and the plastic conducts heat poorly. Exactly as described in post #4, the heating must be done long and slow. So the plastic needs to be clamped to a form so that the bend will come out right.
Using a flame can work BUT it is easy to overdo and create bubbles and melted edges. So using a flame is what I suggest avoiding, unless appearance does not matter at all, or you have had lots of practice. Or if you can get MAX to bend it for you.

I have done a fair amount of bending thicker plastic and have used a hot-air gun to heat it That takes quite a few minutes and it is able to soften an area not just a line. So it is possible to make wider radius bends without distortions or wrinkles. A hot wire will be way too hot in a small area and will do damage rather than soften all the way through.. It is the wrong tool for the job.
 
Last edited:

LowQCab

Joined Nov 6, 2012
4,022
In addition to all of the above ........
Find a Plastics-Dealer and get some "Lexan" Sheet,
or use whatever the business recommends for your application,
they may have a superior product they can recommend,
AND they might even be able to bend it for You, or
recommend a shop that can bend it for You.

You can use coiled Nichrome-Wire,
just keep in mind that it will probably sag quite a bit when it heats-up,
so it will need to be supported at regular intervals along a ~36-inch length.
Look at how close the Supports are in the Heater that You are scrounging from,
You need to duplicate that spacing and support.

Then, measure the total length of the Element ...........
what percentage of that length will You be using ?,
You need to reduce the Voltage applied to the partial Element section by the percentage measured,
and then reduce that number by at least half, because there will be NO-AIRFLOW over the Element.
A Car-Battery just might work, but it won't last very long with that much Load.

Is it worth it ?, only You can say.
.
.
.
 

MrSalts

Joined Apr 2, 2020
2,767
Find a Plastics-Dealer and get some "Lexan" Sheet,
"Lexan" was a brand name of GE Plastics and used to be THE Polycarbonate in North America. A Saudi Arabian company (SABIC) bought GE Plastics and still uses then Lexan name. Other global suppliers have set up plants in the US to make sheet polycarbonate from various manufacturers around the world - all are roughly the same for your application.

Hyzod®
Lexan®
Makrolon®
Susta® PC
Tecanat™
TUFFAK®
Unicar®

Also, if using a hot air gun, place some 1x3 or 1x4" wood strips on either side of the bend to shield the rest of the flat from heating. The gap between the wood strips should be about 3x the thickness. In your case, about 3/4". Heat from about 2" above the plastic for polycarbonate and 3 to 4" for acrylic. If the wood is charring/"toasting", you are at about the right temp for poly carbonate, ir you see any fumes or bubbling on acrylic you're too hot.

Pull on the bottom edge of your sheet, if possible, to feel when it "gives" a bit, then it is soft enough to form.

Keep it clamped for more than 5-minutes to cool into shape.

To test which you have PC or acrylic, shave off some edges that you don't care about to make some strands or chips. Put a match or lighter on them. If they burn with a visible flame that keeps going, it's acrylic. If it turns black and/or melts into a ball or bead and/or makes some black smoke, it's polycarbonate.
 

Thread Starter

robismod

Joined Sep 22, 2015
217
"Lexan" was a brand name of GE Plastics and used to be THE Polycarbonate in North America. A Saudi Arabian company (SABIC) bought GE Plastics and still uses then Lexan name. Other global suppliers have set up plants in the US to make sheet polycarbonate from various manufacturers around the world - all are roughly the same for your application.

Hyzod®
Lexan®
Makrolon®
Susta® PC
Tecanat™
TUFFAK®
Unicar®

Also, if using a hot air gun, place some 1x3 or 1x4" wood strips on either side of the bend to shield the rest of the flat from heating. The gap between the wood strips should be about 3x the thickness. In your case, about 3/4". Heat from about 2" above the plastic for polycarbonate and 3 to 4" for acrylic. If the wood is charring/"toasting", you are at about the right temp for poly carbonate, ir you see any fumes or bubbling on acrylic you're too hot.

Pull on the bottom edge of your sheet, if possible, to feel when it "gives" a bit, then it is soft enough to form.

Keep it clamped for more than 5-minutes to cool into shape.

To test which you have PC or acrylic, shave off some edges that you don't care about to make some strands or chips. Put a match or lighter on them. If they burn with a visible flame that keeps going, it's acrylic. If it turns black and/or melts into a ball or bead and/or makes some black smoke, it's polycarbonate.
Thanks much for all the info and guidance. I have already built a “bending table” that clamps the piece in place. An aluminum U-channel is sandwiched between it and an outboard piece, which is hinged and intended to be lifted up to make the bend. The U-channel houses the hot wire along it’s approx 32” length, and has a spring supporting one end for the heated stretch. I’ve tried wire from hair dryers with various power supplies and haven’t had any real success with getting wire to glow red. Best power option so far has been a PC supply, but it either runs but doesn’t get hot enough, or it immediately goes into protect shutdown depending on whatever configuration I’d came up with…
When I ran across these big strip assemblies I figured surely there’s a way to make them work (short of hooking up 220 ? to them as they were used in the HVAC unit)
 

MrSalts

Joined Apr 2, 2020
2,767
Thanks much for all the info and guidance. I have already built a “bending table” that clamps the piece in place. An aluminum U-channel is sandwiched between it and an outboard piece, which is hinged and intended to be lifted up to make the bend. The U-channel houses the hot wire along it’s approx 32” length, and has a spring supporting one end for the heated stretch. I’ve tried wire from hair dryers with various power supplies and haven’t had any real success with getting wire to glow red. Best power option so far has been a PC supply, but it either runs but doesn’t get hot enough, or it immediately goes into protect shutdown depending on whatever configuration I’d came up with…
When I ran across these big strip assemblies I figured surely there’s a way to make them work (short of hooking up 220 ? to them as they were used in the HVAC unit)
You're going to have to engineer this pretty carefully. I'd say you'll likely need 1200 watts to heat an 18" long heater and get the work piece to 150 to 200°C range (will need to be well beyond published VICAT temp which is the temp the material yields under a weight).

You'll be losing a lot of heat into the table if there is any contact on the backside of the sheet. Ideally, you'll be able to heat from both sides. This is not as easy as it seems when you watch an expert with professional tools.

If you are trying to heat an element with 12v power supply when the element is designed for 220v, then you'll need about 20x more amperage to get it to a similar heat output. "Temperature" is not a good measure alone because it really depends on temp difference and air flow and thermal conductivity of materials near your bend-line. Note that aluminum has about 200x more thermal conductivity than acrylic or polycarbonate so your aluminum frame may need to be insulated or somehow avoid it from acting as a heat spreader and draw heat away from your bend-line.
 

MisterBill2

Joined Jan 23, 2018
18,167
All the reasons given in post #11 are why I have used the industrial strength hot air device, the one that will melt soft solder on a PCB if given time. Heating from both side does speed it up a lot but heating from only one side allows more working time. A single wire can be hot enough but it will not deliver enough heat to bend 1/4 inch plastic in a reasonable time.
 

Thread Starter

robismod

Joined Sep 22, 2015
217
You're going to have to engineer this pretty carefully. I'd say you'll likely need 1200 watts to heat an 18" long heater and get the work piece to 150 to 200°C range (will need to be well beyond published VICAT temp which is the temp the material yields under a weight).

You'll be losing a lot of heat into the table if there is any contact on the backside of the sheet. Ideally, you'll be able to heat from both sides. This is not as easy as it seems when you watch an expert with professional tools.

If you are trying to heat an element with 12v power supply when the element is designed for 220v, then you'll need about 20x more amperage to get it to a similar heat output. "Temperature" is not a good measure alone because it really depends on temp difference and air flow and thermal conductivity of materials near your bend-line. Note that aluminum has about 200x more thermal conductivity than acrylic or polycarbonate so your aluminum frame may need to be insulated or somehow avoid it from acting as a heat spreader and draw heat away from your bend-line.
No, I didn’t plan on 12v in an attempt on this Strip Heater wire…I was curious what 110 might do…(I’m just not brave enough to mess with 220, even though I’d rig it in a way where I’d never be close to the setup—but still, any big spark or flash would make my heart jump LOL)
 

MisterBill2

Joined Jan 23, 2018
18,167
A step-down transformer is a good idea, even if it does not provide isolation. Surplus transformers are often worth the effort of searching for them.
ARC FLASH damage is much faster than shock damage. Copper vapor is nasty stuff. Not only is it very hot, it is also a very good electrical conductor.
 
Top