Forming Polycarbonate

Strip heaters are indeed the answer, especially if you need to repeat a few times. My father built one years ago using three pieces of 1/4 inch thick Transite (a concrete material made of cement with asbestos fibers instead of sand, and no larger ingredients as aggregate; today they use a silica sand instead, but I believe that it will still handle the temperature very nicely). The first, wide piece went down onto a heavy plywood base, followed by two narrower strips spaced about 3/8 inch (1cm, roughly) apart. Between them ran a 1/4" OD coil of resistance heating wire. (1/4" = 6.35mm). He had a large Variac, and set it where the coil got to perhaps 200 degrees F. Typically, for a job like this, there would be a couple of thin spacers placed parallel to the heating element, with the plastic resting on them. Usually, it was possible to see visible sag and thermally-induced changes to the optical properties along the line; then it was time to bend. Slow heating is good; especially if the material has any absorbed moisture, to gain best control over the process.

If you buy resistance heater material from an appliance repair shop, they should be able to tell you what will work for, say, a 12 volt battery supply.

Depending on the length; Alternately, if you cant get a strip heater, and have a jigsaw and some nails/screws, you could make two moulds, one the size of your outside dimensions of the u-piece, and one the thickness of your material smaller, then put your material in any old oven, and when it becomes ductile, wedge it between the large and small mould til it goes hard. Sounds pretty caveman-ish, i know, but it will work.

A hair dryer or heat gun is equally good, particularly if you are only using 60mm wide PC.

All sorts of useful information here:

http://distributionbizwiz.wordpress.com/2007/08/22/machining-forming-polycarbonate/

5mm sheet is pretty thick. My experience is with injection molding rather than forming sheet stock, but I found polycarbonate to be cranky stuff to work with. The temperature range between soft-enough-to-manipulate and devolving-to-shapelessness is fairly narrow. Be prepared to experiment.

You can bend Polycarbonate cold, I don't know how you would go with 5mm.

I have seen a heater using the wire spring used for curtains, shown in red, this can be heated with a home welder or car battery depending on its length and thickness, you need to experiment. Wrap some fibre glass tape around the top block to retain the elements. You may be able to use wood if the elements don't get too hot.

Tony

A welder? haha, that sounds pretty safe. Are you going to take responsibility for someone electrocuting themselves cause they have tried to make a heating element from a stick welder they picked up Bunnnings? Not trying to insinuate that the original poster is stupid and wouldnt know how to do such thing, but what if they didint know? "ill just put this positive and negative on this curtain wire an make myself a strip heater, like someone on CR4 told me....it sounds easy" BANG! your hooked up to 140 amps, and your dead, or getting defribulation from the ambos. Make sure you check you have a safety switch on your premises first.

Bahahahahahhaha......a welder.....

The original poster asked for an electric heater, I have assume some electrical knowledge.

They can also receive burns from other heaters suggested or crush their fingers bending the material. Worse still they could burn out the curtain stringer and their wife could beat them with a large hammer.

Apparently you are not familiar with electricity. Generally, voltage kills not current (amperage) and welders, both domestic and industrial, are designed to run at a non-lethal voltages.

I suggest you research your subject before posting silly comments.

Tonymech - naughty that is. Current kills, but a potential great enough to cause it, is required against the bodies resistance.

Not that I disagree with your conclusion; but if you are going to call "posting silly comments", you first need your own 'ducks in a row'.

Sorry, I probably lost my cool, but I'm too old for nannying.

I would rather suffer a shock of 12v at 1000A than 1000v at 12A, that would certainly knock the ducks out of line.

Tony

Ok, this is a bad analogy, but just because i go to an automotive paint shop and ask to buy a spray gun, doesnt necessarily mean i would have any idea how to use it. Does it?

Whilst you are correct in assuming my missus would most likely beat me with a hammer if i destroyed her curtains whilst trying to form polycarbonate, you are incorrect in stating that i am unfamiliar with electricity. Dont get me wrong, im no guru, but i think i got the basics.

Ohms law: V=IR

Voltage is proportional to current, and current is the thing that will most likely kill you when you you are dealing with "low voltage" (below 1000 volts) "non lethal" domestic appliances, welders, etc. The worst 1000 volts with no current will do is sting a little, but if you get hit with as little as 30 miliamps then there is a good chance your heart will go arrrythmic (into fibrillation). If that happens and your body shuts down, your lucky enough to have someone around that knows CPR, and they are nice enough, then they will administer CPR until the ambulance arrives with the difibrillator and shocks your heart back to "normal". Or alternately (and unlikely) they may just pronounce you dead at the scene.

If you suffered either a 12V hit at 1000A or a 1000V hit at 12A and you were on your own somewhere, then its more than likely that you wouldnt be around any more to reply to my post. Personally i wouldnt like either if i had a choice.

Thats why someone can shock you with 1000V from a megger (thats an insulation resistance tester) and you dont die or suffer any ill side effects besides a small stinging sensation (very little to no amps). Or an elctric fence is another example that springs to mind, im not sure what current they run at, but id say its low, and they pulse, so your not exposed to the current for a period long enough to do you damage.

As for welders being "non lethal", i know of 4 instances here just in my town with both 3-phase and single phase welders where people have been electrocuted (dead). With that being said they were probably in the hull of a boat, with no rubber matting, covered in sweat, whichs means their resistance was markedly lower than normal (somewhere between 4000-40000 ohms).

Im no nazi, and i really dont care if someone goes playing around with elctricity and ends up killing themselves, just as long as they didnt do it because of some advise i game them, and that, was my original point. Now where are these ducks? :)

Small duck, 12 V won't generally overcome the bodies resistance, or a common car battery would kill people with its ~ 100 - 300 cranking amps, and probably 1000 + short circuit current.

32 V is regarded as 'industrially safe'. Most common stick welders ~ 50 V, so sometimes shock the careless and take out fools.

But you could electrocute yourself with a car battery if you're prepared to work at it.

What you need to do; is first insert the electrodes ....

"Small duck", haha, thats brilliant!.....i wholeheartedly concur.

I have had 3mm thick Polycarbonate sheet bent into a large U shape using a series of cold bends done in a conventional sheet metal bender. As I remember the included angle was ~150°, so 3 bends about 50mm apart to get to 90°. I was building custom radomes for a cellphone phase station site. I painted the material with a 2 part linear polyurethane and as far as I know it's still there after 15 years.

I have bent PC using cooking oil to heat the sheet it is inexpensive and heats uniformly remember to not overheat the oil 150-160deg C is good

It's not the answer to your question, but: PET is a remarkable material, and can be bent cold. Certainly 3mm would be easy at your width, just fold it like paper really. At 5mm it would need some kind of jig to hold it firm, but still not hard to bend.

IF your U shape is close-sided, like the sleeves that are in estate agents windows, containing one sheet of paper, then you will need heat to remove the tendency of any material to spring open, if the U is wider, you will need to overbend so it relaxes into a 90.

PET remains beautifully clear at the bend.

I haven't done it with PC, but with ACM, how about routing most of the way through, with a 90 included angle, with a say 2mm flat on it, then bending and glueing?

The look of this corner wouldn't be great, if your PC is clear, but it's an idea you can reject freely.

CNC Jim

Depending on your average humidity, you'll have some water in the polycarbonate. It can take up to 8 hours of soaking at 90-95C to dry it to avoid bubbles at forming temperature. You can do this in a kitchen oven. After that, you can use the ordinary oven element as a strip heater. Just hold the plastic over it, close but not touching, until it starts to sag. Then make your bend.

I've also made dedicated heaters by using nichrome wire from old fashioned hot plates and some scrap sheet insulation from wood stove installations. Really old stoves have handy porcelain insulators that are good for cobbling up all sorts of custom heaters, like hot wire cutters. A heater element can be used to regulate the heat and reduce the voltage of the working portion to a safe level.

Who ever mentioned a hair dryer... you can't use a hairdryer to soften polycarb. You need about 300°F ± 10° to soften polycarb to proper bending temp. Otherwise you'll risk cracking. Hair dryer is no where near that.

Wrong

No, actually it's right. Either that, or I dreamed all those projects where I formed polycarb sheets over all these years.

Hi OBE

Would you agree that any suggestions made here have forgotten about the timing involved? Maybe I missed someone pointing that out. Just too lazy to search all day and to find out if I am plagiarizing and hurting someones feelings. Bloody purple brigade has a lot to answer for, I'm ^{[allzeit betreit}] just in the mood for conflict

If I may, and I have done a bit of forming, suggest to do every thing at a very slow pace. Long and stepped up heating and long and slow cooling. This avoids fissures which are hardly ever seen with the naked eye immediately but only show up as annoying reflections of ones impatience, maybe months or even years later.

If its only something to be used or handled go for it. 150 of that size in a day. If you want good long term results, take your time. No, not you OBE, I mean the OP. You seem to have been there.

Do you agree?

Happy bending, Ky.

And it never blistered, or broke out in micro-bubbles?

Remarkable.

I have always had success with an adjustable heat gun. I have used it with plaster molds and a press to mold very small parts out of HDPE. You should be able to experiment and get the temp right for your needs.

Over the years, I have bent PC with a sheet metal bender (3mm and less, and bends of less than 45 degrees). I first did this in the 70s. I have also used a 13mm diameter propane soldering torch, moved quickly along a wooden straight-edge (in the early 80s). This made a nice smooth, 7mm radius bend, and voila, I had a 3mm PC cover for the nose of my 356 Porsche. No more bugs and rocks on my paint, and the car's colour shows through, so it did not look like the car had a black garbage bag over its nose, the look of those vinyl 'bra' covers.

Last year, I made a canoe out of 5mm PC. Bends were with a parabolic reflector heater (1940 vintage) and a digital remote IR thermometer. It is a bit blobby looking, because PC expands so much as it heats, and will solidify based on heat losses, not on the pattern of your heating. I should have taken the time to make a mold and a heated box. With a huge 200 C oven, and a full-size wooden mold, it would have been rather elegant. Maybe next time.

David

Thank you all for the ideas. I have printed them all off and I will rummage through them. Great response, thanks again. Rex Devantier.

You have some great ideas from all...

From personal experience, used a heat gun with mdf jig (rounded edge).

worked on 1/8 and 1/4" pc. good luck!

OK. I saw one in a fabricating workshop.

IT was just a slot in the middle of an 8' by 4' table. the slot was about 10mm wide, and was lined with aluminum ( aluminium). in the middle of this slot about 5mm down was what looked like the element from a storage heater that had been straightened out.

There are some nice clear vhb tapes. if your u shape is very narrow

CNC jim

Lots of good ideas, most of which will work. As many have mentioned, the heatgun will work fine. As far as cost, it might be your cheapest option. You can get one at a DIY store for $30-$40.