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View Full Version : How do you bend Lexan or polycarbonate?



Buckshot
08-09-2008, 04:16 AM
I bought some .125" x 12"x 24" sheets to use for making chip guards. However I need to bend it for some designs. I thought boiling water might be hot enough but it just made it hot and wet. No bendie :-)

I'm assuming a heat gun type deal?

Rick

jacampb2
08-09-2008, 04:42 AM
A heat gun will work, but you will not get sharp bends in material that thick. I believe that the production method used for thinner material is with a heated wire, and for thicker material it is a quartz heating element (like a laser printer fuser). I have a friend who had some good luck bending and welding using solvent. I believe he used chloroform, but several solvents should make it malleable. I would experiment with some clear PVC cleaning solvent and see if that softens it enough to be workable.

I have used the heat gun method for .125" material, and it makes a nice rolling radius, but depending on how sharp you need it, I doubt it will be satisfactory.

Later,
Jason

darryl
08-09-2008, 05:45 AM
Surprisingly enough, it can be bent at room temperature in a sheet metal bender, though it might also pick up marks from the machine. At that thickness it might crack since most benders would like to bend it to a tighter radius that it would like. A test with a scrap might be in order.

Otherwise it can be bent with heat as described, but more than boiling temperature is needed, around 275F or so. Polycarb will also absorb moisture and if it has done so to any extent it will require drying before the full heating is done, otherwise there can be crazing and bubbling, etc, and the transparency will suffer. The drying can be done at something near boiling temperature for a period of time. Moisture is more likely to be a problem the older the material is, and if the protective covering has been off.

For a line bend, you want the heat to enter the plastic quickly to minimize the softened part for a clean tight bend, but you don't want to raise bubbles in the plastic. Again, an experiment might be in order on some scrap to determine the distance from the heater to the plastic, and the time it takes to soften enough for a good bend.

A fully workable strip heater can be made from an old stove element, the kind that are coiled up and where the element wire is encased within the metal tube. They can be uncoiled and straightened without destroying the element inside, and are certainly powerful enough to heat even 1/4 thick plastic to the bending point. A suitably rated light dimmer can be used to control the heat.

Where the edges of the plastic pass over the heating element, the element should be bent downwards somewhat so the edges don't heat more than the rest of the plastic. If you're using a taut wire to create the heated line, this won't be as easily done.

In any event, avoid both under and overheating the plastic. If it's not hot enough, it obviously won't bend as expected, and if you take too long to soak the heat in, the heated area will become wider than you'd want. If you heat too fast or overheat, there will be some interesting bubbling results. Some experimenting on scrap should be done before committing the project piece.

You can use a propane torch to do the heating if you're patient and diligent. Use two pieces of aluminum flat bar or angle spaced apart on the plastic to define the desired heated zone, then wave the torch evenly across the entire line, without pausing at any spot. Pass it right off the plastic as you pass the edges so they don't get overheated before the rest of the plastic is soft. Obviously a flame shield would be a good idea under the edges.

It's good to have a jig set up so you can quickly make the bend to the desired angle or just past it, and hold it there while the corner is cooling.

Evan
08-09-2008, 05:48 AM
Lexan is a regular thermoset plastic and can be bent by heating. There is a major problem with trapped water in the material. Lexan must be baked at a low temperature at around 250 F for several hours to dry it out. Time depends on thickness and and for 1/8 material a minimum of three hours is required. If you try to bend it without drying it first the trapped water will turn to steam and create 1000s of bubbles in the plastic making it resemble a plastic turd.

How do I know? I use flame polishing on Lexan without drying first and it is a very tricky process. I hit it with a high temperature such as a propane bottle torch and then cool as quickly as possible with compressed air. Even then it is very easy to go too far with the heat.

Try a test piece in the kitchen oven by drying it at 250 for several hours. Use a polished aluminum mold for the Lexan to droop on. After the drying interval ramp the temperature up to 550 F. (not a typo, we are talking pizza temps) The deflection temperature of Lexan is 539 F.

JCHannum
08-09-2008, 07:32 AM
Lexan is a regular thermoset plastic and can be bent by heating.

Lexan is a termoplastic, thermosets cannot, as a rule, be bent or reformed by heat.

Evan
08-09-2008, 09:02 AM
That is correct Jim. I interchanged the terms.

Also, the melting temperature of Lexan depends greatly on what grade it is as there are a wide range of different grades. If the Lexan in question is the water clear optical grade without scratch resistant coating then an oven temperature of around 300F should be sufficient to cause it to droop to conform to a simple convex mold. If it does not then ramp up the temperature in 25 degree increments giving several minutes for the oven to reach the new setting. Once the material is formed turn off the heat and wait until it has cooled for 10 or 15 minutes before opening, then allow it to cool without disturbing until it can be handled.

GKman
08-09-2008, 09:30 AM
Reminded of a couple of things I saw at Oshkosh 20 years ago. Demo on pulling a bubble canopy over a male mold. demonstrator said that the heated plastic had similar elastic and strength properties as same thickness of rubber. In other words a lot. About eight guys were tugging on the edges to get it tight on the mold. The other I didn't see but sounded great. The inventor of the KR experimental aircraft formed his canopies with air pressure. The edges of the sheet was clamped down on a table with plywood with a canopy base shaped hole in it. The builder skillfully heated (torch or heat gun) and applied air pressure under it to blow the desired shape. Think I'll try some motorcycle side covers /number plates today.

Evan
08-09-2008, 09:35 AM
Light aircraft windscreens and canopies are generally made with acrylic plastic which has very different properties than Lexan polycarbonate. Acrylic is often vacuum formed in that sort of application. You can build a vacuum form system using a shop vac as the source of negative pressure. The reason for using acrylic is mainly scratch resistance. Plain polycarbonate is very easy to scratch.

J Tiers
08-09-2008, 10:28 AM
Plain polycarbonate, along with some other plastics, is also not very UV resistant, you will sometimes see lexan with a coating, and the label shows which side should be "out" for windows.

Another thing. Lexan is very strong. You can actually hammer-forge it cold. Although it won't be useful after that, the point is that it is strong and doesn't shatter.

However, some solvents (and possibly oily materials with solvents in them) will change that, and apparently can dramatically weaken it, to the point that a lexan window can simply be punched out with a fist almost like glass.

Haven't investigated that, but a chemist of my acquaintance mentioned it with respect to a different project, suggesting that it might not be suitable due to certain conditions.

Techtchr
08-09-2008, 10:33 AM
I made a protective machine guard from 1/4" thick lexan. I used the following method: Draw a line on the sheet where bend is to occur with dry erase marker. Heat along the line with a heat gun...both sides. When the lexan started to flex and before bubbles occur in the plastic, I put it in a sheet metal break and bent it. I went past 90degrees a bit...maybe 95, then let it cool. It cooled close to 90degrees.
Matt

Swarf&Sparks
08-09-2008, 11:23 AM
"However, some solvents (and possibly oily materials with solvents in them) will change that,"

Have to second that, JT.
Some time ago, I made a splash guard for my lathe from PC.
(because it was what I had on hand, no impact resistance required, just keep the suds in the tray).
Within weeks, it was clouded, then starred. Within months it fractured at the hinge fixing.
The acrylic replacement has now been in place for at least 3 years with no probs.
As I said, no impact resistance is required, this is just a splash stopper.
FWIW, the suds is just standard soluble oil "white water".

Evan
08-09-2008, 12:40 PM
The Lexan product by the name of Mar-Gard is craze resistant since it is coated with an entirely different material on the surface. Whatever it is it's harder than brass as a brass brush doesn't scratch it.

I suspect, although I haven't tried it, a wipe down using silicone oil whould protect polycarbonate quite well against the effects of various solvents. There aren't many solvents that can remove polydimethylsiloxane and once applied to a surface it is there to stay even if the film is only a few molecules thick.

Scishopguy
08-09-2008, 02:07 PM
I have made bends in lexan using an old sheet metal pan brake we had at the shop. I had a piece .125x 12"x 24" that I creased in the middle to make a safety shield out of. I didn't heat it but I did adjust the brake so that there was a little more than 1/8" of radius (the paper was still on both sides). and it came out just fine. No bubbles or scratches either. I was amazed that it stayed bent without any springback. Try it on a small piece.

Swarf&Sparks
08-09-2008, 02:19 PM
Evan, IIRC, certain brake fluids are largely PDMS?
If so, are they likely to protect in the same way?

JCHannum
08-09-2008, 03:47 PM
However, some solvents (and possibly oily materials with solvents in them) will change that, and apparently can dramatically weaken it, to the point that a lexan window can simply be punched out with a fist almost like glass.

Haven't investigated that, but a chemist of my acquaintance mentioned it with respect to a different project, suggesting that it might not be suitable due to certain conditions.
Many of airline accessories are fitted with polycarbonate bowls, airline filters and oilers primarily. They are not resistant to some compressor oils, they usually develop a leak first, but can deteriorate to the point that they shatter.

Peter N
08-09-2008, 03:47 PM
The Lexan product by the name of Mar-Gard is craze resistant since it is coated with an entirely different material on the surface. Whatever it is it's harder than brass as a brass brush doesn't scratch it.

I suspect, although I haven't tried it, a wipe down using silicone oil whould protect polycarbonate quite well against the effects of various solvents. There aren't many solvents that can remove polydimethylsiloxane and once applied to a surface it is there to stay even if the film is only a few molecules thick.

Interestingly enough, the Mar-Gard coating is a modified Polysiloxane applied over the base polycarbonate, then UV or thermal cured.
The taber abrasion resistance of polysiloxane hard coats is very good indeed, and also protects the PC from just about all the common chemicals that attack it so badly, as PC has very poor resistance to even light chemical attack.

However, PC is a major-ly notch sensitive material, and if you lightly score it it should break as clean as a whistle along the score line.

Peter

Evan
08-09-2008, 03:53 PM
Based on Peter's information I would try using a PDMS product on polycarbonate to give it some protection. You can buy a product called Rain-X intended to wipe on windshields to make it easier to clean off bugs and to make rain bead up and blow off the windscreen. It does work, I once drove about 500 miles in the rain with it without needing to use my wipers but it causes streaking if you do use the wipers so I didn't put it back on when it eventually wore off.

It is PDMS and will undoubtedly help to protect polycarbonate from solvents.

Swarf&Sparks
08-09-2008, 04:31 PM
<ping>
sound of penny dropping.
Didn't "rain-X" hit the civvy market not long after the Bell-47?

J Tiers
08-09-2008, 07:05 PM
It does work, I once drove about 500 miles in the rain with it without needing to use my wipers but it causes streaking if you do use the wipers so I didn't put it back on when it eventually wore off.

It is PDMS and will undoubtedly help to protect polycarbonate from solvents.

I use it all the time.

Wipe the wiper blades with it when you've finished applying it, that will prevent streaking.

lugnut
08-09-2008, 08:31 PM
Lexan, My son works for the Pepsi Company and he got and gave me several (10) of the front panels from their vending machines. It's supposedly lexan and very tough stuff. the sheets are about 3'X 6' and .125 thick. I have use the heck out of the stuff. Made garden carts, whirligig propellers, table saw inserts and lots more. When ever I need to make a sharp bend, I clamp the piece between two boards and use a heat gun to heat and bend the stuff. Works great. Just have to be careful not to get it too hot. I've not had too much luck gluing it though.
Mel

Buckshot
08-09-2008, 11:09 PM
............Great responses, and good info about the Rain-X. I love that stuff and will use some on the shields. I guess maybe I should have used Acrylic material instead of the 'PC'? My neighbor said he has an industrial heat gun I can borrow. I will clamp both sides of the material using 1" doug fir, leaving about a 1/2" gap to apply the heat through.

Rick

Evan
08-09-2008, 11:18 PM
I have good luck with ordinary cyanoacrylate glue. If that doesn't work for you then this absolutely will. It even glues Teflon securely as I can attest.

http://www.acehardware.com/sm-loctite-all-plastics-super-glue-loctite-all-plastics-super-glue--pi-1390287.html

lugnut
08-10-2008, 01:47 AM
Thanks for the heads up on the cyanoacrylate glue, Evan. I had tried some el-cheap-o super glue with little luck, but I know that locktite makes great stuff and will give it a try.
Check out your local soda vending company and see if they will part with some of their old pop machine front panels. great stuff.
Mel

HTRN
08-10-2008, 11:07 AM
Guys, you might want to check some Aquarium sites, because building custom acquirums is a fairly popular hobby.

Here's a page (http://ozreef.org/diy_plans/techniques/gluing_acrylic.html) on bonding acrylic for acquirium builders..


HTRN

Evan
08-10-2008, 11:53 AM
Acrylic and polycarbonate are entirely unrelated plastics so methods that work with one usually don't apply to the other.

HTRN
08-10-2008, 12:39 PM
Commercially, the most common method appears to be Solvent Adhesives, notably Methyline Chloride(used for both).

Craftics (http://www.craftics.com/) is a major supplier for working with plastics, you can probably find what your looking for there.

Weldon #3, mentioned in the above link, will bond both Acrylic and Polycarb, as well as a number of other plastics.


HTRN

Evan
08-10-2008, 02:13 PM
Here is the last word on working with Lexan sheet products from General Electric. I note that while it mentions various adhesives that may be used to bond Lexan sheet the method of solvent welding is not even discussed. I presume that is because it would seriously compromise the strength of the resulting product.

http://www.theplasticshop.co.uk/plastic_technical_data_sheets/lexan_polycarbonate_sheet_processing_guide.pdf

The reference covers everything from heat draping to milling and drilling.

snowman
08-10-2008, 06:12 PM
Most solvents in general will cause crazing with lexan. While you may create a good mechanical bond, you will drastically reduce the strength of the base material while solvent welding. This by no means suggests that you can't glue or adhere things to lexan, it just wont be a solvent weld.

Lexan does not score cut well, acrylic does. Lexan does not cut well period, even using quality sharp tools, lexan has a tendancy to chip weld, grab and kick back at you.

The Tg of Lexan is right around 146 deg C IIRC. It can be thermoformed and vac formed quite well, but the process is a bit different. It is currently the window material of choice in the smart car, but this window has had a hardcoat layer applied to it.

The absolute best way to bend it is by using a heat tape. You can purchase these at plastics supply houses. It will be about an inch wide and say, 6 feet long. You adhere the tape on the bend line, on both sides of the plastic, heat slowly, then just wait. If you don't want bubbles, you wait longer.

You can cold bend polycarbonate, but it will create a lot of stress in the bend. If your application allows it, who cares. Most applications allow it, especially if it doesn't have to retain it's optical characteristics.

I personally hate the stuff, but I worked specifically with it and no other polymer for two years, I've learned it's limitations.

If I've got an application where I am protecting myself, I'll use it...sandwhiched between layers of tempered glass.

Evan
08-11-2008, 07:15 AM
Lexan does not score cut well, acrylic does. Lexan does not cut well period, even using quality sharp tools, lexan has a tendancy to chip weld, grab and kick back at you.


I machine a lot of Lexan and I find it very easy to machine. It's all a matter of feeds and speeds as well as adequate cooling. The best cooling is just a high volume stream of compressed air which also clears the chips. It's chip buildup and recutting that causes most of the problems after melting the work. Air prevents that and keeps the tooling below the melting point of the work.

This is made from Lexan and most of the machined surfaces are straight off the mill with no additional polishing or other treatment.

http://vts.bc.ca/pics4/maggearbig1.jpg

NickH
08-11-2008, 07:36 AM
To bend sheet plastics build yourself a line heater, you can use a linear halogen bulb, reflector and a shield to allow exposure of only a thin line of your sheet.
This is a technique used for much display point plastic bending,
Regards,
Nick

Evan
08-11-2008, 08:20 AM
A good source of linear halogen heat lamps is an old photocopier. If you are lucky and find a really old one you can also get what is called a "radiant fuser" unit like this one. It's about 17 inches long and it's ideal for line heating as that is it's intended purpose. It has a housed 600 watt halogen bulb and ceramic feet on each end to stand off from the material. The bulb is protected by a quartz window and it runs from 117 vac. With an appropriate light dimmer you are all set.

http://vts.bc.ca/pics4/fuser.jpg

The parts that look like gold are only gold plated. It's actually pretty thick though. It has to take a lot of wear and abuse in service. :D

gellfex
08-12-2008, 10:44 PM
Reminded of a couple of things I saw at Oshkosh 20 years ago. Demo on pulling a bubble canopy over a male mold. demonstrator said that the heated plastic had similar elastic and strength properties as same thickness of rubber. In other words a lot. About eight guys were tugging on the edges to get it tight on the mold. The other I didn't see but sounded great. The inventor of the KR experimental aircraft formed his canopies with air pressure. The edges of the sheet was clamped down on a table with plywood with a canopy base shaped hole in it. The builder skillfully heated (torch or heat gun) and applied air pressure under it to blow the desired shape. Think I'll try some motorcycle side covers /number plates today.

I worked in a lighting factory in Berkely once, and one of the jobs was vacuuforming and blow molding covers. We had a vertical oven with a rolling track going into it on which you clipped a sheet of acrylic up to 4x8 and 1/4" thick, and rolled it in. Then you took it out floppy as a sheet of rubber and slid it onto the press, slammed the form atop it and brought down the press. If it was a dome you hit the air and blew the bubble till it approached a stick coming down from the press. There were diffusers that had multipart molds that you used both vacuum and pressure to form.

Comment on flame polishing since it was brought up. Best results come from an oxy-hydrogen flame since you get no carbon trapped in the surface.

wshelley
08-13-2008, 06:25 PM
Since no one else asked and I'm curious. Even, what was the whirlygig gizmo you made? It appears to have a lot of magnets in it?

Ward

Evan
08-13-2008, 09:14 PM
Search back a couple of weeks for my thread on magnetic gears. The one in the photo is the new improved version with ten times the torque transfer capability.

Buckshot
08-14-2008, 04:59 AM
I am successfull at bending Lexan :-) My needs were modest at first, as all I wanted to do was to provide a shield on the rear of my milling vise. It was to sit down over the two 1/2-13 socket head bolts and 1 inch past the vise on either side was to be bent forward to form wings. This was just to keep chips from being flung backwards. The position the mill is in makes cleaning in that area almost impossible.

My neighbor is in construction and after hearing of the use of a heat gun I asked if he had one. Myself only having the wife's hair dryer as being the closest tool to that required (short of a torch). He's one of those guys who is just tickled to death if you ask to borrow something, so I had it immediately. I drew the bend lines on the plastic with a Sharpie and clamped it between two 6"x6" pieces of 1" Doug Fir.

I ran it slowly in a circular pattern, off one edge then circled back around to the other side, rather then simply back and forth. Since the wing area is only 4" long I felt it better to test the softness with finger pressure out at the end, rather then waiting for it to droop of it's own weight.

That Milwaukee heat gun was flat putting out some HOT air so I played it easy. I guess it was a bit over a minute and finger pressure on the end had it give. Since the curve was gentle I got off the heat and just pressed it down to an eye appealing angle. The other side went much faster, but just as well.

The Lexan seemed to retain the heat for quite some time so I'd think if you were doing something complicated (bend wise) some tepid water on hand would be good. I had just cut a slot across a new set of soft jaws in the vise so laid the plastic in and used the same 3/8" rougher endmill to mill the slots out. Worked like a champ!

Rick