Working with Plastics

[Tiberius]

Hi guys,

I tried some experiments with bending various plastics. I had some clear acrylic sheet lying around so I set about bending that with the aid of a hot air gun. The first experiment hand bending a piece in the vice was ok. I also tried lining my metal bending machine with plywood and bending hot acrylic. I managed a really tight bend that way without cracking the sheet. But the best result I got was when I worked it over a wooden former.

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Another interesting thing was with PVC. Using a section of the duct I started with, I found it quite easy to hot work this. But I also found I could cold form a bend in it just using a normal metal bending machine with a little care.



BTW, the wooden former is the shape of my prototype battery box. It was built as a "plug" to take a mould from, in order to make a glass fibre box. The hot air gun I used is a fairly serious one, with adjustable temperature and a fishtail nozzle so it can concentrate the heat along a line.

Nick

 

[Link]

Isn't coroplast that corrugated plastic stuff? Yeah, I guess that would work, but I wouldn't trust it with a foil-pouch cell in a fall.

I bet it's nice and cheap, though. :wink:

I'd think it provides better impact and thermal insulation than 1/8" ABS.
Hot glue works for fold and flap construction but I wouldn't trust it without a few layers of nylon packing tape or clear duct tape banding.
I'd not bolt through it without a substantial backing plate.

I dunno. The stuff I got seems pretty tough in terms of impact resistance. I don't think I could do too much damage to it without really trying. And it probably is roughly equal in terms of thermal insulation, but that's not a good thing in hot Southern California sun. :?


Anyway, I scrounged around for some scrap wood and found a 24"x24"x1/2" and unknown-sized piece of plywood. I'll try to cobble together a strip heater with some nichrome wire tomorrow.

 

[marty]

I am feeling the need for some 1/4 inch thick plastic to build a top secret invention. OK I will tell you...... Building a rocket ship to fly to the moon. I AM JOKING!

I can tell the difference of different types of wood and metal with my nose. I know very little about plastics. Bought 5 sheets of plastic from Grainger. Did not shop around. Only went to Grainger because they are local and I can return 4 sheets. For what I am building, want a stiff flat hard plastic that can be glued.

Here are details the 5 plastics that I bought. Each sheet is 12 x 24 x 1/4 inches. Grainger sells lots of different sizes. Chose these 5 types because they were the lowest cost.

POLYPROPYLENE $8.90
2.75 pounds
.24 inches thick
Cloudy white. Light goes through it. Feels soft.

HDPE High-density polyethylene $9.77
2.5 pounds
.24 inches thick
White. Stiff flat hard. This one is the winner. If I don't change my mind, will use HDPE. Want to see how this plastic behaves and smells when cutting with wood working tools. Also will test how hot melt glue works with this. Not to concerned with glue strength. Want glue to be fast drying and easy to work with.

LDPE Low-density polyethylene $12.63
2.5 pounds
.24 inches thick
White. Most see through of all these plastics. Rubbery.

UHMW-PE Ultra-high-molecular-weight polyethylene. Tivar Eco Recycled $18.17
3 pounds
.26 inches thick
Black. Feels soft. Seems strong? Not smooth like the others. Rough scratched surface.

PVC Polyvinyl chloride $18.36
3.5 pounds
.22 inches thick
Dark grey. Heavy, hard, feels similar to HDPE. I like HDPE mostly because it costs less.

I be interested in learning more about working with different types of plastics. Gluing, welding, bending, cutting, sanding and polishing.

 

[friendly1uk]

I really like pvc and solvent welding.
I don't like polycarb. It gets used in police vans as bullet proofing, and windows as vandal proofing. However screw it to anything and the slightest nip of the screw cracks it. So while large panels transmit shocks nicely if hit centrally, I think that is about it's limit. I find it very weak, and only of use when optical clarity is required. Many disagree, but it is what it is. Brittle.

Coroplast is a trade name often used by Americans. Here we use another trade name I forget. The same continues globally. Where the term corrugated often has no local language variant. Even in other Germanic languages.


Is hdpe an ass to bond? It has good chemical resistance. Perhaps beaten only by ptfe where alcohols are concerned.

 

[cwah]

what's the best plastic then?

 

[friendly1uk]

what's the best plastic then?

Gold Card lol

It depends what your doing with it. I find PVC useful as it re-shapes easy, machines nicely, and solvent welding is just like using glue, but actually melts the surfaces together to make a real bond. It's great to have at hand.

PVC makes rubbish windowpanes and is not rigid. It also needs doping to be UV resistant. Don't like working temps above 70c as it softens enough to take a new shape.

Wire is often PVC insulated and windows often UV resistant PVC. We all have first hand experience with it. Other plastic can be a bit mysterious, and I find looking at recycling labels a good way to identify samples around the home. Because I have limited experience.

 

[Dauntless]

Best plastic. Most people would say which plastic sucks the least.

That Polypropylene (Recycling number 5) is a good, tough, outdoor plastic. This is what Pelican Cases are made of. Nothing sticks to it. That includes superglue. When they print on coroplast (PP) to make signs it takes special ink. You'll get it real hot to shape it.

HIgh and Low Density Polyethylene (#2 and #4) isn't as hard to bond but it's not easy either from what I've seen. Boiling water won't really melt it but it'll get soft enough to shape. So if you had one, say, butter tub made of PP and one of PE and ran them both through the washing machine, which would come out better? Gallon milk jugs, motor oil containers, old Mattel toys made of 'Tuff Stuff' are all PE. Grinds up in your blender, melts in your oven, there are ways. But it's not easy. You can even turn grocery bags into solid objects.

PolyVinylChloride (#3, at least sort of.) I don't suggest you casually heat it, especially indoors. Chloride - You know what chlorine is, right? Go to the plumbing dept. and get that PVC and glue and you can make some rather solid frames out of it.

Polystyrene (#6) is dang easy to shape. You can turn those white coffee cups into whatever you want. Use some citrus oil, or some less healthy acetone on those things and they melt. Same with the white packing material that you can tell are little balls. You can make things out of that which will hold the shape once the citrus oil evaporates. Not particularly strong stuff. PS doesn't do well in the Sun, Toyota I think it was made rear view mirror covers of it and they didn't last.

Not NOT to work with plastic: (Great fun to watch, though.)

[youtube]vO2b9iMitQY[/youtube]

 

[amberwolf]

what's the best plastic then?

For what?

There is no "best" unless you know what you want it for.

 

[d8veh]

None of the plastics in the list are suitable for what you want. You should look for high impact polystyrene sheet, which can be heat-bent, glued and drilled. You can also use acrylic sheet, but it's very brittle, so be careful not to bang it, and, if you have to drill it, be very careful when the drill breaks through the back side. Acrylic doesn't have the strength of polystyrene, so if your project needs structural strength, you'd need to go thicker with it.

 

[fechter]

You might try ABS. The stuff old school telephones were made of. It forms easily when heated and glues well.

 

[kfong]

I would build a 3D printer and just extrude it with ABS, but composites would be my preferred choice for battery boxes.

 

[marty]

You might try ABS. The stuff old school telephones were made of. It forms easily when heated and glues well.

Where I live, we mostly use PVC for plumbing drains. White pipe. PVC is Polyvinyl chloride. In some parts of the USA, I see black ABS drain pipes. ABS is All Black Stuff :lol:

 

[hydro-one]

coroplast. there maybe different types. political signs around here are the floppy cardboardy type. still very strong. it canalso be bought at home depot for 20$ for a 4x8 sheet. i have used this along with tape to build an under downtube lipo battery box and used this for years. other than the odd bit of water ingress, i have never had a physical issue with the the battery getting dented and i crash alot. i use two layers of it....i would use a rigid plastic but thats all i could find and it was free

i have seen some samples of corrogated plastic that are alot more rigid than the political sign coroplast and they would appear to be excellent materials structurally and perhaps thermally

 

[amberwolf]

most of the coroplast I've recycled from signage seems to be PE or HDPE of some type, cuz it won't take paint (not permanently, it flakes or peels off), won't dissolve with any of the solvents that work on all the other plastics, etc.

Some of it seems to be some type of styrene, based on how it's surface reacts with Krylon paint (xylenes) and polystyrene-type-solvents.

 

[docnjoj]

Polycarbonate honeycomb is used to built greenhouses and is very strong. Not sure about the price but it can also be glued with solvent cement. Prolly better to edge it with alloy angle and screws.
otherDoc

 

[Dauntless]

If it is coroplast, it is polypropylene. Fluted plastic from HDPE wouldn't be called coroplast, though online you see names of all sorts of things screwed up. PP is near impossible to paint, I don't know that the commercial plastics paint lasts, it is supposed to work well on PE. (Krylon Fusion, etc.) If you have a torch you can try flame treating it, can't walk you through that. If it says it's "Corona Discharge" treated it is supposed to be paintable.

A whole bunch of how to videos, basically how to do things they market supplies for. http://www.smooth-on.com/media.php Casting is how you are most likely to get healthy looking results without an injection molder of your own.

http://www.reynoldsam.com/seminars/categories/lta

 

[John in CR]

I made a battery for my van using A123 M1's and 2 coke bottles, which are PET and PET heat shrinks to some extent. Otherwise I have little use for plastic on an ebike other than wire insulation, unless you consider epoxy a plastic.

 

[marty]

None of the plastics in the list are suitable for what you want. You should look for high impact polystyrene sheet, which can be heat-bent, glued and drilled. You can also use acrylic sheet, but it's very brittle, so be careful not to bang it, and, if you have to drill it, be very careful when the drill breaks through the back side. Acrylic doesn't have the strength of polystyrene, so if your project needs structural strength, you'd need to go thicker with it.

Is this high impact polystyrene sheet?
http://www.mcmaster.com/# part number 8734K37
Easy-to-Machine Polystyrene Sheet
1/4" Thick, 12" x 24"
Color - Opaque to semi-clear white
Temperature Range - 0° to 155° F
Tensile Strength - Poor
Impact Strength - Good
$15.07

 

[marty]

You might try ABS. The stuff old school telephones were made of. It forms easily when heated and glues well.

Compared to the other plastics I looked at, ABS costs more.
ABS is Acrylonitrile butadiene styrene

 

[t3sla]

www.azom.com is your best friend!

 

[marty]

Bought this on Amazon.

HIPS (High Impact Polystyrene) Sheet, Opaque White, Standard Tolerance, ASTM D1892, 1/4" Thickness, 12" Width, 24" Length $19.63 + $6.93 Shipping & Handling + Tax
Part Number HIS-190335-F-01
2.75 pounds
.22 inches thick
White. Hard stiff. Sheet is warped. Experimenting with weights to see if I can get it to be flat.

Would this be a good glue for this plastic?
Testors Plastic Model Cement

 

[docnjoj]

The cement that you picture should work OK, but there are a number of solvent cements that have high concentrations of MEK or Methylene Chloride that really weld this type of plastic. Needless to say they must be used in a well ventilated area, or preferably outdoors. Here are some examples. I used their Lexan (polycarbonate) cement for my battery holder and it is still OK 5 years later. For the warpage, a carefully applied heat gun on low while the plastic is on a flat surface should flatten it. Don't go crazy with the heat or you can melt the sheet.
otherDoc

http://www.eplastics.com/Adhesives?gclid=COqakZbSkcQCFeFj7Aodv0gADg

 

[nutnspecial]

I was under the impression that most of the more widely useful plastics required 'welding' for the best joining. I repaired many pieces of street bike plastic a few years ago with a cheapy welder. came with rods for 8 different plastics, and I think I bought a book too that was helpful.
For actual fabrication or heavy mods to existing things, I believe they carry some nice welders that use hot air and welding rods- mine is just good for repairs (a glorified wood burner almost).
Found the case- it's by 'urethane supply company'
*And I agree, plastic is a great medium to get excited about manipulating- from fairings to boxes, light structural to repairs. check out their site, I'm looking forward to see what y'all come up with.
http://www.urethanesupply.com/

 

[marty]

Polymer Science Learning Center

More About Plastics
View attachment 8574KAC.pdf
Glass transition
Glass transition temperature (Tg) - the temperature at which a polymer changes from hard and brittle to soft and pliable.

Will try boiling water in a pot on the stove. Then pouring in on the Polystyrene Sheet in the bathtub to see if I can get the warp out of it.

 

[marty]

You might try ABS. The stuff old school telephones were made of. It forms easily when heated and glues well.

Compared to the other plastics I looked at, ABS costs more.
ABS is Acrylonitrile butadiene styrene

I was wrong.
http://www.grainger.com
ABS Sheet Stck, 12 In. W, 48 In. L, 0.250 In. T
$28.70

About the same price per square inch as the other plastics. Sheet is bigger. At Grainger one side had a texture. I no want texture. Looked and did not purchase from Grainger.