"Forming" Custom Size Battery Cases

Theory
Heat rises - An open bottom box will retain heat nicely,
Using a rotary dimmer powering multiple light bulbs (4-6? 100w bulbs) should provide precise temperature control
While temperature can be precise, direct observation is recommended


Parts:
Rotary light dimmer
light bulbs
digital meat thermometer
300 ºF safe, open bottom "box" w/glass observation window (Plywood, even cardboard, is fire-safe to ~451 ºF)
( PET (Polyethylene terphthalate) is about 250—260 ºC = 500 ºF is too hot - requires fire safe materials!)
wood paint stirrer sticks, spatula, any smooth or desired shape shaping tools
hairdryer, heat gun ?
hack saw or jig saw w/fine wood or coarse metal blade

Method
Place PVC (or other material) sheet on top of "form" (desired shape item.)
Raise into "oven", or place oven over project.
Adjust heat to proper temperature
Observe temperature rise and watch for indication of PVC wilting-melting
When near optimal temperature, remove from oven and form shape using wooden paint stirrer sticks etc
Use heat gun etc. for additional, or finishing, formability

Tips
Cut corners, but leave material for a fold or overlap - a bulky "apron" at corners is difficult to deal with
Heat gun is excessively hot, overheating PVC will create brittleness, use low setting and keep distance from material. It takes time for heat to saturate material ... have patience! Oven preferred, with heat gun for additional or finish forming

Experiment and practice with scraps
This is as much akin to Art ... as it is to Science!

Applicable to different "plastics", just vary temperature.

DrkAngel said:
Various melting points of different types of plastic:

The melting point of HDPE (High Density Polyethelyne) is about 130 ºC
The melting point of LDPE (Low Density Polyethelyne) is about 110 ºC
The melting point of PET (Polyethylene terphthalate) is about 250—260 ºC - Danger - too hot - 500 ºF
The melting point of PP (Polypropylene) is about 160—170 ºC
The melting point of PS (Polystyrene) is about 70—115 ºC
The melting point of PVC (Polyvinyl Chloride) is about 75—90 ºC
Source:
http://www.goedjn.com/essays/botplas.html

The melting point of PMMA (poly(methyl methacrylate)) - Plexiglas is about 180 ºC 356 °F

ABS (Acrylonitrile butadiene styrene) (chemical formula (C8H8)x· (C4H6)y·(C3H3N)z) is a common thermoplastic. Its glass transition temperature is approximately 105 °C (221 °F).[1] ABS is amorphous and therefore has no true melting point.

POLYCARBONATE (Makrolon®, Lexan®, Zelux®) Melting point : 300 - 310° F (149 - 155° C)

Forming, or shaping temperatures, are several degrees cooler.
Click to expand...
 
cwah said:
What do you use for structural duty then?

I was thinking to only use the 5mm pvc foam sheets, but what would you advise?
Click to expand...

Sorry, I was a little unclear. Reforming ducting and domestic downpipes won't give good results. It is quite weak and even folding over quite a long radius can stretch the outer skin enough to cause lesions

Sheet material supplied for modeling is a lot thicker and more suitable for working with
.
Fence posts offer a sturdy construction. However loaded with cells they will still flex. You can pad them out with foam to stop chaffing, but that brings thermal problems to some builds.

I use 5ah 4s bricks as they are cheap and easier to package than most other options. Thus I have given this no thought. I just have experience with reforming finished goods. Bad experience. Although a heat gun is far from ideal, the oven method is better if you have space in the oven.

Edit: Foam board has low working temperatures. It could go supple left in the car on a hot day. It is perhaps quite a good thermal insulator too, when compared to solid board. I'm not sure, but I would look that up.
 
Went shopping locally for PVC etc, for forming and was disappointed at the lack of material.
Till I stopped at the local hardware-surplus store.
"Plastic"! 40-55gal barrels - $15 each
Great variety, blue, white ... from 1/8" to 3/8" sidewall thickness.
Flat might be nicer, but I'll be re-forming anyhow.
Possibly 18-20 sq feet of slightly curved material - less than $1 per sq foot. Plus top and bottom.
 
Continuing with my stories of doing things badly, It is very difficult to move a sheet of floppy plastic. Impossible you might say. It's worse than an uncooked pizza base. Your leaving finger prints the moment you poke at it. It will just stretch if you try to lift a corner up. You could perhaps get a sheet out the oven still on a baking tray though, if you did want to drape it over something.

It's akin to working with them cheese slices made of an as yet unidentified plastic.


Maybe I'm just not very good at it. I recently sleeved my seat post with a section of 1.5" waste pipe reformed with my heat gun. It was only a short sleeve, about 40mm long. At lower temperatures I had to roll it firmly enough that it caused that plastic cheese slice appearance. At higher temperatures I think it actually was a cheese slice for a moment. The job was satisfactory, but not factory standards
 
friendly1uk said:
Continuing with my stories of doing things badly, It is very difficult to move a sheet of floppy plastic.
Click to expand...
I recommended producing a "form", then let the plastic drape over it.
Form can be something as simple as folded cardboard fastened with staples.
PVC forms at ~175 ºF, cardboard is safe past 400 ºF

Keep an eye on it, remove from oven when it begins to sag ... before it starts to flow.
"Finish" with heat gun or hair dryer.
"Shape" with flat paint stick or spatula.
 
I am working with some acrylic sheets. I am planning on using a piece of felt to move my limp sheet. My acrylic is thick, so I will also use some wood to clamp the edges, and turn the whole piece for more even heating. I read that felt is good for handling sheets. I am using a sheet of aluminum foil on the other side of the felt to even out/absorb some of the heat. Dad on one side, me on the other. Draping over a form. I have aluminum lined masonite to hold/evenly focus my heat. I am doing it outside on coals from a fire. I am hoping I can spread coals evenly from a big fire and use an IR thermometer and intuition to get it right.

Not sure if the felt will work for every plastic, but I have some PVC bits around, so I will try.

Enjoyed the vacuum forming video.
 
I have build my vacuum former just dont have enough time to experiment with different thermoplastics. PP is hard to work with, after forming it shrinks somewhat. I am yet to try ABS, perhaps it will be better. The crucial thing i think is the mold. Square battery case will be hard to form to satisfactory standards. For this, probably concave mold would be best. Here is couple of my vids on the machine and some test forming. Since that video i have attached digital thermometer but need to place it near heating element for more accurate readings:
Vid 1
[youtube]SIpotcZzD-c[/youtube]

Vid 2
[youtube]sbol6J8nGe0[/youtube]
 
DrkAngel said:
Went shopping locally for PVC etc, for forming and was disappointed at the lack of material.
Till I stopped at the local hardware-surplus store.
"Plastic"! 40-55gal barrels - $15 each
Great variety, blue, white ... from 1/8" to 3/8" sidewall thickness.
Flat might be nicer, but I'll be re-forming anyhow.
Possibly 18-20 sq feet of slightly curved material - less than $1 per sq foot. Plus top and bottom.
Click to expand...
Found more material sources.
30gallon garbage cans, durable with large sq footage, multiple colors and a variety of thicknesses.
13ga waste baskets, some rectangular have reasonable sq footage with large flat surfaces.
Either, supplies good donor material for less than $1 per sq foot.
 
Why not go with polycarbonate? I've made some pretty complex shapes for battery boxes just using two heat guns, some straight pieces of metal to act as straight edges, and a couple vice grips.

Plus you get the added benefits of its lack of brittleness, unlike acrylic or PVC. It is also what they use to form complex shapes like teeth retainers.
 
spinningmagnets said:
Would you happen to know the melt-temp of polycarbonate?
Click to expand...
POLYCARBONATE (Makrolon®, Lexan®, Zelux®)
THERMAL PROPERTIES:
Melting point : 310° F (155° C)
Heat deflection at 66 psi (ASTM D 648) : 285° F
Heat deflection at 264 psi (ASTM D 648) : 270° F
Maximum serving temperature for short term : 275° F
Maximum serving temperature for long term : 240° F
Thermal conductivity (ASTM C 177) : 1.35 Btu-inch/hr-ft~2- ° F
Specific heat : 0.30 Btu/lb- ° F
Coefficient of linear thermal expansion (ASTM D 696) : 3.7x10~5
Applicable temperature range for thermal expansion : 0-200° F

Other sources:
Melting Point: 300°F 149°C; Tensile Strength: 10,000 psi.
Melting temperature (Tm), 155 °C (311 °F)
 
A local acquaintance is experimenting with forming "plastics" into a shell-windscreen for his recumbent trike.
With Polycarbonate as his material of choice.
He is experimenting with lower temperature-cheaper material ... first.

His Method (as described to me)
Stencil oven
Oven is a large box with an open top.
Heat source is a gas burner with circulation fans.
"Plastic" is held in a "stencil" (2 sheets of plywood(?) with a large hole the shape of his desired windscreen) and placed on top of his oven.
As heat increases, plastic sags in a reasonably aerodynamic shape.

Method could obviously use some refining!
For instance:
Basic electric heater, supplemented with light bulbs on dimmer, to precisely regulate temperature.
Additional heat regulation - heat gun vs hair dryer on cool, from above, to accelerate or slow forming.
 
If your using radiant heat you may want an infrared thermometer to accurately measure your works temperature.
 
friendly1uk said:
If your using radiant heat you may want an infrared thermometer to accurately measure your works temperature.
Click to expand...
Cheap IR Meter < $15
 
eHow links
How to Melt Plexiglass
How to Melt Plexiglas Together
Melting Plexiglas together involves using Solvent Cement drawn into a precise gap via capillary action, that dissolves and "resolves" the Plexiglas together. Varying the "gap" increases-decreases the depth of bond.
It cannot be "melted" together by heat. ... ?
 
Perhaps it won't mingle till it is liquid, and if it is liquid it is ruined. Solvent welding causes this liquid state but can't act deeply in to the plastic. Too much can really mess up pvc pipe though, I have seen it go very soft. So much so that the action of slipping the fitting on collapsed the pipe. That was kitchen waste size stuff.


I shouldn't of seen this thread. I'm planning my next plastic forming disaster now. I have a solid frame triangle, and I'm thinking of a box that slots in the bottom. A triangle box with concaved sides to sit around the bikes tubes. A box I can drop in and it stays, although I would still fix through it to both bottle locations. I could take my 1.5" waste and cut it lengthways to form a smaller gutter. Use heat to shape to my tubes. Hold them at the bottle mounts, and also a little metal bracket to hold the sides on my box while I bond them there. I quite like milliput for that job. I'm still thinking about the lid.
 
spinningmagnets said:
Would you happen to know the melt-temp of polycarbonate?
Click to expand...

Where the plastic becomes malleable but before the bubbles start to form. :lol:

I wouldn't recommend my method where anything relies on its structural integrity, since overheating the polycarbonate compromises its structural integrity since the plastic boils and creates air cavities in the plastic. It is a bit of a fine line between the melting point and the boiling point; but there is certainty plenty of room for safety for making general items like covers, battery boxes, etc.

But you cant beat vacuum forming for overall finish and consistency.

DrkAngel said:
A local acquaintance is experimenting with forming "plastics" into a shell-windscreen for his recumbent trike.
With Polycarbonate as his material of choice.
He is experimenting with lower temperature-cheaper material ... first.

His Method (as described to me)
Stencil oven
Oven is a large box with an open top.
Heat source is a gas burner with circulation fans.
"Plastic" is held in a "stencil" (2 sheets of plywood(?) with a large hole the shape of his desired windscreen) and placed on top of his oven.
As heat increases, plastic sags in a reasonably aerodynamic shape.

Method could obviously use some refining!
For instance:
Basic electric heater, supplemented with light bulbs on dimmer, to precisely regulate temperature.
Additional heat regulation - heat gun vs hair dryer on cool, from above, to accelerate or slow forming.
Click to expand...

Sounds like a good way to go through a lot of polycarb before you get an acceptable shape. :wink: Instead of all of that, get some sheets of blue board then glue them together to get the appropriate height of your aerodynamic shell (I think spray adhesive works well to glue the boards but don't quote me on that). Then make a hot knife out of a few pieces of wood, a heating element from a toaster and a light dimmer (use with care). Rough cut the foam into the shape you want. Use sand paper to smooth out the shape.

Then use your foam form to drape your polycarb over, if you are proud of your shape you can try to make a vacuum former, otherwise you can just let it drape over the form and call it good. It should give the more of the aerodynamic shape that you want vs. hoping gravity and some heat guns will do the trick.
 
For my form I used a sheet of plywood and some 11/2" pink polystyrene? insulation foam. I doubled the plywood over so there would be uniformity in cut shape, and I alternated plywood and foam. The plywood provides good rigidity and anchoring for sandwiched sheets. I just use a drywall saw to shave the foam to the contours created by the plywood, and I put tape on the finished shape for smoothing. Felt over everything and for handling the plastic sheets.
 
Hot Melt Glue
Interesting to note is that Hot Melt Glue is typically a formulation of Polypropylene and various resins.- (Melts at 380°F - 193°C)

It should be useful for reinforcing or filling seams on Polypropylene and probably some other plastics*.

Lo Temp Glue
Is typically formulated from Styrene block copolymers (SBC)
(Melts at 250 °F - 121 °C)

It might be usable on lower temperature plastics:
PS (Polystyrene) is about 70—115 ºC
PVC (Polyvinyl Chloride) is about 75—90 ºC
LDPE (Low Density Polyethelyne) is about 110 ºC

For a good "bond", material temperature should be near to melting temperature?

*Plastic, originally, refers to the substances with formability-shapeability characteristics.
 
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1. Why are people using ovens? The fumes in the house are freaky and don't see why you need to heat all of the plastic anyway. You only need to heat a corner line and bend it, repeat till you have a box. A cheap heat gun can do it or I've even done it with my solderer. the solderer is actually the neatest as it heats a perfect thin line...

2. I am getting into plastic welding but can't for the life of me make the pvc drainpipe weld by heat.

any ideas?

In time will see if abs is easier.

EDIT

More research, shows oxidation requires scraping back all plastic, if the temp is too low no bond, too high you kill it irreversibly... Now after ordering my hot air equipment I discovered injection welding :cry:

[youtube]kUAre-f0lmQ[/youtube]
 
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