Vacuum Forming

[He Who Shall Not Be Named]

Yeah, Mike ... what Virgial said! Chop-chop!

[Kazzer]

I have a small fan from when I remodeled my lounge and took it out of the fireplace.

before after

I'd kept both fans, in a 'come-in-handy' cupboard, and I had actually pulled one out yesterday afternoon. The frame is a bit long but I have a sheet metal bender, so I think I can tweak it a little.
As soon as I've had my morning 'cuppa' I'm off to the basement to get this going.
These fans have seen 20 years in service pushing very hot air out of the firebox, so I'm happy they won't melt. I looked at Muffin Fans, but Grainger only had ones with plastic housings and so I am a little reluctant to go that route.

Keep your fingers crossed guys.

[Kazzer]

There's a submarine under there somewhere.

It's now official! GAS SUCKS!

I put a fan in and it made a huge difference, but I still had one end 70 degrees hotter than the end. Overall the temperature varied all along the plastic. I melted a hole in one end and by the time I'd flipped it over, the stuff had hardened.

I'm going to drop this idea, the place stinks, the missus reckons I'm going to burn the house down, and I am in the dog-house. (Talking of dogs she who rules has gone out and bought a damned puppy! I put my foot down and said NO-ooooooo! PLEASE NO-O-O-O! but the only thing that did was get me in more trouble. I've told my cats and they are in agreement - no flippin' dogs! We're conspiring as I speak to find a concrete block, some rope and make the boat-dock very slippery. Anyhow! But enough of my personal problems.

I've found a company who looks like they know what they are doing regarding electric heating of vacuum forming systems.

Here's what they say

Yes, we have several options on mounting. Have a look at our
Accessories page on our website store:

http://www.quartzinfrared.com/Merchant2/merchant.mvc?Screen=CTGY&Category_Code=ACC

Since this is experimental, you should consider a smaller mock-up unit
before committing to the full size. For example, if the 10 w/in2 is
considered then you could do a 1' x 1' section at 1/6 the total
wattage (1440w) which would be fine on 120 volts, and use an element
we have in stock - for example 50714 an 800 watt at 120 volts with a
heated length of 13.5 inches. This would be 1600 watts total, but
still fine on 120 volts. This would give you a much better feel for
the power need before going full length. You can reduce the power with
a variable transformer, or an SCR Power Control (www.payneeng.com,
model 18D).

You can see this element specs (and order it) here:

http://www.quartzinfrared.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=50714&Category_Code=HOL

A better picture can be found on our soon to be open updated store here:

http://dev.quartzinfrared.com/mm5/graphics/00000001/holman.jpg

This element is normally mounted with metal tabs which have a hole for
the ceramic tip (and wire of course) to pass through, capturing it
between the metal tabs.

Hope this helps.


Regards,
John Eaton
Quartz Infrared, Inc

[He Who Shall Not Be Named]

Don't give up so easily, you just started ****ing this dog, Mike. Baffles, more heat sources, etc. You've just started to work this oven out. Keep at it. You'll eventually find the magic combination.Chop, chop!

[trout]

David offers some sound advice. Baffles would offer a way to shield the heat closest to the source and allow more heat to the far end giving a balancing of heat distribution. Adding additional heat ducting and keeping your heater in the center so that the ducting equidistant would help. Placing a metal sheet (between the heat source and plastic sheet) with holes and allowing the metal to heat up prior to placing the plastic sheet over it would allow time to distribute the heat along the metal, then when the sheet is placed over it, it will have a better chance to melt evenly. If flipping your frame holding the plastic causes issues, you might want to consider moving your frame along a horizontal plane. Like this:

Where the black bars represent your frame holding the plastic sheet. Plus the two of you can each have a hot gun in hand and while the vacuum is on touch up areas that may have cooled down.

Just do not give up, keep trying some new ideas. Personally, I liked the wire heating element idea. For what it's worth.....

Peace,
Tom

[Subculture]

I'm thinking of the way the old gas fires used to work with the cermaic elements, that spreads the heat well. Think you're best of with electric heaters for vac-forming though.

You could always go into the kebab business if it doesn't work out 'You want chilli sauce on that.....?!'

[trout]

p.s. same for vacuuming. You will need a baffle in there to evenly pull air. Usually it is a table with holes in it. Do you already have that on the vacuum side?

[Kazzer]

I have found some electric elements that might do the job, and have ordered some. We'll try them in a few days. In the meantime, I had to try to get this all working, so decided to do something small.

I purchased a few strips of L shaped aluminum extrusion and made a simple frame. No welder, so I used those angle brackets and screws, then later pop rivets as these were easier.

My frame is a foot square. Simple G clamps and more angle kept the plastic sheet in place. Once this was rigged, I blanked off my vacuum chamber to just give me enough space for the frame, and fired up the gas heater.

After about 5 minutes, the plastic was pretty soggy, so, with the vacuum on, I pulled the frame over to the vacuum chamber.
It worked! Not perfectly- but it worked! I'm so happy I could spit!~




Here's the frame sat on the heater, getting hotter by the minute!



There she goes! If only I knew when enough was enough!




And the finished job! Almost had me a T Class Conning Tower!

Not quite enough 'hot' or maybe too little vacuum?

I could get addicted to this! What fun!

[Subculture]

You're trying to draw a very deep part there. I would split that mould in two, and form the tower in two halves laid flat.

[He Who Shall Not Be Named]

getting there, Mike.

[Scott T]

Curious. Are you heating the parts/buck so it does not remove the heat from the plastic prematurely?

Scott T

[Kazzer]

All of those things I did wrong. But my expectations weren't high. My equipment was VERY flawed. I used a big vacuum table 6' x 1' and blanked off 5' of it with tape and plastic sheet. It must have leaked all over the place. Then I still think the plastic wasn't heated evenly, or long enough.

I'll do better tomorrow! Your critiques are welcome.

[Virgil]

Mike,

From what I can tell, it looks as if the plastic was unevenly heated.


I don't know if you do this or not but make sure you use a timer and keep a log of the time it takes to get the plastic hot enough to give a good finished product. Keep a record of the plastic thickness and good working time needed. Very important and makes life much easier when working with different plastics (Styrene, ABS etc.). I keep a note book with all the info I need as a handy reference.


Also, if you might use different types of plastics, they all have different reactions when heated. For example "lexan" will sag and then tighten up again when it's ready. It also needs to be dryed before using or the chances are good that the finished pull will have bubbles in it.

You're getting close...Keep at it.

Virg

[Kazzer]

I made a new, smaller Vacuum Platen, and the first few goes showed that the edges were leaking air



Here's all the scrap attempts - the learning curve.





This pull was pretty good, but I'm beginning to think I am putting too many items on the platen. See the gap on the right. I'll fix the edge better on the next one.







Next attempt!

OK! Back to the cave!

[trout]

Mike,
Accidents happen! but your vacuum setup is looking good!
As the vacuum is going, and it looks like it will not get enough details, try using a heat gun to warm the plastic in that area. I have used a heat gun before to finish a pull that cooled too much. You won't get details unless there is a vacuum pull. If your parts are covering the holes, it will hamper the pulling of the plastic in. More holes or try putting some washers under your parts to slightly lift them allowing the air to continue be pulled out. taller items in the center might help as well.

Peace,
Tom