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View Full Version : heating source for 48x48 VF-1/4 ABS



edwardpic
06-14-2007, 02:21 PM
Hi guys,
New to the thermoforming threads (usually on the CNC Plasma). We are building a 48" x 48" vacuum former. I have the everything 80% figured out for the gantry-frame-sliding heat box but need advice on a heat source. Do I want to use ceramic-Quartz-infrared etc? Ill post a link in here for the machine we are mirroring.

http://www.belovac.com/model_c_class_4x4.html

i also would like advice on a vacuum pump to use. I found a 3/4 HP rotary vane pump at Grainger but thats $597!! Any ideas on a cheaper model?

Thanks in advance guys.

drcrash
06-15-2007, 03:00 AM
Hi guys,
New to the thermoforming threads (usually on the CNC Plasma). We are building a 48" x 48" vacuum former. I have the everything 80% figured out for the gantry-frame-sliding heat box but need advice on a heat source. Do I want to use ceramic-Quartz-infrared etc? Ill post a link in here for the machine we are mirroring.



If you're doing it on the cheap, I'd recommend a nichrome coil heater, with the coils arranged in a rectangular spiral, a la Thurston James's plans in his book The Prop Builder's Molding and Casting Handbook, which has plans for 2 x 2 foot and 4 x 4 foot bottom heaters. For a top heater, I'd use aluminum flashing to line the oven, and no millboard. (It's cheap and works very well.) You'll just need some kind of rigid-enough framework to attach the flashing to. It doesn't have to be heavy duty.

You can get 22-gauge nichrome coil from www.infraredheaters.com (http://www.infraredheaters.com).

There's a bunch of people who've made Thurston James type machines over at tk560.com. You should sign up on the discussion board over there. It's a good place to ask for advice on making cheap vacuum formers.



i also would like advice on a vacuum pump to use. I found a 3/4 HP rotary vane pump at Grainger but thats $597!! Any ideas on a cheaper model?


Have a look at the surplus Thomas piston pumps Doug is selling over at www.build-stuff.com (http://www.build-stuff.com). If they're the pumps I think they are, I have two, and they're nice pumps.

cod
06-15-2007, 04:13 AM
hmmm. let's see. 2x2 oven calls for 2000-2400 watts.

So 4x4 would be .... four times that ? thats almost 10k watts !

Doesnt sound like it will ever be cheap to me !(electric bill)

I calculate you need at least 10cfm pump and at least 50 gallon tank also.

good luck!

p.s - I second the motion for nichrome wire ... that other stuff is definitely not gonna be cheap.

edwardpic
06-15-2007, 09:02 AM
Thanks guys,
10K sounds about right, I built a 4x4x6 powdercoat oven and that has 12K of strip heaters running off 3 phase. I found a guy to build an array for the 4x4 using the cramic heaters for $900 including the J coupler and insulated box.
Its a business expense and i will be making alot of interior parts for the vehicles i build (faster and cheaper the carpet time/labor wise)
I made the molds already using a 3 axis wood mill a buddy has, now just need to get the machine built and start pulling parts.

Anyone know where to get ABS in colors other then black and white, and cheaper then buying 3K worth to get colored sheets?

kayaker43
06-15-2007, 04:23 PM
Well there certainly is a wide range of specs used for vacuum forming, and they all work to some degree. The Belovac machine looks way out there with an undersize vacuum system and a grossly overdone oven.

The Proto-Form 2x4 use 9600 watts which is about half of the industry standard, but its an optimized design. The reason bottom oven machines can get away with less is that they often seal the chamber with the plastic sheet, and let the air temperature build. The top oven design is more open and uses Infrared primarily. You should use more like 20,000 watts if the elements put out the correct IR, and something more if they don't.

60K watts is crazy but that's how its sometimes done If they don't want to go through the development of an oven, just throw on way too much heat, and use expensive controls to turn it down until it works.

One of Many
06-15-2007, 06:58 PM
We used on average 1500 watts/sqft of plastic surface area as a general rule. Some machines were as high as 2400 watts/sqft, but that is full on heat and rarely of ever ran at 100%. Higher wattage cal-rods would last much longer if run at a lower on time.

As for the heater controls. They were the least high-tech. Nothing more than an Eagle-Signal percentage timer controlling a mercury wetted relay in either single or 3phase systems. In most cases these ran at around 50-70%. No need for temp feedback. One percentage timer for the top and one for the bottom heaters. Wider ovens used 2 percentage timers top and bottom that seperated the outer rods from the inner. No sense running all the rods for smaller sheets and also allowed control near the frame compared to the center.

DC

edwardpic
06-15-2007, 07:23 PM
You are correct in the wide range of specs on the net between machines and designs. Thats why I am here asking like I did before I built the powdercoat oven. Retailed for 12K and built it for 1400, al with digital thermostat and 3 phase wiring run in Delta series. Needless to say I have coated enough parts to make 85K so it was well worth the money.
Now I am attempting to do the same price wise to build a vacuum former. Purchased a 3/4 HP Gats rotary vane vacuum pump today for $235 and a 24 gallon tank for the vacuum for $101. Now to just peg down the heating elements I will be ok. I appreciate all the help so far.
Look forward to more opinions and ideas.

edwardpic
06-21-2007, 04:36 PM
Oh on a side note the 48x48 shown on belovacs website? The website has a typo and says 60K in reality its 20K in heater wattage. Thought id throw that out there.