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Working with very thin Styrene...short forming cycle.

 
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RFC
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Joined: 22 Aug 2011
Posts: 19
Location: Western PA

PostPosted: Sun Oct 09, 2011 5:39 pm    Post subject: Working with very thin Styrene...short forming cycle. Reply with quote

Hi Guys and thanks for your help with my first foray into vacuum forming.
I am asking this question because as you know I am not getting the full pull
using only a shop vac. I am going to have to invest in a small vacuum pump and storage tank.
My question is this. Since I am using .020 flocked styrene I notice that I have virtually no working
time with this material. We are talking seconds from the time the hot plastic hits the tool to the time it will not move anymore and is cool.

How will a vacuum pump help me? Do you still use the shop vac to get the initial pull and then quickly hit the vacuum tank?
Or do you just use the vacuum tank only?
And, how do you control the amount of vacuum with a tank so as not to rupture the plastic?

Should I be preheating my tooling to slow the cool down?

I appreciate any reply's. Thanks
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IMMark
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Joined: 18 Nov 2010
Posts: 185
Location: Columbus, Ohio

PostPosted: Mon Oct 10, 2011 8:24 am    Post subject: Reply with quote

I think that you will find you have a longer working time, if you have a much stronger vacuum. I have done a lot of HIPS .060, and have plenty of time when it heated to work with it.
I use a 2 stage system, with a ball valve on my tank (41 gal.)
So I pull about a 20 on my tank (I could go higher, but I have never even emptied it on a single draw). If needed I could also finish off with the pump too, but again for me...the tank alone has been more than enough.
With the valve, you can apply the vacuum very slowly and controlled. And again, with the greater vacuum numbers...I have found I have more than enough working time, so I have never needed to preheat my tool.
I would add that I have never used flocked plastic, so I can't comment on any effect that may have.
Mark
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RFC
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Joined: 22 Aug 2011
Posts: 19
Location: Western PA

PostPosted: Mon Oct 10, 2011 5:07 pm    Post subject: Reply with quote

Thanks Mark,

I have been thinking about moving up one size in thickness to .030" which is still half the thickness of what you are working with as my finished parts are kind of flimsy after stretching so much.
Would you think that a 5 gal tank would be large enough for the small parts that I am making?
I guess that at least with out the shop vac drawing cool air around the plastic before it hits the tooling, it may give me a second or two longer to work the ball valve.

Are the little vacuum pumps they sell on Ebay sufficient to do small parts like mine?

Still more questions to come...thanks again.
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IMMark
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Joined: 18 Nov 2010
Posts: 185
Location: Columbus, Ohio

PostPosted: Tue Oct 11, 2011 8:11 am    Post subject: Reply with quote

I would think 5 gal. to be on the small side. Although it mostly has to do with the size/shape of the mold and how much air needs to be removed.
If you are not doing production runs, it may not matter how long it takes to put a vacuum on your tank. So if you use a larger tank, perhaps it will take 10 mins. of the pump running...but for a couple of parts, that may not be a big deal? There are plenty of deals on eBay (that is where I got my pump from as well). I have also often seen them on local Craig's list, a lot are used in the AC industry. Also, Harbor Freight has a small (1.5cfm, IIRC) for a reasonable price. As for larger tanks, many use old water heaters (the down side is dirt, etc. in them...but many have had good luck with them). I bought used air compressor tanks (again on Craig's List)..but in reality, although less gunk in them...these to can build up rust deposits, etc.
Also, Doug as some info on pumps at his site if you haven't seen it?
http://www.build-stuff.com/vacuum_pumps.htm

Mark
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jdougn
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Joined: 18 Mar 2009
Posts: 702
Location: Louisville KY area

PostPosted: Fri Oct 14, 2011 3:28 pm    Post subject: Reply with quote

RFC wrote:
Thanks Mark,

I have been thinking about moving up one size in thickness to .030" which is still half the thickness of what you are working with as my finished parts are kind of flimsy after stretching so much.
Would you think that a 5 gal tank would be large enough for the small parts that I am making?
I guess that at least with out the shop vac drawing cool air around the plastic before it hits the tooling, it may give me a second or two longer to work the ball valve.

Are the little vacuum pumps they sell on EBay sufficient to do small parts like mine?

Still more questions to come...thanks again.


If I remember your parts are fairly small compared to Doug Walsh's ProtoForm 2'x4' vac former table? If so, a 5 glln tank should be good. It's usually not too hard to add additional tanks if more storage capacity is needed. Don't use the shop vac with the vac former.

Here's a decent two-stage design that allows the tank to be isolated after the initial pull.

For what I do, this is important since the intial pull uses up a lot of my 30 gallons of vacuum reserve. By isolating the tank the vac pump is only working on the space underneath the hot plastic and not trying to evacuate the wasted tank too.

It sounds like the plastic you're working with has a very short operational window so you will need a tank to quickly slam the plastic to shape. Also, if the plastic is cooling too quickly, it will help to preheat the mold. Your plastic supplier should be able to provide some information on the preheat temp. If not, try Professional Plastics website.

IMMark posted a good link for vac pump information. Harbor Freight sells cheap HVAC vacuum pumps. http://www.harborfreight.com/25-cfm-vacuum-pump-98076.html
When shopping around, be aware that there is a lot of different terminology related to vacuum that can get really confusing. If the vacuum pump is designed for HVAC use it should get close to 30inHg (30 inches of mercury). Other vacuum pumps will work but confirm that they will pull at least 20inHg or they'll be a waste.

If you have the room, the ProtoForm vac former design by Doug Walsh is great. He has smaller designs too. http://www.build-stuff.com/index.htm
Consider getting vac former plans if you're serious about this hobby. The plans will save you hours of frustration and the parts source list will save money and time. Here's a link to a great build thread for the ProtoForm:
http://www.tk560.com/phpBB2/viewtopic.php?t=1162&postdays=0&postorder=asc&start=0

Keep posting up. It's always good to see new projects and ideas!
DougN
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RFC
Newbie


Joined: 22 Aug 2011
Posts: 19
Location: Western PA

PostPosted: Sat Oct 15, 2011 12:42 pm    Post subject: Reply with quote

Thanks Doug for the very informative post. I spent the whole morning reading the articles and looking at the photos. I really appreciate the schematic of a vacuum system. I will let you know how it all works out. Thanks again.
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jdougn
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Joined: 18 Mar 2009
Posts: 702
Location: Louisville KY area

PostPosted: Mon Oct 17, 2011 10:56 am    Post subject: Reply with quote

I should note the diagram is not something I did but cut & paste from another post. The two-stage vacuum pump/tank diagram and a variant have been around for awhile and I don't know who the author is. Hope it all works out for you!
dn
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