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Newbie aiming at polypropylene bubble

 
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BG79



Joined: 02 Oct 2012
Posts: 3

PostPosted: Thu Oct 04, 2012 10:56 am    Post subject: Newbie aiming at polypropylene bubble Reply with quote

Hi all,

First post here, but Iīve been reading a lot. This is a great forum.

My first vaccum project is an hemisphere with 30cm diameter. I want to use polypropylene because I already work with this polymer. The final piece will be used for luminaires, so It needs to be translucent and resistant.

I made a prototipe table for tests (using a vacuum cleaner and my kitchen oven) before come to this forum, but had problems with the oven and the plate size (37x37cm - useful area). Basically the PP wasnīt heated evenly and the sheet could not be streched to the end because it was to small for the mold. I tryed with 1mm and 6mm sheets.

Then I read about freeforming, so I tryed another oven (really slow one) with 3mm sheet. I made a "shy" bubble (about 5cm high. I need 15cm), and Iīm not sure if the sheet couldnīt get the right temperature or the vaccum wasnīt strong enough. With the other oven the sheet got transparent in some spots and sagged. This time It was just soft, like a strong rubber.

So hereīs the question(s):

If I build an oven, should the v.cleaner be able to suck the 3mm (1/8") PP sheet?

Is it viable to use freeforming for small productions (50 pcs each size) or should I prefer molds?

Already thanks.
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jegner
Site Admin


Joined: 30 May 2003
Posts: 2144
Location: Texas, USA

PostPosted: Thu Oct 04, 2012 1:08 pm    Post subject: Reply with quote

Welcome to the board! Sounds like a fun project. Not a lot of PP formers here, but there are a few. I think ANH Trooper did some PP forming some years back.

Jim
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BG79



Joined: 02 Oct 2012
Posts: 3

PostPosted: Fri Oct 05, 2012 12:51 pm    Post subject: Reply with quote

Thanks Jim.

I read PP is a bit tricky, so i donīt wanna buy "pro stuff" before be sure Itīs doable.
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ANH trooper
Master


Joined: 20 Oct 2005
Posts: 305
Location: UK

PostPosted: Wed Oct 17, 2012 1:51 am    Post subject: Reply with quote

I did form a few pieces of PP with not so good results. I managed to form it but I kept getting hot spots that would turn transparent and ultra thin. The secret to successful forming is all down to the heating. PP needs to be heated more uniformly and is definitely less forgiving than ABS or HIPS.

I hear heating both sides is a benefit and I have read about others heating it in their household ovens with a top and bottom heater.

Start off with thin gauge PP to practise with since it is much cheaper and I believe PP-C is easier to work with rather than PP-H.

Good luck! Let us know how you get on Smile
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BG79



Joined: 02 Oct 2012
Posts: 3

PostPosted: Thu Oct 18, 2012 12:37 pm    Post subject: Reply with quote

Hi ANH,

I did some other tests before you post, and I believe Iīll have to go pro even for the tests.

I tryed to freeform 3mm PP with the slower oven and It seems I was getting a good heat distribution. I went to the vacuum and It was going fine (the bubble was about 8cm high), but suddently the vac cleaner triggered some safety system that radically decreased the vacuum. The result was the same shy bubble I got before.
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