Re: [PSUBS-MAILIST] acrylic viewport thickness

["Rick and Marcia" <empiricus@telus.net>]

Speaking of perfection, how many dips to test depth is the norm for a
pressure hull?

It's been a long time since I've read Busby.

Rick
Vancouver



----- Original Message -----
From: "Phil Nuytten" <pnuytten@compuserve.com>
To: <personal_submersibles@psubs.org>
Sent: Tuesday, February 22, 2005 6:37 PM
Subject: Re: [PSUBS-MAILIST] acrylic viewport thickness


> Hullo, Emile:
>        Forming temp for acrylic ( 'plexi G', 'perspex', etc.,) is 290-320F
> (142-160C0. A one inch thick hardboard frame works well for dome -
blowing.
> Two sheets of hardboard, with one cut- out to  desired diameter and other
> with airline, gauge, control valve, vent valve, etc.. Number of
> quick-acting clamps - or bolts and wingnuts. Heat hard board frame to
about
> 180-200F to  minimize stress and distortion from diff. temp. Heat acrylic
> sheet ( separately)by ni-chrome wire elements, quartz lamps, or any even
> heating that will go to about 350F - (need to overheat because of temp
loss
> transferring sheet to frame. Use a plastics pyrometer on sheet surface.
>         Open air valve - make sure you run thru filter if from
compressor -
> not required if from clean,dry, scuba air. ( much more common now, than
> 'bad ol' days'!)Pressure fairly quickly until stretching starts - then can
> slow,  but don't stop until depth is achieved (have line suspended from
two
> posts at desired height/depth). If you blow to quickly you will induce
> excessive stresses in material. If too slow, it may not form evenly if one
> area is even a few degrees colder than another Best slightly too hot than
> too cold.
>         Perfection is achieved in the same fashion that musicians get to
> Carnegie Hall: (Practise, practise, practise!)
> Phil Nuytten
>
>
>
>
>
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