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PVC Water Absorption: fallacy?
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From: Pete [SMTP:casius-at-cyberserv.co.za]
Sent: Saturday, May 30, 1998 1:50 PM
To: Tesla List
Subject: Re: PVC Water Absorption: fallacy?
Hi all,
If one examines the morphology of PVC during the manufacturing stage one finds
that the PVC granules have a certain porocity. The granules are not perfect
little ball but are quite rough and have many convolutions. (Nice little
"crevices" for moisture to hide in)
When the virgin PVC is mixed with heat stabilisers, UV retardents, colorants,
calcium carbonate fillers ect, and extruded into pipe, the PVC still retains
some degree of porocity. Hope this is useful info
Regards
Pete
Tesla List wrote:
> ----------
> From: D.C. Cox [SMTP:DR.RESONANCE-at-next-wave-dot-net]
> Sent: Friday, May 29, 1998 1:37 PM
> To: Tesla List
> Subject: Re: PVC Water Absorption: fallacy?
>
> to: Rich
>
> They don't absorb it like a sponge but they absorb on surface through
> adhesion and cohesion properties. I did a lot of experiments with this
> property and strongly recommend a good sealing process of PVC -- or else
> pay the price especially with RF currents which are great "creepers".
>
> DR.RESONANCE-at-next-wave-dot-net
>
> ----------
> > From: Tesla List <tesla-at-pupman-dot-com>
> > To: 'Tesla List' <tesla-at-pupman-dot-com>
> > Subject: PVC Water Absorption: fallacy?
> > Date: Thursday, May 28, 1998 10:33 PM
> >
> >
> > ----------
> > From: R M Craven [SMTP:craven-at-globalnet.co.uk]
> > Sent: Thursday, May 28, 1998 2:49 PM
> > To: Tesla List
> > Subject: PVC Water Absorption: fallacy?
> >
> > Many people recommend that PVC coilforms should be varnished inside and
> out,
> > in order to seal them against water ingress.
> >
> > Having spent an hour or so in our library with various materials
> handbooks,
> > I see no mention of any significant water absorption of any of the rigid
> > PVCs which are encountered. It is a very good plastic, comparable with
> HDPE
> > (rigid polythene, alkathene). The volume resistivity is not affected by
> > immersion in water, and the surface resistivity is only marginally
> worsened
> > (same is true for most amterials: even touching the test sample will
> cause
> > an OM change in ohms per square). Nylon and PTFE do suffer, but pretty
> well
> > all of the thermoplastics are not prone to absorption. They are
> impermeable.
> >
> > So, why is it recommended that PVC in particular is treated inside and
> out
> > with varnish? Is it actually the case that, in doing so, we create a more
> > tacky surface on which to wind our secondary wire? Is it so that the wire
> > will slightly embed itself in the varnish, get a grip, and thus exclude
> > air-pockets which might harbour water vapour?
> >
> > I think the reason for varnishing might well be moisture related, but it
> is
> > to exclude air pockets, nothing to do with water absorption. If so, then
> > surface prep. should be carried out on all coilforms (which I acknowledge
> is
> > recommended by the experienced builders on the list)
> >
> > If someone can quote me a BS or ASTM or other document that states
> > hygroscopicity of PVC, then I guess i'm wrong!
> >
> > Any comments from people who've built an untreated PVC secondary and been
> > able to do a comparison with a varnished one?
> >
> > Richard Craven, Malvern, England
> >