From: arno@nitro.pp.utu.fi (Arno Hahma)
Subject: Re: Solid content in propellants
Date: Mon, 19 Aug 1996 23:41:37 +0300 (EET DST)

> How is it possible to "pour" a resin with in excess 
> of 75% filler? My HTPB is thick like syrup even with

By selecting a suitable particle size distribution of the solids and
using additives, such as nonionic tensides and lecithing (to prevent
sedimentation). I regularly cast propellants with 84 % solid loading
and they are very pourable, in fact, sedimentation is more of a problem
than pourability. I could go down to 10..12 % binder content, but the
maximum Isp is at 16 % so I try to go with that. It also gives better
mechanical properties.

Also remember, that you need to mix the batch long enough to wet every
single particle with the binder and to obtain a uniform mass. It may
take anything from minutes to several hours of mixing to reach that.

> The experts tell me that 50% is the max filler that
> can be added to polyurethanes.

It depends on the filler. I usually mix 82 % of oxidizer to a
polyurethane (polyol based, not HTPB) if Al is present or 77 % if Al is
absent.

> adding the oxidiser? How long does the resin take to
> cure? I get from 2 weeks down to five min with the addition

HTPB takes about 5 days, if you tune it for best mechanical properties.

> of a mercury cat.

What kind of compound is that? I use chromium or cobalt compounds.

> Steve Kennedy
 
ArNO
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