From: escargo@sbcglobal.net
Date: Fri Apr 18 2003 - 19:13:59 EEST
Interesting thread to see on the RP list. Usually I see this on the APMM's
"MILE", (mail list). It is for members only but members have a wealth of
knowledge on this and other model making subjects.
In the late '90s I was shooting parts, up to several pounds, in 50 second
CIBA resins(now Vantico) and BJB materials, in custom reworked paint
pressure pots. We would directly meter-mix dispense the material into the
mold (using Ashby-Cross eqpt.) while under vacuum, and then reverse to
pressure as soon as the mold was filled. While I consider this more closely
resembling a black art form, if you were good at using the process, and
properly designing the molds, it worked beautifully. Parts could be
demolded in, say, 10-15 minutes. We also heated the materials prior to
dispensing, to lower viscosity and speed the process. If you had several
molds, the process was continuous, except for the need to keep the molds
cool enough.
Glyn
-----Original Message-----
From: owner-rp-ml@rapid.lpt.fi [mailto:owner-rp-ml@rapid.lpt.fi] On Behalf
Of Andrew Miller
Sent: Friday, April 18, 2003 10:02 AM
To: Michael Tsenter
Cc: rp-ml@rapid.lpt.fi
Subject: Re: Pressure tank wanted
> However, there are situations when the presence of vacuum (or negative
pressure)
> during filling of the mold is extremely useful.
> Many of our Protomix machine users inject the resin into the mold using
> cartridges or meter-mix machines while the mold is sitting under vacuum.
Yep I agree...
we will do that on ocasion as well however we usually just pull about 20in
of vacuum in the pressure vessle before filling and then just pressurize the
tank.....skips the Out of one into the other step...
We've also done a lot of work with the flow path of the resin to ensure the
minimization of voids that may be too large to compress once presurization
occurs...if we can't solve the problem with flow path then we have vaccuum
as a fall back...
I guess it mostly comes down to "Air is your enemy"
Whether trapped or mixed in (which is just little tiny trapped bubbles)
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