Re: [PSUBS-MAILIST] Rudders

[greg cottrell <jgcottrell2002@yahoo.com>]

To illustrate the importance of annealing, I'd like to pass on something from George Kittredge.

 

General Dynamics did a few experiments with domes when they built the Star-1. What they found out surprised them. When testing one of the domes (that had NOT been annealed) in a chamber, it imploded at only 50 ft. So they annealed the domes and the Star-1 was able to go much deeper (I don't recall how deep)

George designed the VAST sub with a similar annealed dome (formed from 1" starting thickness) and had the sub tested in a chamber to destruction. The dome reached a depth of 823 ft! I know this was true because George showed me the test results.

 

So, the point is, acrylic domes after forming are full of internal stress that needs to be released. In fact, unformed acrylic sheet from the factory also has internal stress from the casting process that needs to be released. This heating process also completely polymerizes the sheet and reduces residual monomer that can caused the sheet to break down prematurely from UV exposure. Even flat viewports should be annealed for best performance.

 

Greg

--- On Mon, 5/24/10, Jon Wallace <jonw@psubs.org> wrote:

From: Jon Wallace <jonw@psubs.org>
Subject: Re: [PSUBS-MAILIST] Rudders
To: personal_submersibles@psubs.org
Date: Monday, May 24, 2010, 11:31 AM

Annealing is interesting stuff.  Stachiw shows a hold time of 14 hours at 170F and cautions on page 838 that spherical and cylindrical shapes which are thermoformed (as opposed to machined to the desired shape) can lose their shape somewhat if annealed at temps above 180F.  I was wondering the other day if annealing via water immersion would be a reasonable alternative to air convention, for the home owner.  Annealing ovens tend to be expensive and home ovens just won't work.  It seems like good temperature control could be achieved with water immersion and such a unit shouldn't be very difficult or expensive to build using propane as a heat source.

Jon



Greg Cottrell wrote:
Make sure that the fabricator is going to anneal the dome- this is where the strength comes from. Ask them to give you the annealing schedule. For a 1" thick dome it should be 179 F held for 24 hours in a convection oven, Then cool at no more than 10 F per hour for 6 hours, fan off. If you're not convinced that they know how to do this then give me a call and I'll do it here.



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