Re: [PSUBS-MAILIST] Rudders

[greg cottrell <jgcottrell2002@yahoo.com>]

It's true- over 179 F is risky as far as deformation in a stressed part. The advantage to a well design forced air oven is that the rate that it transfers heat into/ out of the material is very slow compared to a medium like water. But you're on the right track- some stress relieving processes use an oil bath. Because of the rapid rate of transfer, the temperature control has to be very precise.

With forced air, the foot per minute speed of the air is very important and much research has been done. As far as the 14 hour estimate goes, this is the minimum suggested time. You can leave it in the oven too short a time but not too long. I usually do an overnight heat cycle and then cool the next day.

 

 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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