[PSUBS-MAILIST] annealing acrylic

Wed Apr 2 08:30:35 EDT 2014

At one time I was going to go down this road, I researched the hell out of it.  I recall that a circulation fan with a given air speed was absolutely essential.  I would research the ovens that the pro's use. 
Hank
On Tuesday, April 1, 2014 8:09:05 PM, Brian Cox <brian at ojaivalleybeefarm.com> wrote:

Well at least I have a piece of acrylic that can serve as a temperature block now !

--- cast55 at telus.net wrote:

From: "Sean T. Stevenson" <cast55 at telus.net>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>
Subject: Re: [PSUBS-MAILIST] annealing acrylic
Date: Tue, 01 Apr 2014 19:57:59 -0600

To be clear on terminology, additional thermal mass does not decrease stability, but rather increases the time constant of the system response. Controllers simply need to be tuned in accordance with the system characteristics, and there are control algorithms which can account for the long delays typical of thermal control loops. 
An unstable, or underdamped system with oscillation, is more typical of a controller with too much gain, or a highly non-linear control element which is not accurately modeled in the control algorithm. 
As far as the oven goes, a simple solution might be to add a convection fan to even out the oven air temperature, and measure the surface temperature of the acrylic for the control variable as opposed to the oven air temperature. 
Sean

On April 1, 2014 7:40:34 PM MDT, Marc de Piolenc <piolenc at archivale.com> wrote:
Adding thermal mass inside an oven actually destabilizes closed loop 
>control, as you have just learned.
>
>With open loop control it can help a bit by ironing out fluctuations.
>
>Best,
>Marc
>
>On 4/2/2014 2:02 AM, Alan wrote:
>
>Brian,
>>I was going to suggest earlier that you build a larger oven next to your
>>small
>>oven & use the small oven to heat it. That way the temperature fluctuations
>>would be less dramatic.  Possibly make it out of insulation batts &
>>aluminium foil.
>>you could still use the control unit I suggested.
>>Alan
>>
>>Sent from my iPad
>>
>>On 2/04/2014, at 3:49 am, "Brian Cox" <brian at ojaivalleybeefarm.com
>><mailto:brian at ojaivalleybeefarm.com>> wrote:
>>
>>
>>Epic Fail !    my attempt to anneal a viewport did not go well.   The
>>>temps swings were so great that it was impossible to regulate.  The
>>>mass in the oven that I had hoped would moderate the swings made it so
>>>the lag time between the heating cycle and when the thermometer sensor
>>>saw the temperature change uncontrollable.   And the heat was not even
>>>though out the oven as well.
>>>Brian
>>>
>>>--- hanker_20032000 at yahoo.ca <mailto:hanker_20032000 at yahoo.ca> wrote:
>>>
>>>From: hank pronk <hanker_20032000 at yahoo.ca
>>><mailto:hanker_20032000 at yahoo.ca>>
>>>To: Personal Submersibles General Discussion
>>><personal_submersibles at psubs.org <mailto:personal_submersibles at psubs.org>>
>>>Subject: Re: [PSUBS-MAILIST] annealing acrylic
>>>Date: Tue, 25 Mar 2014 05:35:51 -0700 (PDT)
>>>
>>>Brian,
>>>I say when in doubt, test.  If your!
  not
building a test chamber , you
>>>can make your sample window to fit my chamber and I will test it for you.
>>>Hank
>>>
>>>
>>>On Monday, March 24, 2014 7:23:18 PM, Brian Cox
>>><brian at ojaivalleybeefarm.com <mailto:brian at ojaivalleybeefarm.com>> wrote:
>>>Hank,
>>>I have the book, that's where the annealing schedules are,
>>>they vary quite a bit, there is an absolute minimum time and then
>>>there is the original recommended time. The recommended time comes out
>>>to be around 51 hours where as the shortened time is maybe half that.
>>>I'm just doing one test piece to start off with.  I was also using the
>>>same oven ( a toaster oven I got from Sears for $75 bucks) to heat the
>>>welding rod to 250 degrees F before we used the rod ( it had been
>>>sitting out for a few days).  I was able to keep the temperature
>>>fairly even for the welding rod at 250.
>>>Brian
>>>
>>>--- hanker_20032000 at yahoo.ca
<mailto:hanker_20032000 at yahoo.ca> wrote:
>>>
>>>From: hank pronk <hanker_20032000 at yahoo.ca
>>><mailto:hanker_20032000 at yahoo.ca>>
>>>To: Personal Submersibles General Discussion
>>><personal_submersibles at psubs.org <mailto:personal_submersibles at psubs.org>>
>>>Subject: Re: [PSUBS-MAILIST] annealing acrylic
>>>Date: Mon, 24 Mar 2014 17:39:27 -0700 (PDT)
>>>
>>>Brian,
>>>Do you have the Stachiw book of Acrylics, I can send you mine if you
>>>don't have a copy.  There is some pretty important stuff in there.
>>>Hank
>>>
>>>
>>>On , hank pronk <hanker_20032000 at yahoo.ca
>>><mailto:hanker_20032000 at yahoo.ca>> wrote:
>>>Brian,
>>>How thick is your acrylic?  should take more than a night?
>>>Hank
>>>
>>>
>>>On Monday, March 24, 2014 6:33:09 PM, Brian Cox
>>><brian at ojaivalleybeefarm.com <mailto:brian at ojaivalleybeefarm.com>> wrote:
>>>Yes, I have the annealing schedules.!
   I have
an electric oven and two
>>>digital thermometers, one I'm going to put in a piece of acrylic and
>>>the other one I'm going to use to monitor the oven temperature itself
>>>.  I'm worried that the thermometer in the acrylic won't register
>>>until it gets heated throughout, and so then the oven temp might go
>>>higher than it should.  So between the two readouts I can heat it
>>>gradually up.  It'll be a long night.
>>>Brian
>>>
>>>--- hanker_20032000 at yahoo.ca <mailto:hanker_20032000 at yahoo.ca> wrote:
>>>
>>>From: hank pronk <hanker_20032000 at yahoo.ca
>>><mailto:hanker_20032000 at yahoo.ca>>
>>>To: Personal Submersibles General Discussion
>>><personal_submersibles at psubs.org <mailto:personal_submersibles at psubs.org>>
>>>Subject: Re: [PSUBS-MAILIST] annealing acrylic
>>>Date: Mon, 24 Mar 2014 17:22:32 -0700 (PDT)
>>>
>>>Brian,
>>>Are you going to anneal your windows yourself?
>>>Hank
>>>
>>> On
Monday, March 24, 2014 6:03:10 PM, Brian Cox
>>><brian at ojaivalleybeefarm.com <mailto:brian at ojaivalleybeefarm.com>> wrote:
>>>Used my polarized lenses on the newly cut piece and it appears clouded
>>>throughout the whole piece.  Where as another piece I have, you can
>>>clearly see a stress area around where it has been drilled.
>>>Brian
>>>
>>>--- emile at airesearch.nl <mailto:emile at airesearch.nl> wrote:
>>>
>>>From: "Emile van Essen" <emile at airesearch.nl <mailto:emile at airesearch.nl>>
>>>To: "'Personal Submersibles General Discussion'"
>>><personal_submersibles at psubs.org <mailto:personal_submersibles at psubs.org>>
>>>Subject: Re: [PSUBS-MAILIST] annealing acrylic
>>>Date: Mon, 24 Mar 2014 22:40:46 +0100
>>>
>>>As far as I know it is only cast.
>>>Regards, Emile
>>>*Van:*Personal_Submersibles
>>>[mailto:personal_submersibles-bounces at psubs.org] *Namens *Brian Cox
>>>*Verzonden:* maandag!
  24
maart 2014 20:37
>>>*Aan:* PSubs
>>>*Onderwerp:* [PSUBS-MAILIST] annealing acrylic
>>>I'm planning on annealing my viewports,  does anyone know if the
>>>acrylic from the factory is pre-shrunk ?
>>>Brian

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