[PSUBS-MAILIST] question

Fri Feb 7 20:41:17 EST 2025

 Thanks.  BTW, did you use the normalization schedules in the Stachiw Handbook of Acrylics or the table in the PVHO table that Sean sent?  I am not sure how I would support a larch flat disk viewport to prevent this sag and not mar the surface.
    On Friday, February 7, 2025 at 02:05:35 PM CST, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

  Cliff, I made an oven with computer controlled temerature and automatic ramp up and down.  It took over 100 hrs, and the 3 inch material did sag 1\8 of an inch.  That was fine in my case because it allowed me to make my dome 1\8 inch thicker.  You will need to support the center or let it sag and you will have a slight dome.  
Rick, it was not the end of the world to make the oven and I am sure you can manage it.  The charts are in the Handbook Of Acrylics.Hank
    On Thursday, February 6, 2025 at 06:26:46 PM MST, Sean T. Stevenson via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

 PVHO-1-2023 has this to say on annealing:
2-4.5 Annealing
All window material shall be annealed after all forming, machining, and machine polishing have been completed. All annealing shall take place in a forced-air circulation oven. Annealing shall be in accordance with Table 2-4.5-1. Time and temperature data for all annealing cycles shall be entered into PVHO-1 Form VP-1. A copy of the final anneal’s time/temperature chart shall be attached to PVHO-1 Form VP-1.
See attached for the Table 2-4.5-1 excerpt from PVHO-1-2023.

Sean
 On Thursday, February 6th, 2025 at 17:56, Cliff Redus via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

  Rick,  it was a lot easier for all of us when Greg Cotrell was fabricating and annealing our viewports.  Now, we have to figure all this out for ourselves.  I am in the build stage for the R400.  As such this topic is near to my heart.
I have attached a PDF file of a spreadsheet I created for a normalization and annealing schedule for my flat disk viewports for my new boat. I got this information from two sources: Jerry Stachiw's " Handbook of Acrylics" and ASME PVHO-1-1997  Safety Standard for Pressure Vessels for Human Occupancy.  Also, I have been in contact with Jon Wallace on this who has quite a bit of knowledge on the topic.
If you cannot get Greg Cotrell to heat-treat your viewports, my suggestion is to read the appropriate sections of these two references to determine the normalization (prior to final machining of the rough cut) and annealing (after machining and surface polishing) schedules. You can then tailor a normalization and annealing schedule to give to the guy who is going to heat treat your acrylic viewports.
The last time I spoke with Jon on this topic, he had done quite a bit of the work on building a microprocessor-controlled annealing oven.  
As to material for the bearing gasket for a flat viewport, both references say that these should be slightly oversized, of at least 80 -durometer hardness, and from 0.020 to 0.125 inches thick.  ...  Since the function of the gasket as primary or secondary seals, they should preferably be made from non-permeable elastomeric material.   Parker Haniffin's o-ring site has a material selection calculator.  This indicates Nitrile (Buna-N), EPDM and Viton are all unaffected by seawater and are applicable.   This is for a flat viewport.  I don't know what you have for your boat.
To be honest with you Rick, the initial normalizing heat treatment schedule scares me to death!  Even though it calls for 266 F in Stachiw's book, I am afraid the 266 F is to high and that the 21.5" diameter x 3" thick acrylic disk will sag.  The plan is to mount in the oven horizontally.
Best
Cliff

     On Thursday, February 6, 2025 at 01:19:33 PM CST, Rick Patton via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

 As mentioned before, I had to have my large viewport turned down on a lathe and I have contacted a couple of places that anneal acrylic and they said that they needed a specific procedure for my particular application. I had Greg Cottrell do it last time but was looking for someone say on the West coast if possible. I don't want to tell the companies I contacted how they will be used as that has been problematic in the past. Can anyone help me with this?I also forgot what type of rubber O ring material I should use. Was it Nitrile or Buma? All that's left now is to install the viewports and she's ready to get wet!
Thanks
Rick _______________________________________________
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