[PSUBS-MAILIST] Clearances

Wed Dec 11 05:04:03 EST 2024

 I had a look in the Hand Book Of  Acrylics, but could not find anything about number of annealing cycles allowed.  I then looked under machining of acrylic.  It says you can sand out blemishes and  scratches with water for cooling, and no mention of annealing.   I also looked under removing crazing.  It is the same thing, you can sand and polish it out, but it will return unless it is annealed.  The conclusion to me is, you can sand and polish without an annealing cycle if the temperature is kept low.  You can also do another annealing cycle, so I must be wrong about not being able to repeatedly do annealing cycles.  At the same time, a very gentle machining seems to fall into the sanding category, to me at least.  Hank
    On Wednesday, December 11, 2024 at 02:27:40 AM MST, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

  Alec,I wish I could remember where I heard or read that there is a limit to how many times it can be annealed.  My understanding is, it needs an annealing cycle to stress relieve the blank, and a second after machining due to heat from machining.  My memory may be failing me.Hank
    On Tuesday, December 10, 2024 at 09:56:51 PM MST, Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

 Hank, what you're proposing sounds totally logical to me. However, I have asked Greg this very question in the past (whether we really have to anneal a viewport.) I'm not sure what the underlying causality is, but he has enough professional experience in the field that I just take his word for it. "You need to re-anneal it whenever any machining has been done on a viewport." Annealing is pretty straight forward. 
I'm currently working on forming acrylic headlight covers and windows for an antique car restoration. It's a new skill I'm trying to develop, so fortunately I'm not making anything safety-critical like viewports. But one interesting detail is that Greg strongly recommended annealing even for this, because it'll make the covers and windows less likely to crack (there could be stresses caused by mounting screws or flying pebbles, for instance.) He had two basic points he stressed for the things to last:
1) That not all acrylic was equal. The only one he will use is "cell cast" acrylic, and he warned me emphatically to stay away from the cheap stuff which can be referred to as extruded or "continuous cast." I know this has not been mentioned on this thread, but I bring it up because it seems to be key information.2) Annealing
Next time I speak to him, I'll ask about machining with light passes and coolant.
Best,Alec
On Tue, Dec 10, 2024 at 1:35 PM hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 Rick, I would do some more research on annealing your port again.  If I recall, a window is only allowed one annealing cycle.  The reason for annealing after machining is due to heat build up for machining.  I have machined and tested ports without an annealing cycle.  The trick is to take super small passes .005 and even spray water on it as its  cutting.   I was talking to a machinist one time about machining domes and he put ice water in the dish to keep it cool.Its been a while since I worked on this, so check it out, in case my memory is off.Hank
    On Tuesday, December 10, 2024 at 10:55:04 AM MST, Rick Patton via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

 Hey Sean,The viewports are flat. Thanks for the data.
On Tue, Dec 10, 2024 at 6:12 AM Sean T. Stevenson via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Rick, is this a flat disc viewport, and not a dome?
See an excerpt from ASME PVHO-1-2023 below. Do, where referenced, is the window major diameter.
2-2.11.4 Flat Disk Windows
2-2.11.4.1 Window External Diameter. 
The dimensional tolerance of the external diameter of the window shall be based on the type of sealing arrangement for the window.
(a) The external diameter of the flat disk window shall be within +0.000/−0.010 in. (+0.000/−0.25 mm) of the nominal value if the window is to be sealed in the seat cavity with a radially compressed O-ring.
(b) The external diameter of the flat disk window shall be within +0.000/−0.060 in. (+0.000/−1.5 mm) of the nominal value if the window is to be sealed in the seat
cavity with a seal ring wedged into the annular space between the retaining ring, the window’s bevel, and the cylindrical surface of the seat cavity.
(c) The external diameter of the flat disk window shall be within +0.0/−0.125 (+0.0/−3.2 mm) of the nominal value if the window is to be sealed in the seat cavity with a flat elastomeric gasket axially compressed by the retaining ring.
(d) The external diameter of the flat disk window shall be within +0.00/−0.02 Do of the nominal value if the window is to be sealed in the seat cavity with a room temperature curing elastomeric compound injected into the annular space between the edge of the window and the cylindrical surface of the seat.
(e) The plane bearing surface of the flat disk window shall not deviate more than 0.001 Do from an ideal plane.

2-2.11.4.2 Seat Cavity Diameter.
The dimensional tolerance on the external diameter of the window seatcavity shall be based on the type of sealing arrangement for the window.
(a) The diameter of the seat cavity for a flat disk window shall be within +0.01/−0.00 in. (+0.25/−0.00mm) of the nominal value if the window is to be sealed in the seat cavity with a radially compressed O-ring.
(b) The diameter of the seat cavity for a flat disk window shall be within +0.06/−0.00 in. (+1.5/−0.00mm) of the nominal value if the window is to be sealed in the seat cavity with a seal ring wedged into the annular space between the retaining ring, the window’s bevel, and the cylindrical surface of the seat cavity.
(c) The diameter of the seat cavity for a flat disk window shall be within +0.125/−0.000 in. (+3.2/−0.00mm) of the nominal value if the window is to be sealed in the seat cavity with a flat elastomeric gasket axially compressed by the retaining ring.
(d) The diameter of the seat cavity for a flat disk window shall be within +0.01 Do /−0.000 of the nominal value if the window is to be sealed in the seat cavity with a room-temperature curing elastomeric compound injected into the annular space between the edge of the window and the cylindrical surface of the seat.
(e) The plane bearing surface of the seat cavity shall not deviate more than 0.002 Do from an ideal plane when measured with a feeler gauge inserted between the mating plane surfaces of the flat disk window or a circular plug gauge and the bare seat cavity. The axial force used to seat the window or the plug gauge shall not exceed 10 Do lb (4.53 Do kg) applied uniformly around its circumference.
Sean
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