Re: [PSUBS-MAILIST] Aqua Jet Cutting Acrylic

[Jonathan Wallace <jon@psubs.org>]

Hi Wil,

There's no need to guess (educated or otherwise) when the Stachiw book has 
tons of information about acrylics.  You'll have to bear with me since I've 
only had mine for about three days, but I believe his book answers all the 
questions/statements in your post.


> The core of the problems seems to be that many of us just want to use
> a simple acrylic disc piece that you can get in a normal acrylic store
> - where they do decorative items more than submarines - and use it as
> a viewport.

Don't do this.  Your life may depend upon using acrylic designed for 
submersibles, not decorative items.  This is similar to a skydiver saying 
that he just wants to find a piece of fabric from a normal department store 
to use as a parachute.

Here is a quote from Stachiw's book, page 1035...
"It is worth remembering, that since its inception in 1977, the Standard (ASME 
PVHO) has maintained a perfect safety record over -14.5 to 20,000 psi (-0.1 
to 138 MPa) pressure range in hundreds of different manned and unmanned 
applications.  It would, therefore, be foolhardy to ignore the guidelines for 
acrylic window installations in pressure vessels for human occupancy 
presented by the Standard."

Page 1027
"Continuous cast or extruded acrylic sheet do not meet the Standards criteria 
for mechanical properties and, therefore, are not accepted by the Standard 
for fabrication of windows"



> The truth is when you get your arcylic disk you do not 
> know exactly what process it is trough or not - it looks good - and
> you do not want to build a computerized heating facility just to be in
> peace with the Professor or ABS you also do not want to convert in
> acrylic scientific you just want to know what is safe.

If you purchase acrylic from a manufacturer that follows the ASME PVHO 
standard, you know exactly what process it has been through.

You do not have to build a computerized heating facility, you simply have to 
follow the prescribed annealing process with any oven that can accurately 
obtain and hold certain prescribed temperatures for certain prescribed 
durations.  This process is detailed in the Stachiw book and I recommend you 
purchase one.  Give me a little time and we'll share the annealing details.

If you want to know what is safe, follow the ASME PVHO standards and/or 
purchase the Stachiw book.  Those sources provide detailed information on 
what is safe.


> The question that arises is : IF they did NOT anything right in the
> factory - (which is a remote or not so remote posibility) what is the
> depth i can do with this - and still be on safe side. Is it fine to do
> half of stachiew and ABS and forget about all those complicated
> proeedings? - or should it be 1/3 ?

No. No. No.  It is not fine to do half of Stachiw or ASME PVHO.  It is not 
fine to forget about all those complicated proceedings.  You must design and 
build to the standard.  If you find the standard too complicated, you must 
either hire a qualified person to perform the work or cease continuation of 
your project because the science/fabrication is beyond your capability.


> So i would suggest somebody who has a water yet and a hydraulic pump
> available cuts out a model series 1:2 from sheet material and tests it
> to destruction in a simple mounting inside a hydraulics cylinder -
> with and without annealing...shrinking...

Page 837.
"Annealing is a thermal treatment intended primarily to relieve surface 
stresses on an acrylic component whose surfaces were machined, sanded, and/or 
machine polished."

Water jetting is machining by definition, and according to Stachiw would 
require annealing.  You have nothing to lose by annealing, and annealing 
multiple times (if necessary) does not have any negative impact on the 
acrylic when performed in accordance with the ASME annealing procedure.


> And hopefully publishes this - of course no guarantee - on this forum.

One of the things many people were talking about at the convention was 
adherence to existing industry standards.  I understand fully the argument 
that if nobody ever experimented, there would be no progress, and I agree 
with that manner of thought.  However, R&D into non-standard procedures 
should be exercised by those that have the means to do so.  Given the time 
and expense necessary to have ASME approve some new procedure that might not 
require annealing after machining (14 months and $150,000 according to 
Stachiw), we are better served at this point to continue manufacturing to 
existing standards.  Instead of publishing water-jet results to PSUBS, any 
person undertaking such work would serve our community better by publishing 
those results to ASME in hopes of establishing a new procedure or standard 
that we can all then implement with assurance that the proper testing and 
quality controls have been addressed in the resulting data.

> What is of interest for us all is what is the DIFFERENCE - and a
> educated guess on that.

I agree and echo a statement made by Jeff Jeffries in a previous post.  We are 
not served well by guesses, educated or otherwise.  If we limit our 
recommendations to information that is known to be valid and can be verified 
as so, then we all will enjoy a safer recreation.




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