Re: [PSUBS-MAILIST] Acrylic laminating

We've got some really deep holes here off the Channel Islands! I would love to destroy something!

A question I have is it really necessary to anneal a piece of flat sheet acrylic if it has been machined with the proper tool and at the proper speed?

Brian

----- Original Message -----

From: Emile

To: personal_submersibles@psubs.org

Sent: Friday, January 16, 2004 8:38 AM

Subject: Re: [PSUBS-MAILIST] Acrylic laminating

Dan, Brian

The vacuum form production method sounds good to me but the white papers on the site tell its not suitable for 1 atm subs. little wall thiknes or bad out of roundness??

For to the slice production method; when heat threadment is done after cutting the donuts stress is gone.If properly machined after bonding (sharp tool,coolant) the residual stress must be very small for a material with such a low youngs modulus.

I still think the advantages of producing relative easy a thick walled spherical viewport are great. Disadvantage: as there are no models we have to do some (scaled down) destruction tests.

Regards , Emile

----- Original Message -----

From: Dan H.

To: personal_submersibles@psubs.org

Sent: Friday, January 16, 2004 3:01 PM

Subject: Re: [PSUBS-MAILIST] Acrylic laminating

Brian,

First you can rough cut to your desired shape, leaving extra. You then ramp up to a shrinking heat, hold temp for a few hours and then ramp down to near room temp. This will actually shrink and toughen the acrylic. It will shrink 2 or 3% in size. Then, after your finished machining, you do the same but to a lower temp to stress relieve the stresses caused by machining.

If you think about what happens when your machining anything, there are very high temperatures created at the tool tip. This heat is concentrated at the surfaces being machined. The interior of the part gets warm but isn't heated to the surface temp at the tool tip. The post machining heat evens this out.

The times and temps can be found in PVHO. You need an oven with precise temp settings and it takes HOURS if your dealing with a thick piece. I did my 2 inch thick K-350 main view port. I don't remember the temps I used off hand but I started the process one evening and finished the next afternoon, changing temps every half hour for the ramp up and ramp down.

Dan H.

----- Original Message -----

From: NeophyteSG@aol.com

To: personal_submersibles@psubs.org

Sent: Friday, January 16, 2004 1:51 AM

Subject: Re: [PSUBS-MAILIST] Acrylic laminating

In a message dated 1/15/04 10:41:39 PM Pacific Standard Time, ojaibees@ojai.net writes:

How would you "stress-relieve" it after machining? I not sure what process you are referring to?

Machining leaves residual stresses. As I understand it from the white paper "Window Considerations", the process is to heat treat the acrylic prior to machining to remove residual moisture, machine it, then heat treat again (~300F for several hours with slow ramps) to relieve the machining stresses that can cause cracks and crazing.

Warm Regards

Shawn

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