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Read density data from data sheet [message #59401] Mon, 31 December 2012 10:26 UTC Go to next message
avatar shapeyou  is currently offline shapeyou
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Registered: January 2012
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The material data sheet for PA 2200 at http://www.shapeways.com/rrstatic/material_docs/mds-strongfl ex.pdf says:

Bulk density EN ISO 60 0.45 g/cm³
Density of laser-sintered part EOS method 0.93 g/cm³

So the density of a printed part is 0.93g/cm3. Correct?
Why this difference for the bulk density? The bulk density is the density before the material is processed?

I want to make a part that will be inside water but almost floating.
Re: Read density data from data sheet [message #59402 is a reply to message #59401 ] Mon, 31 December 2012 11:03 UTC Go to previous messageGo to next message
avatar stop4stuff  is currently offline stop4stuff
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Yes, that is correct, 0.93g/cc is for the printed part.
The bulk density is for the loose powder before it is sintered. If I understand correctly, the powder is laid down in the printer under vacuum before being zapped by a laser, hence a more dense printed part.

Paul


Re: Read density data from data sheet [message #59445 is a reply to message #59402 ] Tue, 01 January 2013 15:07 UTC Go to previous messageGo to next message
avatar Magic  is currently offline Magic
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Have also a look to this post.
Basically, for Nylon (White Strong and Flexible) solid material is 0.93g/cm3 while trapped material is 0.45g/cm3.
So it floats anyways...


So many things to design, so little time...
Re: Read density data from data sheet [message #59462 is a reply to message #59445 ] Wed, 02 January 2013 09:31 UTC Go to previous messageGo to next message
avatar shapeyou  is currently offline shapeyou
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Thank you for the asnswers. Very interesting the density test but the density you got in (http://www.shapeways.com/model/329987/density-test.html) is 0.98 and the data sheet says 0.93.
.
I worry a little about this because I want to tune a part to have the water density, not to float (almost floating, the expression I used). And there are little metalic weights I need to append to that part. So I need to make calculatations with precision.

Can someone tell me if the porous PA 2200 absorbs water or other liquids? If it absorbs water the density will change. And that's a problem because I need to use it inside water.
And what type of varnish do you advice for this material?
Thank you
Re: Read density data from data sheet [message #59464 is a reply to message #59462 ] Wed, 02 January 2013 10:24 UTC Go to previous messageGo to next message
avatar stop4stuff  is currently offline stop4stuff
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Registered: June 2010
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The PA2200 will absorb water over time - it may take weeks to become fully saturated depending on the thicknes of the part.

As water density varies with temperature (the principle behind the Galileo thermometer) you'd need to fine tune your just floating parts in situ to the temperature of the water you are using.

Several coats of a Spray on acrylic paint or varnish would make an effective waterproff seal - expect the first couple of coats to soak into the model and leave each coat to fully dry between re-coats.

Paul


Re: Read density data from data sheet [message #59508 is a reply to message #59464 ] Wed, 02 January 2013 19:45 UTC Go to previous message
avatar stannum  is currently offline stannum
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Brushable paint or varnish will do too, and save you from the smell and the issues that normally happen with sprays (bad humidity is the typical one). Some of them have a milk or thinner consistency and seal the parts fast. You can even use floor polish by J&J (it's pretty much like urethane varnish), old modeler trick.

 
   
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