# Read density data from data sheet

Discussion in 'Technologies and Hardware' started by shapeyou, Dec 31, 2012.

1. shapeyou New Member
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/cmÂ³
Density of laser-sintered part EOS method 0.93 g/cmÂ³

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.

2. stop4stuff Well-Known Member
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
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3. Magic Well-Known Member
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...

4. shapeyou New Member
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

5. stop4stuff Well-Known Member
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
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6. stannum Well-Known Member
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.