🚀 go-pugleaf

In article <1k6fs0INNo19@elroy.jpl.nasa.gov>, gwalsh@kilroy.Jpl.Nasa.Gov
(Gerald J. Walsh) wrote:
> 

> I started by just asking people and so far, I have had Lexan or ABS
> suggested as a possible solution.  If I choose one of those, or whatever
> I choose for that matter, I will have to describe the crystal structure
> (Face Center Cubic, Body Center Cubic or Hexagonal Closed Pack).  I
> also have to discuss the market, price and my intended distribution
> channels.  I will have to identify the materials that make up the
> plastic I choose.  Finally, the process steps need to be discussed and
> the companies that can provide the choosen plastic or its components.

Lexan or ABS are not cyrstalline, they are polymers, and while portions may
be 'crystalline', the majority of it is not crystalline (amorphous is the
proper term) in the sense that you are using it.  Think of them more as a
bowl of spagetti; many long chains of atoms intertwined.


> Is Lexan or ABS a good choice?  Too expensive?  Where can I get information
> on the crystal structure for the choosen plastic?  Any good sources I
> could look for in the library?

Lexan is much more expensive than ABS.  You might also consider cellulose
acetate; that's what they make many soap dishes and the like out of.  Here
are some prices (they should be considered as relative; they may not be
current actual prices):

ABS                     $1.75 / lb
Cellulose Acetate       $1.71 / lb
Lexan                   $2.62 / lb

Some things to look for:

Price
Impact Strength (so it can withstand some abuse)
Processibility  (can it be molded into the desired shape)
Wheatherability  (Lexan beats ABS on this one)
Assembly  (will it be glued, or snapped together.  Cellulose is poor if you
need it to snap together; doesn't bend very well.)
Color and colorability (Don't want a clear case, or do we?)

(Perhaps readers could suggest more)

Overall I think ABS probably has the best combo of what you're looking for.
 Lexan is better stuff but a bit expensive.

For information try reading sections on 'polymers' in basic chemistry books
as a start.  Then perhaps the "Modern Plastics Encyclopedia".

KEVIN

Gerald J Walsh wrote: 
>> I started by just asking people and so far, I have had Lexan or ABS
>> suggested as a possible solution.  If I choose one of those, or whatever
>> I choose for that matter, I will have to describe the crystal structure
>> (Face Center Cubic, Body Center Cubic or Hexagonal Closed Pack).  I
>> also have to discuss the market, price and my intended distribution
>> channels.  I will have to identify the materials that make up the
>> plastic I choose.  Finally, the process steps need to be discussed and
>> the companies that can provide the choosen plastic or its components.

and Kevin Weber replied: 
> Lexan or ABS are not cyrstalline, they are polymers, and while portions may
> be 'crystalline', the majority of it is not crystalline (amorphous is the
> proper term) in the sense that you are using it.  Think of them more as a
> bowl of spagetti; many long chains of atoms intertwined.

[With much more good information about polymers deleted.]

I *think* that Gerald needs information about the actual electronics of his
proposed calculator as well as the case material.  I'd guess that for a 
variety of reasons he's going to have to use Silicon (unless its for DoD,
in which case he can make it out of GaAs with a gold foil liner inside of
a radiation hardned case!).  Information about Si is available just about
anywhere, so there shouldn't be any problem finding out about the crystal
structure.

The other possibility is that whoever assigned this paper is enough of a 
goof not to know about the amorphous properties of plastics and polymers.

-Bill Gawne,  Space Telescope Science Institute