[Beowulf] materials for air shroud?

Lux, Jim (337C) james.p.lux at jpl.nasa.gov
Tue Sep 13 16:51:23 PDT 2011

> -----Original Message-----
> From: beowulf-bounces at beowulf.org [mailto:beowulf-bounces at beowulf.org] On Behalf Of mathog
> Sent: Tuesday, September 13, 2011 1:06 PM
> To: beowulf at beowulf.org
> Subject: Re: [Beowulf] materials for air shroud?
> FYI,
> Some sheets of 1/16" polypropylene were obtained from smallparts.com.
> (This is very similar or identical
> to the case plastic used on DLT and other larger tape cartridges.)  So
> far this material is
> relatively easy to work with.
> I tried bending a sample two ways.  First, just putting it on the edge of a desk and then
> folding it.  That worked but it turned white and thinned somewhat at the bend, and it
> slowly opened back up again from 90 to about 100 degrees. That edge was then melted by
> gently rubbing it with the barrel of a soldering iron.  (Find the point ust below where
> it smokes).  

A hot air gun works nicely for this. A couple pieces of wood laid on TOP of the plastic where you are blowing the hot air forms a nice channel so that the width of the heated strip is uniform.  After you get it soft, you pick it up and put it on your form (i.e. the desk edge). A 1 cm gap works nicely.

> Neither piece of plastic
> was distorted where the glue had been, so clearly not melted.  There
> are specialty hot melts made
> of polyethylene or polypropylene, and those may actually weld this
> material.

Plastic welding uses what looks like a big soldering iron with an air hose and a hollow tip. The tip usually has a sort of flat spoon sticking out, maybe 1 cm long and 0.3-0.5 cm wide that you can use to push the melted/soft plastic around.  You hold the welder in one hand and the rod in the other and it's much like regular welding (except easier). You get the parent material really soft, and then feed the rod in to make a fillet, just like in regular welding.

The trick is welding, not brazing (i.e. the parent material has to melt enough to mix with the melted rod.. otherwise you're basically hot gluing two pieces of plastic together) 

Jim Lux

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