The Outside of the Chamber
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Who would have believed you could use a propane tank for a vacuum
chamber J The tank was
new from Home depot, and fabricated from mild steel. I cut the bottom of the tank off with a skill saw and an abrasive
blade. The above picture was during
initial leak testing, and I’m using a ¾” thick piece of plate glass for a
temporary base plate.
Starting from the top of the image
1.
Brass tee screws into
tank where original propane valve used to reside. I’ve since replaced this plumbing with a simple threaded plug
which I use as a “Valve” to vent the chamber (Much easier than trying to find
an appropriate vacuum capable valve at Home Depot J)
2.
On the top of the
chamber to each side of the plumbing is the electrical pass thru for the
tungsten evaporator. These were
constructed as follows
a.
Drilled a 1” hole in the
chamber wall
b.
Brazed a ¾” ID Fender
washer to the Chamber using Bronze brazing rod
c.
Glued a ¼” thick plate
glass disk to the fender washer. The
glue I used was a two part adhesive originally intended to glue automotive
weather stripping onto auto body parts.
I think its some type of silicone.
I choose this as it was flexible, seemed to make a good seal, resisted
heating with a blowtorch, and didn’t “SMELL” prior to, or after curing.
d.
The Glass disk as a ¼”
ID hole in it, through which passes a ¼-20 stainless bolt, with an O-ring
between the head of the bolt and the piece of glass. (BTW, the O-ring is from
the plumbing isle of Home Depot, no idea what its made of, but it works!)
3.
The Big red thing is the
sending unit for the Penning Cold Cathode Ion Gauge. This gauge measures the low pressure (High Vacuum) from 1x10-3
torr and less (or more depending on how you want to think about it J)
4.
Towards the bottom on
the left side is the electrical pass thru for the high voltage Glow Discharge
cleaning system (Yes, it really is just an automotive spark plug! But it’s a
Bosh Platinum spark plug J) There’s another plug just like it on the
other side. No idea if the platinum
plug vs. a standard plug makes any difference, but it does the job. Glow discharge cleaning is pretty
interesting stuff, see further down
this page for more details!
5.
To the right of the
spark plug is the viewing window. To
create the window I used a cutting torch to rough out a piece of ½” thick steel
to the approximate shape, cleaned it up with a grinding wheel, and matched the
curve of the tank. I then brazed the
this steel square to the tank, and glued a ¼” thick plate glass window to
finish it off, again using the Automotive weather strip adhesive.
6.
At the bottom of the
tank, was the hardest part to create, the flange
a.
To start with I didn’t
have a large enough piece of ½ steel plate to create a single piece flange out
of!
b.
I cut two the halves out
of some scrap steel I had, using a cutting torch mounted in a make shift circle
cutter
c.
Next I welded the two halves
together, and of course the welds warped!
To straiten the mess out I learned about heat shrinking steel (another
amazing piece of physics in action!) Basically you heat the convex side of the
warped steel, as the steel cools it contracts and straightens the curve
out. Pretty neat stuff!
d.
After welding, I
couldn’t figure out how to make an O-ring groove, so I didn’t J Instead I
allowed the walls of the tank to extend past the flange 3/16” inch, and left
the outer edge of the O-ring exposed.
Works pretty well other than occasionally the o-ring falls out while
setting the tank on the base-plate. I
found if I lubed the o-ring with just the right amount of pump oil, I can get
it to stay in place pretty well.
That pretty much covers the outside of the chamber lets have a look
inside J
Inside the Chamber
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image
Here we are looking inside the chamber after several aluminizing
runs. Starting from the top of the
image.
1.
Viewing window, which I
really need to add a shroud around to keep the Al vapor off!
2.
The hole goes to the
Penning Gauge
3.
Next you see my attempt
at a tungsten evaporator. I really need
to re-think this area, especially since my tank is so short.
4.
On the left and right
sides of the tank you see the tips of the spark plugs (after removing unnecessary
material)
5.
Surrounding the tank
wall is the one and only REAL vacuum rated O-ring I purchased from Lesker.com
(great vacuum site!)
6.
Also in this image, you
can see my flange was entirely too wide.
Next tank only gets a ½ wide flange, which will be MUCH lighter!
Glow Discharge Cleaning
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I don’t know a lot about Glow discharge cleaning, other than it’s a
mighty impressive thing to see in person J From what I’ve read, the high voltage ionizes the residual gases in
the chamber (Nitrogen and Oxygen mostly).
These ionized gases apparently don’t like being this way, and readily
search for something to react with. The
result is organic residue like fingerprints and what not, are removed from the
chamber (Somehow). I’ve also read that
glow discharge cleaning is good at removing the molecular layers of water that
like to adhere to everything inside the chamber helping to produce a lower
ultimate pressure. All I know is it
“KOOL” !