Vacuum experimenter in Pittsburgh

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Rob MacLachlan
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Joined: Sun Sep 24, 2017 12:19 pm
Real name: Rob MacLachlan

Vacuum experimenter in Pittsburgh

Post by Rob MacLachlan » Thu Nov 30, 2017 4:53 pm

Hi, I'm Rob MacLachlan. I'm interested in vacuum technology, and have a chamber with a rotary pump. This is currently set up as an induction furnace, and I am messing around with vacuum casting and high temperature.
setup_all_scale.jpg
The chamber is inspired by the cooking-pot chambers on ebay, but I reconfigured in a more typical belljar arrangement. The base is an aluminum plate with the vacuum connections and feedthrus. I cut a hole in the bottom of the pot and glued on a glass disk using high-temp silicone RTV. The pot gasket and glass both came from "slickvac" on ebay.
chamber_tilted_scale.jpg
Because of the vacuum casting, this chamber has one stupid trick. It tilts so I can pour metal from the crucible into the mold, without having to worry about something like the rotary feedthrus for induction current + water used on full-size induction furnaces.
heater_feedthru_scale.jpg
heater_inverter_scale.jpg
This is a detail of the feedthrough for the heater and the heater inverter (power supply not shown). Max input is 500W.
interior_scale.jpg
This is a view of the interior. A photodiode under the copper platform does pyrometric temperature measurement. The copper can to lower right holds an Arduino compatible controller which acquires the pyrometer signal, thermocouple temperature probe, and from a piezoresistive pressure sensor (measuring rough vacuum). The thermocouple is used to calibrate the the pyrometer, but can only be used up to 1200C.
argon_meter_scale.jpg
I have an argon tank setup, and also a large precision analog pressure gauge (which is mostly for coolness).
chrome_whatsit_scale.jpg
I succeeded in melting chromium, which means that the temp got up to at least 3,465°F or
1,907°C. Something else happened also, though. Color changed from your usual chrome color to gold (maybe due to trace residual copper from previous melt?) and there is also this cool iridencent violet stuff at the top (maybe a carbide layer)? According to my homebrew pyro the temp gets up to 2300 °C, but have to take this with a grain of salt due to calibration only up to 1200 °C. I want to try casting titanium, 1,668°C. The Ti is so reactive that even in a pretty good vacuum it tends to become something else before it melts.

I am working now on adding a diffusion pump (My Christmas present!) to get the pressure down faster, get the oxygen out.

I'm also interested in plasma processing, especially sputtering and plasma cleaning.

Rob
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heater_inverter_scale.jpg

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Dennis P Brown
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Real name: Dennis P Brown
Location: Glen Arm, MD

Re: Vacuum experimenter in Pittsburgh

Post by Dennis P Brown » Thu Nov 30, 2017 7:55 pm

Please move this to the Image du Jour section. This is only for introductions.

Tom McCarthy
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Re: Vacuum experimenter in Pittsburgh

Post by Tom McCarthy » Thu Nov 30, 2017 9:54 pm

Welcome to the forum Rob.

Looks like a cool setup. If you decide to build a Fusor, most of your equipment should be helpful - your expertise and experience with vacuum definitely will. Check out the Images Du Jour section for some examples of Fusor Chambers.

We generally don’t undertake any extended discussion in the Introduction forum, but people often post some pics here of their initial status when joining. I see you’ve figured out how things work already though, with your Diffstak post.

Best of luck!

Tom

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Dennis P Brown
Posts: 1389
Joined: Sun May 20, 2012 2:46 pm
Real name: Dennis P Brown
Location: Glen Arm, MD

Re: Vacuum experimenter in Pittsburgh

Post by Dennis P Brown » Fri Dec 01, 2017 9:22 am

Again, do post this in one of the other threads so it is not lost (posts here are purged after a while); and do post more details or as you do more work either in the vacuum thread or again, the "Image du Jour" thread. And yes, welcome and a very nice vacuum furnace system and interesting work.

Aside: consider purging the oven a few times with argon gas (available at welding supplies.) That is: vacuum, a few torr argon, vac again, argon and so on for three cycles, You will get better results with oxygen sensitive metals. Ditto with sputtering - improves coatings

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