Vacuum experimenter in Pittsburgh
Posted: Thu Nov 30, 2017 11:53 am
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.
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.
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.
This is a detail of the feedthrough for the heater and the heater inverter (power supply not shown). Max input is 500W.
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.
I have an argon tank setup, and also a large precision analog pressure gauge (which is mostly for coolness).
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
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.
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.
This is a detail of the feedthrough for the heater and the heater inverter (power supply not shown). Max input is 500W.
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.
I have an argon tank setup, and also a large precision analog pressure gauge (which is mostly for coolness).
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