For our experiments, we need a vacuum oven able to reach 130°C but that equipment was not available in our lab. Vacuum ovens are very expensive, see for instance this model. We decided to fix a broken oven and a broken vacuum chamber.
We had an old VWR oven, 45L with a temperature range of 40 to 240°C. The model is relatively similar to this one, but we have an older version without digital displays. For some reasons, the bottom of the oven was completely rusty and it's the location of the electronics. The knob for the temperature adjustment was blocked by the rust, so that the temperature could not be adjusted. After disassembling this part, we could find the reference of the thermostat and buy a new one for 250$ on grainger. The manufacturer (Robertshaw) reference is 5210-363. It came with a new knob. We just had to replace the thermostat, the wires and some connectors. We also replaced the hinges because they were also completely rusty and one of them broke. After that, we got a shinny oven that looks new.
But that's only half of the story. Now, we need a vacuum chamber. Our temperature requirements cancel any use of plastic. We had a glass vacuum chamber in the lab, but a part was broken. Basically, a cap connected to a vacuum pipe is supposed to fit on the top of the lid and extract air through a small hole. The two parts must be covered with vacuum grease to be efficient.
First, we tried various solutions to connect a valve on the lid, to maintain vacuum. However, the temperature makes strong restrictions on the choice of materials and glues. After some failures, we decided to get rid of the lid and keep only the bowl. The bowl edge is really thick to seal the chamber, that will be helpful.
We bought a aluminium sheet (about 1cm thick) and a pipe connector (Male stud push-in fitting) that fits in a nylon tubing. The aluminium sheet has been drilled and tapped in its center, and we screwed the connector. The bowl and the aluminium lid are covered with vacuum grease and we could vacuum the chamber.
However, we cannot expect the chamber to hold vacuum for hours. So, we need to connect the chamber to the vacuum supply in the oven. The oven has a hatch on the top, which is a millimeter thick stainless steel sheet. We drilled that sheet at the tubing diameter. This tubing resists well at a temperature of 130°C, even if it becomes slightly softer.
You can check below the pictures. Basically, a thick aluminium sheet could replace any broken lid of a vacuum chamber and save quite a lot of money.
- This page has been realized by Sepideh Khodaparast and François Boulogne.