Earlier this year we put together a kiln to melt some aluminum and the lid we made was good enough, but not perfect. It was made of soft refractory bricks, held to a metal plate with fireplace adhesive. The adhesive failed so this time we decided to cast a lid in refractory cement. This video shows the casting process and testing process. There was a lot of cement left over so we smeared in on the inside of the kiln. One lesson we learned is that a thin layer of cement will crumble at the temperatures we use in our kiln.
During one of our Tuesday evening meetings we experimented with creating plasma.
How do you make plasma? Well, usually air insulates electric charges, so it requires high voltage to break apart the molecules. In a partial vacuum, however, this breakdown potential may decrease enough that two uninsulated surfaces with different potentials might induce the electrical breakdown of the surrounding gas. For example, the exposed tips of two big screws, such as we have in our experiment.
When there are molecules and free electrons floating around inside a chamber like ours, there is the chance of collision between an electron and a molecule, which could ionize the molecule. Electric fields need either very high temperature or very low pressure to break down a gas so we used an old pump to suck as much air as we could from a sealed PVC tube. Of course it wasn’t completely sealed – it’s impossible to create plasma in a pure vacuum because plasma is defined as ionized gas. As you’ll see in the video, we control the amount of gas in the chamber by fidgeting with the release valve. After a few trials we discovered the amount of air pressure required to ignite the plasma then we decreased pressure to maintain the pretty purple lights.
Once upon a time in Tübingen a gentleman named Friedrich Paschen wrote a physics paper about the potential difference for sparking air at various pressures. The formula he magicked from the ether became known as “Paschen’s Law” and it’s an equation that gives the voltage necessary to start a discharge between two electrodes in a gas as a function of pressure and gap length.
If you are curious, follow this link to a web site where you can calculate the breakdown of your own gas!
This video details the process we completed in order to cast a hammer from aluminum, from making the kiln through making our own foundry tools, testing, and finally pouring in our handmade cast. The product would be a hammer that would not produce sparks if dropped on concrete, but the goal of the project was to learn how to cast metal. We worked on evenings and weekends during the month of October with help from several makery members and in the end we made a pretty good hammer. If you would like to see the beautiful shiny hammer live in person and grip it by the finely-detailed handle, just come on by Omaha Maker Group whenever you see the “open” sign indicated here on the web site. We also have meetings on Tuesday nights.
OMG has had a kiln made of high quality refractory brick for a while now but recently Kevin led an effort to rekindle it. After a couple weeks of preparation we spent Saturday morning making last minute adjustments and then fired it up. In all, it only took a half hour or so to turn a bucket of scrap aluminum into ingots of metal, ready for casting. Several members stopped by to watch and help out. The weather was perfect and the procedure went smoothly – hopefully this is the first of many times the kiln will be used, now that we have streamlined the process and assembled all the necessary tools.
Here’s a link to a quick edit of video footage from a camera stationed on the dock behind OMG. A more complete video of the process is forthcoming.
I damaged a CD4093BE and instead of throwing it away I decided to satisfy my curiosity regarding its guts. I used Omaha Maker Group’s belt sander to grind away the top layer of material and it revealed a tiny chip embedded within. The slightly orangey color on the right side is where I sanded away a little too much of the tin protecting the copper legs. In the closeup view, you can just make out where filamentous wires must connect the legs to the chip.
For a variety of reasons, Patrick and I took it upon ourselves today to build a new aluminum-melting furnace based on some old refractory (insulating) firebricks we had in the shed. I’d watched a few videos on Youtube and sort of dove in. Here’s some photos of the results.
We did eventually replace the ziptie on the lower course of bricks with more plumber’s strap, and build some legs for the burner that aren’t made of clamps. We also need to finish up the lid and finish tidying up a bit, but I’m super happy with how it turned out for 3 or 4 hours of work. The biggest time-suck was recutting all the bricks to make a 6-sided structure (the original kiln was 8-sided, so the angles needed changed). The most entertaining part was learning to use the plasma cutter to cut out the steel base plate.
A big thanks to Tech Omaha for recording a local meetups talk. Several organizations around Omaha gave their pitch at a OJUG/WITH co-sponsored event, including ours truly! Sarah Kladstrup stepped up to get our name out there. Here’s a good overview of our organization: