PrefaceMy newest need for a tool has arouse from the need to heat treat some knives that I plan on making. I already own torches and have heat treated a few things in that matter in past, but the knives that I would like to make are out of S30V Stainless steel. This steel needs proper heat treatment so I thought that I would make an oven to do so. I have also been doing some outdoor aluminum casting, it is now getting cold here in Canada so I would like to move inside. My current foundry weighs a ton and is oil fired. This means is it not possible to bring it inside. What to do? Why not build the foundry into the heat treat oven. I don't know why more people have not thought of this! But how to do this considering the heat treat needs to be front loading and the foundry top loading. Rotate it, Thats it! Now for a Plan!!
The OvenSince this Oven/Foundry will be inside and I want to hold precision temperatures, I have opted to make it PID controlled. I also need to be able to have it top loading(foundry) and front loading(heat treat). The internal dimensions are then determined by the length of knife I want to make(12") and the size of the crucible I plan on using (8-1/2"Tall, 6-7/8" Dia). The internal dimensions would then be a minimum 13" tall x 8" Dia. I found a local supplier of Grooved K23 Firebrick which measured 2.5"x 4.5"x 9". I figured then if I stacked one fire brick lengthwise on top another third of a fire brick and then the same side by side I could make a wall the would measure 12" Tall x 9" Wide (without corners). I would make the corners by 2.5"x2.5" squares that were 12" tall (total) out of regular firebrick. (see diagrams below). I then added 1" thick by 2" wide firebrick to the bottom and to the top of the walls, in order so that the kenthal wire has some room to go from one groove to the next.
|Top View Of Walls|
|View Of Front or Back Wall|
|View Of Side Walls (Front and Back walls not shown here)|
This design now needs a floor and a door, which both are of the same design (see diagram below)
Diagram to come soon
With the fire brick out of the way next to design was the metal outer case to protect the fire brick. This out case I decided would be a simple box made of angle iron covered in sheet metal. I ended up finding some scrap 1-1/4" angle iron which would work nicely. I would also build the frame for the door from this. (see diagram below)
Diagram to come soon
ElectricalWith the basic mechanical oven structure design finished it was time to consider the electrical needs. I am not an electrical engineer, only a technologist, and these plans have not been certified. So if one chooses to use these plans, please proceed with caution.
I want to be able to set the temperature very precisely, so I will be using a cheap PID controller. An SSR will be used to switch on the Kenthal heating elements. The SSR can overheat, so a thermal switch will be mounted nearby for safety purposes. On the topic of safety, a door switch will also be installed, as well as a main disconnect switch and fuses. Originally I planned for 4 elements(one on each side) but that will require too much power and may get damaged when mounted on its side. In that matter I decided to go with 2 elements instead of the 4.
The PID I am using is the T series from Mypin (ebay), the kenthal elements are also from ebay and are rated at 3KW. The parts will be listed in the bill of materials (BOM) below.
I measured the resistance of one and it comes to 30ohms. This gives me a total resistance of 15ohm when installed in parallel. 240Vac/15ohm=14.7A which is 3226W total. My 240V circuit is 20A so the 14.7A will work nicely.
BOM to come soon
|I may change how this works!!|
The frame is the most unique part of this build as it will allow me to go from a top loading foundry into a front loading heat treat oven. The idea here is to rotate and lock the oven into position. Some angle iron should work nicely to build this.
Diagram to come soon
I will finish this blog in time as the furnace is being completed at the same time. Pictures of progress and updates will follow