I am currently in the planning phase to build a replacement furnace. The outer shell is going to be part of a 120lb gear oil drum. The diameter of the drum is approximately 14" and it will have 2" thick walls. Taking the advice I received on here earlier, my current plan is for a 1" hot face of Kast-o-Lite 30 backed by 1" of fiber insulation. While my current plan is to cast the base as a solid 2" thick disc, would it be better to add 1" of ceramic fiber to back the cast base as with the walls or would it not make much of a difference?
I think for most hobbyists, a lower mass furnace is better because it heats faster, so my vote would be 1". Insulating Fire Brick (IFB) would be a good choice to support and insulate underneath the base. It could even be 1/2" with IFB backing. Best, Kelly
Thank you for your advice. I have revised my plans to use IFB underneath a 3/4" layer of refractory for the base of the furnace. Now to wait for my shipment of refractory to arrive. I have attached a picture of my planned design for the base and lid lifting mechanism.
Is that a parallelogram type lifting mechanism? You might want to take a look at Mark's furnace. IIRC, he has a pretty nifty yet simple and effective version of same. Mark, have a picture for Andrew? Best, Kelly
After doing a lot of research and looking at side-swing lid and traditional lid designs, I felt that a parallelogram lift offered a more stable design compared to a side-swing lid design with my base design while not aiming a scorching hot lid at me while the lid is open. Mark's post on another thread was actually the one that had me considering a parallelogram-type lifting mechanism.
Some of the pics are here: https://forums.thehomefoundry.org/i...g-furnace-build-thread.2450/page-2#post-48641
Hi, I just read this thread for the first time and wanted to add some experiences with using the parallelogram lid for a few years: I built mine by welding the lid mounting points and pivot points in place and then making the arms to suit the measured distances. This results in four arms that are all slightly different in length which is not necessarily bad but does require you to number the parts and always reassemble in the original position. The next thing I noticed between the original 1958 vintage furnace lid and my recent copy is that a bit of sloppiness in the holes is an advantage to getting a good seal between the lid and the furnace: you can sort of jog the lid a bit if flames are coming out a gap and get a better seal. That way all the lid weight is borne on the furnace walls and the four arms take no weight when in the closed position. I cast the furnace walls first and cast the lid in place to get matching surfaces, the top of the furnace lining could have benefited from some smoothing with a masonry wheel in an angle grinder to get out the irregularities. Also the disc used to cover the bore when casting the lid in situ needs to be rigidly in place so it can't move from all the vibration or you'll get places where the lid refractory goes into a bore a slight amount and binds when opening the lid. In fact the disc over the bore could be slightly higher say 6mm 1/4" or so than the furnace wall lining. The current form is 1.5 beer kegs tall with 2.5 inches/65mm of dense castable inside the keg shell and 3"/75mm of insulating fibre outside the shell. This is a kludge to compensate for the outside keg shell reaching 300 deg C in operation but actually works great as the dense castable is contained by a steel shell so the inevitable cracks in the dense castable can't leak oil vapours into the insulating fibre as the stainless shell contains the vapours. This would not be an issue for a propane furnace.
Mark, thank you for the photos and information on your furnace and the lifting mechanism. I am wondering if it would be worth it to cast a port into the side of the furnace for a thermocouple probe to slide into in order to measure the temperature inside the furnace during operation. I am trying to finalize the design and it occurred to me the other night that knowing the temp inside may be useful. Would knowing furnace temp be worth it or is it more important to find a way to measure the actual temperature of the metal?
I later fitted a thermocouple, only a K type good to 1350 degrees C though a drilled hole in the furnace wall. It gives good data on tuning fuel and airflow for maximum temperatures. I've only melted iron twice and have been unable to duplicate those temperatures again. Here's a discussion of my experiences so far: https://forums.thehomefoundry.org/i...-to-help-fuel-air-mix-tuning.2313/#post-46864
I cast the base and lid of my new furnace this weekend. All told, it took about 65lbs of Kast-o-Lite 30. The lid is solid refractory while the walls and base have a 1" hot face backed by 1" of ceramic fiber insulation and fire brick. The cast tuyere came out much better than I thought it would. While it is curing, my next task is to mock up the frame and lifting mechanism with scrap wood. The final drying-out process will have to wait until it warms up a little here.
Yes, that is just a cap I made with the leftover refractory from casting the lid. I didn't have enough mixed up to cast another correct-size plinth.
