"Making a Coffee Tin Furnace"
Melting Metals in a Home-Made Furnace – Part 1 About 10 years ago I became interested in making a range of metal alloys to test their effect on gasoline (petrol) – a result of reading various patents claiming to improve the combustion characteristics of hydrocarbon fuels. Interestingly, a tin based catalyst was added to airplane fuel tanks or fuel lines in the 1940’s enabling British aircraft to operate on a low-octane and wax forming fuel supplied by Russia for English fighter aircraft sold to Russia. Various catalysts containing mercury were developed to work in a similar way and to reduce the incidence of algal contamination. A number of catalysts were patented in the 1990’s claiming to improve combustion, engine corrosion and in some cases reduce exhaust gas pollution. However, I don’t wish to get into any great detail as it is not the purpose of this article. I should point out though, that metal alloy catalysts have been made containing for example: tin, antimony, lead and mercury (traces of platinum added) tin, antimony, lead and mercury tin, antimony, lead, mercury and thallium tin, lead, mercury, nickel and bismuth tin, copper, silver, nickel and copper The list is by no means complete and there are later patents that were developed for a similar purpose. Initially I borrowed an old Muffler Furnace with excellent temperature control – I could set the maximum temperature and automatically raise the temperature by one degree Celsius increments. I o had no trouble melting copper at 1084 o C and iron at 1535 C. Unfortunately, the element eventually burnt out and I was unable to replace it and to make matters worse, the insulation material surrounding the core was asbestos. I decided not to get an element specially made and to scrap the oven. Not prepared to give up, I searched the Internet for information about constructing another small furnace and found an article that explained how to make a gas-fired small furnace from a large coffee tin (6 x 7 inches – 15.5 cm x 17.5 cm). The coffee tin shown in the photograph is the actual size used as is the propane gas burner torch. The original screw-on fitting was taken off and replaced with the larger one inch (2.5 cm) diameter fitting so as to provide a larger heat source. A larger tin may be even better if size is important. The construction process is very simple. Cut off the top one third of another coffee tin and keep the lid on. This will eventually be used as the lid of the furnace. I poured refractory cement into the bottom 2 inches (5 cm) of the coffee tin and allowed it to set. A circular hole was cut in the side of the coffee tin, level with the surface of the new cement base and of a diameter slightly larger than the head of my gas torch (1 inch – 2.5 cm). The hole was then sealed with a piece of plastic tubing packed with paper but wooden dowel is also suitable. Next, and this is a variation on the published plan, I placed a round plastic jar inside the coffee tin, around which I poured refractory cement, keeping the jar in a central position and its lid on whilst pouring. When the cement had set overnight, I then used a gas torch to soften the plastic and removed it – much easier than using an overlapping, pinned metal former. The plastic tubing may also be removed. The hole is where the propane gas burner fits. Now for the lid made from the second can... secure the lid tightly and then fill it with refractory cement. Push a small piece of greased wooden dowel down through the centre of the cement until it touches the lid. This will provide an inspection hole. Gently shake or vibrate the container to compact the setting cement. Finally, when the cement solidifies but is still damp, the wooden dowel can be carefully screwed out. Take the lid off the next day. That’s it! Finished! Note: If you want metal handles on the lid bolt them on securely before pouring the cement. Regretfully I did dispose of my coffee tin furnace when I decided to clean out my shed but it did work well for small quantities of different metals for example, aluminium, lead and alloys containing bismuth and tin. I even started experimenting with ruby crystal growth but that’s another article! Crucibles can be ceramic, steel, carbon and if you really need something special like I did ... platinum. In conclusion, the coffee tin furnace is great project for anyone wanting to melt small quantities of metal or to make alloys particularly for casting jewellery items. As always safety comes first, so be prepared to do adequate research about using small furnaces to melt and cast metal. For those readers wondering why I disposed of my own coffee tin furnace, I graduated to a larger one – a compact electrical resistance Shop Furnace (below) but more to say in part 2. Handy References: http://www.backyardmetalcasting.com/index.html http://www.backyardmetalcasting.com/ccfurnace01.html