Coles, Continued from pg 17
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How do you approach the design and development process for a furnace using alternate fuel sources?
A lot of it was trial and error through research. Once we had settled on a burner design and modified it to suit our needs we then started to test it to see how well/evenly it heated the melt. We also experimented with different waste oils, as well as different ways of treating the waste oil to make it a more reliable and efficient fuel. Once we found a methodology that suited us, we went about recording our operating times and procedures in order to know how to recognise if there was an issue with the melt.
What challenges have you faced in developing furnaces that use alternate fuel sources and if so, how did you
overcome them?
The biggest issue initially with our furnace was learning how to not burn the metal. As the furnace runs a few hundred degrees hotter then a propane furnace it can be easy to burn the metal. Since starting to work with this system we have developed a methodology that compensates for a quicker melt. On average we can melt a pot of metal anywhere from 20-30% quicker then a standard propane crucible furnace. The other large issue with working with a waste oil furnace
is ensuring the waste oil you are using is fit for purpose. You will be surprised at the amount of french fries, chicken skin and hair!! You can get in a batch of waste cooking oil. The other big issue can be water in the oil, as such we have developed a system for screening out the coarser materials and separating the water from the oil. Our burner design allows for some particulate to be present in the oil, we found through our research that a number of oil burners will clog if the oil is not clean, fortunately we do not have this problem.
I think our biggest success with our furnace and our melting methodology is that it allows us to produce crucible iron. Using some basic metallurgy we are able to produce a good quality grey iron that we have used in a number of projects and commission work. This was the initial appeal of this technology as I was looking for a greener more sustainable way of melting iron than using a traditional cupola furnace. One project we are involved in currently that requires a
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good grey iron, is in conjunction with the silversmithing and metallurgical department at West Dean College, Chichester, UK. We were asked to produce a series of silversmithing stakes cast in iron for their silversmithing courses. We have successfully produced some nice anvils using a set of custom patterns that were produced for us, the college is currently trialing the stakes to see how they fare. We are hoping to be able to offer these to silversmiths going forward.
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Can you provide an example of a successful project where you also used this process? What were the key factors that contributed to its success?
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How do you ensure the efficiency and effectiveness of using a furnace with an alternate fuel source?
Due to the nature of the oil we are firing with we run our furnace in a reducing atmosphere, this ensures a good
melt for the range of metals that we work with. In particular, cast iron requires a reducing atmosphere to successfully melt in, if there is too much oxygen present within the melt then it will burn the carbon off of the iron and you will be left with a very hard white iron. This is something we are keen to avoid as a number of our castings go on to be machined and finished after they have been cast. To ensure efficiency throughout the melt we will bring the heat up in stages and when the furnace is running at temperature we tend to use very little fuel as the blast needs to be kept to an optimal ratio of fuel to air. Too much fuel and the heat will be uneven and will struggle to reach temperature.
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Do you see this as a possibility to be used on a larger scale?
I would say certainly, as the technology involved is fairly robust. Our furnace in house produces a 60kg melt in our crucible, there is a foundry not too far from us who are running a similar technology to produce a 90kg melt. We found with our furnace that using a twin burner array helped, as the burners were working in tandem this meant that the atmosphere within our furnace was much more stable. As such we were able to achieve a far more even heat. I think if you were to significantly scale upwards it would be well to introduce further burners to ensure the heat is spread evenly throughout the melt zone on the furnace. Certainly for our scale and applications our burner arrangement works very well.
March 2024 ❘ 19
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