Discussion on "Modern heat treatment" at the Luton Section of the Institution

MR. TINKER: I congratulate Mr. Toplis on this very interesting paper. He certainly has had great experience and it has been a pleasure listening to him. The most modern furnaces are the electric furnaces. He showed us the chart of B.T.U. comparisons and of the thermal efficiency percentages. On a normal supply, say, 2s. 6d. per thousand cubic feet of gas and fd. per unit of electricity, the electric furnace shows a comparable efficiency. Taking everything into account, however, including labour cost and advantages of cleanliness, etc., probably there is not much in it. In some cases electric furnaces are the better proposition. Referring to Mr. Toplis´s remarks that gas furnaces heat up quicker than electric, I do not agree that this is necessarily the case. Regarding carburising, we have now developed a recuperative type of electric furnace, which has proved to be very much cheaper owing to a much higher thermal efficiency. The cost for carburising with a recuperative type electric furnace is .04 to .05 pence per gross lb. treated against .09 pence per gross lb. for the non-recuperative furnace. With regard to boxes, there are a number now being used which are only 1.8 inch thick, made up of fabricated nickel-chromium sheet, and these very quickly repay themselves, taking far less time and fuel to heat up.