Carbon Dioxide as a Coolant

Abstract

ATTEMPTS have been made in the past to use liquid carbon dioxide as a cutting coolant, notably in the U.S.A. However, results were not in general very satisfactory, and this may have been because the material was applied by people who were more familiar with machine tools than with carbon dioxide. Recently considerable progress has been made, however, by The Carbon Dioxide Company—a Division of the Distillers Company Ltd. The earlier attempts had taken the form of spraying a relatively large jet of the liquefied gas on to the work and tool generally. This proved to be wasteful of the gas, and in any case cooled the chip as much as the tool, which to a large extent cancels out the benefits gained from keeping the tool cool. The most important property of carbon dioxide as a coolant is that, when expanded to the atmosphere, a portion of the liquid becomes gas, while the consequent cooling, due to the absorption of the latent heat of vaporization, converts a further portion of the liquid to solid CO2 in the form of ‘snow’. This solid exists, under atmospheric pressure, at—78 deg. C., and under these conditions will sublime directly into gas, with a latent heat absorption from the surroundings of 250 B.T.U. per lb. of solid gasified. It can be seen that, if full use is made of these properties, very high rates of heat removal can be achieved.