The Viscosity and Working Characteristics of Glasses. Part IV. Some Observations on the Rate of Cooling and Viscosity of Glasses during Manipulation by Automatic Machines
JSGT 1945 V29 T199-T232
The previous measurements by us of the temperature and viscosity of glasses at different stages in the processes of gathering and shaping by hand have been supplemented by a study of the temperatures and viscosities during the shaping processes as carried out by gravity-fed automatic machines of different types. The two glasses studied had the percentage compositions, respectively: Colourless, SiO2 74·1, R2O3 0·85, CaO 9·7, MgO 0·1, Na2O 15·2; amber, SiO2 73·75, R2O3 1·25, CaO 9·4, Na2O 15·6. Depending largely on accessibility of the glass at different stages of machine operation, thermocouple, optical pyrometer and calorimetric methods of temperature measurement were applied. The machines included the Hartford Fairmont press-and-blow, the Lynch LA, the Lynch 10 and a mechanical press. The weights of the various types of containers produced by them during these studies ranged between 3 and 23 oz. The temperatures, and corresponding viscosities, of the glass at each stage of operation were found to be influenced by the conditions of manipulation (type of machine), the weight and the colour of the glass. There is a range of temperature and viscosity within which each shaping operation can be accomplished. The ranges of viscosity (in poises) of the glasses were : Gob formation, 2000-11,000; when leaving the parison mould, 1·8×104–6×104 (mean values) with viscosities in the hot interior at 6×103–8×103; entry into blow-mould, 9×104–2·3×105 (mean values), with viscosities in the hot interior of 1·5×104–5×104; when discharged from the blow-mould, interior values in the base of the bottle 106–108. These values, which are wide enough to embrace both glasses examined, are derived from methods of operation at a single works. The conditions of temperature and viscosity suitable at each stage for optimum efficiency of production when using any one glass and a particular type of machine need to be worked out by further systematic study. The need is emphasised for careful determination of the specific heat of glasses over a wide temperature range.
James Boow & W. E. S. Turner
