Transfer of Heat in Glass During Forming

Abstract

The transfer of heat in glass during glass‐container machine‐forming operations is characterized by extremely high rates of heat removal from relatively thin sections of the material. Evidence is presented to show that, under these conditions, the transfer of heat within the glass is almost 100% by true conduction; the contribution of radiative transfer to the thermal distribution is almost nil. This conclusion was reached by the application of experimental forming and glass properties data to radiation and conduction theory through the use of a high‐speed digital computer. It is apparent further that the thermal conductivity of commercial container glass varies slowly with temperature in the forming range, increasing from about 14 B.t.u.‐ft.−2‐hr.−1‐in.1‐°F.−1 at 1200°F. to about 19 B.t.u.‐ft.−2‐hr.−1‐in.1‐°F.−1 at 2000°F. The heat‐transfer coefficient between glass and mold surfaces decreases rapidly with time of contact.