Thermal treatment of glass in a fluidized bed

In a method of thermally treating glass wherein the glass is heated to a temperature above its strain point and is immersed in a gas-fluidised bed of particulate material, and wherein the gas enters the bed from a plenum chamber, the improvement wherein, prior to said immersion, said gas-fluidised particulate material is placed in a quiescent uniformly expanded state of particulate fluidisation through control of the plenum pressure such that the gas velocity while the glass is being contacted by the bed is between that velocity corresponding to incipient fluidisation and that velocity corresponding to maximum expansion of the bed.

In a method of thermally treating glass in which the glass is heated to a temperature above its strain point and is immersed in gas-fluidised particulate material to effect heat transfer between the surfaces of the glass and the fluidised material, the improvement wherein said gas-fluidised particulate material in which the glass is immersed is placed, prior to said immersion, in a quiescent uniformly expanded state of particulate fluidisation through flow control of fluidising gas to engender a uniform distribution of fluidising gas in the particulate material at a gas flow velocity through the particulate material between that velocity corresponding to incipient fluidisation and that velocity corresponding to maximum expansion of the particulate material.

In a method of thermally treating glass in which the glass is contacted with a gas-fluidised particulate material to effect heat transfer between the surfaces of the glass and the fluidised material, and wherein fluidising gas is fed to said particulate material through a membrane from an external source, the improvement wherein said gas-fluidised particulate material with which the glass is contacted is placed in a quiescent uniformly expanded state of particulate fluidisation through control of gas fed through the membrane to provide uniform distribution of fluidising gas flow upwardly from the membrane at a gas velocity between that velocity corresponding to incipient fluidisation and that velocity corresponding to maximum expansion.

In a method of thermally toughening glass in which the glass is heated to a temperature above its strain point and is immersed in a gas-fluidised bed of particulate material, and wherein the gas enters the bed through a membrane from a plenum chamber, the improvement wherein, prior to said immersion, said gas fluidised material is placed in a quiescent uniformly expanded state of particulate fluidisation by regulation of the plenum pressure in the plenum chamber such that the velocity of the flow of fluidising gas upwardly from the membrane is between that velocity corresponding to incipient fluidisation and that velocity corresponding to maximum expansion.

In a method of thermally toughening a glass sheet wherein the glass sheet is heated to a temperature above its strain point and is lowered into a gas-fluidised bed of particulate material, the improvement wherein said gas-fluidised particulate material of the bed is placed, prior to immersion of the hot glass in the bed, in a quiescent uniformly expanded state of particulate fluidisation with a quiescent surface by control of gas feed to the bed such that the gas velocity in the bed is between that velocity corresponding to incipient fluidisation and that velocity corresponding to maximum expansion and the lower edge of the hot glass sheet is uniformly chilled as it enters the quiescent surface of the expanded bed.

In a method of thermally toughening a glass sheet wherein the glass sheet is heated to a temperature above its strain point and is lowered into a gas-fluidised bed of particulate material, the improvement wherein said gas-fluidised bed is placed, prior to immersion of the hot glass in the bed, in a quiescent uniformly expanded state of particulate fluidisation by control of gas fed to the bed such that the gas velocity in the bed is at least that velocity at which the expanded bed has a horizontal quiescent surface which chills the lower edge of the hot glass sheet uniformly as the lower edge enters the horizontal quiescent surface.