Transparent infrared absorbing glass and method of making

Claim 1

A method of manufacturing soda-lime-silica flat glass having a luminous transmittance of at least 65 percent and an infrared transmittance of no more than 15 percent in a continuous process including feeding raw materials to a melting operation, passing from the melting opera­tion to a flat glass forming operation a continuous stream of molten glass and forming the glass into a flat glass product wherein the glass has 0.45 to 0.65 percent by weight iron expressed as Fe₂O₃ and the oxidation-re­duction conditions in the melting and refining operation are controlled so as that at least 35 percent of the iron is in the ferrous state expressed as FeO characterized by the absence of remarkable amounts of tin in the composi­tion and a sequence of discrete liquefying and refining stages, wherein the raw materials being fed to the mel­ting operation include an iron source in an amount suffi­cient to yield the desired iron content of the glass pro­duct or a source of iron is added to molten glass down­stream from the melting operation and reducing conditions are pro­vided in the melting operation by operating the burners with an excess amount of fuel relative to the amount of oxygen being supplied or by including reducing agent in the batch mixture being fed to the melting operation.

Claim 2

A method of manufacturing soda-lime-silica flat glass having a luminous transmittance of at least 65 percent and an infrared transmittance of no more than 15 percent in a continuous process including feeding raw materials to a melting operation, passing from the melting opera­tion to a flat glass forming operation a continuous stream of molten glass and forming the glass into a flat glass product wherein the glass has 0.45 to 0.65 percent by weight iron expressed as Fe₂O₃ and the oxidation-re­duction conditions in the melting and refining operation are controlled so as that at least 35 percent of the iron is in the ferrous state expressed as FeO characterized by the absence of remarkable amounts of tin in the composi­tion and a sequence of discrete liquefying and refining stages, wherein the raw materials being fed to the mel­ting operation include an iron source in an amount suffi­cient to yield the desired iron content of the glass pro­duct or a source of iron is added to molten glass down­stream from the melting operation and reducing conditions are pro­vided in the melting operation by operating the burners with an excess amount of fuel relative to the amount of oxygen being supplied or by including reducing agent in the batch mixture being fed to the melting operation.

Claim 5

The method of claims 1 or 2, wherein a substantial portion of the iron added to the molten glass downstream from melting is in a reduced state relative to Fe₂O₃.

Claim 6

The method of any of claims 1 to 4, wherein the glass has 0.45 to less than 0.60 percent by weight iron expressed as Fe₂O₃.

Claim 7

The method of any of claims 1 to 5, wherein the oxida­tion-reduction conditions are controlled so as to provide at least 40 percent of the iron in the ferrous state.

Claim 8

The method of any of claims 1 to 5, wherein the oxida­tion-reduction conditions are controlled so as to provide at least 50 percent of the iron in the ferrous state.

Claim 9

The method of any of claims 1 to 5, wherein the oxida­tion-reduction conditions are controlled in the melting operation to yield a glass product having at least 0.22 percent by weight iron expressed as FeO.

Claim 10

The method of any of claims 1 to 8, wherein a sulfur content of the glass product less than 0.02 percent by weight expressed as SO₃ is provided by avoiding sulfur containing refining aids and deliberate inclusion of sulfur in the batch material or reducing the sulfur con­tent in the refining stage.