The device and method of manufacturing

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Provided are apparatus and a method for producing plate glass, wherein a sulfate protective layer for preventing defects can be formed efficiently on the glass ribbon. The protective layer forming part of the plate glass production apparatus is upstream of the slow-cooling furnace and the temperature of the glass ribbon is set in the 500°C to 750°C zone which is favorable for the reaction between sulfurous acid gas and alkaline earth metals.  The protective layer forming part is maintained in an essentially sealed state, being separated off by an upstream barrier member which makes contact with the lower surface of the glass ribbon on the upstream side in the direction of travel of the glass ribbon and a downstream barrier member which may or may not be in contact with the lower surface of the glass ribbon on the downstream side in the direction of travel of the glass ribbon.  The upstream barrier member is in contact with the glass ribbon and so there is no leakage of the oxidizing atmosphere in the protective layer forming part into the non-oxidizing atmosphere in the float bath and dross box located upstream of the protective layer forming part.  Furthermore, disturbance of the protective layer forming part due to the intrusion of the atmosphere on the upstream side into the protective layer forming part (20) can be prevented and so the sulfurous acid gas and alkaline earth metals react effectively.