Precision glass roll forming process and apparatus

A glass or glass-ceramic roll forming apparatus comprising:

• a glass feed device for supplying a supplied stream of molten glass;
• a pair of forming rolls maintained at a surface temperature of about 500° C. or higher, the forming rolls being spaced closely adjacent each other defining a glass forming gap between the forming rolls with the glass forming gap located vertically below the glass feed device for receiving the supplied stream of molten glass and thinning the supplied stream of molten glass between the forming rolls to form a formed glass ribbon having a formed thickness;
• a pair of sizing rolls maintained at a surface temperature of about 400° C. or lower, the sizing rolls being spaced closely adjacent each other defining a glass sizing gap between the sizing rolls with the glass sizing gap located vertically below the forming rolls for receiving the formed glass ribbon and thinning the formed glass ribbon to produce a sized glass ribbon having a desired thickness and a desired thickness uniformity;
• the sizing rolls comprising;
• an insulating cylinder having an outer glass sizing surface,
• a first pair of spacer rings mounted adjacent each end of the insulating cylinder of the first of the sizing rolls, and a second pair of spacer rings mounted adjacent each end of the insulating cylinder of the second of the sizing rolls, the first and second sizing rings comprising outer cylindrical bearing surfaces extending radially beyond the outer glass sizing surface of the respective insulating cylinder;
• and
• a translational drive device for pressing the outer cylindrical bearing surfaces of the first and second sizing rolls together with the first pair of spacer rings engaging the second pair of spacer rings and thereby defining the glass sizing gap between the pair of sizing rolls.