Overflow downdraw glass forming method and apparatus

A method for manufacturing glass sheets using an apparatus that includes a trough for receiving molten glass that has sides attached to a wedged shaped sheet forming structure that has downwardly sloping sides converging at the bottom of the wedge, at least one inlet end support block located at an inlet end of the trough, wherein the inlet end support block is positioned at a bottom end of the trough and supports the trough, at least one far end support block located at an opposite end of the trough as the inlet end support block, wherein the far end support block is positioned at the bottom end of the trough and supports the trough, such that a glass sheet is formed when molten glass flows over the sides of the trough, down the downwardly sloping sides of the wedged shaped sheet forming structure and meets at the bottom of wedge, wherein the method comprises the step of:

• a) applying a force to the far end support block to place a bottom of a far end of the trough in compression in a longitudinal direction;
• and
• b) maintaining an applied force to the inlet end support block by periodically adjusting an inlet end adjustment screw to maintain a bottom of the inlet end of the trough in compression in an opposite longitudinal direction to the compression at the far end;
• such that any deformation of the forming trough that results from thermal creep has a minimal effect on a thickness variation of the glass sheet.

An improved apparatus for forming sheet glass, wherein the apparatus includes a trough for receiving molten glass that has sides attached to a wedged shaped sheet forming structure that has downwardly sloping sides converging at the bottom of the wedge such that a glass sheet is formed when molten glass flows over the sides of the trough, down the downwardly sloping sides of the wedged shaped sheet forming structure and meets at the bottom of wedge, and wherein the improvement comprises:

• a) at least one inlet end structure located at an inlet end of the trough, comprising:
• i) at least one inlet support block which supports the weight of the trough, wherein an inlet end compression force is applied to a bottom of the trough by the inlet support block;
• and
• ii) at least one adjustable inlet end force motor, wherein the inlet end force motor generates the inlet end compression force;
• and
• b) at least one far end structure located at an opposite end of the trough as the inlet end structure, comprising:
• i) at least one far end support block which also supports the weight of the trough, wherein a far end compression force is applied to the bottom of the trough by the far end compression block;
• and
• ii) at least one adjustable far end force motor, wherein the far end force motor generates the far end compression force;
• wherein the inlet end support block and the far end support block each are shaped to distribute force into a bottom of the trough such that an applied force maintains the refractory that comprises the trough under substantially equal compression stress in a longitudinal direction throughout a life of a production campaign independent of thermal creep deformation of the trough at each end;
• and any deformation of the forming trough that results from thermal creep has a minimal effect on a thickness variation of the glass sheet.

A method for manufacturing glass sheets using an apparatus that includes a trough for receiving molten glass that has sides attached to a wedged shaped sheet forming structure that has downwardly sloping sides converging at the bottom of the wedge such that a glass sheet is formed when molten glass flows over the sides of the trough, down the downwardly sloping sides of the wedged shaped sheet forming structure and meets at the bottom of wedge, wherein the method comprises the step of:

• maintaining a substantially equal and opposite compression force to each end of a bottom of the trough, independent of thermal creep where the force is applied, such that any deformation of the forming trough that results from thermal creep has a minimal effect on a thickness variation of the glass sheet, wherein the substantially equal and opposite compression force is maintained using at least one inlet end structure located at an inlet end of the trough, comprising at least one inlet support block which supports the weight of the trough, wherein an inlet end compression force is applied to a bottom of the trough by the inlet support block, and at least one adjustable inlet end force motor, wherein the inlet end force motor generates the inlet end compression force, and at least one far end structure located at an opposite end of the trough as the inlet end structure, comprising at least one far end support block which also supports the weight of the trough, wherein a far end compression force is applied to the bottom of the trough by the far end support block, and at least one adjustable far end force motor, wherein the far end force motor generates the far end compression force.

A method for manufacturing glass sheets using an apparatus that includes a trough for receiving molten glass that has sides attached to a wedged shaped sheet forming structure that has downwardly sloping sides converging at the bottom of the wedge, at least one inlet end support structure located at an inlet end of the trough which supports the trough, wherein the inlet end support structure includes a support block which is positioned at a bottom end of the trough, at least one far end support structure located at an opposite end of the trough as the inlet end support structure which supports the trough, wherein the far end support structure includes a support block which is positioned at the bottom end of the trough, such that a glass sheet is formed when molten glass flows over the sides of the trough, down the downwardly sloping sides of the wedged shaped sheet forming structure and meets at the bottom of wedge, wherein the method comprises the step of

• a) applying a force to the far end support block to place a bottom of a far end of the trough in compression in a longitudinal direction;
• and
• b) maintaining an applied force to the inlet end support block by periodically adjusting an inlet end adjustment screw to maintain a bottom of the inlet end of the trough in compression in an opposite longitudinal direction to the compression at the far end;
• such that any deformation of the forming trough that results from thermal creep has a minimal effect on a thickness variation of the glass sheet.

An improved apparatus for forming sheet glass, wherein the apparatus includes a trough for receiving molten glass that has sides attached to a wedged shaped sheet forming structure that has downwardly sloping sides converging at the bottom of the wedge such that a glass sheet is formed when molten glass flows over the sides of the trough, down the downwardly sloping sides of the wedged shaped sheet forming structure and meets at the bottom of wedge, and wherein the improvement comprises:

• a) at least one inlet end structure located at an inlet end of the trough, wherein the inlet end structure supports a weight of the trough;
• b) at least one far end structure located at an opposite end of the trough as the inlet end structure, wherein the far end structure supports the weight of the trough;
• and
• c) a top end force motor, wherein the top end force motor is located at a top end of the far end of the trough;
• wherein the inlet end structure and the far end structure each include at least one compression block shaped to distribute force into a bottom of the trough, inducing a moment to counteract the effect of the weight of the trough such that an applied force maintains all of the refractory that comprises the trough under substantially equal compression stress in a longitudinal direction throughout a life of a production campaign independent of localized thermal creep deformation of the trough at each end;
• such that any deformation of the forming trough that results from thermal creep has a minimal effect on a thickness variation of the glass sheet.

An improved apparatus for forming sheet glass, wherein the apparatus includes a trough for receiving molten glass that has sides attached to a wedged shaped sheet forming structure that has downwardly sloping sides converging at the bottom of the wedge such that a glass sheet is formed when molten glass flows over the sides of the trough, down the downwardly sloping sides of the wedged shaped sheet forming structure and meets at the bottom of wedge, and wherein the improvement comprises:

• a) at least one inlet end structure located at an inlet end of the trough, comprising:
• i) at least one inlet support block which supports the weight of the trough, wherein an inlet end compression force is applied to a bottom of the trough by the inlet support block;
• and
• ii) at least one inlet end adjustment screw, wherein the inlet end adjustment screw fixes a horizontal location of a bottom of the inlet end of the trough;
• b) at least one far end structure located at an opposite end of the trough as the inlet end structure, comprising:
• i) at least one far end support block which also supports the weight of the trough, wherein a far end compression force is applied to the bottom of the trough by the far end support block;
• and
• ii) at least one adjustable far end force motor, wherein the far end force motor generates the far end compression force;
• and
• c) a support structure for an inflow pipe, wherein the support structure is stiff enough to maintain a glass seal, and also yields enough to allow horizontal movement of the seal with minimum change in a sealing force;
• wherein the inlet end structure and the far end structure each include at least one support block shaped to distribute force into a bottom of the trough, inducing a moment to counteract the effect of the weight of the trough such that an applied force maintains the refractory that comprises the trough under substantially equal compression stress in a longitudinal direction throughout a life of a production campaign independent of thermal creep deformation of the trough at each end;
• such that any deformation of the forming trough that results from thermal creep has a minimal effect on a thickness variation of the glass sheet.

An improved apparatus for forming sheet glass, wherein the apparatus includes a trough for receiving molten glass that has sides attached to a wedged shaped sheet forming structure that has downwardly sloping sides converging at the bottom of the wedge such that a glass sheet is formed when molten glass flows over the sides of the trough, down the downwardly sloping sides of the wedged shaped sheet forming structure and meets at the bottom of wedge, and wherein the improvement comprises:

• a) at least one inlet end structure located at an inlet end of the trough, comprising at least one inlet end compression block, wherein the inlet end structure supports a weight of the trough, wherein an inlet end compression force is applied to the bottom of the trough by the inlet end compression block;
• b) at least one far end structure located at an opposite end of the trough as the inlet end structure, comprising at least one far end compression block, wherein the far end structure supports the weight of the trough, wherein a far end compression force is applied to the bottom of the trough by the far end compression block;
• c) at least one adjustable far end force motor, wherein the far end force motor generates the far end compression force;
• and
• d) a cage connected to both the far end force motor and the inlet end compression block, wherein the cage applies a force to the inlet end structure and mounts to the far end force motor to apply an equal and opposite force to the far end structure;
• wherein the inlet end and far end compression blocks are shaped to distribute force into the bottom of the trough, such that an applied force maintains the refractory that comprises the trough under substantially equal compressive stress in a longitudinal direction throughout the life of a production campaign independent of thermal creep deformation of the trough at each end and any deformation of the forming trough the results from thermal creep has a minimal effect on a thickness variation of the glass sheet.

An improved apparatus for forming sheet glass, wherein the apparatus includes a trough for receiving molten glass that has sides attached to a wedged shaped sheet forming structure that has downwardly sloping sides converging at the bottom of the wedge such that a glass sheet is formed when molten glass flows over the sides of the trough, down the downwardly sloping sides of the wedged shaped sheet forming structure and meets at the bottom of wedge, and wherein the improvement comprises:

• a) at least one inlet end structure located at an inlet end of the trough, comprising at least one inlet end compression block which also supports the weight of the trough, wherein an inlet end compression force is applied to the bottom of the trough by the inlet end compression block, wherein the inlet end structure supports a weight of the trough;
• b) at least one far end structure located at an opposite end of the trough as the inlet end structure, wherein the far end structure supports the weight of the trough;
• c) at least one adjustable inlet end force motor, wherein the inlet end force motor generates the inlet end compression force;
• and
• d) a cage connected to both the inlet end force motor and the far end compression block, wherein the cage applies a force to the far end structure and mounts to the inlet end force motor to apply an equal and opposite force to the inlet end structure;
• wherein the inlet end and far end compression blocks are shaped to distribute force into the bottom of the trough, such that an applied force maintains the refractory that comprises the trough under substantially equal compressive stress in a longitudinal direction throughout the life of a production campaign independent of thermal creep deformation of the trough at each end and any deformation of the forming trough the results from thermal creep has a minimal effect on a thickness variation of the glass sheet.

An improved apparatus for forming sheet glass, wherein the apparatus includes a trough for receiving molten glass that has sides attached to a wedged shaped sheet forming structure that has downwardly sloping sides converging at the bottom of the wedge such that a glass sheet is formed when molten glass flows over the sides of the trough, down the downwardly sloping sides of the wedged shaped sheet forming structure and meets at the bottom of wedge, and wherein the improvement comprises:

• a) at least one inlet end structure located at a first end of the trough, wherein the inlet end structure supports a weight of the trough;
• b) at least one far end structure located at an opposite end of the trough as the inlet end structure which also supports the weight of the trough;
• c) at least one adjustable force motor attached to a first compression block at an end of the trough, wherein the force motor generates a compression force;
• and
• d) a cage connected to both the force motor and a second compression block at an opposite end of the trough as the force motor, wherein the cage applies an equal and opposite compression force to the inlet end structure and the far end structure;
• wherein the inlet end structure and the far end structure each include at least one compression block shaped to distribute force into a bottom of the trough, such that an applied force maintains the refractory that comprises the trough under substantially equal compression stress in a longitudinal direction throughout a life of a production campaign independent of thermal creep deformation of the trough at each end and any deformation of the forming trough the results from thermal creep has a minimal effect on a thickness variation of the glass sheet.