MXPA96002134A - Method for heating and forming glass sheet - Google Patents

Abstract

A method for heating and forming a glass sheet includes the steps of heating a glass sheet to at least a first predetermined temperature, applying microwave energy to the glass sheet to heat the glass sheet to at least a second predetermined temperature cooling an outer surface of the glass sheet to at least a third predetermined temperature and forming the glass sheet using forming rollers to a predetermined configuration.

Description

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"METHOD TO HEAT AND FORM A GLASS SHEET" BACKGROUND OF THE INVENTION 1. FIELD OF THE INVENTION The present is generally related to glass sheets and, more specifically, to a method for heating and forming a sheet of glass. 2. DESCRIPTION OF THE RELATED TECHNIQUE It is known how to heat glass sheets using a "crucible" or "annealing tunnel". In general, the annealing tunnel is an oven and may be of the continuous roller type, the fixed roller type or the gas type. For example, a roller-type annealing tunnel has a plurality of rollers placed beneath a plurality of radiant heaters. Typically, a glass sheet is placed inside the annealing tunnel where it is heated by conventional radiation, convection and conduction heat. The glass sheet is moved along the rollers at a predetermined rate which depends on the thermal conductivity of the glass sheet to reach a temperature within its formation scale. When the glass sheet is at a temperature within its formation scale, the heated glass sheet is formed to a predetermined configuration using a plurality of forming rollers to bend the glass sheet to a desired curvature. Once it has formed, the glass sheet cools quickly, recoils or warms. Even though the aforementioned annealing tunnel and the forming rollers have worked well to heat and form a glass sheet, they suffer from the disadvantage that the annealing tunnel must be of long length to allow the glass sheet to be heated to the regime predetermined. They also suffer from the disadvantage that the process capacity is limited due to the heating of the glass sheet with only radiant heat. They also suffer from the disadvantage that the forming rollers are limited to a single radio capacity at a time. As a result, there is a need in the art to heat a glass sheet rapidly in a controlled manner and to form the glass to a predetermined configuration using the forming rolls.

SUMMARY OF THE INVENTION Accordingly, the present invention is a method for heating and forming a glass sheet. The method includes the steps of heating a glass sheet to at least a first predetermined temperature and applying microwave energy to the glass sheet to heat the glass sheet to at least a second predetermined temperature. The method also includes the steps of cooling an outer surface of the glass sheet to at least a third predetermined temperature and forming the glass sheet using the forming rolls to a predetermined configuration. An advantage of the present invention is that an improved method for heating and forming a glass sheet is provided. Another advantage of the present invention is that the method uses microwave energy to heat the glass sheet rapidly at or above its softening temperature. Yet another advantage of the present invention is that the method uses pressure rollers to form the glass sheet to a desired curvature. Yet another advantage of the present invention is that the method utilizes a series of pressure rollers with handle of different radii to form the glass sheet towards a desired curvature. A further advantage of the present invention is that the method allows heating and cooling of the glass sheet at the same time. Yet a further advantage of the present invention is that the method reduces the length of the annealing tunnel resulting in less floor space and increased performance (speed and yield) of the formed glass sheets. Other features and advantages of the present invention will be readily appreciated as it is better understood after reading the subsequent description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a fragmentary perspective view of an annealing tunnel used in conjunction with a method for heating and forming a glass sheet, in accordance with the present invention. FIGURE 2 is a sectional view taken along line 2-2 of FIGURE 1. FIGURE 3 is a sectional view taken along line 3-3 of FIGURE 1. FIGURE 4 is a view in section taken on line 4--4 of FIGURE 1. FIGURE 5 is a graph of the temperature versus the rate of a sheet of glass heated by a method for heating and forming a glass sheet, in accordance with the present invention.

DESCRIPTION OF THE PREFERRED MODALITY (S) Referring to the drawings and in particular to FIGURE 1, an embodiment of an annealing tunnel 10 to be used in conjunction with a method for heating and forming a glass template or sheet 11, in accordance with the present invention, has been shown. As illustrated, the annealing tunnel 10 is of a roller type continuous furnace. The annealing tunnel 10 includes a longitudinally extending upper housing 12 and having a plurality of heaters 14 spaced longitudinally therealong. The heaters 14 are of the radiant type as is known in the art. The annealing tunnel 10 also includes a longitudinally extending lower housing 16 and having a plurality of the rollers 18 positioned longitudinally therealong. It should be noted that the glass sheet 11 is moved by the rollers 18 as is known in the art. It should also be appreciated that, up to this point in the description, the annealing tunnel 10 is conventional and known in the art.

Referring to FIGURE 1, the annealing tunnel 10 includes a microwave energy apparatus, generally indicated at 20, positioned at a position along the length of the annealing tunnel 10. The microwave energy apparatus 20, which is partially shown, includes a longitudinally extending conduit 22 and having a reflector 24 at the corner thereof, for directing the microwave energy through a downward portion of the conduit 22. Microwave energy apparatus 20 includes a shield 26 at one end of the conduit 22 to column the microwave energy and form a transverse microwave energy curtain (e.g., 15.24 centimeters) toward the rollers 18. The energy apparatus 20 Microwave is an integral unit that has a microwave energy frequency of two (2) to forty (40) gigahertz. Preferably, the frequency of the microwave energy is less than thirty-six (36) gigahertz. The annealing tunnel 10 includes lifting doors 28 and 30 at each longitudinal end of the shield 26 to allow entry and exit of the glass sheet 11 to an area contained for microwave energy. The annealing tunnel 10 also includes air blowers 32 and 34 above and below the rollers 18 and placed in the area between the lift doors 28 and 30. The air blowers 32 and 34 are placed in two rows to direct the cooling air towards the glass sheet 11. It should be appreciated that the microwave energy apparatus 20 is a Gyrotron type commercially available from Continental Electronics of Dallas, Texas. It should also be appreciated that a temperature measuring device is used to measure the temperature of the glass sheet 11, which is conventional and known in the art. The annealing tunnel 10 further includes a plurality of forming rolls 36 for forming the glass sheet 11 heated to a predetermined configuration. The forming rollers 36 are sleeve pressure rollers as is known in the art. As illustrated in Figures 2 to 4, the forming rollers 36 include a plurality of first radius rollers 36a, second radius rollers 36b and third radius rollers 36c having a curvature of varying degrees to form the glass sheet 11 toward a predetermined curvature as is known in the art. For example, the first radio rollers 36a have a radius of two hundred sixty-four point sixty centimeters (264.60), the second radio rollers 36b have a radius of two hundred twenty point fifty centimeters (220.50) and the third radio rollers 36c have a radius one hundred twenty-two point fifty centimeters (122.50). It should be noted that on one pair of rollers 36, one roller is fixed and the other roller is adjusted relative thereto. It should also be appreciated that the forming roll 36 of the smaller radius is further downstream. During operation, the annealing tunnel 10 can be used to form the glass sheet 11 as a glass door or glass cleaner for a motor vehicle (not illustrated) by a method, in accordance with the present invention. The method includes placing a flat or flattened glass sheet 11 on the rollers 18 at one end of the annealing tunnel 10. The method includes moving the glass sheet 11 along the rollers 18, at a predetermined rate, and heating the glass sheet 11 to a predetermined temperature with the heaters 14. For example, the glass sheet 11 is heated by the heaters 14, using an ambient heat of more than 760 ° C as the glass sheet 11 travels a certain distance through time to heat the glass sheet 11 to a predetermined temperature. In one embodiment, the predetermined temperature is the softening temperature of the glass sheet 11 which is from about 482 ° C to 509 ° C. As illustrated in FIGURE 5, a curve 38 represents the temperature of the glass sheet 11 as it moves above the distance / time through the annealed tunnel 10, as is well known in the art. When the glass sheet 11 is at its softening point, the glass sheet 11 is placed between the lifting doors 28 and 30. The method includes applying microwave energy to the glass sheet 11, when the glass sheet 11 is at a temperature or above its softening temperature, as represented by the curve 40 and as illustrated in FIG. 5. method includes moving the glass sheet 11 at a predetermined rate below the curtain of the columned microwave energy by the shield 26 and rapidly heating the glass sheet 11 with the microwave energy to a predetermined temperature. In one embodiment, the predetermined temperature of the glass sheet 11 is in its forming scale from about 621 ° C to 676 ° C. For example, the temperature of the glass sheet 11 may rise from 482 ° C to more than 649 ° C in less than ten (10) seconds, as illustrated in FIGURE 5. The microwave energy heats the glass sheet 11 directly, generating heat at the molecular level creating a polar orientation movement very rapidly, resulting in instantaneous and uniform heating through the thickness of the glass sheet 11. The method also includes cooling an external surface of the glass sheet 11 to at least a third predetermined temperature of approximately 482 ° C simultaneously while applying the microwave energy. For example, air is blown into the glass sheet 11 by the air blowers 32 and 34 to provide the glass sheet 11 with a cold hard coating such that the outer surfaces of the glass sheet 11 will not be marked by the forming rollers 36, while the interior of the glass sheet 11 is within its forming scale. It should be appreciated that if the glass sheet 11 is less than its softening temperature, the microwave energy can break the glass sheet 11. It should also be appreciated that microwave frequencies as low as two gigahertz can be used when the glass sheet 11 is at a temperature of 482 ° C. It should be appreciated that the predetermined rate is based on the intensity of the microwave energy and the engagement rate of the glass sheet 11. It should further be appreciated that the ambient temperature of the annealing tunnel 10 before the lifting door 28 is approximately 649 ° C and the ambient temperature of the annealing tunnel 10 after the lifting door 30 is approximately 676 ° C in order to keep the glass sheet 11 at its formation temperature. - li ¬ When the glass sheet 11 passes beyond the lifting door 30, the method includes forming the glass sheet 11 to a predetermined configuration or curvature. The glass sheet 11 passes through the forming rollers 36a which begin to bend the glass sheet 11 to a curvature of large radius and passes through the forming rollers 36b and 36c to fold the glass sheet 11 in order to achieve a curvature of smaller radius until reaching the predetermined curvature. The method includes cooling the glass sheet 11 with cold air once the glass sheet 11 leaves the annealing tunnel 10 at less than its softening temperature as represented by the curve 42 illustrated in FIG. 5. Accordingly, the The method of the present invention provides a very rapid way to heat the movable glass sheet 11 by providing a curtain of microwave energy through which the glass sheet 11 is passed within the annealing tunnel 10. The microwave energy is applied based on the size and thickness of the glass sheet 11 to bring the temperature of the glass sheet 11 up to its formation scale for the forming process. In addition, the method allows the glass sheet 11 to achieve a smaller radius by changing from one radius to another simply by using the appropriate set of forming rollers 36. The method of the present invention uses a microwave energy curtain to heat the glass sheet 11 and at the same time to cool the outer surface thereof which allows the folding of the glass sheet 11 using a succession of rollers 36 of pressure with cuff. As illustrated in FIGURE 5, the method of the present invention heats the glass sheet 11 to the forming scale at a shorter distance / time of conventional radiant heating in an annealing tunnel. The present invention has been described in an illustrative manner. It must be understood that the terminology that has been used is intended to be within the nature of description words rather than limitation. Many modifications and variations of the present invention are possible in view of the teachings mentioned above. Therefore, within the scope of the appended claims, the present invention may be practiced in a manner other than that specifically described.

Claims (20)

CLAIMS:

1. A method for heating and forming a glass sheet, the method comprises the steps of: heating a glass sheet to at least a first predetermined temperature; applying microwave energy to the glass sheet to heat the glass sheet to at least a second predetermined temperature; cooling an outer surface of the glass sheet to at least a third predetermined temperature; and forming the glass sheet using forming rollers to a predetermined configuration.

A method according to claim 1, wherein the heating step comprises heating a glass sheet to at least a first predetermined temperature, using radiant energy.

A method according to claim 1, wherein the heating step comprises heating a glass sheet to at least a first predetermined temperature of about 482 ° C to 509 ° C.

4. A method according to claim 1, wherein the heating step comprises heating a glass sheet to at least a first predetermined temperature at a first predetermined rate.

5. A method according to claim 1, wherein the application step comprises applying microwave energy to the glass sheet when the glass sheet has reached at least the first predetermined temperature.

6. A method according to claim 1, wherein the application step comprises applying microwave energy to the glass sheet at a second predetermined rate.

A method according to claim 1, wherein the application step comprises applying the microwave energy to the glass sheet, and heating the glass sheet to at least a second predetermined temperature of about 621 ° C to 676 ° C.

8. A method according to claim 1, wherein the cooling step comprises cooling the outer surface of the glass sheet simultaneously with the application step.

9. A method according to claim 1, wherein the cooling step comprises cooling an outer surface of the glass sheet to at least a third predetermined temperature of about 482 ° C.

A method according to claim 1, wherein the forming step comprises moving the glass sheet through a plurality of forming rollers, to bend the glass sheet to a desired curvature.

A method according to claim 1, wherein the forming step comprises moving the glass sheet through a plurality of forming rollers having different areas to bend the glass sheet towards a desired curvature.

12. A method for heating and forming a glass sheet, the method comprising the steps of: heating a glass sheet to at least a first predetermined temperature at a first predetermined rate; applying microwave energy to the glass sheet to heat the glass sheet to at least a second predetermined temperature; cooling an outer surface of the glass sheet to at least a third predetermined temperature during the application step; and forming the glass sheet using forming rollers towards a predetermined configuration.

13. A method according to claim 12, wherein the application step comprises applying the microwave energy to the glass sheet when the glass sheet has reached at least the first predetermined temperature.

14. A method according to claim 12, wherein the application step comprises applying microwave energy to the glass sheet at a second predetermined rate.

15. A method according to claim 12, wherein the application step comprises applying microwave energy to the glass sheet and heating the glass sheet to at least a second predetermined temperature of about 621 ° C to 676 ° C. .

16. A method according to claim 12, wherein the cooling step comprises cooling an outer surface of the glass sheet to at least a third predetermined temperature of about 482 ° C.

17. A method according to claim 12, wherein the forming step comprises moving the glass sheet through a plurality of forming rollers to bend the glass sheet to a desired curvature.

18. A method according to claim 12, wherein the forming step comprises moving the glass sheet through the plurality of forming rollers having different radii to bend the glass sheet towards a desired curvature.

19. A method according to claim 12, wherein the heating step comprises heating a glass sheet to at least a first predetermined temperature using radiant energy.

20. A method for heating and forming a glass sheet, the method comprising the steps of: heating a glass sheet to at least a first predetermined temperature with radiant energy, at a first predetermined rate, applying microwave energy to the sheet of glass at a second predetermined rate for heating the glass sheet to at least a second predetermined temperature; cooling an outer surface of the glass sheet to at least a third predetermined temperature, during the application step; and moving the glass sheet through a plurality of forming rollers having different radii to bend the glass sheet to a desired curvature.