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1. (WO2019046676) IMPROVED CERAMIC ROLLER BED AND MEASUREMENT METHOD
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IMPROVED CERAMIC ROLLER BED AND MEASUREMENT METHOD

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority under 35 U.S.C. § 1 19 of U.S. Provisional Application No. 62/552,825, filed August 31, 2017, the content of which is incorporated herein by reference in its entirety.

FIELD

[0002] The present disclosure relates to apparatuses for producing thermally strengthened glass and particularly to ceramic roller beds having improved flatness for used in heating glass for thermally strengthening and to apparatuses and methods for measuring roller trueness and roller bed flatness and/or alignment.

BACKGROUND

[0003] It is also known to thermally strengthen a glass sheet by quenching (cooling quickly) a glass sheet from an initial elevated temperature To above a glass transition temperature of a glass of the sheet, to a temperature below the glass transition temperature. To maintain sheet flatness, sheet smoothness (i.e., low nano- or micro-scale roughness) and optical and other desired sheet properties during thermal strengthening, both the temperature To and the amount of time which the sheet spends at or above To are generally minimized as much as possible. If thermal strengthening effects are go be maximized, however, To must be sufficiently high, especially for glass sheets below 2 or 3 mm thickness, that the sheet can begin to deform to conform somewhat to the shape and/or period of the rollers when heated on a ceramic roller bed. This "roller wave" deformation can be exacerbated by ceramic roller beds that are not very flat, i.e., having rollers that are not well aligned to each other or having rollers that exhibit excessive runout.

SUMMARY

[0004] The following presents a simplified summary of the disclosure in order to provide a basic understanding of some exemplary embodiments described in the detailed description.

[0005] In embodiments, a roller hearth furnace in an apparatus for the thermal strengthening of glass sheets comprises a ceramic roller bed having a deviation from a plane of not more than 500, 400, 300, 200, 100, or even 75 or 50 or 30 micrometers over an area of

not less than 1, 1.2, 1.3, 1.5, 2, 3, 5 or 10 square meters. Desirably, roller diameters is not more than 75, 50, or even not more than 25 mm. Roller length is desirably not less than 1, 1.2, 1, 1.2, 1.3, 1.5, 2, or even 2.5 meters.

[0006] In embodiments, an adapter is disclosed for measuring and aligning a roller bed, along with methods of constructing and methods of using said adapter. Use of the disclosed adapter enables the excellent alignment and/or flatness of the roller bed of the present disclosure.

[0007] The above embodiments are exemplary and can be provided alone or in any combination with any one or more embodiments provided herein without departing from the scope of the disclosure. Moreover, it is to be understood that both the foregoing general description and the following detailed description present embodiments of the present disclosure, and are intended to provide an overview or framework for understanding the nature and character of the embodiments as they are described and claimed. The accompanying drawings are included to provide a further understanding of the embodiments, and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments of the disclosure, and together with the description, serve to explain the principles and operations thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] These and other features, embodiments, and advantages of the present disclosure can be further understood when read with reference to the accompanying drawings:

[0009] Figure 1 shows cross-sectional diagram of a roller hearth furnace for heating a glass sheet according to an embodiment of the present disclosure comprising an improved ceramic roller bed;

[0010] Figure 2 is a cross-sectional diagram of a glass sheet tempering apparatus comprising a roller hearth furnace comprising an improved ceramic roller bed for heating a glass sheet and a thin-gap gas-bearing quench;

[0011] Figure 3 is a cross-sectional schematic view of an embodiment of measurement adapter according to the present disclosure useful in measuring and adjusting flatness or alignment of a roller bed and/or measuring run-out of rollers in the roller bed;

[0012] Figure 4 is a plan view schematic of an embodiment of the adapter of Figure 3, as viewed from below in Figure 3;

[0013] Figure 5 is perspective view of a ceramic roller and three alternative embodiments of shaft ends for use with any embodiments of the adapter present disclosure; and

[0014] Figure 6 is a cross-sectional schematic view of an embodiment of a process of adjusting the adapter of Figures 3 and 4.

DETAILED DESCRIPTION

[0015] Methods and apparatus will now be described more fully hereinafter with reference to the accompanying drawings in which exemplary embodiments of the disclosure are shown. Whenever possible, the same reference numerals are used throughout the drawings to refer to the same or like parts. However, this disclosure can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

[0016] Figure 1 shows cross-sectional diagram of a roller hearth furnace for heating a glass sheet according to an embodiment of the present disclosure comprising an improved ceramic roller bed. With reference to Figure 1, a roller hearth furnace 30 typically includes upper and lower insulated barriers 32, 34 to help contain heat from a heating means such as resistive electric heating elements (not shown). Insulated gates 40a, 40b are individually raised and lowered to let a glass sheet 14 in and out as needed.

[0017] The glass sheet 14 is transported on a bed 10 of ceramic rollers 12. When the rollers 12 rotate in the direction of the arrow R, the sheet 14 moves in the direction of arrow O, such as to go out of the furnace, to the right in the figure as shown. According to embodiments of the present disclosure, a ceramic roller bed 10 flatter and/or better aligned than previously known is provided. Apparatuses and techniques to measure (and thereby adjust and/or maintain) the improved flatness and/or alignment are also disclosed.

[0018] According to embodiments, the ceramic roller bed 10 can have deviation from a plane of not more than 500, 400, 300, 200, 100, or even 75 or 50 or 30 micrometers. This low deviation can be achieved over a ceramic roller bed area (which may be less than a total ceramic roller bed area of the furnace) of no less than 1, 1.2, 1.3, 1.5, 2, 3, 5 or even 10 or more square meters. This low deviation can also be achieved even with rollers of diameter not more than 75, 50, or even not more than 25 mm, and length not less than 1, 1.2, 1, 1.2, 1.3, 1.5, 2, or even 2.5 meters.

[0019] Figure 2 is a cross-sectional diagram of a glass sheet tempering apparatus comprising a roller hearth furnace 30 comprising an improved ceramic roller bed 10 for heating a glass sheet, similar to that of Figure 1 but without the insulating structures shown, and a thin-gap gas-bearing quench 60 comprising opposing gas bearings 50a, 50b which face each other across a gap G. A ceramic roller bed according to embodiments herein enables a glass sheet 14 to be fed into a thin gap in a thin-gap gas-bearing quench as shown in the figure, for thin gaps as small as not more than 400, 350, 320, 300, 280, 260, 240, 220, 200, 180, 160, 140, 120, 100, or even 80 or 60 micrometers larger than a thickness T of the glass sheet 14.

[0020] To achieve the improved ceramic roller bed 10 of the present disclosure, it is necessary to measure the rollers 12 and the roller bed 10 in situ in the roller hearth 30, without causing measureable deflection of the rollers 12 and while ensuring the measurement sensor is properly positioned with respect both to a reference plane and to the feature and/or roller under test.

[0021] This may be achieved by use of the measurement adapter 100 shown in Figure 3. Figure 3 is a cross-sectional schematic view of an embodiment of measurement adapter 100 according to the present disclosure useful in measuring and adjusting flatness or alignment of a roller bed and/or measuring run-out of rollers in the roller bed. Figure 4 is a plan view schematic of an embodiment of the adapter 100 of Figure 3, as viewed from below in Figure 3.

[0022] With reference to Figures 3 and 4, the adapter 100 which is used to adapt between the rollers 12 of the roller bed 10 and a measurement reference system MR. Although the reference system MR is represented in Figure 3 by a schematic representation of a runout gauge, any suitable reference system MR may be used, such as a laser reference plane system. The L-733 Triple Scan® or L-743 Ultra Triple Scan® measurement system from Hamar Laser of Danbury, Connecticut, USA can be used, for example. What is then required to provide a method to mechanically connect a laser reference target with the rollers to measure any deflection of the measured roller, without causing the very deflection which is to be measured. For example, when aligning and adjusting a roller hearth from EFCO (Electric Furnace COmpany) Furnaces Ltd., multiple ceramic rollers (in excess of 50), on the order of 1 meter in length, need to be aligned and checked for sag. This requires a minimum measurements at three locations of the vertical position (height) of each roller, resulting in more than 150 total measurements.

[0023] Using a laser reference system (such as the The L-733 Triple Scan® or the L-743 Ultra Triple Scan® measurement system) avoids the requirement of a mechanical reference

to the furnace. Use of the measurement adapter 100 provides a reliable, repeatable contact with the points to be measured without causing such deflections as would be caused by typical laser reference targets, which can easily be larger than the variation to be measured. The adapter 100 can fixture a Hamar sensor head onto the a roller with minimal deflection of the roller under test, while ensuring the angle of the sensor head with respect to the reference plane is consistent to within acceptable limits (which can be determined using an error budget). This enables a user to quickly place the measurement sensor on the rollers 12 at each of the 150+ measurement locations and record the value.

[0024] With reference again to Figures 3 and 4, ceramic rollers 12 are to be measured. A shaft, S, is the measurement post attached to the bottom of the measurement sensor (laser target) (not shown). In this case, for generality, the reference system MR, desirably in the form of a measurement sensor (laser target) and laser plane have been represented as an indicator measuring the height of the top of the shaft (post) with respect to some external reference ground. The shaft slides up and down in a bearing, B. Bearing B has very low stiction to ensure good contact to the roller with minimal deflection. In embodiments, bearing B is an air bushing with essentially zero friction, to eliminate essentially all stiction. The bearing B is attached to a base plate, BP, having pads P on the bottom thereof. Steps are taken (discussed below) to ensure that the shaft is perpendicular to the pads, P, on the bottom of the base plate BP.

[0025] The bearing B and the pads P are both attached to the base plate in the same step and are fixed in place with a low shrinkage adhesive such as a low shrinkage epoxy.

[0026] There are 3 pads P on the bottom of the base plate BP. (The third pad P is not seen in the view of Figure 3). The pads P and the bearing B should be bonded to the base plate at the same time, in the process described below. Four (4) Dowel pins DP are also affixed to the base plate BP. These dowel pins DP are intended for rough alignment and to keep the pads on adj acent rollers and the shaft on the roller under test. The location of these pins is not critical and only need to be as good as the shaft tip tolerance, which is discussed below in relation to Figure 5.

[0027] The arrangement of the pads and the dowels can be noted in Figure 4. The adapter 100 also comprises a counter balance system to ensure little force is exerted on the roller under test during a measurement. There are many ways the counterbalance can be achieved. In the embodiment shown in Figure 3, a spring SP is used along with a nut N. In its

simplest form the shaft S is threaded at the top and the nut N is used to control the distance from the bottom of the nut N to the bottom end of the shaft S. This enables the amount of interference between the shaft S and the roller under test to be controlled and thus also the probing force. If needed a load cell can be inserted between the shaft S and a contact point with the roller to quantify the measurement force. Note that it is also very important to minimize the height from the roller under test to measurement sensor, H, to ensure that Abbe errors are minimized.

[0028] Figure 5, shows 3 embodiments of shaft tips in contact with a roller 12 under test.

[0029] Shaft tip A is flat tip which is perpendicular to the axis of the shaft S. This tip needs to be placed within one radius of the shaft S diameter with respect to top dead center (TDC) of the roller 12. A flat in contact with a cylinder will exhibit a line contact area which is over constrained and can thus result in measurement error, and so tip A requires high certainty in angular alignment of the shaft S to the roller 12.

[0030] Shaft tip B is a bullnose radius tip with a single point contact between the shaft S and the roller 12. This tip must me precisely aligned to TDC of the roller 12, but is not over constrained and has relatively loose tolerance on angular alignment.

[0031] Shaft tip C produces a perpendicular pin on pin contact with the roller 12, which results in a single point contact between the shaft S and the roller 12. This arrangement is not over constrained and does not require high precision alignment to TDC (must be aligned to a tolerance equal to half the length of the cross shaft) or angularly. However, the cross shaft must be perpendicular the main shaft and must be keyed to prevent large rotations about the main shaft. Keying the shaft will increase the chance of stiction which complicates adapter and the assembly of the adapter. A configuration like shaft tip C is presently preferred for the shaft tip.

[0032] To bond the measurement adapter together, two precision squares are used to ensure that the shaft and pads are perpendicular. Two approaches can be used in this process. The first approach is to attach all three pads P with adhesive AH simultaneously using a flat surface plate to ensure they are all planar. Once the adhesive AH is dry, then the pads P can be hand lapped to ensure that any non-planarity is addressed. The adapter can then be used with the two squares to ensure the shaft is perpendicular to the pads and the bearing then bonded into place. The second approach uses a non-permanent adhesive to temporally attach the pads P and the shaft S to the squares, and then both the pads P and the bearing B are affixed in place with the permanent adhesive. The first approach is more time consuming but eases assembly and enables the "correction" of any out-of-flatness of the pads P.

[0033] The present disclosure provides an adapter that allows measurement of a roller, in situ in a ceramic roller bed of a roller hearth furnace, which adapter and the use thereof require little training for an operator, and which adaptor can be cheaply built with off the shelf components using the replication/assembly described herein.

[0034] It will be appreciated that the various disclosed embodiments can involve particular features, elements or steps that are described in connection with that particular embodiment. It will also be appreciated that a particular feature, element or step, although described in relation to one particular embodiment, can be interchanged or combined with alternate embodiments in various non-illustrated combinations or permutations.

[0035] It is to be understood that, as used herein the terms "the," "a," or "an," mean "at least one," and should not be limited to "only one" unless explicitly indicated to the contrary. Thus, for example, reference to "a component" includes embodiments having two or more such components unless the context clearly indicates otherwise.

[0036] Ranges can be expressed herein as from "about" one particular value, and/or to "about" another particular value. When such a range is expressed, embodiments include from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent "about," it will be understood that the particular value forms another aspect. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint.

[0037] Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not actually recite an order to be followed by its steps or it is not otherwise specifically stated in the claims or descriptions that the steps are to be limited to a specific order, it is no way intended that any particular order be inferred.

[0038] While various features, elements or steps of particular embodiments can be disclosed using the transitional phrase "comprising," it is to be understood that alternative embodiments, including those that can be described using the transitional phrases "consisting" or "consisting essentially of," are implied. Thus, for example, implied alternative embodiments to an apparatus that comprises A+B+C include embodiments where an apparatus consists of A+B+C and embodiments where an apparatus consists essentially of A+B+C.

[0039] It will be apparent to those skilled in the art that various modifications and variations can be made to the present disclosure without departing from the spirit and scope of the disclosure. Thus, it is intended that the present disclosure cover the modifications and variations of this disclosure provided they come within the scope of the appended claims and their equivalents.