APPARATUS AND PROCESS FOR DETERMINING THE DISTANCE BETWEEN A GLASS SUBSTRATE AND A COATER

Abstract

A combination of a chemical vapour deposition (CVD) coater and at least one capacitive proximity sensor, comprising: a CVD coater, and at least one capacitive proximity sensor attached to the CVD coater, wherein the at least one capacitive proximity sensor is arranged to determine the distance between a glass substrate and the CVD coater.

Claims

1.-20. (canceled)

21. A combination of a chemical vapour deposition (CVD) coater and at least one capacitive proximity sensor, comprising: a CVD coater, and at least one capacitive proximity sensor attached to the CVD coater; wherein the at least one capacitive proximity sensor is arranged to determine the distance between a glass substrate and the CVD coater.

22. The combination according to claim 21, wherein the capacitive proximity sensor comprises a sensor unit, a control unit and a cable, wherein the sensor unit and the control unit are arranged to be electrically coupled to each other by the cable when in use.

23. The combination according to claim 22, wherein the sensor unit and the cable can operate at temperatures of at least 650° C., more preferably at least 700° C., even more preferably at least 750° C., most preferably at least 800° C.

24. The combination according to claim 21, wherein the CVD coater is arranged to move to change the distance between a surface of the glass substrate and a surface of the CVD coater.

25. The combination according to claim 21, wherein the combination comprises more than one capacitive proximity sensor attached to the CVD coater.

26. The combination according to claim 22, wherein the sensor unit is at least partially surrounded by a housing, wherein part of the CVD coater constitutes part of the housing, wherein the temperature of the part of the coater that constitutes part of the housing is regulated using a coolant means, and wherein the temperature of the sensor unit is regulated by the part of the coater that constitutes part of the housing.

27. The combination according to claim 22, wherein at least part of the sensor unit is protected from the surrounding atmosphere by an anti-fouling coating and/or an anti-fouling sheet.

28. The combination according to claim 27, wherein any part of the sensor unit that would otherwise be exposed to the surrounding atmosphere is protected from the surrounding atmosphere by an anti-fouling coating and/or an anti-fouling sheet.

29. The combination according to claim 27, wherein the anti-fouling coating comprises a non-conductive material, preferably one or more of bicarbonates such as sodium bicarbonate and calcium bicarbonate, sulphates such as sodium sulphate and calcium sulphate, nitrides such as boron nitride and aluminium nitride, low boiling point hydrogen treated naphtha, silazanes such as polysilazanes, alkali silicates, silicas and/or organo silicas.

30. The combination according to claim 27, wherein the anti-fouling coating and/or anti-fouling sheet is removable.

31. The combination according to claim 27, wherein the anti-fouling sheet comprises one or more of alumina, quartz, zirconia, and/or a non-conductive ceramic.

32. The combination according to claim 27, wherein the housing or the sensor unit comprises a holder suitable for holding the anti-fouling sheet, preferably wherein the holder comprises a slot arranged to accept the anti-fouling sheet.

33. The combination according to claim 22, wherein the control unit provides means for an operator to control the distance between the glass substrate and the CVD coater.

34. The combination according to claim 22, wherein the control unit is arranged to warn an operator if the CVD coater is closer to the glass substrate than a pre-determined minimum distance.

35. The combination according to claim 22, wherein the combination is suitable for use during the float glass manufacturing process.

36. A capacitive proximity sensor for attaching to a CVD coater, comprising: a sensor unit; and a control unit; wherein the capacitive proximity sensor is arranged to determine the distance between a glass substrate and the CVD coater, and wherein at least part of the sensor unit is protected from the surrounding atmosphere by an anti-fouling coating and/or an anti-fouling sheet.

37. A process for determining the distance between a glass substrate and a CVD coater, comprising the following steps: i) providing a glass substrate and a combination of a CVD coater and a capacitive proximity sensor in accordance with claim 21, and ii) utilizing the capacitive proximity sensor to determine the distance between the glass substrate and the CVD coater.

38. The process according to claim 37, wherein the process is carried out when the glass substrate is at a temperature in the range 450° C. to 800° C., preferably in the range 550° C. to 770° C.

39. A method of determining the distance between a glass substrate and a capacitive proximity sensor to determine the distance between a glass substrate and a CVD coater utilizing a capacitive proximity sensor.

Description

[0057] The invention will now be further described by way of the following specific embodiments, which are given by way of illustration and not of limitation, with reference to the accompanying drawings in which:

[0058] FIG. 1 is a schematic view, in vertical section, of an installation for practicing the float glass process which incorporates several CVD coaters to which capacitive proximity sensors are attached in accordance with the present invention;

[0059] FIG. 2 is a perspective view of the lower surface, the back surface and a lateral surface of a CVD coater to which capacitive proximity sensors are attached in accordance with the present invention;

[0060] FIG. 3 is a perspective view of a capacitive proximity sensor in accordance with the present invention;

[0061] FIG. 4 is a cut away perspective view of an end of a sensor unit of a capacitive proximity sensor in accordance with the present invention; and

[0062] FIG. 5 is a graph of distances determined with a micrometer versus distances recorded with capacitive proximity sensor in accordance with the present invention.

[0063] As discussed above, the present invention may be utilized in conjunction with the manufacture of the glass substrate in the float glass process. The float glass process is typically carried out utilizing a float glass installation such as the installation 10 depicted in FIG. 1. However, it should be understood that the float glass installation 10 described herein is only illustrative of such installations.

[0064] As illustrated in FIG. 1, the float glass installation 10 may comprise a canal section 20 along which molten glass 19 is delivered from a melting furnace, to a float bath section 11 wherein the glass substrate is formed. In this embodiment, the glass substrate will be referred to as a glass ribbon 8. However, it should be appreciated that the glass substrate is not limited to being a glass ribbon. The glass ribbon 8 advances from the bath section 11 through an adjacent annealing lehr 12 and a cooling section 13. The float bath section 11 includes: a bottom section 14 within which a bath of molten tin 15 is contained, a roof 16, opposite side walls (not depicted) and end walls 17. The roof 16, side walls and end walls 17 together define an enclosure 18 in which a non-oxidizing atmosphere is maintained to prevent oxidation of the molten tin 15.

[0065] In operation, the molten glass 19 flows along the canal 20 beneath a regulating tweel 21 and downwardly onto the surface of the tin bath 15 in controlled amounts. On the molten tin surface, the molten glass 19 spreads laterally under the influence of gravity and surface tension, as well as certain mechanical influences, and it is advanced across the tin bath 15 to form the glass ribbon 8. The glass ribbon 8 is removed from the bath section 11 over lift out rolls 22 and is thereafter conveyed through the annealing lehr 12 and the cooling section 13 on aligned rolls. The deposition of coatings preferably takes place in the float bath section 11, although it may be possible for deposition to take place further along the glass production line, for example, in the gap 28 between the float bath 11 and the annealing lehr 12, or in the annealing lehr 12.

[0066] As illustrated in FIG. 1, four CVD coaters 9, 9A, 9B, 9C are shown within the float bath section 11. One or more additional coaters may be provided. Also, a description of a CVD coater suitable for practicing the present invention can be found in U.S. patent application Ser. No. 61/466,501. Not depicted in FIG. 1 are sixteen capacitive proximity sensors, each located in a region of a corner of the lower surface of each CVD coater. One or more CVD coaters combined with capacitive proximity sensors may alternatively or additionally be located in the lehr gap 28. Any by-products are removed through coater extraction slots and then through a pollution control plant.

[0067] A suitable non-oxidizing atmosphere, generally nitrogen or a mixture of nitrogen and hydrogen in which nitrogen predominates, may be maintained in the float bath section 11 to prevent oxidation of the molten tin 15 comprising the float bath. The atmosphere gas is admitted through conduits 23 operably coupled to a distribution manifold 24. The non-oxidizing gas is introduced at a rate sufficient to compensate for normal losses and maintain a slight positive pressure, on the order of between about 0.001 and about 0.01 atmosphere above ambient atmospheric pressure, so as to prevent infiltration of outside atmosphere. For the purposes of describing the invention, the above-noted pressure range is considered to constitute normal atmospheric pressure.

[0068] CVD is generally performed at essentially atmospheric pressure. Thus, the pressure of the float bath section 11, annealing lehr 12, and/or in the gap 28 between the float bath 11 and the annealing lehr 12 may be essentially atmospheric pressure. Heat for maintaining the desired temperature regime in the float bath section 11 and the enclosure 18 is provided by radiant heaters 25 within the enclosure 18. The atmosphere within the lehr 12 is typically atmospheric air, as the cooling section 13 is not enclosed and the glass ribbon 8 is therefore open to the ambient atmosphere. The glass ribbon 8 is subsequently allowed to cool to ambient temperature. To cool the glass ribbon 8, ambient air may be directed against the glass ribbon 8 by fans 26 in the cooling section 13. Heaters (not shown) may also be provided within the annealing lehr 12 for causing the temperature of the glass ribbon 8 to be gradually reduced in accordance with a predetermined regime as it is conveyed therethrough.

[0069] FIG. 2 shows an underside perspective view of a CVD coater 9 to which four capacitive proximity sensors 29 are attached in accordance with the present invention. CVD coater 9 is generally cuboid-shaped with lateral surfaces 30 connected to front (not shown) and back surfaces 31. Lower surface 32 has a gas distributor passage 33 extending across the lower surface 32 between and perpendicular to the lateral surfaces 30. A glass substrate 34 is shown in outline below the CVD coater 9 adjacent the lower surface 32. In use, if the glass substrate 34 is moving (e.g. in a dynamic process like the float glass manufacturing process) the direction of travel is from the front surface to the back surface 31 of the CVD coater 9 i.e. parallel to the lateral surfaces 30. Two capacitive proximity sensors 29 are attached to each of the front surface and the back surface 31 of the CVD coater 9 such that an end of each sensor electrode 35 is level with the lower surface 32 of the CVD coater 9. The capacitive proximity sensors 29 are attached to the CVD coater 9 by means of sensor units 37 partially surrounded by housings (associated cable and control unit are not depicted). The capacitive proximity sensors 29 are attached to the front or back surface 31 of the CVD coater 9 adjacent to where said surface meets a lateral surface 30. This frequency and location of capacitive proximity sensors 29 is beneficial since it counteracts situations where the glass substrate 34 and/or the CVD coater 9 is not level (i.e. the glass substrate and/or the CVD coater are positioned in non-parallel planes), such that the CVD coater could conceivably contact the glass substrate even though a sensor indicates that it is spaced apart from the glass substrate.

[0070] FIG. 3 shows a perspective view of a capacitive proximity sensor 29 in accordance with the present invention. Sensor 29 comprises sensor unit 37 partially surrounded by a housing connected to control unit 38 via cable 39. Control unit 38 has a touchscreen 40 which is arranged to display information regarding the proximity of the sensor unit 37 to a glass substrate 34. In use, the sensor electrode 35 is arranged to detect the distance between a glass substrate 34 and the CVD coater 9. The sensor unit 37 is arranged to send signals to the control unit 38 via the cable 39, wherein said signals indicate the distance between the glass substrate 34 and the CVD coater 9. In addition to controlling the operation of any sensor units 37 to which it is connected, the control unit 38 may also control the operation of the CVD coater 9 or may be connected to a separate control unit for controlling the CVD coater 9. The control unit 38 allows an operator to control the distance between the glass substrate 34 and the CVD coater 9, e.g. the control unit 38 is arranged to automatically maintain a constant distance between the glass substrate 34 and the CVD coater 9 if desired. The control unit 38 is also arranged to audibly and/or visually warn an operator if the CVD coater 9 is closer to the glass substrate 34 than a pre-determined minimum distance of e.g. about 2-30 mm, preferably about 2-10 mm.

[0071] Cable 39 is a triaxial cable with a fine copper wire thermally insulated with ceramic beads and successively surrounded by copper tubing, fibreglass and braided stainless steel mesh. Sensor unit 37 comprises a cylindrical copper sensor electrode 35 partially surrounded successively by mica, a copper guard ring and a second layer of mica. The sensor unit 37 is contained in a stainless steel housing.

[0072] FIG. 4 shows a cut away perspective view of an end of a sensor unit 37 of a capacitive proximity sensor 29 in accordance with the present invention. Sensor unit 37 is partially surrounded by a cuboid-shaped housing. Shown in outline at one end of the sensor unit 37 is the end of cylindrical sensor electrode 35, which would be exposed to the surrounding atmosphere but for the presence of an anti-fouling sheet 40 in the form of a 0.5 mm thick, 30 mm circumference alumina disc. This anti-fouling sheet 40 is held in place by holder 41 which is a square-shaped frame with a slot 42 for easy insertion and removal of sheet 40 when it needs replacing, which can conveniently be undertaken between CVD coating runs.

EXAMPLES

[0073] Testing Sensor Variation Over Time in Float Bath Section

[0074] A capacitive proximity sensor in accordance with FIG. 3 was attached to a CVD coater such that the sensor electrode was level with the lower surface of the CVD coater. The coater was then tested in a float bath section set to a temperature of 755° C. The CVD coater was lowered towards the surface of the float bath until it was 5-6 mm from the surface. The variation of the readings provided by the capacitive proximity sensor was then assessed over the course of several hours. The results are shown in Table 1 below.

TABLE-US-00001 TABLE 1 Distance between capacitive proximity sensor and glass ribbon detected by sensor over time Time (hrs:mins) Distance (mm) 10:26 5.42 10:32 5.44 10:36 5.4 10:43 5.36 11:30 5.36 11:42 5.28 11:49 5.28 14:41 6 14:44 6.02 14:53 5.99 14:54 6.07 15:44 5.97 15:46 6 15:47 5.94 16:36 6.11

[0075] As can be noted from Table 1, there was no drift in the detected values over the six hours. The only significant shift occurred around 14:30 when there was a change in the height of the glass ribbon which was duly detected by the sensor. The tiny fluctuations detected over the rest of duration are consistent with typical variations in ribbon surface height.

[0076] Comparing Capacitive Proximity Sensor with Micrometer in Presence of Alumina Disc

[0077] A capacitive proximity sensor in accordance with FIG. 3 incorporating an alumina anti-fouling sheet in accordance with FIG. 4 was attached to a CVD coater such that the sensor electrode was level with the lower surface of the CVD coater. A micrometer was used to position the lower surface of the coater at a number of predetermined distances from a stainless steel plate. At each predetermined distance the distance detected by the capacitive proximity sensor was recorded and the results are shown below in Table 2 and in FIG. 5.

TABLE-US-00002 TABLE 2 Comparison of distances determined with micrometer and distances recorded with capacitive proximity sensor Distance determined Distance recorded with micrometer (mm) with sensor (mm) 0 0.4 1 1.26 2 2.25 3 3.29 4 4.34 5 5.47 6 6.48

[0078] Table 2 and FIG. 5 show that the presence of the alumina disc affected the distance indicated by the sensor. However this difference was predictable and therefore the sensor could easily be calibrated before use to obtain accurate values.

[0079] The invention is not restricted to the details of the foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.