Field of the invention

The present invention relates to a heat treatment apparatus for thermal processing of a sheet wherein a part of the sheet is temporary heated and cooled according to a predetermined temperature profile, when the sheet is passed through the heat treatment apparatus.

Background art

Such a heat treatment apparatus is known from US 4,401 ,484. In the known heat treatment apparatus a metal strip is moved through the heat treatment apparatus in a floating manner.

Thereto the known apparatus comprises a first and second plenum chambers opposite to each other. Furthermore, the known heat treatment is provided with device strip curving means in the wall of each of the plenum chambers adjacent to the metal strip and arranged over the entire length of the strip passage within the heat treatment apparatus.

A disadvantage of the known device is that the substrate is heated at both sides, where in some heat treatments it is desired that substrates provide with one or more thin film layer of an additional material are thermally treated only at the side of the sheet opposite to that whereon the thin film layers are provided. The sheet can be a metal sheet, a ceramic or glass sheet.

DE1483378B1 discloses a device for transporting a metal sheet provided with a chamber provided with an input port for receiving the sheet and an output port for releasing the sheet; transport means arranged to move the sheet from the input port to the output port in a first direction and a gas bearing in the chamber arranged to guide the sheet from the input port to the output port.

Summary of the invention It is an object of the invention to provide a heat treatment apparatus where a more accurate temperature profile can be obtained. This object can be achieved by the heat treatment apparatus in accordance with the invention, and is characterized in that the heat treatment apparatus comprises a chamber provided with an input port for receiving the sheet; an output port for releasing the sheet, transport means arranged to move the sheet from the input port to the output port in a first direction; a gas bearing positioned between the input port and the output port and arranged to guide the sheet from the input port to the output port, the gas bearing being provided with an inlet for receiving the heated gas; a gas flow controller connected to the gas bearing via a channel, the gas flow controller being arranged to control a gas flow through the gas bearing, and heating elements around the channel arranged to heat the gas flow when provided to the gas bearing, wherein the input port, the gas bearing and the output port are arranged in a triangle, when viewed in an operation position.

The invention is based on the recognition that heating one side of the substrate may introduce buckles in the moving substrate, for example, a metal sheet. In the new arrangement, the gas bearing is arranged between the input port and the output port, wherein the gas bearing is positioned in a top angle of the triangle formed between the input port and the output port, when viewed in an operation position. Due to the bend induced by the gas bearing in a transverse direction with respect to the moving direction of the substrate buckle forming in the substrate is prevented. Furthermore, the gas flow through the gas bearing towards the sheet provides a counter force to balance a force induced by the tension in the sheet, when moving around the gas bearing. In this way a small distance can be adjusted between a supporting surface of the gas bearing and the sheet. This small distance induces a turbulent flow of gas to the sheet. A further advantage is that this turbulent heated gas flow provides an efficient heat transfer from the gas flow to the sheet and enables contactless one-side heating of the sheet.

In a particular advantageous embodiment of the heat treatment apparatus, the gas bearing is provided with a bar directed in a direction transverse to the first direction, the bar is provided with an inlet connected to the channel for receiving the heated gas and orifices for venting the gas to the sheet. The bar provides a supporting surface to carry the moving sheet.

In a further embodiment of the heat treatment apparatus the gas bearing is provided with a further bar parallel to the first bar, the further bar is provided with an inlet connected to the channel for receiving the heated gas and orifices for venting the gas to the sheet, and wherein the heating elements are further arranged to adjust the heat transport to different portions of the sheet to a desired temperature-time trajectory of a portion of the sheet. In this arrangement the desired temperature-time trajectory can be set by the different temperatures of the respective gas flows through the two or more bars and the speed of the moving sheet through the apparatus.

In a further embodiment of the heat treatment apparatus the face of the bar directed to the sheet has a rounded shape, when viewed in a second direction transverse to the first direction. The rounded shape provides a smooth, contactless transport of the moving sheet along the air bearing.

In a further embodiment of the heat treatment apparatus a part of the orifices are positioned along a straight line at the face directed to the sheet.

In another embodiment of the heat treatment apparatus, the bar consist of porous material. An advantage of the porous material is that the bar can be manufactured in a simple way. The porous material can comprise stainless steel, ceramics or graphite.

In a still further embodiment of the heat treatment apparatus, the transport means comprises an input reel positioned near the inlet port and arranged to roll off the sheet and an output reel positioned at the output port and arranged to wind up the sheet. The input reel and the output reel enables processing of a rolled sheet.

In a still further embodiment of the heat treatment apparatus, the transport means comprises a first motor arranged to drive the input reel and a second motor arranged the output reel to move the sheet at a predetermined speed.

In a still further embodiment of the heat treatment apparatus, the heat treatment apparatus further comprises a controller connected to the gas flow controller and the first and second motors, the controller is configured to adjust a gas flow and a speed of the moving sheet. The moving speed can be adjusted in the range between 0.1 m and 6 m per min. In a still further embodiment, the controller is connected to the heating elements, and the controller is further arranged to control the heating elements according to the desired temperature trajectory- time trajectory. In this arrangement the controller set the temperature of the gas flow in the channels by controlling the respective heating elements and the speed of the moving sheet.

In a further embodiment a cross-section of adjacent faces of the first and second bar directed to the sheet are conforming a circle segment. This shape provides a smooth transport of the sheet from one bar to the next bar in the gas bearing.

In a further different embodiment of the heat treatment apparatus, the heat treatment comprises a further gas bearing positioned between the input reel and the gas bearing or the gas bearing and the output reel.

Short description of drawings

The present invention will be discussed in more detail below, with reference to the attached drawings, in which

Fig. 1 schematically shows schematically an embodiment of the heat treatment apparatus according to the invention;

Fig. 2 schematically shows a first embodiment of the gas bearing provided in the heat treatment apparatus according to the invention;

Fig. 3 schematically shows a front view in the longitudinal direction of the bar in a first embodiment of the invention;

Fig. 4 schematically shows a front view in the longitudinal direction of the bar provided in a second embodiment of the invention;

and

Fig. 5 schematically shows an example of a graph representing a temperature variation of a sheet passing the heat treatment apparatus.

In the figures like reference numbers indicate like parts.

Description of embodiments

The invention is described with reference to figs. 1 to 5. Fig. 1 shows schematically an embodiment of a heat treatment apparatus according to the invention.

The heat treatment apparatus 1 comprises a frame 2 , a chamber 3 defined by a furnace wall 4 and provided with an input port 5 for receiving a sheet 7, and an output port 6 for releasing the sheet 7, wherein the frame supports the chamber. The furnace wall 4 may comprise isolating material.

The sheet can be for example, a metal plate, a ceramic or glass plate. The metal can be for example stainless steel or INOX. The thickness of the plate can be for example in the range between 0.2 and 0.6 mm. The width of the sheet can be for example 40 cm. The sheet can be a roll of metal. The metal can be steel or INOX. One side of the sheet 7 can be provided in an earlier process step with, for example, a semiconductor printed on the sheet. The semiconductor can be for example doped silicon. In the heat treatment apparatus in this description the side of the sheet opposite to that whereon the semiconductor layer is provided, can be heated.

The heat treatment apparatus 1 comprises a gas bearing 8 positioned between the input port 5 and the output port 6 and arranged to guide the sheet 7 from the input port to the output port.

Furthermore, the heat treatment apparatus comprises transport means arranged to move the sheet from the input port to the output port in a first direction. The transport means may comprise an input reel 9 positioned near the inlet port 5 and arranged to roll off the sheet and an output reel

10 positioned at the output port 6 and arranged to windup the sheet. Furthermore, the gas bearing 8 is connected to a gas flow controller 1 1 via a channel 23.

In this embodiment the gas bearing 8, the input port 5 and the output port 6 are arranged in a triangle, when viewing in an operation position transverse to the moving direction of the sheet. In this arrangement the gas bearing 8 is positioned in a top angle of the triangle formed with the input port 5 and the output port 6. The heat treatment apparatus is based on a flow of heated gas for heating the one side of the sheet directed to the bearing. Furthermore, the gas bearing forms a floating bed for the moving sheet 7.

Advantages of this configuration are that the bend induced by the gas bearing 8 in a transverse direction with respect to the moving direction of the sheet, prevents buckle forming, when the sheet is heated. Furthermore, the small distance in the gas bearing between the supporting surface and the moving sheet provides a turbulent gas flow to the sheet. An advantage of the turbulent gas flow that it improves heat transfer from the heated gas to only one side of the sheet.

Furthermore, in this configuration the force of the gas flow acting on the moving sheets counterbalances a force induced by the tension of the moving sheet. In an embodiment this force is about 10N per meter width of the sheet.

Furthermore, the heat treatment apparatus may comprise a gas flow controller 11 connected to the gas bearing 8 for supplying the gas and a controller 12.. The gas flow controller

1 1 may be connected to the controller 12 arranged to control the gas flow through the gas bearing.

Furthermore, the heat treatment apparatus can be provided with motors 13,14 arranged to drive respectively the input real 9 and the output reel 10. The motors can be electrically connected to the controller 12. The controller is arranged to adjust a speed of the moving sheet and a predetermined tension in the moving sheet by controlling the rotating speed and torque of the respective motors 13, 14. The gap in the gas bearing to the sheet 7 is controlled by the gas flow and the rotating speed and toque of the respective first and second motors. The distance can be smaller than 1 .0 mm preferably smaller than 0.8 mm.

In order to obtain a desired temperature variation of a portion of the moving sheet, when the portion of the moving sheet is moving along the gas bearing 8 in the heat treatment apparatus, the temperature of the heating element, the gas flow through the gas bearing and speed of the moving sheet can be adjusted. Fig. 2 schematically shows a cross-section 20 of the gas bearing 8 provided in the heat treatment apparatus 1 according to an embodiment of the invention. |The gas bearing may comprise one or more bars 21 ,26,27,28. The first bar 21 is provided with an inlet 24 for gas intake and venting orifices 22 in the face of the bar 21 facing the sheet 7. The venting orifices 22 are connected to the inlet 24 by an inner channel in the bar.

Furthermore, the heat treatment apparatus is further provided with a channel 23 connecting the inlet 24 of the bar 21 to the gas flow controller 1 1 .

Fig. 2 shows also the three further bars 26,27,28 positioned parallel to the first bar 21 . The further bars 26,27,28 are similar to the first bar 21 .

In this embodiment the bars 26,27,28 can be arranged beside each other in the chamber

4, wherein the faces of the bars directed to the sheet 7 are conforming to a fictive segment of a circle with a predetermined radius to obtain a smooth rounded surface to support the moving sheet 7. The radius of the circle can be for example 500 mm. The apertures between the bars 20,26,27,28 can be used to drain the expelled gas redirected from the sheet.

Furthermore, in an embodiment the heat treatment apparatus can be provided with heaters

250, 251 , 252, 253 around the channel 23. In an embodiment the channel 23 can be divided in sub channels which are connected to the respective inlets of the first bar 21 and the further bars 26, 27 and 28 and the heaters can be arranged around the respective sub channels.

Furthermore, the controller 12 can be connected to the heaters 250, 251 ,252 and 253 in order to control the heaters. In this arrangement the heat transport to different portions of the moving sheet can be adjusted by the respective heaters 250, 251 , 252, 253, wherein the gas flows to the first bar 21 and the further bars 26,27,28, are flowing. So, a predetermined temperature variation in subsequent steps of a desired temperature-time trajectory of the portion of the moving sheet can be obtained.

Fig. 3 schematically a front view in the longitudinal direction of the bar 21 on the face directed to the sheet in a first embodiment of the invention. Fig. 3 shows that the orifices 22 are positioned along a fictive straight line 30 of the face of the bar 21 .

Fig. 4 schematically shows a front view in the longitudinal direction of bar 21 provided in the heat treatment apparatus according to a second embodiment of the invention. The bar shown in fig. 4 comprises porous material, e.g. stainless steel, ceramics or graphite. The bar can provided with an inner channel between an inlet and the orifices formed in the face of the bar facing the moving sheet.

Fig. 5 shows an example of a graph representing a temperature time trajectory or variation of a moving sheet passing through the heat treatment apparatus according to an embodiment of the invention. In the heat treatment apparatus the sheet is heated from a first temperature e.g. 100 °C, to respectively 300 ⁰ C and 700 ⁰ C. According to the invention the sheet can be heated rapidly from 300 ⁰ C and 700 ⁰ C without introducing buckling of the sheet.

According to an embodiment the heat treatment apparatus can be provided with further gas bearings between the input reel and the inlet port and/or between the bar and output port to guide the sheet respectively from the input reel to the inlet port and from the output port to the output reel. In the description of the figures, the invention has been described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the scope of the invention as summarized in the attached claims.

In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.

In particular, combinations of specific features of various aspects of the invention may be made. An aspect of the invention may be further advantageously enhanced by adding a feature that was described in relation to another aspect of the invention.