Curing furnace and method of controlling a curing furnace

Abstract

A curing oven (1) for curing a mineral wool web (2), the curing oven comprising an air-permeable conveyor (3) for advancing the mineral wool web (2) through an essentially closed cabinet (4) from a mineral wool web inlet (5) provided at one end of the cabinet to a mineral wool web outlet (6) provided at the other end of the cabinet, the curing oven (1) further comprising a hot air inlet (7) arranged for guiding a flow of hot air through the conveyor (3). The curing oven comprises at least one deformation detector (12, 13).

Description

BACKGROUND

[0001] The production of mineral wool, such as man-made vitreous fibre (MMVF), comprises the fiberization of a rock or glass melted into fine fibres and the collection of these fibres on a conveyor, forming a fibrous web. Man-made vitreous fibres can be produced in different ways, such as in a spinning cup, typically used for the production of glass wool fibres, or on a cascade spinner, typically used for the production of stone wool fibres. At or after the fibre formation, a binder for binding the fibres together is applied to the fibres and the fibrous web is heat treated in a curing oven to cure the binder, forming a coherent fibrous web.

[0002] The curing oven is an important element in the production of mineral wool, as it has a large influence on the quality of the finished mineral wool mat, which in turn has an influence on the manufacturing cost of the mineral wool product. Typically, a range of different mineral wool products are produced using the same curing oven. Depending on the desired use of the finished mineral wool product, the density of the produced mineral wool can vary from for example 20 kg / m 3 to 250 kg / m 3 and the thickness of the web can vary from for example 40 mm to 200 mm. Furthermore, the production of many different products in an ordered and timely manner to avoid large stocks of products, which are often bulky, means that many different products with different specifications are produced on the same production line in one day, requiring fast changeovers from one product to another. The melt production and the melt flow are not easily adjusted in a short time, so the melt flow and the fibre production are typically quite stable (up to 20 tons per hour), so the conveyor speed is adjusted to accommodate the thickness and density of the produced product (the conveyor speed can be up to 40 m / s), accordingly, the residence time of the web in the curing oven will depend on this. Therefore, the operator should constantly adjust the settings of the curing oven to ensure full curing, avoiding for example overheating damaging the fibrous web. Finally, the curing oven often becomes a bottleneck in the mineral wool production, especially with the increase in fibre formation, requiring higher production, and the shift to other types of binders that impose limits on the maximum curing temperature. The curing oven is not easily extended, as the length of the curing oven is typically 20-40 meters, there is usually no extra space within the existing building to extend the curing oven, and the modification of the existing curing oven is a time-consuming and costly matter, considering the heavy mechanical parts before and after the curing oven. These different requirements for the curing oven pose some challenges and there is a need for an improved curing oven.

[0003] The curing oven and its optimization has been the subject of numerous patents for at least 60 years. Examples of such earlier curing ovens include US Patent Nos. 2997096, 3096161, 4263007, 9664443 and European Patent No. 1794383. SUMMARY

[0004] One of the challenges related to the curing of mineral wool is that the mineral wool should be fully cured at the exit of the curing oven. Care should be taken during the curing process to avoid damage or deformation.

[0005] The invention relates to a curing oven for curing a mineral wool web, the curing oven comprising a gas permeable conveyor for advancing the mineral wool web through an essentially closed cabinet from a mineral wool web inlet provided at one end of the cabinet to a mineral wool web outlet provided at the other end of the cabinet, the curing oven further comprising a hot air inlet for guiding a flow of hot air through the conveyor.

[0006] It is an object of the invention to provide a curing oven that enables an increased production.

[0007] To achieve this object, the curing oven according to the invention comprises at least one wool deformation detector configured for detecting a wool deformation inside the curing oven.

[0008] Detailed description

[0009] Wool deformation refers to the creation of an unwanted compression in a part of the web. If the hot air pressure on the web is too high, wool deformation can occur in the curing oven, which means that the air flow resistance of the web causes the pressure on the web to exceed the compressive strength of the web, which yields and further compresses the web. The compressive strength of the uncured web is lower than the compressive strength of the cured web, so in the curing oven the web is prone to deformation in the uncured or partially cured stage. The production of mineral wool is a rather disordered process, and the produced mineral wool web often has some variation in parameters, so it can occur that areas cure slower than other areas, and the uncured areas deform. The curing starts from the side of the web facing the hot air inlet and develops through the core of the web to the other side of the web until the whole web is fully cured at the end of the passage through the curing oven. In case of wool deformation, the web will have areas of unsuitable thickness, so should be discarded. A slight deformation of e.g. 95% of the thickness is acceptable, and the rejection also depends on the size of the surface area with the deformation. The general target is to detect wool deformations (compressions) of at least 4 mm of the thickness of the web.

[0010] The cotton deformation detector can for example be a device that detects the thickness of the web at different positions across the width of the web, such as using laser thickness measurements. Laser thickness measurements can be achieved by using a laser to detect the distance to the surface of the cotton web. If the detected distance increases, it means that the cotton web is not in contact with the conveyor and is subject to unwanted compression. Of course, the laser needs to be able to reach the cotton web, which poses some challenges in terms of the conveyor, so suitable openings should be arranged in the conveyor, at least at suitable intervals. Alternatively, pressure or contact sensors can be arranged on the conveyor to detect whether the cotton web is in contact with the conveyor and thus whether the cotton web is subject to unwanted compression.

[0011] The cotton deformation detector can immediately provide information to an operator or to a control system to change process parameters of the mineral wool production line, such as the pressure of the hot air. As a result, the curing oven can be operated closer to the maximum curing oven capacity limit, thereby reducing the amount of waste and / or increasing the production rate and / or improving the energy consumption in the curing oven. Previously, the operation of the curing oven has been based extensively on the experience and knowledge accumulated over the years by the operators. Visual inspection, measurements and / or tests of the finished product show whether there are problems with the deformation of the cotton in the curing oven, without it being clear whether the curing oven could have been operated closer to the limit, which typically results in the curing oven being operated with a maximum wide safety margin, thereby resulting in relatively high costs and / or low production capacity.

[0012] According to one embodiment, the cotton deformation detector comprises a transmitter arranged at a first edge region of one side of the conveyor and a receiver arranged at a second edge region of the opposite side of the conveyor to transmit an electromagnetic signal laterally through the web. The transmitter and the receiver can be arranged outside the cabinet of the curing oven. Within the curing oven cabinet, there is typically an adverse environment with relatively high temperatures, fumes, dust and high air flow, which is adverse for the cotton deformation detector.

[0013] The electromagnetic signal can be any signal suitable to pass through the mineral wool web across the width of the web. X-rays are preferred because they are known to be able to pass through the mineral wool web and are used for other purposes on the mineral wool production line, such as density measurements. Alternatives include gamma rays or isotopic-based techniques.

[0014] According to one embodiment of the curing oven, the receiver has a vertical extension of 10-20 mm. If the receiver has a much larger vertical extension, there is a risk that the cotton deformation is difficult to detect due to averaging, whereas if the vertical extension is much smaller, there is a risk of misalignment or non-detection.

[0015] In its simplest form, the curing oven has only one zone, but advantageously, the curing oven comprises a plurality of zones, and the cotton deformation detector is arranged in at least one zone, preferably in the front half of the curing oven as seen in the conveying direction of the conveyor. Typically, the cotton is most vulnerable at the entrance of the oven where the binder has not yet cured, so here the hot air pressure should be low, while the pressure can be increased as the cotton cures during its passage through the curing oven.

[0016] One aspect of the invention relates to a curing oven control system for a curing oven as described above, wherein the control system is configured to adjust the pressure of the hot air stream based on input from the cotton deformation detector. This feedback makes it possible to operate the curing oven close to the limit of deforming the web, thereby maximizing the curing capacity of the curing oven.

[0017] The control system can be part of the curing oven disclosed by the invention. That is, one embodiment of the curing oven comprises a gas permeable conveyor for advancing a mineral wool web through a substantially closed cabinet from a mineral wool web inlet arranged at one end of the cabinet to a mineral wool web outlet arranged at the other end of the cabinet, the curing oven further comprising: a hot air inlet arranged for directing a hot air stream through the conveyor; at least one cotton deformation detector configured for detecting cotton deformation, preferably cotton deformation within the curing oven; and a control system configured to adjust the pressure of the hot air stream based on input from the at least one cotton deformation detector.

[0018] Another aspect of the invention relates to a method for controlling a curing oven, comprising the steps of: advancing a mineral wool web through a substantially closed cabinet from a mineral wool web inlet arranged at one end of the cabinet to a mineral wool web outlet arranged at the other end of the cabinet; directing a hot air stream through the conveyor and into the mineral wool web; detecting potential cotton web deformation in the curing oven. The detection of potential cotton web deformation can be used to inform an operator to adjust the pressure of the hot air stream, or it can even be used in an automatic system for adjusting the pressure.

[0019] One embodiment of the method comprises emitting an electromagnetic signal transversely across the web from a first edge region; receiving the electromagnetic signal at a second edge region opposite the first edge region; analyzing the received electromagnetic signal to provide a control value, generating a first signal if the control value indicates cotton deformation, generating a second signal if the control value indicates no cotton deformation, adjusting the hot air pressure at the hot air inlet based on the first signal or the second signal.

[0020] The method makes it possible to automate the operation of the curing oven and optimize the curing oven performance by operating the curing oven close to the limit of deforming the mineral wool web.

[0021] Another aspect of the invention relates to a curing oven according to the invention for curing mineral wool with a density in the range of 15-50 kg / m 3Use of mineral wool webs within the specified range. It has been found that the challenge of mineral wool web deformation is most prevalent in the curing of relatively low density mineral wool, so the greatest advantage of the curing oven is found in relation to the use of the curing oven to cure mineral wool having a specified range.

[0022] The present invention can be used to cure any kind of mineral wool, but the embodiments relate to the use of the curing oven to cure mineral wool webs made from fibres having a median diameter below 3 pm. The challenge of mineral wool web deformation is found to be most prevalent for the curing of mineral wool having a relatively small diameter. Mineral wool made from fibres having a relatively small diameter is preferred in view of providing the best thermal performance. A disadvantage of mineral wool made from relatively fine fibres compared to mineral wool made from coarser fibres is that the air flow resistance is higher, which means that curing by hot air flow is more difficult and requires higher pressure, resulting in an increased risk of mineral wool web deformation.

[0023] The median diameter of the fibres can be obtained automatically using a scanning electron microscope (SEM) to measure the diameter of the fibres and count the number of fibres in the sample.

[0024] The median diameter of the fibres can be obtained by a method which is precise and minimizes the breakage of fibres. The method can be automated without introducing errors. About 2 mg of fibres are extracted from a sample of fibres that do not contain any binder. Typically, the binder is removed by heating the fibres to 590 degrees Celsius for at least 20 minutes. The fibres are dispersed on a glass flake using implosion initiated by vacuum. Images of the dispersed cotton fibres are then obtained by light microscopy in transmission mode. Prior to thresholding (see below), the images are convolved with a neighbourhood Gaussian filter to reduce background noise and bring uniformity along the fibre intensity values.

[0025] Thresholding is then performed: high grey level values correspond to fibres, low grey level values are associated with background or residual noise. Isolated clusters of less than a few pixels or pixels having a eccentricity less than 0.5 (i.e. particles having a roughly circular shape) are removed as they correspond to noise or speckles. BRIEF DESCRIPTION OF DRAWINGS

[0026] In the following, the present invention will be described in more detail with reference to examples and drawings, in which:

[0027] Figure 1 is a longitudinal section of a part of a prior art mineral wool production line,

[0028] Figure 2 is a cross-sectional schematic view of a curing oven,

[0029] Figure 3 is another cross-sectional schematic view of a curing oven,

[0030] Figure 4is another cross-sectional view of the curing oven, and

[0031] Figure 5 is a schematic view of the method steps. DETAILED DESCRIPTION

[0032] Figure 1 The production of mineral wool is shown in longitudinal section. Figure 1 The production of fibres 9, the application of binder 10, the collection of the fibres as a mineral wool web 2 on a collection conveyor 11 is shown. The mineral wool web 2 is conveyed to a curing oven 1 having a cabinet 4 (shown in longitudinal section), enters a mineral wool web inlet 5 into the cabinet 4, through the curing oven 1 on a gas permeable conveyor 3 to a mineral wool web outlet 6. Hot air enters the curing oven 1 through a hot air inlet 7 and is forced through the conveyor 3 into the web 2 to cure the binder 10 of the mineral wool web 2. Exhaust air from the curing oven passes through an outlet 8 and the air can be recirculated and reheated or subjected to exhaust air treatment. In the example shown, the curing oven comprises two zones 16, 17, but there can be only one or there can be more, such as seven.

[0033] Man-made glass fibres can be produced in different ways, such as in the way of a spinning cup, typically used for the production of glass wool fibres, or in the way of a cascade spinner, typically used for the production of rock wool fibres.

[0034] In Figure 2 a cross-section of a curing oven 1 can be seen. The curing oven 1 comprises a set of conveyors 3 arranged in a cabinet 4 of the curing oven 1. The conveyors 3 are gas permeable, for example using perforated slats or panels. A mineral wool web 2 is arranged between the conveyors 3 and is conveyed through the curing oven 1 here. Hot air at high pressure is forced into the mineral wool web 2 to heat the web and cure the binder. The temperature of the air can be adjusted to ensure drying of the web and curing of the binder. Suitable temperatures depend, inter alia, on the specific binder and can be in the range of 180-260°C, although higher and lower temperatures are feasible and can be advantageous in some cases.

[0035] If the pressure of the hot air in the curing oven is too high, there is a risk of unwanted deformation of the mineral wool web, as the web can lift from the conveyors and be compressed in the area shown by the gap 14 between the web and the lower conveyor as shown in Figure 3 In this case, the mineral wool web is deformed before curing and the mineral wool web will be cured in the deformed state, which means that the product is below standard and has to be discarded.

[0036] At one edge region of the web, an emitter 12 is provided to emit an electromagnetic signal transversely across the web to a receiver 13 arranged at the opposite edge region of the web, as shown in Figure 4The signal received by the receiver 13 will depend on the mineral wool between the transmitter 12 and the receiver 13. In the case of unwanted compression resulting in the web of mineral wool not being in contact with the conveyor, there is suddenly less mineral wool in the signal path from the transmitter 12 to the receiver, and thus the signal received is different from when the signal has to travel all the way from the transmitter to the receiver through the mineral wool. The signal can be analysed in a processor 15, providing a control value and a first signal indicating web deformation or a second signal indicating no web deformation. Based on the first or second signal, the hot air pressure can be adjusted down or up, respectively, to maximize the curing oven performance.

[0037] As Figure 4 shown, the transmitter 12 and the receiver 13 should be arranged close to the conveyor 3, into which the hot air is forced.

[0038] The method steps of operating a curing oven comprise providing a sensor system, feeding a signal from the sensor system into a signal analyser to produce a value, and using an output generator to generate an output based on the value, as Figure 5 schematically shown in. The sensor system can be an X-ray transmitter and an X-ray receiver. The output from the output generator can be used in a control system for adjusting the pressure of the hot air.

[0039] The estimated potential of the present invention is to increase the curing oven capacity by up to 20% if the curing oven is controlled closer to the limit of web deformation of the mineral wool web.

Claims

1. A curing oven for curing a mineral wool web, comprising: a gas permeable conveyor for advancing the mineral wool web through a substantially closed cabinet from a mineral wool web inlet arranged at one end of the cabinet to a mineral wool web outlet arranged at the other end of the cabinet; a hot air inlet arranged for directing a flow of hot air through the conveyor; at least one wool deformation detector configured for detecting wool deformation within the curing oven; and a control system configured to adjust a pressure of the flow of hot air based on input from the wool deformation detector.

2. The curing oven according to claim 1, wherein the wool deformation detector comprises a transmitter arranged at a first edge region of one side of the conveyor and a receiver arranged at a second edge region of an opposite side of the conveyor to transmit an electromagnetic signal laterally through the web.

3. The curing oven according to claim 2, wherein the electromagnetic signal is X-rays.

4. The curing oven according to any one of claims 2 or 3, wherein the receiver has a vertical extension of 10-20 mm.

5. The curing oven according to any one of claims 1-3, wherein the curing oven comprises a plurality of zones and the wool deformation detector is arranged in at least one of the zones.

6. The curing oven according to claim 5, wherein the wool deformation detector is arranged in a front half of the curing oven as seen in a conveying direction of the conveyor.

7. A method for curing mineral wool in a curing oven, comprising the steps of: advancing a mineral wool web through a substantially closed cabinet from a mineral wool web inlet arranged at one end of the cabinet to a mineral wool web outlet arranged at the other end of the cabinet; directing a flow of hot air through the conveyor and into the mineral wool web; detecting potential wool web deformation in the curing oven; and adjusting a pressure of the flow of hot air based on the detected potential wool web deformation.

8. The method according to claim 7, wherein the step of detecting potential wool web deformation comprises: emitting an electromagnetic signal laterally through the web from a first edge region, receiving the electromagnetic signal at a second edge region opposite the first edge region, analyzing the received electromagnetic signal to provide a control value, generating a first signal if the control value indicates wool deformation, generating a second signal if the control value indicates no wool deformation, the method further comprising the step of adjusting a pressure of hot air at the hot air inlet based on the first signal or the second signal.

10. The use according to claim 9, for curing a mineral wool web made of fibers having a median diameter below 3 pm. ​ 9. Use of the curing oven according to any one of claims 1 - 6 for curing a mineral wool web, wherein the density of the mineral wool web is in the range of 15 - 50 kg / m 3 . ​

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