A METHOD AND A DEVICE FOR APPLYING OF AN INSULATING LAYER ON A SURFACE OF AN OBJECT

Abstract: According to a method for applying of an insulating layer to a surface fibres of an inorganic material is sprayed onto said surface under simultaneous wetting of the fibres with water and/or a binder so that the fibres stick to the surface whereafter the layer is formed and dryed/hardened. Prior to or after the drying/hardening a binder can be sprayed to the surface for the purpose of achieving a dustless and mechanically resistant surface layer. A device for applying of an insulation to a surface of an object (10), making use of the method, comprises a store (41) of fibres of an inorganic material, a conduit means (20) for the transfer of fibres from the store (41) to a spray nozzle (21) and means for generating of an air flow in the conduit means (20) directed towards the nozzle (21). Further, the device comprises first ejector means (22) provided at the end of the conduit facing the store (41) for introducing air jets into said conduit means (20) in the direction of the fibre stream but at an inclination with respect to said stream, second ejector means (23) disposed at the end of the conduit means facing the spray nozzle (21) for the introduction of air jets directed so as to bring the fibre stream into rotation, and means (24) disposed adjacent to the spray nozzle (21) for introducing into the fibre stream, but outside of the spray nozzle, of liquid jets in the direction of the fibre stream but forming an angle with said stream, said liquid jets comprising a mixture of water and a binder.

Description: A method and a device for applying of an insulating layer on a surface of an object The present invention refers to a method and a device, respectively, for applying of an insulating layer to a surface of an object. In connection with oven cavities used in ranges or built-in ovens the oven cavity has to be provided with a heat insulation surrounding said cavity which prevents the heat energy supplied to the oven from unnecessarily leaking out to the environment and, at the same time, assures that surrounding parts do not reach such high temperatures at which there is a risk of fire or other damage to occur. Traditionally, a heat insulation of the kind referred to have the shape of mats and plates of glass-wool or mineral wool cut out and secured to the outer surfaces of the oven by means of steel straps or the like or, at the rear side of the oven, by means of an adhesive. The most common insulating material is glass-wool which consists of glass fibres kept together by a phenol-based binder. In manufacturing ovens in the factory these mats or plates of glass-fibre have to be cut out and otherwise handled in a way creating glass fibre dust which appears in large quantities. This disadvantage is strengthened by the use of tools driven by compressed air. In addition, the manual handling itself of the glass-wool mats and plates involves the risk of skin irritations and eczema to develop. Another drawback is the creation of nasty-smelling gases emitted from the phenol containing binder of the heat insulation when the finished oven is used. Accordingly, it is an object of the invention to make possible the application of an insulation of the kind referred to in such a way as to remedy the drawbacks indicated. The object is achieved by a method having the characterizing steps indicated in claims 1-6 and in a device having the features indicated in claims 7-17. The invention will now be described more in detail in connection with an embodiment with reference to the enclosed drawings in which: Fig. 1 schematically shows a production facility for appli¬ cation of an insulating layer according to the invention onto the outer surfaces of an oven cavity; Fig. 2 schematically shows the oven cavity supported by the gripping tool of a handling robot in the production facility; Fig. 3 schematically shows a device for applying of the insulating layer being part of the facility of fig. 1; Fig. 4a and 4b show an ejector, being part of the device of fig. 2, for providing of a unidirectional air stream; Fig. 5a and 5b show an ejector, being part of the device of fig. 2, for creating a rotating movement of an air stream containing fibres; Fig. 6 is a schematic view taken perpendicular to the outlet of a fibre applying nozzle, being part of the device of fig. 2, showing a preferred arrangement of liquid nozzles; Fig. 7 shows a modified embodiment of the arrangement of fig. 6; Fig. 8 schematically shows, in a top view, the fibre applying and liquid nozzles, respectively, described with reference to figs. 5 and 6; and Fig. 9 schematically shows the distribution of fibres applyed onto an object at different modes of operation with different parameters set which influence on the fibre stream. The embodiment to be described refers to the application of a heat insulating layer to the outside of an oven cavity intended to be mounted in a domestic range. Alternatively, the oven cavity may constitute a separate unit in the shape of a built-in oven. Suitably, the application of the insulating layer is carried out in an automatic work station of a suitable design. In Fig. 1 the design of such work station is schematically shown. In the embodiment a method is being used according to which fibres of a inorganic heat insulating material is sprayed onto the external surface of the oven cavity under simultaneous wetting of the fibres with an aqueous binder causing the fibres to stick to the cavity. The fibres are glass-wool fibres and the binder is of the silicate type and in the example described the binder is EKA Thorsil, having 14 percentage by weight of Silicon and 86 percentage by weight of water. After the application of the glass-wool fibres on the outside of the cavity the layer is formed and compressed against surfaces having insignificant adhesiveness, for example having a coating of PTFE. Then, the water contained in the layer has to be removed for the silicate binder to harden. This drying process can take place in a convection oven at temperatures below 600 °C or by means of infrared radiation elements. Finally, an acetate-based binder can be applied to the insulating layer in order to prevent or substantially limit the creation of dust during the handling of the oven cavity and, in addition, to improve the mechanical strenght of the layer. Alternatively, the application can take place prior to drying if the drying temperatures do not exceed- about 200 °C. An example of such binder is National ML 7224 which is to be applied as an aqueous solution. The continued description will be concentrated on those parts of the application process concerned with the transfer of fibres from a store to an application nozzle and to the application itself of the fibres to the surface of the oven cavity via said nozzle. However, the subsequent forming and surface treatment of the insulating layer thus applied will not be discussed in detail. In Fig. 1 an establishment is shown in which an insulating layer of the kind referred to can be applied to the outside of an oven cavity designated by 10. The establishment is built up around a handling robot 11 which collects an oven cavity from a collecting station 12 and brings it to a work station 13 where the application is to take place. After the application the robot moves the cavity to another collecting station 14 for further transport within the production establishment. The fibre to be applied to the oven cavity is obtained from a fibre tearing machine 15 of a kind known per se. A fibre bale 16 is inserted in the machine to be fed by a feeding means 17 towards rollers 18, 19 of a shape so as to convert the bale into a stream of fibre bundles which, by means of air, are blown towards the inlet of a hose 20 the outlet end of which opens into an application nozzle 21. In the figure there are also shown two ejectors, one of which, designated 22, disposed at the inlet of the hose and another one, designated 23, disposed at the outlet end of the hose. The function of the ejectors will be described more in detail in the following. The application nozzle 21 emits a stream of fibres which is directed towards the oven cavity. In order for the fibres to stick to the surface of said cavity the fibres are being wetted with liquid from nozzles 24 disposed around the outlet opening of said nozzle. The liquid is provided from a liquid system comprising a container 25 and a pump 26. As indicated above, the liquid consists of a slicate binder and water and to prevent sedimentation when the nozzle is not operating the liquid is circulated in the system and, in addition, a stirrer 27 is provided in the container 25 which is activated during the circulation process. A pumping device can also be used which continuously adds water. During the application the robot 11 is arranged to move the different sides of the cavity past the application nozzle, which is fixed. In doing so, the gripping tool of the robot performs the different movements in synchronism with the way of working of the nozzle so that layers of a predetermined thickness are applied to the sides of the cavity. The application process is controlled by a control unit 28 programmed to perform a number of different programs to be selected by a keyboard 29 or the like. Further, the figure contains a hydraulic pump 30 which operates the fibre tearing machine 15 and a unit 31 comprising valves and regulators for air and liquid to the ejectors 22 and 23 and to the liquid nozzles 24, respectively. Subsequent to the application the humid loose fibre layer on the sides of the cavity has to be formed or compressed which takes place in a forming station 32 where forming parts coated with PTFE are brought into contact with said sides. After the forming the insulating layer has to be dryed which, as already mentioned, can take place in a convection oven or by means of infrared radiation elements. Such drying devices have been omitted in Fig. 1. However, a spraying equipment 33 is shown by means of which an additional layer is applyed to the formed and dryed insulating layer. As mentioned above, the purpose of this coating is to prevent dust emission from the insulating layer and in addition the layer is given a higher mechanical strength. During the application of the insulating layer to the external surfaces of the oven cavity, to a certain extent glass fibres will find their way into said cavity and stick to the interior surfaces of the cavity. To prevent this the gripping tool of the robot 11 has been designed as shown in Fig. 2. The cavity is hold by the gripping tool by two parts 34, 35 pressing against two opposite surfaces inside of the cavity and the open end of the cavity is closed by a wall 36 which, via an intermediate sealing gasket 37, bears against a flange 38 surrounding the open end of the cavity. By a conduit 39 a gas, suitably air, is itroduced into the cavity to create an overpressure which prevents fibres and binder from entering through remaining minor openings for details to be mounted, such as the opening 40 in the rear wall of the cavity. With referens to Fig. 3 the device for applying of the insulating layer to the external sides of the cavity will now be described. Glass fibres are available in a store 41 and, in principle, these fibres can have been delivered in finely divided form. In the embodiment the store is part of the fibre tearing machine shown in Fig. 1 and glass fibres for the machine is delivered in the form of compressed fibre bales. In the way described, the machine operates to tear the fibre bale into small fibre bundles which by means of air are blown into the conduit 20 to create in this conduit a fibre stream mixed with air. The means for generating said air stream have not been shown in the figure. In order to facilitate the blowing of the fibres into the conduit air jets are introduced in the ejector 22 from different sides so that a vacuum is established sucking the fibres into said conduit and so that additional air is introduced into the conduit for the transport of fibres through same. In figures 4a and 4b an embodiment of the ejector is shown in which four bores 42 open in an aera of reduced cross-section, said bores being disposed crosswise. The bores extend in the direction of the fibre stream through the ejector but intersects this direction at an angle of about 30 degrees. The number of bores can be increased and in a modified embodiment, not shown, said number has been doubled and the bores have been evenly distributed along the periphery. A number of such modifications can be made within the scope of the idea of invention. As appears from figures 1 and 3, between the conduit 20 and the application nozzle 21 an additional ejector is provided for the purpose of creating a suitably shaped fibre stream leaving the nozzle. The nozzle has an outlet opening which is mainly rectangular in order that the insulating layer applied be given the shape of a swath of a corresponding rectangular cross- section. Therefore, the object is to distribute the fibre flow evenly along the whole of the outlet opening and, accordingly, the ejector 23 is designed so as to apply a rotational movement of sufficient magnitude to the fibre stream in the conduit. In figures 5a and 5b an embodiment is shown in which, as in the ejector 22, four bores 43 open inside the injector in an area of reduced diameter. Here, the bores are directed tangentially to the circular inner wall of the ejector but also at an angle with respect to the direction of the fibre stream through the ejector, said angle, preferably, being at about 45 degrees. As in the ejector 22 the number of bores can be varied as well as the disposition of same without departing from the idea of invention. For example, a modified embodiment, not shown, has been tested in which eight bores have beeen evenly distributed along the periphery of the ejector. The ejectors 22 and 23 also contribute in additionally reducing the size of the fibre bundles leaving the fibre tearing machine. When, by means of the ejector 23, the fibre stream from the nozzle 21 has been given a suitable shape another problem arises, namely the problem of wetting in a correct way the outflowing fibres so that they stick to the surface to be coated. To that " end a number of liquid nozzles 24 have been disposed adjacent to the rectangular nozzle opening so that the two rectangular sides of the fibre stream be wetted as evenly as possible. In Fig. 3 two rows of three nozzles each have been arranged vertically along the sides of the nozzle. The jets from the nozzles overlap so that complete coverage is achieved. Modified embodiments are shown in figures 6 and 7. In Fig. 6 four liquid nozzles 44 and 45, respectively, have been arranged at each side of the application nozzle 21 to form vertical rows whereas at the bottom and at the top liquid nozzles 46 and 47, respectively, have been disposed so that the corresponding jets are directed upwards and downwards, respectively, " to prevent fibre losses in these directions. In the embodiment according to Fig. 7, at both sides of the outlet opening of the application nozzle three liquid nozzles each, 48 and 49, respectively, form vertical rows while at the bottom two liquid nozzles 50 and 51 and at the top corresponding liquid nozzles 52 and 53 are provided. The nozzles 50, 51, 52 and 53 are directed at an angle to the fibre stream giving a good wetting of the corresponding parts of the fibre stream in addition to their preventing of fibre losses. In this embodiment the peripheral parts of the application nozzle have a greater cross-section than the central parts adjacent to the inlet opening of the nozzle. The embodiments accordning to figures 6 and 7 both have shown to result in a good distribution of the fibre flow in the nozzle opening at the same time as the wetting is good and the fibre loss is insignificant. In order to improve the adhesion of fibre to the surface of the oven cavity it is an advantage if said surface be wetted with the mixture of water and binder prior to being hit by the wetted fibres. In Fig. 8 two liquid nozzles 54, 55 are disposed at each side of the application nozzle 21. The nozzle 55 forms with the fibre stream an angle B which is smaller than the corresponding angle for the nozzle 54 resulting in that part of the liquid jet hits the part of the oven cavity being about to be hit by the fibre stream. The angle B is optimized so that wetting of the surface takes place without negatively influencing on the wetting of the fibre stream. As appears from the figure another angle A has been drawn in indicating a certain inclination of the direction of the fibre stream from said nozzle with respect to the normal to the surface of the oven cavity. The purpose of this inclination is to minimize the fibre loss during application. In connection with the embodiments shown in the drawings it has been shown that a good result be dependent on a number of parameters being optimized correctly. In Fig. 9 another such parameter is shown, namely the inclination of the conduit 20 vertically at the passage to the ejector 23. Tilting of the conduit upwards causes an increase of the amount of fibre at the lower part of the application nozzle whereas tilting of the conduit downwards gives the opposite effect. In the case designated 1 an even coverage of the surface is obtained which can be expected at the optimal setting of the various parameters, such as air quantity and the directions in the ejectors, the inclination of the conduit mentioned, the design of the applica- tion nozzle and the positioning of the liquid nozzles and the flow charateristics of same. In case No. 2 an uneven distribution is achieved due to incorrect inclination of the conduit to the ejector 23. Here, the conduit is too high, that is the conduit leans downwards towards the ejector. In case No. 3 too small quantity of fibre is present at the centre possibly due to too much air in the rotational ejector 23 or insufficient quantity of air in the ejector 22. In case No. 4 the fibres are concentrated in the centre, at the top and at the bottom which could be caused by too much air both in the rotational ejector 23 and in the ejector 22. The case No. 5 gives a concentration of fibres in the centre possibly due to insufficient amount of air to the rotational ejector 23. In case No. 6 there is shown the dis¬ tribution resulting from both ejectors 22 and 23 being left out. The flow is instable and a fibre concentration is achieved at the surface.

Claims: C l a i m s 1. A method for applying of an insulating layer to a surface of an object, characterized in that fibres of an inorganic material be sprayed onto the surface under simultaneous wetting of the fibres with water and/or a binder so that the fibres stick to the 5 surface, whereafter the layer is formed and dryed/hardened. 2. A method according to claim 1, characterized in that after the forming and prior to or after the drying/hardening of the insulating layer a binder is sprayed to the surface creating a mechanically resistant surface layer. 10 3. A method according to claim 2, characterized in that the. surface layer consists of an acetate-based binder. 4. A method according to any of the preceding claims, charac¬ terized in that during the application the fibres are wetted with a mixture of water and a silicate-based binder. 15 5. A method according to any of the preceding claims, charac¬ terized in that the fibres are glass fibres. 6. A method according to any of the preceding claims, charac¬ terized in that the object is an oven and that the insulating layer is a heat insulation. 20 7. A device for applying of an insulation to a surface of an object (10), charaterized in that it comprises a store (15) of fibres of an inorganic material, a conduit means (20) for the transfer of fibres from the store (15) to a spray nozzle (21), means for generating of an air flow in the conduit means (20) 25 directed towards the nozzle, first ejector means (22) provided at the end of the conduit facing the store (15) for introducing air jets into said conduit means (20) in the direction of the fibre stream, second ejector means (23) disposed at the end of the conduit means facing the spray nozzle (21) for the introduction 30 of air jets directed so as to bring the fibre stream into rotation, and means (24;44-47;48-53) disposed adjacent to the spray nozzle (21) for introducing into the fibre stream, but outside of the spray nozzle, of liquid jets in the direction of the fibre stream but forming an angle with said stream, said 35 liquid jets comprising a mixture of water and a binder. 8. A device according to claim 7, characterized in that the first ejector means (22) comprise a number of nozzles (42) distributed along the periphery of the conduit means, said nozzles being directed so that the air jets from said nozzles form an angle with the passing fibre stream of about 30 degrees. 9. A device according to claim 8, characterized in that eight nozzles (22) are provided which are evenly distributed. 10. A device according to claim 7, characterized in that the second ejector means (23) comprise at least four nozzles (43) disposed crosswise and being directed so as to have the jets from said nozzles inciding tangentally in the conduit means (20), forming an angle of about 45 degrees with the passing fibre stream. 11. A device according to claim 7, characterized in that the spray nozzle (21) has a cylindrical inlet part and an outlet part which is mainly rectangular where the shorter side is mainly of the same magnitude as the diameter of said inlet part of the nozzle whereas the longer side has a size which is considerably greater. 12. A device according to claim 10, characterized in that a number of liquid nozzles (24;44,45;48,49) are disposed in a row along the longer sides of the spray nozzle (21) at both sides of said nozzle. 13. A device according to claim 12, characterized in that at at least one of the shorter sides of the spray nozzle (21) there is provided at least one liquid nozzle (46,47;50-53) . 14. A device according to claim 12, characterized in that at least one liquid nozzle (46,47;50-53) is provided at each of the shorter sides. 15. A device according to any of claims 11-14, characterized in that means (11) are provided to move the surface of the object (10) past the spray nozzle (21) which is directed so that the fibre stream from said nozzle hits the surface (10) at an angle to the direction of movement of said object which is slightly greater than 90°. 16. A device according to claim 13, characterized in that the liquid nozzles (55) in the forward row, as seen in the direction of movement of said object (10), are directed so that the liquid jets from said nozzles are wetting also the surface of said object prior to the application of the fibres. 17. A device according to claim 7, characterized in that the binder is of the silicate-based type. 18. A device according to claim 10, characterized in that the conduit means (20) is connected to the spray nozzle (21) such that the outlet direction of the fibre stream can be set within a range limited by the shorter sides of the outlet opening of the nozzle. 19. A device according to any of the preceding claims, charac¬ terized in that it comprises means for forming of the wetted fibre layer applied to the object (10) and means for the subsequent drying of said layer. 20. Oven, provided with a surrounding heat insulation comprising fibres of an inorganic material, preferably of the type glass fibres or mineral fibres, characterized in that the heat insulation is produced and applied by means of a device according to any of claims 7-19.

Inventors: NYBERG CURT ELIS TAGE, TROBERG HENRIK EVALD, NYBERG, CURT, ELIS, TAGE, TROBERG, HENRIK, EVALD
Applicants: ELECTROLUX AB, AKTIEBOLAGET ELECTROLUX
Application year: 1992
Main classification: F16L59
IPC codes: B29C70, D04H1, F16L59