DEVICE AND METHOD FOR WRAPPING SOFT ELEMENTS

Abstract: The invention relates to a method for wrapping a plurality of soft elements, comprising the steps of stacking the elements, compressing the stack in a direction of stacking, and thus forming a package, inserting in a feeding direction the package into a film, preferably a plastic film, which at least partly consists of a thermoplastic material and which in an at least partly overlapping manner surrounds the package, sealing the film in the feeding direction, and cutting and optionally sealing the film transversely of the feeding direction. The method is characterised in that the step of sealing the film in the feeding direction is carried out by supplying from a nozzle means towards the film a pressurised heated gas towards the portions of the film that overlap each other, so that they change into an at least partly molten state and are joined. The invention also relates to a device for carrying out the method.

Description: DEVICE AND METHOD FOR WRAPPING SOFT ELEMENTS Field of the Invention The present invention relates generally to a method and a device for wrapping a plurality of soft elements, and specifically for wrapping boards of fibrous insulat- ing material . Background Art As a rule, equipment for wrapping insulating material is connected directly to a production line where the material is sawn and/or cut in specified sizes. This is a continuous process where the boards are usually supplied at a rate of one board per second or faster. When wrapping pads or boards of a soft material, such as insulating material, a method has since long been applied, in which rectangular boards are stacked into a stack, compressed in the direction of stacking into a package, and then provided with a coating of a thin flexible material, such as plastic, which maintains the package in its compressed state. According to a frequently used method, the packages are inserted in their longitudinal direction into an opening of a sack or tube of plastic, which is then possibly welded together at its open end. To automate the handling and eliminate the need for a sack or tube, an alternative method is used, in which each package, while being continuously fed, is coated with a surrounding, but not sealed plastic material, which is first welded along the long sides of the package. Subsequently welding and cutting between the pack- ages are carried out. By welding is here meant all kinds of joining where at least part of the wrapping material is heated during joining. The welding along the long sides of the package is difficult to accomplish in a satisfactory manner, and complicated devices are necessary to weld the packages in a quick and reliable manner. In particular, t is difficult to apply in a satisfactory manner the necessary pressure to the joint without it being weakened, espe- cially if tne surrounding material is a plastic material. In certain embodiments of the above method, the sides of the packages are, perpendicular to the direction of compression, subjected to a mechanical pressure, which results in an unfavourable pressure gradient. There is a risk that the fibres of the material, if any, will be damaged if excessive mechanical pressure is applied to the package This is a major problem since most insulating materials consist of fibre materials which are sensitive to pressure being applied transversely of the fibres. Furthermore, the compressed package, while being fed, frequently passes irregularities m the conveying paths, such as bumps or gaps. These irregularities are propagated through a plurality of boards m the compress- ed package and result m additional pressure gradients and damage the fibres. Summary of the Invention A first object of the present invention is to pro- vide automatic wrapping, which m every respect is satisfactory, of an insulating material, without the material being subjected to detrimental pressure gradients. A second object of the present invention is to provide a simple and strong seal of packages of compressed insulating material. These objects are achieved by a method which comprises the steps of stacking the elements, compressing the stack m a direction of stacking, thereby forming a package, inserting the package m a feeding direction into a film, preferably a plastic film, which at least partly consists of a thermoplastic material and at least m a partly overlapping manner surrounds the package, sealing the film in the feeding direction, and cutting and optionally sealing the film transversely of the feeding direction. The method is characterised in that the sealing of the film in the feeding direction is carried out by applying heat to the portions of the film which overlap each other so that they change into an at least partly molten state, and by supplying, from a nozzle means m the direction of the film, a pressurised fluid so that the portions are joined. The expression film relates to a thin and flexible material, which is capable of tightly surrounding the compressed material . The method can be accomplished by means of a device according to independent claim 8. By the compression of the overlapping portions occurring by means of pressurised fluid, mechanical action is avoided and the risk of weakening the joint is eliminated. In a preferred embodiment of the invention, a nozzle supplies a heated, pressurised gas, pre- ferably air, in the direction of the overlapping portions of the film. In this manner, the gas flow causes both heating and compression of the film. To prevent overheating of the joint, which may result m reduced strength and holes m the film, the heating is interrupted preferably in connection with an interruption of the feeding of the package. If the heating occurs by means of heated gas, the interruption may take place by the gas flow being diverted through an outlet of the nozzle means. The diverted flow of air then produces a negative pressure outside the nozzle means, so that the flow through the nozzle means is reversed. Thus, surrounding, cooler air is made to flow past the heated joint and cool it. Downstream of the compression of the heated por- tions, these can be cooled, for example by supplying According to a preferred embodiment of the invention, a negative pressure is produced between the film and the package. This negative pressure contributes to holding the film in place during sealing. Downstream of the sealing, the negative pressure in the partly wrapped package makes the film fit close to the package and counteract expansion of the insulating material in the wrapping process. This implies that the package can be transported past irregularities in the conveying paths without the fibres being damaged. According to an embodiment, the negative pressure is produced with the aid of a suction means on each side of the feeding path, said suction means preferably being a double-walled metal sheet which extends along a distance of the package in the feeding direction, said sheet being formed with recesses towards the package and connected to a source of negative pressure. Such a sheet can be fixedly arranged at its upstream end and, downstream together with the package, be wrapped by the film. At the downstream end of the metal sheets, where the sealing of the film has at least begun, a connection between the metal sheet and the surroundings would therefore be impossible, which means that the metal sheet will be slightly yielding in the lateral direction. A package which is fed past the suction means may thus be allowed to vary in width to some extent without causing too much resistance . It is preferable, downstream of the sealing along the feeding direction according to a technique which is known per se, to carry out sealing and cutting transversely of the feeding direction. When a package is sealed at its downstream end, it is thus wrapped by film on all sides except one, and therefore the negative pressure from the suction means gives a still greater join- ing effect. Each sealing operation transversely of the feeding direction occurs in this way between two packages which are located in a kind of tube, m which a relatively nigh negative pressure prevails. This results in a further advantage as the fed packages in level with the transverse sealing along a distance have no contact with the feeding assembly. Since the packages are firmly compressed, the absence of contact between continuous surfaces in this joint normally results in the material in the packages being allowed to expand, with the ensuing great pressure gradients. However, according to the described embodiment of the invention, the negative pressure in the tube which is fed over the joint contributes to resisting the expansion pressure, so that the material is not allowed to expand significantly. Pressure gradients wnich are detrimental to the material will thus be avoided. Brief Description of the Drawings The present invention will now be described m more detail with reference to the accompanying drawings, wnich for the purpose of exemplification illustrate preferred embodiments of the invention. Fig. 1 is a schematic side view of a device according to the invention adapted to carry out the method according to the invention. Fig. 2 is a schematic cross-sectional view of tπe device in Fig. 1. Fig. 3 is a schematic front view of a nozzle means according to the invention. Fig. 4 is a schematic rear view of the nozzle means Fig. 5 is a longitudinal section of the nozzle means in Figs 3-4 along lines V-V, and a package passing the nozzle means. Description of a Preferred Embodiment 1. General Description Wrapping of material takes place according to an embodiment of the invention along a process chain accord- mg to Figs 1-2. The material, which in the example shown consists of boards 1 of a fibrous insulating material, is fed on a conveyor belt 2 to a compressing assembly 3 where the boards are stacked and compressed. The compressed package 4 is then introduced by a feeding assem- bly 5 into a thin and flexible wrapping material 6 and further to a sealing arrangement 7 according to the invention, where the packages are sealed, first along the feeding direction and then transversely of the feeding direction. The entire device is held together by a stand 8, preferably consisting of a plurality of welded- together beams . 2. Compressing Assembly The compressing assembly 3 may comprise a compress- mg shaft 14 where a stack 26 of boards 1 forms so as to be compressed. The compressed stack is then removed from the shaft, for example by driven belt conveyors 23, 24 being arranged at the upper and lower side of the stack. 3. Feeding Assembly In direct connection with the compressing assembly 3. a feeding assembly 5 is arranged to transport the package a feeding direction B, past the sealing arrangement which will be described below. The feeding assembly 5 comprises a plurality of feeding segments, each segment having at least an upper and a lower conveyor. In the preferred embodiment, the feeding assembly has four segments 30, 31, 32, 33 and all conveyors consist of belt conveyors 30a, 30b, 31a, 31b, 32a, 32b, 33a, 33b. The first feeding segment 30 is arranged in direct connection with the compressing shaft 14 and adapted to receive a compressed package 4 which is discharged from the shaft by the conveyor belts 23, 24 a-c. The belt con- veyors 30a, 30b m this segment are parallel with each other and do not affect the compression of the package. The subsequent feeding segment 31 has belt conveyors 31a, 31b converging in the feeding direction, the distance a between them being at its maximum m connection with the preceding segment, and then decreasing successively. This segment therefore compresses one more package 4, which is conveyed between the belt conveyors. The third feeding segment 32 is arranged to convey a package 4 while being compressed, past the sealing arrangement 7. In the embodiment shown m Figs 1-2, the segments 31 and 32 consist of joint belt conveyors, but it is also possible to make a division into separate belt conveyors . The fourth feeding segment 33 is positioned down- stream of the sealing arrangement 7 and is arranged to feed the wrapped packages 4 to further handling. The feeding assembly 5 is further adapted to supply, during feeding, a wrapping material 6 which is to surround each package. The wrapping material is preferably th and flexible and consists at least partly of a thermoplastic material which after heating is jomable. For example, the wrapping material consists of a possibly transparent plastic film, for example of polyethylene plastic, which is supplied from one or more rolls 34a, 34b. The plastic film 6 runs from each roll 34a, 34b round the edge of one of the belt conveyors 31a, 31b and then between the belt conveyor and the package that is being fed. The plastic film 6 s thus entrained along with the package during feeding. In the illustrated case, the plastic film is fed from two rolls 34a, 34b, a first film 6a covering the upper side of the package and a second film 6b covering its underside. The two films βa, 6b overlap each other along the sides of the package. Fig. 1 shows how the film runs at the beginning of the converging feeding segment 31, but an alternative embodiment (not shown) the film runs between the second 31 and the third 32 segment, i.e. at the beginning of the sealing arrangement 7. At the upstream end of the sealing arrangement 7, turning-down elements 35 are arranged on each side of the feeding path, which are adapted to turn down the plastic film round the sides of each package. Since a continuous film 6 surrounds a plurality of successive packages, it is important for the packages to be fed with a space in between, which allows the below described sealing of the ends. Transducers (not shown) are used to control the feeding, so that, when a package has been completely fed between the converging conveyors, the feeding is discontinued while waiting for the next package. When this arrives from the compressing shaft 14 through the first feeding segment 30, the feeding starts again. In combination with the interruption feeding which arises connection with the sealing of the ends of packages and which will be described below, two mter- ruptions in the feeding of each package thus arise. For a certain length of the packages, these interruptions may, of course, coincide, in which case there will be only one interruption for each package. 4. Sealing Arrangement A sealing arrangement 7 according to the invention is illustrated in Figs 3-5 and comprises means for sealing each package along the sides and means for sealing each package at the ends. The sealing operations are car- ried out in different ways. The sealing along the sides is carried out by the thermoplastic material being heated to at least a part- ly molten state, and then by means of a fluid being compressed under pressure. In connection with the compression, the heated material is cooled, thereby forming a durable joint. According to the preferred embodiment, a suction means is arranged on each side of the conveying path along the segment 32. The suction means may consist of a double-walled metal sheet 40 which is connected to a source of negative pressure 39 and which wholly or partly is coated with Teflon or like material. The inside of the metal sheet 40 is perforated by a plurality of apertures 41, and its downstream end wall 40a is open for transferring the negative pressure. The metal sheet 40 is at its upstream end 40b, ust before the position where the plastic film is turned round the fed packages 4, suspended, for example, from the stand 8 that supports the feeding assembly. There is otherwise no fixed anchoring. The suspension can be completely fixed but can alternatively be articulated in one direction. Outside each metal sheet 40 a nozzle means 42 is arranged, preferably yieldingly loaded against the metal sheet 40. In the shown example, each nozzle means 42 consists of an elongate metal case 43 which is suspended from a pendulum construction 44. The pendulum construc- tion is provided with a control means m the form of a rotatable supporting wheel 45 which operation abuts against the metal sheet 40 and thus holds the case 43 correctly spaced from the film 6. To this end, the metal sheet 40 can be formed with a groove 46 for improved guiding of the supporting wheel 45 (see Fig. 5) . In the side facing away from the conveying path, the case 43 has at least one connection 49 for a feeding means 50 for pressurised, heated fluid, preferably heated compressed air, and at least one connection 51 for a feeding means 52 for a cold fluid, preferably air. Moreover, the case 43 has an outlet 53. In its side facing the conveying path, the case 43 also has a plurality of openings 47, 48 for feeding the fluid in the direction of the metal sheet 40 and the film 6. Preferably, the recesses consist on the one hand of an elongate slot 47 and, on the other hand, a slotted opening 48 positioned the downstream end. When a package 4 is fed m between the belt conveyors in the feeding segment 32, they are simultaneously guided m between the metal sheets 40. The plastic film 6 which has up to now been extended an essentially planar state immediately above and below the package 4, is now by the turning-down elements 35 turned down round the package and the metal sheets m the manner which is best shown in Fig. 5. The negative pressure to which the metal sheet 40 is connected contributes to minimising any space between the package 4 and the metal sheet 40, and to the plastic film 4 being kept place against the metal sheet. Since the metal sheets are only suspended at their upstream ends, they can move down- stream in the lateral direction and thus be adapted to variations the width of the packages. Subsequently the package 4 passes the slot 47 which is formed each case and which supplies heated compressed air 54 from the feeding means 50. The compress- ed air 54 puts the thermoplastic material m an at least partly molten state, and at the same time presses the overlapping portions 55a, 55b against each other so as to accomplish a joining. By partly molten state is meant that the portions 55a, 55b are joined by adhesion to each other or by being completely combined. The Teflon coating of the metal sheets 40 prevents molten plastic from adhering to the metal sheets. Cold air is supplied through the opening 48 from the feeding means 52, thus cooling and curing the portions 55a, 55b. According to a preferred embodiment, the double- walled metal sheets 40 extend along essentially the entire length of the nozzle means 42 and consequently constitute a firm abutment during the entire sealing process . The nozzle means 42 is arranged to interrupt the feeding of heated gas 54 in each interruption the feeding of packages. According to the embodiment illustrated, the feeding is interrupted by the flow of air being diverted to the outlet 53 by means of a diverting element, such as a throttle 56, arranged m each case. The flow of air is preferably diverted such manner that the flow through the gap 47 is reversed and thus air is conveyed away from the welded joint, and surrounding cooler air is made to replace the removed hot air. The sealing at the ends 4a of the package, trans- versely of the feeding direction, occurs in a manner known per se by means of two welding jaws 60 (see Fig. 2) which are movable towards each other and, arranged therebetween, a cutting means, for instance m the form of a cutting thread (not shown) . The jaws 60 and the cutting means are positioned between feeding segments 32 and 33. In the example shown, the aws are arranged above and below the feeding path, but they could, of course, just as well be positioned on both sides of the path. The feeding is discontinued when a transducer (not shown) signals that the last hot -sealed package has reached the downstream end of the segment 32, and the anteriorly positioned package, which is located in the segment 33, is then moved back a distance to achieve a play m the wrapping material 6 between the packages 4. Then the welding jaws 60 are moved towards each other, and the ends 4a of the packages are sealed and separated from each other (see Fig. 2) . The package 4 which is located the segment 33 is now completely wrapped and is fed for continued handling, for example joint wrapping, stacking and loading on pallets. However, the package 4 which is still located in the segment 32 is only surrounded by plastic film on five of its six sides and thus is located in a plastic tube. The tube is fed past the welding jaws 60 to the next welding position, in which the tube contains two packages, one on each side of the welding jaws (see Fig. 1) . In the tube a negative pressure prevails, which is produced by the suction means, and prevents the material in the packages from expanding in level with the welding jaws. 5. Conclusion It will be appreciated that the invention as defined in the appended claims is not restricted by the above description of preferred embodiments. For instance, the feeding assembly can be allowed to be of different design and extent. Moreover, additional steps can be added to the process for adaptation to different needs. The described devices may vary in respect of form as well as material, and the person skilled in the art is expected to make the adaptations as required by a particular situation. The film 6 can be made of an arbitrary, flexible material, such as textile, paper or metal foil. It may be sufficient for the overlapping portions 55a, 55b to be coated with a thermoplastic material, such as plastic or adhesive.

Claims: CLAIMS 1. A method for wrapping a plurality of soft ele- ments (1) , comprising the steps of: stacking the elements, compressing the stack (26) in a direction of stacking, thereby forming a package (4), inserting the package (4) in a feeding direction into a film (6) , preferably a plastic film, which at least partly consists of a thermoplastic material and at least in a partly overlapping manner surrounds the package, sealing the film in the feeding direction, and cutting and optionally sealing the film transversely of the feeding direction, c h a r a c t e r i s e d in that the step of sealing the film (6) in the feeding direction is carried out by applying heat to the portions (55a, 55b) of the film which overlap each other so that they change into an at least partly molten state, and by supplying, from a nozzle means (42) in the direction of the film (6) , a pressurised fluid (54) so that the portions (55a, 55b) are joined. 2. A method as claimed in claim 1, wherein the heating is interrupted in case of interruption of the feeding of the package (4) . 3. A method as claimed in claim 1, wherein the step of sealing the film (6) in the feeding direction is car- ried out by supplying, from a nozzle means (42) in the direction of the film, a fluid having such a temperature and such a pressure that the overlapping portions (55a, 55b) change into an at least partly molten state and are joined. 4. A method as claimed in claim 3, wherein the fluid (54) is diverted in case of interruption of the feeding of the package (4) . 5. A method as claimed in any one of the preceding claims, further comprising the step of cooling the joined portions (55a, 55b) downstream of the nozzle means (42) . 6. A method as claimed in any one of the preceding claims, further comprising the step of producing a negative pressure between the film and the package. 7. A method as claimed in claim 6, wherein the negative pressure is produced upstream of the step of cutting the film transversely of the feeding direction. 8. A device for wrapping a plurality of soft elements, comprising stacking means (12) for stacking the elements, a compressing assembly (3) for compressing the stack, feeding means (30, 31, 32, 33) for inserting a feeding direction the compressed package (4) into a film (6), preferably a plastic film, which at least partly consists of a thermoplastic material and at least in a partly overlapping manner surrounds the package (4) , and a sealing arrangement (7) for sealing the film, c h a r a c t e r i s e d in that the sealing arrangement (7) comprises means (42) for heating the portions of the film which overlap each other and nozzle means (42) for supplying a pressurised fluid for joining the portions. 9. A device as claimed m claim 8, wherein the nozzle means (42) is adapted to supply heated fluid the direction of the film. 10. A device as claimed m claim 9, wherein the nozzle means (42) comprises means (56) for diverting the fluid flow case of interruption of the feeding of the package . 11. A device as claimed claim 9 or 10, wherein the nozzle means (42) is adapted to reversibly supply the fluid. 12. A device as claimed m claims 8-11, wherein the nozzle means (42) further is adapted to supply a cold fluid the direction of the film. 13. A device as claimed in claims 8-12, wherein the nozzle means (42) is yieldably loaded in the direction of the side of the package (4) . 14. A device as claimed in claim 13, wherein the nozzle means (42) is arranged in a pendulum construction (44) to be pivotable towards and away from the side of the package. 15. A device as claimed in claims 8-14, wherein the sealing arrangement (7) further comprises a suction means (40) which is adapted to produce a negative pressure between the package (4) and the film (6) . 16. A device as claimed in claim 15, wherein the suction means on each side of the feeding path comprises a double-walled metal sheet (40) which extends along a part of the package (4) in the feeding direction, said metal sheet (40) being formed with apertures (41) in the direction of package and being connected with a source of negative pressure (39) . 17. A device as claimed in claims 8-16, wherein the sealing arrangement (7) further comprises means (60, 61) for sealing and cutting the film transversely of the feeding direction. 18. A device as claimed in claim 17, wherein the means (60, 61) for sealing and cutting the film trans- versely of the feeding direction is positioned downstream of the suction means (40) .

Inventors: GUSTAFSSON GLENN, GUSTAFSSON, GLENN
Applicants: GUSTAFSSON GLENN, GUSTAFSSON, GLENN
Application year: 2000
Main classification: B65B51
IPC codes: B65B51, B65B63