Improvements in pocketed springs

Abstract

A pocketed spring unit (100, fig.1) including a plurality of strings (110, fig.1) of pocketed springs 1100 joined together, wherein each string comprises two portions of pocketing material 1200 joined

Description

The present invention relates to a pocketed spring unit, and to a method and apparatus for manufacturing a pocketed spring unit. Pocketed springs, otherwise known as encased springs, are used as core units in upholstered articles such as mattresses. Most pocketed spring units comprise coil springs of wire encased individually in pockets of fabric or other material formed by folding over a sheet of fabric to create two leaves that envelope the springs, and then joining the leaves together between the springs so as to form a linear string of springs. The strings are then joined together to form an array of springs as a pocketed spring unit. The joining of the strings together to form an array may be achieved for example by gluing or welding the strings together along the cylindrical surfaces of the pocketed springs, one string to the next, and so on until the unit is formed, or else by arranging the strings beside each other in the manner of an array, and then attaching a cover sheet of fabric to one or both of the axially spaced ends of the pocketed springs, above and below. When such a unit reaches the end of its useful life there is a need to recycle as much as possible of its material. The coil springs of wire, typically of steel, inside the pockets are recyclable, but with previously considered units it can be labour intensive and therefore expensive to remove them from their pockets. 5 In our UK Patent Number GB 2576216 B we describe a method of perforating the pockets of springs to create a line of weakness that can be used to open the pockets at a time of recycling. 10 In other example of the prior art, methods of manufacture of pocketed spring units have utilised a perforation step, in which a device has been used to perforate the pockets of springs in order to promote the circulation of air therein. 15 Embodiments of the present invention aim to provide an improved pocketed spring unit and method and apparatus for making a unit. The present invention is defined in the attached independent 20 claims, to which reference should now be made. Further, preferred features may be found in the sub-claims appended thereto . According to one aspect of the present invention, there is 25 provided a pocketed spring unit including a plurality of strings of pocketed springs joined together, wherein the string comprises two leaves of pocketing material that are joined together at a plurality of positions to form a plurality of spring pocket sides, and an axial end seam 30 extending longitudinally along the string and forming axial spring pocket ends, which seam comprises an intermittent weld for acting as a tear guide when the string is to be forced open. The seam preferably comprises an intermittent ultrasound weld. According to another aspect of the present invention, there is provided a pocketed spring unit including a plurality of strings of pocketed springs joined together, wherein the string comprises two leaves of pocketing material that are joined together between the springs to form pockets, and an axial end seam extending longitudinally along the string, and closing it substantially at the axial ends of the springs, wherein one or more of the pockets has at least one ventilation aperture in an axial end region of the spring. The leaves, or plies, of pocketing material preferably comprise a single sheet of material that is folded in two. Preferably the ventilation aperture comprises a discontinuity in the pocketing material and may include a flap of pocketing material. In a preferred arrangement, at least one axial end region of the spring has a pair of ventilation apertures, which pair of apertures preferably exhibit symmetry. According to another aspect of the present invention, there is provided a method of manufacturing a pocketed spring unit comprising a plurality of strings of pocketed springs joined together, wherein the method comprises joining together two leaves of pocketing material at a plurality of positions to form a plurality of spring pocket sides, and joining the leaves at an axial end seam extending longitudinally along the string to form a plurality of axial spring pocket ends, wherein the seam is formed by an intermittent weld to create a tear guide when the string is to be forced open. The method preferably includes forming the seam as an intermittent ultrasound weld. According to another aspect of the present invention, there is provided a method of manufacturing a ventilated pocketed spring unit comprising a plurality of strings of pocketed springs, wherein the method comprises forming a string of pockets for the springs by joining two leaves of pocketing material at a plurality of positions to form spring pocket sides, forming an axial end seam extending longitudinally along the string to close an axial end of the string of pockets, and making a cut in the pocketing material at an axial end of at least one pocket before inserting a spring into the pocket. In a preferred arrangement, the method includes making a cut through both leaves of pocketing material prior to inserting the spring. Once the spring is inserted, the or each cut forms a ventilation aperture for the pocket. In a preferred arrangement, the cuts are made by an ultrasonic welding apparatus. The pocket sides and axial end seam(s) are also preferably formed by an ultrasonic welding apparatus, which may conveniently be a common ultrasonic welding apparatus. The invention may include any combination of the features or limitations referred to herein, except such a combination of features as are mutually exclusive, or mutually inconsistent. A preferred embodiment of the present invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, in which: Figure 1 shows schematically a part of a previously considered core unit of pocketed springs; Figure 2 shows a part of a single string of springs forming part of the core unit of Figure 1; Figure 3 shows in schematic perspective view a part of a string of springs in accordance with an embodiment of the present invention; Figure 4 shows the string of Figure 4 in plan; and Figure 5 shows a part of a string of pockets prior to inserting springs, in accordance with an embodiment of the present invention. Turning to Figure 1, this shows generally at 100 a part of a pocketed spring unit, such as is used in a mattress core. Only a relatively small number of springs are shown and the unit would typically contain many more springs in a real mattress . The unit 100 is made up of a plurality of linear strings 110, each comprising a plurality of springs 120 encased within a pocket of material, such as non-woven polyester. The pockets have been formed by joining together two plies / leaves / portions of pocketing material at positions between the springs and around the edges. Figure 2 shows a part of one of the strings. The strings are joined together either by gluing them along their cylindrical sides where the strings meet, or else may be welded together or connected to a common cover sheet (not shown). Figure 3 shows generally at 1000 a short part of a string of springs according to an embodiment of the present invention. The string comprises springs 1100 (one is shown in broken lines) encased within pockets formed between leaves / plies / positions 1200 of pocketing material joined together between the springs at positions P, and at edges E and top seam S. In this example, the leaves are portions of a common sheet that has been folded at one axial (bottom) end, though in an alternative embodiment (not shown) the leaves could be from separate sheets, which would require welding to form a bottom seam. The joining of the leaves 1200 is done by ultrasonic welding, in which the leaves are pressed together between a sonotrode and an anvil (not shown), before applying an electrical signal to the sonotrode. This causes the material sheets to vibrate together and the friction liberates heat energy which fuses together the sheets. Whereas the welds P between the pockets and at the edge E are substantially continuous, the weld forming the top seam S is intermittent, i.e., the weld has spaces where there is no fusing of the pocketing material. This is depicted as a broken line in the drawing. When a mattress core comes to the end of its usable life and must be recycled, the pockets may be readily torn open by pulling them, leading to a neat tearing of the pockets along the top seam. The intermittent welds guide the direction of the tear and facilitate the ready opening of the pockets. At axial ends of the pockets are ventilation apertures V which allow air to circulate within the core during normal use. The act of compressing and decompressing the springs in their pockets, such as happens when a user sits or lies on the mattress, forces air through the ventilation holes, which helps to prevent the build up of moisture in the interior of the core. Figure 4 shows the ventilation apertures V from above. It can be seen that the apertures each comprise a cut in the pocketing material - which in this example is an arc-shaped cut - leaving a small flap of material to open and close with the airflow in use. The apertures are arranged in this example two to a pocket and either side of the longitudinal seam S. Figure 5 shows a part of a string of pockets in an earlier stage of production, prior to insertion of the springs. The ultrasonic tools have made substantially continuous welds at positions P to create the sides of the pockets and at the edge E. The apertures V have been made with ultrasonic tools (which may advantageously be parts of the same tools). The parts of the ultrasound tools that are used to make the apertures V are sharp and the pressure and energy release causes the material of both superposed sheets 1200 to become cut. When a spring 1100 is subsequently inserted (in the direction of Arrow A - towards the folded end), the pocket opens out into the approximately cylindrical shape shown in Figures 3 and 4, leaving two symmetrical apertures on either side of the seam S. Other shapes and numbers of apertures can be used. Finally, the intermittent weld is made to form the longitudinal seam S closing the pockets, which will ultimately be used to tear open the pockets at the end of life. Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance, it should be understood that the applicant claims protection in respect of any patentable feature or combination of features referred to herein, and / or shown in the drawings, whether or not particular emphasis has been placed thereon.

Claims

l.A pocketed spring unit including a plurality of strings of pocketed springs joined together, wherein the string comprises two portions of pocketing material that are joined together at a plurality of positions to form a plurality of spring pocket sides, and an axial end seam extending longitudinally along the string and forming axial spring pocket ends, which seam comprises an intermittent weld for acting as a tear guide when the string is to be forced open.

2. A unit according to Claim 1, wherein the seam comprises an intermittent ultrasound weld.

3. A pocketed spring unit including a plurality of strings of pocketed springs joined together, wherein the string comprises two portions of pocketing material that are joined together between the springs to form pockets, and an axial end seam extending longitudinally along the string, and closing it substantially at the axial ends of the springs, wherein one or more of the pockets has at least one ventilation aperture in an axial end region of the spring.

4. A unit according to Claim 3, wherein the ventilation aperture comprises a discontinuity in the pocketing material and may include a flap of pocketing material.

5. A unit according to Claim 3 or 4, wherein at least one axial end region of the spring has a pair of ventilation apertures, which pair of apertures preferably exhibit symmetry.6.A method of manufacturing a pocketed spring unit comprising a plurality of strings of pocketed springs joined together, wherein the method comprises joining together two portions of pocketing material at a plurality of positions to form a plurality of spring pocket sides, and joining the portions at an axial end seam extending longitudinally along the string to form a plurality of axial spring pocket ends, wherein the seam is formed by an intermittent weld to create a tear guide when the string is to be forced open.7 . A method according to Claim 6, wherein the method includes forming the seam as an intermittent ultrasound weld.

8. A method of manufacturing a ventilated pocketed spring unit comprising a plurality of strings of pocketed springs, wherein the method comprises forming a string of pockets for the springs by joining two portions of pocketing material at a plurality of positions to form spring pocket sides, forming an axial end seam extending longitudinally along the string to close an axial end of the string of pockets, and making a cut in the pocketing material at an axial end of at least one pocket before inserting a spring into the pocket.9.A method according to Claim 8, wherein the method includes making a cut through both portions of pocketing material prior to inserting the spring.10.A method according to Claim 9, wherein the cuts are made by an ultrasonic welding apparatus.

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