Core for an endless web of a plastic film

Abstract

A core which can be plugged onto a winding shaft for winding an endless, flexible material web to form a reel ( 10, 60, 70 ), wherein the core has means for adjusting the diameter of its surface to be wound between a rest state of reduced diameter and an expanded working state, and wherein the winding surface is of jointless configuration in the expanded state. A reel can therefore be stored until it is used up, and the core can then be pulled out of the reel and the reel can be surrendered, with the result that the circulation of sleeves is dispensed with.

1 . A winding core which can be plugged onto a winding shaft for the winding of a continuous, flexible plastic film to form a reel ( 10 ,  60 ,  70 ), characterised in that the winding core comprises means for adjusting the diameter of its surface to be wound on between a diameter-reduced rest state and an expanded operating state, with the internal diameter remaining constant, wherein the winding surface in the expanded state is constituted gapless and is supported inwardly all round against the operating pressure in a dimensionally stable manner that is essentially uniform. 
     
     
         2 . The winding core according to  claim 1 , wherein the means comprises a secondary core ( 80 ) elastically expandable in the periphery, the outer surface ( 81 ) whereof forms the surface to be wound of the winding core, and wherein there are moulded-in at its inner side supporting elements running on it over at least the length of the surface to be wound and, in the expanded operating state, lying at a predetermined distance from one another. 
     
     
         3 . The winding core according to  claim 2 , wherein the supporting elements are constituted as shells ( 83  to  85 ), the inner surfaces whereof form sections of the inner surface of the secondary core ( 80 ) and wherein the shells ( 83  to  85 ) preferably run in the form of a helical line along the inner side of the secondary core ( 80 ). 
     
     
         4 . The winding core according to  claim 2  or  3 , wherein the secondary core ( 80 ) comprises an elastically expandable material, preferably a plastic such as polyurethane or rubber, the expandability whereof permits the change in the circumferential length between the rest state and the operating state. 
     
     
         5 . The winding core according to  claim 4 , wherein the supporting elements ( 83  to  85 ) comprise a material which is harder than the expandable material of the secondary core ( 80 ), and are preferably made of sheet metal or glass fibre-reinforced plastic. 
     
     
         6 . The winding core according to  claim 1 , wherein the means comprise a secondary core ( 20 ) elastically expandable in diameter, the length whereof corresponds at least to the windable surface, and which comprises over its length at least one insertion ( 21 ) which permits the change in the length of the circumference of the secondary core ( 20 ) between the rest state and the operating state and, in the expanded states, essentially has the thickness of the secondary core ( 20 ). 
     
     
         7 . The winding core according to  claim 6 , wherein the insertion ( 21 ) runs in the form of a helical line over the length of the secondary core ( 20 ) and the helical line in the region of the windable surface extends over less than a half, preferably less than a third, particularly preferably less than a quarter of a full revolution. 
     
     
         8 . The winding core according to  claim 6  or  7 , wherein the material of the insertion is elastic and preferably elastically deformable with a constant volume. 
     
     
         9 . The winding core according to any one of  claims 6  to  8 , wherein the secondary core ( 20 ) has a hard surface and is preferably made of sheet metal, particularly preferably of sheet steel. 
     
     
         10 . The winding core according  claim 1 , wherein the means comprise a wedge arrangement with a cone ( 50 ) and at least two, preferably at least three segment shells ( 30  to  32 ) constituted as a mirror image of the cone ( 50 ), said segment shells being constituted such that the outer faces of the segment shells ( 30  to  32 ) lying operationally on the cone ( 50 ) lie on a common cylindrical lateral surface and enclosed between them in each case a gap ( 39  to  41 ) of predetermined width, wherein the length of the segment shells ( 30  to  32 ) and preferably that of the cone ( 50 ) corresponds at least to the length of the windable surface of the winding core and the cone ( 50 ) comprises a concentrically axially running drill hole ( 52 ) which permits it to be plugged onto a winding shaft. 
     
     
         11 . The winding core according  claims 2  and  10  or  6  and  10 , wherein the secondary core ( 20 ) is positioned on the segment shells ( 30  to  32 ) in such a way that the supporting elements each overlap an associated gap ( 39  to  41 ) or the at least one insertion ( 21 ) rests completely on one of the segment shells ( 30  to  32 ). 
     
     
         12 . The winding core according  claim 1 , wherein the means provides a pneumatic element constituted as a hollow cylinder and disposed concentrically with the longitudinal axis of the winding core ( 100 ), said pneumatic element extending along the windable surface of the winding core, preferably forming the windable surface with its outer face ( 103 ) and, under operating pressure, expanding the winding core into the expanded operating state, wherein the winding core assumes the diameter-reduced rest state in the pressure-relieved state of the pneumatic element. 
     
     
         13 . The winding core according  claim 12 , wherein the pneumatic element comprises inner peripheral ribs ( 104 ), which limit its maximum external diameter in a predetermined manner, and wherein a hose made of flexible, non-expandable fabric is preferably provided on the outer side of the pneumatic element, said fabric surrounding the latter tightly and keeping it in a cylindrical shape in the expanded state of the pneumatic element. 
     
     
         14 . The winding core according  claim 1 , wherein the means comprise a hose ( 71 ) made of an elastic material, preferably polyurethane, the outer surface ( 72 ) whereof forms the windable surface, wherein the elastic material can be stretched in such a way that the hose ( 72 ) can be expanded from the diameter-reduced rest state to the expanded operating state. 
     
     
         15 . The winding core according  claims 10  and  14 , wherein the hose ( 71 ) surrounds the segment shells ( 30  to  32 ) and, expanded by the latter in the expanded operating state, lies on the latter. 
     
     
         16 . The winding core according  claim 14 , wherein the means comprise a secondary core ( 20 ) expandable in diameter and slit over its length, the length whereof corresponds at least to the windable surface, wherein the slit is preferably constituted in the form of a helical line and permits the change in the circumference of the secondary core ( 20 ) between the rest state and the expanded operating state and wherein the hose surrounds the secondary core ( 20 ), is widened by the latter in the expanded operating state and lies on the latter. 
     
     
         17 . The winding core according  claims 2 ,  6  and  10 , wherein the hose surrounds the secondary core ( 20 ), which in turn rests on the segment shells ( 30  to  32 ). 
     
     
         18 . The winding core according  claim 2 , wherein the supporting elements are constituted as supporting shells, which run in the interior of the winding shaft core on a common diameter between the surface to be wound and its inner surface and, in the expanded state of the winding shaft, lie side by side at a distance from one another, and wherein the supporting shells are disposed in respect of the radially expandable segments in such a way that each intermediate space between the radially expandable segments is overlapped by an associated supporting shell. 
     
     
         19 . The winding shaft according  claim 18 , wherein the supporting shells taper from a central region between the longitudinal edges towards the latter.