An apparatus for tube forming

Abstract: Apparatuses for reforming web-shaped packaging material into tube form operate, in prior art packaging machines, with the aid of annularly disposed forming rollers which cause the longitudinal edges of the web to overlap so that they can be sealed to one an­ other. In order to prevent the packaging material tube from being en­ trapped between the rollers (12), the rollers may be provided with one chamfered and one straight roller edge (18, 19) which cooperate such that the nip therebetween is directed more or less tangentially to an adjacent portion of the packaging material tube.

Description: TECHNICAL FIELD The present invention relates to an apparatus for reforming of a web-shaped flexible material into tube form by means of rotary forming rollers which define a material aperture. BACKGROUND ART In modern packaging machines for the manufacture of, for example, parallelepipedic packages or cartons for liquid contents such as juice or milk, a web-shaped flexible packaging material is progressively reformed into tube form in that its both longitudinal edges are united and sealed together. After the supply of the desired contents to the packaging material tube, this is transversely sealed at even spacing and is severed for the formation of individual packages or cartons which, by possible additional forming processing, may be given parallelepipedic configuration. The reforming of the originally planar packaging material into tube form takes place with the aid of forming devices which, int. al. include forming rollers which are annularly disposed about a substantially circular aperture for the packaging material. The forming rollers are freely rotary and together force the packaging material to assume a substantially circular cross-section so that its longitudinal edges may be sealed to one another. The annularly disposed forming rollers have hitherto normally had conical end surfaces which are located slightly spaced from one another or substantially abut against one another along a line directed from the centre of the rollers towards the centre of the packaging material tube (see, for example, SU-889 538). In particular in the employment of thin and highly flexible packaging material - as is the case in the manufacture of small carton sizes - it may happen, in such a situation, that the packaging material is entrapped in the nip between the end walls of two mutually adjacent forming rollers so that a longitudinal crease line is formed on the packaging material tube, which occasionally results in rupture of the entire material web or, in any event, gives the subsequent tube the incorrect configuration. With a view to obviating this drawback, attempts have been made in the art to adjust the mutual spacing of the forming rollers so that minimum clearance, or even no clearance occurs between the ends of the forming rollers, but such attempts have enjoyed only limited success and this problem still defies solution in the employment of extremely thin packaging material types. There is, hence, a need in the art to devise, in that type of packaging machine which manufactures packages or cartons from web-shaped flexible material, an apparatus for forming the tube which does not suffer from the above-considered drawbacks. OBJECTS OF THE INVENTION One object of the present invention is, therefore, to devise an apparatus for reforming of web-shaped flexible material into tube form by means of rotary forming rollers which define a material aperture, the apparatus being so designed that the packaging material may freely and without hindrance be formed into tube form without longitindal crease formation occurring and without the packaging material web becoming entrapped or otherwise damaged during the reforming process. A further object of the present invention is to devise an apparatus of the above-mentioned type which, in a conventional manner, operates with freely rotary forming rollers and, consequently, is readily capable of being integrated into existing packaging machines. Yet a further object of the present invention is to realise an apparatus of the above-mentioned type in which the forming rollers included therein are simple and economical to manufacture. SOLUTION The above and other objects are attained according to the present invention in that an apparatus of the type described by way of introduction is characterised in that the forming rollers have partly mutually facing end surfaces which substantially abut against one another at the portion of the rollers facing the material aperture, each pair of mutually facing roller edges including one chamfered and one straight roller edge. Preferred embodiments of the apparatus according to the present invention have further been given the characterising features as set forth in the appended subclaims. By designing, in accordance with the present invention, the forming rollers with cooperating pairs of chamfered and straight roller edges, the direction of the space or nip occurring between the rollers will extend partly tangentially to the packaging material tube and not, as previously, radially - which entails that the rollers no longer "grasp hold of" the tube material but instead guide the tube material down through the tube forming apparatus without crease formation or other damage. This effect may be achieved in two different ways, viz. either in that each roller has one chamfered and one straight end edge, or in that every second roller has chamfered edges and every other roller has straight edges. Whichever option is chosen may, for example, be determined by the size of the apparatus as a whole or by particular requirements, the important feature simply being that the above-mentioned angle is retained. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS One preferred embodiment of the apparatus according to the present invention will now be described in greater detail with particular reference to the accompanying, schematic Drawings which merely illustrate those details which are indispensible for an understanding of the invention. In the accompanying Drawings: Fig. 1 illustrates the principles for reforming a packaging material web into individual packages or cartons in a packaging machine of per se known type; and Fig. 2 shows, partly in section, one preferred embodiment of the tube forming apparatus according to the present invention. DESCRIPTION OF PREFERRED EMBODIMENT The apparatus according to the present invention is applicable to all types of packaging machines which manufacture packages or cartons by reforming a web-shaped flexible packaging material into tube or cylinder form. The progressive reforming and processing of a packaging material web during the manufacture of parallelepipedic packages or cartons of known type are illustrated in Fig. 1, in which the outer contours of a prior art packaging machine are intimated. This machine is supplied with flexible, web-shaped packaging material in the form of a reel 1, from which the packaging material web 2 is unwound and fed substantially upwardly through the packaging machine with the aid of guide rollers 3 of known type. At the uppermost region of the machine, the packaging material web 2 passes over a bending roller 4 and is thereafter guided substantially vertically downwards through the packaging machine with the aid of various types of forming devices 5, int. al. a tube forming apparatus 6 according to the invention. By means of the tube forming apparatus 6, the packaging material web is folded such that its two longitudinal edges overlap one another and may be sealed with the aid of a longltudinal sealing device 7 which, in the simplest case when the packaging material web is coated with thermoplastic material, may consist of a hot air nozzle. A filler pipe 8 extends down concentrically in the tube, the pipe extending in through the upper open end of the tube and discharging in the tube immediately above that point where the tube is reformed into individual packages or cartons. This is effected by means of forming and sealing jaws 9 which cooperate pairwise for compressing together and transversely sealing the packaging material tube. The forming and sealing jaws 9 also cater for a certain reforming of the packaging material tube which, thereafter, is severed transversely in the sealing zones so that individual packages or cartons 10 are created which, by possible additional forming work, may be given, for example, the illustrated substantially parallelepipedic configuration. The tube forming apparatus 6 according to the present invention, disposed in the above-described, prior art packaging machine or a similar packaging machine, is illustrated in greater detail in Fig. 2, in which the apparatus is viewed straight from above, i.e. substantially seen from the position of the bending roller 4 (Fig. 1). A material aperture 11 is disposed centrally in the apparatus according to the present invention, the aperture being substantially circular and through which the packaging material is, during the reforming process, displaced substantially continuously downwards through the packaging machine. The circular material aperture 11 is formed by a number of forming rollers 12 which, in order to impart to the material aperture 11 its desired circular configuration, are of progressively increasing diameter towards their end surfaces. The forming rollers 12 are freely rotatably suspended about shafts 13 which, in the illustrated number of forming rollers, six in all, have a mutual angle of 120 o . The shafts13 are annularly disposed in a bracket 14 which, by means of an anchorage 15, is rigidly connected to the frame of the packaging machine proper. Each forming roller 12 includes two substantially planar end surfaces 16 and a working surface 17 disposed between the end surfaces and engaging with the packaging material. Between each respective end surface 16 and the working surface 17, each forming roller 12 displays one chamfered edge 18 and one straight edge 19 which, because of the mutual spacing of two adjacent forming rollers, substantially abut linearly with one another and form a nip 20 along a rolling radius extending towards the packaging material tube. While direct abutment would be desirable, this is normally not possible for practical reasons (tolerances, wear etc.), but instead the nip is set with the smallest possible clearance, for example between 0.1 and 0.5 mm. In the illustrated embodiment, each forming roller 12 has one chamfered edge and one straight edge, and the rollers 12 are turned in such a manner that each straight edge 19 cooperates with an adjacent chamfered edge 18 on the neighbouring roller. However, it is also possible to provide the forming apparatus according to the present invention with two different types of forming rollers, namely one roller type with chamfered edges at both ends and one roller type with straight edges at both ends, which, in such instance, are placed alternatingly so that, also here, one chamfered edge meets and cooperates with a neighbouring straight edge. This latter version of the present invention (not shown) may be advantageous in packaging material tubes of very small diameter, but may also be preferred for other reasons. Each chamfered roller edge 18 should, where it borders with the packaging material tube, extend towards the surface of the packaging material tube as tangentlally as possible so as to avoid the risk that the packaging material tube becomes entrapped between the rollers, and preferably each chamfered roller edge is at an angle to the centre axis of the roller which is equal to the angle v indicated in Fig. 2 between the end surface of an adjacent roller and the above-mentioned centre axis 13 (60 o in the illustrated embodiment of the present invention). As a result of this design, the nip 20 between one chamfered edge 18 and the end surface 16 of an adjacent forming roller 12 will extend partly tangentlally to the packaging material tube, which has proved in practice to greatly reduce the risk that the packaging material be entrapped by the nip and clenched under longitudinal crease formation during the downward displacement of the packaging material through the tube forming apparatus. On operation of the apparatus according to the present invention, the packaging material web 2 is progressively displaced by the packaging machine proper from the reel 1, via the guide rollers 3 and bending roller 4 and, thereafter, during reforming into tube form, substantially vertically downwards through the packaging machine to the forming and sealing jaws 9. When the packaging material approaches the tube forming apparatus according to the invention, it first passes the forming devices 5 which, as a preparatory measure for the tube formation, fold both of the longitudinal edges of the packaging material web slightly towards one another. When the packaging material web 2 reaches the tube forming apparatus 6 according to the invention, it passes through the substantially circular material aperture 11 between the working surfaces 17 of the forming rollers 12 and is hereby given a substantially circular cross-sectional configuration with partially overlapping longitudinal edges which are sealed to one another by means of the sealing device 7. Since the nip 20 between the mutually adjacent forming rollers 12 does not extend radially to the centre of the material aperture 11 but substantially tangentially to the surface of the packaging material 2, the packaging material will be guided down through the material aperture 11 without being nipped between the rollers 12 and without being damaged or otherwise disrupted on its passage. In practice, this has proved to function most satisfactorily even in extremely thin packaging material of the type which is employed for very small packages or cartons.

Claims: An apparatus for reforming web-shaped, flexible material into tube form by means of rotary forming rollers (12) which define a material aperture (11) characterised in that the forming rollers (12) have partly mutually facing end surfaces (16) which substantially abut against one another at the portion of the rollers (12) facing towards the material aperture (11), each pair of mutually facing roller edges (18, 19) consisting of one chamfered and one straight roller edge. The apparatus as claimed in Claim 1, characterised in that a chamfered roller edge (18) is at an angle to the centre axis (13) of the roller which is equal to the angle between the end surface (16) of an adjacent roller and said centre axis. The apparatus as claimed in Claim 1 or 2, characterised in that each roller (12) has one chamfered and one straight end edge (18, 19 respectively). The apparatus as claimed in Claim 1 or 2, characterised in that every second roller (12) has chamfered end edges (18) and every other roller (12) has straight end edges (19). The apparatus as claimed in any one or more of the preceding Claims, characterised in that the forming rollers (12) are substantially annularly disposed in a bracket (14). The apparatus as claimed in any one or more of the preceding Claims, characterised in that the forming rollers (12) are freely rotatable. The apparatus as claimed in any one or more of the preceding Claims, characterised in that the forming rollers (12) are of increasing diameter towards the end surfaces (16). The apparatus as claimed in any one or more of the preceding Claims, characterised in that the material aperture (11) is substantially circular. The apparatus as claimed in any one or more of the preceding Claims, characterised in that the end surfaces (16) of the forming rollers (12) are planar.

Inventors: ANDERSSON HELGE, ANDERSSON, HELGE
Applicants: TETRA LAVAL HOLDINGS & FINANCE, TETRA LAVAL HOLDINGS & FINANCE S.A.
Application year: 1990
Main classification: B65B9
IPC codes: B65B9