Apparatus for Shirring a Tubular Casing

Europaisches Patentamt J European Patent Office © Publication number: 0159 159 B1 Office europeen des brevets

® Priority: 30.03.84 GB 8408330 Proprietor: DEVRO, INC. One Johnson & Johnson Plaza @ Date of publication of application: New Brunswick New Jersey 08933(US) 23.10.85 Bulletin 85/43 Inventor: Temple, Stephen © Publication of the grant of the patent: 66 Girton Road 11.09.91 Bulletin 91/37 Girton Cambridge(GB) Inventor: Jones, Nigel John © Designated Contracting States: 3 Gladeside CH DE FR GB LI SE Bar Hill Cambridge(GB) Inventor: Syrop, Alan Nigel (55) References cited: 35 St. Barnabas Road EP-A- 0 077 065 DE-A- 2 140 682 Cambridge(GB) FR-A- 1 601 519 FR-A- 2 504 894 GB-A- 922 908 US-A- 3 688 343 Representative: Jones, Alan John et ai CARPMAELS & RANSFORD 43 Bloomsbury Square London, WC1A 2RA(GB)

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Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition LLJ shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid (Art. 99(1) European patent convention). Rank Xerox (UK) Business Services EPO 159 159 B1

Description

This invention relates to an apparatus for shirring a tubular casing such as collagen or regenerated cellulosic casing of the kind employed in the manufacture of sausages. 5 It is known to pass a casing, inflated by air pressure, over a mandrel and between shirring belts or toothed wheels (also known as paddles) having teeth designed to produce a particular fold formation during shirring. It has been proposed in the past that the teeth should be so designed as to produce a helical primary fold in the casing. DE-A-21 40682 shows a shirring apparatus having toothed rolls in which the surfaces of w contact of the teeth with the tubular casing form a helicoidal surface around the mandrel. Three rolls are used in conjunction so aligned as to form a helix when the teeth contacting the casing are diametrically opposite each other and at the position of closest to the adjacent wheel, i.e. on a line joining the centres of the paddles or a position called for convenience, bottom, dead centre position. It might be assumed that to do this the teeth of a pair of rolls or of three rolls used in conjunction should be so aligned as to form a 75 helix when the teeth contacting the casing are diametrically opposite each other and adjacent to each called for convenience the "bottom dead centre position". We have found that this assumption is incorrect. We have found this assumption to be incorrect since the sweep of the paddle leaving the mandrel and continuing on its rotation immediately interferes with, and deforms the helical pattern. Also the helical pattern is formed on the casing at the previously described position while the slug is formed downstream of 20 this point. An object of the invention is to provide a configuration of shirring wheels and a method of operating those wheels which will enable a shirred stick to be produced substantially without discontinuities in the primary fold which occur in use of prior art machines. In accordance with the present invention there is an apparatus for shirring a tubular casing in which 25 there is at least one pair of toothed shirring wheels in which the teeth of the wheels together form a helical surface relative to a mandrel characterised in that the wheels sweep a helical line along a circle of a predetermined radius 'r\ and the teeth on said shirring wheels are so designed that at the point of contact of the leading edge of a tooth of a shirring wheel with the outside diameter of the shirred casing i.e. at the point where the casing has already been pushed into a fold and the fold is about to be ironed, the leading 30 edges of teeth on adjacent wheels are in substantially helical alignment, the geometry of the teeth being such that, in use, after a fold has been formed in the casing, the newly formed fold is pressed down, or ironed, into its final shape thus forming the sharply defined crease or fold line known as the primary fold, said point of contact occurs when the leading edges of the adjacent teeth of the wheels are at an angle 'A1 of a few degrees past the bottom dead centre position, i.e. the point of closest contact between the wheels 35 where

A = Cos"1 R - r ; R

A being the angle in degrees of the leading edges of the adjacent teeth past the bottom dead centre position; R being the minimum distance of the tooth surface from the shirring wheel axis; and 45 r being the predetermined radius of the shirred casing, and R being greater than r. The helical pattern in DE-A-21 40682 is formed at a diameter equal to the mandrel diameter which is the inner diameter of the slug while the primary fold is on the outer diameter of the slug. Therefore the geometry of the cut out and the flexibility of the paddles are arranged to match the outside diameter of the slug. The helical alignment should be precise, but if three wheels are used it may be sufficient that the so tooth form is a straight line. Each tooth is preferably formed with a groove of substantially semi-circular section, in a radial plane, in its outer face and "R" is then the radius through the shirring wheel axis of the base of the groove in the tooth. The form of the teeth is a very important aspect of the present invention, the teeth are spaced round 55 the wheel at a circumferential distance apart so that the mark/space ratio lies in the range 3:4 to 4:3. The preferred mark/space ratio is 1:1. The mark/space ratio is defined as the nominal ratio between the tooth thickness and the gap between teeth measured in the same direction, i.e. a mark/space ratio of 1:1 means that half the circumference of the EP 0 159 159 B1

paddle roll is tooth and half the gap between the teeth. The features which dictate the selection of the mark/space ratio are that a bubble must be allowed to form in the space, which leads to shirr formation, and so there must be sufficient space between the leading edge of one tooth and the trailing edge of the next one to allow a buckle or bubble to form. On the other hand if a very thin tooth is adopted it becomes more 5 difficult to prevent the casing from re-inflating. The active part of the tooth, that is the surface of the tooth which comes into contact with the casing or shirred material, is enclosed by concavo-convex surfaces.called for convenience the face of the tooth, and the flanks of the tooth. The intersections of the face, or crest, of the tooth and the flanks are termed, for convenience the edges. For a given direction of rotation one edge will lead the other and for convenience 10 they are differentiated as the leading and trailing edges. In accordance with the invention the curvatures of the crest or face surface are derived from the diameter of the paddle and the desired slug diameter as follows: The crest surface is part of a groove of substantially semi-circular cross section in a radial plane and is uniform at all points around the shirring wheel. The radius of the radical cross section of the groove is that 75 of the desired finished slug outside diameter less a factor which takes account of the flexing of the teeth during shirring. This factor will depend upon the stiffness of the paddle material and the thickness of the tooth forms employed but will result in a radius noticably smaller than the casing. The amount by which the radius of the cross section of the tooth is reduced may be between 15 and 30% and in a typical case would be 20 between 20 and 30%. The leading edge of each tooth is defined by a series of points on the groove which cross the outside diameter of the slug coincidentally with the desired fold line on the casing, normally a helical fold. The trailing edge of each tooth is defined by a series of points approximately parallel to the leading edge such that on any circular section perpendicular to the axis the ratio of the circumferential length 25 between successive points where the leading and trailing edges cut that section and the circumferential length between either point and the next such point is constant. Each flank surface of each tooth is formed so that it meets the crest or face of the tooth at a nominally constant angle, called for convenience the rake angle. Thus a flank surface at a nominally constant angle is presented to the casing at all points around its periphery. 30 The shirring wheels or paddles perform three different functions. Firstly they move the casing along towards the shirring area and this is known as driving the casing. Secondly they displace the casing to initiate a fold in the casing which is known as layering. Thirdly they press down the initially formed fold into its final shape forming the sharply defined crease or fold line which is known as the primary fold. This process is known as ironing. 35 Driving the casing is difficult particularly when only two wheels or paddles are used. In order to improve the drive it is preferable, in accordance with the invention, to introduce a controlled degree of flexibility in the wheels or paddles in the cylindrical direction of the paddle wheel whilst retaining the torsional stiffness of the wheel. Thus, in accordance with another aspect of the invention the wheels or paddles are provided with 40 flexible teeth. Preferably this flexibility is brought about by means of a series of selected cut-outs in the outer walls of the wheel and by selection of a suitable rubber or rubber like material for the wheel. The cut- outs in the wheel are designed to produce uniform flexibility throughout the circumference of the wheel. The flexibility is preferably related to the flexibility of the material of the casing so as to produce sufficient interference between the wheel and the casing to drive a casing. 45 Having achieved the necessary drive we found that the interference between the wheel and casing is far too great during the formation of each primary shirr fold. By making the wheel flexible we overcome this problem in that sufficient interference is provided for drive without an excess of interference during the formation of the primary folds. Although the clearance between wheels particularly with two wheels in accordance with the preferred 50 embodiment of this invention, is preferably nominal, i.e. the wheels are almost touching, it is also possible and a feature of this invention that the wheel might be locked in phase by inter-engaging teeth on the two wheels. In prior art constructions the teeth are in the form discrete teeth attached to the wheel or formed on the wheel without connecting circumferential walls. 55 To control the strength and flexibility of the wheel we have found it desirable to join the helical teeth by circumferential walls so that in effect the teeth are cut out from a solid wall. Formation of these walls also helps to control the flexibility. When a casing is shirred the resultant compact shirred casing, known as a stick, may contain a EP 0 159 159 B1

considerable length e.g. 24 metres of casing in a relatively short length of "stick", e.g. 23 cms. The ratio between the original length of the casing and the length of the shirred stick is defined as the compression ratio, the length of the shirred stick being measured between the peaks on the first and last of the primary folds. 5 A more accurate way of indicating the amount of casing which is included in a given shirred stick, taking account of the thickness of the material of which the casing is made, is to define in terms of "packing efficiency". The packing efficiency is the ratio of the volume of a casing when laid flat (before shirring) divided by the effective volume of the annular slug or stick, expressed as a percentage. It is calculated by the following formula: 10

Length of unshirred casing x 2 x wall thickness x width of laid flat casing x 100 Stick or slug length x PI x (outside diameter of stick2 75 4 - bore of stick2 )

(Width of laid flat casing is known as "lay-flat"). 20 The thickness of the material is preferably measured by use of an Elcometer thickness monitor. By use of the present invention it is possible to produce sticks having increased compression ratios compared with those produced by other machines. In accordance with the present invention a shirred stick has a compression ratio in the range 95 to 140. This is achieved without reduction of the bore or detriment to the run-out properties of the shirred stick. Run-out is the de-shirring of the stick during filling in a 25 sausage making process. Also in accordance with the invention it is possible to produce a shirred stick having an increased packing efficiency, the packing efficiency being in the range 45 to 90%. The advantage of the increase in compression ratio and packing efficiency is that more rigid shirred sticks, despite increased internal bore diameters, can be produced. 30 In the accompanying drawings:- Figure 1 is a side elevation showing portions of a shirring machine embodying the present invention; Figure 2 is a plan of the central part only of the machine illustrated in Figure 1 ; Figure 3 is an enlarged diagrammatic plan of a portion of the machine illustrating the tapered mandrel used in the present invention; 35 Figure 4 is an enlarged portion of the tapered mandrel shown in Figure 3; Figure 5 is a circumferential development of a portion of one of the shirring wheels shown in Figures 1 to 3; Figure 6 is a side elevation of a portion of one of the shirring wheels; Figure 7 is a part sectional plan on the line 7-7 shown in Figure 6; 40 Figure 8 is a section on the line 8-8 shown in Figure 5; Figure 9 is an enlarged diagrammatic illustration of the central portion of Figure 3 showing the tapered mandrel and its relationship to the teeth of the shirring wheels; Figure 10 shows diagrammatically the formation of a primary fold; and Figure 11 is a further stage in the formation of the fold shown in Figure 10. 45 The shirring machine shown in Figures 1 and 2 is diagrammatically represented and includes only those parts of the machine which are essential to an under standing of the invention. As seen in Figure 1, on the left of the machine is a drier 10 from which prepared collagen or cellulose casing is led through guide rollers 14, which grip the casing fairly tightly so that air which is put in the casing from the far end will not pass beyond rollers 14. The inflated casing is shown at 15 and is seen to so pass through pairs of rolls 16 and 17 and through a guidance block 18 to a pair of drive rolls 19,20. The casing then enters the nip between the pair of shirring wheels 21 ,22. The casing as it passes through the drive rolls 19,20 and shirring wheels 21,22 passes over a mandrel 23. The mandrel has an internal passage 24 through which air is supplied under pressure from a source not shown via a pipe 25 and mandrel end fitting 26. The air flowing through pipe 25 and bore 24 enters the casing and keeps it expanded as shown in 55 Figure 1. The shirring wheels 21 and 22 shirr the casing and the shirring takes place along a tapered portion 27 of the mandrel 23, which will be described in more detail later. The shirred casing is compressed because the casing passes through compression rolls 28,29 which are rotated at about 100th of the speed of the drive rolls 19,20, and in the same direction of rotation as the drive rolls 19 and 20. The shirring rolls EP 0 159 159 B1

rotate in the same direction as the drive rolls but at about twice the speed of the drive rolls. The range of speeds within which they may rotate according to the physical characteristics of the casing is from about 1 .5 to 2.5 times the speed of the drive rolls. It will be seen that the outside edges of the wheels are almost touching, the spacing between them being of the order of 1 to 2 mm. 5 The compression of the casing takes place entirely during the formation of the shirr and as the shirred stick or slug compresses between the shirring wheels and the compression rolls. The shirred stick emerges from the compression rolls and when a suitable length has been formed can be cut off, slid along the mandrel 23 and off the end of the mandrel after removal of the end fitting 26, the air being cut-off temporarily while this occurs. io The shirring wheels 21,22 are driven by a shirring wheel motor 29A which, through a gear-box 30 drives shirring wheel 21. Shirring wheel 22 is driven at the same speed by means of a belt drive 31 and pulleys 32,33. The drive rolls 19 and 20 are also driven through a system of pulley wheels and belts 34,35. The compression rolls 28,29 are driven by a separate electric motor 36 via belts 37 and 37A. The shirring wheels 21 and 22, which form an important aspect of this invention, are molded or 75 otherwise formed from elastomer such as synthetic rubber or natural rubber, or polyurethane. The two wheels are identical and have at their outer periphery teeth 38 (see Figures 5 to 8) separated by spaces 39, the ratio of the tooth thickness (B in Figure 5) to the space or gap between the teeth measured in the same direction (shown as A) is the mark/space ratio which as shown is about 1:1. Each tooth 38 has a face or crest surface 40. As seen in Figures 5 and 8 the face or crest of the tooth 39 has a semi-circular cross 20 section in a radial plane and is uniform at all points around the shirring wheel. This point is seen clearly in Figure 6 wherein the two outer teeth have the semi-circular cross section referred to above, and it is also seen in Figure 8. Each tooth has two flank surfaces 41 and 42. Where the flank 42 joins the face or crest 40 is the leading edge 43 of the tooth 40, assuming rotation to be in the direction shown by the arrows in Figures 5, 6 and 7 of the drawings. Similarly where the flank 41 meets the crest 40 is the trailing edge 44. 25 The flank 41 meets the crest 40 at a nominally constant angle and similarly the flank 42 meets the crest 40 at a nominally constant angle. The edges 43 and 44 are of substantially helical formation as can be seen in Figures -5 and 6 the teeth 39 are joined by walls 45 portions of which are cut away at 46 to improve flexibility. An important aspect of this invention is that the compression of the shirred stick takes place between 30 the shirring wheels 21,22 and the compression rolls 28, 29, the compression, and the folding of the shirred stick, being controlled by the taper 27 on the mandrel 23 (see particularly Figures 3 and 4). The mandrel is tapered so that there is a 1mm change in diameter for every 5mm length of the mandrel. This tapered mandrel is described and illustrated in more detail in our copending European patent application No. 85302222.6 35 The formation of a helical primary fold in the casing, which is part of the shirring process, is illustrated in Figures 10 and 11. The initial fold form is shown at 47 and this fold will be ironed or compressed into a helical primary fold by a subsequent tooth of the wheel. The leading edge of the tooth shown at 43 will create this ironing contact as shown in Figure 1 1 . We have found that it is most important that when this first ironing contact between the teeth of the wheels and the partially formed fold occurs the leading edges 40 of the tooth should form a true helix and the leading edges of adjacent teeth should be aligned. This is illustrated in Figure 9 where the leading edge 43 of a tooth of one of the shirring wheels 22 is aligned (shown as joined by a nominal straight line 48) with the leading edge 43 on the adjacent tooth on the other shirring wheel 21 . It will be seen that this occurs not when the teeth are in the bottom dead centre position but at a point some degrees after the bottom dead centre, the line 49 indicating the bottom dead centre 45 position. The amount by which the teeth have passed the bottom dead centre position is determined as previously described by the formula given. Figure 9 also illustrates the position of the taper 27 of the mandrel and it is seen that the taper 27 commences just before the bottom dead centre position at 50. A fairly typical case is when the point of alignment is 8 to 10° past bottom dead centre. 50 The improved shirred stick which results from use of the improved apparatus and method described above is characterised by a minimum of random folds and increased packing efficiency compared with prior art shirred sticks. An advantage of the tapered mandrel used in conjunction with the shirring wheels of this invention is that slippage of the primary folds which enables high packing efficiency to be achieved can be closely 55 controlled and the axial symmetry around the circumference of the stick or slug is maintained and this results in straight slugs. The tapered mandrel also enables minor changes in the material thickness etc. to be catered for without altering the machine. EPO 159 159 B1

Claims

1. Apparatus for shirring a tubular casing in which there is at least one pair of toothed shirring wheels (21,22) in which the teeth of the wheels together form a helical surface relative to a mandrel 5 characterised in that the wheels sweep a helical line along a circle of a predetermined radius Y, and the teeth on said shirring wheels (21 ,22) are so designed that at the point of contact of the leading edge of a tooth of a shirring wheel with the outside diameter of the shirred casing i.e. at the point where the casing has already been pushed into a fold (47) and the fold is about to be ironed, the leading edges (43) of teeth on adjacent wheels (21 ,22) are in substantially helical alignment, the geometry of w the teeth being such that, in use, after a fold has been formed in the casing, the newly formed fold is pressed down, or ironed, into its final shape thus forming the sharply defined crease or fold line known as the primary fold, said point of contact occurs when the leading edges (43) of the adjacent teeth of the wheels (21,22) are at an angle 'A' (50) of a few degrees past the bottom dead centre position (49), i.e. the point of closest contact between the wheels where 75

Cos"1 A = R - r ; R

2. Apparatus according to claim 1 characterised by this, that each tooth (38) is formed with a groove (40) of substantially semi-circular section, in a radial plane, in its outer face 'R' is then the radius, through the shirring wheel axis, of the base of the groove in the tooth. 30 3. Apparatus according to claim 1 or claim 2 and characterised in that the teeth (38) of each wheel (21 ,22) are spaced round the wheel at a circumferential distance apart so that the mark/space ratio lies in the range 3:4 to 4:3.

35 4. Apparatus according to claim 3 characterised in that the mark/space ratio is 1:1.

5. A shirring wheel (21 ,22) or paddle which has teeth (38) characterised in that the curvature of the crest or face surface of each tooth (38) is derived from the diameter of the wheel (21 ,22) and the diameter of a desired shirred casing or slug as follows: 40 (a) the crest surface is part of a groove of substantially semi-circular cross section in a radial plane and is uniform at all points around the shirring wheel; and characterised by this, that (b) the radius of the radial cross section of the groove is that of the desired finished shirred casing or slug outside diameter less a factor which takes account of the flexing of the teeth during shirring, said factor taking into account the stiffness of the paddle material and the thickness of the tooth 45 forms employed and is such as to result in a radius noticably smaller than the casing.

6. A shirring wheel according to claim 5 characterised in that the amount by which the radius of the cross section of the tooth is reduced is between 15 and 30%. so 7. A shirring wheel according to claim 6 characterised in that the radius is reduced by between 20 and 30%.

8. A shirring wheel according to claim 5 or claim 6 characterised in that the leading edge of each tooth is defined by a series of points on a line which crosses the outside diameter of the slug coincidentally 55 with a desired helical fold line on the casing.

9. A shirring wheel according to claim 10 characterised in that the trailing edge of each tooth is defined by a series of points approximately parallel to the leading edge such that on any circular section EP 0 159 159 B1

perpendicular to the axis the ratio of the circumferential length between successive points where the leading and trailing edges cut that section and the circumferential length between either point and the next such point is constant.

5 10. A shirring wheel according to any of claims 7 to 12 characterised in that each flank surface (41) of each tooth (38) is formed so that it meets the crest (40) or face of the tooth at a nominally constant angle known as the rake angle so as to provide improved driving of the casing.

11. A shirring wheel (21,22) or paddle according to any of claims 5 to 10 characterised by being provided 10 with flexible teeth.

12. A shirring wheel (21,22) or paddle according to claim 11 characterised in that the flexibility is brought about by means of a series of selected cut-outs (46) in the outer walls of the wheel (21,22) and by selection of a suitable rubber or rubber like material for the wheel. 75 13. A shirring wheel or paddle according to claim 12 characterised in that the cut-outs (46) in the wheel are designed to produce uniform flexibility throughout the circumference of the wheel.

14. A shirring wheel or paddle according to any of claims 9 to 13 characterised in that said flexibility is 20 related to the flexibility of the material of the casing so as to produce sufficient interference between the wheel and the casing to drive a casing.

15. A shirring wheel or paddle according to any of claims 9 to 14 characterised in that, to control the strength and flexibility of the wheel, the teeth (38) are joined by circumferential walls (45) so that in 25 effect the teeth are cut out from a solid wall.

Revendications

1. Appareil destine au plissage d'un boyau tubulaire dans lequel il existe au moins une paire de roues 30 dentees de plissage (21 , 22), dans lequel les dents des roues torment ensemble une surface en helice par rapport a un mandrin caracterise en ce que les roues balaient une ligne en helice le long d'un cercle de rayon "r" predetermine, et les dents disposees sur lesdites roues de plissage (21, 22) sont d'une structure telle que, au point de contact du bord avant d'une dent d'une roue de plissage avec le diametre exterieur du boyau plisse, c'est-a-dire au point ou le boyau a deja ete pousse dans un pli (47) 35 et ou le pli sera bientot etire, les bords avant (43) de dents sur des roues adjacentes (21 , 22) sont en alignement sensiblement helicoTdal, la geometrie des dents etant telle que, en utilisation, apres qu'un pli ete forme dans le boyau, le pli nouvellement forme est appuye, ou etire, dans sa forme finale, en formant ainsi une ligne de froncement ou de plissage defini de fagon aigue connue comme le pli primaire, ledit point de contact se produit lorsque les bords-avant (43) des dents adjacentes des roues 40 (21 ,22) sont a un angle A (50) de quelques degres au-dela de la position (49) de point mort bas, c'est- a-dire du point du contact le plus voisin entre les roues ou :

A etant I'angle en degres des bords avant des dents adjacentes au-dela de la position de point mort inferieur; R etant la distance minimale de la surface de dent a partir de I'axe de la roue de plissage; 50 r etant le rayon predetermine du boyau plisse, et R etant plus grand que r.

2. Appareil selon la revendication 1 caracterise en ce que chaque dent (38) comporte une rainure (40) de section sensiblement semi-circulaire, "R" est alors, dans sa face exterieure, dans un plan radial, le rayon, a travers I'axe de roue de plissage, de la base de la rainure dans la dent. 55 3. Appareil selon la revendication 1 ou la revendication 2 et caracterise en ce que les dents (38) de chaque roue (21 , 22) sont espacees autour de la roue a une distance circonferentielle entre eiles de telle facon que le rapport marque/espace est situe dans la plage de 3:3 a 4:3. EPO 159 159 B1

4. Appareil selon la revendication 3 caracterise en ce que le rapport marque/espace est 1 :1 .

5. Une roue ou pale de plissage (21 , 22) qui comporte des dents (38) caracterise en ce que la courbure de la face de crete ou de face de chaque dent (38) est derivee, a partir du diametre de la roue (21 , 22) 5 et du diametre d'un boyau ou billette plisse souhaite, de la maniere suivante: (a) la- surface de crete fait partie d'une rainure de section transversale sensiblement semi-circulaire dans un plan radial et est uniforme a tous les points autour de la roue de plissage; et caracterise par le fait que: (b) le rayon de la section transversale radiale de la rainure est celui du diametre exterieur du boyau 10 ou de la billette plissee finie souhaitee moins un facteur qui prend en compte la flexion des dents pendant le plissage, ledit facteur prenant en compte la rigidite de la matiere de pale et I'epaisseur des formes de dents employees et etant propre a amener un rayon sensiblement plus petit que le boyau.

75 6. Une roue de plissage selon la revendication 5 caracterisee en ce que I'ampleur de la reduction de rayon de la section transversale de la dent est comprise entre 15 et 30%.

7. Une roue de plissage selon la revendication 6 caracterisee en ce que le rayon est reduit de 20 a 30%.

20 8. Une roue de plissage selon la revendication 5 ou la revendication 6 caracterisee en ce que le bord avant de chaque dent est defini par une serie de points sur une ligne qui traverse le diametre exterieur de la billette en coincidence avec la ligne de pli en helice souhaitee sur le boyau.

9. Une roue de plissage selon la revendication 10 caracterisee en ce que le bord avant de chaque dent 25 est defini par une serie de points, approximativement parallele au bord avant de sorte que, sur une section circulaire quelconque perpendiculaire a I'axe, le rapport de la longueur circonferentielle entre des points successifs oCi le bord avant et le bord arriere coupent cette section et la longueur circonferentielle entre chacun des points et le point semblable suivant est constant.

30 10. Une roue de plissage selon I'une quelconque des revendications 7 a 12, caracterisee en ce que chaque surface (41 ) de f lane de chaque dent (38) est formee de facon qu'elle rencontre la crete (40) ou face de la dent selon un angle nominalement constant connu comme angle de dent chevillee de fagon a procurer un entrafnement ameliore du boyau.

35 11. Une roue (21, 22) ou pale de plissage selon Tune quelconque des revendications 5 a 10 caracterisee en ce qu'elle comporte des dents flexibles.

12. Une roue (21, 22) ou pale de plissage selon la revendication 11 caracterisee en ce que la flexibility est realisee au moyen d'une serie de decoupes (46) dans les parois exterieures de la roue (21 , 22) et par 40 un choix, pour la roue, d'un caoutchouc ou d'une matiere semblable au caoutchouc appropriee.

13. Une roue ou pale de plissage selon la revendication 12 caracterisee en ce que les decoupes (46) dans la roue sont realisees de fagon a produire une flexibilite uniforme sur toute la circonference de la roue.

45 14. Une roue ou pale de plissage selon I'une quelconque des revendications 9 a 13 caracterisee en ce que ladite flexibilite est reliee a la flexibilite de la matiere du boyau de facon a produire une interference suffisante entre la roue et le boyau pour entraTner un boyau.

15. Une roue ou pale de plissage selon I'une quelconque des revendications 9 a 14 caracterisee en ce 50 que, pour commander la force et la flexibilite de la roue, les dents (38) se raccordent par des parois circonferentielles (45) de sorte que, en fait, les dents sont decoupees a partir d'une paroi massive.

Patentanspriiche

55 1. Vorrichtung zum Raffen einer schlauchformmigen Hiille, bei der mindestens ein Paar gezahnter Raffrader (21,22) vorgesehen ist, deren Zahne in bezug auf einen Dorn eine Schraubenflache bilden, dadurch gekennzeichnet, da/3 die Rader eine Schraubenlinie entlang einem Kreis mit einem vorbe- stimmten Radius 'r' uberstreichen und die Zahne auf den Raffradem (21 ,22) so gestaltet sind, da/3 am

8 EP 0 159 159 B1

Beruhrungspunkt der Vorderkante eines Zahnes eines Raffrades mit dem Au/tendurchmesser der gerafften Hulle, d.h. an der Stelle, wo die Hulle bereits in eine Falte (47) gedriickt wurde und die Falte im Begriff steht geglattet zu werden, die Vorderkanten (43) der Zahne benachbarter Rader (21 ,22) im wesentlichen eine schraubenformige Ausrichtung aufweisen, wobei die Geometrie der Zahne derart ist, 5 da/3 im Betrieb, nachdem eine Falte in der Hulle geformt worden ist, die neu geformte Falte in ihre endgtiltige Form abwarts gepresst oder geglattet wird und damit die scharf definierte Krausel- oder Faltlinie gebildet wird, die als Primarfalte bekannt ist, wobei der Beruhrungspunkt auftritt, wenn die Vorderkanten (32) der benachbarten Zahne der Rader (21,22) in einem Winkel 'A' (50) von wenigen Grad hinter der inneren Totpunktlage (49), d.h. der Stelle der engsten Beruhrung zwischen den Radern, 70 angeordnet sind, wo

A = Cos -1 * - ■" ist;

75 R

wobei A der Gradwinkel der Vorderkanten der benachbarten Zahne hinter der inneren Totpunktlage;

R der Mindestabstand der Zahnflache von der Raffradachse; 20 r der vorbestimmte Radius der gerafften Hulle, und R grower als r sind.

2. Vorrichtung nach Anspruch 1 , dadurch gekennzeichnet, da/3 jeder Zahn (38) in einer radialen Ebene mit einer Nut (40) von im wesentlichen halbkreisformigen Querschnitt versehen ist, wobei dann in seiner 25 Au/3enseite 'R' der durch die Raffradachse hindurchgehende Radius der Nutbasis in dem Zahn ist.

3. Vorrichtung nach Anspruch 1 oder 2, dadurch gekennzeichnet, da/3 die Zahne (38) jedes Rades (21 ,22) rund um das Rad in einem Umfangsabstand voneinander derart angeordnet sind, da/3 das Teilungsver- haltnis im Bereich von 3:4 bis 4:3 liegt. 30 4. Vorrichtung nach Anspruch 3, dadurch gekennzeichnet, da/3 das Teilungsverhaltnis 1:1 ist.

5. Raffrad (21,22) oder -haspel, welches mit Zahnen (38) versehen ist, dadurch gekennzeichnet, da/3 die Krummung der Kopf- oder Stimflache jedes Zahnes (38) von dem Durchmesser des Rades (21,22) und 35 dem Durchmesser einer gewunschten gerafften Hulle oder Rohlings wie folgt gewonnen wird: a) die Kopfflache ist Teil einer Nut von im wesentlichen halbkreisformigem Querschnitt in einer radialen Ebene und ist an alien Punkten um das Raffrad herum gleichformig; und dadurch gekennzeichnet, daS b) der Radius des radialen Querschnitts der Nut derjenige des Aufiendurchmessers der gewunsch- 40 ten fertiggestellten gerafften Hulle oder des Rohlings abzuglich eines Faktors ist, der das Biegen der Zahne wahrend des Raffens berucksichtigt, wobei der Faktor die Steifheit des Haspelmaterials und die Dicke der verwendeten Zahnformen in Rechnung stellt und derart bemessen ist, da/3 sich ein merklich kleinerer Radius als die Hulle ergibt.

45 6. Raffrad nach Anspruch 5, dadurch gekennzeichnet, da/3 die Gro/3e, durch die der Radius des Zahnquerschnitts reduziert ist, zwischen 15 und 30% betragt.

7. Raffrad nach Anspruch 6, dadurch gekennzeichnet, da/3 der Radius um zwischen 20 und 30% reduziert ist. 50 8. Raffrad nach Anspruch 5 oder Anspruch 6, dadurch gekennzeichnet, da/3 die Vorderkante jedes Zahnes durch eine Reihe von Punkten auf einer Linie definiert ist, welche den Auflendurchmesser des Rohlings in Ubereinstimmung mit einer gewunschten schraubenformigen Faltlinie auf der Hulle kreuzt.

55 9. Raffrad nach Anspruch 10, dadruch gekennzeichnet, da/3 die Hinterkante jedes Zahnes durch eine Reihe von Punkten definiert ist, die angenahert parallel zu der Vorderkante derart verlauft, da/3 auf einem beliebigen kreisformigen Querschnitt, der senkrecht zur Achse lauft, das Verhaltnis der Um- fangslange zwischen aufeinanderfolgenden Punkten, wo die Vorder- und Hinterkanten diesen Quer- EP 0 159 159 B1

schnitt schneiden sowie die Umfangslange zwischen jedem Punkt und dem nachsten derartigen Punkt konstant ist.

10. Raffrad gema/3 einem der Anspruche 7 bis 12, dadurch gekennzeichet, da/3 jede Flanke (41) jedes 5 Zahnes (38) so geformt ist, da/3 sie den Kopf (40) Oder die Stirnseite des Zahnes in einem nominal konstanten Winkel trifft, der als Spanwinkel bekannt ist, derart, da/3 ein verbesserter Antrieb der Hulle erreicht wird.

11. Raffrad (21,22) Oder -haspel gema/3 einem der Anspruche 5 bis 10, gekennzeichnet durch biegsame w Zahne.

12. Raffrad (21,22) oder -haspel gema/3 Anspruch 11, dadurch gekennzeichnet, da/3 die Flexibilitat durch eine Reihe ausgewahlter Ausschnitte (46) in den Au/3enwanden des Rades (21 ,22) sowie durch Auswahl eines geeigneten Gummi- oder gummiahnlichen Materials fur das Rad erreichbar ist. 75 13. Raffrad oder -haspel nach Anspruch 12, dadurch gekennzeichnet, da/3 die Ausschnitte (46) in dem Rad so gestaltet sind, da/3 eine gleichma/3ige Biegsamkeit uber den gesamten Umfang des Rades vorhan- den ist.

20 14. Raffrad oder -haspel nach einem der Anspruche 9 bis 13, dadurch gekennzeichnet, da/3 die Biegsam- keit auf die Flexibilitat des Hullenmaterials bezogen ist, urn eine ausreichende gegenseitige Beeinflus- sung zwischen dem Rad und der Hulle fur den Antrieb einer Hulle hervorzurufen.

15. Raffrad oder -haspel nach einem der Anspruche 9 bis 14, dadurch gekennzeichnet, da/3 zur Steuerung 25 der Festigkeit und Flexibilitat des Rades die Zahne (38) durch Umfangswande (45) verbunden sind, so da/3 im Endergebnis die Zahne aus einer vollen Wand ausgeschnitten sind.

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/T&.2.

4S es dd 21,22-j

/7&6.

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14 EP 0 159 159 B1

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