Method and apparatus for severing shirred tubular food casing

Abstract: Severing a shirred stick of sausage casing from casing feed stock joined to the stick is accomplished by perforating a section of the casing across its flat width prior to moving the section through a shirring zone (14). The section is then moved to a shirring zone where longitudinal movement of the casing is restrained to put the casing in tension across the line of perforations (50). The resulting tension tears the casing apart along the line of perforations. In one embodiment the shirring rolls (120) are operable to incorporate a torn end of the casing into the shirred stick by gathering the torn end up into a pleat at the last-shirred end of the stick.

Description: Technical Field The present invention relates to the production of shirred casing sticks and more particularly to a method and apparatus for severing a shirred stick from the casing feed stock. Background Of The Invention Food casings of regenerated cellulose are widely used for the production of various stuffed food products. The present invention is concerned primarily with thin walled unreinforced cellulosic casing as may be used in the production of small diameter sausages such as frankfurters and the like. For convenience of handling, food casings which may be 20 to 50 meters or more in length are shirred and preferably compressed to produce what commonly are referred to as "shirred casing sticks". Shirring machines for producing these shirred sticks are well known in the art and are disclosed in U. S. Patent Nos. 2,983,949 and 2,984,574 among others. Cellulosic casing for the shirring operation is supplied in reels. Flat casing feed stock, drawn from the reel, is fed into the mandrel of a shirring machine where it is inflated with low pressure gas, usually air. Inflation is maintained by passing the feed stock through the nip of feed rolls located in advance of the shirring mandrel. The inflated casing is moved onto and along the mandrel and through a shirring zone where a shirring mechanism gathers the inflated casing about the mandrel into generally conical pleats nested one tightly against another. The inner folds of the pleats are formed against the mandrel and define the surface of an axial bore through the stick. When a preselected shirred length has been attained, it is severed and moved longitudinally away from the shirring mechanism for further processing. Such further processing may include, for example, a compaction operation where the shirred length is reduced and an operation where a closure is formed and inserted to stop or plug the bore at one end of the casing thereby forming a "closed" end. The other end of the casing is left open to permit mounting of the shirred stick onto a stuffing horn. In many cases, the severing operation produces a tail of loose casing 6 to 25 mm long extending from the tightly nested pleats at the stick open end. This tail not only detracts from the appearance of the stick, but also interferes with the functionality of the stick by interfering with the passage of a stuffing horn into the stick bore. The compaction operation presses this loose casing against the tightly nested pleats of the stick open end but often the compressed tail of casing loosens and sags across the bore opening. Various operations have been devised to prevent this. For example, the tail may be peeled manually from the end of the stick so only tightly nested pleats remain. In U.S. Patent No. 4,594,274 a heated die is used to press and iron the loose tail against the end of the stick. In U.S. Patent No. 4,873,748 a rotating cup is used to burnish the tail against the tightly nested pleats of the stick open end. Severing a shirred length has been accomplished both manually and by automatic means located after, (i.e., downstream) the shirring zone. For example, one general method is to wait until some length of shirred casing has accumulated and then separate off a desired length from this accumulated shirred length as disclosed for example in U.S. Patent No. 3,112,517. Another general method is to shirr only a desired length and then separate this shirred length from the feed stock. This general method is disclosed for example in U.S. Patent Nos. 3,936,909; 4,547,932 and 4,885,821 among others, the latter disclosing a method and an apparatus as defined in the pre-characterizing portions of claims 1 and 9. Whatever the severing means, it is desired that the casing be cut cleanly to avoid so called "shards" or "flags" which are ragged pieces of casing attached to one or both the severed ends. When tensioning is relied upon to sever the casing, shards are often formed on one or both of the severed ends. U.S. Patent No. 4,885,821 illustrates that in a casing under tension, a tear, which initiates at some point on the casing, propagates in opposite directions around the casing. If the ends of the tear propagation fail to meet in the same transverse plane, they overlap and run past one another. As the tear continues to propagate, one end of the tear eventually will run into the other which causes a loose piece or so called "shard" or "flag" of casing to form on one of the severed ends. If tears initiate at a plurality of points around the casing, then several shards may be formed. Shards at the severed ends of the casing are objectionable because they may separate from the casing and become incorporated into the food product being stuffed into the casing. This is especially the case when using the casing for stuffing frankfurters. After a shirred stick is stuffed with a frankfurter emulsion, it is common for the operator to squeeze out emulsion from the ends of the casing so the ends can be tied off. When this is done, shards at the end of the casing can rip free. Since the emulsion squeezed out of the casing is recovered and recycled, any shard of casing ripped off the casing may become incorporated into the emulsion supply. Accordingly, it is most desirable to sever the shirred stick from casing feed stock in a manner which at least reduces the size of shards on the severed ends of casing, and preferably eliminates their formation. Various severing methods have been proposed to reduce the instances of forming shards on the ends of the severed casing. U.S. Patent No. 4,885,821 discloses closing three arcuate members about the shirring mandrel to provide a knife edge in the form of a closed circle at a location after, i.e., downstream of the shirring zone. This edge is pressed against the end face of the shirred stick to push the stick longitudinally along the mandrel and this causes the feed stock to tear away along the knife edge. In U.S. Patent No. 3,936,909 three arcuate members, also located downstream of the shirring zone, are closed about the circumference of an inflated section of the feed Stock casing close to the end face of the shirred stick. The arcuate members form a closed circle about the casing and weakens the casing either by heating or by perforating it about substantially the full circumference of the casing. Subsequent longitudinal displacement of the shirred casing along the mandrel will cause the feed stock to separate from the stick at the weakened section. The operation of closing arcuate members about the casing presents certain problems. If the casing and arcuate members are not on the same center, the casing may not be uniformly severed so that shards on one or both severed ends results. Also, the casing which passes through the shirring zone is creased and folded. Accordingly, severing after the shirring zone may involve a casing that is not uniformly round. This means that the arcuate members closing about the casing may not uniformly engage the casing circumference, or a casing crease or fold may become pinched between adjacent arcuate member. As a further problem, tears initiated about the circumference of the creased casing may tend to follow along the fold or crease lines and this interferes with the formation of a clean, shard-free transverse severing of the casing. In the present invention, severing occurs in the shirring zone. Problems associated with the proper closing of arcuate members about the casing and shirring mandrel as well as the severing problems associated with attempting to sever casing creased and folded by shirring are minimized by preparing the casing feed stock for severing prior to entering the shirring zone. In particular, the casing is prepared by weakening the feed stock along a narrow transverse band at a defined location along its length prior to entering the shirring zone. As the casing moves through the shirring zone, a tensile stress applied to the feed stock casing will easily sever it at the weakened area. In one embodiment of the present invention, the severing is accomplished in a manner which incorporates the severed end portion of casing into the shirred stick so further operations to remove or dress a loose tail may not be needed. Objects Of The Invention One object of the present invention is to provide an improved method and apparatus for separating a length of shirred casing from the feed stock of unshirred casing. Another object of the present invention is to provide a method and apparatus for severing a length of shirred casing from the feed stock which minimizes or eliminates the presence of objectionable shards on the severed ends of casing. Another object is to provide a casing severing method and apparatus which leaves little or no loose casing extending from the last-shirred end of the shirred length. A further object is to provide a casing severing method and apparatus wherein the feed stock is weakened prior to shirring, and severing is accomplished during or after shirring. Yet another object of the present invention is to provide a casing severing method and apparatus wherein severing shirred casing is facilitated by transversly perforating the feed stock casing prior to shirring and then separating the casing after shirring along the line of perforations. Yet another object is to provide a casing severing method and apparatus which draws a severed casing end up against the last-shirred end of a shirred length so as to provide the last-shirred end with a dressed, tail-free appearance. Summary of the Invention In one aspect, the subject of the invention is a method of severing a shirred casing stick from a length of feed stock casing, comprising the steps of: a) drawing feed stock casing in the direction of the casing longitudinal axis on to a shirring mandrel towards and through a shirring zone and conducting a shirring operation in the zone which gathers the feed stock casing into pleats about the shirring mandrel to form the shirred stick; and b) tensioning the casing and tearing apart the casing thereby separating the shirred stick from the feed stock casing; characterized by c) weakening a section of feed stock casing prior to shirring to form a frangible band of casing extending transverse the casing longitudinal axis and around its circumference; d) continuing the conducting of the shirring operation until said frangible band is at the shirring zone; and e) thereafter tensioning the casing across the frangible band and tearing apart the casing along the frangible band. In another aspect, the subject of the invention is an apparatus for severing a stick of shirred tubular food casing from feed stock casing comprising: a) shirring means defining a shirring zone; b) first means for feeding tubular feed stock casing in a longitudinal direction through said shirring zone where said feed stock is gathered into pleats to form a shirred stick of casing; c) tensioning means for tensioning the feed stock casing and tearing apart the casing; characterized by d) second means located prior to the shirring zone for transversly weakening but not severing a section of said feed stock casing to provide a narrow frangible band of casing extending about the circumference of the feed stock casing; and e) said tensioning means being designed for tensioning the feed stock casing across said frangible band and tearing apart the casing along said frangible band. In one embodiment, the casing is put into tension across the frangible band by a member which pushes the shirred stick along the mandrel. In another embodiment, the shirring operation itself crates the tension for severing the casing. In accordance with the present invention, the feed stock casing is weakened, but not severed, prior to shirring to provide a narrow frangible band extending around the casing. The frangible band remains strong enough to withstand the rigors of shirring but will tear under tension. The frangible band is provided by any suitable means operating to perforate, score, thin, abrade or otherwise degrade the tubular wall of the casing along a narrow transverse band that extends about the circumference of the casing. A method according to the present invention, is to weaken the casing transversely by making a line of perforations that extends across the flat width of the feed stock casing before the casing enters a shirring zone. Thereafter, when the casing is subjected to a tensile stress, the casing will tear apart along the line of perforations. The tear propagates from one perforation to another so the likelihood of forming a shard is reduced, and in any event, shards or flags of casing which may be produced tend to be so minute that they will not detract from the commercialization of the shirred casing. Preferably the line of perforations in the feed stock should be made while holding the casing feed stock in a flattened condition. This allows the perforating means to penetrate completely through the casing. Also, in accordance with the present invention the perforations should extend across the entire flat width of the casing. The result is that when the casing is inflated for shirring, a line of perforations will extend around the entire circumference of the casing. In one embodiment, the perforation extends at an oblique angle relative to the longitudinal axis of the casing. The perforations can take several forms. For example, a row of closely spaced sharpened pins can be used to make round perforations. Using a knife with a serrated edge will make a straight row of perforations across the casing. A preferred perforating means has a sharpened edge provided with straight-sided teeth. With this arrangement the length of each perforation is constant regardless of the depth of penetration. Whatever the shape of the perforating means, an important consideration is the number and length of perforations relative to the lands between the perforations. As noted above, the casing should not be so weakened by the number and length of the perforations that the forces applied to pull the casing onto the shirring mandrel and along the mandrel towards the shirring zone will cause the feed stock to sever prematurely. Conversely, if the casing is not sufficiently weakened, the casing may not cleanly sever along the line of perforation during the subsequent severing operation. Putting the casing in tension may be accomplished by stopping the shirring operation and reversing the rotation of the feed rolls. Preferably, however, increasing the tension is accomplished by restraining the longitudinal movement of the feed stock casing by braking the feed rolls to slow or stop the casing. Tension then is moved may be created by pushing the shirred stick along the mandrel or by continuing to operate the shirring means. In either case, the casing at one side of the frangible band is moved while the casing on the other side of the frangible band is restrained from moving by the braked feed rolls. The resulting tension on the casing causes it to tear along the line of perforations. If the tension is created by operation of the shirring means, a torn end of the casing is drawn and gathered into the last-shirred end of the stick. If the casing is not sufficiently weakened and the casing does not sever cleanly, the result may be severed edges so ragged with loose shards as to be unacceptable for the stripping operation that may follow stuffing. Whether a product is acceptably free of loose shards or flags of casing is subjective and depends in part on their number, size and distribution along the severed edge. The color of the casing also may enter into a consideration of acceptability since shards of a clear casing may be less noticeable than shards of a colored casing. The ultimate goal is to have a clean, shard free severed end. However, the goal of an acceptable casing is considered achieved if shards which are formed are so small that they do not readily detach from the casing during a conventional stripping operation. According to the present invention, the perforations can be made at any point before the feed stock casing feeds onto the shirring mandrel. For example, the casing unwinds from a supply reel and is inflated after passing through a pair of nip rolls. The inflated casing then is laced onto the shirring mandrel. At any point prior to the shirring mandrel, the casing is, or may be, pressed to a flat width. Thus, the perforations can be made on the flat feed stock casing at a location between the supply reel and nip rolls or at the nip rolls or after the nip rolls. If the casing is perforated after inflation, a section of the inflated casing preferably is pressed flat and perforated. It also is possible to determine the length of casing to be contained in a stick and then perforate the casing at intervals corresponding to this length as casing is wound onto the supply roll. However, this is not preferred because in this case some accommodation must be made to control the operation of the shirring machine so the length shirred for each stick is coordinated with the length of the casing in the interval between the transverse perforations. Description of the Drawings Figures 1-6 illustrate in schematic fashion the method steps of one embodiment of the present invention; Figures 7-9 illustrate method steps of an alternative embodiment. Figure 10 is a full scale view showing the end of a casing severed according to a prior art method; Figures 11a and 11b are full scale views showing the end of a casing severed according to embodiments of the present invention; Figures 12 and 13 are each magnified views, of a portion of the severed end of the casing juxtaposed to a serrated knife blade used in preparing the casing for severing; and Figure 14 is a magnified view showing portions of the adjacent ends of casing severed in accordance with the present invention. Detailed Description of the Invention Referring to the drawings, Figure 1 shows several elements of a conventional shirring machine as modified to incorporate components for severing the casing according to the present invention. The shirring machine itself is conventional. Only those components necessary to an understanding of the present invention will be described in detail. For example, a conventional shirring machine includes a mandrel 12 and a shirring head 14. It should be appreciated that the shirring machine can be either of the two types in general commercial use including a so-called "floating mandrel machine" of the type generally described in U. S. Patent No. 3,766,603 or a "withdrawing mandrel" machine as generally described in U. S. Patent No. 2,583,654. Flattened feed stock casing 16 is drawn from a supply reel (not shown) and is fed onto the mandrel through the nip of driven feed rolls 18. As the casing passes onto the mandrel, it is inflated by a stream of air 15 issuing from an axial passage 17 in the mandrel. Lubricants and/or moisture or other treatments incorporated into this air stream may be applied to the casing inner surface as is well known in the art. The inflated casing moves in the direction of its longitudinal axis along the mandrel and into the shirring head 14. The shirring head defines a shirring zone in which the inflated casing is gathered, eg. shirred, into pleats about the mandrel 12 to form a shirred stick 22 which exits from the shirring zone. The innerfolds 24 of the pleats are formed against the mandrel and define a longitudinal bore 26 through the shirred stick. The shirring head 14 may comprise any of the known shirring means as described, for example, in U. S. Patent Nos. 3,461,484, 4,185,358, 4,370,780 or 4,374,447 among others. For purposes of illustration, the shirring head 14 is shown as comprising a plurality of toothed shirring rolls 20, usually three in number of a general type which is described in U. S. Patent No. 3,461,484. It should be appreciated that the shirring proceeds in conjunction with conventional and known shirring techniques including the application of lubricants to the external surface of the casing and in conjunction with known shirred casing holdback means (not shown). This holdback means retards the advance of the shirred pleats along the mandrel in order to provide a substantially regular pleat formation wherein the pleats are laid tightly one against another. In a preferred embodiment the shirring rolls lay the pleats at an angle of about 30° with respect to the longitudinal axis of the mandrel so that the overall shirred length is somewhat like a stack of interconnected nesting cones. In a conventional shirring operation, the outside diameter of the shirred stick 22 is larger than the inflated diameter of casing feed stock 16. After a desired length of casing has been shirred, the shirred stick must be separated from the feed stock. Once the shirred stick is separated, it may be subject to further operations (not shown) such as a compaction step to further reduce its length and a step to provide one end of the stick, e.g., the first shirred end 25, with a closure means. For purposes of separating the shirred stick 22 from the feed stock 16, Figure 1 shows a means generally indicated at 28 for working the casing to weaken it. Preferably the casing is weakened by perforating it so the means 28 is referred to as a perforating means. The perforating means 28 is positioned on the upstream side of the shirring zone, i.e. to the left of shirring head 14 as viewed in the figures. Preferably, the perforating means is located, as shown, between shirring head 14 and nip rolls 18 so it operates on casing which is at least partly inflated or expanded from its flattened condition. However, the perforating means also may be located upstream of the nip rolls or even at the nip rolls, in either case, so it operates on flat casing prior to inflation. As will be described further hereinbelow, the perforating means 28 functions to prepare the feedstock casing for severing. This preparation occurs prior to drawing the casing onto the shirring mandrel and facilitates the severing which occurs after the casing is on the mandrel and before it passes completely through the shirring zone. As shown in Figure 1, one component of the perforating means is an anvil 30 at one side of the feed stock casing. A second component of the perforating means is a knife blade 32 which is located on the opposite side of the casing from the anvil. The blade is oriented perpendicular to the anvil and transverse the longitudinal axis of the casing. The edge 34 of the knife which is towards the casing is the knife cutting edge. The knife 32 and anvil 30 are movable one towards the other from an open position as shown in Figure 1 to a closed position shown in Figure 2. At the closed position, the knife blade 32 is closed against the anvil surface 36. The knife edge 34 is not a continuous cutting edge, but is serrated as shown in Figures 12 and 13. Thus, when the knife closes against the anvil, the casing between the serrated knife edge and anvil is perforated. The serrations 38 along the knife edge 34 preferably have straight sides so the cutting edge is crenellated. With this arrangement the length of each perforation is not dependant upon the depth of the penetration of each serration through the casing. It has been found that a suitable knife blade is about 0.406 mm thick. The serrated edge has a pitch of about 0.508 mm wherein each straight sided serration 38 is each about 0.254 mm wide and each space 40 between serrations is about 0.254 mm wide. Such a blade is made by electro discharge machining the cutting edge of a conventional slotted razor blade to provide the serrated edge. To properly perforate the casing, the structure or material of the anvil surface must permit the knife serrations to pass cleanly through the casing engaged between the knife and the anvil. For example, a hard, rigid anvil surface may prevent the serrations from passing completely through the casing and may quickly dull the knife. A soft anvil surface may not provide the resistance needed to permit the knife serrations to penetrate the casing and will wear quickly. A preferred anvil surface is sufficiently resilient to permit some "give" as the knife serrations are pressed against it so that they can pass through the casing, yet is hard enough to avoid excessive wear. A possible alternative is to provide the anvil surface 36 within a transverse groove (not shown) to receive the knife edge. The casing would bridge the groove and be supported as the knife serrations penetrate the casing and enter the groove. As noted above, the perforations preferably are made across the flat width of the casing. Accordingly, to press the expanded feed stock casing to a flat width, Figure 1 shows that perforating means 28 includes a pad 42 having a central opening 44 to accommodate the knife blade so that a portion of the pad is located at each side of the knife blade. The pad moves slightly in advance of the knife blade so the knife does not perforate the casing until after the pad 42 has contacted the casing and pressed it against the anvil surface 36. Coil springs 46, 48 bias the pad which allows the knife to continue to travel through opening 44 and against the anvil after the pad has seated against the anvil. The result is a line of perforations 50 which extend across the flat width of the casing. In a preferred embodiment the perforating means is disposed at an oblique angle with respect to the longitudinal axis of the casing. With this arrangement the resulting line of perforations 150 (Figure 7) extends slantwise across the casing flat width for purposes described further hereinbelow. In operation, the shirring of the inflated feed stock 16 as illustrated in Figure 1 progresses until the desired length of shirred stick 22 accumulates on mandrel 12. The feeding and shirring operations stop and several events occur in rapid sequence. The severing means 28 closes against the casing to the position shown in Figure 2. Preferably, the inflating air is turned off, but the air pressure may be only reduced prior to flattening. In either case, as the severing means closes, anvil 30 and pad 42 first engage and then collapse the casing to substantially the flat width of the casing in advance of the knife edge 34. When the serrated knife edge reaches the anvil 30, it presses the casing to the anvil surface and the serrations penetrate the casing to provide a line of perforations 50, 150 which extend straight across the casing (Figure 3) or slantwise, eg. at an oblique angle, across the flat width of the casing (Figure 3). The severing means 28 then opens. While some inflating air may escape through the perforations, the air flow nevertheless is sufficient to reinflate the casing. In its reinflated condition, as shown in Figure 3, the perforations made by the serrated knife edge now form a line of perforations 50 which extends about substantially the entire circumference of the casing. The feeding and shirring operations start again and proceed until the line of perforations 50 has reaches a location indicated at "A" which is just upstream from the shirring zone. Before the line of perforations can pass through the shirring zone, the feeding and shirring operations stop and the inflating air is turned off or at least the pressure is reduced. Figure 4 shows that the mandrel 12 then is displaced several inches in the shirring direction (longitudinally to the right as shown in the figures). The longitudinal displacement of mandrel 12 carries the shirred stick 22 away from the shirring rolls 20 and, at the same time, the shirring rolls 20 and feed rolls 18 rotate so a section 52 of casing containing the line of perforations 50 is pulled through the shirring zone. The result, as shown in Figure 4 is twofold. First a space 54 is provided between the shirring rolls 20 and the last-shirred end face 23 of the shirred stick. Second, the section 52 of feed stock casing in this space and which contains the line of perforations 50 is not shirred so it is relatively free of creases and folds. Providing a section of casing 52 which is not shirred also can be accomplished by rotating the feed rolls 18 to provide slack casing between the feed rolls and shirring head 14. Now, when the mandrel is displaced longitudinally to the right to the Figure 4 position, this slack casing is pulled through the shirring head and forms the casing section 52. The purpose of providing the clearance space 54 is to expose the last-shirred end face 23 of the stick so a stick transfer means 56 can contact and press directly against the end face. Exposure of the end face 23 also can be achieved by translating the shirring rolls 20 forward (to the left as viewed in the figures) or by opening them radially. Next, the casing feed stock is prevented from moving in the shirring direction by braking the feed stock reel or by clamping the feed stock to the mandrel. Preferably, it is accomplished by holding the feed stock at the nip provided by the stopped feed rolls 18. The shirred stick transfer means 56, including a set of jaws 58, 60 closes radially into the space 54 and towards the mandrel 12. After the jaws close, the mandrel returns to its start position (to the left as viewed in the Figures) which seats the end face 23 against the jaws as shown in Figure 5. The shirred stick 22 is not seized on the mandrel so the mandrel moves relative to the stick after the end face 23 is seated against the closed jaws. A split ring 62 closes about the outside surface of the shirred stick and a drive means (not shown) is operated to move the closed jaws 58, 60 longitudinally in the shirring direction to move the stick 22 along the mandrel 12 and away from the shirring head 14. The inside diameter of split ring 62 is slightly smaller than the outside diameter of stick 22. Accordingly, the closed split ring will resist, but not prevent, the movement of the stick by the closed jaws. It should be appreciated that closing the split ring 62 about the stick creates a drag to resist the movement of the shirred stick which, in turn, keeps the end face 23 of the stick seated tightly against the jaws 58, 60 as the transfer means 56 moves the shirred stick to the right as viewed in the figures. This prevents shirred casing from deshirring off the end face 23 of the stick. On one hand, the nip at the feed rolls 18 holds and prevents the movement of the feed stock casing 16 in the shirring direction as the stick moves. On the other hand, the pressing engagement of the jaws 58, 60 against the end face 23 of the stick acts to hold the casing against the end face. The result, as the stick is pushed in the shirring direction, is that the portion of the casing feed stock 16 between the nip of feed rolls 18 and the jaws 58, 60 is put into tension. Since the line of perforations 50 has weakened the casing, the tension created across the line of perforation causes the casing to tear apart wherein the tear propagates along the line of perforations as shown in Figure 6. The shirred stick now separated from the feed stock casing is transferred down the mandrel. The shirring machine components return to a start position, the inflating air is turned on and the next shirring cycle is started. The line of perforations 50 forms a frangible band extending around the circumference of the casing. As the casing parts along this frangible band, it is speculated that tears initiate at many locations simultaneously around the casing at stress concentration points at the ends of the perforations. These tears however, propagate only a short distance before either running into an adjacent perforation or into a tear emanating from an adjacent perforation. The result as illustrated in full scale in Figure 11a is a casing end 72 having its terminal edge 74 extending normal to the longitudinal axis of the casing. Figure 11a is a full size view of a severed casing end 72 wherein the casing has been slit longitudinally and laid flat so the full circumference of the severed end can be examined. This end corresponds to the casing end at the last shirred end face 23 of the shirred stick. Figures 7-9 illustrate an alternative embodiment. As shown in Figure 7, the perforations are made at an oblique angle. After the perforations are made, the feeding and shirring operations start again and proceed until the leading edge of the oblique line of perforations 150 reaches a location indicated at "A" which is just in advance of the last-shirred end 123 of shirred stick 122. Before the line of perforations can pass through the shirring zone, shirring stops and the movement of the feed stock casing is restrained by applying a brake to feed rolls 118. Now when the shirring rolls 120 are rotated, they draw on the feed stock casing and put it into tension across the line of perforations so the casing tears along the line of perforations. As best seen in Figure 8, a torn end 150A of the feed stock casing is drawn away from the restrained feed stock casing torn end 150B. As shirring rolls 120 continue to rotate, the torn end 150A is drawn through the shirring zone and is incorporated into the last shirred end 123 of the shirred stick 122. Shirring stops and, as shown in Figure 9, the mandrel 112 is displaced several inches in the shirring direction (longitudinally to the right as shown in the figures). The longitudinal displacement of mandrel 112 carries the severed stick 122 away from the shirring rolls 120. At the same time, the shirring rolls 120 and feed rolls rotate so a section 152 of the feed stock casing containing end 150B is pulled through the shirring zone. By displacing the mandrel, a space 154 is provided between the shirring rolls 120 and the last-shirred end 123 of the shirred stick so a transfer means 156, including a set of jaws 158, 160 can close radially into the space 154 and towards the mandrel 112 for moving the shirred stick 123 down the mandrel. As the shirred casing is transferred down the mandrel, the shirring machine components including the mandrel return to a start position, the pressure of the inflating air is returned to an operational pressure and the next shirring cycle is started. By perforating and subsequently tearing the feed stock casing at an oblique angle relative to the casing longitudinal axis as shown in Figure 7, the total length of the torn end is greater than the circumference of the feed stock casing. This greater length allows the shirring rolls 120 to draw the severed end 150A up into a pleat which lies relatively flat against the end of the stick (Figure 8). This provides the last-shirred stick end 123 with a neat appearance and avoids a loose tail of casing which may droop or sag from the end of the stick to partly occlude the bore opening so that additional operations to form or mold the last-shirred end of the stick may not be necessary. The measure of the oblique angle relative to the longitudinal axis of the casing is important for insuring a proper incorporation of the torn end 150A into the last-shirred end of the stick. For example, if the angle is too shallow the torn end 150A will be excessively long. This may result in a portion of the torn end extending from the outer surface of the shirred stick or along the stick outer surface. If the angle is too steep, the length of the torn end 150A may be so short as to prevent the proper gathering of the torn end up against the last-shirred end of the stick. An appropriate angle depends upon such factors, among others, as casing diameter, the outside diameter of the stick and the cone angle of pleats formed by the shirring means. For purposes of the present invention an angle of about 15° from vertical (eg. perpendicular to the longitudinal axis of the flattened casing) has proved suitable. However, it would be well within the skill of the art to determine the angle most appropriate for a given shirring condition. Figure 11b is a full size view showing an end 172 of a casing severed at an oblique angle. The casing is shown laid flat so the full width of the severed end can be examined. Casing end 172 has a substantially straight terminal edge 174 extending at an angle relative to the longitudinal axis of the casing. Shown in phantom line in Figure 11b is the adjacent severed end 172' with its terminal edge 174'. One end 172 or 172' will be located at a first-shirred end of a stick while the other end 172 or 172' will be at the last shirred end of a shirred stick. In contrast to both Figures 11a and 11b, Figure 10 shows an end 76 of a casing severed in accordance with a conventional severing method. The casing in Figure 10 has been slit longitudinally and laid flat so the full circumference of the casing is visible. The casing in each instance is a Viskase Corporation NOJAX cellulosic casing having a nominal diameter of about 21.08 mm. The casings are both shirred in the identical fashion on the same shirring machine. Severing to produce the prior art casing as shown in Figure 10 is in accordance with the teachings of U.S. Patent No. 4,885,821. In the '821 Patent, an annular knife edge is closed about the end of the shirred stick and then is moved longitudinally and pressed against the end of the shirred stick while holding the feed stock casing at the nip rolls. This puts the casing in tension so it tears along the annular knife edge. The terminal edge of the prior art severed end 76 as seen in full size in Figure 10 includes a shard 70 measuring approximately 7.36 x 15.87 mm. In contrast, the casing severed according to the present invention, also seen in full scale, (Figures 11a, 11b) has a transverse terminal edge 74, 174 which is considerably sharper and less ragged than the casing end of Figure 10. Figures 12 and 13 each show a portion of a severed casing end of the invention under 20 x magnification juxtaposed with the knife blade used to perforate the casing as described above. In Figure 12, the blade used has teeth 0.254 mm wide separated by a space of 0.254 mm. Figure 13 is similar to Figure 12 except the knife blade shown juxtaposed to the severed end has teeth 0.177 mm wide separated by a space of 0.330 mm. Thus, the pitch of the serrated edge of this blade is similar to that shown in Figure 12, but the individual teeth are narrower. In each case (Figures 12 and 13) one or more shards can be identified as for example at 68 in Figure 12 and at 78 in Figure 13. However, the shard 68 measures only about 0.178 x 0.203 mm and the shard 78 measures only about 0.229 x 0.279 mm. These shards apparently formed when a tear propagated slightly around an adjacent perforation rather than into it. These shards, as seen under 20 x magnification would not detract from the commercial use of the casing because shards of this size are not likely to be grasped and torn free from the casing edge by a conventional stripping operation. The straight, sharp edge segments 64 produced by the serrated knife blade edge perforating the casing are readily identified at various locations along the severed ends. Between edge segments 64 there are land segments 66 that are raised slightly above the plane of the segments 64. These land segments 66 represent the unperforated casing which has torn between the perforations. In some instances these land segments 66 are relatively flat and in other instances, they are more triangular. Figure 14 shows the profile of a portion of two adjacent severed ends magnified about 20 x. Casing end 71 is the end associated with the last-shirred end. Casing end 73 is the end associated with the feed stock casing. This end 73 will become the end of a shirred length formed to an end closure and accordingly, it corresponds to the end of a shirred length identified at 25 in Figure 1. Figure 14 illustrates the opposite ends of a shirred casing article according to the present invention will each have a transverse terminal edge. The straight edge segments produced when the casing is perforated by the knife edge define the lands 75 on severed end 73 and the valleys 75' on the opposite severed end 71. Conversely, the torn casing between the perforations define the valleys 77 on the severed end 73 and the lands 77' on the opposite end 71. In any event, shards which may appear along either edge, are not likely to detract from the commercial use of the casing so that both ends can undergo a stripping operation. Thus, it will be appreciated that the present invention provides a method and apparatus for severing casing which produces a straight transverse edge extending at an oblique angle to the longitudinal axis of the casing wherein the edge is substantially free of shards or flags of casing likely to pull or tear free of the casing during use. Also, perforating at an oblique angle and relying on rotation of the shirring means to provide the tension for tearing the casing along the line of perforations allows a torn end of the casing to be incorporated into the last-shirred end of the stick. It is possible to stop the flow of inflating air prior to closing the serrated knife against the casing. However, the inflating air can be left on if a pressing means is provided to press and hold the inflated casing to a flat width prior to moving the serrated knife against the casing. Moreover, while the description herein refers to stopping the shirring operation to perforate the casing, a knife that tracks along the casing for a short distance or a rotary knife may be used to perforate the casing without stopping the movement of the casing in the shirring direction.

Claims: A method of severing a shirred casing stick (22, 122) from a length of feed stock casing (16), comprising the steps of: a) drawing feed stock casing (16) in the direction of the casing longitudinal axis on to a shirring mandrel (12, 112) towards and through a shirring zone and conducting a shirring operation in the zone which gathers the feed stock casing into pleats about the shirring mandrel to form the shirred stick (22, 122); and b) tensioning the casing and tearing apart the casing thereby separating the shirred stick (22, 122) from the feed stock casing (16); characterized by c) weakening a section of feed stock casing prior to shirring to form a frangible band of casing extending transverse the casing longitudinal axis and around its circumference; d) continuing the conducting of the shirring operation until said frangible band is at the shirring zone; and e) thereafter tensioning the casing across the frangible band and tearing apart the casing along the frangible band. A method as in claim 1 wherein weakening comprises perforating a section of casing to provide a succession of closely spaced perforations (50, 150), the succession of perforations forming the frangible band. A method as in claim 1 wherein said weakening comprises perforating a section of casing at an oblique angle relative to the longitudinal axis of the feed stock casings (16) to provide a succession of closely spaced perforations (150), extending slantwise across the casing and forming the frangible band. A method as in claims 2 or 3 wherein said perforating step is accomplished while maintaining the section of casing in the flattened condition. A method as in claim 1 wherein moving the frangible band of casing through the shirring zone is accomplished without shirring said frangible band. A method as in claim 1 or 5 wherein tensioning occurs after accumulating a shirred length of casing which, at a first end (25), extends from the shirring zone and at a second end (23, 123) merges with feed stock casing (16) in the shirring zone, said tensioning being accomplished by: a) longitudinally separating the shirring zone and the second end of the shirred length to provide a space (54, 154) therebetween and locating the frangible band of casing in said space; and b) holding the feed stock casing (16) at one side of the frangible band of casing while pressing a driven member (56, 156) longitudinally against the second end (23, 123) of the shirred length thereby tensioning the feed stock casing and tearing it from the shirred length along the frangible band. A method as in claims 1, 2 or 3 wherein tensioning is accomplished by restraining the feed stock casing (16) from moving and utilizing said shirring operation for drawing on said casing and creating the tension to tear apart said casing. A method as in claim 7 including continuing said shirring operation after tearing apart the casing for gathering and incorporating a torn end of the feed stock casing into the last-shirred end of the stick. Apparatus for severing a stick (22, 122) of shirred tubular food casing from feed stock casing (16) comprising: a) shirring means (14) defining a shirring zone; b) first means (18, 118, 20) for feeding tubular feed stock casing (16) in a longitudinal direction through said shirring zone where said feed stock is gathered into pleats to form a shirred stick (22, 122) of casing; c) tensioning means (14, 18, 56, 118, 156) for tensioning the feed stock casing (16) and tearing apart the casing; characterized by d) second means (28) located prior to the shirring zone for transversly weakening but not severing a section of said feed stock casing (16) to provide a narrow frangible band of casing extending about the circumference of the feed stock casing; and e) said tensioning means (14, 18, 56, 118, 156) being designed for tensioning the feed stock casing (16) across said frangible band and tearing apart the casing along said frangible band. Apparatus as in claim 9 wherein said second means (28) is a perforating means for forming a succession of closely spaced perforations (50, 150) across the flat width of the casing, said succession of perforations defining said frangible band. Apparatus as in claim 10 wherein said perforating means (28) forms said perforations (150) at an oblique angle across the flat width of the casing. Apparatus as in claim 10 or 11 wherein said weakening means includes an anvil (30) and a casing perforator (32) disposed on opposite sides of the casing (16), said anvil and casing perforator being movable one towards the other and against the casing. Apparatus as in claim 12 wherein said feed stock casing (16) is expanded to an open position and said perforating means (28) includes members (30, 42) adjacent said casing perforator which move in advance of said casing perforator for engaging and flattening the open casing to substantially its flat width. Apparatus as in claim 12 wherein said casing perforator is a knife blade (32) having a serrated cutting edge (34). Apparatus as in claim 14 wherein said serrated knife (34) edge comprises a plurality of straight sided teeth. Apparatus as in claim 9 wherein said tensioning means comprises said shirring means (14) and a cooperating restraining means (56) for restraining the feed stock casing (16) when said frangible band is adjacent said shirring means, said shirring means and said restraining means cooperating for tensioning the feed stock casing across said frangible band and tearing apart the casing along said frangible band. Apparatus as in claim 16 wherein said shirring means (14), after the tearing apart of the casing, is operable to shirr and incorporate a torn end of the feed stock casing into a last-shirred end (23, 123) of said stick (22, 122).

Inventors: FARKONAS JOHN, FELDT RAYMOND AUGUST, KAZAITIS MICHAEL PAUL, FARKONAS, JOHN, FELDT, RAYMOND AUGUST, KAZAITIS, MICHAEL PAUL
Applicants: VISKASE CORP, VISKASE CORPORATION
Application year: 1992
Main classification: A22C13
IPC codes: A22C13