referring to the drawings , fig1 to 3 schematically show a conventional shirring mechanism for the manufacture of packing skins shirred to form caterpillars from a hose - type wrapper strand of any desired length . the hose - type wrapper strand 10 emerging from a reel ( not shown ) in flat condition first passes a pair of pressing rollers 12 which seal the hose - type wrapper . behind the pair of rollers 12 , the hose - type wrapper strand 10 is opened through a shirring tube 16 provided with a bore 14 . inflating air is passed through the bore 14 and , as shown by arrows 18 , is blown into the open hose - type wrapper strand 10 . the inflated hose - type wrapper strand 10 finally passes a shirring tool 20 , schematically shown by two shirring rollers 22 , which constricts the inner diameter of hose - type wrapper strand to the shirring tube size and at the same time advances it during rotation thereof . shirring tools of the afore - described type are known in the art . in lieu of the two shirring rollers 22 as shown , three or even more shirring rollers can be distributed along the wrapper perimeter . alternatively other types of shirring tools may be employed , such as a rotatingly actuated internal worm of the type as shown and described , for example , in de - ps 21 47 498 . the type of shirring tools have in common the advance of the hose - type wrapper material for shirring purposes . fig1 shows the initial position of the hose - type wrapper strand prior to shirring of a new hose - type caterpillar . the crushing rollers 12 and the shirring tool 20 , to wit , shirring rollers 22 , are in the standstill position . the hose - type wrapper strand 10 extends slightly beyond the shirring rollers where it is held in the open position through the inflating air admitted as shown by arrows 18 at an approximately equal circumferential distance from the shirring tube 16 . the shirring tube 16 , with the other end thereof , is attached to a holding mechanism 24 shown in fig1 to 3 in the form of a plate capable of being displaced in the longitudinal direction of the shirring tube 16 through a power cylinder ( not shown ). in lieu of the plate , the shirring tube may also be attached together with one or several other shirring tubes to an axially displaceable revolver mechanism of the type as shown , for example , by de - os 29 24 059 . displaceably guided on the shirring tube 16 is a stop sleeve 26 exhibiting a cylindrical section 28 tapering toward the shirring tool 20 . a collar 30 of greater diameter on the opposite end of the stop sleeve 26 can be seized by a fork - type gripper 32 and displaced , in controlled manner , through the latter by a power cylinder ( not shown ) along the shirring tube 16 . in the illustration according to fig1 in which the shirring tube 16 is completely pushed into the open end of the hose - type wrapper strand 10 , the tapering section 28 of the stop sleeve 26 is positioned immediately ahead of the opening end of the hose - type wrapper strand . thus , in view of the inflating air centering the strand taper , section 28 can be pushed into wrapper strand 10 to a position directly ahead of the shirring tool 20 . after positioning the shirring rollers 22 ( through a drive not shown ) are caused to rotate , thereby pushing forwardly the hose - type wrapper material toward the stop sleeve 26 . first , an initial section 34 of the hose - type wrapper strand 10 is slid on the tapering section 28 of the stop sleeve 26 , the cross - section of which is only irrelevantly smaller than the internal cross - section of the opened hose - type wrapper strand remaining unshirred . once the front - sided end of the hose - type wrapper strand 10 strikes the collar 30 , the hose - type wrapper strand 10 starts to fold itself behind the tapered section 28 of the stop sleeve 26 . this forms a hose - type caterpillar 36 growing in proportion to the increasing advance of the hose - type strand , while the stop sleeve 26 at the same time moves to accommodate such a growth in length in a manner controlled by gripper 32 . when finally the desired caterpillar length is reached as shown in fig3 the rotary actuator for the shirring rollers 22 is turned off and the shirring tube 16 with the stop sleeve 26 is moved forwardly a short distance . then , the caterpillar 36 is separated from the hose - type wrapper strand 10 by a cutter , such as a pair of knives 38 or a rotating cutting disk , to form a shirred packing wrapper 40 . the severed packing wrapper 40 on the shirring tube 16 , for example with the aid of the afore - mentioned revolver , can now be placed in a position in laterally staggered relationship to the shirring tool 20 . next , as shown in fig4 packing wrapper 40 is seized by a holding mechanism 42 in a manner that the unshirred hose - type wrapper portion 34 at the front - sided end of the packing wrapper 40 protrudes from the holding mechanism 42 . the holding mechanism 42 is composed of two oppositely movable semi - sleeves 42a , 42b which , in the front - sided end , are each provided with a radially inwardly projecting collar 44a and 44b , respectively . once the semi - sleeves 42a , 42b have engaged the packing wrapper , the stop sleeve 26 and the shirring tube 16 are drawn out of the packing wrapper 40 . then , the holding mechanism 42 with the packing wrapper 40 caught therein is placed ahead of a closing tool to close its front - sided end -- as explained hereinafter with reference to fig5 to 11 . fig5 shows the front - sided end of the packing wrapper 40 rigidly clamped within the holding mechanism 42 , in longitudinal section , ahead of the closing tool composed of a first winding element 46 in axial alignment with the packing wrapper 40 and a second winding element 48 pivotally hinged thereto . the elements 46 , 48 form the elongated , thin legs of a pair of tongs 50 attached to the end of a shaft - type tool carrier 52 . the first winding element 46 which is non - pivotable in relation to the tool carrier 52 substantially coincides with the axis of the tool carrier 52 and , hence , with the axis of the packing wrapper 40 . the tool carrier 52 along with the pair of tongs 50 is part of a closure mechanism to be explained in greater detail hereinafter , in conjunction with fig1 to 16 . the axial and rotating movements of the tool carrier as described hereinafter and the opening and closing of the tongs , are generated and controlled with the aid of that mechanism . in the initial position as shown in fig5 the tongs 50 are in an open position in which the movable tong leg 48 encloses an angle of about 25 ° to 30 ° with stationary tong leg 46 . in that position of the tong legs , the tool carrier 52 along the axis thereof is moved forwardly toward the packing wrapper 40 clamped onto the holding mechanism 42 , thereby causing the stationary leg 46 to move into the packing wrapper 40 . once the free end thereof has penetrated into the folded stock of the packing wrapper 40 ( fig6 ) to a depth of about 5 to 10 mm , the forward movement of the tool carrier 52 is discontinued . the tool carrier 52 is then rotated instead , thereby causing the tongs 50 to close approximately during the first half rotation in a manner to be described hereinafter . upon the closure movement of the tongs 50 , the movable leg 48 thereof which is of substantially shorter length ( e . g ., about 12 mm shorter ) than the stationary leg 46 , seizes the unshirred initial portion 34 of the packing wrapper 40 protruding from the holding mechanism 42 from the outside along a surface line . this causes a folding of the unshirred portion 34 inwardly under simultaneous drive in the circumferential direction , thereby forming a twist off 54 , as shown in fig7 of the hose - type material of the initial section 34 at the front - sided end of the tong leg 48 . the twist - off 54 forms the beginning of a twisted plait 56 . twisted plait 56 is thus formed by a continuous rotation of tongs 50 ( now closed ) and , as the advance movement of the tool carrier 52 is recommenced , twisted plait 56 is formed as it travels or builds up along the two tong legs 46 , 48 under a continued withdrawal of wrapper material from the fold stock of the packing wrapper 40 toward the tong hinge 58 . simultaneously with the formation of the twisted plait , the unshirred initial section 34 is drawn into the twisted plait 56 to be rigidly enclosed thereby . the advance movement of the tongs 50 , initially , is relatively rapid . approximately midway of the distance , the movement is substantially delayed in the manner to be described hereinafter . this causes a reinforced knot 60 to be formed on the outer end of the twisted plait 56 , keying itself in the opening end of the packing wrapper ( fig8 ). that condition will be attained , depending on the dimensions of the packing wrapper and the strength of the hose - type material , after about 5 to 10 revolutions of the tongs . at that time , advance movement and rotation of the tongs 50 is stopped . as shown in fig9 a retainer 62 is then moved to a position before the opening end of the holding mechanism 42 . the retainer 26 includes a slot 64 of a width such that the tong legs can be accommodated thereby . once the retainer 62 has reached its end position , the tong legs 46 , 48 ( whose clamping force upon termination of the tong rotation was reduced ) are withdrawn as shown in fig1 . this is done by a retraction movement of the tool carrier 52 , without rotation , from the twisted plait 56 as twisted plait 56 is prevented by retainer 62 from being also withdrawn . left in twisted plait 56 , as shown in broken lines at 66 and 68 , respectively , are two channels . channel 68 is formed by leg 48 of reduced length and terminates at the afore - mentioned twist - off point 54 . however , channel 66 is formed by leg 46 of greater length and is continuously open , thereby forming the desired vent channel within the twisted plait 56 . once the tool carrier 52 with closed tongs 50 according to fig1 has reached its rearward end position , it is rotated temporarily in the opposite direction , thereby causing tongs 50 to open . at the same time , retainer 62 is swivelled back into its resting position , thereby causing all parts to retake their initial position according to fig5 for closing another packing wrapper . as mentioned before , the tool carrier 52 with tongs 60 and retainer 62 form components of a closure device to be described hereinafter in closer detail in conjunction with fig1 to 16 . the closure means cooperates with a holding mechanism disclosed , for example , by de - os 29 26 543 , wherein a shirred packing wrapper provided with an unshirred initial section is firmly clamped . according to fig1 to 15 , the closure mechanism exhibits a housing 70 laterally substantially open . the housing 70 is composed of a base plate 72 , two front walls 74 and 76 , a cover plate 78 , and two narrow lateral bearing plates 80 , 82 . the bearing plates with the ends thereof , are inserted into recesses of the base plate 72 and the cover plate 78 , respectively . the afore - mentioned parts 72 to 82 are interconnected ( not shown ), as by screws . secured in the front walls 74 , 76 are the ends of two guide rods 84 located at the same level in symmetry with the vertical central longitudinal plane of the housing 70 . a sledge - type bridge 88 is mounted on guide rods in a manner longitudinally displaceable with ball sleeves 86 . a dual - acting pneumatic power cylinder 90 , the housing of which is secured in a bore provided in the rear front wall 76 , serves to displace the bridge . the front - sided wall 74 , within a circular , central break - through below the guide rods 84 , accommodates a bipartite bearing housing 92 in which is seized the external ring of an anti - friction bearing 94 . the internal ring of the anti - friction bearing 94 encloses a sleeve 96 provided with a multiple - spline shaft 98 forming the tool carrier 62 . the shaft 98 ends in an axial force transmitting ball bearing 100 which is inserted in an axially non - displaceable manner into a bore 102 of a portion of the bridge 88 extending downwardly and midway between guide rods 84 . the sleeve 96 behind the anti - friction bearing 94 carries a toothed pulley 104 . a second toothed pulley 106 along with a counting disk 108 circumferentially provided with fins is seated on the driving shaft 110 of a reversible geared electromotor 112 fixed to the cover plate 78 of the housing 70 . a belt 114 is wound about the two pulleys 104 , 106 , with the belt extending through an opening 116 in the cover plate 78 . the multiple - spline shaft 98 , on the front - sided end thereof , contains a threaded bore into which are screwed the tongs 50 with a threaded end 118 . the tongs 50 are locked , in suitable manner as by a transverse pin , to prevent them from being unscrewed . the tongs 50 include a shaft - shaped part 120 having the threaded end 118 and having rotatably located thereon a brake drum 122 between a collar 124 rigidly attached to the shaft and a sliding disk 126 of suitable material , such as polytetrafluoroethylene . the sliding disk is supported on the front side , against the multiple - spline shaft 98 . the brake drum 122 is clamped , as especially shown in fig1 and 16 , by two brake levers 128 , 130 configured as brake jaws and swivably disposed on a bearing sleeve 132 . the bearing sleeve 132 is located in a manner to be displaceable in the longitudinal direction on a guide rod 134 on the outer side of the front - sided housing front wall 74 . a helical spring 136 loaded between the ends of the brake levers 128 , 130 generates the required brake force to form a friction brake for the brake drum 122 , slipping once a predetermined torque is exceeded . the front - sided section 138 of the shaft - type part 120 of tongs 50 is flattened on either side , and at the end thereof carries the stationary leg 46 forming the first winding element . the movable leg 48 forming the second winding element is molded approximately perpendicular to a stretched dual lever 140 . the dual lever 140 , with a slot 142 contained mid - way therein , is provided on the flattened section 138 of the shaft - type part 120 of tongs 50 and is swivably mounted by a bolt forming the joint 58 . a ring - shaped cam disk 144 secured by screws 146 to the brake drum 122 serves for swivelling the movable tong leg 48 . formed on the free front side of the cam plate 144 are two cams 148 , 150 ( fig1 ) respectively extending across half the perimeter . the cams 148 , 150 cooperate with a respective cam follower 152 , 154 at each end of the dual lever 140 when the shaft 98 with the braked brake drum 122 is turned into one or the other direction . formed between the ends of the cams 148 , 150 , by the different axial levels thereof , are stop shoulders 156 , 158 . the stop shoulders 156 , 158 are hit , depending on the direction of rotation of the shaft 98 , by one or the other of said cam followers 152 and 154 , respectively at the end of its path . the respective cam follower thereby drives , due to the continued rotation of the shaft 98 and in the same direction of rotation , the cam plate 142 with the brake drum 122 under friction slip in relation to the brake levers 128 , 130 . the bearing plates 80 , 82 by means of articulated pins 160 carry within the housing 70 respectively one leg 162 of a u - shaped damping lever 164 . the bridge portion 166 of the damping lever 164 , by means of a centrally provided pressure member 168 , cooperates with a damping cylinder 170 . the damping cylinder 170 is located on the base plate 72 of the housing 70 and is adjustably secured by a clamping socket . the damping cylinder 170 is filled with oil and includes a restoring spring ( not shown ) forcing the bridge 166 , in the resting position , against an angular stop 174 on the base plate 72 . a crossbar 176 is welded between legs 162 . the upper end of the legs 162 are reinforced and , with their rounded - off rear edges , form stop faces 178 . the stop faces 178 are hit by the bridge 88 during advancing of the tool carrier 52 prior to reaching its front - sided end position , thereby causing a substantial slow - down of the movement of bridge 88 and , hence , of the tongs 50 in the direction of advance . as shown by fig1 , a bearing block 180 is fastened by screws to the left hand edge of the housing front wall or as viewed from the front side . located on bearing block 180 are two non - rotationally interconnected levers 182 , 184 . the levers 182 , 184 enclose an obtuse angle . the upper lever 182 , by an articulated bolt 186 , is coupled to the piston rod 188 of a dual - acting power cylinder 190 . the housing of power cylinder 190 is pivoted to the cover plate 78 by means of another bearing block 192 . the lower lever 184 carries a cross sheet 194 forming the afore - mentioned retainer 62 with the slot 64 . by extension and retraction of the power cylinder 190 , the cross sheet 194 is swivelled from its resting position shown in fig1 into the operating position shown in fig1 and back into the resting position , respectively . viewed from the front side , an angle section ledge 196 is provided on the right hand side of the housing 70 . the ends of ledge 196 are secured to the bearing plate 80 and the rear front wall 76 , respectively . the angle section ledge 196 , in its horizontal profile leg , contains an oblong aperture 198 for adjustably securing three electrical pulse generators 200a , 200b , 200c . these generators cooperate in contact - free manner with an actuating member 202 fixed to the bridge during its displacement . the counting disk 108 on the driving shaft 110 of the geared motor 122 cooperates , contact - free , with a transmitter ( not shown ). the pulses of the transmitter as well as the pulses of pulse generators 200a , 200b , 200c are supplied to an electrical control unit ( not shown either ) to be processed therein . the control unit controls the device according to the time diagram shown in fig1 in the manner described hereinafter to carry out the movements of the tongs 50 for forming the end closure as described with reference to fig5 to 11 . at the time t 0 , the device is in its initial position where the power cylinder 90 is retracted and holds the tongs 50 in their retracted position as shown in fig5 ; motor 112 is switched off ; the damping cylinder 170 , with the built - in restoring spring , maintains the damping lever 164 in abutment with the stop 174 ; and the power cylinder 190 is extended so that the retainer 62 takes its resting position . tongs 50 , in that position , are opened . once the holding mechanism 42 with a packing wrapper 40 clamped therein is placed ahead of the closure tool , the electrical control unit by a control signal is activated . the control unit switches by means of a control valve , the power cylinder 90 to advance . this thereby forces the bridge 88 on the guide rods 84 forwardly , driving tongs 50 ( through the anti - friction bearing 94 and the multiple - spline shaft 98 ) so that the stationary tong leg 46 moves into the packing wrapper 40 through the unshirred initial part 34 . moreover , the bridge 88 drives the actuator member 202 along the angle ledge 196 . after an advance of , for example , 40 mm , the actuator member 202 , at the time t 1 , reaches the pulse generator 200b . pulse generator 200b then transmits to the control unit a pulse turning off the advance movement of the power cylinder 90 . hence , the position of tongs 50 according to fig6 has been reached . at the same time t 1 that the feed movement is stopped , the motor 112 is turned clockwise , closing by its first half rotation tongs 50 ( fig7 ). the control unit counts the rotational angle pulses generated by the transmitter 204 in cooperation with the rotating counting disk 108 and switches on again the feed movement of the power cylinder 90 at time t 2 after about 1 . 5 revolutions . this forms the twisted plait 56 on the tong legs 46 , 48 . the feed movement at first is undamped so that the twisted plait 56 migrates relatively quickly along the tong legs toward the tong joint 56 . at t 3 , however , the bridge 88 strikes the damping lever 164 and the feed movement is slowed down by the damping cylinder 170 so that knot 60 is formed on the twisted plait 56 ( fig8 ) as described in the aforegoing . at the time t 4 , the actuating member 202 reaches the pulse generator 200c , thereby switching off the feed movement of the power cylinder 90 . at the same time , the electromotor 112 is rendered inoperative while the power cylinder 190 is actuated in the retracting direction thereby swivelling the retainer 62 to a position in front of the packing wrapper 40 ( fig9 ). upon lapse of a predetermined period of time , through a time member in the control unit , at the time t 5 the power cylinder 90 is switched over to the retraction direction . this causes a withdrawal of the tong legs 46 , 48 out of the twisted plait 56 which twisted plait is prevented by the retainer 62 from being also withdrawn . at the same time , the built - in restoring spring of the damping cylinder 170 swivels the damping lever 164 into the stop position against the stop 174 . it should be appreciated that this is done slowly in view of the oil damping of damping cylinder 170 . at the time t 6 , the actuating member 202 reaches the pulse generator 200a , causing the power cylinder 90 to be switched off . at the same time , the electromotor 112 is switched to an anti - clockwise run with the result that the braked cam plate 144 opens tongs 50 . after two revolutions at most ( whereafter opening of the tongs is , in fact , safeguarded ), the motor 112 is turned off at time t 7 so that the mechanism has reached its initial position . the hose - type wrapper with the end closure formed therein can now be released by the holding mechanism 42 to be fed to a store rack to make room for a new packing wrapper having an unshirred initial section .
a method and apparatus are disclosed for forming a vent hole in an end closure in the form of a twisted plait on a hose - type packing wrapper , especially a sausage skin , shirred to form a caterpillar with an unshirred wrapper section . a first elongated winding element is introduced into the packing wrapper 940 ) to behind the first shirring folds . subsequently , the unshirred wrapper section is seized along an axial surface line by a second elongated winding element of a length shorter than that of the first winding element which is moved radially towards the latter . thereupon , the winding elements are actuated in rotating manner and , at the same time , are axially advanced . the twisted plait is thus generated from the free end of the winding elements in a manner progressing to the rear . at the end , by retraction of the winding elements , a vent channel or hole remains in the twisted plait .