Apparatus and method for producing bags

Abstract

 This application discloses an apparatus for perforating a plurality of web segments provided with holes received on stacking posts serving to retain the segments in a stack. The apparatus comprises a pair of simultaneously operable linear actuators (68) mounted on a support (70) located above the stack and through which support the output rods (74) project, a crosshead (76) fixed to the actuator rods, means (94) carried by said crosshead for compressing the stack, and means (84) also carried by said crosshead for perforating the stack, while compressed, to provide a line of weakness to facilitate separation of a portion of each web segment.

Description

[0001] This invention relates to bag-making apparatus for producing plastics bags from segments, each segment being dimensioned to produce two bags, said apparatus comprising elongate upstanding members arranged to hold the segments as a stack, perforating means operable to produce two parallel, spaced lines of perforations, and cutter means operable to sever and seal the segments of the stack.

[0002] The disclosure of the present application is related to and is an improvement to the subject matter disclosed in co-pending United Kingdom application No. 81.28656, publication No. 2089286.

[0003] This prior application discloses a bag making procedure in which the elongate strip of thermoplastic web is provided with lines of perforation located centrally of the web strip. Each segment produced by the action of the seal bar contains the centrally located lines of perforation. In transporting the web segment by a rotary transfer device, from the pickup -station to the stacking station containing the upwardly projecting pins, partial or full separation along a line of perforation sometimes occurs. if full separation occurs while the web segment is in transit to the stacking station, stacking of that web segment cannot be achieved since registration with the stacking post is no longer possible. In the event partial separation occurs and stacking on the post is achieved a portion of that web segment may not lie in a position to produce a bag stack having the edges of each individual bag overlying each other.

[0004] The problem to be overcome is, therefore, to provide bag-making apparatus in which the risk of perforations provided in a web becoming effective to divide the web prematurely is eliminated.

[0005] According to the present invention the problem is solved by the provision of bag-making apparatus characterized in that the perforating means are located so that operation is effected on the stacks of segments while the segments are held by said upstanding members.

[0006] Preferably in order to facilitate engagement of the segments on the upstanding members, means are operable -on the web to provide each segment with at least two apertures located adjacent to and on either side of the median, considered in the longitudinal direction of the web, of each segment, the segments produced being transferred to a stacking device incorporating the upstanding members on which successive segments are stacked, the upstanding members extending through the aligned apertures of the stacked segments.

[0007] In the preferred construction of the apparatus, the perforated means are operative while a stack of segments is retained on the stacking device for producing lines of perforation enabling subsequent division of each segment to define two bags, and cutter means being operable concurrently or subsequently to the perforating means.

[0008] According to another aspect of the present invention apparatus is provided for perforating a plurality of web segments provided with holes received on stacking posts serving to retain the segments in a stack, the apparatus being characterized by a pair of simultaneously operable linear actuators mounted on a support located above the stack and through which support the output rods project, a crosshead fixed to the actuator rods, means carried by said crosshead for compressing the stack, and means also carried by said crosshead for perforating the stack, while compressed, to provide a line of weakness to facilitate separation of a portion of each web segment.

[0009] In order further to facilitate the production of the perforations a holder is provided for supporting the perforating means and means carried by the holder serve to heat the perforating means to a temperature sufficient to encourage softening of the material of the segments. The holder also serves to support the perforating means in the form of an elongate flat bladelike member clamped to a recess formed in the holder and provided with a series of slots interrupting the sharpened bleeding edge thereby to produce a series of incissions and uncut bond portions, the latter being sufficiently weak to allow easy separation of a layer of the material of the segments.

[0010] If compressing means are provided then preferably the compressing means are operable before the perforating means.

[0011] United Kingdom Application No. 81.28656 discloses, in Figures 9 and 10, a cutting station substantially -similar to the cutting station disclosed herein.

[0012] The invention will now be described by way of example with reference to the accompanying diagrammatic drawings, in which:

Figures lA and 1B, considered together, is a side elevation of a web processing machine constructed, and operating in accordance with the present invention;

Figure 2 is a perspective view illustrating a mechanism forming a part of the machine of Figure 1 involved for transferring a web segment from a transfer station to the stacking station of the machine;

Figure 3 is a perspective view illustrating a stack of web segments deposited on pins carried by a stacking plate;

Figure 4 is similar to Figure 3 but additionally shows perforating knives of the machine after perforation of the stacked web segments has occurred;

Figure 5 illustrates the web segments being cut between the pins by a knife to produce two bag stacks;

Figure 6 is a side elevation of the knife supporting and actuating means;

Figure 7 is a section of Figure 6 taken substantially along the line 7 - 7;

Figure 8 is an elevation of the perforating mechanism; and

Figure 9 is a side view of Figure 8 as viewed along the line 9 - 9.

[0013] Referring first to Figure lA it will be seen that a web roll WR is mounted on a transverse shaft 20 rotatably supported by an unwind stand 22 carried by a frame structure 24. The web strip unwound from the web roll WR passes over a series of rolls collectively identified by the numeral 26 and then progresses over a series of rolls rotatably mounted in a tower structure 28 which includes gusseting devices 30. Unreeling of the web strip from the web roll is accomplished by drive rolls 32 and thereafter the web is passed over a series of rolls comprising a web tensioning device 34. A turning roll 36 directs the web strip to draw rolls 37 which are intermittently operated by the drive of a bag machine 38.

[0014] The thermoplastic film TF is advanced by the draw rolls to a severing and sealing station 40 and the portion of web advanced is momentarily retained on a series of belts 42 generally describing a triangular path and defining a transfer station TS. On creation of a web segment WS located at the transfer station (Fig. 2), a rotary transfer mechanism 44, which includes a plurality of regularly spaced radially extending tubular bars 46, connected through a hub 48 to a source of vacuum, engages and retains a web segment at the transfer station and translates it through an arc for reception by one of a series of stacking devices 50 located at a stacking station 52.

[0015] Reference to Figure 2 will reveal one style of web segment in which each segment has a central medial strip removed from one panel and the remaining panel is provided with four holes 54 through which project stacking pins or posts 56 projecting upwardly and fixed to a base plate of the stacking devices 50. The posts 56 are located to correspond to the spacing of the holes 54 so that each web segment is retained on the stacking devices 50 by the posts 56. During machine operation a selected number of web segments are stacked on the stacking devices 50 and when the predetermined number of web segments has been stacked operation of the bag machine 38 is arrested and concurrently therewith a successive stacking device 50 is positioned at the stacking station 52.

[0016] Reference to Figure 1B will reveal the provision of a conveyor 58 that is intermittently driven by drive mechanism 60 such that the upper reach of the conveyor is incrementally advanced from right to left as viewed in Figure lB. Also, as revealed by this Figure, the stacking devices 50 are mounted on the conveyor and successive stacking devices are positioned at the stacking station 52 for a period of time required to accumulate a selected number of web segments.

[0017] In accordance with the principle feature of the preferred embodiment the problem of premature partial or complete detachment of a portion of a web segment WS, along a line of perforation, does not arise since the web segments produced by the bag machine do not include perforations. Accordingly, forces created by air pressure in the course of transferring a web segment by the transfer device 44 from the transfer station TS to the stacking station 52 are easily tolerated by the web segment. As will be explained presently, the bag stacks produced include perforations but their creation occurs while a stack of web segments is retained on the stacking posts 56 carried by the stacking devices 50.

[0018] Further processing of the web segments WS to produce two perforated bag stacks from each group of web segments is achieved by perforating means 62 and cutting means 64 being carried by a frame structure 66 straddling and overlying the conveyor 58. The cutting means 64 are in substantial respects similar to the cutting means disclosed in the above referenced Application.

[0019] During the time when a stack of web segments is being accumulated on the stacking device 50 located at the stacking station 52 the conveyor 58 is inactive. During this time period the perforating means 62 and the cutting means 64 are rendered operative, sequentially or concurrently, to effect, respectively, perforation and separation of the accumulated web segments to produce two individual bag stacks each of which contain a line of perforation.

[0020] The preferred construction of the perforating means 62 comprises linear actuators 68 secured to a flat plate 70 which is in turn adjustably secured to horizontal supports 72 (Figure 1B) of the frame structure 66. The plate 70 is provided with bores through which extend the rods 74 of the linear actuator 68. The extremity of each rod 74 is fixed to a crosshead 76 carrying downwardly projecting perforating knife holders 78. The knife holders 78 are secured to the crossheads 76 by a series of bolts 80 passing through insulating spacer blocks 82 and threaded into the perforating knife holders 78. Perforating knives 84 are secured to the holders 78 by a series of fasteners 86 and the perforating knives 84 extend beyond the holders 78 sufficient to penetrate a stack of web segments. Figure 8 shows the general configuration of each of the perforating knives, and it will be seen that each knife is provided with a series of slots ₈8 creating an interruption in the line of cut defined by a cutting edge 90 which may take the form of a jagged edge which experience has shown requires less force to penetrate each stack of web segments. To enhance penetration of the knife 84 each of the perforating knife holders 78 is provided with a slug heater 92 which can be energized to produce a given temperature to each of the knives 84. Heating of the knives 84 has been found to reduce the amount of force necessary to penetrate a stack of web segments and yet the tendency to form a blocked stack does not arise when a sufficiently low temperature level is selected.

[0021] Before the perforating knives 84 make contact with the -uppermost web segment of the stack of segments, means 94 are provided for compressing the stack to prevent upward bulging of the stack when the knives 84 come into pressure engagement with the stack. As shown in Figures 8 and 9 the compressing means 94 include elongate offset bars 96 which are substantially equal in length to the perforating knives 84 and make contact with the stack adjacent the line of perforation established by the knives 84. The bars 96 are connected to the crosshead 76 by spring biased rods 98 which slidably extend through bushings 100 mounted in the crosshead 76. A stop member 102 is secured to the upper end of the rod 98 by a fastener 104 to limit and retain the rods 98 in the bushings 100.

[0022] According to the above described arrangement when the actuator 68 is energized to effect operation of the perforating means 62 the elongate bars 96 come in contact with the stack of web segments forcing them downwardly onto the stacking devices 50 and immediately thereafter the perforating knives 84 penetrate and accordingly perforate the stack of web segments.

[0023] In order to enhance the longevity of the knives 84 the stacking devices 50 are provided with inserts 106 which can be made of wood or plastic material which will allow penetration of the knives 84 and yet have a minimal effect in rendering the cutting edge of the knives dull.

[0024] As shown in Figure 2 the cutting means 64 is located downstream and adjacent the perforating means 62 and if desired the perforating means and the cutting means can be actuated simultaneously or sequentially at the option of the user. Figures 6 and 7 illustrate the cutting means 64 in greater detail and it will be seen to comprise linear actuators 108 also mounted on the flat plate 70 being suitably bored to accommodate reciprocating movement of rods 110 having their lower ends threaded to receive a nut 112 fastening the rods to a crosshead 114. A knife holder 116 is in turn connected to the crosshead 114 by bolts 118 extending through insulating spacers 120. In similar respects the cutting means is provided with stack compressing means 122 which include presser bars 124 rigidly connected to rods 126 having their upper ends slidably disposed, by means of bushings 128, to the crosshead 114. Tension springs 130 are associated with each of the rods and serve to bias the presser bars 124 downwardly.

[0025] The knife holder 116 is formed to receive and retain a cutting knife 132 and rod heaters 134 serving to heat the knife 132 to a desired temperature to facilitate cutting of the web segments, while they are retained on the pins 56, into two bag stacks each of which includes a line of perforation previously made by the perforating means 62. As with the perforating means, cutting means 64 includes, in the stacking device 50, an insert 136 selected of a material such as previously indicated to prevent dulling of the cutting edge of the knife 132. The knife 132 is retained in the holder 116 by a plurality of fasteners 138.

[0026] Reference to Figures 3, 4 and 5 shows the condition of a stack of web segments at the stacking station 52, the perforating station 62 and the cutting station 64. When the conveyor positions a stack of web segments WS at the perforating station 62 and the actuators 68 are operated to drive the perforating knives 84 to cut the web segments, lines of perforation 85 are produced adjacent the stacking posts 56. As previously mentioned, the cutting station 64, operating the parting knife 132 may be concurrently or subsequently operated to produce two bag stacks BS by cutting the web segments along a line PS, located between the -stacking posts 56.

[0027] In view of the above described construction and the mode of operation of the over-all machine, and more particularly the perforating means 62 and the cutting means 64, it should be evident that performing the perforating and cutting function after a selected number of web segments have been stacked eliminates the problem of the prior art of premature separation along one or more lines of perforation formed in the web segment before stacking.

Claims

1. Bag-making apparatus for producing plastics bags from segments, each segment (WS) being dimensioned to produce two bags (BS), said apparatus comprising elongate upstanding members (56) arranged to hold the segments as a stack, perforating means operable to produce two parallel, spaced lines of perforations, and cutter means (132) operable to sever and seal the segments of the stack, characterized in that the perforating means (84,88) are located so that operation is effected on the stacks of segments (_WS) while the segments are held by said upstanding members (56), the severed line of the segment stack lying intermediate the parallel lines of perforations.

2. Apparatus according to claim 1, characterized by means operable on the web to provide each segment (WS) with at least two apertures located adjacent to and on either side of the median, considered in the longitudinal direction of the web, of each segment, the segments produced being transferred to a stacking device (52) incorporating the said upstanding members -(56) on which successive segments are stacked, the upstanding members extending through the aligned apertures of the stacked segments.

3. Apparatus according to claim 1 or claim 2, characterized in that the perforating means are operative while a stack of segments is retained on said stacking device (52) for producing lines of perforation enabling subsequent division of each segment to define two bags (BS), and the cutter means being operable concurrently or subsequently to the perforating means (84,88).

4. Apparatus for perforating a plurality of web segments provided with holes received on stacking posts serving to retain the segments in a stack, said apparatus being characterized by a pair of simultaneously operable linear actuators (68) mounted on a support (70) located above the stack and through which support the output rods (74) project, a crosshead (76) fixed to the actuator rods, means (94) carried by said crosshead for compressing the stack, and means (84) also carried by said crosshead for perforating the stack, while compressed, to provide a line of weakness to facilitate separation of a portion of each web segment.

-5. Apparatus according to any one of claims 1 to 4, characterized by a holder (78) supporting the perforating means (84) and means (92) carried by said holder for heating said perforating means thereby to facilitate penetration of the web material.

6. Apparatus according to claim 5 characterized in that said perforating means comprise an elongate flat bladelike member (84) clamped to a recess formed in said holder (78) and provided with series of slots (88) interrupting the leading sharpened edge to thereby produce a series of incisions and uncut bond portions being sufficiently weak to allow easy separation of a layer of thermoplastic material.

7. Apparatus according to claim 4,5 or 6 further characterized in that said compressing means (94) operate to engage the material of the segments before it is engaged by said perforating means.

Drawing