AU707975B2 - Plastic net bag sealing apparatus - Google Patents

Description

ST

2 Field of the Invention This invention relates to a plastic net bag sealing apparatus and to a method of sealing plastic net bags.

Background of the Invention Plastic net bags are commonly used to hold fruit and vegetables but can also be used as packaging for such diverse objects as sausages, bottles of wine, cheeses and toys.

The netting for making plastic net bags is produced as a continuous plastic web in the form of an expandable tube which when unexpanded is generally cylindrical and rope-like having a diameter of approximately 6mm and which is sold wound on spools.

To make a net bag the web of netting is unwound from the spool and cut into appropriate lengths usually around 30 40 cm long, but which can vary depending upon the size of bag required. One (first) end of the length is 15 then sealed to make a plastic net bag having one sealed end. A packer or a distributor then fills the bag with produce and seals or closes the other, open, end of the bag. The sealing of that open end is not a particular feature of this Sinvention.

There are two common ways of sealing the first end of the length of web to make a plastic net bag.

The first method is using a metal clip to seal the first end of the bag.

Although bags sealed with a metal clip are strong, metal clips can be sharp and often when bags of fruit are stacked for transport or display to customers, the clips cut or damage fruit in adjacent bags. Since the major market for 25 plastic net bags is for packing fruit and vegetables this is a major fault. A second, though less serious problem is that metal clips can rust.

Heat sealing of the first end of the length of web is also known.

Guimatra SA of Brazil make a plastic net bag bonding/sealing apparatus (model GSG700) in which the web is cut into lengths then a hot plate is applied to the cut end of the length and a heat bonded seal is formed. Bags made by this apparatus have two problems. First the seal is not very strong, and, in particular, is considerably weaker than sealing with a metal clip.

Secondly, the seal formed is bulky and has sharp edges which can cut and damage fruit.

SV I 3 The invention seeks to provide an improved method and apparatus for seeking net bags which can produce a seal/bond of sufficient strength and also produce a seal/bond which is less likely to damage soft goods such as fruit, vegetables and the like.

Summnary of the Invention According to the present invention there is provided a net bag sealing apparatus including: means for winding a continuous tubular web of plastic netting for making a net bag around a frame each winding of the web being spaced from an adjacent winding; means for allowing the cutting of the tubular web of plastic netting into a series of discrete lengths having a first end and a second end; and means for enclosing a length of the web at or adjacent said first end in a enclosure which is approximately the same diameter as the unexpanded 15 diameter of the tubular web; the arrangement being such that when heat is applied to the first end of the plastic webbing the webbing forms a seal or node whose size is not substantially larger than the width of the enclosure, preferably less than 1.3 times the width of the enclosure.

Thus the present invention allows the manufacture of the seal for a net bag whose diameter and shape can be at least partly governed by the 0* configuration of the enclosure, thus enabling the seal to be much smaller than existing heat bonded seals. Typically the seal will be at most 20% larger than S* the enclosure. Uniform, identical seals can be made which are smooth and 25 without sharp edges which have a much reduced likelihood of damaging fruit during transport.

In a preferred embodiment the heat applied may be provided by a flame of a blowtorch, oxy-acetylene torch, or the like.

In a preferred embodiment the frame is defines a series of grooves into which adjacent windings of the web locate when the web is wound around the frame and which from part of the means for enclosing a length of the web.

Conveniently the frame defines two parallel spaced apart plates each plate defining a series of grooves.

The plates may be spaced between 10 and 20mm apart.

Preferably an upper part of the mould is provided which is locatable over the two spaced apart plates to define a series of upper mould parts, lower parts of the moulds being defined by the grooves, which upper part is separable from the frame but which can be placed on the frame before the application of heat to the web.

Typically the mould or enclosure is generally cylindrical.

The frame is rotatable about its central longitudinal axis and a feeder whose movement is linked to the rotation of the frame moves along a worm drive aligned parallel with the longitudinal axis for feeding web into the grooves.

In a related aspect, the invention provides a method of making plastic .net bags comprising the steps of:a) winding a web of unexpanded tubular plastic net bag webbing around a frame, successive windings placing the web into adjacent grooves on 15 the frame; 1 h.e b) placing a lid or upper part over the grooves to define an enclosure around one or more of the windings c) making a cut through the webbing to define a series of individual lengths of web; d) applying heat to the winding adjacent to each enclosure to cause the web to melt and shrink to define a node which is less than 1.3 times, preferably less than 1.15 times, the diameter of the enclosure.

.Brief Description of the Drawings The invention will now be described by way of example only and with reference to the accompanying drawings in which: Figure 1 is a schematic plan view of a bag sealing apparatus embodying the present invention; Figure 2 is a schematic side elevation of the apparatus shown in Figure 1; Figure 3A is a side view of a detail of the apparatus of Figure 1 showing an enclosure/mould in which a length of web is retained while being heat sealed; Figure 3B is a view on line IIIB shown in Figure 3A; Figure 3C is a similar view to Figure 3B but which shows an upper part of the mould separated from a lower part of the mould; Figure 4 is an end view of a frame of the apparatus of Figure 1; Figure 5 is a schematic drawing of a net bag made by the apparatus of Figure 1; Figure 6A is a schematic section through a clutch which forms part of the apparatus shown in Figure 1; and Figure 6B is a front elevation of the clutch of Figure 6A.

Detailed Description of a Preferred Embodiment Referring to the drawings, the overall layout of the plastic net bag sealing apparatus will first be described with references to Figures 1 and 2 before a more detailed description of the method of sealing of the plastic net bags is discussed.

The plastic net bag sealing apparatus, generally indicated at includes a frame 12 supported on a centrally located axle 14 for rotation of the frame about longitudinal axis 14A of the axle. Referring to Figure 1, and Figure 4, in particular, the frame, viewed from one end is in the form of a 15 cross, with beams 16, 18, 20, 22 supported at the four points of the cross by cross beams 24 and 26 which extend perpendicularly from the axle 14 to the beams. One pair of cross beams is located at each end 12A, 12B of the axis/frame. As can be seen from Figure 4, cross beams 24 and 26 are also oriented perpendicular to each other.

The uppermost beam 16, as oriented in Figure 4, is shown in more detail in Figures 3A to 3C. Beam 16 includes two parallel, spaced apart plates 28 and 30. Each plate, 28, 30 defines a generally saw tooth pattern shown in detail in Figure 3C. The saw tooth pattern extends along the length of the beam/frame from a first groove 32A at the first end 12A of the frame to the other, second, end 12B, where end groove 32B is defined. The base of each groove 32 between the points 34 of each adjacent tooth has a generally semicircular cross section hence the base of each groove is semicylindrical.

Further plates 28A, 30A, respectively are fixed adjacent to plates 28, Those plates define semicylindrical grooves which match the grooves in the plates, to lengthen the grooves. The centre of each groove is spaced apart from the centre of the adjacent groove by a fixed distance D The lower most beam 20, (as oriented in Figure 4) comprises two spaced apart metal beams 20A, 20B, which define a longitudinally extending gap 20C between them, which gap extends along substantially the entire length of the beam The spacing between beams 16 and 20 is adjustable as is the spacing between beams 18 and 22 by adjusting the location of the beams on the cross beams 24 and 26, so that the size of the frame can be adjusted for manufacture of net bags of differing lengths, as will be explained later. The dotted outline 33 illustrates the winding of a web of net bag webbing around the frame.

The frame is rotated about its longitudinal axis 14 by a drive arrangement comprising a three phase motor 100 a reduction gear box 102 together with a clutch mechanism 104 and belt drive 106, which controls the stopping and starting of the rotation of the frame 12. The clutch mechanism is shown in more detail in Figures 6A and 6B and includes a driven shaft 200, a spring 202 and a clutch plate 203 moveable by the spring. An annular wheel 204 is mounted on one end of shaft 200. A further annular wheel 206 is located around wheel 204, which wheel carries the belt for the belt drive 106. A circular plate 208 is located over the one end of the axis which is mounted on the axis 200 for rotation with the axis by means of pin 209 and adjustable screw 210. The circumference of the plate defines an annular rim *oo or projection 212 which rim, when annular wheel 206 is moved towards the plate 208 by clutch plate 203, frictionally engages with the wheel 206 to turn the wheel and hence drives the belt 106. The adjustable screw 210 allows the clutch to be adjusted so that is slips easily if resistance to movement of the belt increases above what is expected during normal use of the apparatus. A chain and sprocket drive 108 links the rotation of the axis 14 of the frame 12 with rotation of a worm drive 110 which in turn controls movement of a feeder 112, threaded on the worm drive, relative to the rotation of the frame 12. The gearing of the sprocket and chain drive and the thread angle of the worm drive 110 is such that for every complete rotation the frame makes, the feeder travels along the worm drive in the direction of the longitudinal axis 14A, a distance equivalent to the distance D between two adjacent grooves in beam 16 of the frame.

In use, the feeder is located at the first end 110A of the worm drive adjacent to the first end 12A of the frame. The beam 16 which carries the grooves is normally located at the top of the frame and approximately above the axle 14. Figure 2 shows a roll or spool 120 of plastic net bag web 122.

One end of the web 122 is fed from the roll 120 through the feeder 112 and is placed in the end groove 32A defined in the beam 16. The apparatus is then 7 switched on and the clutch operated to commence rotation of the frame and simultaneous travel of the feeder along the worm drive 110. For each rotation of the drive the feeder 112 moves distance D between two grooves along the longitudinal axis of the worm drive and on each rotation of the frame the web 122 is fed consecutively into adjacent grooves. Figure 1 illustrates the start of this procedure after the web has been fed around the frame four times into four consecutive grooves. The frame continues to rotate and the feeder moves along the worm drive until webbing has been fed around and along the length of the frame into all the grooves. Net web can become stuck on the spools 120 of web so the adjustable clutch is set so that it slips if the resistance to movement of the frame increases significantly, due to the web being stuck on the spool for example. This prevents damage to the apparatus occurring.

'A limit switch 124 is defined on the second end 110B of the worm drive. Once the feeder touches this switch, travel of the feeder and rotation of 15 the frame ceases. When the operation stops the beam 16 which carries the grooves is preferably located substantially vertically above the axis 14 at the top of the machine, although the frame 14 can be rotated manually, if Snecessary.

Referring now to Figures 3A to 3B an upper mould or enclosure part 130 is then placed on top of the frame 16. As can be seen in Figure 3A, the upper part of the mould includes two parallel spaced-apart metal plates 132, 134 defining V-shaped grooves which are adapted to interfit with the Vshaped grooves defined in the plates 28, 30 of beam 16. The lower part of each V of the upper part 130 defines a semi-cylindrical groove so that, as is best seen in Figure 3B a cylindrical mould or enclosure is defined around a portion of the web 122. The upper grooves are lengthened by additional plates 132A, 134A the same way as the lower grooves. The diameter of the cylindrical mould is preferably slightly larger than the diameter of the unexpanded web. Thus, with reference to Figure 3A, two cylindrical metal mould portions spaced approximately 10 to 20mm apart are disposed around a length 122A of web 122.

Once the upper part 130 of the mould is in place, the web of net roll is cut to define a series of individual lengths of net roll by slicing through the web where it is wound around the frame at the bottom of the frame 16 by inserting a knife in the gap 20C between the two parallel metal plates which define the lowermost beam 20 and cutting along the length of the 4 4 8 frame. Next the flame from a blow torch, oxyacetylene torch or the like is applied to melt or burn the lengths of web 122A disposed between the two parts of the upper mould which causes the web to melt (parts may burn) and form a smooth cylindrical node or seal of a diameter only slightly larger than the unexpanded web and the mould itself. Figure 5 illustrates a typical seal/node 150 made by the apparatus of the present invention. The end of the seal does not have to be formed in the enclosure itself and may be contiguous to it and will still form a smooth generally planer seal which is rounded and small. Th function of the mould enclosure may be merely to retain the web in position and provide a nucleus or for the formation of the seal. The upper part of the mould can then be removed and the net bags removed from the machine. The number of net bags made in a single forward cycle of operation of the machine is twice the number of grooves. The net roll is then inserted into the other end groove 32B, the device operated in reverse and the feeder 15 travels from the second end 110B to the first end 110A, feeding web 122 into the frame as it goes before the same process of applying the upper part of the mould cutting the webbing and heat sealing the nodes is carried out.

Although the specific embodiment describes the use of a single feeder, it would be possible to have two feeders operating in series or parallel on the same principles as set out above. For example, in one embodiment, a second feeder could be spaced a fixed distance from being linked to and moved by feeder 112 on a smooth rod rather than the worm drive adjacent a further frame or an extension of the frame 12 and fed from another spool of web so that twice as many bags can be made at the same time.

25 The size of the frame and the number of grooves in the frame may also be varied to provide an apparatus which can make more, or less, net bags at a time. Typically an apparatus embodying the present invention may make 100 bags each cycle of operation.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

I I 9 THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:- 1. A net bag sealing apparatus including: A frame; means for winding a continuous tubular web of plastic netting for making a net bag around the frame each winding of the web being spaced from an adjacent winding; means for allowing the cutting of the tubular web of plastic netting into a series of discrete lengths; and means for enclosing a length of the web in a enclosure or mould which is approximately the same diameter as the unexpanded diameter of the tubular web; the arrangement being such that when heat is applied to the first end of the plastic web adjacent to the enclosure the web forms a seal or node whose size is less than 1.3 times, preferably less than 1.15 times, the width of 15 the enclosure or mould.

2. Apparatus as claimed in claim 1 wherein the frame is defines a. series of grooves into which adjacent windings of the web locate when the web is wound around the frame and which from part of the means for enclosing a length of the web.

3. Apparatus as claimed in claim 2 wherein the frame defines two parallel spaced apart plates each plate defining a series of grooves.

4. Apparatus as claimed in claim 3 wherein the plates are spaced between 10 and 20nmm apart.

U. 5. Apparatus as claimed in claim 2 or claim 3 wherein an upper part of U 25 the mould is provided which is locatable over the two spaced apart plates to define a series of upper mould parts, lower parts of the moulds being defined by the grooves which upper part is separable from the frame but which can be placed on the frame before the application of heat to the web.

6. Apparatus as claimed in any preceding claim wherein the cross section of the mould or enclosure is generally cylindrical in cross section.

7. Apparatus as claimed in any preceding claim wherein the frame is rotatable about its central longitudinal axis and a feeder whose movement is linked to the rotation of the frame moves along a worm drive aligned parallel with the longitudinal axis for feeding web into the grooves.

Claims (5)

1. 8. A method of making plastic net bags comprising the steps of:- a) winding a web of unexpanded tubular plastic net bag webbing around a frame, successive windings placing the web into adjacent grooves on the frame; b) placing a lid or upper part over the grooves to define an enclosure around one or more of the windings c) making a cut through the web to define a series of individual lengths of web; d) applying heat to the winding adjacent to each enclosure to cause the web to melt and shrink to define a node which is less than 1.3 times, preferably less than 1.15 times, the diameter of the enclosure.
2. 9. A method as claimed in claim 8 wherein heat is applied by means of a blowtorch flame or the like. 10 A method as claimed in claim 9 or 10 wherein heat is applied to a 15 length of web held between two spaced apart enclosures or moulds.
3. 11. A plastic net bag made by apparatus as claimed in any one of claims 1 to 7.
4. 12. A plastic net bag made by a method as claimed in any one of claims 8 I to
5. 13. Apparatus for making plastic net bags substantially as hereinbefore .described with reference to and as shown in the accompanying drawings. Dated this third day of June 1997 VAN TRI HUYNH Patent Attorneys for the Applicant: F.B. RICE CO. ABSTRACT A net bag sealing apparatus includes a frame, and means for rotating the frame to wind a continuous tubular web of plastic netting for making a net bag around the frame, with each winding of the web being spaced from an adjacent winding. The apparatus also includes means for allowing the cutting of the tubular web of plastic netting into a series of discrete lengths by a knife, or the like and means for enclosing a length of the web in a enclosure or mould which is approximately the same diameter as the unexpanded diameter of the tubular web. When heat from a blow torch is applied to the plastic web adjacent to the enclosure the web melts and forms a seal or node whose size is less than 1.3 times, preferably less than 1.15 times, the width of the enclosure or mould. °o. S SSoC