GB2124579A

GB2124579A - Method of wrapping, and wrapping apparatus

Info

Publication number: GB2124579A
Application number: GB08320468A
Authority: GB
Inventors: Peter Gordon Wilson
Original assignee: Baker Perkins Ltd
Current assignee: Baker Perkins Ltd
Priority date: 1982-07-30
Filing date: 1983-07-29
Publication date: 1984-02-22
Also published as: JPS5926409A; IT8348755A0; IT1173746B; GB2124579B; DE3325996A1; FR2531034A1; GB8320468D0

Abstract

In wrapping successive falling charges of product item in a vertical form-fill-seal wrapping machine so much of a bag length of a tube 13 of wrapping material 10 as is in a suction chamber 31 immediately above sealing jaws 15,17 operation to form a lower transverse seal of the bag length is held open by establishing within the chamber and externally of the tube a gas pressure which is less than ambient air pressure and the simultaneous pressure within the tube. <IMAGE>

Description

SPECIFICATION Method of wrapping, and wrapping apparatus This invention reiates to a method of wrapping and wrapping apparatus and more particularly but not exclusively concerns bagging of charges of snack foods, especially potato crisps, at high speeds in a vertical, form-fill-seal, wrapping machine.

The Assignees of the present Inventor have found that in conventional crisp bagging, vertical form-fill-seal machines with a pair of transverse sealing jaws which reciprocate vertically, the free fall of the crisps is hindered by the progressive narrowing of the open cross-section of the wrapping material tube, immediately above the sealing jaw position, that is brought about by the coming together of the flat faces of the sealing jaws as they bring together the wrapper tube sides for formation of the transverse seal.

More particularly, the Assignees found that successive charges of the crisps fall free until the wrapper side walls restrict further downward falling motion, but then, as the sealing jaws open and stroke upwardly to the top position of their range of movement, the open cross-section of the tube widens to allow the crisps to drop to the bottom of their bag.

It is an object of the present invention to reduce or eliminate the above-mentioned restriction on product fall.

According to a first aspect of the present invention there is provided a method of wrapping successive falling charges of product item in a vertical, form-fill-seal, wrapping machine characterised by the step of holding open, for receiving said charge, a bag length of a tube of wrapping material in a region immediately above a lower transverse seal of the bag length by establishing on so much of the external surface of the bag length as is within said region a gas pressure which is less than ambient air pressure and the simultaneous pressure within the tube.

It might be thought that substantially the same increase in freedom of movement of the failing product item could be achieved by increasing the pressure within the wrapper tube above ambient, rather than reducing the pressure outside the tube.

It is not. This is because any pressure increase within the wrapper tube acts over much more than one bag length, and so will not pull open to the same extent the otherwise narrow portion immediately above the sealing means.

Furthermore, gas currents within the tube will tend to interfere with free fall of low density product items.

According to a second aspect of the invention there is provided vertical, form-fill-seal, wrapping apparatus including transverse wrapper tube sealing means and means to draw a tube of wrapping material downwardly for wrapping successive falling charges of product item in bags formed from successive sealed bag lengths of the tube characterised by suction means to hold to tube open in a region immediately above the sealing means the suction means comprising a suction chamber, surfaces at the upstream end of the suction chamber which define a bag-filling entry orifice and surfaces at the downstream end of the suction chamber which define a filled bag exit orifice the disposition of which varies between a closed disposition in which the orifice has a narrow width appropriate to fit around the transverse seal and an open disposition in which the exit orifice is wide enough to permit passage of the filled bags therethrough, means to move in an operational cycle of the apparatus the surfaces defining the exit orifice to the closed disposition prior to bag filling and maintain the closed disposition during the period when filling commences, and from the closed disposition to the open disposition prior to movement of the filled bag downstream relative to the suction chamber, and means to establish within the suction chamber during the period when filling commences a pressure of gas which is lower than ambient air pressure and the simultaneous pressure within the tube whereby, during the bag filling portion of the cycle of operation of the apparatus, the tube is in the suction chamber urged outwardly so that a terminal length of the tube is held, by the pressure difference across the tube in the chamber, open for filling.

It will generally be convenient for the terminal length to extend upwardly from the sealing means no more than a distance of the same order of size as the diameter of the wrapping tube, regardless of the size of the bag length.

By holding open the bag length immediately above the transverse seal, in the manner provided by the present invention, the charge of product item can fall with less interference from the wrapper tube. The increased freedom of falling movement leads to a possibility of increased rate of formation of bags. Any such increased rate can be utilized to take fuller advantage of the potential of computer-controlled batch weighers to deliver to the wrapping apparatus at great speed a succession of charges of product item.

Reference will now be made, by for example, to the accompanying drawings; in which: Fig. 1 is an elevation, partly in section, of certain essential components of a vertical, formfill-seal, bagging machine; and Figs. 2 and 3 are details showing the interaction of the tube with the rim of the bagfilling entry orifice of the suction chamber.

With reference to Fig. 1, those skilled in the art will recognise certain basic machine parts and the underlying mode of operation on the machine.

Thus, a web 10 of bag-forming synthetic plastics material is fed from a reel (not shown) over a roller 11 and on to the exterior surface of a hollow former 12 which forms the web into a tube 1 3. Associated with the former 1 2 is a longitudinal seal former 14. A pair of sealing jaws comprising a first jaw 1 5 actuated by a cylinder 1 6 and a second jaw 1 7 actuated by a cylinder 1 8 are reciprocable in a horizontal plane both to pinch the bag material between them and so form in it a transverse seal, and also to sever the material at the seal. The severing means comprises a knife 151 in the jaw 15 which cuts into a gap 171 in the jaw 17. The knife 1 51 is actuated by means not shown.

The jaws also reciprocate in a vertical plane.

They move through a cycle, moving when open to an upper position G shown chain dotted, then closing to pinch the bag material at said upper position, then, still closed and holding the bag material, moving downwardly to a lower position R thereby drawing a fresh bag length on to the former 12. At the lower position R, the knife 1 51 is actuated to sever the bag material. The jaws then open to release downwardly a severed bag.

In synchronism with each downward jaw movement, a bag-filling charge of product is dispensed into the internal flow channel 19 of the former 12. It then falls freely under gravity downwardly into the tube 1 3 sufficiently far that it comes to rest between the upper G and lower R positions of the jaws 1 5 and 1 7 so that it becomes sealed within a pillow-type bag generated by the cyclical operation of the jaws 15 and 17.

Turning now to a more particular description of the present invention, the carriage 30 to which the jaw cylinders 1 6 and 18 are mounted carries, upstream of the jaws, a box structure 31 which defines a suction chamber. The suction chamber includes a bag-filling entry orifice 32 in the flat top 33 of the box structure, that is to say, an upstream end 33 of the chamber, and an open downstream end 34 through which filled bags leave the chamber 31. The diameter of the entry orifice 32 is slightly larger than the diameter of the tube 1 3 of wrapping material, when the material 10 is not under tension, so that there is a small annular gap 35 between the tube 13 and the rim 36 of the entry orifice 32.

A pair of shutters, one 37 mounted to the jaw 1 5 and the other 38 to the jaw 17 occlude the open bottom of the box structure 31. As is to be seen in Fig. 1, the leading edges 39 of the shutters almost touch when the jaws 1 5 and 1 7 are in the closed disposition, but the gap 40 between them is sufficiently wide that the shutters do not crush the wrapping material 10 between them. When the jaws 1 5 and 1 7 are in the open disposition, the leading edges 39 of the shutters are at least as far apart from each other as the side walls of the box structure. The gap between the shutters 37 and 38 constitute the exit orifice of the suction chamber.

A vacuum supply 48, typically produced by a fan, is connected to a vacuum line 41 which in turn is fitted to a spigot 42 on the suction chamber 31. The source 44 of lower than ambient pressure is capable of establishing across the walls of the suction chamber 31 a pressure differential of around 4.5 to 9.0 cm/Hg. A baffle 45 within the chamber 31 smoothes the pressure distribution within the chamber 31.

In operation, the jaws 1 5 and 1 7 execute a repeated macl-,ine cycle, as follows.

1. With the carriage 30 at a lower, release station R, actuation of a pneumatic control means 46 provides a flow of compressed air from a source 44 to the cylinders 16 and 1 8 to move the jaws 1 5 and 1 7 to their open disposition. The consequent increased flow of air into the suction chamber around the shutters 37 and 38, results in dissipation of the above-mentioned pressure differential across the tube 13, despite the continuing suction along the line 41. The tube material relaxes and the small gap 35 mentioned above forms between the tube 10 and the rim 36 of the entry orifice 32.

2. With the downstream end 34 of the chamber 31 completely unobstructed, and with the small gap 35 (see also Fig. 3) between the tube and the rim 36, the carriage 30 carrying the chamber 31 and the jaws 1 5 and 1 7 is moved upwardly by crank-driven link 47 to the gripping station G, shown chain dotted. During this movement, the tube 10 does not move either upstream or downstream in the machine.

3. At the gripping station G, the cylinders 1 6 and 1 8 of the jaws are actuated by the control means 46 to move the jaws 15 and 17 to the closed disposition at which the tube sides are brought together and the two faces of the tube material are sealed together. The knife 151 carried within the jaw 1 5 is, however, not yet actuated to sever the material in the middle of the seal so formed. During the time when the jaws are moving together, the pressure within the suction chamber 31 falls. The developing pressure differential across the tube 13 keeps it taut, and this reduces the likelihood of creases in the transverse seals. This is a valuable improvement, because creases in a bag seal can render the seal imperfect.

4. With the closure of the jaws 15 and 1 7 and their attached shutter plates 38 and 39, the exit orifice is substantially blocked and the continuing removal of air along the vacuum line 41 establishes the chosen full pressure differential inside the chamber 31. The resulting pressure differential across the walls of the suction chamber puts the tube material under such tension that it stretches a little.The difference of diameter of the former 12 and the entry orifice 32 and the elastic modules of the tube material are chosen such that, under the influence of the pressure difference, the tube contacts the rim 36 of the entry orifice 32 as shown in Fig. 2, and pulls the length of the tube within the chamber 31 outwardly so that it is fully open throughout much of the depth of the suction chamber, narrowing to the seal in the jaws 15 and 1 7 only in the zone immediately above the jaws 1 5 and 1 7. The pressure differential thereby holds open for filling the tube lying within the chamber 31. Usually, the diameter of the relaxed tube is in a range of from 80 to 99% of the diameter of the entry orifice 32.

5. The tube being held open, the jaws are then moved by the control means 46 downstream, back to the release station R. Such movement puts the tube material under longitudinal tension and draws another bag length off the reel of material, over the roller 11 and past the former 12. The relationship between the pressure differential and the longitudinal tension is such that there is during the downward movement substantially no upward longitudinal movement of the tube material over the rim 36 of the entry orifice 32. (Any such longitudinal movement would tend to reduce the degree of openness of the bag length in the region within the suction chamber, and therefore be undesirable.) 6. Synchronised with the downward movement, a charge of product is dispensed to the bag length of which a lower portion is held open within the suction chamber 31.In the absence of any pressure differential in the suction chamber 31, the width of the bag length would not be maintained below the former 12 but would steadily decrease in the zone below the former thereby impeding product flow. However, by virtue of the holding-open action, the product can fall more or less unimpeded to the bottom of the bag length.

7. With the jaws now at the release station R, knife 151 is actuated to sever the bag material in the middle of the transverse seal formed by the action of the jaws 1 5. The cycle is repeated, opening of the jaws 1 5 and 1 7 allowing the severed bag length suspended from the closed jaws to fall from beneath the release station R on to a conveyor or further processing means.

The present invention and another which is the subject of our copending British Patent Application No. 8222122 filed 30 July 1982 and entitled "Charging of Containers" are related, in that, in general, greater speed and efficiency in bagging snack foods is obtainable using the two inventions together than is obtainable with either invention by itself.

Not all vertical form-fill-seal wrapping machines have a single pair of sealing jaws which reciprocate in a vertical direction to draw down lengths of the wrapping tube. It is envisaged that the present invention would have application to forms of vertical, form-fill-seal wrapping other than the one herein illustrated, for example, apparatus in which the sealing means do not move vertically (other means being provided to draw down the tube), or apparatus in which sealing devices are carried on at least one endless loop carrier means and undergo a downward movement adjacent the wrapper tube and a return upward movement less closely adjacent the wrapper tube. The loop carrier means would normally be constituted by a lefthand chamber wall portion carried on the lefthand loop carrier and a righthand chamber wall portion carried on the righthand loop carrier.

It will be appreciated that a gusset at each end of the transverse seal is not usually required when bagging snack foods. Nevertheless, the invention is applicable to the bagging of product items other than snack foods, and in bags with or without gussets. The tendency for the reduced likelihood of crease formation mentioned hereinabove, would also tend to improve consistency and reliability of the seal in any gussetted area.

Claims

1. A method of wrapping successive falling charges of product item in a vertical, form-fill-seal, wrapping machine comprising the step of holding open, for receiving a said charge, a bag length of a tube of wrapping material in a region immediately above a lower transverse seal of the bag length by establishing on so much of the external surface of the bag length as is within said region a gas pressure which is less than ambient air pressure and the simultaneous pressure within the tube.

2. Vertical, form-fill-seal, wrapping apparatus including transverse wrapper tube sealing means and means to draw a tube of wrapping material downwardly for wrapping successive falling charges of product item in bags formed from successive sealed bag lengths of the tube and comprising suction means to hold to tube open in a region immediately above the sealing means the suction means comprising a suction chamber, surfaces at the upstream end of the suction chamber which define a bag-filling entry orifice and surfaces at the downstream end of the suction chamber which define a filled bag exit orifice the disposition of which varies between a closed disposition in which the orifice has a narrow width appropriate to fit around the transverse seal and an open disposition in which the exit orifice is wide enough to permit passage of the filled bags therethrough, means to move in an operational cycle of the apparatus the surfaces defining the exit orifice to the closed disposition prior to bag filling and maintain the closed disposition during the period when filling commences, and from the closed disposition to the open disposition prior to movement of the filled bag downstream relative to the suction chamber, and means to establish within the suction chamber during the period when filling commences a pressure of gas which is lower than ambient air pressure and the simultaneous pressure within the tube whereby, during the bag filling portion of the cycle of operation of the apparatus, the tube is in the suction chamber urged outwardly so that a terminal length of the tube is held, by the pressure difference across the tube in the chamber, open for filling.

3. Apparatus as claimed in claim 2 wherein the sealing means comprises a pair of sealing jaws which open and close in a direction transverse to the movement of the tube of wrapping material through the apparatus.

4. Apparatus as claimed in claim 3 wherein the surfaces which define the exit orifice are mounted for movement with the jaws, so that said transverse movement of the surfaces with the jaws effects the said variation of the disposition of the exit orifice between the open and closed dispositions.

5. Apparatus as claimed in claim 4 wherein the suction chamber is defined by a box structure with a flat top, and an open base within the lower edges of sidewalls of the box, which sidewalls are fixed relative to each other and to the box top, the transversely moving, exit orifice surfaces being located below the lower edges and any gap between the exit orifice surfaces and the said lower surfaces being insufficiently large to prevent attainment of the required pressure differential.

6. Apparatus as claimed in any one of the preceding claims wherein the sealing means include means to sever the tube within the width of the transverse seal thereby to divide the tube into unit bag lengths.

7. Apparatus as claimed in any one of the preceding claims wherein the sealing means are mounted for cyclic movement, in use of the apparatus, in vertical directions relative to stationary components of the apparatus.

8. Apparatus as claimed in claim 7 wherein the means for drawing the tube downwardly include clamping means which are mounted for movement with the sealing means and which grip the tube.

9. Apparatus as claimed in claim 8 wherein the sealing means constitute the clamping means.

10. Apparatus as claimed in claim 7, 8 or 9 wherein the sealing means are mounted on a carriage which reciprocates in said vertical direction.

11. Apparatus as claimed in any one of the preceding claims wherein the means to establish a lower than ambient gas pressure is capable of establishing a pressure in the chamber which is less than that within the tube by an amount of from 4.5 to 9.0 cm/Hg.

12. Apparatus as claimed in any one of the preceding claims including means for forming said tube adapted to establish a diameter of the tube which is, when the tube material is in the relaxed condition, in a range of from 80 to 99% of the diameter of the entry orifice whereby selection for use as the tube of a material which is capable of stretching eiastically by at least the difference in diameters of the tube and the entry orifice permits the gas pressure differential to bring the tube into contact with the periphery of the entry orifice all around the circumference thereof.

13. Wrapping apparatus substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.

14. A method of wrapping charges of product item substantially as hereinbefore described with reference to the accompanying drawings.