GB2260114A

GB2260114A - Sealing head for a packaging machine

Info

Publication number: GB2260114A
Application number: GB9120595A
Authority: GB
Inventors: Stewart Atkinson
Original assignee: WEIGH SYSTEMS Ltd SA
Current assignee: WEIGH SYSTEMS Ltd SA
Priority date: 1991-09-27
Filing date: 1991-09-27
Publication date: 1993-04-07
Also published as: GB9120595D0

Abstract

A packaging machine comprises a sealing head (2 fig 1) which may be rotated relative to a sleeve forming head (1,fig 1) in which the longitudinal edges of a length of sheet material are brought together and joined to form a sleeve. The sealing head comprises heated jaws 25, 26 one of which or both may close on the sleeve at intervals along its length to form transverse seals across the sleeve. The jaws are mounted in a frame 11 which can be mounted in either of two mutually perpendicular positions by plates 14, 14' so that the position of the longitudinal seam in the finished bag or wrapper can be moved from the middle to the side of the bag or wrapper. One or both jaws 25, 26 are each secured to a pair of bobbins 22b which are magnetically coupled, to prevent jamming on obstructions, with a respective shuttle which is movable inside a cylinder 19, 20 by fluid pressure, eg liquid or gaseous. The jaws are longitudinally divided into upper and lower halves (25a, 25b, 26a & 26b, fig 5). A cutter blade 28, is mounted between the two halves of one of the jaws 25 extending 27 along the length of the jaw and projecting through a slot in the carrier 23. A pneumatic actuator 29 operates the blade via a push rod 30 so as to sever the sleeve across its width dividing it into separate bags or wrappers. The lines connecting the cylinders, actuators and electrical cables are all flexible. <IMAGE>

Description

PACKAGING MACHINE TECHNICAL FIELD OF THE INVENTION This invention relates to a packaging machine of the kind which includes a sleeve-forming head in which the longitudinal edges of a length of sheet material are brought together and joined to form a sleeve, and the machine further includes a pair of heated jaws which close on the sleeve at intervals along its length to form transverse seals across the sleeve. The sections of sleeve between adjacent seals may be used as wrappers or bags for food or other products. Such a packaging machine is referred to below as "a machine of the kind set forth".

BACKGROUND In existing machines of the kind set forth the heated jaws close on the sleeve in a fixed direction so that the seam formed at the longitudinal edges of the length of material extends along either the side edge or along the front or rear face (usually the rear) of the finished bag or wrapper, depending on the particular machine in question. Thus, once a particular machine has been purchased, if an application should arise which requires a seam in a different position the user is faced with the prospect of having to purchase another machine at considerable expense.

An aim of the present invention may be viewed as being to overcome this problem; SUMMARY OF THE INVENTION The present invention proposes a packaging machine of the kind set forth in which there is provision for adjusting the relative positions of the sleeve-forming head and the jaws such that the position of the longitudinal seam in the finished bag or wrapper can be changed relative to the transverse seals.

The necessary adjustment could be achieved either by rotation of the sleeve-forming head, or by rotation of the jaws, about the general direction of travel of the sleeve through the head or jaws respectively. In general however, it will be easier to make provision for rotation of the jaws whilst the sleeve-forming head remains in a fixed position.

It is possible within the scope of the invention for the sleeve-forming head or the jaws to be continuously rotatable through at least 900 so that the position of the seam can be adjusted to any position between, say, the centre of the transverse seal and one end thereof (i.e. between the transverse centre of the bag and one side edge of the bag). In practice however it will be easier to arrange for the head or jaws to be mounted in either of two mutually perpendicular positions, and in fact this will meet most, if not all, of the users requirements.

In order to form the transverse seal the heated jaws will be arranged to move together. One of the jaws may move relative to a fixed jaw, or more commonly, both of the jaws will move into contact with the sleeve. In a case where it is the jaws that can be rotated rather than the sleeve-forming head, relative movement between the jaws could be achieved by various means such as pneumatic pistons for example.However, in order to permit a reduction in the size of the head and thereby make it easier to provide for rotation of the jaws it is preferred that the or each movable jaw is magnetically coupled to a shuttle which is movable within a cylinder by fluid pressure. (The respective fluid may be liquid or gaseous.) An additional advantage of such an arrangement is that if the jaws should close on an obstruction the magnetic coupling can be overcome so that the jaws become dissociated from the shuttle. The or each movable jaw is preferably magnetically coupled to a pair of shuttles located at opposite ends of the respective jaw.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is exemplified in the accompanying drawings, in which: Figure 1 is a diagrammatic side view of part of a packaging machine of the invention, Figure 2 is a plan view of a sealing head of the machine, Figure 3 is a side view of the sealing head, Figure 4 is a similar view to Fig. 2 but showing the jaws in a closed position, and Figure 5 is a transverse section through the jaws of the sealing head, shown in an open position.

DETAILED DESCRIPTION OF THE DRAWINGS Referring to Fig. 1, the packaging machine comprises a sleeve-forming head 1 and a sealing head 2.

The sleeve-forming head 1, which may be of any known form, operates to bring together the longitudinal edges of a length of sheet material, and a heated bar 4 which is reciprocable in direction A, co-operates with the head 1 to form a continuous seam along the longitudinal edges, thereby forming the material into a sleeve coming off the lower end of the head 1.

The sealing head 2 is mounted below the sleeve-forming head 1 on two pairs of parallel arms, of which only one pair is visible 5, 6. The arms are arranged to move angularly so that the sealing head 2, which is mounted on the arms by respective bearings 7 and 8, is moved vertically in direction B. The sealing head 2 contains a pair of heated jaws (see below) which, when the sealing head is in an upper position, close on the sleeve to form a transverse seal across the width of the sleeve. The sealing head 2 moves downwardly to draw the sleeve through the sleeve-forming head 1 whereupon the jaws move apart to release their grip on the sleeve. The jaws then move upwardly and re-close on the sleeve at a different position to make a further transverse seal in a repetition of the above-described cycle. The sections of sleeve between adjacent seals are separated to form wrappers or bags.

As thus far described the machine operates conventionally, but the sealing head is different and this will now be described in detail.

Referring to Fig.s 2 and 3, the sealing head 2 includes a square frame 11 having a pair of mounting plates 14 secured centrally to opposite sides of the frame by bolts 15. The plates project above and below the frame 11 to carry parallel spindles 16 and 17 for reception in the bearings 7 and 8 of Fig. 1. As shown in the drawing, the mutually perpendicular sides of the frame 11 carry a pair of similar plates 14' having spindles 16' and 17', although in practice one pair of plates and spindles may be mounted in the two alternative positions as required.

Internally of the frame 1, two pairs of cylinders 19, 20 are mounted on opposite sides of the frame with each pair being axially aligned in end-to-end relationship.

The cylinders have pneumatic couplings 21 at each end and each contain a magnetically attractable metal shuttle (not shown) which can be moved axially within the cylinder by air pressure applied via the couplings 21. A magnetic bobbin 22 is slidably mounted on each cylinder 19, 20 and each bobbin is magnetically coupled to the respective shuttle to move with it. Each opposed pair of bobbins 22 are secured to a U-shaped carrier 23, 24 to which a respective electrically heated jaw 25, 26 (referred to above) is secured via spacers 27. Thus, by suitable application of pneumatic pressure to the cylinders 19 and 20 the bobbins can be moved to urge the jaws together, as shown in Fig. 4, and make a transverse seal across the sleeve.

Referring to the sectional view of Fig. 5, it will be noted that, the jaws are longitudinally divided into upper and lower halves 25a, 25b and 26a, 26b. A cutter blade 28 is mounted between the two halves of one of the jaws 25 extending along the length of the jaw and projecting through a slot in the carrier 23. A pneumatic actuator 29 is mounted on the respective carrier 23 to operate the blade 28 via a push rod 30.

When pneumatic pressure is applied to the actuator 29 it causes the cutting edge of the blade to project from the jaw 25 (as indicated in outline in Fig. 2) so that, when the jaws are closed onto the sleeve, the blade enters the gap between the opposite jaw sections 26a and 26b to sever the sleeve across its width and thus divide the sleeve into separate bags or wrappers.

The relatively compact form of the sealing head enables it to be mounted in the bearings 7 and 8 in either of two mutually perpendicular positions by mounting the plates 14 and spindles 15, 16 in either of the two positions described above. In these two positions the the jaws 25 and 26 will close on the sleeve in either of two mutually perpendicular positions so that the longitudinal seam falls either along the side of the bag or wrapper or along its centre, as required.

The pneumatic lines to the cylinders 19, 20 and to the actuator 29 are made via flexible plastics pipes.

Similarly, flexible electrical cables are used to supply the heated jaws, so that the position of the sealing head can be changed without the need to break any connections.

The use of the magnetically coupled shuttles and bobbins provides the machine with an additional safety feature, as already noted. If the jaws should close on an obstruction the jaws become dissociated from the shuttle so that their closing force is limited.

Claims

1. A packaging machine of the kind set forth in which there is provision for adjusting the relative positions of the sleeve-forming head and the jaws such that the position of the longitudinal seam in the finished bag or wrapper can be changed relative to the transverse seals.

2. A packaging machine according to Claim 1, in which the head or jaws is/are arranged to be mounted in either of two mutually perpendicular positions.

3. A packaging machine according to Claim 1 or 2, in which the sleeve-forming head is fixed and the jaws are arranged such that they can be rotated about the general direction of travel of the sleeve therepast.

4. A packaging machine according to Claim 3, in which the or each movable jaw is magnetically coupled to a shuttle which is movable within a cylinder by fluid (liquid or gaseous) pressure.

5. A packaging machine according to Claim 4, in which the or each movable jaw is coupled to a pair of shuttles located at opposite ends of the respective jaw.

6. A packaging machine substantiually as described with reference to the drawings.