Device for joining films of heat-shrinkable plastic material in a machine using said film

Abstract: In order to make it possible the bobbin (11A) of heat-shrinkable plastic material film to be replaced without stopping the machine which uses it, the device (1) substantially comprises, listed in the direction of film (A-B) unwinding, one pair of parallel reels (2A, 2B), respectively supporting the bobbins (11A, 11B) on which the film (A-B) is wound, two sucking mouths (3A, 3B), two cutting devices (4A, 4B), a welding device (6) and an accumulation device (7).

Description: The present invention relates to a device for joining heat-shrinkable film in a machine using said film. In the presently used packaging machine, the film of heat-shrinkable plastic material is taken from a bobbin which, when is emptied, must be replaced with a full bobbin. The replacement operation furthermore requires that the trailing end of the film which is being unwound from the empty bobbin is joined (heat-welded) to the leading end of film coming from the full bobbin. During the above operations, the packaging machine has to be stopped and therefore the production is penalized by a dead time which, on the contrary, should desirably be avoided. US-A-3 266 968 relates to a device according to the preamble of claim 1. US-A-4 219 378 shows a similar device having a sucking device, acting on the film, and an accumulator for the film which is being wound. The purpose of the present invention is of obviating the above mentioned drawback, i.e., providing a device for heat-shrinkable film joining which is capable of making it possible the empty bobbin to be replaced by a full bobbin and the film joining to be carried out without that the machine has to be stopped. Such purposes are achieved by means of a device according to claim 1. The invention is illustrated, for merely exemplifying, non-limitative purposes, in the figures of the accompanying drawing tables. Figure 1 is a schematic view of a device according to the present invention, during the normal film unwinding step; Figure 2 is a schematic view of the device according to Figure 1, in which the pressing element keeps the film coming from the full bobbin and the film coming from the bobbin which is going to be emptied pressed towards each other, stopping the latter immediately before the intervention of the welder bar; Figure 3 is a schematic view of the device according to Figure 1, in which the cutting device is operating on the film coming from the bobbin which is being emptied; Figure 4 is a schematic view of the device of Figure 1, in which the device according to the present invention has ended operating and the film is being normally unwound from the replaced bobbin. Referring to the above mentioned figures, the device for film joining according to the present invention, generally indicated with (1), comprises, listed in the direction of unwinding of both films (A) and (B), a first unwinding reel (2A) and a second unwinding reel (2B), first return rollers (12A) and (12B), a first sucking mouth (3A) and a second sucking mouth (3B), and a first cutting device (4A) and a second cutting device (4B), a welding device (5), a set of second return rollers (6), and a film accumulation device (7). The unwinding reels (2A) and (2B) are each associated with respective brakes (8A) and (8B) and sensors (9A) and (9B). The sensors (9A) and (9B) send their signals to a central control unit (10) suitable for commanding, according to a pre-established operating cycle, the operation of the device (1). By means of brakes (8A) and (8B), the unit (10) can control the unwinding speed and/or the tension both films (A) and (B) are subject to. The reels (2A) and (2B) support bobbins (11A) and (11B), which, in the herein exemplified case, are, respectively, close to get emptied and full. The first return rollers (12A) and (12B) cooperate with the second return rollers (6) in such a way that the portions of film (A) and film (B), when unwound, result to be taut and adhering to the sucking mouths (3A) and (3B), which, however, do not operate simultaneously. The first and the second cutting devices (4A) and (4B), respectively, are identical to each other and substantially comprise actuator cylinders (13A) and (13B) acting by means of the interposition of springs (14A) and, respectively, (14B) and blades (15A), and, respectively, (15B). At the cutting time, the blades (15A), (15B) penetrate respective seats (16A) and (16B) of a shoulder element. The cutting devices furthermore comprise pressing elements (21A), (21B) elastically acting on films (A) and (B) so as to keep them clamped in the nearby of the action line of blades (15A), (15B). The welding device (5) comprises a stationary shoulder (17), a pressing element (18), a welder bar (19) and an actuator cylinder (20). The pressing element (18), which has a width equal to the width of films (A) and (B) is elastically installed on the actuator cylinder (20) and bears a plurality of nozzles (22) from which cooling air is blown. On the contrary, the welder bar, which also has a width equal to the width of films (A) and (B), is rigidly mounted on the stem of the actuator cylinder (20). The stationary shoulder (17) is formed by a support of rigid material (23) and a layered portion (24) consisting of a plurality of mutually overlapped layers of elastically yielding material. In order to favour the operating effectiveness of the welder bar (19), the layered portion (24) is subdivided into a central portion (25) and two mutually identical side portions (26), which are layered according to a different pattern and as a function of the fact that the side portions (26) are destined to act as shoulders for the pressing element (18) (cold), whilst the central portion is destined to act as a shoulder for the welder bar (19) (hot). The side portions (26) comprise, listed from outside inwards, at least one layer of soft, however not necessarily heat-resistant, rubber. The central portion (25) comprises, listed from outside inwards, a Teflon (R) layer, at least one layer of heat-resistant silicone rubber and at least one soft rubber layer. The accumulator device (7) is of the type comprising a first set of stationary rollers (27) and a second set of sliding rollers (28), which can so slide as to move away from, while remaining coplanar with, the above stationary rollers, under the action of a constant force which can be applied either by a weight (29), or a hydraulic actuator, not shown in the drawings. The larger the distance between both roller sets, i.e., the stationary and the sliding roller sets, the larger the amount of accumulated film. During the operation, the film (A) is fed to the user machine from the bobbin (11A) which is going to get emptied (Figure 1). The film (A) path is between the various elements of the device, clearly visible in Figure 1. The bobbin (11B) is stationary, in stand-by step. The leading end of the film (B) lays freely overhanging beyond the welding device, get clamped by the depressure generated by the sucking mouth (3B). When the sensor (9A) sends to unit (10) the signal that the bobbin (11A) is close to get emptied, the brakes (8A) and (8B) are enable in order to block films (A) and (B). The film (A), which continues to be pulled by the packaging machine, is supplied by the accumulation device (7), thanks to rollers (28) progressively moving towards rollers (27). The welding device (5) is enabled (Figure 2). The pressing element (18) elastically compresses the film (B) head against the end portion of film (A). Subsequently, the welder bar presses both films (A) and (B) against each other for the necessary time, in order to weld them along at least one seaming line. The cutting device (4A) is enabled, thus cutting the film (A) (Figure 3). The free end of the portion of film (A) still wound of bobbin (11A) is clamped by the sucking mouth (3A) enabled at the time of disabling of the sucking mouth (3B). The enabling of the cutting device (4A), of the sucking mouth (3A) and the disabling of the sucking mouth (3B) preferably take place at the same time. When the necessary time to carry out the welding has elapsed, the welder bar (9), and consequently, also the pressing element (18), are moved backwards. Simultaneously, from nozzles (22) air is blown in order to cool the welded seam. The pressing element (18) is moved backwards, releasing the film (B), which can start again to freely unwind from bobbin (11B). The accumulation device (7) makes it possible the film supplied soon before the future bobbin replacement, to be recovered. Simultaneously, the operator, possibly warned by the same machine, removes from reel (2A) the bobbin (11A) and replaces it with a full bobbin. The leading end of the film wound on said full bobbin will be arranged as displayed in Figure 4, i.e., clamped in stand-by position by the sucking mouth (3A). The next bobbin replacement will involve the bobbin (11B), and also it, like all preceding and subsequent replacements, will be carried out without that stopping the machine is necessary.

Claims: Device (1) for automatically joining films (A-B) of heat-shrinkable plastic material in a machine using said film, said device substantially comprising, listed in the direction of film unwinding: -- one pair of reels (2A, 2B) with parallel axes, suitable for respectively housing a first bobbin (11A) of heat-shrinkable film from which said film (A) is being unwound, and a second bobbin (11B) which is in stand-by step and is ready to supply the film (B) as soon as the first bobbin (11A) gets emptied, -- one pair of cutting devices (4A, 4B), each of which is capable of independently acting on either of both films (A, B), -- a welding device (5) suitable for simultaneously acting on both films (A, B), -- means (9A, 9B) for detecting the emptying degree of bobbins (11A, 11B), connected with a central control unit (10) capable of commanding, according to a pre-established operating cycle, the operation of the sucking devices (3A, 3B), cutting devices (4A, 4B), welding device (5) and reels (2A, 2B), characterized in that said device further comprises -- one pair of sucking devices (3A, 3B), acting on the whole width of films (A, B) and suitable for keeping the film (A) coming from the first bobbin (11A) and the film (B) coming from the second bobbin (11B) independently clamped by means of their sucking action; -- an accumulator device (7) for accumulating the film which is being unwound, wherein each cutting device (4A, 4B) comprises a pressing element (21A, 21B) elastically acting on the film (A, B), so as to keep it blocked in the nearby of the line of action of the cutting blade; said welding device (5) comprising: -- an actuator device (20), a pressing element (18), a welder bar (19) and a stationary shoulder (23), in which the actuator cylinder (20) simultaneously acts: elastically on the pressing element (18); and rigidly on the welder bar (19) contained inside the interior of said pressing element (18), wherein -- said pressing element (18) is provided with air blowing nozzles (22) for blowing air for welded joint cooling, and -- said stationary shoulder (17) is formed by a support (23) of rigid material and a layered portion (24) provided with a plurality of mutually overlapped layers of elastically yielding material. Device according to claim 1, characterized in that the layered portion (24) is subdivided into two side portions (26) identical to each other and a central portion (25) which comprises, listed from outside inwards, a Teflon (R) layer, at least one layer of heat resistant silicone rubber, and at least one layer of soft rubber, -- the side portions (26) comprise, listed from outside inwards, at least one layer of soft rubber.

Inventors: GATTESCHI EMANUELE, GATTESCHI, EMANUELE
Applicants: OCME SRL, OCME S.R.L.
Application year: 1993
Main classification: B65H19
IPC codes: B29C65, B29C35, B65H19