Wrapping machine

Abstract: A wrapping machine for winding a web (1) of wrapping film from a roller (2) around an object to be packaged. The wrapping machine has a film dispenser (3) which comprises a frame (4) provided with at least one guide means (5, 11) in contact with the first side (1 1 ) of the film 1 to guide the film; an openable gate section (7) provided with at least one guide means (8, 12) which is in contact with the opposite side (1 2 ) of the film relative to the first side, said gate section (7) being pivoted on the frame so that it can be turned between an open position (I) and a closed position (II); and a pre-stretching device (10) for preliminary stretching of the film. The pre-stretching device comprises a first pre-stretching roller (11) and a second pre-stretching roller (12). One of the pre-stretching roller (11, 12) is connected to the frame (4) and the other one is connected to the gate section (7) in such manner that one of the pre-stretching rollers in contact with the first side (1 1 ) of the film while the other one is in contact with the other side (1 2 ).

Description: The present invention relates to a wrapping machine as defined in the preamble of claim 1. From EP 0 293 352 A2 is known such a wrapping machine for winding a web of wrapping film from a roll around an object to be packaged. The wrapping film consists of a thin plastic film. The wrapping machine is provided with a film dispenser. The film dispenser comprises a frame provided with at least one guide element for guiding the film, which guide element is in contact with the first side of the film. Further, the film dispenser comprises an openable gate section which is provided with at least one guiding device which is in contact with the second side of the film opposite to the first side. The gate section is pivoted on the frame so that it can be turned between an open position and a closed position. Moreover, the film dispenser comprises a pre-stretching device for preliminary stretching of the film. The pre-stretching device comprises two pre-stretching rollers, a first pre-stretching roller which can be run at a first circumferential velocity and a second pre-stretching roller which is disposed at a distance from the first pre-stretching roller and can be run at a second circumferential velocity differing from the first circumferential velocity. The pre-stretching of the film occurs as a result of the two different circumferential speeds over the film portion between the pre-stretching rollers, which are brought into frictional contact with the film. In the known apparatus of EP 0 293 352 A2, both pre-stretching rollers are attached to the frame of the film dispenser. Connected to the gate part are guide elements, such as backup rollers, which, in the closed position of the gate, are pressed against the pre-stretching rollers while the film is passing between them along a W-shaped path so that each pre-stretching roller is in contact with the first side of the film on the same side of it and the backup rollers in the gate are in contact with the second side of the film. A problem with this prior-art apparatus is that it has a complex structure containing many different parts, such as guiding means, rollers, power transmission elements etc., so the structure is expensive. The film is narrowed too much by the pre-stretching system as the distance between the pre-stretching rollers is relatively long. As the film narrows too much, the film area covering the object being wrapped becomes smaller. The object of the present invention is to eliminate the drawbacks mentioned above. From EP 0 243 861 B1 is known an apparatus for spiral wrapping a load. It comprises a carriage which is mounted moveably in the vertical direction on a fixed base-mounted stand and to which two prestretch rollers each coupled with simultaneous rotation with a frictionally engageable wheel and a film supply roll are secured. The downstream prestretch roller and its associated frictionally engageable wheel are carried by a two-arm assembly moveable around a vertical axis and may be moved by moving the member in order to engage or to disengage the frictionally engageable gearing mechanism. From EP 0 467 729 A1 is known a wrapping machine with a film dispenser including two adjacent prestrech rollers. The prestrech rollers are fixedly mounted on the dispenser frame. The apparatus does not contain an openable gate section. A specific object of the invention is to present a wrapping machine whose film dispenser has a simpler structure and contains fewer parts than earlier machines. Another object of the invention is to present a wrapping machine whose film dispenser can be implemented as a smaller and lighter structure than before. A further object of the invention is to present a wrapping machine in which the film does not undergo excessive narrowing. The wrapping machine of the invention is characterized by what is presented in claim 1. According to the invention, one of the rollers on the frame is the first pre-stretching roller and one of the rollers on the gate section is the second pre-stretching roller, such that one of the pre-stretching rollers is in contact with the first side of the film while the other one is in contact with the other side. The invention has the advantage that the film dispenser can be implemented as a simpler structure than before, using fewer parts, so it becomes small and light. In the film dispenser of the invention, the film passes along an S-shaped path between the pre-stretching rollers and in contact with their external surface, so the pre-stretching rollers can be placed very close to each other, preventing excessive narrowing of the film. In an embodiment of the wrapping machine, the film dispenser comprises a power means provided with a rotating shaft, the power means being connected to the frame; a first set of power transmission elements for transmitting power from the shaft to rotate the first pre-stretching roller and a second set of power transmission elements for transmitting power from the shaft to rotate the second pre-stretching roller. In an embodiment of the wrapping machine, the first set of power transmission elements comprises a first wheel connected to the shaft of the power means, a second wheel connected to the first pre-stretching roller, and an endless driving element fitted to run over the first and second wheels as an endless loop. In an embodiment of the wrapping machine, the second set of power transmission elements comprises a third wheel, which is mounted with a bearing on the frame so that it can be rotated by the power means, and a fourth wheel, which is connected to the second pre-stretching roller and so fitted that it comes into power transmitting contact with the third wheel in the closed position of the gate section. In an embodiment of the wrapping machine, the third wheel is connected to the first pre-stretching roller on the same axle with the second wheel. In an embodiment of the wrapping machine, the second set of power transmission elements comprises a fifth wheel, which is connected to the first pre-stretching roller on the same axle with the second wheel, a sixth wheel, which is connected to the same shaft with the third wheel, and an endless driving element fitted to run as an endless loop over the fifth and sixth wheels. In an embodiment of the wrapping machine, the second set of power transmission elements for transmitting power to the second pre-stretching roller consists of an endless driving element and a fourth wheel, which is connected to the second pre-stretching roller and fitted to come into driving engagement with the driving element in the closed position of the gate section. In an embodiment of the wrapping machine, the endless driving element is an open-link chain, a cogged belt, a trapezoidal belt or the like, and, correspondingly, the fourth wheel is a chain wheel, a cogged pulley, trapezoidal belt wheel, a toothed gear or the like. In an embodiment of the wrapping machine, the third wheel and the fourth wheel are toothed gears whose tooth systems are adapted to each other. In an embodiment of the wrapping machine, the transmission ratio of the power transmission elements is so chosen that the circumferential velocity of the posterior pre-stretching roller as seen in the running direction of the film web is higher than the circumferential velocity of the anterior pre-stretching roller as seen in the running direction. In the following, the invention is described in detail by the aid of embodiment examples by referring to the attached drawing, in which Fig. 1 presents a side view of an embodiment of the wrapping machine of the invention, Fig. 2 presents the wrapping machine of Fig. 1 in top view, Fig. 3 presents the film dispenser of the wrapping machine of the invention in side view, Fig. 4 presents detail A of Fig. 3 in a magnified form, Fig. 5 presents a top view of the film dispenser of an embodiment of the wrapping machine of the invention with the gate section in its open position, Fig. 6 presents the film dispenser of Fig. 5 with the gate section in its closed position, Fig. 7 presents a top view of the film dispenser of another embodiment of the wrapping machine of the invention with the gate section in its open position, Fig. 8 presents the film dispenser of Fig. 7 with the gate section in its closed position, Fig. 9 presents an axonometric diagram illustrating the principle of the power transmission system of the pre-stretching device of the film dispenser in Fig. 5 and 6, Fig. 10 presents a diagram illustrating the principle of the power transmission system of the pre-stretching device of the film dispenser in Fig. 5 and 6, and Fig. 11 presents a diagram illustrating the principle of a third embodiment of the power transmission system of the pre-stretching device of the film dispenser. Figures 1 and 2 show a wrapping machine designed for winding a web of wrapping film 1 from a roll 2 around a stationary object to be packaged. The wrapping machine comprises a film dispenser 3. In this example embodiment, the film dispenser 3, carried and guided by a circular guide track 25, moves along a circular path around the object to be wrapped up. However, it is to be noted that the film dispenser 3 described in the following can be applied in conjunction with any wrapping machine, such as e.g. one in which the film dispenser 3 is connected to a revolving crank which moves the film dispenser around the object to be wrapped up, or with a wrapping machine in which the film dispenser 3 is connected to a fixed post and the film is passed around an object that is revolved around the dispenser. Figure 3 and also in Figures 5-8 show a film dispenser 3, which comprises a frame 4. In the embodiments in Fig. 5 and Fig. 6, the frame 4 is provided with supporting elements 26 allowing the film roll to be detachably mounted. In the apparatus in Fig. 6 and Fig. 7, these supporting elements are located in the openable gate section 7. The frame 4 is provided with at least one guide means 5, 11, which is in contact with the first side 1 1 of the film 1, for guiding the film. Furthermore, the film dispenser 3 comprises an openable gate section 7, which is provided with at least one guide means 8, 12, which is in contact with the opposite side 1 2 of the film relative to the first side. The gate section 7 is pivoted on the frame so that it can be turned between an open position I and a closed position II. Moreover, the film dispenser 3 comprises a pre-stretching device 10 for preliminary stretching of the film. The pre-stretching device 10 comprises two pre-stretching rollers, viz. a first pre-stretching roller 11 and a second pre-stretching roller 12. The first pre-stretching roller 11 is rotated so that it has a first circumferential velocity v1. The second pre-stretching roller 12 is located at a distance from the first pre-stretching roller 11 and it is rotated in the opposite direction relative to the first pre-stretching roller 11. The second pre-stretching roller 12 is rotated so that its circumferential velocity v2 differs from the circumferential velocity of the first pre-stretching roller 11. In the running direction of the film web, the circumferential velocity of the posterior pre-stretching roller is higher than the circumferential velocity of the first pre-stretching roller. The pre-stretching of the film takes place as a result of the different circumferential velocities over the film portion between the pre-stretching rollers 11, 12, which are in frictional contact with the film. A sufficient contact area between the film and the pre-stretching rollers is achieved by using backup rollers pressing the film against the pre-stretching rollers. As shown in Figures 5 - 8, one of the pre-stretching rollers 11, 12, in this case the first pre-stretching roller 11, is connected to the frame 4 and the other pre-stretching roller 12 is connected to the gate section 7, so that the first pre-stretching roller 11 is in contact with the first side 1 1 of the film and the second pre-stretching roller 12 is in contact with the second side 1 2 . The main difference between the embodiment in Figures 5 and 6 and the embodiment in Figures 7 and 8 is the manner in which power is transmitted from the motor 13 to the pre-stretching device 10 and especially to the second pre-stretching roller 12 located in the openable gate section 7. A feature common to both embodiments is that the film dispenser 3 comprises a motor 13 with a rotating shaft 14. The motor 13 is connected to the fixed frame 4. Furthermore, the film dispenser comprises a first set of power transmission elements 15 for transmitting power from the shaft 14 to rotate the first pre-stretching roller 11 and a second set of power transmission elements 16 for transmitting power from the shaft 14 to rotate the second pre-stretching roller 12. The first set of power transmission elements 15 comprises a first wheel 17, which is connected to the shaft 14 of the power means 13, a second wheel 18, which is connected to the first pre-stretching roller 11, and an endless driving element 19 fitted to run as an endless loop over the first and second wheels. Fig. 9 shows a diagram illustrating the principle of how the power transmission is implemented in the embodiment presented in Fig. 5 and 6. The second set of power transmission elements 16 comprises a third wheel 20, which is mounted with a bearing on the frame 3 and so arranged that it can be rotated by the power means 13, and a fourth wheel 21, which is connected to the second pre-stretching roller 12 and adapted to come into power transmitting contact with the third wheel 20 in the closed position II of the gate section 7. The third wheel 20 is connected to the first pre-stretching roller 11 on the same axle with the second wheel 18. The third wheel 20 and the fourth wheel 21 are toothed gears with tooth systems adapted to each other. The teeth mesh when the gate section 7 is closed. The same thing can be seen from Fig. 3 and 4. The detail illustration A in Fig. 4 shows that there are two different third gear wheels 20 mounted successively on the same axle at the end of the first pre-stretching roller 11 to allow a change of transmission ratio. By replacing the fourth gear wheel 21 mounted on the end of the second pre-stretching roller 12 with a different-sized gear wheel that engages the upper third gear wheel 20, a suitable transmission ratio can be selected, thereby changing the speeds of rotation of the pre-stretching rollers. The transmission ratio to be selected depends on the thickness and quality of the film and on the desired degree of preliminary strain. Fig. 10 presents a diagrammatic illustration of the power transmission application of Fig. 7 and 8. The second set of power transmission elements 16 comprises a fifth wheel 22, which is connected to the first pre-stretching roller 11 on the same axle with the second wheel 18, a sixth wheel 23, which is connected to the same axle with the third wheel 20, and an endless driving element 24 fitted to run over the fifth and sixth wheels as an endless loop. Here, too, the third wheel 20 and the fourth wheel 21 are toothed gears with tooth systems adapted to each other. The teeth mesh when the gate section 7 is closed. Fig. 11 shows yet another embodiment, in which the second set of power transmission elements 16 for transmitting power to the second pre-stretching roller 12 consists of an endless driving element 19 and a fourth wheel 21 connected to the second pre-stretching roller 12, this fourth wheel 21 being fitted to come into driving engagement with the driving element 19 when the gate section 7 is in its closed position II. The endless driving element 19 is an open-link chain, a cogged belt, a trapezoidal belt or the like. The second wheel 18, which comes into driving engagement with the driving element 19, is a chain wheel, a cogged wheel, a friction wheel or the like, respectively. The invention is not limited to the examples of its embodiments described above, but many variations are possible within the framework of the invention as defined by the claims.

Claims: Wrapping machine for winding a web (1) of wrapping film from a roll (2) around an object to be packaged, said wrapping machine comprising a film dispenser (3) which comprises: a frame (4) provided with at least two guide rollers (5, 11) which are in contact with the first side (1 1 ) of the film (1), for guiding the film; an openable gate section (7) provided with at least two guide rollers (8, 12), said gate section being pivoted on the frame so that it can be turned between an open position (I) for changing a web roll in which its guide rollers (8, 12) are spaced from the guide rollers (5, 11) on the frame, and a closed position (II) in which its guide rollers (8, 12) are in contact with the opposite side (1 2 ) of the film relative to the first side and intermesh with the guide rollers (5, 11) on the frame (4); and a pre-stretching device (10) for preliminary stretching of the film, said pre-stretching device comprising pre-stretching rollers, viz. a first pre-stretching roller (11), which can be driven at a first circumferential velocity (v1), and a second pre-stretching roller (12), which is disposed at a distance from the first pre-stretching roller and rotated at a circumferential velocity (v2) differing from the first circumferential velocity (v1), so that the preliminary stretching of the film takes place in the film portion between the pre-stretching rollers as a result of the different circumferential velocities, characterized in that one of the rollers (5, 11) on the frame (4) is the first pre-stretching roller (11) and one of the rollers (8, 12) on the gate section (7) is the second pre-stretching roller (12), such that one of the pre-stretching rollers is in contact with the first side (1 1 ) of the film while the other one is in contact with the other side (1 2 ). Machine as defined in claim 1, characterized in that the film dispenser comprises a power means (13) provided with a rotating shaft (14), said power means being connected to the frame (4); a first set of power transmission elements (15) for transmitting power from the shaft to rotate the first pre-stretching roller (11); and a second set of power transmission elements (16) for transmitting power from the shaft to rotate the second pre-stretching roller (12). Machine as defined in claim 2, characterized in that the first set of power transmission elements (15) comprises a first wheel (17) connected to the shaft (14) of the power means (13), a second wheel (18) connected to the first pre-stretching roller (11), and an endless driving element (19) fitted to run over the first and second wheels as an endless loop. Machine as defined in claim 2 or 3, characterized in that the second set of power transmission elements (16) comprises a third wheel (20), which is mounted with a bearing on the frame (4) and arranged to be rotated by the power means (13), and a fourth wheel (21), which is connected to the second pre-stretching roller (12) and so fitted that it comes into power transmitting contact with the third wheel (20) in the closed position (II) of the gate section (7). Machine as defined in claim 4, characterized in that the third wheel (20) is connected to the first pre-stretching roller (11) on the same axle with the second wheel (18). Machine as defined in claim 4, characterized in that the second set of power transmission elements (16) comprises a fifth wheel (22), which is connected to the first pre-stretching roller (11) on the same axle with the second wheel (18), a sixth wheel (23), which is connected to the same shaft with the third wheel (20), and an endless driving element (24) fitted to run as an endless loop over the fifth and sixth wheels. Machine as defined in any one of claims 1 - 3, characterized in that the second set of power transmission elements (16) for transmitting power to the second pre-stretching roller (12) consists of an endless driving element (19) and a fourth wheel (21), which is connected to the second pre-stretching roller (12) and fitted to come into driving engagement with the driving element (19) in the closed position (II) of the gate section (7). Machine as defined in any one of claims 3 - 5, characterized in that the endless driving element (19 is an open-link chain, a cogged belt, a trapezoidal belt or the like, and that, correspondingly, the second wheel (18) is a chain wheel, a cogged pulley, trapezoidal belt wheel, a toothed gear or the like. Machine as defined in any one of claims 1 - 3, characterized in that the third wheel (20) and the fourth wheel (21) are toothed gears with tooth systems adapted to each other. Machine as defined in claim 9, characterized in that the transmission ratio of the power transmission elements (15, 16) is so chosen that the circumferential velocity (v2) of the posterior pre-stretching roller as seen in the running direction of the film web is higher than the circumferential velocity (v1) of the anterior pre-stretching roller.

Inventors: DIEHL WERNER, PAAVOLA JARI, DIEHL, WERNER, PAAVOLA, JARI
Applicants: HALOILA M OY AB, OY M. HALOILA AB
Application year: 1997
Main classification: B65B11
IPC codes: B65B11