EP1020390A2

EP1020390A2 - Feeding calender in welding machines for plastic materials

Info

Publication number: EP1020390A2
Application number: EP99204427A
Authority: EP
Inventors: Giorgio Mainini
Original assignee: Elba SpA
Current assignee: Elba SpA
Priority date: 1999-01-12
Filing date: 1999-12-20
Publication date: 2000-07-19
Also published as: ITMI990031A1; EP1020390A3; IT1306936B1

Abstract

An instantaneously controlled feeding calender in welding machines for plastic materials, comprising an upper feeding cylinder (12) and a lower feeding cylinder (13) superimposed on each other and mounted on parallel axles, between which a plastic or thermoplastic film (14) is fed so as to form a bag or similar, a welding group downstream of the cylinders (12, 13) comprising an upper welding arm (15) and a lower welding arm (16), and a collecting area (18, 20, 21, 22) for finished bags (19), where each cylinder (12, 13) is equipped with an independent motor (27, 28).

Description

This invention refers to an instantaneously controlled feeding calender in welding machines for plastic materials.
In the present welding machines for plastic or thermoplastic materials generally used for the production of plastic bags, such as "shoppers", garbage bags, open-mouth bags etc., the plastic material is fed in a forward motion by at least a pair of superimposed rollers or cylinders, known as calenders.
The two main rollers forming the feeding calender leading to a downstream welding unit are presently controlled in two different ways.
In a first case, one of the rollers is controlled by a kinematic device and a mechanical transmission, linked in turn to a central drive unit and to the welding unit, in addition to the second roller.
In a second case, one of the rollers is simply and directly actuated by a motor controlled by and electronically linked to the welding unit, and the other roller is phase-connected to the first by gears or some other form of transmission.
This means that the proper maintenance of the ratios of all the mechanical transmission components (gears, toothed belts, etc.) between the two rollers must be assured in both cases.
It is evident, however, that due to their ever increasing operating speed the interposed mechanical elements are ill-suited to support an ever growing number of cycles, and that some problems of improper synchronization may arise between the two rollers.
It is also worth noting that precisely in order to promote the forward feeding motion of the plastic material, some blowing elements such as air jets have been fitted downstream of these feeding units, so as to encompass the plastic material from both an upper and a lower side and promote its proper forward motion in an essentially planar manner.
Even this arrangement fails to suffice to ensure the required and desired planar forward motion, also because it is difficult to achieve blown air streams uniformly distributed over the two feeding and forward moving planes mentioned above.
The purpose of this invention is to produce a feeding calender in welding machines for plastic materials capable of overcoming the mentioned technical problems, by eliminating any out of phase feeding and improper forward motion with respect to the welding and stacking units of the welding machine.
According to the present invention, this purpose is achieved by producing an instantaneously controlled feeding calender in welding machines for plastic materials, according to the principles outlined in claim 1.
Further characteristics of this invention are outlined in the subordinate claims.
A calender according to this invention has thus made it possible to achieve a practical embodiment with the utmost simplicity, as it can be attained by using elements of a simple construction and assembly, even available on the open market.
Such a calender can also be easily adapted to any type of application.
The characteristics and advantages of an instantaneously controlled feeding calender in welding machines for plastic materials according to this invention will be more clearly evident in the following description, offered for exemplifying and non-limiting purposes and in reference to the simplified drawings attached, where:
Figure 1 is a schematic elevated lateral view of part of a welding machine for plastic materials which includes an instantaneously controlled feeding calender according to this invention, shown in a welding and cutting phase,
Figure 2 is a schematic sectional view showing the calender pictured in the previous Figure 1, in a different forward moving operating phase of the film,
Figure 3 is a partial front view merely showing the feeding calender with its relative motors,
Figure 4 is an elevated view comparable to those shown in Figure 1 and 2, depicting a second embodiment according to this invention.
The reference to these figures shows part of a welding machine for plastic materials including an instantaneously controlled feeding calender, indicated in its overall form by the number 11.
The feeding calender 11 comprises an upper cylinder 12 and a lower cylinder 13, superimposed on each other and mounted on parallel axles, between which a plastic or thermoplastic film (14) is fed so as to form a bag or similar. For instance, the film 14 may be fed from a roll, not shown here, of a continuous tubular plastic material.
Moreover, the cylinders 12 and 13 are associated with air feeding nozzles 10 capable of favoring the maintenance in a flat plane of the filmy material 14 fed by and passing through the interior of the cylinders 12 and 13.
It can also be seen that a welding unit is positioned downstream of the two cylinders 12 and 13, comprising an upper welding arm 15 and a lower welding arm 16. These two welding arms 15 and 16, which are for instance both moved in an alternating manner by a known cinematic device not shown here, are working together to perform the transversal welding operation of the tubular material and provide a cutting blade 17 which acts between the two welding lines set up by the welding arms when engaging with each other.
An area for collecting the finished bags, shown in a simplified manner by the number 19, is provided downstream of the welding units. In the example given, this collecting area is formed by a supporting element 18 designed to stack these bags 19, after being welded and expelled from the two welding arms 15 and 16.
In the simplified form shown, the supporting element 18 is equipped with a few needles 20 (only one of which shown) on which the bags 19 are permanently positioned by using a pressing element 21 provided in the upper part. It can be seen that the bags 19 are stretched out on a subsequent table or similar supporting element 22.
The figures 1-3 show how according to this invention the two cylinders 12 and 13 are each supported on terminal cushions 23, inserted and fastened to the shoulders 24 of the welding machine. An additional bracket 25, firmly attached by some rods 26 to the shoulders 24, supports a motor 27 and 28 on either side of the machine.
Each of the motors 27 and 28 is directly coupled by a corresponding coupling 29 to the corresponding upper cylinder 12 and lower cylinder 13.
The two motors 27 and 28 are connected to an electronic control panel, shown in a simplified manner by the number 30, which performs and coordinates the movement depending on the feeding requirements.
The motors 27 and 28 may for example be of a "brushless" type, of a alternate current vectorial inverter type, of a direct current or other type.
The electronic control panel 30 may therefore actuate the two motors 27 and 28 in a perfectly phased and coordinated or in a pre-established out-of-phase manner. The second type makes it possible to achieve a correction of the feeding motion of the film 14.
In fact, if for example the motor 27 connected to the upper cylinder 12 is made to rotate at a slower speed than the motor 28 connected to the lower cylinder 13, the film 14 tends to be rotated in an upward direction.
This makes it possible to compensate the feed of a film of heavy material which would tend to fall in a downward direction. This also happens in the presence of an air feed generated by the nozzles 10, which would on their own tend to maintain the filmy material 14 in a planar position, after being fed and passed through the interior of the cylinders 12 and 13.
Such a feeding system, which can also adjusted based on a possibly separate and independent control of the two cylinders, also proves advantageous in the event of producing a bag of particular length, made of a particular plastic or thermoplastic material, at a high feeding speed.
Such an arrangement eliminates every potential out-of-phase movement due to a wear of the drive transmission acting between the two feeding cylinders.
It is moreover possible, for the purpose of minimizing the encumbrance due to the presence of the two motors 27 and 28 associated with the two cylinders 12 and 13 of the feeding calender, to arrange the motors at the two extremities, by placing them on the opposite sides of the shoulders 24 supporting the two cylinders 12 and 13.
It is in any case possible to achieve a similar positioning without fully keying the two cylinders, the upper cylinder 12 and the lower cylinder 13 which constitute the feeding calender.
As shown by Figure 4 in a highly simplified manner, it may already suffice to provide two independent motors 27 and 28 in place of the single motor used in the machines built to this date.
In a further embodiment, this figure in fact shows that the motors 27 and 28 are placed on shafts parallel to those of the two cylinders 12 and 13 to which they are connected by an interposed transmission, as shown in a simplified manner by the numbers 31 and 32.
Even in this case, the arrangement of two different motors for each feeding cylinder is used in an advantageous manner, despite a transmission being interposed between the motor and its respective cylinder.
It is natural that an expert in the trade may also find further embodiments, all falling within the scope of protection of this invention.

Claims

An instantaneously controlled feeding calender in welding machines for plastic materials, comprising an upper feeding cylinder (12) and a lower feeding cylinder (13) superimposed on each other and mounted on parallel axles, between which a plastic or thermoplastic film (14) is fed so as to form a bag or similar, a welding group downstream of the cylinders (12, 13) including a welding unit placed downstream of said cylinders (12, 13) comprising an upper welding arm (15), a lower welding arm (16), and a collecting area (18, 20, 21, 22) for finished bags (19), characterized in that each cylinder (12, 13) is respectively equipped with an independent motor (27, 28).
A calender according to claim 1, characterized in that said motor (27, 28) is directly associated and aligned with each of the said feeding cylinders (12, 13).
A calender according to claim 1, characterized in that said motor (27, 28) is directly associated and aligned with each of the said feeding cylinders (12, 13) by the interposition of a couping (29).
A calender according to claim 1, characterized in that said motors (27, 28) are placed on shafts parallel to those of said two cylinders (12, 13), to which they are connected by an interposed transmission (31, 32).
A calender according to claim any of the preceding claims, characterized in that said motors (27, 28) are of a "brushless" type equipped with an alternate current vectorial inverter, of a direct current and other type.
A calender according to any of the preceding claims, characterized in that said motors (27, 28) are associated to control said two cylinders (12, 13) of said feeding calender on opposite sides of the shoulders (24) supporting said two cylinders (12, 13).
A calender according to any of the foregoing claims, characterized in that said cylinders (12, 13) are associated with air feeding nozzles (10) capable of maintaining said film (14) in a flat plane.