Abstract:
Various embodiments of the present disclosure provide a pre-stretching device for a stretch-film wrapping machine that enables quick and easy modification of the pre-stretch level. Specifically, in various embodiments, the two power transmission gears that control the rotation of the two pre-stretch rollers (and thus the pre-stretch level) are located outside of the housing of the pre-stretching device. This enables an operator to easily access those gears when the operator desires to swap those gears with a set having a different transmission ratio (and thus corresponding to a different pre-stretch level).

Description:
PRIORITY CLAIM 
       [0001]    This application is a national stage entry of PCT/US2013/056633, filed on Aug. 26, 2013, which claims priority to and the benefit of Finland Patent Application No. 20126039, filed on Oct. 5, 2012, the entire contents of each of which are incorporated herein by reference. 
     
    
     FIELD 
       [0002]    The present disclosure relates to changing the pre-stretch level of a plastic stretch-film used to wrap palletized loads or articles with a stretch-film wrapping machine. More precisely the present disclosure relates to a method for changing the pre-stretch level of a stretch-film by changing the transmission ratio between the first pre-stretching roller and the second pre-stretching roller of the pre-stretching device of the wrapping machine, and to such a pre-stretching device. The present disclosure also relates to a stretch-film wrapping machine equipped with such a pre-stretching device, and to a gearbox for such a pre-stretching device. 
       BACKGROUND 
       [0003]    When a palletized load and articles are wrapped in a plastic stretch-film, the film is usually pre-stretched to a certain degree prior to wrapping the film around the load. The stretched film provides secure protection of the wrapped load and helps to keep the wrapped products at their places on the pallet. The stretching of the film also lowers the thickness of the film and thus less film material is used in the wrapping of the load. 
         [0004]    Normally the pre-stretching of a film in a wrapping machine is carried out in the pre-stretching device of the wrapping machine, such as a film carriage, into which device a roll of plastic wrapping film is inserted. Depending on the construction of the wrapping machine, the pre-stretching device can be stationary in relation to the load to be wrapped, or the pre-stretching device can be movable in relation to the load to be wrapped. The pre-stretching device generally comprises two pre-stretching rollers, which rollers are rotated at different rotating speeds in order to obtain desired level of pre-stretching to the film prior to wrapping the film on the load to be wrapped. The two pre-stretching rollers are coupled to each other via transmission gears. Publication EP 1 542 192, for example, discloses this type of a known wrapping machine having a pre-stretching device configured to pre-stretch a film web drawn from a film roll before its being wrapped around an object, where the pre-stretching device comprises a first pre-stretching roller and a second pre-stretching roller, which rollers are tractively coupled via power transmission gears. 
         [0005]    Changing of the pre-stretch level of the film to be wrapped is required since different types of wrapping films endure different amounts of pre-stretching. And since the pre-stretch level is kept close to the maximum for each type of wrapping film in order to save wrapping material, the pre-stretch level need to be adjusted when the type of the wrapping film is changed. 
         [0006]    The changing of the pre-stretch level of the film in these types of known stretch-film wrapping machines generally required at least partial dismantling of the pre-stretching device in order to change the transmission ratio of the two pre-stretching rollers by changing the power transmission gears coupling the rollers. This action generally takes about 1-2 hours and thus causes significant downtime to the wrapping machine. 
         [0007]    Another known solution for changing the pre-stretch level of the film in stretch-film wrapping machine is to equip both of the pre-stretch rollers with separate motors. This way the pre-stretch level of the film can be changed by adjusting the rotating speeds of the motors. These types of arrangements however provide more complex and costly construction of the pre-stretching device of the wrapping machine. 
         [0008]    Publication GB 2 395 165 discloses a pre-stretching device for use in pre-stretching plastic wrapping film, where the transmission ratio between the two pre-stretching rollers can be changed without removing and replacing the relating gears. In this arrangement each roller has at least two coaxially mounted gear wheels coupled to the roller, one of these gear wheels on each roller is fixed for rotation with the roller and the other gear wheel is mounted for non-fixed free rotation relative to the roller. The arrangement also comprises coupling means for selectively coupling a fixed gear wheel to a non-fixed gear wheel on one or other roller in order to change the pre-stretch level of the device. This arrangement also provides complex and thus costly construction of the pre-stretching device of the wrapping machine. 
         [0009]    Publication EP 0 653 352 discloses an incrementally variable transmission between pre-stretching rollers in a stretch-film wrapping machine. In this arrangement pre-stretching rollers are coupled via a reduction gear and a transmission unit with variable transmission ratios. The required reduction gear and transmission unit makes the construction of a pre-stretching device according to this arrangement complex and thus costly. 
       SUMMARY 
       [0010]    The present disclosure provides a simple and cost effective arrangement for changing the pre-stretch level of a pre-stretch wrapping machine, where the change of the pre-stretch level can be carried out quickly and easily. The present disclosure also provides reliable and stable arrangement for changing the pre-stretch level of a pre-stretch wrapping machine, where the changing of the pre-stretch level can be carried out without tools and dismantling of the machinery and without any special technical knowledge so that anyone can carry out the changing process. 
         [0011]    In the present disclosure the pre-stretch level of the stretch-film wrapping machine is changed by replacing the power transmission gears coupling the first and second roller located on an outer surface of the pre-stretching device. Since the power transmission gears in the present disclosure are located on the outer surface of the pre-stretching device, and not inside the construction of the pre-stretching device as in the prior-art devices, the power transmission gears are easily accessible and can be quickly changed to another set of transmission gears providing different transmission ratio and thus different level of pre-stretching of the film. 
         [0012]    The pre-stretching device according to the present disclosure comprises a first pre-stretching roller and a second pre-stretching roller, which rollers are substantially parallel and comprise parallel rotating shafts for rotating the rollers, which rotating shafts are coupled to each other with power transmission gears. The ends of the rotating shafts extend through an outer surface of the pre-stretching device and the power transmission gears are connected at the portions of shafts extending from the surface of the pre-stretching device. 
         [0013]    The transmission gears are advantageously connected to the shafts of the pre-stressing rollers with mating cross-sectional forms so that the ends of the shafts of the pre-stretching rollers have cross-sectional forms that deviate from circle, and the respective gears have center holes corresponding to the cross-sectional forms of the respective ends of the shafts for connecting respective gears to respective shafts. This way the replacement of the gears can be easily carried out simply by pulling the first transmission gears away from the ends of the shafts and pushing second transmission gears on the ends of the shafts, in the length direction of the shafts. 
         [0014]    The power transmission gears are advantageously located in a separate housing, which housing is connected detachably to the pre-stretching device through the connection between the power transmission gears and the ends of the shafts of the pre-stretching rollers. This way the different sets of power transmission gears can be assembled in different housings for obtaining different transmission ratios, and thus different pre-stretching levels for the pre-stretching device, whereby the change of the pre-stretching level is achieved simply by replacing the whole transmission housing. 
         [0015]    The proper positioning of the housing with gears can advantageously be achieved with mating forms or surfaces, where the form of the housing fits is a respective mating form or surface of the pre-stretching device and/or another part of the wrapping machine. This helps with the changing of the gears and in proper alignment of the gears in relation with the ends of the shafts of the pre-stretching rollers. 
         [0016]    Advantageously the power transmission gears in certain embodiments of the present disclosure consist of only two intermeshing gears, which are connected to respective ends of the shafts of the pre-stretching rollers. Thus different sets with different transmission ratios can be manufactured cost-effectively. 
         [0017]    The present disclosure also provides a stretch-film wrapping machine, which is equipped with a pre-stretching device according to the present disclosure. 
         [0018]    Further, the present disclosure also provides a detachable gearbox for a pre-stretching device of a stretch-film wrapping machine, where the power transmission gears are located inside the gearbox, wherein the outer surface of the gearbox comprises at least one hole, and in certain embodiments two holes, for inserting two parallel ends of shafts of pre-stretching rollers of the pre-stretching device, and the power transmission gears comprise two gears equipped with means for connecting the gears to the parallel ends of the shafts of the pre-stretching rollers, which means are located substantially in the areas of the respective holes of the housing. This type of detachable gearbox be easily and quickly attached and detached from the pre-stretching device for changing the pre-stretching level of the wrapping machine, and plurality of gearboxes with different preset transmission ratios can be provided for different pre-stretch levels. 
         [0019]    In a detachable gearbox according to the present disclosure, the means for connecting the gears to the parallel ends of the shafts of the pre-stretching rollers advantageously consist of center holes in the two gears, which center holes have cross-sectional form that deviates from circle and which cross-sectional form fits to corresponding cross-sectional form of the parallel ends of the shafts of the pre-stretching rollers. This enables the attachment and detachment of the gearbox by simply moving the gearbox in the direction of the shafts of the pre-stretching rollers. Thus the detachable gearbox according to the present disclosure can be changed to another without use of tools or without dismantling of the machinery when the pre-stretch level of the wrapping machine needs to be changed. Therefore anyone can carry out the changing process. 
         [0020]    The power transmission gears of the detachable gearbox according to the present disclosure advantageously consist of two intermeshing gears. Thus the construction of the gear box is very simple and cost-effective. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0021]    Exemplifying embodiments of the present disclosure and their advantages are explained in greater detail below in the sense of examples and with reference to attached drawings. 
           [0022]      FIG. 1A  shows an upper portion of a film carriage utilizing the gearbox of the present disclosure. 
           [0023]      FIG. 1B  shows enlargement A of  FIG. 1A  showing the pair of gears defining the pre-stretching level of the wrapping machine. 
           [0024]      FIG. 2  shows schematically a cross-section of a detachable gearbox of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]      FIG. 1A  shows an upper portion of a film carriage  1  of a rotating ring wrapping machine, where the film carriage is connected fixedly to the rotating ring of the wrapping machine in order to rotate the film carriage around the load to be wrapped. 
         [0026]      FIG. 1B  shows enlargement A of  FIG. 1A  where the casing  2  is removed in order to show gear pair formed of gears  3  and  4 . 
         [0027]    In the embodiment of  FIGS. 1A and 1B , an electric motor  5  rotates first and second pre-stretching rollers through a belt  6  and belt pulley  7 . The belt pulley  7  in connected to the shaft  8  of the first pre-stretching roller, which shaft  8  extends from the upper end of the first pre-stretching roller. Above the belt pulley  7  and on the top end of the shaft  8  of the first pre-stretching roller is gear  4 , which gear  4  is connected through a gear coupling to the gear  3 , which gear  3  is located on the top end of the shaft  9  of the second pre-stretching roller. The shaft  9  extends from the upper end of the second pre-stretching roller. 
         [0028]    In this embodiment the pre-stretch level of the film to be wrapped is defined by the transmission ratio of the gear coupling formed by gears  3  and  4 , and the pre-stretch level of the wrapping machine is adjusted and controlled by changing the transmission ratio by changing both of the gears  3  and  4 . 
         [0029]    The changing of the gears  3  and  4  are done simply by lifting the gears  3  and  4 , advantageously simultaneously, upwards in the direction of the upper ends of the shafts  8  and  9  until these gears slide off from the ends of these shafts. Then new pair of gears, again advantageously simultaneously, can be slid on the ends of the shafts  8  and  9 . In this embodiment, protrusions  10  and  11  on the outer surfaces of the ends of the shafts  8  and  9 , or alternatively on the inner surfaces of the gears  3  and  4 , are positioned in the corresponding grooves in the inner surfaces of the gears  3  and  4 , or alternately in the outer surfaces of the ends of the shafts  8  and  9 , in order to rotate the shafts  8  and  9  together with gears  3  and  4 . 
         [0030]    The gear pair formed of gears  3  and  4  is advantageously located inside casing  2 . This way the gear pair can be replaced simply by replacing the whole casing  2 . Further, different casings  2  with different gear pairs  3  and  4  defining different pre-stretching levels for the wrapping machine can be provided for quick changing of the pre-stretch level. 
         [0031]      FIG. 2  shows a schematic cross-section of a gearbox  12  according to the present disclosure, comprising a pair of intermeshing gears  13  and  14  inside housing  15 . 
         [0032]    The housing  15  has detachable end surface  16 , which can be detached for changing the pair of gears  13  and  14  inside the gearbox  12 . At the lower surface of the housing  15  is provided two holes  17  and  18 , which holes are located in the area of the center holes  19  and  20  of the gears  13  and  14 . The holes  17  and  18  of the housing  15  are substantially larger than the center holes  19  and  20  of the gears  13  and  14 , and the holes  17  and  18  have substantially same center axis than the respective center holes  19  and  20 , so that ends of the rotating shafts of the pre-stretching rollers can be inserted through the holes of the housing into the center holes of the gears. 
         [0033]    Instead of the two holes  17  and  18  provided in the housing  15 , the access to the center holes  19  and  20  of the gears  13  and  14  can be provided with a single hole covering both of the center holes. In that kind of embodiment enough of the lower surface of the casing  15  needs to be maintained so that the gears  13  and  14  are retained inside the casing when the gearbox  2  is slid off the ends of the rotating shafts of the pre-stretching rollers. 
         [0034]      FIG. 2  also shows grooves  21  and  22  formed in the inner surface of the center holes  19  and  20  of the gears  13  and  14 . The grooves  21  and  22  are utilized when connecting ends of the rotating shafts of the pre-stretching rollers unrotatably to the gears  13  and  14  in a way evident to a person skilled in the art. 
         [0035]    Inner surfaces of the housing  15  of the gearbox  12  are advantageously provided with protrusions that guide the gears  13  and  14  to their proper places inside the housing. The housing  15  is advantageously made from plastic. 
         [0036]    The specific example provided in the description given above should not be construed as limiting. Various changes and modifications to the present embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present subject matter and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims.