IES20020874A2

IES20020874A2 - A pre-stretching device

Info

Publication number: IES20020874A2
Authority: IE
Inventors: Christopher Belton
Original assignee: Arboc Ltd
Priority date: 2002-11-11
Filing date: 2002-11-11
Publication date: 2004-05-19
Also published as: GB2395165B; GB2395165A; AU2003261529A1; GB0325524D0

Abstract

The invention concerns a pre-stretching device for use in pre-stretching plastics wrapping film. The pre-stretching device comprises two parallel rollers which are spaced apart to define a film pre-stretching zone through which a web of plastics film may be drawn. Each roller has at least two coaxially mounted gear wheels. One of the gear wheels on each roller is fixed for rotation with the roller, while the other non-fixed gear wheel can rotate freely relative to the roller. A coupling means allows a fixed gear wheel to be coupled to a non-fixed gear wheel, on one or orther roller, thereby allowing drive to be transmitted through a non-fixed gear wheel. The gear ratio between the two rollers can be changed, depending on which gears the coupling means couples together. There may be more than two coaxially mounted gear wheels on each roller, allowing a plurality of gear ratios to be selected by the coupling means. <Figure 1>

Description

The invention relates to a pre-stretching device for use in pre-stretching plastics wrapping film. The device is particularly suitable for use in pre-stretching webs of plastics film used in agricultural bale wrapping machines for wrapping bales of fodder. Thus the invention is particularly concerned with a pre-stretching device for use with machines for wrapping bales of agricultural silage, grain, hay, straw, maize, beet pulp, beet tops, and the like (hereinafter referred to as “fodder”) with a plastics film, which preferably is air tight and water tight. The device of the invention may also be used with machines for compacting and wrapping general farm and agricultural waste products, such as waste plastics and the like, and for wrapping other loose materials and objects such as comminuted peat moss, saw dust, wood shavings, wood chippings, brewery waste, bricks, blocks, cartons and the like.

Background to the Invention It has become conventional practice in agriculture to form harvested fodder into cylindrical-shaped bales, and square or rectangular bales, which are then wrapped in a plastics film. This is particularly suitable method of manufacturing silage because the silage is kept air-tight within the wrapped bale which, typically, is wrapped with up to six plies of plastics film. The cylindrically shaped bales are commonly called “big round bales”. Machines for wrapping big round bales with a plastics film are described, for example, in GB 2191984 A, GB 2228246A, EP 0208034A (GB 2159489B), EP 0 539 549 and WO 99/04613.

Bale wrapping machines of the kind described are usually provided with a film dispenser which holds a roll of plastics wrapping film. The film dispenser is usually rotated about the bale to be wrapped to apply several layers of plastics film to the bale IE 0 2 OR 7 4 until it is fully wrapped. Film dispenser units are disclosed for example in EP 0 426 308 A and EPI 115 276 B.

In order to ensure that the plastics film fits tightly over the bale, conventional film dispensers usually include a film pre-stretching device which pre-stretches the film so that when the pre-stretched web of film is applied to the bale it remains under tension to provide air-tight and water-tight covering. An example of a pre-stretching device is disclosed in EP 0 291 483 B. Conventional pre-stretching devices comprise a holder on which a reel of film is rotatably mounted. Two rollers are provided adjacent the film reel between which the film web is drawn by rotation of the bale wrapping apparatus. The first of these rollers is rotated by friction between the drawn film web and the roller. Alternatively, it may be power driven. A gear on the end of the first roll meshes with a complementary gear on the top of the second roll to provide a drive connection between the first driven roller and the second roller. The gearing is such that the second roller is driven at a different speed than the first roller, usually a lower speed. Thus as the film web is drawn through a film stretching zone between the two rollers the different peripheral speeds of the rollers cause pre-stretching of the film.

Different stretch ratios must be used depending upon the type of film being used and also the kind of bales which it is intended to wrap.

The plastics may be manufactured for example from polymide, polypropylene, PVC, polybutene, polyethylene, or copolymers or mixtures of such materials. Using such film the pre-stretch unit is designed to pre-stretch the film by typically up to 70% (or more) of its length in the case of standard round bales, and 55% of its length for wrapping square bales. Film manufacturers now supply a pre-tensioned film which has an inherent elasticity, for example a film of the type sold under the tradename “Volac Enduro”. The use of this film is described in a publication entitled “Volac Silowrap Enduro News, Vol. 2, Issue 1, May 2002”.

Users face a problem in using conventional pre-stretching units where different stretch ratios are required depending on the kind of bale to be wrapped or the IE 0 2 08 7 4 specification of the wrapping film, because the gear ratio on the pre-stretching unit must be altered. In the “Volac Silowrap Enduro News”, referred to above, directions are given as to how various pre-stretching units can be modified for use with “Enduro” prestretch film. This involves removing the inter-meshing gears on the pre-stretching unit and replacing the gears with a pair of gears of a different gear ratio. This is quite a cumbersome task as it involves removing the gear housing, loosening nuts that retain the gears in position, removing the larger gear using a bearing pullers or levers, then removing the smaller gear and finally replacing the gears with a different set of gears.

Object of the Invention It is an object of the invention to provide pre-stretching unit having intermeshing gears in which the gear ratio can be changed without removing and replacing the gears.

Summary of the Invention The invention provides a pre-stretching device for pre-stretching plastics film comprising two rollers mounted for rotation on a frame in parallel relationship and spaced apart to define a film pre-stretching zone through which a web of plastics film may be drawn about said rollers, and a first gear wheel coupled to a first roller which meshes with a second gear wheel on the second roller to drive the second roller at a different peripheral speed than the first roller to stretch a web of plastics film drawn around the rollers characterised in that each roller has at least two coaxially mounted gear wheels coupled to the roller, one of said gear wheels on each roller being fixed for rotation with the roller and the other gear wheel being mounted for non-fixed free rotation relative to the roller, and coupling means is provided for selectively coupling a fixed gear wheel to a non-fixed gear wheel on one or other roller whereby drive may be transmitted through a non-fixed gear wheel.

In accordance with another aspect, the invention relates to a pre-stretching device for pre-stretching a web of plastics film before applying the film as a wrapping to IE 0 208 7 4 a bale comprising a support on which a reel of plastics film is mounted for rotation about a longitudinal axis of the reel, and two pre-stretching rollers laterally spaced from the reel, and having longitudinal axes which extend substantially parallel to the longitudinal axis of the reel, the pre-stretching rollers comprising a first roller and a first gear wheel coupled to the first roller which meshes with a second gear wheel on the second roller to drive the second roller at a different peripheral speed than that of the first roller to stretch a web of plastics film drawn about the rollers, characterised in that each roller has at least two coaxially mounted gear wheels coupled to the roller, one of said gear wheels on each roller being fixed for rotation with the roller and the other gear wheel being mounted for non-fixed free rotation relative to the roller, and coupling means is provided for selectively coupling a fixed gear wheel to a non-fixed gear wheel on one or other roller whereby drive may be transmitted through a non-fixed gear wheel.

One or both rollers are adapted to be driven by withdrawing the web of film from the reel about at least part of the periphery of the rollers.

In another embodiment, the pre-stretching device of the invention comprises three coaxially mounted gear wheels, positioned one above the other, on each roller, and one of the gear wheels on one roller is fixed for rotation with the roller and the other two gear wheels on that roller are non-fixed; and two of the gear wheels on the other roller are fixed and the other gear wheel is non-fixed, and the gear wheels are so arranged that a fixed gear wheel on one roller meshes with a non-fixed gear wheel on the other roller.

Suitably each inter-meshing gear wheel set on the two rollers has a different gear ratio. The coupling means for coupling superimposed gear wheels preferably comprises a removable pin, bolt, screw or the like which is passed through aligned holes in the gear wheels. Thus, it is very simple for the user to remove the pin from one set of aligned holes and insert it in a different set to change the gear ratio.

The term “gear wheel” as used throughout the description and claims is intended to be interpreted broadly to cover mechanical equivalents. For example, it is envisaged IE 0 2 08 7 4 that the gear wheels might be substituted by sprocket wheels which are meshed by means of endless chains, or by pulleys and toothed or v-belts.

The pre-stretching device of the invention offers a number of advantages over known systems including the following: • The gear ratios can be changed by changing the location of only a single pin and no manual changing or engaging of gears is required.

• The device can utilise standard off-the-shelf gear wheels and does not require a special floating pair of gear wheels to be machined in the various ratio options.

• The pre-stretching device of the invention can be retro-fitted to older machines without any machining being required.

• The device of the invention is suitable for use in applications where space is limited.

• Also, the device is relatively weatherproof unlike some systems utilising floating gear pairs which are prone to seizing because they are exposed to the elements.

Brief Description of the Drawings Some embodiments of the invention are hereinafter described with reference to the accompanying drawings wherein: Figure 1 is a perspective view from above of one embodiment of a pre-stretching device in accordance with the invention; Figure 2 is an elevation showing the pre-stretching device of Figure 1 mounted in a film dispenser; Figure 3 is a diagrammatic plan view showing the path of the film web in the dispenser of Figure 2; Figure 4 is an elevation of inter-meshing gears as used with a conventional prestretching device; Figures 5 and 6 are elevations of one embodiment of gearing used with the prestretching device of the invention; Figure 7 is a elevation of another embodiment of gearing used with the pre-stretching device of the invention; and IE 0 2 08 7 4 Figure 8 is a elevation of another embodiment of gearing used with the pre-stretching device of the invention.

Detailed Description of the Drawings Figure 1 shows a first embodiment of a pre-stretching device 1 of the invention, and Figures 2 and 3 shows the device 1 mounted in a film dispensing assembly 2.

Referring firstly to Figures 2 and 3 these illustrates a film dispensing assembly 2 comprising a reel 3 of plastics film which is supported for rotation between two vertically aligned spigots 4 and 5 which are mounted between arms 6 and 7 which extend laterally from a support member 8 suitably made from steel box section. Frustoconical bearings 9,10 are rotatably mounted on the ends of the spigots 4,5 respectively, and engage the centre of the reel 3 to enable the reel to rotate about the central axis of the spigots 4, 5. Two pre-stretching rollers 11,12 are laterally spaced from the reel 3 and are disposed parallel to the reel 3. The rollers 11,12 are freely rotatably between brackets 13,14, located one at each end of the rollers. The brackets 13,14 are mounted on an upright support 15 which is held between the arms 6, 7.

In use, a web 30 of plastics film is drawn from the reel 3 by rotation of the bale wrapping apparatus. As shown in Figure 3 the web passes about the rollers 11 and 12. The roller 11 is rotated by friction between the drawn film web 30 and the roller. Alternatively, the driven roller 11 may be power driven (not shown). Drive is also imparted to the other roller 12 by the film web 30. Gearing coupled to the top of the driven roller 11 transmits drive to gearing on the top of the roller 12 as hereinafter described. The gearing causes the roller 12 to rotate at a different speed than the roller 11, usually at a faster speed. The rollers 11 and 12 are spaced apart a distant, typically of the order of 10mm to 20mm, to define a stretching zone 16 between the two rollers. Because of the different speeds of the rollers 11 and 12, the plastics film is stretched in the stretching zone at a stretch ratio which is at least partly determined by the gearing. It should be noted that the pull on the film web 30 caused by the wrapping apparatus also causes stretch in the film.

IE 0 208 7 4 The outer surfaces of the rollers 11 and 12 may be knurled, spiral cut, ribbed or may be provided with a coating or polyurethane cover, to increase friction between the film and the roller. The rollers 11,12 have axial shafts 17,18, respectively which are rotatable with the rollers. Gear wheels are mounted on the shafts as described hereinafter. The gear wheels are provided with a cover 19.

Referring now to Figure 4, this shows the prior art gearing which typically is used on conventional pre-stretching devices. A first toothed gear wheel 20 is keyed to the first shaft 17 so as to rotate with the shaft. The gear wheel 20 meshes with a complementary gear 21 keyed to the second shaft 18. The arrows in Figure 4 show how the drive from the first shaft 17 is transmitted to the second shaft 18. The gear wheels 20, 21 have a different number of teeth (n) and have different radii (r). The number of teeth is proportional to the corresponding radius of the gear wheel. Thus, the speed ratio may be calculated by the formula: ω. ω. where na is the number of teeth in the first gear wheel, nb represents the number of teeth in the second gear wheel, rc is the radius of the first gear wheel, rb is the radius of the second gear wheel and w is the speed of rotation.

Referring now to Figures 5 and 6, these show one embodiment of gearing for the pre-stretching device of the invention. In this embodiment there are two gears on each of the shafts 17 and 18. Thus, on the first shaft 17 there is a first gear 33 which is keyed or otherwise fixed to the shaft 17 by keys 23, in well know manner, so that the gear wheel 33 rotates with the shaft. Superimposed on the gear wheel 33 is a second gear wheel 31 of different radius. In this case it has a larger radius and a proportionally larger number of teeth than gear 33. The gear wheel 31 is freely rotatable (i.e. nonfixed) on the shaft 17 by means of suitable bearings (not shown). A complementary set of gears 34, 32 is mounted on the shaft 18. The lower gear wheel 34 is freely rotatable IE 0 2 08 7 4 on shaft 18 whereas the upper gear wheel is keyed to the shaft 18 by keys 24. Again, these gear wheels have different dimensions and proportionally different numbers of teeth. The top gear wheel 31 of shaft 17 meshes with the top gear 32 of shaft 18 and likewise the lower gear 33 of shaft 17 meshes with the lower gear 34 of shaft 34. Each of the gear wheels has a hole 25 drilled axially through the gear wheel spaced from but extending parallel to the axis of rotation of the wheel. The holes 25 are so positioned that they may be aligned with each other. A screw or pin 26 may be inserted through aligned holes 25 of either of the sets 31,33 or 32, 34. In Figure 4, the pin 26 is inserted in the aligned holes 25 of gears 31 and 33 so as to couple the gears together for corotation.

Thus, because gear wheels 31 and 33 are coupled the drive from the first shaft 17 is transmitted as shown by the arrow in Figure 5. That is, the drive is transmitted from fixed gear wheel 33, through the coupling pin 26, to gear wheel 31 which in turn meshes with gear wheel 32 to transmit the drive to shaft 18 of roller 12. Thus, the speed of rotation of roller 12 is determined by the radii of gears 31, 32 and the proportional number of teeth in these gear wheels. The gear wheel 34 is free to idle because it is not keyed to the shaft 18.

When it is desired to change the gear ratio so as to vary the stretch ratio of the film all that needs to be done is to remove the pin 26 from the holes 25 of gears 31 and 33 and to insert the pin in the corresponding holes 25 of gears 32 and 34, as shown in Figure 6.

In the arrangement shown in Figure 6, drive is transmitted from the shaft 17, in the direction of the arrows, from the keyed gear 33 to non-keyed gear 34, which in turn is coupled by the pin 26 to gear 32 which is keyed to shaft 18. In this arrangement the gear ratio is determined by the radii and teeth number of inter-meshing gears 33 and 34.

Thus in this embodiment inter-meshing gears 31 and 32 provide for gear ratio (A) whereas inter-meshing gears 33 and 34 provide for gear ratio (B).

IE 0 208 7 4 A second embodiment of the invention is shown in Figure 7. In this embodiment there are three superimposed gear wheels on each shaft 17,18. The top sets of gear wheels comprise gear wheels 31, 32, 33 and 34 as described above. Two further gear wheels are provided on each shaft namely inter-meshing gear wheels 35, 36. In this embodiment gears 31, 33 and gears 32, 34 may be coupled by pin 25 as described above to provide for gear ratios (A) and (B).

A third gear ratio (C) may be obtained by coupling keyed gear wheel 33 with a freely rotatable gear wheel 35 on shaft 17. This is achieved by inserting a coupling pin 26 through aligned holes 25, from the underside of gear 35. Thus, drive is transmitted, in the direction of the arrows, from shaft 17 to fixed gear wheel 33, which in turn transmits the drive through the pin coupling 26 to gear 35, which meshes with fixed gear 36 keyed to shaft 18.

Gear wheel 31 is idle and so no drive is transmitted between it and gear wheel 32.

Different sized gear wheels may be selected to achieve different relative speeds of rotation of rollers 11 and 12, and hence different stretch ratios for the film web 30.

For example, in the embodiment described in relation to Fig. 7, the following gear ratios may be used: First Roller Second Roller Stretch Ratio 60t 35t 71% 54t 41t 32% 59t 38t 55% t = number of teeth on gear wheel. ΙΕ η 2 08 7 4 A further embodiment is illustrated in Figure 8, in which there are four superimposed gear wheels on each shaft 17,18. This enables a fourth gear ratio (D) to be obtained.

The words “comprises/comprising” and the words “having/including” when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

Claims

1. A pre-stretching device (1) for pre-stretching plastics film comprising two rollers (11,12) mounted for rotation on a frame (13,14) in parallel relationship and spaced apart to define a film pre-stretching zone (16) through which a web of plastics film may be drawn about said rollers (11,12), and a first gear wheel coupled to a first roller (11) which meshes with a second gear wheel on the second roller (12) to drive the second roller (12) at a different peripheral speed than the first roller to stretch a web of plastics film drawn around the rollers (11,12) characterised in that each roller (11,12) has at least two coaxially mounted gear wheels (31,32, 33, 34) coupled to the roller (11,12), one of said gear wheels (33,32) on each roller (11,12) being fixed for rotation with the roller (11,12) and the other gear wheel (31,34) being mounted for non-fixed free rotation relative to the roller (11,12), and coupling means (26) is provided for selectively coupling a fixed gear wheel (33, 32) to a non-fixed gear wheel (31, 34) on one or other roller (11,12) whereby drive may be transmitted through a non-fixed gear wheel (31, 34).

2. A pre-stretching device as claimed in claim 1 characterised in that there are three coaxially mounted gear wheels, positioned one above the other, on each roller (11, 12), and one of the gear wheels (33) on one roller (11) is fixed for rotation with the roller (11) and the other two gear wheels on that roller (11) are non-fixed; and two of the gear wheels (32, 36) on the other roller (12) are fixed and the other gear wheel (34) is non-fixed, and the gear wheels are so arranged that a fixed gear wheel (33, 32, 36) on one roller meshes with a non-fixed gear wheel (34,31,35) on the other roller.

3. A pre-stretching device as claimed in claim 1 or claim 2, characterised in that each inter-meshing gear wheel set (31,32; 33, 34; 35, 36) on the two rollers (17,18) has a different gear ratio.

4. A pre-stretching device as claimed in any of the preceding claims, characterised in that the coupling means comprises a removable pin (26) which is passed through aligned holes (25) in the gear wheels. IE Ο 208 7 4

5. A pre-stretching device for pre-stretching plastics film substantially as hereinbefore described, and as illustrated in, one or more of the accompanying drawings.