UNWINDER FOR WEB MATERIAL, PROVIDED WITH SYSTEMS FOR REDUCING DYNAMIC VACUUM DURING UNWINDING, AND RELATED METHOD

DESCRIPTION

TECHNICAL FIELD

[0001] The invention relates to unwinders for unwinding reels or rolls of web material, for example, although not exclusively, paper, tissue paper, non-woven and other materials that are partially air-permeable. The invention also relates to methods for unwinding web materials from a reel.

BACKGROUND ART

[0002] In many industrial applications, it is required to unwind a continuous web material from a reel, for example for feeding it to a converting line or a rewinder. Typically, web materials are unwound from parent reels and rewound in reels or rolls of smaller radial and/or axial dimensions, that are then used for producing articles intended for the final consumption. If the web material is tissue paper, the reels may be used, for example, for producing rolls of toilet paper, rolls of kitchen towels, napkins and the like. If the web material is non-woven fabric, the reels obtained by rewinding the web material may be used, for example, for producing baby or adult diapers, sanitary napkins or similar products.

[0003] When a roll or reel of web material is unwound, the continuous detachment of the web material from the reel in tangential direction generates a depressurization in the approximately wedge-shaped region delimited by the peripheral surface of the reel and the web material tangent to said peripheral surface of the reel. Depressurization is practically generated by the air dragged by the surface of the web material being unwound that faces the reel, and by the outer surface of the outermost turn of the reel, the dragging being caused by the movement of the two diverging surfaces. Due to this aerodynamic phenomenon, in the detachment area depressurization is generated, called “dynamic vacuum”.

[0004] Due to the dynamic nature of the phenomenon, the depressurization degree is null when the unwinding speed is null, and tends to increase as the unwinding speed increases.

[0005] The dynamic vacuum phenomenon is also ruled by geometrical factors; especially, by how many degrees is the acute angle formed at the detachment point where the side surface of the reel detaches from the web material tangent thereto. The more acute the detachment angle (and therefore the approximately wedge-shaped space), the higher the vacuum. The larger the reel diameter, the smaller the width of the wedge; for this reason, the phenomenon is more significant when the unwinding begins, i.e. when the reel diameter is maximum.

[0006] The depressurization generated in the area where the web material detaches from the reel, and the consequent pressure difference between the outer surface and the inner surface of the web material in the segment tangent to the reel, have two effects.

[0007] The first effect is a return of air from the area extending along the bisecting line of the wedge. This air flow, opposite to the flow of the dragged air, generates high turbulence. Turbulence creates instability in the web material (flattering) that, if not controlled, can cause folds in the downstream process. In most cases, flattering is controlled by increasing the tension of the web material.

[0008] The second effect is a pressure on the rectilinear portion of web material detaching from the reel. The pressure generates a load on the web material in a direction substantially perpendicular to the movement direction. This load tends to bend the web material towards the reel. The bending results in that a higher tension is required for proper operation, given the same speed difference between the unwinder and the subsequent section of the line (calender, cut or winding).

[0009] These inconveniences adversely affect the processing of web materials of various type.

[0010] A higher tension applied to the web material can jeopardize the features of the downstream article. For example, if the web material is tissue paper, the higher tension exerted thereon to control flattering causes a reduction in paper scraping and therefore a loss of the physical characteristics imparted to the paper in the production process that is detrimental to the quality of the finished product. [0011] Higher tension negatively affects also the processing of other types of web materials, for example non-woven fabric. Indeed, non-woven fabric tends, when tensioned, to shrink transversally, which results in inconveniences in the product (reels or rolls) obtained by rewinding the web material unwound from a parent reel.

[0012] The object of the present invention is to provide an unwinder and a method for unwinding a reel of web material, which entirely or partly overcome the drawbacks of the previous art.

SUMMARY

[0013] In order to reduce the dynamic phenomena described above, using an active device is suggested, which is associated with the unwinder and has the function of blowing air in a controlled manner in the wedge where the web material being unwound detaches from the reel, thus preventing the pressure drop caused by the aerodynamic processes mentioned above, and in this way preventing or reducing instability and bending of the web material when detaching from the reel.

[0014] In practice, according to one aspect, an unwinder is disclosed for unwinding reels of web material, comprising unwinding members for unwinding a reel of web material towards a feed path for feeding the web material unwound from the reel, and a device with at least one nozzle, adapted to blow pressurized air in an area where the web material geometrically detaches from the reel.

[0015] The nozzle can be advantageously provided on board a moving system that ensures that the position and direction of the nozzle are always geometrically consistent with the displacement of the area where the web material detaches from the reel, the displacement being due to the progressive decrease in the diameter of the reel being unwound.

[0016] In the field of reel unwinders the use of air nozzles forming an air curtain is known, but for different purposes and having a different structure. For instance EP 1444154 discloses an unwinder wherein a nozzle generates an air blade for detaching the leading edge of the web from the body of a new reel and ensure that the leading edge be placed on the trailing portion of an exhausted reel. This publication does not mention the use of a nozzle to eliminate or reduce the above described dynamic phenomena.

[0017] In many applications, the web material can be unwound in the unwinder in both directions of rotation (clockwise and counterclockwise direction). It is therefore advantageous that the device is double, for clockwise and counterclockwise unwinding. In other embodiments, a same device can be repositioned and redirected according to the direction of rotation of the reel being unwound. Many solutions can be suitable to this end. Some of them will be described in more detail below, with reference to the attached drawing.

[0018] For proper operation of the device, it is advantageous that the position thereof is always consistent with the instant diameter of the reel being unwound. For this purpose, the absolute position of the device can be controlled according to the reel diameter. This can be achieved, for example, by continuously acquiring the value of the reel diameter, measured by a system provided outside the device. Through this value, the values for the positioning parameters of the device are calculated. A simple example is to calculate the reel diameter as the ratio between the unwinding speed of the web material, that is the machine speed, and the angular speed of the reel at the same time instant, measured by a common speedometer coaxial with the roll.

[0019] In other embodiments, the distance between the device and the outer surface of the reel is measured instantaneously and directly. This can be done through various systems, both contact systems, such as rolling or sliding mechanical feeler, and non- contact systems, such as laser or optical systems.

[0020] In many applications, the unwinder is arranged upstream of a rewinder, where the web material (unwound from a parent reel in the unwinder) is rewound into one or more smaller reels. In many cases, the rewinder is a discontinuous machine characterized by steps of acceleration, constant speed, deceleration and stop for changing the set of smaller reels and/or changing the parent reel. It is therefore advantageous that the air for saturating the dynamic vacuum is blown in modulated fashion according to the vacuum intensity and therefore to the peripheral speed of the parent reel.

[0021] To this end, the members supplying air to the nozzle are provided with a system for automatically adjusting the airflow rate from zero to a maximum. In some embodiments, air is supplied by one or more fans. In this case, the airflow rate of the fans may be adjusted based on the speed of the web material, for example by motors provided with converters or potentiometers.

[0022] In further embodiments, air is supplied to the nozzle by a centralized system; in this case the airflow rate, and therefore the air supply speed, can be adjusted by proportioning valves for partializing the supply line of the device.

[0023] Further features and embodiments of the unwinder and the nozzle device to supply pressurized air in the area where the web material detaches from the reel being unwound are defined in the attached claims. [0024] According to a further aspect, a method for unwinding a web material from a reel is disclosed, including the step of driving the reel into rotation and unwinding the web material from a reel unwinding point towards a feed path. Characteristically, the method comprises the step of blowing pressurized air in an area where the web material detaches from the reel. [0025] Further features and embodiments of the method according to the invention are indicated in the appended claims.

BRIEF DESCRIPTION OF THE DRAWING

[0026] The invention will be better understood by following the description below and the attached drawing, showing non-limiting embodiments of the invention. More specifically, in the drawing:

[0027] Fig. l is a schematic view of an unwinder according to a first embodiment;

[0028] Fig.2 is a simplified axonometric view of a nozzle according to a first embodiment;

[0029] Fig.3 a simplified axonometric view of the nozzle in a further embodiment; [0030] Figs.4A-4C show a diagram of an operative sequence in an embodiment;

[0031] Fig.5 shows a diagram of the moving members of the nozzle in an embodiment; [0032] Figs.6A-6E show a diagram of an operative sequence in a further embodiment; and

[0033] Fig.7 shows a further diagram of an embodiment.

DETAILED DESCRIPTION

[0034] Fig.l schematically shows an embodiment of an unwinder 1 for unwinding parent reels B of web material, for example and typically non-woven or paper, for instance and especially tissue paper. N indicates the web material being unwound, moving forwards according to the arrow F due to rotation (arrow R) of the reel B.

[0035] The web material N moves forwards along a feed path 3 towards a processing station 5 arranged downstream of the unwinder 1. In the embodiment of Fig.l, the processing station 5 downstream of the unwinder 1 comprises a rewinder. Just by way of example, the rewinder 5 comprises a pair of lower motorized winding rollers 7, 9 that define a winding cradle where the web material N is rewound to form one or more reels B1 with diameter and/or axial dimension smaller than that of the parent reel B. Reference number 10 indicates a rider roll, or movable roll, that can be motorized similarly to the lower rollers 7, 9 to facilitate and control the rotation of the reel B 1.

[0036] Cutting blades are provided along the feed path of the web material N for slitting the web material into two or more longitudinal strips, with which two or more reels B 1 are formed in parallel. In Fig.l, the cutting blades are schematically indicated with reference number 11 and co-act with corresponding counter-blades 13. Practically, more pairs of blades and counter-blades may be provided, that can be arranged transversally to the feed direction of the web material N, so as to slit the latter in a variable number of longitudinal strips of suitable width according to the preset production orders.

[0037] The parent reel B is driven into rotation by unwinding members. The unwinding members can be peripheral unwinding members, central unwinding members, or a combination thereof. Just by way of schematic example, in Fig.l the unwinding members are indicated with reference number 15 and represented as peripheral unwinding members. The unwinding members 15 comprise idle rollers or pulleys 19 and motorized rollers or pulleys 21, around which continuous flexible elements 17, for example belts, are driven. The motorized rollers or pulleys 21 are associated with a motor 23 controlling the rotation of the rollers or pulleys 21 and therefore the movement of the continuous flexible members 17. These latter rotate the parent reel B around the axis thereof by friction. To this end, the parent reel B is suitably supported by support members, not shown.

[0038] An encoder 25 is associated with the motor 23 and interfaces a control unit 27 that receives information on the motor 23, for example data allowing to detect the peripheral speed of the parent reel B, for purposes that will be detailed below.

[0039] D indicates the point where the web material N detaches from the parent reel B. V indicates a wedge-shaped space delimited by the web material N and the side surface, i.e. the approximately cylindrical peripheral surface, of the parent reel B, the space ending with a vertex in the detachment point D and representing the area where the web material N detaches from the parent reel B.

[0040] For the reasons illustrated above, depressurization, i.e. a decrease in air pressure, tends to form in the space V. To prevent this phenomenon, the unwinder 1 comprises a nozzle 31 generating an airflow A directed towards the wedge-shaped space V, i.e. in the area where the web material N detaches from the parent reel B. More particularly, the airflow blown by the nozzle 3 is preferably directed towards the detachment point D. The nozzle 31 is fluidly connected to an air source 33 supplying air at the required flow rate and pressure (and therefore at the required speed).

[0041] In the diagram of Fig.1, the air source 33 is a fan 35 combined with a control valve 37, for example a proportioning valve 37. Actually, the fan 35 may be part of an air-supply system serving also other users. In this case, the flow rate and/or the pressure of the air fed by the source 33 along a duct 39 to the nozzle 31 is controlled by the control valve 37. In further embodiments, the fan 35 is dedicated for the nozzle 31. In this case, the flow rate and/or pressure can be controlled by acting directly on the fan motor.

[0042] Thus, in practical embodiments, a connection 41 may be provided connecting the control valve 37 to the control unit 27, or a connection 43 connecting the motor of the fan 35 to the control unit 27. In Fig.l both connections are shown by way of example. [0043] The nozzle 31 can have any shape suitable to generate an air knife investing the entire length of the space V, along the extension of the axis of the parent reel B. To this end, the nozzle 31 may have an opening in the form of a continuous or discontinuous slit, schematically indicated with number 31A in Fig.2. In other embodiments, the nozzle 31 comprises a series of openings that can be circular, rectangular, square or of any other appropriate shape, aligned parallel to the axis of the reel B, as schematically indicated with number 3 IB in Fig.3.

[0044] As the airflow rate and speed along the linear extension of the nozzle 31 shall be as uniform as possible, it is useful that the duct 39 is multiple, for example double, as indicated with 39A, 39B in Figs.2 and 3, so as to supply air to several points (for example to the ends) of the nozzle 31.

[0045] Whilst the parent reel B is unwound, the diameter thereof gradually decreases. Therefore, as the diameter of the parent reel B decreases, the nozzle 31 adequately moves following the detachment point D where the web material N detaches from the parent reel B. The sequence of Figs.4A, 4B, 4C shows the movement of the nozzle 31 as the diameter of the parent reel B decreases.

[0046] As shown in Figs.4A, 4B e 4C, the movement of the nozzle 31 is advantageously a combined roto-translation movement, so as to keep approximately constant also the direction of the jet of air A with respect to the wedge-shaped space V ending with the vertex defined by the detachment point D.

[0047] Various mechanisms can be used to achieve the movement of the nozzle 31.

[0048] Just by way of non-limiting example, Fig.5 shows a moving mechanism that combines a translation movement along two translation axes and a rotary movement to be imparted to the nozzle 31. Reference number 51 indicates the moving mechanism as a whole.

[0049] The moving mechanism 51 comprises a first guide 53, for example horizontal, and a second guide 55 not parallel to the first guide 53, for example vertical. A first slide 54 moves along the first guide according to a numerically controlled axis Fx. The second guide 55 is integral to the first slide 54, thus performing a movement according to the double arrow Fx (numerically controlled horizontal axis of translation). A second slide 57 is movable on the guide 55, the second slide being able to perform a movement along a second numerically controlled vertical axis of translation according to the double arrow Fy. The nozzle 31 is provided on the slide 57, so as to perform a rotation movement (arrow FR) according to a numerically controlled axis of rotation.

[0050] As shown in the diagram of Fig.5, the three combined movements Fx, Fy, FR allow the nozzle 31 to track the detachment point D of the web material N while the parent reel B is unwound. In Figs.4A, 4B, 4C unwinding takes place by rotating the parent reel B clockwise. Fig.5 shows that the moving mechanism 51 allows the nozzle 31 to keep the correct position during the unwinding movement.

[0051] However, as shown in Fig.5, the moving mechanism 51 is also able to make the nozzle 31 perform a movement tracking the detachment point D even if the parent reel B is unwound counterclockwise. The reference number 3G indicates the initial position of the nozzle 31 when the parent reel B is unwound clockwise, and 31" indicates the initial position of the nozzle 31 when the parent reel B is unwound counterclockwise. Fig.5 also shows, for both unwinding directions, the trajectory followed by the nozzle 31, which can be obtained in both cases by appropriately combining the movements along the axes Fx, Fy and FR.

[0052] The airflow rate required for balancing the dynamic vacuum phenomenon is a function of the feed speed of the web material N and therefore of the peripheral speed of the parent reel B and, consequently, of the angular speed and the diameter of the parent reel B. Appropriately, the control unit 27 receives information from the unwinder 1 for modulating the airflow rate (through signals to the valve 37 and/or the fan 35 on the connection 41 and/or 43) and for controlling the moving mechanism 51 (connection X, Figs.l and 5).

[0053] The unwinding speed can be detected by the encoder 25 associated with the motor 23. Alternatively, or in combination, a speed sensor can be provided that reads the peripheral speed of the reel B, or of the web material N, or of the continuous flexible member 17, for example through a laser system.

[0054] By continuously detecting (or by detecting through instant measurements repeated over time) the speed of the web material N, the airflow rate can be modulated correctly to balance the effect of the dynamic vacuum and to reduce or to eliminate the related drawbacks.

[0055] In other embodiments, in addition, or as an alternative, to the control based on the speed of the web material N, it is possible to detect, through a laser sensor or other sensor 63, for example, any oscillations or vibrations of the web material N in the detachment area. A signal Y is transmitted to the control unit 27 for controlling the airflow rate. The signal Y can either be an alternative to the signal of linear speed of the web material N, or be used in combination therewith, for example as a subordinate signal, if, despite the control based on the speed, abnormal oscillations or vibrations of the web material are detected.

[0056] To check the position of the nozzle 31, the diameter of the parent reel B can be detected. To this end, the value of the peripheral speed of the parent reel B can be used together with a value of the angular speed of the parent reel B, which can be detected by a sensor or encoder 61 (Fig.1) associated with the winding core of the parent reel B and connected to the control unit 27.

[0057] In addition, or as an alternative, to detecting the diameter of the parent reel B in order to control the movement of the nozzle 31, it is also possible to detect, directly or indirectly, the distance of the nozzle 31 from the cylindrical surface of the parent reel B. This distance can be detected by a sensor 67 integral to the nozzle, or by a device independent of the nozzle.

[0058] Figs.6A-6E show a sequence of positions of the nozzle 31 during the clockwise unwinding of the parent reel B in a different embodiment of the moving mechanism 51. In this embodiment, the moving mechanism 51 comprises a four-bar linkage with two rockers 51 A, 5 IB hinged to a fixed structure and connected to a connecting rod 51C. The nozzle 31 is fastened to the connecting rod 51C. The two rockers 51 A, 5 IB have different lengths, calculated so that the connecting rod 51C performs such a roto-translation movement as to make the nozzle 31 perform the correct movement with respect to the detachment point D. In the illustrated embodiment, the nozzle 31 has a central point coaxial to the hinge that joins the connecting rod 51C and the shorter rocker 51 A.

[0059] In this embodiment, the four-bar linkage that comprises the rockers 51 A, 5 IB and the connecting rod 51C is not able to impart to the nozzle 31 the correct movement for counterclockwise unwinding of the parent reel B. If the unwinder 1 shall be able to unwind the parent reel B in opposite direction, it is necessary to provide a second four- bar linkage, with a respective second nozzle 31, arranged in mirror-like fashion with respect to the first four-bar linkage and the first nozzle. Fig.7 graphically shows the trajectory of the two nozzles, indicated with 3 IX and 31Y, which can be used for clockwise and counterclockwise unwinding of the parent reel B.