The present invention relates to a machine for severing a web of material and, more particularly, to a simplified and improved apparatus and process for severing a web of cushioning material, especially a web of gas-containing cushioning material, such as foam or Bubble Wrap® cushioning material.
There often arises a need to sever a predetermined length of web from a larger supply of such material. For example, articles to be shipped in a container, e.g., a cardboard box, are often wrapped in a cushioning material inside of the container in order to protect the article during shipment. Such material often is supplied in the form of a continuous web from a source such as, e.g., a roll or folded stack. In order to sever an appropriate length of the material from the web, the packaging professional must make a transverse cut across the web or simply tear the web in a general direction which is transverse to the longitudinal dimension of the web, i.e., the direction from which the web is withdrawn from its source. Alternatively, the web of cushioning material may have a series of transverse perforation lines to facilitate tearing. In the case of Bubble Wrap® cushioning material, or other types of cushioning material containing individual cells or pockets of trapped gas, perforations are disadvantageous because any gas pockets contacted by the perforation lines become deflated, thereby reducing the number cells that are available for cushioning. In addition, the perforation lines are spaced at arbitrary intervals, which results in a lesser or greater length of cushioning material being torn from the web than would otherwise be desired in order to properly wrap the particular article in question.
As a result, various machines have been developed to provide automated severance of webs of cushioning material. One such machine, sold by Sealed Air Corporation under the trade name Instasheeter™ High-Speed Converting System, employs a pair of horizontally-oriented, counter-rotating conveyor belts that contact respective upper and lower surfaces of a horizontally-oriented web of cushioning material to convey such web through the machine. Downstream of the conveyor belts is a guillotine-type knife to sever the web into selected lengths. While this machine has worked well, it is more complex and expensive than would otherwise be desired for certain segments of the protective packaging market.
Accordingly, there is a need in the art for a simpler and less expensive web-severing machine, particularly one adapted to convey and sever webs of cushioning material, yet one that operates reliably and at a sufficiently high rate of speed to satisfy the requirements of the end-use packaging environment.
Those needs are met by the present invention, which, in one aspect, provides a machine for severing a web, comprising:
a) a movable surface positioned such that the web may exert gravitational force against the movable surface, the movable surface providing frictional force against the web such that movement of the surface causes movement of the web, wherein, the gravitational force exerted by the web on the movable surface and the frictional force between the web and the movable surface are sufficient to allow the movable surface to convey the web; and
b) a severing mechanism to sever the web into selected lengths, the severing mechanism including a severing device that urges the web against the movable surface to effect the severance of the web.
Another aspect of the invention pertains to a machine for severing a web, comprising:
a) a movable surface positioned such that the web may exert gravitational force against the movable surface, the movable surface providing frictional force against the web such that movement of the surface causes movement of the web;
b) a guide member adjacent the movable surface to define a path for movement of the web between the movable surface and the guide member, the guide member being in sliding contact with the web; and
c) a severing mechanism to sever the web into selected lengths, the severing mechanism including a severing device that urges the web against the movable surface to effect the severance of the web.
Still another aspect of the invention is directed to a device for severing a web, comprising:
a) a heating element capable of reaching a temperature sufficient to sever the web when electrical current flows therethrough, the heating element being configured such that only a contact portion thereof makes contact with and effects severance of the web; and
b) two or more electrical nodes that are connectable with a source of electricity and in electrical communication with the heating element, the nodes being positioned relative to the heating element such that electrical current flows substantially only through the contact portion of the heating element.
These and other aspects and features of the invention may be better understood with reference to the following description and accompanying drawings.
Referring to
Alternatively, web 12 may comprise an inflatable cushioning web that is inflated and sealed on-site, and is fed from an inflation/sealing apparatus directly or indirectly, e.g., via a hopper or supply roll, to machine 10. Inflatable cushioning material of this type, as well as a machine and method for its inflation, is disclosed in U.S. Ser. No. 10/057,067, the disclosure of which is hereby incorporated herein by reference thereto. Such an inflatable web and inflation system is sold by Sealed Air Corporation under the trade name NewAir I.B.™ 200 packaging system. Machine 10 in accordance with the present invention may be used as a component of, or adjacent to, e.g., downstream of, such packaging system.
As a further alternative, web 12 may comprise a foam cushioning material, such as a web of polyolefin foam sheet comprising, e.g., polyethylene or polypropylene foam. Such material is sold by Sealed Air Corporation under the trade name Cell-Aire® Polyethylene Foam.
Web 12 may, in general, comprise any flexible material that can be manipulated by machine 10 as herein described, including various thermoplastic materials, e.g., polyethylene homopolymer or copolymer, polypropylene homopolymer or copolymer, etc. Non-limiting examples of suitable thermoplastic polymers include polyethylene homopolymers, such as low density polyethylene (LDPE) and high density polyethylene (HDPE), and polyethylene copolymers such as, e.g., ionomers, EVA, EMA, heterogeneous (Zeigler-Natta catalyzed) ethylene/alpha-olefin copolymers, and homogeneous (metallocene, single-cite catalyzed) ethylene/alpha-olefin copolymers. Ethylene/alpha-olefin copolymers are copolymers of ethylene with one or more comonomers selected from C3 to C20 alpha-olefins, such as 1-butene, 1-pentene, 1-hexene, 1-octene, methyl pentene and the like, in which the polymer molecules comprise long chains with relatively few side chain branches, including linear low density polyethylene (LLDPE), linear medium density polyethylene (LMDPE), very low density polyethylene (VLDPE), and ultra-low density polyethylene (ULDPE). Various other polymeric materials may also be used such as, e.g., polypropylene homopolymer or polypropylene copolymer (e.g., propylene/ethylene copolymer), polyesters, polystyrenes, polyamides, polycarbonates, etc. The web may be a monolayer or multilayer film and/or foam, and can be made by any known extrusion process by melting the component polymer(s) and extruding, coextruding, or extrusion-coating them through one or more flat or annular dies.
Machine 10 generally includes a movable surface 16 positioned such that the web 12 may exert gravitational force against the movable surface 16. Further, movable surface 16 provides frictional force against the web such that movement of surface 16 causes movement of the web. In this embodiment, the combination of the gravitational force exerted by the web 12 on movable surface 16 and the frictional force between the web 12 and movable surface 16 are sufficient to allow the movable surface to convey the web.
Machine 10 also includes a severing mechanism 18 to sever the web 12 into selected lengths. Severing mechanism 18 generally includes a severing device 20 that urges the web 12 against movable surface 16 to effect the severance of the web. Severing device 20 may include a heated wire or other appropriate means, depending upon the composition of web 12, to melt, cut, or otherwise sever the web.
Many configurations for machine 10 are possible. In the embodiment shown in
By proper selection of material(s) for the movable surface 16, the combination of the gravitational force exerted by the web 12 on movable surface 16 and the frictional force between the web 12 and movable surface 16 is sufficient to allow the movable surface to convey the web, e.g., as the cylinder rotates. In this manner, additional conveyance machinery, such as a counter-rotating nip roller or conveyor belt as has been conventionally required, are not necessary in accordance with the present invention. As a result, the present machine is less complex and less expensive than conventional web-severing machines.
In the embodiment shown in
A bin 38 may be employed as shown to collect the cut sheets 36 as they are produced. Alternatively, machine 10 may be positioned over a work station or conveyor to dispense sheets 36 of cushioning material at their point of use, e.g., directly into shipping containers.
Referring now to
Regardless of the specific configuration, shape, or form assumed by the movable surface 16, it is advantageous that the movable surface comprise a material that 1) provides sufficient static and/or dynamic frictional force against the web to carry or otherwise propel the web in a desired direction upon movement of surface 16, and 2) has sufficient durability to withstand repeated contact thereagainst by the severing device 20. In one embodiment, the frictional force between the movable surface 16 and web 12 is sufficient for the surface 16 to convey the web based on only the weight of web 12 on surface 16. When severing device 20 employs a heating element such as a heatable wire, surface 16 ideally comprises a material with sufficient heat-resistance to withstand the temperatures generated by such heating element. Such heat-resistance is desirably sufficient to prevent the heating element from melting through the material when the severing device 20 urges web 12 against the movable surface.
Suitable materials for the portion of movable surface 16 that will be in direct contact with web 12 may be selected from the family of materials known as “elastomers,” particularly thermoplastic elastomers, which are also known as elastic polymers. Non-limiting examples of such elastomeric materials include:
In the embodiment shown in
Coated or otherwise disposed on substrate 40 may be a contact surface 42, which may comprise any of the elastomeric materials described above, or blends thereof. Advantageously, the particular elastomeric material selected may be matched with the web to be conveyed such that a desired level of friction between the contact surface 42 and web 12 is achieved in order to provide conveyance by the movable surface/cylinder 16. Ideally, material selection for contact surface 42 will also take into account the particular severing device 20 to be employed, with heated severing devices necessitating a relatively high degree of heat-resistance, for example, and cutting devices requiring a relatively high degree of impact toughness.
As an example, when conveying a web of inflated Bubble Wrap® cushioning material, having a width of 16 inches and comprising primarily polyethylene, contact surface 42 comprised a coating of Silastic® M RTV silicone rubber (from Dow Corning), having a Shore A durometer hardness of 59 and a thickness of ⅛ inch. Such a coating was manufactured ed by Precision Elastomers, Inc. of Ipswich, MA, which applied the coating in liquid form to substrate 40, whereupon it cured into a solid coating in adherence with the substrate. Cylindrical substrate 40 was made from aluminum tubing having an inner diameter 9.5 inches, a wall thickness of ⅛ inch, and a length of 16 inches.
In
Referring to
Machine 10 in accordance with the present invention may generally operate in two primary modes:
1) a “conveyance mode,” wherein the movable surface 16 moves, e.g., rotates, to convey web 12 in a forward direction; and
2) a “severance mode,” wherein the severing mechanism severs web 12 into selected lengths.
Severing device 20 may move into pinching relationship with movable surface 16 (to effect severance of web 12) in a direction that is substantially perpendicular to surface 16. Further, severing device 20 may move in a substantially linear path of travel as shown. These features are particularly advantageous when web 12 comprises a gas-containing, cellular cushioning material, such as Bubble Wrap® cushioning material because a minimum number of gas-cells or bubbles are contacted by the severing device, thereby minimizing the number of gas-cells that are deflated by melting or cutting. In contrast, a severing device that moves into severing relationship in a pivotal or rotatable fashion would approach the web at a more acute angle, thereby adversely affecting all gas-cells in the path of approach and causing the deflation of more cells that would otherwise be necessary to effect severance of the web.
After the severing operation is complete and severed cushion 36 is separated from the rest of web 12, the severing device 20 returns to its starting position as shown in
Referring now to
Guide member 60 may advantageously provide a measure of safety, by reducing the likelihood that an operator's hand will come in contact with the severing mechanism 18. In addition, particularly when severing device 20 employs a heated element to effect severance, the guide member facilitates the return of the severing device 20 to its starting position above the web, in the event that a portion of the web melt-bonds or otherwise adheres to the severing device.
Inclusion of guide member 60 may also be advantageous when the combination of the gravitational force exerted by the web 12 on movable surface 16 and the frictional force between the web 12 and movable surface 16 is insufficient to allow the movable surface to convey the web. In this instance, guide member 60 may be positioned relative to movable surface 16 such that it is in sliding contact with web 12 to facilitate the creation of additional traction between the web and the movable surface. More specifically, with reference to
In some embodiments of the invention, the weight of the guide member resting on upper surface 68a of web 12 keeps the web in contact with movable surface 16. This, in conjunction with the frictional force between the movable surface 16 and web 12, insures that the web moves forward at the speed of the movable surface as it moves, e.g., rotates. In other embodiments, guide member 60 may exert additional force, i.e., a force that is greater than just the weight of the guide member, against the upper surface 68a of the web 12. This may be accomplished in any suitable manner, e.g., by adding extra weight to the guide member, via spring tension or compression, by pulling or pushing on the guide member with actuators (e.g., pistons) that are powered pneumatically, hydraulically, electromagnetically, etc.
As with the embodiments of the invention discussed above that do not employ a guide member, the use of a guide member still provides web conveyance without the need for a separate drive mechanism, such as a drive belt or nip roller in driving contact with upper web surface 68a. Thus, guide member 60 is preferably a relatively simple device with no moving web-drive components. The material and size of the guide member is desirably chosen to provide enough contact force for consistent drive, without adding undue friction between the guide member and the web. Preferred materials are those having a relatively low coefficient of friction, such as metals or crystalline plastics. For example, when using a cylindrical movable surface as described above, guide member 60 may comprise acrylic plastic having a thickness of ⅛ inch and a length such that it covers approximately 100° of the circumference of the cylinder. A curved or upwardly-angled section 70 near leading edge 66 may be provided to prevent the web from getting caught on the leading edge as the web enters path 62. This may be particularly advantageous when web 12 comprises bubble-containing cushioning material as shown.
Also when web 12 comprises bubble-containing cushioning material, slotted mounting tabs 64a, b may have elongated slots 72 that allow for vertical movement of the guide member. This allows for variations in the height of web 12, so that the guide member may continue to ‘float’ on top of the web as different heights are encountered.
Referring now to
Referring now to
Referring specifically to
Drive/driven wheels 48/50 may be manufactured of metal, e.g., aluminum, or other suitable material. If desired, e.g., to provide improved traction against the inner surface of movable surface 16 (e.g., to cylindrical substrate 40) and/or to reduce the operating noise of machine 10″, a resilient material may be included around the circumference of each wheel. For example, a rubber O-ring 96 may be included around the circumference of each wheel as shown (o-ring 96 omitted from
Idle rollers 52 may be provided as a pair 52a, b, which may be rotatably mounted to idle shaft 98. Idle shaft 98 is attached to end plates 78a, b as shown. Rollers 52a, b may each comprise a metallic material, which is rubber-coated for quiet operation when rolling inside the cylinder/movable surface 16.
In some embodiments of the invention, drive mechanism 46 produces both of the following actions:
a) the movement of movable surface 16 to convey web 12, and
b) the movement of severing device 20 against movable surface 16 to sever web 12 (i.e., when the web is positioned between the severing device 20 and movable surface 16).
In those embodiments, therefore, only a single drive source, e.g., motor 84, is needed to perform both actions. This may be accomplished in accordance with the present invention when the drive source for drive mechanism 46 is a reversible drive source, which is capable of producing a driving force in a first direction and in an opposing second direction. For example, motor 84 may be a reversible motor, e.g., a reversible DC motor, which may produce a driving force at drive shaft 86 in two opposing directions, e.g., clockwise and counterclockwise, by reversing the polarity of the current supplied to the motor. The above-described DC-powered gear motor, for instance, may be driven in a forward or a reverse direction.
Drive mechanism 46 may also include a drive transmission that interconnects movable surface 16 and severing mechanism 18 to the reversible drive source, e.g., motor 84, such that
a) motor 84 or other drive source causes movable surface 16 to move when the motor produces a driving force in the first direction, and
b) motor 84 causes severing device 20 to urge web 12 against movable surface 16 when the motor produces a driving force in the opposing, second direction.
As will be described in more detail immediately below, the reversible drive source, e.g., motor 84, may be movably, e.g., pivotally, supported by the drive transmission for movable adjustment of drive mechanism 46 between
a) the “conveyance mode,” which may occur when motor 84 produces a driving force in the first direction, and
b) the “severance mode,” when motor 84 produces a driving force in the second direction.
On the opposite end of drive mechanism 46, driven wheel 50 rides on a bearing 110, through which the driven wheel shaft 94 passes and mounts securely to the driven wheel bracket 92. The driven wheel 50 can rotate freely about shaft 94. Shaft 94 passes through a clearance 112 in cam plate 100a and into a bearing 114 in end plate 78a. Bearing 114 may be a plain bearing that allows shaft 94 to rotate in either direction. Thus, driven wheel shaft 94 may rotate with any rotation of bracket 92, but rotates against (relative to) end plate 78a via bearing 114. As may be appreciated, drive mechanism 46 is thus rotatably suspended by bearings 108 and 114 in end caps 78a, b.
With respect to the foregoing description of drive mechanism 46, motor 84 serves as the drive source while the other components to which motor 84 is operably and physically connected serve as a drive transmission to enable the drive mechanism to function in both the conveyance mode and in the severance mode.
In some embodiments, drive mechanism 46 may alternate between the conveyance mode and the severance mode.
Once the desired amount of web 12 has been dispensed, drive mechanism 46 may be movably adjusted to assume the severance mode. This may be accomplished by reversing the polarity of the voltage to motor 84 with an appropriate switching device (not shown), e.g., a circuit board or PLC w/switching relays, via power-supply wires 117. This reversal of the voltage polarity causes motor 84 to produce a driving force in a second direction, which is different from, e.g., opposite to, first direction 54. For example, while first direction 54 is counter-clockwise, the second, opposing direction may be clockwise. In this example, motor 84 thus attempts to rotate drive wheel 48 in the second, clockwise direction (i.e., opposite to that of direction 54), but the one-way clutch bearing 108 prevents the drive wheel from turning in that direction. The resultant counter-rotational force on drive mechanism 46 causes the drive transmission to rotate in a counter-clockwise direction 118 as shown in
When severance is complete, the motor polarity may once again be reversed. When this occurs, the drive transmission rotates in clockwise direction 116 until link arm 90 makes contact with and stops against base plate 76, whereby drive mechanism 46 once again assumes the conveyance mode shown in
Referring back to
While drive mechanism 46 has been described above in connection with a specific embodiment in accordance with the claimed invention, many other configurations are possible. In order to minimize the space occupied by the machine, in any such alternative configuration, movable surface 16 will desirably comprise a continuous surface that moves about a defined path, with the drive mechanism positioned interiorly of said path. In a particularly space-saving configuration, the movable surface is in the form of a rotatable cylinder as illustrated in the drawings, and the drive mechanism is positioned inside of the cylinder such that the cylinder rotates about the drive mechanism as also shown in the drawings. Moreover, although advantageous from the standpoint of cost and simplicity, it is not a requirement of the present invention that only one motor be employed to operate by the movable surface and severing mechanism. Instead, these devices may be operated by separate power sources, e.g., one motor dedicated to operation of the movable surface and another motor dedicated to operation of the severing mechanism.
Severing device 20 may comprise any conventional device for severing a web of material, including a heating element such as one or more wires, knives, bands, or other electrically-heatable material; a cutting element such as a guillotine-type knife, a rolling, swinging or translating blade, a serrated blade; etc. In the presently-illustrated embodiment, severing device 20 comprises a heating element 139 capable of reaching a temperature sufficient to sever web 12 (
Advantageously, movable surface 16 is employed not only as a conveyance surface but also as a surface against which severance device 20 urges web 12 during the severance operation. This greatly simplifies and reduces the number of required components of the web-severing machine, thereby minimizing cost and improving reliability. A potential downside of using movable surface 16 in such a dual-function role is that repeated impact by a severance device, either a heating or cutting type, can rapidly degrade a surface that is soft and flexible enough to also convey a web. However, because movable surface 16 starts, stops, and is cut upon at random intervals, based on operator and/or automated control of machine 10 (or 10′, 10″, etc.), the impingements by severing device 20 are made at random locations on the surface, e.g., circumference, of movable surface 16. As a result, cuts are rarely made at the same location on surface 16, and it has therefore been found to possess a relatively high degree of longevity.
Referring now to
As illustrated in
Severing device 20′ may also include a support member 152 to provide physical support for heating element 146. This may be advantageous when heating element 146 is in the form of a wire or band as shown. As also shown, electrical nodes 150a, b may space the contact portion 148 of heating element 146 from support member 152. Alternatively or in addition, electrical nodes 150a, b may resiliently bias the contact portion 148 of heating element 146 away from support member 152.
In some embodiments, heating element 146 may be attached to support member 152 by a pair of tension-control units 154a, b. Such units, e.g., a pair of coil springs as shown, may be selected to maintain tension in heating element 146 over a predetermined temperature range at which the heating element is operated. For example, the material of construction, length, spring force, etc. of the coil springs may be selected based on the expansion and contraction of the heating element throughout the temperature range at which the heating element will be operated such that tension is maintained in the heating element over the entirety of such range, i.e., when the heating element is at full thermal contraction and also when it is at full thermal expansion.
As also shown, electrical nodes 150a, b may be positioned between tension-control units 154a, b. Thus, tension-control units 154a, b may be positioned at opposing ends of heating element 146 while electrical nodes 150a, b are positioned therebetween. In this manner, electrical current flows substantially only through contact portion 148, which lies between each of the electrical nodes 150a, b.
Referring now to
In some embodiments, electricity to power heating element 146 is supplied through the conductive pins 156. In
Electrical isolation of conductive pins 156 from connector arms 158a, b may be achieved by positioning a pair of non-conductive (e.g., plastic) shoulder washers 164 in an orifice 163 in each of the connector arms, and inserting pins 156 through the shoulder washers 164 as shown in
Accordingly, heating element 146 may be energized, for example, by causing electrical current to pass from wire 162a and into contact tab 166 via connector 168a, whereupon the current flows through conductive pin 156 at orifice 160a, and into heating element 146 via electrical node 150a (described in further detail below). The current may exit heating element 146 at electrical node 150b, whereupon it flows through the pin 156 of connector arm 158b at orifice 160b, and into wire 162b via contact tab 166 and connector 168b.
Referring collectively to
The firmness of pad 170 and amount of pad compression may be selected to provide a desired amount of force with which the heating element is urged against the web and movable surface. Maximum pad compression may be set by including a step 174 at each end of support member 152 (
As noted above, severing device may include tension-control units 154a, b, attached to the opposing ends 175a, b of heating element 146. As shown perhaps most clearly in
Within slots 176a, b, tension-control units 154a, b may be attached to support member 152 via pins 178a, b. When heating element 146 is in the form of a wire, the tension-control units may be attached to the ends 175a, b of the heating element by twisting the element upon itself at each end to form a loop, which engages with a hook, loop, or other attachment device on each of the units 154a, b as shown.
Each end 180a, b of support member 152 may include a groove 178, which retains the portions of heating element 146 that extend around the ends 180a, b of the support member (
As noted above, electrical nodes 150a, b may be configured to space the contact portion 148 of heating element 146 from support member 152. Alternatively or in addition, electrical nodes 150a, b may resiliently bias the contact portion 148 of heating element 146 away from support member 152. In some embodiments, electrical nodes 150a, b may take the form of ‘j-shaped’ leaf springs as shown in
The portion of the spring-type electrical nodes 150a, b in contact with heating element 146 may be biased outwards, i.e., away from support member 152, thereby holding the heating element at a predetermined distance away from the support member, e.g., away from resilient backing pad 170 as shown. In some embodiments, such spacing between the heating element and support member may be advantageous. For example, when web 12 is comprises a thermoplastic material, the heating element 146 may become coated with polymeric material from repeated contact with the web during severance, wherein molten polymer from the web solidifies on the heating element. Such polymeric residue may be conveniently removed from time to time by causing the heating element to effect a ‘burn-off’ cycle, in which the heating element is heated while severing device 20′ is in the conveyance mode, i.e., wherein the heating element is not in contact with a web or with movable surface 16. This causes the polymeric residue to vaporize off of the heating element. If the heating element is in contact with support member 152 during this process, much of the heat will be transferred to the support member, e.g., to pad 170, requiring excess heat to effectively remove the polymeric residue.
Another advantage of spacing the heating element from the support member is that the heating element can be heated more quickly than if it is in contact with the support member. This is because the support member acts as a heat sink when the heating element, particularly the contact portion thereof, is in direct contact with the support member. When the contact portion 148 is spaced from the support member as shown, very rapid heating of the contact portion is possible. For example, when the heating element comprises a nickel/chromium wire having a diameter of approximately 0.015 inch, the wire can be fully heated by the time it makes contact with the web by applying a 24 volt current across the wire just as the severing mechanism 18′ begins to move the severing device 20′ towards the web. The current can then be stopped just before the severing device 20′ is retracted such that the total current-flow time is 1−1.5 seconds/cycle. As can be appreciated, this relatively short period in which current flows is advantageous from the standpoint of both reduced energy usage/cost, and also reduced thermal fatigue on the heating element, thereby providing increased service life.
As can be seen in
Advantageously, with this embodiment, the portions of the heating element 146 between electrical node 150a and tension-control unit 154a, and between electrical node 150b and tension-control unit 154b, including the tension-control units themselves, remain relatively cool, i.e., are not heated because substantially no electrical current flows through those portions. Thus, no precautions are necessary to keep these portions, nor the tension-control units 154a, b or any other components in contact therewith, from overheating. In general, it is desirable to minimize the amount of time that the heating element is maintained at a high temperature, e.g., a temperature high enough to sever the web, because heat is the primary cause of failure of the heating element (due to heat stress or heat fatigue). Stated somewhat differently, heating elements generally have a maximum amount of time at which they can be maintained at a given temperature before failure, with greater temperatures generally allowing less time before failure. Since the contact portion 148 can be heated quickly as noted above, and transfers its heat to the web 12 and/or movable surface 16, it stays at an elevated temperature for a relatively short duration. If the other portions of the heating element that do not contact with web were heated, such portions would either remain hot, and therefore fail prematurely, or transfer excessive heat to support member 152, which could damage or otherwise shorten the service life of the support member. Thus, inexpensive materials, e.g., plastics that do not have a high heat tolerance, may be used for support member 152.
In some embodiments, outward biasing of heating element 146 by electrical nodes 150a, b may be advantageous by reducing physical stress on the heating element as it makes contact with the web, i.e., by allowing the heating element to resiliently move towards the support member 152 as contact is made with the web. In other embodiments, the inclusion of pad 170 continues the resilient movement of the heating element into support member 152 until full contact is made, e.g., when the pad is compressed to the level of steps 174. As contact is made with the web, the leaf spring-type nodes 150a, b may flex inward into longitudinal slot 172 in the support member so that the final urging of the heating element against the web can be performed by the resilient pad. Advantageously, tension-control devices 154a, b take in the resultant slack in the heating element to maintain tension therein.
Referring now to
Another alternative embodiment to conductive pin 156 is shown in
Other embodiments may include a latching mechanism to secure the support member 152 to the connector arm. One such latching mechanism is shown in
One of the advantages of severing device 20′ is that when replacement is necessary, it can be accomplished quickly and easily. An operator can keep a supply of the severing devices on hand, and machine downtime due to heating element failure is minimal. At a convenient time, the support members can be rebuilt with new heating elements, but the machine remains running.
A further alternative embodiment for the severing mechanism may be used when the web is a bubble-type cushioning material, wherein the severing mechanism seals the bubbles that are severed, thereby making partial bubbles at the edges of the resultant cushion. The advantage of this embodiment is that the entire cushion contains air-filled bubbles, rather than a row of deflated/severed bubbles at the severed edges of each cushion. In order to seal at least some of the gas inside the bubbles that are being severed, the web may be completely compressed against the movable surface by the severing device prior to energizing the heating element to effect severance. In order to seal the gas within the severed bubbles, both plies (upper and lower) of the bubble material must be in intimate contact before heating, or the heating element will burn through the upper ply and the gas will escape. To accomplish this, the severing device may compress an inflated bubble row, rather than burning through and deflating such bubbles during advancement of the severing device, as may occur when the heating element is at a temperature sufficient to sever the web when initial contact with the bubbles is made. Once the bubbles are sufficiently compressed to bring both plies of film together, the heating element may be energized to effect severance and sealing, thereby retaining the inflation gas in the resultant partial bubbles in either side of the sever/seal line created by the heating element.
Having now described various aspects of severing machines in accordance with the present invention, e.g., machines 10, 10′, 10″, and 10′″, the operation of such machines will now be described. The machines may be operated in a variety of ways. For instance, an electronic controller (not shown), e.g., in association with control panel 34 (
Alternatively, the machines may be controlled by the controller but with operator intervention, e.g., manually via a foot pedal, hand switch, or other manually-actuatable device. An operator may thus be able to select the length and number of cushions desired via control panel input to the controller, or may choose to depress a foot pedal or other means to manually select cushion lengths.
The following examples describe three different operating sequences for machine 10″, which conveys and severs a web of Bubble Wrap® cushioning material: single mode, batch mode and manual mode.
In this mode of operation, machine 10″ makes one cut sheet of cushion having a length of 12 inches, which an operator selects via an electronic controller. Machine 10″ then performs three basic sub-operations:
When another sheet is selected, these 500 pulses will be subtracted from the total target length, so that the length will be correct. In some embodiments, the entire cut-off and return cycle takes less than 1 second to complete, with the movable surface conveying about 2 feet of web per second.
In this mode, machine 10″ makes a pre-determined quantity of sheets of a pre-determined length, which an operator selects via an electronic controller. Machine 10″ then performs three basic sub-operations:
In manual mode, the operator steps on a foot switch, or presses a button, which conveys the web until the foot switch or button is released. Severance is then performed as in the single mode of operation as described above. In manual mode, the operator can make sheets of varying length as desired.
The foregoing description of preferred embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention.