TECHNICAL FIELD

[0001] The present invention relates to a system and method of producing a coil for a mattress. In particular, the present invention relates to pre-heating a metal wire prior to forming the metal wire into a coil for use in an innerspring of a mattress.

BACKGROUND

[0002] Innerspring assemblies for mattresses, furniture, seating and the like, are typically assembled by arranging coils or springs in a matrix and interconnecting them with lacing coils. The coils are produced from steel wire stock which is fed through a die and bent or coiled at designed radiuses by cam-controlled forming guides. When forcing the relatively cool wire through the die, temperatures differences are created within the wire due to the thermoelastic effects of the plastic deformation of the wire as well as friction between the wire and the die. In particular, a temperature differential is created between those portions of the wire which are stretched and those portions of the wire that are compressed through the formation process. These temperature differences result in anisotropic residual stress throughout the wire which can lead to undesirable characteristics in the coils and ultimately result in an inferior mattress.

[0003] Typically, some of the residual stress is removed by heating the coil after formation through either resistive heating of the coil, or annealing the coil in an oven. Resistive heating does not relieve all of the residual stress and can, in some instances, result in case hardening. Furthermore, and in particular for the case of oven annealing, the extra step is costly in terms of both labor and fuel. Another known method of relieving the residual stress which does not involve post-formation heating of the coil is repeated load cycling of the spring, but this results in degradation of long-term performance of the coil within the finished mattress.

SUMMARY

[0004] The present invention is a system and method of producing a coil. In particular, the present invention is a system and method of producing a coil for a mattress and that has minimal residual stress.

[0005] In one exemplary embodiment of the present invention, a wire coil manufacturing system comprises a source of a metal wire; a heater configured to receive the metal wire and heat the metal wire as it passes through the heater; and a coil formation device positioned down-line of the heater and configured to bend the metal wire into a coil while the metal wire is still hot.

[0006] In one exemplary implementation of a method of producing a coil, a spool of wire is provided which includes a substantially continuous length of metal wire. The substantially continuous metal wire is then advanced through the heater such that a portion of the metal wire exiting the heater is at or above a target temperature. In particular, a portion of the metal wire entering the heater is at, or around, an initial temperature, such as room temperature, and as the portion of the metal wire passes through the heater, the portion of the metal wire is progressively heated so that when the portion of the metal wire exits the heater, the portion of the metal wire is at the target temperature that is greater than the initial temperature. In some implementations of the methods of the present invention, It is contemplated that the metal wire is continuously advanced through the heater, and so it should be understood that at any given moment the metal wire has a temperature gradient along the length of the metal wire extending through the heater, where the temperature of the metal wire progressively increases from the initial temperature at a portion of the metal wire at the entrance of the heater to the target temperature at a portion of the metal wire at the exit of the heater.

[0007] An exemplary heater of the present invention is an induction heater that includes a plurality of induction coils that the metal wire passes through and a power source that is electrically connected to the plurality of induction coils. An induction heater generates heat inside the metal wire itself, which advantageously allows the metal wire to be rapidly heated without requiring any direct contact between the plurality of induction coils and the metal wire. Furthermore, the rate at which the metal wire is heated by the induction heater can be adjusted through means well known in the art of induction heaters, such as, for example, controlling the power provided by the power supply to the plurality of induction coils. Of course, other types of heaters are also contemplated and can be used with the system and method of the present invention without departing from the spirit and scope of the present invention.

[0008] Regardless of the particular configuration of the heater, as mentioned above, the portion of the metal wire exiting the heater is at the target temperature. Depending on multiple design factors, including but not limited to, the composition of the metal wire, the design of the resulting coil, and the intended use of the resulting coil, the target temperature can be set to a variety of different temperatures. For example, in some implementations of the method of the present invention, the target temperature is below a recrystallization temperature of the metal wire such that the subsequent formation of the coil from the metal wire is performed under conditions typical of warm forging. For a steel metal wire, the recrystallization temperature is typically between about 400° C and about 1000° C. As such, in implementations where the coil is formed from steel metal wire through warm forging, the target temperature is in a range from above room temperature to below the recrystallization temperature, or about 1,000° C. However, in some implementations, a narrower range is contemplated for the target temperature from about 530° C to about 720° C. In some particular implementations, the target temperature is about 600° C. Regardless of the particular temperature, warm forging advantageously increases the ductility of the metal wire which makes it much easier to form the metal wire into the coil. Furthermore, pre-heating the metal wire prior to forming the coil reduces or eliminates the creation of residual stress in the coil. This in turn eliminates the need for post-formation treatment of the coil to reduce the residual stress in the coil prior to installation and use in a mattress.

[0009] In other implementations of the method of the present invention, the target temperature is at or above the recrystallization temperature of the metal wire such that the subsequent formation of the coil from the metal wire is performed under conditions typical of hot forging. In a hot forging process, the plastic deformation of the metal wire is at a temperature where recrystallization occurs simultaneously with deformation, thus avoiding strain hardening. As compared to warm forging, hot forging increases the formability of the metal wire even further which also lowers the forming forces.

[0010] After the metal wire passes through the heater, the metal wire is then advanced from the heater and into the coil formation device where the metal wire is bent to form a coil while the metal wire is still at or above the target temperature. With regard to the coil formation device, an exemplary coil formation device can be, for example, one of several known wire formation machines or coilers, such as a Spuhl LFK coiler manufactured by Spuhl AG of St. Gallen, Switzerland. The exemplary coil formation device feeds the metal wire through a series of rollers and wire-formers, including a forming block or die, which bend the wire into the designed coil formation. Once a sufficient amount of wire has been fed through to form a complete coil, a cutting tool is advanced against an opposing cutting blade mounted on the forming die to sever the coil from the remainder of the metal wire.

[0011] In some implementations of the present invention, the metal wire is continuously fed into the coil formation device with the cutting tool severing each coil from the remainder of the metal wire without interrupting the feed of metal wire. In such implementations, the metal wire is also continuously advanced through the heater at a rate that is adjustable and which can range from about 1 ft/min to about 500 ft/min. In order to ensure that the portion of the metal wire leaving the heater is at or above the target temperature, it is necessary, at least in some embodiments, to adjust the rate at which the heater heats the metal wire. In the case of an induction heater, this can be accomplished by adjusting the current passing through the induction coils or by adjusting the amount of power supplied by the power source to the induction heater. It is contemplated that in some embodiments, the current passing through the induction coils is directly related to the rate at which the metal wire is advanced through the induction heater so that the portion of the metal wire leaving the induction heater is always at the target temperature.

[0012] In some implementations of the method of the present invention, after the coil is formed but while the coil is still hot, the coil is quenched. In particular, a water curtain or a water bath are positioned down-line of the coil formation device so that the coil can be quenched by either advancing the coil through the water curtain, or by submerging the coil in the water bath. A water curtain can be used when the coil is long enough that it is desirable to quench a forward portion of the coil while a rear portion of the coil is still being formed by the coil formation device. By comparison, shorter coils can be completely formed before appreciably cooling and the completed coil can then be submerged in a water bath in order to simultaneously quench the entire coil. [0013] Further features and advantages of the present invention will become evident to those of ordinary skill in the art after a study of the description, figures, and non -limiting examples in this document.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 is a schematic representation of an exemplary wire coil manufacturing system of the present invention; and

[0015] FIG. 2 is a flowchart showing an exemplary implementation of a method of producing a coil.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0016] The present invention is a system and method of producing a coil. In particular, the present invention is a system and method of producing a coil for a mattress and that has minimal residual stress.

[0017] Referring first to FIG. 1, a wire coil manufacturing system 100 of the present invention comprises a source 120 of a metal wire 110; a heater 130 configured to receive the metal wire 110 and heat the metal wire 110 as it passes through the heater 130; and a coil formation device 140 positioned down-line of the heater 130 and configured to bend the metal wire 110 into a coil 112 while the metal wire 110 is still hot.

[0018] Referring now to FIGS. 1 and 2, in one exemplary implementation of a method of producing a coil, a substantially continuous length of wire is first provided, as indicated by step 200. In the exemplary wire coil manufacturing system 100 shown in FIG. 1, the source 120 of the metal wire 110 is a spool of wire 120 which includes a substantially continuous length of metal wire 110. As used herein, "substantially continuous " refers to any 1 ength of wire which allows the metal wire 110 to pass through the wire coil manufacturing system 100 continuously so that multiple coils can be produced by the methods of manufacturing of the present invention without having to provide a new source 120 of metal wire 110 for each coil produced. As such, although a spool of wire 120 is shown in FIG. 1, it is of course contemplated that other sources of wire may also be provided without departing from the spirit and scope of the present invention. Furthermore, a piece of metal wire that is not substantially continuous may also be used in some implementations of the method of the present invention wherein each of the steps of the present invention can be performed on each discrete piece of metal wire.

[0019] Referring still to FIGS. 1 and 2, upon providing the substantially continuous length of metal wire 110, the metal wire 110 is then advanced through the heater 130 such that a portion of the metal wire 110 exiting the heater is at or above a target temperature T ₂ , as indicated by step 210. In particular, it is contemplated that the spool of wire 120 is provided at an initial temperature To such as, for example, the ambient temperature of the facility at which the wire coil manufacturing system 100 is located. A portion of the metal wire 110 entering the heater 130 is therefore at, or around, the initial temperature To. As the portion of the metal wire 110 passes through the heater 130, the portion of the metal wire 110 is progressively heated so that when the portion of the metal wire 110 exits the heater 130, the portion of the metal wire 110 is at the target temperature T ₂ that is greater than the initial temperature T ₀ . In some

implementations of the methods of the present invention, it is contemplated that the metal wire 110 is continuously advanced through the heater 130, as further discussed below, and so it should be understood that at any given moment the metal wire 110 has a temperature gradient along the length of the metal wire 110 extending through the heater 130, where the temperature of the metal wire 110 progressively increases from the initial temperature T ₀ at a portion of the metal wire 110 at the entrance of the heater 130 to the target temperature T ₂ at a portion of the metal wire 110 at the exit of the heater 130.

[0020] With regard to the heater 130 in the exemplary embodiment of the wire coil manufacturing system 100 shown in FIG. 1, the heater 130 is an induction heater 130 that includes a plurality of induction coils 134 that the metal wire 110 passes through and a power source 132 that is electrically connected to the plurality of induction coils 134. An induction heater, such as the one shown in FIG. 1, heats an electrically conductive object, such as the metal wire 110, through electromagnetic induction. More specifically, the power source 132 provides an alternating current through the plurality of induction coils 134 which act as an electromagnet (i.e., a solenoid). The alternating current through the induction coils 134 produces a rapidly alternating magnetic field which penetrates the metal wire 110 passing through the plurality of induction coils 134. The alternating current creates eddie currents within the metal wire 110 which subsequently heat the metal wire 110. Heat is thereby generated inside the metal wire 110 itself, which advantageously allows the metal wire 110 to be rapidly heated without requiring any direct contact between the plurality of induction coils 134 and the metal wire 110.

Furthermore, the rate at which the metal wire 110 is heated by the induction heater 130 can be adjusted through means well known in the art of induction heaters, such as, for example, controlling the power provided by the power supply 132 to the plurality of induction coils 134. Although in exemplary embodiment shown in FIG. 1 the plurality of induction coils 134 have two loops, it is contemplated that any number of loops can be used with the number of loops also affecting the rate at which the metal wire 110 is heated. Of course, other types of heaters 130 are also contemplated and can be used in the methods of the present invention without departing from the spirit and scope of the present invention. [0021] Regardless of the particular configuration of the heater 130, as mentioned above, the portion of the metal wire 110 exiting the heater 130 is at the target temperature T ₂ . Depending on multiple design factors, including but not limited to, the composition of the metal wire 110, the design of the resulting coil 112, and the intended use of the resulting coil 112, the target temperature T ₂ can be set to a variety of different temperatures. For example, in some implementations of the method of the present invention, the target temperature T ₂ is below a recrystallization temperature of the metal wire 110 such that the subsequent formation of the coil 112 from the metal wire 110 is performed under conditions typical of warm forging. For a steel metal wire, the recrystallization temperature is typically between about 400° C and about 1000° C. As such, in implementations where the coil 112 is formed from steel metal wire 110 through warm forging, the target temperature T ₂ is in a range from above room temperature to below the recrystallization temperature, or about 1,000° C. However, in some implementations, a narrower range is contemplated for the target temperature T ₂ from about 425° C to about 800° C. In some particular implementations, the target temperature T ₂ is about 600° C. Regardless of the particular temperature, warm forging advantageously increases the ductility of the metal wire 110 which makes it much easier to form the metal wire 110 into the coil 112. Furthermore, pre-heating the metal wire 110 prior to forming the coil 112 reduces or eliminates the creation of residual stress in the coil 112. This in turn eliminates the need for post -formation treatment of the coil 112 to reduce the residual stress in the coil 112 prior to installation and use in a mattress.

[0022] In other implementations of the method of the present invention, the target temperature T ₂ is at or above the recrystallization temperature of the metal wire 110 such that the subsequent formation of the coil 112 from the metal wire 110 is performed under conditions typical of hot forging. In a hot forging process, the plastic deformation of the metal wire 110 is at a temperature where recrystallization occurs simultaneously with deformation, thus avoiding strain hardening. As compared to warm forging, hot forging increases the formability of the metal wire 110 even further which also lowers the forming forces.

[0023] Referring still to FIGS. 1 and 2, after the metal wire 110 passes through the heater 130, the metal wire 110 is advanced from the heater 130 and into the coil formation device 140 where the metal wire 110 is bent to form a coil 112 while the metal wire 110 is still at or above the target temperature T ₂ , as indicated by step 220. In particular, the metal wire 110 is bent at or above the target temperature T ₂ so that the resulting coil 112 has minimal residual stress. To this end, in some implementations of the present invention, instead of exiting the heater 130 at the target temperature T ₂ exactly, the portion of the metal wire 110 exiting the heater 130 is at an exit temperature T ₁ which is above the target temperature T ₂ . The higher exit temperature T ₁ accounts for and accommodates at least some cooling of the metal wire 110 as it travels from the heater 130 to the coil formation device 140 so that when that portion of the metal wire 110 reaches the coil formation device 140, it is still at or above the target temperature T ₂ .

[0024] With regard to the coil formation device 140, which is shown schematically in FIG. 1, an exemplary coil formation device 140 can be, for example, one of several known wire formation machines or coilers, such as a Spuhl LFK coiler manufactured by Spuhl AG of St. Gallen, Switzerland. The exemplary coil formation device 140 shown in FIG. 1 feeds the metal wire 110 through a series of rollers and wire-formers to bend the wire into the designed coil formation. The radius of curvature in the helical segments of the coil is determined by the shapes of cams (not shown) in rolling contact with a cam follower arm 148. The metal wire 110 is fed to the coiler by feed rollers 142 into a forming block or die 144. As the wire is advanced through a guide hole or exit point 1441 in the forming die 144, it contacts a coil radius forming wheel 146, attached to an end of the cam follower arm 148. The forming wheel 146 is moved relative to the forming die 144, toward and away from the line of feed of the metal wire 110, by travel distances defined by rotating cams which the follower arm 148 follows. In this manner, the radius of curvature of the helix of the coil 112 is formed as the wire emerges from the forming die 144 against the forming wheel 146.

[0025] A helix is formed in the wire stock after it passes the forming wheel 146 by a helix guide pin 150 which moves in a generally linear path, generally perpendicular to the wire stock guide hole 1441 in the forming die 144, in order to advance the wire in a helical path away from the forming wheel 146. Once a sufficient amount of wire has been fed through the forming die 144, past the forming wheel 146 and the helix guide pin 150, to form a complete coil 112, a cutting tool 152 is advanced against an opposing cutting blade 154 mounted on the forming die 144 to sever the coil 112 from the remainder of the metal wire 110. This is, of course, just one exemplary coil formation device 140, which can be used in the system and methods of the present invention, and it is contemplated that other coil formation devices can be used without departing from the spirit and scope of the present invention. Regardless of the particular form of the coil formation device 140, according to the methods of the present invention, the metal wire 110 is still hot when it is bent to form the resulting coil 112. As discussed above, the elevated temperature increases the ductility of the metal wire 110 which not only makes it easier to form the coil 112 but also prevents the formation of residual stress in the resulting coil 112.

[0026] With further respect to the coil formation device 140 shown in FIG. 1, in some implementations of the present invention, the metal wire 110 is continuously fed into the coil formation device 140, through the forming die 144, forming wheel 146, and helix guide pin 150 with the cutting tool 152 severing each coil 112 from the remainder of the metal wire 110 without interrupting the feed of metal wire 110. In such implementations, the metal wire 110 is also continuously advanced through the heater 130 at a rate that is adjustable and which can range from about 1 ft/min to about 500 ft/min. In order to ensure that the portion of the metal wire 110 leaving the heater 130 is at or above the target temperature T ₂ , it is necessary, at least in some embodiments, to adjust the rate at which the heater 130 heats the metal wire 110. In the case of an induction heater 130, this can be accomplished by adjusting the current passing through the induction coils 134 or by adjusting the amount of power supplied by the power source 132 to the induction coils 134. It is contemplated that in some embodiments, the current passing through the induction coils 134 is directly related to the rate at which the metal wire 110 is advanced through the induction heater 130 so that the portion of the metal wire 110 leaving the induction heater 130 is always at the target temperature T ₂ . Of course, for other types of heaters, the rate at which the metal wire is heated can also be similarly controlled.

[0027] Referring still to FIGS. 1 and 2, in some implementations of the method of the present invention, after the coil 112 is formed but while the coil 112 is still hot, the coil 112 is quenched, as indicated by step 230. As shown in FIG. 1, a water curtain 160 or a water bath 162 is positioned down -line of the coil formation device 140 so that the coil 112 can be quenched by either advancing the coil 112 through the water curtain 160 or by submerging the coil 112 in the water bath 162. A water curtain 160 can be used when the coil 112 is long enough that it is desirable to quench a forward portion of the coil 112 while a rear portion of the coil 112 is still being formed by the coil formation device 140. For example, lacing coils that are used within innersprings of mattresses are typically several feet in length and therefore it can be

advantageous to quench a forward portion of the lacing coil shortly after it is formed in order to prevent the forward portion of the lacing coil from cooling in the air before the entire lacing coil is finished being formed. By comparison, shorter coils, such as the compression coils used within innersprings of mattresses, can be completely formed before appreciably cooling and the completed coil 112 can then be submerged in a water bath 162 in order to simultaneously quench the entire coil 112. Of course, a combination water curtain 160 and water bath 162 can also be used without departing from the spirit and scope of the present invention. Similarly, it is contemplated that other mediums, such as oil, air, or some other gas can be used to quench the coil 112 by means known in the art.

[0028] Regardless of how the coil 112 is quenched, by quenching the coil 112 it is contemplated that the resulting coil 112 is stronger and less prone to plastic deformations.

Furthermore, quenching the coil 112 inhibits grain growth and locks dislocations in place which provide for increased strength in the final coil 112. Of course, depending on the design and intended use of the resulting coil 112, quenching may not be desired in which case this step may not be performed at all and the coil 112 is instead allowed to gradually cool.

[0029] One of ordinary skill in the art will recognize that additional embodiments are also possible without departing from the teachings of the present invention or the scope of the claims which follow. This detailed description, and particularly the specific details of the exemplary embodiments disclosed herein, is given primarily for clarity of understanding, and no unnecessary limitations are to be understood therefrom, for modifications will become apparent to those skilled in the art upon reading this disclosure and may be made without departing from the spirit or scope of the claimed invention.