EP2719307A1

EP2719307A1 - Spring, spring core unit and method of producing a spring core unit

Info

Publication number: EP2719307A1
Application number: EP13000880.8A
Authority: EP
Inventors: Peter Vogel; Markus Beerli
Original assignee: Spuehl AG
Current assignee: Spuehl AG
Priority date: 2012-10-11
Filing date: 2013-02-21
Publication date: 2014-04-16
Anticipated expiration: 2033-02-21
Also published as: WO2014057085A3; PL2719307T3; AU2013328591A1; DK2719307T3; EP2719307B1; CN104869870B; AU2013328591A8; CN104869870A; WO2014057085A2

Abstract

A spring (2) for a spring core unit (1), the spring (2) having a spiral body and an end ring (3) with a substantially straight leg (4). The leg (4) is provided with at least one V-shaped bending (5) or at least one U-shaped bending.

Description

Embodiments of the invention relate to a spring, especially a so-called "open end" spring, and a spring core unit comprising a plurality of such springs. Embodiments of the invention also relate to a method of producing a spring core unit.
Conventional spring core units comprise a plurality of open end springs arranged in rows and columns with a group of springs in one row or one column being connected by a helical lacing wire. In particular, the helical lacing wire connects respective end rings of two adjacent springs.
In conventional spring core units, the end ring of each open end spring has a free leg with a relatively long bent tail. This bent tail may cause problems with roll packing of such spring core units.
A roll packing system bales bulky spring core or inner spring units into easy to ship and easy to open compressed paper rolls. When opening the bale, the bent tails of the open ends springs can hook themselves into an opposite lacing wire or into end rings of other springs. If this happens, the spring core cannot assume its original shape any more so that such spring cores become unusable.
It is therefore an object of the invention to provide an improved spring for use in a spring core unit which avoids the above problems and in addition allows saving wire during the manufacturing of the spring. Furthermore, it is an object of the present invention to provide a corresponding spring core unit, in particular a spring core unit which may be used for bedding or seating components.
According to embodiments of the invention, this object is achieved by a spring as defined in independent claim 1. The dependent claims define preferred and advantageous embodiments of the invention.
According to the invention, the spring has a free leg which is relatively straight and is provided with at least one V-shaped stamping or bending or with at least one U-shaped stamping or bending. When the spring is used in a spring core unit in which two end rings of the springs are connected by a helical lacing wire, this V-shaped bending prevents a lateral shifting of the two connected end rings within the helical lacing wire. The V-shaped bending or U-shaped bending may be oriented in any direction, so that it may be bent inwards, outwards, upwards or downwards, etc.
The spring may have two end rings, each of which has a free leg which is relatively straight and is provided with at least one V-shaped stamping or bending or with at least one U-shaped stamping or bending.
Spring core units using this end ring design are suitable for roll packing as the respective end rings cannot hook themselves into opposite end rings or helical lacing wires when opening the respective bale. Furthermore, by omitting the bent tails on the free legs of the end ring, a significant amount of wire per spring can be saved.
According to a preferred embodiment of the invention, the substantially straight leg of the end ring of the spring is arranged substantially completely within the respective helical lacing wire so that the end tip of the free leg does not extend beyond the windings of the helical lacing wire.
The helical lacing wire may have a pitch. The leg around which the helical lacing wire winds may have a first portion and a second portion with the V-shaped bent portion disposed therebetween. The first and second portions may be straight. The first portion may extend from an end tip of the spring.
The first portion may have a length which is equal to or greater than the pitch of the helical lacing wire. The first portion may have a length which is at least two times the pitch of the helical lacing wire. The first portion may have a length which is at least three times the pitch of the helical lacing wire. Such a configuration allows adjacent springs to be secured reliably while also allowing springs to be reliably attached to a circumferential outer support wire.
The second portion may have a length which is equal to or greater than the pitch of the helical lacing wire. The second portion may have a length which is at least two times the pitch of the helical lacing wire. The second portion may have a length which is at least three times the pitch of the helical lacing wire. Such a configuration allows adjacent springs to be secured reliably while also allowing springs to be reliably attached to a circumferential outer support wire.
An apex of the V-shaped bending may be offset from a center of the respective spring in a direction along the longitudinal axis of the helical lacing wire.
Further embodiments of the invention also relate to a spring core unit which includes springs which are comparatively hard and to a method of producing such a spring core unit. The springs of the spring core unit may have a small height of, e.g., less than 70 mm. Such a spring core unit may be particularly suitable for use in seating furniture.
The characteristics of a spring may be adjusted by using a suitable wire gauge and/or by selecting a specific spring geometry. Conventional methods for automatically producing a spring core unit may prevent the use of springs having small heights. This applies in particular when so-called high speed transfer systems are used for transferring springs between different processing stations. In such conventional methods for producing a spring core, a spring is coiled and both end rings of the spring are subsequently modified using a bending tool. The spring is supported by a gripper of the high speed transfer system while bending tools act on the two end rings, either sequentially or simultaneously. In order to provide sufficient room for the bending tools without interfering with the gripper, there is a lower bound on the height of the spring.
It is an object of embodiments of the invention to provide a method of producing a spring core unit and a spring core unit which address these shortcomings. In particular, it is an object to provide a spring core unit in which springs having smaller heights and, thus, higher spring rate may be used.
This object is achieved by a method as defined in claim 10 and a spring core unit as described below. The dependent claims define embodiments.
In a method of producing a spring core unit, a spring is coiled. The coiled spring has a first end ring and an opposite second end ring. The spring is supplied to an assembly station which assembles the spring with at least one other spring. At least one bend is formed in only one of the first or second end ring of the spring using a bending tool before the spring is supplied to the assembly station.
In the method, a bending tool acts on only one of the end rings of the coiled spring after the spring was coiled and before the spring is assembled with other springs to form the spring core unit. The other end ring of the spring, in the state in which the spring is assembled with other springs to form the spring core unit, has a shape as formed by a coiler without any additional bends introduced therein. Because a bending tool acts on only one end ring of the spring before the spring is assembled with other springs, the springs may have smaller heights compared to conventional methods and may still be transferred using a high speed transfer system. Further, an amount of wire may be reduced.
Each spring of the spring core unit produced by the method may be coiled and may be provided to an assembly station with bends formed in only one of the two end rings of the respective spring. The spring core unit may be composed of springs which have an end ring with a geometry which corresponds to the end ring geometry formed by a coiler, without any additional bends formed therein prior to assembling the springs.
A gripper may support the spring while the at least one bend is formed. The gripper may abut on a portion of the spring which is offset from an axial center of the spring towards the other one of the first or second end ring, i.e. towards the end ring on which no bend is formed by a bending tool before the spring is assembled with other springs. When the gripper is positioned in this way, there is more room for the bending tool which forms at least one bend in one of the first or second end ring even when the spring has a small height.
The spring may have a spiral body which extends from the first end ring to the second end ring. The spiral body may consist of at most 1.25 active turns. The spiral body may consist of at least 0.75 active turns. A high spring rate can be attained using such a configuration.
The spring may have a height of less than 70 mm, in particular of at least 40 mm and less than 70 mm, when in an unloaded condition. The spring may have a height which may be less than 40 mm.
In other embodiments, the method may be used to produce springs with different end ring configurations, with the springs being produced so as to have a greater number of active turns and/or a greater height. For illustration, the spiral body between the end turns may consist of equal to or less than 3.25 active turns. The spiral body between the end turns may consist of 1.25, 2.25 or 3.25 active turns. The spiral body between the end turns may consist of 0.75, 1.75 or 2.75 active turns.
The at least one bend which is formed with the bending tool may include a V-shaped bending or a U-shaped bending in a free leg of the one of the first or second end ring. This allows the spring to prevent shift of the leg relative to a helical lacing wire.
The springs of the spring core unit may be assembled such that an end tip portion of the end ring in which at least one bend is formed extends from an interior of a helical lacing wire. The springs of the spring core unit may be assembled such that an end tip portion of the end ring in which at least one bend is formed is positioned in an interior of the helical lacing wire.
The springs of the spring core unit may be assembled such that a free end tip portion of the other one of the first or second end ring, i.e. of the end ring in which no bend is formed by a bending tool, is completely arranged within a volume defined by a helical lacing wire. This end ring may have a free leg, or tail, which extends in the interior of the helical lacing wire.
The one of the first or second end ring in which the bend is formed may have a geometry defined such that at least a portion of this end ring has a concave shape. This end ring may have a shape such that it includes both convex and concave portions.
The other one of the first or second end ring, i.e. the end ring in which no bend is formed, may be convex throughout its length.
According to another embodiment, there is provided a spring core unit which comprises a plurality of springs which respectively have a first end ring, an opposite second end ring, and a spiral body extending from the first end ring to the second end ring. The first and second end rings have different configurations.
One of the first or second end rings may respectively have at least one bend formed therein. This end ring may have a geometry such that at least a portion of this end ring has a concave shape. This end ring may have a shape such that it includes both convex and concave portions.
The other one of the first or second end ring, i.e. the end ring in which no bend is formed, may have be convex throughout its length.
Adjacent springs may be attached to each other by a helical lacing wire. At least the other one of the first or second end ring, i.e. the end ring in which no bend is formed, may have a free leg terminating at a free end, with an end tip of the free leg being located in an interior of the helical lacing.
The spiral body may respectively consist of at most 1.25 active turns. The spiral body may respectively consist of at least 0.75 active turn. The springs may respectively have a height of less than 70 mm, in particular of at least 40 mm and less than 70 mm, when in an unloaded condition. A high spring rate can be attained using such a configuration.
In other embodiments, the springs of the spring core unit may have a greater number of active turns. For illustration, the spiral body between the end turns may consist of equal to or less than 3.25 active turns. The spiral body between the end turns may consist of 1.25, 2.25 or 3.25 active turns. The spiral body between the end turns may consist of 0.75, 1.75 or 2.75 active turns.
Embodiments of the invention will now be described in more detail with respect to a preferred embodiment.

Fig. 1 shows a spring core unit having a plurality of springs according to an embodiment of the invention.
Fig. 2 shows an enlarged view illustrating a connection of two springs by a helical lacing wire in the embodiment of Fig. 1.
Fig. 3 shows a cross-sectional view of an end ring of a spring used in the spring core unit of Fig. 1.
Fig. 4 shows a plan view of adjacent springs of the spring core unit of Fig. 1.
Fig. 5 is a plan view of adjacent springs of the spring core unit of Fig. 1.
Fig. 6 shows an arrangement of a free leg of a spring installed in a spring core unit of another embodiment.
Fig. 7 shows a free leg of a spring according to another embodiment.
Fig. 8 is a side elevation view of a spring of another embodiment.
Fig. 9 is a schematic block diagram representations of a method and apparatus for producing a spring core unit according to an embodiment, in which the springs of Fig. 8 are assembled to form the spring core unit.
Fig. 10 is a plan view of first end rings of adjacent springs of a spring core unit produced with the method of Fig. 9 according to an embodiment.
Fig. 11 is a plan view of second end rings of adjacent springs of a spring core unit produced with the method of Fig. 9 according to an embodiment.
Fig. 12 is a plan view of first end rings of adjacent springs of a spring core unit produced with the method of Fig. 9 according to another embodiment.
Fig. 13 is a plan view of a first end ring of a spring as produced by the coiler in the method of Fig. 9.
Fig. 14 is a plan view of a second end ring of a spring as produced by a coiler in the method of Fig. 9.

Fig. 1 shows a spring core unit 1 which, for example, may be used for bedding or seating components. The spring core unit 1 comprises a plurality of springs 2 which are arranged in rows and columns. In Fig. 1, helical lacing wires 6 extend in the transverse direction of the spring core unit 1 in order to connect respective two adjacent springs 2.
The springs 2 shown in Fig. 1 are open end springs which have a spiral body and an end ring or end turn 3 with an unknotted free leg 4.
The free leg 4 of each spring 2 may be substantially straight so that it does not include a bent tail or end tip portion. Furthermore, the free straight leg 4 of the end ring 3 of each spring 2 is provided with a V-shaped stamping or bending 5. As will be explained with reference to Fig. 7, the free leg 4 may also be provided with a U-shaped bending.
As shown in Fig. 2, in an assembled state of the respective spring core unit 1, the helical lacing wire 6 connects two springs 2 or the respective end rings 3 thereof such that the free straight leg 4 of one of the end rings 3 is arranged completely inside the helical lacing wire 6. The tip or end portion of the free straight leg 4 does not extend beyond the helical lacing wire 6. In addition, the V-shaped bending 5 of the free straight leg 4 is aligned with one of the windings or turns of the helical lacing wire 6 so that the V-shaped bending 5 retains itself on the helical lacing wire 6 to prevent lateral shifting of the end rings 3.
While the springs 2 shown in Fig. 1 and Fig. 2 include only one V-shaped bending 5, the free legs 4 of the end rings 3 thereof may also be provided with two or more of such V-shaped bendings.
The free leg 4 may include a first portion and a second portion on opposite sides of the V-shaped bending 5. The first and second portions may respectively be straight. Both the first and the second portion may have a length which is selected such that the helical lacing wire 6 is wound at least twice around the first portion and that the helical lacing wire 6 is wound at least twice around the second portion of the V-shaped bending 5.
Fig. 3 is a cross-sectional view of the end ring of the spring 2 which may be used in the spring core unit shown in Fig. 1 and Fig. 2. The free leg 4 has a first portion 11 which extends from an end tip 13 to the V-shaped bending 5. The free leg 4 has a second portion 12 which extends from the V-shaped bending 5 towards the spiral body. The first portion 11 and the second portion 12 are respectively straight. The first portion 11 and the second portion 12 may be substantially aligned with each other. Both the first portion 11 and the second portion 12 may be completely arranged in an interior of the cylindrical volume defined by the helical lacing wire 6. The end tip 13 is also located in the interior of the cylindrical volume defined by the helical lacing wire 6.
The helical lacing wire 6 has a pitch 17. The first portion 11 has a length which may be equal to or greater than the pitch 17 of the helical lacing wire 6. Similarly, the second portion 12 has a length which may be at least twice the pitch 17 of the helical lacing wire. Such dimensions allow adjacent springs to be securely attached to each other and also provide sufficient attachment length for attaching springs to a circumferential wire at an outer boundary of the spring core unit.
As also shown in Fig. 3, the V-shaped bending 5 may be formed in the free leg 4 such that it is offset from a center axis 10 of the spring. For illustration, an apex 15 of the V-shaped bending 5 may be offset from a center plane of the spring by a distance 16. The apex 15 of the V-shaped bending 5 may be offset from this plane in a direction along a center axis of the helical lacing wire 6.
Fig. 4 shows a partial plan view of a spring core unit according to an embodiment. The end rings of adjacent springs respectively have a free leg 4 with a V-shaped bending 5 formed therein. The free leg 4 has a first portion 11 extending from the end tip 13 to a base point 23 of the V-shaped bending 5. The free leg 4 has a second portion 12 extending from another base point 22 of the V-shaped bending 5 to another bend 21. In the spring core unit of Fig. 4, the second portion 12 of the free leg has a length which is at least two times or at least three times the pitch 17 of the helical lacing wire 6. Accordingly, at least two turns of the helical lacing wire 6 are wound around the second portion 12. The first portion 11 has a length which is also at least two times the pitch 17 of the helical lacing wire 6. Accordingly, at least two turns of the helical lacing wire 6 is wound around the first portion 11. Other dimensions may be used. For illustration, the first portion 11 or the second portion 12 may have a length which is equal to or greater than the pitch 17 of the helical lacing wire 6.
Fig. 5 shows a partial plan view of a spring core unit according to another embodiment. The free leg 4 has the first portion 11 which extends from the V-shaped bending to the end tip 13. The first portion 11 has a length which is at least three times the pitch 17 of the helical lacing wire 6. While the first portion 11 is extended compared to the embodiment of Fig. 4, the end tip 13 is still located in an interior of the helical lacing wire.
The V-shaped bending 5 or a U-shaped bending of the free leg 4 may also be positioned in other ways relative to the helical lacing wire when the springs are assembled to form a spring core unit.
Fig. 6 shows an end ring of a spring when the spring is attached to another spring (not shown) by a helical lacing wire 6. The end ring has a free leg 4, in which a V-shaped bending 5 is formed. The V-shaped bending 5 of the leg 4 protrudes to an exterior of the cylindrical volume defined by the helical lacing wire 6. The V-shaped bending 5 is positioned in between two helical turns of the helical lacing wire 6. By abutment of two turns of the helical lacing wire 6 on the V-shaped bending 5 , the free leg 4 is positioned relative to the helical lacing wire 6. The V-shaped bending 5 is retained on the helical lacing wire 6. The two legs of the V-shaped bending 5 abut on different turns of the helical lacing wire. This mitigates the risk that the free leg 4 will become caught when the spring core unit is roll-packed, for example.
Fig. 7 shows an alternative configuration of the free leg 4 of a spring. Springs having a free leg 4 configured as explained with reference to Fig. 7 may be used in the spring core units explained with reference to any one of Fig. 1 to Fig. 5. The free leg 4 has a U-shaped bending 5'. The U-shaped bending 5' has a base section 14. The base section 14 may be arranged at an external side of the helical lacing wire 6. Several windings of the helical lacing wire 6 may pass through the U-shaped bending 5', so that the U-shaped bending 5' retains the free leg 4 on the helical lacing wire 6. The base section 14 may have a length which is equal to or greater than the pitch 17 of the helical lacing wire 6. The base section 14 may have a length which is equal to the pitch 17 or equal to an integer multiple of the pitch 17. A first portion 11 and a second portion 12 of the free leg 4 may extend on opposite sides of the U-shaped bending 5'. The base section 14 of the U-shaped bending 5' may be parallel to the first portion 11 and the second portion 12.
A method of producing spring core units having a configuration as explained with reference to Fig. 1 to Fig. 7 comprises attaching at least two adjacent springs to each other using a helical lacing wire such that an end tip portion of the leg of the end ring of at least one of the springs is completely arranged inside the helical lacing wire. The V-shaped bending 5 or U-shaped bending 5' of the leg 4 may protrude to an exterior of the volume defined by the helical lacing wire, such that the end ring is positioned relative to the helical lacing wire 6 and is retained thereon by the V-shaped bending 5.
To attach two adjacent springs to each other, a tool may hold the leg of one spring and a portion of the end ring of an adjacent spring. The helical lacing wire may be pre-formed and may be advanced through the tool in a threading manner. Thereby, the helical lacing wire may be arranged such that it winds around the first and second portions 11, 12 of the leg 4, while the V-shaped bending 5 or U-shaped bending 5' is retained on the helical lacing wire 6.
A spring of an embodiment may have an end ring configuration with a free leg 4 in which a V-shaped bending 5 or U-shaped bending 5' is formed on both end rings. I.e., a spring of an embodiment may have one or two end rings having a free leg 4 in which a V-shaped bending 5 or U-shaped bending 5' is formed. Accordingly, the attachment of adjacent springs as explained with reference to Fig. 1 to Fig. 7 may not only be used on one end, but also on both ends of the springs assembled to form the spring core unit.
Irrespective of whether a V-shaped bending 5 or a U-shaped bending 5' is formed on one end ring or respectively on both end rings of the spring(s), the V-shaped bending 5 or U-shaped bending 5' may respectively project from the free leg 4 in a direction towards the longitudinal axis of the spring. When several springs are assembled to form a spring core unit, the V-shaped bending 5 or U-shaped bending 5' on an end ring of a spring may project from the helical lacing wire towards the longitudinal axis of the respective spring. The V-shaped bending 5 or U-shaped bending 5' may be formed in the free leg 4 such that it is located in a plane which is transverse to the longitudinal axis of the spring. The V-shaped bending 5 or U-shaped bending 5' may define a plane which is perpendicular to the longitudinal axis of the spring.
The spring core units using the end ring design as described with reference to Fig. 1 to Fig. 7 mitigate the risk of end rings hooking into opposite end rings or helical lacing wires. This spring core units are particularly suitable for being roll-packed. Accordingly, in a method of an embodiment, the spring core unit may be roll-packed for shipping or storing.
With reference to Fig. 8 to Fig. 13, spring core units, methods, and springs according to further embodiments will be described. While these spring core units may comprise springs having the configuration described with reference to Fig. 1 to Fig. 7, other end ring configurations may also be used.
Generally, in the spring core units and methods for producing spring core units described with reference to Fig. 8 to Fig. 13, springs having different first and second end rings are assembled to form a spring core unit. The techniques described with reference to Fig. 8 to Fig. 13 are particularly suitable for being used with springs which have small heights, such as heights of less than 70 mm, and/or a small number of turns in the spiral body, but may also be used with other springs.
Fig. 8 is a side elevation view of a spring 100 used in the spring core units of embodiments. The spring 100 has a first end ring 101 and a second end ring 102. A spiral body 103 extends from the first end ring 101 to the second end ring 102. The spiral body 103 may include a small number of turns, e.g. at most 1.25 active turns or at least 0.75 active turns to provide a high spring rate. A height 105 of the spring 100 may be at most 70 mm. The height 105 of the spring 100 may be as small as 40 mm or less, for example.
When producing a spring core which comprises a plurality of such springs, a bending tool acts on only one of the first end ring 101 or the second end ring 102 of each spring, before the spring 100 is supplied to an assembly station which assembles plural springs to form a spring core unit. A gripper may support the spring 100 while a bending tool forms one or several bends in the first end ring 101, for example. The gripper may be a gripper of a high speed transfer system for springs. The opposite second end ring 102 may have a shape which remains the same from completion of the coiling process until assembly of plural springs to form a spring core unit. I.e., the second end ring 102 may have a shape when lacing plural springs together which is identical to the shape at the time at which a coiler completed the coiling process of the respective spring.
When a bend is formed in the first end ring 101, for example, the gripper may hold the spring 100 at a portion 108 located between an axial center 104 of the spring and the second end ring 102. With the gripper being positioned in a spatial region 107, there is sufficient room 108 for the bending tool which acts onto the first end ring 101 even when the spring 100 has a small height.
The spring is provided to the assembly station with first and second end rings which have different shapes. The shape of the second end ring 102 may remain the same from coiling the respective spring until several springs are attached to each other, e.g. using a helical lacing wire. As will be explained in more detail with reference to Fig. 10 to Fig. 14, the first end ring 101 may have bends when the springs are assembled to form the spring core unit, such that the first end ring includes convex and concave portions. A center of curvature for a concave portion may be located on an exterior side of the first end ring 101. The second end ring 102 may be convex throughout its length. A center of curvature may respectively be located in an interior of the second end ring 102 throughout the length of the second end ring 102. Both the first end ring 101 and the second end ring 102 may have free end tips.
Fig. 9 is a schematic diagram representing a method 110 of producing a spring core unit and the corresponding processing stations. At 111, a coiling station coils springs. The coiling station may comprise a coiler having a coiling head which forms the springs. The springs may be formed to have a first end ring, a second end ring, and a spiral body extending therebetween. The spiral body may consist of a small number of turns, e.g. at most 1.25 active turns or at least 0.75 active turns.
At 112, at least one bend is formed in one end ring of the spring using a bending tool. Forming of the bend is performed on only one end ring of the spring, e.g. the first end ring 101. In the process 112, a gripper may support the spring while the bending tool forms the bend in the first end ring 101. The gripper may hold a portion of the spring which is arranged towards the second end ring 102, so as to leave sufficient room for the bending tool.
Step 112 may be performed while the spring is arranged on a high speed transfer system. In such a system, a gripper which is moveably mounted may hold the spring and may transport the spring between various processing stations without releasing the spring while it is being processed in these processing stations. The gripper may receive the spring directly at the coiling station.
At 113, several springs are assembled to form a spring core unit. The springs have different first and second end rings when they are assembled. The first end rings of adjacent springs may be attached to each other using a helical lacing wire. The second end rings of adjacent springs may be attached to each other using another helical lacing wire. The spring core unit may be used for seating furniture.
Fig. 10 is a partial plan view of a spring core unit formed with the method explained with reference to Fig. 8 and Fig. 9, the partial plan view showing the first end rings 101 of adjacent springs. When the springs are assembled to form the spring core unit, the first end ring 101 includes several bends. One or several concave portions 121, 122 may be formed in the first end ring 101. The first end ring 101 may also have several essentially straight portions 124, 126 along which adjacent springs are attached to each other by a helical lacing wire 116. The first end ring 101 may have a convex portion 127 adjacent at least one concave portion 121, 122. A center of curvature 123 of the concave portion 121 is respectively located on the exterior of the first end ring 101. The concave portion(s) 121, 122 may be formed using a bending tool which acts onto the first end ring 101 while a gripper holds the spring at a location disposed towards the opposite second end ring 102.
The first end ring 101 has a free end tip 125. The free end tip 125 may project from the helical lacing wire 116, as shown in Fig. 10, or may also be arranged in an interior of the helical lacing wire 116, as explained with reference to Fig. 12 below.
Fig. 13 illustrates the shape of the first end ring 101 at a time at which the coiling process is completed and before bends are formed in the first end ring 101. The shape of the first end ring 101 is modified using a bending tool prior to assembling springs to form the spring core unit.
Fig. 11 is a partial plan view of a spring core unit formed with the method explained with reference to Fig. 8 and Fig. 9, the partial plan view showing the second end rings 102. When the springs are assembled to form the spring core unit, the second end ring 102 of the respective springs may have a convex shape throughout its length. The shape of the second end ring 102 when the spring is assembled with other springs to form the spring core unit may still be the same as the shape of the second end ring 102 at the time at which coiling was completed, which is illustrated in Fig. 14 for comparison.
The second end ring 102 includes a free end 129. The second end ring 102 includes a leg 128 or tail 128 which extends from the free end 129. When the springs are assembled to form the spring core unit, the free end 129 of the second end ring 102 may be located within a cylindrical volume defined by the helical lacing wire 116. The leg 128 may be substantially straight or may be a bent tail of the end ring. The leg 128 may extend in the cylindrical volume defined by the helical lacing wire 116, such that the helical lacing wire 116 is wound around the leg 128 several times.
Other configurations of the first end ring 101 and/or the second end ring 102 may be used. For illustration, the first end ring 101 may include a leg which extends along a straight line and a V-shaped bending formed therein, as explained with reference to Fig. 1 to Fig. 5.
Fig. 12 is a partial plan view of a spring core unit of another embodiment formed with the method explained with reference to Fig. 8 and Fig. 9, the partial plan view showing the first end rings 101. When the springs are assembled to form the spring core unit, the first end ring 101 includes several bends. The first end ring has a leg 134 which extends from a free end tip and which essentially extends along a straight line. A V-shaped bending 135 is formed in the leg 134. The V-shaped bending 135 is positioned on the helical lacing wire 116 such that the V-shaped bending 135 retains the leg 134 on the helical lacing wire 116. The opposite second end ring 102 of the springs may respectively be configured as explained with reference to Fig. 11. Both the end tip 139 of the first end ring 101 and the end tip 129 of the second end ring 102 may respectively be positioned within the cylindrical volume defined by the associated helical lacing wire 116.
When plural springs are assembled to form a spring core unit as described with reference to Fig. 8 to Fig. 14, the springs may be arranged in rows and columns. Spring orientations may alternate between adjacent springs in a row and/or in a column. Alternatively or additionally, a last spring in a row or column may be arranged such that it is rotated relative to an adjacent spring in the respective row or column. This reduces the risk that a free end tip of a spring causes damage to a fabric in which the spring core unit is enclosed.
Spring core units as described with reference to Fig. 8 to Fig. 14 and the methods for producing the same allow springs having a high spring rate to be combined to form a spring core unit even when a high speed transfer system is used for transferring springs. Spring core units as described with reference to Fig. 8 to Fig. 14 and the methods for producing the same also allow the amount of wire required for forming the spring to be reduced, because bends are formed only in one of the two end rings of a spring.
Spring core units as described with reference to Fig. 8 to Fig. 14 and the methods for producing the same may be used for producing spring cores for seating furniture without being limited thereto.

Claims

Spring (2) for a spring core unit (1), the spring (2) comprising a spiral body, and
an end ring (3) having a free leg (4),
characterized in that
the free leg (4) of the end ring (3) extends in an essentially straight direction and is provided with at least one V-shaped bending (5) or at least one U-shaped bending (5').
Spring (2) according to claim 1,
wherein the free leg (4) of the end ring (3) of the spring (2) extends in the straight direction such that it does not include a bent end tip portion.
Spring (2) according to claim 1 or claim 2,
wherein the spring (2) is an open end spring.
Spring core unit (1) comprising a plurality of springs according to any one of the preceding claims.
Spring core unit (1) according to claim 4,
wherein the spring core unit (1) comprises at least one helical lacing wire (6) which connects the end rings (3) of at least two adjacent springs (2) in the spring core unit (1).
Spring core unit (1) according to claim 5,
wherein the springs (2) are arranged in the spring core unit (1) such that the V-shaped bending (5) or the U-shaped bending (5') of the leg (4) of the end ring (3) of at least one of the springs (2) is aligned with a winding of the helical lacing wire (6).
Spring core unit (1) according to claim 5 or claim 6,
wherein the springs (2) are arranged in the spring core unit (1) such that an end tip portion of the leg (4) of the end ring (3) of at least one of the springs (2) is completely arranged inside the helical lacing wire (6).
Spring core unit (1) according to any one of claims 5-7,
wherein the at least one helical lacing wire (6) has a pitch (17), and
wherein the leg (4) has a first portion (11) and a second portion (12), the first portion (11) extending from an end tip (13) of the leg (4), the V-shaped bending (5) or U-shaped bending (5') being disposed between the first portion (11) and the second portion (12), the first portion (11) having a length which is equal to or greater than the pitch (17) of the helical lacing wire (6).
Spring core unit (1) according to claim 8,
wherein the second portion (12) has a length which is at least two times the pitch (17) of the helical lacing wire (6).
Method of producing a spring core unit, the method comprising:
coiling a spring (100), the coiled spring having a first end ring (101) and an opposite second end ring (102), and

supplying the spring (100) to an assembly station which assembles the spring with at least one other spring,

wherein at least one bend (121, 122; 121, 122, 135) is formed in only one (101) of the first or second end ring (101, 102) of the spring (100) using a bending tool before the spring (100) is supplied to the assembly station.
Method according to claim 10,
wherein a gripper supports the spring while the at least one bend is formed, the gripper abutting on a portion (108) of the spring which is offset from an axial center (104) of the spring (100) towards the other one (102) of the first or second end ring (101, 102).
Method according to claim 10 or claim 11,
wherein the spring (100) has a spiral body (103) extending from the first end ring (101) to the second end ring (102), the spiral body (103) consisting of at most 1.25 active turns.
Method according to any one of claims 10-12,
wherein the spring (100) has a height (105) of less than 70 mm, in particular of at least 40 mm and less than 70 mm, in an unloaded condition.
Method according to any one of claims 10-13,
wherein the at least one bend includes a V-shaped bending (135) in a free leg of the one (101) of the first or second end ring (101, 102), and
wherein the spring is assembled such that a free end tip portion (128, 129) of the other one (102) of the first or second end ring (101, 102) is completely arranged inside a helical lacing wire (116).
Method according to any one of claims 10-14,
for producing a spring core unit of any one of claims 4-9.