US20180249842A1

US20180249842A1 - Spring, spring core and method for producing the same

Info

Publication number: US20180249842A1
Application number: US15/753,046
Authority: US
Inventors: Wolfgang Grothaus
Original assignee: Agro Holding GmbH
Current assignee: Agro Holding GmbH
Priority date: 2015-08-20
Filing date: 2016-07-25
Publication date: 2018-09-06
Also published as: CN108271344A; BR112018002377A2; WO2017029077A1; MX2018001977A; DE102015113857A1; EP3337354A1

Abstract

A spring for a spring core, wherein the spring has helical windings and a first end winding and a second end winding, wherein at least the first end winding has a free end and the free end has at least one passage and the opening of the passage is directed outwardly with respect to the end winding of the spring, is distinguished by the fact that the passage is inclined out of a horizontal plane preferably about an angle α in the compression direction of the spring.

Description

The present invention relates to a spring, a spring core and a method for its manufacture.
Springs for open spring cores such as so-called Bonell or light spring cores for the manufacture of mattresses or cushions are known from the state of the art. Open spring cores have the essential characteristic of a more flat distribution of forces that a user exerts on the core, as opposed to pocket spring cores. This means that when using such an open spring core, more springs deflect per unit area than with a comparable pocket spring core.
This property is achieved, for example, by the connection of a row of springs of an open spring core through a respective connecting spring, which open spring core extends in a is column or row of the open spring core. The connecting spring connects the free ends of the springs by twisting or winding around the free ends. A pocketing or complete encapsulation of each individual spring of the spring core by a non-woven fabric for example—as is the case with a pocket spring core—therefore does not take place with open spring cores.
The spring core is usually rolled up after completion to achieve a smallest possible, space-saving packing size for shipping. In order to ensure trouble-free handling during further processing of the spring cores into mattresses or cushions, measures must be taken because of the absence of pockets in order to avoid hitching of respectively adjacent springs of the spring core when the spring core is compressed during the rolling-up process or when the spring core is extended when handling the spring core during further processing of the spring core into mattresses or cushions.
For this reason, the spring core is covered with a layer of wrapping paper before the rolling-up process. However, this measure is often not sufficient to avoid hitching of the springs during the rolling-up process. Therefore, various measures are known from the state of the art to avoid hitching of the springs of the spring core during the rolling-up process.
According to EP 2 719 307 A1 it is provided that the free end of the end winding of a spring is extended in a straight direction and provided with at least one V-shaped or U-shaped passage. The V- or U-shaped passage is intended to prevent the end windings of the springs from coming out of the connecting spring. So-called light spring cores are also known from the state of the art, which solve this by a further spring leg.
In the following, the term “passage” refers to the result of a penetration by forming of a section of a spring steel wire from one plane or surface to another plane or surface.
These and other measures have also improved the handling of a spring core during further processing of the spring cores into mattresses or cushions according to the technical teaching of EP 2 719 307 A1, so that hitching of the springs occurs less frequently during the rolling-up process, but this state of the art technology also provides cause for further optimisation.
Accordingly, it is the object of the present invention of further improving the manageability of a spring core when further processing the spring cores into mattresses or cushions and, in particular, to further reduce the possibility of hitching the springs when rolling up the spring core and/or when handling the spring core during further processing of the spring core into mattresses or cushions.
This object is achieved by the invention by a spring of claim 1, a spring core of claim 11 and a method according to claim 14.
Accordingly, it is intended that the passage is preferably inclined by an angle α in the compression direction of the spring from a horizontal plane in relation to the installation position.
The invention is thus based on the idea of arranging a passage in such a way that the passage forms a “deflector” inclined into the spring, which prevents a first end winding and the remaining resilient windings of the spring from hitching when the spring is compressed, e.g. during the packing process.
The inclination of the passage in the compression direction of the spring further advantageously creates an inclined sliding plane, which optimises the deflector function of the passage advantageously, so that with high probability hitching of the passage with the other resilient windings of the spring is prevented.
In one embodiment of the invention, the first end winding and the second end winding of the spring have a free end. The free end has a curvature smaller than the curvature of the other resilient windings of the spring.
Due to the curvature of the free end of the first end winding or the second end winding, the free end in the assembled state of the spring core touches the side of a connecting spring, which forms the inner diameter of the connecting spring, in a two-point contact or three-point contact.
This ensures advantageously a defined position of the spring relative to the connecting spring, wherein the free end of the first end winding or the second end winding can carry out a rotational movement relative to the connecting spring when the spring is compressed.
In a further embodiment of the invention, the first end winding and the second end winding each have a reciprocal indentation.
Due to the indentation, the connecting plane of the respective end winding with the respective connecting spring is arranged outside the outer diameter of the respective end winding. This allows the end windings to respectively accommodate the remaining part of the spring in an advantageous manner when being compressed during the rolling-up process, when the spring almost retracts to the block, so that the mutual jamming of neighbouring springs between the spring windings moving towards each other in the vertical direction during the compression of the spring can be avoided to the highest possible extent.
In another embodiment, the first end winding and the second end winding of the spring have an indentation. The topology of the indentation is reminiscent of a bus stop bay. Due to the indentation, the connection section of the first and second end winding is advantageously designed in such a way that it lies outside the outer diameter of the first end winding or second end winding.
In another embodiment of the invention, the spring comprises a last resilient winding before the first end winding or before the second end winding, which is wound in such a way that its diameter continuously increases within a half winding in a defined section of the last resilient winding.
The increase in diameter for this section is preferably in a range of 5% to 30%, especially from 15% to 20%, based on the diameter of the other resilient windings of the spring.
This allows the end windings to respectively accommodate the remaining part of the spring in an advantageous manner during the rolling-up process, when the spring almost retracts to the block, so that the mutual jamming of neighbouring springs between the spring windings moving towards each other in the vertical direction during the compression of the spring can be avoided to the highest possible extent.
The spring according to the invention results in a spring core in which a hitching of springs during the packaging process is advantageously avoided to the greatest extent possible.
Further advantageous embodiments of the invention can be found in the subclaims.

The invention is described below with reference to the enclosed figures, wherein:

FIG. 1: shows a section of a spring core in accordance with the invention with a plurality of springs according to the invention;

FIG. 2: shows an enlargement of a section of a connection of two springs through a connecting spring in the spring core according to FIG. 1;

FIG. 3: shows an enlargement of a section of a front view of a spring of a spring core from FIG. 1;

FIG. 4: shows a top view of a spring of a spring core from FIG. 1;

FIG. 5: shows a top view in the sectional view of an end winding of a spring of a spring core from FIG. 1;

FIG. 6: shows a top view of an end winding with an embodiment variant of a free end of s a spring inserted into a spring core as shown in FIG. 1;

FIG. 7: shows a top view of another embodiment variant of a free end of a spring inserted into a spring core as shown in FIG. 1;

FIG. 8: shows a top view of an embodiment variant of a respective first end winding of two springs of a spring core arranged next to each other;

FIG. 9: shows a top view of a respective second winding of two springs of a spring core arranged adjacent to each other.

FIG. 1 shows a spring core 1 for mattresses or cushions. The spring core 1 has a plurality of springs 2, which are arranged side by side or below each other in rows and columns. The springs 2 are spirally wound springs made of spring wire with a round cross-section.
The spring 2 respectively has a first end winding 201 at its respective one end and respectively a second end winding 202 at the respective other end. The springs 2 are alternately mutually inserted into the spring core 1. In this respect, the springs 2 are arranged in the spring core 1 in such a way that the first end winding 201 is respectively arranged next to the second end winding 202.
The first end winding 201 and the second end winding 202 each have a diameter greater than the remaining part of the spring 2. Thus the spring 2 has a progressive spring characteristic curve. Due to the larger diameter, the end windings 201,202 can each take up the remaining part of the spring 2 during compression during the rolling-up process, when the spring 2 almost retracts to the block, so that due to the increased diameter of the end windings 201, 202 the mutual jamming of neighbouring springs 2 between the spring windings moving towards each other in the vertical direction during the compression of the spring 2 can advantageously be avoided to the highest possible extent.
The first end winding 201 and the second end winding 202 of springs 2 respectively arranged adjacent to each other in the spring core 1 are connected to each other by a respective connecting spring 3. The connecting spring 3 is a spiral wound spring with a round wire cross-section. The connecting spring 3 preferably has a lead greater than the wire diameter of the connecting spring 3. The connecting springs 3 can be arranged in row or column direction of the spring core 1. However, an arrangement of the connecting springs 3 in line direction of the spring core 1, i.e. transverse to the longitudinal extension of the spring core 1, is preferred.
The connecting springs 3 and the absence of pockets, in which a spring of a spring core is inserted in each case and by which a spring is respectively enclosed, characterize the spring core 1 as the so-called Bonell spring core.
FIG. 2 shows an enlarged section of a connection of two springs 2 by a connecting spring 3 in the spring core 1 according to FIG. 1. FIG. 2 clearly shows how the connecting spring 3 connects the first end windings 201 and the second end winding 202 of two springs 2.
The first end winding 201 of the spring 2 has a free end 203. The free end 203 of the first end winding 201 has a curvature smaller than the curvature of the other resilient windings of the spring 2.
Due to the curvature of the free end 203 of the first end winding 201, the free end 203 in the assembled state of the spring core 1 touches the inside of the connecting spring, i.e. the side of the connecting spring 3 which forms the inner diameter of the connecting spring 3, in a two-point contact or in a three-point contact.
This ensures advantageously a defined position of the spring 2 relative to the connecting spring 3, wherein the free end 203 of the first end winding 201 can rotate relative to the connecting spring 3 when the spring 2 is compressed.
The free end of the end winding 201 also has a V-shaped passage 204. The passage 204 can alternatively also be U-shaped. The V-shaped passage 204 is arranged in the free end 203 of the first end winding 201 in such a way that the opening of the “V” is directed outwards with respect to the first end winding 201 of the spring 2.
The V-shaped passage 204 is inclined from a horizontal plane preferably by an angle α of 5° to 25°, particularly preferred by an angle α of 10° to 15° in the compression direction of the spring 2 (see also FIG. 3).
By the arrangement of the V-shaped or U-shaped passage, in such a way that a “deflector” inclined into the spring 2 is formed by the passage 204, there is a high to probability that hitching of the first end winding 201 and the remaining resilient windings of the spring 2 is prevented, for example, during the packing process. In addition, the inclination of the passage 204 in the compression direction of the spring 2 advantageously creates an inclined sliding plane, which optimizes the deflector function of the passage 204 advantageously, so that with high probability hitching of the passage 204 with the other resilient windings of the spring 2 is advantageously prevented.
The free end 203 of the first end winding 201 is wound around by the connecting spring 3, so that the free end 203—with the exception of the V-shaped or U-shaped passage 204—is within the clear inner diameter of the connecting spring 3.
The free end 203, around which the connecting spring 3 is wound or coiled, acts in combination with the connecting spring 3 as a hinge-like connection between the spring 2 and the connecting spring 3.
The hinge action results in a largely vertical compression of the spring 2, as the free end 203 can rotate relative to the connecting spring 3, so that this “hinge effect” also makes an advantageous contribution to preventing the resilient windings from hitching when the spring 2 is compressed, since the spring 2 is not deflected out of the vertical during the compression process.
The second end winding 202 of the spring 2 has an indentation 205. The topology of the indentation is reminiscent of a bus stop bay. The indentation 205 has a first leg section 206, a second leg section 207 and a connection section 208. Due to the indentation 205, the connecting section of the second end winding 202 is advantageously designed in such a way that it lies outside the outer diameter of the second end winding 202.
The connecting section 208 has a curvature which is smaller than the curvature of the remaining resilient windings of the spring 2.
The connecting section 208 of the second end winding 202 is wound around by the connecting spring 3, so that the connecting section 208 is within the clear inner diameter of the connecting spring 3.
The connecting section 208, around which the connecting spring 3 is wound or coiled, acts in combination with the connecting spring 3 as a hinge-like connection between the spring 2 and the connecting spring 3.
As a result of the hinge action, the spring 2 has a largely vertical compression, as the free end can rotate relative to the connecting spring, so that this “hinge effect” also is makes an advantageous contribution to avoiding hitching of the resilient windings when the spring 2 is compressed.
FIGS. 3 and 4 each show a spring 2 without an adjacent spring 2 and without a connecting spring 3.
In FIG. 3 the first end winding 201 and the V-shaped or U-shaped passage 204, which is inclined from a horizontal plane into the spring 2, are clearly visible.
In FIG. 4 the spring 2 is shown in a top view. The first end winding 201 and the second end winding 202 each have alternately the V-shaped or U-shaped passage 204 inclined from a horizontal plane into the spring 2. The first end winding 201 and the second end winding 202 each also have alternately the indentation 205.
Due to the indentation 205, the connecting plane of the respective end winding 201, 202 with the respective connecting spring 3 is arranged respectively outside the outer diameter of the respective end winding 201, 202. This allows the end windings 201, 202 to respectively accommodate the remaining part of the spring 2 in an advantageous manner when being compressed during the rolling-up process, when the spring 2 almost retracts to the block, so that the mutual jamming of neighbouring springs 2 between the spring windings moving towards each other in the vertical direction during the compression of the spring 2 can be avoided to the highest possible extent.
FIG. 4 clearly shows that the last resilient winding 209 of the spring 2 is wound before the first end winding 201 in such a way that its diameter continuously increases in a defined section 210 of the last resilient winding 209 within half a winding.
The increase in diameter for this section 210 shall preferably be in a range from 5% to 30%, in particular from 15% to 20%, based on the diameter of the other resilient windings of the spring 2.
Section 210 is followed by the first leg section 206 of the indentation 205, wherein the first leg section is already on the plane of the first end winding 201 of spring 2.
The second end winding 202 respectively also has a last resilient winding 209 before the second end winding 202 alternately to the first end winding, the diameter of which also continuously increases in a defined section 210 of the last resilient winding 209 within half a winding.
The increase in diameter for this section 210 preferably lies in a range from 5% to 30%, more preferably from 15% to 20%, based on the diameter of the other resilient windings of the spring 2.
This allows the end windings 201, 202 to respectively take up the remaining part of the spring 2 in an advantageous manner when being compressed during the rolling-up process, when the spring 2 almost retracts to the block, so that the mutual jamming of neighbouring springs 2 between the spring windings moving towards each other in the vertical direction during the compression of the spring 2 can be avoided to the highest possible extent.
FIG. 5 shows a top view in a section of the first end winding 201 of the spring 2 of the spring core 1. The section passes through the connecting spring 3 in a plane of the largest spring outside diameter to be measured. For the sake of clarity, only the wire cross-sections 301 of the resilient windings in the free end area 203 with the V-shaped or U-shaped passage 204 of the first end winding 201 are shown of the connecting spring 3.
The free end 203 has a first section 210 extending from one end 211 of the free end 203 to the V-shaped or U-shaped passage 204. The free end 203 also has a second section 212 extending from the V-shaped or U-shaped passage 204 to the first end winding 201.
The connecting spring 3 has a pitch p. The length of the first section 210 of the free end 203 has a length equal to or greater than the pitch p of the connecting spring 3. The second section 212 has a length of at least 2 p. Such a design of the sections 210 and 211 with corresponding lengths enables a safe and therefore advantageous connection of two adjacent springs 2 by a connecting spring 3.
The V-shaped or U-shaped passage 204—formed in FIG. 5 by way of example as a V-shaped passage 204—is arranged in the free end 203 of the end winding 201 in such a way that there is an offset 213 between an apex 214 of the passage 204 and a central plane X-Y of the spring 2 in the arrangement direction of the central axis of the connecting spring 3.
By arranging the passage 204 with the offset 213 from the middle plane of the spring 2, an arrangement of the passage 204 is advantageously obtained which effectively and thus advantageously prevents the spring from hitching the resilient windings of the spring during compression to the highest possible extent.
FIG. 6 shows a top view of the first end winding 201 with an embodiment variant of the free end 203 of the spring 2 inserted in spring core 1. For a better overview, only the first end winding 201 of a spring 2 is shown. In FIG. 6, the V-shaped passage 204 is dimensioned in such a way that it is arranged between two windings of the connecting spring 3. The two windings of the connecting spring 3 serve as abutments for the two legs 215, 216 of the V-shaped passage 4, thus securing the V-shaped passage 204 to the connecting spring. The free end 203 of the first end winding of the spring 2 is thus positioned relative to the connecting spring 3.
FIG. 7 shows an alternative design of the free end 203 of the first end winding 201 of the spring 2. The passage 204 here is designed as U-shaped passage 204. The U-shaped passage 204 has a connecting section 217. The connecting section 217 is positioned at the circumference of the outer diameter of the connecting spring 3. The U-shaped passage 204 is dimensioned in such a way that it spans—by way of example—two windings of the connecting spring 3. In an alternative embodiment variant of the U-shaped passage 204, the U-shaped passage 204 can also span less or more than two windings of the connecting spring 1.
The two windings of the connecting spring 3 serve as abutments of the two legs 218, 219 of the U-shaped passage 204, thus securing the U-shaped passage 204 to the connecting spring. The free end 203 of the first end winding of the spring 2 is thus positioned relative to connecting spring 3.
FIGS. 8 to 13 show an alternative embodiment of the spring 2. In order to avoid repetitions, only deviations and/or additions to the spring 2 according to FIGS. 1 to 7 will be described below.
When manufacturing the bends in the end windings 201, 202 of the spring 2, the problem with low springs 20 is that a relatively low spring 20 is too low to provide enough working space for a bending tool to produce bends in both end windings 2001, 2002 without significantly reducing the cycle time of a spring production machine.
The spring 20 in FIG. 8 according to the alternative embodiment therefore only shows bends in the first end winding 2001. The first end winding 2001 thus shows a free end 2003, analogous to the first end winding 201 of the spring 2, wherein the free end 2003 is curved. The free end 2003 also has a V-shaped or U-shaped passage 2004 and an indentation 2005.
Essential difference to the spring 2 is that the second end winding 2002 of the spring 20 according to the alternative embodiment is not shaped analogously to the second end winding 202 of the spring 2.
According to this, the second end winding 2002 of the spring 20 according to the alternative embodiment shows a free end 2030. The free end 2030 shows a curvature that is smaller than the curvature of the remaining windings of the spring 20 according to the alternative embodiment. The second end winding in 2002 also has a connecting region 2031. The connecting region 2031 also shows a curvature which is smaller than the curvature of the other windings of the spring 20 according to the alternative embodiment.
The connection of two adjacent springs 20 to a spring core 10 is achieved by rewinding the free end 2003 with the V-shaped or U-shaped passage 2004 of the first end winding 2001 of the one spring 20 and the indentation 2005 of the first end winding 2001 of the other spring 20 by a connecting spring 30. The connection is further made by wrapping the free end 2030 of the second end winding 2002 of the one spring 20 and the connecting region 2031 of the second end winding 2002 of the other spring 20 by a further connecting spring 30.
When mounting the springs 2, 20 to form a spring core 1, 10, the springs 2, 20 are usually arranged in rows and columns.
The orientation of the springs 2, 20 can alternate in this case so that two adjacent springs 2, 20 are connected in each case in pairs with their free end 203, 2003 or with their indentation 205, 2005 of the first end winding 201, 2001 by a connecting spring 3. Similarly, a corresponding orientation of the springs 2, 20 is obtained on the second end winding 202, 2002.
Alternatively or additionally, the respective last spring 2, 20 of a row or a column of the spring core 1, 10 is oriented in such a way that it is arranged relative to the adjacent spring 2, 20 rotated by approx. 180° about its vertical axis.
Such arrangements of the springs 2, 20 in the spring core 1, 10 advantageously reduce the risk of hitching of the springs 2, 20 during compression within the scope of the rolling-up of the spring core 1, 10 for shipping.
The following method is specified for the manufacture of the spring 2, 20 and the spring core 1, 10:
A spring steel wire is provided in a first process step.
In a second process step, the provided spring steel wire is used to produce the resilient windings as well as the first end winding 201, 2001 and the second end winding 202, 2002 and respectively the last resilient winding 209 before the first end winding 201 and the second end winding 202 with the defined section 210 of the spring 2, 20. Preferably, the winding of the resilient windings and the first end winding 201, 2001 and the second end winding 202, 2002 of the spring 2, 20 is carried out on a spring winding machine.
In a subsequent method step, at least one bend, in particular the V-shaped or U-shaped passage 204, 2004 and/or the indentation 205, 2005, is produced in the first end winding 201, 2001 of the spring 2, 20. Preferably, the bending takes place in a separate bending tool, which can be integrated into the spring winding machine.
In a subsequent method step at least one bend, in particular the V-shaped or U-shaped passage 204, 2004 and/or the indentation 205, 2005, is optionally produced in the second end winding 202, 2002 of the spring 2, 20. Preferably, the bending takes place in a separate bending tool, which can be integrated into the spring winding machine.
In a further method step, two respective springs 2, 20 are connected at their respective first end winding 201, 2001 and their respective second end winding 202, 2002 to a connecting spring 3 to form a spring core 1, 10. The connection of the springs 2, 20 to form a spring core 1, 10 preferably occurs on an automated assembly system provided for this purpose.

LIST OF REFERENCE NUMERALS

1, 10 Spring core
2, 20 Spring
3 Connecting spring
201, 2001 First end winding
202, 2002 Second end winding
203, 2003 Free end
204, 2004 Passage
205, 2005 Indentation
206 First leg section
207 Second leg section
208 Connecting section
209 Last resilient winding
210 Section
211 End
212 Section
213 Offset
214 Apex
215 Leg
216 Leg
217 Connecting section
218 Leg
219 Leg

Claims

What is claimed is:

1. A spring core (1, 10) comprising at least two springs (2, 20) and at least two connecting springs (3), with which the at least two springs (2, 20) are connected, wherein the springs (2, 20) comprise spiral windings and a first end winding (201, 2001) and a second end winding (202, 2002), wherein at least the first end winding (201, 2001) has a free end (203, 2003) and the free end (203, 2003) has at least one passage (204, 2004) and an opening of the passage (204, 2004) is directed to the outside with respect to the end winding (201, 2001 or 202, 2002) of the spring (2, 20), wherein the passage (204, 2004) is inclined from a horizontal plane by an angle α in the compression direction of the spring (2, 20), wherein the angle α is 5° to 25°.

2. The spring core (1, 10) according to claim 1, wherein the angle α is 10° to 15°.

3. The spring core (1, 10) according to claim 1, wherein the passage (204, 2004) is V-shaped or U-shaped.

4. The spring core (1, 10) according to claim 1, wherein the passage (204, 2004) is arranged in such a way in the free end (203, 2003) of the first end winding (201, 2001) or the second end winding (202) that an offset (213) is obtained between an apex (214) of the passage (204) and a central plane X-Y of the spring (2, 20) in the arrangement direction of the central axis of a connecting spring (3).

5. The spring core (1, 10) according to claim 1, wherein the free end (203, 2003) has a curvature.

6. The spring core (1, 10) according to claim 1, wherein the curvature of the free end (203, 2003) is smaller than the curvature of the remaining resilient windings of the spring (2, 20).

7. The spring core (1, 10) according to claim 1, wherein the free end (203, 2003) in the assembled state of the spring core (1, 10) touches the inner diameter of the connecting spring (3) with a two-point contact or a three-point contact.

8. The spring core (1, 10) according to claim 1, wherein that the last winding (209) before the end winding (201, 2001 or 202) has a section (210) in which the diameter of the last winding (209) increases continuously.

9. The spring core (1, 10) according to claim 1, wherein the increase in the diameter for this section (210) is preferably in a range of 5% to 30%, particularly preferably from 15% to 20%, based on the diameter of the remaining resilient windings of the spring.

10. (canceled)

11. The spring core (1, 10) according to claim 1, wherein the orientation of the springs (2, 20) alternates per row or column, so that two adjacent springs (2, 20) are each connected in pairs with their free end (203, 2003) or with their indentation (205, 2005) of the first end winding (201, 2001) or the second end winding (202, 2002) by a connecting spring (3).

12. The spring core (1, 10) according to claim 1, wherein the respective last spring (2, 20) of a row or a column of the spring core (1, 10) is oriented in such a way that it is arranged relative to the adjacent spring (2, 20) rotated by about 180° about its vertical axis.

13. A method for producing a spring core (1, 10) according to claim 1, characterized by the following method steps:

a) providing a spring steel wire;

b) producing the resilient windings and the first end winding (201, 2001) and the second end winding (202, 2002) of the spring (2, 20), and in each case the last resilient winding (209) before the first end winding (201, 2001) and the second end winding (202, 2002) with the respectively defined section (210);

c) producing at least one bend, in particular a V-shaped or U-shaped passage (204, 2004) and/or the indentation (205, 2005) in the first end winding (201, 2001) of the spring (2, 20);

d) connecting two respective springs (2, 20) at their respective first end winding (201, 2001) and at their respective second end winding (202, 2002) with a connecting spring (3) to form a spring core (1, 10).

14. The method for producing a spring core (1, 10) according to claim 13, wherein after the method step c) the following method step takes place:

producing at least one bend, in particular the V-shaped or U-shaped passage (204, 2004) and/or the indentation (205, 2005) in the second end winding (202, 2002) of the spring (2, 20).