Patent Application
20240026587
Sewing machine needles for industrial sewing machines have been known for many decades and undergo continuous further development. Recent years have seen the growing use of textiles made of synthetic fibres. At the same time, sewing speeds have been increased ever further. A problem in this context is the meltability of synthetic fibres at temperatures that are relatively low for sewing processes. As sewing speeds increase, so too does the heat introduced into the fabric as a result of friction with the needle blade. The consequence is undesirable melting of the synthetic fibre at the needle hole if sewing speeds are too high. In order that sewing speeds may be increased further despite this problem, attempts have already been made to reduce the friction between needle blade and fabric.
EP2896732A1 describes a sewing needle with a double-twist groove, which comprises a scarf in which two bevels are disposed. The bevels reduce the cross section of the needle blade in the area of the scarf but they do not lead to a reduction in friction between needle blade and fabric. This is because they are disposed in the scarf at positions where, even in the case of a needle without such bevels, there is no contact with the fabric during sewing.
DE962949C1 describes a sewing machine needle of this kind, which is intended to reduce frictional heat generated during sewing. For this purpose, the sewing machine needle has longitudinal grooves extending from the level of the needle eye to a conical transition between the needle blade and the shank. These grooves are intended to reduce the contact surfaces of the blade with the fabric, thereby also reducing the friction.
EP1391548A1 describes a sewing machine needle comprising concave recesses at two diametrically opposite lateral surfaces of the needle blade. These concave recesses are intended to reduce the contact surfaces between the needle blade and the fabric, and, in consequence, to reduce the friction.
DE3149383A1 describes another example of a sewing machine needle intended to reduce the friction between the needle blade and the fabric. Seen in cross section, the blade has V-shaped profiling and has ribs which are separated by an indentation—similar to a concave recess. The shape of the indentations is adapted to suit the nature and number of the ribs. For example, one embodiment has a star-shaped cross section with seven ribs that are separated from each other by numerous small indentations. Another embodiment has only four ribs, which are separated from each other in each case by a larger indentation. The indentations are recesses which penetrate into the sewing machine needle in such a way as to reduce the needle blade's cross section. The described “geometry” is intended to reduce the contact surface with the fabric and thus to reduce the friction, but to increase the surface area of the needle blade and thereby increase the speed at which the generated heat is transferred to the surrounding air.
Prior art sewing machine needles of this kind have proved to be considerably more expensive to manufacture than customary sewing machine needles and sometimes require additional production steps.
Starting from the prior art, the objective of the invention is thus to provide a sewing machine needle that reduces the friction between the blade of the sewing machine needle and the fabric and does not require any additional or more complex production steps.
The objective is achieved with a sewing machine needle having the following features:
It is advantageous if the recess has a uniformly shaped section making up at least 10%, preferably, however, at least 20% of the entire reach of the recess in the longitudinal direction and if the height of the recess at every point on the uniformly shaped section corresponds to at least 30% of the height of the blade at the point in question. In this way, friction is reduced over a largish portion of the sewing machine needle. The uniformly shaped section does not include the entry and exit parts of the recess. These are the end portions of the recess, pointing in the longitudinal direction. In the entry and exit parts of the recess, the upper and lower edges generally approach each other in the elevational direction until they are touching. It is advantageous if the height of the recess in the elevational direction is at a maximum at least at one point along the length of the uniformly shaped section. The uniformly shaped section of the recess is a part of the blade—i.e. the blade includes the uniformly shaped section of the recess.
Further advantages are obtained if the upper edge distance is smaller than the lower edge distance. A sewing machine needle in the case of which, at least in the uniformly shaped section of the recess, the upper edge distance is smaller than the lower edge distance is particularly advantageous. A geometry of this kind is especially beneficial if, during at least one production step, the tool performs a movement having a directional component in elevational direction, starting out from the upper edge towards the lower edge, or in lateral direction. The upper edge delimits the recess in the positive elevational direction. The lower edge delimits the recess in the negative elevational direction. The positive elevational direction is the direction from the lower edge towards the upper edge. The negative elevational direction is accordingly the opposite, from the upper edge towards the lower edge. This definition of positive and negative elevational directions applies to all possible embodiments of the teaching according to the invention. In a preferred embodiment, the sewing machine needle comprises at least one scarf and/or at least one thread groove, the scarf being disposed on the upper side, which points in the positive elevational direction, and the thread groove preferably being disposed on the underside, which points in the negative elevational direction. A thread groove may also be disposed on the upper side, which points in the positive elevational direction.
Further advantages are obtained for all embodiments
Scarves in connection with sewing machine needles are already known to persons skilled in the art. Every known embodiment of a scarf is advantageous. By “overlap in the longitudinal direction” is meant that the scarf and the recess are at least partially parallel in the longitudinal direction, i.e. they are not spaced apart in the longitudinal direction. It is particularly beneficial if the recess overlaps with the scarf by at least 10% of the scarf length in longitudinal direction, preferably, however, by at least 70% of the scarf length in longitudinal direction. The scarf length is the length, in the needle's longitudinal direction, along which the surface of the needle in the scarf portion is depressed in elevational direction compared to the surrounding needle portions. The scarf length thus includes an entry and an exit part of the scarf. The blade of a sewing machine needle with a scarf can be divided into two sub-portions, the principal blade portion and the scarf portion. The scarf portion is the portion in which the scarf, including its entry and exit parts, extends in the longitudinal direction. The principal blade portion is the remaining portion of the blade. It is to advantage if the uniformly shaped recess section described above does not overlap with the scarf portion. The uniformly shaped section of the recess advantageously lies completely within the principal blade portion—i.e. it overlaps completely with the principal blade portion in the longitudinal direction. The principal blade portion advantageously has a uniform cross section in the longitudinal direction (cylindrical blade) or a slightly tapering cross section in the longitudinal direction (conical blade). The recesses in a blade may be “conical” as well, i.e. their shape may taper in the longitudinal direction towards the needle eye, irrespective of the blade's shape. However, the recesses may also be “cylindrical”, i.e. maintain the same shape and position in the longitudinal direction, irrespective of how the rest of the blade is shaped. In this case, the lateral distance function s(h) in the uniformly shaped section of the recess is the same at every position along the length of the uniformly shaped section. Accordingly, various different combinations are possible, for example:
It is advantageous for all embodiments of the sewing machine needle if, at least at one point along the length of the recess in the longitudinal direction, preferably, however, at every point along the length of the uniformly shaped section, it holds that the maximum distance in the elevational direction between the upper edge of the recess and the highest point of the blade is 35% of the blade height, preferably, however, 25% of the blade height. In this way, large recesses are obtained, which effectively reduce the frictional surface between sewing machine needle and fabric.
It is advantageous if a lateral distance function s(h), which describes, dependent on a height coordinate h, the distance in the lateral direction between the surface of the sewing machine needle and the axis of the needle eye, decreases monotonically, preferably strictly monotonically, with increasing height over at least 90% of the recess's elevational reach, preferably, however, the entire elevational reach of the recess. The elevational reach of the recess is the extension of the recess in elevational direction. In this way, undercuts are avoided and the production process additionally facilitated. The lateral distance function s(h) is also the function of the sectional curve of the surface of the sewing machine needle in the plane defined by the elevational direction and the lateral direction, which describes, dependent on a height coordinate h, the lateral distance between the surface of the sewing machine needle and the axis of the needle eye in the lateral direction. The height coordinate h increases in positive elevational direction H. It is to advantage if the first derivative of the lateral distance function s′(h) is negative for height coordinates smaller than the height coordinate hO of the upper edge and larger than the height coordinate hU of the lower edge—i.e. s′(h)<0 if hU<h<hO. It is especially beneficial if the second derivative of the lateral distance function s″(h) is less than or equal to zero for height coordinates smaller than the height coordinate hU of the lower edge or larger than the height coordinate hO of the upper edge—i.e. s″(h)≤0 if h>hO or h<hU.
At least one recess which, in lateral direction, is spaced at every point from the position of the axis of the needle eye shows further positive effects. It is to advantage if the distance, in lateral direction, between the recess and the position of the axis of the needle eye is greater than zero at every point of the recess. In this way, a plane defined by the axis of the needle eye and the longitudinal direction does not intersect the recess. A needle having at least two such recesses, which are symmetrical with respect to a plane defined by the axis of the needle eye and the longitudinal direction, is particularly advantageous.
Advantageous embodiments are obtained if an imaginary lead-in tangent to the recess at the upper edge encloses a lead-in angle of 5° to 70°, preferably, however, 10° to 40°, with the elevational direction. The lead-in tangent is a tangent adjoining the surface of the recess in the plane defined by the lateral and elevational directions. The lead-in tangent touches the upper edge. In the upper-edge area, the recess may be rounded to varying extents depending on the manufacturing method. The lead-in tangent is not tangential to roundings of this kind, in which the gradient of the surface in the plane defined by the elevational and lateral directions changes extensively. In a preferred embodiment, the lead-in tangent makes contact with the recess in a concave area of its surface. It is particularly advantageous if an imaginary tangent in the plane defined by the lateral and elevational directions encloses an angle of at least 5°, preferably, however, at least 10°, at every point of the recess surface.
The sewing machine needle may advantageously comprise at least one thread groove, which extends substantially in the longitudinal direction, follows on from the needle eye in the negative longitudinal direction, i.e. in the direction looking from the needle eye towards the blade, and constitutes a depression in the elevational direction. In a preferred embodiment, the thread groove is disposed on the underside of the needle, which points in the negative elevational direction. The thread groove is then “open” in the negative elevational direction—i.e. it is not delimited in the negative elevational direction by material of the sewing machine needle. However, a thread groove may also be disposed on the upper side, which points in the positive elevational direction. The thread groove is then “open” in the positive elevational direction. The thread groove is suitable for receiving a thread running through the needle eye and for guiding it along the blade in longitudinal direction. A thread groove that ends in the needle eye offers advantages. The thread groove and the needle eye then merge into each other in the longitudinal direction—i.e. no needle material is disposed between the needle eye and the thread groove. However, the thread groove may also be spaced from the needle eye. The thread groove is a slot-like depression in the needle blade. The groove is delimited on one side in the elevational direction and on both sides in the lateral direction by needle material. It is advantageous for the sewing machine needle to comprise two thread grooves. A sewing machine needle comprising a first thread groove on its underside and a second thread groove on its upper side is particularly advantageous.
It is advantageous if, at least at one point along the length of the recess in the longitudinal direction, preferably, however, at every point along the length of the uniformly shaped section, it holds that the surface of the sewing machine needle between the lower edge and the upper edge of the recess in a plane defined by the elevational and lateral directions is shaped as a circular arc with a substantially constant radius, wherein the circular arc centre preferably lies outside the cross-sectional area of the sewing machine needle in the plane defined by the elevational and lateral directions. In this sectional plane, accordingly, the surface of the recess has the shape of a circular arc and the radius is the same at every point on this circular arc. This kind of recess shape is easy to produce, both with cutting and with forming production methods. Additional advantages are obtained if, in a plane defined by the elevational and lateral directions, the surface of the sewing machine needle between the lower edge and the upper edges of the recess has a shape made up of a circular arc and, adjoining the circular arc, a straight line. This straight line preferably adjoins the circular arc tangentially.
Further advantages are offered by a sewing machine needle in the case of which, at least at one point along the length of the recess in the longitudinal direction, preferably, however, at every point along the length of the uniformly shaped section, it holds that the recess height, which corresponds to the distance between the upper and lower edges in the elevational direction, is 60% to 170% of the maximum lateral distance function s(h), preferably, however, 75% to 160% of the maximum lateral distance function s(h). The selection ranges mentioned have proved advantageous for sewing machine needles having customary dimensions because they enable the use of simple production methods and simultaneously make for sewing machine needles which generate little friction with the textile during sewing. Advantages are also offered by a sewing machine needle in the case of which, at least at one point along the length of the scarf, preferably, however, for at least 20% of the length of the scarf, the recess height, which corresponds to the distance between the upper and lower edges in the elevational direction, is 25% to 150% of the maximum lateral distance function s(h), preferably, however, 35% to 105% of the maximum lateral distance function s(h). Particularly advantageous is a sewing machine needle in the case of which, at least for 20% of the length of the scarf portion, it holds that the recess height, which corresponds to the distance between the upper and lower edges in the elevational direction, is 35% to 60% of the maximum lateral distance function s(h).
Further advantages are offered by a sewing machine needle in the case of which, at least at one point along the length of the recess in the longitudinal direction, preferably, however, at every point along the length of the uniformly shaped section, it holds that the upper edge distance O is 10% to 60% of the maximum lateral distance function s(h), preferably, however, 25% to 45% of the maximum lateral distance function s(h). The upper edge distance O corresponds to the value of the lateral distance function at the position of the upper-edge height coordinate hO. In other words, O=s(hO). The selection ranges mentioned have proved advantageous for sewing machine needles having customary dimensions because they allow a recess of maximum possible size, thus making for the maximum possible reduction in friction, and yet are easy to manufacture, and because they guarantee sufficient stability of the sewing machine needle. Advantages are offered by a sewing machine needle in the case of which, at least at one point along the length of the scarf portion, preferably, however, for at least 20% of the length of the scarf portion, the upper edge distance O, is 10% to 75% of the maximum lateral distance function s(h), preferably, however, 35% to 65% of the maximum lateral distance function s(h).
Further advantages are offered by a sewing machine needle in the case of which, at least at one point along the length of the recess in the longitudinal direction, preferably, however, at every point along the length of the uniformly shaped section, it holds that the lower edge distance U is 50% to 100% of the maximum lateral distance function s(h), preferably, however, 70% to 95% of the maximum lateral distance function s(h). The lower edge distance U corresponds to the value of the lateral distance function at the position of the lower-edge height coordinate hU. In other words, U=s(hU). The selection ranges mentioned have proved advantageous for sewing machine needles having customary dimensions because they allow a recess of maximum possible size, thus making for the maximum possible reduction in friction, and yet are easy to manufacture, and because they guarantee sufficient stability of the sewing machine needle. Advantages are offered by a sewing machine needle in the case of which, at every point along the length of the scarf portion, it holds that the lower edge distance U is 50% to 100% of the maximum lateral distance function s(h), preferably, however, 70% to 95% of the maximum lateral distance function s(h).
A method for the production of a sewing machine needle having a blade, which extends substantially in a longitudinal direction, and a needle eye, which extends through the sewing machine needle in an elevational direction that is at right angles to the longitudinal direction, achieves the objective of the invention in that
A tool movement which is limited to two or even just one movement direction makes for a particularly efficient production process. Large numbers of sewing machine needles can be produced in series with a method of this kind. A method of this kind is particularly advantageous for a sewing machine needle in the case of which the recess has, at least at one point along its length in the longitudinal direction, a height which corresponds to at least 30% of the height of the blade at the point in question.
Further advantages are offered by a method in which the at least one recess is produced by a separating process, preferably by milling. If the milling cutter has a contour corresponding to that of the recess, the recess can be produced by a movement in horizontal and longitudinal direction. An additional movement in lateral direction is unnecessary. This procedure may be used to advantage with other separating-type manufacturing methods as well—for example grinding or spark erosion.
Further advantages are offered by a method in which the at least one recess is produced by a forming process, preferably by pressing. If the press consists of an upper die and a lower die which copy the contour of the at least one recess or of a plurality of recesses, the recess can be produced by a tool movement exclusively in the elevational direction. This is a particularly easy and efficient way of making the recess in the sewing machine needle. However, the recess may also produced by forming with a press having more than two dies—for example a press having three, four or five dies.
s=f(h)=s(h). A lead-in tangent 14 which adjoins the curve of the lateral distance function s(h) tangentially at the upper edge 6 of the recess 5, in the end area thereof, encloses a lead-in angle 15 greater than 5° with the elevational direction H. However, the selection ranges for the lead-in angle 15 which have been mentioned in the earlier paragraphs are advantageous for all embodiments of the sewing machine needle 1.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20214663.5 | Dec 2020 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/081981 | 11/17/2021 | WO |
