Sewing – Elements – Needles
Reexamination Certificate
2000-09-12
2001-12-25
Izaguirre, Ismael (Department: 3765)
Sewing
Elements
Needles
Reexamination Certificate
active
06332417
ABSTRACT:
This application claims the priority of German Application No. 199 21 913.3 filed May 12, 1999, which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
This invention relates to a sewing machine needle, particularly for rapidly operating sewing machines which have high stitch output.
As a rule, the output of current industrial sewing machines is 5,000 stitches per minute; in some applications even 8,000 or more stitches per minute are reached.
During the sewing operation the sewing machine needle penetrates the workpiece (hereafter referred to as fabric) to produce a stitch hole. The time available for opening the stitch hole is the period from the moment the needle point touches the fabric to the moment when the needle eye passes the stitch hole. Such an opening period is approximately 0.5 ms for a stitching machine which operates with 5000 stitches per minute. The opening of the stitching hole occurs as a rapid, almost explosion-like lateral displacement of the fabric During such an occurrence, high frictional forces are generated and thus high penetrating forces as well as high operating power for the sewing operation are required.
Sewing with a very high number of stitches per minute involves the risk of mechanical and thermal damage to the fabric. Fibers or even fiber bundles (yarns) may be torn apart as stitch holes are being formed. Further, the high friction forces may heat the needle to temperatures which, within a few seconds, may cause the usual synthetic fibers to reach their melting point. Such fibers then are melted or fused in the stitching zone. A further consequence may be frequent ruptures of the sewing thread.
The fusing of laminates and layers as well as color or other components may lead to further disturbances during the sewing operation. The discussed problems may lead to a deteriorated seam quality and may adversely affect the strength of the manufactured apparel.
Further, needles for sewing machines, particularly those which operate at high machine speeds, are exposed to relatively large mechanical stresses. Increasing machine speeds cause dynamic problems to an increased extent. The masses rotating in the sewing machine may cause vibrations which affect particularly the sewing machine needles clamped at one end. The sewing machine needles furthermore have to withstand external forces such as the pull of the thread, lateral excursions upon contacting the fabric as well as forces derived from handling the sewing machine by the operating personnel. If, for achieving an increased stability, thicker needles are used, the above-outlined problems become even more pronounced.
During sewing the thread must be protected from being damaged as it is pushed through the fabric by the needle. Therefore, in industrial sewing machines it is a desideratum that the needle, even in case of extremely high reciprocating speeds, ensures a substantially frictionless run of the thread during the entire stitch forming cycle. Since the thread thickness is in most cases predetermined for providing the desired seam strength, the sewing machine needle must guide the thread of predetermined thickness with low friction and must adequately protect the thread even in the high-speed range. Also, an excessive motion caused friction between the thread and the fabric is to be avoided in the high-speed range. In case such a requirement cannot be ensured, uncontrollable thread ruptures and misses in the stitching operation result.
German Offenlegungsschrift (application published without examination) 30 27 534 discloses a sewing machine needle having a laterally bent blade. A thread trough provided along the needle blade leads to a needle eye which is positioned in the vicinity of the needle point. The thread trough is defined by two lateral walls which extend into the eye region. The needle contour is substantially linear in the region of transition from the laterally bent zone to the needle point. The above-described difficulties during high-speed sewing operations may involve sewing machine needles of the above-outlined conventional type.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an improved sewing machine needle which is adapted for high-speed operation.
This object and others to become apparent as the specification progresses, are accomplished by the invention, according to which, briefly stated, the sewing machine needle includes a central longitudinal axis; a blade extending at least partially coaxially with the axis and terminating in a point; and an eye passing through the blade transversely to the axis and having an opening direction. The eye has opposite openings on opposite sides of the blade. Two mutually spaced walls forming part of the blade have respective inner faces bounding the eye. An indentation is provided in the blade in a region of at least one of the eye openings. The indentation reduces the height of at least one part of the eye walls as measured from the axis.
The sewing machine needle according to the invention has a reduced volume of the eye cross section while the eye width remains the same and, at the same time, exhibits improved thread protecting characteristics. As a result, the stitch hole for the thread of a given thickness needs to be opened less wide than required conventionally, whereby friction effects on the sewing machine needle and the fabric are reduced. The reduction of the eye cross section is achieved by the indentation formed on the trough-side of the needle blade. Such an arrangement does not adversely affect the eye width and thus threads of usual or predetermined thicknesses may be used.
The indentation changes the deployment characteristic of the piercing force. The first force peak which dominantly occurs during the passage of the eye of a normal needle is in most cases significantly reduced. The maximum stitch hole widening occurs relatively gently only as the upper needle blade penetrates, that is, when the lowering motion of the needle becomes slower and approaches zero. The explosive effect which in case of a conventional needle occurs by virtue of the maximum stitch hole widening at the highest penetration velocity is minimized or prevented altogether.
According to the invention, advantageously a lesser piercing force is present, and thus a lesser energy input is required for the stitching process, accompanied, at the same time, by a lesser needle heat-up and a stitch hole opening process which treats the material gently. Further, the eye may be configured such that a high degree of thread protection is obtained, resulting in fewer stitch misses and thread breakage.
The indentation is preferably dimensioned in such a manner that at least at one location the eye walls have a total height which is slightly less than the height of a region which is situated between the needle point and the eye. As a result, it is feasible to equalize to some extent the width increase of the needle from the needle point to the needle eye by a simultaneously slight flattening to thus achieve an overall, only small cross-sectional increase of the needle. This feature reinforces the above-discussed advantages.
In accordance with an advantageous feature of the invention, the sewing machine needle has at least in one certain region of the eye a substantially constant overall height; this contributes to the delay of the stitch hole opening process during needle penetration.
The indentation of the sewing machine needle has, according to another advantageous feature of the invention, a substantially constant radius; the center of the curvature may be situated approximately at the height of the eye (that is, in a linear extension of the eye). The radius of curvature is preferably relatively large and is, according to an advantageous example, approximately three to four times the nominal needle thickness to be measured in a blade region of unreduced thickness.
While the sewing machine needle according to the invention has an indentation at the needle eye on the side where the thread trough extends, the eye walls at the opp
Groz-Beckert KG
Izaguirre Ismael
Kelemen Gabor J.
Venable
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