GB1596619A

GB1596619A - Latched needles

Info

Publication number: GB1596619A
Application number: GB5331676A
Authority: GB
Original assignee: Needle Industries Ltd
Current assignee: Needle Industries Ltd
Priority date: 1977-12-19
Filing date: 1977-12-19
Publication date: 1981-08-26

Description

(54) IMPROVEMENTS RELATING TO LATCHED NEEDLES (71) We, NEEDLE INDUSTRIES LI MITED, a British Company of, Central Works, Studley, Warwickshire, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to latched needles (hereinafter referred to as being of the kind specified) comprising an elongate shank portion of generally flat strip-like form generally defining a longitudinal axis and having a pair of side faces and upper and lower edge faces, a hook portion at one end of the shank portion, a latch element pivotally mounted on the shank portion for movement between closed and open positions with respect to the mouth of the hook portion, and a butt portion spaced along the shank portion from the hook portion.

A latched needle of the kind specified is normally made of strip metal in the form of flattened metal wire and the side face of the shank portion have depths which are greater than the thickness of the shank portion, that is, the width of the edge faces. In the following description, for convenience, it will be assumed that the side faces of the needle lie in vertical planes and that the upper and lower edge faces of the needle are approximately horizontal, the hook portion is at the forward end and the butt portion is at or adjacent to the rearward end of the shank portion.

Needles of the kind specified are used in knitting machines. In such an application the needles may be mounted in grooves or, as they are termed, tricks, which extend longitudinally in the outer surface of a mounting cylinder for the needles, and the latter are reciprocated longitudinally in the tricks by cooperation between the needle butts and a cam.

For high productivity it is a requirement that the knitting machines shall be operated at the highest speed consistent-with satisfac tory knitting operation and service life of the component parts of the machine, but one of the limitations in this respect is failure of the needles which often takes place by fracture of the hook portion with or without part of the shank portion attached from the shank portion or the remainder of the shank portion.

It is known that this particular form of failure increases with increasing working speed of the knitting machine. Many studies have been made and experiments conducted in an endeavour to analyse or ascertain the cause or causes of this mode of failure with a view to developing solutions without any large measure of success having been achieved.

The present invention is based upon recognition that the principal cause of nee dle failure in the mode referred to is excitation of shock waves originating at the butt of the needle as a result of impact between the butt and the operating cam, and the reflection of such waves from the end of the needle at which the hook portion is situated. When a shock wave is reflected as aforesaid it travels reversely along the shank portion towards the butt and at some position along the needle spaced from the end of the hook portion, the needle is subjected simultaneously to shock stress arising from the leading end of the reversely travelling shock wave and the trailing end of the forwardly travelling shock wave, the stresses respectively being of opposite kind, e.g. compressive and tensile, so that they are additive.

The present invention is further based upon the concept that if the head (and possibly the tail of the travelling shock wave can be modified from a form in which it lies in a plane at right angles to the longitudinal axis of the shank portion to some other configuration, then at the crossing position between the reflected and reversely travelling head and the forwardly travelling tail, the peak stress will be reduced with consequent reduction in the failure rate of the needles.

According to the invention there is provided a needle of the kind specified wherein the shank portion has a web or section of reduced thickness defined by a recess in a part of the shank portion situated between the butt portion and the hook portion; and wherein an unrecessed full thickness section of the shank portion extends generally longitudinally and uninterruptedly along that part of the shank portion between the butt portion and the region in which the latch element is pivotally mounted and past said recess.

The recess may be formed in a part of the shank portion part of which one of the edge faces presents a ramp defining a gradual decrease of depth between the edge faces over at least part of the length of said part in a forward direction longitudinally of the shank, the recess being formed in one only of the side faces of said part and the depth of the recess being less than the depth of the shank portion, leaving said unrecessed full thickness section extending past the recess.

The needle may have two recesses provided in the shank portion between the butt portion and the hook portion, each of the recesses beginning at an edge face of the shank portion and terminating at a boundary spaced depthwise from the other edge face, the recesses being such as to leave said resulting unrecessed full thickness section extending generally longitudinally and uninterruptedly along the shank portion past each of said recesses.

According to a further feature of the invention, the needle may include recesses provided at respective longitudinal positions in the part of the shank portion between the butt portion and the hook portion, each of the recesses beginning at an edge face of the shank portion and terminating at a boundary spaced depthwise from the other edge face, with successive recesses being formed in oppositely presented side faces respectively, and the respective boundaries of the recesses being so disposed as to leave said unrecessed full thickness section extending generally longitudinally and uninterruptedly along that part of the shank portion between the butt portion and the region in which the latch element is pivotally mounted, and past each of said recesses.

A further feature of the invention is that the needle may comprise a shank portion which is reduced in thickness over part only of its depth so as to define an integral web or section which is asymmetrical with respect to a median plane parallel to said side faces and a median plane parallel to said edge faces, so as to leave said unrecessed full thickness section of the shank portion, the depth of the web or section and of the full thickness shank portion being such as to define a progressive reduction of transverse cross-sectional area along the recessed part of the shank from its rearward towards its forward end.

Further features of the invention will appear in the following description and appended claims.

The invention will now be described, by way of example, with reference to the accompanying drawings wherein: Figure 1 is a view in side elevation of one embodiment of latched needle of the kind specified in accordance with the invention; Figure 2 is a view in side elevation and on an enlarged scale showing a fragment of the shank portion of the needle of Figure 1 to which the modification of transverse crosssectional shape in accordance with the present invention is applied; Figure 3 is a graphical view plotting transverse cross-sectional area as ordinate against needle length as abscissa; Figures 4, 5 and 6 show transverse crosssections at lines 4-4, 5-5 and 6-6 of Figure 2; Figure 7 shows a second embodiment of latched needle of the kind specified in accordance with the invention.

The latched needle shown in Figure 1 comprises a shank portion 10 which is integrally connected at one end to a hook portion 11 and adjacent to its other end integrally connected to a butt portion 12.

Starting at the left-hand end of the needle the hook portion occupies a length indicated at a which is integrally joined with the adjacent part of the shank portion which is slotted medially to form two cheeks between which a latch element 13 is pivotally connected for movement between a closed position, as shown, and an open position in which the latch element lies back along the shank portion.

Continuing along the needle, the shank portion includes a second part occupying a length c for which the depth dimension is equal to, or a little less than, the maximum depth dimension afforded by the first part b.

Next, the shank portion includes a junction part d which serves to join part c to the part e, the latter having a depth which substantially exceeds that of the part c. The junction part d in a conventional needle provides a more or less gradual change of depth by way of a ramp edge 14, usually of somewhat concave form.

Likewise a further junction part f serves to connect the part e with a fourth part g of still greater depth than the part e and from which the butt 12 projects laterally as shown. In a conventional needle all of the parts b, c, d, e and g have the same thickness. The thickness of the hook portion a is normally less than that of the part b but may, if desired, be deformed with respect to the blank of strip form in a manner to undergo some enlargement in thickness, i.e.

the dimension at right angles to the planes of the side faces of the shank portion. In transverse cross-section the hook portion may be of circular or oval form.

Endwise reciprocating movement imparted to the needle by way of cam faces engaging contact faces 12a and 12b of the butt portion produce shock waves which travel lengthwise along the shank portion of the needle to the hook portion 11 and are then reflected. The shock wave may consist at its leading end of a local compressive stress followed at its tail end by tensile stress. Upon reflection from the terminal or end face of the hook portion one of these forms of stress, e.g. a compressive stress, "crosses" the opposite form of stress, e.g. a tensile stress, forming the tail of a shock wave and at the crossing point a high value of stress is produced. When this occurs at a relatively slender portion of the needle, i.e.

one where the transverse cross-sectional area is at a minimum. for example near the junction of the parts a and b, fracture of the needle is apt to occur.

The peak value of stress for each crossing point depends not only upon the magnitude of the stresses in the head and tail portion of the shock wave but also upon the shape of the wave fronts. Thus, if on a simplified analysis the wave front of the head portion of the shock wave is regarded as being more or less planar and at right angles to the longitudinal axis of the needle and the trailing wave front at the tail is of like form, then at the crossing point, high additive stress will be produced across the entire transverse cross-section of the needle.

If, however, the form of the wave fronts can be modified, without significantly or seriously weakening the needle, then the value of the peak stress at the crossing point can be reduced.

With this object a part of the shank portion has its transverse cross-sectional area and shape modified. Satisfactory results have been achieved by modification in respect of the part identified at d as above mentioned.

For this purpose, and as seen particularly in Figures 2 and 4 to 6, the thickness of the part d is reduced for part of the depth of the part d leaving an upper section or web 15 connected integrally to a lower section and projecting upwardly therefrom, such web having a thickness which is less than the lower section 16. In transverse crosssection, as seen especially in Figures 4 to 6, the part d of the shank portion is thus of stepped shape in cross-section, as distinct from the rectangular shape presented by the adjoining parts c and e of the shank portion.

The web 15 may be about one-third of the thickness of the lower section 16 but need not be of uniform thickness, e.g. it could be tapered towards its upper edge. Starting from the end nearest the butt portion, the depth of the metal removed from the web 16 increases up to the point 15a coinciding with the cross-sectional line 5-5. The depth of the lower section 16 decreases and that of the web 15 increases relatively without change in the overall depth of the shank portion.

Thereafter, and continuing towards the hook portion, the depth of the web 15 is decreased while that of the lower section 16 decreases slightly at first and then begins to increase. The web may thus be formed by cutting away part of the shank using a circular milling cutter or the like tool having a peripheral radius r corresponding to the radius of curvature of the surface 17. The cross-sectional shape of the part d considered in any of the planes 4-4, 5-5- and 6-6 is asymmetrical about a vertical median plane 19 parallel to the side faces 21 of said part d of the shank portion (considered before any cutting away is effected to produce the section 15). It is also asymmetrical about a median plane 20 parallel to the edge faces and midway between them (again considered before any cutting away has taken place).

This asymmetry is considered to be an important factor in modifying the shape of the wave front of the shock wave.

It will be noted that the modification of the wave front of the shock wave brought about by the characteristic cross-sectional shape of the part d occurs in a portion of the needle where the depth, and hence the cross-sectional area as a whole. provides relatively low stressing compared with that which will exist at the junction of the hook part in the region a and the part b at the shank portion. Therefore, such modification can be carried out without detriment to the overall strength of the needle.

It will be noted from Figure 3, in which the cross-sectional area is plotted as ordinate against length as abscissa, that the portion D of the curve corresponding to the part d of the shank portion shows a gradual decline in cross-sectional area from the value existing in respect of the part e to that existing in respect of the part c without abrupt changes.

It will be appreciated that in forming the part d of modified cross-section. two or more needle blanks may be clamped in side by side relation with their side faces in contact, and a milling cutter or other suitable tool having a width equal to twice the width of the surface 17 may be utilised simultaneously to cut away the shank portion of adjacent needle blanks which are then formed either left-handed or righthanded.

The needle may be formed from any suitable metal, for example plain, carbon or alloy steel of a composition in either case suitable for hardening and tempering. The thickness of the blank portions of the needle may typically range from 0.015 inches to 0.040 inches according to usage. The depth of the second part c of the shank portion may be approximately one half of the depth of the fourth part e which in turn may be approximately half the depth of the part g.

The part c may range typically from 0.025 inches to 0.060 inches depending upon the usage to which the latch needle is to be put.

Referring to Figure 7, parts corresponding to those already described with reference to the embodiment of Figures 1 and 2 are designated by corresponding references with the prefix 1 in the case of numerals and the suffix 1 in the case of letters, and the preceding description is to be deemed to apply.

In this embodiment the shank portion of the needle includes a further part d2 which is offset longitudinally of the shank portion from the part dl, and of which the thickness is reduced for part of the depth to provide a web or upper section 122 and a lower section 123 of reduced thickness. The web 122 is offset laterally with respect to the vertical median plane parallel to the side faces 121 of the shank portion on the side of this median plane opposite to that from which the web 155 is offset. The thickness of the web 122 and the web 155 may, as in the case of the first embodiment, approximate to one third of the thickness of the reduced lower sections 123 and 116 respectively, and in this case it would be possible for the webs 122 and 115 to overlap longitudinally to some extent at their adjacent ends.As illustrated, the web 122 follows on immedi ately after the web 115 in a rearward direction along the shank portion of the needle but there may, between the two parts dl and d2 occupied respectively by the webs 115 and 122, be a short length of the shank portion of dimensions corresponding to those in respect of the part el, i.e. which is not cut away to provide a web or portion of reduced thickness.

It will be evident that the transverse cross-sectional shape in any transverse plane throughout the part d2 is also asymmetrical about a horizontal median plane parallel to the edge faces of the shank portion of the needle.

Conveniently the cutting away of the shank portion of the needle to form the web 122 may be effected by a milling cutter which may have the same peripheral radius as that for cutting away the shank portion to form the web 115.

Tests which have been conducted have shown that the incorporation of a part d having the cross-sectional shape of the embodiment illustrated in Figures 1, 2 and 4 to 6 have very considerably extended needle life before failure occurs due to the shock wave effect already described. The incorporation of two parts dl, d2 of the form shown and described with reference to Figure 7 has the effect of further extending the life before failure from the shock wave effect.

WHAT WE CLAIM IS: 1. A needle of the kind specified wherein the shank portion has a web or section of reduced thickness defined by a recess in a.

part of the shank portion situated between the butt portion and the hook portion; and wherein an unrecessed full thickness section of the shank portion extends generally longitudinally and uninterruptedly along that part of the shank portion between the butt portion and the region in which the latch element is pivotaly mounted and past said recess.

2. A needle according to claim 1 wherein the recess is formed in a part of the shank portion, of which one of the edge faces presents a ramp defining a gradual decrease of depth between the edge faces over at least part of the length of said part in a forward direction longitudinally of the shank, the recess is formed in one only of the side faces of said part, and the depth of the recess is less than the depth of the shank portion, leaving said unrecessed full thickness section extending past the recess.

3. A needle according to claim 2 wherein the ramp is presented by the upper edge face.

4. A needle according to claim 2 or claim 3 wherein the shank at the recess comprises integrally connected upper and lower sections, and has a transverse crosssection of stepped form with a step being defined collectively by one side face of the upper section, one side face of the lower section, and a step face between the upper and lower sections, the other side faces of the upper and lower sections being coplanar.

5. A needle according to claim 4 when appendant to claim 3 wherein the recess and the resultant web or section of reduced thickness being at a position rearwardly of the ramp and continue forwardly along said ramped part of the shank portion, and said step face inclines downwardly in a forward direction longitudinally of the shank portion but at a less steep inclination than is presented by said ramp.

6. A needle according to claim 5 when appendant to claim 3 wherein the step face

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

simultaneously to cut away the shank portion of adjacent needle blanks which are then formed either left-handed or righthanded.

The needle may be formed from any suitable metal, for example plain, carbon or alloy steel of a composition in either case suitable for hardening and tempering. The thickness of the blank portions of the needle may typically range from 0.015 inches to 0.040 inches according to usage. The depth of the second part c of the shank portion may be approximately one half of the depth of the fourth part e which in turn may be approximately half the depth of the part g.

The part c may range typically from 0.025 inches to 0.060 inches depending upon the usage to which the latch needle is to be put.

Referring to Figure 7, parts corresponding to those already described with reference to the embodiment of Figures 1 and 2 are designated by corresponding references with the prefix 1 in the case of numerals and the suffix 1 in the case of letters, and the preceding description is to be deemed to apply.

In this embodiment the shank portion of the needle includes a further part d2 which is offset longitudinally of the shank portion from the part dl, and of which the thickness is reduced for part of the depth to provide a web or upper section 122 and a lower section 123 of reduced thickness. The web 122 is offset laterally with respect to the vertical median plane parallel to the side faces 121 of the shank portion on the side of this median plane opposite to that from which the web 155 is offset. The thickness of the web 122 and the web 155 may, as in the case of the first embodiment, approximate to one third of the thickness of the reduced lower sections 123 and 116 respectively, and in this case it would be possible for the webs

122 and 115 to overlap longitudinally to some extent at their adjacent ends.As illustrated, the web 122 follows on immedi ately after the web 115 in a rearward direction along the shank portion of the needle but there may, between the two parts dl and d2 occupied respectively by the webs

115 and 122, be a short length of the shank portion of dimensions corresponding to those in respect of the part el, i.e. which is not cut away to provide a web or portion of reduced thickness.

It will be evident that the transverse cross-sectional shape in any transverse plane throughout the part d2 is also asymmetrical about a horizontal median plane parallel to the edge faces of the shank portion of the needle.

Conveniently the cutting away of the shank portion of the needle to form the web

122 may be effected by a milling cutter which may have the same peripheral radius as that for cutting away the shank portion to form the web 115.

Tests which have been conducted have shown that the incorporation of a part d having the cross-sectional shape of the embodiment illustrated in Figures 1, 2 and 4 to 6 have very considerably extended needle life before failure occurs due to the shock wave effect already described. The incorporation of two parts dl, d2 of the form shown and described with reference to Figure 7 has the effect of further extending the life before failure from the shock wave effect.

WHAT WE CLAIM IS: 1. A needle of the kind specified wherein the shank portion has a web or section of reduced thickness defined by a recess in a.

part of the shank portion situated between the butt portion and the hook portion; and wherein an unrecessed full thickness section of the shank portion extends generally longitudinally and uninterruptedly along that part of the shank portion between the butt portion and the region in which the latch element is pivotaly mounted and past said recess.
2. A needle according to claim 1 wherein the recess is formed in a part of the shank portion, of which one of the edge faces presents a ramp defining a gradual decrease of depth between the edge faces over at least part of the length of said part in a forward direction longitudinally of the shank, the recess is formed in one only of the side faces of said part, and the depth of the recess is less than the depth of the shank portion, leaving said unrecessed full thickness section extending past the recess.
3. A needle according to claim 2 wherein the ramp is presented by the upper edge face.
4. A needle according to claim 2 or claim 3 wherein the shank at the recess comprises integrally connected upper and lower sections, and has a transverse crosssection of stepped form with a step being defined collectively by one side face of the upper section, one side face of the lower section, and a step face between the upper and lower sections, the other side faces of the upper and lower sections being coplanar.
5. A needle according to claim 4 when appendant to claim 3 wherein the recess and the resultant web or section of reduced thickness being at a position rearwardly of the ramp and continue forwardly along said ramped part of the shank portion, and said step face inclines downwardly in a forward direction longitudinally of the shank portion but at a less steep inclination than is presented by said ramp.
6. A needle according to claim 5 when appendant to claim 3 wherein the step face

is of concave arcuate form longitudinally of the shank and extends from the level of the upper edge face at a position rearwardly of the ramp to the level of the upper edge face at the forward end of the ramp.
7. A needle according to claim 6 wherein said upper section has an upper edge face which, in the forward longitudinal direction, extends substantially parallel to the lower edge face of the shank portion up to the mid region of the length of the recessed part and then extends forwardly and downwardly by way of said ramp.
8. A needle according to claim 1 wherein two recesses are provided in the shank portion between the butt portion and the hook portion, each of the recesses begins at an edge face of the shank portion and terminates at a boundary spaced depthwise from the other edge face of the shank portion, the recesses being such as to leave said resulting unrecessed full thickness section extending generally longitudinally and uninterruptedly along the shank portion past each of said recesses.
9. A needle according to claim 8 wherein each recess begins from the upper edge face of the shank portion.
10. A needle according to claim 9 wherein, at each recess, the shank portion has a cross-section of stepped form provided by a reduced thickness upper section and a full thickness lower section, the latter presenting a step face at its upper end, the upper and lower sections being integral with each other and coplanar at the side face of the shank remote from said step face.
11. A needle according to claim 10 wherein each of said boundaries is of concave arcuate form in a direction longitudinally of the shank portion.
12. A needle according to claim 1 wherein recesses are provided at respective longitudinal positions in the part of the shank portion between the butt portion and the hook portion, each of said recesses begins at an edge face of the shank portion and terminates at a boundary spaced depthwise from the other edge face, with successive recesses being formed in oppositely presented side faces respectively, and the respective boundaries of the recesses being so disposed as to leave said unrecessed full thickness section extending generally longitudinally and uninterruptedly along that part of the shank portion between the butt portion and the region in which the latch element is pivotally mounted, and past each of said recesses.
13. A needle according to claim 12 wherein each recess begins from the upper edge face of the shank portion.
14. A needle according to claim 13 wherein, at each recess, the shank portion has a cross-section of stepped form provided by a reduced thickness upper section and a full thickness lower section defining a step face at a respective one of the side faces of the shank, the upper and lower sections at each recess being coplanar at the respective other side face of the shank.
15. A needle according to claim 14 wherein each of said boundaries is of concave arcuate form.
16. A needle according to any one of claims 12 to 15 wherein the lower edge of the shank portion is parallel to the longitudinal axis of the shank portion and the upper edge face includes a ramp which slopes downwardly in a forward longitudinal direction and overlaps longitudinally with the forwardly situated one of said recesses.
17. A needle according to claim 1 wherein the shank portion is reduced in thickness over part only of its depth so as to define an integral web or section which is asymmetrical with respect to a median plane parallel to said side faces an a median plane parallel to said edge faces, so as to leave said unrecessed full thickness section of the shank portion3 the depth of the web or section and of the full thickness shank portion being such as to define a progressive reduction of transverse cross-sectional area along the recessed part of the shank from its rearward towards its forward end.
18. A needle according to claim 17 wherein the recess defining the reduced thickness web or section starts from the upper edge face of the shank and extends down to a lower boundary, the reduced thickness web or section being of substantially uniform thickness down to said boundary.
19. A needle according to claim 17 or claim 18 wherein both the reduced thickness web or section and the residual full thickness section of the shank are respectively or substantially uniform thicknesses and the depth of said reduced and full thickness sections vary longitudinally of the shank collectively in a manner to provide said progressive reduction in transverse crosssectional area.
20. A needle according to any preceding claim wherein the sections of reduced and full thickness each have a substantially uniform thickness and that of the reduced thickness section or sections is or are approximately one third of that of the full thickness section.
21. A latched needle substantially as hereinbefore described with reference to and as illustrated in Figures 1, 2, 4, 5 and 6 of the accompanying drawings.
22. A latched needle substantially as hereinbefore described with reference to and as illustrated in Figure 7 of the accompanying drawings.