Abstract:
A clothing wire for mounting on a clothing roll of a carding machine has a base section ( 1 ) and a blade section ( 4 ). A gradient dh/db of the height (h) as a function of the width (b) of at least a first section ( 10 ) of at least one blade-section side face ( 5, 6 ) is greater than the gradient dh/db of a second section ( 11 ) of the at least one blade-section side face ( 5, 6 ). The second section ( 11 ) is closer to the base section ( 1 ) than the first section ( 10 ). The sign of the gradients dh/db is the same. In a region which extends to a vertical distance of at most ⅛ of the overall height of the blade section beneath the at least one second portion ( 11 ), there no protrusions or indentations cause a gradient sign change on the at least one blade-section side face ( 5, 6 ).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This patent application is the national phase of PCT/EP2015/055057 filed Mar. 11, 2015, which claims the benefit of European Patent Application No. 14159263.4 filed Mar. 12, 2014. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention relates to a sawtooth wire for a roll of a carding machine. 
       BACKGROUND 
       [0003]    Carding machines are used to open (individualize) and align fibres of a fibrous material, e.g. of wool, cotton, synthetic fibres or of a fibre blend, to homogenize them (for fleece production) and/or to parallelize them (for yarn production). The carding process may be used to produce a fibre mat from a fibrous material. The fibre mat consists of a loose collection of ordered individual fibres. A nonwoven, for example, may be produced from a fiber mat of this kind. During carding, the fibre mat is formed by removing the fibres, by way of a removal means, from a large carding roll known as the swift and combining them. 
         [0004]    The carding machine may have various carding rolls, each of which has teeth, serrations or spikes projecting outwards in approximately radial direction. The number and/or size and/or density of the teeth, serrations or spikes, as well as their shape and configuration, may vary. 
         [0005]    Carding rolls are generally provided with all-steel card clothing. This consists of a profiled sawtooth wire wound under tension onto the carding roll in question. The sawtooth wire has a foot segment and a blade segment. The foot segment may have, for example, a rectangular or square cross section. In the operating position, the blade segment projects away from the foot segment at approx. right angles to the curved surface of the carding roll. The blade segment has a sawtooth profile for the formation of teeth or serrations. The sawtooth wire is wound, under longitudinal stress, around the curved surface of the carding roll, and the two ends are attached to the carding roll. Sawtooth wires are known per se. For example, CN 201512617 U describes a sawtooth wire with obliquely slanting teeth on the blade segment. 
         [0006]    In U.S. Pat. No. 5,096,506 A, a sawtooth wire is shown where one side of the blade segment (blade-segment lateral surface) is perpendicular to, and the other blade-segment lateral surface is inclined relative to the base area of the foot segment. The inclined blade-segment lateral surface is flatter on the side further away from the foot segment than on the rest of the surface. Accordingly, the thickness of the blade segment increases faster on the side further away from the foot segment than in the remaining area of the blade segment. 
         [0007]    U.S. Pat. No. 6,185,789 B1, EP 1 408 142 A1 and EP 2 567 010 A1 show sawtooth wires having blade-segment lateral surfaces with a plurality of convexities. One of the advantages listed for these sawtooth wires is that, during the carding process, they are better able to separate non-spinnable fibres and other foreign substances from the spinnable fibres than are conventional sawtooth wires. 
         [0008]    In DE 19 44 251 U and WO 2006/136480 A1, a sawtooth wire is described whose one blade-segment lateral surface has a first, upper area that is very steep. A second planar area adjoins this first portion and is considerably flatter than the first area. The transition between the first and second areas is at a height much less than half the height of the blade-segment lateral surface. 
         [0009]    In practice, it has been found that especially the tips of the teeth are subject to severe wear. Since the tips of the teeth become rounded with time, the quality and efficiency of the carding process decrease. A countermeasure consists in regrinding the carding wires mounted on a drum (carding roll). Rounded teeth tips may be resharpened in this way. 
         [0010]    However, the latter measure, too, is only able to slow down, but not stop, the long-term loss in quality and efficiency. 
       SUMMARY 
       [0011]    For the reasons cited, the objective of this invention is to create a sawtooth wire which enables optimal homogenization and parallelization of the fibres over a lengthy operating period during production of the fibre mat. The fibres must sustain no or only negligible damage during the carding process. 
         [0012]    Either staple-fibre yarns or nonwovens may be formed from staple-fibre fleeces. 
         [0013]    Among the characteristics of sawtooth wires according to the invention are foot segments, which serve for seating the wire on a carding roll. The foot-segment surface in contact with the carding roll (when the sawtooth wire has been wound onto it) is referred to as the base area. As a rule, the foot segment is the widest segment of the wire. When the wire has been wound on the carding roll, the lateral edges of the foot segments of adjacent wires usually touch each other. 
         [0014]    The base area of the foot segment extends in the wire&#39;s longitudinal direction Z (first spatial direction: is defined by the sawtooth wire&#39;s longitudinal extension) and in the lateral direction B (second spatial direction: is perpendicular to the wire&#39;s longitudinal direction). The third spatial direction is the height direction H, which is perpendicular to the base area of the foot segments and extends towards the exterior surface of the sawtooth wire (i.e. towards the side of the blade segment facing away from the foot segment). Measured from the base area, the height values (i.e. the values in the direction of the height) increase to a maximum blade-segment height. Accordingly, the (height) position of points close to the base area is referred to as being “down” and the position of points close to the exterior surface (of the sawtooth wire) as being “up”. 
         [0015]    The longitudinal, height and lateral directions of the wire are (pairwise) mutually perpendicular. The three directions thus define a Cartesian coordinate system. 
         [0016]    The blade segment running in the height direction tapers as a rule towards the top, i.e. the breadth of the blade segment often decreases steadily with increasing height. The blade segment is confined in the lateral direction by a first and a second blade-segment lateral surface. One of the two blade-segment lateral surfaces frequently (but not always) has a gradient dh(b)/db (henceforth: dh/db) of height as a function of breadth, the value of which is infinitely large, i.e. the blade-segment lateral surface in question is parallel to the perpendicular dropped to the base area of the foot segment. If this is the case, the aforementioned taper is effected in that the other blade-segment lateral surface (in the language of this publication “at least one blade-segment lateral surface”) has a finite gradient dh/db, i.e. the angle between it and the aforementioned perpendicular is not 0°. 
         [0017]    The height value at which the blade segment has its greatest reach in the height direction is referred to as the blade segment&#39;s maximum height. The height value at which the blade segment begins (at the bottom thereof) is referred to as the minimum height. The span (in the height direction) between the minimum height and the maximum height is the overall height of the blade segment. The minimum and maximum heights are thus individual height values. The overall height is a distance (a length) in the height direction. 
         [0018]    The manufacture of the sawtooth wire commences with the drawing of a wire. The wire is subsequently rolled, during which process a wire with a broad foot area and a less broad blade area is formed. The cross section of the wire is constant, within the manufacturing tolerances, over its length. In the blade-area parts further away from the base area it is customary to periodically punch out recesses, thereby forming teeth. At least the toothed part of the blade area is hardened. Usually, therefore, at least the toothed part of the blade area is of greater hardness (is harder) than the foot area (this is softer). Sawtooth wires typically have a length of several hundred metres to several kilometres. 
         [0019]    When a sawtooth wire has been wound onto the carding roll, the foot segments form a closed area (except for the narrow gaps between the sawtooth wires). Above the foot segments, carding gaps, as they termed, are formed between adjacent blade segments (the latter being thinner than the foot segments). As the blade segments (usually) taper towards the top, the carding gaps bordered by the blade segments accordingly widen steadily towards the top. 
         [0020]    The foot area may have planar lateral surfaces. Each foot area may, however, have (profiled) elevations and/or recesses on one lateral surface and be provided, on the other lateral surface, with inverse (geometrically corresponding) elevations and/or recesses which, when the sawtooth wire is wound onto a carding roll, engage the lateral surface of the adjacent wire segment (i.e. the wire segments are interlinked/interlocked). 
         [0021]    The foot segment is clearly distinguishable from the blade segment, since, firstly, it has a geometry (greater breadth) that enables the formation of a (largely) closed area when a sawtooth wire is wound onto a roll. By contrast, the geometry of the blade segment is such that (when a sawtooth wire has been wound onto a roll) open carding gaps are formed, i.e. the blade segments are always less broad than than the associated foot segments. Secondly, the blade segments have teeth (i.e. the blade segments end with a serrated outer contour in the height direction), whereas foot segments always end, in respect of height, with a largely planar base area. Thirdly, the blade segments are usually (at least partly) hardened (i.e. they are comparatively hard), whereas the foot segments are less hard. 
         [0022]    In the case of the sawtooth wire according to the invention, the absolute value of the gradient dh/db at least of a first portion at least of one blade-segment lateral surface is greater than the absolute value of the gradient dh/db at least of a second portion of the same blade-segment lateral surface. 
         [0023]    All the height values of the at least one second portion are smaller than all the height values of the at least one first portion, i.e. the at least one second portion is below the at least one first portion. The two portions do not overlap. 
         [0024]    The at least one first portion and the at least one second portion each extend between a smallest height value, which is at the bottom of the portion in question, and a maximum height value, which is at the top of the portion in question. 
         [0025]    The algebraic signs of the gradient dh/db of the at least one first and of the at least one second portion are the same. In other words, a first portion (at least of one blade-segment lateral surface), which is located higher up, is steeper relative to the base area of the sawtooth wire (i.e the gradient of this portion is steeper) than is a portion of the same blade-segment lateral surface located further down. Both portions should either rise or fall (i.e. the gradient sign should be the same for both portions). Whether both portions rise or fall depends on which of the two blade-segment lateral surfaces they are located on. 
         [0026]    According to the invention, the gradients dh/db of those portions on the same blade-segment lateral surfaceside whose height values are in a range extending between the smallest height value of the at least one second portion and a further height value which is, at the most, ⅛ of the overall height of the blade segment below the aforementioned smallest height value of the at least one second portion, have the same sign as the gradients dh/db of the at least one first and of the at least one second portion. 
         [0027]    In other words, there should be no elevations (“humps”) or indentations (“dents”) beneath the lower end of the second portion that cause a change in the sign of the gradient. A change in gradient sign should by all means be ruled out within an height range (below the at least one second portion) whose height dimension is ⅛ of the blade segment&#39;s overall height. Preferably, the height range in question is ⅕ of the blade segment&#39;s overall height. It is also possible to rule out gradient changes (elevations or indentations) over the entire area of the respective blade-segment lateral surface which is beneath the lower end of the at least one second portion. A further valuable refinement of the invention may consist in that the gradient dh/db of the at least one blade-segment lateral surface also has the same sign everywhere above the at least one first portion (i.e. above the highest height value of the first portion). Alternatively or in addition, provided that the first portion does not border directly on the second portion, the gradient dh/db of the at least one blade-segment lateral surface in the area between the at least one first and the at least one second portion (i.e between the smallest height value of the at least one first portion and the highest height value of the at least one second portion) has the same sign everywhere. 
         [0028]    Elevations/indentations in the flat, rounded transition area between the (comparatively steep) blade segment and the foot segment are irrelevant. Consequently, the term “blade segment” always refers exclusively to the relatively steep area of the blade segment (and not to the flat transition area). 
         [0029]    Changes in gradient sign can also be ignored if they are caused by very small elevations or indentation attributable to manufacturing inaccuracies or manufacturing flaws. 
         [0030]    During the carding process, elevations (indentations) which are sizable and accordingly not attributable to manufacturing flaws/manufacturing tolerances can prevent the fibres from penetrating (in the case of elevations) or penetrating deeper (in the case of indentations) into the carding gaps, thereby impairing the process efficiency. 
         [0031]    If the elevations/indentations have narrow radii or even sharp edges, they can cause substantial damage to the fibres. Such damage leads to quality shortcomings in the end product (e.g. yarns or fleeces) and must by all means be prevented. 
         [0032]    Since, in the case of the sawtooth wire according to the invention, the at least one first portion located further up on the at least one blade segment is steeper (steeper gradient dh/db) and the at least one second portion is flatter (flatter gradient dh/db), the fibres to be carded can enter the carding gaps more easily than with conventional sawtooth wires (whose blade-segment lateral surfaces customarily have a constant gradient). At the level of the smallest height value of the at least one second portion, the carding gaps are usually already very narrow, in particular, substantially narrower than in the height area of the blade-segment lateral surface just beneath its maximum height. Accordingly, elevations/indentations that directly adjoin the at least one second portion or lie only slightly below this very often cause serious damage to the fibres being carded (on account of the narrow carding gap), and usually prevent them from penetrating further into the carding gaps. 
         [0033]    Surprisingly, it was found that elevations/indentations located at a greater height distance (typically at least ⅛ of the blade segment&#39;s overall height) below the at least one second portion cause either negligible or no damage to the fibres being carded. It is, furthermore, no longer necessary for the fibres to enter further into the respective carding gap at this point; i.e. even if the elevations/indentations were to prevent further penetration of the fibres there, this would have practically no influence on the carding process. 
         [0034]    Elevations/indentations located above the at least one first portion or between the at least one first and the at least one second portion cause no or only negligible damage to the fibres being carded and do not prevent these fibres from penetrating the carding gaps because they are in an height area in which the the carding gaps are comparatively wide. 
         [0035]    It is advantageous to select precisely the upper end of the blade-segment lateral surface, i.e. the point on the blade-segment lateral surface whose height corresponds to the maximum height of the blade segment, as the maximum height of the at least one first portion. Alternatively, it is also possible to select a point which (in the height direction) lies slightly below the upper end, e.g. at the most 0.2 (preferably at the most 0.1 mm) below the upper end of the blade-segment lateral surface. Or else a point in the upper quarter, preferably in the upper tenth, of the respective blade-segment lateral surface is selected as the maximum height of the at least one first portion. The smallest height value of the at least one first portion is in an area which is 50% to 98%, advantageously 60 to 90%, of the (blade section&#39;s) overall height above the blade section&#39;s minimum height. 
         [0036]    The at least one first portion is usually positioned longitudinally at a point on the blade-segment lateral surface at which the height (reach in height direction) of the latter is comparatively great. It is advantageous to select, for the at least one first portion, a longitudinal position at which a tooth tip is located. 
         [0037]    For the smallest height value of the at least one second portion, a position is preferably selected in the lower part of the blade segment (nearer the foot segment), e.g. in the bottom tenth of the blade segment. It suffices, however, if the greatest height value of the at least one second portion is less than the smallest height value of the at least one first portion. In a preferred variant, the smallest height value of the at least one first portion borders on the greatest height value of the at least one second portion. 
         [0038]    In the longitudinal direction, a position for the at least one second portion is selected at which the sawtooth wire is existent, i.e. not a position at which the sawtooth wire has a recess (due to the punching out of teeth). 
         [0039]    It should always be assumed that the sawtooth wire runs longitudinally. In particular, the sawtooth wire should not have any deformations in the plane defined by the longitudinal and the lateral directions which could lead to parts of the blade-segment lateral surface being considered as curved which are planar in the case of a longitudinally straight sawtooth wire. 
         [0040]    The at least one first and the at least one second portion are preferably selected such that they are on planar parts of the at least one blade-segment lateral surface. The two portions then run straight in the plane defined by the height and the lateral directions, i.e. the gradient dh/db is constant in each of the two portions and corresponds in each case to the gradient of the secant which runs in the plane defined by the height and lateral directions and through the at least one first or the at least one second portion. 
         [0041]    The at least one blade-segment lateral surface may, however, also be curved in such a way as to preclude the presence, on the blade-segment lateral surface in question, of at least one first and/or at least one second portion located at a “suitable” height (at a height between suitable height values). What is considered as a suitable height has already been explained in earlier sections dealing with the height position of the at least one first and the at least one second portion. 
         [0042]    In a case of this kind, the at least one first portion and/or the at least one second portion may be infinitesimally small (especially in the height direction), i.e. in the case of the infinitesimally small portion concerned, the gradient can no longer be determined in a finite straight/planar portion but at a point. To persons skilled in the art, this situation is known from the introduction to differential calculus, since here the differential quotient for the limit value observation of infinitesimally close arguments (here breadth values) expresses the gradient at a point: 
         [0000]    
       
         
           
             
               
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                      
                     b 
                   
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                   0 
                 
               
                
               
                 
                   Δ 
                    
                   
                       
                   
                    
                   h 
                 
                 
                   Δ 
                    
                   
                       
                   
                    
                   b 
                 
               
             
             = 
             
               
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                 h 
               
               
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                 b 
               
             
           
         
       
     
         [0043]    For this case (infinitesimal portion breadth), the tangent is a special case of the secant through a planar portion, and the value of the secant gradient is the value of the derivative of the function describing the course of the contour of the blade segment in question, or, expressed more simply, the value of the gradient at this point. 
         [0044]    The two portions may (but need not) lie one above the other in the height direction. If one were able to use the starting profile for these sawtooth wires, i.e. the original shape of the sawtooth wire prior to the generation of teeth (e.g. by punching or by a method producing the same effect) as a basis, it would be easy to select the two portions such that they are disposed one above the other in respect of height. However, sawtooth wire teeth are often oblique, i.e. they are shaped like the teeth of a saw, which slope. When determining the tooth&#39;s angle of slope, it is customary to use the slope of the tooth face (working angle). The working angle is defined as the angle enclosed between the tooth face and the perpendicular. On account of the tooth&#39;s slope, many sawtooth wires have no position at which a complete and gapless cross-section (through the original profile) can be found. It is then necessary not to arrange the portions one above the other in respect of height (i.e. the two portions lie at different points of the sawtooth wire&#39;s longitudinal reach). 
         [0045]    A length of 1/100 mm may be preferable as minimum length of the portions (in the lateral direction), although a length of 5/100 or 1/10 mm may also be to advantage. 
         [0046]    The other blade-segment lateral surface (the blade-segment lateral surface opposite the at least one blade-segment lateral surface) is preferably almost completely in a plane defined by the height and longitudinal directions, i.e. its gradient dh/db is infinite. It may, however, have a different geometry, e.g. it could be inclined relative to the height direction by a small angle, e.g. of less than 3° (i.e. its gradient dh/db may have a finite value). Or it could be mirror-symmetric to the at least one blade-segment lateral surface. 
         [0047]    In the case of customarily used sawtooth wires (or in the case of their starting profiles), both blade-segment lateral surfaces (with the exception of curved transition areas) are virtually completely planar, with one blade-segment lateral surface extending in a plane defined by the height and longitudinal directions and the second blade-segment lateral surface extending (likewise in the longitudinal direction but) inclined in respect of height. With sawtooth wires of this kind, the breadth (lateral spread) of the sawtooth wire increases linearly over the entire blade segment. 
         [0048]    By virtue of the blade-segment geometry (of the at least one blade-segment lateral surface) proposed in the invention, the breadth of the blade segment increases more slowly (or not at all) in the upper area (farther away from the foot segment) and then, in the lower area, increases more rapidly (than in the upper area). The transition between the small (or non-existent) increase in breadth and the stronger increase may be continuous or take place in one or more steps, e.g. by way of a succession of several planar portions, e.g. a maximum of 4, preferably 2 to 3. The technical implementation of each of these variants will be explained in more detail below. 
         [0049]    The breadth of the carding gaps formed by a sawtooth wire according to the invention and mounted on a carding roll accordingly decreases—with decreasing height—less quickly (or not at all) in the upper area (nearer the teeth of the sawtooth wire) of the carding gaps, and more quickly in the lower area. 
         [0050]    Surprisingly, it was found that when the sawtooth wire according to the invention is used, the loss in quality and efficiency of the carding process over time (due mainly to necessary regrinding of the teeth) is significantly less than is the case with conventional wires. The sawtooth wire of the invention thus enables optimal homogenization and parallelization of the fibres (during the production of a fibre mat) over a lengthy operating period. 
         [0051]    The sawtooth wire usually has an exterior surface which bounds the sawtooth wire (in the height direction) on the side facing away from the foot segment, and which also extends in the height direction. In so doing, it (often) defines at least one tooth (usually many teeth) of the sawtooth wire. In other words, the blade-segment lateral surface has a serrated contour, at least in its upper area. 
         [0052]    At the tip of the at least one tooth, the exterior surface extends substantially in the longitudinal direction (Z) and the lateral direction (B). The exterior surface of the tooth flanks, by contrast, is inclined in respect of height. 
         [0053]    In one embodiment of the invention, the two portions of the at least one tooth are typically arranged such that they are longitudinally staggered. In this way it is ensured that each of the two portions is located at a point of the sawtooth wire where no material has been removed (by punching during tooth production). This arrangement makes it possible to locate the topmost portion at or near the tip of the at least one tooth and, simultaneously, to locate the at least one second portion at the lower end, or at least in the vicinity of the lower end, of the blade segment (in the area of the respective tooth). The entire (or almost the entire) height of the blade segment can hereby be encompassed by the two portions. 
         [0054]    Arranging the two portions such that are longitudinally staggered, as described above, is unproblematic because sawtooth wires are made from profiled wires the cross-sectional profile of which remains practically the same over their length. 
         [0055]    In principle, the at least one first and the at least one second portion may also be located at a single longitudinal position of the sawtooth wire, i.e. they are arranged one above the other in the height direction, as described above. This is possible in cases where no hollow (punched out) areas exist beneath the tooth tip in question, i.e. if the line connecting the (at least one) first and the (at least one) second portion runs completely within the sawtooth-wire material. 
         [0056]    In a preferred embodiment, at least the part of the blade-segment lateral surface reaching from the blade segment&#39;s maximum height to a point which is 2%, preferably 5% or, best of all, 10% of the blade segment&#39;s overall height above the minimum height of the blade-segment lateral surface is made up of at least two planar surface portions. Expressed differently, the at least one blade-segment lateral surface (of the sawtooth wire) has at least two planar surface portions, which extend straight in the plane defined by the lateral and height directions. The two surface portions preferably follow each other in succession (adjoin each other) in the height direction and enclose an angle (which does not equal 0°) in the plane defined by the lateral and height directions. 
         [0057]    It is also possible for more than two planar (straight) surface portions to follow each other in succession in the height direction, e.g. three or four straight surface portions. Two or three planar surface portions are preferred. The planar surface portion furthest from the foot segment (the highest surface portion) and the second surface portion bordering thereon (the one nearer the foot segment) preferably adjoin each other at a height in the range between 5/10 and 9/10, preferably ⅖ and ⅘ of the blade segment&#39;s overall height. 
         [0058]    The invention is particularly advantageous for (fine) sawtooth wires with comparatively low blade segments, i.e with heights of the blade segments (alternatively: of the teeth) ranging from 0.3 to 1 mm. Sawtooth wires of this kind are customarily used for the manufacture of staple-fibre yarns, e.g. of cotton and/or synthetic fibres. 
         [0059]    For coarser fibres, sawtooth wires are used that may have blade segments with a height of up to 3 (in exceptional cases up to 4) mm. 
         [0060]    In the case of fine sawtooth wires it is to advantage that the portion furthest away from the foot segment (the at least one first portion) usually has a height (reach in h direction) of 0.1 to 0.5 mm, preferably of 0.2 to 0.3 mm. This preferred planar portion preferably begins at a maximum distance of 5/100 mm or 1/10 mm below the tooth tip, i.e. the upper height value of the at least one first portion is, at the most, 5/100 or 1/10 mm smaller than the blade segment&#39;s maximum (height) value. 
         [0061]    If the aforementioned ranges are selected, carding quality and efficiency losses due to necessary regrinding of the teeth of the sawtooth wire are significantly less than is the case when conventional wires are used. 
         [0062]    In order to prevent sawtooth wires, i.e. the gaps formed by sawtooth wires, from becoming blocked with fibres (when the wires are in service on a carding roll), at least in a sufficiently large area of the sawtooth-wire the blade segments must taper sufficiently fast in the height direction. Conventional sawtooth wires practically always fulfill this requirement. However, if the area in which the breadth of the sawtooth wire according to the invention only increases slightly or not at all (small angle of slope relative to the height direction) were to extend over the entire blade-segment lateral surface concerned, blocking of the gaps would have to be anticipated. Via suitable selection of the respective height range, the sawtooth wires are prevented from becoming blocked with fibres despite the (at least first) blade-segment lateral surface being very steep in part (correlating with little-pronounced tapering of the blade segment). 
         [0063]    The at least one first portion (the portion in which the breadth of the sawtooth wire increases less) of the at least one blade-segment lateral surface usually makes an angle of less than 5°, preferably 0°-2°, with the perpendicular dropped to the base area of the foot. Accordingly, since 0° are also possible, the (at least one) first portion of the (at least one) blade-segment lateral surface may also be parallel to the perpendicular dropped to the base area of the foot. 
         [0064]    The at least one second portion of the at least one blade-segment lateral surface usually makes an angle of more than 6°, preferably, however, of more than 8°, with the perpendicular dropped to the base area of the foot. This angle is typically less than 15°, preferably less than 12°. 
         [0065]    In an alternative embodiment, the portions of the at least one blade-segment lateral surface may extend curvilinearly in the plane defined by the lateral and height directions. In particular, the entire blade-segment lateral surface may be curved, preferably concave (as seen from the exterior). Curved means the absence of kinks in the portion concerned. Kinks are points at which discontinuities or singular points occur in the gradient (of the portion concerned). 
         [0066]    Ultimately, variants are also conceivable in which the at least one blade-segment lateral surface is formed from a combination of curved surface portions and planar surface portions. 
         [0067]    In this embodiment (curved surface portions), too, it is possible to maintain comparatively high efficiency of the carding process for longer than is possible when conventional sawtooth wires are used. At the same time, it is also possible to prevent the carding gaps formed by the sawtooth wires from becoming blocked with fibres. For this purpose (by analogy with the embodiment having planar portions), a height in the range between 5/10 and 9/10, preferably ⅗ and ⅘, of the blade segment&#39;s maximum height is selected for the point at which the surface portion in which the breadth of the sawtooth wire increases faster and the surface portion in which it increases more slowly border on one another. If the entire blade-segment lateral surface is curved, a suitable limiting value (for the maximum breadth increase per unit of height) may be specified for determination of this point. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0068]    The invention is explained in more detail below on the basis of three embodiments. The drawing in 
           [0069]      FIG. 1 : is a perspective view of a sawtooth wire, 
           [0070]      FIG. 2 : shows a cross section of a sawtooth wire having a blade-segment lateral surface with two planar surface portions; for reasons of clarity, the wire is shown enlarged in the lateral direction. 
           [0071]      FIG. 3 : shows a profile of a sawtooth wire having a blade-segment lateral surface with two planar surface portions; 
           [0072]      FIG. 4 : shows a cross section of a sawtooth wire having a blade-segment lateral surface with four planar surface portions; for reasons of clarity, the wire is shown enlarged in the lateral direction. 
           [0073]      FIG. 5 : shows a profile of a sawtooth wire having a blade-segment lateral surface with four planar surface portions; 
           [0074]      FIG. 6 : shows a cross section of a sawtooth wire the blade-segment lateral surface of which is a concave curve; for reasons of clarity, the wire is shown enlarged in the lateral direction. 
           [0075]      FIG. 7 : shows a profile of a sawtooth wire with a concave blade-segment lateral surface; 
           [0076]      FIG. 8 : shows the determination of contour gradients in the plane extending in the height direction H and lateral direction B; 
           [0077]      FIG. 9 : shows a blade segment and choice of position for the first and second portions on the blade segment; 
           [0078]      FIG. 10 : shows an alternative shape for the foot segment; 
           [0079]      FIG. 11 : shows a first shape for the second blade-segment lateral surface; 
           [0080]      FIG. 12 : shows a second shape for the second blade-segment lateral surface; 
           [0081]      FIG. 13 : shows a further cross section of a sawtooth wire. 
       
    
    
     DETAILED DESCRIPTION 
       [0082]    The section of sawtooth wire shown in  FIG. 1  consists of a foot segment  1  featuring a base area  2  and two lateral surfaces  3 , and a blade segment  4  which adjoins the foot segment  1  and has a first blade-segment lateral surface  5  and a second blade-segment lateral surface  6 . On the side further away from the foot segment  1  (facing upwards), the blade segment  4  is delimited by an exterior surface  7 , which undulates along a serrated path in such a manner as to form teeth  8 . 
         [0083]    The sawtooth wire runs in the longitudinal direction Z; its height extends in the height direction H and its breadth in the lateral direction B (B is perpendicular to both Z and H). 
         [0084]    The height value at which the blade segment  4  has its greatest reach in the height direction H is referred to as the blade segment&#39;s maximum height h max . The height value at which the blade segment begins (at the bottom thereof) is referred to as the minimum height h min . The span (in the height direction) between the minimum height h min  and the maximum height h max  is the overall height H max  of the blade segment. 
         [0085]    The second blade-section lateral surface  6  extends (apart from manufacturing tolerances) in a plane spanned by the longitudinal direction Z and the height direction H. 
         [0086]    The first blade-segment lateral surface  5  is made up of a first portion  10  located higher up on the blade segment  4  (further away from the foot segment  1 ) and a second portion  11  located lower down on the blade segment (nearer the foot segment  1 ). As already explained earlier, the comparatively flat, rounded transition area  9  between the foot segment  1  and the blade segment  4  is not part of the blade segment  4 . The first portion  10  is practically parallel to the plane defined by the longitudinal direction Z and the height direction H (accordingly, it is also parallel to the second blade-segment lateral surface  6 ), i.e. its gradient is infinitely large. The first portion  10  may alternatively enclose a small angle not exceeding 2° with the height direction H (i.e. dh/db assumes a finite value) and, except for manufacturing tolerances, run parallel to the longitudinal direction Z. 
         [0087]    The second portion  11  is also parallel to the longitudinal direction Z (except for manufacturing tolerances) but, compared with the first portion  10 , encloses a substantially larger angle of 8° to 12° with the height direction H. In other words, the first portion  10  is steeper than the second portion  11 . A steep run generally means that dh/db is large. For a flat run, dh/db is accordingly small. 
         [0088]    On account of the particular geometry of the blade-segment  4 , its breadth B initially increases very slowly (or not at all) from the top downwards, e.g. starting from one of the tooth tips  12  (technically speaking, the tip is a short edge), as its height decreases (i.e. towards the foot segment). At the transition  13 , at which the first portion  10  merges into the second portion  11 , the breadth of the blade segment  4  then increases faster (or commences to increase) with decreasing height. The sawtooth wire&#39;s property of featuring a blade segment  4  the breadth of which, starting from the top, initially increases more slowly and then, towards the bottom, increases more quickly, is essential to the invention and is shown by a multiplicity of advantageous embodiments thereof. Of course, this applies only to those areas of the sawtooth wire in which the material of the original profile is still there, i.e. in which no material was punched out. 
         [0089]    In  FIG. 2  the cross section of the sawtooth wire shown in  FIG. 1  is illustrated, and in  FIG. 3  the associated starting profile (corresponding to the sawtooth wire without teeth). The sectional plane (of the cross section) extends in the lateral direction B and the height direction H. In  FIG. 2 —as in  FIGS. 4 and 6 —the lateral direction B is shown enlarged (i.e. the overall breadth B max  of the sawtooth wire is shown enlarged compared to the overall height H max ,) in order to enable the viewer to recognize the angles and gradients. 
         [0090]    As is apparent from  FIG. 2 , the first portion  10  (in the respective sectional plane) is delimited by the end points  14  and  15  and the second portion  11  by the end points  15  and  16 . The first secant  17 , which runs along the first portion  10  (i.e. through the end points  14 ,  15  of the first portion  10 ) in the sectional plane defined by the lateral direction B and the height direction H, has a steeper gradient than the second secant  18 , which runs in the same plane and along the second portion  11  (through the end points  15 ,  16  of the second portion). 
         [0091]      FIG. 4  shows the cross section (and  FIG. 5  the associated profile) of a sawtooth wire the first blade-segment lateral surface  5  of which is made up of four planar surface portions following each other in succession in the height direction H. The uppermost planar surface portion (furthest from the foot segment  1 ), which (in this sectional plane) is delimited by the end points  20  (with the height value h 11 ) and  21  (with the height value h 12 ), has been selected here as the first portion  10 . The second uppermost planar surface portion, which is delimited by the end points  23  (with the height value h 21 ) and  24  (with the height value h 22 ) has been selected as the second portion  11 . The first secant  22  runs through the end points  20  and  21 , the second secant  25  through the end points  23  and  24 . Both secants  22 ,  25  run in the plane defined by the lateral direction B and the height direction H. Here too, the secant  22  has a steeper gradient than the secant  25 , i.e. the secant  22  encloses a smaller angle α 1  with the perpendicular  19  dropped to the base area  2  of the foot segment than does the secant  25  (angle α 2 ). 
         [0092]    Beneath the end point  24 , with the height value h 22  of the at least one second portion, is the further height value h 3 . The further height value h 3  is located (at a distance in the height direction H) approximately ⅛ of the overall height H max  beneath the lower height value h 22  of the at least one second portion. No change in the sign of the gradient dh/db is allowed in the area between these two height values, i.e. no elevations or indentations are allowed in this area. 
         [0093]      FIG. 6  shows the cross section (and  FIG. 7  the associated profile) of a sawtooth wire the first blade-segment lateral surface  5  of which (seen from the outside) is a concave curve (with no kinks). In  FIG. 6 —as before in  FIGS. 2 and 4 —the lateral direction B is once again shown enlarged so that the viewer is able to recognize different angles between the perpendicular  19  and the tangents  27  and  30 . It remains to be mentioned that in  FIGS. 2, 4 and 6  the points  14 ,  15 ,  16 ,  20 ,  21 ,  23 ,  24 ,  26  and  29  are represented by horizontal strokes, which intersect the contour of the sawtooth wire  1 . The respective point lies at the intersection between the horizontal stroke and the contour of the sawtooth wire  1 . 
         [0094]    An infinitesimally small surface portion  26  in the height direction H (punctiform relative to the selected sectional plane) has been selected as the first portion  10 . Here, the tangent  27  to the first blade-segment lateral surface  5  at the surface portion/point  26  takes the place of the otherwise customary secant running along a planar portion (in the plane defined by the lateral and height directions). The second portion  11  is formed analogously by the point  29 , with the tangent  30  in place of the secant along a planar portion. Here too (as with the respective secants) the gradients of the tangents correspond in each case to the derivative dh/db at the respective point. As in the two preceding examples, the tangent  27  has a steeper gradient dh/db than the tangent  30 , i.e. the tangent  27  encloses a smaller angle α 1  with the perpendicular  19  dropped to the base area  2  of the foot segment than does the tangent  30  (angle α 2 ). 
         [0095]      FIG. 8  shows the contours of two first blade-segment lateral surfaces  5  in the plane defined by the height direction H and the lateral direction B. The one first blade-segment lateral surface  5  running in the respective plane is entirely curved  31 , the other first blade-segment lateral surface  32  is made up of two planar surface portions  33 ,  34 . The lateral direction B is again shown in enlarged form. 
         [0096]    In the case of the blade-segment lateral surface  32 , which comprises two planar surface portions, the first portion  10  may be selected as the surface portion  33 , which extends between the points with the coordinates (b 11 , h 11 ) and (b 12 , h 12 ), and the second portion  11  as the surface portion  34 , which extends between the points with the coordinates (b 21 , h 21 ) and (b 22 , h 22 ). The gradient of the secant through the end points of the first portion  10  is then (h 12 -h 11 )/(b 12 -b 11 ), the gradient of the secant through the end points of the second portion  11  is (h 22 -h 21 )/(b 22 -b 21 ). 
         [0097]    For the blade-segment lateral surface  31 , which is entirely curved, the first portion  10  and the second portion  11  are selected (at least in the viewing plane) to be infinitesimally small (i.e. punctiform). The gradient of the first portion  10  equals the derivative dh/dh at the point b 11  (or at the point b 12 , since the two end points of the infinitesimally small portion  10  coincide), the gradient of the second portion  11  equals the derivative dh/db at the point b 21  (or b 22 ). 
         [0098]      FIG. 9  shows a tooth  8  whose height corresponds to the overall height H max  of the blade segment  4 , i.e. the overall height of the tooth  8  equals the overall height H max  (=h max −h min ) of the blade segment  4 . 
         [0099]    The tooth has, in the area of the tooth tip  12 , a first planar surface portion  35 , which is steeper, and, further down, a second planar surface portion  36 , which is flatter. The two surface portions  35 ,  36  border on each other at the partition line  37 . 
         [0100]    It is possible to select either a first portion  110   b , which extends between the height values h′ 11  and h′ 12 , and a second portion  111  (which extends between the height values h 21  and h 22 ), which have the same reach z 1  in the longitudinal direction Z. Or it is possible to select a first portion  110   a , which extends between the height values h 11  and h 12 , and the second portion  111 , the two portions  110   a  and  111  having different reaches z 1 , z 2  in the longitudinal direction Z. 
         [0101]    As is evident from  FIG. 10 , the foot segment  1  may be shaped such that adjacent wire sections interlock (linked configuration). The gradients of the side walls  38  of the foot segment are not subject matter of this application. 
         [0102]    In  FIGS. 11 and 12 , embodiments of the second blade-segment lateral surface  6  are illustrated. The second blade-segment lateral surface  6  shown in  FIG. 11  is approx. mirror-symmetric to the first blade-segment lateral surface  5 .  FIG. 12  shows a blade-segment lateral surface  6  which is slightly inclined relative to the height direction H. 
         [0103]      FIG. 13  shows that the at least one blade-segment surface  5  of the sawtooth wire showing the feature essential to the invention may also lie on the “other” side of the sawtooth wire  1 . 
       LIST OF REFERENCE NUMERALS 
       [0000]    
       
           1  Foot segment 
           2  Base area of foot segment 
           3  Lateral surface of foot segment 
           4  Blade segment 
           5  First blade-segment lateral surface 
           6  Second blade-surface lateral surface 
           7  Exterior surface of blade segment 
           8  Tooth 
           9  Rounded transition area between blade segment and foot segment 
           10  First portion 
           11  Second portion 
           12  Tooth tip 
           13  Transition between first and second portions 
           14  First end point 
           15  Second end point 
           16  Third end point 
           17  First secant 
           18  Second secant 
           19  Perpendicular dropped to the base of the foot 
           20  First end point 
           21  Second end point 
           22  First secant 
           23  Third end point 
           24  Fourth endpoint 
           25  Second secant 
           26  Infinitesimally small first surface portion/first point 
           27  Tangent to the first surface portion 
           29  Infinitesimally small second surface portion/second point 
           30  Tangent to the second surface portion 
           31  Curved contour of the blade-segment lateral surface 
           32  Contour of the blade-segment lateral surface, which is made up of two planar surface portions 
           33  First planar surface portion 
           34  Second planar surface portion 
           35  Steeper planar surface portion 
           36  Flatter planar surface portion 
           37  Dividing line between the steeper and the flatter planar surface portions 
           38  Side walls of the foot 
           110   a  First portion 
           110   b  First portion (alternative) 
           111  Second portion 
         Z Longitudinal direction 
         B Lateral direction 
         H Height direction 
         B max  Overall breadth of blade segment 
         b 11  Upper lateral value of first portion 
         b 12  Lower lateral value of first portion 
         b′ 11  Upper lateral value of first portion (alternative) 
         b′ 12  Lower lateral value of first portion (alternative) 
         b 21  Upper lateral value of second portion 
         b 22  Lower lateral value of second portion 
         H max  Overall height of blade segment 
         h max  Maximum height of blade segment 
         h min  Minimum height of blade segment 
         h 11  Upper height value of first portion 
         h 12  Lower height value of first portion 
         h′ 11  Upper height value of first portion (alternative) 
         h′ 12  Lower height value of first portion (alternative) 
         h 21  Upper height value of second portion 
         h 22  Lower height value of second portion 
         h 3  Further height value 
         z 1  First longitudinal reach value 
         ′z 2  Second longitudinal reach value 
         α 1  Angle between the first portion and the perpendicular dropped to the base 
         α 2  Angle between the second portion and the perpendicular dropped to the base 
         α 3  Angle between the first and second portions