RU2137869C1 - Metal cord and metal cord manufacture method, metal cord fabric and apparatus for deforming reinforcing member of metal cord - Google Patents

Abstract

FIELD: reinforcement for elastomeric products. SUBSTANCE: metal cord has reinforcing members, each twisted at predetermined pitch. Projection on plane perpendicular to longitudinal central axis of metal cord of each reinforcing member is curved, with radius of curvature varying from maximum to minimum value. Curved line is extending lengthwise through at least one twisting pitch. Curved line of at least one reinforcing member is made convex. Microspaces defined between curved reinforcing members and adjoining reinforcing members serve to receive rubber, which may penetrate into them. Method for manufacture of metal cord having at least one reinforcing member involves bending at least one reinforcing member, whose definite curved line has curvature radius varying between maximum and minimum values; putting this member together with other members so that distance between two minimum curvature radii of mentioned predetermined curved line measured along longitudinal central axis is different from half the pitch of reinforcing member, or predetermined curved line is different from curves circumscribed by other members. EFFECT: wider operational capabilities and enhanced reliability in operation.

Description

 The present invention relates to steel cord and metal cord fabric for reinforcing elastomeric products, such as rubber tires, conveyor belts, synchronizing belts of polyurethane or rubber, hoses, mandrels, etc.

 The present invention also relates to a method for producing metal cord for reinforcing rubber products and to a device for deforming a reinforcing element of metal cord.

State of the art
One of the main requirements for steel cords is the complete penetration of an elastomer, such as rubber. This means that rubber should be able to penetrate the cord between its constituent elements and fill all possible gaps in order to reduce friction corrosion and stress between the elements and to prevent moisture from moving along the cord, which can lead to significant corrosion and significantly reduce the life cord service and rubber product.

 Solutions have already been proposed that provide cords having good permeability to rubber. For example, the solution proposed in US-A-4258543 and US-A-4399853 consists in preliminary mechanical shaping of steel monofilaments constituting a metal cord outside their elastic base in such a way that the resulting metal cord acquires an open shape: due to the plastic deformation of steel threads along the length Such metal cords appear "macrogaps", which guarantee the penetration of rubber into the cord. The considered steel cords, however, have a very significant drawback: in order to guarantee the full penetration of rubber, a high degree of plastic deformation and, therefore, a large degree of openness are required. This leads to the production of steel cords having too large a diameter of the cord and too high elongation at partial load (UFN), which can lead to structural instability of twisted cords. When embedded in the tire’s tire layer, such steel cords may adversely affect the directional stability of the tire and its service life.

 Patent Application EP-A-0462716 proposes a solution to the problem of structural instability of cords described above. This application proposes a steel cord having steel threads that are deformed in such a way that they take the form of a spiral with a pitch that is less than the pitch of the steel cord, and with a spiral diameter that is slightly larger than the diameter of the thread. Due to the fact that the spiral pitch of such a deformed spiral steel thread is smaller than the pitch of the metal cord, more than one micro-gap opens on one bend. The term "microgap" is used in the present description to determine the difference between the above-mentioned concept of "macrogap". Micro-gaps are smaller than macro-gaps, but their number is greater. The dimensions of the micro-gaps are significantly lower than the pitch of twisting of the metal core. Due to the presence of such micro-gaps, rubber can completely penetrate into the metal cord, while such a metal cord does not have the previously mentioned drawback - too large diameter of the cord and too high elongation at partial load. However, spiral filaments are obtained using deforming fingers driven by an external force, which must rotate at a speed more than two times higher than the rotation speed of a double twisting machine twisting a metal cord. This method is a fairly energy-intensive and expensive production method.

 In yet another prior art, US Pat. No. 5,020,312 discloses another method for deforming part or all of the steel filaments constituting a metal cord in order to obtain a metal cord with good permeability to rubber. Part or all of the steel threads pass between the surfaces of the teeth of a pair of elements similar to gears, so that they acquire a zigzag shape. The distances between two teeth of elements similar to gears can be selected in such a way that in this case, on one bend of the steel cord, it is also possible to obtain more than one micro-gap between the steel threads. As a result, full penetration of the rubber is also guaranteed in the absence of a relatively large elongation at partial load. Two gear-like elements are not driven by external forces, but by the action of the steel threads themselves. Thus, this method is less energy intensive and less expensive. However, such an implementation of the method for producing metal cord also has a drawback: the tooth-like elements can flatten the threads to some extent, which can lead to damage to steel threads, especially a thin coating layer (usually copper or zinc with a thickness much less than 1 micron), and / or abrasion of the gear-like elements themselves. Damage to the coating of steel threads can significantly reduce the fatigue resistance and adhesion of these steel threads.

SUMMARY OF THE INVENTION
The aim of the present invention is to provide a steel cord, which does not have the disadvantages characteristic of prior art steel cords. Another objective of the present invention is to provide a steel cord with full permeability to rubber and with low UCH, upon receipt of which there is no damage to its constituent elements and the production of which does not require large expenses.

 Another objective of the present invention is to provide a metal cord with increased bending resistance and increased resistance to repeated tensile loads.

 According to a first aspect of the present invention, there is provided a metal cord comprising at least one reinforcing element and having a longitudinal central axis.

 Each element is twisted with a twisting step into a cord and has a projection onto a plane perpendicular to the longitudinal axis. These projections have the shape of a curved line. At least one of these curves is a convex curve with a radius of curvature that varies from maximum to minimum. The cord is also characterized by the following features: the distance between the two minimum radii of curvature of the above convex curve, measured along the longitudinal central axis, differs from half the pitch of the element that creates the convex curve, or at least one curve differs significantly from other curves.

 The term "metal cord" does not mean that all the constituent elements must be steel, but means that steel elements make up most of the cord. Other elements, such as nylon or aramid, can also be used as reinforcing elements or filler elements.

 The term "element" refers to both single yarns and veins consisting of a large number of steel monofilaments. There are practically no restrictions on the specific form of elements. It is convenient when the elements have an almost circular cross section, but the use of elements with flat, rectangular or oval cross sections is not excluded.

 The term "reinforcing element" refers to an element (monofilament or core) that makes a significant contribution to increasing the total breaking load of steel cord. The term "reinforcing element" does not apply to the covering thread, since the covering thread does not contribute to an increase in the breaking load on the metal cord. In this regard, we can point out the difference between the claimed steel cord and the metal cord described in the application P-A-63-110002, in which the projection of the covering thread only forms a convex and polygonal curve on a plane perpendicular to the longitudinal axis of the steel cord.

 The term "step" refers to the step of twisting a separate reinforcing element of the cord. A cord can have more than one torsion step: for example, a cord with two layers around a rod has one torsion step for the structure of the rod, one torsion step for the intermediate layer and another torsion step for the outer layer. The specific value of the twisting steps can vary from a few millimeters, for example from 5 mm to an infinite amount. In the latter case, the corresponding reinforcing elements are not twisted. In the case where the cord has only one reinforcing element, the pitch is also equal to an infinite value.

 Sign (II), that is, a substantially different curve, means that either the amplitude or phase, or the amplitude and phase of this curve is significantly different from the amplitude or phase of other curves.

 Distinctive features (I) and (II) clearly define the difference between the inventive cord from the cord of the prior art, which is described in application EP-A-0363893. EP-A-0363893 discloses a cord including all the features of a restrictive part. In this cord, all three to six steel strands form a convex elliptical curve in a plane perpendicular to the longitudinal axis of the cord. The distance between the two maximum radii of curvature of these ellipses, measured along the longitudinal axis of the cord, is equal to half the pitch of the twist of the cord, and the projection of all three to six strands essentially forms the same ellipses. This means that all threads run parallel to each other and that, as a result, micro-gaps do not form.

 Preferably, in the inventive cord, the distance between the two minimum radii of curvature is less than half the pitch of the element that creates a convex curve. This is necessary in order to exclude the receipt of a corrugated cord with too high an arc height.

 Typically, a convex curve represented by the projection of at least one reinforcing element onto a plane perpendicular to the longitudinal axis takes the form of an approximately polygon with rounded edges and is equal in length to the twisting step of the corresponding element. This polygon can be a triangle, a quadrangle, a pentagon, a hexagon, etc.

 The specified convex curve can give all the composite reinforcing elements of the cord or only part of them.

In a first embodiment of the inventive cord, the reinforcing element is a steel core that includes a plurality of individual steel threads. Examples of such cords are the following multi-core designs:
- 3 x 3, which means three cores with three threads each;
- 4 x 4, for example, in the modification with high elongation (WU);
- 4 x 2, which means four cores with two strands in each, for example, in a modification with extension (Y);
- 4 x (1 + 5), which means four cores, where each includes a core thread and five covering threads;
- 7 x 3;
- 3 x 7, for example, in the modification with high elongation (WU);
- 7 x 4;
- 4 x 7, for example, in the modification with high elongation (WU);
- 7 x 19;
- 19 + 7 x 7, which means a core core of 19 threads and seven covering cores each of 7 threads;
- 7 x 31;
- 1 x 3 + 5 x 7.

 In accordance with the present invention, the projection of the entire core onto a plane perpendicular to the longitudinal axis of the cord has the shape of a convex curve in order to allow the penetration of rubber between the wires. However, each core may contain one or more threads, the projection of which, in turn, also has the shape of a convex curve to ensure the penetration of rubber between the individual threads inside the core.

In a second embodiment of the inventive cord, the reinforcing element is a separate steel thread. Examples of such inventive cords are:
- 1 x (where n represents the number of threads, which takes values from one or more to five or less);
- l + m (where l corresponds to the number of threads in the rod, and m - to the number of covering threads around the rod, for example 1 + 6, 3 + 9, 3 + 6, 3 + 7, 2 + 7, 2 + 8, 3 + 8 );
- l + m + n (where l corresponds to the number of threads in the core, m - the number of threads in the intermediate layer around the core and n - the number of threads in the outer layer, for example, 1 + 6 + 12, 3 + 9 + 15, 3 + 8 + 13, 1 + 4 + 10);
- l x n SS) - the so-called compact cord, where all n threads have the same twisting pitch and the same twisting direction, with n taking values from six to twenty seven).

 If the inventive cord is 1 x 2-, 1 x 3-, 1 x 4- or 1 x 5-cord, then each individual steel thread has an extension at partial load with a tensile force of 50 N, which differs by no more than 0, 20%, and preferably not more than 0.10% (absolute values and non-relative values) from the UCH of each other steel thread, regardless of whether the projection of the steel thread is in the form of a convex curve. This feature, namely, that the cord consists only of threads for which UCH values are within a small interval, provides structural stability of the cord. The cord described in the application EP-A-0462716 does not have this feature, since the spiral-shaped filaments have an RFI significantly larger than the non-spiral filaments, and since not all the filaments of this cord are spiral-shaped. The cord described in US Pat. No. 5,020,312 has this feature only when all the constituent strands are deformed to a zigzag shape. This applies to UCHN at the thread level.

 As for the UCH at the cord level, the claimed 1 x 2-, 1 x 3-, 1 x 4 or 1 x 5-cords preferably have UCH-cord less than 0.30%, and preferably less than 0.25%, for example less 0.20%. As shown above, such a low UFN value at the cord level also contributes to the structural stability of the cord.

 UCHN both at the cord level and at the level of threads is defined as the increase in the length of the test sample (cord or thread), which is the result of a certain force (usually 50 N) from a certain preliminary stretching (usually 2.5 N) upward. Elongation is expressed as a percentage of the initial length of the sample.

 If the inventive cord is a 1 x n SS compact cord, then its cross-section is characterized by a densified configuration of the cross-sectional surfaces of individual threads. According to such a cross-section, the cord can be divided into combinations of three strands each, where three adjacent strands form a triangle delimiting the central void space. If the three threads of each such combination are mutually in contact with each other, then the rubber cannot penetrate into the central empty space and moisture can move along this cord along the entire cord. Therefore, in accordance with a particular embodiment of the inventive cord, at least one thread of each such combination has a convex curve projection so that micro-gaps between the three threads are formed and allow the rubber to penetrate into the central void during vulcanization.

 In accordance with a second aspect of the present invention, there is provided a fabric comprising weft and warp. The weft or warp or weft and warp are at least partially made of steel cord in accordance with the first aspect of the present invention.

In accordance with a third aspect of the present invention, there is provided a method of manufacturing a steel cord having a longitudinal axis and consisting of reinforcing elements, each of which is twisted with a twisting step into the above cord. The inventive method includes the steps of:
- bending of at least one of the elements to thereby obtain at least one element, the defined curve of which has a radius of curvature that varies between the maximum and minimum;
- the introduction of at least one element together with other elements with the formation of the above steel cord.

The method also differs in one or two of the following features:
(I) the distance between the two minimum radii of curvature of the curve, measured along the longitudinal central axis, is different from half the pitch of the element, which creates a convex curve; or
(Ii) a certain curve is significantly different from the curves described by other elements.

In accordance with a fourth aspect of the present invention, there is provided a device for deforming a reinforcing member of a steel cord. The inventive device includes a housing having a Central axis and a peripheral surface. The housing rotates around a central axis when the reinforcing element is fed at an angle of at least 90 ^° along its peripheral surface. The peripheral surface has a radius of curvature that varies between maximum and minimum in order to give the reinforcing element that passes along it a curve with a radius of curvature that varies between maximum and minimum.

The inventive metal cord can be manufactured mainly in two ways:
1) the inventive device, which gives the shape of a convex curve of the projection of the element, does not rotate with a twisting device (although it rotates around its axis), and the twisting device is a single twisting machine or double twisting machine, which makes individual steel elements rotate around their longitudinal axes;
2) the inventive device, which gives the shape of a convex curve of the projection of the element, rotates with a twisting device (as well as around its central axis) and the twisting device does not cause individual steel elements to rotate around their longitudinal axes; An example of such a twisting device is a cylindrical twisting machine.

 In both cases, a plastic compression zone and a plastic tension zone can be created in the cross section of the element, at least with the smallest radius of curvature.

 In the first case, the compression zone and the tension zone remain motionless with respect to the steel element. Steel thread rotates around a central axis.

 In the second case, the steel element itself does not rotate around its central axis, but the compression zone and the tension zone rotate around the steel element along the length of this element.

Brief Description of the Drawings
In more detail, the invention can be illustrated using the following drawings, where
in FIG. 1 shows a stage in which at least one of the elements of the inventive cord is subjected to bending in accordance with the inventive method;
in FIG. 2a and 2b schematically show another embodiment of the invention in which at least one element of the inventive cord is bent in accordance with the claimed method;
in FIG. 3a and 3b respectively represent a front view and a side view of a reinforcing element of the inventive cord, which has been processed in accordance with the claimed method;
in FIG. 4 shows a cross section of the inventive steel cord containing steel wires as a reinforcing element;
in FIG. 5 shows a cross section of the inventive 1x4 metal cord containing steel threads as reinforcing elements;
in FIG. 6 shows a curve of elongations at partial load for the inventive 1x4 metal cord;
in FIG. 7a, 7b, 8a, 8b, 8c and 9 show cross-sections of the inventive steel cords;
in FIG. 10 is a schematic representation of the claimed fabric;
in FIG. 11a and 11b schematically show how measurements are taken that determine the differences between the prior art cords and the claimed cords;
in FIG. 12, 13, 14, and 15 show the YZ curves of the inventive cords; and
in FIG. 16, 17, and 18 show the YZ curves of prior art cords.

Description of a preferred embodiment of the invention
In accordance with FIG. 1, a cold drawn steel thread 100 with a diameter of 0.28 mm extends from the top of the inventive deforming device 102. This deforming device 102 includes a series of deforming fingers 104 that are firmly connected to the deforming device 102. The deforming device 102 is characterized, along with other features, with a circle diameter D that limits all deforming fingers 104, as well as the number of deforming fingers 104. Diameter D determines the UCH. For yarn 100 with a diameter of 0.28 mm, the diameter of the deforming fingers 104 is less than 5 mm. Deforming fingers having a diameter of more than 5 mm result in a too small tensile strength, which is necessary in order to completely close the cord. For yarns with a diameter of 0.28 mm, the diameter of the deforming fingers is preferably 2 mm or more. Deforming fingers with a diameter of less than 2 mm should lead to too large a decrease in the tensile strength of the steel thread due to too high local deformations.

 In a more general case, a suitable range of values for the diameter of the deforming fingers depends on the tensile strength and on the diameter of the element to be deformed. The higher the tensile strength of the element, the smaller the diameter of the deforming fingers, and vice versa. The smaller the diameter of the element, the smaller the possible diameter of the deforming fingers, and vice versa.

 The diameter of the deforming finger determines the minimum spatial (three-dimensional) radius of curvature of the deformed thread. This minimum spatial radius of curvature is larger than the diameter of the deforming finger, since there is some stretching during twisting after deformation. The maximum spatial radius of curvature can take on an almost infinite value, since the deformation between the deforming fingers is not so great. It should be understood that the radii of curvature referred to in the claims are two-dimensional or planar radii of curvature in the YZ plane and, therefore, they have a much smaller value.

 The entire deforming device 102 is mounted so that it can rotate, but without using an external energy source. The deforming device 102 is driven by the thread 100 itself. There is no slipping between the thread 100 and the deforming device 102, so the wear of the deforming device 102 is limited, and the steel thread 100 is not damaged. This is mainly before the cord prior art described in US patent US-A-5020312. As a result of passing around a special deforming device 102, the thread 100 is bent in a certain way: the radius of curvature varies from the minimum at the level of the deforming fingers 104 to the maximum between the deforming fingers 104. Removing the tensile force from the thread so bent in this way no longer leads to the so-called impression of an almost round shape , but leads to an impression 106 having approximately the shape of a polygon with rounded edges. The rounded edges of the polygon correspond to the minimum radii of curvature, while the sides of the polygon correspond to the maximum radii of curvature. The minimum radius of curvature is determined by the diameter of the deforming fingers 104, and the length of the sides of the polygon is determined by the distance between the deforming fingers 104.

 Another deforming device may be provided, which is structurally different from the deforming device shown in FIG. 1, but which provides similarly deformed threads. For example, a single rotating deforming finger 102 made of hard metal with a cross-section in the form of a polygon with rounded edges 108 and sides 110 (Fig. 2a) or elongated shape (Fig. 2b) can also be used to deform a steel thread according to the method of the present invention .

 Thus deformed steel thread 100 is then twisted using a double twisting machine with other steel threads, which may be deformed in the same way or may be undeformed, with the formation of a cord. This results in a steel thread 100, which is shown in FIG. 3a (side view) and in FIG. 3b (front view). The X axis is parallel to the longitudinal and central axis 112, while the Y axis and the Z axis lie in a plane perpendicular to the central axis 112. It can be seen that in FIG. 3b also shows a substantially polygon with rounded edges, not a circle (it should be understood that the scale in the Y- and Z-directions is much larger than the scale of the X axis). The radius of curvature of this thread 100 varies between two extreme values: from the minimum at the point of highest curvature to the maximum at the point of least curvature. As a result of rotation of the yarn 100 around its longitudinal axis, the radius of curvature of such a yarn is always directed along the central axis 112 of the cord and, therefore, along the length of the cord. This means that the polygon has a convex shape. In other words, after deformation, after twisting and after removal of all external loads, the zone of plastic direction of the steel thread is always radially inward, while the zone of plastic compression is radially outward.

 This is the main difference from the thread, which is subjected to deformation between two gear-like elements described in US patent US-A-5020312; The zigzag shape of the steel thread has a bending radius that constantly changes direction. This leads to the fact that the front view (in the YZ plane) has a convex-concave shape.

 In the general case, and theoretically, at a distance between two minimum radii of curvature, which is equal to one third of the twist step, a triangle forms, with a distance between the minimum radii of curvature equal to one fourth of the twist step, a quadrangle, etc.

 In FIG. 4 shows a cross-section of a multi-strand 7 x 19 steel cord, intended, along with other possible applications for reinforcing conveyor belts. The metal cord 114 includes a core strand 116, which is surrounded by six covering veins 118. The core strand 116 consists of a core filament 120, six intermediate filaments 122 surrounding the core filament 120, and twelve outer filaments 122 surrounding the intermediate filaments 128.

 In order to achieve full penetration of the rubber between the cores 116 and 118, one or more of the cores may undergo a deformation operation, which is described above for a single thread 100. Thus, the deformed cores form a certain convex curve in the YZ plane, which leads to the creation of a large number of micro-gaps between them and other veins and provides effective penetration of rubber.

 In FIG. 4, as well as in FIG. 5, 7a, 7b, 8a, 8b, 8c and 9 of the yarn that underwent the warping process shown in FIG. 1, and which form a certain convex curve in the YZ plane, have a cross-hatching, and they are called "specially deformed threads", while other threads are shaded in the same direction.

 Returning to FIG. 4, it should be noted that to ensure complete penetration of rubber into each core 116, 118, the following guidelines of the present invention can be used: three of the six intermediate threads 122, 128 are specially deformed threads and alternate with other threads of the intermediate layer of each core 116, 118 ; six of the twelve outer threads 124, 130 are specially deformed threads and alternate with other threads of the outer layer of each core 116, 118.

 In FIG. 5 shows a cross-section of a steel cord 114 in accordance with the present invention, which has one core. The inventive cord 114 consists of a specially deformed thread 100 and three "normal" steel threads 132. In order to obtain structural stability of the steel cord 114, in which all (four) threads are the same length, the three "normal" steel threads 132 are also plastic deformed (although not in a special way in accordance with the present invention). That is why in FIG. Figure 5 shows the gaps even between steel threads 132. These gaps, which are actually macro-gaps, are, however, within acceptable limits due to the straightening operation of the cord thus obtained. The straightening process reduces the UFN and improves the arc of the metal cord.

 In FIG. 6 shows the elongation curve at partial load 134 of the inventive 1 x 4-cord. It should be emphasized that the point 136, at which the straight section extends from the upper part of the curve - UCHN 134, lies above the initial voltage of 20 N. This means that the point 136, where the individual threads of the steel cord come together and where the penetration of rubber is no longer possible, lies above the original voltage of 20 N, which is usually used when embedding steel cord in rubber. In other words, with an initial voltage of 20 N, the penetration of rubber into the cord is still guaranteed.

 In FIG. 7a and 7b show a cross-section of two embodiments of a 1 + 6 cord according to the present invention. The metal cord 114 includes a core thread 138 and six covering threads 140, 140 ′ that surround the core thread 138. In the embodiment of FIG. 7a, only the core thread 138 is a specially deformed thread, while the other threads 140 were not subjected to special deformation. In the embodiment of FIG. 7b, three yarns of six covering yarns 140 'are specially deformed yarns, while core yarn 138 and other yarn yarns 140 were not subjected to special deformation. Specially deformed filaments 140 'alternate with normal filaments of layer 140.

 In FIG. Figure 8a shows a cross section of an SS or SZ twisted 3 + 9 cord, but not its compacted modification, Cord 114 includes a three-strand core 142 surrounded by a nine-strand layer 144. Three core strands 142 are specially deformed steel threads covering 144 are normal. Thus, there is no central empty space between the three core threads 142, and rubber may surround each individual thread 142, 144.

 In FIG. 8b shows a cross section of a 1 x 12-CC cord in a sealed modification, and FIG. 8c shows a cross section of a 1 x 10-CC cord in a compacted version. The core threads 146, 150 may or may not be larger in diameter than the cover threads 148, 152. The core threads 146, 150 are specially deformed threads, and other threads are normal. For each possible combination of three threads, which in cross section forms a triangle of adjacent threads, at least one thread is a specially deformed thread so as to exclude the appearance of a central empty space and to ensure full penetration of the rubber.

 In FIG. 9 shows a cross section of a 1 x 19-SS cord in a sealed version. The core thread 154 may or may not be larger in diameter than the other threads 156, 158. Three of the six intermediate coating threads 156 'are specially deformed threads and alternate with the normal threads 156 in the intermediate layer. Six of the twelve outer threads 158' are specially deformed filaments and in the outer layer alternate with normal filaments 158.

 The present invention is not limited to the examples of cords described above, but can be applied to other types of steel cord in which penetration of rubber can be a problem.

 In accordance with FIG. 10, the inventive cord can also be used as an element of fabric, for example, to reinforce conveyor belts. Weft elements 160 or warp elements 162 or both are metal cord, which includes special deformed steel threads.

Example 1
Four steel cords are manufactured and tested in accordance with the present invention:
- N 1: 4 x 0.28 cord with one specially deformed thread;
- N 2: 4 x 0.28-cord with two specially deformed threads;
- N 3: 4 x 0.28-cord with three specially deformed threads;
- N 4: 4 x 0.28-cord with four specially deformed threads.

 Although it has been found that it is possible to use a large twist pitch for these specially deformed threads, all of the above cords 1-4 have a pitch of 12.5 mm.

 The special deforming device 102, which is used in this example, has six deforming fingers 104 with a diameter of 2 mm each.

The table at the end of the description lists the results. To assess the penetration of rubber, a cord sample 12.7 mm long with an initial tensile strength of 20 N is embedded in a small rubber bar, which is then held at a pressure of 1 bar (105 N / m ² ). Pressure drop is recorded. A decrease in pressure indicates the degree of penetration of the rubber. No pressure drop means full penetration of the rubber.

 The penetration of rubber in all four embodiments of the invention is complete, regardless of the relatively low elongation at partial load at 50 N: all UCH values remain below 0.25%.

Example 2
In a second example, the two inventive cords are compared with prior art cords in terms of resistance to repeated bending and resistance to repeated tensile loads.

The following cords were tested:
1) the inventive 4 x 0.28-cord with four specially deformed threads and a twisting step of 16 mm;
2) the claimed 4 x 0.28-cord with four specially deformed threads and a twisting step of 12.5 mm;
3) a dense 4 x 0.28-cord, that is, a cord in which in the cross section all the threads are in contact with each other, the twisting step is 12.5 mm;
4) open 4 x 0.28-cord, that is, the cord in accordance with US patent US-A-4258543, the twisting step is 12.5 mm;
5) 4 x 0.28-cord, in which one thread is previously deformed to a spiral shape in accordance with the application EP-A-0462716, twisting step - 12.5 mm;
6) 4 x 0.28-cord, in which one thread has a zigzag shape in accordance with US patent US-A-5020312, twisting step - 12.5 mm;
7) 4 x 0.28-cord with four threads having a zigzag shape in accordance with US patent US-A-5020312, twisting step - 12.5 mm;
8) 2 + 2 x 0.28-cord in accordance with US patent US-A-4408444, the pitch is infinite and 12.5 mm.

 Resistance to repeated bending loads is measured by repeated bending along a wheel with a diameter of 26 mm of a rubberized cord sample with a tensile force of 1200 MPa until the cord breaks. The tests are carried out twice, once without pre-conditioning the test sample with water and once with pre-conditioning the sample with water. Such conditioning (humidification) with water is carried out by attaching one side of the test sample, where a piece of cord protrudes from the rubber, for 5 minutes to a water pipe with a water pressure of 1.5 bar (approximately 1.5 atm).

 Resistance to repeated tensile loads is measured when a rubberized cord of tensile stress is applied to the sample, which periodically changes between 880 MPa - x% from 880 MPa and 880% MPa + x% from 880 MPa. The initial value of the amplitude x is 50%, i.e. 440 MPa. After 100,000 cycles, the amplitude x increases by 10%, etc. to complete destruction of the cord. This test is repeated three times.

 The inventive cords 1) and 2) are particularly characterized by a very high resistance to repeated bending and the fact that this high resistance does not decrease after preconditioning the rubberized cord with water.

 The resistance to repeated tensile loads of the inventive cords 1) and 2) is higher than or equal to the resistance of the cords of the prior art.

 In FIG. 11a and 11b schematically illustrate equipment that is used to distinguish between cords of the prior art and the inventive cords.

To this end, a sample of steel thread 100 with a length of approximately 10 cm is released from the twisted cord without plastic deformation of the steel thread 100. A sample of steel thread 100 is placed horizontally between the fixed points 166 and 168 with a slight tension, which is sufficient only to keep the thread in a horizontal position and to exclude its deformation at least in the middle part of the sample. If the thread is not installed horizontally, soft correction is possible. Then, a sample of steel filament 100 is carefully studied in the longitudinal X-direction using a KEYENCE LS3034 laser head, which consists of a laser emitter 170 and a laser radiation receiver 172. Using the laser head 170, 172, the distance between the reference level and the lowered side of the sample of filament 100 is measured ( = distance Z). The measurement is carried out using the KEYENCE LS3100 element. After measuring the distance Y for the entire length, the yarn sample is rotated 90 ^° and the distance Y is measured for the entire length. Using a personal computer, a YZ curve is obtained.

 The difference test described above is carried out on seven 1 x 4 x 0.28 metal cords that have a twist pitch of 16 mm. Four of these seven metal cords are cords according to the present invention, and their YZ curves are shown in FIG. 12-15, the three metal cords are metal cords of a prior art and their YZ curves are shown in FIG. 16-18.

 In FIG. 12 shows the YZ curve of a specially deformed steel thread extracted from the claimed 1x4x0.28 metal cord, and only for the distance between two fixed points 166 and 168, namely, for a length X = 17 mm. The maximum value in both the Y direction and the Z direction is +0.385 mm, and the minimum value in both the Y direction and the Z direction is -0.133 mm. The diameter D of the deformation device 102 is 10 mm, and the deformation device has six fingers 104 with a diameter of 3 mm and a distance between the fingers of 5 mm. Theoretically, the YZ curve should have the shape of a polygon with rounded edges 16 mm / 5 mm = 3.2 at one step of twisting the cord. More generally, the twisting step divided by the distance between the deforming fingers determines the shape of the polygon.

 Curve 178, which is shown in FIG. 8 almost takes the shape of an aligned triangle with three rounded edges. The alignment is a consequence of the straightening operation carried out on the cord after receiving it, and the three rounded ribs essentially correspond to the theoretically obtained coefficient 3.2. Thus, the curve is a convex polygon without concave sections.

 In FIG. 13 shows a YZ curve of a specially deformed steel thread extracted from the claimed 1x4x0.28 metal cord for a length X = 16.9 mm. The diameter D of the deforming device 102 is 8 mm, and the deforming device has nine fingers 104 with a diameter of 2 mm and a distance between the fingers of 2.5 mm. Theoretically, the YZ curve should have the shape of a polygon with rounded edges 16 mm / 2.5 mm = 6.4 at one step of twisting the cord. Curve 180, which is shown in FIG. 13 has the shape of an aligned hexagon with six rounded edges. Alignment is the result of a straightening operation carried out on the cord after receiving it, and six rounded edges almost correspond to the theoretically calculated coefficient 6.4.

 In FIG. 14 and 15 show other YZ curves of specially deformed steel threads taken from the inventive steel cords.

 All FIG. 12-15 have a common feature: they show more or less aligned polygonal shapes with rounded edges. Their shape, with the exception of measurement errors, is always convex and never concave. This is the result of a special deformation method in accordance with the invention, in which a tension zone is created on each cross section, which is directed to the central axis of the cord. It should be noted that the polygon does not have to be closed at every twisting step.

 In FIG. 16 shows a YZ curve of a 186 cord in accordance with US Pat. No. 4,285,543. In this case, the deforming device consists only of a cylindrical deforming device, which gives a thread with a constant radius of curvature, therefore, the YA curve should theoretically have the shape of a circle. The shape of curve 186 is very close to the shape of a circle.

 In FIG. 17 shows a YZ curve 188 of a prior art cord in accordance with EP-A-0462716 (helical deformation). Curve 188 has a number of concave sections 190.

 Finally, in FIG. 18 shows a YZ curve 192 of a prior art cord according to US Pat. No. 5,020,312 (zigzag shape). In this case, curve 192 also has a series of concave portions 194.

 Concave sections 192 and 194 are a consequence of the fact that the location of the extension zone along the length of the thread varies. At one point, the stretch zone is radially inward, and at another position, radially outward.

 Obviously, the invention described above is applicable to all types of threads that can be used to reinforce elastomers, regardless of their exact diameter, specific steel composition, their tensile strength or coating.

 In this regard, it should be noted that steel threads typically have a diameter in the range from 0.03 mm to 0.80 mm, preferably from 0.15 mm to 0.45 mm. Steel threads have a composition that is characterized by the following values: the carbon content is from 0.70 to 0.98%, the manganese content is in the range from 0.10 to 1.10%, the silicon content is from 0.10 to 0.90%, while the sulfur and phosphorus content is limited to 0.15%, preferably 0.010%; additional elements such as chromium (up to 0.20 - 0.40%, copper (up to 0.20%), nickel (up to 0.30%), cobalt (up to 0.20%) and vanadium (up to 0.30%) can be included.

 The final tensile strength of the threads Rm depends on their diameter: for example, 0.2 mm thread with normal tensile has Rm above about 2800 MPa, 0.2 mm thread with high tensile has Rm above about 3400 MPa, 0.2 mm thread with ultra-high tensile has Rm above about 3600 MPa, 0.2 mm ultra-high tensile thread has an Rm above about 4000 MPa.

 Steel threads are coated with a layer that promotes adhesion of rubber. Copper alloy coatings such as brass (or with a low copper content of 63.5%, or with a high copper content of 67.5%), or complex brass coatings (nickel + brass, brass + cobalt) are especially recommended (these coatings can even be applied by plasma spray technology).

Claims (16)

 1. A metal cord containing a plurality of reinforcing elements, each of which is twisted with a twisting step into a cord, the projection onto a plane perpendicular to the longitudinal central axis of the metal cord of each reinforcing element, has a curve shape with a radius varying from maximum to minimum, passing through at least one step of twisting along the length, characterized in that the curve of at least one reinforcing element is convex, while between the convex-curved reinforcing element and other adjacent micro-gaps are formed with reinforcing elements, which serve to penetrate rubber into them.  2. The metal cord according to claim 1, characterized in that the convex curve is similar to a polygon.  3. The metal cord according to claim 1, characterized in that all the reinforcing elements form a convex curve.  4. The metal cord according to claim 1, characterized in that the reinforcing element is a core consisting of many steel threads.  5. The metal cord according to claim 1, characterized in that the reinforcing element is a steel thread.  6. The steel cord according to claim 5, characterized in that it contains 3 to 5 steel threads.  7. The steel cord according to claim 6, characterized in that each of the threads of the specified cord has an elongation at partial load at a tensile stress of 50N, excellent by no more than 0.20% of the elongation at partial load of each other steel thread.  8. The metal cord according to claim 6, characterized in that it has an elongation at partial load with a tensile stress of 50 N below 0.3%.  9. The metal cord according to claim 5, characterized in that it contains more than five steel threads.  10. The metal cord according to claim 9, characterized in that the threads have the same pitch of twisting and the same direction of twisting.  11. The metal cord of claim 10, characterized in that in each combination of three cord threads that form a cross-section of a triangle of adjacent threads, at least one of these threads gives a convex curve.  12. The metal cord according to claim 1, characterized in that the twisting step equals an infinite value.  13. The metal cord according to claim 5, characterized in that it contains only one steel thread.  14. Metal cord fabric consisting of weft and warp, characterized in that the weft or warp or weft and warp are at least partially made of steel cord according to claims 1 to 13.  15. A method of obtaining a metal cord having a longitudinal axis and containing at least one reinforcing element twisted with a twisting step into a cord, characterized in that it involves folding at least one of the elements to obtain at least one element, a certain curve of which has a radius of curvature varying between the maximum and minimum, the installation of at least one element together with other elements with the formation of the specified metal cord, while the distance between the two minimum The total radii of curvature of the specified specific curve, measured along the longitudinal central axis, differs from half the pitch of the element forming the specified specific curve, or the specified specific curve differs from the curves described by other elements. 16. A device for deforming a reinforcing element of a metal cord, comprising a housing having a central axis and a peripheral surface, the housing being rotatable around its central axis when the reinforcing element is pulled at an angle of at least 90 ^° along said peripheral surface of the housing, characterized in that the peripheral surface has a radius of curvature varying between the maximum and minimum so as to give a reinforcing element that extends along the above peripheral surface, the shape of a curve with a radius of curvature that changes between maximum and minimum.

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