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Lifetime improvement of radial tires with the help of steel cords.



Modern radial radial /ra·di·al/ (ra´de-al)
1. pertaining to the radius of the arm or to the radial (lateral) aspect of the arm as opposed to the ulnar (medial) aspect; pertaining to a radius.

2.
 tires are expected to deliver a long service life without losing their integrity, even, at times, under improper
In mathematics
  • Improper rotation
  • Improper integral
  • Improper fraction
  • Improper prior
  • Improper distribution
  • Improper point
  • Improper limits
Other
  • Improper English
  • Improper motion
  • Improper noun
 conditions. Steel cord reinforcement reinforcement /re·in·force·ment/ (-in-fors´ment) in behavioral science, the presentation of a stimulus following a response that increases the frequency of subsequent responses, whether positive to desirable events, or  is used at the belt area of all fires and carcass carcass, carcase

1. the body of an animal killed for meat. The head, the legs below the knees and hocks, the tail, the skin and most of the viscera are removed. The kidneys are left in and in most instances the body is split down the middle through the sternum and the vertebral
 area of track tires, basically due to the excellent properties and favorable fa·vor·a·ble  
adj.
1. Advantageous; helpful: favorable winds.

2. Encouraging; propitious: a favorable diagnosis.

3.
 cost/performance ratios it offers. However, it is essential to select the steel cord type designed to meet those requirements dictated dic·tate  
v. dic·tat·ed, dic·tat·ing, dic·tates

v.tr.
1. To say or read aloud to be recorded or written by another: dictate a letter.

2.
a.
 by the function in the tire. Long service life would require a high resistance against corrosion and resistance against fretting fret·ting
n.
A hole, or worn or polished spot made on metals by abrasion or erosion.
 in the case of carcass cords of track tires which easily receive a few retreads until they are discarded dis·card  
v. dis·card·ed, dis·card·ing, dis·cards

v.tr.
1. To throw away; reject.

2.
a. To throw out (a playing card) from one's hand.

b.
 for good. The first part of this 'article deals with the corrosion aspect by comparing two cords for passenger tire belt reinforcement, and explains the underlying differences in cord designs. The second part handles the fretting issue by giving comparative data on two popular types of truck carcass cords, and introduces a new type developed using organic elements The so-called organic elements are molecule fragments often encountered in organic chemistry. For ease of notation, they are marked similarly to elements.

Me CH3 methyl
Et CH2CH3 ethyl
Ac acetyl (not acetate!) CH2CO, e.g. acetate AcO-
Tf F3CSO2 trifyl
 in the cord.

Steel cord and corrosion resistance

Steel cord is prone to corrosion in the case of extended exposure to moisture. Most rubber types or rubber compounds, on the other hand, are very good insulators, and they provide excellent protection against corrosion. It is, therefore, very important to have a good rubber coverage around all of the filaments forming a steel cord, especially for belt reinforcement where the chance of exposure to moisture is higher. Actually, extensive research at Bekaert has proven that the "rubber penetration" is by far the most effective protection against corrosion.

Rubber penetration and evaluation methods

Rubber penetration is dependent on compound and cord characteristics, as well as the tire production process conditions:

* Compound viscosity;

* compound scorch time;

* vulcanization vulcanization (vŭl'kənəzā`shən), treatment of rubber to give it certain qualities, e.g., strength, elasticity, and resistance to solvents, and to render it impervious to moderate heat and cold.  pressure; and

* cord geometry geometry [Gr.,=earth measuring], branch of mathematics concerned with the properties of and relationships between points, lines, planes, and figures and with generalizations of these concepts. .

As a mere steel cord producer, Bekaert can only influence the last factor and therefore indulge in·dulge  
v. in·dulged, in·dulg·ing, in·dulg·es

v.tr.
1. To yield to the desires and whims of, especially to an excessive degree; humor.

2.
a.
 in activities to improve the cord geometry without adversely "affecting the other properties. It is also very important to have evaluation techniques that have a good repeatability, correlation with the reality and efficiency. The following tests have proven themselves in all these respects.

Visual evaluation of rubber coverage

The filaments are carefully unraveled and the rubber coverage degree was evaluated. The decisive factor Noun 1. decisive factor - a point or fact or remark that settles something conclusively
clincher

causal factor, determinant, determining factor, determinative, determiner - a determining or causal element or factor; "education is an important determinant of
 is the status of core or internal filaments. It is a more valuable test when used to evaluate samples in a comparative manner.

Photos of cord cross sections

Sections (4-8 per lay length) are cut of the rubber embedded Inserted into. See embedded system.  and vulcanized vul·ca·nize  
tr.v. vul·ca·nized, vul·ca·niz·ing, vul·ca·niz·es
To improve the strength, resiliency, and freedom from stickiness and odor of (rubber, for example) by combining with sulfur or other additives in the presence of heat
 cords and close-up photos are taken. The existence and size of air pockets indicate the extent of rubber penetration. This test is also more meaningful for comparison purposes.

Pressure drop across embedded cords

It is a kind of air-wicking test known in the tire industry. The air at a certain pressure is applied at one end of the rubber embedded and vulcanized cord sample, and the pressure drop between up and down streams is measured after one minute. This test is quite severe when the sample lengths are short (e.g., lay length-10%). A high number of samples cut consecutively from a long block of embedded cord further improves the reliability of the test. The results are not only useful for ranking of comparative samples, but also as separate absolute values.

Comparative fatigue testing of embedded cords (dry and wet conditioned)

The rubber embedded cold samples are kept at dry and wet conditions for a certain time and then fatigue tested until failure. The fatigue performance of steel cords at humid hu·mid  
adj.
Containing or characterized by a high amount of water or water vapor: humid air; a humid evening. See Synonyms at wet.
 conditions deteriorates considerably. The drop in fatigue level of a sample should indicate existence of moisture around the steel, and therefore less than full rubber penetration. The results as percentages of wet vs. dry fatigue levels are used to rank the samples for the degree of rubber penetration.

The preparation of samples in all of these tests is very important. For instance, the applied tensions during vulcanization can change the results for many types of cords. It is also crucial to use the right amount of compound for the mold mold, name for certain multicellular organisms of the various classes of the kingdom Fungi, characteristically having bodies composed of a cottony mycelium. The colors of molds are caused by the spores, which are borne on the mycelium.  cavity cavity /cav·i·ty/ (kav´i-te)
1. a hollow place or space, or a potential space, within the body or one of its organs.

2. in dentistry, the lesion produced by caries.
.

Betru process

The cord construction design parameters, such as the number of filaments, the filament filament, in astronomy: see chromosphere.  diameters, lay lengths and directions, as well as the preformation pre·for·ma·tion  
n.
1. The act of shaping or forming in advance; prior formation.

2. A theory popular in the 18th century that all parts of an organism exist completely formed in the germ cell and develop only by increasing in
 type and degree are important to determine the cord geometry for good rubber penetration.

The Betru process shapes the filaments very lightly with polygonal pol·y·gon  
n.
A closed plane figure bounded by three or more line segments.



po·lygo·nal adj.
 pro-formers to generate micro gaps along the cord without excessively opening the cord in the radial direction. These gaps do not close under moderate calendering calendering, a finishing process by which paper, plastics, rubber, or textiles are pressed into sheets and smoothed, glazed, polished, or given a moiré or embossed surface.  tensions. and good rubber penetration is still achieved. This process does not affect the basic efficiency of cord making as it does not require an additional production step. It is a combination of on-line tooling for plastic deformation plastic deformation,
n any irreversible deformation of tissues.
 and the instrumentation instrumentation, in music: see orchestra and orchestration.
instrumentation

In technology, the development and use of precise measuring, analysis, and control equipment.
 for consistency control. It is also verified that the process only brings a negligible This article or section is written like a personal reflection or and may require .
Please [ improve this article] by rewriting this article or section in an .
 loss on properties such as tensile strength tensile strength

Ratio of the maximum load a material can support without fracture when being stretched to the original area of a cross section of the material. When stresses less than the tensile strength are removed, a material completely or partially returns to its
 and fatigue level.

Characterizing the cords

It is not possible to visually distinguish the cords made with the above process from the classical cords. There is, however, a technique developed based on Keyence laser scanning which characterizes the shape of the filament along its length. This device follows the path of the filament, measures the distance from a fixed point in other two directions and creates a (y, z) graph. Figures 1 and 2 demonstrate the difference between two passenger belt cords; 3X0.30 Betru and 3X0.30 O.C. The Betru processed filaments have non-round travel paths and are always with convex Convex

Curved, as in the shape of the outside of a circle. Usually referring to the price/required yield relationship for option-free bonds.
 portions, whereas the classical cords have round paths and sometimes with concave Concave

Property that a curve is below a straight line connecting two end points. If the curve falls above the straight line, it is called convex.
 portions as demonstrated in a competition cord (figure 3).

[FIGURES 1-3 OMITTED]

Results

The mechanical properties of the subject cords given in table 1 show that the breaking load of Betru cord is only slightly less, whereas the fatigue level is considerably higher than the open cord. Other clear differences are on the diameter and elongation elongation, in astronomy, the angular distance between two points in the sky as measured from a third point. The elongation of a planet is usually measured as the angular distance from the sun to the planet as measured from the earth.  potential of the open cord, which are considerably higher than Betru cord. High wet/dry fatigue ratio of the latter is also an indication of good rubber penetration.

For extensive rubber penetration evaluation, an experiment has been designed with these two cords by making strips at a Steelastic unit and vulcanizing test pieces in the laboratory. Two levels of Steelastic let-off tension (1 kg and 2 kg), and four levels of vulcanization tension preload preload /pre·load/ (pre´lod) the mechanical state of the heart at the end of diastole, the magnitude of the maximal (end-diastolic) ventricular volume or the end-diastolic pressure stretching the ventricles.  (0, 10, 30 and 50 N) were included in the design, and the rubber penetration was evaluated using pressure drop and cross section porosity porosity /po·ros·i·ty/ (por-os´it-e) the condition of being porous; a pore.

po·ros·i·ty
n.
1. The state or property of being porous.

2.
 check methods.

The results of the pressure drop method, shown in table 2, clearly indicate that the increasing Steelastic and vulcanization tensions lead to some pressure drop (all figures larger than zero) across 3x0.30 O.C., indicating the existence of a capillary capillary (kăp`əlĕr'ē), microscopic blood vessel, smallest unit of the circulatory system. Capillaries form a network of tiny tubes throughout the body, connecting arterioles (smallest arteries) and venules (smallest veins).  channel (incomplete rubber penetration): whereas the 3x0.30 Betru has 0% pressure drop at all samples. This point is also proven on the cross-section photos shown in figure 4 (only some of the pictures are shown here due to space limitations).

[FIGURE 4 OMITTED]

Since all sections are similar, only the 50 N vulcanization tension, the most critical situation is shown hem. Despite these high tensions, the cords are not closed and the rubber could totally surround all the filaments.

In the aged adhesion adhesion /ad·he·sion/ (ad-he´zhun)
1. the property of remaining in close proximity.

2. the stable joining of parts to one another, which may occur abnormally.

3.
 tests, plies plies 1  
v.
Third person singular present tense of ply1.

n.
Plural of ply1.
 were prepared on a drum with a winding tension of 30 N, two-ply patches have been vulcanized and one inch (25.4 mm) width strips have been cut for ply/ply separation measurements (strip adhesion):

* Cord end count in ply (mathematics, data) ply - 1. Of a node in a tree, the number of branches between that node and the root.

2. Of a tree, the maximum ply of any of its nodes.
: 70 ends/dm;

* vulcanization temp.: 160[degrees]C;

* vulcanization time: 20 minutes;

* ply/ply separation speed: 125 mm/min.

Adhesion results are shown in table 3.

Conclusions

Rubber penetration of 3X0.30 O.C. is highly dependent on processing and vulcanization tensions of the cords, which can not be modified easily due to other requirements.

Aged adhesion results (table 3) also confirm the superiority of 3X0.30 Betru cords with respect to 3X0.30 HT O.C., in case the rubberized cords are exposed to a salt water solution.

Optical diameter of Betru cord is smaller requiring less compound in ply making, which results in weight savings in the tire.

Steel cords and fretting resistance

Fretting and evaluation methods

Fretting is the material erosion at the contact areas of filaments due to their relative movement during flexing of cords, such as in the carcass of truck tires. This is a long term, dynamic phenomenon. For instance, large multi-layer cords having S/Z type lay directions have point contacts, which result in serious fretting. Compact cords, on the other hand, have line contacts and better fretting performance.

There is an established laboratory simulation test called the endless belt test. The sample cord is wound around a drum to form a belt with a certain width, rubberized and vulcanized. This endless belt, then, is mounted around two pulleys, which rotate at a constant speed (1,200 cycles/minute), exerting bending stresses to the sample. Additionally, an axial axial /ax·i·al/ (ak´se-al) of or pertaining to the axis of a structure or part.

ax·i·al
adj.
1. Relating to or characterized by an axis; axile.

2.
 load can also be applied. The test conditions of a fretting evaluation are:

* Pulley pulley, simple machine consisting of a wheel over which a rope, belt, chain, or cable runs.

A grooved pulley wheel like that used for ropes is called a sheave.
 diameter: 143 mm;

* axial load: 400 N/ [mm.sup.2]; and

* test duration: stop after 40-100-150 million cycles.

Evaluation of fretting damage:

* Loss of breaking load in filaments

* loss of bending ductility ductility, ability of a metal to plastically deform without breaking or fracturing, with the cohesion between the molecules remaining sufficient to hold them together (see adhesion and cohesion). Ductility is important in wire drawing and sheet stamping.  in filaments (dynamic bending test); and

* visual analysis/erosion in filaments.

Compact cords vs. multi-layer cords

As can be seen in table 4, large multi-layer cords having S/Z type lay directions have point contacts, which result in serious fretting. This is demonstrated by the property losses of filaments, as well as the visual evaluation results. Compact cords, on the other hand, have line contacts and better fretting performance. Existence of a spiral wrap heavily contributes to fretting, as it cuts into the outside layer filaments and causes important damage to the cord.

Further improved contact cords

The fretting performance of compact cords can only be improved if the contacts between the filaments can be eliminated or minimized with the help of a medium such as rubber or plastic which is placed there. The cords mentioned below were designed based on this idea and tested at an endless belt machine, with the normal compact cord as reference, for fretting evaluation:

* 0.22 PF+6X0.175+(6X0.175+6X0.15) cc NT Betru 12.5/Z PF = polymer filament in the core; smaller filaments (0.15 mm) are used intermittently in·ter·mit·tent  
adj.
1. Stopping and starting at intervals. See Synonyms at periodic.

2. Alternately containing and empty of water: an intermittent lake.
 in addition to Betru pre-forming to increase the rubber penetration.

* 0.20+6X0.15PC+12X0.175 cc NT Betru 12.5/Z; PC = polymer coated steel filaments; polymer coating on two-layer filaments eliminate metal/metal contacts between same layer filaments as well as those between two- and three-layer filaments. Table 5 shows the results and mechanical properties. Figure 6 shows cord cross-section photos before and after endless belt testing.

[FIGURES 5-6 OMITTED]

Conclusions

Extended endless belt test results (table 6, figure 6) clearly indicate a superior fretting performance for the newly designed cords having organic elements in the core with respect to normal compact cords which are already very resistant to fretting.

These cords also offer considerably good tenacity (breaking strength/linear density), compactness (breaking strength/ cord diameter) and the fatigue resistance, which is essential for the carcass usage (table 5).

The cords with organic elements were made on an experimental basis only. With the information available at this moment, the version with a polymeric polymeric /poly·mer·ic/ (pol?i-mer´ik) exhibiting the characteristics of a polymer.

pol·y·mer·ic
adj.
1. Having the properties of a polymer.

2.
 filament in the core is to be preferred, considering the economics of cord making.
Table 1--mechanical properties

Cord construction                   3X0.30 HT   3X0.30 HT
                                         O.C.       Betru

Lay direction/length, -/mm           S / 16      S / 16
Diameter, mm                          0.92        0.71
Linear density, g/ m                  1.68        1.68
B. Load (Bare), N                      660         650
Elongation at break, %                 2.9         2.3
E Modulus, kN/[mm.sup.2]               204         203
LLE (low load elongation), %          0.54        0.19
3 P Ben. stiffness, N/[mm.sup.2]       266         283
Compression resist., N/[mm.sup.2]      500         496
Impact force, N                        180         200
Impact energy, Nm                     0.77        0.86
Bending fatigue
Dry, cycles to failure               18,272      24,674
Wet, cycles to failure               13,081      25,813
Wet/dry fatigue level, %               71          104

Table 2--pressure drop results

Pressure drop (%)

                      3X0.30 OC

          1 kg Steelastic    2 kg Steelastic
          tension            tension

Preload   0   10   30   50   0   10   30   50
          0    0    9   35   0    0   33   11
          0    0    3    3   0    0   19   13
          0    0   19   19   0    0   46   12
Avg.      0    0   19   19   0    0   33   12

                      3X0.30 Betru

          1 kg Steelastic    2 kg Steelastic
          tension            tension

Preload   0   10   30   50   0   10    3   50
          0    0    0    0   0    0    0    0
          0    0    0    0   0    0    0    0
          0    0    0    0   0    0    0    0
Avg.      0    0    0    0   0    0    0    0

Table 3--adhesion results

                       3X0.30 HT O.C.           3X0.30 HT Betru

Strip adhesion     Separation     Rubber     Separation     Rubber
                     force      coverage *     force      coverage *
                      (N)          (%)          (N)          (%)

Initial adhesion      202           90          232           90

Aged adhesion ** salt water exposure

1 week                188           60          229           80
2 weeks               193           70          233           75
3 weeks               185           65          201           75

* Rubber coverage around the cords
100%: No exposed cord surfaces--very good adhesion
0%: Bare cord surfaces/no rubber on cords--bad adhesion

** 20% NaCl solution at room temperature

Table 4--fretting evaluation--endless belt test

Construction        Layer    Loss of       Loss of       Visual
number of cycles            filament      filament   evaluation
                            breaking       bending     filament
                              load %   ductility %      erosion

3+9+15X0.175+1          3          0                          1
5/10/16/3.5 SSZS        9          1                          1
40X[10.sup.6]          15          8                 2 (3 wrap)

3+9+15X0.175            3         16            18            2
5/10/16 SSZS            9         13            40       2-3(4)
100X[10.sup.6]         15         21            37            1

3+8+13X0.175            3          1            11          1-2
5/10/16 SSZ             8         16            46            4
100X[10.sup.6]         13          6            22            1

0.20+18 X0.175 cc       1          7             6            2
12.5 Z                  6          6            16          1-2
100X[10.sup.6]         12          8            17            1

CC: compact cord
Visual evaluation criteria

Code:              0       1         2           3
Fretting level:   None   Little   Moderate   Significant

Code:               4         5
Fretting level:   Heavy   Very heavy

Table 5--results--mechanical properties

                              0.20+18X0.175cc NT   0.22PF+6X0.175+
                                  12.5 mm/Z        (6X0.175+6X0.15)
                                                        cc NT
                                                    Betru 12.5mm/Z

Tensile test
Breaking load (N)                   1,331               1,048
Elongation at break (%)              2.5                 1.7
Cord diameter (mm)                   0.90                0.83
Linear density (g/m)                 3.64                3.13
Tenacity (N-m/g)                     365                 335
Compactness (N/mm)                  1,479               1,263
Bending fatigue test *
Cycles to fracture - Avg.           77,179              94,768
                  -St. Dev.         7,533               8,319
Bending stiffness
Ek (N-mm)                            191                 152

                              0.20+6X0.15PC+
                              12X0.175cc NT
                              Betru 12.5mm/Z

Tensile test
Breaking load (N)                 1,146
Elongation at break (%)            1.9
Cord diameter (mm)                 0.91
Linear density (g/m)               3.51
Tenacity (N-m/g)                   326
Compactness (N/mm)                1,259
Bending fatigue test *
Cycles to fracture - Avg.         88,371
                  -St. Dev.       7,233
Bending stiffness
Ek (N-mm)                          171

* Bekaert internal test

Table 6--fretting evaluation--extended endless belt test

Construction              Layer   Loss of      Loss of       Visual
100X[10.sup.6] cycles *           filament    filament     evaluation
                                  breaking     bending      filament
                                   load %    ductility %    erosion

0.20+18X0.175 cc NT         1        7            6            2
12.5 mm/Z                   6        6           16           1-2
                           12        8           17            1
0.22PF+6X0.175+             1        /            /            /
(6X0.175+6X0.15)            6        4            2            1
cc NT Betru                 6        0           12            1
12.5 mm/Z                   6        1            8            1

0.20+6 x 0.15PC+            1        -3          -6            1
12X0.175 cc NT              6        2            5            1
Betru 12.5 mm              12        3           10           1-2

* Corresponds to almost 500,000 km running time of a
truck tire in service.
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No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2003, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

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Author:Basaran, Murat
Publication:Rubber World
Date:Sep 1, 2003
Words:2641
Previous Article:Dynamic testing of elastomeric materials.
Next Article:New reinforcing materials for rising tire performance demands.



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