TYRE CORD PROCESSING.pptx

About Tyre cord processing

1. TYRE CORD REINFORCEMENT Dr.K.RAVICHANDRAN Professor Department of Rubber and Plastics Technology MIT Campus Anna University Chennai

2. Tyre is a Structural Composites Reinforcement of Textile Fabrics in rubber composites : Impart loading carrying capacity Serve as a medium of stress transmission Provide dimensional stability Determines basic strength and durability Also Carbon black / Silica in rubber composites improves rubber modulus

3. Requirements for Reinforcing Materials Rubber composites used for Dynamic flexing Applications ( Tyre Carcass): Modulus Tensile strength Dimensional stability Fatigue resistance Hysteresis Adhesion

4. Requirements for Reinforcing Materials Rubber composites used for Tyre Belt Applications (In addition to carcass): Compression modulus Moisture c ontent Chemical stability Impact strength Less brittleness

5. Tyre Cords

6. Truck Radial Tyre Casing Components

7. Tyre Cord Constructions

8. Hysteresis loops of four different textile cords, loaded by the force of 20 N and then unloaded

9. Cord Size Comparison

10. Tyre Structure The term tyre structure defines the number, location and dimension of the various components used in it’s composition. The primary components which govern the performance of the tyre are the casing plies, bead construction, belts, sidewall and tread . The secondary components are chaffers, flippers and overlays, which are strips of fabric located in the bead and crown areas, protect the primary components by minimising stress concentration

11. CORD ANGLE ANGLE OF THE CORD PATH TO THE CENTRE LINE THE TYRE, THE PREDOMINANT FACTOR AFFECTING THE TYRE SHAPE OR CONTOUR The term equilibrium shape or neutral- contour shape is used in conjunction with cord angle to describe specific tire dimensions

12. Functions and Requirements of Tyre cords Functions Maintain durability against bruise and impact Support inertial load and contain inflating gas Provide tire rigidity for acceleration, cornering, braking Provide dimensional stability for uniformity, ride, handling . Cord Requirements Large length to diameter ratio , eg , long filaments High axial orientation for axial stiffness and strength Good lateral flexibility (low bending stiffness) Twist to allow filaments to exert axial strength in concert with other filaments in the bundle Twist and tire design to prevent cord from operating in compression.

13. Ideal cord properties for a radial tire belt High tensile strength High bending modulus High stiffness High compression modulus High adhesion to rubber Good resistance to chemical attack

14. Tyre Fabrics History

15. History of Tyre Reinforcement

16. Cord reinforcement for different Tyres

17. Reinforcement and Tyre Properties

18. Tyre Cord Applications

19. Textile Terminology Cord Structure: consisting of two or more strands when used as plied yarn or an end product . Denier: The weight of cord expressed in grams per 9000 meters. EPI: Ends of cord per inch width of fabric. Fibers: Linear macromolecules orientated along the length of the fiber axis. Filaments: Smallest continuous element of textile, or steel, in a strand. Filling: Light threads that run right angles to the warp (also referred to as the "pick ") that serves to hold the fabric together. LASE: Load at a specified elongation or strain

20. Textile Terminology Length of lay: Axial distance an element or strand requires to make a 360 ~ revolution in a cord. Ply twisting: Twisting of the tire yarn onto itself the required number of turns per inch; two or more spools of twisted yarn are then twisted again into a cord: for example , if two 840-denier nylon cords are twisted together, an 840/2 nylon cord construction is formed ; if three 1300-denier polyester cords are twisted together,they give a 1300/3 cord construction. Rivit Distance: between cords in a fabric; high rivet typically describes a fabric with a low EPI.

21. Textile Terminology Tenacity: Cord strength, frequently expressed in grams per denier. Tex: Cord weight expressed in grams per 1000 meters. Twist: Number of turns per unit length in a cord or yarn; direction of twist can be either clockwise ("S" twist) or counterclockwise ("Z" twist); twist imparts durability and fatigue resistance to the cord, though tensile strength can be reduced. Warp: Cords in a tire fabric that run lengthwise. Weft: Cords in a fabric running crosswise. Yarn: Assembly of filaments.

22. Fabric reinforced in rubber Square woven linen fabric Cords embedded in rubber

23. Tyre Cord Construction To use the range of fibers for tire applications , the yarns must be twisted and processed into cords. First , yarn is twisted on itself to give a defined number of turns per inch, i.e ., ply twisting. Two or more spools of twisted yarn are then twisted into a cord . Generally, the direction of the twist is opposite to that of the yarn; this is termed a balanced twist .

24. Tyre Cord Construction

25. PLY TWISTING The plies are twisted on itself and with another ply before it is formed into a cord. The ply twisting directions are denoted by “Z” and “S ”. If the direction of twist is from right to left, then it is called “Z” twist and if the direction of twist is from left to right, then it is called “S” twist. Usually , the individual ply is twisted in the “z” direction and two plies are twisted together in “s” direction to form a cord

26. Designation of twist direction

27. PLY TWIST

28. Reasons for Twisting of Tyre Cord 1. Twist imparts durability and fatigue resistance to the cord, though tensile strength can be reduced. 2. Without twist, the compressive forces would cause the cord outer filaments to buckle. 3. Increasing twist in a cord further reduces filament buckling by increasing the extensibility of the filament bundle. 4. If the twist is irregular, the phenomenon of “bird caging” or filament un-winding can occur, where the cord is flexed during in-service tire rotation

29. Tyre Cord Twisting Durability reaches a maximum and then begins to decrease with increasing twist. This can be explained by the effect of stresses on the cord as the twist increases . As the twist increases, the helix angle or the angle between the filament axis and the cord axis, increases. In addition to twist, the cord size may be varied to allow for different strengths, depending on the application or tire line.

30. Twist multiplier The amount of twist relates to both tenacity and compression fatigue resistance. To obtain equivalent fatigue performance in a product when changing cord size, cords must be twisted to the same helix angle using a “twist multiplier” relationship: For the same material: Cord Atpi x √Cord A denier = Cord B tpi x √Cord B denier. [For example: Cord A of 2000/2 construction at 8 tpi would be equal to Cord B of 1000/2 at 11.3 tpi .] For different materials specific gravity must also be considered Cord Atpi x √Cord A denier/ √Cord ASpGr = Cord B tpi x √Cord B denier /√Cord B SpGr . [For example, an 840/2 nylon (1.14 SpGr ) at 11.0 tpi would have the same helix angle as a 1100/2 aramid (1.44 SpGr ) at 11.3 tpi .]

31. Ply Twisting

32. Weaving After twisting yarns into cords, 1000 to 1500 cords are woven into a coherent sheet using a very light “pick” fabric as the weft at a very low fill count of one to two picks per inch. Rolls of this fabric (which is about 1.5 to 1.75 meters wide - the practical width of rubber-cord calenders ) are transferred for further operations. The function of the pick is to maintain a uniform warp cord spacing during the downstream operations, such as, shipping, adhesive dipping and heat treating, calendering , tire building and lifting . The core ensures uniform cord distribution as the tire is shaped and the sheath holds the cord spacing during adhesive treatment and calendering but breaks readily during tire lifting and shaping .

33. Weaving

34. Weaving

35. Tyre Cord Construction Generally, three-ply cords have the greatest durability. After cable twisting, the cords are woven into a fabric, using small fill threads. These threads are also referred to as picks This weaving process introduces an additional construction variable, i.e., the number of cords per inch or EPI (ends per inch) that are woven into the fabric . High-end-count fabric gives greater plunger strength or penetration resistance . Low-end-count fabrics have more rivet (distance between cords) and give better separation resistance because of the greater rubber penetration around the cords. In addition, the weight savings may enable reductions in rolling resistance with equivalent tire strength factors

36. Tyre Cord Construction Normally all fabric will have a balanced twist which means that S and Z twists will be equal. The usually given twists in turns per meter are 840/2 —- 472 TPM (turns per metre) 1260/2 — 394 TPM 1680/2 — 335 TPM by twisting, we lose tensile strength but gain flex fatigue resistance . Hence the twist factor must by decided by striking a compromise between tensile strength and flex fatigue resistance . By twisting, the cord acts as a single unit, and gains good abrasion resistance.

37. Tire cord processing Downstream cord processing of tire cords can profoundly influence tire performance and dimensional stability of the cords through the various environments D ipping , adhesive baking, heat stretching, relaxation, and tire vulcanization- is necessary to control and predict variations in such factors as tire size, tire uniformity, cord-to-cord uniformity, flat spotting, side-wall indentations, and creep during operation. Steel , aramid and rayon are minimally affected during cord processing while the thermoplastic fibers, nylon and polyester, must be very carefully controlled. The radial tire with its high-modulus restrictive belt has greatly alleviated many of the cord growth problems previously seen in bias tires, leading for example to tread groove cracking . A goal of process engineers concerned with dimensional stability when working with the thermoplastic cords is to maximize tensile modulus (often characterized by EASL - elongation at specified load) while minimizing thermal shrinkage. Care must be taken to optimize tensile strength and fatigue properties in these procedures.

38. Rayon and aramid cord processing The processing of these cords is relatively simple since they are thermally stable and do not change significantly in downstream operations . Rayon must be carefully protected from moisture regain at all processing stages, especially at roll ends to avoid uneven shrinkage across a fabric roll. An optimum treatment for processing rayon has been reported .Rayon cord made with a higher than specification twist is dipped in cord adhesive under relaxed conditions to open the twist for good dip penetration and to completely wet the cord with the aqueous adhesive. The cord is then tensioned to achieve the specification twist and dried at 130-150C before being baked under tension at 155-175C to cure the adhesive. Heat treatment for aramid 230-260C is generally at low tension (8.8cN/ tex ) and with very low stretch to standardize modulus. As with polyester, adhesive application is a two step procedure.

39. Nylon and polyester cord processing Thermoplastic fibers, such as nylon and polyester, are considered to be composed of a mixture of crystallites, extended (aligned) non-crystalline molecules, and amorphous “tie” molecules. Crystallization occurs principally during fiber drawing. Cord processing, carried out below the crystal melting temperature, modifies the non-crystalline portion. In the process of applying and baking a cord adhesive the amorphous portion of a thermoplastic cord will tend to become less oriented, resulting in shrinkage which will, in turn, adversely affect tire uniformity.

40. Heat treatment Heat treatment temperatures can cause polymer flow and molecular weight degradation. Heat treatment of nylon, for example, varies in temperature between 177 o C and 246 o C, between 7% and 16% stretch, and between 20 and 60 seconds residence time . For Polyester cord recommended a treatment temperature of 246 o C, 4% stretch in the first zone and 3% relaxation in the second zone, with 90 seconds residence time in both zones for optimum fatigue resistance . Nylon is generally used at 3-7% net stretch, and polyester at 0 - 4%.

41. S tretching Shrinkage is partially controlled by stretching the fabric in the heat-setting zone and relaxing it under controlled tension in a second zone. In general, higher relaxation results in lower shrinkage. Net stretch (the difference between stretch in the first zone and relaxation in the second) is often used as a measure of shrinkage and growth potential. This can be deceptive, however, for a number of reasons: Additional crystallinity can occur that will lower shrinkage and/or growth potential, Equilibrium orientation is seldom reached in allotted treatment times, especially with heavy cords

42. Nylon cords

43. Postcure inflation On release from the tire curing press, viscoelastic cords in the hot tire are almost completely free to shrink . Postcure inflation (PCI) is therefore employed to stabilize tire size and uniformity. All-steel or all-rayon tires do not require a postcure treatment. Because the postcure inflating equipment is expensive to install and maintain, some companies have minimized or eliminated PCI for their radial tires by predictive mold sizing, control of cord properties, and controlled cooling. The use of PCI entails the following: Passenger and light truck tires are automatically ejected from the press after the usual 12 to 24 minute cure time, depending on size, and then immediately loaded onto a postcure inflator which re-inflates the tire to 200 to 400 kPa (30 - 60 psi). This loads and stretches the hot cords. Post inflating controls the size, shape, uniformity, and growth of the finished tire. However , the results depend on the time, temperature and load applied to the cords during the inflation process. Moreover , the cords should be cooled evenly to below their glass transition temperature before release from the inflator

44. Postcure inflation Lim has reported on studies that simulate PCI and non-PCI conditions by measuring EASL (elongation at specified load - the inverse of modulus). For R ayon the modulus is constant for cords heated to 177C under 0.06N/ tex and cooled to RT with or without tension. No modulus change took place. Under the same conditions Nylon showed a 20% increase in modulus and PET a 30% increase. Equilibrium times for the cords were 30 minutes. A practical cooling time for factory tires is usually about two cure cycles. Also, it should be noted that uneven cooling, e.g., from one side to the other, can result in tire distortion, so that tires may be rotated during the PCI treatment. Skolnik has reported a “coefficient of retraction” for loaded cords in a simulated postcure inflation study. Cords were loaded to 0.9 g/den., heated to 165C, and cooled to various temperatures where the load was released. The coefficient of retraction (CR) is the percent length change per degree C.

45. Cord Construction Depending on the speed rating of the tire, the overlay can take one of several lay-ups, a) One layer or two layers b) Covering the immediate top belt c) Full belt coverage and partially extending over the shoulder wedge

46. RFL Formulations

47. one layer or ply of textile is used (as is generally the case) each ply will only contribute approximately 70-80% of its strength as measured before incorporation into the composite.

48. Designation: D 885 – 03 Standard Test Methods for Tire Cords, Tire Cord Fabrics, and Industrial Filament Yarns Made from Manufactured Organic-Base Fibers1

49. Choice of a textile cord Chemical composition of textile Cost per unit length and weight (cost in tire) Denier – filament size and strength Cord construction – number of yarn plies Cord twist Number of cords per unit length in ply Number of plies in the tire

50. Cotton Cotton is a natural fibre, consisting of the seed hairs of a range of plant species in the Mallow family (Genus Gossypium ). The plants are grown, mainly as an annual crop, in many countries around the world between latitudes 40°N and 40°S.

51. Cotton

52. Rayon Rayon is a man-made fibre, based on regenerated cellulose Rayon is used as a body ply cord or belt reinforcement made from cellulose produced by wet spinning. It is often used in Europe and in some run-flat tires as body ply material. Advantages: Stable dimensions; heat resistant; good handling characteristics. Disadvantages: Expensive; more sensitive to moisture; environmental manufacturing issues. Rayon is used in both carcass and belt of passenger radial tires but lacks strength for durable heavy-duty tires

53. Rayon Rayon - Tire cord strength has been improved 300% since its introduction by improved coagulation and heat treatment . The low- shrink, high-modulus, good-adhesion properties of rayon make it an excellent choice for use in passenger tires. However , rayon has lost market share to polyester due to higher cost and environmental concerns with production facilities. Rayon had historically been used in truck tires but has been displaced by nylon with higher strength and impact resistance. Rayon is used for racing tires and has gained renewed interest in the development of an extended-mobility self-supporting passenger tire.

54. Rayon

55. Nylon Nylon type 6 and 6,6 tire cords are synthetic long chain polymers produced by continuous polymerization/spinning or melt spinning. The most common usage in radial passenger tires is as cap, or overlay ply, or belt edge cap strip material, with some limited applications as body plies. Advantages: Good heat resistance and strength; less sensitive to moisture. Disadvantages: Heat set occurs during cooling ( flatspotting ); long term service growth .

56. Nylon Fabrics N ylon fabric comes in different deniers like 840/2, 1260/2, 1680/2, and 1260/3 . The nomenclature can be explained by taking an example. If we take 1260/2, it means that two plies make one cord (represented by the digit 2 in the denominator) and 9,000 meters of one yarn will weigh 1260 grams.

57. Flatspotting In instances where nylon 6 is used, the tire will show “flat spotting”, i.e., when the vehicle is parked, particularly in hotter environments, the loaded tire footprint will flatten. On start-up, the vehicle driver will experience severe vibration, due to this distorted section of the rotating tire. As the tire continues in service, the increase in operating temperature will allow the nylon 6 cords to relax and the temporary distortion in the tire may be mitigated. High-end tires tend to use overlays with a 1400 × 2 construction, whereas broad-market tires use overlay reinforcements, such as 840 × 2.

58. Nylon Cap ply Nylon finds use in the tire overlay or cap ply. When the new tire is cured, the nylon overlay will shrink, thereby locking the belts in place . Under high-speed tire service conditions, the belts show strong centrifugal forces but with a firmly positioned overlay, so that such forces are contained, the long-term durability of the tire is improved. The key properties for an overlay fabric are tensile strength and modulus, adhesion, shrinkage, and heat and fatigue resistance. For these reasons, nylon 6,6 is preferred

59. Polyester Polyester tire cords are also synthetic, long chain polymers produced by continuous polymerization/spinning or melt spinning. The most common usage is in radial body plies with some limited applications as belt plies. Advantages: High strength with low shrinkage and low service growth; low heat set; low cost. Disadvantages: Not as heat resistant as nylon or rayon

60. Polyester Polyester Tyre Cord Fabrics   are used as reinforcing materials for tyres and designed to keep tyres in shape and support vehicle weight, having a significant impact on tyre performance . Nylon has high strength and excellent fatigue resistance. However, owing to its low glass transition temperature and lower modulus, it is not suited for high-speed application. Polyester on the other hand, being superior to nylon tyre cord fabric in these respects, is preferred in radial and high-speed tyres. Polyester tyre cord fabrics are available in 1000/2,1300/2,1500/2 and 2000/2

61. Polyester General comments on cord usage in various types of tires Polyester – Polyester is the condensation polymerization product of ethylene glycol and terephthalic acid. Newer modifications resulting from increased molecular weight and revised processing are called DSP-PET (dimensionally stable PET), with 50% increased modulus and 50% reduced shrinkage, bringing it close to rayon for dimensional stability. It has become relatively inexpensive making it a good choice for passenger and small light truck tires. Polyester must be used with carefully designed rubber adhesion systems and carcass rubber compounds to prevent cord deterioration in use. Polyester cord is not recommended for use in high-load/high-speed/ high-temperature applications, as in truck, aircraft and racing tires, because of rapid loss in properties at tire temperatures above about 120C.

62. Aramid Aramid is a synthetic, high tenacity organic fiber produced by solvent spinning. It is 2 to 3 times stronger than polyester and nylon. It can be used for belt or stabilizer ply material as a light weight alternative to steel cord. Advantages: Very high strength and stiffness; heat resistant. Disadvantages: Cost; processing constraints (difficult to cut).

63. Aramid Aramid is a wholly aromatic polyamide. The most common commercial material is poly(p-phenylene terephthalamide ), eg , Kevlar™ or Twaron ™. Aramid cords have very high strength, high modulus, and low elongation. The relatively high cost has slowed adoption as a general radial belt material where steel cord is performing well. It is particularly suited where weight is important, such as in the belts of radial aircraft tires or in overlay plies for premium high-speed tires. In a multiply carcass construction, aramid’s low elongation will prevent the outer ply from adjusting to the average curvature, thus placing the inner plies into compression. This reduces the contribution of the inner plies to the total strength, but, more seriously, early failures of the inner ply are encountered due to the poor dynamic fatigue resistance of aramid in compression.

64. Glass fiber Glass fiber – fiber glass was introduced to the US tire industry in the 1960s with Goodyear’s development of a belted-bias tire. This tire was soon replaced by the radial tire, however. Some attempts were made to use fiber glass in the belts of radial tires but in spite of its excellent credentials, fiber glass quickly lost out to steel as the premier belt material. Premature failures were encountered, both in cold weather use and with inappropriate tread designs that put the top belt into compression . However, a review of its properties gives glass fiber an excellent rating as a belt material if proper tread design and latex adhesive dips are used. Its specific stiffness and strength are equal to those of steel, whereas the specific gravity is only 2.54 compared to 7.85 for steel. The initial modulus is 2150 cN / tex compared to 1500 for steel. Rubber adhesion is excellent with no problems with rusting due to water in the belt. Each filament of fiber glass is coated with a latex dip before the filaments are twisted into a yarn. It has been established that this latex must be formulated from a low glass transition polymer to prevent the premature glass breakage seen in the early glass fiber development

65. Polyethylene Naphthalate ( PEN) Polyethylene Naphthalate (PEN) - PEN is similar to the standard polyethylene terephthalate (PET) polyester, being a copolymer of ethylene glycol and naphthalic acid. This new textile has been developed by Allied-Signal (presently Honeywell High Performance Fibers) and is being evaluated for tires. Its properties have been reported by Rim . It is claimed to surpass DSP-PET for use in the carcass of passenger car tires, having lower shrinkage, higher modulus, and higher Tg (120C vs. 80C ). It also has potential as a restrictive overlay belt for light truck and high-speed passenger tires, replacing nylon overlays. A disadvantage is the high price, about 2.5 times that of polyester.

66. Chafer Fabrics Chafer Fabrics  are speciality fabrics used in manufacture of heavy duty tyres, specially to protect the side wall of tyres. The fabric is offered in both wicking and non wicking types in construction of 420, 840 and 1260 denier. It protects the tyre from damages during the fitting or removal operations by Rim and Wheel assembly, also by the tools during these operations .

67. Advantages Advantages It saves tyres from damages during fitting or removal operations by rim and wheel assembly, also by the tools used during these operations. It saves tyres bead area from chafing effects and damages caused by rim. It saves tyres carcass plies from damage from rim friction. Additionally, the chafer fabric should ensure that pressurized air inside the tubeless tyres does not wick through it. Our wide range of chafer fabric meets the performance requirements of all kinds of tyres, be it passenger tyres or light and heavy duty truck / bus tyres or aircraft tyre besides industrial and agricultural tyres.

68. Steel Cord Steel cord is carbon steel wire coated with brass that has been drawn, plated, twisted and wound into multiple-filament bundles. It is the principal belt ply material used in radial passenger tires. Advantages: High belt strength and belt stiffness improves wear and handling. Disadvantages: Requires special processing (see figure 1.16); more sensitive to moisture.

69. Bead wire Bead wire is carbon steel wire coated with bronze that has been produced by drawing and plating. Filaments are wound into two hoops, one on each side of the tire, in various configurations that serve to anchor the inflated tire to the rim

70. Bias cutting

71. Steel Cord

72. Shear Strain on Radial Tyre Belt (greater at the edges of the belt)

73. Change in Tyre Shape When Under Load

74. Gum Strips: These are different types of rubber strips, all made of the same compound, located at belt endings, ply endings, and other component endings, and serving as a transition compound between two different tire parts. They provide a modulus gradient, improve component-to-component adhesion, and minimize potential for crack formation and propagationThe

75. Cord-rubber adhesion The adhesion of rayon, nylon, polyester, and aramids has been reviewed extensively. Takeyama and Matsui (24) reviewed adhesives for rayon, nylon, and polyester. Solomon (25) updated this work in 1985 to include aramid adhesion and the effects of environmental exposure on degradation of adhesion. Chawla (17) summarized both cord processing and adhesive dip treatments. Dipping and baking of the adhesive is intimately tied in with cord stretching and relaxation procedures. There are many variations in cord dipping procedures, e.g., one-step vs two-step dipping, dipping in the tire-plant vs in the cord-plant, surface activation of the cord, etc. We consider here only the goal of using adhesives, general operating procedures, and potential problem areas. The prime goal of the cord adhesive is to avoid separation at the cord-adhesive interface, at the rubber-adhesive interface, or within the adhesive itself. This objective is achieved by using proper dipping procedures. Tire carcass failures that were initially attributed to failure at the adhesive interface were often shown on microscopic examination to be due either to fatigue failure of rubber close to the cord, caused by high stresses resulting from improper construction or irregular cord spacing, or to cord fatigue from excessive compressive stresses

76. Mechanism of cord-rubber adhesion It is generally accepted that the adhesive provides both chemical bonding between the rubber and the cord surface and by mechanical interlocking as the rubber penetrates within the cord interstices. The adhesive must also accommodate the large differences in the two materials: -high-polarity polymers in cords vs. low polarity of rubber - high modulus of cords vs. low modulus of rubber. -Good adhesive durability is achieved by minimizing the abrupt change in modulus at the cord-rubber interface by introducing an adhesive layer of intermediate modulus

77. Requirements for cord-to-rubber adhesives Good bonding to both cord and rubber Intermediate modulus between cord and rubber Rapid rate of bond formation High fatigue resistance in the cured adhesive No chemical deterioration of cord by the adhesive Compatibility with a range of rubber compounds No brittleness or flaking in processing

78. resorcinol-formaldehyde-rubber latex system ( RFL) The resorcinol-formaldehyde-rubber latex system (RFL) developed in the 1940s for use with nylon and rayon is still used throughout the tire industry. A synthetic 2-vinyl pyridine-butadiene-styrene copolymer latex, developed for nylon, has replaced the natural rubber latex originally used for rayon, in all modern dips. Resorcinol and formadehyde react in the dip to give a strong polar polymer with good adhesion the polar tire cord, while the rubber component of the latex provides good bonding to the rubber . RFL is used for rayon and nylon exclusively and as the outer dip for polyester and aramid cords . Typically, rescorcinol and formaldehyde are mixed and “matured” for up to 24 hours. The latex is blended and the cord is dipped before tensioning. Dip formulations contain 2 5% total solids and dip pickup is controlled to about 6 - 8%. The cord is then tensioned and baked. Complete total wetting of the cord is necessary to prevent spotty adhesion. Good dip penetration is important for good adhesion and cord compaction. Dip penetration of 2 - 3 filament layers is optimal.

79. Polyester and aramid polymers are much less reactive to standard RFL and must be pretreated to obtain good adhesion. A common practice is to employ a multistage dipping process . The cord is first dipped in an aqueous solution of a reactive chemical, such as an epoxide, e.g., the diglycidyl ether of glycerol or a blocked isocyanate , e.g., phenol-blocked polyisocyanate [“ Hylene MP”], along with a small amount of wetting agent to give uniform dip pickup. After tensioning and baking the cord is again dipped in a standard RFL for final baking and relaxation. Processing times through each of the steps is generally 30-60 seconds.

80. The dip formulation, amount of dip pickup and the curing conditions can all affect adhesion and must be optimized. Strict quality control must be implemented once optimum conditions are established. Problems that must be avoided are: inadequate wetting of the cord, inadequate dip pickup, excessive dip pickup (which can result in flaking off of the adhesive), or overbaking during heat treatment. Any of these conditions can reduce adhesion. The finished cord must be protected from nitrous oxides (if gas or oil heating ovens are used) and from exposure to sunlight, humidity, or ozone if the cords are stored or shipped before being calendered with rubber. The treated cords are generally protected by storing them in polypropylene cloth liners and sealing them in black polyethylene film

81. FABRIC PRODUCTION The most critical stage in preparing a cord or fabric for use in tires is fabric treatment, which consists of applying an adhesive under controlled conditions of time, temperature, and tension . Required properties are: 1.Adhesion for bonding to rubber 2. Optimization of the physical properties of strength, durability, growth, and elongation of the cord for tire application 3. Stabilization of the fabric 4. Equalization of differences resulting from the source of supply of the fiber

82. Processing consists of passing the fabric through a series of zones 1. Adhesive application zone or first dip zone 2. First drying zone 3. First heat treatment zone 4. Second dip zone 5. Second drying zone and then second heat treatment zone 6. Final cooling zone

83. To obtain optimum cord properties of strength, growth, shrinkage, and modulus, specific temperatures and tensions are set at various exposure times within the fabric processing unit . The temperature and tensions determine, in part, the ratio of crystalline and amorphous areas within the fiber, and the orientation of the crystallites, which, in turn, determines the physical properties of the cord . For example, polyester, when heated, tends to revert to its un-orientated form and the cord shrinks . Stretching the cord in the first heating zone and then allowing the cord to relax in a controlled manner in the second heat treatment zone, i.e., stretch relaxation, will control shrinkage

84. An increase in temperatures can decrease cord tensile strength and modulus but will improve fatigue life which may be necessary for some tire constructions. However, not all cord properties behave similarly with changes in processing conditions. It is thus necessary to determine the processing conditions that optimize the specific cord properties needed for the required tire end use. When two or more diametrically opposed properties have to be optimized, more complex processing operations could be required

85. CORD-TO-RUBBER COMPOUND ADHESIVE There are three aspects to adhesion of tire cord to the elastomer treatment: molecular, chemical, and mechanical. Molecular bonding is due to absorption of adhesive chemicals from the adhesive dip or elastomer coating onto the fiber surface by diffusion and could be achieved by hydrogen bonding and van der Waals forces. Chemical bonding is achieved through chemical reactions between the adhesive and the fabric and rubber, i.e., crosslinking and resin network formation. Mechanical adhesion is a function of the quality of coverage of the cord by the rubber coating compound; the greater the coverage, the better the adhesion. The fiber properties of primary importance to adhesion are reactivity, surface characteristics, and finish . Rayon has many reactive hydroxyl groups . Nylon is less reactive but contains highly polar amide linkages, whereas polyester is quite inert. Thus, an adhesive system must be designed for each type of fiber.

86. adhesive system must conform to a rigid set of requirements : 1. Rapid rate of adhesion formation 2. Compatibility with many types of compounds 3. No adverse effect on cord properties 4. Heat resistance 5. Aging resistance 6. Good tack 7. Mechanical stability The adhesive bond between the rubber and cord is achieved during the tire vulcanization cycle. The rate of adhesive formation should give maximum adhesion at the point of pressure release in the cure cycle