RUBBER COMPOUND (1): POLYMER

A tire is mainly made of "rubber" and cords. Rubber in this context means the rubber compound to be exact. The

compound is made by mixing polymer, reinforcement material, softener and various chemicals.

Different characteristics are required for every type of tire or tire part. For example, a TBR tire requires heat, wear

and cut resistance for the tread rubber, while the sidewall requires good weather resistance. Therefore many kinds of

rubber compounds are needed.

Polymers, their types, characteristics and uses, which all perform very important functions, are explained.

The main polymers used for tires are as follows:

1. Natural Rubber (NR)

2. Styrene Butadiene Rubber (SBR)

3. Butadiene Rubber (BR)

4. Isoprene Rubber (IR)

5. Halogenated Butyl Rubber

All of the above except natural rubber are synthetic.

1. Natural Rubber (NR)

NR is made from latex taken from rubber trees, mainly grown in Southeast Asia. Although there are now various kinds of synthetic rubber available, natural rubber is still used extensively in tires.

Characteristics of Natural Rubber

Advantage Disadvantage

Tear StrengthWear Resistance Impact ResilienceLow Heat Generation

Uniformity of qualityAging ResistanceFatigue ResistanceOzone Resistance

2. Styrene Butadiene Rubber (SBR)

SBR is now the most common synthetic rubber being used in tires. It is made by polymerizing Styrene and Butadiene together, it is also possible by changing styrene content and polymerization

Characteristics of Styrene Butadiene Rubber

process to make various types of SBR's with different characteristics. Advantage Disadvantage

ProcessabilityUniform qualityAging by heatFrictional Forc

Impact ResilienceHeat Generation

3. Butadiene Rubber (BR)

Like SBR, BR is a common synthetic rubber used in tires. However unlike NR or SBR there is less interaction among the molecules, and for this reason, a compound of BR only or high BR content has high flexibility but poor elongation resistance. BR however has good resistance to both wear and low-temperatures and therefore is generally used by mixing with either NR or SBR to compensate for its disadvantages.

Characteristics of Butadiene Rubber

Advantage Disadvantage

Impact ResilienceWear Resistance Low Temperature PropertyFatigue Resistance

Tear Strength

4. Isoprene Rubber (IR)

IR is produced by artificially synthesizing Isoprene which is a principle constituent of NR. Its characteristics are

naturally quite similar to those of NR. The main difference between the two being, that the quality of IR is more

consistent than NR since it dose not contain natural impurities. The downside however is the cost is higher than NR.

5. Halogenated Butyl Rubber

Halogenated Butyl Rubber is made by halogenating (adding chlorine or bromine) to Butyl Rubber. The molecular structure of Butyl Rubber gives a high air impermeability. Its disadvantage is it needs a long vulcanization time, however by halogenated the Butyl Rubber this can be overcome.

Characteristics of Halogenated Butyl Rubber

Advantage Disadvantage

High Air Impermeability Impact Resilience

Characteristics of Halogenated Butyl Rubber

Advantage Disadvantage

Ozone ResistanceFatigue Resistance

Heat GenerationAdhesion

Main Use for Tire

1 Natural Rubber (NR) General Use, TB Tread

2 Styrene Butadiene Rubber (SBR) PC Tread

3 Butadiene Rubber (BR) Sidewall

4 Isoprene Rubber (IR) Partially Used to Replace NR

5 Halogenated Butyl Rubber Inner Liner

Characteristics of Various Polymer

PolymerNatural Rubber /Isoprene Rubber

Styrene ButadieneRubber

ButadieneRubber

Halogenated ButylRubber

Impact Resilience

Tear Strength

Wear Resistance

Fatigue Resistance

Aging Resistance

Main Use for Tire

Weather Resistance

Ozone Resistance

High AirImpermeability

: Excellent    : Good   : Fair   : Inferior

Use for Tire

PC Tread(Cap)

Tread(Base)

Sidewall

Belt

Carcass Ply

Inner Liner

TB Tread(Cap)

Tread(Base)

Sidewall

Belt

Carcass Ply

Use for Tire

Inner Liner

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RUBBER COMPOUND (2): ANTIOXIDANTS AND WAXES

As commonly known, rubber is a main constituent of tires and, regardless whether natural or synthetic, it suffers

aging like any other substance as a result of usage over a long period. Aging is recognized as deterioration in

physical properties. Namely, aged rubber becomes either hardened or softened causing cracking or loss of adhesion.

The main causes of rubber aging in tires are Ozone, Heat and Deflection. To protect rubber from aging, Antioxidants

and Waxes are generally used in the rubber compounding.

Functions of Antioxidants and Waxes as Anti-Aging Agents in Tires

Cause Antioxidant Wax

Ozone

Antioxidants come out to the surface of the tire where chemical reactions take place with the attacking ozone. Thus ozone is rendered inactive to age rubber.*

Waxes migrate to the tire surface and form a thin film covering the surface. Thus the rubber is physically protected from the attack of ozone.**

Heat/Deflection

Tire deflection and heat generation in the tire weaken and finally cut the polymer (rubber molecule) linkage which results in aging. Antioxidants in the rubber work to chemically bond with polymers in order to prevent the polymer linkage from being extensively cut.

Wax has no effect against heat and deflection aging.

*When you find the tire surface "reddish", this means Antioxidants have come out to the surface and effectively fought

against ozone.

**When you see the tire with a "whitish" color, this is evidence of a layer of wax protecting the tire from ozone.

(However the effectiveness of the wax layer is lost once the tire becomes rolling because the wax layer is broken.)

Type and Property Requirements of Antioxidants

Tire parts where wax is used are as follows: Tread, Sidewall, Rim Strip and Tread Strip.

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STEEL CORDS

Tire cords play an important role in the "reinforcement of rubber". They are an important factor in tire construction and

have a major influence upon the tire's performance. The below chart shows the trends in tire cord material and

organic fibers such as cotton, rayon, nylon and polyester, were used for tire cord for some time. Within the last 25

years the increase in steel cord can be seen and this is due to the increase in radial tire manufacture.

The steel cords are mainly used in the following parts of the tires.

"Carcass" of LT/TB/OTR tires. (In PC tires, polyester is used in the majority of passenger tire carcasses.)

"Belt" of PC/LT/TB/OTR tires. "Bead wire" of PC/LT/TB/OTR tires, which reinforces bead area.

Some basic knowledge of steel cords currently used in the "carcass" of LT/TB tires and "belt" of PC/LT/TB tires is

explained.

1. The Material of Steel Cords

In general, high level carbonaceous steel wire is used.Carbon content: around 0.7%←Diameter: 5.5m/m

2. Manufacturing Method of Steel Cords

(1) The manufacturing process runs high level carbonaceous steel wire through a die numerous times.

But in the middle of this process, the steel manufacturer has to carry out the following;

→The heat treatment must be carried out once or twice because steel wire becomes hard by running it through the

die.

→The plating with "brass" must be carried out so that the steel wire can easy adhere to rubber.*

*Brass plating: In general, copper (Cu) and zinc (Zn) are used. The ratio is usually between 60:40 to 70:30

(2) By repeatedly drawing the wire through the extruder die the wire finally←(Diameter: 0.2m/m - 0.38 m/m)

3. Characteristics of Steel Cords

(1) Excellent tensile strength

(2) High modulus of elasticity per uniform section area

By utilizing the characteristics of steel cord, it is easy to see where it is suitable for certain tire categories, components and operating conditions.

Steel cord construction and the effect on requirement performance is shown below

Notes

*General diameter of filament: 0.2 to 0.38m/m per filament

**Pitch of twist (turn/cm): The length of cord, strand or wrapping per one twist. Strand is like a rope where several

filaments are twisted while wrapping, known as "fret wire", is the filament wrapped around the cord bundle in a spiral.

The main purpose that the steel wire is twisted is to keep the wire's form. This form prevents

the twist of the steel wire from becomeing loose. (Wrapping also assists.)

The popular construction of steel cord used in the belt of PC tire and the belt and carcass of TB tire is shown below.

A) Characteristics of Steel Cord for Passenger Tire (Belt)

(a) Diameter of filament is smaller.→This provides improve ride comfort and durability of belt.

(b) Pitch of twist (turn/cm) is longer.→Durability (deflection) is not as important for the steel belt when compared with the carcass.

B) Characteristics of Steel Cord for Truck Tire (Belt)

(a) Diameter of filament is bigger.→This is required to improve the strength of the belt. (More difficult to deflect the belt.)

(b) Pitch of twist (turn/cm) is longer.→Durability (deflection) is not as important for belt by comparison to carcass.

C) Characteristics of Steel Cord for Truck Tire (Carcass)

(a) Diameter of filament is smaller.→The purpose is to improve the durability of carcass. Additionally, strength for the carcass is improved by increasing the number of filaments.

(b) Pitch of twist is shorter.→Durability is very important for carcass when compared to the

belt wire.

As with most things in the world steel cord has its good and weak points. The most commonly known weak point of

steel cord is "rust". Rust resistance can be improved by improving rubber penetration.

D) High-Tensile* Open Construction Carcass-Cord*

Regular steel cord

 

 

Open-type steel cord

Regular steel cord:

There is a very small opening between filaments. ↓Rubber penetration is poor. ↓(a) Air or water enters easily → Steel cord rust. (b) Steel cord to steel cord contact occurs. → Fretting occurs. 

Open-type steel cord:

There is an opening between filaments. ↓Rubber penetration is good. ↓(a) Air or water has difficulty entering → Steel cord resists rust.(b) Steel cord maintains separation. → Fretting is eliminated.

*High-Tensile Steel Cord (High strength steel cord):

Carbon content of high level carbonaceous steel wire (steel cord material) is increased to about 0.8%. (Regular

carbon contents is around 0.7%) This results in a High-Tensile Steel Cord with greatly improved strength as a result

of the increasing carbon content.

Tire Shape A tire gets it shape from layers of fabric and adhesive that comprise the body of

the tire. The layers are called plies, and belts consist of cords of metal, nylon, kevlar or similar material. The plies are wrapped in an outer and inner layer of rubber. The rubber layers make a tire hold the air, and the ply layers give the shape. To maintain the tire's integrity, all of the layers are permanently bonded together during the manufacturing process.

Causes of bubbles The underlying cause of a bubble in the side of a tire is a separation between

the cords and plies in the body of the tire. The damage to the plies allows air to seep through and form a bubble in the flexible rubber outer layer of the tire. A

bubble is a sign of internal damage to the tire. Several factors can cause bubbles, including manufacturing defects, under-inflation and tire impacts.It is possible that a tire may be manufactured with bad or contaminated materials, or the curing process bonding the components may have not been fully completed. If the cord and plies are not properly bonded together, they will eventually separate, and a tire bubble will result.An under-inflated tire will flex significantly more than if it is properly inflated. The flexing causes excess heat to build up in the tire, and this heat will break down the materials that hold the plies and cords together. This heat caused separation is another source of bubbles.Hitting a curb or pothole hard enough will cause internal damage to the plies of a tire. The blow could break cords or cause plies to separate. Once again, when you get this type of separation in the body of a tire, the external sign will be a bubble in the sidewall.

Bubble Prevention and Remedies Once you have a bubble in the sidewall of a tire, the only safe solution is to

replace the tire. A bubble that is the result of a manufacturing defect should be covered by warranty if the tire is still in the warranty period. Bubbles due to manufacturing problems usually show up within a few months of driving on the tire. Bubbles from under-inflation or impact damage may not show up until months after the abuse occurs.There are steps you can take to prevent bubbles or prevent a bubble from leading to a tire blowout. First, visually inspect your tires regularly. Walk around your car and give the tires a close inspection. Remember the tires have inner sidewalls too and these need to be inspected regularly. Second, check your tire pressure at least once a week. Have tires with slow leaks repaired promptly. Finally, most impact damage can be avoided by driving with caution near curbs and on bad roads.

Pneumatic tires are manufactured according to relatively standardized processes and machinery, in

around 450 tire factories in the world. With over 1 billion tires manufactured worldwide annually, the tire

industry is the major consumer of natural rubber. Tire factories start with bulk raw materials such

as rubber, carbon black, and chemicals and produce numerous specialized components that are

assembled and cured. This article describes the components assembled to make a tire, the various

materials used, the manufacturing processes and machinery, and the overall business model.

The tire is an assembly of numerous components that are built up on a drum and then cured in a press

under heat and pressure. Heat facilitates a polymerization reaction that crosslinks rubber monomers to

create long elastic molecules. These polymers create the elastic quality that permits the tire to be

compressed in the area where the tire contacts the road surface and spring back to its original shape

under high-frequency cycles. Typical components used in tire assembly are listed below.

Inner liner

The inner is liner an extruded halobutyl rubber sheet compounded with additives that result in low air

permeability. The inner liner assures that the tire will hold high-pressure air inside, without the air

gradually diffusing through the rubber structure.[1]

[edit]Body ply

The body ply is a calendered sheet consisting of one layer of rubber, one layer of reinforcing fabric, and a

second layer of rubber. The earliest textile used was cotton; later materials include rayon,nylon, polyester,

and Kevlar. Passenger tires typically have one or two body plies. Body plies give the tire structure

strength. Truck tires, off-road tires, and aircraft tires have progressively more plies. The fabric cords are

highly flexible but relatively inelastic.

[edit]Sidewall

Sidewalls are non-reinforced extruded profiles with additives to give the sides of the tire good abrasion

resistance and environmental resistance. Additives used in sidewall compounds

includeantioxidants and antiozonants. Sidewall extrusions are nonsymmetrical and provide a thick rubber

area to enable molding of raised letters

[edit]Beads

Beads are bands of high tensile-strength steel wire encased in a rubber compound. Bead wire is coated

with special alloys of bronze or brass. Coatings protect the steel from corrosion. Copper in the alloy

and sulfur in the rubber cross-link to produce copper sulfide, which improves bonding of the bead to the

rubber. Beads are inflexible and inelastic, and provide the mechanical strength to fit the tire to the wheel.

Bead rubber includes additives to maximize strength and tougness

[edit]Apex

The apex is a triangular extruded profile that mates against the bead. The apex provides a cushion

between the rigid bead and the flexible inner liner and body ply assembly. Alternatively called "filler" (as in

the diagram above).

[edit]Belt package

Belts are calendered sheets consisting of a layer of rubber, a layer of closely spaced steel cords, and a

second layer of rubber. The steel cords are oriented radially in radial tire construction, and at opposing

angles in bias tire construction. Belts give the tire strength and dent resistance while allowing it to remain

flexible. Passenger tires are usually made with two or three belts.

[edit]Tread

The tread is a thick extruded profile that surrounds the tire carcass. Tread compounds include additives to

impart wear resistance and traction in addition to environmental resistance. Tread compound

development is an exercise in compromise, as hard compounds have long wear characteristics but poor

traction whereas soft compounds have good traction but poor wear characteristics.

[edit]Cushion gum

Many higher-performing tires include an extruded component between the belt package and the tread to

isolate the tread from mechanical wear from the steel belts.

[edit]Other components

Tire construction methods vary somewhat in the number and type of components, as well as the

compound formulations for each component, according to the tire use and price point. Tire makers

continuously introduce new materials and construction methods in order to achieve higher performance at

lower cost.

[edit]Materials

Natural rubber, or polyisoprene is the basic elastomer used in tire making

Styrene-butadiene  co-polymer (SBR) is a synthetic rubber which is often substituted in part for

natural rubber based on the comparative raw materials cost

Polybutadiene  is used in combination with other rubbers because of its low heat-buildup properties

Halobutyl rubber is used for the tubeless inner liner compounds, because of its low air permeability.

The halogen atoms provide a bond with the carcass compounds which are mainly natural rubber.

Bromobutyl is superior to chlorobutyl, but is more expensive

Carbon Black , forms a high percentage of the rubber compound. This gives reinforcement and

abrasion resistance

Silica , used together with carbon black in high performance tires, as a low heat build up

reinforcement

Sulphur  crosslinks the rubber molecules in the vulcanization process

Vulcanizing Accelerators  are complex organic compounds that speed up the vulcanization

Activators  assist the vulcanization. The main one is zinc oxide

Antioxidants  and antiozonants prevent sidewall cracking due to the action of sunlight and ozone

Textile  fabric reinforces the carcass of the tire

[edit]Manufacturing process

Tire plants are traditionally divided into five departments that perform special operations. These usually

act as independent factories within a factory. Large tire makers may set up independent factories on a

single site, or cluster the factories locally across a region.

[edit]Compounding and mixing

SB R rubber compound to with chemicals formulations

1. SB Rubber 100 k.g.

2. carbon 220 150 k.g.

3. zinc oxide 20.5 k.g.

4. static acid 13.5 k.g.

5. accelerator 11.2 k.g.

6. Oil 33.5 k.g.

Compounding is the operation of bringing together all the ingredients required to mix a batch of rubber

compound. Each component has a different mix of ingredients according to the properties required for

that component.

Mixing is the process of applying mechanical work to the ingredients in order to blend them into a

homogeneous substance. Internal mixers are often equipped with two counter-rotating rotors in a large

housing that shear the rubber charge along with the additives. The mixing is done in three or four stages

to incorporate the ingredients in the desired order. The shearing action generates considerable heat, so

both rotors and housing are water-cooled to maintain a temperature low enough to assure that

vulcanization does not begin.

After mixing, the rubber charge is dropped into a chute and fed by an extruding screw into a roller die.

Alternatively, the batch can be dropped onto an open rubber mill batchoff system. A mill consists of twin

counter-rotating rolls, one serrated, that provide additional mechanical working to the rubber and produce

a thick rubber sheet. The sheet is pulled off the rollers in the form of a strip. The strip is cooled, dusted

with talc, and laid down into a pallet bin.

The ideal compound at this point would have a highly uniform material dispersion; however in practice

there is considerable non-uniformity to the dispersion. This is due to several causes, including hot and

cold spots in the mixer housing and rotors, excessive rotor clearance, rotor wear, and poorly circulating

flow paths. As a result, there can be a little more carbon black here, and a little less there, along with a

few clumps of carbon black elsewhere, that are not well mixed with the rubber or the additives.

Mixers are often controlled according to the power integration method, where the current flow to the mixer

motor is measured, and the mixing terminated upon reaching a specified total amount of mix energy

imparted to the batch.

[edit]Component preparation

Components fall into three classes based on manufacturing process: calendering, extrusion, and bead

building.

The extruder machine consists of a screw and barrel, screw drive, heaters, and a die. The extruder

applies two conditionspressure. The extruder screw also provides for additional mixing of the compound

through the shearing action of the screw. The compound is pushed through a die, after which the

extruded profile is vulcanized in a continuous oven, cooled to terminate the vulcanization process, and

either rolled up on a spool or cut to length. Tire treads are often extruded with four components in a

quadraplex extruder, one with four screws processing four different compounds, usually a base

compound, core compound, tread compound, and wing compound. Extrusion is also used for sidewall

profiles and inner liners.

The calender is a set of multiple large-diameter rolls that squeeze rubber compound into a thin sheet,

usually of the order of 2 metres wide. Fabric calenders produce an upper and lower rubber sheet with a

layer of fabric in between. Steel calenders do so with steel cords. Calenders are used to produce body

plies and belts. A creel room is a facility that houses hundreds of fabric or wire spools that are fed into the

calender. Calenders utilize downstream equipment for shearing and splicing calendered components.

[edit]Tire building

Tire building is the process of assembling all the components onto a tire building drum. Tire-building

machines (TBM) can be manually operated or fully automatic. Typical TBM operations include the first-

stage operation, where inner liner, body plies, and sidewalls are wrapped around the drum, the beads are

placed, and the assembly turned up over the bead. In the second stage operation the belt package and

tread are applied and the green tire is inflated and shaped.

All components require splicing. Inner liner and body plies are spliced with a square-ended overlap. Tread

and sidewall are joined with a skived splice, where the joining ends are bevel-cut. Belts are spliced end to

end with no overlap. Splices that are too heavy or non-symmetrical will generate defects in force variation,

balance, or bulge parameters. Splices that are too light or open can lead to visual defects and in some

cases tire failure. The final product of the TBM process is called a green tire, where green refers to the

uncured state.

Pirelli Tire developed a special process called MIRS that uses robots to position and rotate the building

drums under stations that apply the various components, usually via extrusion and strip winding methods.

This permits the equipment to build different tire sizes in consecutive operations without the need to

change tooling or setups. This process is well suited to small volume production with frequent size

changes.

The largest tire makers have internally developed automated tire-assembly machines in an effort to create

competitive advantages in tire construction precision, high production yield, and reduced labor.

Nevertheless there is a large base of machine builders who produce tire-building machines.

[edit]Curing

An opened tire mold being cleaned. The deflated rubber bladder is on the central post.

Curing is the process of applying pressure to the green tire in a mold in order to give it its final shape, and

applying heat energy to stimulate the chemical reaction between the rubber and other materials. In this

process the green tire is automatically transferred onto the lower mold bead seat, a rubber bladder is

inserted into the green tire, and the mold closes while the bladder inflates. As the mold closes and is

locked the bladder pressure increases so as to make the green tire flow into the mold, taking on the tread

pattern and sidewall lettering engraved into the mold. The bladder is filled with a recirculating heat

transfer medium, such as steam, hot water, or inert gas. Temperatures are in the area of 350 degrees

Fahrenheit with pressures around 350 PSI. Passenger tires cure in approximately 15 minutes. At the end

of cure the pressure is bled down, the mold opened, and the tire stripped out of the mold. The tire may be

placed on a PCI, or post-cure inflator, that will hold the tire fully inflated while it cools. There are two

generic curing press types, mechanical and hydraulic. Mechanical presses hold the mold closed via

toggle linkages, while hydraulic presses use hydraulic oil as the prime mover for machine motion, and

lock the mold with a breech-lock mechanism. Hydraulic presses have emerged as the most cost-effective

because the press structure does not have to withstand the mold-opening pressure and can therefore be

relatively lightweight. There are two generic mold types, two-piece molds and segmental molds.

Large off-road tires are often cured in ovens with cure times approaching 24 hours.

[edit]Final finish

After the tire has been cured, there are several additional operations. Tire uniformity measurement is a

test where the tire is automatically mounted on wheel halves, inflated, run against a simulated road

surface, and measured for force variation. Tire balance measurement is a test where the tire is

automatically placed on wheel halves, rotated at a high speed and measured for imbalance.

Large commercial truck/bus tires, as well as some passenger and light truck tires, are inspected by X-

ray machines that can penetrate the rubber to analyze the steel cord structure.

In the final step, tires are inspected by human eyes for numerous visual defects such as incomplete mold

fill, exposed cords, blisters, blemishes, and others.

[edit]Tire manufacturing companies