tyres what are they and what they can do

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Presentation

April 2009, Durban

Kevin Emmett

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Topics to be covered:

Global overview of Earthmover tyres

•Technical aspects

•Temperature and pressure monitoring

•TKPH

•Weight Studies

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What is a tyre?

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From a person on the street….

“A round, black rubber thing that holds my vehicle up!”

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From a tyre expert……

“a visco-elastic toroid comprised of, high modulus flexible filaments, embedded in and bonded to, a low modulus matrix, which forms an anisotropic shell structure”

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What do we expect from a tyre?

The tyre designer’s challenge is to design a tyre that has:

•Load carrying capacity

•Speed capability

•Grip (during acceleration, braking and steering)

•Handling (steering response)

•Good ride (shock absorption)

•Durability (long life, damage resistance)

•Good appearance

•At a low cost!

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Cross ply and Radial constructions:

Two types of tyre exist for off highway use

Radial and Cross ply (bias)

Radial•More technologically

Advanced solution

•Offers many performance

Advantages

•More expensive to purchase but has lower cost per hour than bias

Cross-Ply•No steel used in casing or

Crown

•Cheaper to purchase

•Generally lower life potential

•Higher cost per hour than steel braced Radial

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A tyre is a high tech and a complex product………

Making a Radial tyre……..

The very short version

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Tyre materials:

•Rubber, both synthetic and natural

•Chemicals

•Carbon black

•Cord materials

A typical tyre uses 47 or more different products

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Radial Earthmover Tyre Building:

First step: The casing (air bag)

Various rubber products are

Assembled on a cylindrical drum

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Second step: The Belt is applied

The cylinder of rubber products is inflated, then the belt plies and tread rubber are applied:

Two independent working parts

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Third step: Curing

The tyre is placed in a mould where it is ‘vulcanized’

(under high temperature and pressure) to bond the rubber products. The finished product, including the

tread pattern, is also formed during this stage

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Tread rubber

Steel protection plies

Working plies

Inner liner

Bead wire

Carcass ply

Turn up ply

Bead area

Sidewall

Shoulder zone

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Factors affecting tyre life:

Tyre performance is shown as a function of factors found in two key areas:

• The tyre itself

• The site parameters

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Tyre selection

Conditions = advice of

Your tyre specialist based

On site conditions

Site= factors fixed by the

operation

Tyre Performance

Tyre maintenance

Site maintenance

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Tyre selection: advice of your tyre specialist, based on site conditions:

•Tread design

•Tread depth

•Tread rubber compound

•WDAS (speed capability)

•TKPH

•Air pressure recommendation

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•51”

•XDR

•B4

•20 Km/hr WDAS

•740 TKPH

•Tyre ideally runs at 6 bar (600 kpa) and will carry 46,250 kg. The max permitted for this tyre is 51,000 kg at 7.5 bar (750 kpa)

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Site conditions: fixed factors

•Type of equipment

•Weight distribution

•Site speed (average and max)

•Haul lengths

•Wheel position

•Ambient temperature

Variable factors

•Underfoot conditions

•Operator habits

•Utilisation of support equipment

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Therefore we must act on Tyre maintenance and Site maintenance both critical in overall tyre performance

Tyre maintenance:

•Air pressure maintenance

•Tyre matching

•Rotation policy and scheduled changes

•Tyre record/analysis

•Mounting procedures

•Repair procedures

•Workmanship and materials

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Air pressure maintenance:

•Frequency of checks….daily weekly….?

•Accuracy of gauges…how often is the calibration checked?

•Recording of pressures

•Plan for correction

•A tyre will build up pressure during operation; as an example a tyre inflated at 750 kpa cold should build in pressure between 15% and 18% (less could mean that the cold pressure is too high, more that cold pressure is not correct, tyres are mismatched, one sided loading, struts………..)

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3% Circumference

0.5% circumference or 10% of RTD

Rigid Dump Truck

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Maximum permissible differences in diameter

6%

3%

Loader

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- 2% +

1.5%

1.5%

Articulated Dump Truck

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PERFORMANCE

TYREMAINTENANCE

APPLICATION

Type of equipment

Speed in turns

Hours of operation

Average speed

Maximum speed

Operators

Haul length

Weight distribution

Ambient temperature

Tyre matching

Machine modifications

Working surfaces

Air pressures

Pit areas

Tyre rotation/matching

Tyre repair process

Tyre records/analysis

Tyre fitting

Tread compound

Cold pressure recommendation

Tread depth

Tread design

Quality of tyre workmanship and materials

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Factors affecting tyre life:•Operators

•Overloads

•Loading areas

•Haul roads (drainage, undulations,materials

•Grades

•Turns (super elevation, speed in turns)

These can all be monitored with the application of Site Severity Studies

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Site Severity Studies:These include inspection and analysis of the following:

•Roads

•Loading Areas

•Waste dumps

•Ore dumps

•Loading efficiency

Case study: Improvement in tyre life from 4100 hrs in 2005 to 8000 hrs ytd 2008 (33.00R51) and from 3900 hrs to 6500 hrs ytd 2008 (37.00R57)

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Rocks lying in Berm, see rubber marks….

Ore dump. Water, best cutting agent for rubber, and large rocks to reverse over….

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Underfoot conditions in the waste dump area, where are the tailings?

Road width, 2.5X width of truck? Undulations, cause spillage, one sided load causes tyre overload situations…

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Trucks reversing into waste pile

Poor underfoot, no drainage, no super elevation, banking apparent…

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One sided loading creates massive overload factors (or underinflation) and causes this….

No clean up at shovel, loading point.

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Examples of Loading:

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TKPH:What is TKPH?

•It is an expression of the working capacity of a tyre.

•It is a function of the maximum allowed structural operating temperature of the tyre

•TKPH is calculated to agreed international standards

Why do we calculate TKPH?

•So that we are able to keep the tyre operating within it’s safe working zone

•To obtain the highest productivity while still in the safe working zone (Highest speed with the heaviest load)

•To choose the most suitable tyre for the site so as to decrease the costs per tonne Kilometre/Mile

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Why does the tyre get hot?As the tyre rotates, it deflects, and this causes the structure to flex. As the

tyre rolls the area that makes contact with the ground compresses, as it leaves the ground it returns to it's original shape.

The energy produced through this action and the flexing cause heat. If this process is too rapid, heat builds up in the tyre. If the process continues the acceptable working zone is exceeded.

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Elastic rubber All the energy produced is retained Viscoelastic mixtures

Part of the energy is transformed int heat..

The rubber elements store the energy..

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TKPH:A tyres TKPH depends upon its design and varies according to size and type.

It is a function of load and the number of Kilometres covered per hour at an ambient temperature of 38° C

Pages 106 107 in the data book give a full example of calculating a TKPH

Michelin use 5km as the base length for a haul. (page 108) gives you two tables for K1 (length of haul) and K2 reference between WDAS (speed) and ambient temperature these coefficients need to be applied in order to make the correct calculation.

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There is no magic in improving tyre life and managing tyres in a fleet. Too often due to familiarity we stray away from the BASICS.

Get the BASICS correct and tyre life will improve

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Any questions…………………

tyres what are they and what they can do

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