tyres what are they and what they can do
TRANSCRIPT
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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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Radial Earthmover Tyre Building:
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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Radial Earthmover Tyre Building:
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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Factors affecting tyre life:
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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Factors affecting tyre life:
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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Factors affecting tyre life:
•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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Factors affecting tyre life:
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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Factors affecting tyre life:
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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Factors affecting tyre life:
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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FF FF
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FFFF
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FF FF
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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…………………