Tyres What Are They and What They Can Do

Download Tyres What Are They and What They Can Do

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Presentation April 2009, DurbanKevin EmmettPage 1 /Topics to be covered:Global overview of Earthmover tyres Technical aspects Temperature and pressure monitoring TKPH Weight StudiesPage 2 /What is a tyre?Page 3 /From a person on the street.A round, black rubber thing that holds my vehicle up!Page 4 /From a tyre experta visco-elastic toroid comprised of, high modulus flexible filaments, embedded in and bonded to, a low modulus matrix, which forms an anisotropic shell structurePage 5 /What do we expect from a tyre?The tyre designers 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!Page 6 /Cross ply and Radial constructions:Two types of tyre exist for off highway useRadial and Cross ply (bias)RadialMore technologically Advanced solution Offers many performance Advantages More expensive to purchase but has lower cost per hour than biasCross-PlyNo steel used in casing or Crown Cheaper to purchase Generally lower life potential Higher cost per hour than steel braced RadialPage 7 /A tyre is a high tech and a complex productMaking a Radial tyre.. The very short versionPage 8 /Tyre materials: Rubber, both synthetic and natural Chemicals Carbon black Cord materials A typical tyre uses 47 or more different productsPage 9 /Radial Earthmover Tyre Building: First step: The casing (air bag) Various rubber products are Assembled on a cylindrical drumPage 10 /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 partsPage 11 /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 stagePage 12 /Shoulder zoneTread rubberSteel protection plies Working plies Inner linerSidewallCarcass plyTurn up plyBead wireBead areaPage 13 /Factors affecting tyre life:Tyre performance is shown as a function of factors found in two key areas: The tyre itself The site parametersPage 14 /Factors affecting tyre life:Tyre selection Conditions = advice of Your tyre specialist based On site conditions Site= factors fixed by the operationTyre PerformanceTyre maintenance Site maintenancePage 15 /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 recommendationPage 16 /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)Page 17 /Factors affecting tyre life:Site conditions: fixed factorsType of equipment Weight distribution Site speed (average and max) Haul lengths Wheel position Ambient temperatureVariable factorsUnderfoot conditions Operator habits Utilisation of support equipmentPage 18 /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 materialsPage 19 /Factors affecting tyre life:Air pressure maintenance: Frequency of checks.daily weekly.? Accuracy of gaugeshow 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..)Page 20 /Rigid Dump Truck3% Circumference0.5% circumference or 10% of RTDPage 21 /LoaderMaximum permissible differences in diameter6%3%Page 22 /Articulated Dump Truck- 2% +1.5%1.5%Page 23 /APPLICATIONType of equipment Operators Speed in turns Haul length Hours of operation Weight distribution Average speed Ambient temperature Maximum speedTyre matching Tyre rotation/matching Machine modifications Working surfaces Air pressures Pit areasPERFORMANCETread designTyre repair process Tyre records/analysisTread compoundTread depth Cold pressure recommendationTyre fittingMAINTENANCETYREQuality of tyre workmanship and materialsPage 24 /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 StudiesPage 25 /Site Severity Studies:These include inspection and analysis of the following: Roads Loading Areas Waste dumps Ore dumps Loading efficiencyCase 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)Page 26 /Rocks lying in Berm, see rubber marks.Ore dump. Water, best cutting agent for rubber, and large rocks to reverse over.Page 27 /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 situationsPage 28 /Poor underfoot, no drainage, no super elevation, banking apparentTrucks reversing into waste pilePage 29 /One sided loading creates massive overload factors (or underinflation) and causes this.No clean up at shovel, loading point.Page 30 /Examples of Loading:Page 31 /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 its 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/MilePage 32 /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.1 4 3 2F 2 13 The rubber elements store the energy. . Part of the energy is transformed int heat. .4 1tElastic rubber All the energy produced is retained Viscoelastic mixtures F 3 F F F F F 2 4 1Page 33 /xxTKPH: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.Page 34 /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 improvePage 35 /Any questionsPage 36 /