177 Selecting Haul Truck Bodies


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Paper on the issues surrounding selection of a haul truck tray or body. Covers Technical and organisational matters.

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177 Selecting Haul Truck Bodies

  1. 1. 177- Selecting Haul Truck Bodies Increasing Mine Productivity with an Appropriate Mine Truck BodyBy: Richard LangDate: October 2010 Page 1 of 13
  2. 2. Increasing Mine Productivity with an Appropriate Mine Truck BodyIntroductionAchieving Mine Productivity requires input from all levels of management, Innovativethought, a detailed understanding of the mine application, working with the supplier toget the right result including providing correct information, correct application of what isquite simple maths and an understanding of the pitfalls of using SAE volumes.A truck body needs to suit the purpose rather than be a general purpose device. Itneeds to be selected to match the particular environment of the mine. The first part ofthat selection is matching the technical environment and the second part is making surethat the supplier and the mine have a common understanding.But first, look at who in the organisation should understand this process and the conceptof the calculation. This paper is intended for a wide range of personnel.The main points covered are: • The importance for all levels of management to have an understanding • The huge financial payoffs possible • Traps for the unwary in angles of repose and loose bulk density as they effect achievable tray payload.OrganisationTake a typical organisation structure as depicted below. Managing Director General Manager General Manager General Manager Commercial Technical Operations or Mine Manager Specialist Supt Mobile Supt Mining Mining Equip Services Maintenance Figure 1: Typical Organisation StructureInitiative, analysis and recommendations on equipment like truck bodies tend to happenat the Superintendant level. Is this a good idea? The short answer is yes but.........These people have to be heavily involved as they live with the consequences of thedecision for years afterwards. Page 2 of 13
  3. 3. However, I believe that people up the line need to understand the concepts in order forthe organisation to achieve Mine Productivity. Mine haulage is a substantial cost in thescheme of things as shown in Table 1 below. TYPICAL OPEN CUT MINING COSTS Haulage 32% Drill & Blast 25% Loading 17% Other 26% Table 1: Mining CostsGiven the substance of the issue, the top levels of management should understand thebasics of haulage. Furthermore if you look at the responsibilities of the managementlevels in Table 2 below, there is an argument that because haulage decisions impactover many years, there is a need for senior management to take an interest.Level Time Horizon & Thinking PatternsV - Managing Director 5-10 Yrs & Conceptual Thinking – Creative, positioning the business as it sits in the industry.IV - General Manager 2-5 Yrs Reviewing recurring Issues, undertaking investigations and generally directing traffic.III - Superintendant 1-2 Yrs Action Focused on issues in front of them Table 2: Management Levels and their FocusThe Company’s Board of Directors has delegated responsibilities for taking care of theshareholders money to the Managing Director and in turn the General Manager. So it isincumbent upon them to consider innovation especially when there are significantshareholder benefits to the decision.The level IV and V people in large organisations don’t need to be involved in the detailbut they should understand enough to raise issues and make critical assessments onanalysis presented. They also have a critical role in communicating the organisationsappetite for risk and in which areas the company needs to move ahead to be in thelower quartile of the cost to revenue ratio curve for the industry. The averageSuperintendant left to their own devices will deal competently with the issues thatpresent themselves for action in the 1-2 year time frame. The leadership task for thelevel IV and V people is to encourage the Level III people out of their comfort zone. Inorder to perceive the opportunities in mine haulage as well as to promote some criticalthinking, the level IV and V people need to understand the basics of haulage analysis.Going straight to an example; a mine had been running for many years with thefollowing empty truck weights which are driven by the tray weight. Page 3 of 13
  4. 4. Reduction in Tray Weight Truck Empty Truck Possible - Number Weight Tonnes Tonnes 400 171 21 401 180 30 403 172 22 404 181 31 405 180 30 406 179 29 407 180 30 408 181 31 409 182 32 411 172 22 412 177 27 413 177 27 414 150 0 415 178 28 417 177 27 418 179 29 419 180 30 420 174 24 421 176 26 422 180 30 423 178 28 424 172 22 425 175 25 426 172 22 427 179 29 428 173 23 429 178 28 430 177 27 431 178 28 432 175 25 433 180 30 472 150 0 Average 27 Table3: Potential Reduction in Tray weight = Payload increaseCan you imagine the financial implications if you carried 27 tonnes more or even justhalf of that every load on every truck.Truck Operating Hours per annum 5,500Cycle time 40 minsLoads per annum per truck 8,250Extra Tonnes carried per load 27 or say 20 to be conservativeExtra Tonnes per annum per truck 165,000 - This is about 9% increase but potential is around 13%Number of trucks 30Extra Tonnes per annum for the mine 4,950,000 OR park 3 trucksImagine the extra revenue associated with that!! or Imagine the cost and capital savings of parking up between 2 and 4 haul trucks!! Table 4: Calculation of SavingsSo who in the organisation is going to come up with the creative thought to look atreplacing the 30 odd trays with one that weighed less and lasted without increasedmaintenance?For years the people at the lower levels kept maintaining what was in front of them untila creative Superintendant / Manager came along and asked the question and started Page 4 of 13
  5. 5. the assessment process. Soon the profits will be flowing to the shareholders as aresult. So the point is that while the maths is very simple, it takes someone with acapacity for level IV or V thought processes to make it happen. That person may besomeone on the rise through the ranks from Superintendant level or a level IV – Vincumbent. So to achieve Mine Productivity everyone in the organisation needs to bepaying attention to haulage at an appropriate level of detail commensurate with theirposition and the capacity of the people around them.Technical AssessmentThe designer has to make the body suitable for the impact loading, the abrasiveenvironment and the nature of the material being loaded. Very large loading tools fillingthe body in a small number of passes will impart more “damage” than a smaller tool.Dropping the load from further away will also increase the “damage”.1So in environments where the loading will be rugged, we suggest a 25mm floor for theDT truck body. We have not seen damage in the loading impact area with this policy.For less arduous environments we suggest a 19mm floor. The trade off is weight andlongevity.With material having a Bond Abrasiveness Index of 0.34 (eg hard rock – gold mine) ,we expect that over the rear 2-3M of the floor, all but the last 100mm of the body willwear at 0.85mm/1,000 Hrs. The treatment here is to let the body wear and then addwear tiles in the worn areas to bring the body back to the original weight.In less abrasive environments, the wear process will take longer but the tile solution isthe same. In coal, the body may only ever get three rows of tiles at the rear over its life.In aggressive environments where the material is sharp and harder than the materialwith Bond Abrasive Index 0.34; then specific tile packages can be provided.DT HiLoad offers canopy protection plates and rear support rails for toughenvironments. In addition, the body comes with 19mm or 25mm thick floors. The traymanufacturer can’t do much about haul road condition, even though it does impact onbody life. As the truck twists and slides over rough and slippery haul roads enormousforces are applied to the body and the chassis of the truck. Where all other factors arepointing in the direction of specifying a 19mm floor, poor haul roads may cause the mineto choose a 25mm floor to help cope with the higher stressed environment. Abrasivematerial will also push the body selection towards a 25mm floor model.For optimum Mine Productivity, the body needs to be rugged enough. Options selectionis important for matching the application.1 Damage is a term used in fatigue analysis whereby the number of stress cycles undergone by the materialexpressed as a fraction of the total number to cause failure allows “rainflow diagrams” to be drawn which relatethe stress level and the frequency to the damage created during the loading. This allows the designer to seewhether a large number of low stresses or a few large impacts are source of the “damage” which is consuming thebody life. Page 5 of 13
  6. 6. The sizing of the body is mathematically simple. Gross Vehicle Mass set by 384,000Kg the manufacturer: Less: Chassis Weight 118,000Kg Less: Weight of the body 30,000Kg Equals: Payload Allowable 236,000Kg Loose Bulk Density of 1.6 material: Volume of body required for 147M3 material Fill Factor 0.9 Volume of body required 163M3 Body size to order 170M3 Table 5: Body Volume calculationTwo questions arise from this calculation, firstly the loose bulk density number and thevolume. What volume and what density?Loose Bulk DensityIf the mine supplies the supplier with a loose bulk density number from the feasibilitystudy done for the original mine development analysis – that can be risky becausetoday’s reality may be different. An error of 10% in the bulk density will result in amatching error in the target truck body size.The build up from Bank Density (the density in the unfired material) to the density in thetruck is shown in Table 6 below. Bank Density 2.2 T/M3 Swell Factor 1.30 (say) Bulk Density as fired 1.69 Swell Factor 1.05 Loose Bulk Density in the truck 1.61 Table 6: Example of relationship of Bulk DensitiesAccurate numbers can be obtained using a scanner in conjunction with a set of truckscales. The trucks are scanned and weighed empty and again when full. The increasein weight and the volume difference yields the material density. If the mine isprocessing different materials, the density needs to be calculated for each material egoverburden and ore. Reconciliations between surveyed volumes and weightometerreadings at the plant will calculate bank Density. Knowing the number of truckloads willallow calculation of Bank M3 per truck load but don’t be confused as using that densitywill result in the wrong sized tray. Note also that there will be a small density differencebetween material in a shovel dipper and the truck or as shot. Furthermore, you need tomeasure the moisture content at the time of calculation as if done in summer at 2%moisture, there will be a difference in payload in winter at say 6% moisture. Themoisture will not usually increase the volume measurably but it will add to the weight. Page 6 of 13
  7. 7. Figure2: Scanning and weighing of empty and Full Trucks by Transcale of Queensland Australia Ph +61732170311Unless the mine wants dedicated haulage fleets for each material, then the body shouldbe sized to the lightest material. This yields the biggest body so there needs to beloading control when the most dense material is carried. If the amount of light materialis relatively small, it may be decided that the optimum solution is for a smaller body.This illustrates how managing Mine Productivity involves some tradeoffs and theimportance of getting the loose Bulk Density right. Readers should be aware thatmistakes have been observed in practice associated with the above points – otherwisehow does a mine get a body that is too small for the task?Body VolumeThe 147M3 body volume calculated in Table 5 above, is not enough as we can’t havethe load spilling over the sides, leaving rocks at the loading area. Also when the truckclimbs a 10% grade on the haulroad, there needs to be some free space at the tail sothat rocks don’t roll off onto the haulroad. The 90% fill factor allows for this andvariations in density in order to target the allowable payload of the truck. Depending onthe expected variations in loading and material density it is quite important to thinkabout what size of body to order. The loading tool operator needs to be able to get the+10% and the +20% loads in the tray in order that the truck will average the designpayload. The OEM loading rule is generally that 10% of the loads can be 10% over thetarget payload while no load should be more than 20% over and the average of all loadsshould be the Allowable payload or less.At one mine site, we looked at 22,000 truck loads from 11 loading tools and theStandard Deviation of each load overall was 9.8%. That means that it is impossible toachieve the average without a policy of tipping off the +20% loads. Overloads wouldbe 2.5% of the total according to the theory of normal distributions where the band Page 7 of 13
  8. 8. within two standard deviations (ie +2*9.8 = 20%) is covering all but 2.5% at the end ofthe distribution. In fact, this set of data had 89 loads =0.4% of loads over the +20%target. This indicates that the loading tool operator was taking some care not tooverload, making the distribution not a classical normal distribution. To manage thesituation, the policy of tipping off the +20% load needs to be adhered to or the loadingtool operator is given a lower target payload so that the natural variation in loads doesnot drift over the +20% target.The data also illustrates that if the body is merely sized to the target payload, then howwill your average achieve that target? When the truck has the +10% load on board,assuming that it is sized to 90% fill factor, the material will be spilling over the edges.Fragmentation can help reduce the variation and increase fill factor in the dipper. Instatistical terms, this means that if you reduce the standard deviation of the dipperpasses, the standard deviation of the truck payloads will tighten up and that means thechance of overload is less. Improved fragmentation can sometimes be achieved bymore careful placing of the explosives and managing the timing rather than using moreexplosives.The next thing effecting body volume is the angle of repose. Different materials willstack at different angles depending on the way the particles interlock and rill. Moisturecontent can affect this angle as well.When calculating the volume of a body you need to assume this angle. So there is apoint of difference possible from different suppliers.There is a standard which is widely used in the industry called SAE J1363.That calculates haul Truck Tray Volume by the following means:It takes the “Struck volume” which is conceptually a water holding capacity and thenyou add a volume of a pyramid shape with sides sloping at 2:1 (if that is the standardcomplied with).So it looks like Figure 3 below. Figure 3 : SAE 2:1 Volume representationWe all know that material doesn’t stack like that. You might think that it doesn’t matterbecause all trays being considered having the same “error”. But that is not true. Trayswith different shapes will have different actual carrying volume ratios to their SAE 2:1heaped volume. Then to add confusion there is a thing called SAE Field Heap. Page 8 of 13
  9. 9. Furthermore, not everyone is “tight” in their use of the standard. One contractor we dealwith filled truck bodies to overflowing and measured the volume showing that the actualwas 15% less than SAE. We had one mine site that was confused by suppliers claimingtray volumes which made no relative sense to each other. The reason was that onesupplier had used an inappropriate angle of repose.Figures 4 and 5 below show the extent of the volume difference. The angles in Figure 4are actual from a field example! The 38degrees was the angle that a competitor trayvolume was calculated at. The 26 degree line represents 2:1 stacking angle .Figure 4: Representation of Volume Difference with variation of Angle of Repose Repose angle vs. Load cone volume (m3) 210 210.2 Body Capacity (m3) 200 194.4 190 180 180.2 170 170.9 25 30 35 40 Repose angle (deg) Figure 5: Impact on Stated Volume of Change in Angle of ReposeWhat you really want to know is how much will the tray hold. We all have computers atour disposal now so we don’t need techniques rooted in the days when we added upsquares on graph paper to calculate the volume of things. Figure 6: A representation of how Material Stacks – DT Volume Page 9 of 13
  10. 10. Given the volume, if you assume 90% fill factor and multiply by the loose bulk density,you will get the payload mass. We find that theory matches reality pretty well asdepicted in Figure 7 below. Figure:7: 244Tonne in a body with a target payload of 240TonnesJust in case the argument is not convincing enough just yet. Below is a table thatshows the stacking angles or Angles of Repose of various materials. Note that the SAE1:1 and 2:1 slopes used in the calculations can give answers a long way from reali reality.The angle used should be the angle that the material sits at in the truck after beingagitated or shaken as that may be flatter than the angle it will freely sit at when carefullypiled on the ground. Angle of Repose θ Distance along Typical Range of Angle of Repose for Materials horizontal To 1 up Degrees tan 20.0 0.36 2.7 22.5 0.41 2.4 25.0 0.47 2.1 SAE angle for 26.6 0.50 2.0 wet sand Top heap soil & clay 27.5 0.52 2 1.9 30.0 0.58 8 1.7 32.5 0.64 1.6 soils 35.0 0.70 0 1.4 coal 37.5 0.77 1.3 Gravel 40.0 0.84 4 1.2 & small Crushed SAE angle for bottom 42.5 0.92 1.1 material section (struck Vol) 45.0 1.00 1.0 47.5 1.09 0.9 50.0 1.19 0.8 Table 7: Angles of Repose Page 10 of 13
  11. 11. So to achieve Mine Productivity care needs to be taken when interpreting the volumeof a tray. What you really want to know is how much material it will carry given the loosebulk density and angle of repose settings. Now that we have computers, the industryshouldn’t be using approximations like the SAE method.Some Other ThingsUnder sized bodies can be selected by merely looking at the payload calculation asdepicted in the Table 5 ie 236,000Kg. Yes the truck will carry it but if the body can’t fitthe volume in, then you won’t be averaging that payload. It seems straight forward butthis error has been seen in the field.As suppliers, we get concerned when confronted by assessment spreadsheets built bycustomers like the one below in Table 8The concerns of this, from a supplier viewpoint are: • What is the customer interpreting from the SAE volume? Do they think that the truck will be carrying this amount? You can bet the level IV and V managers who don’t have a detailed background in this area, think it will be. • The payload is calculated without options and wear pack. So how is that number relevant in comparing suppliers? The analyst says they will take it into account later – but will they recalculate the payloads? The weight of the wear pack and accessories are part of the Empty Vehicle weight and are significant. Unit of Detail for Company measure XYZ Supplied Information Gross Vehicle Weight tonnes 384.0 Chassis Weight tonnes 138.1 Unit of Tray Tray Volume measure Supplier XYZ Co Make & Model of Tray text *****-150-19 3 Volume of Payload SAE m 160.0 Payload tonnes 221.0 Tray Weight (before options/wear pack) tonnes 24.5 Check - Payload Must = 0 0 Table 8: Worrying Assessment by a CustomerThe point is that to get good decisions and achieve Mine Productivity, attention to detailis vital and not always easy when information comes from numerous sources.Secondly, this is not a process which is undertaken every year so people forget. Page 11 of 13
  12. 12. Economic EvaluationIn some organisations this is where the investment decision that has the potential toincrease Mine Productivity can go astray. It is the part of the process where commercialpeople are dealt into the team. If they do not understand the issues, the spreadsheetswill not bring out the salient points. Focus on capital cost; unless the company isartificially constrained, is rarely going to maximise the shareholders position. One minewe know has been analysing the issue for over eighteen months. If they had bought thetrays, six months after they started the analysis, they would be paid for by now throughcost savings. So how your company goes about managing change and analysingprojects also impacts the potential for improving Mine Productivity.Floor thicknessIf a body with lots of buttressing or bolsters is the same weight as a body without them,you need to ask how that can be so. Figure 8: Butressing consumes weight that has to be saved elsewhereUsually it will be found that the floor thicknesses are quite different in bodies like thoseillustrated in Figure 8. With a thinner floor, there is less wear allowance. That can onlymean less life or more maintenance cost unless the body is carrying benign materialwhich never wears the body.ImplimentationChange is a process which needs to be managed and if you are looking to buysomething other than the stock standard repeat of what you have been using, there willbe people to be managed as depicted in Figure 8 below. Figure 8: The Change Bus Source: Strategic Partnering by Tony Lendrum Page 12 of 13
  13. 13. Percentage of people in a Typical Organisation Terrorists Followers Early Adaptors Innovators 16% 68% 13% 3% Table 9: Seating Arrangements on the Change BusSo spare a thought for the innovative person who is trying to manage this change. If itis the level V manager, it is easier as their position has a significant degree of power butif it is an innovative Superintendant, it is much harder and they need help from top level.That help just needs to be taking an interest in the project to nudge the innovation andthe naval gazing along, so that the terrorists in the organisation don’t derail theimprovements that will increase Shareholder returns.To do this, the level IV and V managers need to understand the basics contained in thispaper. One of our customers achieved this change process from the Superintendantlevel by building a multi disciplinary team who worked on the project. This produced astrong coalition of knowledgeable people to drive the project forward. The amount ofsuch firepower required depends on where the organisation sits on the scale ofmoribund to agile and innovative.ConclusionThe selection of haul truck bodies to achieve Mine Productivity with an Appropriate MineTruck Body requires: • Attention from all levels of the management, • Innovative thought, • A detailed understanding of the mine application, • Working with the supplier to get the right result. This includes providing correct information, • Correct application of what is quite simple maths • An understanding of the organisations inner workings and who the innovative free thinkers are, • An understanding of the pitfalls of using SAE volumes and • An ability to conduct economic analysis and technical evaluation to ensure that the best value for shareholders is purchased rather than just the cheapest.ii Richard Lang is Chief Executive Officer of DT HiLoad Australia Pty Ltd. The company manufactures haultruck bodies in Australia and there is an operation in South America. They have sold some 1000 bodiesin the world with over 150 in Australia. He is a graduate of the University of Queensland EngineeringSchool and holds a Master of Administration from Monash University. Richard is also a GraduateMember of The Australian Institute of Company Directors. He has managed a Shipping business forPatricks and was Managing Director of a manufacturing and maintenance business servicing the miningindustry. Prior to that, he was Sales & Marketing Manager for Argyle Diamonds. Page 13 of 13