P&Q University Lesson 12- Maintenance & Optimization

Equipment maintenance is an important consideration at any aggregate operation. Properly maintaining equipment prevents costly downtime, and new technologies allow for better equipment optimization to further reduce costs and increase production. One example is the maintenance and optimization of screens and other vibrating equipment.

When vibrating screens and feeders aren’t performing well, the first thing aggregate producers may check is the stroke – the measure of the total vibrating motion of the vibratory machine. Is the stroke magnitude correct? However, in addition to the magnitude, other factors should be examined, such as the stroke angle, direction of rotation, and stroke consistency.

The stroke can be in the form of a circular pattern, an elliptical pattern, or it can be linear. The stroke pattern will be based on the type of vibratory machine. On most machines, it will be circular or elliptical. If the vibratory machine has two motors (or a dual drive), or is a two mass type of drive, it will be linear, or nearly linear.

For a circular or elliptical pattern, the stroke is the measure of the diameter of the circle or the long axis diameter of the ellipse. For linear stroke vibratory machines, it is the measure of the total movement, back and forth, of the machine. For instance, if the stroke is 1/4 in., the trough moves 1/8 in. forward and 1/8 in. back, for a total movement of 1/4 in.

All vibratory machine manufacturers will provide stroke plates and the recommended stroke magnitude for their particular machines. Usually, these are permanently attached to the sides of the trough. Ideally, there will be one stroke-indicating plate on both sides of the trough inlet and both sides of the trough outlet. The manufacturer will also indicate how to read the stroke plate. Different manufacturers use different types of stroke plates, and the owner’s manual will illustrate how to read them.

In addition to providing the magnitude of vibration, the stroke plate will indicate the angle of vibration (if the stroke pattern is not a circle). This is the angle of the ellipse or line, as viewed against the horizon. It will also indicate the direction of rotation. If the stroke is an ellipse or circle, it will have a direction of rotation, either clockwise or counter-clockwise. Also, the stroke plate will indicate any inconsistency of the stroke. (i.e., if the stroke varies erratically or if it cycles high and low).

The stroke should be observed both when the trough is empty and when it is fully loaded. If a vibratory machine is operated with an adjustable speed drive, such as a variable frequency drive, it is better to remove the drive for the purpose of troubleshooting the stroke. This eliminates the drive as any source of a problem.

STROKE MAGNITUDE

The magnitude, as recommended by the manufacturer, should be the same, or nearly the same, when the vibratory machine is operated empty and when it is operated under full load. If it diminishes under load, it may be an indication that the driving horsepower is insufficient for the given load. If it significantly increases under load, it is an indication that material may be sticking to the trough or that the machine is not correctly tuned.

The magnitude should be the same, or nearly the same, on all four corners of the machine (both sides of the inlet and both sides of the discharge). If the magnitude is not the same, it is an indication that the vibratory machine is not balanced with respect to its center of gravity, or that it is incorrectly installed. In this case, the manufacture or a knowledgeable consultant should be contacted.

STROKE ANGLE

The stroke angle should be the same, or nearly the same, when the vibratory machine is operated empty or under full load. Additionally, the stroke angle should be the same on all four corners of the trough. If the stroke angle changes, under load, it is an indication that the machine is not aligned with its center of gravity, it may be underpowered, or that material may be sticking to the trough.

If the stroke angle is different at the inlet and discharge of the machine, this can be a cause of poor performance, material sticking to the trough and premature wear to the trough. This is because the conveyed material will be trying to convey at different speeds along the length of the trough.

For example, if the stroke is normal, say 30 degrees from the horizontal, at the trough inlet and very shallow, say 5 degrees, at the discharge, the material will be trying to convey fast at the inlet and will be conveying slow at the discharge.

This can cause severe wear on the trough discharge, it can cause material to stick to the trough, and it is inefficient. When this occurs, the material depth may be deep at the discharge, where it is conveying slow and shallower at the inlet. The manufacturer or a vibratory machine consultant should be contacted.

DIRECTION OF ROTATION

If the machine has an elliptical or circular stroke, the rotation of the stroke should be the same on all four corners of the trough. If the stroke rotation is not the same on all four corners, it can cause a similar reaction as described above regarding the stroke angle.

For instance, if the rotation is in the direction of material flow at the inlet and counter to the direction of flow, at the discharge, the material will try to convey faster at the inlet and slower at the discharge, causing wear, sticking and inefficiency.

It is an indication that the vibratory machine is not correctly aligned with respect to its center of gravity, or it may be installed incorrectly. The manufacturer or a consultant should be contacted.

STROKE CONSISTENCY

The stroke should remain uniform. If the stroke goes up and down or has an erratic motion, it is an indication that the vibratory machine is bumping into a stationary structure, that the motor (or drive) is not operating correctly, or that the vibratory machine is not receiving a constant power supply (varying volts or a changing hertz). Make sure the adjustable drive is removed and that the power supply is consistent.

These simple checks will tell you how efficient the machines are performing and if any modifications are required.

Motors and bearings

Motors account for a high percentage of the electricity consumed in the U.S., at a very high yearly cost. Simple arithmetic: Every 1-percent reduction in motor demand cuts 0.64 percent off the industry-wide bill. High-efficiency motors also run cooler, which lightens the load on air-conditioning systems and further reduces plant demand. Lower total demand can lead to lower rates by helping to minimize peak-demand surcharges. As rates increase over time, these savings get even bigger.

But electricity bills aren’t the only place where savings will show up. Premium-efficiency motors are built better and provide longer service life backed by longer warranties, which means lower maintenance costs. On the other hand, because they’re built better, premium-efficiency motors typically cost up to 25 percent more than a comparably rated standard motor.

WHY EFFICIENCY RAISES PRICE

Motors lose energy in several ways. Biggest among them are the “copper” losses that result naturally from current passing through the copper-wire windings.

Premium-efficiency design employs larger-diameter wire, increasing the volume of copper by 35 to 40 percent. To accommodate larger wire, the steel laminations that support the windings need larger wire slots, which reduce the amount of active steel in each lamination. To compensate for the loss of steel, more laminations must be added. Consequently, the rotor and stator core must be lengthened, and the motor’s shell length increased. More metal adds more cost.

Next comes magnetic core loss-technically divided into eddy-current and hysteresis losses. In premium-efficiency designs, the longer rotor and core generally help decrease magnetic losses, but the makeup of the laminations is the key factor.

Most standard-efficiency motors use low-carbon steel laminations around 0.025 in. thick, rated for electrical loss at 3.0 watts per lb. Premium-efficiency motors use high-grade silicon steel laminations around 0.018 in. thick, having an electrical loss of 1.5 watts per lb. The chemical makeup and thinner gauge of premium-efficiency laminations, plus a coating of inorganic insulation on each piece, combine to greatly reduce eddy current losses. However, better steel costs more.

Hysteresis losses, a result of molecular magnetic alignment properties too complex for this brief discussion, are reduced in premium-efficiency motors by special annealing and plating of rotor and stator components, plus use of high-purity cast aluminum rotor bars.

Friction losses are reduced by higher-grade bearings, and windage losses in fan-cooled motors are reduced by smaller, more efficient fan designs. Overall, generally tighter tolerances and more stringent manufacturing process control are applied to minimize losses from unplanned conducting paths and stray load phenomena, both of which are common among motors.

While all the above differences in material and manufacturing discipline combine to increase motor price, they also combine to make premium-efficiency motors run cooler than their standard-efficiency counterparts.

Aside from cutting down the ambient air-conditioning costs, cooler operation lengthens the motor’s service life in two important ways. For every 10 degrees Celsius reduction in temperature, motor insulation life doubles; premium-efficiency motors tend to operate 10 to 20 degrees Celsius cooler than their standard-efficiency counterparts. Heat also is the primary cause of grease breakdown, which shortens bearing life; premium-efficiency motors tend to run 10 to 15 degrees Celsius cooler at the bearings. Consequently, premium-efficiency motors can provide up to four times longer winding life and twice the lubricant life of standard motor designs.

BEST CANDIDATES FOR CHANGE

When evaluating a changeover to premium-efficiency motors, look first at two main factors: cost of electrical power and the hours of operation.

The utility cost benefit of premium-efficiency motors begins to diminish when industrial power rates drop below 6 cents per kWh. Note that the true kWh cost very often is 1 to 2 cents higher than the actual base rate, due to the addition of peak demand charges and other penalties. True kWh cost is most easily determined by dividing the facility’s total electric cost by its kWh usage.

Rates can vary widely by geographic area; wherever true kWh cost moves above 6 cents, the economic argument for changeover gains strength. In such areas, hours of operation will indicate which motors in your plant might provide the quickest and best opportunities to save money with higher efficiency. Motors that run at least 2,000 hours per year (eight hours per day, five days per week) are your best candidates.

As operating hours increase, payback period shrinks. Remember that lower rates and shorter running times should not automatically rule out a change. Many local utilities offer energy-saving rebate programs that might shorten payback sufficiently to make premium-efficiency motors more cost-effective. Also, consider that the other benefits of better construction, cooler operation and longer life might still make premium-efficiency motors attractive, regardless of how much they help cut utility bills.

The third factor to review is the size and type of motor involved. The potential for premium-efficiency cost savings is greatest in motors rated 1 through 125 hp. The ratings that are most readily replaced are T-frame, NEMA design A, B or C and which operate at 3,600, 1,800, 1,200 or 900 rpm. In those applications where changeover to T-frame is difficult, premium-efficiency direct replacements for older U-Frame motors are available, which eliminate the need for adaptations on the replacement motor to match the original mounting dimensions.

Any application where seasonal or peak-load requirements must be accommodated by an oversized motor, but non-peak periods will force the motor to run at less than 50 percent of rated load throughout most of its duty cycle, usually cannot be justified on utility cost basis alone.

BEARINGS

If properly selected, handled, lubricated and maintained, bearings will play a vital role in sustaining reliable operation. If, however, they are neglected, the health of the operation will suffer. This is one area where a small investment in proper care can provide a big benefit in reduced downtime and operating costs.

This is particularly true in pits and quarries, which present bearings with one of their most severe operating environments. Dust and grit are everywhere, temperatures vary over a wide range, and exposure to the weather means that water will have to be dealt with. Some types of equipment present additional challenges.

An example of this is vibratory screens, whose rotating weight places unusual loads on bearings and amplifies the need for good lubrication. The need to perform some maintenance work at remote locations is another challenge. Anyone who has changed a bearing on top of a tower, with dust in the air and a stiff, cold wind blowing, can tell you that care for the bearing was not their first concern. All of these factors can contribute to bearing problems, and all are common in the aggregate industry.

GET THE RIGHT BEARING

Bearing selection is critical. While getting a bearing that fits in the hole left by the previous bearing is important, it is not the only consideration that affects bearing performance and reliability. For every standard bearing size, there are many possible variations in seals, internal clearance, accuracy class, material, cage type and other special features. All of these have an impact on how the bearing performs. Making sure you get the right bearing is the first step in avoiding problems. The following tips will help you get the right bearing.

1. Get to know your equipment. Many pieces of equipment use common bearings that can be replaced from readily available stock. Others require bearings that may appear to be standard but actually have special features that are not obvious.

A good example of this is the bearings used in some makes of vibrating screens. Certain screen makers use slightly oversized shafts. This difference is large enough to require that the inside diameter of the bearing also be oversized. If a standard bearing is used instead, the excessively tight fit will cause a loss of bearing internal clearance. In this case, the bearing will run hot and may fail in a matter of hours or even minutes. Get to know your equipment, and keep a record of the bearings that your equipment requires.

2. When requesting replacement bearings, make sure you’ve got the complete part number. Most bearing manufacturers place the basic size information on the exterior of bearing components. This information, however, may relate only to the part of the bearing on which it is marked and not to the entire bearing. There are also part number codes that may be included only on written documentation and not on the bearing itself. Checking equipment documentation and getting all markings from the exterior of the bearing will help to ensure you get the right replacement.

3. Consider premium and/or improved bearings in your toughest applications. The bearings that came with your equipment may not be the best available. The conditions under which some of your bearings operate may be more severe than what the equipment maker anticipated. There may also be optional bearing features that the equipment builder did not include because they added cost or because they just weren’t available at the time the equipment was made.

In any case, bearings with special improvements are often available for the toughest applications. When applied properly, dramatic increases in value will outweigh the small increase in price.

In the aggregate industry, debris-resistant bearings are particularly attractive. Hard-particle contamination that enters bearings dramatically shortens operating life. Seals reduce the amount of contamination, but cannot prevent it. A new solution is bearings that are made of debris-resistant materials. The properties of these materials have been tailored to minimize the damage created when contaminant particles get caught between rollers and raceways.

4. Purchase bearings from a reliable source. Seek a distributor who is an authorized source for major bearing makers. These distributors are not only more likely to have the bearing you need, but they will also be knowledgeable about a wide variety of applications and will be able to draw on the technical resources and expertise of their suppliers.

DON’T BREAK IT BEFORE YOU START

It’s no secret that many bearings fail to reach their expected life because they were not handled properly. This next group of tips will help you ensure your bearings live a long, productive life.

5. Store bearings properly. Bearings should be left in their original packaging until they are to be used and should be stored in a clean, dry place with a minimum of vibration and temperature fluctuation. Improper storage can result in corrosion and false brinelling of the raceways.

6. Keep the work area as clean as possible when changing bearings. It’s understood that some bearings must be changed at the equipment site, regardless of where that may be. In such cases, remember there is a payoff for efforts to keep dirt and moisture out of the bearings and housings, and then take whatever precautions are practical. When a shop area can be used, make sure work surfaces are clean and dry, and keep bearings wrapped or covered with plastic until ready to mount them.

7. Use proper tools and techniques. Whether mounting on a tapered adapter, pressing onto a shaft or into a housing, or using heat to shrink-fit parts, proper care must be taken to not damage bearings. Avoid use of hard objects to strike bearings. Never use a torch to heat a bearing, and when pressing onto a shaft or into a housing, apply pressure only to the ring that is being fitted. Use tools that are designed to distribute pressure evenly around the face of the bearing without contacting seals, shields or cages. Hot plates, ovens, heated oil baths and temperature-controlled-induction heaters are recommended for heating bearings. Distributors usually offer a variety of mounting and dismounting tools that not only protect the bearing from damage, but also make installation much easier.

KEEP IT RUNNING SMOOTHLY

Once the bearing is installed, you’re only half done. Proper lubrication is essential for reliable operation. While many ball bearings are sealed and lubricated for life, most other bearings require that the user supply and replenish lubricant. Without proper lubrication, excessive wear, smearing of raceway surface material and bearing seizure can be expected.

8. Use the right lubricant and quantity. The proper choice of grease or oil is dependent on operating conditions such as temperature, speed, load and need for resistance to moisture or chemicals. Fortunately, many lubricants can handle a wide range of conditions. A little planning can help you determine the minimum number of lubricants needed to meet your varying needs. For oils, matching the viscosity to the normal operating temperature of the equipment is the key factor.

Temperature is also a big factor in selecting the right grease, but speed, load and other concerns also play a role. The most popular greases for general bearing applications are ones with mineral base oils and lithium-soap thickeners. When conditions are extreme, other oils (silicone, ester, synthetic) and thickeners (sodium, calcium, aluminum, urea, bentonite.) are often used. Consult with your bearing or lubricant supplier if you are unsure.

Getting the right amount of grease can be just as important as getting the right type of grease. In addition to lubricating the bearing, grease also forms a barrier that restricts entry of contaminants. If there is not enough, contaminants may enter freely, and the bearing may run dry. On the other hand, if there is too much grease, the churning created by the bearing’s movement will generate excessive heat.

In general, grease amount is decided based on bearing speed. If the bearing operates at less than half of its limit speed, the bearing may be packed full and the remaining space inside the housing at half to two-thirds. If the bearing speed exceeds half of the limit speed, the remaining space in the housing should only be packed one-third to half full. Consult your bearing supplier regarding grease fill for equipment that operates at extremely high speeds or is sensitive to rises in temperature.

9. Replenish the lubricant at proper intervals. Grease deteriorates in use due to the effects of temperature, contamination and mechanical stress. Eventually, it loses its ability to properly lubricate. Bearing suppliers can provide general guidelines based on the bearing type, size, speed and temperature. Because conditions vary widely, your practical experience is also valuable here. Higher speeds, heavier loads, higher temperatures and the presence of moisture or dirt are all factors that call for more frequent replenishment of grease. Some applications, such as vibrating screens, may require replenishment on a daily basis. In general, more frequent replenishment of smaller quantities is better than occasional replenishment of larger quantities. Experimentation and careful observation are the best way to determine the proper interval for a particular application.

Telematics

Most aggregate operations live and die by the mantra of “lower cost per ton.” This often conjures up visions of “bigger, faster, stronger” when, in reality, most companies need to think “smarter.”

Telematics, a web-based software technology that takes critical operating information transmitted from equipment in the field and presents it in easy-to-understand reports, is one such tool to help companies operate more intelligently. Operating a mixed fleet? That’s fine, as many manufacturers offer consistency in data output for application programming interface solutions that enable you to aggregate data from several telematics systems into a single database.

The most obvious benefit of telematics for most aggregate applications is a complete overhaul of the way equipment maintenance and service takes place. But there are other operational benefits related to productivity, equipment utilization and performance that can significantly lower operating costs and the bottom line.

GETTING STARTED

One of the most important things to understand about telematics is that the barriers to entry are very small. Most heavy equipment is now built telematics ready, meaning it comes equipped with what it needs straight from the assembly line.

As a web-based service, a telematics solution does not require added computers or servers in the office. The program can be accessed from the devices you already have that allow for web access. Fleet managers can access the program in the office, on the road or from their computers at home. Reports are easily formed within the program, and access can be granted throughout the organization as needed.

Most telematics programs are purchased through a monthly subscription on a per-unit basis, but some manufacturers are now offering telematics as a standard service at the time of purchase on select models. Case Construction Equipment does this, for instance, for the first three years of operation under its ProCare program.

STREAMLINING MAINTENANCE

Managing and performing planned maintenance on large fleets of equipment is time intensive. In the past, this required visits to the machine and phone calls to operators to determine data such as current engine hours, fluid levels and operating temperatures. All of this takes significant time and resources and can complicate efforts to schedule downtime for planned maintenance at times that are both optimal to machine health and site workflow.

Telematics provides fleet and maintenance managers with real-time maintenance data on each machine in a fleet. The data is automatically aggregated and saves significant time in collecting data and creating reports – including long-range historical reporting and analysis.

Alerts can also be created that are sent to the maintenance team if certain machine health functions are operating out of acceptable parameters. All of that data helps managers better plan, schedule and perform maintenance without having to rely on operators or site visits.

The accurate and current information also helps ensure a machine isn’t pulled out of service too early or too late, and is done at a time that is most convenient for production.

Equipment dealers can also be given access to the data produced by a telematics program. This allows the dealer’s service department to see what you see and be proactively engaged in the upkeep of each machine and possibly help identify problems before they happen.

BENCHMARKING PERFORMANCE

Telematics offers a wealth of insights into your operation, as long as you know what to do with the information. Engines, for instance, aren’t built to idle. Engine idling indicates an inefficient use of that machine, but what else does it tell us about machine performance and workflow?

Data made available by a telematics program helps raise red flags that will help you diagnose other systemic problems that may be robbing you of productivity. For instance, one possible cause of excessive engine idling is operator inactivity. If observed, this can be turned into an opportunity to coach an operator on best practices and efficient machine operation.

A second cause of excessive idling is that the equipment is not optimally matched to the application. For instance, a wheel loader with a 6-yd. bucket may be matched with a hopper that can’t handle that much material at once. As such, that loader may be completing a fairly simple cycle but then sitting and waiting for the material to cycle through the hopper before it can dump the next bucket. This idling is not an efficient use of the machine and may indicate a number of improvements your operation should make.

For instance, do you need that large wheel loader with the 6-yd. bucket, or would a smaller wheel loader with a 3-yd. bucket be more efficient and ultimately offer a lower owning and operating cost? Telematics helps determine the right machine for the job.

Also, are there improvements you can make to your plant to allow it to process more material faster? This particular example may be an oversimplification, but identifying a piece of equipment not operating to its full potential can expose other efficiencies that can be implemented upstream or downstream of that machine. Maybe the problem is not with the machine, but with the workflow.

Similarly, telematics may help identify underutilized assets and allow companies to make more intelligent equipment-purchasing decisions. Larger pit and quarry operators with multiple sites may be able to identify underutilized machines at one location and put them to work at another location where the added production is needed, instead of making a redundant equipment purchase while an underused machine sits idle elsewhere.

At its most basic level, a telematics program helps you set benchmarks for operation and makes you aware of changes in data that may signify other issues. If your fuel use or engine hours suddenly change from one week to the next, there must be a reason. Telematics gives you that evidence to investigate and improve your business in real time.

DEMYSTIFYING TIER 4

With waves of new Tier 4 Interim and Tier 4 Final technologies hitting the market, much is made of how these solutions differ and what it means to the operator. The two primary solutions available to heavy equipment operators are selective catalytic reduction (SCR) and cooled exhaust gas recirculation (CEGR). Each has its place, and both affect engine operation in different ways.

SCR, optimally matched with machines such as wheel loaders, requires the use of diesel exhaust fluid (DEF) to help eliminate pollutants. Telematics can monitor critical operating factors related to this technology, such as DEF fluid levels and dosing rates.

CEGR engine solutions commonly found in excavators and other heavy earthmoving equipment feature additional components, including a diesel particulate filter, and require the engine to go through regeneration to burn off excess particulate matter. Telematics can monitor regeneration cycles and provide additional insights into CEGR engine performance and health.

MEETING CHANGING DEMANDS

One of the best features of some telematics programs is the ability to configure data to help best address the concerns of each individual operation. For instance, what one operation may want to record and note in relation to idling may be different than what another operation wants to record. Having the ability to edit the parameters and tolerances of the reporting structure helps ensure it provides the most useful data to help set trends and make changes that benefit the business.

There are also important functions available related to equipment security and safety. Alerts can be established if a machine is started after hours, or if a machine is moved outside of its geo-fence – a virtual perimeter around the machine. This helps identify and stop unauthorized equipment use.

When viewed holistically, telematics is an extremely powerful new tool that has the potential to help fleet managers and business owners change the way their equipment fleets run. As the technology progresses, it will eventually become a standard way of doing business and critical in managing fleets of all sizes.

Fleet management

Financial constraints often force fleet managers to make tough equipment decisions. Should I repair a vehicle or replace it? If I do repair it, how much work should I do: just enough to get by or a complete overhaul? Is it better to replace two low-cost units or one higher-cost unit?

In far too many cases, the answers to these questions are based on educated guesses or are driven by external decision makers with their own agendas. One of the best financial-analysis tools available to fleet managers for making decisions of this nature is the net present value (NPV) life cycle cost analysis. Instead of relying on guesswork, and not being able to fully defend your position, a NPV life cycle cost analysis will show you the true total cost of each alternative.

Many fleet managers have used life cycle cost studies for years. Unfortunately, the usual study only considers direct cash flows. A typical logic thread might be something like: If I spend $1,000 today, I will save $250 a year, which means I will recoup my investment in four years. There are two faults with this type of analysis. First, it does not consider the time value of money. Secondly, decisions made by a fleet manager working for a taxpaying entity have a direct impact on the taxes the entity pays. An after-tax NPV life cycle cost analysis addresses both of these issues.

WHAT IS THE DIFFERENCE?

The time value of money is directly related to an entity’s cost of money. A taxpaying business’ cost is normally considered to be its minimum acceptable internal rate of return. For a government agency, it is typically the weighted cost of debt (direct loans, bonds, etc.). This cost of money, which is normally expressed as a percentage, means that one dollar at some point in the future is worth less than a dollar in hand today. For a given cost of money, the current value of a dollar at some point in the future is known as its present value. The total present value of a series of related expenditures, spread over a period of time, is referred to as the net present value.

If an entity pays taxes, the fleet manager must also consider the true bottom-line cost of an expenditure after taxes. Ordinary expenses reduce gross income, which in turn reduces tax liabilities. This effect is known as a tax shield. For example, if your entity has a total effective tax rate of 30 percent, a dollar of ordinary expenses only costs 70 cents after taxes. Capital expenditures, on the other hand, must be depreciated over a period of years, so the NPV of the series of depreciation allowances is less than the actual capital expenditure.

The following is a very basic example of a tax shield. Let’s say that your business has a tentative gross profit of $1,000 for a period, and the effective tax rate is 10 percent. That means that you will owe $100 in taxes for the period, leaving you with a net income of $900. If you incur an expenditure of $100, your gross profit will drop to $900 and your tax liability will drop to $90. That means that your net income will be $810, so the additional $100 expenditure actually only costs you $90 after taxes. Many businesses have total effective tax rates in excess of 40 percent to 50 percent, so the impact of a tax shield can be very significant to the bottom line.

AFTER-TAX NPV ANALYSIS

Admittedly, most fleet managers are not familiar with this type of financial analysis, but available spreadsheet programs perform the calculations for you once you input the necessary information. The biggest single issue the fleet manager faces with this type of analysis is that it documents the total cost to the entity, as opposed to just the fleet manager’s budget. However, your financial people are probably very familiar with the concept, so if you are in a position to work with them, you may be able to use this type of analysis to document your stewardship of the entity’s budget and get additional funds when justified by your analysis.

When you make an NPV analysis of a series of expense options, the NPVs of the various alternatives will be negative. The option with the least negative cost is the best alternative from a purely financial point of view. Some NPV life cycle cost spreadsheet programs, such as the NTEA’s Vehicle Life-cycle Cost Analysis Program, will also show your annualized cash flows. If the NPVs of two options are very close, these annualized cash flows may be more important than the total cost.

In the case of revenue-producing alternatives, the NPV will be positive if the alternative being considered is earning more than the established cost of money and negative if it is earning less. An alternative can be revenue generating even if there are no direct income flows associated with it. For example, you may be considering upgrading a new truck in such a way that will be more productive. If the operations associated with the existing truck incur a significant amount of labor overtime, the increased efficiency may eliminate that overtime. The loaded overtime rate (say $50 per hour), multiplied by the total hours of overtime eliminated (say one hour per day times 260 days per year), generates a direct labor savings for the company – which can be treated as additional revenue. Using the hypothetical numbers stated, the annual savings (revenue) would be $13,000.

If you can increase the productivity of a new unit to the point that it will replace two existing units, the potential savings (revenue) may be even greater since you will be eliminating the total labor costs of a driver (and possibly a helper), as well as the maintenance and operating costs of the second truck. The opposite of this scenario applies when people in your entity want to downsize a vehicle to reduce fuel costs. If this downsizing increases over time, or forces the addition of a second vehicle to get the work done, the fuel savings will probably be less than the other costs incurred.

Even replacing a high-cost unit with a new unit that has a lower life-cycle cost can be considered revenue producing, since it may reduce total life cycle expenditures. For example, if you have a vehicle with a lifetime average operating cost of $1.50 per mile, and the truck runs 15,000 miles per year, your annual costs will be $22,500. A new, more fuel-efficient vehicle may have a projected average annual operating cost of $1.10 per mile or $16,500 per year. Therefore, the cost reductions (revenues) associated with the new unit will be $7,000 per year.

Of course, as we have seen, the actual bottom line in these examples is not without some complexity. If you work for a taxpaying entity, the reduction in labor payments will eliminate a tax shield. In addition, the cost of the upgraded vehicle must be depreciated over time as opposed to being treated as a one-time expense. In all cases, the carrying costs (time value of money) must also be taken into account. However, a properly applied NPV life cycle cost analysis will take all of these factors into consideration and the true costs of each option.

RANKING ALTERNATIVES

If you have a number of revenue-producing alternatives, and only enough money to fund part of them, you can perform an NPV analysis and determine the actual return for each alternative. The individual rates of return can then be used to rank the alternatives. For example, let’s say you have five projects, with a total cost of $450,000, but you have only been allocated $360,000. An NPV analysis provides the following information:

In this case, Project 2 has the highest return on investment (ROI) (20.3 percent) and should be funded first. Next would be Project 1 at 18.2 percent. The remaining projects are returning less than the desired ROI, but may still be perfectly valid, and necessary. Unless there are some overriding requirements, such as regulatory compliance, the next project funded should be No. 5, at 15.1 percent. Lacking an ROI analysis, you may have been tempted to fund Projects 3 and 4, which have the same total cost as project 5, but provide a lower ROI.

Off-highway tires

Tires play a major role in any quarry’s productivity and, ultimately, its profitability. Simply by knowing and observing simple basic tire facts and techniques a quarry can make a noticeable difference in the life of its tires and the performance they deliver while in operation. Choosing the correct tires for the application, maintaining those tires through proper maintenance techniques, and educating machinery operators about tire basics are just some of the ways that a quarry operation can realize significant savings and uptime.

The importance of a proper understanding of tires and their place in any operation cannot be underestimated. Any quarry that ignores its tires and the significance of their proper selection, maintenance, and usage is virtually guaranteed to encounter tire failures, downtime and a significant loss to its bottom line.

CHOOSING THE CORRECT TIRE

Not every tire is capable of optimal performance on every surface or terrain. Some tires are capable of operating adequately in multiple applications, but most tires are designed to deliver the best possible performance based on the requirements of a specific application. That is why it is vital to know, as accurately as possible, what demands the quarry’s terrain will make on the equipment and its tires. This knowledge will greatly help when deciding which tires to fit on equipment.

As part of the tire-choosing process, another issue to consider is whether the equipment will be used primarily off-road, on-road or an even mix of both. To be classified as off-road, a specific piece of machinery would generally spend at least 80 percent of its operation time off-road, with only 20 percent of operation occurring on-road. The opposite is true to be classified as on-road – 80 percent of operation on-road, with 20 percent coming off-road. Some equipment may truly be considered on-/off-road, if its operation time is spent almost equally between applications. It is important to know this information, because the use of the tire will determine what rubber compounds in the tread are recommended, as well as the tread depth and tread design. An on-road tire is engineered differently to be optimized for road travel, with more attention to using softer rubber compounds, shallower tread depth and less aggressive tread designs. Off-road tires will feature more robust sidewalls, harder compounds and aggressive treads to guard against damage, provide increased traction and handling and evacuate debris or stones from the tread.

When deciding between radial tires and bias-ply tires, there are some important factors to be aware of. In the 1940s, almost all construction, mining and quarry equipment ran on bias-ply tires. A bias-ply tire is made up of textile plies, usually nylon or rayon, crisscrossed on top of one another and bonded together by a rubber compound. This design is prone to damage from poor heat conduction and punctures. In addition, sidewall distortion can lead to uneven wear and reduced adhesion between plies.

In 1959, Michelin brought radial tire technology to the heavy equipment market. The biggest difference between a radial and a bias-ply tire is that the sidewall of a radial is separate from the crown, allowing each component to work independently, thereby enhancing performance. In a radial tire, metallic casing plies hold the sidewall and the crown together, reinforcing the strength of the tire. In addition, the metal allows for greater heat dispersion and impact resistance. Since the sidewalls can flex independently of the crown, a radial tire maintains a consistent contact patch and offers exceptional operator comfort without compromising stability and performance.

“To improve upon the radial design, modern radials incorporate a special butyl rubber layer that eliminates the need for a tube in the tire,” said Todd Ramsey, director of replacement market sales for Michelin North America’s Earthmover division. “Tubeless earthmoving tires provide several advantages by eliminating the risk of puncturing the inner tube and also the risk of air becoming trapped between the tire and the inner tube.

“In addition, when a puncture does occur, there is less likelihood of a sudden deflation. With a tubeless tire, air loss is slower, allowing an operator more time to reach the repair workshop,” said Ramsey.

Once a specific tire has been chosen for an application, avoid mixing tires on a given piece of equipment, such as placing a deep-treaded tire next to a regular or shallow tread tire or a radial tire and bias-ply tire next to each other in a dual configuration. Different tires will not work well together, sacrificing traction and performance and possibly leading to the damage of vehicle components.

Understanding the differences between radial and bias-ply tires and determining the correct application will enable quarries to make the best decision when choosing which tire to put on their equipment.

MACHINERY OPERATION

It is essential that a tire not only be correctly chosen, but also the machine on which the tires appear correctly operated. All operators should have a basic knowledge of tires and how they work. With this knowledge they will be better equipped to operate the machinery that the tires run on, reducing the wear-and-tear effects on the tire and increasing the overall life of the tire.

“A good understanding of tire basics and the role of tires in a quarry should be mandatory for every machinery operator on a site,” said Ramsey. “Properly educated and trained drivers will aid in ensuring the safe and productive operation of equipment. This will inevitably lead to the tires and the equipment lasting longer.”

Operators need to understand that tires are not bulletproof and should not treat them as such. Whenever possible, they should avoid hitting any debris, such as rocks, while traveling along haul roads. Even a small rock can cause significant damage to a large tire if the conditions are right. Speed, distance, load, curves and slopes all play a part in how a tire performs. These are all areas that are controlled by the driver. Drivers have to understand that if they are going to drive a long distance, then it is important that they slow down so not to overheat the tires. A little knowledge about tire limits can help any driver make the tires last a long time. If drivers know that the rubber compound being used in the tires on the vehicle is for protection and not speed, it helps them to understand why they must slow down. If the compound is for speed and not for protection, then they understand why they need to be even more wary about avoiding potential hazards.

“No matter how well the tires are made, it is the driver that has the final say as to how the tires perform,” said Ramsey. “The site needs to educate the drivers as to the importance of what the tires do and how important they are to the site’s productivity. If a driver takes pride in the equipment, that should include the tires. The driver being sure the equipment is running up to speed needs to include the tires. The tires and the engine are the two things that keep the machine running.”

In the dump areas, when a driver slows down when approaching, the vehicle is capable of a wider radius turn, which reduces spillage and the possibility of riding on the shoulders of the tires. This reduces the wear and tear on the tires and prolongs their life. By approaching at a slower speed, drivers are better able to navigate rocks or other debris in the area and protect the tires. At dump areas, it is very important to avoid debris, because the tires have been working very hard to carry the load and have probably reached their maximum temperature, making them more susceptible to damages. Approaching the loading areas at a slower rate improves the ability of the driver to spot the truck in a better position to get a well-centered load and avoid any spillage that might be in that area from previous loading.

MACHINERY AND SITE PREPARATION

Other areas that should be considered to keep tires in top shape and operating at their best are haul roads and chains. The preparation of a site and the set-up of machinery can be utilized to prevent unnecessary wear and tear on the quarry’s tires and improve equipment’s overall performance.

“When designed and maintained properly, haul roads have a very significant impact on tire life,” said Ramsey. “Quarry planners and haul road maintenance personnel should pay special attention to road surface conditions, super elevation curve radius and speed in curves, as well as the cleanliness of loading and dumping areas to eliminate potential puncture hazards.”

The design of haul roads needs to match up to the rubber compounds of the tires being used on the machines of that particular site. Certain compounds are better suited to short hauls as opposed to longer hauls. If used in the wrong application, the tires can be damaged beyond serviceability.

Wet haul roads have a higher tendency to cut tires than do dry roads. Water acts as a lubricant in this case, aiding any debris in cutting or damaging the tire. Because of this fact, spot watering an operation’s haul roads is a better idea than continuous flooding to keep dust down. Flooding is not recommended because it can erode and deteriorate the road base as well as cause the formation of puddles. Puddles have a propensity to hide rocks and other debris that are serious hazards to tires. They also leave the road uneven, increasing the risk of damage to the vehicle’s suspension, frame and bed.

One benefit to crowning a haul road is that it provides drainage for the water and keeps it from puddling. If the roads are sloped or banked appropriately, it can greatly aid the turning radius of the vehicles. There are limitations to crowning the roads. If the crown is too great, it will cause the load to transfer to one side of the vehicle, making the tires carry more load on that side and reducing their potential life.

Hauling on steep grades causes a load shift to the front or rear of the vehicle depending on which direction the load is being hauled. If hauling the load down, pay special attention to the air pressure adjustment of the front tires and set them according to the operating conditions. This compensation should be done only after consulting with a tire manufacturer representative to ensure proper air pressure setting. When designing haul roads, try to avoid grades higher than 8 percent to reduce the effect of load transfer.

Sometimes, when designing roads, the equipment that is going to be running on those roads is not taken into consideration – only the equipment being used to build the road. The materials used to build roads play a very important part, particularly when the sites are in rainy areas.

When the roads are built, they should be maintained in good operating condition, because it would be more expensive to rebuild them than to maintain them. To maintain the roads does not take a lot of effort or investment. Operating the motor grader on a daily basis, filling the potholes and applying the correct amount of water is all it takes to keep a road in good condition.

The greatest benefits of maintaining smooth haul roads will be even wear patterns on the tires, increased wear and potential life, less damage to the suspensions and frames of the vehicles, more comfort for the vehicle operator and, ultimately, greater productivity and safety.

Tire chains are typically used in only the most severe of applications and are often used in applications that really do not require their use. Chains can do some damage to the tires fitted under them, but the protection that they provide the tires outweighs the minor damage and sidewall wear. There are other factors that come into play when running chains. Because of the mass of the chains, there is a huge amount of weight added to the equipment, causing tremendous wear and tear on the drive train, the braking system and the engine. Chains are very expensive and require continual upkeep and maintenance to keep them tight on the tire. By running a good radial tire that is designed to take the abuse of the specific application, quarries can virtually eliminate the need for chains.

TIRE-MANAGEMENT PROGRAM

Every quarry should have a tire-management program. This program will not only enable personnel to better maintain the tires, but also provide site management with vital data for tracking performance and purchasing decisions. Each tire that an operation owns should be included in the management program and should be tracked “from the cradle to the grave.”

The tires should be monitored on a regular basis. Information such as air pressure, wear patterns, operation hours and machinery, damage and repairs should be recorded. When a tire is removed from service, an end-of-life examination of the tire should be conducted. The tire should be inspected for damage, tread wear or other factors that may have caused it to come out of service. This information should be contained in the tire-management program.

Cross-referencing tires that come out of service due to similar causes may uncover a reoccurring problem with a certain piece of equipment, maintenance technique or site layout. Analyzing tires at end of life can shed light on these problems and allow them to be fixed, increasing the life of the quarry’s other tires.

There are many ways to handle a tire-management program, from using paper and pencil for gathering tire data to using electronic-monitoring systems. The quarry must remain actively involved in the program whether it keeps the program in-house or outsources it to a service dealer or tire manufacturer.

A tire-management program should also stipulate maintenance practices, such as tire rotation and alignment, inspection procedures, specified air pressures, pull points and more. If a quarry plans to retread its tires, paying close attention to the pull point is vital to ensure the casing will be capable of withstanding the retread process. For the tire-management program to succeed, it must be written, communicated, monitored and enforced.

RETREADING

Retreading OTR tires in North America has become a more viable option for sourcing an operation’s tire needs. However, not all tires should be retreaded. All tires should be subjected to rigorous inspection processes to be considered for retreading. Any damage that could compromise the tire’s casing should be careful analyzed. Without verifying the integrity of the casing, no tire should be accepted for retreading.

Some tires are capable of being retreaded only after going through an even more stringent type of testing known as NDT (non-destructive testing). In NDT, tires are tested to confirm the strength of the casing and the tire’s ability to undergo retreading.

Still, other tires should never be retreaded. Certain sizes and tread designs should not be retreaded due to the application and the demands that are made of the tires on a regular basis. A tire that experiences difficult operating applications, and therefore significant wear and tear, will not be capable of safely and successfully going through the retread process because of the fatigue and stresses the casing has endured.

Tires will always play a major role in any quarry. This means that the importance of a proper understanding of tires and their place in the operation cannot be overemphasized. Ignoring tires and their significance, proper selection, maintenance, repair and usage will put a quarry and its employees in a dangerous work environment, as well as virtually guarantee a rise in tire failures and a downturn in ultimate profitability.

UNDERSTANDING OTR

The best way to understand OTR tires is to be trained about them. Many manufacturers offer training classes that can help you understand what you need to know. Realize that you will be making an investment in this training. You will be investing your own time away from your job and maybe away from your family. Also, there may be costs in getting there, etc., so make sure that you attend a seminar that will really help you. Often times, the best way of knowing how valuable a seminar will be is to solicit input from those that have already attended.

Just exactly what do you need to know? Probably the most important thing for you to know is how to maintain what you already have. Now is the time to consult with your local suppliers and your tires’ manufacturer to find out how you can do a better job of keeping what you have running as long as possible. Keep in mind that tires and rims are a pressure vessel. Do not run any tire or rim/wheel that is unsafe.

To have a complete, effective OTR tire-maintenance program you must have several different systems in place and working efficiently. The first thing you should do is to review your air-pressure maintenance program to see if you are doing everything you can. Remember, it’s the air in the tire that supports the load. But also remember, it’s the air pressure that ensures the tire is operating at the shape the tire’s manufacturer designed it to operate. When a tire operates at its designed shape, it delivers all those things you buy the tire to do for you: provide traction and braking, ensure optimum control of the vehicle while cornering, provide the maximum level of cut resistance possible, wear at the slowest possible rate, and provide the best ride possible for the operator and the machine, etc. Operating the tire out of its designed shape, even for a short time, affects all those productivity functions just mentioned but also increases the fatigue within the tire and shortens its overall life.

To give the tire a chance to provide those things it was designed to provide means that you must carefully check and correct the air pressure in OTR tires at least once a week. I know, you are thinking that you can’t do that; the cost and hassles aren’t worth it. Well, let’s think about how much production you may lose if a tire fails.

My unofficial nationwide survey confirms that the average downtime associated with a flat tire is approximately four hours. That includes the time required to get somebody to the flat, fix it, air it back up and for you to get an operator on it again to get back to work. How much production do you lose in those four hours? What does it cost you to make up that lost production? Pretty expensive, if you can do it. The longer you can go between flat tires means that much more production.

Have you ever considered how important traction is on your OTR machines? Have you ever put the white lines on the sidewall of both the front and rear tires on a machine and then watched it go up a grade? Have you ever watched a loader while in the face? If those white lines don’t stay parallel on a straight stretch, your tires are slipping and your vehicle is not moving as fast as it could. In other words, you are losing production. Even if you buy the right tire with the best pattern available for your operation, that tire can’t deliver all the traction you need unless it is operated at its designed shape. Could you use one more load per day? That is very possible if you will give all your tires a chance to deliver their best traction by maintaining the tire’s designed shape with the correct air pressure.

Okay, so you agree you need to check air pressures weekly; now you want to make sure that they are inspected the proper way. Number one, all air pressures must be taken with a calibrated air-pressure gauge. It really doesn’t make much difference how much you spend on an air-pressure gauge or who made it because they all can be wrong thanks to the dust, grime and water that finds its way into the tire’s air chamber. If you start with an accurate gauge it can become very inaccurate after only a few tires. What do you think the possibility is that the air gauge you have is still accurate after all these years? The only way to make sure air pressure gauges are accurate is to compare them to a known source such as your main compressor’s gauge. This may not be perfect, but is probably better than never comparing the gauges to one source. My recommendation is that whomever is going to check air pressures for you should stop by the shop, calibrate their gauges with your main gauge and then go make sure your air pressures are correct.

When someone checks your air pressures, make certain they have a compressor with them of sufficient capacity to correct any incorrect pressures. Make certain that you receive a written report that lists what the air pressure was and what it was corrected to. Someone, you or the site’s “tire boss,” should then compare this week’s inspection with last week’s to look for tires that are losing air pressure. Someone has to have the responsibility to spot these leaking tires and then to decide what to do about it and when.

Put yourself in the shoes of the person checking air pressures. How do you know what air pressure the tire should have? Remember, the goal is to maintain the tire’s designed shape. The correct shape is determined by analyzing the amount of load on the tire and the speed the tire must travel. All major tire manufacturers have OTR tire data books that will help you figure out how much air pressure is needed for each OTR vehicle you have. Now, the next problem is how to communicate this information to anyone who might have occasion to check air pressures. By far, the best thing to do is to stencil the recommended air pressure on the fender or on the hub or somewhere near the tire. Every tire should have this information readily available so there is no confusion as to what air pressure you want in the tire.

OK, so you are moving toward a “perfect” air-pressure program that will ensure peak productivity. One thing, though: How often are your air pressures going to be checked when they are “cold?” The air pressures that tire manufacturers recommend are based on a tire that is “cold,” not run for at least 24 hours. If you are like most operations, this condition isn’t always available. So, what do you do when you have to check a “hot” tire? My recommendation is that you develop a “hot” air pressure recommendation. How do you do this? Well, you will usually find that air pressure builds up by 10 to 15 percent as the tire runs. If you apply this figure to the “cold” pressure recommendation, you will have a “hot” tire pressure target or reference point. If you stencil this pressure on the vehicle as well, whomever checks your pressures will know what they should find.

The next important thing you must do in your tire-maintenance program, especially because of the shortage of OTR tires, is to manage this precious asset. You no longer can be reactive, you must take control. You really can’t wait for the tire to go flat to decide you could have repaired that tire. The key to managing your OTR tires is information. You can’t manage what you don’t know about.

There are a couple of tools that can help you manage your OTR tires. An important thing you need is a very thorough inspection and reporting system that give you fresh and accurate information about tire conditions and performance. The best way to get fresh information is to get your operators and mechanics actively involved in looking at OTR tires and rims, and then passing this information up the chain to the “tire boss.”

Tires that all of a sudden have a big cut or new bulge or are missing a lug are things that the “tire boss” needs to be aware of so he/she can take action to prolong that tire’s life. Somebody needs to decide if the tire can be repaired, moved to a less strenuous position or replaced.

Obviously, it won’t take long before all the information coming in will get out of hand. The solution to keeping track of your OTR tires’ conditions is to maintain some kind of database. Years ago, most efficient OTR companies kept tire information on 5×7 cards. Today, there are computerized programs, such as Bridgestone’s Treadstat Tire and Rim Management software program, that not only store the information but make the retrieval and analysis of the information simple.

Tire-and-rim management software can provide you the need-to-know information that matters. Not only can it provide the necessary data for safer tire operation, but it is an excellent management tool for inventory control and forecasting, selecting appropriate tires for site operating conditions and matching. If you are not keeping accurate records of your OTR tire performance and conditions, you should start today.

One of your toughest jobs today is to anticipate your tire needs. If you get lucky and have your local supplier call you with an offer of some tires, you need to be able to make an informed decision as to whether or not to buy them. Once the information about your tires is in one of the tire-tracking systems, you can easily tell how many tires you can expect to use over the next few months.

Whatever you do with and for your OTR tires, a word of caution: there is enough explosive force contained within an OTR tire to do very serious damage to people and machines. Do not use an unsafe tire. Make certain that everyone on your operation knows that a tire and wheel is a pressure vessel; that they know not to apply heat to a brake drum or stud if the tire is still on the wheel. They have a need to know.

Tire maintenance

Downtime can cost significant money. While there are some instances of downtime that are unavoidable, there are measures you can take with your equipment that can help avoid those associated costs.

Air-pressure maintenance. All tires should be kept at the pressure specified by the tire and vehicle manufacturers. The correct tire pressure for a radial tire will vary widely depending on the machine type, manufacturer model type and weight. It is always a good idea to consult the tire manufacturer to ensure that each axle is properly weighed and the correct pressure is set.

Any vehicle with properly inflated radial tires carries its load in a noticeably different way. Radial tire technology separates the work done by the sidewall and tread areas, allowing the tire to conform to the terrain by running at lower air pressures than bias tires. This lower air pressure yields a more even footprint and higher levels of traction for radial tires. The constant footprint ensures that the lugs strike the contact patch simultaneously, reducing vehicle vibration.

Driver awareness. Because the operators are on-site all the time, they see problems that need to be fixed, whether it’s in their pre-trip inspection or while operating the equipment. Managers and supervisors can draw their operators into the equation by asking for input and cultivating a team approach to tire and vehicle maintenance. Operators should be kept in the loop on situations with their equipment or tires, so they are aware when they conduct inspections or operate the equipment.

It is crucial that operators report any spillage, whether from their vehicles or other vehicles.

■ Tire and rim inspection. All vehicle operators should do a thorough walk-around inspection of their vehicle before beginning operation. They should look for cuts, holes, cracks or any other damage to tires or wheels. The constant inspection of a rim and tire helps to minimize and detect any issues in a timely manner and ensure they are dealt with before becoming major maintenance issues or going beyond the point of serviceability.

■ Haul road maintenance. Maintaining the site’s haul roads can help prevent tire punctures and other damages. When designed and maintained properly, haul roads can reduce negative impacts on tire life. Site planners and haul road maintenance personnel should pay special attention to road surface conditions, super elevations, curve radii and speed in curves.

Hauling on steep grades will cause the load to shift toward the front or rear of the vehicle. If hauling downhill while laden, pay special attention to the pressures of the front tires and set them according to the operating conditions. This compensation should be done only after consulting with the tire manufacturer representative to ensure proper tire pressure settings. It is best to avoid grades higher than 8 percent to reduce these load-transfer effects.
When designing haul roads, it is also important to use the appropriate curve radii in turns, so they are not too tight. Build a crown into the roads at approximately 3 percent to help with water runoff.

■ Mechanical vehicle maintenance. When it comes to tire life optimization and avoiding downtime, maintaining the vehicle is critically important. Brakes, struts, rock knockers and alignment all need attention to function properly and not have an adverse effect on a vehicle’s tires. Ensuring the vehicle is correctly aligned helps to prevent uneven wear on the steer axle tires. It is also important to check the suspension regularly through a comprehensive strut maintenance program and to evaluate the rock ejectors for any potential problems.

■ Load management. Load management is another crucial area because of the significant weights carried by just six tires. When a load is not centered, it can often put too much weight on one corner of the truck, causing an overload on that corner’s tires. Overloading tires will lead to shorter tire life or downtime. Even if properly centered, every load should stay within total gross vehicle weight compliance. Michelin, for example, suggests conducting weight studies regularly.

■ Support equipment. The role of support equipment on a mine site should not be minimized or overlooked. They are key pieces of equipment that play a vital role in keeping haul roads clear of rocks or other debris that could damage tires. A motor grader or rubber-tired dozer should be used on a regular basis, not just for the haul roads, but also for the loading and unloading areas to clean up any spillage. As mentioned previously, operator training should include communicating and reporting work area spillage.

■ Scrap tire analysis. Tires will normally display what happened to them to cause them to come out of service. Inspecting scrap tires as they come out of service can help prevent future tire loss and indicate the need for tire or vehicle repairs or adjustments in vehicle operation.

It is an important step to analyze the history of scrap tires and evaluate and determine the type of tire damage, the vehicles on which the tires were operating, as well as the area of the site. Also key to the evaluation are load distribution, weight transfers or misalignment.

■ Tire performance improvement committee. Establishing a monthly tire performance improvement committee can benefit a site by forcing discussion on how tire assets are being used and maintained. The committee should be composed of personnel from different areas of responsibility at the site. Maintenance, operations, production and operators should each have a voice and provide their input to improve and enrich the meeting.

■ Communicating/reporting. The last area that can help improve tire performance and avoid downtime is to generate clear and specific policies and reports of all the initiatives and progress made in any meetings. For tire maintenance to succeed, policies must be written, communicated, monitored and enforced.

Oils and lubes

When considering the importance of reliability in lubricant performance, there is always room for improvement when it comes to housekeeping issues. Keeping lubricants in machinery clean can be compared to the work of the kidneys in the human body. When the blood is efficiently cleaned, the body runs efficiently and lasts longer.

There are some basic and simple solutions to enhance the life of your equipment and machinery. These are simpler than you might imagine. The fact is you are ahead of the game if you are monitoring your systems on some level. To find out where you stand on this issue, give some thought to your own operation, and how you view your treatment of lubricants on an everyday basis:

1. Do you monitor system or equipment failures, and how is the data managed?
2. How and where do you currently store your oils and lubricants?
3. Is contamination of your lubricants a concern?
4. Do you sample your stored lubricants regularly?
5. Have you upgraded your current storage and handling program?

INDUSTRY TRENDS IN CLEANLINESS LEVELS

OEMs have determined that a large part of the equipment-failure rate, especially while under warranty periods, can be traced to problems with cleanliness.

Premature component failure has been attributed to these causes:
■ Dirt: 45 percent.
■ Misassembly: 13 percent.
■ Misalignment: 13 percent.

Today’s systems run at higher pressures and higher volumes. Systems have more horsepower, are faster and are manufactured in more compact sizes with even higher breakout forces. External contaminants are responsible for 45 percent of premature component failure.

It is estimated that preventing dirt ingress is about one-tenth the expense of repairing a system once it has been damaged. In many applications the cost of that damage escalates when downtime and lost productivity are included.

■ Were you aware that more than 75 percent of hydraulic-system failures result from contaminated fluid (caused by particulate and water introduction through the breather cap)?
■ Did you know lubrication failure is the top reason for gearbox returns during the warranty period?
■ How about the fact that industry spends upwards of $200 billion annually fighting the problem of mechanical wear occurring as a result of contamination?
■ And, were you aware that the most common cause cited for denial of warranty claims in hydraulic systems is contamination?

WHERE DOES IT ALL COME FROM?

These are the main sources of particulate contamination:
■ Originated from system components.
■ Generated by system components.
■ Entered from outside the components.
■ Introduced during oil sampling.
■ Caused by inadequate reservoir covers.
■ Added by routine maintenance.

Dirt may enter a system from a variety of routes. Some dirt is built in at the time of machine construction; some wear is generated as the machine operates. Dirt can come in from leaky seals, or open, inadequate covers; it may be introduced while taking samples; and it can be introduced while adding new oil.

New oil itself is not absolutely clean, because oil is manufactured in open containers and pumped through metal piping into containers with varying degrees of cleanliness.

Oil can be filtered at the place of manufacture, but the minute the container is opened by a customer, the ingress of contaminants begins and negates the fluid cleanliness.

HOW CLEAN ARE YOUR LUBRICANTS?

Which of these samples do you think is the cleanest? Note the sample with the 14/13/10 International Standards Organization (ISO) cleanliness level code. That sample is transparent and the cleanest in the quartet. When free water has emulsed or dispersed in the oil, the result is what you see in the 22/20/16 sample: a milky appearance and poorly performing oil.

It is an industry statistic that a water content as little as 400 parts per million reduces bearing life by 85 percent. Be proactive and set a target for your stored oil, based on recommendations from your OEMs.

TIPS FOR ATTAINING A GOOD ISO LEVEL

The following is a logical path to a favorable fluid performance:
1. Ensure the proper fluid is chosen for the application.
2. Ensure the storage container is clean and dry.
3. Vent the storage container with the proper vent filter.
4. Establish a reasonable target cleanliness level.
5. Filter the fluid whenever it is transferred into or out of the container.
6. Set up a monitoring schedule.
7. Submit representative samples for testing.
8. Circulate the test results to everyone within the operation.

SYNTHETIC LUBRICATION

Considerable attention has been focused on synthetic lubricants because of their introduction to the retail market for automotive engine oils. Although these products are relatively new, the use of synthetic-base lubricants in aviation and very specific industrial applications extends back over many years.
The terms “synthetic” and “synthesized” are both used to describe the base fluids used in these lubricants. A synthesized material is one that is produced by combining or building individual units into a unified entity.

The production of synthetic lubricants starts with synthetic base stocks that are often manufactured from petroleum. The base fluids are made by chemically combining low molecular weight compounds to produce a range of viscosities for use as lubricants.

Unlike mineral oils, which are a complex mixture of naturally occurring hydrocarbons, synthetic base fluids are manmade and tailored to have a controlled molecular structure with predictable properties.

With synthetic lubricant base stocks, the process of combining individual units can be controlled so that a large proportion of the finished base fluid is either one or only a few compounds.

In either case, the special properties of the finished synthetic lubricants prepared from the compound may justify the additional cost in applications where mineral oil lubricants do not provide adequate performance.

The primary performance advantage of synthetic lubricants is the extended range of service temperatures, outstanding flow characteristics at extremely low temperatures and their stability at extremely high temperatures.

Synthetic lubricants in addition to providing a wider temperature range application can provide advantages in the following areas:
■ Oxidation stability.
■ Filterability.
■ Higher flash points.
■ Energy savings.
■ Lower maintenance.
■ Extended equipment life.
■ Easier product consolidation.
■ Environmental aspects.

Are synthetic lubricants available for all of the equipment applications? The answer is yes. Are synthetic lubricants needed for all of the equipment applications? This answer is obviously no.

This has to be judged on economics for each application. For example, a proper synthetic oil may span the summer/winter lubricant requirements while at the same time giving a three-year change cycle.

This not only saves six oil changes and associated manpower requirements but also reduces disposal of the used oil. In this application, the use of a synthetic could be easily justified.

Generally, synthetic lubricants will provide three to five or more times the life of comparable premium mineral-oil-based lubricants. Synthetics cost about five times the cost of mineral-oil-based lubricants, so often you cannot cost justify their use based solely on oil cost and change interval.

Look at the advantage in the list above to see if any of these apply and has a qualifiable benefit. There are many applications today using synthetics where they are not needed. They are used because of a desire to have that extra assurance of using the best.

Similarly, there are many equipment applications where use of synthetic lubricants could save thousands of dollars annually. Be sure when selecting a synthetic that you understand its limitations as well as its capabilities.

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Sources

Contributors to this chapter include the following, in alphabetical order:

Bridgestone Americas

Chevron Corp.

Bob Johnson
Director of Fleet Relations
NTEA

Mobil Oil Co.

Hugo Morales
Mining & INFRA Business Segment Manager
Michelin Earthmover Tires

Brad Stemper
Solutions Marketing Manager
Case Construction Equipment

Steve White
Market Segment Manager
Michelin Earthmover Tires

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Lesson 12 Quiz

1. If a vibrating screen or feeder isn’t performing well, what is the first thing that should be checked on it?

2. What does it indicate if stroke magnitude diminishes under load?

3. How much will tire life decrease if tires are overinflated by 20 psi?

4. What is the biggest difference between a radial and a bias-ply tire?

5. What are some things that quarry operators should record regarding their tires in their tire-management program?

6. For a tire to be classified as off-road, what percentage of that tire’s time should be spent off-road?

7. What are some causes of premature component failures?

8. Where should bearings be stored?

 

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