 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
|
|||||||||||||||||||||||||||||
 |
|
||||||||||||||||||||||||||||||
|
While construction companies have long conceded the importance of tire management, few of them have liked the routine checking and recordkeeping needed for good tire management. Now help is on the way to relieve them of these chores. By Charles D. Bader
|
||||||||||||||||||||||||||||||
|
Off-the-road tires must operate under a wide variety of conditions that cause wear and other damage. According to information supplied by Don Stretch, senior sales consultant for Caterpillar in Peoria, IL, these conditions can range from dry "potato dirt" to wet, severe shotrock. "Speed conditions vary from less than 1 mile per hour average to 45 miles per hour. Gradients may vary from 75% favorable to 30% adverse. Climatic conditions, operator skills, maintenance practices, et cetera can all have a profound effect on tire life and unit costs." The vehicle type may also have a significant impact on tire wear and life. Kelly Moore, product manager for skid loaders at Gehl Company in West Bend, WI, contends that skid loaders are particularly hard on tires. "By its very nature, a skid loader turns by skidding, so tires routinely scrape against a variety of surfaces. Unquestionably, tires represent the highest-wear item on a skid loader." Notes Stretch, "Proper tire selection, application, maintenance, and operator training are very important factors in earthmoving economics. Wheel tractors, loaders, scrapers, trucks, motor graders, et cetera are earthmoving vehicles whose productivity and payload unit cost depend greatly on tire performance." Tire Selection and Application Dennis Munns, market and product manager for John Deere Construction Equipment in Moline, IL, wholeheartedly agrees. "In fact, tire selection has been shown to affect production as much as 30%. That’s because the wrong tires can cause handling problems, including instability and frequent slippage. In addition, the selection can lead to excessive downtime, resulting from excessive flats, sidewall failures, and even premature drive-train wear. "But how does a user find the right tire? First he must ask himself some basic questions: What material will be handled? What’s the weight of the heaviest anticipated load? What are the ground conditions? What’s the cycle time? What’s the carry distance? Are there any special considerations?" These are application considerations, and Tomas Bennett, market segment manager of Michelin North America in Greenville, SC, regards application considerations as paramount in the selection process. "Whereas one tire type might work fine in a soil-intensive environment, that same tire might not fare nearly as well in a rock construction environment. And there are tradeoffs to be considered too. You can buy an almost bulletproof tire that will give you great protection on a site, but the huge amounts of steel and rubber in such tires will lower the average speed of the vehicle. That will cut down the amount of material that can be moved in an hour. Add those costs to the difference in the original cost of the tires, and that might change the selection decision." Heat is another important matter. Serious problems occur when tires are operated at temperatures that exceed their design capabilities. Separation and related failures can occur. Stretch explains, "A tire generates heat as it rolls and flexes." Heat generated faster than it can be radiated into the atmosphere gradually builds within the tire and reaches maximum level at the outermost ply or belt. As a tire’s operating temperature increases, the rubber and textiles within significantly lose strength. The tire becomes susceptible to failures from cornering, braking, impact, cuts, and fatigue. Over time, enough heat can develop from overflexing to actually reverse the vulcanizing temperature, thereby causing ply separation and complete tire failure. "What does this have to do with tire selection?" asks Stretch. "A formula (described in the Ton - Miles per Hour sidebar) has been developed to predict temperature buildup and to rate tires. Thus, a knowledge of probable job conditions can prevent a contractor from selecting a tire with inadequate temperature capabilities." With the application information firmly defined, one of the first selection decisions is whether to use bias-ply or radial tires. Explains Munns, "Bias-ply tires feature layers of nylon-ply cord applied at opposing angles from bead to bead to form the casing of the tire. In radial tires, a single layer of steel cord is applied radially [at a 90° angle] from bead to bead." Table 1 shows some of the distinct advantages of each type of tire.
"Both radial and bias-ply tires are rated to indicate tire capacity and strength," Munns continues. "For bias, a ply rating is used. This rating is determined by the number of cords used. The higher the ply rating on bias tires, the higher the load capacity and the higher the initial cost. Also expect better side-to-side stability and a stiffer ride with a high-rated bias. Radials use a star rating to indicate the capacity and strength. As a general rule, a one-star rating equals the strength and capacity of most bias-ply tires." A determination of the best tire size and capacity for a given application is heavily influenced by the expected load on each tire. This depends on the total vehicle weight and weight distribution. The total weight is the sum of the weight of the typical load of material being hauled and the bucket size added to the empty weight of the vehicle. The weight distribution between the front and rear tires varies depending on the vehicle. For example, when a wheel loader is fully loaded, it is estimated that 80% of the total weight will be borne by the front tires and only 20% by the rear tires. The resultant calculation of the tonnage each tire can be expected to carry is then compared with the tire manufacturers’ tire-load and inflation charts to determine which tires have the capacity to handle that load. "You might find that your first choice of tire size does not have the capacity to handle the loads you’re demanding," Munns warns. "So you’ll be forced to consider a larger-tire option. Or perhaps you’ll find that smaller loads will handle the loads nicely. The point is, these charts will give you firm capacity numbers on which you can base your final decision." "Contrary to what some might think, the lightest tire and the least expensive tire you can put on to meet the demands of the job is the one you want," claims Lorne Fleming of RDO Equipment in San Diego, CA. "That’s because you want to keep the weight down, which in turn helps keep down the heat. Heat is the enemy of all tires. And the farther you have to carry the load, the more heat you generate." The air-filled pneumatic tire is by far the most widely used type of tire in construction applications, but it is not the only type. For applications where frequent punctures are liable to be encountered, for example, foam-filled tires might be preferable to the air-filled pneumatics. Galaxy Tire and Wheel produces just such a tire, although the company uses a polyurethane fill that it insists is much superior to conventional foam fills. "Our Soft Flex-Super Fill tires also provide 100% protection against flats, but they ride like air-filled tires," claims Neil Ganz, managing director of Galaxy Tire West in Hayward, CA. Polyurethane-filled tires cost more than pneumatic tires, but they provide a number of offsetting savings:
"Galaxy’s poly-filled tires are approved for use by every major equipment manufacturer that has tested them as well as by suppliers of critical components such as axles. What’s more, they do not void the warranties of these OEMs [original equipment manufacturers]. And both the cost of the tire and the cost of the fill are covered by Galaxy’s warranty, which extends through multiple retreadings." Polyurethane-and foam-filled tires are not the only nonpneumatic tires available for construction vehicles, points out Moore. For severe environments, Airboss of South Haven, MI, manufactures a segmented tire. This consists of a large steel rim onto which 18 or 20 thick segments of rubber tread are bolted. Not only are these segments much thicker than typical pneumatic tire treads, but individual tread segments can be replaced as they wear out. The manufacturer also claims that its segmented tires have an average of 55% greater traction and double the shock absorption of comparable-size pneumatic tires. And, of course, they are completely punctureproof. Again the main drawback is cost. Setco of Idabel, OK, manufactures a totally solid rubber tire for even more severe environments. The 100% natural rubber is adhered directly to a rim. The rubber is reinforced with shredded, 70,000-psi tensile-strength wire for strength, cut resistance, and extended tire wear. To quote the manufacturer, "If you do cut the tread face of a Setco tire, you’ve simply added another tread void for traction." These solid-rubber tires are punctureproof and impervious to most other failure modes. As might be expected, Setco tire/rim assemblies are quite expensive, but since they are claimed to last three to five times longer, they might well be the most cost-effective tires available for certain applications and workloads. The key to effective preventive maintenance of tires is maintaining proper tire pressure. "Air pressure maintenance is equal to goodness," remarks Ganz. And while Michelin’s Bennett doesn’t restrict his tire maintenance recommendations to just air pressure (see his tire maintenance checklist in the adjacent sidebar), he does say, "Correct air pressure is very important. Every OEM’s performance handbook lists air pressure recommendations for both front and rear tires on all their vehicles, so the information is readily available to any user. If you don’t maintain the right air pressure, you decrease the life of the tire, pure and simple. If you do maintain the right air pressure, you’ll reduce wear and enable your tires to withstand punctures better. Every day, users should do a visual inspection to look for any damage to sidewalls or tread, and once a week they should measure the air pressure." The Caterpillar Performance Handbook gets even more specific, sternly warning, "All tires should be operated at the tire manufacturer’s recommended inflation pressure for a given application. Inflation should be checked every working day with an accurate Borden tube - type gauge. This gauge should be checked against a known standard such as a dead-weight tester at least once a month. "Excess loads may result from factors such as varying material density, field modifications to equipment, mud accumulation, load transfer, et cetera. Only under these conditions may the actual in-service tire load exceed the rated machine load. When excess loads are encountered, cold inflation pressures must be increased to compensate for higher loads. Increase tire inflation pressure 2% for each 1% increase in load.
"The above loads will result in reduced tire performance and must be approved by the tire manufacturer."
That’s all very good advice, but in the real world most users don’t check their tire air pressures as frequently or thoroughly as this. That’s why there are such high hopes for the long-awaited tire chips. Having an electronic chip with a battery and transmitter in each tire "will be the greatest thing since sliced bread," Stretch comments. "The chip will send out signals that give a reading of the temperature and air pressure of each tire as the vehicle drives by a receiver. We’re looking forward to having a wireless tie from the chips to our Vital Information Management System in our big haul trucks. That way, the driver can directly read the temperature and air pressure of each of his vehicle’s tires so he can take corrective action before a tire goes soft and/or before overheating occurs. Either of these conditions can cause serious, perhaps irreparable, damage to a tire before the next inspection is made." Chips are in the testing phase by at least one tire manufacturer. Until the tire chip is perfected, however, many users will probably neglect rigorous tire inspection and other preventive maintenance of their fleet’s tires–particularly at remote construction sites. But now, notes Stretch, tire dealers appear to be stepping in to fill this need through the use of maintenance contracts. "Tire dealers are doing a better job of offering total maintenance packages that include tire management as part of the guarantee," he observes. "Some tire dealers are sending out service trucks to customer locations, even remote job sites, on a regular basis. They’re inspecting, rotating, and checking air pressures as part of their maintenance contract. It’s a good deal for the customer; he gets vital preventative maintenance done without any labor cost or downtime, so he gets longer wear on his biggest-wear item. "I envision the day when a dealer will say, ‘I’ll sell you the tires for your fleet, guarantee them, and do all the preventive maintenance for so much money a month.’ Eventually the customer might not even know or care what the raw cost of each tire is. Instead, he’ll be evaluating the life cycle cost of his fleet’s tires." While preventive maintenance is an important aspect of tire management, tracking of tires on vehicles, undergoing repair, or in spares inventory is equally important. It is tracking that permits proactive management of this important asset. Knowing the cost per hour of different tires, being able to predict the useful life remaining for every tire (until retreading or failure), and knowing the damage patterns of tires in the fleet so you can at least evaluate corrective action all enable the user to decrease the life cycle costs of his tires and increase the productivity of his operations. This is difficult to achieve with file cards or even a general spreadsheet program like Excel. But now Bridgestone has developed a second-generation tracking system it calls Tire Management 2000 (TM2000), which has recordkeeping and tracking software specifically designed for the off-road-vehicle industry. Operating on a PC with 32 megabytes of RAM, 200 megabytes of free disk space, and a color monitor displaying at least 800 x 600 pixels, the TM2000 enables users to scrutinize tire utilization and comprehend tire-wear trends and costs by organizing normal tire inspection data and outputting them in a series of custom reports and graphs. It uses click-and-drag technology to minimize input time, and it is laid out so that most tire management functions can be done from a single-screen format. System features include the ability to search for tires by serial number or brand, rotate tires between vehicles, and write reports. "The system can store baseline data on a user’s entire fleet," explains Jeff Asay, Bridgestone’s manager for technology services. "To input data into the program for a particular site, the user can pull from the extensive preloaded database of vehicles and tires. After initial creation of the tire and vehicle fleet [database], the daily maintenance of the data-consisting of timely inspections and tire changes-takes just a few minutes a day. Based on the remaining tread depth and calculated wear rate in hours or miles per thirty-second, the software can quickly project the remaining tire life. On the system display, each tire will be color-coded in one of four colors to indicate the remaining tread wear. As a result, the user can see at a glance which tires need to be replaced or retreaded and approximately when. With this early warning, the user can schedule retreading or order replacement tires in a timely fashion. "When a tire is taken out of service, the user can mirror the actual actions by clicking on the appropriate icon and dragging it from the vehicle icon to spares, retread, or other function, thereby automatically updating the records of that tire. Then, if desired, reports, line graphs, pie charts, or other easy-to-comprehend graphics can be displayed and/or printed out to show fleet status or any activity that is needed." While this tracking system is designed for ease of use and relevance to the end user, most of the systems placed so far have been with Bridgestone dealers that use them to track tires for their customers. While dealers typically provide this as a free service to their customers, they benefit too. Dan Stroup, purchasing manager of Bridgestone dealer Cobre Tire Inc. in Gillette, WY, explains, "We can use the system to detect such things as improper wheel alignment that would affect warranty disputes, and we can see when they should be buying replacement tires. It’s a service for us as well as for them." Dwight Day of Tufco Inc., a Bridgestone dealer in Eveleth, MN, agrees. "I hope we will be able to do the tire tracking for all of our customers. We’ve learned that anything we can do to make them perceive us as more valuable to them is important. And, of course, we get a heads-up on repair, retreading, and replacement requirements, so the system generates business for us while we’re providing a service for them." Thus, a tracking system like Bridgestone’s fits right in with the trend of tire dealers expanding their maintenance contracts to take a more proactive role with their customers. And it also fits right in with the move to tire chips. Joe Rayna, director of mining tires for Bridgestone, says the company’s "tire tag" sensor product will have a user-friendly interface that will look and feel like the TM2000. "Using real-time as well as historical data, the two products will work in tandem to deliver enhanced tire management capabilities that will cut user downtime, improve user productivity, and save the user money." Charles D. Bader is with Dateline II Communications in Los Angeles, CA.
|
|||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||
