Dozer undercarriage selection profoundly impacts owning and operating costs. "Remember, 45% to 60% of the repair and maintenance costs associated with maintaining a dozer over its life is undercarriage," says Bruce Boebel, product manager, crawler dozers, Komatsu America Corp. "This is unavoidable, but can be minimized with proper operation practices and machine selection."
Mid-size machines usually have the widest choice of undercarriage options, including shoe width, moderate or extreme service and standard and premium options for rollers, idlers and chains, says Antonio Pela, technical support manager, Berco. "Carefully evaluating the type of application, ground condition and environment of the jobsite, and how they may change during development of the job, will lead to the best undercarriage solution," he adds.
SHOE WIDTH SELECTION
"Proper shoe width is directly correlated with the machine weight and wheelbase," says Pela. "The wheelbase defines how many shoes are in contact with the terrain. The machine weight with the required attachments defines the ground pressure.
"Usually, wider shoes are indicated when the flotation of the machine is key or when there is a restriction on the maximum ground pressure allowed," he continues. "In events where good soil penetration is required to provide good grip for the machine, it's better to consider shorter shoes."
According to Jeff Powell, general product manager - earthmoving equipment, Liebherr Construction Equipment, "The proper selection of track shoes depends mainly on ground conditions. For hard and abrasive material, take narrow shoes; for soft ground such as clay, take wider shoes. If you have swamp or peat, an LGP (low ground pressure) undercarriage with extreme wide shoes is necessary."
Most undercarriage experts advise using the narrowest shoe possible. "That is for structural reasons -- joint life, oil life, etc.," says Tim Nenne Sr., undercarriage specialist, Caterpillar. "The wider the shoe the harder it is going to be on the undercarriage structurally."
Yet, it's important to understand the trade-offs. Wider shoes provide a better ride, traction and flotation, and shoes that are too narrow can create their own problems. "For example, if you put a 28-in. shoe in really soft underfoot conditions, you allow the machine to sink," says Nenne. "It is going to be harder on the powertrain, which results in higher fuel consumption. It will also bring more material into the undercarriage during turns. which reduces undercarriage wear life."
"Width equates to ground pressure," adds Boebel. "Determine the narrowest shoe that will support the machine's weight above ground. Go wider only when it is absolutely necessary. Match shoe type to material and the type of work. The wider the shoe, the greater the stress on the chain if you run over an obstacle."
MODERATE, EXTREME AND BEYOND
Mid-size dozers offer a dizzying array of shoe types. "If you look at our part sales kit, the number of shoe choices for a D6 alone is amazing," says Nenne. This high number of choices allow a Caterpillar machine to be best matched with its underfoot conditions.
Moderate Service (MS) shoes are recommended for use in soft and non-abrasive material, says Powell. In more abrasive conditions, Extreme Service (ES) shoes are typically the more cost-effective choice.
"Using the extreme service shoe usually reduces the operating cost on really abrasive terrain due to the need for less frequent replacement," says Pela. "[They] are therefore suggested on high-abrasive terrain like sand or tar sand."
"The ES shoe helps you from a structural standpoint. [It] will resist breaking because of the plate thickness. It has a taller and wider grouser," Nenne explains. "Not only do you get better durability, you also get better wear life. But that does come at a cost. With the grouser being taller and wider, it is harder to get into the ground, so you could suffer penetration problems." ES shoes also add significant weight to the machine, which could affect flotation.
"The grouser works like a blade on the soil, so the thinner the grouser shape, the easier the ground penetration, which results in a smoother ride," Pela elaborates. "ES shoes are not recommended in applications where a smooth ride is the key or where the soil provides very high impacts to the undercarriage."
Boebel advises using extreme service shoes only when they are actually needed. "They are for rock, shot rock applications or pioneering dozers (with oscillating track frame). They are hard on the chain joints, so use them sparingly," he emphasizes. "Most larger dozers use severe service shoes, but smaller machines do not benefit from their use, since they add cost and affect smoothness of travel. Severe service shoes affect grading performance, since they can create vibrations that can be transferred to the blade."
Many shoes have options such as trap holes to get material to flow out of the link box. "In a condition where you have tacky mud where it would cause a tight track incident, we recommend you use a trap hole shoe," says Nenne. "The sprockets will eject the mud out of the link box and give you proper track tension.
"On the other hand, a trap hole shoe can be detrimental," he continues. "That shoe is there for flotation. If you punch a hole in the middle of it and it is in soft underfoot conditions, all of that material will eject up through that hole and come right into that link assembly, which can reduce wear life. Instead of helping to get rid of material, you actually bring it in."
"Specialty shoes are exactly that -- special," says Boebel. They are higher cost and harder to obtain. "Only use when absolutely required."
Clipped corner shoes are often used for fine grading. "That clipped corner gives you less ground disturbance when you are making turns," says Nenne. "It allows the tractor to turn more easily."
"A wider shoe also makes turning more difficult. This is the reason Berco recommends wide shoes with clipped corners," Pela comments. "This prevents the shoe from bending too much and reduces the risk of links breaking."
Often, versatility trumps a single application. "If you go into a wide range of applications where you get into some rocks or stumps, as well as doing finish grading, I would tell you to run an ES shoe because of the bending protection. You have better joint protection [due to] a thicker leading and trailing edge. We recommend most of our D6s with System One to run ES shoes because you get a better balanced undercarriage," says Nenne.
"It must be remembered that there is not one combination of tracks/shoes that will work in all applications," says Powell. "Depending upon geography, climate and soil condition, a track combination can vary widely even in a small geographic area. The best a contractor can do is determine where the dozer will perform the majority of its operating life and configure the unit to perform for these conditions."
DESIGNED TO CUT WEAR AND COSTS
The longevity of undercarriage components is driven by wear.
"Different components in contact with each other wear with different speed. Links wear at a slower speed compared to pins and bushings," says Pela. "All of the pulling effort that comes from the sprocket and track adjuster are sustained by the pin and bushing. Lubrication between these elements greatly benefits the speed at which they wear out. Lubricated chains are indicated for machines that are constantly moving because the oil is able to create a constant film between the pin and bushing."
"Sealed and lubricated track (SALT) is required for most applications," Boebel asserts. It reduces the internal friction in the undercarriage by providing internal oil lubrication, resulting in a long life.
"If the track is maintained properly, a contractor could see up to a 50% increase in bushing life due to the ability to get the same life out of the second side of the bushing after being turned," Powell explains. The system can be used in almost any application, except in high heat, such as hot slag applications.
"There are more advantages than disadvantages with SALT," says Nenne. "Having that oil in the joint substantially lengthens the time the assembly will be able to run before service needs to be performed. The only time we would not recommend using SALT would be applications working in steel mills because the seals can't handle that kind of ambient temperature."
Of course, there are still applications for dry track. "Whether for oil or grease, seals reduce the distance that a bushing fits into a link. Dry track is stronger against torsional stress and twisting types of movement," Boebel says. "But internal pin and bushing wear will become the No. 1 reason for service work, replacing external bushing wear."
Rotating bushing designs are another means to extend component life. "Any time we talk to customers or dealers about managing undercarriage, the whole idea is to get the maximum life out of the link that you can," says Nenne. "A rotating bushing track allows you to do that because you don't wear out a bushing before you can wear out your link."
Rotating bushing designs can eliminate costly maintenance. "Rotating bushings reduce or eliminate internal pin and bushing wear," says Boebel. "Less service intervals equal more uptime and less cost per hour."
One example is the Komatsu PLUS undercarriage, which gets its name from its configuration. "The links run in a parallel layout as opposed to an offset link used on conventional undercarriage systems," says Boebel. "PLUS uses a rotation bushing that does not require the machine to be taken out of service to have a service technician turn or rotate the pins and bushings, which reduces maintenance cost and downtime. The design goal is to balance the wear of the undercarriage components so they wear out at about the same time.
"Customers who are in the most abrasive applications will see the most reduction in repair and maintenance costs," he adds. "Repair and maintenance cost savings range from 10% to 40%."
"When you purchase an undercarriage, typically the purchase of a moving component is the highest part of that cost, followed by the maintenance costs," says Nenne. "Performing a bushing turn halfway through the track assembly life and rebuilding an idler near the end of the undercarriage life so you can use the cores again drive your expenses."
Nenne believes a large percentage of customers benefit from Caterpillar's System One rotating bushing design. "Typically the guys who get 6,000 hours or less on the heavy-duty undercarriage benefit the most and see the greatest reduction in owning and operating costs," he states. "With System One, you get to reuse the sprocket segments for at least two link assemblies. You get to reuse the idlers. Just not having to buy those two components or refurbish the idlers, you save significant money."
Similar to other designs, Berco's ROBUSTUS rotating bushing track doesn't require pin and bushing turns.Its life is defined by complete wear on all of the components.
Yet, not all applications are suited for a rotating bushing track design. "One recommendation would be to avoid systems with rotating bushings in applications with heavy impact shock loads (rocks and stones), especially when ripping," says Powell. "These impact loads tend to crack and break the rotating bushing portion of the track system, which results in costly track repairs and replacement."
Roller design also impacts undercarriage life. "The roller is the component transmitting the weight between the main frame and the chain," says Pela. "The more stable the roller, the longer the chain life."
"Compare single vs. dual flange rollers," says Boebel. "Dual flange helps guide the track to reduce wear, especially on slopes. Also compare center thrust vs. end thrust bearings. Typically, center thrust bearings have an advantage on side slope work, but it really depends on the overall design of the roller, not just the bearing type."
Caterpillar offers multiple roller choices and configurations. "Typically, when a tractor comes out of the factory, it will have a mix between single- and double-flange rollers," says Nenne. This provides better guiding for work on slopes to keep the track underneath the machine.
On larger machines with a suspended undercarriage, single flange rollers are bigger in diameter and provide the greatest life, but offer the least amount of guiding. "Some customers can run all single-flange rollers to get a better overall link/roller system life in certain applications where additional guiding is not a necessity. If you are slot dozing most of the time, you can run all singles and get better system life," Nenne indicates.
But most customers need double-flange rollers for guiding. And in some cases, extreme guiding may be required. "Caterpillar has what we call high double-flange rollers," says Nenne. "Those go on machines that do a significant amount of side sloping. That high double flange is about 30% bigger than a standard roller's flange. It's whole job is to keep that link assembly on the roller system. If the link assembly gets outside of the roller system, it is going to cause internal damage."
Another area that can save maintenance cost is the use of segmented sprockets. "Replacing a full sprocket wheel requires taking off the chain, usually in a shop because a crane is needed," says Pela. "Replacing a segment is an operation that can be done in the field without the need for a complete tear down of the chains."
CONSIDER ALL ALTERNATIVES
"All available track systems have their advantages and disadvantages depending on the application and the ground conditions," says Powell.
Equipment suppliers can offer guidance. "We are just completing an online undercarriage application guide," says Nenne. "It will help customers with a D3 through D8 to choose the proper undercarriage. It will help them choose their shoe type and size, guiding recommendations and the type of undercarriage they should be running based on tractor size, underfoot conditions and tractor configuration."
Modify Shoes to Cut Costs
Bruce Boebel, Komatsu America Corp., suggests it is sometimes practical to perform modifications to standard shoes. "If you need improved turning performance for your application, why not save money and torch the corners of the shoes yourself and clean up with a grinder?" he asks. "This method results in a less expensive parts price, since high-volume 'common track shoes' are used and you can keep labor costs lower by doing the work yourself."
Mud holes can also be added using a cutter torch, but care is required. "If you cut a hole in the shoe, you also reduce flotation," Boebel points out. "Know how much you can afford to lose before getting 'hole crazy.' This also saves parts lead time and cost. Anytime you can use a standard shoe over a specialty shoe, you can save money."