But too loose also causes its own set of problems. “We really emphasize the tight track, but sometimes a loose track is a real issue as well from the standpoint of slapping,” says Neeley. “On an elevated machine without a carrier roller, you might have the track sitting down on the frame, which is not good.”
Shoes play crucial role
There are many factors that influence shoe selection. For example, wide shoes are intended for flotation, but they also provide additional track on the ground for improved blade control in some applications.
“Any choice of track shoe features is a compromise,” explains Koester. “Selecting the correct track shoe for a specific application has a significant effect on machine productivity. It is common that the selection of track shoes is based only on machine productivity, while the effects on potential undercarriage life are ignored. Productivity may be increased, but the life of the undercarriage may be reduced.”
Using wide shoes serves as a perfect example. “Our research shows that for every 2 in. the shoe width is increased, the stress on the chain is increased 20% to 25%,” says Neeley. This varies by chain size. “But if shoe width is increased by 6 in., it puts about 60% more bending stresses in that chain. A tractor that is working in high-impact [conditions] with wide shoes may sacrifice two-thirds of its undercarriage life.”
“The general rule of thumb when you are looking at track shoes is you want to use the narrowest pad that maintains adequate flotation,” says Schaeffer. “The table of the shoe should be fully resting on the ground. The grouser should be fully penetrated into the ground without material coming up over the top of the shoe. You want the full weight of the crawler tractor resting on the table of the shoe, not on the tips of the grouser.”
What dictates your choice is the environment that the tractor is most likely going to be operated in.
The environment also effects shoe style. “Include shoes with open centers when running in materials that are extrudable, such as mud or sand,” says Koester. “Use extreme service shoes in areas where abrasive soils are the norm and where high-impact conditions may cause structural damage to the shoes.”
Determining when to change shoes is another issue that deserves close attention. You need to look at more than grouser condition when evaluating shoe life. “Customers will sometimes judge shoe life strictly on the remaining life on the grouser,” says Neeley. But if you’re working in a highly abrasive environment, it’s possible the grouser still has life remaining, while the leading and trailing edge of the shoe exhibit significant wear.
This allows sand and abrasives to enter the system and decrease undercarriage life. “So you should not only look at the grouser wear, but you should also consider the amount of wear on the plate of the shoe, particularly the leading and the trailing edge,” he adds.
To guard or not to guard
Full or partial roller guards serve a couple of purposes — as guides and to keep non-extrudable materials out. The downside is they can trap extrudable materials in the undercarriage. “The disadvantage of using roller guards in packing materials, such as mud or sand, is that they usually will not keep this material out but in fact, tend to keep the material in,” says Koester. This, in turn, accelerates wear.
Therefore, roller guards should only be used when absolutely necessary. “Track guards should be used only if there is a need to keep rocks, tree limbs or other non-extrudable material from entering the roller areas,” advises Koester.
In some instances, partial roller guards can be useful. “End guiding guards may be used with partial length guides to help guide track chains as they enter and leave the sprockets and idlers,” says Koester. “Center guiding guards may be used in the middle of the track to help maintain track alignment while allowing for packing material to fall free.”