Heavy-duty plain bearings from igus ensure a maintenance-free drive of the PowerBully

Whether in the forest, the mud, the moor, or the desert, Kässbohrer Geländefahrzeug AG developed its PowerBully for the most impassable terrain. The track-driven vehicle battles its way to its destination wherever a wheeled vehicle would despair. Unique challenges also arise for the plain bearings used in the vehicle. These bearings have to withstand dirt, moisture, and dust without fail. For this, the designers rely on the heavy-duty material from igus in XXL format: iglide® TX1. 

Headquartered in Laupheim, Baden-Wuerttemberg, Kässbohrer Geländefahrzeug AG develops and manufactures vehicles for preparing slopes and cross-country ski trails, beach cleaning equipment, and track-driven utility vehicles for use in low ground pressure applications.

The company’s PowerBully family of special-purpose track-driven vehicles is designed for work and transport deployments to impassable terrains and can accommodate very high payloads up to 16.6 tons. PowerBullys are used to maintain oil pipelines, power and telephone lines, firefighting, and soil investigations. The vehicle’s extremely low ground pressure and high-performance off-road characteristics make it ideal for operations in rough, difficult-to-access, or remote areas.

Extreme operating conditions

The tracked vehicles operate with low ground pressure and, therefore, have a minimal environmental impact. The environmental conditions of a PowerBully are extreme due to the PowerBully being in demand on any surface where a wheeled vehicle cannot make any headway. 

“Mud and slush, as well as isolated, steep, stony, and dusty environments, are where it operates,” explains Simon Holland, Business Development Manager PowerBully at Kässbohrer Geländefahrzeug AG. 

The challenge when working in remote areas is clear: you have to be able to rely on the PowerBully when the next road is miles away. Accordingly, all vehicle components must work reliably, be fail-safe, and have low maintenance.

 

Tech up, Cost down

In a new design of the PowerBully, Marius Holder, development engineer at Kässbohrer, scrutinized the previously chosen plain bearings. The hand-turned special plastic bearings were too expensive and time-consuming to manufacture. Bronze and coated steel bushings were also available but were eliminated due to the even higher costs and special requirements. 

“The plain bearings in the vehicle’s chassis are particularly exposed to extreme conditions. Wetness, sand, and stones surround the axes,” says Holder. “The chains inevitably introduce additional contaminants onto these assemblies.” 

Keeping dirt out of the bearing points is not always possible despite seals. A seizure of the plain bearings would cause severe limitations, ranging from the loss of terrain adaptability to the chain slipping out and the vehicle coming to a complete stop.

In search of the right material

“Due to the good experiences with igus plain bearings in other projects, I approached Reiner Nusser at igus,” recalls Holder. 

“We then set up a trial test with three different igus materials as well as a metallic bearing and the turned plastic bearing of the competitor,” explains Reiner Nusser, technical sales consultant at igus GmbH. “We did a long-term test under real conditions on the shaft from Kässbohrer, and it turned out that iglide TX1 is the optimal material for the application in the PowerBully.” 

The tests were carried out on the standard heavy load pivoting test rigs in the 3,800 square meter igus in-house laboratory in Cologne. To determine the wear rate, the inner diameter of the bearings was measured before and after the test using an outside micrometer in the direction of force. 

The test shows that the iglide TX1 material has a service life eight times longer than the previous plain bearing. In numbers: The turned plastic bearing has the highest wear rate in dry conditions with approximately 832µm/km, the lowest iglide Q2 with approximately 73.5µm/km. In the lubricated condition, the metallic bearing shows the highest wear rate (≈ 199µm/km), iglide TX1 the lowest (≈ 70µm/km).

iglide TX1: Heavy-duty material for the PowerBully

Like all iglide plain bearings, the iglide TX1 is a wound plain bearing that is self-lubricating and dry-operating. In individual cases, such as with the PowerBully, the bearing can also be lubricated in order to maintain the corrosion protection of the shaft. iglide TX1 combines excellent coefficients of wear and friction with high dimensional stability. 

“Due to the long fiber winding, plain bearings made of iglide TX1 absorb even strong shocks and impacts and remain very dimensionally stable,” confirms Reiner Nusser. 

Therefore even heavy-duty applications can be equipped with iglide plain bearings as an alternative to metallic solutions – which always require permanent lubrication or where a lack of lubrication can cause maintenance and repair costs, and even machine breakdowns. 

TX1 is also highly resistant to temperature, chemicals, and moisture and is therefore ideally suited for the various application scenarios of the PowerBully. The low maximum water absorption of less than 0.1 percent by weight in combination with seawater resistance predestines plain bearings made of iglide TX1, for example, even for applications in bogs or rivers.

Bearings undertake important tasks

The PowerBully’s oscillating axles feature four iglide TX1 plain bearings. During travel, the axles compensate for unevenness. The bearings can endure high surface pressure and a combined weight of 30 tons.

In addition, mud, moisture, dirt, and fine-pored sand can enter the bearing points. The same applies to the two iglide TX1 plain bearings in the tensioning axle of the chain. The bushings were manufactured for this purpose in the dimensions 131 and 156 millimeters inside diameter, especially for Kässbohrer Geländefahrzeug AG.

Golden manus award for the PowerBully

Kässbohrer Geländefahrzeug AG was also able to convince the jury of the 10th manus award with the application of the iglide TX1 plain bearing in the PowerBully. The award honors the exciting and creative use of polymer plain bearings. A total of 582 entries from 41 countries were received this year. The jury, consisting of representatives from the specialist media, business, and research, selected four applications that stand out for their technical, economic efficiency, and creativity. Kässbohrer was delighted to receive the golden manus award and 5,000 Euros in prize money.

“The award confirms the good collaboration with our supplier igus and encourages us that we have found an optimal solution here, both technically and economically,” sums up expert Marius Holder.