A major US steel mill contacted us about some bearing problems on a piece of equipment called a straddle carrier. These are large, powered gantry-style lifts that pick up and move big loads of steel bar from one location to another. As you can imagine, a steel mill is not the cleanest operating environment and contamination from dirt and debris was significantly reducing the service life of some of the bearings in the equipment − resulting in increased cost and downtime.
Several Key Locations on the Straddle Carriers Were More Prone to Failure Than Others
The customer identified several specific locations on the straddle carrier where the bearings were failing prematurely. The first of these were the upper and lower large column bushings. These had started as greased bronze, which routinely failed at around 2-3 weeks of use. The customer then tried greased nylon, which still lasted only 5-6 weeks. The second location was on the steering gear bushing which went through the same bronze-to-nylon pathway without success. Finally, they were seeing rapid wear on thrust washers and sleeve bearings on the column roller sheaves.
Digging into Cause and Effect
The loads present in this application are extremely high, leading to routine issues with vibration and impact. Additionally, these straddle carriers endure constant use throughout the average workday, with operations being influenced by temperature fluctuations and various environmental factors.
In response to these challenges, TriStar engineering undertook a comprehensive analysis to identify the root causes of the failure. A significant part of the issue was discovered to be related to the grease present in the bronze and nylon bushings. This grease tends to attract airborne debris present under the rig, allowing it to infiltrate the bearings swiftly. Such contamination transforms the grease into a lapping compound, accelerating the wear on the bearings and drastically reducing their lifespan. This finding underscored the need for a reevaluation of the lubrication strategy to enhance the durability and reliability of the system.
The Solution – Self-Lubricating, Composite Ultracomp Bearings
We chose two of our composite bearing materials – Ultracomp UC300AX in the upper and lower column bushings and Ultracomp UC200 on the steering bushings, chain sheave thrust washers, and sleeve bearings. Ultracomp has a compressive strength nearly 5X higher than SAE 841 bronze and 4X greater than cast nylon. In addition, Ultracomp has an impact strength 25X greater than nylon, so for applications where extreme loads are being applied in vibrating and bouncing conditions, Ultracomp is an ideal choice.
A few more benefits: Ultracomp does not absorb moisture, does not need lubrication, is easy to install and remove, and is thermally stable under variable operating temperatures.
Ultimately, it was determined that the new Ultracomp components improved the lifetime by 10X on the column bushings and 4X on the steering gear. The plant maintenance team was thrilled with the result and this success opened the door for several other applications in the plant, including components for overhead cranes, guide rollers, bar flippers and other line equipment where greased bronze or nylon was in place before.
If you have questions about an application in a challenging environment, we encourage you to reach out to our team with the details. We’re eager to put our experience to work for you.