Lubrication contamination and the effect on pin bushings

When it comes to maximising the profitability of capital equipment, uptime and throughput are the keys to success. However, when excessive contamination comes into play, equipment downtime due to damaged pin bushings can have a severely negative impact on the bottom line.

Pin bushing bearing joints have been around for thousands of years, and some historians call them the first form of a bearing. Bushings were originally used in applications such as rotating wheels on wooden axles; however, today’s bushings are used in thousands of machines throughout the world utilising various materials and configurations. Although material construction has changed since the original wood plain bearings, eliminating contamination and lubricating between the pin and bushing have not.

Today’s construction and mining equipment use the most sophisticated form of bronze pin bushings and their ability to reduce wear is impressive. The problem lies within the nature of the material itself — bronze. Bronze is extremely reliable and very durable, yet is designed to be a “wear” material. The purpose of wearing is to reduce damage to structural steel components. The bronze bushing is much less expensive to replace than something like a wheel loader boom arm and is therefore used as a wear material to reduce damage to other rotating components.

The effect that contamination has on pin bushings is directly related to scarring, skidding/plowing and smearing. When excessive contamination builds up between a pin and bushing surface, the rotation of the pin and the pressure load begins to dig contamination into the bronze bushing. Over time this contamination builds up and begins to restrict the movement of the pin by increasing friction. Due to increasing friction and the load pressure, the pin will eventually gouge the bronze and start removing material from the bushing to allow the pin to rotate. This material then becomes additional contamination between the pin and bushing and the problem worsens.

If this process continues, the space between the pin and bushing will increase allowing additional contamination and wear to occur. Eventually the bronze bushing material is worn away and the pin begins digging into the steel structure of the equipment. Under these conditions, production machinery is generally pulled out of service and the bushings replaced. If only the bushing is damaged, the repair might only require replacing a pin and bushing set. If the bushing is completely worn away and the pin has damaged the structural steel of the equipment, a “line bore” is traditionally required which can increase the cost of the repairs exponentially.

If proper lubrication maintenance is practised, the replacement and/or repair of pin bushings can be virtually eliminated except in the case of bushing deformation due to impact loading. Most pin bushings today have “grease grooves” on the inner diameter which aid in purging contamination from the bushing by forcing out unwanted materials while providing a film thickness for the pin to rotate on. These grease grooves can also house contamination if proper greasing intervals are not maintained, and therefore wear can occur if the bushings are not purged frequently.

Using an automatic lubrication system provides a means of frequently purging contamination from a pin and bushings on mobile equipment while it is operating. They are designed to dispense consistently accurate doses of lubricant to extend equipment life and reduce downtime due to lubrication maintenance and equipment repair. By greasing during equipment operation, the entire pin is coated and equal purging of the pin’s circumference is obtained. This increases equipment life and extends Performance of the machine.

Graco manufactures automatic lubrication systems specifically designed for yellow iron construction and mining equipment. Whether you are looking for heavy-duty G3 lubrication systems for small and medium-sized construction machines or mining-grade Dyna-Star lubrication systems for the world’s most demanding equipment, Graco has you covered.

For additional information on how to increase your equipment reliability through automatic lubrication solutions, contact Graco or your local Graco distributor.