CAT 785 / 789 / 793 Rear Axle
Mag-Shield®X on CAT 789C haul truck surpassed rear axle cleanliness targets without extra maintenance or downtime.
Challenges
Like all mechanical components, CAT Haul Truck rear axles are subject to wear. Over the life of a machine, bearings & gears in differentials and final drives generate ferrous contaminants initiating the wear cycle.
CAT haul trucks are the only mechanical drive trucks fitted with a rear axle filtration system. There is good reason – it is well understood that ferrous contaminants generated during normal operation reduce the life of components impacting the reliability and availability of the trucks.
The CAT rear axle filtration system is very well designed and effective, but as rear axle components wear the volume of debris generated can overwhelm it. Typically, this will reveal itself as a degradation in ISO cleanliness levels, initiating a course of action that leads to availability robbing downtime.
Solution
Traditional means of cleaning contaminated rear axles includes fitting finer grade filters, renewing oil more frequently, or both. While the approach is logical it results in very significant waste & cost. Finer filters plug frequently causing filter alarms and filter bypass events. Additionally, renewing oil cannot remove stubborn contaminants from intricate areas of the axle housing.
This case study examines how fitting a Mag-Shield® X to a CAT 789C haul truck not only cleaned the rear axle but exceeded targeted reference cleanliness levels without increasing maintenance activities & impacting machine availability.
Results
A Mag-Shield® X was fitted to a 789C haul truck as shown in Figure 1 on the left. Services were carried out on a 550 hr schedule. At each service the Mag-Shield® X was weighed pre & post cleaning enabling the amount of material collected to be calculated.
A summary of the overall program & results is shown in Figure 3:
The sample SOS report extract in Figure 4 shows the first 2 samples following fitment of the Mag-Shield® X
At the time the Mag-Shield® X was installed ISO cleanliness levels were unacceptable. A final drive failure occurred almost immediately initiating a repair. Actions taken as part of the repair included cleaning the axle compartment and renewing the oil. By the next scheduled service (220 hrs post failure) the Mag-Shield® X had captured 100g of material despite the repair actions taken.
The following service saw another 88g of material captured proving that residual material from the failure was still circulating. Details of material captured at subsequent services are shown in Figure 3. ISO cleanliness levels improved by 97% from March through to July, exceeding the reference sample cleanliness by 45%. The trend downward indicates that cleanliness levels are likely to improve further. It is important to note that Mag-Shield® X captures ferrous contaminants down to 0.1 microns in size which is not represented on the ISO cleanliness scale. Critically, the cleanliness level improvements occurred without triggering filter alarms or initiating additional maintenance activities.
Mag-Shield® X is designed to complement CAT’s rear axle filtration system. It improves the system’s ability to keep oil clean reducing costly downtime. The benefits of clean oil are well understood and in the case of CAT rear axles increased reliability, service life & lowered cost of ownership can be expected.
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