ACOPOStrak shuttles’ wheels are intended to be a wear item, but the rate of wear can be rapidly accelerated by several factors. Severe wheel wear can lead to several severe issues if not properly monitored. The purpose of this post is to document as many sources of accelerated wheel wear as possible, as well as how to spot them and how to correct them.
ACOPOStrak shuttle wheels should be regularly measured for wheel wear using the wheel wear gauges (8F1TCA.SWGS0000I-1). New wheels are typically slightly over-sized, so they should not fit all the way in to the gauges. It is recommended to replace the wheels when wear is measured at 0.15 mm, and wheels must absolutely be replaced if the measured wear is 0.25 mm. The rate of wheel wear varies depending on the application, including the shuttles’ payload, velocity, and acceleration, so the typical replacement interval should be noted for each specific application. If the wheel replacement interval begins to significantly shorten, the following points can be checked as possible sources of this accelerated wheel wear.
A common source of accelerated wheel wear is out-of-tolerance alignment points. It should be noted that each alignment tolerance discussed in this post should be observed during the initial installation of the track, but can and should be re-checked and adjusted if wheel wear begins to become an issue. The following mis-alignment points can lead to accelerated wheel wear:
- Rail Transition Gap
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The gap between adjacent rails must be 0.5 mm +/- 0.2 mm as checked with feeler gauges. Note that the gap must be checked for both the double-v rails and the flat rails.
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If the gap is larger than 0.7 mm, shuttle wheels crossing these transitions will experience a dip and can lose small flakes of material each time they cross.
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If the gap is severe enough, you can begin to see wheel flakes build up below these large rail gaps (see image below). This wheel flake build-up is an indicator that the rail transition should be checked and adjusted.
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- Rail Alignment in the Direction of Travel
- The transition between rails should be aligned both horizontally and vertically with a tolerance of +/- 0.05 mm, as checked with the ACOPOStrak measuring shuttle (8F1TCA.GMS00000I-1).
- A mis-aligned transition can cause a sharp bump between rails. Depending on the direction shuttles travel over these bumps, the wheels must either move away from the segments and risk losing small flakes of material, or move toward the segments and impact the rail after the transition. In either scenario, the wheels are experiencing more wear than they would over a smooth transition.
- Shuttles will typically make more noise as they pass over these mis-aligned transitions. This noise and/or visible wheel flakes are good indicators that alignment must be adjusted at a transition.
- Divert Alignment
- The gap between two opposite rails in a divert area should be 30.2 mm +/- 0.1 mm, as measured with the divert adjustment and control blocks (8F1TCA.DCB00000I-1). In addition, the height offset of two opposing rails must be less than 0.05 mm, as measured with the divert height offset measuring tool (8F1TCA.DHOMD000I-1).
- If the gap is larger than 30.3 mm, shuttles have a larger distance to “jump” between rails, which causes the wheels to experience impacts during each divert. If the gap is smaller than 30.1 mm, shuttles’ wheels may lose flakes of material each time they pass through the divert area. The height offset being larger than 0.05 mm can also cause wheels to lose flakes of material when entering the divert area.
- If the gap is too large, shuttles will make an audible sound as they divert. This sound or visible wheel flakes are indicators that the divert alignment should be checked and adjusted.
Another common source of accelerated wheel wear is maintenance-related issues. If the recommended maintenance intervals are not observed, several factors can arise that can lead to accelerated wheel wear. Recommended maintenance intervals can be found in both the ACOPOStrak User’s Manual and the ACOPOStrak Maintenance Manual. It should be noted that the recommended maintenance intervals are heavily application-dependent, and should be adjusted according to the specific application. The following sources of accelerated wheel wear can be avoided by observing the recommended maintenance intervals and practices:
- Debris and/or Particulate Buildup on the Guide Rails
- Particles building up on the rails can act as an abrasive and cause the wheels to wear down more quickly as they travel around the track.
- It is recommended to clean the rails of an ACOPOStrak system regularly using 70% isopropyl alcohol and a soft cloth. B&R recommends to clean the rails at a minimum of every six months for a lower usage system, but this interval should be adjusted depending on the application and cleanliness.
- Bent Shuttles
- A bent shuttle can cause the wheels to be mis-aligned with the direction of travel. This mis-alignment can cause the wheels to slide along the rails instead of rolling, increasing the amount of friction the wheels experience.
- If a shuttle is dropped, it should be inspected for any damage. To check if a shuttle is bent, stand it up on a flat surface next to a known-good shuttle to compare. The top and bottom surfaces of the shuttle should be parallel to one another.
- Bent shuttles should be immediately removed from the track and replaced, as they can also lead to damage on other components of the track system.
- Seized Wheel Bearings
- If wheels are unable to spin freely, this can cause wheels to slide along the rails instead of rolling, potentially wearing a flat spot in the wheels.
- Seized bearings can be caused by multiple factors, including corrosion from water intrusion and over-tightening of the wheel assembly. Always check whether the assembly has been over-tightened by loosening the wheel assembly and seeing if the wheel can spin. It is recommended to use the pin-type bit (8F1TCA.SPTB0000I-1) to torque the wheel assembly to 4 Nm.
- If a wheel does not spin freely after loosening, the wheel should be replaced.
- Lubrication
- If the lubrication felts are not lubricated at the recommended interval, the wheels can experience increased friction on the guide rails. In addition, if the lubrication felts have particulate built up, this can also directly lead to more abrasion on the wheels.
- Lubrication felts should be inspected each time the wheel wear is measured, and should be replaced if they are dirty. The felts should be lubricated with one drop of ISO grade 46 or SAE grade 20 oil at the specified intervals. It should be noted that lubrication should also occur after each time the guide rails are cleaned.
The seven points mentioned in this post are the most common sources of wheel wear I have encountered as a field service engineer, but this is likely not an exhaustive list. If anyone has encountered other sources of accelerated wheel wear, feel free to comment on this post to build both my knowledge and the Community’s.
