Saturday, March 30, 2019


One of the most challenging cases came when one of the product dryers started creating high impact sounds from the non-drive side/outlet side support rollers. The equipment is a big rotary drum supported by 2 rollers each at inlet and outlet side. The drums are fitted with a replaceable component called rider rings one each at inlet and outlet side, which rests on the two support rollers. A slope of 1 deg. is maintained so that the dried product moves down by gravity. Hot air is blown through the drum, to facilitate the product drying. Gland packings are provided at inlet and outlet sides to prevent hot air leakage. The drum is rotated by a motor through gearbox, which transfers power through a spur gear arrangement provided on the drum. Many suggestions came from the maintenance like it is because of eccentricity in drum rotation, bearing damage etc. Due to high market demand, stoppage of equipment without identifying the root cause would lead to severe wastage of time and will incur huge losses. But the correct problem was identified by thorough observation and teamwork.

Impacts are large forces acting over a short time, which can lead to fracture failure/breakage of the impacted component.
In this case, large hammering sounds were observed from the outlet support rollers. It was very difficult to identify the cause of the problem due to access restrictions. The whole support roller assembly was guarded and only a small inspection window was available to check the ring and roller condition on one side.

The dryer rollers were inspected through the available inspection window. Vibration readings were not collected. On observing, it was noticed that the impacting sound recurred in every single support roller rotation. So the problem was narrowed down to the support roller assembly. It was also noticed that the sound was more from one of the two support rollers. So our concentration was on the specific support roller.
Since it recurred in one revolution and was periodic, it was concluded that the issue is not related to bearings. Bearing issues will lead to frequent random impacting, and once the bearing fails, the roller gets seized than rolling with a broken bearing roller or races. Moreover, the chances of bearing failure are less as it was heavy-duty, double row spherical roller bearings.
Recommendations were provided for the inspection and repair of the associated support roller.

After proper planning, the equipment was stopped for identifying and solving the issues. On inspection, it was found that the mentioned support roller got detached from the shaft. The roller was attached on the shaft by welding and the weld has failed, making the roller free on the shaft. Continuous running with free movement of the roller on its shaft further damaged its ID (Inner Dia.) thus opening up the radial gap between roller and shaft causing the impact sounds. The impacts were produced when the worn-out roller got lifted by key in every rotation and got down due to the weight of the drum when the key passes the contact line. The roller surface was found to be worn due to prolonged running/ageing.

The only solution was to replace the support rollers as the radial gaps cannot be built up. But the support roller spares were not available, which compelled us to provide temporary solutions.
Recommendations were provided to re-weld the support roller on the shaft by maintaining concentricity. The repairs were done and the rollers were reinstalled. The equipment was started and the sounds have completely vanished. The equipment ran smoothly for four months after which slight impact sound resurfaced, indicating weld joint failure.
In the next shutdown opportunity, the support rollers were replaced with a new one and the equipment is restored to a reliable condition. No abnormal impacting observed after the correction.

1. Support rollers will be hardened. Any welding might induce additional stresses which might lead to failure of the shaft. So it is always preferred to buy new roller assembly in case of damage.
2. PWHT on the welded joints will remove residual stress.
3. Support roller/trunnion diameters should be checked every year to understand the wear rate so that proper planning can be done for procuring and allocating the budget.
4. Heavy-duty bearings should be cleaned and re-greased during the available opportunities.

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