Case Study: Application of a Locking Assembly in a Ball Mill for Cement Production

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In this article we take a brief look at a locking assembly solution of RINGFEDER POWER TRANSMISSION which was developed for a cement plant after the mill operator had experienced repeated failures of its equipment.

The Challenge

After maintenance engineers had examined the ball mill unit thoroughly, the cause of the problem seemed to be the shaft-pinion connection, or to be more exact, the locking assembly that connected the solid shaft with the pinion. Measurements showed the assembly to be out of tolerance by a whopping 300 to 400 µm.

To identify the reason for this abnormally high run-out value, the decision was taken to remove the locking device and to re-install and tighten it again. However, the removal turned out to be impossible and neither the manufacturer of the ball mill nor the local supplier of the locking assembly were able to support the maintenance engineers in this task.

The General Problem

The purpose of a locking assembly is to lock a connection. Yet, it is not sufficient to just use any material and to comply with the dimensional drawing.

The selection of the right material and the right manufacturing processes along with the expert knowledge of the application and installation procedure are the essential prerequisites for providing a locking assembly that will reliably deliver its desired performance throughout its life cycle.


The Solution

As the supplier of the installed locking device was not able to provide a solution and as production downtimes of the plant caused substantial losses to the mill’s operator, RINGFEDER was contacted for help and assistance. An engineer from RINGFEDER visited the plant immediately to find out the reason for the problems.

Not only did the first analysis reveal that the customer had spent a substantial amount of money for maintenance operations that were in no relation to the miniscule savings by using the competitor’s locking assembly, it also showed that they had a locking assembly that could not be unlocked when needed.

It took 5 to 6 maintenance engineers a whole day to remove the damaged component.

It turned out that the faulty product that had been installed was a replica of RINGFEDER’s 5-part locking assembly RfN 7015.0-340 x 425. This replica had broken into several pieces which was one of the reasons for all of the trouble.


After the shaft and the pinion had been thoroughly cleaned, they were mounted again and connected with a RINGFEDER locking assembly. The measurements carried out after the start-up of the plant were more than satisfactory: in addition to reducing the run-out to a value as little as 80 µm, the vibration level had also greatly decreased.

Further Development

Fully satisfied with the excellent results and the professional support furnished by RINGFEDER, the customer ordered further locking assemblies from RINGFEDER to replace the ones in four other ball mills.

RINGFEDER now has an ongoing project with the Ball Mill OEM, supplying and replacing locking assemblies in mills in various customer locations.


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