Mounts bring shakers back to full capacity

Edited by the Engineeringtalk editorial team Oct 22, 2003

A change of suspension has solved a long-standing problem at a southeast US coal-mining operation.

A major aggregate producer involved in coal mining operations in the southeast USA recently developed a serious problem: one of its tower shaker screens was vibrating so badly that it was unsafe to operate at full capacity.

In the aggregate industry, excessive vibration in a shaker screen is a common problem, due to the basic technology and lower-cost parts used in shaker screen construction.

In a large operation there might be as many as ten screens operating at any one time, used to sift the aggregate so smaller particles shift to the bottom.

To protect the tower from collapsing, some possible solutions in this case could include: reinforcement of the tower site, running the shaker at slower speeds or a complete screen replacement.

The first solution, reinforcing the tower site, may or may not be possible, depending on the shaker location and could involve expensive materials, parts and labour.

The second potential solution, running the shaker at slower speeds, causes a corresponding reduction in efficiency and profits.

In addition, even at a lower speed, the problem could very well reoccur.

The third possibility, replacing the screen, provides an interim solution that more than likely will reoccur at a future date, because the shaker screen design, in that same situation under the same level of stress, more than likely will continue to vibrate at an excessive rate.

Unwilling to settle for any of these conventional alternatives, the aggregate company contacted Lovejoy in Downers Grove, Illinois, for a solution.

Lovejoy's application engineers recommended replacement of the conventional coil spring suspension with Rosta AB oscillating mounts.

Unlike coil springs, Rosta AB oscillating mounts use the vibration damping properties of engineered rubber to reduce peak transmitted forces generated by the screen.

This leads to vibration isolation exceeding 95% and resultant increased life of side plates, frames, supporting steelwork mechanisms, bearings and belts.

After a quick retrofit that minimised downtime, the producer now operates at full capacity with no worry of the tower being shaken apart.

According to John Anthony, Rosta Senior Product Manager at Lovejoy: "This would be a classic application for the Rosta AB oscillating mount.

This particular product is made specifically to replace coil springs, the standard, basic technology or part used in a shaker screen so common in aggregate operations.

In this particular case, the screen was vibrating so violently, the entire structure was in danger of collapse and we were able to salvage the situation to everyone's satisfaction.

However, even in a normal operation, excessive vibration causes wear and tear on the equipment and surrounding support items as well.

Using the Rosta product to reduce vibrations can help extend the life of other components on site as well".

The Rosta line of oscillating mounts offers customers the most options and the largest size mounts in the market, able to replace any size coil spring suspension and fit into larger spring mount applications.

With four different size oscillating mounts to mix and match, the Lovejoy applications engineers can tailor a custom solution to any screen vibration problem.

Another benefit of using the Rosta AB oscillating mount is the noise reduction.

"This has become a critical characteristic in most aggregate operations", says Anthony, "with the MSHA regulations regarding noise requirements.

When the operating equipment rises above a certain critical decibel level, mining workers can only be exposed for so many hours.

Reducing the noise level in an aggregate operation can help that company run its business more efficiently and realise an economic benefit by being able to run a complete shift while still complying with MSHA noise regulations".

Anthony said that when comparing the basic shaker screen with spring coil suspension to a shaker screen outfitted with Rosta AB oscillating mounts, internal testing demonstrated significant noise level reductions.

When comparing decibel levels, even a 2-3dB drop can have a significant impact on an operation.