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Nov 3, 2016

Avoid burnout of your HP crusher's eccentric bushing with proper maintenance

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In a crushing plant, failures may occur, requiring a crusher to be shut down for unscheduled maintenance. Once these stoppages happen, certain precautions need to be taken to avoid repeated occurrence.

Unscheduled stoppages

One possible failure is the burnout of the eccentric bushing. Generally, three conditions will indicate that there has been a bushing burnout:

  • Total lockup of the crusher
  • Overheating of the lubricating oil
  • Bronze filings in the screen of the hydraulic unit

A few factors that can cause eccentric bushing burnout are:

  • Use of improper lubricating oil
  • A failure in the lubricating system (oil pump)
  • Improper liner configuration
  • Use of inferior quality liners
  • Closed side setting (CSS) too small
  • Off-center or segregated feed
  • Excess fines in feed material
  • Incorrect rotation

 

What should be done when a bushing burnout occurs?

First, it is necessary to identify the main cause of the failure to know which actions can be taken to avoid the same problem in the future. Then the damaged bushing must be removed immediately so that a new one can be installed.

A few precautions should be taken: when the bushing becomes ‘seized’ (stuck) to the main shaft of the equipment (see picture below), it must be cut for removal.

Bushing that is stuck to the main shaft of the equipment
Caution: take care not to cause scoring (etching) to the main shaft when you are cutting the bushing.

What is the next step?

Next, it is necessary to clean and polish the main shaft and the inner diameter of the eccentric.

Following clean-up, it is necessary to measure the main shaft and the internal diameter of the eccentric at a minimum of four heights and two positions separated by 90 degrees from each other, as seen in the following example (picture below).

Metso expert measuring the main shaft and the internal diameter of the eccentric

After taking these measurements, they must be submitted to Metso’s technical assistance to assess whether they are within tolerance limits.

If so, the new bushing may be installed. If not, Metso will advise on the type of repair that is possible or whether one of the two components must be replaced. Installation will be performed according to the instructions in the equipment manual.

Prior to resuming normal equipment operation, it will be necessary to “break-in” the bushing as established below:

  • Run the crusher free of any load for 1 hour
  • Run the crusher for 2 hours with a full chamber, but with the equipment open far enough to reach 50% of the motor’s nominal power rating (or 60% of its nominal amperage)
  • Close the crusher until 75% of the crusher’s nominal power rating is reached (or 80% of its nominal amperage) and run for another 4 hours
  • Close the crusher until 100% of the nominal amperage is reached and run for 1 hour

Between these four steps, always inspect equipment to ensure that operating conditions are normal and that the adjustment ring is not “knocking” during crusher operation.

Tip: All crusher bushings should be inspected at the time of liner replacement. This precaution can help to avoid unexpected stoppages of your equipment.

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