2 years delivery time in case your gear ring fails

A good maintained crane slewing gear ring it can be seen from afar.

When I start the work, first thing I do is to check the condition of the crane from outside. When the outside surface below the slewing ring is clean then the ring is at risk. The outside area of a proper maintained ring has to be with visible trace of grease.

There are 2 types of slewing bearings: with balls and with rollers. And is either bolted or welded to the pedestal and rotating platform of the crane.

Slewing bearing with rollers is used for smaller cranes up to 30 tones and the bearing with balls is for bigger type of cranes.

Measurements should be taken regularly to overtake the wear over the slewing ring.

The wear in the bearing may be checked by taking periodic grease sample.

The grease sample should be taken properly.

Follow this:
- Clean the areas where the sample will be taken.
- Push new grease into the grease point and collect the first used grease which will come out at the seal.

All the time a struggle to take grease sample. It’s a complicated procedure because of the narrower space between the bearing and crane platform. Find proper tools, check the drawings for location and dimension of the grease point and prepare to make an effort to take sample of grease.

I would say that at least 4 points to be selected to obtain a suficient grease sample. Macgregor Crane Division says one sample should be taken in the area under jib and one sample 180° in opposite direction.

For a piece of mind follow these basic rules for proper lubrication of the slewing bearing:

1. Use the recommended grease;
2. Check the manual of the crane for location and dimension of the grease point;
3. Follow the maintenance and lubricating chart inside the crane manual;
4. Heavily grease until overlap of greasing is achieved and the whole bearing circumference is filled with new grease.

During my work often I meet slewing bearing neglected.

slewing gear ring


Measuring the gear ring play or rocking test

The measuremnts has to be taken when the ship have as little list/trim as possible.

Not any load or cargo handling equipmet (e.g. grab) should be on the crane hook.

I remember once I attended to a ship for inspections of deck cranes. Among others I had to measure the gear ring. It was the first time when I was doing the test.

I knew the procedure from the maker manual and I also got all the needed information from some experience colleagues. I was prepared.

But I was using a vernier caliper instead of dial indicator and the result was wrong. With the dial indicator the measurement is more accurately.

Procedure

On the cranes bottom plate two reference point need to be marked. The reference points have to be always used for the future measuring. The marked surfaces should be on the front and rear bottom plate of the crane.

It is important to use about the same position for all further measurements to be able to compare the measurements.

The dial indicator should be positioned between the rotating and nonrotating bearing races and crane jib must be raised maximum up and maximum down.

Measurements shall be taken on four positions of the slewing bearing. With the jib pointing:forward, starboard, aft, port side.

Set the indicator at zero then raise the crane jib at maximum up and record the value. The indicator of dial indicator should return to zero when the crane jib is lowered back to its original position.

Above I presented one method that I am familiar with, but out there are others method of slewing gear ring measuring like: rotation method or tilt method.

That’s why before doing the test you should become familiar with the crane and maker recommendations shall be checked.


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