Answer MEP Question 6

Q. What is the Rocking test of Deck Crane? Explain the procedure of the rocking test. Tabulate and indicate a fault-finding procedure. What is the action taken if the deviation is out of the limit? 

Rocking test is carried out to ascertain the wear down of the sleeve bearing of the deck cranes by measuring the play (relative movement) between the inner and outer bearing race. This measurement indicates the rate of wear. Slewing bearing is one of the most important components of a deck crane, so It is very important to grasp the condition of slewing bearing periodically in order to prevent unexpected trouble.

Interval of the test is Every 6 month. If the class has other requirement of Rocking test interval, that should be followed. And if wear amount close to tolerance, more frequent inspection is required.

– The Rocking Test needs to be carried out according to manufacturer recommendation.

No loads shall be to the crane hook, positions below are usually marked and used always as a datum reference.

Measurements are typically taken in four positions on the slew bearing, with the jib pointing towards the fore side, starboard side, stem side, and port side.

Procedure of rocking test.

Fix the dial gauge on the outside surface of the fixed post, and apply the probe to the bottom surface of the outer ring of the slewing ring. (The measurement point is "measuring point -1" on the rear of the deck crane.)

If the measurement is performed inside the fixed post, place the dial gauge on the inside surface of the fixed post and apply the probe to the bottom surface of the base plate of the deck crane.

Perform the initial setting (direct the top of the jip upward.)  Direct the top of the jib upward by luffing operation. (Minimum reach) Adjust the dial gauge to zero.

Lower the jib to the maximum reach by luffing operation. Record the indicated value of the dial gauge at the measuring point of the rear side of the deck crane.

Check that the bottom surface of the pinion doesn’t contact with the top surface of the fixed post top flange.

Be sure to measure without load. If the wear volume is measured with load, the contact position between the ball of the bearing a raceway varies, the dial indicated value fluctuates greatly. Measure the wear volume at the 0 point position without slewing the deck crane.

Make a diagnosis of the measured result. The result of the measurement of step 3 is the wear volume including the clearance between the ball of the bearing and raceway. If any one of the results of the measurements towards 4 sides, the fore side, starboard side, stem side and port side, exceeds +3mm from the initial value (allowable wear volume), replace the bearing. The allowable wear volume is same regardless of outside measurement/inside measurement