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Pitting erosion of Main Bearings


1.ONE POSSIBLE CAUSE IS "SPARK EROSION"

2.IN THE EARLY STAGES SPARK EROSSION APPEARS AS SMALL PITTING EROSION.LATER, AS ROUGHNESS INCREASES, THE SMALL CRATERS WILL SCRAPE OFF AND PICK UP WHITE METAL (THE LATTER GIVES A SILVERY WHITE APPEARANCE TO THE BEARING).

3.SPARK EROSION IS CAUSED BY A VOLTAGE DISCHARGE BETWEEN JOURNAL & BEARING.

4.THE CRANKSHAFT IS ELECTROSTATICALLY CHARGED WHEN THE ENGINE IS RUNNING. TO ENSURE PROTECTION AGAINST SPARK EROSION AN EARTHING DEVICE IS USUALLY FITTED ON THE INTERMEDIATE SHAFT.

5.THE EARTHING DEVICE CONSISTS OF THE FOLLOWING:
 -A CLAMP WITH A COPPER LINING.
 -CARBON BUSHES WHICH ARE PRESSED ON THE COPPER LINING WITH SPRINGS.
 -CABLE CONNECTING CARBON BUSH TO SHIP'S HULL

6.IF SUCH AN EARTHING DEVISE IS ALREADY FITTED
 CHECK ALL THE COMPONENTS AND THEIR CONNECTIONS AS MENTIONED IN PARAGR. 5.

7.IF THE SHAFT IS NOT FITTED WITH EARTHING DEVICE  THEN PLS ADVISE INTERMEDIATE SHAFT DIAMETER.
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