Main Damage of 250kVA Diesel Generator Crankshaft

The main damage to the crankshaft of 250kVA diesel generator is shaft wear, crankshaft cracks, and fracture.

Cracks originate from the oil hole and develop in a direction of 45° to 55° with the axis, causing the fracture of the main shaft and connecting rod; Cracks are generated at the rounded corners and develop towards the crank arm, causing the crank arm to break, often occurring at 2/3 of the total length of the crankshaft. In addition to the above, the crank will also experience bending and twisting deformation.

Inspection and repair of 250 kva diesel generator set crankshaft

1. Use a magnetic flaw detector to check the crankshaft for cracks and damage

After inspection with a magnetic flaw detector, the crankshaft oil cannot be further used under the following conditions:

1) The damage should be removed from the rounded corners of the crankshaft.

2) There are cracks or damages at the intersection of the 45° crossing line crossing the oil hole or entering the chamfer with holes.

3) Cracks longer than 6mm appear.

4) There are more than 4 cracks on one axis.

If there are any of the following conditions in the surface lower part of the crankshaft, it cannot be used.

1) There are circumferential cracks and damages in the shaded area of the crankshaft fillet.

2) There are cracks with a length of more than 25mm in the circumferential direction.

3) There are cracks with a length of 9.5mm in the axis direction.

4) There are cracks with a chamfer distance close to 1.5mm from the hole.

5) Cracks with a 45° cross line crossing the oil hole.

Please note that the crankshaft that has undergone magnetic testing must be completely demagnetized and cleaned at the bottom of the pool before use.

2. Measurement of worn parts of the crankshaft

1) Measure the roundness error and cylindrical error of the crankshaft main shaft journal and connecting rod journal. If the roundness error is greater than 0.05mm or the cylindricity error is greater than 0.013mm, it is necessary to grind the crankshaft journal.

3. Measurement of crankshaft curvature

The bending degree of the crankshaft refers to half of the total reading of the dial indicator measured at the middle main shaft when the crankshaft is supported by its two ends of the shaft, which is the different center degrees of the bending degree or the entire length.

The runout of the journal refers to the difference between the total reading of the dial gauge of one spindle machine and the total reading of the dial gauge of another adjacent journal when the spindle force rotates along a common axis, which is the runout of the adjacent journal.

Measurement of bending measurement: Support the journals at both ends of the crankshaft on V-shaped iron, place the measuring rod of the dial gauge at the centerline of the journal, and make the contact contact contact the measured shaft force. Rotate the crankshaft, measure each journal, and make a record. Divide the dial gauge reading of the measured middle main shaft force by 2 to determine the bending degree. The maximum bending degree of the crankshaft: 0.267mm for K38 diesel engines; The K50 diesel engine is 0.356mm.

4. Repair of crankshaft of 250kva generator

1) Clean the oil passages in the crankshaft. The method is to remove all hole plugs; Clean the oil passages in the crankshaft with a drill rod, a cloth, and a cleaning solution; Use clean SAE20 or 30W engine oil to lubricate the oil hole and replace the hole plug.

2) After the crankshaft journal is worn, it can be repaired using grinding methods.

When grinding the crankshaft, mark the crankshaft arm at the front end to indicate the exact size of the main or connecting rod bearing shells to be installed, and mark the size and position of the thickened thrust ring to be installed on the crankshaft arm at the rear end.

Before grinding the crankshaft, check if its curvature is within the specified range. If it is not within the specified range, it must be scrapped. If the crankshaft is not rounded off, it can be straightened.