Crank Shaft Final Inspection

Main engine - Crank shaft final inspection Contents    

1 General 2 Purpose 3 Procedure 4 Example

General

Crankshaft The crankshaft with the connecting rod is that part of an engine which trans lates linear  piston motion into rotation. The The relative timings of piston movements are adjusted to give smoother delivery to shaft. The angle between cranks depends on the relative timing of piston movement. The crank is fitted to the shaft or journal b y ‘Shrink Fit’ method. The crank with the crank pin is one-piece finished product.

Purpose To check the deflection of crank pin, run out of jounals, dimensions, parallellism,  NDT, and contact.

Procedure The crankshaft is placed horizontally and firmly above the ground so that it can be rotated easily at different given angles. The dimension of shaft is checked in six steps:        

1. Deflection and run-out 2. Diameter check 3. Parallelism 4. NDT 5. Contact test 6. Roughness test 7. Trueness test 8. Dimension of crankshaft

Example In this example a MAN B&W 6S50MC Main Engine is chosen. Tests Illustration

Description Deflection and run-out

The deflection of crank pins(P) and run-out of  journals(J) are checked by by dial gauge. The The deflections of crank pins are measured at eight different angles (0, 45, 90…. 315, 360). The measured maximum deflection(0.01) should be within the tolerance limit (max +-0.02 mm). Similarly run-out measurement is carried out for four different angles and the maximum deviation(0.015) is checked to be within the tolerance limit (max 0.04). The data is noted down in the following format. (Photo: Crankshaft reading format) Diameter check 

A standard rod of length equal to the diameter of crank  pin or journal (560 mm) is used to set the screw gauge gauge at zero error. Then the diameter is measured and the error is noted down. The error in diameter must be within the tolerance range (0 to –  to  – 0.07 0.07 mm). The diameter check for pin is noted down in the following format described in the photo.) Parallelism

For minimum vibration of crankshaft and better contact

with bearing, the crankshaft should be aligned properly. To check the alignment ‘parallelism’ test is performed. A level checker is kept at different points on the shaft to get the inclination in mm per meter. The reading must  be within the tolerance (0.06/ (0.06/ 1m). NDT (Non Destructive Test) - Magnetic Particle Test

The crank with the crank pin is a one-piece finished  product. So the joining part of pin and crank are tested for internal cracks. This is done by Magnetic particle test method. For crankshaft, AC Yoke type wet method is used. The test area is rinsed with magnetic particle fluid, which contains mineral oil and magnetic particles. Lifting a specified weight made of magnetic material tests the strength of the magnetizer. Before testing, the magnetic particle field indicator is used to check the adequacy or the direction of magnetic field. The continuous electromagnetic field (yoke method) is applied on the test object. The magnetic particles in the fluid align themselves to identify abnormalities in the ferrous metal component. This test can measure internal cracks up to a depth of 6mm. The part is then rinsed with a mineral oil solution not containing magnetic  particles. Contact test

One of the basic purposes of a bearing beari ng is to provide a frictionless environment to support and guide the rotating crankshaft. Properly installed and maintained,  journal bearings have have essentially infinite life. For proper proper transfer of weight and force of crankshaft, the j ournal  bearing contact should be be maximum. The contact  percentage is checked by applying a dye on journal and sliding the test-piece of bearing on it. Any abnormality in dye shows the contact is not proper. Roughness test

The roughness of the thrust bearing is measured on both sides. Accepted roughness was 3.2 Ra. Before measurement the instrument is calibrated with a standard piece of 3.29 Ra. During measurements it was found to be 0.29 Ra in the t he ahead and astern side. Ra is the measure of average roughness and is the most common measure of roughness used in engineering.

Trueness test

The trueness of the thrust bearing is measured in the ahead direction side by using a scale.

Dimension check 

The overall length of the shaft is measured by steel tape ruler through the inner most hole passing all through the shaft.

Conclusion

The outcome of the test has to be noted down and any suggestion has to be mentioned in the inspection report.