crank shaft final inspection

8/13/2019 Crank Shaft Final Inspection

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Main engine -Crank shaft finalinspection

Contents

1 General 2 Purpose 3 Procedure 4 Example

General

Crankshaft

The crankshaft with the connecting rod is that part of an engine which translates linear

piston motion into rotation. 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 by 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.
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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 dial gauge. 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

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 to0.07 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
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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/ 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 methodis 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, themagnetic 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 is to provide a

frictionless environment to support and guide the

rotating crankshaft. Properly installed and maintained,

journal bearings have essentially infinite life. For proper

transfer of weight and force of crankshaft, the journal

bearing contact should 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 ahead and astern side. Ra is

the measure of average roughness and is the most

common measure of roughness used in engineering.
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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.
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crank shaft final inspection

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