The crankshaft flywheel set is mainly composed of crankshaft, main bearing and flywheel, as shown in Figure 1.
The function of the crankshaft is to turn the force from the connecting rod into torque. And then output power outward through the flywheel, and drive the diesel engine through the gear or belt wheel each mechanism and each system to work.
The crankshaft consists of five parts: the main shaft journal, the connecting rod journal, the crank, the front end of the crankshaft and the back end of the crankshaft.
The gas pressure from the piston connecting rod group is converted into torque output.
Also used to drive the engine valve mechanism and other auxiliary head.
Working conditions: gas pressure, inertia force, inertia moment.
Withstand the impact of alternating loads.
Crankshaft material: medium carbon steel (steam), alloy cast iron (wood), nodular cast iron.
Crankshaft classification: integral (common)
Combined type (usually used in small gasoline engines with connecting rod big head as integral and engines with rolling bearing as main crankshaft bearing
(1) Spindle journal — used to support the crankshaft.
Full support: the number of crankshaft neck than the number of cylinders more than one.
Good strength and stiffness, reduce wear;
Diesel and most gasoline engines are used.
Incomplete support: the number of crankshaft necks is less than or equal to that of cylinders.
The load is large, shortening the total length of the crankshaft.
Journal surface strain, ablated crankshaft bending or distortion, crack or fracture.
Wear law of crankshaft
The maximum wear of the journal of the connecting rod is also near the journal side.
The former is mostly transverse crack, serious will cause crankshaft fracture, should focus on inspection.
The latter are mostly axial cracks, which develop along the sharp edge of oblique oil hole.
(1) The transverse and axial cracks of crankshaft are mainly caused by stress concentration.
(2) The crack at the oil hole on the journal is mainly caused by the asymmetrical distribution of the stress at the oil hole caused by the oblique position of the oil passage.
1, wear using outside diameter micrometer.
(1) Oil penetration percussion method: the cleaned crankshaft is soaked in kerosene, and then the crankshaft is removed and cleaned, the surface is sprinkled with white powder. And then the crankshaft is hit along the axis of the non-working face with a hand hammer. If there is obvious crack-like oil mark in the white powder, there is a crack there.
(2) magnetic flaw detection method: magnetize the parts with the help of flaw detector, and sprinkle some magnetic powder on the parts where cracks may occur. When the magnetic force line passes the edge of the crack, the magnetic powder will be adsorbed at the crack, so as to show the part and size of the crack.
When the roundness and cylindricity error of crankshaft journal exceeds 0.01~0.0125mm, grinding should be carried out on a special crankshaft grinder.
Crankshaft radial circular runout, generally not more than 0.04~0.06mm.
If more than 0.10mm, correction is required.
Methods: cold pressing straightening method, knocking method
Crack: magnetic crack detection method, oil immersion percussion method.
(1) Repair size of crankshaft journal:
General crankshaft journal and connecting rod journal have standard size and 2-4 reduced repair size, and with the corresponding size of bearings.
Some engines are fitted with maintenance bearings of 0.05mm.
A few crankshafts have no repair dimensions.
The actual repair size selected should be less than or equal to the maximum journal size that can be obtained after grinding.
(2) Grinding of crankshaft:
The technical requirements and key points of crankshaft journal grinding are as follows:
1) The grinding size of the journal shall be in accordance with the selected repair size and the actual size of the bearing bush, and ensure the specified matching clearance.
2) The main shaft journal and connecting rod journal of the same crankshaft should be ground into the same repair size, otherwise the dynamic balance of the crankshaft will be destroyed.
3) The roundness and cylindricity error of the journal should be less than 0.005mm, the surface roughness value should be less than 0.2um, and the dimensional tolerance should not be greater than 0.02mm.
4) A transition fillet with a radius of 1~3mm should be processed at both ends of the journal working face and the connection of the crank. The oil hole on the journal should be chamfered with a radius of 0.50mmx45~ 1.00mmx45, and burrs should be removed.
1, crankshaft crack repair
When cracks occur in non-stressed parts or cracks do not extend, they can be repaired.
Crankshaft cracks in the crank arm and journal and other stress parts, should be replaced with new parts.
(1) surface percussion method: this method is applicable to the crankshaft with a bending amount not greater than 0.30-0.50mm.
In case of development of taper and ovality, crankshaft repair is undertaken by grinding of crankshaft.
Excessive rough surface finish, bearing marks, pitting requires crankshaft repair.
RA Power Solutions undertakes crankshaft repair of damaged crankshaft counter weight and bolts thread. The combination of metal stitching, metal locking and use of helicoil thread inserts is done for successful repair of crankshaft.
The loss of alignment of crankshaft by penning process is undertaken. We have experienced technicians to undertake crankshaft repair successfully.
Correction of radius fillet of crank pin and crank main journal is undertaken as per manufacturer’s standards.
All crankshaft repair procedures followed by RA Power Solutions are approved by class and are guaranteed for satisfactory performance. Ours is the only company which can undertake crankshaft repair by vibration free onsite crankshaft grinding machine. Crankshaft repair is also undertaken while sailing of vessel and on low cost.
In case there is some accident takes place in the engine, now you do not need to remove the crankshaft from engine block then send it to the workshop. Please contact us and we will send our senior technicians having seaman passport in very short notice to your site for repair of crankshaft. They will inspect and repair crankshaft onsite by using portable crankshaft grinding machine.
We undertake crankshaft repair and repair of crankpin for land based diesel engines in power plant, cement plants, etc. and for marine engine also.
Onsite repair of crankshaft results in substantial savings in terms of downtime and money. With the experience of 40 years of working experience on crankshaft our trained technicians go to the site and undertake repair of crankshaft and other necessary engine repairs while the vessel is sailing.
We have successfully done 10,000 jobs of crankshaft repair all over the world like Qatar, Dubai, Sudan, Indonesia, Singapore, South America, Malaysia, Jordan, Kenya, Maldives, Nigeria, etc.