Skip to main content

Material of connecting rod bolt ,importance of elongation, nature of stresses in this component and why should these bolts be replaced after some time in service

The connecting rod bolt in service is subjected to: 
a. A dynamic tension loading due to centrifugal force of the mass of connecting rod 
rotating with the crank pin 
b. A dynamic tension loading owing to inertial forces of the reciprocating mass of the 
piston which is fluctuating with angular displacement of the crank and having the 
peak value at an instant of 360˚ after the firing TDC in a cycle of operation 
c. A dynamic shear stress at the parting of the two halves of the bearing housing 
Dowel pins with fitted bolts or serrations at the face or both are used to reduce shear loading  on bolts and possibility of fretting. 
Bolts should be constructed of materials having high resilience and should not be stiffer w.r.t  bearing housing. 

Pretension of the bolts should be regarded as the single most important factor which 
contributes towards the fatigue life of the material of the bolt. Pretension must be kept high 
enough, so that the increase in stress owing to dynamic loading remains within the range of 
stress already given by pretension. 

Some routine checks on this part are (rejection criteria of the bolt) 
a. Check for corrosion by acidic lube oil, discard if any present on shanks 
b. Check the length of the bolt against a new or bolt tolerances. If longer, yielding of 
the material should have taken place. Renew the bolt in this circumstance 
c. Check for mechanical damage, especially on shanks 
d. Check for fractures by NDT 
e. Check the landing faces for uneven tightening 
f. Discard the bolt when either designated life, over speed failure or piston seizure has 
occurred

Comments

Post a Comment

If you have any doubts.Please let me know

Popular posts from this blog

Differences between MC/MC-C and ME/ME-C engines

The electrohydraulic control mechanisms of the ME engine replace the following components of the conventional MC engine: Chain drive for camshaft Camshaft with fuel cams, exhaust cams and indicator cams Fuel pump actuating gear, including roller guides and reversing mechanism Conventional fuel pressure booster and VIT system Exhaust valve actuating gear and roller guides Engine driven starting air distributor Electronic governor with actuator Regulating shaft Engine side control console Mechanical cylinder lubricators. The Engine Control System of the ME engine comprises: Control units Hydraulic power supply unit Hydraulic cylinder units, including: Electronically controlled fuel injection, and Electronically controlled exhaust valve activation Electronically controlled starting air valves Electronically controlled auxiliary blowers Integrated electronic governor functions Tacho system Electronically controlled Alpha lubricators
9 comments
Read more

Why is a man hole door elliptical in shape?

Any opening in a pressure vessel is kept to a minimum and for a man entry an elliptical hole  is lesser in size than the corresponding circular hole. More over it is prime concern to have a  smoothed generous radius at the corners to eliminate stress concentration. Hence other  geometrical shapes like rectangle and square are ruled out.  To compensate for the loss of material in the shell due to opening, a doubler ring has to be  provided around the opening. The thickness of the ring depends on the axis length along the  dirrection in which the stresses are maximum and the thickness of the shell. It is important to  align the minor axis along the length of the vessel, as the stress in this direction is  maximum. Longitudinal stress: Pd/2t where P= pressure inside the vessel, d= diameter of the arc, t=  thickness of the shell plating  Circumferential stress: Pd/4t  More over a considerable material and weight saving is achieved as minor is along the  direction of maximum stress.
21 comments
Read more

Shell Expansion Plan

It is a two dimensional drawing of a three dimensional surface of the ship’s hull form. This plan is very useful for the following information:It is used for marking the location of a hull Damage on this plan by identifying the strake number , letter and frame number so that the exact location of the damage and also suggested repairs are marked in a localised copy. The shell expansion can be used for finding areas of painting surfaces such as topside, boot topping and bottom areas by applying Simpsons rules directly.  In the shell expansion the vertical scale used is different from the horizontal scale and a suitable adjustment has to be made when calculating areas. This becomes useful in solving disputes concerning areas of preparation and painting. It gives information on the thickness of the original strake which is indicated by the number in the circle shown in the strake.  The quality of steel used is also shown by letters A,B,D E and AH, BH,DH, EH.
20 comments
Read more