Skip to main content

Scuffing

Piston ring scuffing is consists of local micro welding, or material adhesion, between a piston ring and a cylinder liner. Various causes of Scuffing are following

Lack of Lubrication
If the engine doesn't have enough oil, the cylinders will not be properly lubricated. As the ring rubs against the liner of the cylinder, dry spots will cause it to scuff. Symptoms of scuffed piston rings include dirty exhaust and excessive oil consumption.
Engine Dry Starts
If an engine has sat idle for even a short time, it may have a "dry start" when next used. This occurs because the existing lubricant sheen in the engine has dried up, and these dry parts of the engine run without lubricant in the first few seconds after the engine starts before lubricant is fully circulated. If an engine is dry-started after a new piston ring is installed, scuffing could result. To avoid this, lubricate the ring before installing it or add a secondary engine oiler that squirts oil into the engine before start-up.
Liner Surface Glaze
Engine cylinders that are overheated by insufficient lubrication can break down the little bit of oil that is present, which then accumulates as a glaze on the interior of the cylinder. This glaze can scuff the edges of a piston ring as it scrapes by, as the glaze won't allow oil to flow properly in the cylinder. Getting rid of this may require a professional reconditioning of the cylinder.
Liner Roundness Faults
If the liner of a cylinder is uneven, some points will rub against the piston ring and cause it to scuff. Here, too, a reconditioning of the cylinder may be necessary.

Comments

Popular posts from this blog

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.

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.