LINER

Cylinder block is grey cast iron

A simple symmetrical design fosters low lubricating oil consumption and low wear rates. With increase in rating of the engine, the liner must be made thick to accommodate the hoop stresses but the effective cooling is also important.

The liner is bore cooled on the larger engine models and available in two different configurations— with or without insulation of the cooling water jet pipes so as to match the cooling intensity closely to the different engine ratings.

For this, holes are bored from the underside of the flange formed by the increase in inner dia. The holes are bored upwards and tangential to the internal surface of the liner. Holes are then bored radially at the top of the liner so that they join with the tangentially bored holes. For engines originally specified with cast-in cooling pipes in the liners, the later design with oval pipes has stopped the occurrence of cracks.

Cracked cylinder liners are now rarely reported thanks to the successful introduction of countermeasures, such as bore-cooled liners and (for smaller bore engines) slim liners.

MAN B&W

The original MC-type liners with cast in pipes unfortunately suffered from cracks but the introduction of the bore-cooled liner solved the problem. The standard specification for new engines is a bore-cooled type made of Tarkalloy C grey cast iron.

The inside surface temperature of the liner greatly influences the general cylinder condition. Traditionally, the cooling system has been laid out to match the maximum continuous rating load but there is an advantage in controlling the inside liner surface temperature in relation to the load.

Man completely avoided cooling of the lower part.

NOTE- One system simply adjusted the cooling water flow through the original cooling ducts in the liner but the results were not promising. Another system features different sets of cooling ducts in the borecooled liner, the set deployed depending on the engine load. At nominal power and high loads the inner row of ducts is used to cool the liner, yielding the highest cooling intensity. In the intermediate load range the cooling function is shifted to the next set of ducts which are located further away from the inner surface; this means that the cooling intensity is reduced and the liner surface temperature is kept at the optimum level. At very low loads both rows of cooling ducts are bypassed in order to further reduce the cooling intensity.

SULZER

Mid stroke insulation of the liner and the insulating tubes optimized the liner temperatures and avoided corrosion.

 

1.    After liner calibration found liner oval in FWD aft dir. Reason and action.(Battu) one unit liner wear aft and fwd, why? And it's remedy(Mitra)

Piston is aligned in fore-aft direction by the guide strips, which are bolted onto the inner side of the guide shoes. Liner wears more in the fore-aft direction if it is misaligned. Alignment can be changed by changing the shims between the guide strip and guideshoe.

2.    cylinder liner wear which direction more wear and y?(KM Rao)

Liner wear is more in the port-starboard direction. It can be due to continuous rolling of the ship in the p-s direction.

3.    Liner wear in full detail—(Sarkar)

4.    what is cloverleafing? causes?(Bhowmick)

5.    what is cloverleafing..draw top view in liner showing cloverleafing(Battu)

i)             Corrosive wear

COLD CORROSION

Corrosion occurs due to the condensation of Sulphur dioxide, which is a combustion by-product, when the combustion component temperature drops below its dew point (approx. 110-180 degrees). The Sulphur dioxide mixes with the water to form sulphuric acid and is termed as cold corrosion.

The main cause is due to the inadequate alkalinity reserve in the cylinder oil. It can also happen if the piston rings sticks inside the groove and the combustion gases blowpast the rings and result in corrosion.

HOT CORROSION

If Vanadium:Sodium in the fuel is 3:1, during combustion it forms eutectic compounds like pento sodium vanadate (5Na₂Ov₂O₄11V₂O₅) which adhere to metal surfaces. This has low melting point as low as 450degrees­­. These deposits are corrosive by itself and build up on hot surfaces like liner, exh vv.

i)             Cloverleafing

Is a kind of corrosive wear which happens due to the improper distribution of the oil. It usually happens at the farthest points from the lubricating oil quills, i.e. in the middle of the quills. This produces an irregular circumferential wear pattern in the liner so that the rings are unable to conform to it totally.

ii)            Abrasive – scoring

This is due to abrasives in the fuel oil which are greater in size than the oil film thickness. Ex cat fines-alumina and silica, soot, rust or wear particles.

iii)           Adhesive wear-scuffing / microseizure

It is a localized welding happening due to the piston ring pressing against the liner without the cylinder oil separation. This localized welding of hot spots  tear apart as piston travels and acts as abrasives.
It is caused due to the insufficient l.o. supply or distribution; excessive gas pressure behind the piston ring which breaks the l.o. film; improper cooling which will burnaway the l.o film. Liner too smooth or water on liner surface.

It is indicated by the scratching/tearing in the vertical direction; localized hardening of the ring and liner.

i)             what is deep honed liner in sulzer eng(Battu)

A key element of TriboPack is the cylinder liner manufactured in cast iron, which needs a controlled hard-phase content and the best grain structure in the running surface for both good strength and running behaviour. Careful machining followed by full deep honing to remove all damaged hard phase from the liner surface reportedly delivers an ideal running surface for the piston rings, together with an optimum surface microstructure. Deep honing of the full liner running surface is a prerequisite for maximizing the benefits of TriboPack, says Wärtsilä: its experience has shown that plateau honing of a wave-cut liner is not adequate because, once the plateau is worn down, the rings run on liner metal whose hard phase structure was damaged during machining. This damaged hard phase must be removed by deep honing.

ii)            liner calibration, wear,etc(Chakravarty)

Gauging a liner is carried out for two reasons:

-      To establish the wear rate of the liner

-      To predict if and when the liner will require changing.

A liner is gauged by measuring the diameter of the liner at fixed points down its length using a template to ensure accurate comparisons may be made. It is measured from port to stbd (athwartships) and fwd to aft. An internal micrometer is used because of its accuracy (within 0.01mm). accurate comparisons may be made, a flat bar is hung down the side of the liner with holes drilled through where the measurements are to be taken.

Measurements are taken at more frequent intervals at the top of the liner where wear rate is expected to be highest.

To ensure accuracy, the micrometer gauge is checked against a standard, and the liner and micrometer should be at ambient temperature. To ensure micrometer and liner are at the same temperature, lay the micrometer on the entablature for a few minutes before starting. If the temperature is higher, then a correction factor can be applied.

The readings can be recorded in tabular form, and from the data obtained the wear rate/1000 hours can be calculated.

On a large 2 stroke crosshead engine - about 0.05mm/1000 hours.                                On a medium speed trunk piston engine-  around 0.015mm/1000 hours.

Manufacturers quote max wear for a cylinder liner at about 0.6-0.8% of original diameter. Ovality is limited to 1mm

Cylinder Number: 1 Nominal Dia: 840mm			Total  Running hours: 60000		Running hours since last calibration: 15000
Gauging  point	P - S	F - A	Wear rate (average) P - S	Wear rate (average) F - A	last calib. P - S	wear rate P - S	last calib. F - A	wear rate F - A
1	841.2	841.26	0.02	0.021	840.95	0.017	841	0.017
2	841.38	841.44	0.023	0.024	841.1	0.019	841.17	0.018

iii)           what all checks on  cylinder liner

·         Excess wear on liner due to insufficient lube oil, abrasives in the fuel, liner too cool

·         Cracks on liner wall due to fuel impingement (fuel injector fault or fuel oil too cold)

·         Deposits on liner coolant side due to insufficient water treatment or oil in water

·         Lubricator quills condition such as poor or nil operation due to supply system defect

·         Criss Cross surface pattern can be maintained as per the engine manufacturer recommendation reducing the lub oil consumption. 

Well if you see a mirror sort of dry finish then do not be happy about it because ideally the surface should appear worn-bright and a bit oily, which gives an indication that all is well within the liner. The mirror finish means that local lubrication has failed in that region and severe galling action has occurred.

if you see black patches on the liner, it indicates that the piston rings are leaky and should be changed accordingly.

Since the piston moves in a to and fro fashion, there might be a ridge or sharp edges at the extreme points and/or ports and these need to be removed by proper grounding. Any other scoring marks and ridges should also be removed using grind stones or oil stones as appropriate.

iv)           m.e cyl liner crack.if there is no liner onboard then what all things u do.how u repair the liner.how u will do metal locking onboard (Bhowmik)(meatal striching)

The process of Metal Locking is based on mechanical insertion of metal alloy parts, with special shapes appropriate to each situation.   Used in T/c casings, pump casings, piston and cyl liner.

Benefits are

• Dampens and absorbs compression stresses
• Provides a good ‘expansion joint’ for such castings as cylinder liners, diesel heads or any vessels subject to thermal stresses
• Distributes the tension load away from fatigue points
• Maintains relieved conditions of inherent internal stresses where rupture occurred
• Maintains alignment and original surfaces, since lack of heat produces no distortion
• The vast majority of repairs can be done in situ, with consequent savings in time with little or no dismantling.

At the end of the process, the piece goes through finishing, getting tough as before, they do not use welding or heating suffers during the restoration process.

PROCESS
- Jigs are used to drill holes across the crack till the depth of the casting and the holes are joined to form shape of metallock key.
- Individual layer of keys are inserted into the apertures and peened to metal to metal condition.
- Holes are then drilled along the line of fracture, Tapped and fitted with studs such that 30% overlap with the previous stiched stud.
- The surface is then peened and excess material removed

HONING

Before honing, the coke deposits and the Ridge formation are removed by scraping. The honing is made by means of a flex honor (honing brush) with fineness grains 80 to 120. Revolution speed between 80 to 160 RPM is chosen. In order to achieve the required angle between the honing grooves the vertical speed is adjusted to about 1 metre per second for one move. The procedure is to be continued until about 25% of the surface is covered by honing grooves. This is achieved only after a few vertical movements. Gas oil should not be used as it promotes scratches and uneven surface roughness. After the honing, the liner is carefully cleaned and it must be ensured that the all abrasive particles have been removed.

RUNNING-IN

The running in process is a prerequisite for the reduction of adhesive wear, and it enables proper gas sealing and lubrication.

When the liner is new, it is very rough(surface asperities) and the ring is not at embedded. Consequently there will be no proper Sealing, risk of blowby is substantial, leading to disturbance of the oil film and adhesive wear. Also the hot gases due to blow by break the lube oil film and this results in ring sticking which leads to adhesive wear and ring breakage.

Some engine manufacturers recommend using the straight Mineral oil without additives like the crankcase lubricating oil for cylinder lubrication during running in. The unneutralised acids help in faster wear (hence bedding) also.

Under reduced power, if regular cyl oil with High TBN is used, the unconsumed alkaline additives might form sticky deposits leading to ring sticking.

For running in purpose a profile ring such as KNP profile ring or minute ring is used, whose ring pressure is 1/5th of the conventional ring.

The engine is run at 10%MCR for 6hrs, then 24%MCR for 2hrs.... In this way increase the load to 100%MCR for 24hrs.