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In an internal combustion engine, an air fuel mixture in a certain ratio is drawn inside the engine cylinder. The charge is then compressed and ignited by a spark, which on explosion generates considerable amount of heat and pressure. These burnt gases expand pushing the piston away from the cylinder head causing the piston to displace. This displacement of the piston is transmitted by means of a connecting-rod to the crank shaft which converts the linear motion of the piston to rotary motion of the crankshaft.
Description : It is that part of the engine which translates reciprocatory linear motion of the piston into rotational motion. In order to do this the crankshaft has "crank throws". These are additional bearing surfaces whose axis are at an offset from that of the crank. Â This offset converts the reciprocating (up and down) motion of the piston into the rotary motion of the crankshaft. Â The amount of offset determines the stroke of the engine.
Description : The connecting rod connects the piston to the crankshaft. The big end is connected to the crank and the small end to the piston. As it rotates at both the ends, its angle changes as the piston moves and crank rotates.
Location : Inside the engine
To convert the reciprocatory motion of the piston to rotary motion of the crank shaft.
Forged steel or duralium.
Malleable or spheroidal graphite cast iron.
The piston assembly comprises of 3 components i.e
Description : A piston is a component of the reciprocatory engine. It moves up and down in the cylinder and is made gas-tight by means of piston rings.
Location : inside the engine
To transmit the gas pressure to the crankshaft.
To take the side pressures due to angularity of the connecting rod.
To seal the inside of the cylinder from the crankcase.
To dissipate heat absorbed by the piston top during early part of expansion and combustion.
Description : A piston ring is an open ended ring that fits into slots provided on the circumference of a piston. The number of rings used depend on the requirement. Usually 3 rings are used, two compression rings, one oil ring.
Location : On the piston.
To prevent the leakage of the high pressure gasses from the combustion chamber to the crank case.
To allow heat to flow easily from the piston crown to the cylinder wall.
To maintain sufficient lubricating oil on the cylinder walls thus preventing ring and cylinder wear at the same time preventing oil from entering into combustion chamber.
Description : The gudgeon pin is what connects the piston to the connecting rod and serves as a bearing for the connecting rod to pivot about as the piston moves up and down.
Location : inside the piston.
The main function of the gudgeon pin is to avoid a discontinuity between the connecting rod small end and piston.
It should have high strength and stiffness to withstand high loads in modern engines , and should offer opportunities for downsizing and weight reduction.
It should be rigid to keep the deflection as low as possible.
It should be stastiscally and dynamically balanced.
It should be resistant to fatigue in torsion and bending.
It should have enough stiffness to resist the stresses due torsional vibration of shaft.
It should resistant to wear in bearing areas.
It should have low heat expansion in order to main the clearance between the crank cheeks and bearing shells.
It should be resistant to corrosion.
It should be as light as possible.
They should have high strength in both tension and compression.
They should have high fatigue strength.
They should be light in weight to facilitate engine balancing.
It should have high strength, particularly at its head.
It should have the shortest possible length to reduce the overall size of the engine.
It should be light in weight.
It should have high thermal conductivity for efficient heat transfer.
It should offer sufficient resistant to corrosion.
The design should be as such that seizure is prevented.
It should have a long life & be silent in operation.
They should have high strength
They should have good wear characteristic.
They should have high thermal conductivity for effective heat transfer.
They should be resistant to corrosion and micro welding.
It should have high strength to withstand bending and shearing load.
It should be light in weight.
High fatigue & wear resistance.
Problem: Progressive fracture
Cause : repeated bending or reversed torsional stresses.
Remedy : an over lap on the journal bearing& crankpin to increase endurance strength.
Problem : high wear rate.
Cause : broken springs of vibration dampers giving rise to torional stresses, oil absence, high operating oil temperature, improper use of engine.
Remedy : replacing broken springs, use of good quality oil, avoiding over revving of engine.
Problem: Crank shaft scorring
Cause : contaminations in engine oil with sand, metal & other grit material.
Remedy : check oil filter.
Problem : overloading of crankshaft thrust bearing.
Cause : poor surface finish.
Remedy : ensure good surface finish.
Problem : bending of connecting rod.
Cause : detonation.
Remedy : check ignition setting & use manufacture recommended fuel.
Problem : failure of connecting rod bolts.
Cause : faulty or improper tightening of bolts.
Remedy : use of highly skilled staff in assembly.
Problem : scorring of connecting rod bearing.
Cause : presence of debris like sand, metal in engine oil.
Remedy: checking oil filter.
Problem : Stretched connecting rod big end bearing.
Cause : loading and flexing at high speeds.
Remedy : use of better quality material & process in manufacturing.
(((((PROBLEM GIVES RISE TO CAUSE)))))) CHECK ****?????????
Refer following link make changes..( http://boatracingfacts.com/forums/showthread.php?t=5472)
PROBLEM: Deposits on piston surface( oil ash, brown, tan, carbon)
Cause: deposits on piston dome are due to oil ash ,fuel ,contaminations and un burnt carbon.
Remedy :use of better quality oil and fuel.
Problem : heat seizure.
Causes : excessive heat, over 1200f/659 c. Lean jetting.
Remedy: adjustment of carburettor so that a proper air fuel mixture is drawn inside the engine cylinder.
Problem : cold seizure.
Causes : thermo-imbalance.
Remedy : servicing and checking lubrication system.
Problem : oil flash.
Causes: poor quality oil, unsuitable temperature stability.
Remedy : better quality oil & cooling system.
Problem: piston scuffing.
Causes : insufficient lubrication on cylinder wall due to poor quality
Remedy: inspect lubrication system & use good quality oil.
Problem: piston dome breakout.
Cause: ignition timing failure, pre ignition leading leading to detonation ,spark plug heat rate too high, low value octane fuel.
Remedy: check spark plug and ignition system setting.
Problem : piston scorring.
Cause: debris getting through the air filtering system and collecting between piston and wall.
Remedy : check air filter.
Problem: Piston fracture.
Cause: excessive wear, excessive RPM with no load, excessive clearance fitting.
Remedy : adjusting the idling speed, using manufacture recommended spare parts.
Problem : piston ring scuffing
Cause : high base pressure, oil combustions & possible piston scorring.
Remedy : check air filter & oil injection system or amount of oil mixed.
Problem : fatigue failure
Cause : surface irregularities
Remedy : gudgeon pins should be lapped to a very fine surface finish to about 0.1 micro metre.
Problem : worn out gudgeon pin
Cause : excess noise & decreased life.
Remedy : replace it with appropriate size manufacture recommended pin.
The material used to manufacture the crankshaft should have the following characteristics.
High melting point.
Good thermal conductivity.
Material used: Speroidal-graphite iron
Material description : ( ces chart data)
Crankshafts materials should be as such that it is readily shaped, machined and heat-treated, and has adequate strength, toughness, hardness, and high fatigue strength. The crankshaft are manufactured from steel/iron either by forging or casting. Forged crankshafts are stronger than the cast crankshafts, but are more expensive. Forging makes a very dense, tough shaft with a grain running parallel to the principal stress direction. With the casting process the crankshaft material and machining costs are reduced because the crankshaft may be made close to the required shape and size including counterweights. Cast crankshafts can handle loads from all directions as the metal grain structure is uniform and random throughout. Counterweights on cast crankshafts are slightly larger than counterweights on a forged crankshafts because the cast metal is less dense and therefore somewhat lighter. Taking into consideration the properties of steel and cast iron, the material selected is nodular cast iron which is commonly called as speroidal-graphite iron. Speroidal-graphite iron has high wear resistance, high strength, can be easily machined, harden ability & is much cheaper than the expensive forged steel.
The material used to make connection rod should have the following characteristic :
high fatigue strength.
high endurance limit.
high yield strength.
high corrosion resistance.
light in weight.
Material used: forged steel( c 70)
C70 is widely used for making connecting rods. C70 is a type of crackable forging steel. The alloying elements in the material enable hardening of forged connecting rods where they undergo controlled cooling after forging. Analysis of forged steel show that it is 10% lighter, 25% less expensive than other forged steel rods & 15 % less than powder forged with same or better fatigue strength. The following accompanied with high endurance limit, high yield strength & high corrosion resistance have lead to selecting this material.
Various materials have been used in making con rods like aluminium alloys, titanium & steel. However forged steel ( c70) satisfies all the needful conditions.
Characteristics of forged steel :
(give ces chart)
Pistons are mostly made of cast iron because of good wear qualities, but this does nor serve the purpose. Cast aluminum alloy on the other hand is much lighter than cast iron & has high thermal conductivity which allows the piston to cool don much faster, hence material selected is cast aluminum alloy.
Characteristic of cast aluminum alloy :
high thermal conductivity
easy to machine
high dimensional stability
high specific strength.
Material characteristic :
high breakage resistance.
high heat resistance.
high mechanical stress resistance.
wear resistance ( ring side and groove side).
Material used : SAE 9254 HIGH ALLOY STEEL.
Description : ( ces chart data )
Piston rings are always operating in a high temperature region and are subjected to high pressures. The material used for making these rings is steel. Steel is stronger than ductile iron and is capable of withstanding high speeds and loads that would destroy rings made of ordinary grey cast iron. Steel piston rings can be easily formed into extremely narrow bands between piston and cylinder wall. Rings made of cast iron will easily snap on bending, but not steel piston rings. Steel is harder, has a higher tensile and fatigue strength than ductile or grey cast iron. Steel rings also provide reduced wear on the ring side and groove side along with a long life.
The material used for making gudgeon pins should have the following characteristic
high strength to withstand bending and shearing load.
High yield strength.
High fatigue and wear resistance
Material used: low carbon case hardened steel
Material description: (give ces chart)
Gudgeon pins operate under some of the highest temperatures experienced by the engine. Considering the location, lubrication is difficult. A material which is light in weight, compact and can withstand heavy shear and bending loads along with highest bearing pressure that any bearing can take. Low carbon steel satisfies all these criteria's. Some of the other unique properties of low carbon steel are high hardness, low friction, high surface conformance & high heat transfer.
Surface considerations for crankshaft: Cracking thermal stresses corrosion.
Cracking: Factographic studies indicate fatigue as a dominant mechanism of failure of crankshaft. Fatigue initiations were seen in the crankpin-web fillet region at high values of stresses.
How is it addressed: to avoid failure, machining and final grinding has to be done to prevent formation of discontinuities or crack-like defects in the fillet region.
Corrosion : corrosion of crankshaft is mainly due to contamination of the engine oil by sand, metal and other grit material. Oil in poor condition can also damage the bearing surfaces. This is due to dilution of lead in the alloy by a compound produced by oil degredation.
How is it addressed : Thermal spray coating is widely used in preventing corrosion of many materials. Anodic coating is a type of thermal spray coating which is preffered in case of iron parts.
Induced stresses : stresses are induced in crankshaft due conventional threading, milling and other finishing operations.
How is it addressed : replacing the conventional processes with some other process.
Surface considerations for con-rod:
Cracking : steel con rods are quiet prone to fatigue cracks if there are surface imperfections from machining.
How is it addressed : use of processes which give better surface finish, usually shot penning should be carried out to avoid crack initiation .
Abrasion : abrasion of the connecting rod is mainly caused due to contamination of the engine oil with abrasive materials like sand metal & other grit material. Abrasive wear takes place when hard material, metals & grit move along the surface under load indenting the surface. The surface material is removed by gouging chipping or fatigue cracking.
How is it addressed : in order to prevent the above, a polytetrafluoroethylene coating, PTFE is given to the connecting rod.
Geometrical stress : stresses are originated in sharp edges which lead to cracks being developed.
How is it addressed : shot penning is done to reduce crack initation.
Surface consideration of piston :
Cracking : thermal fatigue cracks arise due to cyclic thermal gradient. There are two ways through which thermal gradient act on stresses, thermal stresses due to different temperatures at the head of the piston & thermal stresses due to vertical distribution of the temperature along the piston. In the first case cracks are developed in specific areas of piston head, in the second case several fatigue radial cracks over the whole piston head.
How is it addressed : a graphite- modified polymer coating is given. This coating optimizes the skirt reliability, reduces friction. Hard anodising of the piston crown is used to prevent thermal fatigue crack initiation.
Abrasion : the working temperature inside the engine cylinder are highest, at these high temperatures aluminium may melt thus causing dust, sand or other grit material to impinge on the piston thereby causing abrasion.
How is it addressed: checking the oil & air filter for any leakages or damages.
Static stresses: static stresses concentrate mainly at pin holes, thus causing crack initiation at pin holes and rim this was related to Mechanical fatigue. The crack always starts at the same point and the same plane which contains the hole. Stresses at the piton head are higher.
How is it addressed: rounding of the corners in the undercut region to reduce the stress concentration.
Surface consideration of piston ring:
Cracking : steel piston rings usually break on over stressing due to shock loading, fatigue.
How is it addresses: this is caused by incorrect size piston ring, insufficient end gap. In both cases exact size rings should be used.
Abrasion : abrasive materials present inside the cylinder will cause excess ring wear by scraping action.
How is it addressed : checking the oil and air filter for leakages or damages.
Surface consideration of gudgeon pin:
Cracking : the contact surfaces between the pin and its hub, although cylindrical when not stressed, will bend and tilt, causing local surface pressure peaks. This along with the tensile forces which acts along the circumference of the pin hub, will lead to fatigue cracking in the apex of the pin hubs.
How is it addressed : it can only be prevented by the use of low-deformation rings with thick walls. This solution however runs counter to the attempt to keep the dimension of the mechanism driven by the i.c engine as small as possible.
Ovalisation: ovalisation can be defined as swelling of the gudgeon pin inner and outer diameters. This swelling is due to compression of the gudgeon pin & rapid pressure being transmitted to gudgeon pin. Excess ovalisation causes partial seizure or scuffing of the oscaillating gudgeon pin. This scuffing causes welding of localised material and increases wear rates and eventually seizure
How is it addressed : in order to maintain ovalisation to a low value, thicker material sections are necessitated.
Manufacturing process for crank shaft :
Spheroidized Graphite Cast Iron bar is first sheared into a billet to adjust the weight.The billet is then heated to around 1000 Â°C by rapid induction heating. This causes less decarburization. The material is then evenly distributed by rough forging.A forging roll is then used to shape the crankshaft. Simultaneously the bending of the crankshaft is carried out to distribute volume along the direction. Hot forging can shape intricate forms, but cannot give high dimensional accuracy because oxide scale accumulates on the surface, so milling is carried out to give the required shape. This is followed by die forging. Forging makes the grain flow continuous thus increasing the strength of the material An intricate shape of the crankshaft is obtained by the rough stamping process. Finishing is given to the final part to obtain dimensional accuracy. This is followed by Deburring and then straightening to remove any bends.
Manufacturing process for connecting rod:
The forged steel con-rods are made from closed die-forging. Closed die forging also known as impression die forging involves the movement of metal blank through a set of dies shaped in the required part design. There are two dies, stationary and moving die. Initially the material is cut to the required length and heated in an induction billet heater to a temperature above the Ac3 transformation point ,this is a preparatory treatment of steel before a final hot forging to improve the mechanical properties and attractive appearance with a minimum formation of scale on the surface of forging. The conventional closed die hot forging to a temperature of about 450 degree Celsius to Ac1 transformation point is done to achieve the non -symmetrical configuration with a high degree of workability which cannot be achieved with cold forging. These combined treatments produce a steel free from warping or residual strain and homorgenized grain structure. This process is followed by piercing, trimming & shot penning. Shot penning is a process in which the surface of the metal is bombarded with spherical particles formed from stainless steel. Penning creates a uniform compressive stress layer on or near the surface of the metal which prolongs service life under cyclic loading conditions by resisting fatigue failure.
This is followed by deburring, machining, grinding the side faces & drilling the piston end, bolt holes and tapping. The big end of the connecting rod is then fracture split & the connecting rod is assembled followed by final finishing.
Manufacturing process for piston:
The foundry is the beginning of the piston. At the foundry , die is prepared by heating it to operating temperature for approximately one hour. This process allows the die to readily accept the molten material when it is poured. The dies are made from cast iron with steel inserts for gudgeon pin holes and cores. At the start the material is heated to about 700 degrees celcius well above the metling point but below the boiling point. The material is then scooped with a ladle and poured into the die through the sprue. The material is then allowed to cool. Before removing it from the die, it is dipped in water which facilitates and even settling of the hot metal. After the casting is cooled, it is placed into a heat treatment plant over night. The heat treatment process is a three step process:
Solution heat treatment:- the objective is to take into solid solution the maximum practical amount of the soluble hardening elements in the alloy. This process consists of soaking the alloy at a sufficiently high temperature till the time the a homogenous solid solution is obtained.
Quenching :- the main objective of quenching is to preserve the solid solution at the solution heat-treating temperature and then cooling to a lower temperature( close to room temperature). Quenching increases the hardness, corrosion resistance and generates a uniformly distributed matrix with decreased grain size.
Annealing :- Annealing is a heat process whereby a metal is heated to a specific temperature /colour and then allowed to cool slowly. Annealing increases corrosion resistance, formation of sub grains with re arrangements of dislocation.
This is followed by pin boring, where the casting which has the gudgeon pin hole roughly machined. This is followed by the bung and pin boring process which allows the reamer to enter the gudgeon hole. The turning of the casting is carried out on a CNC (Computer numeric control ). The final finishing processes like drilling, grinding, reaming & pin fitting are carried out later.
Manufacturing of piston rings: ( high alloy steel )
The first step in manufacturing of piston rings is forging a blank of piston ring member separately, this is followed by heat treatment to the blank. The blank is thermally treated by heating it to a temperature of 830 degrees Celsius for 1.5 hours and then oil cooling it. The tempering temperature is 600 degrees Celsius and holding time is 2 hours. This is followed by shot penning as it improves the fatigue strength of the material under a number of load cycles.
Manufacture of gudgeon pin: ( ask kalpesh)
The process of manufacturing of gudgeon pin begins with machining a cylindrical pin. This pin is of maximum permissible length and has to be faced on the ends as it is in contact with cylinder wall. The ends are usually faced with a material different from that of the pin itself. The facing material used is aluminium bronze which is deposited by plasma gun. This is followed by plasma nitriding. Nitriding not only improves the surface hardness( increase resistance to abrasion and erosion), it will also increase the corrosion resistance, mechanical & thermal fatigue strength all of which are vital physical properties for a gudgeon pin. Plasma nitriding is a ready to use process and does not require any machining, polishing or post nitriding operations. It is a fast process and produces very little distortion.
http://www.freepatentsonline.com/5255592.html for alternate material use aluminium..
http://www.freepatentsonline.com/3575089.html for checking above written process.
( pleagirism check http://ed.grammarly.com/editor/view?analyzeJustCompleted=true )
Alternate material for crankshaft : Composite steel (Cr-Mo alloy steel).
Description : A composite steel material consists of two metallically joined steel components having different chemical composition. The composite steel contains 0.4-0.45 weight percent carbon,0.40-1.0 weight percent silicon,0.40-1.0 weight percent manganese,2.5-4.0 weight percent chromium, 0.50-1.50 weight percent molybdenum,0.20-0.45 weight percent vanadium. This characterises a high alloy tool steel having high hardness & wear resistance.
High hardness & toughness
High wear resistance
High temperature resistance
High oxidation & corrosion resistance
Very poor corrosion resistance as compared to stainless steel.
Initially the steel is hot forged and subjected to a solution treatment to have a shape which includes the pin and the journal at a temperature equal or greater than 900 degrees Celsius. The steel is then cooled at a rate of 0.3 degrees/ second whereby the area percentage of the bainite structure is the steel is equal to 80 percent. It is then sent for cutting. Finally the surface of the steel is subjected to nitrocarburizing treatment.
Alternate material for connecting rod: titanium.
Description : a typical powder base alloy using titanium alloy powder is processed to produce a connecting rod. They have a comparatively high strength with a lower density value.
High melting point ( 1649 degrees Celsius ).
High strength to weight ratio.
Titanium has excellent corrosion resistance.
It is hard, but not as hard as heat treated steels.
Poor conductor of heat.
Machining requires precaution as the material will soften n gall if sharp tools and good cooling system is not used.
In manufacturing the connecting rod, a mold of the connecting rod defining a large bore for the large bearing , a small bore for the small bearing & both these bores connected by an arm member. The powder comprises of a titanium powder base alloy. The powder is then compressed to form a perform and then sintered to form the connecting rod. Sintering is generally carried out in a temperature range of 1400- 2200 degrees F. The cap portion is then fractured along the fracture plane.
Alternate material for piston: Carbon - carbon composites.
Description : With the ever increasing demands in the automotive sector for light weight parts, a new material was introduced, carbon carbon composite. Carbon carbon composites are members of a family of materials which contain carbon fibres in a carbon matrix. The properties of these materials can be easily altered to give any desired physical and mechanical properties by a definite orientation of continuous fibres in the composite materials, selection of additives & thermal treatment of fibres and matrix before, during or after fabrication. This material can be easily cast, moulded or machined. The surface material can also be treated with oxidation protection or sealing material.
Low co efficient of thermal expansion, thus giving high stability at elevated temperatures
Capable of withstanding high temperature and pressure
Low co efficient of thermal expansion
High abrasion resistance.
Carbon carbon composites are very expensive as compared to other materials.
In oxidizing atmosphere at temperatures above 500 degrees Celsius, the material oxidizes thereby loosing mass and strength rapidly.
The carbon carbon composites piston architecture with a slight improvement is mentioned. This improvement refers to replacing the knitted fibre three dimensional piston perform with a two dimensional mould of carbon fibre fabric. Initially these carbon fabric is prepregged with a carbonaceous organic resin and layed up or molded about a mandrel to form a carbon fibre reinforced organic matrix composite. This composite is then pyrolized in an inert atmosphere to convert the organic matrix material to carbon. Cylindrical piston blanks are then densified by reimpregnation with resin which is subsequently carbonized. The densification is also accomplished by direct infiltration with carbon by vapour deposition. Once the required density is achieved, the piston billets are machined to the final piston dimension coated with oxidation sealants or catalyst.
Alternate material for piston ring: cast iron.
Description : Cast iron piston rings have a pearlitic base structure with spherical or vermicular graphite sediments and comprises of
2.5-4.0 wt. % of carbon,
1.5-4.0 wt. % of silicon,
0.2-2.0 wt. % of manganese,
a maximum of 0.35 wt. % of phosphorous,
a maximum of 0.03 wt. % of sulfur,
a maximum of 3.0 wt. % of chromium,
a maximum of 1.5 wt. % of vanadium,
a maximum of 2.5 wt. % of molybdenum,
a maximum of 0.2 wt. % of nickel,
1.0-3.5 wt. % of copper,
0.02-2.5 wt. % of aluminum,
0.005-0.04 wt. % magnesium, and remainder iron.
Alternate material for gudgeon pin : bi- material.
Description :A bi- material gudgeon pin includes a cylindrical ceramic core. Surrounding this cylindrical core is a tubular shell which is fixedly secures the core in relation to the shell. This hell rotatably cooperates with the piston and is fixed in relation to the connecting rod.