4RD SEMESTER, MECHANICAL
PRROJECT REPORT:
SLIDER CRANK MECHANISM. GROUP MEMBERS: 1. SYED
ANIS BADSHAH
ME-001
2.
SHAFIQUE AHMAD
3.
SAYED SHAHID RAZA
ME-034
4.
SYED IBRAHIM HASSAN
ME-035
5.
SANAUALLAH KHATTAK
ME-044
SUBMITTED TO:
ENGR; MUAZAMA ARSHAD
DEPARTMENT; MECHANICAL ENGG;
ME-032
4RD SEMESTER, MECHANICAL
OUTLINE: — Introduction and Working of crank mechanism. — Working principle of crank mechanism — Terminology and kinematics of crank mechanism. — Types of crank mechanism. — Applications and uses. — Failure in crank. — Design consideration. — Conclusion.
Crank mechanism: Mechanism in which rotary motion of crank is converted into the linear motion of the piston or any other integral element. “
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Crank is the main element used in crank mechanism.
A slider crank (see illustration) is most widely used to convert reciprocating to rotary motion (as in an engine) or “
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to convert rotary to reciprocating motion (as in pumps), but it has numerous other applications. ”
Parts of crank mechanism: I.Gide frame. II.Slider III.Wrist pin IV.Connecting rod V.Crank pin VI.Crank VII.Crank shaft
Principal parts of slider-crank mechanism
Positions at which slider motion reverses are called dead centers. When crank and connecting rod are extended in a straight line and the slider is at its maximum distance from the axis of the crankshaft, the position is top dead center (TDC); when the slider is at its minimum distance from the
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axis of the crankshaft, the position is bottom dead center (BDC).
The conventional internal combustion engine employs a piston arrangement in which the piston becomes the slider of the slidercrank mechanism. Radial engines for aircraft employ a single master connecting rod to reduce the length of the crankshaft. The master rod, which is connected to the wrist pin in a piston, is part of a conventional slider-crank mechanism. The other pistons are joined by their connecting rods to pins on the master connecting rod.
Principle of crank mechanism. To convert rotary motion into reciprocating motion, the slider crank is part of a wide range of machines, typically pumps and compressors. Another use of the slider crank is in toggle mechanisms, also called knuckle joints. The driving force is applied at the crankpin so that, at TDC, a much larger force is developed at the slider.
Terminology used in crank mechanism: Terminology used in crank mechanism is; 1. Linkage 2. Crank angle 3. Connecting rod 4. Crank shaft geometry and kinematics.
1)- linkage:
A set of rigid bodies, called links, joined together at pivots by means of pins or equivalent devices.
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Linkages are used to transmit power and information. They may be employed to make a point on the linkage follow a prescribed curve, regardless of the input motions to the linkage. They are also used to produce angular or linear displacement. If the links are bars the linkage is termed a bar linkage. A commonly occurring variation of the four-bar linkage is the linkage used in reciprocating engines (see illustration).
Slider C is the piston in a cylinder, link 3 is the connecting rod, and link 4 is the crank. (Link 1 is the fixed base, A and D are pivots, R is the length of the crank, L is the length of the connecting rod, and τ denotes the angle of the crank.) This mechanism transforms a linear into a circular motion, or vice versa. The straight slider in line with the crank center is equivalent to a pivot at the end of an infinitely long link.
2)- crank angle: The angle between a crank and some reference direction. Specifically, the angle between the crank of a slider crank mechanism and a line from crankshaft to the piston.
3)- connecting rod:
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A rod that transmits motion or power from one moving part to another, especially the rod connecting the crankshaft of a motor vehicle to a piston. Also called pitman.
4)-crank geometry and kinematics : Definitions l = rod length (distance between piston pin and crank pin) r = crank radius (distance between crank pin and crank center, i.e. half stroke) A = crank angle (from cylinder bore centerline at TDC) x = piston pin position (upward from crank center along cylinder bore centerline) v = piston pin velocity (upward from crank center along cylinder bore centerline) a = piston pin acceleration (upward from crank center along cylinder bore centerline) ω = crank angular velocity in rad/s
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Diagram showing geometric layout of piston pin, crank pin and crank center
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Types • • • •
of crank mechanism:
1)- CRANK AND LEVER MECHANISM. 2)-DOUBLE CRANK MECHANISM. 3)-SINGLE SLIDER CRANK CHAIN MECHANISM. 4)- MULTIPLE SLIDER CRANK MECHANISM.
1)- CRANK AND LEVER MECHANISM. • •
This mechanism is basically used in “BEAM ENGINE ”. This mechanism consists of four links as shown.
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4RD SEMESTER, MECHANICAL
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In this mechanism when the crank rotates about the fixed center, the lever oscillates about a fixed center. The end of the lever is connected to a piston rod which reciprocates due to the rotation of the crank.
2)- double CRANK MECHANISM.
This mechanism is used for a coupling rod of a locomotive.
In this mechanism the links having equal lengths act as crank and are connected to the respective wheels.
One link act as a coupling rod and the other link is fixed in order to maintain a constant center distance between them.
The main purpose of this mechanism is to transmit rotary motion from one wheel to the other wheel.
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3) - single slidED crank CHAIN mechanism.
This mechanism consist of one sliding pair , and three turning pairs. Usually found in reciprocating steam engine. Its main purpose is to converts rotary motion into reciprocating motion and vice versa.
4)- multiple slider cra nk mechanism.
It consist of more than one sliding pair. Usually found in Gnome rotary engine.
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Applications and uses.
Used in in diesel engines. Used in petrol engines. Used in rotary engines. Used in beam engines Used for coupling rod of locomotives Used in steam engine. Used in toggle mechanism i.e. knuckle joints. Used in bull engine. Used in shaping and slotting machines. Used in Oldham’s coupling. Used in quick return mechanism. Used in spring mechanism to store energy. Used in pedals of bicycles. Used in bucket pulley system in well.
Failure in crank mechanism: 1. Fracture initiated in a segregated region near the neutral bending axis of pin and produced a woody fracture plane perpendicular to the direction of imposed piston loading. This woody fracture existed prior to machining and induction hardening. The woody fracture location, orientation, and size are similar in both crankshafts. 2.The large woody fracture region was produced by stresses that acted in a cross planar direction as evidenced by the orientation of secondary cracking. 3.The woody fracture pre-existed final machining and heat treatment, as evidenced by the disruption of tool withdrawal markings in the oil hole on crank. (A similar determination was not possible on crank because the material containing the oil hole and woody fracture intersection was not available.) 4. Regions of segregated material, including MnS inclusions and higher carbon, tempered marten site bands, Existed throughout the crankshaft with some segregated areas extending to or near the journal surface. 5. Cracking continued from the edges of the woody fracture plane through the hardened case to the journal surface in service by low cycle fatigue.
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6. Fatigue propagation was by combined bending and torsional stresses. The actual level of these stresses as Compared to design or expected stress levels in this engine is unknown. 7. When the fracture reached the bearing interface, spilling and localized seizure caused bearing failure and engine outage. Lubrication conditions appeared nominal as evidenced by bearing, piston, and oil Examination.
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Design consideration: Diameter of crank= 3 inch Length of connecting rod= 6 inch Length of piston = 2.5 inch Bed ways length= 10 inch Bearing for bed ways= small 10 ball bearings.
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Operations performed: Following operations are done on the construction of this project i.e. Slider cranks mechanism.
Drilling. Lathe machines operations(facing, turning, cutting) Rough turning. Finishing.
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4RD SEMESTER, MECHANICAL
Conclusion: •
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We conclude that crank mechanism is much important in all types of engines especially in ic engines, and reciprocating engines. Proper design is carried out rather failure will occur Material is used according to the kind of load. For high duty high carbon steel is used and for low duty cast iron is used. Proper adjustment is carried to between the piston and cylinder side wall in order to avoid striking, and for long life of machine. Size of crank is taken according to the desired rpm, and size of connecting rod is taken according to the crank.
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