This is a labreport on chemical kinetics... From this labreport students of chemical engineering and chemistry students can get a huge advantage in working in their lab..Full description
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INTRODUCTION
The sole intention of this experiment is to gain in-dept h details of a four bar chain mechanism. The four bar chain is a very important mechanism where relative motion can occur between adjoining links. This mechanism is widely used in real life app lications due to the fact that t hat lot of variations could be obtained by altering the lengths of the link. A four bar linkage consists of four rigid members on which the input motion is applied is known as the crank. The output motion link is known as the follower and t he middle link which connects both follower and crank is known as the coupler. The fourth link is known as a frame which is fixed. Also it was identified from the Gruebler ’s equation that it has a degree of freedom of one. According to the arrangements of the links, four bar linkages could be divided into into different types of groups. There are four main types of link arrangements such as the, Parallelogram linkage, crank rocker linkage, drag linkage and double rocker linkage. Each of it has differe nt characteristics of its own o wn and has its own style of coupler curves. I n parallelogram linkage the crank and the follower are of the same length and, coupler and the frame are of o f the same length. In the crank rocker linkage, crank can rotate rotat e through 360⁰ but due to the length of the follower it can only rock or oscillate. The T he drag linkage is formed when both crank and the follower could rotate t hrough 360⁰. An important characteristic of this mechanism is that the follower has variable angular velocity for constant angular ve locity of the crank. Finally in the double rocker linkage, neither the crank nor the follower can make a full rotation.
OBJECTIVE
Main objectives of this experiment are to investigate invest igate a four bar chain and to find the linkages that ensure same input output relationship or coupler curve geometry. Also to come to an understanding of the times taken for the outstroke and in st roke via drawing graphs.
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Mechanics of Machines
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SUMMARY
A four bar chain was analyzed and the readings were recorder in a table as shown in Table 1. It was an easy experiment to understand but there were lot of readings to be taken. Initially a rocker length had to be set and the lengths of each component of the mechanism had to be measured using a ruler. Then by changing the crank angle by 10 ⁰ intervals, its corresponding position of the rocker was measured. Then the distance OAD was measured using the extra link with the scale. V B was measured using the equation,
Where VA was assumed to be 1. This process was repeated until crank angle reached 360⁰.
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Mechanics of Machines
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RESULTS AND OBSERVATIONS Table 1 - Readings from the experiment θ⁰
VB has a maximum instroke value of 1.15 mm/s at 90 ⁰
VB has a maximum outstroke value of 1.625 mm/s at 220 ⁰
VB has zero velocity at both 160⁰ and 320 ⁰
Dead centre is the position of the mechanism when the ro cker is at a limit position. Hence in this case the dead centre occurs when θ is at 160⁰
Time ratio is usually calculated using the equation, TR = φ/360-φ. Hence from the VB vs φ graph it
was identified that,
Time ratio for instroke as 0.395
Time ratio for outstroke as 0.423
TR = 0.423/0.395 = 1.07
DISCUSSION
As you can see the graph in figure 1 has the shape of a polynomial function. The initial velocity of B is at 0.5 mm/s and it reaches gradually upto 1.15 mm/s when the angle is at 90 ⁰ then it slowly decreases to 0 mm/s when at the dead centre. Then when the rocker starts to move in opposite direction again the same process happens with a maximum velocity of 1.625 mm/s at 200⁰ and it goes to 0 and again climbs up to 0.475 mm/s when the angle is 360 ⁰. Graph in figure 3 has two quadratic shaped curves w ith maximum velocities at 1.15 mm/s and 1.625 mm/s. There are two identical curves is because of instoke and outstroke. There are few errors in the graphs such as velocity not coming to 0.5 mm/s in figure 1 and the ma ximum value for outsroke is at two points on the graph. These errors could be due to the mistakes made while taking readings off the scales in the four bar chain. Also there could be few
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Mechanics of Machines
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machine errors. Even though the readings may not be that accurate we could come to a conclusion and get an idea on how the four bar chain mechanism works.
EN 13 5180 42
Mechanics of Machines
Dahlan A.A.S.
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REFERENCE World Wide Web
“Four Bar Mechanism”, C.S. Kumar, Accessed March 04, 2014. http://vlabs.iitkgp.ernet.in/ “Mechanism Basics”, MIT class 6.S080, Accessed March 02, 2014. http://courses.csail.mit.edu/ “Four Bar Mechanism”, OCW press, Accessed March 02, 2014. http://ocw.metu.edu.tr/
