OCTOBER 19-20, 2012 - YMCA University of Science & Technology

Proceedings of the National Conference on
Trends and Advances in Mechanical Engineering,
YMCA University of Science & Technology, Faridabad, Haryana, Oct 19-20, 2012
1. Compression range-635mm
2. Extension range-533mm
3. Platform diameter-305mm(equipped with three load cells for maximum off centre load capacity)
4. Operating system-MS Windows XP
5. Software-FLASH Pro Spring
6. Load cell capacity-1361 kg, 3000lb
7. Power-240VAC, 50Hz
8. Emergency stop button is provided in case of overloading
9. Least count of the machine is 1 N
4.3 Experimental testing procedure
The operation of the Larson testing machine is as follows-
1. As the machine is powered on an automatic self check takes place to ensure that the machine is working
properly.
2. The top and the bottom surfaces touch and thus zero calibration is automatically done so that the machine
knows the exact location of the top surface.
3. The end seats are fixed on both the top and bottom surfaces of the testing machine.
4. The spring is now placed on the bottom end seat and the top end seat is made to just come in contact with
the top part of the spring.
5. The shackle height is calculated and the total offset height is fed into the computer.
6. Now the load is gradually applied on the spring and values are directly read off the screen.
7. The spring height is decreased in steps of 25mm and the loads values are taken.
8. When the shackle is placed on the machine along with the load readings the turn in Degrees is also noted
down from the laminated circular scale on the shackle.
4.4 Shackle Design
Under normal testing conditions in the Larson testing machine, the coiling and uncoiling motion of a compression
spring is restricted. The end seats which are used under normal testing conditions fits snugly into the end
coil profile. The top plate and the bottom test bed of the machine are fixed, thus preventing the uncoiling of the
spring. To allow the coiling and uncoiling motion we have designed a shackle [7]. It also measures the degree to
which the spring coils and uncoils under normal compressive load. The shackle has been designed with a thrust
bearing. The thrust bearing takes the load on the spring but allows free rotation along the axis of the spring. The
shackle consists of a base plate, the thrust bearing and a top plate. The bottom plate is fixed to the bottom test
bed of the Larson testing machine with the help of a bolt made to specification. The thrust bearing itself is made
up of two hardened steel circular plates, both of which have grooves to account for the ball bearings which are in
the middle of the two circular plates. The two circular plates of the thrust bearing rotate because of the ball bearings.
The bottom circular plate of the thrust bearing is press fitted onto the base plate of the shackle and the top circular
plate of the thrust bearing is press fitted onto the top plate of the shackle. A laminated circular measuring
scale is fixed onto the base plate of the shackle which measures the degree of rotation of the compression spring
being tested in Degrees. The top plate of the shackle has a pointer attached to it. When the bottom end of the
spring rotates the top plate of the shackle also rotates and the pointer gives the reading on the circular scale. The
top and bottom plates of the shackle are made of mild steel. The top and the bottom plates of the shackle have
holes with M20 screw threads which fit firmly into the top and bottom test beds of the Larson testing machine.
The set up of the shackle is as follows-
1. The bottom plate of the shackle along with the laminated circular scale are placed on the bottom test bed of
the Larson testing machine and is bolted using M20 bolt to make sure that it is fixed firmly.
2. The ball bearing ring is then placed on top of the bottom circular plate of the thrust bearing. Oil is then applied
to ensure smooth rotation.
3. Now the top circular plate of the thrust bearing which is press fitted onto the top part of the shackle is put on
top of the ball bearing ring. The top part of the shackle also has a pointer attached to it.
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