Question

machine design please answer ASAP

15. Ball and Roller Bearings a. What is the major difference in the design of ball and roller bearings? b. Why does a roller bearing have more load carrying capacity than a ball bearing? 16. How is the Rotational Rating Life of a ball bearing related to the applied load? 17. What is the Fundamental Law of Gearing? 18. Why doesn't a spur gear produce an end thrust? 19. Why is backlash required in the manufacture of a gear set?

Answer 1

15 a) Ball bearing is spherical in shape while roller bearings are cylindrical in shape. The major difference in the design of both bearings lies in the contact surface between bearing and inner rail. Ball bearings have a point contact while roller bearings have a line contact.

15 b) Roller bearings have line contact while ball bearings have a point contact between bearing and inner rail. The contact surface area in roller bearing is greater than ball bearing. Hence, roller bearing have more load carrying capacity than ball bearing.

16) We can calculate rotational life of ball bearing by the following formula -

$L_{10}=( \frac{C}{P_{e}})^{3}$

C = Dynamic load rating of bearing

P_e= Equivalent load on bearing

L₁₀= Life of bearing in million revolutions

17) For a pair of gear to transmit constant angular velocity ratio, the tooth profiles of mating gears is designed in such a way that common normal passes through the pitch point on the line of centres.

18) The teeth of spur gears are parallel to the axis of gear. So when it meshes with another spur gear, only axial force acts radially trying to separate the two gears but there is no thrust (axial) force.

19) Backlash is clearance between mating gear teeth. It prevents jamming of gears and making contact on both sides of their teeth simultaneously. It reduces noise while gears are meshing.