TABLE OF CONTENTS Mechanical Design, or Machine Design as it is often called, combines all of the disciplines in the study of Mechanical Engineering. A typical design problem requires first the development of a mechanism to perform the desired function. Next it has to be demonstrated that the device will perform without failing and without imperilling the user or the public. Attention should also be paid to the cost of the device including material, manufacturing, operating, and maintenance costs.
Q:
Design a square key for a gear wheel attached to a 2.5 cm diameter shaft to transmit 10.0 kw of power at a speed of 1750 rpm. The gear wheel is 1.5 cm thick. If the key is to be made of steel with an allowable shear stress of 200 MPa, what size key should be used if a safety factor of three is required assuming shear stress controls?
Answers
Q:
The allowable stress on the key material would equal 200/3 = 66.67 MPa. 10.0 kW = 10.0 kJ/s and a joule is a N m. Power = 2 ? (rev/sec) Torque = watts
The shaft rotates at a speed of 1,750/60 = 29.17 rev/s and transmits energy at the rate of: 10,000 J/s = F m/s) F ( ? 0.025 29.17) = 2.2910 F = 10,000 N m/s
where F = force on key in newtons. F = 10,000 watts/2.2910 = 4,364.9 N
The required shear area of key = 4,365/66.67 ...
