Question

Problem 2: A) Explain 1) Different types of Keys 2) Interference fit 3) Couplings. 1151 B) A simply supported shaft is shown in the following Figure. A constant magnitude distributed unit load pis applied as the shaft rotates. The shaft is also subject to a steady torque of Tmax=2000-N m., find the diameter of shaft required to obtain a safety factor of 2.5 in fatigue loading if the shaft is steel of Sut= 814 MPa and Sy = 703 MPa. The dimensions are in cm, the distributed force in N/cm, and the torque is in N-m. No stress concentrations are present, the shaft is machined, the required reliability is 90%, and the shaft operates at room temperature. [20] Figure: 1 = 20 cm, b = 18-cm: a = 16-cm Applied distributed load p = 1000-N.cm': IN ----- ----- ------

Answer 1

A]

1)

A key is a machine element which is used to connect pulley or hub (machine element) to the shaft so as for the transmission of torque.

Common types of keys are the following:

1. Square key
2. Rectangular key
3. Woodruff key
4. Saddle key
5. Tangent key

Based on the shape and key accomodation, keys are differentiated as

1. Sunk key

• Rectangular sunk key
• Square sunk key
• Parallel sunk key
• Gib headed sunk key
• Feather sunk key
• Woodruff key

1. Saddle key

• Flat saddle key
• Hallow saddle key

1. Tangent key
2. Round key
3. Splines

All the detailed explanations can be procured from internet along with neat figures.

2)

A fit can be defined as the degree of tightness and looseness between two mating parts. 3 types of fits are there,namely

• Clearance fit
• Transition fit
• Interference fit

Interference fit

A negative difference between the diameter of the hole and diameter of the shaft is known as interference

(Diameter of Hole) - (Diameter of shaft) = (- Clearance)

(Diameter of Hole) - (Diameter of shaft) < 0

Diameter of Hole < Diameter of the shaft

Interference occurs between low limit of the shaft and high limit of hole.

3 types of interference are

1. Shrink fit / Heavy force fit - Maximum negative allowance
2. Medium force fit - Medium negative allowance
3. Tight fit / force fit - Slight negative allowance

3)

Coupling is a device used to connect 2 shafts at their ends so as to transmit power.

Its functions are

• Power transmission
• Mounting errors absorption - Absorb misalignment
• Vibration absorption - surrounding products are safe
• Ceases heat transmission

Types of Couplings are the following

1. Muff / Sleeve coupling
2. Split muff coupling
3. Flange coupling
4. Bush pin type flexible coupling
5. Gear coupling
6. Fluid coupling
7. Universal joint / Hooke's joint
8. Rzeppa joint

The detailed explanations and figures can be referred from internet.

While writing the answer, the student must make sure that as it is a total of 15 marks, each section will be carrying 5 marks alone. Hence write and draw the matters only which are most relevant.