Design of Machine Elements - I Assignmnet No I

Assignments No – I

Topic-Basic Machine Design, Design of Shaft, Keys & Coupling

Date of Issue: 8^th August, 2013                                                    Date of Submission: 14^th August, 2013

1.      Explain the different stages in the design of machine elements.

2.      A armature shaft of a 40 kW, 720 rpm electric motor, mounted on two bearings A and B as shown in figure. Total magnetic pull on the armature is 7 kN and it can be assumed to be uniformly distributed over a length of 700 mm midway between the bearings. The shaft is made of steel with a ultimate tensile strength of 770 N/mm² and yield strength of 580 N/mm².  Determine the diameter of shaft if K_m =1.5 and K_t=1.0, assume that the pulley is keyed to the shaft.

3.      The problem is shown in the given figure. A pulley drive is transmitting power to a pinion, which in turn is transmitting power to some other machine element. Pulley and pinion diameters are 400mm and 200mm respectively. Shaft has to be designed for minor to heavy shock

ASME code for shaft design is suitable in this case as no other specifications are provided.  In absence of any  data  for material  property,  the  allowable  shear  for  commercial  steel  shaft may  be  taken  as 40 MPa, where keyway is present in the shaft.  For the given condition of shock, let us consider K_m = 2.0 and K_t = 1.5.

4.      What is key? How are the keys classified? Draw neat sketches of different types of keys and state their applications.

5.      Discuss the function of couplings and effect of key way cut into shaft. Explain the difference between rigid and flexible coupling.

6.      Design a cast iron protective flange coupling to connect two shafts in order to transmit 7.5 kW at 720 rpm. The following permissible stresses may be used:

Permissible shear stress for shaft, bolt and key material = 33 MPa

Permissible crushing stress for bolt and key material = 60MPa

Permissible shear stress for the cat iron = 15 MPa

7.      Design  a  bushed  pin  type  flexible  coupling  for  connecting  a  motor  shaft  to  a  pump  shaft  for  the following service conditions:

Power to be transmitted = 40 kW; speed of the motor shaft = 1000 r.p.m.; diameter of the motor shaft = 50 mm; diameter of the pump shaft = 45 mm. The bearing pressure in the rubber bush and allowable stress in the pins are to be limited to 0.45 N/mm2 and 25 MPa respectively.

Note: On the last date of submission of your assignment, a minor test of 20 marks will be conducted

DESIGN  OF SHAFTS

1.  Define shaft.

A shaft is a rotating machine element which is used to transmit power from one place to another.  Shaft is used for the transmission of torque and bending moment.

2.  Differentiate between shaft and axle.

An axle, through similar in shape to the shaft, is a stationary machine element and is used for transmission of bending moment only.  It simply acts as a support for some rotating body.

3.  What is spindle?

A spindle is a short shaft that imparts motion either to a cutting tool or to a workpiece. 

4. What are the materials used for shafts.

For ordinary shafts – mild steel

            For high strength shafts – alloy steel such as Nickel, Ni-Cr steels (or) Cr – V steels.

5. What are the types of shafts and their importance?

1. Transmission shafts – These shafts transmit power between the source and the machines absorbing power.  These shafts carry machine parts such as pulleys, gears etc.  they are subjected to bending in addition to twisting.

2. Machine shafts – these shafts form an integrated part of the machine itself.  The crankshaft is an example of machine shaft.

6. What are various types of stresses induced in the shafts. .

1. Shear stresses due to transmission of torque.

2. Bending stresses.

3. Stresses due to combined torsional and bending loads.

7.  What are standard sizes of transmission shafts?

1. 25mm to 60mm with 5mm steps.

2. 60mm to 110mm with 10mm steps.

3. 110mm to 140mm with 15mm steps.

4. 140mm to 500mm with 20mm steps.

Standard length – 5m, 6m and 7m.

8.  On what basis the shafts are designed.

1. Based on rigidity and stiffness       2. Based on strength   3. Based on critical speed.

9.  Differentiate the hollow shaft and solid shaft.

The hollow shafts are used in marine work.  These shafts are stronger per kg of material and they may be forged on a mandrel, thus making the material more homogenous than a solid shaft.

10. Give examples for shafts subjected to axial load in addition to torsion and bending loads.

a. propeller shafts of ships                              b. shafts for driving worm gears

c. main shaft of Kaplan turbines.

11.  What are the desirable properties for the materials for shafts and axles?

a. sufficient high strength

b. a low sensitivity to stress concentration

c. ability to withstand heat and case hardening treatment.

d. good machinability

12. How the shafts are designed when it is subjected to twisting moment only?

When the shaft is subjected to torque only, then it is designed based on torsion equation.

13.  Why rotating shaft are generally made with circular cross section?

Stress distribution pattern will be uniform throughout the circular cross section.

14. Define Torsional stiffness of shaft.

It is defined as the resisting strength of a shaft to torsional load.

Mathematically it can be calculated by the formula.

15. If the shaft is subjected to torsion and bending moment, the shaft diameter can be determined based on the two theories namely _________

Ans: Guest’s theory and Rankine’s theory.

16. What are the ways of improving lateral rigidity of shafts?

1. maintaining proper bearing clearances

2. correct gear teeth alignment.

17. Define critical speed of a shaft.

Rotating shaft tends to vibrate violently in transverse direction at certain speeds known as critical (or) whirling speed.  When the natural frequency of vibration is equal to the speed of the shaft, resonance will occur.  Such a value of natural frequency is called critical or whirling speed.

18. State any two reasons for preferring hollow shaft over solid shaft.

1. for some weight of shaft, hollow shaft can transmit 1.5 times the torque transmitted by solid shaft.

            2. for a particular power transmission hollow shaft requires minimum weight.

19. What is column factor?

If a long shaft subjected to axial load (compressive load) in addition to torsion and bending, a factor must be introduced to take the column effect into account.

MV Assignment No 3

Assignement No III Total Quality Management (TQM)

CTIEMT, SHAHPUR

MECHANICAL ENGINEERING DEPARTMENT

Total Quality Management (TQM)

Assignment No # III

Date of Issue: 27^th March, 2013                                                       Date of Submission: 4^th April, 2013

1.      Discuss in detail seven basic problem solving tools and seven new tools for problem solving.

2.      What is benchmarking? What is it process? Explain its various types.

3.      Explain the registration procedure for ISO 9001.  Also explain the elements of ISO 9001.

4.      Explain the FMEA technique of TQM in details along with its advantage and limitations.

5.      Write a short note on

a.      Taguchi Methods.

b.      Signal to noise ratio

c.       Difference between ISO 9000 and  ISO 14000