# GTU previous question papers -BE- Sem-Vth – Machine Design-I -May/June -2012

GTU previous question papers

GUJARAT TECHNOLOGICAL UNIVERSITY

BE- Vth SEMESTER–EXAMINATION – MAY/JUNE – 2012

Subject code: 151905

Subject Name: Machine Design-I

Instructions:

1. Attempt all questions.

2. Make suitable assumptions wherever necessary.

3. Figures to the right indicate full marks.

Q.1 (a) (i) Explain the importance of Wahl’s stress factor in spring design.

(ii) State and explain the factors affecting selection of spring materials.

(b) Design a helical compression spring from the following data:

Minimum load = 100 N

Maximum load = 225.6 N

Compression of spring = 10 mm

Permissible shear stress for spring material = 440 Mpa

Spring end – square and ground ends

Modulus of rigidity for spring material = 0.80 x 105 MPa

Q.2 (a) (i) Explain the friction materials used in friction clutches.

(ii) Explain the difference between single plate and multiplate clutch.

(b) The following specification refers to a centrifugal clutch:

Power to be transmitted = 15 kW

No. of shoes = 4

Angle subtended by the shoe at centre = 600

Inner radius of drum = 150 mm

Distance of C.G. of shoe from the centre of the spider =120 mm

Coefficient of friction the shoe and drum = 0.25

Running Speed = 900 r.p.m.

Shoe engagement starts at Speed = ¾ th of the Running Speed

Permissible pressure intensity = 0.10 MPa

Find (i) capacity of the clutch Mass of each shoe and (ii) size of each shoe.

OR

(b) Design a single plate clutch considering uniform wear criterion and

effective

one pair of contacting surfaces from the following specification:

Power to be transmitted = 18.5 kW

Speed = 750 r.p.m.

Outer diameter = 2 times internal diameter

Permissible pressure for the lining = 1 MPa

Coefficient of friction = 0.20

Permissible stress for shaft material = 45 MPa

Q.3 (a) (i) Explain the different types of stresses induced in a belt with neat sketch.

(ii) Write a note on belt materials.

(b) The following data refers to flat belt drive

Power to be transmitted = 15 kW

Motor speed = 1440 r.p.m.

Speed of driven pulley = 480 r.p.m.

Density of belt material = 950 Kg/ m3

Centre distance between two pulleys = 810 mm

belt speed = 20 m/sec

Modulus of elasticity for belt material = 100 MPa

Coefficient of friction=0.35

Permissible stress for belt material = 2.25 Mpa

Belt thickness = 5 mm

Calculate (i) pulley diameters (ii) length and width of the belt

OR

Q.3 (a) (i) Explain the step by step procedure used for chain drive selection.

(ii) State the different belt tension adjustment devices and explain one of

them in detail with neat sketch.

(b) V-belt drive has the following specification:

Power to be transmitted = 30 kW

Motor speed = 1440 r.p.m.

Machine pulley speed =480 r.p.m.

Centre distance between two pulleys = 1 m

Approximate Allowable belt speed = 20 m/sec

Coefficient of friction=0.20

Density of belt material = 1000 Kg/ m3

Cross sectional area of V belt = 700 mm2

Find the no. of v-belts required and pulley diameters neglecting the slip of the belt.

Q.4 (a) State the different equations used for thick cylinder design with their conditions and limitations.

(b) Design a journal bearing from the following data:

Radial load = 20 kN

diameter of journal =100 mm

Speed of journal =900 r.p.m.

oil SAE 10 with viscosity at 550 C = 0.017 kg/m-sec

ambient temperature =15.50 C

maximum bearing pressure = 1.5 Mpa

permissible rise in oil temperature = 100 C

heat dissipation coefficient = 1232 W/m2/0C

L/D ratio = 1.6

Design parameter ZN/p = 28

clearance ratio = 0.0013

specific heat of oil = 1900 J/kg/0C

OR

Q.4 (a) (i) State and Explain the factors affecting the selection of a suitable

antifriction bearing.

(ii) Explain the effects of the L/D ratio and C/D ratio parameters on the

performance of journal bearing.

Q.4 (b) A hydraulic press has the following specifications:

Capacity = 80 kN

Fluid pressure = 16 MPa

Stroke = 80 mm

Permissible tensile stress for pillar and ram = 75 MPa

Permissible stress for C.I. cylinder = 30 MPa

Distance between the center line of pillars = 800 mm

Distance between top supporting platform and bottom of top plate when the ram is in the down most position = 800mm

Design the ram, cylinder and pillars.

Q.5 (a) Explain Goodman’s and Soderberg’s diagram with neat sketches.

(b) Answer the following (any TWO)

(i) Explain the wear considerations in design.

(ii) Explain the important considerations to be considered in casting design.

(iii)Explain Hertz contact stresses in detail.

OR

Q.5 (a) (i) What do you meant by standardization? Explain the use of standardization in

design.

(ii) Explain the assembly considerations in machine design.

(b) The following data refers to a transmission shaft :

I torsional moment that varies from = -100 Nm to + 600 Nm.

ultimate tensile strength = 630 Mpa

yield strength = 360 MPa, stress

load correction factor = 0.6

size correction factor = 0.85

Surface finish factor = 0.8.

reliability factor = 0.897

factor of safety = 2

Calculate the shaft diameter using distortion energy theory of failure.

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