adv.design of weldments seme1 2004

7/27/2019 Adv.design of Weldments Seme1 2004

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Ex/MME/6135/57/2004

MASTEROFMECHANICALENGG.EXAMINATION,2004

1st Semester

ADV. DESIGN OF WELDMENTS

Time : Three hours Full Marks : 100

(50 marks for each part)

Use a separate Answer-Script for each part.

PART-I

Assume relevant data and underline them.

Answer question No. 1 and any two from the rest.

1. a) State the factors which affect the welding cost.

b) Two mild steel plates each of 2000 500 12 are tobe gas welded. A 60 vee joint is to be hand cut by

gas cutting as edge preparation. The costs of oxygen and

acetylene per cu.m. are being Rs. 10.00 and Rs. 55.00

respectively, the cost of filler rods is Rs. 20.00 per kg

and the cost of mild steel plate is Rs. 10.00 per kg. The.

density of the filler rod is 8.0 gm/cu.cm. Calculate thefactory cost of the job, assuming (i) time for personal

allowance as 25% over the labour cost (ii) welder's

charge as Rs. 12.00 per hour and (iii) overhead charges

are 400% of the labour cost. 5+13

[Turn Over]


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( 2 )

2. a) Show that the volume of material required for cast iron

structure is 4.5 times that required for mild steel

structure of a cantilever of rectangular section for equal

loading capacity and stiffness, if the working stresses

for cast iron and mild steel are 30 MN/m2

and

90 MN/m2

respectively and modulus of elasticities of

cast iron and mild steel are 1105

MN/m2

and 2l05

MN/m2

respectively.

b) An I section cantilever, d mm deep and b mm wide

consists of two identical flanges of 20 mm thickness and

a web of 10 mm thickness (d40) mm depth. What

will be the optimum volume if the 2.0 m long cantilever

is loaded with 300 KN at its free end? Allowable

deflection is 1 mm, allowable stress is 90 MN/m2

andmaterial is St42 steel. 6+10

3. a) Joint preparation is independent of welding process

employedComment.

b) Importance of width to depth of weld in a single vee

joint preparationExplain.

c) What is hardfacing? What are its advantages? Name

at least three electrodes used for hardfacing. 4+4+8

4 a) Explain any one with neat sketch :

i) Electroslag welding

ii) Thermit welding

b) What are the factors involved in selecting electrodes

name them with brief explanation. 16


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Table 1 (Approx Values)

Plate

thickness

(mm)

Nozzie size

Dia (mm)

Cutting Speed

(m/hr)Gas Consumption in m

3

Hand M/C Oxygen Acetyene

Hand M/C Hand M/C

3 0.8 30-45 30-50 1.3-1.4 1.2-1.4 0.2-0.25 0.18-0.25

5 1.0 20-30 18-31 0.85-2.1 0.82-2.1 0.15-0.20 0.13-0.2

10 1.2 15-25 15-30 1.2-2.4 1.1-2.4 0.2-0.25 0.15-0.25

15 1.5 18-27 18-30 3.3-4.0 3.3-4.5 0.33-0.45 0.33-042

25 1.6 15-28 18-30 3.6-4.5 3.6-5.0 0.36-047 0.36-0.47

50 2.0 9-18 10-18 5.0-6.5 5.0-6.8 0.45-0.56 0.45-0.58

Table 2 (Approx Values)

Plate

thickness

(mm)

Filler rod dia

(mm)

Edge

preparation

C2H2Consumption

cu. m/hr.

Welding Rate

m/hr.

Filler rod

used/m of

weld (mm)

Using Leftward Welding Technique

1 1.0 Square 0.0525 6.5 1.0

2 2.0 Square 0.1 6.0 1.5

3 2.5 Square 0.165 5.5 1.6

4 3.0 80V 0.325 5.0 2.6

5 3or4 80V 0.325 4.0 4 or 1.8

Using Rightward Welding Technique

5 2.5 Square 0.445 3.75 3.3

6 3.0 Square 0.600 3.33 3.48 4.0 Square 0.775 3.00 3.6

10 5.0 60V 1.15 2.25 4.5

15 6.0 60V (Top) 1.60 1.35 6.8

20 6.0 80V (Bottom) 1.85 1.00 10.0

25 6.0 -do- 2.25 0.65 16.0

* Oxygen consumption is 1.1 times that of acetylene for neutral flame conditions


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( 3 )

PART-II

Do not answer more than 50 marks.;

5. a) What do you mean by residual stress ?

b) Mention the effects of residual stresses.

c) State and explain different methods of relieving residual

stresses. 3+4+8=15

6. a) What is pre-heating of welds ?

b) Why and how are pre-heating done?

c) Mention the factors producing cracking. 3+8+4=15

7. Starting from fundamental deduce the relations

i)

and

ii)

All notations carry usual meaning. 10+10=20

8. Write notes on (any three) : 35=15

a) Friction welding

b) Straight polarity and Reverse polarity

c) Submerged Arc welding

d) Parameters affecting weldability

adv.design of weldments seme1 2004

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