mechanical engineering 1

7/29/2019 Mechanical Engineering 1

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SI. N-DTN-M-NFDAMECHANICAL ENGINEERINGPaper I

Time Allowed : Three Hours Maximum Marks : 300INSTRUCTIONSEach question is printed both in Hindi and in English.

Answers must be written in the medium specified in theAdmission Certificate issued to you, which must bestated clearly on the cover of the answer-book in thespace provided for the purpose. No marks will be givenfor the answers written in a medium other than thatspecified in the Admission Certificate.Candidates should attempt Question Nos. I and 5 whichare compulsory, and any three of the remaining ques-tions selecting at least one question from each Section.The number of marks carried by each question isindicated at the end of the question.Symbols/notations carry their usual meanings, unlessotherwise indicated.If any data is considered insufficient, assume suitablevalue and indicate the same clearly.Newton may be converted to kg using the equality1 kilonewton (1 kN) = 100 kg, if found necessary.Neat sketches/diagrams may be drawn in the answer-book itself wherever required.Important : Whenever a Question is being attempted,all its parts/sub-parts must be attempted contiguously.This means that before moving on to the next Ques-tion to be attempted, candidates must finish attemptingall parts /sub-pans of the previous Question attempted.This is to be strictly followed.Pages left blank in the answer-book are to be clearlystruck out in ink. Any answers that follow pages leftblank may not be given credit.earsrfe. - t i r c i


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Section 'A'1. (a) The critical buckling load of a cast iron hollow

cylindrical column 3 m in length when hingedat both the ends is equal to P kN. When thecolumn is fixed at both the ends, its criticalload increases to (P + 300) kN. If the ratioof external diameter to internal diameter is1.25 and E = 100 GPa, determine the externaldiameter of the column.2

(b) A stuntman drives a motorcycle around acircular vertical wall 30 m in diameter. Thecoefficient of friction between the tyre andwall is 0-6. Determine the minimum speed thatwill prevent sliding down the wall. Determinethe angle also by which the motorcycle isinclined to the horizontal.2

(c) A hypoeutectoid plain c-steel is heated to1540C and then cooled slowly to 725C.What is the percentage of ferrite and austenitein steel after the process ? Mark the process onIron-carbon diagram.2

(d) An 1-beam with the following dimensions issubjected to a shearing force of 20 kN.Flange : breadth = 50 nun, thickness = 5.5 mmWeb : depth = 109 mm, thickness = 3.5 mmArea of cross-section = 9.4 x 104 mm2M.I. = Ixx = 220 x 104 mm4.Calculate the value of the transverse shearstress at the neutral axis x-x and at the top ofthe web.2

F-DTN-M-NFDAContd.)


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(e)

A band brake is used to stop a machine. Thebrake band is in contact with the brake drumthrough an angle of 250. The coefficient ofthe friction is 0.3. Determine the force Prequired to develop the braking torque ofmagnitude 400 Nm. The arrangement is shownin the above figure.2

2. (a)i) 1. Define interference in involute gears.2. How do you prevent interference ?3. Determine the minimum number of

teeth required on a pinion, in order toavoid interference which is to gearwith an equal wheel. The pressureangle is 20 and a standard addendumof 1 module for the wheel may beassumed.+3+10=15

F-DTN-M-NFDAContd.)


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F - D T N - M - N F D AC o n t d . )


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(ii) 1. Sketch the arrangement of a revertedgear train comprising of gears A andD mounted on co-axial driving anddriven shafts, respectively. Gears Band C are mounted on a parallelcounter shaft to mesh with gears Aand D, respectively.

2. The speed ratio (driving speed driven speed) in the reverted geartrain of above arrangement is to be 14.The module pitch of gears A and Bare 3-125 mm and of gears C and D are2.5 mm . Calculate the suitable num bersof teeth for the gears. No gear is to haveless than 24 teeth. The centre distancebetween the counter-shaft and drivingshall is 200 mm.+10=15

(b) A cylinder having mass 40 kg is hungby means of cables Al? and AC which areattached to the top of the vertical wall. Thedistance of points B and C on the wall from aline along the wall parallel to the axis ofcylinder are 8 m and 10 m respectively. Ahorizontal force along the line perpendicular tothe wall has been applied at the cylinder whichpulls it by a distance 1.2 m away from thewall. The point A is on the cylinder and it is10 m below BC. Determine tension in eachcable and the force applied at the cylinder.

20

F-DTN-M-NFDAContd.)


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F - D T N - M - N F D AContd.)


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(c) (i) How are the thermosetting plastic pro-ducts processed ?

(ii) Name two polymerization processes. 103. (a)

22 cm

25 cm

Compute second moment of area of the planelamina shown in the above figure about an axisparallel to the base and passing through thecentroid.0

(b) (i) A hollow shaft having an inside diameter50% of its outer diameter is to replace asolid shaft transmitting the same powerat the same speed. Calculate the per-centage saving in material if the materialto be used is also the same.0

F-DTN-M-NFDAContd.)


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(ii) A dose coiled spring has coil diameterto wire diameter ratio of 6. The springdeflects 30 rnm wider a load of 500 Nand the maximum shear stress is not toexceed 350 MPa. Find the diameter andlength of wire required. Modulus ofrigidity of wire material = 80 GPa. 10

(c) Compare the main characteristics with regardto their hardening and magnetic properties ofarious stainless steels.0

(d) Four masses mini2, rn3 and m4 are 160 kg,225 kg. 200 kg and 312 kg, respectively.The corresponding radii of rotation are 0.25 m,0.2 m, 0.3 m and 0.25 m, respectively. Theangles between the successive masses are 45,75 and 135. Find the position and magnitudeof the balance mass required. if its radius ofrotation is 0.25 m. Presume that all massesincluding the balance mass rotate in the sameplane.0

4. (a) (i) Compare the flexural strengths of thefollowing three beams of equal weight.I. I-section 300 mm x 150 mm with

flanges 20 mm thick and web 12 mmthick.

2. Rectangular section having depthtwice the width.

3. Solid circular section.5F-DTN-M-NFDA0Contd.)


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(ii) A cantilever. 3 in long, and of symmetri-cal section 250 mm deep carries auniformly distributed load of 30 kNper m run throughout, together with apoint load of 80 kN at a section 12 mfrom the fixed end. Find the deflectionat the free end. Take, E = 200 GPa andI = 54,000 cm4 .5

(b) (i) Discuss criteria of stability for springcontrolled governors.

(ii) The sleeve arm and the ball arm of aHarme11 governor are 9 cm and 10 cmlong respectively. At mean position ofthe sleeve, the equilibrium speed is300 rpm and balls rotate at the radius of12 cm. The mass of each ball is 2 kg andthe sleeve movement is 2 cm from themean position. The minimum speed is96% of the mean speed. Determine thestiffness of the spring and the maximumspeed of the governor.5

(c) A part ic le has init ial veloc i ty of 30 m /s towardsthe right at 30 with the horizontal. The retarda-tion along horizontal axis is 1 m/s2 and alongupward vertical axis is 6 m/s2. Determine thehorizontal distance covered until the particlereached a point 30 m below its original eleva-t ion.0

F - D T N - M - N F D A2Contd.)


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Section 'B'

S. (a) Define "tool life" and list down four methodsfor quantitative measurement of tool life. 12

(b) (i) With the help of an example, clarify thefunction of a clamp in a fixtures

(ii) Sketch a cam type clamp and suggest itstwo applications.2

(c) Explain how flatness of a surface is measuredwith an optical flat.2

(d) Following table shows the predecessorrelationship of the activities in an assemblyline. The output is 200 units per day andoperating time is 450 minutes per day. Usingthe most successors rule to assign tasks towork centre and longest work time rule as a tiebreaker,

(a) group the tasks into work centres and

F-DTN-M-NFDA4Contd.)


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(b) compute balance efficiency, idle time andbalance delay.Taskredecessorime(sec)A None0B 0C None0D 0E 0F None5G None5H 0I 0

12(e) What are the principles of motion economy

related to work place ? If these principles areadopted in design of work place, what will bethe advantages ?2

6. (a)i) A hole is to be drilled in a high-strengthcopper alloy workpiece with a 10 mm bitat a feed of 0.2 mm/rev. The spindlespeed is 500 rpm. Estimate the materialremoval rate and the torque required forth is op erat ion. Take sp ec if ic energ y v alueof the work material as 1.9 w.s./mm3.

10(ii) Discuss in brief the mechanism involved

in grinding wheel wear. Why aluminiumoxide and cubic boron nitride abrasivesare suitable for grinding of steel, butsilicon carbide or diamond are not ? 20

F - D T N - M - N F D A6Contd.)


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(b) (i) Explain in brief, with sketches, thepressure and vacuum gap flushingtechniques used in EDM.0

(ii) Which one of the above will result in amore accurate cavity ? Give reason. 5(iii) Also discuss how the gap flushing condi-tions may be improved while drilling

small holes.(c) Find the sequence that minimises the total

elapsed time required to complete thefollowing jobs. Each job is processed in theorder ACB.

Processing times in hoursJob No. 1 2 3 4 5Machine A 5 7 6 9 5Machine B 3 7 5 6 7Machine C 2 1 4 5 3Determine the sequence of the jobs, mak esp anand idle time of machines. Illustrate themethod of solution and assumptions taken. 10

7. (a) (0 What is understood by the statement"Process under statistical control" ?

(ii) State the conditions when the process isconsidered statistically out of control onthe basis of theory of runs ?

(iii) What is JIT ? What are its objectives andkey elements ? Illustrate in brief thesingle card Kanban and two cardK anban systems.+10+15=30



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F-DINI-M-NFDA9Contd.)


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(b) (i) Compare the process capabilities ofShielded Metal-Arc Welding (SMAW)and Submerged Arc Welding (SAW)processes.5

(ii) How thick jobs (> 20 mm) may bewelded by SMAW process ?

(c) What are the objectives of an efficient facilitylayout ? What are the principles to be adoptedto achieve these objectives ? Compare product,process and cellular layout.0

8. (a)i) What is the significance of (1) angle ofnip, and (2) angle of bite during rollingoperation ? How are they related to rollfriction ?0

(ii) Classify the process of extrusion withthe help of sketches. Enumerate theconditions under which central burst mayoccur. Where does a 'pipe' occur ? 15

(iii) What is "friction hill" ?(b) (i) A firm manufactures a product whose

selling price is0. It has a capacityof 10.000 units. The variable costs are

2.50 per unit. The fixed costs areestimated at aT 30,000 up to 50% capacityutilization, T 36,000 above 50% level,and 42,000 if the utilization is 80% orabove.



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23/24

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F-DTN-M-NFDA3


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mechanical engineering 1

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