gtu paper analysis chapter 1 gear design · 2019-11-19 · worm is to be made of hardened steel and...

GTU Paper Analysis

Machine Design (2171909) Department of Mechanical Engineering Darshan Institute of Engineering & Technology

Chapter 1 – Gear Design

Sr. No. Questions

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Theory

1. Explain the following terms used in helical gears: (a) Helix angle; (b) Normal pitch; (c) Axial pitch; (d) Normal Pressure angle

04

2. Explain in detail: (i) Law of gearing (ii) Gear tooth failures. 07

3. Explain: (i) Thermal rating of worm gearing (ii) Efficiency of worm gearing. 07

4. Why dissimilar materials are used for worm and worm wheel? And explain the designation 4/29/10.6/2.5/50 used for the pair of worm and worm gear.

03

5. Explain: Interference and undercutting of gears 02 04

6. How are the gears classified? Explain the role of pressure angle in the gears. 03

7. Explain different types of gear tooth failures. 04

8. Give classification of gears. 03

9. Prove that “The common normal to the tooth profile at the point of contact should always pass through a fixed point, in order to obtain constant velocity ratio”.

07

10. What is the minimum number of teeth on spur gear? Why? 03

11. Why are worm gear reduction units not preferred over other types of gearboxes for transmitting large powers?

03

12. What is herringbone gear? State two advantages of herringbone and double helical gear. 04

Examples

1. A pair of straight teeth spur gears, having 20° involute full depth teeth is to transmit 12 kW at 300 r.p.m. of the pinion. The speed ratio is 3:1. The allowable static stresses for gear of cast iron and pinion of steel

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GTU Paper Analysis


are 60 MPa and 105 MPa respectively. Assume the following: Number of teeth of pinion = 16; Face width = 14 times module; Velocity factor (Cv) = 4.5/ (4.5 + v), v being the pitch line velocity in m / s; and tooth form factor y = [0.154 – (0.912/No. of teeth)]. Determine the module, face width and pitch diameter of gears. Check the gears for wear; given σes = 600 MPa; EP = 200 kN/mm2 and EG = 100 kN/mm2.

2.

A 90° bevel gearing arrangement is to be employed to transmit 4 kW at 600 r.p.m. from the driving shaft to another shaft at 200 r.p.m. The pinion has 30 teeth. The pinion is made of cast steel having a static stress of 80 MPa and the gear is made of cast iron with a static stress of 55 MPa. The tooth profiles of the gears are of 14.5° composite form. The tooth form factor may be taken as y' = [0.124 – (0.684 / TE)], where TE is the formative number of teeth and velocity factor, Cv = 3/ (3 + v), where v is the pitch line speed in m/s. The face width may be taken as 1/3rd of the slant height of the pitch cone. Determine the module, face width and pitch diameters for the pinion and gears, from the standpoint of strength and check the design from the standpoint of wear. Take surface endurance limit as 630 MPa and modulus of elasticity for the material of gears is EP = 200 kN/mm2 and EG = 80 kN/mm2.

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3.

The speed reducer unit is to be designed for an input of 2 KW at 1600 rpm. The velocity ratio is 25. The worm is to be made of hardened steel and the gear of phosphor bronze having a static stress of 70 MPa. The approximate distance between two shafts is 120 mm. Taking a velocity factor Cv = 6/ (6 + v), Tooth form factor, y = [0.154 – (0.912/No. of teeth)] and a wear factor of a 0.7. Find Standard module of gear, Face Width of the gear & length of worm and Check the design for wear load. Take tooth system 20° full depth involute.

10

4.

A pair of bevel gear with 20° pressure angle consists of a 20 teeth pinion meshing with a 30 teeth gear. The module is 4 mm, while the face width is 20 mm. The material for pinion and gear is steel 50C4 (σut=750 N/mm2). The surface hardness of gear is 400 BHN. The pinion rotates at 500 rpm and receives 2.5 kW power from the electric motor. The service factor is 1.5. Determine the factor of safety against bending failure and against pitting failure.

07

5.

A 17-tooth 20° pressure angle spur pinion rotates at 1800 rev/min and transmits 4 HP to a 52-tooth disk gear. The diametral pitch is 0.4 teeth / mm, the face width is 38 mm, and the quality standard is No. 6. The gears are straddle-mounted with bearings immediately adjacent. The pinion is a grade-1 steel with a hardness of 240 Brinell tooth surface and through-hardened core. The gear is steel, through-hardened also, grade 1 material, with a Brinell hardness of 200, tooth surface and core. Poisson’s ratio is 0.30, JP = 0.30, JG = 0.40, and Young’s modulus is 208 x 103 N/mm2. The loading is smooth because of motor and load. Assume a pinion life of 108 cycles and a reliability of 0.90, and use load cycle factor YN =1.3558 N-

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GTU Paper Analysis


0.0178, ZN = 1.4488 N-0.023. The tooth profile is uncrowned. This is a commercial enclosed gear unit. Consider following factors in the AGMA design of gear as per usual notations. k0=1, kB=1, km=1.22, (ks) P =1.043, (ks) G=1.052, kT=1, kR=0.85, (St) P=31350, (St) G= 28260, kv=1.377. (a) Find the factor of safety of the gears in bending. (b) Find the factor of safety of the gears in wear.

6.

A worm drive transmits 15 kW at 2000 rpm to a machine carriage at 75 rpm. The worm is a triple threaded and has 65 mm pitch diameter. The worm gear has 90 teeth of 6 mm module. The tooth form is to be 20° full depth involute. The coefficient of friction between the mating teeth may be taken as 0.10. Calculate: 1. Tangential force acting on the worm 2. Axial thrust and separating force on worm 3. Efficiency of the worm drive.

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7.

Design a spur gear drive to transmit 30 HP at 900 r.p.m. Speed reduction ratio is 2.5. Material for pinion and wheel are C.I steel and Cast Iron respectively. Take pressure angle of 20. Design bending stress for pinion material is 85 N/mm2 and surface endurance limit for pinion material is 620 N/mm2. Take the following data for the given gears: Quality of the gears to be - Grade 12 Service factor = 1.5

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8.

Design the bevel gear pair for the following specification using Carl Barth velocity factor and wear consideration: Power transmitted: 40 kW Input speed: 360 rpm Reduction ratio: 3 Shaft angle: 90 Application: Agitator

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9. A pair of spur gears consists of a 20 teeth pinion meshing with a 120 teeth gear. The module is 4 mm. calculate (i) the center distance, (ii) the pitch circle diameter of the pinion and gear, (iii) the addendum and dedendum, (iv) the tooth thickness, (v) the bottom clearance, and (vi) the gear ratio.

07

10. A pair of bevel gears transmitting 7.5 kW at 300 rpm is shown in Figure 1. the pressure angle is 20. Determine of the components the resultant gear tooth force and draw a free body diagram of forces acting on the pinion and gear.

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GTU Paper Analysis


Figure 1

GTU Paper Analysis


Chapter 2 – Design of Gear Box for Machine Tools

Sr. No. Questions

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Theory

1. What is structure diagram? Explain the method of drawing structure diagram of gear box. 07

2. What are the major advantages of using geometric progression of for speed regulation in a gear box? And explain the design procedure of 8-speed gear box for machine tool application with the assumption of suitable and necessary data.

07

Examples

1. Draw the ray and speed diagram for a 9 speed gear box. State the necessary assumptions taken. 05

2. A 2 x 2 drive is required to be designed for transmitting speeds starting from 400 rpm with a geometric progression of 1.4. Draw a suitable structure and speed diagram. Also draw the layout of the gearbox and determine the number of teeth on each gear.

09

GTU Paper Analysis (New Syllabus)


Chapter 3 – Journal Bearing

Sr. No. Questions

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Theory

1. Explain the performance of a hydrodynamic bearing with neat curve of coefficient of friction versus

bearing characteristic number. 07

2. Explain the thermal consideration in Journal Bearing design. 04

3. Classify the bearing and explain the properties of bearing lubricant. 07

4. Give the classification of hydrodynamic bearings based on lubrication. 03

5. Explain the significance of L/D ratio and minimum oil-film thickness in hydrodynamic bearings. 04

6. What are the difference between Hydrodynamic and Hydrostatic bearings. 03

7. Derive the “ Petroff’s equation with assumptions made there in. 04

Examples

1.

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 550C = 0.017 kg/m-sec, Ambient temperature =

15.5 C, Maximum bearing pressure = 1.5 MPa, Permissible rise in oil temperature = 100C, Heat

dissipation coefficient = 1232 W/m2/ C, L/D ratio = 1.6, Design parameter ZN/p = 28, Clearance ratio

=0.0013, Specific heat of oil = 1900 J/kg/ C.

09

2.

A 80 mm long journal bearing supports a load of 2800 N on a 50 mm diameter shaft. The bearing has a

radial clearance of 0.05 mm and the viscosity of the oil is 0.021 kg / m-s at the operating temperature. If

the bearing is capable of dissipating 80 J/s, determine the maximum safe speed.

07



3.

The following data is given for a 3600 hydrodynamic bearings:

Radial load : 3.1 kN

Journal diameter : 50 mm

Bearing length : 50 mm

Journal speed : 1440 rpm

Radial clearance : 50 microns

Viscosity of lubricant : 25 cP

Density of lubricant : 860 kg / m3

Sp. Heat of lubricant : 1.76 kJ / kg 0C

Assuming that the total heat generated in the bearing is carried by the total oil flow in the bearing.

Calculate:

i) Sommerfeld Number

ii) Minimum oil-film thickness

iii) The coefficient of friction

iv) The power lost in friction

v) The total flow rate of lubricant in liter /minute

vi) Side leakage

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4.

A Petroff’s sleeve bearing consists of a sleeve having a bore diameter of 100.1 mm and a length of 100

mm. A shaft having 100 mm diameter supports a load of 4000 N. A shaft runs at 2880 r.p.m in the sleeve.

If the frictional torque on the shaft is 10 N-m, find

i) The absolute viscosity of lubrication

ii) The bearing pressure

iii) The coefficient of friction and

iv) The power lost in bearing.

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5.

The dimensions of a hydrostatic thrust bearing with a rectangular oil groove A, are shown in Fig-2. The

pressure distribution can be assumed to be linear, varying from supply pressure at the inner edge of the

groove to atmospheric pressure at the outer edge of the pad. The flow over the corners can be neglected.

The thrust load is 100 kN and the film thickness is 0.02 mm. the viscosity of the lubrication oil is 300 cP.

07



Calculate: (i) supply pressure, and (ii) requirement of flow.

Fig. 2



Chapter 4 – Rolling Contact Bearing

Sr. No. Questions

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Theory

1. Explain the static load capacity, dynamic load capacity and equivalent dynamic load capacity of bearing. 05

2. Explain in detail the selection procedure of rolling contact bearing from manufacturer’s catalogue. 05

3. Static and Dynamic load carrying capacity of rolling contact bearings. 03 03

4. Derive the equation for equivalent dynamic load for bearing under cyclic loads. 04

5. Classify the rolling contact bearings. And explain how they are designated according to ISI code of practice.

03

6.

Define the following terms: (9) Rating life of rolling contact bearings (ii) Median life (iii) Equivalent dynamic load (iv) Reliability of bearing

04

7.

Establish the following relationship between the life and reliability of the rolling contact bearing;

𝐿

𝐿10= [

𝑙𝑜𝑔𝑒 (1

𝑅)

𝑙𝑜𝑔𝑒 (1

𝑅90)]

1

𝑏

07

8. Give selection criteria of bearings in a particular application. 04

9. Explain Load-Life relationship in context with bearing. 04



Examples

1.

It is required to select a ball bearing suitable for a 50 mm diameter shaft rotating at 1500 rpm. The radial and thrust loads at the bearing are 4500 N and 1600 N respectively. The value of X and Y factors are 0.56 and 1.4 respectively. Select a proper ball bearing from the following table for the rating life of 22500 hr. the inner ring rotates and the service factor is 1.

Bearing No. 6010 6210 6310 6410 C (N) 21600 35100 61800 87100

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2.

A ball bearing is operating on a work cycle consisting of three parts – a radial load of 3000 N at 1440 rpm for one quarter cycle, a radial load of 5000 N at 720 rpm for one half cycles, and radial load of 2500 N at 1440 rpm for the remaining cycle. The expected life of the bearing is 10000 h. Calculate the dynamic load carrying capacity of the bearing.

07

3.

A single-row deep groove ball bearing operated with the following work cycle. If the expected life of the bearing is 13000 hours with reliability of 90%. Calculate the dynamic load rating of the bearing and determine reliability of a system consisting of four such bearings. The work cycle is as follows:

Gear Axial load

Radial load

Radial Factor

Thrust factor

Race rotation

Cs N

rpm % time

engaged

I 1.5 5 0.56 1.1 Inner 1.25 960 30 %

II 0.73 3.7 0.56 1.3 Outer 1.4 1440 40 %

III - - - - Outer - 720 50 %

07

4. A single row deep groove ball bearing No. 6002 is subjected to an axial thrust of 1000 N and a radial load of 2200 N. Find the expected life that 50% of the bearing will complete under this condition.

07

GTU Paper Analysis


Chapter 5 – I. C. Engine Components

Sr. No. Questions

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Theory

1. Why an I-section is usually preferred to round section in case of connecting rods? 04

2. Explain the design procedure of cylinder of an I. C. engine. 04

3. Explain the construction and working of valve gear mechanism with neat sketch. 05

4. Why the cylinder liners are being used in I. C. Engine? What are the desirable properties of the materials for the cylinder liners.

03

5. What are the functions of I. C. Engine piston? List the elements involved in the I. C. Engine piston. 04

6. What is the criterion for design of push rod? 03

7. Name the materials used for engine cylinder and engine piston. 04

8. Why is the area of inlet valve port more than that of an exhaust valve? 03

9. What are the design requirements of piston? 04

10. When do you use Johnson’s equation for buckling columns? 03

Examples

1.

The following data is given for a single cylinder four stroke diesel engine having CI Piston: Cylinder bore = 0.30 m Stroke length = 0.375 m Speed = 500 rpm Break Mean effective pressure=1.15 MPa Maximum gas pressure = 8 MPa Allowable tensile stress = 37.5 N/ mm2

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GTU Paper Analysis


Break specific fuel consumption = 0.22 kg/ kW –h Temperature difference between centre and edge of piston head is 220° C Assume 5% of the total heat is developed in cylinder is transmitted by piston. Design (1) Piston Head (2) Piston pin.

2.

Determine the dimensions of an I-section connecting rod for a petrol engine from the following data: Diameter of the piston = 110 mm; Mass of the reciprocating parts = 2 kg; Length of the connecting rod from centre to centre = 325 mm; Stroke length = 150 mm; R.P.M. = 1500 with possible over speed of 2500; Compression ratio = 4: 1; Maximum explosion pressure = 2.5 N/mm2.

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3.

The following data is given for a connecting rod having I-cross-section dimensions (4t x 5t): Engine speed = 1800 rpm, Length of connecting rod = 350 mm, Length of stroke = 175 mm, Density of material = 7800 kg/m3, Thickness of web or flanges (t) = 8 mm, Mass of reciprocating parts = 2.5 kg, Permissible tensile stress for bolts = 60 N/mm2. Calculate: (i) Nominal diameter of bolts (ii) Whipping stress in the connecting rod.

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4.

Design the following parts of a cast iron piston for a single acting four stroke engine for the below given data. (i) Piston Head (ii) Piston Skirt (iii) Piston Pin. Cylinder bore=100 mm, Stroke=125 mm, Maximum gas pressure= 5 N/mm2, Indicated mean effective pressure=0.75 N/mm2, Mechanical efficiency=80%, Fuel consumption=0.15 kg per brake power per hour, Higher calorific value of fuel=42 x 103 kJ/kg, Speed=2000 rpm. Take for cast iron material σt=38 N/mm2, Thermal conductivity (k) =46.6 W/m/°C and TC - TE=220 °C.

09

5.

The following data is given for the piston of a four-stroke diesel engine: Cylinder bore: 250 mm Material of piston rings: Gray C. I. Allowable tensile stress: 100 N/mm2 Allowable radial pressure on cylinder wall: 0.03 MPa Thickness of piston head: 42 mm No. of piston rings: 4 Calculate: i) Radial width of the piston rings ii) Axial thickness of the piston rings iii) Gap between the free ends of the piston rings before and after the assembly iv) Width of the top land v) Width of the ring grooves

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GTU Paper Analysis


vi) Thickness of the piston barrel

6.

The bore of a cylinder of the four-stroke diesel engine is 150 mm. the maximum gas pressure inside the cylinder is limited to 3.5 MPa. The cylinder head is made of grey cast iron FG 200 (Sut = 200 N/mm2) and the factor of safety is 5. Determine the thickness of the cylinder head. Stud are used to fix the cylinder head to the cylinder and obtain a leakage proof joint. They are made of steel FeE (Syt = 250 N/mm2) and the factor of safety is 5. Calculate (i) number of studs, (ii) nominal diameter of studs, (iii) pitch of studs.

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Machine Design II (2171909) Department of Mechanical Engineering Darshan Institute of Engineering & Technology

Chapter 6 – Design of Cranes

Sr. No. Questions

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1. Explain design procedure of wire rope drum. 07 07

2. What do you understand by 6 x 37 ropes? Explain with neat sketch the different rope section. 07

3. Describe the basic objectives of material handling system. State the basic principles in selection of material handling equipment.

07

4. What are the basic objectives of material handling systems? 03

5. What are the different types of ropes used in EOT cranes? How they are designated and selected in the hoisting mechanism.

04

6. Draw rope sheave and drum with usual notations. 03

7. Give classification of cranes. 04

8. Discuss stresses in wire rope with usual formulae. 07

9. When do you use Johnson’s equation for buckling columns? 03

10. Write advantages of wire rope. Draw cross section of 7, 19 and 37 wires in strand of wire rope. 04

11. Give Classification and application of various Material handling equipment. 07

Examples

1. Design a crane hook for lifting capacity of 50 KN. It is made from forged steel and has triangular section. Take permissible tensile stress 80 N/mm2. Select the most suitable cross section for the hook.

10 07

2. Design the following components of EOT cranes for the following requirements: Application : class – II Load to be lifted : 8 tones

07


Machine Design II (2171909) Department of Mechanical Engineering Darshan Institute of Engineering & Technology

Hoisting speed : 4 m / min Maximum lift of the load : 12 m (i) Select through design procedure a suitable wire rope (ii) Sheave in a snatch block assembly of crane.

gtu paper analysis chapter 1 gear design · 2019-11-19 · worm is to be made of hardened steel and...

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