Design Of Machine Members - II Assignment 1

Department of Mechanical Engineering

DVR & Dr. HS MIC College of Technology

DESIGN OF MACHINE MEMBERS-II

Assignment – I

1. A rolling contact bearing is subjected to the following work cycle:

(a) radial load of 6000N at 150 r.p.m for 25% of the time;

(b) radial load of 7500N at 600 r.p.m for 20% of the time; and

(c) radial load of 2000N at 300 r.p.m for 55% of the time.

The inner ring rotates and loads are steady .Select a bearing for an expected average life of 2500hours.

2. Journal bearing with a diameter of 200mm and length 150mm carries a load of

20kN, when the journal speed is 150r.p.m. The diametral clearance ratio is 0.0015.

If possible, the bearing is to operate at 350C ambient temperature without external

cooling with a maximum oil temperature of 900C. If external cooling is required, it

is to be as little as possible to minimize the required oil flow rate and heat exchanger

size.

(a) What type of oil do you recommend?

(b) Will the bearing operate without external cooling?

(c) If the bearing operates without external cooling, determine the operating oil temperature?

(d) If the bearing operates with external cooling, determine the amount of oil in kg/min required to carry away the excess heat generated over heat dissipated,

when the oil temperature rises from 850C to 900C, when passing through the

bearing.

3. (a) Explain the following terms:

i. Rated life

ii. Basic load rating

iii. Dynamic load.

(b) Select the suitable dimensions for a journal bearing which is subjected to

3.5kN radial load. The diameter and length of the bearing are 75mm each.

The journal rotates at 400r.p.m.

4. Design a mild steel connecting rod with an I section for a single cylinder spark

ignition engine from the following data :

Diameter of piston, D=0.104m

Weight of reciprocating parts =18.2N

Length of connecting rod from centre to centre=0.314m

Stroke length=0.14m

Speed of the engine=1500rev/min

Maximum explosion pressure = 2.28MPa gauge

Assume that the maximum thrust takes place at T.D.C. during the explosion stroke.

5. Design a suitable connecting rod for Fiat 1100 car for the following data:

Diameter of piston, D=68mm

Weight of reciprocating parts/cylinder=2.5kg

Length of connecting rod =150mm

Stroke =75mm

Speed=4,400rpm

Compression ratio=8:1

Maximum explosion pressure = 3.5MPa

Allowable bearing pressure for big end =7MPa

Allowable bearing pressure for small end =14MPa

Assume any other data. Rod is made of 37Mn2 alloy steel.

6. (a) How the piston head of an IC engine is usually cooled? What are the advanta

ges of cooling ?

(b) A horizontal four stroke diesel engine has the following speciation:

Break Power =5kW

Speed = 1200 rpm

Imep = 0.35 N/mm2

Mechanical efficiency = 80%

Calculate the dimensions of the cylinder and the cylinder head.

7. (a) What are the requirements of a piston material?

(b) Design a CI piston for a single acting four stroke petrol engine of the following

specifications :

Cylinder bore = 100mm

Stroke Length =120mm

Maximum gas pressure = 5MPa

Break mean effective Pressure =0.65MPa

Fuel Consumption = 0.17kg/bhp/min

Speed =220rpm

8. Design a trunk type cast iron piston for an I.C. Engine from the following data:

Diameter of the Cylinder = 10cm

Stroke = 15cm

Maximum explosion pressure = 3.5MPa

Maximum permissible tension for cast iron for the design of head thickness is 30MPa

and the flexural stress for the pin may be taken from 90 to120Mpa. The gudgeon

pin should be hardened and ground and should turn in phosphor bronze bushing.

Bearing pressure should be limited to 20MPa.

Sketch the piston inserting important dimensions of the piston with piston pin,

piston ring and scraper ring in position. Check the design from heat transfer view

point.

9. Design an overhang crankshaft with two main bearings for an I.C engine

with the Following data:

Cylinder bore = 250mm

Stroke length =300mm

Flywheel weight =27kN

Maximum pressure=2.5N/mm2

Maximum torque is at crank rotation 300, the pressure at that instant = 1.7 N/mm2

10. Starting from the fundamentals derive an expression for radius of neutral axis of a trapezoidal c/s curved beam.

11. Determine the stresses at point A and Bin the C frame shown in fig.

12. A ring is made of 2.5 cm diameter steel bar carries a pull of 15KN.caluculate the maximum tensile and compressive stress in the material of the ring the mean radius of the ring is 15 cm,as shown in fig.

Prepared by

K.SRINIVAS