DMM-2 1st Mid Questions

Department of Mechanical Engineering

DVR & Dr. HS MIC College of Technology

Design Of Machine Members-2

1st Mid Questions

1) Design a suitable journal bearing for a centrifugal pump from the following available data :

    Load on the bearing = 13.5 kN; Diameter of the journal = 80 mm;

    Speed = 1440 r.p.m.; 

    Bearing characterisitic number at the working temperature (75°C) = 30 ;

    Permissible bearing pressure intensity= 0.7 N/mm2 to 1.4 N/mm2;

    Average atmospheric temperature = 30°C.

    Calculate the cooling requirements, if any.

2) A journal bearing with a diameter of 200 mm and length 150 mm carries a load of 20 kN, when the

    journal speed is 150 r.p.m. The diametral clearance ratio is 0.0015.  

    If possible, the bearing is to operate at 35°C ambient temperature without external cooling with a

    maximum oil temperature of 90°C. If external cooling is required, it is to be as little as possible to

    minimise the required oil flow rate and heat exchanger size.

   1. What type of oil do you recommend ?

   2. Will the bearing operate without external cooling?

   3. If the bearing operates without external cooling, determine the operating oil temperature?

   4. 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

      85°C to 90°C, when passing through the bearing.

3) A rolling contact bearing is subjected to the following work cycle :

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

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

   (c) Radial load of 2000 N 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 2500 hours.

4) A ball bearing operates on the following work cycle : 

    Element No. Radial load Speed Element time

      (N)       (R.P.M.)  (%)

   1. 3000     720        30

   2. 7000    1440       40

   3. 5000     900        30

  The dynamic load capacity of the bearing is 16 600 N. 

  Calculate 

  1. the average speed of rotation ;

  2. the equivalent radial load ; and 

  3. the bearing life.

5) A four stroke internal combustion engine has the following specifications:

    Brake power = 7.5 kW; 

    Speed = 1000 r.p.m.;

    Indicated mean effective pressure = 0.35 N/mm2;

    Maximum gas pressure = 3.5 N/mm2; 

    Mechanical efficiency = 80 %.

    Determine:

   1. The dimesions of the cylinder, if the length of stroke is 1.4 times the bore of the cylinder;

   2. Wall thickness of the cylinder, if the hoop stress is 35 MPa; 

   3. Thickness of the cylinder head and the size of studs when the permissible stresses for the cylinder head

       and stud materials are 45 MPa and 65 MPa respectively.

6) Design a cast iron trunk type piston for a single acting four stroke engine developing 75 kW per

    cylinder when running at 600 r.p.m. The other avialable data is as follows:

    Maximum gas pressure = 4.8 N/mm2;

    Indicated mean effective pressure = 0.65 N/mm2; 

    Mechanical efficiency = 95%;

    Radius of crank = 110 mm; 

    Fuel consumption = 0.3 kg/BP/hr; 

    Calorific value of fuel (higher) = 44 × 103kJ/kg; 

    Difference of temperatures at the centre and edges of the piston head =200ºC;

    Allowable stress for the material of the piston = 33.5 MPa; 

    Allowable stress for the material of the piston rings and gudgeon pin = 80 MPa; 

    Allowable bearing pressure on the piston barrel = 0.4 N/mm2 and allowable bearing pressure on 

    the gudgeon pin = 17 N/mm2.

7) A connecting rod is required to be designed for a high speed, four stroke I.C. engine. The following

    data are available.

   Diameter of piston = 88 mm; 

   Mass of reciprocating parts = 1.6 kg; 

   Length of connecting rod (centre to centre) = 300 mm; 

   Stroke = 125 mm;

   R.P.M. = 2200 (when developing 50 kW); 

   Possible overspeed =3000 r.p.m.; 

   Compression ratio = 6.8 : 1 (approximately); 

   Probale maximum explosion pressure (assumed shortly after dead centre, say at about 3°) = 3.5 N/mm2.

8) Design a plain carbon steel centre crankshaft for a single acting four stroke, single cylinder engine for

    the following data:

    Piston diameter = 250 mm; 

    Stroke = 400 mm; 

    Maximum combustion pressure = 2.5 N/mm2; 

    Weight of the flywheel = 16 kN; 

    Total belt pull = 3 N; 

    Length of connecting rod = 950 mm.

    When the crank has turned through 30° from top dead centre, the pressure on the piston is 1 N/mm2

    and the torque on the crank is maximum.

    Any other data required for the design may be assumed.

9) Design a side crankshaft for a 500 mm × 600 mm gas engine. The weight of the flywheel is 80 kN and

    the explosion pressure is 2.5 N/mm2. The gas pressure at maximum torque is 0.9 N/mm2 when the

    crank angle. is 30º. The connecting rod is 4.5 times the crank radius.

    Any other data required for the design may be assumed.

10) The dimensions of 100KN crane hook are shown in fig . Determine the stresses at the inside and 

      outside  fibres of the hook on a horizontal diameter passing through the centre of curvature.

11) An open ring having T-section as shown in fig is subjected to a compressive load of 100KN.Determine the stresses at A and B

12) A chain link is subjected to a pull of 200KN . It is composed of steel 2.5 cm diameter and has a mean radius of 3 cm. Its semi-circular ends are connected by straight pieces 2.5cm long.Estimate maximum compressive stress in the link and tensile stress at the same section

Note:The diagrams related to the above questions will be drawn 

          on the board in the classroom tomorrow