Final Year Exam May 2008 2 nd Year Prod

Suez Canal University

Faculty of Engineering

Production Engng & Mechanical Design Dept

Machine Elements Design ( Code : PRD 214 )

Port Said

Total Exam Time 3. Hour

2 ^nd Year

Final Exam May 2008

Answer All the questions and assume any missing data you find it necessary to complete your answer

Question No. 1 10 Marks

Describe the design procedure of the cotter joint ( Draw a neat sketch to show the general layout of the final design of the cotter joint )

Question No. 2 20 Marks

Design a knuckle joint for a tie rod of a circular section to sustain a maximum pull of 70 kN The ultimate strength of the material of the rod against tearing is 420 MPa. The Ultimate tensile and shearing strength of the pin material are 510 MPa and 396 MPa respectively. Determine the tie rod section and pin section. Take factor of safety = 6. (Support your answer with neat sketch of the final joint )

Question No. 3 20 Marks

A solid steel shaft is supported on two bearings 1.8 m apart and rotates at 250 r.p.m A 20° involute gear D, 300 mm diameter is keyed to the shaft at a distance of 150 mm to the left on the right hand bearing. Two pulleys B and C are located on the shaft at distances of 600 mm and mm respectively to the right of the left hand bearing. The diameters of the pulleys B and C are750 mm and 600 mm respectively. 30 kW is supplied to the gear out of which 18.75 kW is taken off at pulley C and 11.25 kW from pulley B. The drive from B is vertically downward while from C the drive is downward at an angle of 60° to the horizontal. In both cases the belt tension ratio is 2 and the angle of lap is 180°. The combined fatigue and shock factors for torsion and bending may be taken as 1.5 and 2 respectively. Design a suitable shaft taking working stress to be 42 MPa in shear and 84 MPa in tension

Question No4 5 Marks

A rectangular base plate is fixed at each of its four corners by a 20 mm diameter bolt and nut as shown in Fig 1. The plate rests on washers of 22 mm internal diameter and 50 mm external diameter. Copper washers which are placed between the nut and the plate are of 22 mm internal diameter and 44 mm external diameter.

If the base plate carries a load of 120 kN (including self- weight, which is equally distributed on the four corners), calculate the stress on the lower washers before the nuts are tightened.

What could be the stress in the upper and lower washers, when the nuts are tightened so as to produce a tension of 5 kN on each bolt ?

Question No 5 20 Marks

A bracket in the form of a plate is fitted to a column by means of four rivets A, B, C and D in the same vertical line, as shown in the Fig. AB=BC=CD=60 mm. E is the mid-point of BC. A load of 100 KN is applied to the bracket at a point F which is at a horizontal distance of 150 m from E. the load acts at an angle of 30° to the horizontal. Determine the diameter of the rivets which are made of steel having a yield stress in shear of 240 MPa . Take a factor of safety of 1.5.

What would be the thickness of the plate taking an allowable bending stress of 125 MPa for the plate, assuming its total width at section ABCD as 240 mm?

Question No 6 25 Marks

A screw jack is to lift a load of 80 kN through a height of 400 mm. The elastic strength of screw material in tension and compression is 200 MPa and in shear 120 MPa. The material for nut is phosphor-bronze for which the elastic limit may be taken as 100 Mpa in tension, 90 MPa in compression and 80 MPa in shear. The bearing pressure between the nut and the screw is not to exceed 18 N/mm². Design and draw the screw jack. The design should include the design of 1, screw, 2, nut, 3, handle and cup, and 4, the body.