Question 6

(a) Why is it necessary to balance rotors? What is a "rigid rotor"? Can rigid rotors be

balanced at any speed? If not, why not?

(6 marks)

(b) A shaft carries three pulleys, each of mass 12 kg, in planes A, B and C, the eccentricity of

the mass centres of these pulleys being 5 mm, 4 mm and 3 mm respectively. The

bearings are positioned in planes L and M. The relative axial positions of these planes

are shown in Figure 6 (a), and the relative angular positions of the mass centre of each of

the pulleys are indicated in Figure 6 (b). The shaft rotates at 1000 rad/s.

Determine the dynamic force exerted by this shaft on each of the bearings.

A

B

HLU

200 mm

100 mm

100 mm

--ھ۔

240⁰

90⁰

Figure Q6 a and b

A

C

100 mm

(14 marks)

M