Gaps in Stacked Rotor - Stacking by Shaft Shrinking

Is it possible foreign matter is getting between the laminations causing the gap? Is the gap always in the same place on the shaft, or does it occur at different, random locations?

Hi.,

Thanks for your remarks.

No; the gaps as shown are found in random locations; along the periphery of the rotor.

In some cases the stacked rotor is in good condition.

RAGHU.

Looking at the photographs I think you should be considering putting a compressive load on the stack.

Most probably this is due to the expansion in shaft length, as its temp increases and diameter reaches in tight fit zone it fragment some off laminations and create those random gaps, Leaving stack in compressed condition untill the temp of whole Assembly is not in equilibrium may solve problem.

Nice judgement, equally nice suggestion, GA. However the cooling rate is very high when dipped in liquid nitrogen (-196 degC), it may cause uneven cooling some times. Outer surface cools very fast, inner side is cooled by conduction. Increase in length will be appreciable only when inside is also cooled. So, cooling time is important. May be OP is finding gaps when it is cooled for longer time.

OP can experiment cooling with dry ice (-78 degC), but it takes longer time (minimum 6 hours) for favourable result.

This does NOT look like a problem of axial expansion of the shaft as it warms up (eg a gap caused by the shaft expansion from the point at which it grips the lamination bore). It looks like its caused by the CHANGE IN ORIENTATION of the laminations (eg adjacent laminations stacked 'face' to 'face', or 'back' to 'back' at that point), which results in the slight conical form produced by the lamination reaching a stress balance (which will occur in its most "natural" direction), caused by shaft expansion pushing out the lamination bore.

The amount of coning will depend on the amount the bore is expanded.

Try ensuring all laminations are assembled in the same orientation (or the two halfs of the stack naturally coning inwards)

You could check for this cone condition by sticking shim gauges into the gap and seeing whether it gets more and more narrow towards the shaft.

You may also like to check the concentricity of the shaft. If this changes suddenly, it may cause the gap seen. could you give the dimension of the gap? From the picture it looks to be quite big. Is the stack inserted on the rotor in pressed condition? You may like to increase the pressure and maintain the same till shaft attains room temperature.