Sir,

we were facing high vibration problem in our crusher only at motor bearings exactly at running speed motor(Motor rpm 1500) & crusher vibration was very normal.I recommended for motor pulley unbalance(Because in all H,V,A direction vibration persisted in motor)

 

Our maintenace people inspected the shayaji crusher rotor (hammer type rotor) & some of the hammers found with wear. They replaced all the hammers recently based on ou client advice.Luckily the motor vibration came down after hammer replacement.

 

Before replacing hammer we did not have vibration in crusher at all.Crusher rotor wear means we would get crusher unblance vibration in our curhser bearing, which was not there.Please see the readings before hammer replacement

Before replacement of hammer

Measurement Location

Vibration velocity in mm/sec RMS

    Horizontal

      Vertical

     Axial

Motor Non Drive End

29.10

15.07

16.14

Motor Drive End

26.77

27.50

11.64

Crusher Drive End

1.84

1.01

2.52

Crusher Non Drive End

1.91

0.60

2.37

 

After replacing all hammers then also crusher vibration found normal & motor vibration reduced how? please see the readings after hammer replacement

After replacement of hammer

Measurement Location

Vibration velocity in mm/sec RMS

    Horizontal

      Vertical

     Axial

Motor Non Drive End

11.28

7.08

6.86

Motor Drive End

3.23

4.87

5.19

Crusher Drive End

1.22

1.14

4.22

Crusher Non Drive End

1.38

0.60

2.91

 

Any one can suggest how motor vibration came down.

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Original Post

Hi,

The change in motor vibration doesn't seem to be directly related to the crushers hammers. But there may have happened something to the motor during this maintenance.

The first spectra show not only a high 1X but also some higher harmonics of it. Those are also gone after the maintenance actions. Therefore I think is was caused by some looseness or clearance at the motor which is not there now. Was the motor loosened to remove belts during the maintenance? I think the mounting of the motor had gone a bit loose and is fixed now. Another possibility is that the motor sheeve was a bit loose and it is fixed without you knowing.

 

Hi,

Thanks for the reply.Spectrum before hammer replacement shown the dominated/greater vibration only at 1X rpm of motor in both NDE & DE bearing of motor and 2X,3X amplitude were about lesser 2mm/sec.There was no looseness at all in motor base & bearing and belt was not removed so far.This is crusher A.Let us keep away this discussion for some time.

 

Let me share you another interesting thing about crusher B(Stand by of Crusher A).Compare both crusher behaviour and suggest your opinion.

 

In crusher B also we have higher vibration problem similar like crusher A. When I had checked the vibration of crusher B we found all direction of motor NDE & DE bearing vibration high and crusher bearing vibration was normal. please for your notification i am putting the vibration readings of crusher B 

Crusher B vibration similar like Crusher A(Under load)

Machine points

Vibration velocity in RMS mm/sec

H

V

A

Motor NDE Bearing

36.70

6.26

16.64

Motor DE Bearing

41.67

14.33

19.28

Crusher DE Bearing

2.04

0.84

1.57

Crusher NDE Bearing

2.31

0.89

2.28

 

I suggested maintenance personal to remove the belt and wanted to take crusher B idle run with pulley in motor keyway.I got the results of increased horizontal vibration in Crusher B motor than it was under coupled.

Motor idle run with pulley in key way (After removal of belt)

Machine points

Vibration velocity in RMS mm/sec

H

V

A

Motor NDE Bearing

43.10

10.81

15.96

Motor DE Bearing

54.94

12.06

28.79

 

Further i have instructed our maintenance people to remove the pulley from the keyway of motor and wanted to take further idle run of crusher B motor.My results after removal of pulley from key way

Machine points

Vibration velocity in RMS mm/sec

H

V

A

Motor NDE Bearing

1.07

0.73

0.77

Motor DE Bearing

0.90

0.93

0.64

There was no looseness in base & motor bearings, Crusher bearings are good.I recommended to inspect themotor pulley for unbalance/overweight.This test was carried out in May 2015.

 

In Aug 2015 the same crusherBwas tested in empty at a particular time period i got the readings like 

Crusher B empty load reading at 4.00PM that day i tested 

Machine points

Vibration velocity in RMS mm/sec

H

V

A

Motor NDE Bearing

19.59

5.26

5.16

Motor DE Bearing

26.97

10.8

5.62

Crusher DE Bearing

1.57

0.71

1.84

Crusher NDE Bearing

1.70

0.54

2.60

 

Intentionaly i wanted to test the crusher B under emptyload after 1 hour of time.I tested at 5.00P.M on that same day & shocked.Horizontal vibration of crusher B motor in NDE & DE bearing increased high & i noticed this observation and went out of field without taking other location readings. Under empty load in one hour of time i am getting different in vibration especially in horizontal direction only at 1X rpm of motor. How it is possible? Are the hammers of the crusherBis the reason for this variation of vibration reading in motor.If so why crusherBvibration maintaining normal.This is breaking my head.

Machine points

Vibration velocity in RMS mm/sec

H

V

A

Motor NDE Bearing

27.98

-

--

Motor DE Bearing

36.87

-

--

Crusher DE Bearing

-

-

-

Crusher NDE Bearing

-

-

-

 

I left crusher B bearings & rotor from my analysis view and focussed only on crusher B motor pulley(Because my crusher vibration was normal.So i eliminated crusher side) and told my client to inspect the pulley/replace the pulley.If it succeeded do it for crusher A.

 

After this meeting with client, because of some coal size issue problem our maintenance team opened crusher A first and found some hammer are had wear problem. Eventhough they replaced entire hammers.Then after crusher A motor vibration came down. If they do hammer replacement for crusher B like A will my vibration come down in crusher B motor. This is my question.

 

In Crusher no vibration & vibration is there only in motor.I am not able to relate technically motor & crusher vibration.This case is really breaking my head. I dont have phase angle measurement option with me.

 

Both crusher motor pulleys are indentical.

I assumed the crusher was at lower rpm than the motor. But they have same rpm you say.

You should take a measurement and zoom in on 1X rpm. There will be a small difference in motor and crusher rpm, due to a few % slip on the belt. That way you can determine if the big 1X is from motor or from crusher.

 

You should know that a high vibration on the motor could still come from a source in the crusher. The crushers mounting will be a lot stiffer than the motor mounting. I also have some equipment where imbalance in the driven part shows a big amplitude in motor vibration.

 

And imbalance and/or looseness in the crusher is really normal when hammers are worn.

 

 

My suspection is that they have replaced hammers in Crusher A.there may be a chance of rotor weight increase than the older weight.I don't know what is the each weight of new hammer they replaced.could this be reason for reduction of high vibration in motor. 

 

Let us imagine that motor pulley got unbalance and we get high vibration in motor.If i increase the weight of crusher rotor mass by using higher weight hammers.will my motor unbalanced vibration reduce. 

If yes means is it happening in my case

The force initiated by unbalance only depends on rpm and the unbalance itself. But the actual deflection of the structure can vary because the stiffness of the construction varies with different load. Espesially belt driven.

Whatever happens in the crusher can not influence the unbalance of the pulley. What can happen is that your pulley is worn eliptical. under different loads the belt can be in a different position where this is more ore less present. Also over time (after running one hour) the belt position could change and use another part of the pulley.

 

What type of belt is it? V / flat / powerbelt / ...?

 

A normal v-belt will go deeper into the groove under load and also when over time the belt gets warm and thus softer.

Tell me one think 

 

When motor & crusher(Under coupled by V belt) condition- High vibration in Motor NDE & DE bearing in Horizontal direction comes 30 mm/sec.

 

When i decouple the crusher from motor(By removing V belt)- High vibration in Motor NDE & DE bearing in same Horizontal increased to 55 mm/sec. 

 

Why under motor solo run it is high & why it has halfy reduces under coupled.

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