Skip to main content

Hello Experts,

I request you to please provide me your valuable suggestions regarding the following problems.

1) Our Raw Mill creates too much vibration and mostly it is coming from the grinding rollers running inside when they come in contact with the rotating table. My question here is, as I believe we cannot install sensors on rotating devices so Is there any way/method we can measure the vibration of that specific rollers?

2) Here is another problem. The separator of Raw mill is adjacent to the raw mill vertical structure. When the raw mill runs, the vibration from the Raw mill is being transmitted to Separator (motor and its gearbox), and the whole unit of motor and gearbox moves (like if they are on the hanging foundation). How should we tackle this problem? as the original manufacturers installed separator on this location but we believe that the reducing performance of our raw mill is due to this problem? If there is so much vibration around, Do you think installing vibration sensors on that separator unit would be a good idea?



I would highly appreciate your valuable suggestions and taking the time to help me make the right decision. As this is very critical for our performance and we have to have some credible solution for it.



Thank you all.

Original Post

Replies sorted oldest to newest

1) I think you won't be able to reduce vibration level from the milling rollers.  It's the construction property that can't be changed. So I think it is not reasonable to measure roller vibration because it won't help you much.

2) When you know the separator vibration is too high, it won't do anything good to install sensors. I think you should reinforce the separator's supporting structure. Make it more stiff. Monitor changes with handheld vibration device. After successful adjustments, you could think about online monitoring.

The very nature of these machines is they make a lot of noise and vibration.  What I suggest you do is take a careful look at previous maintenance records and see if you can determine a common mode of failure, then attack the failure looking carefully at root cause.

As an example, I was involved many years ago with a similar machine that employed a combination of bevel and helical gearing, unlike your machine with the planetary stage.  When we reviewed about 5 years of maintenance records, we found a high rate of failures in the lower bearings of the intermediate shaft and output shaft.  When the customer instituted an oil analysis program, they found a great deal of moisture in the lubricant.  In addition, the lower bearings had a well (with a drain line) but the drain lines had never been installed.  After the drain lines were installed, oil was drained on a regular basis from the wells at the lower end of the shafts.  It was not unusual to find debris in the wells.  

The units also ran almost all week, with a shutdown on weekends.  The cooling period when shut down was believed to pull cool air into the gearbox resulting in excess moisture.  The oil was changed to a SHC type oil which had better properties in the presence of moisture.

As best I recall, and this was many years ago, the overhaul period went from being an annual event to something like every two to three years.

 

@Registered Member posted:

The very nature of these machines is they make a lot of noise and vibration.  What I suggest you do is take a careful look at previous maintenance records and see if you can determine a common mode of failure, then attack the failure looking carefully at root cause.

As an example, I was involved many years ago with a similar machine that employed a combination of bevel and helical gearing, unlike your machine with the planetary stage.  When we reviewed about 5 years of maintenance records, we found a high rate of failures in the lower bearings of the intermediate shaft and output shaft.  When the customer instituted an oil analysis program, they found a great deal of moisture in the lubricant.  In addition, the lower bearings had a well (with a drain line) but the drain lines had never been installed.  After the drain lines were installed, oil was drained on a regular basis from the wells at the lower end of the shafts.  It was not unusual to find debris in the wells.  

The units also ran almost all week, with a shutdown on weekends.  The cooling period when shut down was believed to pull cool air into the gearbox resulting in excess moisture.  The oil was changed to a SHC type oil which had better properties in the presence of moisture.

As best I recall, and this was many years ago, the overhaul period went from being an annual event to something like every two to three years.



Indeed John, those are very useful insights. In fact, I would say you read my mind. I am also into reviewing the Oil analysis reports, past failure data, and down time reports. The moisture content you mentioned, yesterday we had to stop the Raw mill and when I observed the bed inside the rolling, I found a very fine powder of material on the bed. The fineness of material troubled me at that time as I believe for a stable operation we need the right thickness of a material layer on the bed neither too fine, nor too thick. As if it get too fine, the material flows over the bed. Vertical grinding pressure The difference is increased, the ventilation is not smooth, and the external circulation and internal circulation are greatly increased. At this time, the material layer will become extremely unstable, the load of the powder separator will increase, the thickness of the material layer will increase, and the load of the mill will increase. If it is not treated in time, the vibration of the vertical mill will be further aggravated and the main motor will be overcurrent.

@Registered Member posted:

The very nature of these machines is they make a lot of noise and vibration.  What I suggest you do is take a careful look at previous maintenance records and see if you can determine a common mode of failure, then attack the failure looking carefully at root cause.

As an example, I was involved many years ago with a similar machine that employed a combination of bevel and helical gearing, unlike your machine with the planetary stage.  When we reviewed about 5 years of maintenance records, we found a high rate of failures in the lower bearings of the intermediate shaft and output shaft.  When the customer instituted an oil analysis program, they found a great deal of moisture in the lubricant.  In addition, the lower bearings had a well (with a drain line) but the drain lines had never been installed.  After the drain lines were installed, oil was drained on a regular basis from the wells at the lower end of the shafts.  It was not unusual to find debris in the wells.  

The units also ran almost all week, with a shutdown on weekends.  The cooling period when shut down was believed to pull cool air into the gearbox resulting in excess moisture.  The oil was changed to a SHC type oil which had better properties in the presence of moisture.

As best I recall, and this was many years ago, the overhaul period went from being an annual event to something like every two to three years.



John, I also got the Oil analysis details. Surprisingly, it shows no moisture contents are present in the oil.

"Our Raw Mill creates too much vibration and mostly it is coming from the grinding rollers running inside when they come in contact with the rotating table."

"I found a very fine powder of material on the bed. The fineness of material troubled me at that time as I believe for a stable operation we need the right thickness of a material layer on the bed neither too fine, nor too thick."

Regarding Question 1: My experience was with vibration measurements and analysis on Raymond vertical coal Mills. That mill design had a rotating table and spring-loaded rollers. Vibration levels can be significantly affected by process conditions that are particularly related to bed material height. Each roll has a substantial mass that is attached to the load spring, and the material on the table compressed by the roll acts as a secondary spring and as a damper. The material height also affects roll traction and speed. There can be certain process conditions (in-feed, out-flow, material properties, and material height) that produce unstable and high vibrations. Vibration monitoring can provide important feedback so that the mill operation can be optimized and extend reliability.

Excessive vibrations can be the result of poor mill condition. Component deterioration can include roll and table surfaces, roll and table bearings, roll load springs, and gearbox bearings and gears. Overall vibration levels can indicate a change in mill condition, and vibration analysis can identify deteriorating components.

In summary, low vibration levels and machine reliability can be maintained by:

1 Optimize machine operation with vibration feedback to the control system and operators.
2 Maintain good machine condition utilizing vibration monitoring and analysis. Make repairs before cascading excessive damage occurs.
3 Maintain good structural condition including tight fasteners and crack control on upper structure and foundation. Visual inspection and vibration measurements can identify weak structural locations.

If these three measures do not control vibrations, then mill and foundation design may have to be evaluated for modifications.

Regarding question 2: The separator structure and foundation may be in poor condition, so that should be investigated and corrected first. The separator structure and foundation may have a natural frequency that matches the excitation frequency from the raw mill. This could be investigated by vibration analysis. Typical vibration control measures include changing the mass or stiffness of the structure. There is no point speculating on the best approach without fully understanding what the problem is.

Walt

Add Reply

Post
×
×
×
×
Link copied to your clipboard.
×