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     Motor

Brook Cromptoon

1440rpm

50hz

5.5kw

     Gearbox

Radicon

inline

156rpm

Highest vibration at NDE Vertical at 50.0hz, which conveniently is also 1x line frequency. pictures should illustrate the mounting position. the file contains the vibration data Not sure if this can be misaligned when its a direct fit into the inline gearbox. any help would be great

thanks alot

Attachments

Images (1)
  • IR000099: Thermal Image showing the motor and gearbox, hot spot was the area where the motor and gearbox connect
Files (1)
Original Post

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Possible misalignment? I don't like to guess. I've these general comments:

1. Thermographic images can be misleading if the scale is not included. They can give an incorrect impression if there is no reference such as the normal temperature profile. My suggestion is to add the scale and have a reference temperature perhaps from sister equipment.

2. Are you sure the vibration readings are reliable and stable? I see a filtered amplitude of about 37 mm/sec (~ 1.5 ips?). Unstable reading like beating can be confusing if one looks only at one reading. My suggestion is to have a longer data sample perhaps for 60 seconds to confirm the stability.

3. I'm not familiar with the equipment you are analyzing but it "looks" flexible and it might be easily excited. If this is true, I would consider the possibility of encountering structural vibrations. My suggestion is to perform an impact test to identify natural frequencies.

4. The spectra look of a low resolution. Are the peaks really at 1450 cpm or 1500 cpm etc? My suggestion is to have high-resolution data to confirm the exact frequencies in the spectra. 

Regards- Ali M. Al-Shurafa

Hiya Ali

Thanks for the information, those are some good points and I will look into them.

The thermal image should have had the temp data on there too, I'll have to upload it with the relevant information.

Unfortunately I can only get a maximum of about 20 seconds using the sensor i have but that's a good idea I will try that.

I'll get a better resolution of the peaks to identify the exact frequency.

Thanks very much

James

What is the drive between gearbox output and auger: V-belt(s), cog-belt, or chain?

I agree that there is probable resonant structure; either local at motor-gear or the entire screw conveyor. An impact test could confirm this.

Excitation force frequency near 3000 cpm could be from one of these sources:

a) 2xMotor speed from motor-gear misalignment or worn coupling

b) Gearbox tooth-mesh, if multi-stage reduction -- get gear info.

c) Chain or cog-belt (if present) tooth mesh frequency -- 19 teeth x gear output speed

d) Friction of screw auger inside conveyor housing

Walt

Last edited by Registered Member

Hi Walt

nice to hear from you

The motor base nuts are tight its just got a penny washer and a spring washer which is giving the illusion of them being loose.

The output drive is a chain and sprocket arrangement, As

thanks for that I'll check the gear mesh and tooth mesh,

below is an example of the bump test i did on the base plate, there was a peak at 56Hz but all over bump tests didn't have anything near that range.

Bump test

Attachments

Images (1)
  • Bump test

Two quick comments:

1- The new spectra do not show any filtered vibration components higher than 8 mm/s. This makes me think more about the instability of the vibration. Your initial data showed 38 mm/s.

2- The thermographic image's maximum reading is 60 deg C (~ 140 F). I'm not sure about your limits but in my world, this is a bit high for indoor applications. The grease could fail with time if it's not selected to handle this temperature.

Regards- Ali M. Al-Shurafa

Hi all

Thanks for the information Walt, I'll conduct an impact test on that area and see if that brings so results.

Thanks Ali for the reply, it does make me wonder how accurate my initial data was, and why its drastically reduced, albeit still high for such a small motor.

Yes the thermal image indicates a hot spot of 60c, this application is outdoors where the ambient temperature was around 10C, it seems unusual warm for such a small motor and it leads me to suspect that it's working harder than it should, I need to see what amps it's pulling to continue that line of thought.

Also I looked at the sprockets today,

Driver sprocket 19 teeth and 156rpm

Driven sprocket 38 teeth and 78rpm IMG_20210224_172541

Attachments

Images (1)
  • IMG_20210224_172541

You confirmed that drive is by chain and the 19 teeth (I estimated) would give a sprocket tooth mesh frequency that is close to the 3000 cpm problem frequency. I notice it is a double wide chain, so sprocket alignment is important. Sprocket offset, angle and twist should all be measured and corrected. A laser belt/chain alignment tool is preferred. Check and correct chain tension and lubrication.

I pointed to where I would conduct impact test that for the motor-gearbox. This location should detect pure vertical (perpendicular to motor shaft) and rocking motion vibration modes. It would also be good to measure (impact and vibration response) in the horizontal direction at the same location.

The appearance of the four threaded rod supports with lock washers suggests that support stiffness might be increased by removing the lock washers and replacing both lock and flat washers with Grade-5 or Grade-8 extra-thick flat washers for better contact between nut and base.

It looks like a new or well cleaned machine, so be proactive with mechanical and structural condition.

Walt

Last edited by Registered Member

How does the chain respond (deflection) to modest thumb pressure at mid span with the equipment locked out and tagged out. I'd rotate the motor manually thru several rotations looking for spots where the chain tension gets super tight.

What does the  O&M manual say about adjusting the chain? I suspect the chain may be adjusted too tight (in addition to the machine structure, by inspection, being highly suspect). Regardless I'd adjust the chain for 1/2" or so sag and repeat the vibration measurements

How old is this equipment? Is it under warrantee, and is acceptance testing complete? Regardless, what does the manufacturer say about these vibration levels?

Can the manufacturer provide references and contacts for users of this device?

Do you have a strobe for your analyzer?

Attached is an image showing my requests for more information about this device and a bunch of additional detailed vibration measurements to help under stand what is going on. "Bearing housing" type measurement are only the start, especially on a structural system as dainty looking as this one.

Attachments

Images (1)
  • auger info request

Thanks Dan and Walt for your replies.

I've been back to do a few more tests on it to see if I can understand what's going on .

This is roughly a month old, used for grain handling, no feedback from the manufacturer as of yet. Have gone back to the manufacturer with concerns.No other information to work off from the manufacturer. Only been used a handful of times. My job is just to show that there is an issue but I want to be able to find the cause too.

No unfortunately I don't have a strobe to use.

I found some unusual issues with it which I'll explain and hopefully can get some insight for you guys as to possible causes.

Firstly on start up,

I've attached a slow Mo video (ignore the horrible audio)  it shows the chain that seems to be moving alot before settling down when up to speed, I assume this is due to it passed through some critical speeds but it still seems rather strange.

Secondly, on spinning the auger by hand , the motor fan blades were found broken and all lying in the bottom of the cowling, as far as I'm aware no one has taken this cowling off before me and there is no evidence of foreign object causing this issue.

When checking the deflection, the chain at its looses was 10mm and at it's tightest point was 5mm. I know this doesn't sound like much but it should be all roughly the same shouldn't it ? This would suggest a tight spot with the auger.

Attachments

Images (5)
  • IMG_20210302_092544: Cowling with the fan blades
  • IMG_20210302_092549: The remaining part of the fan
  • IMG_20210302_091353: 14mm thick galvanised steel
  • IMG_20210302_091359
  • IMG_20210302_091403: Cracked welds?
Videos (1)
VID_20210302_135317

No fan blade; now you know why the surface temperature was high! IR survey had a good result.

Chain oscillation at start of video may be just result of auger torque oscillations from partial load. Otherwise, if the motor has VFD and auger startup was variable speed and went through a torsional resonance. This should not be an issue if normal speed and load avoids the chain oscillation. The auger torque oscillation frequency is number of flytes (usually 1 or 2) times auger speed.

β–· Screw Conveyor : ALL about Sectional Screw Flight and Pitch Types - USA (screwconveyorbega.com)

Broken tack welds on motor support indicated probably vertical/rocking motion as previously discussed. Tack welds are useless to replace, so either good solid weld or none at all; depending on minimizing vibrations.

Variable chain tightness can be from uneven chain stretch or eccentricity of one or both sprockets. Shaft eccentricity/runout can be measured with dial indicator on magnetic base.

Walt

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