Dear Svenson,

A guess could be:

840 rpm corresponds with 2*3.1415 * 840 / 60 = 87.96 Hz

860 rpm corresponds with 2*3.1415 * 860 / 60 = 90.06 Hz

The 2 frequencies are close together and therefore will cause a interference frequency of

90.06 – 87.96 = 2.1 Hz

This frequency of 2.1 Hz could be the resonance frequency of the support or the building.

These type of problems start with measuring the vibration spectra and after that searching for exiting frequencies that match the unwanted vibration frequency.

Specialist work.

Take care

Teus ■

Dear Svenson,

Recreating the original situation should result in the absence of the, now, experienced vibration.

To what extend the old situation can be restored is probably uncertain, as there have probably been made other changes too.

If you can vary the speed of the individual machines, it is an idea to search for those rpm’s that solve the problem.

If there is a natural frequency to be avoided, there will also be the possibility to have that situation during starting.

Then you have to pass this situation as quickly as possible and convince yourself that this, short, event is not damaging to the support or building either.

I still maintain my advice to have the installation evaluated by a vibration expert consultant.

Take care

Teus ■

Originally Posted by Svenson82

href="showthread.php?p=78541#post78541" rel="nofollow">

I currently have 2 Tyler Canada Screens running side by side (1 with Rostas mounts and 1

on springs) They are getting lots of vibration in the structure. With the previous screens they had installed there was no vibration.

1 machine is running at 840rpm and the other at 860rpm. What would you

recommend?

When only 1 machine is running the vibration in the building stops

completely.

Let me know what you think or if you have any experience of this.

If you need anymore information let me know.

Originally Posted by Teus Tuinenburg

href="showthread.php?p=78542#post78542" rel="nofollow">

Dear Svenson,

A guess could be:

840 rpm corresponds with 2*3.1415 * 840 / 60 = 87.96 Hz

860 rpm corresponds with 2*3.1415 * 860 / 60 = 90.06 Hz

The 2 frequencies are close together and therefore will cause a interference frequency of

90.06 – 87.96 = 2.1 Hz

This frequency of 2.1 Hz could be the resonance frequency of the support or the building.

These type of problems start with measuring the vibration spectra and after that searching for exiting frequencies that match the unwanted vibration frequency.

Specialist work.

Take care

Teus

Originally Posted by Svenson82

href="showthread.php?p=78543#post78543" rel="nofollow">

Many thanks for your quick reply. The original machines these replaced were exactly the same and running both at 860rpm. Would you reccomend to change the speed so that both machines are running exactly at the same speed? To me this would be a good starting point as there was no vibration on the original screens. As long as the weight of the screens, speed and amplitude is the same on the new screens as the original machines then this should put the vibration back to the same level as the existing machines.

Originally Posted by Teus Tuinenburg

href="showthread.php?p=78559#post78559" rel="nofollow">

Dear Svenson,

Recreating the original situation should result in the absence of the, now, experienced vibration.

To what extend the old situation can be restored is probably uncertain, as there have probably been made other changes too.

If you can vary the speed of the individual machines, it is an idea to search for those rpm’s that solve the problem.

If there is a natural frequency to be avoided, there will also be the possibility to have that situation during starting.

Then you have to pass this situation as quickly as possible and convince yourself that this, short, event is not damaging to the support or building either.

I still maintain my advice to have the installation evaluated by a vibration expert consultant.

Take care

Teus

AYYY CARAMBA, LUCY YOU GOT PROBLEMS!!!!!!!

A few questions about your screeners;

How many decks per screen?

What are you screening?

How wet is it?

AM I correct in assuming the screeners are horizontal screeners and you have

a center drive motor over the screener body?

Are the screeners set in a cascade pattern or is one screener recirculating oversize?

Are the new screeners the same "exact weight" as the original screeners?

Are the exciter weights the same "original weight" for each screener?

DID you reuse the "original" Rosta mounts and coil springs for the new screeners?

If so Why? Mounting rubber deteriorates with age and coil springs weaken too.

Were airbags out of the question for the installation and if so why?

Is there a specific reason why a wire rope supported sceening suspension was not used?

Have you used stroke check cards to check the orbit of the screens at all four corners

both screens?

If not you can find them here on the forum and print them out and then

glue them to card stock to check the screeners.

Are these screeners controlled with a VFD motor system?

The resonance as Teus has so kindly described is the problem

I think as each screener is separated by 20 Hertz.

The least invasive examinination would be the first thing to do would be to change the frequency and at the same time

plaster all four corners of each screener with the stroke cards running them empty and with product as the stroke check cards

would be the tattle tale for you to detemine the orbit of the screeners.

I have a screener horror story here on the forum that I still laugh at after 17 years because of the manufacturers recommended fix which was Adding steell under the screener until thr excess vibration was canceled-no real resolution to the problem of the poorly designed installation and methodology as the two deck screener was vibrating the 700 tons of steel used to construct the entire screening plant so badly that people could not walk on the screen plants perforated steel deck flooring safely while it was screening.

Attachments

stroke check card (PDF)

■

Have you looked at all the differences between the 2 screens? Drives on same side or opposite sides? They should be on opposite sides to create balance in the structure.

You mentioned the Rosta mounts vs springs. Rostas will dampen more vibration into the structure than the springs will causing a difference in structure resonance. I would look at changing out the one with springs to Rostas or change the one with Rostas to springs. Then you are comparing apples to apples. ■

Originally Posted by Svenson82

I currently have 2 Tyler Canada Screens running side by side (1 with Rostas mounts and 1

on springs) They are getting lots of vibration in the structure. With the previous screens they had installed there was no vibration.

1 machine is running at 840rpm and the other at 860rpm. What would you

recommend?

When only 1 machine is running the vibration in the building stops

completely.

Let me know what you think or if you have any experience of this.

If you need anymore information let me know.

Svenson

One screen is running at 14 Hz and another one at 14.3 Hz - difference is very small and you can have "beating frequency" problem - the vibration comes and goes.

Something has changed as you say the problem is new and you did not have this problem before. Steel springs have better isolation than Rosta mounts and therefore signal transferred to structure will be higher from Rosta. Structure should be checked for frequencies and for structural problems( looseness, corrosion, etc). Really the only option you can do without getting professional help is to reduce you stroke on the screen to the minimum required for the process - very often the acceleration on the screen is much higher than required - and therefore reducing the vibration transferred tot he supporting structure.

That's what I'm doing normally but you a bit far from Australia.

Regards

Ziggy Gregory ■

Svenson

Several option

-change the frequency of one screen - function of natural frequencies of the structure and the screen

-change the stroke of both screen - function of process - very often the screen are run at very high acceleration when there is no need for it. That's the only option available to you without a need for vibration analyst with a frequency analyzer.

-change rosta mounts to steel springs

-install the isolating frames

Regards

Ziggy Gregory ■

Dear Svenson:

I am writing to you from W.S. Tyler. We would be happy to review what may be causing the vibration in your structure, and develop a plan together on how to resolve the issue. Following are some ways to limit vibration, but if you contact us directly, we can zone in on the specific cause in your situation. Our Service Manager, Lui Petrucci, can be reached at 1-800-325-5993, or lpetrucci@wstyler.ca.

Kind regards,

The W.S. Tyler Service Team

1. Structure - Having an adequate support structure is extremely important. This is determined when computing the design load on the structure the standard practice involves three factors. They are as follows:

a) The actual weight of the vibrating screen including all of the auxiliary equipment such as motors, chutes and fines hoppers.

b) A material load on all screening surfaces which is assumed to be a six-inch deep bed depth.

c) Add 40% to the totals of the above to take care of any external impact load, any possible future changes in weight of the screen or any unusual loads that might occur if a heavy overload, such as might happen if a chute was plugged, built up on the screen.

2. Balancing - Having a properly balanced machine will ensure your machine is running within its parameter's which will ensure that your machine is not transferring unnecessary forces into the structure.

3. Mounting systems - Having the proper mounting system installed on your machine is very important to insure that you have sufficient amount of support under your machine which will limit the amount of unwanted forces into your structure.

4. House Keeping - Material build up around the machine will cause your machine not to run freely which will cause unwanted frequency into your machine and into your structure.

5. Type of Machine - Replace your machine to a W.S Tyler F-Class machine why? The F-Class is dynamical balanced causing forces between the body weight and drive assembly to cancel out eliminating dynamic loads going into the structure.

6. Speed - When making the calculations as to the natural frequency of the structure do not overlook the operating speed of other pieces of equipment in the vicinity of the screen. The natural frequency of the structure should not directly coincide with or be a harmonic of the speed of any other piece of equipment. By simply changing the speed of your machine can change the natural frequency into your structure. ■

Originally Posted by W.S. Tyler

Dear Svenson:

I am writing to you from W.S. Tyler. We would be happy to review what may be causing the vibration in your structure, and develop a plan together on how to resolve the issue. Following are some ways to limit vibration, but if you contact us directly, we can zone in on the specific cause in your situation. Our Service Manager, Lui Petrucci, can be reached at 1-800-325-5993, or lpetrucci@wstyler.ca.

Kind regards,

The W.S. Tyler Service Team

1. Structure - Having an adequate support structure is extremely important. This is determined when computing the design load on the structure the standard practice involves three factors. They are as follows:

a) The actual weight of the vibrating screen including all of the auxiliary equipment such as motors, chutes and fines hoppers.

b) A material load on all screening surfaces which is assumed to be a six-inch deep bed depth.

c) Add 40% to the totals of the above to take care of any external impact load, any possible future changes in weight of the screen or any unusual loads that might occur if a heavy overload, such as might happen if a chute was plugged, built up on the screen.

2. Balancing - Having a properly balanced machine will ensure your machine is running within its parameter's which will ensure that your machine is not transferring unnecessary forces into the structure.

3. Mounting systems - Having the proper mounting system installed on your machine is very important to insure that you have sufficient amount of support under your machine which will limit the amount of unwanted forces into your structure.

4. House Keeping - Material build up around the machine will cause your machine not to run freely which will cause unwanted frequency into your machine and into your structure.

5. Type of Machine - Replace your machine to a W.S Tyler F-Class machine why? The F-Class is dynamical balanced causing forces between the body weight and drive assembly to cancel out eliminating dynamic loads going into the structure.

6. Speed - When making the calculations as to the natural frequency of the structure do not overlook the operating speed of other pieces of equipment in the vicinity of the screen. The natural frequency of the structure should not directly coincide with or be a harmonic of the speed of any other piece of equipment. By simply changing the speed of your machine can change the natural frequency into your structure.

========================================================================================

We have yet to hear about what is being screened or the tonnages per his

twin systems so we are in a bit of a fix.

Until we hear more.................................................................................. ■

Originally Posted by Svenson82

Thanks for all the info guys. Please see some more information below:-

- Single Deck, Inclined Screens (20 Degrees Downhill)

- Iron Ore Peletts

- Vibrator Unit is through centre of machine

- Screens are side by side

- I understand screens are same weight as before but I am not 100%

- New Rostas and springs were used. Original screens had 1 spring in each corner.

- Stoke was checked in all 8 corners and was around 10-11mm but it didnt seem like a perfect circular motion. Was more oval

hope this helps.

==================================================================================================== ==================================================================================================== ==============

What you have are elliptical screeners hence the oval orbit.

Were both screeners installed intact or built up on the screen deck???????????????????????????????????????????????????????????????????????????????????????????????? ???????????????????????????????????????????????????????????????????????????????????????????????????? ??????????????

Been there, DONE THAT, lots of torch holes for wire rope shackles, BUTTS UGLY!!!!!!!!!!!!!!!!!!!!!!!!!

AS most screeners throw the material back upon the screen deck for

separation/cut the one question comes to mind;

is one screener throwing material back and the opposing screener

throwing material forward, or are both of the machines throwing the

pellets forward instead of back upon them selves for the cut?????????

With the "shake and bake" as we joke about calling the

screening motion the two front opposing stroke cards

should have identical oval orbits and the rear corners

should have THE SAME identical oval orbits, if they

do not the screener is fighting itself.

IS there any chance you have the old stroke cards

for the old screeners for comparison?

Are the screener motors on opposing sides or the same side as gary has

questioned before?

Here is a bg one:

Are the V Belts tensioned to the same tension or have new and used belts been used OR are the belts all from the same LOT NUMBER. Has a V-belt tension gauge been used to check the V belt tension?

Assuming the motor(s) are tray mounted are the adjusting bolts all the same length/threadcount under tension????

This pains me to say BUT did anyone run an 8 foot level

along the steel work/beams/girders supporting the screener

suspension mounts before the new screens were installed?

Has anyone done any survey work with a transit and run lines to

to check any of the structure?

The other issue is the spring strength and the Rosta mount

strength and whether they are sized properly.

Are the balance weights identical for both screeners?

IF equalizing the motor speeds does not solve the problem I would

want to check how true the steel work is along ALL 4 girders under the

suspension.

IF they are not true..............................., then it becomes an issue

of true balance where an air bag suspension would provide equal height and

eliminate any deformities in the girders that may not have become evident over time.

The use of an airbag suspension creates a level operating platform simply because the

the compressed air in the air bags acts like air shock absorbers and then the screener

should be fine as it eliminates any structural deformities because of the airbag suspension

has an equal air pressure at all suspension points.

If all else fails you can have the screens changed over to a wire rope suspension

if you have the head room and IF the screeners side plates can be used in thier current

design/they already have mounting points/ for wire rope suspension.

IF the stroke check cards have been used to check the screeners when they were running full

and empty and:

IF the stroke length is identical on all eight sides and if cable suspension is not an option

AND the steel is still true OR EVEN IF IT IS NOT true the use of airbags would be an excellent

way to solve the problem IF and only IF the screen loading of pellets is uniform during screening.

IF everything about the 4 screeners is the same it has to be something simple-you will have to examine everything and I mean everything about the two brands of screeners to assure that they are identical in weight and throw distance/orbit length.

It may be something simple that was not evident or overlooked but I would call the manufacturer and have someone come out with tools and a lazer theodelite at least to check the screeners frame and height from

corner to corner and side to side. ■

sound like you in fact are experiencing a "sympathetic vibration" deal with those machines now at or near the NF of the structure and causing erratic vibration.

I would normally try to get the screens plus minus 50 rpm diff between the two....better to kinda slow one down vs speed one up. this would normally calm the structure down.

WS Tyler checking it out would be a perfect solution, they built those and can easily, and professionally TELL you what the structural vibration problem is with a vibration analyzer by an experienced factory REP. how can you go wrong there/ Their machines, best folks to look at it in my opinion.

a transit check idea mentioned in one of the responses also makes perfect sense....because it does actually seems like something has "changed" and we always look for that when a problem occurs especially if it was all fine before with the same kinda of setup. sometimes when we remove and replace vib screens we repair support beams under these things first for prep work and we could be slightly off level side to side...a 1/2" difference will cause you MAJOR VIBRATION PROBLEMS all day long...so must double check by transom check to ensure level all around.

SIDE BY SIDE AND CLOSE...really sound like a possible harmonic vibration could be there with each machine...ramping thru the NF of the structural beam holding it.

The ROSTAS really.....should help dampen the vibration here not hinder. the difference between those and the coil springs basically are: the ROSTAS very very well proven technology disseminate the vibration on shutdown out in a horizontal plane with their scissor action on shutdown and the vibration elimination on the coils is dampened in a linear straight line down thru the coils towards mr structure but, both serve the same purpose.

if not resolved, email me personally or call and we will resolve it for sure. Please keep us up to speed on what goes.

A DIGITAL PIC of your stroke card checks would be excellent...and did you do a tach check to confirm speeds?

GEORGE BAKER Moderator

Originally Posted by lzaharis

========================================================================================

We have yet to hear about what is being screened or the tonnages per his

twin systems so we are in a bit of a fix.

Until we hear more..................................................................................

■

Dear All,

As far as I am concerned, the machine vibration transfers to base from bearings. Hence, the base shall not in fact be very rigid. However, it is mentioned that to reinforce the motor base is okay. Please let me know why?

We think if we reinforce the motor base, then the vibration will affect the bearings and dryer itself instead of base and we may face with bigger issue.

Generally speaking please let me know if base shall be very strong?

On the other hand,if the base is not more strong,this can cause increased vibration.I am confused if the base shall be very strong or weak?

Best Regards

Hamidreza ■