Rekkawar: This will be from my practical field experience, someone smarter can be more scientific.

I have flown to many sites over the years for this exact complaint.

My opinion:

1. You MAY be experiencing sympathetic vibrations. Specifically when 2 vibrating devices of same RPM on same structure are operating at same time. You can in fact encounter, a WAVE of sympathetic vibration............the two units are too close to the same operating frequency and hence cause strong vibrations to the structure on which it is installed.

POSSIBLE FIX: Change operating RPM of one of the units by say 50 RPM to stop this condition between the two machines.

I have this many times when we install say......banks of vibrating screeners in a line and across from one another. say, 5 machines in a row.........and more across.........you get this condition fairly normally when all running the same RPM and fairly CLOSE to each other. We just change RPM on one or more.........to break the chain of vibration between the vibrating screens and the structure.

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2. You MAY be experiencing........vibrating equipment that is installed on steel structure that does NOT have the SAFETY FACTOR built into it to handle the dynamic operating loads put out by the vibrating device.

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You MAY be experiencing.........a transmission of vibration condition, especially if high up in structure......if there is no vertical support under a spring mounting position to the floor for example. YOu will see rampant vibration in the structure

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POSSIBLE FIX: Typically, I find if we throw some more steel at it, for example strategically placed X BRACING below....this will quite often fix this condition. We sometimes cheat on steel ...to save money........and create this condition. On the vertical support under the spring load positions........this can be fixed by installing same from the underside of the support pad to the concrete floor in some instances.

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Plan X............not necessarily applicable here but, if way up high in the structure........and say a very big vibrating unit.....8x20 size.....sometimes a ROSTA MOUNT vs coil springs can really quiet down the whole shutdown mode........substantially.

Hoping this helps......George Baker www.assinck.com ■

Hello again: Are these units cable hung? floor mounted?

If cable hung.......you may need to install ISOLATORS....to eliminate vibration transmission to the structure support steel.

let me know how you make out.......

Keep the faith......George Baker Moderator ■

rekhawar

I addition to George's usefull comments. You should have a structural engineer thoroughly inspect the structure for cracked weld joints on all bracing, loose or missing bolts. Also check for cracked or broken structural components. Anything of this nature will weaken your structure and exaggerate the vibration.

The engineer will be able to determine if more bracing is required such as George suggests.

Good Luck

Gary Blenkhorn ■

As a first step, I would be checking whether the screen is operating too close to a natural frequency of the steelwork, as one of the previous posts recommends.

The installation of ROSTA units underneath the screen will result in a substantial decrease in transmitted vibration, and is often more than adequate to solve problems such as this.

However, if the vibration is caused by vibration modes in the steelwork, the problem will remain until the supporting steelwork is corrected.

We are the Australasian distributor for ROSTA units, and can assist you if required. Alternatively, you may wish to contact a distributor closer to home. ■

Gentlemen

I agree with mr Misterblobby, regarding the ROSTA under the screen.

I had this exact problem with some viration conveyors ( 3 pc)

in a "cheap" steel building where all vibrations were transferred into the steel, causing noise and shaking beams.

We started with reinforcement- beams velded in all possible directions. The funny thing was that we could move the vibrations around in the building depending on how we put in the beams- but it didnt solve it.

Finally we put in rubber damper under the large support springs for the vibrators´, to isolate the noise from the vibrations.

It was made special support for the sping, some standing and some hanging mount, but it was succesfull.

Tthe problem was totally solved- no wibrations at all.

I can recomend this. ■

I agree with others......and have used ROSTAS many many times on vibrating screen PROBLEM APPLICATIONS.

BEAUTIFUL on big ole HORIZONTAL heavy bang crash flat deck vibrating screens THAT shudown like an elephant falling off a cliff. These horizontal screens run at 5.5 or 6 G's and it is hard to shutdown smooth on coil springs.....going to ROSTA...not cheap but it does work.

but. SPECIFICALLY in regards to this particular problem, the main focus point is........IF the structure was in fact engineering properly under this screen.......ie: enough safety factor in the beams supporting it.......the problem should NOT EXIST.

ROSTA is a fix.......yes.......one fix.......but, the structure must be engineering properly in all cases.

Keep shakin' out there........George ■

Daer Mr.P. Rekhawar

Mogensen Sizers are supercritical operating Machines and will not cause vibrations during operation except during transistion over the 0-300 RPM zone & that too at one descrete frequency only.

If you have two exciters ensure both of them are having the same unbalance mass setting.

If you have inly one Directional force exciter; check that all the masses are even and ensure that additional lead masses have not been unevenly placed in one of the rotating segments.

Most often the springs could have settled, which need to be checked: if all the above are Ok, please check the ccardon shaft which drives the Directional force exciter: This may be over streached more than the manufacturer's specified length and consequently it may be causing a hammering effect. This can happen if the cardon shaft is fully collapsed too!! the intermediate cardon shaft between exciters may also be jammed.

If all the above are in order; you have to stop using the equipment and check where the noise arise from and; if required, replace the exciter

There is one other thing you can do : provide a high inertia isolation frame base with its own springs and shock absorbers.

Trust this post will be of help

Let us know how you solved the problem.... Thanks

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Rekhawar

It looks like you have a frequency problem - running frequency of the screen is the same or very close to the natural frequency of the structure.

The simplest way the solve the problem is to do a frequency test on the structure ( impact test) to determine the frequencies and then adjust the running speed of the screens and you have to also do the bump test on the screens - possibly you are running the screens at resonance.

If the problem is structure related changing springs to rosta mounts will make the problem worse as the steel springs give better isolation than rosta mounts - signal that is now transmitted to the structure will have the same frequency and higher amplitude - additionally you can change the natural frequency of the screen and get the screen running at resonance as the rosta mounts are much stiffer in horizontal direction in comparison to the steel springs - the frequency will be still the same as the natural frequency of the structure but the amplitude can get several times bigger.

My advice is - get the someone to do the impact test on the structure and the screen before doing any changes.

Ziggy Gregory ■