Originally Posted by lzaharis

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If you could provide some images that would help a lot.

If your trailer carrier is not very heavy the screen resonance may be

overpowering the mass of the trailer.

Did you consider mounting the screener on a set of airbags for support and

resonance cancellation?

When I test run the screen, the wire cloths haven't been installed yet (but I think there is no issue in balancing the screen without the wire cloths) and it is set horizontally (when it is supposed to be inclined). The screen is mounted on a pair of WF 250 beam, and is laid on the ground without being bolted.

I haven't considered mounting it on airbags support, but then, even without the airbags support the screen runs smoothly (with the arms aren't fix welded to the WF 250). But I am not sure whether the screen is already in balance since it can also run unbalanced but the mounting support (rosta oscillation mounts) is dampening the vibration to the structure (due to unbalanced condition) and making the screen looks like balanced. One of the main problems is that I do not know what an unbalanced/balanced condition of a four bearing single shaft screen looks like, maybe you have reference where I can see videos of such screen running in balanced/unbalanced?

Anyway, below are the photos attached. Thank you for the advise, Izaharis.

Regards,

Chris

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Now that you mentioned about the sagging of the cross member, I wil checked them asap, And have the chassis support under the Lip modified. We have done our best to weld the box as 'square' as possible, but if it is as you said, then we still have to continue until the end since we already put quite an effort here.

About the cross tube bracing at the end discharge, I agree with you though, but why there are some manufacturer (tyler, terex, etc) do not use such bracing...i wonder

The side plates, yes, but unfortunately, in my country, it is very difficult to acquire good materials and good workmanship.

Anyhow, izaharis, maybe you can help me describe how a four bearing single shaft is balanced? And how it looks like under balanced or not balanced condition, at least woth this type of setting..

Thank you for your input...maybe I should really just buy an F-class screen from Tyler..sigh...haha

Regards,

Chris ■

Hi izaharis,

The diagonal distance is the same. Could you describe what are the troublesome factors about this type of screen? I could only think about the maintenance, especially when we have to replace the inner bearing, it woukd be quite troublesome. Our quarry is currently using an inclined two bearing single shaft screen though...with unbalanced weight..it is much simpler...

It happens that I saw the f-class tyler brochure in the internet, so i do a little research...read in the vsma too, mentioning that this type of screen has its stroke independent with the material feed load, hence the tyler saying it heavy duty?? And start/stop smoothly...that picked my interest as i have never seen such screen before and in my country, this type of screen is very very rare...no quarries that i know (about 20 quarries) use this type of screen.

So before taking out quite a sum of money to purchase from the manufacturer, i decided to do a 'fun' project...

But anyway, thanks a lot for the knowledge shared...

Regards,

Chris ■

Dear George,

Yeah, you are right, more than 100 years actually...

Anyway, here's my big question:

What i understand about how a four bearing single shaft screen works is that it works like a crankshaft of an engine. So, the screen actually moves in a constant circular motion with a stroke diameter equals to the eccentricity of the shaft designed. The part of the shaft which is in the main screen body (held by 2 inner bearings) is plain, and the eccentricity part is designed immediately after the shaft part leaves the inner bearing area and held by the outer bearings. Hence, the centerline of each the inner and outer bearings is on different plane with each other as far as half the stroke diameter (in my case, 4 mm, since the stroke is designed to be 8 mm).

The simple design is such that the outer bearings uses simple plummer block fixed/bolted on the main frame (e.g. Wide flange or H beam). The screen body is then mounted on a suspension system (at four corners, could be spring coils, rubber mountings or rosta oscillating mounts; i use the latest). But the problem here is that if you run the screen immediately, the whole screen will vibrates erratically and jumps around like a frog SINCE the nett resultant of the moment of the screen body is equal to the screen weight itself, in other words, the whole screen body acts like a counterweight to the rotating shaft (which is the total weight of the body x the eccentricity distance, i.e. 4 mm). Certainly this cannot work, that is why we have to 'BALANCE' the screen by counter acting the moment delivered by the screen body so that the nett resultant of the moment of the overall vibrating system is zero, in other words, the screen will vibrate due to only the eccentric mechanism designed on the shaft and not because of the unbalanced condition. So, this balancing is done by putting a counter weight between the outer and inner bearings on both sides. The counter weight is set to be 180 degrees from the eccentricity, which means when the screen body throws itself in clockwise manner, the counter weight set oppositely will cancel the moment delivered by the screen body. The weight of the counterweight is determined by calculating the distance from the centerline of the outer bearing to the center of gravity of the counter weight, and then you can design physically the shape of the counter weight. It is preferable to have the counter weight as slim as possible and as close as possible to the screen body, that means you will have a larger area of the counterweight.

I intentionally make a number of different thickness of shims to add additional weights to the counterweights (flexible design). This screen and its balancing is very similar to a jaw crusher (and cone crusher, vertically).

Taking reference from VSMA, since in practical, it is impossible to balance the screen perfectly, usually many manufacturers of this type of screen has the outer bearings mounted on rubber mountings in order to dampen the residual vibration due to the imperfect balancing. So, i assume that if the screen is ideally/perfectly balanced, there should be no vibration whatsoever transfered to the structures (since the nett resultant of the moment is zero).

But then, here i see that this f class tyler screen actually mounts both of its outer bearings on suspension system similar to the one used for the main body. Moreover, the outer bearing is not aimply housed with a plummer block, but is housed inside an extended arm where the suspension system can be placed further away from the center of the outer bearing. With such setting, i believe that eventhough the system is extremely unbalanced, the screen will only run like a normal two bearings single shaft screen (with an additional of circular motion due to the eccentricity of the shaft design). So it vibrates due to both the eccentric design and unbalanced condition. This is what exactly happens in my ase, i believe.

Since i do not know how a balanced four bearing single shaft scren looks like, i do not have a reference data. So, george, i 'think' what you mean by balanced is different from what i meant, your balancing term refer to the finishing step of the screen. Where what i am still wondering is the main concept of the balancing of the system (double eccentric shaft). And i am somehow certain that we are unable to balance the screen like what you meant since we are fabricating this screen with low quality of workmanship. But of course, at least i would be able to see the concept of how the screen works eventhough it will not run in a perfect way.

So, as i stated in my first post, when i test run my screen without installing the wirecloth, i simply want to know how the balancing actually works and looks like. And the type of screen media has nothing to do with the balancing (except its weight). But you have a point there maybe due to that i did not install the wire cloths, the main body has less weight than what it is supposed to be when in complete state, which ruins the balancing. As where there is a possibility that without the screening media and tensioning system installed, even without the whole counter weight additional shim weights added, the outer bearing system (including the whole weight of suspension systems and extended arm housings) has a bigger moment than the main body delivers when run.

Well, this is how i understand the concept of the balancing. Maybe i am wrong in many points. This is he most important part at the moment. All of the other imporant points or aspects of a good design can latter be improvised systematically (in my opinion...perhaps i am wrong?) with helps and advices coming from the more experienced/seniors in is forum

As in the case to my actual problem, please refer to my first post.

Nobody has the video of this type of screen running, eh???

Anyway, thank you, george for your great input, i will certainly look for your advices on many aspects later on...hehe

Regards,

Chris ■

Dear ziggy,

Thanks for the input. But how can i know that the screen is actually running in its natural frequency? What is the distinct characteristic of a screen running in its natural frequency? I mentioned that the screen vibrates eratically, perhaps i used the word wrongly. The screen vibrates eratically in a manner that the whole screen and the chassis it mounts on jumped off the ground continuously due to that the chassis in not bolted to the ground and that due to the suspension system, the whole screen jumped off. So what i meant is that the stroke becomes bigger as the speed increases but i did not see how the stroke goes till the end (whether it reduces gradually until it reaches some point or operational speed or that it stays constant at certain point or that it grows bigger and bigger) as i was afraid the whole screen would be damaged.

But if it is as what you have said, what is the best and/or most economical solution?

Thanks.

Regards,

Chris ■

Dear izaharis,

Yes, they are different animals living on the same farm, my mistake...i was actually referring in a general idea to the concept of dynamic balancing of the shaft of either jaw or cone crusher.

Anyway, thanks for the advice...

Chris ■