This topic is near and dear to my heart.

Your post was quite to the point and actually very correct in that:

- Lots of operations, in fact most, especially stationary, come up to their 6', 7', 8' wide screen boxes with 36" wide troughed belt or maybe a 42" wide if you are lucky and typically try to hit a DEFLECTOR and cast the material down onto a feed box or directly onto the feedbox or even worse, directly onto the first piece of wirecloth.

- Feed to a screen is typically left to chance at best BUT, is highly important

- When you feed with a narrow belt, you will typically feed down onto the length of the box in the shape of an "INVERTED V" missing maybe 6-8" away from each sideplate for maybe a foot or two. This is of course LOSS OF OPEN AREA, equals loss of EFFICIENCY and fines CARRYOVER.

- On portable screening plants, there are a number of companies that actually feed up the FEED CONVEYOR THE FULL WIDTH and come on to the screen box the FULL WIDTH of the screen.....absolutely desirable and equals more efficiency and more TONS PER HOUR by utilizing the full open area of the wirecloth

- Many companies feed with a FLAT BELT and variable and this further improves production and efficiency by controlling the feed to a screen box, putting it onto the screen box "Plowed back" or in other words in a "nice, even, levelled bed depth" which allows the screen to try to do its job humanely....vs trying to screen out with the typical "SURGE LOADED" condition created by feeding with a "35 deg troughing idler belt assembly"

- PROPER BED DEPTH is a critical factor contributing to proper stratification and screening of materials.

- There is a very good company thats screens at very fine meshes....J&H out of the USA......whose screens are installed at 33-36 deg install angle and screen at mesh sizes of 100,200,and finer mesh ranges all the time.

- J&H has a very unique feeder device that controls the feed to their screens and evenly feeds material across the full WIDTH of their screeners in a "CONTROLLED MANNER" this helps their fine screening machines work beautifully.

WS Tyler HAS similar units doing this type of fine screening.

- Feeding a vibrating screen the full width from the zero INCH mark of the front end of the length of the deck if very important to ensures happens.......take the time to readjust the feed conveyor position, speed or setup to make this happen.

on WET: it is common to see folks "spraying water onto their material" as it comes down the screen but, what you will see is much material that is in fact DRY underneath the top material and hence does not get cleaned all that well.

- The forethought to design and install a proper "SLURRY MIXING FEED BOX" in lieu of a standard feed plate arrangement on a WET VIBRATING SCREEN is critical to obtaining a GOOD, CLEAN, MATERIAL at the discharge end of the screen.

EXCELLENT topic........discussed here long time ago..... ■

When we installed a vibroscreen, the vibroscreen supplier was demanding to install a vibrofeeder previous to his screen. He was not relectant to have a dosing conveyor to feed his vibroscreen, for the above reasons. ( Wider feeding, lesser depth , better screening )

Rgds, ■

Part of the problem stems from the end user of the screen often having no understanding of the differences between a "Feeder" and a simple "Conveyor".

A conveyor is designed to move material from A to B in the most efficient, i.e. smallest, manner with regard to belt capacity loading guidelines. No plant designer is going to spec a 48 or 60 inch wide conveyor where a 36 inch one will handle the load just to help spread the material out for the screen at the end. To do so would be using the conveyor improperly and spending a large amount of money in the wrong area.

While feeder can often use the same recognizable components of a conveyor like a belt, idlers, pulleys, etc, but the two are not the same. What you are describing sounds like the common situation of an operation using a 36 inch wide "transfer conveyor" to feed material onto a 72 inch wide screen. This situation is not the fault of the screen manufacturer nor will they have any easy way to fix the problem without the introduction of a proper "feeder" between the transition conveyor and the screen throat. Sure you can rig up some spreader bars or variable geometry pan chutes to try and get the material spread out as it falls from the transfer conveyor but these are only going to give marginally better results.

Portable equipment rarely has this problem because they almost all include a feeder(belt, chain, apron, vibratory, dump pan, etc) that is sized to feed the screen properly. How the feeder is loaded is either by bucket or a transfer conveyor and it is then the job of the feeder to transition the material from a relatively high speed, compact form to a slower speed, spread out form. Imagine the relationship between speed and torque as an analogy of what I mean. The feeder would be like a "gearbox" of sorts that converts the shape and speed of the material to a form the screen needs. ■

Originally Posted by louispanjang

I just viewed a recent thread about screen excitation & have realised that there are many similar threads relating to shafting, fatigue, aperture profiles deck size etc.

I have yet to see the major plant design issue of filling the wide screen deck from a narrow conveyor ever mentioned, let alone addressed, on the forums. Screen manufacturers are either struck dumb or clueless; but usually both, on the topic of recommending a method for spreading material across the deck within a reasonable travel distance. The problem is as bad in the wet as it is dry.

Any takers?

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I second what george has said as I have spent enough time under a typical twin deck Tylers screen-being locked out of course; we always had trouble with both Tylers wearing out to soon in the middle of the welded fabric coarse screens and the trouble was the same with the 8 Derricks' screening the minus 30 mesh pancake flour fines as they did not fix the problem when the Derrick's were installed in 1978.

The BZ screeners replaced by the Derricck's installation was no different flight conveyor carrying plus thirty mesh salt over 8 drop chutes to each individual screener- right down the middle of each screen deck just like hitting number one pin while bowling a guaranteed beer frame every time.

When the new screen plant was installed in 1994-5 they made the same mistake only worse as the tons per hour were increased using an inclined Simplicity ahead of a Spokane impactor to cull rock shale from ROM Halite.

When the new screenplant was commisioned the simplicity was shaking the entire screen plant and walk ways and they called Simplicity and asked why it was doing this and they aaaahhhhhh just weld more steel weight -tons under the floor under the screener and it will stop doing that- Oy Vey!!!!!!!!!!!! I said.

I was referred to as stupid when I suggested using goodyear or another makers airbags to support the Simplicity as is commonly done.

The folks who engineered the screen plant and secondary flow screens which are rotex screens are no better as the impact is still in the middle even though the screeners are swinging left to right to scalp the minus thirty fines. hence the cleaning balls used for all installations.

Do not get me wrong as I am in no way saying the rotex screens are a problem at all as the chutes were and still are the problem. in both cases `14 years after the fact.

lzaharis ■

I don't want to spend too many words on this topic as many of us already did. In general, what I have seen in the field of dry screening so far is that the need for a device that spreads the material across the full width of the screener is very dependent of the type of screener.

What I noticed is that vibratory screeners all need a spreading device because the type of motion does not spread the material at all... In most cases, the spreading device is a feeder which is also a disadvantage of using this kind of screeners: apart from the question which screening motion is the most effective/ efficient one, the need for a feeder means that an extra piece of equipment is needed. An extra piece of equipment means extra investment, extra maintenance, extra failure chance etc.......

A gyratory type screener like the Rotex screener (the inventors of this screening motion!) spreads the material on the screen surface by means of its unique motion. The circular motion at the feed end of the screeners helps spreading the feed accross the full width of the screener.

Of course, the feed material properties play an important role in the process!

You are invited to visit our website www.rotex.com for an explanation of the Rotex principle and how we can improve your business. ■

Originally Posted by Rotex Europe

I don't want to spend too many words on this topic as many of us already did. In general, what I have seen in the field of dry screening so far is that the need for a device that spreads the material across the full width of the screen is very dependent of the type of screen.

What I noticed is that vibratory screen all need a spreading device because the type of motion does not spread the material at all... In most cases, the spreading device is a feeder which is also a disadvantage of using this kind of screen: apart from the question which screening motion is the most effective/ efficient one, the need for a feeder means that an extra piece of equipment is needed. An extra piece of equipment means extra investment, extra maintenance, extra failure chance etc.......

A gyrating type screen like the Rotex screen (the inventors of this screening motion!) spreads the material on the screen surface by means of its unique motion. The circular motion at the feed end of the screen helps spreading the feed across the full width of the screen.

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Of course, the feed material properties play an important role in the process!

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You are invited to visit our website www.rotex.com for an explanation of the Rotex principle and how we can improve your business.

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Greetings, I am certainly glad for the sake of this discussion that you placed the above sentence in your posting on the thread, otherwise I would be commenting on the Rotex and its performance with Halite <>30 mesh screening and screen blinding.

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lzaharis ■

Faced with feeding from a conveyor to an in-line screen twice the width of the conveyor I proposed a distribution chute based on a section of a cone. It seemed to work OK on a model, but the project was not proceeded with so I don't know what would have happened in real life.

Attachments

distributingchute (JPG)

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