How old is this screener?

Maybe the springs supporting the deck are OLD and lazy and this will cause poor screening efficiency.

Maybe your WIRE diameter is a tad too big on the 150m, I assume it is T304 or T316 stainless steel wirecloth?

Maybe the supplier of that mesh, is not supplying a nice TIGHT interwoven wire in the RING FRAME....and yes it happens.

If the ball tray did not keep clean....Ummm sounds like some other problem.

....................................................let's try plan B

1. Where does the mtl come from? A grinder or?

2. Is the product shape angular, cubical or little arrowhead shaped. Look under a magnifying glass, if slivery.....IT WILL PEG or plug.

3. 150 mesh screening is VERY difficult at best of times.

4. May be overloading this deck and pressing or forcing the material into the opening and unable to clear

5. What % of minus 150 is in the TOTAL INFEED. ...BY sieve analysis.....if too much NEARSIZE to 150mesh this could be the problem.

6. Is material absolutely DRY, if not this will blind the holes.

7. The sifter may be undersized in DIAMETER to handle the tonnage being fed. Is this a 4', 5' or 6' diameter? You may need to split feed to units of the same diameter.

8. Do you have clean power to this machine?

....................................

This type of screening can be done many ways by the way......150mesh and finer suits itself nicely to TYLER HUMMER electro magnetic vibrating screens.....or a highspeed DERRICK. ■

Happy New years. George ■

Hello,

A happy New Year to everybody.

I am first time posting, so please excuse any mistakes.

I was selling, testing, starting up, trouble shooting and repairing circular vibrating screens from 1985 to 2003.

The problem you have proves a theory I came to know some time ago.

What you experience on the bottom screen is bridge building (blinding) of the fine material - in German we call it: "Brückenbildung" - a phenomenon well known, and in these days very often additional ultrosonic vibration is suggested. But most probably wouldn't work in your case.

When you worked without top screens you had coarse particels in the material to be screened which bounced around on the bottom screen and which broke the bridge building of the fine particels.

As you installed the top screens you took away the coarse particels and the fine material was alone on the bottom screen and made bridges between the wires and there was nothing to break it up. So, blinding was the result.

As a consequence you have to introduce something larger on top of the bottom screen which will bounce around and break up the bridge building of the fine material.

Introducing balls, rings, etc. under the screen won't help.

In tests I introduced a V-belt on the screen and that helped - a V-belt won't be discharged through the outlet-spout of the oversize.

So, introduce something larger on top of the screen which won't run out of the outlet spout.

Hope you are successful! ■

I agree with GeorgeP the likely explanation is the new upper and middle decks ar removing the coarse particles that kept the material above the screen free flowing and non blinding when it was operating as a single deck unit.

Potential solutions are :-

Pre-screen the fines out and then split the oversize into various fractions , this can be done using two seprate units or using a gyratory screener with internal overize reciculation to the lower decks - if youd like further information on htis please email me at rw@procengtech.co.uk

or

put in some material which will tumble on the surface of the fine deck and break up hte 'bridges' this should be big enough so that it does not pass out of the material outlet - in the past I have used square rubber cubes approx 30mm diameter and a perforated plate with say 10mm holes across the oversize outlet to stop these being rejected . If there is a screen spiral fitted this needs adapting to allow the cubes to recircualte or they will jam at the outlet like a log pile and hte screen will blind in the centre.

Ultrasonics may work - may not as well and are a potential maintenace problem - only trials will tell ■

>> But still the basic question remains : the centre of mass of the suspended body does change when we add decks 2, 3, 4 etc. <<

It is correct, the centre of mass of the suspended body does change when you add decks 2, 3, 4 etc.

But this is not the main cause for blinding, I think.

Though, it will change your overall perfomance - capacity, flow pattern on the screen, vertical bouncing. Therefore you might have to change the amount of weights and the angle setting between upper and lower weight. And/or you might have to live with a lower capacity. Nothing (more decks) is for free.

Literature does not tell too much about circular screening. Not too many people really do know in detail how and why it functions. It's all trial and error and experience. Sorry. ■

Hi waipl,

I am glad to hear you were successful.

The effect you achieved (dust-free oversize) of course is a different effect than we originally tried to achieve (reducing blinding of bottom screen in a multi-deck machine).

But any improvement is a success, isn't it.

The dust free oversize is due to the mechanical action of the V-belt (or any other larger object on the screen) onto the particels of the material to be screened.

You break the adhesion between particel and dust (probably due to static electricity) with the help of the V-belt (or any other larger, bouncing „thing“ on the screen.

An ultrasonic vibration device would serve the same purpose.

One thing though you have to watch. There is a grinding action on the V-belt (or any other „thing“) due to the screen, which means you get a small amount of rubber (or other material) into your material to be screened.

In case you work with very pure powder this might cause a problem.

I am looking forward hearing about your further tests. ■