Dear Shri Anupam Agarwal,

You have asked for the “screen size”. Possibly, it seems that you are asking for the aperture size of the screen deck to suit the cut off size of 10mm. Is it so?

You have mentioned mm size and percentages very close by, this makes it difficult to read them. It seems you have got 99.514% (-) 31mm.

You have to also see your required nominal size (i.e. size for 80% of material) and also the maximum size, i.e. considering both of them to suit your process. Simply considering the maximum size may not be ideal.

Regards,

Ishwar G Mulani.

Author of Book : Engineering Science and Application Design for Belt Conveyors.

Advisor / Consultant for Bulk Material Handling System & Issues.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 25882916 ■

Dear Anupam: Thankyou for your question.

It is common to give the PERCENT passing for screen size calculations. I converted your retained numbers to passing numbers.

MTL: Cement Clinker: Wgt cu/ft = 80-95# convey angle 18 deg

Feed Mtl Sieve analysis is:

mm % Passing

35 100.00

31.5 99.514

25 97.362

20 93.576

10 86.140

6.3 65.08

4.0 64.54

2.0 57.42

1.0 49.40

-1.0 50.60

Using Sizing Formula: IN VSMA guidelines:

On a single deck vibrating screen it is calling up 118 sq ft of screening area to do this job.

The MATH says: 118 sq ft needed or 6x20 single deck. But, now experience from working condition must apply. Typically would make the screen slightly bigger as a safety factor. Say 7x20 or 8x20 screen. Assumes 20 deg angle, takes into these factors:

U = 350STPH

= 118 SQ

feet

2.15 X 1.13 X 1.20 X 1 X 1 X .85 X 1 X 1.20 X 1 Req'd ■

I hit a wrong button.......and posted before I was done.

- THE BED depth appears to be okay by the calculation formula

but, personally i would probably go to a 6x20 double deck screen which would load relieve the 10 mm screening deck which is the critical. A top deck over the 10mm opening would make the 10mm deck more efficient and keep the bed depth down.

I used slotted wirecloth.......with 51% open area to try to keep the size of the unit down. stroke 1/4" circle size at 1000 rpm

minimum.

YOU have about 13.86 % of total feed as over and 86.14 % passing. Basically, you will have lots of material quick trying to pass the 10mm opg and hence a splitter deck may be a good idea here. Keep wire diameters lighter vs heavier and maybe even look at T304 stainless steel if necessary as alternate to Abrasion resistant wire.

Hope this helps a bit............George Baker MODERATOR ■

Dear Shri Anupam,

Referring to your query on screen deck size, there are different types of screens such as :

- Circular throw type

- Elliptical throw type

- Linear motion type etc…

The screen deck size will depend upon type of screen, features specific to make, inclination adopted (allowable) and desired screening efficiency.

As per the analysis of your feed material you have 21.252% retaining while screening for (-) 10 mm product size. This implies that you have 78.748% of material less than 10 mm in feed material. In terms of tonnage this becomes 350 x 0.78748 = 275.618 mtph in feed. You have mentioned you intend to screen-out 175 mtph from feed. This means that your expected screening efficiency is 175 / 275.618 = 63.5%. This is comparatively low efficiency and you may find the screen deck size is comparatively less. Please check whether this efficiency is acceptable and what you intend to do with the useful product going as over-size. Screen deck size increases rapidly as the screening efficiency increases.

The required screening function can be also performed by single deck or double deck (even though if there happens to be only one screen-out size, but provided that the screen-out content is somewhere at the middle in total feed). This type of screen will have two decks but of lesser dimensions. In your case, the screen out content is nearly 80% and therefore possibly double deck may not suit your need.

Above are the general guidelines / salient points. Thus, the adopted screen deck size is a very subjective issue and you may find the recommended size differs from various sources. For specific size you may refer to screen manufacturers.

Regards,

Ishwar G Mulani.

Author of Book : Engineering Science and Application Design for Belt Conveyors.

Advisor / Consultant for Bulk Material Handling System & Issues.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 25882916 ■

I also concur with IG MULANI.......on his salient points

The sizing criteria used by me plugs in 95% efficiency as the rule of thumb by VSMA. I also agree that a smaller screen size by width and length can be used if say 50% screen efficiency is needed.

Going to a double deck......would allow you to maybe drop the screen size to a 6x16 by "in the field experience." The math is interesting for the calculation BUT, the art is more the point which equates to experience on this actual type of material on an actual TYPE of screening device.

As i say in the field.......even if I have a screening device that is NOT WORKING worth a hoot...........it in fact does TELL ME SOMETHING. How not to do it.......which is good info to decide HOW TO DO IT.....

The unit I picked at a 6x20 is a circle throw.........can it be down on a horizontal....absolutely. Can it be done on a smaller, HIGH ANGLE........say 33 or 36 deg screener with say 1800 or 3600 VPM (vibrations per minute) or pull on a armature post...for sure. The art then begins to drive the train here.....what can i physically fit into the space.........HEIGHT WISE, LENGTH WISE, etc.

Many assumptions............and just as many variables.

GOOD LUCK....

George ■