Sandeep: You have just explained the complete theory of evolution in your question.....on vibrating screen sizing.

IT aint easy.........yes their is math.....but, even more so ...there is EXPERIENCE or the ART of screening..knowledge that allows you to SEMI confidentlly alter the setup due to known variables discovered in the designing process.

BE ASSURED.....sizing is simply NOT BLACK AND WHITE answers....it is multi shades of GRAY.

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IF you follow the assumptive guidelines of VSMA.....it will actually keep you pretty DOWN THE MIDDLE.......for sizing......and it will normally size the screen with "safety factor" BIGGER vs UNDERSIZE.

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You will have noted, VSMA.....asks the wgt of mtl.....VSMA allows for this.....IN FACTOR F....and will change the plug in mathematical number to assimulate the weight of COAL.

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So, first we do the calculation for sizing.....with all variables as per the VSMA formula, then before picking a size of screen, we now check BED DEPTH..to see if we are still okay at the same size. BASICALLY, if BEDDEPTH is too deep.....meaning the efficiency will not be at the plug in VSMA rate of 95 EFF as per the rules......the screen must get longer......to become more efficient by adding retention time to BETTER SCREEN.

George ■

Hi Sandeep:

The relationship is:

SPEED: if speed ........too slow.......like 1 RPM vs 850 RPM

material would BUILD UP, foot travel of mtl would be too slow, causing bed depth to INCREASE very deep........which causes the screen to BOG down......and NOT SCREEN EFFICIENTLY.

STROKE: if you stroke too aggressively....the relationship of the stroke to the material is this. THE material stays way too high in air, and never gets down to try to pass the hole opening and thus we carry fines over and we are INEFFICIENT.

If you watch, and I have hundreds of times.......a unit with too large or aggressive stroke. With your eyes at discharge end level, you can clearly see fines..STRATIFIED....up in the air.....and before it can pass......the stroke throws it back up into the air....and it never passes.

BASICALLY: if big stroke....used.......slow RPM should be used. EXAMPLE: COARSE SCREENING...1" opg in wirecloth......inclined setup would be 3/8" circle size stroke at 850 RPM

if small stroke used......faster rpm should be used. EXAMPLE FINE SCREENING....3/8" minus.....at 1/4" circle at 1050 RPM

(So.....what are we doing.......we are throwing the material up in the air NOT AS HIGH, and introducing it to the opening in the wirecloth....1050 times per minute down full length of deck) ■

Hello Sandeep: This theory of screening.....takes some time to absorb and fully understand. After 29 years, I am starting to slightly understand now.

So...... FOOT TRAVEL RATE

horizontal screen: Assuming it is installed a zero degree flat..... the foot travel rate for a straight line 45 deg timed stroke angle....is 45 FPM (FOOT PER MINUTE) down the length of the screen. NO matter how long it is. There is NO gravity to help it go faster, so must all be STROKED by mechanical means - ie: by mechanically driving 2 offset shafts (achieving a 1/2" long stroke length) by Mechanically driving with ELECTRIC MOTORS.

PS: the rules for horizontal screens, is they can also be installed up to and including 10 degree slope downhill. This would increase tonnage and increase FOOT TRAVEL. Most are in fact installed at zero degree flat. FOOT TRAVEL factor in VSMA is 45.

INCLINED screen: Assuming 20 degrees equals 75 FPM. DUE to the help of mother nature....GRAVITY. FOOT travel rate increases.

VSMA allows for this factor....20 being the norm for the formula.

Some inclines go up to 45 deg slope....on port plants.

The VSMA forumula takes slope into the sizing calculation and adjusts size of screen and tph accordingly.

George ■