Comments On Speed, Stroke, Slope
for those openings:
68mm (nominal 2 5/8") TOP DK over 28mm (1.1" nominal) that is fairly easy basic middling screening cuts. Should not be a problem, IF THE SCREEN is in fact setup correctly.
If that was my machine: I would be installed at 20 degree angle, 3/8" CIRCLE THROW STROKE at a speed of 860 RPM. And that would screen all day long.
EFFICIENTLY.
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NEAR SIZE: If the sieve analysis of the INFEED shows lots of near size close to 68mm size.....then, change the wirecloth opg to something TIGHTER....but, i am dubious that is the problem described here.
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is it standard weave, WOVEN WIRECLOTH? if so.......consider using flat top weave or smooth top weave wirecloth as alternate.
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ensure the wire diameter of the top deck is NOT TOO HEAVY OR THICK....could be causing material to stall in holes...you want about 57-63% open area
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A PIC WOULD TELL ME A PILE OF INFORMATION VERY QUICKLY for comment.
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if you are trying to do 150 TPH on a 5x20 or (100 sq feet) of available screening area.......TIMES TWO.....for two decks......you GOT MILES OF SCREEN THERE TO DO THE JOB EASILY AND EFFICIENTLY.
ACTIONS: Please let me know:
TACHED SPEED OF BOX, INCLINE OF DECK. AND STROKE CHECK SIZE. ■
Couple More Pointers
1. Please advise TOP SIZE of feed to screen
2. Please advise mtl BED DEPTH at the discharge end (20') point in inches
3. your drive belts could be loose....
4. your screen SHEAVE OR MOTOR SHEAVE could be worn, if an old screen or
the combo could just be wrong vs what it was setup and sold for originally and
that is highly likely.
5. YOU must ensure the material comes onto the first foot of the TOP DECK FULLY SPREAD ACROSS THE FULL WIDTH OF THE SCREEN or yours fines will carryover the top deck ontop of the HEAVY BED DEPTH of material that is not spread.
GOOD LUCK. ■
Re: Screening Problems
George,
thanks for your informative post and you hit the nail on the head so to speak with point 3 in your second post.
The problem was after running for a number of hours the drive belts stretched some what, resulting in an untrue power performance.
Screen is working fine since we altered this. I run screen at 20 degrees with a circle throw not sure of size though and shaft speed of 900 rpms. What do you think this screen is capable of doing on the feed size described?
Thanks for your help again i was under a little pressure tyring to figure out a solution.
Cheers,
trevor ■
Tonnage Rates Nominal
Using the VSMA (FACTOR A) charts: YOUR SCREEN IS: 5' WIDE X 20' long 2 deck
2 1/2" OPG TOP DECK: 5.52 STPH passing per each SQUARE FOOT
1.1" OPG 2nd DECK: 3.56 STPH passing per each SQUARE FOOT
WHICH of course assumes: basic operating conditions:
feed to screening deck contains 25% oversize and 40% halfsize
feed is granular free flowing material
material weighs 100lbs per cubic ft
Operating slope if inclined design is 18-20 degrees with downhill flow rotation
Objective screening efficiency of 95%
(as quoted by VSMA RULES)
From my practical field experience, i also concur with these assumptive values.
Hoping this helps. Wishing you happy tonnage rates. ■
Loose Belts
Thankyou for that feedback, i always like to know what it actually was that fixed the problem.
With vibrating screens, there are many many variables to consider to fix a problem. ■
Re: Screening Problems
George,
No problem i know, the variables are vast, and thankfully i hadnt gone into to much detail before checking one of the most basic causes of screen problems.
Thanks for your help.
trev ■
Important Troubleshooting Rule Of Thumb
My teacher (Mr Frank Hawley) 50 yrs experience of WS TYLER CANADA fame, taught me this:
"CHANGE ONE THING ONLY at a time"
Lots of people, in there haste to fix, change speed RPM, add wgts, subtract wgts TO increase/decrease stroke, change wirecloth, etc etc all at once....and when it works, you DID NOT know which thing made the difference.
This rule is a superb RULE OF thumb for all.
Frankie knew stuff.....god bless him. ■
Screening Problems
hi all,
ok i ve just comissioned a new secondary crushing plant crushing 10 inch down to inch crushed limstone down to 4inch down.
this material is then run over a 20 * 5 goodwin vitrex double deck screen fitted with 68mm top deck wire mesh screens and 28mm bottom deck wire mesh screens.
both are square openings.
problem i seem to be having is that the material seems to be clogging excessively on the top deck. it looks as if the screen hasnt the power to "throw" or tumble the material enough to stop it from sitting in the appetures. im not sure if its becuase the material has a large percentage of approx 68mm pieces in it or is the screen angle not steep enough.
if screen angle was steeper would this effect seperation performance?
i know that the material could be spreed prior to discharge onto the screen also.
this is quite an old screen and was bought second hand so maybe something wrong mechanically with it? resonance maybe?
i think the screen is not being overloaded as it is only recieving approx 150tph which i feel is well within its capacity.
Also the bottom deck seems to be working fine.
you help would be greatly appreciated here as this plant was commissioned in order to increase throughput being achieved by a smaller mobile arrangment and at this early stage its not performing near whats exspected.
thanks in advance.
trev. ■