Apertures Selection
Sorry, I was kinda out of the loop for about 3 weeks....but, back now.
The use of long slots leads to coarse passing when it should go over.....of course the slots open up and this problem results.
Go to all square but, PEGGING occurs and OPEN AREA decreases.
Maybe try the use of a BALLTRAY deck on a high open area STAINLESS wirecloth at a lower angle of inclination and make sure you are spreading your material the full width of the screen box to ensure you use EVERY BIT of open area.
You could use a nice slotted or square urethane as an alternate also.
One other thing.........your opening that you are trying to CUT AT could very well be affected by the steep ness of the angle of the deck. For example on the 26 deg slope section....if you have a specific opening that you want to pass at.....you should at least TEST a slightly BIGGER opening to get what you actually want.
You see, at a steep angle....MR. MATERIAL DOES NOT ACTUALLY see the FULL opening you installed.....(it sees a FORESHORTEND OPENING OR SMALLER than you want too pass at) So you actually become INEFFICIENT.
Conversely, if i put a specific opg in a flat or horizontal screen, when MR MATERIAL comes up to the opening and decides to try and pass thru that opening.....IT ACTUALLY SEES A FULL OPENING that is in the screening media (rubber, wire or urethane).
So, in conclusion the steeper the angle the more importance it is to every so slightly increase the OPENING in the deck to make the actual opening you really want to PASS.
A slippery slope..........
I will run the numbers and try to give you the VSMA Formula answer to this setup. ■
Re: Aperture Selection
Dear Mr.Baker,
We are already using a urethane deck.
Using a square aperture seems to be the only recourse open to us.Since going for a slotted aperture with long slot along flow will invariably result in overs going as unders I have been thinking of using the long side of the slot across the flow to take advantage of higher % o/a and at the same time limit the overs in unders.Now the problem is what should be the slot length across the flow.Since the width of the aperture is unaffected by the inclination of the m/c,I think selecting the long slot too big even across the flow will lead to some contamination in unders.what do you think of this.I don't wish to force your hands but a nod from you will bolster my confidence.
Regards
A.K.Srivastava
e-mail-aksri@tegaindustries.com ■
Slots Crosswise Or Slots Lengthwise, "That Is The Question"....…
Well.......I am using some interesting WIRECLOTH for the last 6 months which has proven to be very very PRODUCTIVE and has kept our sand products (-6mm) on spec.
So, on this particular screenbox, the longitudinal support rails are basically 15" centre to centre spacing. These rails of course would have the rubber cap material friction fitted on to them.
We ordered and installed custom ordered WIRECLOTH with the slots to be 15" cross slots which did 2 things: greatly increases the OPEN AREA at 15" slots, and lands the interwoven cross wires at the 15" centres (so they are SUPPORTED on the rubber capped rails) and the cross wires are actually then URETHANE CAPPED for strength and integrity of the manufacture.
We get a nice long slot, a strong built screencloth and a nice tight stretch on the side tension and it produces like crazy in our instance. Note: We actually tried a LONG SLOT lengthwise before this cross slot and it PRODUCED zipall for TPH....terrible performance TONNAGE wise and quality of mfr wise.
Now, just for fun we had a ball tray deck setup on this opening and it helped keep the LONG SLOTS UNPLUGGED and clear. We also had an aggressive stroke on this setup (5/8" circle at 12 degrees) all which contradic VSMA but, it works and works well.
By the way, standard wovenwire cross slot lengths from a long time woven wire cloth manufacturing outfit like WS TYLER COMPANY would typically be 3-4" cross slot for their TYROD wirecloth. ■
Aperture Selection
For a Vibrating Screen of Size 1550*6250mm the followings are the feed analysis.The material handled is Limestone with a Bulk Density of 1.6t/m3.
The product requirement is 3mm.
Feed Analysis
+30=0%
-30+20 =1.04%
-20+10 =14.13%
-10+8 =3.48%
-8+6 =9.69%
-6+4 =34.24%
-4+3 =6.58%
-3+2 =7.10%
-2 =23.74%
The feed TPH is 120 although the Screen is presently run at 50 TPH.
Stroke-8-10 at long axis
3-5 at short axis
RPM-800
Inclination-26/18/10 degrees
The Screen was supplied with an aperture of 4*17mm with 17 mm along the flow.The deck was of Cross tension design and the material of the deck was Rubber with a % open area of approx.0f 25..
With the above we find that practically 30% overs is reporting as unders.Presently we are in the process of reselecting the aperture size.
We had a similar problem in a major steel plant in India where we overcame the problem with 6.5mm aperture in one third of the screen and the balance with 4.5mm.The apertures were square and the material of construction of the panel was Polyurethane.
We have been trying to select the aperture size but based on the feedback where 30% overs has reported as unders we have the following constraints.
The feed analysis being what it is,the feed fraction is a whopping 41% between 3 and 6mm and 44% between 4 and 8 mm.There is a large mass of material which is of marginal size.So selecting an aperture which is slotted will present a recurrence of undesirable overs in unders and selecting a square aperture may lead to clogging considering the marginals.
Will a combination of 4*8mm aperture where 8mm is across the flow and 4mm square aperture yield better result.
Can anybody help quickly.I have the moderator of this forum in mind.
Regards
A.K.Srivastava
e-mail-aksri@tegaindustries.com
www.tegaindustries.com ■