Re: Screen Amplitude Whith Multiple Decks
Niff5855
You have to give some informations o the screens - flat or inclined and the rpm is very important as that will tell what g force you are running your screens at.
18mmm amplitude or total stroke ( double the amplitude). 18 mm sounds like stroke to me but even then you have 7.2 g at 850 rpm and that is a big acceleration - normally the screen is designed for 5g.
Regards
Ziggy ■
Screens The Stuff Of Separation
Do you possess operating manuals for these screeners?
Do you have or can you obtain stroke cards to check the screen stoke under load and no load conditions? this has to be done properly!
Are the screen frames square?!!
Have you measured the length of the screen support cables if so equipped?
Who made the bloody things?!!!
What are the drive motor amps/voltage/rpms prior to the driven pullies of the screeners? measure this with a loaded and unloaded screen.
If the drive belts have been changed recently were they changed in matched sets/lots of manufacture ID numbers?
Was a V belt tension guage used to properly tension the belts.
Speculating is fine for the Chicago Mercantile Exchange but screeners are a different matter entirely.
Until you understand what those machines are capable of screening and how much you will not have a knowledge base for any and all decisions regarding anything related to the perfomance of the screeners.
You have not even told us what you are screenning yet!!!!!!!
Do you have a wobble feeder in front of the screeners?
Slowing down the delivery tonnage rate to the screeners will work.
Has any maintenance work been done on the screeners recently?
What are you using for lubrication?
What are the current tonnages delivered to the screeners?
Are you screening wet or dry?
Is the load uniform ACROSS THE TOP SCREEN OF BOTH SCREENERS?
How often do you clean the support area around the screen- screen shaker arm rubbers/build up on the frame/ excess material at the screeener lip, build up on the floor of the screener if any etc.?
You have not mentioned if the screens are blinded at all by build up.
How tight are the drive belts? If they are too tight that will have a dramatic effect on perfomance, and amperage load and , bearing life.
George, john, and Lyn if I missed something I sincerely apologise.
leonZ ■
Re: Screen Amplitude Whith Multiple Decks
Thanks Chaps.
I'm screening dry material on both screens. They're fed by a standard conveyor. the product sizes, feed rates etc are giver in my original post.
The weights of the screens (unloaded) are 13.8Tonnes each.
I've checked that they are square - they are.
The Stroke (sorry, when quoting amplitudes in my post I mean double amplitude - Stroke) spec given on the side of each screen is 8-11mm. We are inside this for both (S1 is at 10mm at 708rpm, S2 11mm at 746rpm - These rpm figures are taken off the side of the screen, I havent started measuring pulleys etc... yet - But I will.).
Actually the screen supplier has gone broke (DOH !) but luckily we have found an engineer from the firm who is giving us advice.
I can work out whether we are running the screens beyond their design limits now, so the advice I'm looking for really is the theoretical stroke and speed that I should be running at for each screen to efficiently screen the products.
So to recap
S1 Top deck is a 30mm - this sends all >30mm to a tertiary crusher off the top
Bottom deck is around 22mm and sends a 31-25mm prodcut off the top.
The feed is 60 - 40mm at 550tph and 30mm down at around 400tph So a total of 900tph - This is at around the max capacity.
S2 (there are 2 of them) has a much reduced feed rate of 250tph (each).
The feed is 25-0mm
Thanks for the help gents. ■
Re: Screen Amplitude Whith Multiple Decks
Niff
S1 at 10mm at 708 rpm it gives you about 2.7 g
S1 at 11mm at 746 rpm - about 3.5 g
Both number s are very low and you can't expect good screening - depends on the duty but I would expect to see more than 4.5 g to get some good results( without getting too much into details).
You have to check what stroke you have in each corner ( if they are even).
You have to increase the acceleration and there are 2 ways of doing it - increase the speed or stroke. Before you play with speed you have to check the location of natural frequencies by performing an impact test.
regards
Ziggy Gregory ■
Screens The Stuff Of Separation Again
Originally posted by niff5855
Thanks Chaps.
I'm screening dry material on both screens. They're fed by a standard conveyor. the product sizes, feed rates etc are giver in my original post.
The weights of the screens (unloaded) are 13.8Tonnes each.
I've checked that they are square - they are.
The Stroke (sorry, when quoting amplitudes in my post I mean double amplitude - Stroke) spec given on the side of each screen is 8-11mm. We are inside this for both (S1 is at 10mm at 708rpm, S2 11mm at 746rpm - These rpm figures are taken off the side of the screen, I havent started measuring pulleys etc... yet - But I will.).
Actually the screen supplier has gone broke (DOH !) but luckily we have found an engineer from the firm who is giving us advice.
I can work out whether we are running the screens beyond their design limits now, so the advice I'm looking for really is the theoretical stroke and speed that I should be running at for each screen to efficiently screen the products.
So to recap
S1 Top deck is a 30mm - this sends all >30mm to a tertiary crusher off the top
Bottom deck is around 22mm and sends a 31-25mm prodcut off the top.
The feed is 60 - 40mm at 550tph and 30mm down at around 400tph So a total of 900tph - This is at around the max capacity.
S2 (there are 2 of them) has a much reduced feed rate of 250tph (each).
The feed is 25-0mm
Thanks for the help gents.
Are you using a 48 inch belt or larger for delivery to the screen?
What are you screening and how big are the screens(length and width of screen fabric decks) and are they horizontal or inclined AGAIN!!!!
If you have a solid plume of material running through the center
of the screens you have to much material contacting the scalping deck. You may be overloading the screener without realizing it. ■
Stroke Chart
Here are VSMA theoreticals......and they are very useable and applicable.
Pls confirm Inclined and angle. Real Important.
I layed your circuit out and I see a number of problems there also. But, could you pls tell us exactly what PROBLEM you are experiencing??? Inefficient, not enough TPH, carryover?
THANKYOU Kindly, George Baker Moderator
Attachments
speed stroke slope pg3 incline screen chart 500 pi (JPG)
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Re: Screen Amplitude Whith Multiple Decks
Once again, thanks for your responses.
The screen is inclined at 20 degrees and the direction of rotation is in line with the direction of material flow.
IzaHarris, The feed is spread fairly evenly across the screen coming off a 1m belt (or could be 1.2m I forget).
The screen decks (which are standard woven wire) are 2400mm o/hx 1250 mm, there are 5 of these per deck.
George, thanks for the chart, thats the one I've been using as a guide.
The problem I'm having is that I know that the S1 screen is close to max capacity and I want to optimise it. Also, I'm sure that the stroke of the S1 screen should be larger than the stroke of the S2 screen as it is handilng larger material. (I understand that the speed will automatically decrease when I increase the stroke-so I'm hoping that will take care of its self). But in reality S2 has a larger stroke than S1, which I know to be wrong in theory. I am nervous of simply increasing the Stroke on S1 for fear of shaking the thing to pieces.
Ziggy, what is the formular for g? I am waiting to hear from the supplier about the max working range with regards to g.
The stroke seems to be equal in all 4 corners of the screens.
The reason I checked the stroke etc.. of these screens in the 1st place is that I have a similar unit which I am about to use temporarily on another plant to screen 0-5mm at a 3mm split. So I was aware that I'd need a high speed and low stroke and out of curiosity decided to check the S1/2 screens. ■
Re: Screen Amplitude Whith Multiple Decks
Niff
Send me an email to
ziggy.gregory@vibfem.com.au
and I will forward a graph with stroke, g and rpm so you do not have to do calcs.
Regards
Ziggy ■
Untitled
Originally posted by niff5855
Once again, thanks for your responses.
The screen is inclined at 20 degrees and the direction of rotation is in line with the direction of material flow.
IzaHarris, The feed is spread fairly evenly across the screen coming off a 1m belt (or could be 1.2m I forget).
The screen decks (which are standard woven wire) are 2400mm o/hx 1250 mm, there are 5 of these per deck.
George, thanks for the chart, thats the one I've been using as a guide.
The problem I'm having is that I know that the S1 screen is close to max capacity and I want to optimise it. Also, I'm sure that the stroke of the S1 screen should be larger than the stroke of the S2 screen as it is handilng larger material. (I understand that the speed will automatically decrease when I increase the stroke-so I'm hoping that will take care of its self). But in reality S2 has a larger stroke than S1, which I know to be wrong in theory. I am nervous of simply increasing the Stroke on S1 for fear of shaking the thing to pieces.
Ziggy, what is the formular for g? I am waiting to hear from the supplier about the max working range with regards to g.
The stroke seems to be equal in all 4 corners of the screens.
The reason I checked the stroke etc.. of these screens in the 1st place is that I have a similar unit which I am about to use temporarily on another plant to screen 0-5mm at a 3mm split. So I was aware that I'd need a high speed and low stroke and out of curiosity decided to check the S1/2 screens.
Ok I will assume that you mean five screens per deck level rather than 5 separate cutting screens per screener- I hope.
Anyway do you want to improve your course screening cut?, is this what you mean by optimizing it?
If you are not happy with the cut of the top screen decks for both screeners slow the feed rate to the top of the screeners with a rock box at the head pulleys of both screeners if you have room. Short of a belt gear box change out or reducing the feed material with a narrower chute you do not have many options short of changing the top screen cloth with a slightly larger cut to reduce the load on the lower 4 screen cloths of the top deck.
Changing the top screen cloth will probably be the least painful if these screens are a common screen design. ■
Re: Screen Amplitude Whith Multiple Decks
Gents,
thank you all for your help and advice.
Just thought I'd give you a bit of feedback.
I've left the main screens alone for the minute, might tinker with them later on.
But on my new 0-5mm screening plant I altered the stroke from 12mm down to 8mm by removing all of the weights from the balancers. I'm sure I could add reduce this further by adding weight to the opposing side to the eccentric but I'll probably leave this for now.(I've fitted the stroke cards with the different diameter circles to all of our screens by the way),
according to the g reference sheet (thanks Ziggy mate) this means I can speed up the screen to around 850rpm to achieve a g of 3.5 (approx). I'm told most screens are manufactured to 4, but seeing as our supplier has gone bust and I cant get any info elsewhere I'll stick to 3.5 to be on the safe side.
I might speed it up, depends on the results of the material trial that I'll run later today or tomorrow.
So thanks again everyone. And what a fantastic forum, I'll be sure to keep my eye on it from now on. ■
Re: Screen Amplitude Whith Multiple Decks
Niff
My suggestion is to run it with current speed - if it's ok - unless you have someone do do an impact test for you. If you change running speed you can get into or too close to the natural frequency. ■
Screen amplitude whith multiple decks
Background:
I have 2 double deck screens. Lets call them S1 and S2.
Feed to S1 is approx 65mm-20mm at 550 tph + recycle (20mm down) at approx 400tph. Total = 950tph.
S1 top deck screens at 30mm to send oversize to a tertiary crusher. (Note - All mesh sizes are approximate)
The bottom deck screens 25-31.5 product with the fallthrough being fed to S2.
S2 top deck is at 15mm with the bottom deck at 4mm. This gives a product of 15-25 off the top deck, 5-15 from the top of the bottom deck and a 0-5 fall through. The feed is 25mm down at a much reduced rate (there are actually 2 S2 screens)
Conventional theory says that for a larger size the amplitude should be larger and the speed slower.
For smaller sizes the amplitude should be smaller but the speed faster.
My Question:
A chart I've gotton my hands on recomends for 25-50mm, around 18mm amplitude at 850rpm.
My S1 screen is running at 10mm ( I dont know the rpm yet)
The chart also says for 25-12.5mm the amplitude should be around 6-8mm at 900 revs.
My S2 screen is running at 11mm.
I would like to alter these amplitudes so that at least the courser material is getting a higher amplitude than the finer stuff. But do these amplitudes on the chart sound reasonable?
Do I need to consider other factors such as screen weight etc....??
Any help gratefully appreciated.
L ■