Dear Sir: Thankyou for the fully detailed question on speed stroke slope and inclined vs horizontal screeners and which is best for what.

Of course, this question comes up over the years to me in my travels a thousand times. I answer most people with the words...if I speak to 10 people - 5 will strongly pick horizontal and 5 will strongly pick inclined. Preference and familiarity is a strong motivator and truly no one is wrong.

So lets talk about the actual PROS & CONS for both:

Inclined: PROS

> Very user friendly, flexible, adjustable typically but, not always*

> we have mother nature (gravity) helping us

> 40-50% less capital cost than horizontal ( + - )

> Material size range: Over 8" down to 50mesh ( + -)* this is a

key DIFFERENCE - top size to bottom end range

> Can stomach some abuse

> simple cartridge bearings, shaft design and housings

> Bearings changeouts in reasonable time

> Adjustable stroke with plate weights, adjustable speed with

sheave changes, adjustable inclination with some work

Inclined: CONS

> Foreshortening of the openings at 20 degrees incline and even foreshortened more if steeper inclination. Material does not see the actual opening in the wirecloth, rubber or urethane on a incline. You can and people do install say 15/16" clear to make a spec -7/8" clear product.

> If switching to a 30mm thick RUBBER panel or urethane - the media opening must be thoroughly investigated taking into consideration foreshortening issues that may be amplified using a thicker media and installed on an incline

> Will not fit everywhere - stance is too high to fit in structue or go under a bridge.......must look at expense of a horizontal screen

HORIZONTALS: PROS

> Very popular in their specific niche applications

> Adjustable stroke & speed on most, within the mfr's limits*

> Material on zero degree installation sees the exact opening installed on the deck (No foreshortening occurs). This is a key point for a lot of people

> adjustable incline up to a max of 10 degrees = (more TPH)

> Higher accelerating force than incline 5.5 to 6 G's

> Excellent for dewatering and rinse jobs

> Excellent when using wire, rubber or urethane, side tension styles of flat deck with say 2' x 2' square panels

> FITS IN TIGHT SPOTS. Most useage on portable plants that must go under 14' bridges and or in lowheadroom situation.

> Makes all structures lower in stationary jobs, less steel, less $$

> More efficient Tons

HORIZONTALS: CONS

- Very high capital costs, higher mtce costs THAN inclined

- Bigger motors needed, gears needed, 4 bearings needed

- Mtce repairs if flow thru oil in common housing - mega $$$$ as

we cross contaminate all drive parts

- Mtce downtime longer, more complex, more problems

- Very tight between decks - Non mtce friendly. On a portable

screener - 9" between top and second deck is not unusual

- Less tph than incline.....45FPM foot travel rate vs 75FPM incline

- Limited accelerating stroke, speed range....a lot of these

units are in thee nominal 1/2" stroke length range at 850rpm

range settings.

- MUST be very careful with these units. The designers make

them run somewhat SLOW with NOT MUCH ADJUSTABILITY -

typically conserative....so we do not CRACK out the sideplate

or run below an acceptable L10 bearing life range.

- You know, the screen will last forever with no problems is the

theory.....except it just doesn't screen very well

- People will install faster sheaves to GIVE ER....and this works

great until the bearings or the sideplate break

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Now, the answers to your specific questions:

1. 34mm separation on a Horizontal, straight line @ 7mm 950rpm

Is this stroke and speed OK? Cross related to imperial, you are

nominal 1/4" opg at 950rpm. VSMA charts are imperial.

Answer: NO. Using VSMA charts for speed, stroke, slope. Your

PREFERRED stroke length is 1/2" long@850rpm and

5/8" long@800rpm is also in that range and also listed

as preferred. 3/4"@750rpm is listed as acceptable.

The 34mm separation dictates the stroke, speed.

This also assumes this is the top deck.

2. For such application, is it preferable to go in for an inclined

screen?

Answer: You job falls nicely into the range a HORIZONTAL should be capable of handling, no problem. Your speed stroke is not correct. What could be happening, is carrots or elongates are stuck in holes as you indicate, hammered in by material passing over them....no chance to get out. This now causes a STATIC load, which actually deadens the stroke from extra load and this AMPLIFIES all of your problems even more. Inclined screen would handle peace of cake for a lot less money.

3. What should be the aperture shape (square, round, slotted or other) ? The opening can any of these and or all. Square is normal pic, as we are trying to pass a sieve analysis spec. slotted equals more OPEN AREA equals more TPH thru per hour. ROUND has less sharp corners and at times will do better at resisting jamming in the hole. ELONGATES or carrots once in are nasty to get out and at times impossible - except for manual sledge.

4. Would rubber panels with sq opgs perform better than polyurethane deck for this application?

I would use RUBBER here:

> Number one reason = More open area vs polyurethane

> More suited for impact abuse than poly

> More self relieving than poly on underside

> See more below

RUBBER is excellent on dry, excellent on impact areas and wear, self relieving underside of aperture is normal. Underside is a little bigger than top surface and this allows near size to PASS thru. If pounded from above actually helps to push thru opg. RUBBER panels normally have SOFT INNER MIDDLE layer that BREATHES and give the rubber MEMORY...or slightly expands and contracts to help clear openings.

POLYURETHANE excellent on wet, excellent on slide wear. Not as good on dry and or impact abuse.

Other comments: I see a number of items of possible problem in your description. An 8x20 horizontal, all in itself is a big, heavy monster which will have trouble throwing its own body weight, let alone material on it. These babies are problematic at best.....when we add polyurethane panels to it and the support rail system below it......we are heavier than a normal setup with wirecloth. DID you ever wonder why there are 100 plus companies that mfr inclined screeners and only about 3-5 good mfrs of big horizontals? It is because they are hard to build, harder to keep together and require huge manufacturing expertise.....not just anyone can make these and make them right.

Coke screening @ 55# cu ft.......lots of material but, not much weight or TPH. A lot of VOLUME to pass, which is harder.

NO PROVISION on present unit to change stroke. THIS IS BAD Of course and not preferred - we have zero flexibility to help ourselves here. If we just speed up this may be helpful as long as the factory gives you the OKAY. It would give you more G FORCES OR ACCELERATING forces.........more ACTION!!

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I would like to see, if possible, the FRONT END of this unit raised to 5-6 degrees***, speed up if possible, have some sort of polyurethane skid rail RISERS added to keep the big stuff sliding down and off the deck.......vs letting them go down to the screening surface and JAM in the hole.

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Something else to consider, IT IS sometimes better to go with 2 screens side by side......a little late now probably.....which are a little less wide.........and able to GET THE RPM UP..and be aggressive enough with the material, yet not break the screen.

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Lastly, an inclined unit with RISER RAILS on the RUBBER would be ideally a very good unit, if looking at replacing.

So, for the long wind, but, "Thar she blows......"

Hoping this helps, George Baker ■

handy chart....................george baker

Attachments

speed stroke slope pg4 horizontal charts (ZIP)

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Handy chart FYI.........on inclined screens. GEORGE Baker

Attachments

speed stroke slope pg3 incline screen chart (ZIP)

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Dear Sir,

In reply to your inquiries:

-stroke 7 mm. with speed 950 rpm is correct for polyurethane application

-the application of inclined or horizontal screen in not influent for blinding mesh problem

-I suggest you slotted size (35 x ...) in relation the oblong raw material dim.) along the material flow

-for to reduce the blinding problems the "elastic" polyurethane is better than the rubber panels

In order to understand better your blinding problems could you let me know:

-thickness of the polyurethane holed panel area (not thick. of polyurethane panel)

-dimension of your conical holes 35x35 mm. on the under surface (conical inclination)

-do you use modular interchangeable panels or tensioned panels?

Looking forward to hearing from you

Best regards

A. MARIO ■

Hello: Please see G FACTOR CHART.....for info purposes.

If we troubleshoot back further in the system.....what is the crusher type that is sending elongates to the screener?

If we could theoretically and probably in practice produce cubical material out of the crusher.........then.....the screener ...in this case horizontal 8x20 1 deck.......would not PLUG with elongates or arrowheads. No elongates, no big problem.

Just another concept to consider.

............................

Suggest doing a BED DEPTH check:

- For a 35mmx35mm sq opg.......the VSMA rules recommend not to exceed MAX 4 times the opening at the discharge end of the screener. (4 x 35mm = 140MM DEEP). More than this means your are carrying fines over that should be going through. From this discovery we know we have a problem of some description in the operation of the deck.

Go to 20' end of the deck.......tape measure the depth of material at the discharge lip area to see how you are doing for bed depth.

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VSMA GUIDELINES:

After completing the exercise of calculating theoretical screening area, the experienced screen application specialist will now proceed to devote some time in reviewing some of the variables that govern screening performaance but cannot be included in a mathematical formula. These variable can contribute to a more favourable or UNFAVOURABLE screening condition. It is the presence of unfavourable conditions that requires attention after calculated screen area is established. Another words: after getting a pick of say `120 sq feet needed to screen X TONNAGE - DO the next step and apply KNOWLEDGE or the ART to the math.

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Some examples: Moisture can effect a separation as it presents problems with BLINDING of the screen surface. The mfr may have an accessory to help here....ball decks, special non blinding wirecloth or other. THINK outside the box.

PECULIAR PARTICLE SHAPES, such as wedges, slivers, elongates, flats......are often difficult to separate. This can have an ADVERSE effect on screen capacity and efficiences. YOUR PROBLEM.

NEARSIZE: if the feed to the deck contains a large amount of nearsize, there is also the DANGER OF PLUGGING. The screen surface specification become very IMPORTANT in making an efficient separation when this condition exists.

CHECK FOR FEED GRADATION ANALYSIS......for above.

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THE VSMA screen size calculations deal wtih a mathematical formula BUT...................there are several factors unaccounted for in this formula. It is IMPOSSIBLE and IMPRACTICAL to assign a numerical value to all of the uncontrollable variables related to the SEPARATION OF MATERIALS. After the calculations by math, now an EXPERIENCED operator knowledge and common sense MUST BE APPLIED to finalize the screen size, speed, stroke, slope PICK. That is why it is very important that the VSMA formula be considered as only a GUIDE.

Regards, George Baker ■

if you check.........the HORIZONTAL speed stroke slope chart...you will see recommended operating parameters.

see G FORCE chart for your actual operating range at 7mm 950 rpm.

Using the G FORCE chart from our field travels........

7mm (.280") nominal 1/4" stroke length,at 950 rpm...using the chart shows you are running at 3.2 G's.

THAT STROKE if original........is A PROBLEM. 1/4" long stroke length measured with a ruler on a STICK ON stroke check card is ZIP ALL....it should normally be minimal 1/2" long 850 rpm RANGE to make the horizontal screen do anything.

1/2" @ 850 is 5.1 G FORCES......more action in other words.

Your present setup: I would do a stroke check with all rocks out of the holes...........and then, one with elongates stuck in holes.

You may have decreased OPERATING G's because of extra static weight......sticking in the holes.......which would decrease the stroke length or deaden it........and make the machine even more inefficient.

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There is some great possiblity to go to plan B.. If you are controlling your topsize abusive material to the deck and screen at1/4" opening.......YOU.......in a new setup would probably be better to setup as a tertiary screening SETUP.

If we keep the loads down.......we can separate finer materials, on faster machines.......with smaller strokes......BUT, at more G FACTORS.....to put some real STING or accelerating force into the deck and hence the material processing. If the vibrating screen is lighter weight,...........the rules allow me to run faster......and put a smaller stroke but, at a much higher speed and NOT break the machine. When we can run at say........1200, 1800, 2400 RPM....now my probability to pass a given opening.....multiples substantially........MY success rate theoretically to pass an opg goes up many times.

...............

More food for thought......George Baker - Moderator

Attachments

shortcut to g force chart 2 (ZIP)

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Just for your information, our company has patented a new coke dewatering process that does not use typical screens and does not plug. If you would like more information, please contact our technical director, Oscar Mathis, at 815-444-3516 or via email at omathis@generalkinematics.com.

Thank you,

Thomas Musschoot

General Kinematics ■