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Thread: Troubleshooting

  1. #1
    George Baker

    George Baker

    Vice President- Corporate Communications

    Assinck Ltd. [eDir]

    Assinck Ltd.

    Professional Experience 39 Years / 9 Month George Baker has 39 Years and 9 Month professional experience

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    Know-How Screening (373) George Baker used this tag 373 times, Manufacturer (110) George Baker used this tag 110 times, Conveying (28) George Baker used this tag 28 times

    Troubleshooting

    VIBRATING screen is not passing enough fine material. WHY?

    I had this one again, in the field this week. It was a 7x20 double deck vibrating screen. CIRCLE THROW, TWO BEARING DESIGN, inclined screen at 20 deg standard downhill slope.

    CUSTOMER COMPLAINT: Not handling the tonnage, TOP DECK carrying fines over that should have went through the 3/4" opening. Wanted to make 100% passing 7/8" spec.


    TROUBLESHOOTED & solution: We do process of elimination. We confirm what is right and then decide what is wrong.

    STROKE CHECK DONE: It actually showed as 3/8" size circle. THIS was acceptable by the VSMA rules or guidelines. The speed I tached out at 851RPM.....perfect correlating RPM to stroke as per VSMA and experience. I used a protracter gauge and the angle was 20 degrees.....also a perfect match for speed/stroke/slope charts of VSMA. Ummmmmmmmmm........NOW WHAT?

    The wirecloth was cross verified at 3/4" clear opening with mid range wire diameter .192 range nice and tightly installed.

    We went to the stockpile and measured the biggest piece of stone in the stockpile. Basically, all the stones measured would be approx. 1/2" minus by tape measure. HOW COULD THIS BE??? The spec calls for 100% passing 3/4" -- the cloth opening was 3/4" so what was the problem here???

    FORESHORTENING OF THE OPENING WAS THE PROBLEM. At 20 degree installation angle the material sees a shorter opening than the one installed in the deck. So, it was seeing with a 3/4" clear opg at 20 degrees.......nominal 5/8"-1/2" range give or take.

    SOLUTION: We installed all 15/16" clear openings down the full deck and the remeasurement in the stockpile was basically 100% minus 3/4" clear. The material does not see the nominally bigger opening. The steeper the angle of slope the more this applies.

    ON A FLAT OR HORIZONTAL SCREEN: The material sees the full opening at zero degree flat installation angle. So the above concept does not cross apply.

    HAPPY SCREENING out there folks !!!!

    GEORGE BAKER, MODERATOR

  2. #2
    Krusher Guest
    George,

    Is there something that I am missing here?

    They have a 3/4 screen on the top deck with a 100% passing 7/8 spec? Why would they not configure 1.25" on the top and 7/8 on the bottom?

    Also you didn't mention the depth of material on the bottom deck. What you say in theory is very true, however, with the proper feed rate on a 20 degree incline the opening of 7/8 would seem to be a good choice.

  3. #3
    George Baker

    George Baker

    Vice President- Corporate Communications

    Assinck Ltd. [eDir]

    Assinck Ltd.

    Professional Experience 39 Years / 9 Month George Baker has 39 Years and 9 Month professional experience

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    Answer to KRUSHER

    Hi Krusher: Do you have a first name?

    Your point is well taken and valid. The bed depth is actually a bone of contention here also. For 3/4" - the max bed depth of 4 times the opg at the discharge end of the screen is infact being exceeded (5" deep by actual measurement). This due to high percentage of NEAR SIZE evident in the feed and recirculated load being dropped onto the feed belt to this screen from an impact crusher circuit.

    Of course, if the bed depth is too heavy as you are aware, the stroke can not LIFT the coarse particles up thru the thickness and makes carryover of minus 3/4 more of a problem.

    By putting in the larger opg we reduced
    bed depth and carryover problems.

    Keep Smiling........George

  4. #4
    Krusher Guest
    George,

    Please keep in mind that I am not being argumenative, but wouldn't the correct solution be to adjust the feed rate? Also would you not stand the chance of getting oversize if the feed rate was reduced? I would be afraid of creating another problem by going to an oversize opening.

    I think on an incline of more than 30 degrees a larger opening would have a better chance of working.

    Best, Roger Young

  5. #5
    George Baker

    George Baker

    Vice President- Corporate Communications

    Assinck Ltd. [eDir]

    Assinck Ltd.

    Professional Experience 39 Years / 9 Month George Baker has 39 Years and 9 Month professional experience

    Discussions 883 George Baker acceded to 883 discussions, Articles 0 George Baker wrote 0 articles, Publications 0 George Baker Baker released 0 publications

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    This is a great discussion....

    Hello Roger:

    We are not arguing, we are discussing our respective theories and we want people to THINK.

    We in fact did, reduce feed rate but, to no avail. We actually diverted recirculating load from another screen off this deck.
    So, this did nil to help in reality.

    We did prove, by testing one section of a slightly larger opening that it did in fact help decrease bed depth, increase efficiency and did not put the product OUT OF SPEC in reality.

    30 degrees here, would increase the FTPM (foot travel per minute)by way too much. It would decrease the bed depth yes but, would definitely speed up the travel rate to a point that the screening efficiency would not be at 95% as outlined by VSMA rules.

    Note: if I am scalping a small percent of stones from a large percent of sand......ie a sand scalper (many brands out there). 30 degree or even steeper would work. At this point I AM NOT screening or using screen SIZING efficiency tables....I am scalping and the efficiency rate drops to something in the range of 80 percent efficient.

    I appreciate your imput very much.

    George

  6. #6
    Krusher Guest
    George,

    I understand that, on an incline screen, the rock sees a smaller opening if dropped vertically. However, once the material forms a bed, and is running parallel to the screen deck does it not see the actual opening?

    Best, Roger

  7. #7
    George Baker

    George Baker

    Vice President- Corporate Communications

    Assinck Ltd. [eDir]

    Assinck Ltd.

    Professional Experience 39 Years / 9 Month George Baker has 39 Years and 9 Month professional experience

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    Know-How Screening (373) George Baker used this tag 373 times, Manufacturer (110) George Baker used this tag 110 times, Conveying (28) George Baker used this tag 28 times

    Roger....

    No it does not.


    George

  8. Hi, Georgre.

    Insuffucuent throughput of a vibrating screen is one of many unavoidable deficiencies of all screeners. The core problem is that they all single-frequency past-resonance linear vibratory systems with low accelerations (4-5 g), weak or no impulse, low amplitudes etc., etc. Absence of principal difference between any traditional industrial screener and a hand sifter causes problems. Hence, insuficienct throughput, blinding, low effieincy...

    Using the Ultimate Screener(TM), the only multi-frequency resonance non-linear vibratory system allows for results unseen before. No wonder with acceleration of 800-1000 g, very strong impulses, dynamic boosting, multi-frequency character of excitation etc. Principal differences in vibratory technology cause principal difference in screening/separation/dewatering results. One very obvious result - no blinding of screens (self-cleaning effect).

    With a multi-frequency machine all problems described in your letter would have been non-existent.

    Thnak you.

    Gregory Feldman

  9. Hi, George.

    Insufficient throughput of a vibrating screen is one of many unavoidable deficiencies of all screeners. The core problem is that they all single-frequency past-resonance linear vibratory systems with low accelerations (4-5 g), weak or no impulse, low amplitudes etc., etc. Absence of principal difference between any traditional industrial screener and a hand sifter causes problems. Hence, insufficient throughput, blinding, low efficiency...

    Using the Ultimate Screener(TM), the only multi-frequency resonance non-linear vibratory system allows for results unseen before. No wonder with acceleration of 800-1000 g, very strong impulses, dynamic boosting, multi-frequency character of excitation etc. Principal differences in vibratory technology cause principal difference in screening/separation/dewatering results. One very obvious result - no blinding of screens (self-cleaning effect).

    With a multi-frequency machine all problems described in your letter would have been non-existent.

    Thank you.

    Gregory Feldman

  10. #10
    George Baker

    George Baker

    Vice President- Corporate Communications

    Assinck Ltd. [eDir]

    Assinck Ltd.

    Professional Experience 39 Years / 9 Month George Baker has 39 Years and 9 Month professional experience

    Discussions 883 George Baker acceded to 883 discussions, Articles 0 George Baker wrote 0 articles, Publications 0 George Baker Baker released 0 publications

    Searching nothing specified

    Know-How Screening (373) George Baker used this tag 373 times, Manufacturer (110) George Baker used this tag 110 times, Conveying (28) George Baker used this tag 28 times

    Hi Gregory.......

    Very Interesting reading: When you say ALL problems discussed would be NON existent. I have a problem with this statement.
    It sounds very BLACK and white. Definitive.

    Of course, screening and screening efficiency is anything but black and white due to constant variable factors of many different influences.

    I also sell what is called a NON-blinding screener. The body actually runs at an accelerating force of 2 G's but, the deck itself runs independantly at 50 YES FIFTY...G'S and it is sold as NON BLINDING. Guess what..........I have done many demos in the field with a portable unit and it is non blinding. EXCEPT, at the times that it actually does blind.......oops. It is non blinding compared to most circle throw inclined applications but, it is not the panacea of screenig....it in fact does blind under certain conditons also.

    Most typical inclined screeners run at 3.5 to 3.8 G's in actual fact and if it is a horizontal screen which is all driven by motor vs with the help of gravity......these units typically run at 5-6 G's .

    I am very interested in further discussing your ULTIMATE screener technology. If you could send me by mail, catalogues for my review, i would be much appreciative.

    BEST REGARDS,

    George Baker - MODERATOR

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