1. P ERFORMANCE A NALYSIS OF V IBRATORY S CREENS AT SCREENING PLANT, DIOM By: S HASHANK J AIN Asst. Manager (Mech.) Screening Plant, DIOM NMDC Limited

2. I NTRODUCTION Mechanical screening, is the practice of separating ore into multiple grades by particle size. Physical principles Vibration: Sinusoidal or Gyratory GravityDensity Electrostatic Force Sizing or Classifying ScalpingGradingDewatering De-sliming or de- dusting Trash removal Objectives of Screening:

3. D IFFERENT T YPES OF S CREENS Vibrating screen: Inclined Vibrating Screens: Horizontal Grizzly screen Resonance screen Dewatering screen Banana screen Modular screen Mogensen sizers High frequency screen Trommel

4. S CREENING P LANT, DIOM At S/Plant, all the screens are Vibratory Screens. Level No. of Screens Make/ Name TypeSpecification Lubrication Type Primary04 TRF (Vibropulse) Inclined Vibratory Double Deck with rubber panel Oil Lubricated Secondary 03 TRF (Vibropulse) Inclined Vibratory Double Deck with PU panels Oil Lubricated 01 TRF (Truflo) Horizontal Vibratory Double Deck with T/D wire mesh & B/D PU panels Oil Lubricated Tertiary02 TRF (Vibropulse) Inclined Vibratory Double Deck with wire mesh One Grease lubricated, other is Oil Dewatering04TRF Horizontal Vibratory Single Deck with Wedge wire panels. Oil Lubricated

5. S CREEN M OTION & M ECHANISM ’ S A single shaft two bearing mechanism is widely used to produce a circular motion. Gravity being relied upon to effect the rate of travel Inclination vary from 16° to 20° Typical shaft speed is in the range of 650 -1100 RPM with 5/8”- 1/8” stroke. Gforce in range of 3.5 to 4.5 G’s. High travel rate (100 - 125 FPM). Moderate to good screening The Vibrating Inclined Screen

6. Conveyor Discharge Chute Screen S CREEN M OTION & M ECHANISM

7. S CREEN M OTION & M ECHANISM ’ S The motion of the horizontal screen can be straight line (linear) or elliptical. Typical shaft speed is in the range of 600-1100 RPM with 7/8”- 3/8” stroke. Gforce in the range of 4.5 to 5.5 G’s on two shaft mechanisms Low travel rate (40 to 60 FPM). Stroke angle from 30° to 60° Lighter than other screens High Screening Efficiency The Vibrating Horizontal Screen

8. S CREEN A PPLICATION Factors Which Effect Screening Tons per hour per square foot Oversize factor Half size factor Bulk Density Aperture shape Particle shape Screen open area Surface moisture Screen feed arrangement

9. S CREEN A PPLICATION Factors Affecting the Screen Performance Particle Size Feed Rate Screen Angle Particle Shape Open Area Vibration Moisture

10. T HE P RINCIPLE OF O PERATION Stratification & Separation

11. T HE P RINCIPLE OF O PERATION Material Bed Depth Bed depth is a measure of load on the screen. The bed depth at the discharge lip of the screen should be no more than 4 times the cloth opening Bed depth can be calculated as indicated below. Bed Depth = ( O x C ) / (5 x T x W) O = STPH oversize in feed C = Cubic feet per ton of material (use 20 for 100pound per cubic foot) T = Travel rate in FPM W = Width of screen in feet (true screen width)

12. T HE P RINCIPLE OF O PERATION Stroke & Speed The stroke size effects how the feed material starts to stratify. It also effects pegging, blinding and screen capacity. Screen speed and acceleration effects the screen performance. Acceleration effects screen body stress and screen capacity.

13. T HE P RINCIPLE OF O PERATION Bearing Life Decreases as speed increases Decreases as throw increases Speed changes affect bearing life more than throw changes Decreases as counterweight increases

14. S CREENING M EDIA Standard Square Wire Cloth Inexpensive, high open area Economical Easy to Install Available in openings from 10 Mesh to 6”. Rubber Panels Resistance to impact and abrasion Reduce blinding and plugging due to its flexibility Lower noise level. Excellent in dry sizing applications. Polyurethane Panels Excellent wear resistant properties. Very tough and resilient material. Excellent wear characteristics in wet applications.

15. F REQUENT B REAKDOWNS Major Breakdown Bearing failure Oil Seal damage Failure of screen structure. Minor Breakdown Panel/ Wire mesh damage Suspension parts damage V belts worn out

16. T ROUBLESHOOTING Bearing & Oil Seal Failure Contamina tion of Lubricants ? Poor Quality of Bearing/ Oil Seal ? Improper Oil Level? Improper fixing procedure ?

17. T ROUBLESHOOTING Fatigue Failure of Screen Body Oversize feed Material ? Interference with structure or material build –up ? Excessive Feed rate? Corrosion & wear? Field modification which concentrate abnormal stresses?

18. T ROUBLESHOOTING Sl. No. BreakdownCause Remedy 1.Screen structure failure Excessive feed rate Reduce feed rate More no. of lines to be operated Corrosion & Wear Periodically painting Replace wear part Screen Operating out of balance Restore Balance Field ModificationInitial specification to adhere to avoid abnormal stresses Interference with structure. Material build-up Eliminate build-up & interference

19. T ROUBLESHOOTING Sl. No. BreakdownCause Remedy 2.Frequent failure of Screen Bearings & Oil Seal Contamination of Lubricants Automation of Lubrication System Heavy Load in dry Circuit. Feed rate to be reduced Improper fixing procedure Use of proper equipments like jacks etc. for fixing the bearing. Proper Training Poor QualityContact Manufacturer

20. D ATA A NALYSIS PositionTypeMakeTonnage Handled Commissioned A LineVibropulse (Inclined) TRF460658525.01.2009 B LineVibropulse (Inclined) TRF542598814.10.2008 C LineVibropulse (Inclined) TRF453879604.06.2008 D LineVibropulse (Inclined) TRF23732112.04.2012 Status of Primary Screens till date from DOC.

21. D ATA A NALYSIS PositionNo. of Bearing Changed No. of Oil Seal Changed Structure Repair Present Condition A Line060804Needs Repair B Line071003Needs Repair C Line030705Needs Repair D Line*Nil01NilSatisfactory Comparison of Breakdowns for Primary Vibropulse Screens * D Line Primary Screen is a comparatively new screen with DOC 08/04/2012.

22. Comparison of Breakdowns for Primary Vibropulse Screens * D Line Primary Screen is a comparatively new screen with DOC 08/04/2012.

23. D ATA A NALYSIS PositionTypeMakeTonnage Handled Commissioned A LineVibropulse (Inclined) TRF137165814.12.2010 B Line*Vibropulse (Inclined) TRF54678824.08.2011 C LineVibropulse (Inclined) TRF287117522.09.2008 D Line Truflo (Horizontal) TRF232329118.05.2009 Status of Secondary Screens as on date 07.08.12 for DOC. * At B line, a spare overhauled screen was commissioned, instead of a new screen at 04/06/2012.

24. D ATA A NALYSIS Position / Type No. of Bearing Changed No. of Oil Seal Changed Structure Repair (No. of time) B /Down Hours Present Condition A Line (Vibro) 0502 130Needs Repair B Line (Vibro) 0510 276Needs Repair C Line (Vibro) 04 09152Needs Repair D Line (Truflo) Nil 0440Satisfactory Comparison of Secondary Screens from 18.05.2009 to till date. Note: New screens were installed at A & C line on 14/12/10 & 22/09/08 respectively. A spare overhauled screen was installed at B Line on 04/06/2012.

25. Comparison of Breakdowns for Secondary A, B & C Vibropulse Screen with D line Truflo Screen Note: New screens were installed at A & C line on 14/12/10 & 22/09/08 respectively. A spare overhauled screen was installed at B Line on 04/06/2012.

26. Comparison of Breakdowns Hours for Secondary A, B & C Vibropulse Screen with D line Truflo Screen

27. D ATA A NALYSIS PositionType No. of Screens Changed No. of Bearing Changed No. of Structure Repair 205 DVibropulse 04* 10 12 209 DTruflo Nil 04 Comparison of Primary Vibropulse Screen v/s Secondary Truflo Screen from 18.05.2009 to till date. * 01 No. Screen changed dues to frequent bearing failure 03 No. Screens changed due to Bucker Frame damage.

28. Comparison of Vibropulse Screen (205D) with Truflo Screen (209D) installed at same line.

29. T ANGIBLE B ENEFITS SL No ParticularsVibropulse Screens (A) Truflo Screen (B) Cumulative Saving (C = A - B) 1.Replacement of Bearing 4 X @ 50000 = 2,00,000 0 X @ 50000 = Zero 2,00,000 2. 2.Replacement of Oil Seal 7 X @20000 = 1,40,000 0 X @20000 = Zero 1,40,000 3.Structure Repair 5 X @50,000 = 2,50,000 4 X @25,000 = 1,00,000 1,25,000 4.Production Loss186 hrs x 400 ton x 4000 = 29,76,000,00 40 hrs x 400 ton x 4000 = 6,44,00,000 23,32,00,000 Total Saving23,78,50,000 Following is the comparison of the cost incurred for the maintenance of a vibropulse screen to that of a truflo screen.

30. C ONCLUSION AND R ECOMMENDATION “ Performance of the Horizontal Vibratory (Truflo) Screens is better that of Inclined Vibratory Screens ” Conclusion T o change the Secondary level Inclined Vibratory Screens with Horizontal Vibratory screens Recommendation

31. O THER T ANGIBLE B ENEFITS Increase in Production High Screening Efficiency High Feed Rate, since Truflo screens have wire mesh at the top deck. Increase in Screen Availability Reduced Spare Consumption Less Manpower Requirement Less screen stoppage time in Dry Circuit DE-MERIT? The only demerit is less space b/w the two decks of the screen, which hinders the B/D maintenance. This can be avoided, by contacting the manufacturer.

32. Sl NoDate Position of Screen Tonnage handled Running Time Condition 125.01.09 to 12.09.09C - Line1315917 08 monthsNew 229.10.09 to 01.08.11B - Line2033398 10 months Overhauled 305.08.11 to till dateA - Line1257270 12 months Overhauled Total4606585 114.10.08 to 23.02.11C- Line3404396 34 monthsNew 222.06.11 to 04.08.11A - Line22308402 months Overhauled 320.08.11 to till dateB- Line91131612 months Overhauled Total4538796 205 A Primary Screen Sl. No 7835 205 B Primary Screen Sl. No 7764 D ATA A NALYSIS

33. 205 C Primary Screen Sl. No 7568 Sl NoDate Position of Screen Tonnage handled Running Time Condition 104.06.08 to 05.09.08C - Line19166603 Months New 206.09.08 to 18.01.09A - Line737174 04 MonthsOverhauled 319.04.09 to 22.06.11A - Line3340053 02 Months Overhauled 415.07.11 to till dateC - line1157095 13 MonthsOverhauled Total5425988 205 D Primary Screen Sl. No 8600 Sl NoDate Position of Screen Tonnage handled Running Time Condition 112.04.12 to till dateD - Line237321 04 MonthsD - Line D ATA A NALYSIS

34. L IFE OF S CREEN AT ITS DIFFERENT STAGES Month

35. C ONCLUSION Average life a screen comes out to be 35 Months. Average life of the screen overhauled after 03 years is 06 Months only From the results of the analysis, following observations are made: To replace the screen after 03 years, rather than overhauling. 02 spare screens should be there for both primary & secondary level. Hence it is suggested,

36. SL No ParticularsVibropulse Overhauled Screen (A) Vibropulse New Screen (B) Cumulative Loss (C = A - B) 1.Replacement of Bearing 5 X @ 50,000 = 2,50,000 1 X @ 50,000 = 50,000 2,00,000 2. 2.Replacement of Oil Seal 7 X @20,000 = 1,40,000 1 X @20,000 = 20,000 1,20,000 3.Cost of Bucker Frame 2 X @6,00,000 = 12,00,000 0 X @6,00,000 = Zero 12,00,000 4.Structure Repair 2 X @50,000 = 1,00,000 0 X @50,000 = Zero 1,00,000 Total Loss 16,20,000 W HAT IF SCREEN RUNS IN THE 4 TH YEAR ? Above loss is just because of the cost of spares only, which when clubbed with production loss, turns out to be much more than the cost of a NEW SCREEN.

37. O IL OR G REASE ? Particulars Oil Lubricated Screen Grease Lubricated Screen Frequency of lubrication/ Filling Daily BasisShift Basis Frequency of Bearing Damage HighModerate Frequency of Seal damage HighVery Low Due to high frequency of failure of Oil seal & bearings, Oil lubricated screens are not economical when compared to grease lubricated screens, where stoppage time is more. Hence, it is preferred to switch back to the Grease Lubricated System.

38. DO’ S & DON’T S DO’s Check Screen daily, make it a practice. Regularly check the Oil level. Check for material buildup around the screen body/house keeping Inspect the screening media for looseness, damage, plugging. Maintain optimum feed rate, speed & stroke. When in operation, check the screen noise level. Check the side plates for loose bolts, excessive wear or cracks. Check for loose screen media hold down bolts. Check the screen box support frames for wear and cracks. Check buffer strips for wear. Check for Sufficient clearance between screen and structure. Check Oil & Bearings temperature. Avoid & Check for Oil contamination. Grease labyrinth seals Check the Alignment of the Motor.

39. DON’Ts хFill excessive amount of Lubricant хProcrastinate, attend the breakdowns immediately хBe in a hurry, give proper attention хIgnore change in noise patterns хIgnore the Misalignment хHammer the bearing, labyrinths unnecessarily.

40. T HANK Y OU