SCREENING PROBLEMS; SOLVED Alex Caruana Aggregate Territory Manager
#1: My Screen and structure keep failing!
#1: My Screen and structure keep failing! Identifying the symptom is a good start: -
Breaking cross members, frames, feedboxes, Repeated premature bearing failures, Fastener failures, Cracked side plates, Structural damages.
The next step‌. Measure it! You can only manage what you’ve measured. -
Orbits (rotation), Amplitude (stroke), Speed, Pedestal movement, Critical Frequency.
Orbits & Amplitudes INCLINE SCREENS & 4 BEARING (CIRCULAR MOTION)
Amplitude/Stroke
Orbits & Amplitudes HORIZONTAL SCREENS (ELLIPTICAL MOTION)
Amplitude/Stroke
Orbits & Amplitudes COMBINATION SCREENS
FAST travel rate
Medium travel rate SLOW travel rate
Orbits & Amplitudes LINEAR MOTION SCREENS
Orbits & Amplitudes
Pedestal Supports – Structural Movement Measuring the pedestals’ movement. -
Excess motion in any of the directions will cause lost energy, Excess motion will also cause fatigue failure perpendicular to it, ISO standard for vibrating equipment on a fixed structure is the baseline.
Critical frequency ‘peak’ @ 13Hz / 780 RPM Operation at or near such peaks result in screen body damages
#2: Quality Control vs. Production – a Saga!
Measuring points
+ Belt Sampler (plant running)
Belt Cut (plant stopped), Useful for tonnages & efficiency. Making changes? Make a new pile!
Loader pad
Making QC performance a little easier Save your work! - Screen layouts, - Crusher settings, - Feed parameters, - Specialty materials, - Don’t look for the magic formula again.
Smaller media = smaller degrees of change. - Double crown wire = 2x as adjustable, - Small modules, 1’x1’, 1’x2’ etc allow for very fine tuning - Quicker repairs when failures occur.
QC Peace of Mind Finding the longest wearing screen media smooths out your gradation variances
Wear Trend vs. Out of Spec Wire
Synthetic
Oversize
120 100
1 oversize occurrence vs. 6.
80 Wear
Real example based on 2 sets of wire cloth per year, vs. 1 set of Rubber modules every 36 months.
60 40 20 0 1 2 3 4 5 6 7 8 9 101112131415161718192021222324252627282930313233343536 Months
#3: I need More Tonnes! 1” opening wire 56 holes across, 180 holes down
1” opening rubber 72 holes across 8’, 180 holes down
Step #1: Find out your actual open area in place – simply count the open holes.
Step #2: Apply the correct open area panel blend. Feed zone, under spray and flow path have different requirements. This is possible with most media types.
24% Wear Life
Tonnes/Hr
35%
44%
52%
Hybrid decks are excellent at blending wear and high open area too.
Check your bed depth and feed distribution to raise efficiency.
Underloaded
Overloaded Wear line = bed depth
#4: My Media isn’t Working! Pegging factors: -
Particle shape, Nearsize, Rotation of machine uphill/counterflow, Lacking stroke for the application.
Solutions: -
Self cleaning media opening style, Flexible media material, Adjust rotation downhill/with flow, Adjust stroke upward if appropriate for application and machine.
Blinding: -
Moisture content, Clay content, Rotation of machine uphill/counterflow, Lacking stroke for the application.
Solutions: -
Self cleaning media opening style, Flexible media material, Adjust rotation downhill/with flow, Adjust stroke upward if appropriate for application and machine, Washing.
#5: It’s got Water, now why isn’t it Working?!
Wet Screening can be a lot more efficient,
-
Biggest efficiency increase in finer sizing,
Efficiency with proper Water Application 2.5
Too fine and water just adds turbulence.
2
2
2
1.75 E (x100%)
-
1.75
1.5
1.5 1.3
1.25
1.2
1
1.1
0.5
0 1/32”
1/16”
1/8”
3/16”
5/16” Opening Size
3/8”
1/2”
3/4”
1”
So‌. How much water? Rule of Thumb: 3-5 GPM per TPH (feed to screen)
@
*Pressure gauge should be placed at the actual spray bars or manifold.
Introduce Water BEFORE the screen!
1/3 of water at headbox
2/3 of water at spray bars
Bottom deck of a triple deck screen with no headbox water L
What is happening in there‌
Head Box Creates Slurry
Feed End Passes Half Sized Material
Discharge End Passes Near Sized Material
Slurry Quickly Passes on Feed End
How do I position my spray nozzles? • 45 Degree Angle • Towards Feed End • Create Water Dam
• Increase Retention Time of Material Under Water • Critical for Deeper Bed Depths (4:1) • Biggest Impact on Decks with Higher Fines Content
THANK YOU! Let’s talk further… Alex Caruana Polydeck 519 774 2813