u-SupplierTip-104:C-Masters_old
11/21/08
12:23 PM
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here are two distinct types of blinding: coating and plugging. Coating occurs in applications where undersize particles adhere to the wires and then cement to each
other until the screening surface is partially or completely closed off. This typically happens when you’re screening sticky or moist materials. Plugging occurs when near-sized
particles wedge into the screen aperture, preventing the passage of undersize particles.
If you’re starting a new project and choosing a screener, it’s important to look at the
amount of force the screener generates and the amplitude of its stroke. Some manufacturers produce screeners that have variable stroke depths, which allow the operator to
change frequency and amplitude to increase efficiency in specific applications.
If you’re having issues with blinding on a machine that’s already in use, try the following steps: First, reduce the feedrate to the screening surface. This allows the screener to
work more efficiently. Second, adjust the frequency and stroke amplitude. Your screener
manufacturer’s engineers can suggest specific adjustments based on your application
and requirements. Third, try changing the screen mesh to a slotted or Z-wire mesh. These
meshes allow plugged particles to clear the screen instead of blinding it. The Z-wire actually expands and contracts with the frequency being generated by the screener, allowing particles to pass through or bounce free of the screen apertures. This wire type may or
may not be available, depending on how fine your separation is. In isolated cases, adding
a ball deck, rope deck, or heating unit is a possibility, but these can turn out to be expensive retrofits.
epending on your material and
process, using a finger-style deck
may reduce blinding issues. Also, a highenergy vibratory unit, such as one that
uses the two-mass principle, could increase stroke and material motion. This
will also help alleviate blinding problems.
D
Thomas P. Musschoot,
director of R&D and marketing,
General Kinematics,
815-455-3222
Randall Stoner,
engineering,
SMICO Manufacturing,
800-351-9088
linding problems are particularly
challenging in fines separation applications because a material bed is always
present on the screen deck. The material
bed’s weight adds force that can wedge
near-size and multiple particles into the
screen cloth openings. Measures to combat this situation include:
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• Using mesh cleaning devices, such as
balls or rings. You can increase these devices’ effectiveness by varying the ball’s
size to increase its mass, altering the rubber type to improve rebound, or changing the quantity of balls per pocket of
screen frame. The screener’s motion is
important as well, since it imparts the
force to move the mesh-cleaning balls.
• Changing to a screen with a smaller wire
diameter but the same opening. This
screen type is more flexible, allowing
mesh-cleaning devices to be more effective. The trade-off is a shorter screen
cloth life.
• Switching to a synthetic monofilament
bolting cloth, such as nylon or polyester.
This screen type offers more flexibility
than metal wire screen cloth and consequently, reduced blinding.
• Using ultrasonic technology that applies
vibration directly to the screening mesh.
This injects a secondary high-frequency
low-amplitude vibration to improve mesh
deblinding and screener performance.
A combination of the above may be the
right answer for your specific fines separation application. Consult an application
engineer at your separation equipment
manufacturer to determine if you’re getting the most efficient process performance from your screener.
Steve Schmidt,
senior application engineer,
ROTEX Global,
513-541-1236
Equipment suppliers are a valuable
source of information about equipment and processes. In light of this,
each month we ask suppliers a question of concern to our readers. Answers reflect the suppliers’ general
expertise and don’t promote the suppliers’ equipment. If you have a question you’d like suppliers to answer,
send it to Alicia Tyznik, Associate Editor, Powder and Bulk Engineering,
1155 Northland Drive, St. Paul, MN
55120; fax 651-287-5650
([email protected]).
Copyright, CSC Publishing, Powder and Bulk Engineering
How can I overcome blinding
problems during fines
separation?