Vibrating Screen Design Features

Jul 13, 2020

Oil Lubrication
Manufacturers will design grease lubrication systems because it simplifies sealing, making it
the most economical choice. In addition, the grease acts as an additional barrier against
contamination. However, grease is not suitable for all applications due to its inability to
operate at higher speeds.
Oil Lubrication allows the bearing to operate at higher speeds, dissipates heat quicker,
improved control of lubricant quantity, use of a filtration system to remove contaminate and
moisture.
Oil lubrication can be applied by several methods, splash and circulating oil being the most
common. Splash systems are most popular and normally provide adequate lubrication in
most cases. In high speed & load applications where the heat generated cannot be
dissipated by a splash system, circulating systems are used. Circulating oil not only carries
away heat, but also any contaminate that may have entered the bearing. Oil coolers may
also be added for additional heat extraction.
Selection of an oil is based upon the viscosity required to generate the proper film thickness
at the bearing operating temperature. For vibrating mechanisms an ISO 220 grade is
normally used during the spring, summer and fall (Ambient > 50°F), and ISO 150 grade
during winter operation (Ambient < 50°F), Lower grades may be required in extreme cold
conditions.
Huck Bolted Joints
To avoid the stresses created by welding (unless they are stress relieved after welding),

many manufacturers are making all permanent joints of the screen’s body using huck bolts.

Use of huck bolts is a more efficient fastening method than standard nuts and bolts. They
are a pin and collar combo that are permanently clamped together making them ideal in
applications that require vibration resistance fasteners.
Snubbers (Friction Check Assemblies)
Any vibrating frame that is supported by resilient springs has a resonance zone (critical
speed area) at which the frame can jump and lurch very erratically. During start-up and shut
down, the unit must pass through this phase as quickly and as smoothly as possible. For
this, screen manufacturers provide snubbers, also called friction check assemblies. The
snubbers restrict large movements that could damage the vibrating frame and chutes or any
stationary structure members yet do not hamper the normal oscillating motion of the unit. In
addition, it also provides dampening of the excessive vibration from getting it transmitted to

the supporting structure / foundation.

Above figure shows typical construction of two types of snubber assemblies. In case of
assembly with retaining straps, the retaining straps restrict large movements of the unit while
in the case of assembly with the spring-loaded horse-shoe-shaped arm, it comes in contact
with the pin extension to restrict the unit’s movement. However, for proper functioning of the
snubber, the spring-loaded horse-shoe-shaped arm of the snubber assembly should be snug
tightened as per manufacturer’s recommendation.
Adjustable Slope Panels
Many times inclined screens with sectioned support decks that enable the sections to be
arranged in an arc shape (banana screens) are provided with adjustable slope panels at the
feed and discharge ends. To improve the efficiency, these panels can be adjusted as per the
process requirement. Raising the feed end section will increase the velocity of the feed and
thin the depth of bed. Whereas raising the discharge end will decrease the velocity and
increase the depth of bed.
Pivoted Motor Base and Belt Tension
In case of V-belt drive, drive motor may be provided with pivoted motor base to provide
uniform belt tension at all times (to take care of belt’s normal stretch and stretch due to
start/stop bounces).
For more information on pivoted motor base, please view the article “Construction and
Working of Pivoted Motor Bases for Belt Drives” at www.practicalmaintenance.net.
Be careful. Belts that are tensioned too tightly can cause much more serious damage. If
belts are over-tightened, the vibrating frame gets pulled out of square with the support frame.
Operating in this twisted position introduces stresses that can lead to spring failure, metal
fatigue, cracking and broken welds in the vibrating frame.
In addition, the twisting will affect the stroke amplitude, thus affecting material flow and
screening efficiency.
Over-tightened belts put an extra load on the mechanism bearings that is unnecessary and
may damage motors and motor bases. Ideally, the belts should only be tight enough that
they do not slip during start-up.
Dust Enclosure
Vibrating screens are available in partially or fully enclosed models if dust or noise is a
problem, or where regulations require such control.
Air Springs

Air springs provide maximum isolation of vibration for structures supporting vibrating
screens. Their action is like that of a bellows, silently expanding or contracting with variations
of load. These air springs are made of the same rugged nylon cord and high strength rubber
used in tubeless automotive tires. Any convenient air supply can be used for inflation.
Sub-frames (Isolation Frames)

Sub-frames (additional anti-vibration frame) are used to reduce the vibrating force
transmitted to the support structure. They are highly recommended for larger screens. Above
figure shows a vibrating screen with the sub-frame.