ROLLER BODY
SHAFT GRINDING OPERATION
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TOPICS
Design Advantages Of Lorbrand Steel Idler Rollers
Lorbrand is able to offer robust steel rollers for CEMA B to CEMA F Load ratings.
The success of the Lorbrand roller is due to the sealing system, method of construction
and accuracy of manufacture.
1. Sealing System
There are many sealing systems in use in conveyor idlers. Most are variations of
the grease filled labyrinth type and others have contact seals. These seals have
a higher friction than non-contact/non-grease filled seals such as the Lorbrand
centrifugal seal. Lower friction means lower electricity costs and cheaper belting
in the case of long overland belts. Lorbrand seals have in fact, zero friction,
and the only contributor to rotating friction is bearing friction which is hugely
advantageous because actual running friction under actual load, speed and ambient
temperature conditions can be calculated accurately from readily available bearing
manufacturer data.
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GREASE FILLED LABYRINTH SEAL |
CONTACT SEAL
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LORBRAND FRICTIONLESS CENTRIFUGAL SEAL
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SEAL FRICTION |
Unknown seal friction. Value is dependent on temperature and rpm and may also increase
with time as seals clog due to grit penetrating the seal grease. |
High and unknown seal friction. Value is dependent on temperature and rpm and may
also decrease with time as contact seal wears out. |
Frictionless seals. |
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TOTAL FRICTION
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Unknown friction. Value is dependent on temperature and rpm and may also increase
with time as seals clog due to grit penetrating the seal grease. |
High and unknown friction. Value is dependent on temperature and rpm and may also
decrease with time as contact seal wears out. |
Low friction, values can be calculated using bearing manufacturer data base or interactive
websites. |
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SEALING EFFICIENCY
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Good until seals clog and collapse. |
Good until contact seal wears out. |
Good. Seals are self cleaning. |
2. Method of Construction
The structural parts of an idler roller are essentially the roller body (can), the
shaft, the bearings and the locking/securing elements.
2.1 Rollerbody
The roller body is the rotating part of the idler and it must accurately rotate
about the bearings whilst supporting the belt load. A roller body is usually composed
of 2 bearing housings which are affixed by various methods to each end of a machined
or cut steel tube. The two most popular methods of affixing these bearing housings
are welding steel housings or press fitting either plastic or cast iron housings
in place. Lorbrand steel rollers have pressed steel housings which are accurately
MIG welded into place to form a strong single structural element that cannot disintegrate
or deform.
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HOUSING TYPE
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PRESS FIT PLASTIC HOUSING
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PRESS FIT CAST IRON HOUSING
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LORBRAND WELDED STEEL HOUSING
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LOAD CAPABILITY
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Light to moderate loads only. Housings will deflect under high load conditions.
Overheating of the housing may occur because the insulating nature of plastic limits
cooling of the bearings. |
Light to high loads. Housings may drift out if axial load limits are exceeded or
there is excess vibration such as from material build-up on the roller. |
Light to high loads. Welded steel housings form a single structural element with
the shell. |
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STRENGTH / ROBUSTNESS
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Poor. Housings may drift out. |
Average. Housings may drift out. |
Good. Welded steel housings form a single structural element with the shell. |
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DIMENSIONAL ACCURACY
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Average for light loads. |
Good. |
Good. Lorbrand’s proprietory design and manufacturing process ensures that there
is no misalignment at the bearing seat due to weld deformation. |
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ROLLER LIFE DUE TO HOUSING
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Average, if heating effects are low and housings do not drift out. |
High, if housings do not drift out. |
High. |
2.2 Idler Shaft
The idler shaft is the stationary part of the idler and must adequately and accurately
support the bearings in place. The idler shaft is typically slotted at each end
for fitting into an idler support frame. Of critical importance is the accuracy
of alignment of each bearing inner (stationary) ring relative to each other. The
greater the degree of this misalignment, either due to load or due to inaccurate
manufacture, the shorter the bearing life. Shaft diameters between bearings may
in some cases need to be increased in order to limit shaft deflection due to load.
The accuracy and quality of the shaft bearing seals also affects bearing life. If
the shaft/bearing interference is too large, the bearing internal clearances are
reduced, and affect the bearings ability to accommodate misalignment. This reduces
bearing life. If there is too much clearance, fretting type failures will occur.
Bearing shaft seats are typically machined or ground or bright “drawn to tolerance”
shaft stock is used. The best shafts are those with machined or ground concentric
bearing seats. Bright bearing size drawn shafts need to be controlled in terms of
straightness tolerance, especially on longer rollers, because there is no rectifying
machining or grinding operation.
SHAFT GRINDING OPERATION
There have, over the years, been many shaft design developments by various manufacturers
in order to cut the costs of manufacture and to increase profitability. These developments
have all resulted in poor quality shafts in terms of accuracy and strength. Some
typical designs are shown below.
Lorbrand uses drawn and machined shafts to increase manufacturing accuracy, minimise
bearing misalignment and maximise roll life.
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SHAFT TYPE
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TYPE 1 - PEENED SHAFT
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TYPE 2 - WELDED SHAFT
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TYPE 3 - MULTIPLE PIECE SHAFT
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TYPE 4 - LORBRAND DRAWN SHAFT
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TYPE 5 - LORBRAND MACHINED / GROUND SHAFT
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LOAD CAPABILITY
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Light to medium loads. Roller will fail if axial load limits are exceeded or there
is excess vibration such as from material build - up on the roller. |
Light to high loads. |
Light loads only due to shaft end deflections. |
Light to high loads. Load capability may be limited by shaft deflection misalignment. |
Light to high loads. |
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STRENGTH / ROBUSTNESS
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Poor. There is a high probability of raised burrs flaking off and causing roller
to fail. |
Good. |
Poor. |
Good. |
Good. |
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DIMENSIONAL ACCURACY
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Depends on shaft preparation. |
Poor. Weld heat creates distortions causing severe bearing misalignment and an increase
in running friction. |
Poor, due to inaccurate assembly causing severe bearing misalignment and an increase
in running friction. |
Average. Shaft straightness and tolerance depends on the drawing operation. Drawn
shaft is acceptable for shorter, light to medium duty rollers |
Good. Machining / grinding operation rectifies any inaccuracies in the bar stock
and greatly reduces running friction. |
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ROLLER LIFE DUE TO SHAFT
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Low. There is a high probability of raised burrs flaking off and causing roller
to fail. |
Low, due to reduced bearing life which in turn is due to bearing misalignment. |
Low, due to reduced bearing life which in turn is due to bearing misalignment |
Average to high. |
High. |
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