Extruders - A Special Supplement from Rubber & Tyre Machinery World

| EXTRUDERS |
Here are 6 other key criteria of a gearbox
evaluation, which you should know
1. Gear Design, Hardness and its
Construction
Each of the individual gears that go into
your gearbox assembly are rated for power
or torque based on their strength and
durability ratings. The calculations would
be according to industry standard AGMA
rating systems. Factors include the gear
tooth pitch, center distance, material and
hardness.
2. Gear Shafts
The shafts must be designed to transmit the
full power and torque capacity of the gears.
The length and diameter of these shafts is
decisive and must match the ability to
transmit this torque without excessive
deflection, fatigue and failure. The diameter
of the input shaft must be adequate to
properly support sheaves (in the case of belt
driven models) or a coupling. The output
shafts must be properly designed to handle
the correct range of screw shanks that will
be inserted. Adequate access to the drive
keys is beneficial when they become worn
or damaged and need to be replaced.
3. Radial Bearings and Seals
The radial bearings support the rotational
forces of the gear shafts and must be
designed to handle the load forces and
speeds effectively. The dynamic load
capacity of these radial bearings must also
be considered when evaluating the design
and durability of the gearbox. Radial
bearings must also be properly lubricated
and sealed.
4. Gearbox Housing Design - Construction
Cast Iron is the cost-effective material of
choice for most manufacturers.
Traditionally, CI gearboxes are made in two
pieces, split either horizontally or vertically.
Newer designs have the gearbox housing
cast as one piece to reduce any potential
leakages.
5. Thrust Bearing
Thrust bearing isolates the backward forces
from the screw. The larger the screw and/or
the higher the back pressure, the greater
the backward thrust forces. There are three
basic types of thrust bearings – cylindrical,
spherical and tapered.
6. Serviceability
When you select a gearbox, you should give
prime importance to the availability to
affordable parts and service. It is best to
select rubber extruder suppliers who
purchase their gearboxes from proven and
reputable manufacturers that specialize
only in gearboxes for better serviceability.
An old gearbox manufactured around
through-hardened process and shaved gears
technology has shafts, bearings and
housings designed accordingly. Replacing
new hardened gears with a higher HP
capacity, does not automatically guarantee
the gearbox rating to increase, if you do not
replace the assembly with stronger shafts,
bearings and housing.
Gear manufacturing technology today has
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Rubber & Tyre Machinery World | FEB 2016