Herringbone Gears
Herringbone
gears are said to be a type of Double helical Gears in fact they are in
essence a two side-by-side, opposite-hand held helical gears. As the tooth
angles of the herringbone gear are reversed on the opposite side, this
results into counterbalance of the thrusts produced by the left hand or
right hand sides. The two sets of teeth is separated at the center by a thin
gap for a proper alignment. The teeth on the mirrored halves of the gear
looks like an arrow head or a "V"
A perfect herringbone contains a helix angle of 30° helix, a 20°
transverse pressure angle. They may or may not contain a center groove
between the left and right hands. These gear generally functions on
non-intersecting parallel shafts. A Herringbone gear is perfectly suited for
operations that are:-
» Quiet
» High-speed
» Low-thrust applications where heavier loads are applied
Gear design
In terms of deign, these gears show a marked improvement over the double
helical gears. Here right and left hand cuts, both are put to optimum use on
the same gear blank. This cancels out any chances of thrust forces. But
attention must be given to the aspect of alignment as it is very critical
for ensuring a correct teeth engagement.
Because of their superior design these gears are often used to transmit
huge amounts of horsepower and a permanent fixture in any power transmission
system.
Manufacturing of Herringbone Gear
A large and diverse type of material is used for the manufacturing of
Herringbone gears. This include both metals and nonmetals. In metals typical
material used are brass, aluminum, bronze, cast iron, varieties of steel
like carbon, hardened or stainless steel. These days Herringbone gears that
are made of plastics are also not uncommon. Material includes nylon, acetal,
and polycarbonate. Gears that feature for example a metal teeth with inserts
made of plastics now combines the best properties of the two. Coming to the
manufacturing process, these gears are quite difficult and costly to make.
These Gears cannot be made using the processes of hobbing or shaping. This
is due to the change in direction taking place in the helical slant.
Two popular method for manufacturing Herringbone Gears are:
(a)
Machining of opposite helix angles on a common gear blank.
(b)
Machine each helix gear separately and afterwards assembling them to a
common shaft for the formation of the Herringbone Gear.
However, the most popular technique is to join the two separately machined
helical gears to a shaft. This forms a Herringbone rotor. Thereafter the
gears can be easily bound by the usual processes of welding, pinning,
brazing, threading, diffusion bonding, cooling the shaft member etc.
Application of Herringbone Gear
These gears are increasingly finding use in external gear pumps. This
preference towards these gears is accentuated by increasingly demanding
application for these Gear pumps. Customers are now using gear pumps for
applications that typically needs higher pressures, larger percentages of
filled materials, and also molecular weights that are higher. By switching
on to one-piece herringbone gears in place of standard gears and bearings
the results have been quite satisfactory. The discharge pressures has
increased and the life expectancy of the gear pump's parts prolonged.
Features of Herringbone Gear
Given here are few of the features that makes the use of Herringbone gears
in Gear Pumps (external) very productive.
- Quiet and pulse-free flow
- Improved load carrying ability
- Greater strength
- Minimal hydraulic shock
- Made mostly with durable Cast iron for wear resistance
- Pump capability is of high speed
- Side thrusts on the wear plates eliminated
- Smooth flow ensured by a gradual and steady gear tooth engagement
insuring
- No occurrence of end thrust and need for thrust bearings eliminated
with an innate hydraulically balanced design
