SB Aug42 drives.qxd 8/8/07 10:59 Page 42
Drives
In the driving seat
Low speed drives - the direct hydraulic drive approach. Brian Holmes of
Hagglunds weighs up the advantages
When faced with a decision about a low speed drive for Some characteristics of hydraulic drives:-
industrial plant and equipment, there is a tendency to follow the Low inertia
traditional line of thinking of some kind of high speed motor or Full torque available from zero to maximum speed
turbine and a gearbox selected for the speed and torque Shockproof
required. This solution will often require other elements in the Perfect load sharing
drive train to complete the installation such as couplings, Can be applied in almost any environment
clutches, pulleys, belts etc and foundations. Sometimes these High power to weight – Compact and weight saving
arrangements are complex with quite high design cost. No problems with EMC or distortions on the power supplies.
However, there is an attractive and simple alternative of using
direct hydraulic drive. Typical applications include steel plate feeders, belt conveyors,
Hydraulic motors have been used to drive all kinds of plant and bucket wheel reclaimers, shredders, mills, mixers, winches,
machines for a long time. The excellent controllability, flexibility drilling and injection moulding machines.
and user friendly nature in use with an unbeatable power to
weight ratio were and still are strong attractive reasons for using
fluid power.
But hydraulic motors have developed and there are now a very
wide range of direct hydraulic drives available up to a massive
250 lt/rev and over 1MW in power from a single unit completely
eliminating the need of gearboxes. The great advantages of
hydraulics with inherent simplicity and flexibility can now be
applied to heavy duty industrial applications operating 24/7
where efficiency, reliability and long life are prerequisites.
Hydraulics offer full control of power, torque and speed by
using axial piston pumps supplying variable flow to the drive
motors thereby providing variable speed, which is essential for
efficient processes. And by controlling pressure, we directly
control the torque. Both can be precisely controlled and
integrated into power control by electrical signals. Thus
complete control of the drive is available bringing high
functionality and versatility to the drive.
ABOVE: A typical drum drive with four motors sharing the load
The hydraulic drive has very low inertia and so can react instantly
giving excellent response and control. For example roll mills can
stop instantly compared to high inertia gearbox drives which take
longer to slow down. This is a significant improvement in the
safety of operators working for example in the rubber and
plastics industry.
On drives with high speed motor and gearbox, a very high
moment of inertia is evident and if the machine is liable to
shocks, for example on a crusher when an uncrushable object
enters, the transient forces experienced can often damage the
machine and the drive, causing costly repair and time in lost
production. The direct hydraulic drive in the same circumstances
stops instantly, the forces limited by fast acting pressure
ABOVE: A typical Hagglunds Drive consists of a drive motor selected controls, are kept within design limits and so no damage and
from the wide range available to give the torque required. A power unit
less wear is caused giving high reliability and low maintenance.
with a variable displacement pump/motor set and necessary tank filters
and instrumentation. A control and monitoring unit and the inter piping.
Hydraulic drives are charged with oil, cushioned so to speak
The arrangement is versatile and flexible which enables customisation
and can therefore be applied on tough applications with
to suit the exact requirements of the application and environment
vibrations and shock without problems.
42 Solids & Bulk Handling • August 2007 www.solidsandbulk.co.uk
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