Drives and motors are used to power an
array of equipment in mining operations,
from conveyors, and crushing/grinding
equipment to flotation cells and pumps.
The major challenges associated with
powering mining equipment is the
increased scale of operations and the
accompanying requirement for increased
power, whilst maintaining reliability. There
are a range of companies that provide
drives and motors for the mining industry,
some of which are mining specific whilst
others cover a range of industries.
Bauer Gear Motors has launched a new Ex-approved, IE4 Super
Premium Efficiency motor. The new S Series is the latest development
to Bauer’s permanent magnet synchronous motor (PMSM) motor
range. The IE4 has the highest achievable energy efficiency rating
within the motor technology, making the S Series the most efficient
motor that can be used in an explosion hazardous area. Motors for
use in explosion hazardous areas are exempt from the EU regulations
on minimum energy efficiency because explosion protection takes
precedence over energy savings. This has traditionally meant that
overall energy efficiency has waned, however, the S Series of Bauer’s
PMSM motor range, available from 0.55 kW to 15 kW are classified for
Zones 1 and 21.
The S Series also has the advantage of maintaining constant
speed independent of the load. PMSM synchronous motors offer
considerably improved efficiency when compared to induction motors
even under partial load conditions; and extremely high efficiency
under rated operating conditions. They also have considerably higher
power density, which, for geared motors, yields higher system
efficiency with minimal installation volume – and also reduced weight.
Importantly, PMSM drives can produce higher torque values for the
same installation volume as conventional induction motors, a factor that
allows cost savings, through the ability to specify a smaller motor size
in some applications.
Protecting drive system components
The IE4 Super Premium Efficiency PMSM
(permanent magnet synchronous motors)
S series can achieve energy savings of up to
40% compared to an IE2 inverter-driven squirrel
Protecting machinery and systems against expensive failures
and costly downtime is indispensable to large scale mining operations;
so many technologies are available to protect machinery against
overloads. Andrew Bargh of Bibby Turboflex, part of Altra Industrial
Motion’s couplings division indicated that “ large machinery and
rotating systems can generate enough rotating energy to cause
significant machine damage during a jam, crash stop, or during
uncontrolled braking due to, for example, a power failure. At very low
speeds, systems can develop a huge amount of unnecessary torque,
which can damage drive system components such as shafts, gearboxes,
chain and couplings.” Some of the technologies available to protect
- Shear pins have protected rotating equipment for centuries, but
lack accuracy and can require extensive repair time following
overload. To maximise plant uptime and improve the accuracy
of release torque, vendors have developed a variety of torque
overload release devices with integral bearings and simple
mechanical reset features.
- Friction clutches are one of the most common types of clutch;
however, as a safety device in a higher load application, they
can slip and wear, producing inaccurate and changeable torque
- Sensing devices, such as current sensors, monitor one particular
aspect of the drive and provide an output or alarm when that
function deviates from preset norms for a preset time period.
- Electronic control devices continuously monitor the machine,
comparing, for example, the difference between actual and
theoretical positions of various components.
The final two points cover electrical torque limiting solutions, which
are increasingly popular in many industries as they offer increased
accuracy and reduced downtime following the overload. A sensor is used
to detect a problem, and initiate corrective actions such as stopping and
reversing the drive, engaging the brake or shutting down the machine.
Bargh states that “the protective functions integrated into today’s sensing
and control units are an expedient supplement to the mechanical torque
limiting clutch, but not a replacement. Thus, mechanical torque limiters
still make sense, but not necessarily for every application.” There is also
the issue concerning the speed of the collision. For ‘hard’ collisions,
when the speed or mass of the rotating components is at a high level,
electronic controls may not be able to react before significant damage
occurs. At these speeds, only a mechanical overload device can react
quickly enough to prevent damage. The complexity of each system
should also be considered, especially in applications which are remote
or have limited access. Electronic monitoring systems need multiple
sensors for data; between the monitoring system and all of its sensors
and other components the system has multiple possible points of failure.
Once installed, a mechanical limiter can be left in-situ with minimal
maintenance, and yet offer complete reliability in the case of overload.
Turboflex’s UEP (Ultimate Extruder Protection)
modular torque limiting devices provide accurate
release torque repeatability, simple manual
re-engagement and low-cost maintenance
Bibby Turboflex has developed a range of UEP modular torque
limiters with an emphasis on simple installation, accurate release
torque repeatability, simple fast manual re-engagement, and low cost
maintenance. The UEP range of modular torque limiters was designed
specifically to offer alternatives to shear pin protection for high torque
drives where it’s accurate release torque repeatability coupled with a fast
reset feature offers a significant reduction in downtime.
The optimised design of the UEP torque limiters also means that
installation is highly flexible, enabling the centre section of the torque
limiter to be removed without the need to move the motor or gearbox.
Similar design versatility ensures that any maintenance of the modules
is a straightforward operation, and that recalibration is a simple removal
operation achieved without having to replace the complete torque limiter
When considering how best to protect machinery from overload it
is important to consider the different scenarios where this might occur.
Electrical monitoring or sensing equipment can initiate corrective actions
prior to overload during a slow torque increase, however, there are times
when the increase is too fast and the electrical system may be too slow to
prevent damage to other components.