COMMINUTION & CRUSHING
Despite these recent orders, HPGRs remain the
exception rather than the rule in hard-rock
comminution circuits.
There are a few reasons for this.
First, it can be quite difficult to slot HPGRs into
existing brownfield circuits. While OEMs are
working on initiatives to make the process easier –
reducing the size of the HPGR equipment or the
amount of civil work involved with installation – it
is still a major task that requires careful planning
and more money than the machine’s price tag
alone.
Second, the introduction of an HPGR may
influence the rest of the comminution circuit,
meaning changes may be required in order to best
optimise the new equipment. Weir’s Dierx said this
change management requires an “integrated
solutions approach”.
He said: “Implementing a HPGR to uplift
capacity in the existing tumbling mills requires
knowledge of not only the HPGR, but also cone
crushers, mills, pumps, cyclones, etc.
“As every stage in the processing plant is
interlinked, every process change has a
consequence, which requires a team of dedicated
process and equipment experts to partner with
our customers and to demonstrate the potential of
lowering the total cost of ownership.”
Weir would know all about this. It booked £72
million ($92 million) of Enduron HPGR orders in
2019.
Third, HPGRs have, in the past, been criticised
for an inability to handle varied feed. Should the
material being fed to the machine change over
time, this can result in either a coarser product
that requires further downstream processing, or
excessive wearing of components.
The benefits of introducing these machines are
starting to outweigh these cons. This is especially
true given the refinement of existing products on
the market and the increased industry demand
placed on energy and water efficient technologies.
HPGR benefits
HPGRs are widely acknowledged to produce more
fine material at a given crush size than
conventional comminution equipment, form micro-
cracks in the crushed rock particles beneficial for
subsequent grinding and leaching, generate less
noise and dust compared with conventional cone
crushers, consume less power per tonne than
conventional crushing plants and offer a dry
processing option. In some cases, they can also
improve liberation.
Weir Minerals’ Dierx said every operation
considering an HPGR installation requires a
specially tailored flowsheet supporting its
objectives and working within the acceptable
boundaries, but, “in the right application, HPGRs
represent energy savings of as much as 40%
compared to conventional circuits whilst reducing
downstream milling
requirements”.
He went on to say of
Weir’s Enduron HPGR,
specifically: “The
patented Enduron tyre
surface technology with
spring-loaded lateral
walls provides long
component wear life and
maximises product
quality.
“Further supporting
grinding performance,
our design philosophy
maximises the width of
the tyre, whilst keeping
the diameter as small as
possible. First, this
allows the pressure to
fully penetrate through
the full operating gap,
exceeding the material’s compressive strength.
And, secondly, it reduces the so-called edge effect
area, which is a result of reduced pressure on the
edges of the rollers.”
The ability for the HPGR rollers to skew –
reducing wear and ensuring optimal grinding
across the whole feed – combined with a fully
controlled oil-lubricated cylindrical bearing
system, increases the longevity of the bearings
and eradicates the need for additional water
cooling, he said.
“Given the global shortage of large engineered
bearings, our clients feel secure knowing that the
Enduron HPGR has never experienced a premature
bearing failure,” Dierx said. “Another major
advantage of the Enduron bearing arrangement is
that it reduces the overall height of the machine,
reducing the structural costs in the overall layout.”
Metso owns the largest fully operating HPGR in
the world, the HRC™ 3000, which comes with an
ore processing capability of over 5,400 t/h.
It, too, thinks its HRC equipment has a few
standout qualities.
By directing the feed material straight to the
crushing zone and adjusting the speed and
pressure, Metso’s HRCs avoid wasting energy and
reduce operating costs, the company says. On top
of this, the grinding rolls are known for robustness
and longevity of wear components, while it has an
anti-skewing arch frame design to prevent
bearings from being damaged due to
misalignment.
Metso says: “The flange design maximises the
amount of material that is crushed by pulling the
feed into the crushing zone. This method prevents
the material bypassing the rollers and increases
efficiency and throughput.”
When used as an independent finish grinding
mill, thyssenkrupp says its HPGR has an energy
By directing the feed material straight to the
crushing zone and adjusting the speed and
pressure, Metso’s HRCs avoid wasting energy
and reduce operating costs, the company says
requirement that is only 40-50% that of a classic
ball mill, making it one of the most efficient
grinding systems on the market.
The company is also finalising the field
implementation of a package of what it says are
“massive design advancements and innovations”
to its HPGR technology ahead of the market
launch of its next generation HPGRs.
Most of these improvements are a result of
learnings from more than 150 units in mineral
applications, more than 50 of which are in hard
rock, it said.
Included in these developments are an oil
lubrication and cooling system for the main
bearings. This system has been successfully used
on vertical roller mills for years, with the first
HPGR retrofits set for existing installations to
allow a further increase of grinding pressure and
roll speed while extending the lifetime of the self-
aligning roller bearings, it said.
A number of design improvements related to
wear, which includes the capability to specifically
adjust roll protection on a case by case basis for
widely differing ore types had already been
implemented in earlier designs. These
improvements extended wear life significantly to
8,000 – 20,000 hours when processing
challenging ores in hard rock applications,
thyssenkrupp said. Additionally available
innovations have the potential to increase wear
life by up to 50%, in general.
A disruptive innovation being tabled by the
company is the application of so-called flanges on
conventional thyssenkrupp HPGRs. While flanges
are starting to replace conventional cheek plates,
APRIL 2020 | International Mining 15