international
construction
september 2013
CRUSHING AND SCREENING
48
Choices, choices
Crusher considerations
CEMCO president Neil Hise explains how to choose the right VSI
U
nderstanding the technology
in today’s vertical shaft impact
crusher (VSI) designs and how it
affects costs and profits is a key element
to finding the right machine for your
operation. VSI crushers can come in one of
four configurations - closed rotor & anvil
ring, shoe table rotor & anvil ring, closed
rotor & rock shelf and shoe table rotor &
rock shelf.
The open shoe table will work best for
softer materials or for processing less
abrasive materials with a larger feed size
- normally 3 inches (76 mm) or larger. Highly abrasive materials would wear the shoes too
quickly – maybe just six hours before they needed replacing. This is of course costly in terms
of both new parts and down time.
When working with the shoes, it is important to either replace them as a complete set
or in pairs to maintain proper balance on the rotor. The shape of the shoe can impact the
production sizes – straight shoes produce more fines, while curved shoes produce coarser
material.
For more abrasive materials, closed rotor designs tend to be most effective. But perhaps
the single most important decision is whether to opt for a rock shelf or anvil ring design.
With a rock shelf, material builds up in an open ring, to form a shelf of the mineral being
crushed. This is designed to protect the ring from abrasion and provides a wall at which
material is hurled at high speeds and with great force to fracture it.
Although this sounds like a good alternative to the cost and expense needed to replace
anvils as they wear, things are not quite that simple. When the material thrown by the rotor
hits the shelf, it absorbs energy that could otherwise be used for breaking – a reduction in
efficiency. As well as lower production, this implies that more force, meaning more rotor
speed and therefore a larger motor, is needed to break the material, increasing purchase and
operational costs.
Anvil rings meanwhile use a series stationary blocks that rock is thrown against by the
rotor – a design that means much more energy goes into crushing the material. Maintenance
costs might be higher, but these can be helped with the systems offered by some
manufacturers that allow anvils to be rotated, meaning the full face is used before they need
replacing.
Distance can be easily altered by either adjusting the rotor diameter or the number of anvils
in the system - the closer the throw distance, the more fines will be produced. Impact energy
can also be adjusted by changing the rotation speed – higher speeds mean more fines – and
with the variable frequency drives available today, this can be a simple change to make.
force which maximises screening efficiency and allows the
equipment to be effective in both wet and dry applications.
Designed for operations that require a smaller footprint and
capacity, the 4-foot F-Class can process up to 300 tons (272
tonnes) per hour while providing accurate sizing. It can screen
any material from 3 in (76 mm) down.
Green field plant
Indeed, when it comes to high output facilities, many mobile
units would struggle to keep up with the throughputs achieved
by static units.
This is illustrated by Metso, which has won the contract to
supply a complete crushing & screening plant to a green field
quarry being opened by road building contractor Colas in
France. The order includes primary, secondary and tertiary stages
along with service contracts and extended guarantees.
Metso Mining and construction sales director for France,
Philippe Portevin, said, “Tailored solutions for high-end output,
reduced costs with energy-efficient machines and automated
treatment are the major benefits we are delivering to our
customer with this supply. Colas wanted not just a supplier, but
a responsible partner for their investment. We’ve set an ambitious
target and we’re confident in achieving it.”
The installation includes a C160 jaw crusher, a HP500
cone crusher, two HP6 cone crushers, more than 12 vibrating
machines from TS, CVB and VF range completed with more
than 2,000 m of Metso conveyors.
The full engineering scope of the installation includes a truck
loading station, automation and power, 2,000 tonne steel
structures, plateworks, de-dusting, erection and commissioning
Shanbao’s latest products include its new DY range of
cone crushers.
