incoming feed can result in the bridging
of the feed material across the crusher
opening. When this occurs, once again,
throughput capacity is diminished and
plugging of the chutes can occur. It is
good practice to size the width of the
rolls to 1.5 – 2 times the size of the
largest feed lump, even though the
capacity requirement of the application
may be lower than what the crusher can
produce.
Next to be considered is the required
product size. When taking this into
account, you must also refer back to the
feed size to see if the ratio of reduction
requires multiple stages of crushing. A
good rule of thumb for single stage
crushers is that a single roll crusher
provides up to a 6:1 ratio of reduction
and a double roll crusher provides up
to a 4:1 ratio of reduction. In the event
that the application requirement
exceeds the guidelines discussed herein,
dictating more than one crushing stage,
then a determination needs to be made
as to whether a single two-stage crusher
or two individual crushers should be
employed. If the two-stage crusher is
selected, consideration has to be given
to the overall headroom available.
When selecting a two-stage crusher,
feed size generally dictates if a triple
roll (Figure 2) or quad roll (Figure 3)
crusher is the appropriate choice. When
larger feed sizes are the norm and
require up to a 6:1 ratio of reduction to
achieve the final product, a triple roll
crusher should be chosen due to the
inherent design, which allows for the
larger feed sizes to be readily grabbed
in the large throat opening between the
top (primary) roll and crushing plate. If
the feed-to-product-size ratio can be
accomplished with 4:1 and 4:1 ratios
then a quad roll crusher can be
considered.
Tooth configuration and
roll speeds
At this point in the selection process,
the tooth configuration required to
produce the desired product size and
the proper metallurgy for the teeth can
be selected.
There are a multitude of tooth
patterns, designs and configurations
available on roll crushers today.
Selecting the correct metallurgy and
tooth configuration is extremely
important to maximise crusher capacity,
product shape and sizing, and wear life.
Improvements in quality to castings and
availability of more exotic metals have
created a desire for better wear elements.
McLanahan worked closely with one of
its suppliers to develop a weld-on
carbide tooth that provides the coal
industry with extended wear life for
crushing elements. Coal operators have
increased the wear life of their crusher
segments by more than double the life
they were previously achieving. One
operator in particular, which normally
averaged 18 – 20 million t through a set
of crusher segments, has been able to
achieve more than 50 million t with the
weld-on tooth design.
Consideration must also be taken
with reference to the flowability of the
feed material and if it has a tacky,
clay-like quality. Are roll scrapers or
differential roll speeds required to
provide a self-cleaning action to prevent
material build-up on the roll surfaces?
Is water being added? The differential
in roll speeds imparts compression
crushing, as well as the added benefit of
a tearing/shearing action. Sticky,
clay-like material can potentially build
up between the stages of a two-stage
crusher, eventually plugging the
crusher between the stages. In many
cases, the only option in instances such
as this is to employ two single‑stage
machines.
Throughput capacity of a crusher
has multiple variables that are taken
into account when calculating crusher
capacity. With roll crushers, 100% of the
material flow is processed between the
roll bodies or roll and crushing plate.
The space created between the width of
the rolls and the distance from
roll‑to‑roll or roll-to-crushing plate
must be calculated using the following
variables:
n
n
Roll diameter.
n
n
Roll width.
n
n
Roll speed.
n
n
Gap setting.
n
n
Bulk density.
n
n
Crushing factor of the feed
material.
Knowing these factors and taking
into account how each material reacts
in the crushing process helps
determine the overall crusher
selection.
Once all the information is
gathered, the proper crusher(s) can be
selected. In some instances, multiple
crusher options and combinations are
available for the same application and
the ultimate decision is left up to the
operator or contractor.
In the end, many factors play a part
in the selection of the proper crushing
Figure 1.
Figure 2.
Figure 3.
40
|
World Coal
|
July 2015
