Jaw crusher is generally
the primary crushing equipment of the whole production line, and its efficiency
has a great influence on the production line. The main purpose of jaw crusher
is to reduce the feed material to a small enough size that it can be
transported by conveyors to the next crushing stages. Feeding is the first step
in crushing and following the proper feeding practices not only increases
component wear life but improves the productivity and efficiency of the entire
production line. Improper feeding is a major cause of slowdown and production
capacity gaps.
In-line
feeding
Jaw crushers should only be
fed in line with a feeder or scalping screen. This means the discharge end of
the feeder should align with the feed opening or gape of the crusher. In-line
feeding limits opportunities for the material to clog the jaw crusher.
Choke
feeding
Jaw crushers should be
routinely choke fed to maximize the production capacity. Choke feeding results
in stone-on-stone crushing, which can help break apart more flaky materials.
Jaw crushers work best when the entire crushing chamber is used for material
size reduction. Choke feeding a jaw crusher maintains a crushing chamber that
is at least 80% full. This will help to draw the material down into the
crushing chamber, as well as create a better material shape and improve overall
efficiency.
However, choke feeding also
often results in a finer output. Trickle-feeding material into the jaw crusher
could achieve fewer fines and result in larger products but this would have an
adverse effect on particle shape, and it also reduces throughput capacity,
hindering the crusher’s efficiency.
Avoid
over and under-sized feed
Both over and under-sized
feed should be avoided for better productivity. The material being fed into the
jaw crusher should be evenly distributed and free from any large chunks.
Material that exceeds the size of the feed opening can clog jaw crushers and
reduce their efficiency or block production altogether. Removing oversize ahead
of the jaw crusher will help to avoid blocking and clogging of the crusher
opening. A good rule of thumb is that the maximum feed size should be 80% of
the crusher opening.
Scalp
out the fines and undersize material
Fines and undersize
material should be scalped out by pre-screening the feed. Fines in the feed can
limit production for several reasons: they can clog the crushing chamber,
reducing the tons per hour and machine efficiency. They can also prevent even
distribution of particle sizes and generate an inconsistent product shape.
Fines can also create unnecessary wear on crusher components. Scalping out this
material ahead of time will help to prolong the life of wear components (jaw
dies and side plates), as well as help to reduce the downtime required to
change out worn components. Scalping screens and grizzly feeders should be used
to remove fines that are below the demanded product size. Feed that’s smaller
than the closed side setting (CSS) won’t get crushed anyway; rather, fines
decrease the percentage of voids in the crushing chamber, reducing
effectiveness and increasing wear.
Avoid bridging
Continuous bridging in the
feeding area of jaw crushers is a common problem. Bridging is a common cause of
inefficiency and time loss in production. This event occurs when a material
enters the feed and becomes lodged, blocking the above material from entering.
A single larger piece typically causes this, but several feed material
happening to wedge against each other may also cause a jaw crusher’s
inefficiency. Blockage of this type is common and may take several minutes to
resolve. Because of the large quantities and sizes of material passing through
a primary crusher, this may cause several short tons per hour to be lost.
Bridging can be avoided by
implementing a tight control of the blasting grid to avoid generating oversize
material, training the truck loader operator to separate the oversize material
at the pit and the primary crushing plant operator visualizing the flow of
material to the crusher and controlling the feed materials’ speed and direction
by varying feeder speed and using the hydraulic hammer installed in the area.
Well-graded
feed
Another best practice for
feeding jaw crushers is to blend the feed material ahead of the crusher to
ensure a well-graded feed. This will produce steady, consistent tons per hour
out of the crusher and will also promote inter-particle crushing to break any
flat or elongated material. A well-graded feed for a jaw crusher includes
material larger than the closed-side setting but no larger than 80% of the feed
opening. Oversize, fines and material equal to the product size should be
removed ahead of time for optimum operation.
Avoid
lightweight and sticky material
Jaw crushers can handle a
wide variety of materials, including hard, abrasive, non-friable and even some
wet materials. However, they are not designed for handling lightweight or
sticky materials. Sticky materials can build up on the jaw plates and reduce
efficiency. Lightweight materials don’t draw down into the crushing chamber
well, which also reduces efficiency. These should be best avoided. Higher
moisture content in the feed material negatively affects the crushing
performance. Feed with higher moisture levels typically ends up just being
compressed, rather than crushed, resulting in a clay-like cake being
discharged.
Limit
steel and other metals in the feed
In aggregate or mineral
processing plants, tramp metal isn’t necessarily expected to be in the feed,
although it may enter in some form. While jaw crushers can handle metal, such
as steel, in a feed, and can even pass the steel without harm to the crusher if
equipped with an automatic tramp relief system, it is best to limit the amount
of metal that enters the crusher. If the crusher does not feature a tramp
relief system, the toggle that maintains the closed-side setting can break,
potentially damaging other components in the plant as it falls out of the
crusher as well as causing unplanned downtime to replace the toggle. It is
always best to remove as much steel as possible via a hydraulic breaker, shear
or concrete processor before feeding into the jaw crusher.
