Introduction
Jaw Crushers are primary crushers used in the first stage of the crushing process. They feature a V-shaped cavity (called the crushing chamber) that is formed by a moving piece of steel and a stationary piece of steel (called jaw dies). Material to be crushed enters the top of the chamber, where it is squeezed between the moving piece of steel and the stationary piece of steel as it makes its way down the chamber toward the discharge at the bottom.
Jaw Crushers typically have a reduction ratio of 6:1, which means a 30” feed will be reduced down to 5” at the smallest size. The product size can be adjusted by opening or closing the gap between the jaw dies at the smallest point. This is referred to as the closed-side setting. If you need a smaller product size, move the jaw dies closer together to decrease the closed-side setting. If you need a larger product size, move the jaw dies further apart to increase the closed-side setting.
A compression-type crusher, Jaw Crushers are ideal for processing hard rock like dolomite, limestone, sandstone and river gravel, as well as material that is fairly abrasive. They are also a good choice for construction and demolition debris recycling applications for processing reinforced concrete, bricks, ceramics and more. Jaw Crushers are not the best choice for lightweight or sticky material.
Jaw Crushers are not a shaping crusher. Because they typically produce an elongated, flat and slabby product, Jaw Crushers are usually followed by a secondary crusher, such as a cone, impactor or roll crusher, for refining and further size reduction.
These crushers come in a range of styles and sizes and are capable of
handling low tonnages, such as in sampling applications, as well as
large lumps at high capacity. If you are considering a Jaw Crusher for
your application, here’s how to choose the right one.
Jaw Crusher sizing and selection
Like other types of crushers, Jaw Crushers are sized based on the material to be crushed. This includes:
- A description of the material to be processed
- Physical characteristics of the material
- Desired product size
- Desired feed rate (or tons per hour)
The characteristics of the feed material are extremely important. Not
only do they help to determine the size of the Jaw Crusher required to
do the job, but they also help to determine the materials of
construction of the wear components.
A Jaw Crusher is sized so that the maximum feed size is 80% of the gape and width openings. The gape is the measurement between the two jaw dies, while the width is the measurement between the two side plates. For example, if the maximum feed size is 29”x49”, the crusher gape would be 32” and the width would be 54”.
By sizing the Jaw Crusher slightly larger than the largest feed size, you reduce the risk of large lumps getting stuck in the crushing chamber or sitting on top of the crushing chamber, stalling production.
The characteristics of the feed material also help to determine if a
Jaw Crusher is even the best type of crusher for the job, or if another
type of crusher would be better suited. Lab testing can provide an
analysis of the material that can be shared with the equipment
manufacturer for sizing the crusher.
Other considerations
In addition to the material to be processed, you also want to consider the environment in which the crusher will be operating. This includes factors such as:
- Method of extracting the raw material
- Method of feeding the raw material to the crusher (typically Jaw Crushers are fed by Vibrating Grizzly Feeders, Wobbler Feeders and scalping screens)
- Does it need to fit into an existing structure or integrate with existing equipment?
- Is it an aggregate plant or a recycling plant?
- Is going to be a stationary structure? Does it need to be installed on a chassis as part of a portable plant? Does it need to be skid-mounted for modularity?
- Future production increases
- Site footprint
- Plant height restrictions, if any
- Operating hours per day
Another consideration is the method of adjusting the closed-side setting: manually with shims or hydraulically with the push of a button. Shim-adjust Jaw Crushers are lower in capital cost, but they require a complete plant shutdown when product-size adjustments need to be made, as well as someone to physically make the adjustments.
You also want to consider if tramp metal relief is necessary. If
there is a chance you could accidentally process a large piece of metal,
such as a bucket tooth, on through to the Jaw Crusher, you may want to
consider a hydraulic Jaw Crusher with tramp relief over a shim-adjust
Jaw Crusher. The toggle on a shim-adjust Jaw Crusher can break in the
event an uncrushable material enters the chamber, whereas the hydraulics
on a hydraulic-adjust Jaw Crusher will relieve to pass the material.
Why choose a Jaw Crusher
Jaw Crushers are effective for crushing a wide range of materials
and are a top choice for primary crushing in a variety of applications
as well as in stationary, portable or modular plants. They provide a 6:1
reduction ratio and can handle small and large tonnages. Jaw Crushers
are a low-wear, low-operation-cost option for material size reduction
with minimal maintenance requirements.
