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What is a Jaw Crusher?

Jaw crushers comprise one fixed and one moving jaw. The material is crushed between the movable jaw and the fixed jaw through the application of compressive force produced by the elliptical motion of the movable jaw. The movable jaw, which is supported from the top by an eccentric shaft, is connected to the tension arm and an angled built-in support plate that absorbs the cyclic loads in the lat section.

Jaw crushers are used as the primary crushers in the first stage of a crushing process for the breaking of large-sized rocks, while jaw crushers with smaller mouth openings are used to break smaller ores into finer sizes.

Two basic jaw crushers types are produced, being single or double-supported, depending on the movement system of the jaw. Single headed jaw crushers are the most common type.

For what processes/applications are jaw crushers used?

Jaw crushers are used as the primary crushers in the first stage of the crushing process. Jaw crushers are preferred for when breaking large rocks is the priority rather than achieving high capacity.

Jaw crushers can be used as first-stage crushers in small- and medium-sized plants, as well as for secondary crushing when necessary.

The oscillation distance of the jaw generally varies between 20 and 40 mm, and the number of oscillations varies between 200 and 350 rpm. That said, the dimensions of the outlet are as important as the inlet of the jaw crusher. Crushers can be adjusted within certain limits.

In jaw crushers, the outlet opening and jaw movement are adjusted to suit the ore being crushed and the desired product size. Chunks of ore crushed between the jaws descend under the force of gravity.  The greater the number of oscillations of the jaw, the more fine product is produced. In high oscillating crushers, the jaws open and close more often and ore does not have the opportunity to get much distance downstream between the jaws with its own weight and the ore is faced with more crushing force along the jaw.

What materials can jaw crushers process?

Jaw crushers are used to break up hard rocks and moist ores of all kinds, but are not suitable for muddy applications.

In eccentric jaw crushers, the jaw facilitates the downward movement of the ore, though these kinds of crushers are not recommended for crushing ores with high abrasive properties, as in addition to the compression force, the shear force provided by the horizontal movement of the jaw is also effective.

In the jaw crushers in which compression force is applied, the internal stresses that occur in the rock to be broken during the crushing process are also observed in the crushed rock. For this reason, the crushed rock produced by the jaw crusher is unsuitable as an aggregate in concrete, especially in the construction sector. If the rocks produced by a jaw crusher are to be used in the construction sector, the internal stresses in the rocks should be released by breaking them up with impact or hammer crushers.

What criteria and advantages are important in the selection of a jaw crusher?

·        These can be used as a primary or secondary crushers, depending on the size.

·        The use of jaw crushers in underground applications is convenient and common, as they can be produced with few parts, and are easy to carry, assemble and maintain.

·        There are no capacity problems, as the desired capacity can be achieved by using more than one crusher side by side when necessary.

·        They are easy to maintain and affordable.

·        The replacement of worn jaws is not time-consuming.

Useful tips for the maintenance and operation of jaw crushers.

·        These crushers operate with a belt pulley system. As long as the electric motor is maintained on time and protected from dust, the probability of failure is very low. Worn belts should be replaced with new ones at the recommended frequencies before breaking.

·        The recommended maintenance of moving parts at the stated intervals and the periodic lubrication of moving parts will minimize the risk of failure of the crusher.

·        Although the crushers operate with a protection system, the entry of hard iron into the crusher mouth should be avoided.

·        The size of the material to be fed into the jaw crusher should not be larger than 80% to 85% of the crusher mouth opening. Feeders that feed material to the crusher should be suitable both for the material size and the width of the crusher feed opening.

·        Large capacity jaw crushers are driven by double electric motors. To ensure continuity in the back and forth movement of the crusher jaw and to keep the applied force size equal, the pulleys that provide the movement are made of large diameter, heavy, and a flywheel is attached to the opposite side of the pulley in single-pulley crushers.

·        Jaw crushers have a material production capacity of up to 1,000 t/h depending on the outlet, and the reduction ratio is generally accepted as 1:5.

·        The maximum product size is 300 mm, depending on the breaker closed part adjustment opening.

·        Grate or pallet feeding systems should be included in the initial investment costs of jaw crushers.

·        Since the vibration and load distribution are not uniform during the operation of the jaw crushers, the concrete foundations required for assembly must be robust.