New Rock Crushing Technologies

By Author: Qiao JingLiang
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As opposed to advances in consumer electronics and computers, the introduction of new rock crushing technologies occurs at a slower pace. There are various kinds of these heavy devices, and one type, the jaw crusher, is virtually unchanged since the 1940s. Another type, called a cone crusher, has improved in build quality and reliability while retaining the same basic design, changing more than the other types, perhaps, due primarily to an increase in rotating speed and improvements to the crushing chamber. A 120 cm (48 inch) cone crusher from the 1960s could crush 170 tons of rock per hour, while the same size machine today will put out 300 tons.

Perhaps the greatest advance with contemporary crushers has been the gradual deployment of hydraulics to protect the crushing chamber in cone crushers from damage by "uncrushable" objects. Steel and other uncrushable materials can damage the cone crusher, even beyond the chamber, and cause additional losses from lost production. With the newer hydraulic relief mechanisms, downtime has been reduced tremendously and the useful life of the cone crushers has been extended.

Jaw ...
... and impact crushers
Occasionally called toggle crushers, jaw crushers grind rocks between two vertical plates, one that moves and one that doesn't, and reduces them through powerful compression. The jaw plates are farther apart up top but closer together at the bottom, making a tapered chute. The plates work in tandem by dint of the gradual inertia created by a heavy flywheel, so as rocks progress down the chute, the tapering creates smaller and smaller pieces before the final product is output at the bottom of the machine. Jaw crushers are able to process materials of different hardness and abrasiveness.

Rather than using pressure, impact crushers use impacts to crush generally softer materials that are less abrasive. There are two types of impact crushers, horizontal shaft and vertical shaft. The former has two huge hammers on a spinning rotor that works well with such materials as basalt, granite, gypsum and limestone. The latter uses velocity to crush various materials, in effect throwing them against an anvil to break them up, and outputs cube-shaped final product that is preferred in highway construction and water conservation applications. Impact crushers process quartz, limestone, granite and bauxite, among other materials.

Cone and gyratory crushers
Cone crushers squeeze rocks between mantles that cover gyrating spindles and enclosed, concave-shaped hoppers. When rocks enter through the top they are wedged between the mantle and the hopper, which breaks up the larger ones so that they fall to a lower level, where they are broken down further until they can fall through a narrow bottom output. Cone crushers are efficient, easy to operate, less prone to wear and tear, and the preferred method for hard and medium-hard rocks from stone mining or building material uses.

Gyratory crushers have stationary, concave surfaces over which conical heads move in a rough circular manner, accomplishing their crushing actions as the gap between the two surfaces is reduced. Like jaw and cone crushers, rocks get progressively smaller as they fall down level to level. Gyratory crushers are typically used in ore processing operations and mines, with such ores as copper and iron.

Roller crushers
For soft and/or fragile materials, like limestone, chalk and clay, roller crushers are indicated. They consist of two rollers, one that is stationary and equipped with a flywheel and another that is adjustable to account for the different sizes of various materials. Raw material is fed through an opening so that it falls between the two rollers, where the pieces are reduced to as little as one-fifth of their original size. The processed product is output through an opening. When any uncrushable objects get caught in or jammed between the rollers, the feed mechanisms are designed to disengage to prevent any damage.

The future
Rock crushers of all types are generally heavy and large pieces of equipment, but emerging technologies foreshadow a new generation of crushers that are portable for on-site work. The benefits are many, including most cost-effective production due to reduced transportation time and expense (no more back-and-forth to fixed-location processing plants). In the usual evolutionary process evident in the history of these machines, some newer models are experimenting with the combination of jaw and roller actions and a range of different compression settings. As the technology continues moving forward, the use of new lighter-but-stronger materials, improved manufacturing techniques, mobility features and ever-more-efficient individual components will add up to good news for operators of these gargantuan machines.
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