The process of mechanical destruction of solid raw materials is called crushing or disintegration. Materials subject to crushing include construction materials, chemical raw materials, solid minerals, abrasive materials, some types of plant raw materials, and secondary solid raw materials.
First Crushing Equipment
The first industrial machines were developed in the late 18th century when the English engineer Blake invented the so-called jaw crusher. The crusher utilized the force of crushing chunks of tough construction raw materials, such as granite, between a stationary armor plate and a moving plate that executes oscillating movements. The jaw crusher had such a brilliantly simple and reliable design that similar machines have been produced for mining enterprises in large quantities for over two centuries. Clearly, the first jaw crushers used a steam engine as a drive, not an electric motor as is common today. Jaw crushers can vary in size from laboratory to industrial crushers for crushing large raw materials. The largest jaw crushers have a feed opening size (“mouth”) of 2.1*2.5 m and can accept ore chunks up to 1.5-1.7 m in size.
Development of Crushing Equipment in Industry
Further development of crushing equipment occurred with the creation of cone crushers, in which the rock mass is crushed by applying forces of compression and shear between a stationary outer cone and an inner cone that rolls along the inner surface of the outer cone. Cone crushers used for coarse crushing have a steeper crushing chamber profile than cone crushers for medium and fine crushing. The maximum size that a large cone crusher can accept is 1.2-1.3 m. Overall, cone crushers have higher productivity than jaw crushers and provide a greater degree of reduction in the size of the crushed material. Cone crushers also have the advantage of being able to operate “under choke feed” conditions, whereas jaw crushers require more precise control of the feed rate. Both cone and jaw crushers have rigid kinematics, determined by the design of eccentric assemblies that provide the trajectory of the crushing elements (jaws, cones). Therefore, these crushers cannot automatically adapt to changes in the strength properties of the crushed material.
The main limitation of jaw and cone crushers is their relatively limited ability to reduce the size of the crushed material. Typically, their reduction ratio does not exceed 4-5. Therefore, ore preparation schemes usually involve three to four stages of crushing, following a clear sequence.
Effective Use of Crushing Equipment
To increase the reduction ratio of ore size in one crushing stage, principles of material destruction mainly through shear and compressive forces can be utilized. These crushing principles ensure the breakdown along the planes of mineral aggregates’ cohesion and along microcracks in their structure, allowing for a reduction ratio of material size by 5-10 times. Among the aggregates implementing the shear principle during crushing with minerals, there are cone vibrating crushers of the KID type and high-pressure roller crushers. Such crushers are mainly used for operations of fine crushing.
For crushing less sturdy material than massive ore raw materials, for example, for crushing limestone, gypsum, or breaking down solid household waste, rotary crushers are used. The most common type of high-speed rotary crushers is hammer crushers, in which the crushing elements are freely suspended on a horizontal or vertical shaft plate hammers made of impact-resistant grades of steel. Precise dosing of the feedstock is a prerequisite for the operation of hammer crushers to avoid overloading the crusher and its emergency stop.
