## 1 Introduction  
During the processing of raw materials in different industries such as the mining and cement sectors, the size reduction of fed rocks is primarily a mechanical process [1]. The rock blasting process is the most primary, and the first significant stage in these industrial sectors through which massive rocks are broken and fragmented into suitable smaller sizes before feeding to the processing plant. This process can be realized in mechanical systems commonly known as crushers. Primary crushers are capable of handling huge rocks of considerable size (typically around 1.5 m) to provide blasted rocks with a size reduction ratio varying from 3 to 10 [2]. The reduction ratio is the feed size to the product size. The crushing process is a multi-stage dry process where each stage has a small size reduction ratio within a range of 3 to 6. Rock breakage is accomplished by crushing, impact, and abrasion corresponding to known modes of rock fracture including compressive, tensile, and shear. The applied mode can be defined according to rock mechanics and the load type. Rocks meet crushing or compressive failure, where rocks of two distinct size ranges are obtained. In this mode, the coarse rocks are produced due to tensile failure, while the small size rocks result from compressive failure occurring at loading points or due to shear stress between projected rocks [3]. In tensile failure mode (impact crushing), the rock possessing a higher stress over the stress needed to achieve fracture has a great tendency to break rapidly, producing smaller rock sizes and shapes. In the final mode, shear failure (attrition mode), the rocks are broken due to the particle-particle interaction producing a significant part of fine size rocks. The later mode can occur when too fast feeding of a crusher is applied, which is usually undesirable. Crushing in closed circuit operations produce more unwanted fine material than open circuit operations. The crushing action comes from stresses applied to rock particles by moving parts of the machine. One of the most famous and oldest crushers is the jaw crusher [4; 5]. Jaw crushers have been in practical usage for about 175 years. There are different types of jaw crushers; these can be distinguished by the presence of two plates where crushed materials are fed between them. One of these plates is fixed while the other swings. Jaw crushers are classified, according to the location of this pivoted swinging plate, into Blake, Dodge, and Universal crushers. The Blake crusher is considered the most common, where the swinging plate is pivoted at the top [6]. This crusher can be a double toggle or single toggle. Due to its simplicity, lower cost, and its higher efficiency, the single toggle jaw crusher is the most realized form in new applications. Jaw crushers achieve size reduction mainly by compressing particles between relatively slow-moving, inclined surfaces. The material being fed into the machine enters from above, where the crushing surfaces are furthest apart, and is crushed into smaller fragments as it descends into the narrowest zone of crushing and is finally discharged by gravity. The crushing surface in a jaw crusher consists of two rectangular plates, one fixed crushing face and an inclined mobile face, which moves a small distance back and forth from the fixed face [7]. The significant variables in jaw crushing are the angle of the jaws, rate of jaw movement, displacement of the movable plate, and the distance between the jaws at the discharge end, which controls the product size as shown in Figure 1[8]. Several studies have dealt with size reduction, focusing on developing a theory or criterion that would be useful during the selection and evaluation of crushing equipment. However, none of these studies has satisfactorily successfully predicted the power consumption, a major source of running costs in crushing equipment.