Optimisation of Motion and Force Transmissions in a Single-Toggle Jaw Crushing Mechanism

Abstract

Jaw crushers are important mechanisms in quarries and construction sites used to reduce rocks and stones into aggregate materials for construction works. These crushers are also used in the mining industry to prepare the ore for secondary milling processing by reducing it to suitable sizes. The single-toggle jaw crusher is the most common crusher and uses a swing jaw which crushes the feed material against a fixed jaw. The crushing process is achieved through the application of both motion and force. The swing jaw moves back and forth towards the fixed jaw while transmitting forces from a motor-coupled eccentric shaft. For the feed material to be crushed, the mechanism must supply enough compressive force to overcome the compressive strength of the feed. This research was concerned with the synthesize of jaw crusher mechanisms which achieves optimal force and motion transmission from the input eccentric shaft to the ouput swing jaw. The aim was to ensure maximum crushing motion for better rock comminution as well as minimising shearing motion for wear reduction. In addition, the research investigated optimal force application on the rocks to overcome their fracture toughness and reduction to small particle sizes. The research involved the use of evolutionary optimisation technique called Genetic Algorithm (GA) to search for optimum link sizes that gave the best transmission results. Genetic Agorithm was implemented using MATLAB software. Motion optimisation was divided into two sections namely, crushing-shearing ratio and crush-travel inverse. Force optimisation was also split into two: static force and dynamic force and an objective function for each was created and fed into the GA solver. All objective functions were developed from first principles and then coded in MATLAB. Four optimised designs were synthesised each corresponding to the crusher motion or force parameter being optimised. The motion crushing-shearing ratio optimised design had 1.18 times higher crushing than shearing. The crushing-only optimised design achieved a production rate of 1.7 ×10−4 m3 . Meanwhile, the static force optimised design gave a total torque of 425 MNm while the dynamic force optimised design resulted in a total dynamic torque of 640GNm. The effect of link lengths on the four criteria were also sought and established. The swing jaw had the highest influence on both motion and force transmission so that a longer swing jaw was preferrable. The findings from this study will assist in the production of a new, optimised and locally fabricated single-toggle jaw crusher with high crushing efficiency, power saving and increased production. These findings will also aid in the modification of the existing ones by varying lengths of the components to increase crusher production via optimised motion and force transmission.