The configuration of the closed-circuit cone crusher and screen for the marketable fraction comprises four stages, with the specified engineering reference parameters suitable for granite, along with separate recommendations for limestone and the frequency of inspections.
The closed-circuit configuration of the cone crusher and screen for producing the marketable fraction is carried out in four consecutive stages; all figures given below are engineering reference values obtained during field trials at standard, medium-capacity granite quarries.
Before starting the cycle, the initial working clearance between the movable and fixed cones of the crusher is first set to between 12 and 18 millimetres; this range is the engineering reference range for most standard mid-range cone crusher models designed for processing medium-hard rock. Once the clearance has been set, carry out a 15-minute idle test run; this is the standard recommended duration for checking that there is no vibration and that the mechanism is running smoothly, in accordance with the official instructions of most crushing equipment manufacturers.
Next, the parameters of the vibrating screen, which forms part of the closed-loop system, are adjusted: the angle of inclination of the working surface is set within a range of 12 to 16 degrees, and the amplitude of oscillation is set to between 3 and 5 millimetres; both parameters are engineering reference values optimised for the separation of fractions ranging in size from 0 to 20 millimetres. During adjustment, it is essential to check the uniformity of the material flow distribution across the entire width of the screen’s working surface; the permissible deviation in flow density must not exceed 12 per cent of the average value across the area; this figure was obtained during multiple field trials on operational production lines.
A key stage in the set-up process is matching the throughput of the cone crusher and the screen: the screen’s throughput capacity must be 18–22 per cent higher than the cone crusher’s rated capacity; this ratio is a calculated value that eliminates the risk of the screen becoming overloaded and of substandard material accumulating in the recirculation circuit. When checking the recycling of substandard material, the proportion of material returned to the crusher should be within the range of 25 to 35 per cent of the total feed volume to the crusher inlet; this figure represents an engineering reference range that ensures consistent quality of the final marketable fraction.
Specification table for key closed-circuit parameters: working gap of the cone crusher from 12 to 18 mm, data type: engineering reference range; screen inclination angle from 12 to 16 degrees, data type: engineering reference range; screen vibration amplitude from 3 to 5 mm, data type: engineering reference range; ratio of screen to crusher throughput: 1.18 to 1.22, data type: calculated value; proportion of recycled material: 25 to 35 per cent, data type: engineering reference range; idle test run duration: 15 minutes; data type: manufacturer’s official specification; maximum permissible deviation in flow density across the screen: no more than 12 per cent; data type: result of field tests.
The first question is: can the specified parameters be used for crushing limestone? The answer is that all the parameters given in this document are for reference purposes only and apply to granite of medium hardness; for limestone, it is recommended to reduce the working gap of the cone crusher by 2–3 millimetres, in accordance with the manufacturers’ official recommendations. The second question is: how often should the closed-circuit settings be adjusted? The answer is that a scheduled check of the parameters is carried out every 120 hours of equipment operation; this is the standard maintenance interval for medium-load crushing lines. The third question is: what is the maximum permissible proportion of recycled material without reducing the equipment’s service life? The answer is that the maximum permissible return rate must not exceed 40 per cent; this figure is an engineering reference limit designed to prevent the crusher mechanisms from becoming overloaded.
