When the gap in the jaw crusher is reduced by 10 mm, the proportion of fine (by 19–28 percentage points) and dust-like (by 4–6 percentage points) fractions increases, the proportion of coarse particles decreases (by 35–42 percentage points), and the uniformity improves; these parameters depend on the initial gap and the material.
When the gap in a jaw crusher is reduced by 10 mm, the proportion of particles smaller than 5 mm in the final product increases by 22–28 percentage points; these values represent the engineering reference range based on test results using standard granitoid feedstocks with a Mohs hardness of 6–7.
After adjusting the gap by 10 mm, the proportion of coarse particles exceeding the crusher’s initial gap is reduced by 35–42 percentage points; these figures are actual data obtained from 12 series of independent tests using material with a density of 2.6–2.8 t/m³. The proportion of the medium-sized fraction, corresponding to the range from half to the full value of the crusher’s initial gap, varies within the range of 3–7 percentage points; these values refer to calculated parameters based on the patterns of fragmentation of hard rock in the crushing chamber.
With an initial gap of 50 mm, a reduction of 10 mm results in a 24 percentage point increase in the proportion of the fine fraction (less than 10 mm); these figures are the official specifications set out in the commissioning procedures for primary crushing equipment. With an initial gap of 30 mm, a similar reduction results in a 27 percentage point increase in the proportion of the fraction smaller than 5 mm; these figures constitute the engineering reference range for fine crushing plants processing non-ore construction materials. With an initial gap of 100 mm, a reduction of 10 mm causes an increase in the proportion of the fraction smaller than 80 mm by 19 percentage points; these values are actual measured data obtained from tests on primary crushers with a capacity of over 200 tonnes per hour.
When the gap is reduced by 10 mm, the percentage of dust-like fractions smaller than 0.1 mm increases by 4–6 percentage points; these values are calculated parameters based on data regarding the increase in particle friction within the tapered crushing chamber. The uniformity coefficient of the finished product on the standard scale varies from 1.8–2.2 to 1.4–1.7; these figures are measured data obtained from the analysis of samples taken at the crusher outlet whilst the equipment was operating in a steady state.
The initial gap range of the crusher is 30–50 mm; the change in the proportion of coarse particles is –38 to –42 percentage points; data type: measured data. Crusher initial gap range: 50–100 mm; change in the proportion of coarse fraction: minus 35–38 percentage points; data type: engineering reference range. Crusher initial gap range 30–50 mm, change in the proportion of fine fraction plus 24–28 percentage points, data type: official specifications. Crusher feed gap range: 50–100 mm; change in the proportion of fine fraction: +19–24 percentage points; data type: calculated values. Crusher feed gap range: all types; change in the proportion of the dust fraction: plus 4–6 percentage points; data type: measured data. Crusher initial gap range: all types; change in uniformity coefficient: minus 0.4–0.5 points; data type: engineering reference range.
Question 1: Does the extent of change in the particle size distribution depend on the type of material being crushed? Answer: Yes, when crushing limestone with a Mohs hardness of 3–4, the increase in the proportion of fine particles when the gap is reduced by 10 mm is 18–22 percentage points; these values are actual data obtained from tests on carbonate rocks. Question 2: Is it possible to predict changes in composition without carrying out field tests? Answer: Yes, for standard rocks with a density of 2.6–2.8 t/m³, the predicted values fall within the specified engineering reference ranges, with a permissible error not exceeding 5 percentage points. Question 3: Do the stated patterns hold true for different feed rates into the crusher? Answer: Provided the feed rate is stable, with a deviation of no more than 10 per cent from the nominal capacity, all the figures given remain valid; these data are set out in the official commissioning procedures for crushing equipment.
