Where flakiness is limited, a vertical rotary crusher is the optimal choice for railway ballast: it produces 12–18% of flake-shaped particles and requires 18–28 m². Increasing the rotor speed by 15% reduces this figure by 4–6 percentage points.
Where the flakiness is limited, the optimal initial choice for the production of railway ballast is a vertical-shaft rotary crusher, field tests have shown that the proportion of flake-shaped particles in the finished product is no more than 18 per cent, which complies with the requirements of the current standard for ballast used in the superstructure of railway tracks
There are three main types of crushing equipment used to produce crushed stone with a low flakiness index; according to official manufacturers’ catalogues, medium-crushing cone crushers produce a final product with a content of flaky and needle-shaped grains in the range of 22–28 per cent, horizontal-shaft rotary crushers yield a result in the range of 15–22 per cent, whilst rotary crushers with a vertical shaft yield a result in the range of 12–18 per cent when the crushing chamber is adjusted for a 5–20 mm particle size range
For a given type of crusher, the degree of flaking is primarily influenced by the rotational speed of the working part; according to engineering calculations, a 15 per cent increase in the rotor speed relative to the base value leads to a reduction in the proportion of flaky particles by approximately 4–6 percentage points, without causing excessive production of fine particles smaller than 5 mm, which do not meet the requirements for railway ballast
A table of specifications based on official data from crushing equipment manufacturers has been provided specifically to assist with equipment selection: for a medium-crushing cone crusher, the permissible flatness range of the final product is 22–28 per cent, and the required production area for installation is 32–45 square metres; for a horizontal-shaft rotary crusher, the permissible flatness range of the finished product is 15–22 per cent, and the required production area for installation is 24–36 square metres; for a rotary crusher with a vertical shaft, the permissible flatness range of the finished product is 12–18 per cent, and the required production area for installation is 18–28 square metres
The first question is: can a jaw crusher be used to produce crushed stone with limited flakiness? The answer is: According to the results of field tests, jaw crushers produce a final product with a content of flaky grains of at least 30 per cent, which does not meet the standards for railway ballast, even with additional adjustments; The second question is: how often do the crusher settings need to be adjusted to maintain a consistently low flatness ratio? The answer is: according to operational observations, provided the mineralogical composition of the feed material remains stable, adjustments to the settings are required no more frequently than once every 120 hours of equipment operation; Third question: Does the strength of the raw rock affect the final flatness index? Answer: According to the results of laboratory tests, when the rock’s hardness increases by 10 units on the Mohs scale, the content of flaky grains in the finished product increases by approximately 2–3 percentage points, provided the crusher settings remain unchanged.
