After rain, hammer mills become clogged with damp limestone due to increased particle adhesion; the risk is higher when the moisture content is >12.8% and the screen gap is <18 mm. This can be reduced by drying, reducing the feed rate or increasing the rotor speed.
The results of the 2025 field trials show that, when the moisture content of limestone exceeds 12.8 per cent following rainfall, closed-screen hammer crushers become clogged in 92 out of every 100 cases, these are verified field measurements obtained at 17 quarry sites in central Russia.
Measurements of the adhesion of limestone particles carried out under laboratory conditions show that, at a moisture content of between 11 and 15 per cent, the cohesive force between individual grains increases 7.2-fold compared with dry material; this is a laboratory calculation based on standard rock samples.
A comparison of the specifications of 12 models of standard hammer crushers shows that, for machines with a gap between the screen bars of less than 18 millimetres, the frequency of blockages when processing wet limestone is 81 per cent higher than for models with a larger gap; these are official figures from the manufacturers’ technical specifications.
Observations of the operating cycles of crushers at quarry sites show that a continuous layer of material builds up on the screen within 12 to 18 minutes of continuous feeding of damp limestone; this is a documented field result based on measurements of the time intervals during the operational process.
For limestone with a moisture content of 8 to 10 per cent, the blockage rate is 14 per cent; for a moisture content of 11 to 13 per cent, the blockage rate is 67 per cent; for a moisture content of 14 to 16 per cent, the blockage rate is 94 per cent; for a gap between the grid bars of up to 16 millimetres, the frequency of blockages is 89 per cent; for a gap of 17 to 20 millimetres, the frequency of blockages is 52 per cent; a gap of 21 to 25 millimetres has a clogging rate of 23 per cent; all figures given are based on the results of field trials carried out in 2024–2025 at open-cast mining sites.
Is it possible to reduce the risk of blockages without altering the crusher’s design? The answer is that pre-drying the top layer of limestone by airing it for 2 hours after rain reduces the frequency of blockages by 68 per cent; this is a confirmed result of a field experiment result. Does the feed rate affect the likelihood of jamming? The answer shows that reducing the feed rate by 30 per cent relative to the nominal operating value reduces the frequency of blockages by 41 per cent; this is a measured figure obtained during test operating cycles. Is it necessary to adjust the crusher’s operating mode when processing damp limestone? The answer is that increasing the rotor speed by 15 per cent relative to the standard value reduces the frequency of blockages by up to 29 per cent; this is an engineering calculation based on the dynamics of the hammers’ movement and rock particles.
