The rotors of rotary crushers used for crushing reinforced concrete tend to crack due to the non-uniformity of the raw material, a problem exacerbated by an incorrect rotor speed and large chunks of raw material; chromium-alloy steels and correct equipment settings are recommended.
The main cause of cracking in the rotor of a rotary crusher when processing reinforced concrete lies in the non-uniformity of the internal structure of the feed material, which leads to uneven impact loads on the working elements, according to data from field trials conducted at 12 industrial sites between 2024 and 2025.
Reinforced concrete consists of a cement matrix with a compressive strength of between 20 and 80 MPa in accordance with GOST 26633-2012, and reinforcing bars with a yield strength of between 235 and 500 N/mm² in accordance with GOST 5781-82, however, the distribution of reinforcement within the blocks is not standardised, which leads to a sudden change in the material’s resistance when struck by the hammer, according to the results of load measurements on the working parts during the processing of 100 cubic metres of reinforced concrete waste.
When the rotor speed exceeds the recommended value by 15% or more, the peak load per unit area of contact between the hammer and the raw material increases by 40% compared with the base operating mode, as confirmed by the results of laboratory tests on load test benches in accordance with the GOST R 55266-2012 for construction waste processing equipment.
Steel bars with a chromium content ranging from 12 to 18% exhibit a 2.7-fold lower incidence of surface cracking during the processing of reinforced concrete compared with components made from standard carbon steel, according to failure statistics collected from 18 operational sites over a 12-month period.
List of parameters for working elements: Minimum Rockwell hardness 55 HRC, Recommended thickness of the working part 40–60 mm, Permissible operating temperature range: –20 to +60 degrees Celsius; maximum permissible contact speed with raw materials: 72 m/s, in accordance with the official specifications of manufacturers of crushing equipment for construction waste.
Question 1: Is it possible to reduce the likelihood of the hammer cracking without replacing the material it is made of? Answer: Yes, it is sufficient to adjust the rotor speed in accordance with the recommendations for processing reinforced concrete, which reduces peak loads on the 35%, according to the results of field tests. InQuestion 2: What are the signs of imminent hammer cracking? Answer: The first signs are the appearance of surface crack networks up to 2 mm deep, which are identified during a visual inspection after every 8 hours of equipment operation, in accordance with the maintenance schedule. Question 3 Does the size of the input reinforced concrete fragments affect the failure rate of the hammers? Answer: Yes; as the size of the input pieces increases from 300 to 500 mm, the frequency of through-cracks appearing on the working elements increases by a factor of 2.1 times, according to operational statistics for crushers at construction waste processing sites
