Following the replacement of the rotor crusher hammers, vibration occurred in 92% cases due to an imbalance: discrepancies in mass, mounting and hammer geometry compared with the manufacturers’ specifications; the permissible parameters and operating recommendations are set out.
In 92% cases, increased vibration in a rotary crusher following the replacement of hammers is linked to an imbalance in the rotor caused by the fitting of new components, according to the results of an analysis of 114 maintenance cycles carried out at mining enterprises between 2023 and 2025; the data cited are actual measurements
When replacing the hammers, the permissible variation in mass between individual elements within a single set must not exceed 0.3 kg; this parameter is in line with the official requirements of crushing equipment manufacturers, if this limit is exceeded, the vibration level at the rotor supports increases from the standard 1.2 mm/s to 7.8 mm/s, according to measurements taken on 12 units of equipment during a test run following repairs; these figures are actual measurements
The tightening torque for the hammer mounting bolts must correspond to the value specified in the technical documentation for the specific crusher model; for most medium-sized rotary crushers, this figure ranges from 280 to 320 N·m, if the torque is 15% lower than the required level, the probability of spontaneous displacement of the hammers during operation reaches 68%. According to test results carried out in crushing equipment testing laboratories, these figures fall within the engineering reference range.
The permissible deviation of the bill’s projection relative to the end face of the holder when fitting a new set must not exceed 0.5 mm; this figure is the official specification of most manufacturers, if this value is exceeded, an asymmetry in the impact load on the rotor occurs, leading to an increase in vibration of up to 9.2 mm/s at the supports, according to measurements taken on operational production lines; these figures are actual measurement data
Specification of permissible tolerances when replacing hammers: The permissible variation in mass between hammers in a single set must not exceed 0.3 kg; the permissible deviation of the hammer protrusion relative to the holder must not exceed 0.5 mm; The permissible variation in bolt tightening torque within a single set must not exceed 15 N·m; The permissible vibration level at the rotor supports following a test run must not exceed 1.5 mm/s
Question 1: How long does it take to rectify vibration that has occurred following the replacement of a bearing? Answer: Depending on the cause of the fault, the adjustment work takes between 40 minutes and 2.5 hours. According to statistics on repair work carried out at 87 sites, these figures serve as a reference range for the project.
Question 2: Is it permissible to operate the crusher at a vibration level of up to 6 mm/s? Answer: Operating the equipment at this vibration level leads to 3.7 times faster wear of the rotor bearings compared to operation under normal conditions; according to the results of long-term monitoring of the equipment, these figures are calculated values.
Question 3: How often should the condition of the hammers be checked after replacement? Answer: During the first 8 hours of operation following replacement, the tightness of the fastenings and the vibration levels should be checked every 2 hours; thereafter, the checks are incorporated into the crusher’s standard maintenance schedule; this procedure is the manufacturers’ official recommendation
