Apparatus for detecting a failure in bearings

An apparatus for detecting a failure in ball-and-roller bearings for a rolling mill comprising:

• a comparison means for comparing an acoustic emission signal indicative of power of an acoustic emission from ball-and-roller bearings with a predetermined threshold value, and for outputting an error signal which expresses a bearing failure when the power of the acoustic emission exceeds the predetermined threshold value;
• and
• a logic circuit for invalidating the output of the comparison means for a specified interval of time during a metal-in time when a metal sheet is loaded into the rolling mill or when the rolling of the metal sheet is started and during a metal-out time when an end of the metal sheet passes out of the mill.

A method of detecting a failure in a bearing to be executed by a machine having an acoustic emission sensor which detects acoustic emission from a bearing, the acoustic emission being related to the failure of the bearing, a bandpass filter which extracts signals in the range of from 100 kHz to 500 kHz from signals outputted by the acoustic emission sensor, a comparison means which compares each of the signals outputted from the bandpass filter with a threshold value, thereby detecting a failure in the bearing based upon the comparison means detecting a signal which is greater than the threshold value, which method comprises the steps of:

• determining by means of a period determination means time intervals in which the output signal from the bandpass filter exceeds the threshold value;
• totaling the number of times that the output signal from the bandpass filter exceeds the threshold value for each time interval determined in the previous step;
• modifying the threshold value in such a manner that the gradient of a straight line generally expressing a distribution of the number of events is approximately equal to zero.