Definition and classification
As defined in Section 220.127.116.11 of the fifth edition of API 541, the low speed roller is a condition of a film bearing motor or generator, ie the rotor speed is between 200 and 300 rpm. At this speed, the dynamic effect is at its lowest level and the vibration is almost non-existent. In this state, the readings of the proximity detector should be closely related to the mechanical defects of the detector trajectory, including out-of-roundness, surface-related defects, concentricity between the detector trajectory and the radial bearing, and shaft Electromagnetic defects in the material of the bend or shaft.
The conditions at which the low speed rolls can be measured include: 1. in an already assembled machine; 2. placed on a rotating assembly on a V-shaped block of a half-shell of the bearing; or 3. on a lathe. The radial runout of low speed rolls comes mainly from two aspects: mechanical and electrical.
Mechanical radial runout (MRO) is the deviation of the cylindrical surface of the measuring shaft from the perfect cylindrical surface and the concentricity with the centerline of the bearing. Deviations include: surface out of roundness, surface mechanical defects (such as surface finish or scratches), and lack of concentricity between the surface and the axial center of the bearing. MRO is a measurement made using a dial indicator or a contact detector.
Electrical radial runout (ERO) measures the deviation between the axial surface conductivity and the magnetic permeability. The non-uniform electromagnetic properties of the shaft interfere with the magnetic field close to the detector, so as the gap voltage changes, it causes a change in the signal being processed.
Please note that in order to ensure the normal operation of the sensing system, the components must be matched. If these components do not match well, the measured amplitude of the vibration will be inaccurate. As a default, proximity detectors are calibrated using AISI 4140 steel. If the types of steel vary widely, it may affect the measurement accuracy. Other materials can be used to calibrate the proximity detector if necessary.
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