press_mechanical — vibration_health (accelerometer-motor-bearing)

Physics

A mechanical stamping press stores its stroke energy in a flywheel spun continuously by an induction main-drive motor, so the motor and flywheel bearings run at constant speed between strokes. A rolling-element bearing with a developing outer-race defect excites impacts at its ball-pass frequency (BPFO, about 3-5x shaft speed for common motor bearings), and as the defect grows the broadband velocity RMS (10-1000 Hz, ISO 20816-3) at the motor drive-end housing rises with it. Main drives of small and mid-size presses are 15-300 kW machines, ISO 20816-3 group 2 on a rigid foundation. The once-per-stroke ram impact is a short transient: taking the median vRMS over each window keeps it from reading as bearing wear. At 1500 RPM (25 Hz) the defect frequencies stay under 200 Hz and their harmonics under 1 kHz, so 4000 Hz acquisition leaves ample Nyquist margin; the edge reduces it to 1 Hz velocity RMS and band features.

Sensor

• Spec: piezoelectric accelerometer, IEPE/4-20mA output, 0.5-10 kHz bandwidth, stud or magnetic mount
• Signal: scalar (mm/s), range n/a

Example parts

• ifm electronic VSA001 vibration sensor with integrated velocity RMS and acceleration output
• SKF CMSS 2200 industrial IEPE accelerometer (100 mV/g, top-exit connector)
• Pepperl+Fuchs VIS-M18-AI-KH1 M18 vibration sensor (acceleration/velocity 4-20 mA output)

Mounting

Stud-mount the accelerometer radially on the main-drive motor’s drive-end bearing housing, on a flat unpainted machined spot close to the bearing, at the stud torque the sensor’s datasheet gives. Never mount on the belt guard, the flywheel cover or any sheet-metal panel: a flexible surface attenuates the bearing-defect signal and picks up the ram impact.

Wiring

2-wire shielded IEPE cable to a vibration input on the edge box (or a 4-20 mA analog input for a current-loop variant), routed away from the main-drive motor cables and any VFD output, strain-relieved clear of the flywheel, belts and the ram’s travel.

Validation

with the press running continuous strokes at its usual rate, compare the detector’s velocity RMS against a handheld calibrated vibration meter at the same bearing-housing point, and confirm the motor nameplate speed matches shaft_hz

Expected: detector velocity RMS within +/-10% of the handheld meter; shaft_hz within 2% of the nameplate speed / 60

Safety notes

• lock out and tag out the press main drive AND let the flywheel coast to a full stop before working near it; a flywheel keeps turning for minutes after the motor is off
• block the ram or slide (die blocks or the press’s safety block) before reaching into the press frame, per the press’s lockout procedure
• the motor housing can be hot after a long run; let it cool before mounting the sensor

Cost

150–700 USD, difficulty 2/5, ~30 min install downtime.