www.rulmecacorp.com TC101: 03/07

Taconite Plant Control Panel- “Before & After” (Minnesota—USA)Left photo shows control panel of taconite plant DC-powered variable speedconveyor control system before 1995 conversion to AC drives. Note SCR's,relay banks, and timer banks.

Right side shows control panel after conversion to AC motorized pulleyscontrolled with variable frequency drives. Elimination of SCR's and relaybanks improved reliability, simplified troubleshooting, and reduced energyloss.

Technical Precaution: The power and current range of the VFD must beselected according to the full load amperage given on the Motorized Pulleydata plate.

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Motorized PulleysVariable Frequency Drives

Taconite Plant - After Conversion (Minnesota—USA)Taconite processor converted limestone feeder conveyor drives from 1975vintage DC motors and chain/sprocket speed reducers to 460 volt 3 phase60 Hz AC-powered Motorized Pulleys in 1995. Photo was taken beforechute and hood were reinstalled. ABB variable frequency drive (VFD) driveseach 19.72” diameter 5.5 HP motorized pulley to a maximum belt speed of120 FPM. Torque loss is limited to less than 5% because operating fre-quencies are between 12 and 66 Hz.

Technical Precaution: When driving motorized pulley with VFD on 460 volt3 phase 60 Hz power supply, always restrict frequencies to allowable fre-quency spectrum of 12 to 66 Hz to avoid torque loss and heat build-up.

Various Limestone Quarries (Georgia—USA)Photo shows two of ten 15.75” diameter Motorized Pulleys installed 1994-1998 to automatically “choke feed” tertiary gyratory crushers. Working incombination with a VFD and an ultrasonic sensor, each Motorized Pulleydrives a 36” wide belt at a maximum speed of 120 FPM to transfer 4” minusproduct from hopper to crusher throat at 425 TPH.

Technical Precaution: When driving motorized pulley with VFD, filter VFDoutput if it is more than 30’ from motorized pulley to avoid resonance-induced voltage spikes.

Taconite Plant - Before Conversion (Minnesota—USA)Prior to 1995 conversion to Motorized Pulleys, old maintenance-prone chain& sprocket units served as DC motor speed reducers. Frequent lubricationof pulley pillow blocks, maintenance of chains/sprockets, expanded metalsafety guards, and DC motors were all eliminated with the installation ofMotorized Pulleys at this location.

Technical Precaution: When converting a system to use a VFD do notundersize the conveyor drive. Make certain conveyor drive provides enoughbelt pull at each end of the desired belt speed range. Remember that horse-power is linearly proportional to frequency (e.g. a 10 HP Motorized Pulley,designed to provide 1,080 lbs of belt pull at 460 volts and 60 Hz, will provideapproximately 1,080 lbs of belt pull at 30 Hz, but this equates to 4.9 HP.)