Motor matters

Vibrating motors: For dewatering screens that use high-frequency vibrating motors, operators need to know that these motors run fast, from 900 to 1,800 rotations per minute, depending on the screen and motor.  Additionally, their linear throw can equal up to 6 g (six times the force of gravity, which means that one ton of sand is equal to six tons – or 12,000 pounds – of force), so they generate a lot of force driving up and down. If these motors and their mounting apparatus are not kept properly maintained, they can destroy themselves rapidly and create safety hazards.

As a standard step in safety and operating the machine efficiently, producers need to maintain the bearings on the motors and should follow manufacturer-recommended intervals. The motor’s manufacturer provides greasing schedules for the bearings, as well as startup procedures, which should be included in the screen manufacturer’s operation and maintenance manual.

Ensure that bolts are tightened to the correct specifications. If the bolts or the frame are cracked, repair them immediately. Most manufacturers will recommend checking the torque on the bolts prior to initial startup when the unit is first installed, followed by regular inspections at least twice a year. Inspect the motor mount regularly; if cracks are found, repair them immediately.

Eccentric drives: For eccentric shaft dewatering screens, the maintenance of the motors and bearings is similar to that of traditional sizing screens. Manufacturers should provide schedules for maintenance, but most recommend checking the belt torque on the wheel case approximately four times a year. It is a good idea to check the drive belt and sheaves daily, as well as for leakage from the drive shaft seal. The pillow block bearings should be greased every couple of weeks or according to recommended intervals. Producers should also check the wheel case oil for contamination after 250 hours of operation and change it according to manufacturer specifications.

While dewatering screens may not be maintenance intensive, a basic understanding of how they perform and what maintenance they require will guarantee long-term success.

Bio: John Bennington is vice president and general manager for Columbus, Neb.-based GreyStone Inc., a manufacturer of sand washing and classifying systems. He also is a past chairman of the National Stone, Sand & Gravel Association’s Manufacturers and Services division. Bennington has more than 15 years of experience in the aggregate industry. He may be reached at 888-346-9274 or johnb@greystoneinc.com.

Headshot: EquipMgmt-AM1008-Bennington.