Using quality motors and gearboxes optimises screen economy

1 August 2019 Electrical switching & drive systems & components

Harsh operating conditions on vibrating screens demand high quality engineering and the strictest tolerances for unbalanced motors and gearboxes, or they simply do not last. According to Kenny Mayhew-Ridgers, chief operating officer at Kwatani, local design and manufacture to the highest standard is therefore a non-negotiable. The company designs its own range of motors and locally manufactures the gearboxes for its vibrating screens.

“We design our own motors with local conditions in mind, giving the customer a high performance and long lasting product,” says Mayhew-Ridgers. “This includes optimal sealing arrangements for keeping electrical components dry and clean. Power cables, for instance, must always enter from the underside to prevent water ingress. The design must consider various orientations of the motor, depending on the angle of installation. Dusty conditions on mines also present a challenge.

“Dust ingress can compromise the sealing configuration of the lid,” he continues. “Our design is therefore like a top hat, so the O-ring is not on a flat surface but rather on a cylindrical, vertical surface. There is even a double sealing arrangement for the lid, which includes a gasket.”

Kwatani’s gearboxes are fully locally manufactured, with only the high quality bearings imported direct from leading global producers. Gearboxes comprise two shafts, each with its own set of unbalanced weights linked to each other by a gear to achieve synchronised motion. Gears and shafts are locally fabricated by selected suppliers, while the housing is cast by a local foundry and machined to exacting specifications.

“We have spent a great deal of effort on the sealing configuration, to ensure no oil leaks,” he says. He notes that Kwatani is probably the only OEM that services its own gearboxes. This ensures adherence to strict tolerances, so that units have sustained performance and longevity. He also highlights the massive centripetal forces that are exerted on the screening machine by the unbalanced motor and gearbox. This makes it vital to secure them well to the screen. “To achieve this, we specify our own fabricated bolts, nuts and washers,” he explains. “If sub-standard fasteners are used, components can come loose and cause extensive damage.”

Unbalanced motors usually have to be installed at an angle. Taking account of the weight of these components, there are rigging points all around the housing to manipulate the angle of installation. The feet are normally larger than those of competitors, for a better contact surface. “If there is the slightest imperfection in the flat surface of the join, this can cause costly damage to the drive and the screen,” says Mayhew-Ridgers. “This is why OEMs like Kwatani have such detailed installation procedures on issues like torqueing of bolts. Installers and maintenance teams need to stick closely to these specifications.”

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