Electricity + Control September 2019

round up

DRIVES, MOTORS + SWITCHGEAR

Long-lasting motors and gearboxes for vibrating screens

He also highlights the massive centripetal forces that are exerted on the screening machine by the unbalanced motor and gearbox. This make it essential to secure them well to the screen. “We specify our own fabricated bolts, nuts and washers for this,” he says. “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 other motors, to provide a better contact surface. Mayhew-Ridgers cautions that if there is the slightest imperfection in the flat surface of the join, this can cause costly damage to the drive and the screen. “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.” Enquiries visit: www.kwatani.co.za

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. Kenny Mayhew-Ridgers, Chief Operating Officer at Kwatani, says local design and manufacture to the highest standard is 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. He highlights some key design considerations. These include optimal sealing arrangements to keep electrical components dry and clean. Power cables must always enter from the underside, to prevent water ingress. The design needs to 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 says. “Kwatani’s 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 a double-sealing arrangement for the lid, which includes a gasket.” Kwatani’s gearboxes are fully locally manufactured, with only the 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. The gears and shafts are locally fabricated by selected suppliers and the housing is cast by a local foundry and machined to exacting specifications. Mayew-Ridgers says Kwatani is probably the only OEM that services its own gearboxes. This ensures adherence to strict tolerances so that the units provide sustained performance and longevity.

Kwatani motors and exciter gearboxes are designed and manufactured locally.

Improved design and efficiency favours HV motor replacement

performance and direct savings in energy consumption. “When motor failures occur, Zest WEG Group has the ability to conduct a detailed on-site analysis,” Spohr says. “Based on a root-cause analysis, we can provide a failure assessment which will enable the customer to make an informed decision.” The assessment includes an energy consumption analysis conducted with specialised software. Taking account of the machine’s application, ZestWEG Group then recommends enhancements for greater control and efficiency. These include motor control options such as variable speed drives for applications such as fans and pumps. “New, more reliable motors also contribute significant productivity benefits,” says Spohr. Enquiries: ZestWEG Group. Visit: www.zestweg.com

“As a leading technology provider of a wide range of motor products, we have the capability to design a replacement motor to match the footprint of the original unit,” Spohr says. “This means there’s no need for the customer to modify mechanical infrastructure or electrical design to accommodate an upgraded motor.” He notes that, with the design lifespan of electric motors ranging from 20 to 30 years, there are still many old units in operation around South Africa. However, technological improvements in motor design and efficiency present a strong case for the replacement of old units rather than repeated repairs. The cost of a major motor overhaul can be up to 60% of the cost of replacement and the advanced technology of the new units offers greater reliability and efficiency, which means improved operational

The applications knowledge of Zest WEG Group, coupled with the design capability of parent company WEG, make it easier for old high voltage (HV) motors to be replaced with new, improved HV machines within the customer’s existing footprint and operational configuration. David Spohr, the group’s newly appointed Business Development Executive points out that, compared to HV machines designed 20 to 30 years ago, advances in technology often allow for new HV units to be manufactured at a smaller scale than the originals. Spohr works with customers to optimise their HV motor operations. WEG’s HV motors are typically purpose- built to meet the needs of the customer. While smaller in dimension compared to the original HV motors, new motors still deliver the required performance at even higher output and efficiencies.

10 Electricity + Control

SEPTEMBER 2019