Tag Archives: Kenny Mayhew-Ridgers

Kwatani large vibrating screen customisation pays off

Process plant designers often underestimate the movement of large vibrating screens when these machines start and stop, a challenge for which Kwatani says it has found an innovative and cost effective solution.

According to Kwatani’s Chief Operating Officer, Kenny Mayhew-Ridgers, the company has achieved considerable improvements in many screening applications by selectively fitting torsional springs alongside coil springs.

“It is well known that the vibrating motion of a screen impacts on the building and structural accessories around it,” Mayhew-Ridgers says. “This vibration is addressed by fitting isolators between the screen and the plant floor, and by constructing the plant building to certain minimum structural specifications.”

However, the focus is often on the frequencies that the screen generates in its steady-state phase – or the normal running phase – rather than during the transient phases when the screen is starting up or slowing down to a stop, Kwatni says.

Mayhew-Ridgers highlights that it is during these transient phases that the screen’s movement becomes amplified and potentially most destructive. Isolators between the screen and the floor – common among which are coil springs and rubber buffers – are meant to absorb vibrations and prevent damage to surrounding infrastructure. However, the transient phases, especially when stopping, can generate considerable sideways movement of the screen, which must be avoided.

“Traditional isolators like coil springs usually perform well in controlling the up-and-down movement of the screen,” he says. “Our experience is that the sideways movement, which is induced most strongly when the machine stops, can be better controlled by torsional springs.”

However, he notes that coil springs retain the advantages of being cost effective and providing a good linear isolation of the screen from the building structure. In this respect, their isolation characteristics are generally better than rubber buffers which excel in terms of their damping qualities.

“The torsional spring provides the best of both worlds, giving a good linear range for compression during operation while also becoming non-linear like the rubber buffer during stopping,” Mayhew-Ridgers says.

Using its experience observing screens operating in the field, Kwatani has developed and trialled various solutions in its dedicated testing centre at its headquarters in Kempton Park, South Africa. By optimising the best combination of coil springs and torsional springs, the company says it has succeeded in achieving the best results for customers.

“It’s not that torsional springs are better than coil springs,” Mayhew-Ridgers says. “It is about finding the right combination – through intensive testing and adaptation – for the customer’s particular requirements; we have both the expertise and the equipment to do this.”

Kwatani breathes new life into scalping screens with rubber, polyurethane wear panels

As mines move towards using one large scalping screen between primary and secondary crushers – rather than a modular approach using multiple smaller screens – Kwatani says it has found ways to triple the panel life in these single mission-critical units.

According to Kenny Mayhew-Ridgers, Chief Operating Officer of Kwatani, any downtime in this single-line stream would require the mine to store several hours of production. While some mines schedule regular weekly production halts during which an exciter or worn screen panels can be replaced, many operations are not so lenient, he said.

“The message from these mines is clear: the longer the scalper can run between maintenance interventions, the better,” Mayhew-Ridgers said. “Our research and development efforts, together with extensive testing in the field, have allowed us to extend the life of screen panels from eight weeks to over six months.”

While smaller screens use wire mesh screening media, Kwatani has evolved larger screens that use rubber or polyurethane screen panels. Although these panels present less open area, they deliver important advantages.

“Key to the success of our design is our integrated approach – which matches the panel design with that of the scalping screen itself,” Mayhew-Ridgers said. “This allows us to achieve a balance between screening area, aperture layout and screen panel life – a result based on a sound understanding of screen dynamics.”

Whereas wire mesh undergoes rapid wear from abrasive materials, the rubber or polyurethane panels are more wear resistant and deliver longer life, according to the company. The latter require gentler declines for effective stratification, but a key factor is the stiffness of the screen bed.

“The stiffness of the supporting structure must go hand-in-hand with the screen panel design to achieve our required results,” Mayhew-Ridgers said.

Polyurethane panels, while strong and lightweight, have screening apertures that tend to be too stiff for heavy-duty scalping applications. This leads to blinding. Rubber overcomes this problem, however, and also delivers improved wear life.

Kwatani has also developed a panel replacement system – with a fastening mechanism on the underframe – that improves safety and saves time, it says.

Kwatani solves the screening equation at South Africa coal processing plant

Kwatani has once again shown its mineral processing expertise in a retrofit project that saw one of the largest coal processing plants in South Africa boost screening throughput.

The South Africa-based company was brought in to consult on possible solutions to assist the plant in not only returning its screening throughput performance to the original design parameters but increasing it further.

Kwatani Chief Operating Officer, Kenny Mayhew-Ridgers, said: “Having evaluated the challenges on site and consulted extensively with the plant personnel, we determined that the suggestion to incorporate a bigger gearbox onto the screen would fail.”

The screen lifespan was in excess of six years and Kwatani determined it would not be able to accommodate substantially larger gearboxes offering 50% more output than the currently installed exciter gearboxes. “This would have resulted in irreplaceable damage to the screens,” Mayhew-Ridgers stated.

Because the customer was also looking for a quick and cost-effective solution, purchasing new screens with larger vibration capabilities was not an option, according to the company.

Kwatani came up with a simple solution, according to Mayhew-Ridgers.

“The plant was achieving 450 t/h on 480 t/h screens and was looking to increase this to about 525 t/h. This equated to roughly a 17% increase in performance. Replacing the screen’s existing gearboxes with those that could deliver greater vibration but would not exceed the output torque that the 37 kW drive motor could provide was the answer,” he said.

With a range of locally designed and manufactured exciters gearboxes in its portfolio, Kwatani was quickly able to provide the customer with two new exciter gearboxes delivered to site, installed and operational in the two-week timeframe the customer was looking for. “The increase in screen throughput was immediate,” Mayhew-Ridgers said.

The success of the retrofit saw Kwatani secure the order to replace three additional screens for the customer with new exciter gearboxes now currently operating at 550 t/h – 22% more than the original requirement. “Our success has proven our capabilities and screening knowledge and we have further secured all the screen repair work as well,” Mayhew-Ridgers added.

“We have positioned this business to offer expertise that extends beyond the supply of screening equipment. Our product knowledge enables us to correctly specify the right equipment and components for the application – in a case-by-case scenario,” he concluded.

Kwatani screens and feeders tackle manganese ore in South Africa

As a vital aspect of a plant expansion at a manganese mine in the Northern Cape of South Africa, Kwatani says it is supplying four heavy duty vibrating screens and 10 feeders to help boost throughput.

According to Kwatani CEO, Kim Schoepflin, this large-scale equipment is custom-designed and engineered for tonnage to meet the mine’s challenging operational requirements.

“Manganese ore is very demanding on vibrating screens as it has a high specific gravity and is also very abrasive,” Schoepflin says. “Our machines are engineered to perform the application’s duty requirement while being robust enough to deliver maximum uptime.”

The units being supplied include a 3.6 m double-deck scalping screen, a 3 m double-deck screen, a 2.4 m screen and a 1.8 m dewatering screen. A local OEM that has designed and engineered vibrating screens for over four decades, Kwatani has built a reputation for world-class expertise and capability, it says.

“Customers choose us for our engineering track record – developing technology that can manage the tonnages they require,” Schoepflin says. “This means understanding each mine’s specific conditions, and then building a design to meet a range of complex mechanical and metallurgical factors.”

The order to the mine is being rolled out on time and on specification to the customer’s satisfaction, according to Kwatani COO, Kenny Mayhew-Ridgers.

“The efficiency and quality of our work process allows us to design, manufacture and deliver custom-designed screens in the same timeframes that other OEMs deliver standard models,” Mayhew-Ridgers said.

This is particularly demanding as custom-designed equipment undergo an intensive design process after being verified by rigorous finite element analysis in-house, Kwatani says. Prior to dispatch, all units endure intensive testing before being commissioned on a customer’s site. For this reason, Kwatani boasts its own in-house advanced testing facilities at its Kempton Park facility, in South Africa. Aligned to ISO 9001 standards, the testing protocols have been developed in-house with decades of experience. This allows full testing similar to cold commissioning, even before delivery to site.

Kwatani makes manufacturing commitment on comminution equipment

Vibrating screen and feeder original equipment manufacturer (OEM), Kwatani, is promoting the need for high-quality engineering and the strictest tolerances for unbalanced motors and gearboxes to ensure components can run over the long term.

The harsh operating conditions that screens face in mining operations makes having these safeguards in place all the more important, it says.

According to Kenny Mayhew-Ridgers, Chief Operating Officer at Kwatani, local design and manufacture to the highest standard is a “non-negotiable”, with the OEM designing its own range of motors, as well as locally manufacturing 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,” Mayhew-Ridgers says.

This includes optimal sealing arrangements for keeping electrical components dry and clean, Kwatani says. Power cables, for instance, must always enter from the underside to prevent water ingress, while the design must consider various orientations of the motor, depending on the angle of installation. Dusty conditions on mines also present a challenge that need to be addressed.

“Dust ingress can compromise the sealing configuration of the lid,” he says. “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 locally manufactured, with only the high quality bearings imported direct from leading global producers, it says. 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, meanwhile, 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.

Mayhew-Ridgers says Kwatani is probably the only OEM that services its own gearboxes. This, he says, ensures adherence to strict tolerances, so that units have sustained performance and longevity.

He also highlights the massive centripetal forces exerted on the screening machine by the unbalanced motor and gearbox, which makes it vital to secure them well to the screen.

“To achieve this, we specify our own fabricated bolts, nuts and washers,” 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 of are normally larger in Kwatani installations than those of competitors, for a better contact surface, the company says.

“If there is the slightest imperfection in the flat surface of the join, this can cause costly damage to the drive and the screen,” Mayhew-Ridgers says. “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.”