Tag Archives: Kwatani

UPS AND DOWNS OF APPLYING THE ‘BANANA’ SCREEN DESIGN

While multi-slope screens – also known as ‘banana’ screens – are commonly used in various screening applications, they need to be carefully designed with the specific purpose in mind, according to Kwatani CEO Kim Schoepflin.

“Multi-slope screens have been in use since the 1970s and have a significant reference base, becoming very fashionable mainly because of the benefit they offered in terms of higher velocity leading to higher capacity ,” says Schoepflin.

At the top of these screens is usually a first slope with a deck angle of at least 35 degrees – allowing material velocities of over 3 metres per second – curving down to end at about 10 degrees.
This original layout, however, is not always ideal for many operations today.

“When we design a banana screen at Kwatani, we are careful to understand exactly what the application is, so that we can align the number of slopes as well as change the angles of each slope to achieve better efficiencies,” she says. “In this way, we have been very successful placing these designs in diamond and coal applications, mainly in dense media circuits as well as for diamond scrubber plants for degritting.”

Failure to adapt the design appropriately to the application can lead to a number of challenges, says Kwatani COO Kenny Mayhew-Ridgers.

“Material velocity is exponentially linked to the wear rate of the panels, and this high panel wear will lead to frequent and costly maintenance,” says Mayhew-Ridgers.

Another design strategy to reduce panel wear is to create a more continuous curvature profile along the screen, with a higher number of slopes making for a gradual change of direction for material.
This is based on the simple principle that the greater the change of direction, the more the panel will wear.

“Insufficient drainage of water can also be an issue at these high deck angles, particularly with apertures of less than 1.0 mm which most are,” he says. “Where retention time on the screen is low, there could be too much carry-over of water to the next phase of processing, with wet product going onto conveyors and into silos, creating various problems related to moisture content.”

Schoepflin highlights that, in dense media processes, it is also important to recover as much of the medium – such as magnetite – as possible, which the steep slope may not allow.
To maximise recovery of the dense medium, the slope and material velocity may need to be reduced.

“The feed arrangements are also critical, as the material is being fed onto a steep angle,” she says. “The material needs to be fed at a low velocity onto the screen, and the application of water needs to be carefully controlled.”

A cost aspect that needs to be considered is that the physical height of a banana screen layout can also add to the screen infrastructure, as this structure also needs to be heightened.
In addition, this height can make the screen more difficult to access for maintenance purposes. All these factors need to be considered by a user when deciding upon whether a multi-slope screen is optimal and – if it is – exactly how the design needs to be fine-tuned.

LOOK OUT FOR KWATANI ‘BEAST’ AT ELECTRA – WITH ADDED SWEETENER

Leading vibrating screen and feeder OEM Kwatani will be showcasing customised products big and small at this year’s Electra Mining Africa exhibition, with live demonstrations showing the value of their laboratory test screen.

With a replica of the nose of its widest screen at its exhibition stand, visitors will sense the scale of these large ‘beasts’ currently at work in the mining industry.
They deliver solid performance not unlike rugby star Tendai ‘Beast’ Mtawarira, whose image will grace the stand. These large screens measure 4,3 metres wide and 11 metres long and are operating in the most arduous screening conditions.

“The design and construction of these screens is a clear indication of Kwatani’s technical capability, with quality ensured by our ISO 9001:2015 certification,” says Kwatani CEO Kim Schoepflin. “Not only must they be robust and fit-for-purpose, but they must also achieve continuous tonnage at the lowest cost of ownership.”

In addition to desktop simulation in the design of customised screening equipment, Schoepflin also emphasises the importance of physical testing to ensure that the equipment delivers the results expected.
A versatile test screen will therefore be on show – a metallurgist’s dream – to give visitors an appreciation of how material can be tested as part of designing the optimal solution for the most challenging screening applications.

The test screen allows all the key screening parameters – such as the speed, deck angle, drive angle, amplitude and screening media – to be changed as part of the research process.

On the other end of the size scale on the stand will be 30-inch round separator, demonstrating the gentle, effective spiral screening motion that reduces breakages in products of high value.
At Electra Mining Africa, however, visitors will be able to sample the separated products: sweets.

This unit is part of Kwatani’s range of smaller screens and separators for industrial and food-related applications, now processing almost 50 different materials and products from sugar and rice to gold slurry and bunker sand.

Schoepflin highlights the importance of suppliers aligning with the Mining Charter: “We are proud to be the first – and still the only – manufacturer of vibrating equipment to be black-owned, allowing us to make a valuable contribution to our mining customers’ transformation efforts.”

INDUSTRIAL, FOOD APPLICATIONS NOW BIG FOR SCREEN SPECIALISTS KWATANI

Known mainly for its large screens and feeders for mining, Kwatani has in recent years expanded substantially into various industrial and food sectors – currently providing screening solutions for almost 50 different materials and products.

According to Warren Mann, Kwatani’s business development manager – industrial division, the company is involved in screening a wide range of materials and foodstuffs from wax beads, carbon and bunker sand to tea, coffee, pet food and rice.

“Our strength is the ability to test the customer’s product or material in our own materials testing laboratory,” says Mann. “This is part of our solution-focused approach to deliver a customised machine that will add optimal value to the customer’s operation.”

These in-house facilities are vital in selecting the correct separator for each application.
By analysing and testing under simulated production conditions it is possible to determine the appropriate machine size and configuration as well as the optimum screen openings.

He highlights that Kwatani has for decades invested heavily in its local design and manufacturing capacity.
In 2012, it also acquired the assets of Lockers Engineers, and continues to supply Lockers customers with the full product range including vibrating screens and feeders, electromagnetic super feeder drives, controllers, vibrating trough conveyors and fluidised bed dryers.

The company’s rectangular R-type separators have a typical application in the sugar industry and are capable of screening 50 to 200 tonnes per hour of sugar to remove lumps and foreign material before grading and packaging.

“Spices and tea processing are other applications where we are actively involved, providing sizing and scalping screens that can handle up to 10 tonnes per hour,” he says.

Food safety comprises a key element in the design and manufacture of the screens that are used in food-related applications, and Kwatani has standardised on using stainless steel.
In addition, its workshop facilities have been optimised accordingly to achieve cost savings in the final assembly.

“We use high-grade stainless steel for any food contact surface, as mild steel tends to rust when exposed to excessive moisture and is not suitable in many food processing applications,” he says. “There are also specific plastics we use that are non-toxic and food-safe, adhering to hygiene and quality standards.
We offer a bonded screen mesh with food-safe epoxy, rather than a bolt down screen mesh, in order to eliminate the risk of bolts coming loose and entering the product stream.”

Kwatani’s S-type round separators are highly versatile and used in many different industries and have a special application in high temperature environments and liquid separation such as removing foreign particles from hot cooking oil.

Industrial products handled by Kwatani screens include the sizing of wax beads that are used in exfoliating creams. Clays such as bentonite and kaolin are also scalped.

“We have screens that can clean the sand in bunkers on golf courses, removing contaminants like grass and soil that have been tramped in by golfers,” says Mann. “In this instance we provide a mobile solution, so the screen can be easily moved to site, and powered by a small generator.”

The range of fine-screen meshes – with apertures of just 38 microns in size – can even separate blood from water and are used in environments like abattoirs.

Kwatani has a low-profile separator option with lower heights than the standard design. This allows it to fit into spaces too small for the standard design where installation space is limited.

Kwatani separators can also be used as safety screens as a last line of defence to remove off-spec product before it is packed.
This reduces the volume of returns and raises satisfaction levels among end-users.

“Manufacturing our own products promotes job creation and skills development, and also gives us the ability to offer high levels of product support, we know the products inside out,” says Mann.

KWATANI’S HUGE SCREEN ORDER INCLUDES LARGEST UNITS YET

In the single largest order for vibrating screens secured from any mine in the past two years, Kwatani has shown its mettle by supplying some of the largest vibrating screens in Africa to the world’s leading opencast coal complex.

According to Kwatani CEO Kim Schoepflin, the contract comprised 44 large screens boasting widths of up to 4,3 metres.

“Our equipment may be large and heavy, but each individual unit has been customised for its specific application, to efficiently handle the ore required,” says Schoepflin. “Moreover, the vibrating unit must be engineered to seamlessly fit into a new or existing building, and must operate in harmony with the rest of the processing plant.”

Among the larger units in the order were two double-deck, run-of-mine screens measuring 3 metres wide by 9 metres long, as well as three 2,4 metres by 6 metres degradation screens which will be installed in the mine’s drum plant. Also being supplied are twenty three screens and three vibrating pan feeders for the cyclone plant.

There are sixteen drain and rinse screens in the contract, four of which are generously sized at 4,3 metres by 7 metres, driven by two large gearboxes which deliver a centrifugal force of over 460 kN each.

“The successful handling of this magnitude of contract is a testament to Kwatani’s technical capability,” she says, “as we can handle these larger contracts while continuing to service all our other customers.”

Schoepflin highlights the skills and passion of the company’s family of 160 employees, combined with its extensive and well-equipped manufacturing facility in Spartan near Johannesburg.

“The vibrating screen comprises of thousands of different parts and components, each requiring precision engineering and a number of fabrication processes, which at the end are carefully assembled by dedicated staff,” she says.

She adds that Kwatani is the only OEM of vibrating equipment to engineer, assemble and test its exciter gearboxes in-house and at full load on its fit-for-purpose test bench – ensuring that every gearbox performs optimally before dispatch to a customer.

KWATANI SCREENS FOR ELIKHULU RETREATMENT PLANT

Engineering group DRA has ordered six large screens from Kwatani for the R1,6 billion Elikhulu gold tailings retreatment plant facility at Pan African Resources’ Evander operation in Mpumalanga.

“Kwatani was involved from an early stage in this project, so we were able to custom design this equipment at the study phase, allowing the EPC to readily integrate the design into the plant design,” says Kwatani CEO Kim Schoepflin. “Our focus here was to deliver a cost effective, fit-for-purpose solution to the customer that is technically appropriate to their needs; which is to retreat 1 million tonnes per month of gold tailings.”

Cognisant of the price pressures on all stakeholders, Kwatani was able to hold the price from the original quote date through to final agreement. Making the customer’s purchasing decision easier was also Kwatani’s substantial reference base in the gold sector, as well as at the Evander operations.

“We also helped the EPC with designs for ancillary equipment, assisting in holding down costs for the overall plant structure,” says Schoepflin.

Four of the six screens – the two trash screens and two carbon safety screens – are in excess of three metres wide, feeding 1,500 tonnes per hour. The remaining units comprise one regenerated carbon screen and one loaded carbon screen, through which some 2,000 m3 of slurry will pass per hour.

“We designed these six large screens to facilitate a commonality of spares in the plant, so that parts will be easily interchangeable. This will reduce the necessity for a holding a large inventory of these items,” she says.

She emphasised the low margins inherent to gold retreatment operations, highlighting the importance of reliability in the way that Kwatani equipment is designed, tested and maintained.

“Uptime of the plant is a key factor in sustaining a profitable operation in this sector, so we place high priority on both the process duty that our units must achieve and their mechanical durability to achieve low cost of ownership over their life-times,” she says.

KWATANI TAKES RUGGED SCREEN DESIGN TO NEW HEIGHTS

Spartan-based vibrating screen specialist Kwatani is building one of its strongest and heaviest screens yet, to undertake punishing duty at a South African iron ore mine.

The 54 tonne scalping screen – measuring over 10 metres in length and with a 3,7 metre width – is a single-line unit that will handle about 7,000 tonnes of run-of-mine iron ore per hour. It will take feed from a primary crusher with a top size of 400 mm, although the dimension of these boulders may still be up to 800 mm long.

“This run-of-mine feed will place tremendous load on the screen, particularly due to the impact and weight of the oversize rocks,” says Kwatani CEO Kim Schoepflin. “Significantly, a large portion of the material – as much as 50% of the feed – will move over the full length of the screen without passing through the apertures, so the screen must effectively ‘convey’ these heavy boulders without incurring damage.”

This also means that the bed depth will be relatively high, requiring the design to accommodate a bed of about 800 mm of material on the feed end and about 500 mm on the discharge end. Iron ore is a heavy material, so a bulk density factor of 2,5 has been applied to the design specifications.

Vibrating with a stroke that applies around five times the gravitational acceleration (5G’s) on the material, the mass of the rocks is effectively increased by five times, according to the Kwatani’s chief operating officer Kenny Mayhew-Ridgers.

“This places a very high requirement on the machine’s technical specifications and durability, so the mine has been very careful to choose a supplier that they trust completely to design and manufacture a unit of this capacity,” says Mayhew-Ridgers. “Even the panels had to be designed with internal structures so they could withstand the magnitude of these forces.”

Kim Schoepflin, ceo of Kwatani.

Schoepflin emphasises that the unit’s single-line status makes it a key item of equipment on site, with several parts of the process plant heavily reliant on its throughput.

“It is therefore vital that the screen runs reliably and continuously, as any stoppage will in turn disrupt the whole plant,” she says. “Uptime is an absolute non-negotiable.”

She highlights Kwatani’s capacity to design, manufacture, test, commission and maintain screens of this capacity and ruggedness.

“Our depth of expertise and experience in the field, combined with our substantial facilities and quality standards, equips us to custom-design and engineer fit-for-purpose machines that handle high tonnages reliably while doing the duty that customers demand,” she says.

KWATANI SAYS ON SPEC AND ON TIME ARE KEYS TO SERVING EPCS AND MINES

Faced with the ongoing challenge of being price sensitive in new capital projects, original equipment manufacturers (OEMs) must also ensure that their product and service offering helps create a sustainable foundation for the end customer’s ongoing profitability and efficiency.

“Being cost competitive upfront includes delivering on time and on specification,” says Kim Schoepflin, CEO of vibrating screen specialist Kwatani. “Once equipment is operational, however, OEMs still need to make sure that their equipment provides the lowest total cost of ownership.”

Meeting all the necessary performance criteria means both the process ‘duty’ requirements – managing the required throughput and product – as well as the structural and mechanical demands of durability, ease of maintenance and reliability.

Kwatani’s extensive in-house technical capacity to custom design and manufacture vibrating screens for a range of different applications allows it to align its equipment not only to closely meet the customer’s process requirements, but also to accommodate the existing plant infrastructure.

“We work closely with the EPC or the mine on the interface between the infrastructure and our equipment,” she says. “This may involve optimising the dynamic loading of a screen, taking into account the features and capacity of the plant structure, to avoid costly and time consuming plant modifications.”

It may even extend to offering advice on resonance issues where there are a number of vibrating screens operating in close proximity. The company’s experts have also been requested on occasion to assist with an appropriate chute design, which can influence the performance and life-span of the screen.

“At Kwatani, we are keenly aware that engineering costs on a mining project must be contained at every opportunity, so we minimise the impact that our equipment has on the number of hours that an EPC must invest in project engineering and implementation,” says Schoepflin. “We work to accommodate the client’s plant design by matching the footprint of our machines to those constraints wherever possible.”

She emphasises that this kind of adaptation is only possible with custom designed equipment, which is a key factor in Kwatani’s focus on engineered solutions rather than off-the-shelf products. Schoepflin also highlights reliability as non-negotiable when it comes to meeting project deadlines, as tight schedules are usually the order of the day in any capital project.

With an extensive reference base across the mining sector, Kwatani has recently constructed a heavy-duty grizzly feeder and a sizing screen for Vedanta Zinc International’s Gamsberg zinc project near Aggeneys in the Northern Cape. Another recent contract will see the company delivering six large screens to Pan African Resources’ Elikhulu gold retreatment plant at Evander.

HEAVY KWATANI SCREEN FOR GAMSBERG

Spartan-based vibrating screen specialist Kwatani, driven by its aggressive cost leadership strategy, is supplying a large exciter-driven grizzly feeder and a sizing screen to the Gamsberg zinc project near Aggeneys in South Africa’s Northern Cape Province.

As the flagship of miner Vedanta Zinc International/Black Mountain Mining, Gamsberg is set to exploit one of the largest known, undeveloped zinc ore bodies in the world, with SA-based ELB Engineering Services conducting the engineering, procurement and construction (EPC) services.

Kwatani was contracted to supply a heavy-duty grizzly feeder capable of feeding over 750 tonnes per hour of ore. Built with cast manganese grizzly bars for durability, this robust unit will withstand maximum lump sizes of up to 1,5 metre in size. Also supplied is a single-deck, motor-driven sizing screen of the same throughput capacity.

“Kwatani has a significant reference base especially in the Northern Cape, where we supply most of the mining vibrating screens,” says Kwatani CEO Kim Schoepflin. “Our installations are particularly well recognised in those areas with arduous applications.”

While price was a key consideration, Schoepflin highlights the customer’s insistence on robust equipment that is fit-for-purpose. Kwatani has been able to meet the project’s tight roll-out schedule, not just with the delivery of equipment but with all the necessary product documentation that will facilitate compliance and safe installation.

“We have completed our part of the project, and are ready to commission the equipment in line with the overall plant construction schedule,” she says. “We also assisted our client with the design of the chute that will feed the grizzly.”

After fabrication, the equipment was fully tested on Kwatani’s in-house test bench at its 17,000 m2 facilities near OR Tambo airport.

The supply of the equipment will come with an extended warranty which will include regular visits by field experts from Kwatani’s fully-fledged branch in the Northern Cape. The capacity of this facility will allow it to conduct both the commissioning of the equipment and the follow-up inspections and interventions.

GROUND RULES FOR REDUCING MAGNETITE LOSSES IN DENSE MEDIUM PLANTS

While the evolution of dense medium separation (DMS) technology has seen various advances since the mid-1900s, there are still a number of “fundamentals” that will allow users to reduce magnetite losses over the life of a DMS plant.

Speaking shortly after the Southern African Coal Processing Society’s biennial conference in Secunda recently where Kwatani, represented by Jeremy Bosman, presented a paper addressing the impact of appropriate screen selection on dense medium recover and highlighted the importance of adhering to certain ground rules.

“Across the different processes, there are basic principles that are common, such as the use of drain and rinse screens to recover magnetite from the product and reject streams,” says Kim Schoepflin, CEO of Kwatani.

She says a concentration of magnetite in the dilute medium must also be achieved to give a suspension of high relative density, or overdense, medium using wet drum magnetic separators.

Schoepflin outlines the fundamentals to be observed in restricting magnetite losses, regardless of which screening arrangement is chosen.

“The feed arrangement onto the screen must ensure that the full width of the screen is utilised,” she says. “Low feed velocities are also critical, as this maximises the drainage rate on sieve bends and multi-slope screens.”

She emphasises that the drain section, which includes both static and vibrating screens, must have sufficient area to recover 95% of the medium being fed to it, and that allowance must be made for potential blinding which will reduce the open area of the screen.

“It is vital to take the average particle size and bed depth into account when selecting the screen width,” she argues. “Running at too high a bed depth will increase medium carry-over from the drain to the rinse section, and will also reduce the efficiency of the rinse water in washing off the medium; this in turn will lead to an increase in magnetite losses.”

Another important aspect to observe is that sufficient rinse water must be used to wash off the adhering medium, without overloading the wet drum magnetic separators. Provision must also be made at the end of the screen – after rinsing – for the clean coal and reject material to dewater before being discharged off the end of the screen, says Schoepflin.