MechChem Africa

MechChem Africa visits the Spartan facilities of Kwatani and talks to COO, Kenny Mayhew-Ridgers, about the company’s industrial offering, the research and development mindset and some key aspects of vibrating product design.

“While mining is still the biggest focus of our business, about three years ago we began to also focus on the industrial side of material sizing, which is now a fast growing area for us,” begins Mayhew-Ridgers.

As well as including much finer screening requirements, the industrial side is often associated with food grade materials and standards. “We typically look at using stainless steel for the aperture screens and contact materials. Powders and dewatering applications are common.”

Kwatani Circular industrial ScreenHe cites Rooibos tea as a typical example, where an evenly fine size distribution is required to give good diffusion and to remove any non-leaf material. “Sugar and salt are other examples, where all the granules must be fine enough to pour without containing powders. Good quality products have particles of very close to equal sizes, carefully packed for easy use and less mess,” he says.

“Then there are the powders, such as limestone, which is used, for example, as an additive to chicken feed to strengthen the bones of heavy broilers,” Mayhew-Ridgers tells MechChem Africa, adding that another industrial application is sizing the additives used in paint manufacturing.

“The requirements of these screens are very different to those in the mining industry and understanding them is another angle for us compared to our core mine screening strength.

Kwatani manufactures two types of industrial screens, one being circular and the other rectangular. The circular screen is driven by an unbalanced motor and exciter mounted on the vertical axis of the machine. This creates a circular vibrating motion in the horizontal plane. While the fines pass through the aperture’s mesh, the ‘overs’ are thrown outwards by centrifugal forces, over the edge of the screen and into a separate chute.

These are low profile machines that are ideal for smaller scale batch sizing of material in the 5.0 mm to 100 µm size range. “This one has a rotating scraper underneath the mesh to prevent the screen from clogging, which is a particular problem. It is also possible to place several different screening rings below each other to sort the material into several size fractions,” Mayhew-Ridgers says.

“If the material is very fine, in the 100 µm range for example, then even the weather will affect the separation accuracy. When tested on a dry day, it might work perfectly, but when the humidity is high, the fines start to bind together and the screening process may significantly be compromised. So, for some applications, we need to install the solution into a controlled environment,” he advises.

Generally speaking, rectangular industrial screens are better suited to finer materials. “These also vibrate in the horizontal plane, with an eccentric shaft creating a to-and-fro movement along the length of the screen. Balls running underneath the screen mesh are bounced against the screen to shake loose material blocking apertures and a slight decline promotes forward movement of the material,” he explains.

The in-line motion of the screen enables a longer screen length to be used, which, compared to circular screens, can offer better screening efficiency for finer materials.

“In both of these systems, the challenge is to keep the mesh clear and clean,” he notes. “In our test laboratory, we have test screens and apertures based on both technologies for sizing material from 12 mm down to 45 µm,” he notes, adding that this is as fine as the muslin cloth used to make cheese.

“We strive to help manufacturers and industry explore different aperture mesh and to test which technologies perform better on the materials they are sizing or using. This helps us to design and manufacture customised solutions optimised for a specific application,” Mayhew-Ridgers informs MechChem Africa.

A flexible mine screen test rig

The most recent addition to the Kwatani laboratory is a test plant for mining applications. “This is a vertical vibrating screen for sizing rock of up to 150 mm – and by using modular screen panels with apertures down to 0.3 mm, we can also do dewatering,” he explains.

“This is a fully adjustable test screen,” he continues. “Several things have to be taken into account when it comes to screening: the drive angle of the exciter beam, which is currently set at a 50° angle from horizontal; the screen or deck angle, currently horizontal; the modular and replaceable screen panels with their different apertures; and the stroke and vibration frequencies. All of these are variables in this system,” he explains. Read more…

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