Capital Equipment News August 2019

TOTAL COST OF OWNERSHIP – VIBRATING SCREENS

equipment is designed with the application and existing infrastructure in mind. When designing, Kwatani considers many factors that affect the life of the screen, efficiency and performance. The aim is always to produce a durable, long-life screen that does the job properly. “These factors have a massive effect on the total cost of ownership equation, and they have to be taken into account, while at the same time meeting the tonnage and process efficiency requirements. It is always important to design a solution that can give the most optimal output at the given infrastructure,” she adds. Correct choices Schoepflin also reasons that the choice of various components of the screen, depending on the application requirements, is important in designing and manufacturing a screen that offers optimal cost of ownership. For example, the correct choice of isolators is significant. “The screen stands on an isolator and it’s an important factor when designing a vibrating screen. It needs to be sized according to the size of screen and type of building structure” says Schoepflin. There are three basic isolators used in vibrating screens – coil spring, rubber buffer and a torsional spring. A coil spring typically gives the best isolation because its stiffness is linear across the stroke range. A rubber buffer, although non-linear, offers a better load handling and damping capacity. A torsional spring can be mounted on the support frame and that completely prevents side-way movements and keeps the machine in line and stable during start-up and stopping. Starting and stopping of a vibrating screen needs to be carefully considered in the design process. In the tests done by Kwatani on a specific screen, a coil spring takes 50 seconds to stop, a rubber buffer stops at 21 seconds, while the torsional spring stops within 12 seconds. “For cost-effectiveness, if the machine needs to be stopped in a certain manner, we can adopt a hybrid approach because a torsional spring is a bit expensive. We can provide the required stability by combining a torsional spring and a coil spring to get the cost element in line – and this has a vast impact on the total cost of ownership,” says Schoepflin. Another important parameter is the testing element. Every Kwatani unit is tested before it’s shipped and all units are commissioned by the company’s experienced and qualified technicians. This process ensures that the unit meets the design parameters that it was designed and fabricated for. “This is done to make sure that the unit meets the desired quality and robustness,” says Schoepflin, adding that in terms of quality, the OEM is

The robust grizzly screen used in an iron ore application being prepared for transportation.

One of the largest screens manufactured by Kwatani for the coal mining sector.

“For me, cost of ownership entails five key parameters: capital cost, maintenance costs, equipment uptime, life of equipment and operating efficiency.”

Kim Schoepflin, CEO of Kwatani

TALKING POINT

and downstream processes,” says Schoepflin. She adds that Kwatani’s engineers and metallurgists engage with the customer to understand what the customer is trying to achieve in terms of their application, what is the ore like and how it behaves, as well as where the vibrating screen will go, because more often these units are supplied on brownfields projects. “It’s not always new plants. New plants are few and far between. We see a lot of improvement projects, plant optimisation, increasing life of mine and brownfield expansions. So we need to understand where the equipment will fit in the existing infrastructure,” says Schoepflin. “It’s about working through each case through the eyes of a consultant; analyse the condition of existing equipment,

the customer’s requirements and the infrastructure. That incorporates the design with the most cost-effective solution,” says Schoepflin, adding that it is pointless to offer a screen that may give better processing efficiency, but not fitting into the existing infrastructure or requires massive plant modification. She reasons that a plant modification can actually cost more than the price of a new screen. Therefore, there is need to consider where the screen will go in the existing plant setup, its impact on the existing infrastructure, for example, power requirements, available headroom, weight restrictions and existing shoots, among others. The information is then disseminated into the mechanical design process where the

CAPITAL EQUIPMENT NEWS AUGUST 2019 18