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Total Cost of Ownership – Vibrating Screens

Discoursing TCO of vibrating screens Large vibrating screens are a critical part of processing plants at mines and quarries. If not correctly engineered, the operating costs can become extremely high – to the detriment of mining operations already operating under severe cost pressures. What are the key design and engineering factors that affect total cost of ownership of vibrating screens? By Munesu Shoko.

Large vibrating screens play an important role in the processing of ore at mining operations. Traditionally, the focus has always been on the capital cost, but Kim Schoepflin, CEO of Kwatani, a leading South African vibrating screen manufacturer, reasons that like any other piece of capital equipment purchase, the cost of owning a vibrating screen should be the principal factor when it is procurement time.

But what are the key factors that affect total cost of ownership of these crucial pieces of equipment? “For me, cost of ownership entails five key parameters: capital cost, maintenance costs, equipment uptime, life of equipment and operating efficiency,” explains Schoepflin. However, she reasons that the design and engineering of vibrating screens has a great bearing on these five factors. If not correctly engineered, the operating costs of a large vibrating screen can tremendously shoot up.

Knowing the exact type of machine that should be inserted in a plant, understanding the requested function and developing a machine that best suits these needs is important. Therefore, when vibrating screens and vibrating processes in general are concerned, it is important to deal with expert companies like Kwatani. Leveraging 43 years of experience, with 15 000 units across 37 countries, Kwatani has over the years lived up to its “engineered for tonnage” philosophy, anchored by the drive to offer its customers the lowest total cost of ownership possible. “We believe that innovation and technology are the most important pillars of our ‘engineered for tonnage’ philosophy,” she says.

 


Fit-for-purpose manufacturing

With uptime in mind, reliability of vibrating screens is key. Reliable vibrating screen designs are dependent upon the proper marriage of the manufacturer’s capabilities and the understanding of requirements of the design. It is for this reason that Kwatani doesn’t offer catalogue sales for its vibrating screens; every unit is customised to meet the unique operational requirements.  

“The in-house design expertise gives us the ability to customise a piece of equipment to the needs at hand. Our knowledge base stems from a mechanical metallurgy expertise. We have to understand how our equipment integrates into the mine’s processes and how it impacts the upstream 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 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 one of the only 5% of local manufacturers of its size to be ISO9001:2015 certified.

Reiterating the company’s testing capabilities, Schoepflin makes special mention of the company’s variable speed drive that has been connected to the test bench with specialised monitoring software. This allows Kwatani to experiment with the gearbox at different speeds. “This allows us to be more accurate when specifying the required drive for the vibrating screen or feeder, so that we can specify the right size and capacity in a more scientific way,” she says.

“For instance, we may find that a smaller drive can provide the motion required without necessarily needing a larger drive, allowing the customer to save on energy costs. We are able to size the drive to the need, because often a larger drive means bigger upfront costs, and higher energy consumption.”

 

Uptime and maintenance costs

Schoepflin says in a sales situation, often customers opt for the cheapest unit in terms of capital cost. However, in most cases the cheapest vibrating screen tends to be the most costly in the end because of lack of required efficiency, breakdowns, maintenance costs and related downtime. 

“The fact of the matter is that customers need to compare the actual efficiency of the units, lifetime costs, downtime and how much and difficult the maintenance is. With Kwatani screens, only wear parts and drive components are maintenance items. Typically a steel part is not a maintenance item because it is built to last,” she says.

“One of the most important things in cost of ownership, especially considering the importance of a screen on a mine, is plant uptime,” says Schoepflin, adding that regular, cost-effective maintenance is essential in ensuring plant uptime. “Regular service is probably one of the most important elements in achieving the optimal cost of ownership.”

Schoepflin reasons that the industry is currently suffering from a lack of skills. To help close this gap for its customers, Kwatani probably has the highest number of tertiary qualified staff of any OEM of its class. In fact, the company has a building that houses highly-qualified engineers only.

When it comes to maintenance, Kwatani offers customised service level agreements. “We offer customised service level agreements because not every customer is the same. In some instances we have to continuously audit the screens and maintain them ourselves. In other cases we can train the customer’s workforce to oversee maintenance,” she says.

“Our service programmes are not catalogued – it depends on the individual needs of the mine, which is an important factor. Together with the design, quality, efficiency and fitting the infrastructure, we find the service element being an important parameter in the cost of ownership equation,” says Schoepflin.

Kwatani also offers a cost per tonne operational basis. “We also have a cost per tonne agreement, where instead of getting paid for our screens, we get paid on a cost per tonne basis.This type of contractual relationship aligns the interests of both the mine and supplier.  This formula of sharing tonnage and risk positions Kwatani as a provider of value.” she says.

To help customers extend the lifetime of their machinery, Kwatani also offers refurbishment programmes. “We refurbish our large screens. They lend themselves to refurbishment. When they come for refurbishment, we also look at the wear patterns and advise the customer on possible changes that can prolong the life of their screens,” concludes Schoepflin.

 

Quick take

The design and engineering of a vibrating screen has a great bearing on total cost of ownership

·         Knowing the exact type of machine that should be inserted in a plant, understanding the requested function and developing a machine that best suits these needs is very important

·         Reliable vibrating screen designs are dependent upon the proper marriage of the manufacturer’s capabilities and the understanding of requirements of the design

·         The choice of various components of the screen, depending on the application requirements, is important in designing and manufacturing a vibrating screen that offers optimal cost of ownership

 

Talking point

 “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