Pulling it all together
Joest is a wholly owned South African company which holds the licence and distributorship for Joest technology in sub Saharan Africa. The company manufactures and supplies vibratory screens and feeders to the bulk materials industry.

Operating out of premises in Spartan, Joest has the necessary resources to design, manufacture and test equipment at its facility. One of the primary differentiators is the company’s ability to select the most appropriate vibrating screen or feeder for a given application.

“We would typically analyse the process requirements and design the machine to suit the application, resulting in better process efficiencies and throughput,” Malcolm Skeen, sales director, Joest, says. “With this focus on custom specific equipment, we were well positioned to be able to offer SEP a cost efficient and viable solution.”

The company secured the full scope of supply in the crushing and screening building at SEP. This included a Joest secondary scalping screen, a secondary feeder and eight tertiary feeders which feed the tertiary screens that were supplied by Schenk Process.

The Joest secondary scalping screen is 3.6 metre wide and 10 metre long and is engineered to screen to 90 mm at 6 500 t/h. The secondary feeder and tertiary feeders are capable of handling between 1 200 to 2 000 t/h and are 2.5 metre wide and 4 metre long. The secondary feeder transfers material into the tertiary crusher, and the tertiary feeders, in turn feed the 3 metre wide by 9 metre long Schenck screens cutting at 27 mm.

During the design stages, the Joest secondary scalping screen, with a 43 ton vibrating mass, required in-depth finite element analysis to ensure optimum strength to mass ratio. “In addition, the metallurgical efficiency of screens is determined by the mechanical characteristic of the screen and this has to be factored into the machine from the start and cannot be retroactively adjusted on the screen,” Skeen says.

The secondary feeders had to be able to withstand significant bunkers loads which were also taken into account during the design and engineering of the feeder.

The jig beneficiation plant at SEP comprises eight modules and each module consists of nine screens in the format of a double deck primary vibrating screen of 3 x
6.1 metre, a 2.1 x 4.8 metre single deck secondary sizing screen, four 1.8 metre wide x 4.88 metre long jig dewatering screens and three 1.2 x 3 metre fines jig dewatering screens. In total, Joest supplied 72 machines for the jig beneficiation plant.

In addition to the SEP, Joest has supplied screen machines to other projects in the Northern Cape including the ASSMANG BKM Project and the company is considered the dominant supplier into hard metal mining in this region.

Skeen says that Multotec polyurethane screen cloth panels were selected for all screens on the plant. “The secondary sizing screen is fitted with 0.8 x 8.8 mm Multotec Hi Flow polyurethane screen panels and both the coarse jig dewatering screens and the medium jig dewatering screens have Multotec Hi-Flow panels, but with 3.5 x 9 mm and 0.6 x 8.8 mm slots respectively.” The fines jig has 0.63 x 8.8 mm aperture Multotec Hi Flow panels.

“The Multotec Hi-Flow screening system offers maximum screen surface area available for apertures as well as high open area, high throughput and efficiency,” Skeen says. In addition to this, the Multotec Saddle Top runners and T-Bar Rail System was selected for the screens capable of accepting such a system (48 off) in the jig beneficiation plant as it significantly increases the lifespan of vibrating screen support frames and screen panels.

“The Saddle Top system is a better solution in terms of maintenance on the runner and wear interface between the stringer and the panel. Similar variations are offered in the marketplace but we believe that the Multotec system is the most cost effective and definitely the best solution for this particular application,” Skeen says.

The Multotec Saddle Top is a saddle that fastens to a vertical laser cut flat-bar runner. This rail system replaces the conventional angled runners on a vibrating screen frame. Its major advantage is that when the fastening holes become worn it is only necessary to replace the saddle top itself and not the complete runner system. This can be accomplished with semi-skilled labour.

Manufactured from polyurethane, the Multotec Saddle Top has improved impact and abrasion resistance especially when compared to conventional angled runners. The excellent wear characteristics result in improved life as well as reduced maintenance and downtime.

The 24 fine jig dewatering screens were unable to accommodate Saddle Tops because of the nature of the deck frame.

“The jig beneficiation plant was an expansion in our market share in the screens business in that we typically supply machines for the front end of the process, so to engineer and supply screens for the downstream processes in beneficiation proves that we are able to offers full scope of screening solutions for a mining process,” Skeen comments.

Dewatering bins
Grinaker-LTA Mechanical & Electrical’s Metals and Minerals division secured the contract to fabricate, construct, install and assist with commissioning of the dewatering bins for the Sishen Expansion Project.

In total, 49 dewatering bins were supplied for the project in a phased approach. Each dewatering bin comprised 30 compartments and these are fitted with a wedgewire screen. The total length of each bin is about 60 metre and it is 14 metre high.

Material is transported via shuttle conveyor to the inlet feed of the dewatering bin, and water is drained through the sides of the dewatering bin which has a sloped angle of 32˚. The water drains through the wedgewire panels into a channel, while the product is gravity fed to a transfer chute.

The inlet section of the dewatering bin has solid panels while various wedgewire panel sizes were used at the outlet end of the bin. These panels were individually tailored to fit the configuration of the dewatering bin with the majority having a surface area of 2 metre x 550 mm.

Fabrication of the dewatering bin formed only a portion of Grinaker-LTA Mechanical & Electrical’s total scope of supply on the SEP. The company’s new Metals and Minerals Division secured two contracts at SEP.

“Our ability to provide a comprehensive multi-disciplinary service and the expertise within our different operating divisions has positioned us to provide a complete service for this type of project,” Marius Botes, general manager Grinaker-LTA Metals & Minerals, says.

The scope of the first contract involved the fabrication, supply and erection of all structural steelwork, platework and related items for the beneficiation and jig plant at the SEP. It also covered the installation of all mechanical items within the plant. Construction work was completed in the second quarter of 2007.

The second contract involved the detailing, fabrication and supply of the structural steelwork as well as the mechanical installations for the conveyors and transfer towers between the primary crusher and the run-of-mine (ROM) bed.

Multotec wedgewire screens, as used by Grinaker-LTA Mechanical & Electrical on the SEP dewatering bins, are made to tight tolerances of between 0 to -5 mm on the 10 metre diameter unit. “Just as important is the profiling of the wedgewire and the robustness of the screen deck itself,” Botes says.

Generally, wedgewire is supplied in stainless steel, as this ensures long life even in abrasive and corrosive applications. The wedgewire screen decking is also designed with high release angles to ensure minimal blinding and pegging. The type and size of profile as well as the slot width and materials are chosen to suit the mechanical and process requirements of the screen of jig concerned and the close tolerances on the aperture sizes ensure a uniform flow rate and dewatering efficiency.

The wedgewire can also be supplied in exotic materials for applications with varied chemical compositions if required. As part of Multotec’s overall service, it offers in-house Finite Element Analysis (FEA) prior to manufacturing, to confirm that the steel support structure and flooring are capable of meeting the full load bearing requirements.

Ultimate control
allmineral, acknowledged as the largest jig supplier in the world, was also involved on the prestigious SEP. “The process technology at SEP was developed specifically for this application and is the heart of the entire project,” Udo Busch, managing director of allmineral, says.

“One of the primary reasons SEP chose allmineral machines was essentially because of the control system, which will ensure optimum efficiency, recovery and grade,” Busch adds.

These alljig® machines are under-bed air pulsed jigs ensuring a physically stable operation and optimal jigging stroke with minimal energy consumption. Other alljigs® in operation in South Africa are at Cato Ridge in a manganese metal from slag recovery plant as well as an installation in Steelpoort for the recovery of chrome-metal from slag.

“Although we have almost 400 jigs in operation globally, this order for SEP is the largest single supply worldwide,” Busch adds.

Busch explains that a pilot plant was bought by SEP and test work was conducted over a period of two years prior to the project. “Following on the data from the pilot plant test work we, in co-operation and in consultation with the metallurgists from Sishen and Kumba Resources, refined the jigging process, especially with regard to the control system, ensuring optimum recoveries at the most appropriate grade.”

SEP ordered 18 jigging machines from allmineral in October 2005 and subsequently placed an order for an additional six alljig® systems. The first of six modules were installed and commissioned at the end of 2007 with the balance due during the second quarter of 2008.

Phase IA comprised the supply of six identical jigs each for the coarse, medium and fine ores with a total throughput of 1 000 t/h. Each module was designed to take the specified export product grade requirements into account. The first and biggest jig, the 4 metre wide coarse jig, was assembled complete with gate discharge system and deck in the local workshop prior to delivery in order to minimise the erection time on site as well as ensure that any possible assembly problems had been eliminated.

Screening solution
The Multotec screen cloth panels for the entire project were delivered in a phased approach to the various OEMs over a three month period. In addition to the supply of the screen panels, Multotec also concluded a maintenance contract with Kumba for all the polyurethane screening media installed on the SEP. This is on a rate per ton basis which will ensure optimum performance of the screens for the mine. Multotec maintenance teams are based on site at SEP and are responsible for monitoring and replacing panels as required.

Monitoring
Monitoring of the screen panels is performed using the Multotec in-house developed Hawkeye Monitoring Programme which effectively monitors screen maintenance processes to provide guaranteed efficiency.

Hawkeye is a Web based application, accessible anywhere in the world, which offers the user an easy-to-use interface to allow accurate and efficient recording of maintenance activities. These entries are stored in a database, and can be called up as required in a number of ways so as to zero in on what is actually happening on the screen. Another critical benefit is that screen panel life expectancy can be determined.

“At the end of the day, the success of the project was achieved through superior teamwork and meeting exacting customer demands,” Skeen concludes.

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