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.
The advantages that a dry-type or cast resin transformer offers played a role in Trafo Power Solutions securing an order for thirteen custom designed units. These dry-type transformers are destined for installation at the large scale Rand Water Zuikerbosch Water Treatment Works.
David Claassen, managing director of Trafo Power Solutions, says that is it most gratifying for the company to have received this order only months after the business was established. Claassen, an electrical engineer with broad ranging and high level experience in many sectors, recently established Trafo Power Solutions to distribute and service transformer products in Africa from Canada-based Hammond Power Solutions (HPS).
The contract to supply all the cast resin transformers for this waste water treatment facility will include units that range from 100 kVA up to 1600 kVA. Included in the scope of supply is the complete earth fault protection system which will be in the transformer enclosures.
Claassen says that the rationale for a project to go the route of using cast resin or dry-type transformers is for a number of reasons. “Prime among these is the inherent safety offered by these units as well as ease of installation given the fact that they are installed inside built substations as opposed to outdoors with associated special bunding and civils.
Dry-type transformers are categorised as F1 in terms of international fire resistance ratings, making them low risk as they are self-extinguishing and flame-retardant by nature. With zero risk of fire, the high safety rating of dry-type transformers allows them to be installed indoors, avoiding the cost and inconvenience of the special structures normally required to accommodate the safety and environmental hazards related to oil-filled units.
“And this results in savings because there is no need for costly civils and site work to be done,” Claassen adds
Less maintenance is another advantage; dry-type transformers are low in maintenance and could last for 25 years without significant attention, while oil-filled transformers require regular maintenance including oil sample analysis to ensure operational consistency and safety.
Claassen says that the units have been witness tested at the manufacturing facility and are scheduled for delivery to site in the first quarter of 2018.
Although transfer points potentially contribute to some of the highest maintenance costs on a mine, engineers seldom view transfer systems as a critical element of the minerals processing system.
So, says Mark Baller, managing director of Weba Chute Systems, who maintains that transfer points — by the very nature of their application — should be viewed with the same level of importance as any other machinery in the minerals processing cycle.
“The uncontrolled discharge of bulk materials through conventional chutes has a history of escalated maintenance and replacement costs, not least of which can be attributed to excessive wear and other related problems,” Baller says. “All of this adds up to unnecessary expenditure and a headache for the engineers concerned.
“Numerous successful installations of Weba Chute Systems have proved that the correct use of our streamlined, scientific approach to the dynamics of bulk materials handling greatly reduces the problems associated with conventional transfer chutes and results in significant cost savings.”
Each Weba Chute System is custom designed for a specific application, considering factors such as belt width, belt speed, material sizes and shape and throughput. Baller says there are numerous advantages to be gained from this locally developed transfer system which, when introduced on a new project, achieves the optimum design configuration for the application with the best belt cleaning arrangement and optimum selection of belt type and size. In addition, spillage can be virtually eliminated.
Further benefits that apply equally to retrofitted Weba Chute Systems and new projects alike include up to 80% reduction in material degradation, greatly reduced levels of dust and noise, reduced production losses owing to fewer blockages, significantly reduced spillage and vastly improved safety levels.
Easy access is provided for inspection and maintenance purposes and the system does not require ongoing supervision, again representing a saving in manpower and related costs.
Baller says Weba Chute Systems should not be compared to conventional chute systems but rather seen as an improved alternative or “upgrade”, because they adopt a completely different and unique approach to control and handling of bulk materials. For instance, the system uses a “supertube” with a cascade scenario, where 95% of the material runs on material at all times.
“When one looks at this process in slow motion, it becomes apparent that the bottom layer of particles in the product stream move in a tumbling motion and do not slide down the chute,” he explains. “This results in significantly reduced wear and in many cases the lip remains completely covered by material and rarely needs replacement.”
This manner of controlling material movement is taken a step further by designing the internal angle of the transfer chute in such a way as to match the product discharge velocity with the belt speed, which either virtually eliminates or greatly reduces spillage.
Extensive experience and technical expertise, coupled with applications knowledge, has positioned Weba Chute Systems as the leader in its field. The Weba Chute System design is accomplished using sophisticated 3D computer software. Data received from the customer is always verified, and in many instances Weba Chute Systems’ highly skilled personnel are in a position to make cost saving recommendations.
The quality of the manufacturing process is strictly controlled by the company’s procedures which are in line with its ISO 9001 certification. Performance guarantees, set in accordance with operational and application parameters, are provided with all Weba Chute Systems.
The largest AC electric motor operating in Zimbabwe drives a reduction mill, and this synchronous motor was recently refurbished by leading rotating machinery repairer, Marthinusen & Coutts, a division of ACTOM.
Estimated to be around 30 years old, the 2150 kW synchronous mill motor, which was in operation at Freda Rebecca Gold Mine, suffered a catastrophic failure caused by its age and metal fatigue. The main hub of the electrical rotor component had sheared off.
Following preliminary repair work undertaken by the mine, Marthinusen & Coutts was called to site by the mine to investigate further and to provide a long term world class solution. A full assessment undertaken by the Marthinusen & Coutts team resulted in the motor being brought back to the division’s facility in South Africa.
It was decided, following negotiations with the mine, to do a design modification instead of replacing the hub. Richard Botton, Divisional CEO of Marthinusen & Coutts, explains that this option was chosen as it would save costs and reduce the lead time without sacrificing the performance of the refurbished motor.
“Our team’s extensive experience and understanding of large rotating machinery enabled us to offer an alternative to the mine that would ensure optimum reliability going forward. One of the solutions was to use the existing rotor superstructure with a bolt-on hub on the motor,” Botton says.
In addition, 18 main pole coils were replaced; these were manufactured by Marthinusen & Coutts at its ISO 9001 accredited facility in Cleveland, Gauteng.
A complete rewind of the stator was necessary due to the extensive damage caused during the failure at the mine. Fortunately, the mine store had a spare set of coils, manufactured 20 years ago, and these were rewound at Marthinusen & Coutts in South Africa.
A compete upgrade and modification to the sleeve bearings also brought these back to OEM specifications.
“The ability to implement enhancements during the repair of critical electrical rotating machinery such as this motor is a major advantage to the mine as it allows for the latest technology and enhancements to be included in the final product solution,” Botton says.
The scope of work included the on-site commissioning of the motor which was facilitated by the Marthinusen & Coutts Zimbabwe operation with technical support from the division’s centre of excellence in Johannesburg.
Through the level of skills and expertise that reside within this leading rotating machinery service provider, Marthinusen & Coutts, a division of ACTOM (Pty) Ltd, has established a strong reference base and reputation for this.
FREDA REBECCA PIC 01 : Marthinusen & Coutts recently refurbished the largest AC electric motor operating in Zimbabwe.
Modern packaging plays an important role in preserving, protecting and selling a host of products, from items tiny enough to need tweezers to be picked up to those that need a forklift to be moved. Packaging also comes in a confusing array of materials and can be very costly if incorrectly selected or processed.
Countapulse Controls offers a broad range of opto-electronic sensors which have been developed to ensure packaging lines operate at peak cost efficiency to the packaging industry. Made by the respected German instrumentation manufacturer Leuze Electronic, the sensors are purpose-designed for the feeding, packing, dosing, detecting, labelling, sealing and other operations that go into the makeup of any packaged product.
Countapulse Controls’ managing director, Gerry Bryant points out that the variety of materials used for packaging, as well as the surface properties and the specialised printing used in the industry require the highest standards of instrumentation and machinery:
“Modern, high-production packaging uses cutting edge technology, and sensors applied to these applications have to be capable of meeting the demanding requirements,” he says.
Leuze is one of the leading developers and manufacturers of opto-electronic systems, which use light in various spectra for sensing, monitoring and controlling products and equipment in the production line.
This includes standard opto-electronic sensors, colour sensors, label detectors and sensors for workplace safety. Also in the range are sensors for foil and glass detection, CCD sensors, forked photoelectric sensors and sensors for differentiating between glass and PET.
These can be effectively applied to hasten and improve quality control in any number of processes. In feeding and conveying, for instance, solid granules, loose goods, paste products, fluids or mixed items are transported, accumulated and passed on. Opto-electronic sensors are used to position products on conveyors, recognise their shapes, measure them for filling and sealing and even check the quality of printing and labelling.
“The many ways used to package products nowadays show the dynamics and bandwidth of the various packaging technologies. Leuze has expended considerable research and development effort in producing its range of opto-electronic sensors, using concepts aimed at improving speed, accuracy and performance in the packaging line,” Bryant says.
The complexity and depth of sensors available on the market can be confusing, and for this reason Countapulse Controls often assist customers in evaluating an application for either the fitment of new sensors or the retrofit of replacement units.
“While the Leuze sensor range is broad enough to offer units of the right type and size for virtually any operation in the line, we have found that in some instances we have sourced alternative sensor solutions for the customer,” he says.
This, he explains, is not unusual at all and with the depth of expertise that resides within Countapulse Controls it is easy to apply best practice sensor technology to an application.
Countapulse Controls has more than 35 years of experience in providing fit-for-purpose sensor solutions on the African continent. The company also operates a 24/7 technical hotline to assist customers.
Andrew Mentis maintains that although supplementary building products are not necessarily essential to building work, they are essential to good quality building work.
“The sad fact is that, unless specified in the original job specifications and costing by the architect, there is little chance that a builder would use these products,” Lance Quinlan, marketing manager for Andrew Mentis, says. “We find that architects are often unaware of these products, but once they know about them, they are extremely keen to use them.”
Specific building products, made by Andrew Mentis for the building industry on special purpose machines, are used mainly as reinforcing to prevent plaster and walls cracking and for strengthening the corners of a building to prevent damage where the building is most vulnerable. The products include Angle Bead, Riblath, Plaster Stop, Mentlath, Strip Mesh and Brickforce.
Mentis Angle Bead provides a true straight edge for forming an arris in plasterwork which resists chipping or cracking. The expanded metal wings anchor securely in the full depth of plaster on either side of the arris. “This is essential on plastered columns as the corners are particularly susceptible to damage both during and after building operations,” Quinlan says. Mentis Angle Bead is supplied in 3 metre lengths and is manufactured from 0.5 mm thick galvanised steel strip.
Mentex Expanded Riblath is ideal in the plaster base for walls and ceilings, and as a permanent shuttering for concrete. It has mechanical retention properties for fire protection plasters and splays. The straight, heavy longitudinal ribs and bead stiffening give Mentex Riblath a tremendously high strength to mass ratio.
“It is highly flexible for a variety of applications, yet rigid enough for others. Mentis Riblath has for many years been an approved and preferred plaster base and concrete shuttering material for suspended ceilings,” Quinlan says.
Mentis Plaster Stop provides a straight edge and finish for plaster at all openings and abutments. Recommended wherever a plastered wall finishes against tiles, face bricks, skirting, exposed steelwork, and all woodwork, it protects and reinforces the plaster and gives a neat finish.
Mentis Mentlath 213 is used to provide a key for plaster and as a reinforcement to minimise cracking. It is used extensively for a key where gunite is applied, and is the most accepted means of keying plaster or vermiculite to steelwork when fire proofing a steel building. It is galvanised to prevent corrosion.
Mentex Strip Mesh is used along lines of potential weakness such as at the corners of doors and window frames and as a backing for plaster over narrow gaps such as service chases. “It is used as a plaster reinforcing to prevent cracking around airbricks, window frames, vents, door arches, electrical conduits, water pipes, and is extensively used to provide a bond between dissimilar materials at crack prone areas,” Quinlan adds.
Reinforced brickwork is preferable to unreinforced in all types of building because steel reinforcement adds tensile strength to the inherent compressive strength of this traditional construction method. “Mentis Brickforce 210 reinforcement greatly reduces the detrimental effects of vibration and changes of temperature. Moreover, considerable savings may be made in the cost of material and labour, and in space and deadweight,” Quinlan says.
He further adds that for optimal effect, Mentis Brickforce should be used in every third course of bricks and, where the strips are joined at the ends, an overlap of not less than 80 mm should be provided.
“Embedded in the normal thickness of brickwork joint Mentis Brickforce gives brickwork increased resistance to tensional stresses. This is important for buildings erected on reclaimed ground or on other ground in which settlement may occur. However, it is equally suitable as a reinforcement for concrete block work, partition slabs, asphalt guttering and in other work,” Quinlan explains.
Other items in the Mentis building products range are Mentex Corner Mesh, Mentex 99 hailguards (prevent gutters from filling up with dirt and leaves), Mentis scaffold planks, storm water gratings and frames, and trench covers.
Being locally registered in Mozambique and well-staffed with 26 highly trained and qualified Mozambican nationals, Multotec Services Mozambique Limitada has secured supply contracts for processing equipment with some of the country’s major role players.
“We were the first mineral processing company to establish a facility in Tete province – back in 2011,” says Thinus Kruger, Multotec’s regional manager for east Africa. “We now have a solid presence with our full range of mineral processing solutions, as well as maintenance and fabrication services.”
Kruger emphasises that the company’s global strategy is to be located close to customers, not just in-country but as near to operational sites as possible.
“Our branch is situated within 20 to 100 kilometres of all our major customers, making for fast response times in terms of maintenance and support services and for the delivery of emergency spares,” he says.
Multotec Services Mozambique’s customer base now includes four major coal players, a graphite mine and a heavy minerals mine, as well as mineral separation plants and harbours. So well equipped is the branch that it is also used as a base for servicing customers in Zimbabwe and Madagascar. Among the full fleet of vehicles to enhance customer service is an eight-tonne crane truck for collection and deliveries, a personnel transporter, double-cab vehicles for service support, two forklifts, an equipped standby trailer, and a rugged HDPE welding trailer for overland installations of HDPE pipes.
Situated just off the main road between Tete and Moatize, the Multotec facility is just 10 km from the airport and 15 km from customs, and boasts a 1,000 square metre fabrication workshop with a bending break, guillotine, pedestal drill, power saw and a variety of welding machines.
“Leveraging the local team’s combined 60 years of experience in mineral processing, our company in Mozambique offers long term maintenance contracts, supply contracts and fixed price agreements to suit customer requirements,” says Kruger. “We also conduct small to medium-scale steel fabrication and specialise in the manufacturing of steel chutes, launders, steel pipes and general fabrication work, including carbon steel, stainless steel, aluminium and welding and installation of HDPE pipes.”
The range of work carried out for customers encompasses service exchanges and refurbishment on cyclones, the retro-fitting of belt cleaners, samplers and cyclone clusters, and preventative or reactive maintenance of screening and other process equipment.
Quality of services is ensured by ongoing investment in local employees through training on-site and advanced training in Multotec’s South Africa-based training centre, which hones employees’ skills in installing and maintaining Multotec products, as well as in the ceramic lining of equipment.
This focus on skills has allowed the company to develop a depth of expertise that – in addition to a commercial manager, accountant and human resources officer – also includes a metallurgical process specialist, an engineering and fabrication specialist, ten artisans or technicians, four HDP pipe welders and nine artisan assistants and installers. The company’s capacity is enhanced by technical support from the Multotec head office in South Africa.
“We regularly fly our Multotec equipment specialists to Mozambique to assist with on-site training for our customers, as well as to conduct audits on their installed Multotec equipment,” says Kruger.
He expects that employment numbers in the company are likely to rise over the coming year as business grows, and a full bursary is being provided for a local university student in the field of teaching education.
In engineering and manufacturing, warehouses and workshops often become heat chambers in a hot summer as is currently being experienced in most parts of the country. Doors left open to allow access for people and equipment also let in hot air, which is trapped in the building and reheated by the greenhouse effect, causing excessive heat build-up.
“It’s a proven fact that a comfortable worker is a productive worker, yet many industrial managers in both large and small operations do not realise they can improve working conditions immeasurably in hot buildings by simply controlling air movement,” says Wim Dessing, managing director of Apex Strip Curtains.
Dessing’s company offers a range of products that make it easy to control the working environment. Locally manufactured Apex SR 900 high impact traffic doors are insulated impact resistant swing doors, designed for efficient long life use in high traffic, impact-opening applications.
Built to withstand traffic from both pedestrians and forklifts, the Apex SR 900 door is a fully gasketed heavy duty impact swing door which opens easily and closes under its own weight. Insulated with polyurethane, this robust impact door is ideal for application where temperature control is vital, or where ingress of dust, insects or noise must be prevented.
The door retains its physical properties in both high and low temperature environments and is impervious to moisture, acid, animal fats, insects, salt solutions and petroleum products. Besides being durable and robust, this door provides excellent sound attenuation.
Another popular option, Dessing says, is the range of high speed roll-up or fold-up doors which includes the Traffic and Sector units. All offer rapid automated opening and closing, as well as efficient thermal insulation and a highly effective wind barrier.
The doors are aesthetically pleasing in a range of colours and are made from durable, flexible polyesters and PVCs. The electronic componentry is modern, compact and self-contained to allow quick and easy installation in doorways and passages.
A variety of activation options, from floor mats to beepers, is available and all doors have a back-up emergency opening capability. Unless otherwise required, doors have a transparent panel for through-vision.
The company is also well-known for its patented, balledged strip curtains, which have proved itself in innumerable applications in South Africa and abroad.
“Strip curtains are a very inexpensive way to cover a door opening to prevent the ingress of hot air yet still allow easy passage. Strips are made from specially formulated PVC that doesn’t become brittle with use and stays transparent for through-viewing and added safety. The balledge on the strips don’t snag or catch on people or goods passing through, strengthening the strips for a long service life as well,” Dessing explains.
“All our products are modular in design, providing flexibility for either retrofitting or greenfields installation. Specifications and advice are readily available, and Apex’s philosophy is to provide the best solution for long-term, cost-effective environment-control,” Dessing concludes.
While a large market remains for rental tower cranes, this has to come to an end at some stage. This is according to Louw Smit, sales director of Crane & Hoist Equipment SA, who says there is already a distinct shortage of rental tower crane units locally.
With more than 12 years’ experience in the tower crane sector, Smit was mentored by Quentin van Breda, the now retired founder and managing director of SA French, and believes there will be a turn in local market conditions towards the purchase of new tower cranes again.
The recently established Crane & Hoist Equipment SA is a specialist operation that will supply new and refurbished cranes as well as construction hoists to the sub-Saharan markets.
“With an eye on being a sustainable business and keeping our customers top of mind, we have to ensure that there are options available for the built environment and infrastructure contractors, some of whom are feeling the effects of the slowdown in contracts being awarded,” he says.
“Tower cranes are definitely not an off-the-shelf product,” he says. “Each tower crane is unique and configured for the exact application requirement of the contract.”
As an example, Smit points to the instance where a contractor is faced with space constraints. This is one of the more frequent challenges being experienced as more and more construction is taking place in heavily built up areas. In many cases, a construction site could be surrounded by buildings on three sides, and this can prove challenging for a contractor in terms of mitigating the materials handling activities while striving for optimum productivity.
“The best option in this scenario would be the use of a luffing jib crane,” Smit says. Essentially, this crane is configured in such a way that the luffing jib is raised and this allows slewing to take place without affecting the surrounding buildings. On a large site, use of these cranes will also allow more than one to be in action at the same time.
With structures becoming taller and taller within the built environment, it is essential to apply optimal material handling solutions to ensure productivity is achieved on the construction site while operating safely.
Smit says that contractors who partner with competent technical tower crane experts are at a distinct advantage as they have access to people with an in-depth understanding of tower cranes configurations. He says that the special configuration of the mast will allow for a higher freestanding height of the tower crane itself, and this is a good solution for high rise structures.
“But what is extremely important,” Louw cautions, “is for contractors to communicate directly with a specialist supplier such as Crane & Hoist Equipment SA prior to site layout to ensure that the materials handling solution is fit for the actual conditions and application.”
“In the above example of the increased free standing height option, this tower crane would not have to be tied into the building or anchored and this will give the contractor both a time and cost saving on the project,” he adds.
“Often when we are involved from the initial site layout, we are able to offer alternate materials handling solutions to the contractor, and in some cases it is preferable from a cost saving perspective to make use of a tower crane in the initial stage of the project and then to use a construction hoist,” Smit says.
Construction hoists have gained traction in the construction sector as these are ideal for the vertical movement of personnel and materials, and significantly reduce the manual handling of equipment and materials. Hoists are not only suitable for almost all lifting activities on a site, but can travel at a speed that is both safe and effective, increasing productivity on site.
Commenting on the new company, Crane & Hoist Equipment SA, Smit says he is excited about future prospects, and that the key to the company’s success lies in the wealth of experience of its management team and the commitment of its people.
Operations director Danie Roos has, with over 18 years’ experience in the industry, has in-depth technical knowledge and will be able to provide sound technical product support to clients.
Significantly, Crane and Hoist Equipment SA strives to be a leader in the lifting industry, and managing director, Brenden Crous says that in the high risk environment in which tower cranes and hoists operate there is no room for error.
“Quality and safety are a priority for Crane and Hoist Equipment SA and this translates to all our products and services,” Crous says. “Further by providing turnkey tower crane management and lifting solutions we offer a major differentiator to industry and this market offering will allow our clients to focus on their core business – construction – knowing that their lifting and materials handling equipment is well maintained and compliant with legislation.”
“We believe the Crane & Hoist Equipment SA team has the depth of experience and technical expertise needed to assist customers in selecting the most appropriate materials handling solution for any given application, whether it is a tower crane or a hoist and we look forward to serving the southern African construction and mining sectors for years to come,” Smit concludes.
The WEG MPW range of motor protection circuit breakers offer customers reliable operation in the harsh operating environment found on the African continent. All motor protection circuit breakers in the WEG MPW range are manufactured in accordance with IEC 60947 and UL 508 international standards giving absolute assurance in terms of operational parameters and quality.
The devices offer the benefit of being compact and modular, facilitating space saving within the electrical panel itself. This means the panel can be smaller or where necessary more components can be included in the panel. The WEG MPW range of motor protection circuit breakers are robustly constructed for optimal reliability.
The WEG MPW range facilitates the protection of a wide range of electric motors from 0.16 A up to 100 A. Significantly, the range has both thermal magnetic versions facilitating protection against potential short circuit and overload conditions as well as magnetic only versions which provide protection against short circuits.
Use of the thermal magnetic device will reduce the number of components required when manufacturing a motor control centre. This can translate into a significant cost saving. The magnetic-only version allows the use of electronic overload protection devices which can reduce costs further.
The WEG MPW motor protection circuit breaker is available with a full range of accessories including auxiliary contacts, shunt trips, under voltage releases, door mounting handles and free standing enclosures. The devices are certified to Type 2 allowing continuous operation until replaced. This is important in a production critical environment.