Weir Minerals Africa has received its biggest order from India to date – seven Linatex vibrating screens of various sizes for RBSSN, a mining and metals company based in Hospet, in northern Karnataka. The order includes the biggest screen Weir has supplied to India, with dimensions of 2.4 m by 4.8 m. Weir Minerals Africa’s Chris Dorlas says the order, which is destined for an iron ore application, is a milestone for the company, since it firmly establishes Weir Minerals’ footprint in India and will serve as a reference base for further sales in that country.The RBSSN order includes three VD18/38, one VD15/38 and one VD21/48 dewatering screens. Linatex dewatering screens incorporate a 45o sloping back section, fitted with slotted apertures across the direction of the flow. Incoming slurry is fed uniformly along the top of this back section, which acts as a vibrating drainage panel. The screen’s main deck slopes upwards at 5o and is fitted with smaller slotted apertures.
“This design achieves exceptionally high dewatering and draining capacity,” Dorlas says, “making it possible in many cases to use smaller units than if one was using conventional dewatering screens. This, in turn, reduces the cost of the initial investment in the screens.”
At the lowest point of the screen, where the sloping back and main deck meet, a pool of partially dewatered slurry forms. Here, solid particles bridge over the apertures and form a cake, which acts as a filtration bed, allowing only very fine particles to pass through. The vibrating action conveys the cake along the screen and out of the pool, where further dewatering takes place, depending on the porosity of the cake, which is finally discharged over the adjustable weir into the product chute.
Vibration is produced by two linear motion low noise exciter motors operating at 980 or 1460 rpm. Alternatively, geared exciters with an external drive motor can be fitted to the larger screens. Both the vibrating motors and the geared exciter have been specifically designed to ensure long life, with minimum maintenance requirements.
Easy adjustment of the amplitude of vibration and deck inclination, as well as the discharge weir plate, are features incorporated to suit changes in process requirements. A high solids recovery is achieved when the screen underflow is kept in closed circuit, with the only solid losses occurring as the very fine material exits in the cyclone overflow.
The two large Linatex HG24/48 screens included in the RBSSN order are horizontal linear motion screens. Linear motion is produced by the action of counterweights on separate shafts, geared together to produce a straight line “throw”. The mechanism’s direction of rotation does not affect the pattern of motion.
“Linear motion provides excellent performance in applications such as wet screening, desliming and dewatering, owing to the ability to break the surface tension between deck apertures and the pulp being screened,” Dorlas says. “Screen capacities vary widely, depending on the material characteristics and the separation required.
“Screen design has evolved and improved over many years of operational experience and industry know-how. However, the company has actively taken these improvements to the next level and introduced the Finite Element Analysis (FEA) method of design to our development technology some years ago. Our in-house FEA capabilities have assisted in optimising the mass and strength of the screens, helping to provide lower cost solutions, both in terms of capital and operational costs.”
The Weir Group acquired the Linatex group of companies in September 2010, now marketed as Lintex® rubber products. Dorlas says that these products are proving a valuable addition to the Weir Minerals product line and assist the company in positioning itself as a solutions provider. The South African Linatex manufacturing facility in Alrode is capable of producing screens up to 4.9 m wide by 10 m in length.
