27 November 2012 – Due to the critical situation with regards to shortages of power in South Africa, a strong effort is being made by the government to explore new sources of energy beyond traditional sources such as coal. As a result, government has set a target to generate up to 42% of the country’s electricity from renewable energy resources by 2030. To date, more than 20 bidders, who are capable of contributing 1,415 MW of power generation capacity, have been selected in the first round of the government’s renewable-energy independent power producer (IPP) programme.
As South Africa continues to place a higher emphasis on renewable energy sources, Bearings 2000 director Nick Stamatiadis points out that that a number of businesses from the private sector have stepped forward to join the government in reaching the set targets.“Renewable energy systems will become increasingly common in the near future and, with that in mind, the need for high quality composite plain bearings is important. In solar energy systems, for example, plain bearings are particularly suitable to the operating conditions, which often involve slow swivelling movements with high loads,” he explains.
Although field work is not currently taking place, Nick points out that a large amount of planning is being undertaken, and he expects the construction of solar farms in South Africa to begin within the next six months. “From the initial outset, I believe that demand for these bearings will stem from the maintenance side, as highly-specialised bearings are required to maintain these technical systems.”
Solar PV systems convert solar energy directly into electrical energy, while solar thermal systems have reflectors that concentrate the sun’s rays into an absorber that generates water vapour by making use of a heat exchanger. The vapour is then used to drive turbines and generators, as in conventional thermal power plants. Both of these types of plants operate at their highest efficiency if the collectors are able to track the course of the sun, where a single-axis or double-axis tracking system is used to continuously align the reflectors with the course of the sun
The Schaeffler range of metal-polymer composite bearings is particularly effective in oscillating applications, where the bearings achieve a higher basic rating life than conventional bearings. These products are available as bushes, flanged bushes and thrust washers and are ideal for applications where there are small radial or axial design envelopes.
Bearings 2000 marketing manager Michael Stamatiadis explains that the metal-polymer composite material provides low-wear sliding characteristics, as well as a high load carrying capacities and thermal conductivity. “With this composite material, static load carrying capacities of up to 250 N/mm2 can be achieved. Composite materials can also be used in water or other media due to its high moisture resistance.”
He adds that the metal-polymer composite bearings are a cost-effective alternative for applications with minimum available space and a comparatively high sliding speed. “The plain bearings are available as bushes and flanged bushes, as well as thrust washers and strips. The material can also be easily formed to specific customer requirements for rotary, linear and oscillating movements. An added benefit is that all Schaeffler metal-polymer bearings are lead-free.”
The Schaeffler range of metal-polymer composite plain bearings is available in E40, E50 and E60 materials. The E40 and E50 materials are similar in composition, as a porous bronze-sintered structure is applied to a steel or bronze backing and impregnated with a special plastic compound. The solid lubricant produces a lubricant film between the sliding surfaces, which provides low-noise operation with a constant low friction coefficient throughout the entire service life of the bearing.
Nick Stamatiadis explains that E40 bearings are generally maintenance-free. “Lubrication is not required over the entire operating life of the bearing, as polytetrafluoroethylene (PTFE) and various other chemically inert additives are used as the lubricant. E40 is recommended for rotary and oscillating motion applications, as well as for short stroke linear movements.”
E50 bearings are low-maintenance, although initial grease lubrication is required at start-up.
“The sliding layer is comprised predominantly of polyoxymethylene (POM), a high-molecular thermoplastic characterised by its low friction properties, as well as chemical and thermal stability. E50 is a low-wear material that has good damping properties and long relubrication intervals. The material is ideal for rotary and oscillating movements and is also recommended for long stroke linear motion applications.”
NickStamatiadis adds that E60 sliding layer bearings are maintenance-free foil bearings. “E60 bearings have a lattice structure in which a sliding layer of PTFE and other additives are rolled and sintered. The structure functions both as a backing and a sliding layer. The PTFE sliding layer is on both sides of the foil, in order to ensure that the sliding motion can take place on the inside and outside of the bushes. A further advantage is that E60 can be easily moulded.”
The Schaeffler range of Elgotex plain bushes provides a variety of technical advantages that stem from the product’s unique entwined double-layer design. Michael Stamatiadis explains that each bush comprises two layers of wound material. “The inner, sliding layer is made from synthetic fibres and PTFE fibres in epoxy resin, while the outer layer comprises continuous glass fibres in epoxy resin. This combined double wound material is stabilised by applying a specific winding angle to the glass fibres, which significantly increases the strength of the bush.”
The result is a host of technical advantages, including extreme robustness, compactness and low wear, due to consistent friction levels. In addition, Elgotex plain bushes are lighter than their bronze equivalents. The bushes are also easy to mount and require no further axial location. Due to their dry-running characteristics, the bushes are also environmentally-friendly and maintenance-free for life, resulting in reduced maintenance costs for the end user.
Michael Stamatiadis highlights the fact that the Elgotex range is also insensitive to shock loads and edge pressures. “The product is available with integrated seals and is resistant to corrosive media, and the bushes also perform well in applications where swivel or axial movement is required.”
INA plain bushes with Elgotex are available with bore diameters from 20 mm to 200 mm, outside diameters from 24 mm to 220 mm, and widths of 15 mm to 250 mm. Custom versions with outside diameters up to 1,200 mm are also available on request.
Michael Stamatiadis highlights the fact that the entire Schaeffler range of bearings has been used in solar PV and solar thermal plants worldwide for a number of years, due to the fact that they are able to effectively move the solar collectors to track the course of the sun in the sky. “These bearings have high rigidity and high load carrying capacity, and are able to operate reliably even under extreme operating conditions.”
Looking to the future, Nick Stamatiadis is confident that the INA, FAG and Elges range of bearings will gain substantial market share in South Africa in the years to come. “Solar farms require considerable capital investments and vast amounts of space. These projects are almost impossible to establish in many developed countries in Europe, due to a shortage of space and limited sunshine. South Africa is in the fortunate position of having all of these resources at its disposal. What’s more, the local market possesses the expertise to manufacture solar panels locally and, as demand for these panels steadily rises, so too will the demand for locally supplied bearings,” he concludes.