African Fusion March 2017

solutions): Thermaspray is the exclusive Southern African repre- sentative of German-based DIA- MANTMetallplastic GmbH. DIAMANT Metallplastic offers the metalwork- ing industry high-quality polymeric solutions to restore functionality to castings, thereby significantly reduce scrap. The DIAMANT poly- meric solution includes products for impregnating and sealing leakages, repairing of blow holes and surface treatments as well as wear protec- tion and services. Typical applications in sugar industry include knife and trash plate replace- ment components in sugar mill, shred- der hammers, crushers rolls, scrapers, pump casings, conveyor screws, valves covers, flanges and bearings and bear- ing journals. Thermaspray , in a joint venture with Cape Town-based Surcotec, offers an extensive portfolio of engineering and thermal spray coating solutions that ex- tend component life cycles to assist OEM and end-user clients across southern Africa in reducing costs and increasing production. The company’s world-class quality wear- and corrosion-resistant thermal spray coatings, Plasma Transferred Arc (PTA) cladding and Polymer coatings are augmented by a host of specialised allied services.

cal run-out can be measured using an electrical run-out indicator apparatus on a lathe or inspection bench. Electrical run-out is measured every 1.0° through 360° and plotted on graphs using special- ised, calibrated equipment andapplicable software. Discussing eddy-current proxim- ity probes for shaft vibration monitor- ing, Hoosain says that the probes are positioned over a specially machined probe track area adjacent to each bearing journal. The signal from the eddy-current proximity probe is a function of the gap between the probe tip and the target ma- terial. If the run-out changes in service, the difference is registered by the probes and will indicate to operators and engineers that the equipment is damaged – worn, out of balance or poorly lubricated, for example. Surface imperfections such as scratch- es, out-of-roundness or non-concentricity with respect to the bearing journal are mechanical imperfections, which will appear as vibrations that will result in measurement errors. Thesewill be picked the rapid solidificationof small globules, flattened from striking a cold surface at high velocities. The different processes include: • High velocity oxy-fuel (HVOF): This process operates on a continuous steady-state basis with continuous powder feed. Thermaspray offers two processes, gas and liquid fu- elled. • Wire Arc Spraying: Also known as the twin-wire arc spray process, in this thermal spray process a direct current (dc) electric arc is used to melt the feedstock. Compressed air behind the arc is then used to atom- ising the molten material. Higher thermal efficiency is achieved as wires are melted directly. Coatings are coarse with higher porosity. • Powder plasma spraying: Plasma, the 4 th state of matter, consists of neutral and positive atoms and free electrons. Plasma gases are heated as they ionise in the arc and high degrees of melting and relatively high particle velocities are achieved. Finely structured coatings with high adhesion strength can result. Plasma Transferred Arc (PTA) welding and hardfacing This is a versatile method of depositing highqualitymetallurgically fuseddepos- its on relatively lowcost substrates. Both

the surface material and the coating material are melted during the process. PTApermits precise control of important welding parameters, such as powder feed rates, gas flow rates, amperage, voltage, and heat input, ensuring con- sistency. Controlled heat input ensures that weld dilutions can be controlled to between 5% and 7%. Polymer applications • Plasma Coatings (non-stick and traction coatings): Thermaspray has undertaken a strategic partner- shipwithPlasmaCoatings in theUSA to offer the South African market a new range of surface technologies and coatings to tackle the sugar, food, printing and packaging, tyre and rubber, paper andpulp, fempro/ diaper and many more industries. These coatings are designed to solve many of the above indus- tries’ problems resulting in reduced maintenance, higher outputs and an increase in cost savings. These coatings combine the advantages of thermal spray (metal base) coatings with polymer top coatings to offer benefits of wear resistance, slip and traction. These coatings can be ap- plied to aluminium, steel, stainless steel, tool steel, copper, ceramics as well as synthetic materials. • Diamant Metalplastic (polymeric

A schematic representation of the burnishing process, which improves surface strength and reduces roughness. Plastic deformation occurs which leads to a smoother surface profile.

Burnishing is used to improve run-out measurement reliability, which can

significantly improve the in-service condition- monitoring accuracy for rotating equipment. up as signals by the eddy-current proxim- ity probes. Typical equipment using probe tracks includeboiler feedpumps, 50%boiler feed pumps, turbine rotors, compressor rotors, blower rotors, pinion shafts and cryogenic pump rotors. Burnishing, de-magnetisation and measuring of electrical run-outs are all routinely performed in Thermaspray’s well-equipped workshops according to the relevant ISO standards.

The typical arrangement of eddy-current proximity probes for shaft vibration monitoring.

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March 2017

AFRICAN FUSION