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2014SumShotcreteEMag

Nozzleman Knowledge destructive results. To the untrained eye, correct and incorrect greasing methods appear the same. Operators and crew must understand the func- tion of grease to properly lubricate wet-mix pump- ing equipment. Grease is typically a petroleum product that is suspended in a soap-like thickening agent. Greases are rated for their temperature and melting rate, the ability to inhibit oxidation and corrosion, and their level of protection for metals in the presence of water. Greases are application- specific (think submerged boat trailer axle versus very hot truck disc brake rotor). It is important to understand the various func- tions that grease must accomplish within wet-mix pumps. If properly applied, grease prevents metal- to-metal contact at the critical internal bearing surfaces of concrete pumping components. Fig. 1: Unnecessary corrosion and wear on critical bearing surface is Greases provide lubrication and corrosion protec- likely caused by improper grease application tion by coating action. Its viscous fluid component lubricates clearances between parts that are rela- tively large, but for small clearances, the molec- through a recirculating oiling system. This method ular soap layers provide the lubrication. Water- is impractical in a wet-mix pump application resistant greases may be used for a wide range of (excluding engine and hydraulic components) equipment and are very good choices for wet-mix due to the constant exposure and potential con- equipment. However, grease must be applied tamination from abrasive, corrosive, concrete properly within a bearing surface, or it will not slurries. Lubrication by grease is common for provide adequate protection. machinery undercarriage components, sliding Unlike typical oils, greases do not easily flow surfaces, and articulating arm pivot bearings. If at normal temperatures. This means that to be grease is applied at the proper interval, it offers effective, grease must be installed by force, excellent lubrication for these applications. But directly to wear surfaces through small ports or greasing requirements differ for wet-mix pump passageways within the bearing surface or applications due to the near-continuous immer- housing. Grease must then completely coat all the sion of components within the abrasive, corrosive, surfaces which require protection from corrosion concrete slurries. and wear, and be routinely replenished as mechan- Wet-mix shotcrete pumps are usually positive ical energy pushes the product aside. As the grease displacement swing valve configurations. Swing coating diminishes, the protective layer is lost. valve designs (swing tube, rock valve, or gate Wear and corrosion begin immediately. valve) use very large sealed shaft bearings that When used properly, grease will reduce or even completely eliminate corrosion and wear at critical surfaces. Many critical bearing surfaces are required on typical wet-mix pump designs. Any component within the material hopper that must rotate or slide will possess some form of bearing surface. All of these surfaces are con- tinuously exposed to abrasive concrete slurries during daily operation. Why Wet-Mix Equipment Requires Specific Lubrication Techniques All machinery applications require some form of lubrication. Typically, lubricants are provided under pressure to critical bearing and seal surfaces Fig. 2: Typical S tube shaft bearing Shotcrete • Summer 2014 33


2014SumShotcreteEMag
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