Plant Services - March 2008 - (Page 38)

Vibration Analysis & Balancing Power transmission Reliability Three failure modes Figure 1. Sheave friction can burn belts. Extraneous machine components can rub a belt raw. A belt that turns over in its sheave is doomed. Sources of drive problems Improper belt storage or handling ngle Twist Improper belt or pulley installation Environmental factors Poor drive design Improper drive maintenance VIBXPERT® Defective drive components Figure 2. Maintenance and installation account for most belt failures. 2 3 4 Bring in the sheaves Tie string Pull string The next step is to measure sheave run-out, which comes in two varieties: rim (radial) and face (axial). Both must be within tolerances before you can perform successful final alignment corrections. sheave diameter (TIR) for high-speed sheaves, and can be raised to about 1 mil per inch for slower sheaves. Check radial runout first. If it’s unsatisfactory, check the shaft runout. If that’s excessive, the shaft might be bent. If so, replace the shaft and check radial runout on the sheave again. If no shaft runout is detected, install a new sheave. If the sheave is mounted on a tapered shaft bushing, remember to inspect and clean the bushing, both inside and out, to ensure proper seating. Next, check for face (axial) runout (wobble) and, if necessary, correct it by repositioning the sheave on its shaft. Once both runout values are within tolerance, install new belts. New belts must be the correct length, material of construction and pitch angle. Never force a belt onto a sheave. Doing so either will damage the tensile members in the belt’s core h Watc O VIDEne Onli VIBSCANNER® Correct any mechanical and structural problems before proceeding with alignment to prevent premature or catastrophic failure. Use the sheave or machine manufacturer’s tolerance recommendations. Otherwise, tolerance for radial or rim runout on high-speed sheaves (1,800 rpm and greater) shouldn’t exceed 5 mils total indicated reading (TIR), and this value can be increased to perhaps 10 mils on slower sheaves. The tolerance for axial or face runout shouldn’t exceed 0.5 mil per inch of www.PLANTSERVICES.com The right tool for every user, job and budget 305-591-8935 • www.ludeca.com 38 or damage the sheave itself. When aligning a multiple-belt drive, replace the belts as a set, not singly. New and used belts that are otherwise identical have greatly different operating and tensile characteristics (Figure 3). Also, never mix and match belts. Instead, only use belts from the same manufacturer, and preferably in a factory-matched set. March 2008 http://www.ludeca.com http://www.PLANTSERVICES.com

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Plant Services - March 2008 Contents From The Editor Letters The PS Files Up and Running Crisis Corner What Works Asset Manager: Enterprise Thinking Technology Toolbox: Hydrogen In Action Cover Story: Get Real Electrical: Reliable Distribution Power Transmission: When the Belt Breaks Web Hunter: Tooting Horns In the Trenches Product Picks Classifieds Fast Facts Energy Expert: Energy versus Sustainability

Plant Services - March 2008

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