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friction clutches - Arten Freios e Embreagens Industriais

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Table of ContentsTENSION CONTROL (UNWIND):A brake is used on unwindstands to apply constant force(or tension) to a web of paper,film, wire or other material.Tension is determined by airpressure. Because of thecontinuous slip operation,brakes are generally sized onthermal characteristics ratherthan torque.“Air Champ” ®◗ SELECTION CONSIDERATIONS:Maximum roll diameter in inchesMinimum roll diameter in inchesWeb speed in FPMWeb width in inchesWeb tension in pounds per inchof web width◗ EXAMPLESize a brake for an unwind stand which has apaper roll 24 inches in diameter; a core size of3 inches in diameter.The line speed is 500 feet per minute. Theweb width is 30 inches wide and the desiredweb tension is 1.5 pounds per inch of web width.Web Tension = Web Width x Tension= 30 in x 1.5 lbs/in = 45 lbsFUNCTION EXAMPLES◗ UNIT SELECTED:A XCB-10 Brake with two calipers and .35coefficient of <strong>friction</strong> facings. Refer to pages206-207.◗ CONTROL CIRCUIT:Nexen has a complete electronic TensionControl System which automatically sensestension in a web and compares it to a setdesired tension level. When the web tensionis more or less than the desired level, theautomatic Tension Control System adjusts theair pressure to the brake which maintains theset tension level.Maximum Brake HP = Web Tension x Web Speed = 45 lbs x 500 FPM33000 33,000 ft-lbs/Min/HPMax Torque = Web Tension x Max Roll Radius = 45 lbs x 12 in = 540 in lb Max◗ “AIR CHAMP”PRODUCT CONSIDERATIONS:DIAPHRAGM BRAKESJ, K, 4K, 8K, & 12KMin Torque = Web Tension x Min RollRadius = 45 lbs x 1.5 = 68 in lb MinMax RPM = Web Speed x 12 = 500 FPM x 12 = 636 RPM MaxMin Core Dia x π 3 x πMin RPM = Web Speed x 12 = 500 FPM x 12 = 80 RPM MinMax Core Dia x π 24 x πCALIPER BRAKESDB, BC, BD, VC500 & SPCNOTE: Effective cooling speed = RPM EFF = RPM MIN + (RPM MAX – RPM MIN )= 80 RPM + (636 RPM – 80 RPM) = 265 RPM33SA & TA450-1000Select a brake from the Thermal horsepower vs.RPM graphs, that dissipates .7 horsepower atthe effective cooling speed of 265 RPM.TCB-7,XTB-10, 12, 14, 18, 22XTBA-10, 12, 14, 18, 22BTBA-10, 12385

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