friction clutches - Arten Freios e Embreagens Industriais

Table of Contents◗APPLICATION ENGINEERING DATA“Air Champ” ®◗ CLUTCH AND BRAKE SELECTIONClutch and brake selection is rathersimple when the functions of themachine are clearly defined. Make surethat the location, shaft size, heatdissipation capacity and speed specificationsare compatible with the clutchor brake selected. Match the machinerequirements to a clutch or brake that islarge enough to handle the load.First, classify the application.Occasional start or stop:Applications where a clutch disconnectsthe prime mover (usually an electricmotor) from the machine at cycle ratesof less than four or five times a minute..Torque and transmitted horsepower areimportant considerations ofapplications of this type.Cyclic start and stop:Applications where the clutch or brakecycles more than five per minute, fallinto this classification. Inertia, torque,energy per cycle, heat sink capacity andresponse time all may requireevaluation.High inertia start or stop:Applications of this type are identifiedby a requirement to start or stop heavyrotating rolls or flywheels in a specificlength of time. Start or stop periods ofmore than 1.0 second are typical of thisapplication type. Thermalcharacteristics and torque are veryimportant considerations when highinertia loads are present.Continuous slip or constanttensioning:Applications of this type appearfrequently in the paper or textileindustries where material is pulled froma roll. A clutch or brake is connected tothe shaft supporting the rolls toprovided tension in the material. Heatdissipation is the primary concern forthe clutch or brake.Many clutch and brake selectionsare successfully made on thebasis of transmitted horsepowerand speed only.For these applications it is a simplematter of solving the basic torqueformulas and selecting a unit from thetorque vs. air pressure graphs in the AirChamp catalog or various other productbrochures.Nexen also provides selection chartsthat suggest specific models at varioustransmitted horsepower and speeds.These charts include an appropriateservice factor for the selected model.Motor frame charts showing modelswhich fit the motor shaft and/or NEMA“C” flanges are provided for somemodels. A general rule-of-thumb formotor mounted applications is: if theunit fits the motor, it will do the job.Nexen units have adequate torque tohandle what the motors deliver.Applications where the clutch or brakedo not fit the motor require anevaluation of inertia, torque and thermalcharacteristics. Thermal characteristicsare very important for high inertia orhigh cyclic applications. Do not select aunit from the catalog selection charts ifhigh inertia loads are present.Location is one of the most importantthings to consider when making aclutch or brake selection. Since torque(in. lbs) equals 63000 x HP , theRPMclutch or brake should be located on thehighest speed shaft in the drive train.An ideal location is directly on themotor shaft. Mounting is easier andmore convenient. Lower torque requirementsmean smaller diameter units,which result in considerable cost savings.Because “Air Champ” Clutches andBrakes are rugged and designed withhigh thermal horsepower ratings, wecan use the following rule-of-thumb forselecting the proper size unit for yourapplication:Ninety percent of the time you canmake your clutch/brake selectionbased on the torque requirementalone. It’s that simple. Sure it’simportant to use a service factor, butfor the most part the torquerequirement is your prime considerationwhen choosing which size clutch to use.For severe applications with high inertialoads and high cycle rates, you alsoneed to consider the thermalhorsepower requirement.◗ CLUTCH & BRAKE SERVICE FACTORA service factor of 1.2 to 2 shouldalways be used when operating at anyair pressure. The service factor isdependent on the severity of theapplication. It is not recommended thata clutch or brake be used in an applicationat its maximum designed torque.360