FRENOS Y EMBRAGUES

Transcription

FRENOS Y EMBRAGUES

FRENOS Y EMBRAGUES
http://profesor.sis.uia.mx/~cosornio/dismaquinas/...
FRENOS Y EMBRAGUES
Clutches rely on mechanical or electromagnetic action for torque transmission. However, they are usually
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identified by their mode of actuation:
mechanical,
electrical,
pneumatic, or
hydraulic.
Although the four operating modes are considered highly competitive, each mode actually is restricted to a
fairly well-defined area of application. Within each area, one method provides definite advantages in terms of
cost, response time, and torque transmission.
http://www.machinedesign.com/bde/mechanical/index.html
FRENOS:
Brakes absorb energy and convert it to heat. Thus, prime concerns in a brake are:
1. Generating a force capable of retarding a rotating shaft.
2. Dissipating or absorbing the heat generated in the process.
Mechanical brakes all act by generating frictional forces as two surfaces rub against each other. The stopping
power or capacity of a brake depends largely on the surface area of frictional surfaces as well as on the
actuation force applied. The friction and wear encountered by the working surfaces are severe. Thus, the
durability of a brake or service life between maintenance depends heavily on the type of material used to line
the shoe or pad.
Brake linings
Most brakes use some type of friction lining. Asbestos, once the accepted friction material, has been replaced
in most cases by nonasbestos materials.
Contents of the new material, largely proprietary, are also fibers molded or woven into pads or discs. Copper
is sometimes added to improve heat dissipation. Cotton-based linings are sometimes used for light-duty
service.
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Electric Brakes
For heavy-duty service, sintered-metal linings perform better than fiber-based linings. Cermet linings are
used for extremely rigorous service.
Linings are attached to the brake shoe either by riveting or bonding. Riveted attachment is simpler, but usable
lining depth depends upon the depth of rivet-head countersink. Also, rivet heads may score the drum if the
linings are not replaced soon enough.
Electric brakes operate according to the same principles as electric clutches. The most commonly used
electric brakes are electrically actuated but rely on mechanical friction for stopping action. Such brakes are
almost the only electrical types suitable when the load must be brought to a full stop. The other electrical
types -- magnetic-particle, hysteresis, and eddy-current brakes -- are primarily used to provide drag or
retarding action where a rapid or precise full stop is not needed.
Ejemplo para selección de Embragues
y frenos
Trig-O-Matic
Model 700
tm
Lite
Overload Release Clutches
APPLICATIONS
Trig-O-Matic Lite
Model 700
Mechanical
This automatic reset, roller detent style overload clutch,
combines Centric's 30 plus years experience manufacturing
the Trig-O-Matic with a simpler design. This combination
yields a reliable, low cost alternative to many of the torque
overload clutches on the market today.
Packaging
Cartoners, Fillers, Case Packers, Cappers, Labelers,
Sealers, Can Forming
Paper Converting
Rewinders, Log Saws, Folders, Slitters, Accumulators
Food Processing
Ovens, Centrifuges, Mixers, Pumps, Extruders
Material Handling
Belt, Drag, Chain, Bucket & Screw Conveyors, Palletizers
Other Industries
Chemical, Printing, Portable Lifting/Lowering Systems
MODEL 700 FEATURES
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MOUNTING
CONFIGURATIONS
For mounting flexibility the Model 700 is available in two
shaft mounted bushing models.
Bore Bushing Model - for easy mounting and stocking.
Taper Bore Bushing Model - for more secure mounting.
OPTIONS
Simple Cost-Effective Design
Large Bore Capacity
Through Shaft or End Shaft Mounting
Bidirectional Operation
Single Position Indexing
Automatic Reset
Accurate & Repeatable Torque Settings of +/-10%
Maximum Torque Limit Stop
Limit Switch Actuating Plate
Operating speeds up to 1000 rpm
Proximity Sensor Plate
Finished Bore & Keyways
Spacer
Bar
CAPACITIES
Size Max. Straight Bore Max. Taper Bore Torque Range
in./mm
in./mm
in.-lb.
Nm
720
1.438/36,5
1.125/28,6
200-700
22,6-79,1
730
2.125/54,0
1.750/44,5
600-2000
67,8-226,0
740
2.750/70,0
2.250/57,2
2000-5000
226,0-565,0
Request Catalog 764-ADV. AutoCAD & DXF Drawings Available.
Centric Main Page | Centrifugal Clutch Couplings
Ameriguard | Pneumatic Series H - Model 2000
...Quality Clutches From Yesterday to Tomorrow
Home
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En la figura se puede apreciar el arreglo de conexión de un embrague que a la vez es cople
GEOMETRIA DE LOS EMBREGUES
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Fn = 2ppmáxri(ro – ri ) (a)
Fuerza para operar el embrague
T = mFnrprom ( b) donde rprom = ½ (ro + ri )
Capacidad de transmisión de Par por sup. De contacto.
Para desgaste uniforme
Para presión uniforme:
Fn = pp( r2o - r2i ) ( c )
T = 2m (r3o – r3i )/3 ( r2o - r2i ) ( d )
GEOMETRIA DE LOS FRENOS DE TAMBOR DE ZAPATA INERNA
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ECUACIONES:
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Variables de Diseño:
Fuerza normal Fn
Coeficiente de fricción
Geometría.
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FRENOS DE DISCO
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Variables de Diseño:
Fuerza normal Fn
Coeficiente de Fricción m
Geometría do, di, q1 y q2.
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Se recomienda la lectura del artículo:
Electronic Braking Control Developments.
Today´s hydraulic braking systems are expected to be replaced by fully electrical systems, despite various
development challenges.
Automotive Engineering International. February 1999.
Para obtener las ecuaciones correspondientes se hace sumatoria de momentos alrededor del punto de pivoteo
de la palanca.
EJERCICIO DE FRENOS Y EMBRAGUES.
Explique paso a paso cómo funciona el mecanismo accionador del sistema de embrague.
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1.- Un motor de un automóvil puede desarrollar un máximo par de freno de 2500 lb-pulg. ¿ Cuáles de los
embragues de disco siguientes que produce un fabricante pueden ser seleccionados para este coche ?.
Dimensiones de las caras en pulgadas:
a.- Do = 8 7/8, Di = 6 1/8, Pa = 34 psi
b.- Do = 10 , Di = 6 1/8, Pa = 30 psi
c.- Do = 11 1/16, Di = 6 1/8, Pa = 26.2 psi.
En cada caso f= 0.3.
2.- La figura representa los arreglos posibles para un freno de zapatas interiores de un auto.
Cara b = 4.5 , r = 8, h = 5, c= 2.5, w = u = 6.5, q = 100°, f = 20°, Para una presión máxima de
120 psi, determine la fuerza Q y el par de freno para
Sentido de giro manecillas en A y B
Sentido de giro contramanecillas en A y en B
Considere un coeficiente de fricción de 0.25
Explique el concepto de la autoenergización en ambos incisao A y B.
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Transcription

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