1. MECH1200 Clutches, Brakes, and Backstops

2. MECH1200 Functions Clutch – Go (or limit torque) Brake – Stop (or slow down) Backstop – Go only one direction Primary function: Stop, slow, or prevent reversal of load in a mechanical system

3. MECH1200 Activation Methods Centrifugal Mechanical Electrical Pneumatic Hydraulic

4. MECH1200 Applications Control Torque Disconnect loads Starting Stopping Prevent load reversal Tension Control

5. MECH1200 Clutch-like operations by Electrics Soft start Servo drives Variable speed drives Positioning systems

6. MECH1200 Application Guide BrakeDescriptionNotes Band Operates by the action of a fixed belt over a rotating cylindrical surface(drum). Action not harsh. Band Drum Works by bringing curved metal plates, lined with friction material(brake shoes) against an external or internal rotating cylindrical surface. Drum Disc Disc brake consists of a disc rotating between two friction pads. When the pads are forced together under hydraulic, pneumatic, electrical or magnetic action then the disc is very effectively stopped. Disk Block/Shoe Probably the first design of brake based on a shoe/block which is forced against the outside of a rotating wheel. A simple design visible on many old vehicles Block/Shoe Fluid A smooth progressive brake action resulting from rotating plates, or vanes in a retained fluid. When the fluid is prevented from flowing the viscous resistance retards the rotation. Magnetic Particle This type of brake includes a fixed cylindrical enclosure housing a coil wrapped around a fixed cylinder. Within the cylinder is a cylindrical rotor mounted on the rotating shaft. The annulus between the fixed cylinder and the rotor is filled with magnetic particles. If there is no current in the coil the rotor is relatively free to rotate. On applying a current the particles coalesce and prevent relative movement. Electric Regenerative Shafts driven by an electric motor often using regenerative braking. When the power to the motor is removed. The motor effectively becomes a generator driven by the shaft. The shaft is slowed as the kinetic energy is converted into electical energy. The recovered energy is often stored when used in electric vehicles.

7. MECH1200 Selection Criteria Function of the application – Stopping – Holding – Braking – Slowing Speed of shaft Horsepower of prime mover Torque requirement Accelerate or Stop time required Cycle rate Environmental conditions Mounting method Maintenance and servicing required or available

8. MECH1200 General Categories Positive mechanical engagement Sliding or friction engagement Electrical engagement Pneumatic or hydraulic engagement Torque limiting Centrifugal actuation One way motion control

9. MECH1200 Positive Engagement Clutches Relies on engagement of a dog or latch to connect two shafts No slippage is possible once engaged Shock loads are directly transferred. Tapered surfaces can permit slow engagement Tend to become replaced with better equipment.

10. MECH1200 Friction Clutches and Brakes One surface has friction lining Surfaces brought into contact by electromagnetic, mechanical, pneumatic, or hydraulic pressure. Radial engagement – Band – Expanding shoe Axial engagement – Disc caliper – Plate – Centrifugal

11. MECH1200 Friction Materials Asbestos no longer used High coefficient of friction Heat resistant Material Combination Coefficient of FrictionTemp.(max) Pressure (Ma x) WetDryDeg.CMPa Cast Iron/Cast Iron0,050,15-0,203000,8 Cast Iron/Steel0,060,15-0,203000,8-1,3 Hard Steel/Hard Steel0,050,15-0,203000,7 Wood/Cast Iron-steel0,160,2-0,351500,6 Leather/Cast Iron-steel0,12-0,150,3-0,51000,25 Cork/Cast Iron- Steel0,15-0,250,3-0,51000,1 Felt/Cast Iron- Steel0,180,221400,06 Woven Asbestos/Cast Iron- Steel0,1-0,20,3-0,62500,7 Moulded Asbestos/Cast Iron- Steel0,08-0,120,2-0,52501,0 Impregnated Asbestos/Cast Iron- Steel0,120,323501.0 Carbon-graphite/Cast Iron- Steel0,05-0,10,255002.1 Kelvar/Cast Iron- Steel0,05-0,10,353253,0

12. MECH1200 Electrical Clutch and Brake Electrically activated friction elements – Uses electromagnet to apply force Magnetic particle – Magnetic particles drawn by coil Eddy current – ?

13. MECH1200 Wet and Multiplate Clutch Multiple plate clutch This type of clutch has several driving members interleaved or "stacked" with several driven members. It is used in race cars including F1, IndyCar, World Rally and even most club racing, motorcycles, automatic transmissions and in some diesel locomotives with mechanical transmissions. It is also used in some electronically controlled all-wheel drive systems. Wet vs. dry A wet clutch is immersed in a cooling lubricating fluid which also keeps the surfaces clean and gives smoother performance and longer life. Wet clutches, however, tend to lose some energy to the liquid. Since the surfaces of a wet clutch can be slippery (as with a motorcycle clutch bathed in engine oil), stacking multiple clutch discs can compensate for the lower coefficient of friction and so eliminate slippage under power when fully engaged.

14. MECH1200 Pneumatic and hydraulic Air pressure expands diaphragm or piston to exert force on the friction material. Springs are used to disengage Hydraulic actuation can supply higher pressure.

15. MECH1200 Torque Limiting Clutches Provide overload protection Pressure is applied to friction discs by spring pressure and adjusting nuts. Intended as an overload protection, not for repetitive starts

16. MECH1200 Fluid Clutch Function to provide soft start, delayed engagement, reduced starting load, and overload protection. Uses a fluid torque converter. Consists of an impeller and running vanes in an oil filled housing. Dry fluid clutch involves the use of shot between the housing and impellers.

17. MECH1200 Overrunning clutches Terms – cam clutch, free-wheeling clutch, backstop, sprag clutch, roller ramp clutch, on- way clutch, or single direction clutch. Allows rotation in one direction and prevents rotation in the opposite direction.

18. MECH1200 Overrunning clutch types Pawl and ratchet – Most primitive – Pawl catches on backside of teeth Ramp clutch – Spring loaded ball engages outer ring via flat ramp Sprag – Special shaped locking cams engage inner and outer ring – Garter spring keeps cams centered Wrap spring clutch – Hubs fit inside spiral wound spring and tighten one direction, slip the other.

19. MECH1200 Overrunning Clutch Applications Overrunning – Two motors (main drive and inching drive) connected to same equipment Indexing Backstopping – Safety mechanism – Prevent load reversal – Can mount within gearbox Holdback – Prevents inclined conveyor from reversing

20. MECH1200 Stopping Torque

21. MECH1200 Stopping Torque

22. MECH1200 Stopping Torque