Alb Mod Clutches and Brakes Flashcards
The purpose of a clutch in a power transmission system is to:
engage or disengage a driven machine without starting and stopping the prime mover
Clutches can connect two shafts together, or connect power to:
A sheave, sprocket or gear
Clutches can be used to provide _____, constant torque, limited torque, automatic disconnection, quick starts or stops
variable speeds
Positive contact clutches depend on ____ for engagement and do not allow slippage
interlocking parts
Positive clutches can be used for timing applications. What are two disadvantages to positive clutches?
- Cannot be engaged at high speeds (shock loads)
- May not line up when at rest
This clutch is a positive contact clutch. Uses square jaws that lock into mating recesses. These are bidirectional. One jaw is splined or keyed and can move axially for engagement. Generates no heat, must be engaged at low speeds (under 10 RPM)
Square jaw clutch
This clutch is a positive contact clutch. It can be engaged at higher speeds than the square jaw, but still causes shock on engagement. Engaging surfaces are square on one side and sloped on the other. Slides axially for engagement. Can drive in one direction only.
Spiral jaw clutch
This clutch is a positive contact clutch. Uses a large number of teeth to provide engagement. Can be engaged at a higher speed than square and spiral jaw, and still causes shock loading on engagement. Activated mechanically or electrically.
Multiple tooth clutch
Friction clutches provide a ____ transfer of power on engagement. Can engage or disengage at any speed.
smooth
Friction clutches can be designed with _____ in the friction plate to reduce shock and torsional vibration
dampening devices (springs)
Friction material may be non-metallic, metallic, or:
A mixture of both
A wet clutch is a:
Clutch flooded with oil
Radial clutches have the pressure applied against the:
rim or drum
axial clutches have contact pressure applied against the:
face
This is a radial friction clutch. Has a set of shoes connected to one shaft. They expand outward and engage the inside of the drum, which is connected to the other shaft. Once engaged, extra force is applied via centrifugal forces.
Expanding shoe clutches
This is a radial friction clutch. Has a drum on one shaft and a rim with the shoes on the other. The shoes are attached to a bladder, which inflates to apply pressure. Can engage and disengage quickly. Disengagement aided by centrifugal force
Contracting shoe clutch
Note: Alignment of the two machines must be accurate
Axial friction clutches use a soft friction disc sandwiched between two:
harder pressure plates
What is the main wearing surface of an axial friction clutch?
friction disc (clutch disc or clutch plate)
Rapid wear of a friction clutch indicates:
clutch is undersize
This is an axial friction clutch. It has a single clutch disc splined to the driven shaft. Has a larger surface area than a drum clutch and occupies less space. Has a single, spring loaded pressure plate connected to a fly wheel. Sandwiches the clutch disc when engaged.
Single disc friction clutch
This is an axial friction clutch. Same as the single disc clutch, but has multiple clutch discs so it can transmit more power. Uses an intermediate pressure plate between the clutch discs.
Multiple disc friction clutch
This style of friction clutch uses clutch plates with external teeth that mate with a ring with internal teeth, and can slide axially within it. The clutch plates are pressed against a pressure plate, which has internal teeth and mates with a splined shaft.
Pneumatically engaged friction clutch
Clutch plates that are in segments have the advantage of:
Being easily replaced
This type of friction clutch uses an activated magnetic field that pulls a friction disc into contact to transfer power
Electromagnetically activated clutch
This clutch is a cross between a radial and axial clutch. It’s contact surfaces are engaged at an angle usually between 10-15°. Smaller the angle, the greater the wedge and grip. Have a tendency to grab and to hold on when disengaging. Can be used submerged in oil.
Cone clutch
The main difference between a fluid clutch and a fluid coupling is the fluid clutch is designed so the amount of fluid is:
Controlled, via scoop tube. Regulates slip
The impeller of a fluid clutch is located on the ___ shaft
input
The turbine of a fluid clutch is located on the ____ shaft
output
Fluid couplings will always slip unless a ___ is used in the design
lock up clutch
Magnetic clutches are ____ clutches
non friction
Engage without any direct mechanical connection
True _____ clutches have no contact at all between driving and driven parts
electromagnetic
The disadvantage of electromagnetic clutches is:
Cannot transmit as much torque
This clutch uses an electromagnetic coil (or permanent magnet) on the input rotor to generate a magnetic field. Actuated by turning on the power supply to the magnet, torque is transferred to the hardened steel drag cup proportional to the current or strength of the magnetic field. Used for light high speed applications. Quick response time
Hysteresis clutch
This clutch contains magnetic metal particles between the input rotor and output housing. When a coil is energized, the particles form a link and transmit torque proportional to the current. Used for high power transmissions and has a quick response time.
Magnetic particle clutch
This clutch has two drums that run close together. Have soft iron rotors. Coupled through a magnetic field, requires slip to develop torque. Torque depends on strength of magnetic field and on slip. Should be liquid cooled for larger HP units. Can have infinite speed regulation. Transfers high HP at moderate speed.
Eddy current clutch
On this clutch, a driven member is held between friction plates under a pre determined pressure. When the clutch is overloaded, the driven member slips. Power transferred adjusted by tightening/loosening nut/bolts
Torque limiting clutch
A one way clutch comes in three types: (3)
- Roller ramp clutch
- Sprag (cam) clutch
- wrap-spring clutch
The wrap spring clutch is used on very low power applications and moderately large torque. It works because it ____ and transfers power in only one direction
tightens
What are the 3 applications for one way clutches? (3)
- Simple overrunning
- Indexing
- Holdbacks/backstops
With a one way clutch, _____ allows multiple drive sources, and allows the shaft to turn even if one is stationary.
-Simple Overrunning
With a one way clutch, _____ allows reciprocating motion to be changed to one way intermittent rotary motion
-Indexing
With a one way clutch, ____ stops a drive, say on a conveyor, from running backwards when the load has stopped.
-Holdback or backstop
____ are a power control device used to stop a machine or control speed or direction
brakes
Most brakes transform mechanical energy to _____
heat
Note: may have fins to aid air cooling, can be cooled by liquids
The friction materials for brake pads are usually made from _____ materials
heat resistant
Brake capacity is expressed in ____
braking torque
Brake effectiveness depends on:
Coefficient of friction of the material
What are the 3 classes of brakes? (3)
- Mechanical
- Hydraulic
- Electrical
A dynamic brake is one that:
Not only holds, but slows and stops a load
A brake used in personal safety is:
overdesigned
If a retarder is used on a braking system, it does:
most of the braking but won’t fully stop a load
The duty cycle of a brake refers to:
how often it is used
The two basic types of brakes are: (2)
- Drum
- Disc
External drum brakes use a brake band, internal drum brakes use:
brake shoes
Does a disc brake or a drum brake have more surface area for braking?
disc
Disc brakes can have ____ force applied vs drum
more,
equal loading on both sides, no warping
Caliper style disc brakes have the advantage of: (2)
- pressure
- heat dissipation
What are the two types of disc brakes? (2)
- Rotating disc (caliper)
- Stationary disc
This type of drum brake has a block that presses onto the side of the drum to stop the machine
block brake
This type of drum brake has a band of material that applies pressure to the drum. braking power can be enhanced by using a differential pivot.
band brake
This type of drum brake has two shoes on the outside, works like two block brakes.
external shoe brake
This type of drum brake has two anchored shoes inside a drum.
Internal shoe brake
Retarders are very similar to fluid couplings, except the ____ is anchored
turbine
Retarders are activated by:
pumping fluid into it.
More fluid, more braking power
Magnetic particle brakes have a stator, a rotor, a coil, and magnetic particles. It works the same as a magnetic particle clutch, except:
One member is held or anchored.
Braking power is determined by the intensity of the magnetic field
Eddy current brakes work like an eddy current clutch, except one member is held or anchored. Works purely on the electrical principle of the:
repulsion of same poles
When installing a clutch, bearings should be _____ to the clutch
as close as possible
