WOOD 356 Part 2

kevchan's version from 2015-11-13 04:09




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brakedevice which turns kinetic energy into heat via friction
dynamic friction resultsfrom two parts moving at different speeds
types of brakesdisk, external drum, internal drum, band
important concepts of brakesself-actuating brake, fail safe brake
fail safe brakeare used for specific applications that require brakes to stop motion in the event of a loss in power. A compression spring pushes against the lever, activating the brake.
fail safe applicationselevator, trains, large trucks, chair lifts, cranes
internal vs external drum brake
band brake applicationswinches
band brake self-actuationcan use to create a system which
windmill brake
What is a clutcha mechanical device that engages and disengages the power transmission typically from driving shaft to driven shaft,
multi-disk clutch - use of multiple clutch plates engaging flywheel
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disk clutch
cone clutch: high surface area of contact for transmitting torque
slip clutch - limits power transmitted to machinery by limiting the amount of torque
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centrifugal clutchuse of springs to disengage the clutch
calculations - delta energy of brake= delta energy of load for rotational, changes in height, and temperature
wear rates dependsmaterials, surface roughness, temperatures, pressure, surface area
wear rate calculations:


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belt drivespower transmission between shafts
belt drive advantagessome stretch and flexibility - shock, vibration, misalignment, slip, can easily vary length, dirt resistance
continuous variable transmission can output different amounts of torque depending on the position of the belt on the tapered sheave
common belt sectionswrapped construction, cog type, timing belt, poly-rib, vee-band, double angle v-belt, flat belt, round belt
factors affecting belt selectionrated power, service factor, centre distance, smaller sheave size, belt length, size of driven and driving sheave, correction factor for belt length, correction factor for wrap length, number of belts, initial belt tension.


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Motor sizesub fractional - < 40 mhp, fractional - 1/20 to 1 hp
Integralsmall and large motors:
Motor specifications - type, power rating and speed, operating voltage, frequency, type of enclosure, frame size, mounting details
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Generation of electricitydirect current and alternating current
AC current60 Hz in Canada, 50 Hz in Britain
The frequency of the AC power setsthe speed of the AC motor
An AC motor will run20% faster at 50 Hz than 50 Hz
For a given motor the synchronous speed depends on the frequency of the electrical supply
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Synchronous-speed definitionthe speed at which an alternating-current machine must operate to generate electromotive force at a given frequency
Most AC motors rotateat speed less than synchronous speed
Slip is the loss of speed
Phase shift: purely in resistive load, current is in phase and purely in inductive load current is recycled, current lags voltage by 90 degrees, in a combined inductive and resistive load lags the voltage by theta some current is recycled
Power factor is cos of the lag angle: for example if theta = 25.8 then cos(25.8) = power factor
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Power factor iscurrent divided by the voltage
Single phase wire connection is one sin function while three wire connections: has three sin functions separated by phase shifts.
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AC induction motorrotor and stator where the stator alternates current due to the ac power supply and the relative motion of the stator and the rotor creates a current in the conductor which is called induced current
breakdown torquethe highest load the motor can achieve while not stopping
full load torque the highest speed the motor can achieve
locked rotor torquestarting immediate torque
pull up torquethe dip into speed/torque before reaching breakdown torque
if motor overheating thanmotor is overloaded and is drawing current excess to the specified current on the nameplate
if overheat continues theninternal mechanism breaks circuit -> then wires melt, short circuits, possible fire
overheating preventioninstall motor with thermal protection, size fuses, circuit breakers, increase melting temperature of insulation, increase cooling


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simple framesomething for your components to sit on
complex framemany holes accommodating hardware coming out
common materials used for woodworking machinesstructural steel - low cost and flexible design, aluminum - light weight, cast iron - damping of high frequency vibration, no welding


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simple circuit for fluidsreservoir, rotary pump with motor, check valve, pressure control valve, directional control valve, check valve with flow control valves