# Shared Flashcard Set

## Details

Machine Design two Chapter 13 & 16
Machine Design two Chapter 13 & 16
79
Engineering
12/11/2013

## Additional Engineering Flashcards

Term
 Helical gears
Definition
 have teeth inclined to the axis of rotation
Term
 • Bevel gears
Definition
 – have teeth formed on conical surfaces and are used mostly for transmitting motion between intersecting shafts.
Term
 • Worms and worm gears
Definition
 worm resembles a screw; the direction of rotation of the worm gear also called the worm wheel depends upon the direction of rotation of the worm and whether the worm teeth are cut right or left handed.
Term
 • Pitch circle
Definition
 theoretical circle upon which all calculations are usually based; pitch circles of a pair of mating gears are tangent to each other.
Term
 • Pitch diameter
Definition
 diameter of the pitch circle
Term
 • Pinion
Definition
 smaller of two mating gears
Term
 • Circular pitch
Definition
 distance measured on the pitch circle from a point on one tooth to a
Term
 • Module –
Definition
 ratio of pitch diameter and number of teeth
Term
 • Diametral pitch
Definition
 ratio of number of teeth on gear to pitch diameter
Term
Definition
 radial distance between the top land and the pitch circle.
Term
 • Dedendum
Definition
 radial distance from bottom land to pitch circle
Term
 • Whole depth
Definition
 sum of addendum and dedendum
Term
 • Clearance circle
Definition
 – circle that is tangent to addendum circle of the mating gear
Term
 • Clearance –
Definition
 amount by which the dedendum in a given gear exceeds the addendum of its
Term
 • Backlash –
Definition
 amount by which the width of a tooth space exceeds the thickness of the engaging tooth measured on the pitch circles
Term
 • Conjugate action –
Definition
 designed so as to produce constant angular velocity ratio during meshing
Term
 • Involute profile –
Definition
 in universal use for gear teeth and is the only one which we should be concerned.
Term
 • Line of action
Definition
 – represents the direction of action of forces normal to the contact.• To transmit motion at a constant angular velocity ratio, the pitch point must remain fixed; that is, all the lines of action for every instantaneous point of contact must pass through the same point.
Term
 • Base circle
Definition
 – circle on which involute is generated
Term
 • Contact ratio
Definition
 – a number that indicates the average number of pairs of teeth in contact
Term
 • Interference
Definition
 contact of portions of tooth profiles that are not conjugate.
Term
 • Undercutting
Definition
 – when gear teeth are produced by a generation process, interference is automatically eliminated because the cutting tool removes the interfering portion of the flank
Term
 • Interference can also be reduced
Definition
 by using a large pressure angle.
Term
 • Ways of forming teeth of gears
Definition
 o Sand castingo Shell modlingo Investment castingo Permanent mold castingo Die castingo Centrifugal castingo Powder metallurgy processo Extrusion
Term
 • Gears that carry large loads
Definition
 in comparison with their size are usually made of steel and are cut with either form cutters or generating cutters
Term
 • Form cutting -
Definition
 tooth space takes the exact form of cutter
Term
 • Generating
Definition
 tool having a shape different from the tooth profile is moved relative to the gear blank so as to obtain the proper tooth shape.
Term
 • Gear teeth may be machined by:
Definition
 o Milling – uses form milling cuttero Shaping – uses either pinion cutter or rack cuttero Hobbing – uses cutting tool called hob
Term
 • Gear teeth may be machined by:
Definition
 o Shavingo Burnishingo Grindingo Lapping
Term
 • Teeth may be finished by
Definition
 o Shavingo Burnishing – used with gears that have been cut but not heat treated; hardened gears with slightly oversize teeth are run in mesh with the gear until surfaces become smootho Grinding and lapping – used for hardened gear teeth after heat treatment.
Term
 shape of the tooth is an involute helicoids
Definition
 • For a helical gear, the
Term
 • The initial contact of helical gear teeth is a point that extends into a line as
Definition
 the teeth come into more engagement.
Term
 • Tooth system
Definition
 a standard that specifies the relationship involving addendum, dedendum, working depth, tooth thickness, and pressure angle.
Term
 • Face width of helical gears should be at least __________ the axial pitch to obtain good ___________ ________action
Definition
 2 timeshelical gear
Term
 • Design of gear trains to accomplish a specific train value is straightforward:
Definition
 o Number of teeth on gears must be integers, better to determine firsto Obtain pitch diameterso Determine number of stages necessary to obtain overall ratioo Divide overall ratio into portions to be accomplished in each stageo To minimize package size, keep portions as evenly divided between the stage as possible.
Term
 • Compound reverted geartrain
Definition
 – Input shaft and the output shaft of two stage compound gear train is in line
Term
 • Planetary or epicyclic gear trains
Definition
 permits some of the gear axes to rotate about otherso Have two degrees of freedom aka must have two inputso In most configurations, one element is fixed to the frameo Elements include Sun gear, arm, and planet gears
Term
 tangential or transmitted midpoint
Definition
 • In determining shaft and bearing loads for bevel gear applications the usual practice is to use the _________ or ___________load that would occur if all the forces were concentrated at the _________ of the tooth.
Term
 • Cone clutch
Definition
 consists for cup keyed or splined to one of the shafts, a cone that must slide axially on splines or keys on the mating shaft, and a helical spring to hold the clutch in engagement.
Term
 disengaged
Definition
 • Clutch is __________ by means of a fork that fits into shifting groove on friction cone
Term
 absorbed heat
Definition
 • Kinetic energy is ____________ during slippage of either a clutch or a brake, and this energy appears as _____
Term
 o Characteristics of the materialo Ability of the clutch to dissipate heat
Definition
 • The capacity of a clutch is limited by two factos:
Term
 • A temperature-rise problem
Definition
 arises when heat is generated faster than it dissipates
Term
 • Clutch operation is completed
Definition
 at the instant in which the two angular velocities become equal.
Term
 directly proportional inversely proportional
Definition
 • Time required for the engagement operation is ______ _________to the velocity difference and _______ _____________to the torque.
Term
 o High and reproducible coefficient of frictiono Imperviousness to environmental conditions such as moistureo Good resiliencyo Flexibility
Definition
 • A brake or friction clutch should have the following lining material characteristics to a degree that is dependent on the severity of service:
Term
 • Woven cotton lining
Definition
 – produced as a fabric belt that is impregnated with resins and polymerized; used mostly in heavy machinery
Term
 • Woven asbestos lining
Definition
 may contain metal particles; not quite flexible; widely used as brake material in heavy machinery
Term
 • Molded asbestos lining
Definition
 contain asbestos fiber and friction modifiers; thermoset polymer used; used in drum brake
Term
 • Molded asbestos pads
Definition
 similar to molded linings but have no flexibility; used for both clutches and brakes
Term
 • Sintered metal pads
Definition
 made of mixture of copper and/or iron particles with friction modifiers.
Term
Definition
 similar to sintered metal pads and have substantial ceramic content
Term
 • Square jaw clutch characteristics (form of positive contact clutch)
Definition
 o Do not slipo No heat generatedo Cannot be engaged at high speedso Sometimes cannot be engaged when both shafts are at resto Engagement at any speed is accompanied by shock
Term
 • _________ used where synchronous operation is required (power presses or rolling mill screw downs
Definition
 Positive clutches
Term
 • Overload release clutch
Definition
 spring loaded so as to release at predetermined torque.
Term
 • Failure by _________will occur when the significant tooth stress equals or exceeds either the yield strength or the bending endurance strength
Definition
 bending
Term
 • A _______ ________ occurs when the significant contact stress equals or exceeds the surface endurance strength
Definition
 surface failure
Term
 • AGMA
Definition
 American Gear Manufacturers Association
Term
 • Wilfred Lewis
Definition
 introduced an equation for estimating the bending stress in gear teeth in which the tooth form entered into the formulation (1892)
Term
 • 4 things to look at when analyzing performance of clutches and breaks:
Definition
 o Actuating forceo Torque transmittedo Energy losso Temperature rise
Term
 • Various types of devices to be studied and may be classified as follows:
Definition
 o Rim types with internal expanding shoeso Rim types with external contracting shoeso Band typeso Disk or axial typeso Cone typeso Misc types
Term
 • Flywheel
Definition
 inertial energy storage device; absorbs mechanical energy by increasing its angular velocity and delivers energy by decreasing its velocity.
Term
 • Self energizing
Definition
 frictions is reducing the necessary actuating force
Term
 • Self locking
Definition
 when critical value of coefficient of friction causes term (b-fa) to become zero; designer must insure this will not occur unless its specifically desired.
Term
 • Fail safe
Definition
 the operating mechanism has been designed so that, if any element should fail to perform its function, no accidents will occur in the machine.
Term
Definition
 from railway industry, refers to locomotive control mechanism which causes engine to come to a stop if operator should suffer a blackout or die at controls
Term
 • A break shoe is __________ _____________ if its moment sense helps set the brake, self deenergizing if the moment resists setting the brake.
Definition
 self energizing
Term
 • Three elements of an internal shoe rim clutch:
Definition
 o Mating frictional surfaceo Means of transmitting torque to and from surfaceso Actuating mechanism
Term
 • Classifications of clutches:
Definition
 o Expanding ringo Centrifugal (used mostly for automatic operation) If no spring used, torque is proportional to square of speedo Magnetic Useful for automatic and remote control systemso Hydraulic Useful for complex loading cycles and in automatic machineryo Pneumatic
Term
 • Hydraulic and pneumatic clutches are available as
Definition
 o Disko Coneo Multiple plate clutches
Term
 • Internal shoe or drum brake
Definition
 mostly used for automotive applications
Term
 • Pressure distribution has interesting and useful characteristics:
Definition
 o Pressure distriubution is sinusoidal with respect to angle thetao If shoe is short, large pressure on the shoe is p¬(a) occurring at end of shoeo If shoe is long, largest pressure on shoe is p(a) occurring at 90 degrees
Term
 • Assumptions implied by analysis:
Definition
 o Pressure at any point on shoe assumed to be proportional to distance from hinge pin, zero at the heelo Effect of centrifugal force neglected; clutch design, this force must be considered in staticso Shoe assumed to be rigido Analysis based on coefficient of friction
Term
 • Operating mechanisms can be classified as:
Definition
 o Solenoidso Levers, linkages, toggle deviceso Linkages with spring loadingo Hydraulic and pneumatic devices
Term
 • When external contracting designs are used as clutches, the effect of __________ ____________ is to decrease the normal force. Thus, as the speed __________ a larger values of the actuating force is required.
Definition
 centrifugal forceincreases,
Term
 • Flexible clutch and brake bands
Definition
 are used in power excavators and in hoisting other machinery
Term
 • Axial clutch
Definition
 mating frctional members are moved in a direction parallel to the shaft.
Term
 • Advantages of disk clutch:
Definition
 o Freedom from centrifugal effectso Large frictional area that can be installed in small spaceo More effective heat dissipation surfaceso Favorable pressure distribution
Term
 • Floating caliper brake
Definition
 caliper supports a single floating piston actuated by hydraulic pressure
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