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kevchan's version from 2015-10-14 15:31

Section

Question Answer
What is a machine? 1an assemblage of parts that transmit force, motion and energy from a stored state
What is a machine? 2an instrument (such as a lever) designed to modify the application of power, force or motion
What is a machine? 3human operated device for performing a task with, a coin operated device
Sources of forcehuman, gravity, magnetic, combustion, friction
Relationship between force and energyforce applied over a distance
Force is used toproduce movement, prevent movement, determine mass
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stressforce/area
strainchange in length/ original length
areaoriginal area before loading
reduced areasmallest area after fracture
ductileincreased deformation before failure
brittleimmediate failure
yield strengtha large increase in strain with little or no increase in stress indicates elongation plastically
proportional limitpoint where stress strain curve deviates from a straight line
true strengththe projection of a material continuing to yield under yield strength indefinitely
ultimate strengthmax amount of strength achieved until failure
elastic modulusrelationship between stress and strain with constant proportionality; indicates stiffness of material
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carbon steel high strength tocost ratio
carbon content range<0.1% to 1%, higher content increases strength, hardness, and decreases ductility
alloy steelsalloying elements added to improve properties
sulfur/phosphorous/lead + steelimproves machinability but increases brittleness
nickel + steelimproves toughness, hardenability and corrosion resistance
chrome is like nickel except alsohas high abrasion resistance and strength at high temperatures.
aluminumhigh conductivity, light strong used in cars and air planes
copper low electrical resistance
brasseasily cast, good machinability
bronzehigh strength, low friction
plasticscan be used for hardness and toughness
composite plasticsnon-structural applications like guards
powdered metalssintering is when powder is raised to the temperature just below melting points to have the powder fuse together
annealingheated, held, controlled heating
normalizinglike annealing but above a critical temperature and cooled in air
through hardening and quench and temperingheated and quenched to form martensite, then tempered to achieve ductility
case hardeningrapid heating of the surface followed by rapid cooling
stress relievingheated to lower the yield strength
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sulfur/phosphorous/lead + steelimproves machinability but increases brittleness
nickel + steelimproves toughness, hardenability and corrosion resistance
chrome is like nickel (good toughness, hardenability and corrosion resistance) except alsohas high abrasion resistance and strength at high temperatures.
aluminumhigh conductivity, light strong used in cars and air planes
copper low electrical resistance
brasseasily cast, good machinability
bronzehigh strength, low friction
plasticscan be used for hardness and toughness
composite plasticsnon-structural applications like guards
powdered metalssintering is when powder is raised to the temperature just below melting points to have the powder fuse together
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toughness ability of a material to absorb energy and plastically deform without fracturing
resilienceability to absorb energy when deforming elastically (constant modulus of elastically) and release the energy
strengthability to withstand deformation before failing
machinabilityease with which a metal can be cut permitting the removal of the material with a satisfactory finish at low cost
hardenabilitydepth at which a metal is able to be hardened through heat treatment
hardnessresistance to permanent shape change
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factors of meritany variable you wish to use to make a decision
factors of safetyquantity that causes failure divided by expected quantity
design factorfactor of safety before final decision is made
stress ratioused to describe varying stresses in a material
stress reversalwhen a member experiences a tensile stress followed by a compressive stress of equal quantity
fatigue loadingrepeated loading
endurance strengthability to resist fatigue loads
endurance limithighest stress level in which a material can withstand infinite number of cycles.
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Question Answer
Three different types of weldingarc, gas, spot
Arc welding usesAC or DC power sources and controls
brazing and solderingjoining similar or dissimilar materials bonded with heating a filler material with a base material without melting the base material
heat-affected zonearea in which the base material has not melted but has been altered in its properties by welding
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Question Answer
power screw applicationsconvert rotary motion to linear motion, speed reduction results in torque which is force multiplication, positioning and measuring, coordinating, has high friction froce.
Pitchthe distance between two successive crest peaks
Leaddistance traveled in one 360 degree turn, steeper angles means more turning to travel a distance lead angle too steep will not hold load
Lead angleangle between helix and plane of rotation
Thread angleangle in between a thread
major diameterdiameter relative to the crests of the thread
minor diameterdiameter relative to the roots of the thread
mean diameteraverage of the major and minor diameter
Thread depthMajor minus minor diameter
RH and LHboth need to tighten screws when in intended functional motion
Ball screwgreatly reduces friction with efficiencies of 90% or higher
Square thread90 degree thread angle
Acme Thread14.5 degree thread angle
self-lockingif friction is greater than tan(lead angle)
square thread vs acme threadacme is cheaper, square needs special equipment to manufacture and is better you need less torque to turn
Back driving torquetorque required to hold the nut from turning when a force is applied LOOSENING THE BOLT
pre-loading boltPreload is the tension created in a fastener when it is tightened
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springs made of different materialelasticity with hysteresis, non-linear elasticity, linear elasticity
spring materialhigh carbon steel, alloy steel, rubber
torsion barquarter elliptical, semi ellipitical, full eliptical
Lead/ multi-leaf springsvehical suspension failure in bending
helical coil torsion springsclothes pegs failure in bending at ends
helical compression springsconstant pitch, conical, variable pitch used in ball point pens failure in buckling
helical tension springsbend springs failure in torsion
spring constantchange in force divided by change in length
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Question Answer
embedibilityability to fuse with the shaft or bearing you want high
journal vs rolling elementjournal quieter, journal faster, journal lower stress, journal less expensive, journal high start friction, journal takes up less radial space, rolling takes up less axial space
types of lubricationhydrodynamic, mixed film, boundary
hydrodynamicsurfaces completely separated by lubricant. no contact
mixed filmintermittent local contact
boundaryextensive local contact
shafttransmits rotational motion and power
bearings allow a shaft to rotate in its support
weargradual removal of surface material
greasestwo-phase compounds - thickener and oil
solid lubricantspolytertrafluoroethylene, molybdenum disulphide, very cheap, lowest speed, lowest maintenance
greaselow speed, cost, maintenance
oil bathmoderate speed, cost and maintenance
oil misthigh speed, cost and maintenance
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Question Answer
ball bearinglow cost, medium radial load, small thrust load
deep grove balllow cost, medium radial load, larger thrust load
angular contact balllow cost, medium radial load, greater thrust load
self-aligning ballself alignment problems eliminated reducing machining costs, medium radial load , medium thrust
cylindrical rollerlower cost, high radial loads, no thrust
needle rollerlow cost, high radial load, no thrust, low radial space, lower speed
spherical roller thrustself-aligning, high thrust, high cost
taper rollerlow cost, very high axial loads, small radial load
spherical rollerself aligning, high radial, moderate thrust loads
taper rollerlow cost, high radial loads, good thrust loads
ball thrustlow cost, moderate axial loads
cylindrical roller thrustlow cost, high thrust loads
need thrustlow cost, very high thrust loads, small space, lower speed
eccentricitythe quality of being more oval
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Question Answer
worm gearno backdriving, high speed reduction, high friction, shafts perpendicular, some thrust
spur gearinvolute profile, shaft parallel, perpendicular teeth, no thrust, backdriving possible, inexpensive, noisy, medium speed reduction
helix gearangled teeth, parallel shaft, thrust, back driving possible, more expensive, quiet, medium speed reduction , smaller than spur
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