103 lines
12 KiB
Plaintext
103 lines
12 KiB
Plaintext
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what are plain bearings - a suitable solid material fitted between shaft and support to reduce friction and wear - bearing may be dry rubbing bearing or lubricated
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what types of lubrication can be used for plain bearings - hydrodynamic - hydrostatic - solid-film - boundary layer
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what is hydrodynamic lubrication the shaft rotating in oil creates the oil pressure to lubricate the shaft
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what are ball and roller bearings the rotating load is converted to rolling contact of the balls or rollers
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what are the parts of a ball bearing
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what is the difference between a journal bearing and a thrust bearing - a journal bearing supports the shaft radially - a thurst bearing supports the shaft axially
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when would one use a plain rubbing bearing low load, low speed applications
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what is the pV factor and what is it the product of a measure of the bearing's ability to cope with frictional heat generation p- pressure V- speed at contact point
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what is the projected area of a radial sliding bearing the area of a journal when looking down from it:
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what is the thrust area of an axial bearing area of the bearing that isn't holey [$]\frac\pi4 \left(D^2-d^2\right)[/$]
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what is the wear volume of an axial sliding bearing the non holey area multiplied by the distance the bearing can wear down without issue [$]YA_\text{thrust} = Y\frac\pi4\left(D^2-d^2\right)[/$]
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what are the main properties of plain rubbing bearings (4) - usually made of polymers - moulded to final shape - dry lubricants added - reinforcements added
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what dry lubricants and reinforcements are added to plain rubbing bearings - PTFE lubricant added - glass fibre reinforement added
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what limits the pressure and speed a plain bearing can be operated at strength and temperature, respectively
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what differentiates oil lubricated porous bearings - manufactured from sintered metal powders - porous and impregnated
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how often does lubricant need to be replenished in porous bearings roughly 1000 hours
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list some of the lowest coefficient of friction bearing materials and their coefficient range - babbitt metal (0.005 to 0.1) - POM (0.05-0.15) - cast iron and lead bronze with grease (0.05 to 0.15)
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list the highest pV bearing materials - babbitt metal (2) - cast iron and lead bronze with grease (1) - porous bronze (1)
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what is the equation for wear factor, [$]K[/$] [$]K = \frac{W}{FVt}[/$] where $W$ is wear volume, $F$ is bearing load, $V$ is sliding velocity, and $t$ is elapsed time
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what is the main issue with hydrodynamic bearings surfaces touch at low speeds
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draw the curve of friction against speed
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describe the properties of boundary lubrication continuoous and extensive contactlubricant is smeared across surfacecoefficient of friction 0.05 to 0.2wear take place & limits life
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what are the properties of mixed lubrication higher surface speedsintermittent contact between surfacepartial hydrodynamic supportcoefficient of friction of 0.004 to 0.10very high local pressures can create elastic deformation of surfaces
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what is elastohydrodynamic lubrication fluid film lubrication where high local pressure create elastic deformation of surfaces
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what are the properties of hydrodynamic lubrication high speedsno contact between surfaces---no wearminimum film thickness of 8 to 20 micronsvery good surface finish and tolerances requiredcoefficient of friction between 0.002 to 0.01
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what is the Sommerfeld number a dimensionless number describing the relationship between a bearings dimensions, speeds, and fluid properties [$]S = \left( \frac R h\right)^2 \frac{\eta n}{P}[/$] where R is radius, h is clearance, [$]\eta[/$] is viscosity, n is angular speed, and P is bearing pressure
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what is the equation for clearance of a bearing [$]h = R_\text{bearing} - R_{shaft}[/$]
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what is petroff's equation and what is it used for [$]\mu = 2\pi^2 \frac{\eta n}{P}\frac{R}{h}[/$] used for lightly loaded bearings
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equation for hydrodynamic journal bearing capacity [$]F = S\eta V \left(\frac{R}{h}\right)^2[/$]
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equation for thrust capacity for hydrodynamic thrust bearing [$]F = 6\eta\left[ \frac{Ln(1+n)}{n^2} - \frac{2}{n(2+n)}\right]\frac{VL^2}{h_\text{min}^2}[/$] where [$]n = \frac{h_\text{max}}{h_\text{min}}-1[/$]
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what causes friction between components in relative motion real surfaces have asperities which stick out and make contact with the other facewhen sliding, asperities catch and must be deformed or brokenthe forces required to do so is friction
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what are the different rolling element types
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what are the types of ball bearings and what are their primary features
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what is the equation for static load carrying capacty [$]s_0 = \frac{C_0}{P_0}[/$] where s is the static safety factor, P, is the equivalent static bearing load, and C is the basic static load rating
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dynamic load carrying capacity [$]L_{10} = \left(\frac CP \right)^q[/$] where L10 is the basic life rating in millions of revolutions, C is the basic dynamic load rating, P is equivalent dynamic bearing load, q is exponent of life: 3 for balls10/3 for rollers
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what are the equations for equivalent dynamic load (4) constant magnitude and direction: P = F axial and radial load: [$]P = XF_r + YF_a[/$] (X and Y from manufacturers data)roller bearings: P = F_rfluctuating loads: [$]F_m = \sqrt[3]{\frac{F_1^3U_1 + \cdots}{U}}[/$]
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when would you have adjust life rating (5) low reliabilityhigh temperaturehigh vibrationrisk of water ingressrisk of corrosion
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why should a locating bearing be used in conjunction with a floating bearing ensures journal does not slide about axially (i think)
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what combinations of bearings can be used to support a shaft (5) 2 angular contact bearings - free sliding housing for axial adjustmentone ball + one roller - roller supports radial, ball supports axial and radial2 taper rollers - both support radial and axial, one bearing adjusted against other to required preload2 balls - radial and axial loads, one clamped axially on both races while other left free2 roller - accepts heavy radial load, some axial, each roller locates axially one in direction
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when should you slide fit the inner race with the shaft when the load rotates with the shaft
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what is the difference between bolts, screws, and studs bolts have an unthreaded core, and a matching nutscrews are threaded all the way and screw directly into a materialstuds do not have heads
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draw a lap joint and the forces they are designed to handle
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draw a butt joint and the forces they are designed to handle
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what is a rivet a non threaded fastener that is deformed around the parts to be joined
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what are the types of rivets (3) solidtubular - have a hole down the axisblind (pop rivets)
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what are the advantages of rivets (5) low costrapid assemblypermanentcan join dissimilar materialswide range of shapes and materials
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what are the disadvantages of rivits (3) slower than welding and adhesivespoor under tensile loadsjoints leak unless sealed
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draw a welded but joint and forces is designed to handle
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draw a welded lap joint and the forces it is designed to handle
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draw a double fillet t joint
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draw a fillet cornet joint
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why are bolts pre tensioned stops faces from separatingreduces fluctuating stresses experienced by bolt -> increases fatigue life
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what is the recommend preload for non permanent joints [$]F_i = 0.75A_s\sigma_p[/$]
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what is the rceommended preload for permanent joints [$]F_i = 0.9A_s\sigma_p[/$]
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what is the tensile area of a bolt [$]A_s = \frac{\pi}{16}(d_p+d_r)^2[/$]
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what is the pitch diameter of a bolt [$]d_p = d-0.6495p[/$]
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what is the minor diameter of a bolt [$]d_r = d-1.0825p[/$]
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what can proof strength be approximated to if unavailable [$]\sigma_p = 0.85\sigma_y[/$]
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"what does the marking ""MX.Y"" mean on a bolt" X - has tensile strength of X*100 MPa Y - has yield strength of Y*X*10 Mpa
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what is the bolt torque pre tension equation [$]T= KF_id[/$] where K is torque coefficient (around 0.2 for most cases), and d is nominal diameter
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how can the stiffness of a bolt be reduced (2) reduce cross sectional areaincrease length
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what stress reserve factor would you want for reliable materials under controlled conditions and known stresses 1.25 to 1.5
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what stress reserve factor would you want for average materials with known loads and stresses 2 to 2.5
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what reserve factor would you want for untried materials in average conditions 3 to 3.5
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what reserve factor would you want for well known materials in uncertain conditions 3 to 3.5
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what are the steps to select a bolt (6) consider permanent vs non permanent, define external load, number of bolts, and reserve factorestimate preload by assuming hard joint (K_c = 3K_b)choose suitable bolt size and determine preload by using table 5 of bs en iso 898-1:2009calculate stiffness of bolts and componentscalculate maximum allowable external loadcalculate reserve factor
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why is a pre tensioned bolted joint beneficial for cyclic loading pre tension raises mean stress which increases fatigue life
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what must be considered when using helical gears axial load generated
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what are the properties of spur gears between parallel shafts (4) cheap to manufacturenoisyfew number number of teeth in contact at any given timesensitive to alignment
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what are the properties of helical gears teeth cut at inclined angle to axis of rotationcontact between teeth more progressive and longercarries higher loadsquietercan be mounted at right anglesdouble helical gears (herringbone) can cancel out axial thrust for smoother power transmission at high speeds
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what is the pitch circle circle upon which all calculations are based
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what is circular pitch the distance between two identical points on adjacent teeth on a gear
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what is the module of a gear, m [$]m = \frac d N [/$] where d is pitch diameter, N is number of teeth
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what is tooth thickness and width of space [$]t = w = 0.5p[/$] where p is circular pitch
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what is the addendum radial distance between pitch circle and top land a = m
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what is the dedendum radial distance between pitch circle and bottom land b = 1.25 m
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what is the clearance c = 0.25m radial distance between bottom land of gear 1 and top land of gear 2
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what is the whole depth of a gear ht = addendum + dedendum = 2.25m
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what is the working depth of a gear hk = addendum + dedendum - clearance = 2m
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what are the conditions for proper meshing between gears module is samepressure angle is same
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what are the common pressure angles 20 degrees14.5 degrees
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what is the equation for centre distance betwen two gears [$]C = \frac m 2 (N_1 + N_2)[/$]
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what is the minimum number of teeth for standard gears of pressure angle 20 degrees 18
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what is a simple gear train each shaft only carries one gear
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what is a compound gear train a gear train where at least one shaft carries two or more gears
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what is a reverted train a compond train in which the input and shaft are colinear
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what is a planetary gear train has a sun gear, planet carrier, and one or more planet gears
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what differentiates planetary gear systems it has two degrees of freedomhas very high gear ratios
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what are the common forms of gear failure bending fatiguepittingmicropittingscuffing
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what is a lower pair joint joint with surface contact (pin in a hole)
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what is a higher pair joint a joint with point or line contact, such as a pin in a slot
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what is rectilinear translation points in the body move in parallel straight lines
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what is curvilinear motion points in the body move along idential curves so the link does not rotate with respect to the ground
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what is the equation for degrees of freedom of a mechanism (gruebler's) M = 3L - 2J - 3G
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what does it mean if a structure has negative degrees of freedom it's preloaded or overconstrained
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what is the grashof condition equation and what does it mean S + L < P + Q: it is a grashof linkage and at least one link can make a full revolutionS + L > P + Q: non grashof and no link capable of making full revolutionS + L = P + Q: special grashof - either double-cranks or crank rockers
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what is a limit/toggle test checks if linkage can reach all positions without encountering a limit of toggle positiontoggle positons may be determined by collinearity of two links
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what is transmission angle angle between output link and coupler
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what is the ideal transmission angle 90 degrees
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what is the minimum transmission angle 40 degrees
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