METAL FITS, TOLERANCES, AND SURFACE TEXTURE 11.13 Downloaded from Digital Engineering Library @ McGraw-Hill www.digitalengineeringlibrary.com METAL FITS, TOLERANCES, AND SURFACE TEXTURE.
Trang 1FIGURE 11-9 Press-fit pressures between steel hub and
shaft (1 psi¼ 6894.757 Pa; 1 in ¼ 25.4 mm) (Baumeister, T.,
Marks’ Standard Handbook for Mechanical Engineers, 8th
ed., McGraw-Hill, 1978.)
FIGURE 11-10 Variation in tensile stress in cast-iron hub
in press-fit allowance (1 psi¼ 6894.757 Pa; 1 in ¼ 25.4 mm).(Baumeister, T., Marks’ Standard Handbook for MechanicalEngineers, 8th ed., McGraw-Hill, 1978.)
FIGURE 11-11 Press-fit pressure between cast-iron huband shaft (1 psi¼ 6894.757 Pa; 1 in ¼ 25.4 mm) (Baumeister,T., Marks’ Standard Handbook for Mechanical Engineers,8th ed., McGraw-Hill, 1978.)
METAL FITS, TOLERANCES, AND SURFACE TEXTURE 11.13
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METAL FITS, TOLERANCES, AND SURFACE TEXTURE
Trang 3METAL FITS, TOLERANCES, AND SURFACE TEXTURE
Trang 5METAL FITS, TOLERANCES, AND SURFACE TEXTURE
Trang 7TABLE 11-12
Tolerancesafor shafts for sizes 500 to 3150 mm
of
basic 500 560 630 710 800 900 1000 1120 1250 1400 1600 1800 2000 2250 2500 2800shaft Limits 560 630 710 800 900 1000 1120 1250 1400 1600 1800 2000 2250 2500 2800 3150
ei þ280 þ310 þ340 þ380 þ430 þ470 þ520 þ580 þ640 þ720 þ820 þ920 þ1000 þ1100 þ1250 þ1400t7 es þ470 þ520 þ580 þ640 þ710 þ770 þ885 þ945 þ1085 þ1175 þ1350 þ1500 þ1675 þ1825 þ2110 þ2310
METAL FITS, TOLERANCES, AND SURFACE TEXTURE 11.19
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METAL FITS, TOLERANCES, AND SURFACE TEXTURE
Trang 8TABLE 11-13
Tolerancesafor holes for sizes 500 to 3150 mm
of
basic 500 560 630 710 800 900 1000 1120 1250 1400 1600 1800 2000 2240 2500 2800hole Limits 560 630 710 800 900 1000 1120 1250 1400 1600 1800 2000 2240 2500 2800 3150
EI 350 380 420 460 520 560 625 685 765 845 970 1070 1175 1275 1460 1610T7 ES 400 450 500 560 620 680 780 840 960 1050 1200 1350 1500 1650 1900 2100
EI 470 520 580 640 710 770 885 945 1085 1175 1350 1500 1675 1825 2110 2310U7 ES 600 660 740 840 940 1050 1150 1300 1450 1600 1850 2000 2300 2500 2900 3200
Trang 9METAL FITS, TOLERANCES, AND SURFACE TEXTURE
Trang 11METAL FITS, TOLERANCES, AND SURFACE TEXTURE
Trang 13METAL FITS, TOLERANCES, AND SURFACE TEXTURE
Trang 14TABLE 11-19
Surface finishavalues (CLA)
Machining process Tolerance grade Finish (lm) Tolerance grade Finish (lm) Tolerance grade Finish (lm)
1m ¼ 0:001 mmOld
Unmachined surface cleaned up by sand blasting, brushing, etc 5–80mSurface to be rough machined if found necessary (to prevent fouling)
Surface obtained by rough machining under turning, planing, millingetc Quality coarser than 9
8–25mFinish-machined surface obtained by turning, milling etc Quality 12–7 1.6–8mFine finish-machined surface obtained by boring, reaming, grinding etc
Trang 15TABLE 11-20
Lay symbols
METAL FITS, TOLERANCES, AND SURFACE TEXTURE 11.27
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METAL FITS, TOLERANCES, AND SURFACE TEXTURE
Trang 16TABLE 11-21
Preferred series roughness average values (Ra) (in lm and lin)
FIGURE 11-13 Application and use of surface-texture symbols (Baumeister, T.,
Marks’ Standard Handbook for Mechanical Engineers, 8th ed., McGraw-Hill, 1978.)
Source: Reproduced from Baumeister, T., Marks’ Standard
Handbook for Mechanical Engineers, 8th ed., with permission from
McGraw-Hill Book Company, New York, 1979
11.28 CHAPTER ELEVEN
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Trang 17TABLE 11-23
Surface roughness ranges of production processes
Source: Reproduction from Baumeister, T., Marks’ Standard Handbook for Mechanical Engineers, 8th ed., with permission
from McGraw-Hill Book Company, New York, 1979
METAL FITS, TOLERANCES, AND SURFACE TEXTURE 11.29
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METAL FITS, TOLERANCES, AND SURFACE TEXTURE
Trang 18TABLE 11-24
Application of surface texture values to surface symbols
placed at the left of the longleg; the specification of onlyone rating shall indicate themaximum value and anylesser value shall beacceptable
produce the surface; the basicamount of stock provided formachining is specified at theleft of the short leg of thesymbol
by the lay symbol placed atthe right of the long leg
Maximum waviness heightrating is placed above thehorizontal extension; anylesser rating shall beacceptable
2:5 ð0:100Þ Roughness sampling length
or cutoff rating is placedbelow the horizontalextension; when no value isshown, 0.80 mm is assumed
Maximum waviness spacingrating is placed above thehorizontal extension and tothe right of the wavinessheight rating; any lesserrating shall be acceptable
? 0:5 Where required, maximum
roughness spacing shall beplaced at the right of the laysymbol; any lesser rating shall
Trang 19Slideways and gibsPress-fit partsPiston-rod bushingsAntifraction-bearing seatsSealing surfaces for hydraulictube fittings
O-ring grooves (static)Antifraction-bearing boresand faces
Camshaft lobesCompressor-blade airfoilsJournals for elastomer lipseals
Engine cylinder boresPiston outside diametersCrankshaft bearingsJet-engine stator bladesValve-tappet cam facesHydraulic-cylinder boresLapped antifriction bearingsBall-bearing races
Piston pinsHydraulic piston rodsCarbon-seal mating surfacesShop-gauge faces
Comparator anvilsBearing ballsGauges and mirrorsMicrometer anvilsMETAL FITS, TOLERANCES, AND SURFACE TEXTURE 11.31
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METAL FITS, TOLERANCES, AND SURFACE TEXTURE
Trang 20TABLE 11-26
Range of surface roughnessa
Trang 214 Black, P H., and O Eugene Adams, Jr., Machine Design, McGraw-Hill Publishing Company, New York.
5 Baumeister, T., Marks’ Standard Handbook for Mechanical Engineers, 8th ed., McGraw-Hill Publishing Company, New York, 1978.
6 Maleev, V L., and J B Hartman, Machine Design, International Textbook Company, Scranton, Pennsylvania, 1954.
7 Shigley, J E., Machine Design, McGraw-Hill Publishing Company, New York, 1956.
8 Vallance, A., and V L Doughtie, Design of Machine Members, McGraw-Hill Publishing Company, New York, 1951.
9 British Standard Institution.
10 Bureau of Indian Standards.
FIGURE 11-14 Symbols for tolerances of form and position FIGURE 11-15 Rivet symbols
METAL FITS, TOLERANCES, AND SURFACE TEXTURE 11.33
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METAL FITS, TOLERANCES, AND SURFACE TEXTURE
Trang 2212
DESIGN OF WELDED JOINTS
SYMBOLS2;3;4
A area of flange material held by welds in shear, m2(in2)
A0¼ l! length of weld when weld is treated as a line, m (in)
b width of connection, m (in)
c distance to outer fiber (also with suffixes), m (in)
cx distance of x axis to face, m (in)
cy distance of y axis to face, m (in)
c1 distance of weld edge parallel to x-axis from the center of weld,
to left, m (in)
c2 distance of weld edge from parallel to x-axis from the center of
weld, to right, m (in)
c3 distance from farthest weld corner, Q, to the center of gravity of
weld, m (in) (Fig 12-8)
d depth of connection, m (in)
ex eccentricity of Pzand Pyabout the center of weld, m (in)
ey eccentricity of Pxabout the center of weld, m (in)
h thickness of plate (also with suffixes), m (in)
i number of welds
Ix, Iy, Iz moment of inertia of weld about x, y, and z axes respectively,
m4, cm4(in4)
J moment of inertia, polar, m4, cm4(in4)
J! polar moment of inertia of weld, when weld is treated as a line,
m3, cm3(in3)
Kf fatigue stress-concentration factor (Table 12-7)
l effective length of weld, m (in)
lt total length of weld, m (in)
Mb bending moment, N m (lbf in)
Mt twisting moment, N m (lbf in)
na actual factor of safety or reliability factor
Na fatigue life (for which sfais known) for fatigue strength sfa,
cycle
Nb fatigue life (required) for fatigue strength sfb, cycle
P load on the joint, kN (lbf )
Px component of P in x direction, kN (lbf )
Py component of P in y direction, kN (lbf )
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Trang 23Pz component of P in z direction, kN (lbf )
r distance to outer fiber, m (in)
R ratio of calculated leg size for continuous weld to the actual leg
size to be used for intermittent weld
t throat dimension of weld, m (in)
V shear load, kN (lbf )
w size of weld leg, m (in)
Z section modulus, m3(in3)
Z! section modulus of weld, when weld is treated as line (also with
suffixes, m2(in2)
normal stress in the weld (in standard design formula), MPa
(psi)
0 force per unit length of weld (in standard design formula) when
weld treated as a line, kN/m (lbf/in)
sfa fatigue strength (known) for fatigue life Na, MPa (psi)
sfb fatigue strength (allowable) for fatigue life Nb, MPa (psi)
d design stress, MPa (psi)
e elastic limit, MPa (psi)
shear stress in the weld (in standard design formula), MPa (psi)
0 shear force per unit length of weld (in standard design formula)
when weld is treated as a line, kN/m (lbf/in)
The allowable load on the weld
FIGURE 12-1 Fillet weld
BUTT WELD
The average normal stress in a butt weld subjected to
tensile or compression loading (Fig 12-2)
12.2 CHAPTER TWELVE
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DESIGN OF WELDED JOINTS
Trang 24The average shear stress in butt weld
The allowable load on the weld
TRANSVERSE FILLET WELD
The average normal tensile stress
The average normal tensile stress for the case of
trans-verse fillet weld shown in Fig 12-3.
A double fillet lap weld joint.
FIGURE 12-3 A transverse fillet weld
PARALLEL FILLET WELD (Fig 12-5)
The average shear stress in the weld
The shear stress in a reinforced fillet weld
The throat dimension (h) does not include the reinforcement.
Refer to Fig 12-4.
FIGURE 12-4 A double-fillet lap-weld joint
where w ¼ dimension of leg of weld.
w can be replaced by h (thickness of plate) when w and
h are of same dimension.
Either symbol F or P can be used for force or load depending on symbols used in figures in this chapter.
¼ P
where throat t is taken as 0.85w
DESIGN OF WELDED JOINTS 12.3
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Trang 25LENGTH OF WELD
The effective length of weld (Fig 12-5)
The total length of weld (Fig 12-5)
The relation between the length l1and l2(Fig 12-5)
FIGURE 12-5 Parallel fillet weld
ECCENTRICITY IN A FILLET WELD
The bending stress due to fillet weld placed on only
one side of the plate (Fig 12-6)
The stress due to tensile load
The combined normal stress at the root of the weld
The shear stress
The maximum normal stress
The maximum shear stress
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DESIGN OF WELDED JOINTS
Trang 26ECCENTRIC LOADS
Moment acting at right angles to the plane of
welded joint (Fig 12-6)
Direct load per unit length of weld
Load due to bending per unit length of weld
The resultant load or force
Moment acting in the plane of the weld
(Fig 12-7)
Load due to twisting moment per unit length of weld
The resultant load (Fig 12-7)
DESIGN OF WELDED JOINTS 12.5
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Trang 27The shear stress due to torsion
Combined bending and torsion
The resultant or maximum induced normal force per
unit throat of weld
The resultant induced torsional force per unit throat
of weld
The required leg size of the weld when weld is treated
as a line
The resultant normal stress induced in the weld
The resultant shear stress induced in the weld
The required leg size of weld when the weld area is
considered
FATIGUE STRENGTH
The fatigue strength related to fatigue life can be
expressed by the empirical formula
¼ Mtr
wJw
ð12-23aÞ or
0¼ Mtr
Jw
(treating weld as a line) ð12-23bÞ
0 max¼ 1 2
2 4
3
5 ð12-24Þ
0 max¼ 1 2
ð12-25Þ
w ¼ actual force permissible force ¼ 0maxor 0
max
0
aor 0 a
ð12-26Þ
max¼ 1 2
2 4
3
5 ð12-27Þ
max¼ 1 2
k ¼ 0:13 for butt welds
¼ 0:18 for plates in bending, axial tension,
or compression
12.6 CHAPTER TWELVE
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DESIGN OF WELDED JOINTS
Trang 28DESIGN STRESS OF WELDS
The design stress
The design stress for completely reversed load
THE STRENGTH ANALYSIS OF A TYPICAL
WELD JOINT SUBJECTED TO ECCENTRIC
LOADING (Fig 12-8)2;3;4
Throughout the analysis of a weld joint, the weld is
treated as a line
Area of cross section of weld
The distance of weld edge parallel to x axis from the
center of weld, to left
The distance of weld edge parallel to x axis from the
center of weld, to right
The distance from farthest weld corner, Q, to the
center of gravity of weld
The moment of inertia of weld about x axis
The moment of inertia of weld about y axis
The moment of inertia of weld about z axis
The section modulus of weld, about x axis
The section modulus of weld, about y axis
The section modulus of weld, about z axis
d¼ a
na
ð12-31Þ where
na¼ actual safety factor or reliability factor
2s
DESIGN OF WELDED JOINTS 12.7
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Trang 29Pz component
Throughout the analysis of this problem the weld is
considered as a line
The force per unit length of weld due to direct force Pz
The force per unit length of weld an account of
bend-ing at the farthest weld corner, Q, due to eccentricity
exof load Pz
The force per unit length of weld an account of
bend-ing at the farthest weld corner, Q, due to eccentricity
eyof load Pz
The total force per unit length of weld due to bending
The combined force per unit length of weld due to
Zwy
ð12-43Þ
0 zb2¼ Pzey
Zwx
ð12-44Þ
0
zb¼ 0 zb1þ 0
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DESIGN OF WELDED JOINTS
Trang 30Px component
The force per unit length of weld due to direct shear
force Px which acts in the horizontal direction (Fig.
12-8)
The twisting moment
The shear force per unit length due to twisting
The resultant shear force per unit length of weld in the
horizontal direction due to Pxonly
Pycomponent
The direct shear force per unit length of weld parallel
to y direction due to force Py(Fig 12-8)
The twisting moment
The shear force per unit length of weld due to twisting
moment Mty
The vertical component of 0
ty
The horizontal component of ty0
The resultant shear force per unit length of weld in the
vertical direction due to Pyonly
tyh0 ¼ ty0 sin ð12-57Þ
0 tyrv¼ 0
ydþ 0
DESIGN OF WELDED JOINTS 12.9
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Trang 31COMBINED FORCE DUE TO Px, Py, AND Pz
AT POINT Q (Fig 12-8)
From Eqs (12-46), (12-50), (12-52), (12-57), and
(12-58)
The total shear force per unit length of weld in the x
direction (Fig 12-8) from Eqs (12-52) and (12-57)
The total shear force per unit length of weld in the y
direction (Fig 12-8) from Eqs (12-50) and (12-58)
The resultant shear force per unit length of weld at
point Q due to Px and Py forces (Fig 12-8) from
Eqs (12-59) and (12-60)
The resultant actual force per unit length of weld
(treating weld as a line) due to components Px, Py,
and Pzat point Q from Eqs (12-46) and (12-61)
The leg size of the weld
For the AWS standard location of elements of
welding symbol, weld symbols and direction for
making weld
0
x¼ 0 tzrhþ 0
y0¼ txv0 þ tyrv0 ð12-60Þ
0¼ ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 02
x þ 02 y
q
ð12-61Þ
0 actual¼ ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 02
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DESIGN OF WELDED JOINTS