Sujetadores y Tornillos de Potencia

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Sujetadores y Tornillos de Potencia
Engineers need to be continually reminded that
nearly all engineering failures result from
faulty judgments rather than faulty
calculations. Eugene S. Ferguson, Engineering
and the Minds Eye.
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Perfile roscado
Parámetros empleados para definir un perfil
roscado Diámetro mayor, d. Paso por pulgada
p1/n, nº roscas por pulgada Diámetro de cresta,
dc Diámetro de paso, dp Diámetro de raiz, dr
Text Reference Figure 15.1, page 667
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Roscado
(a) Simple, (b)
doble, y (c) triple.
AVANCE l tipo roscado x p
Text Reference Figure 15.2, page 667
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Perfiles de rosca
UN -- M
ACME
Uso potencia, máquina - herramienta
UN 8 series de rosca de paso constante Roscas
de paso C-basto F-Fino EF-Extra Fino
M Roscas de paso C-basto F-Fino Ej.MF8X2-G6
dc/roscas/pulg/ajuste
Ej.UNF1/2X16-1B dc/roscas/pulg/ajuste
Text Reference Figure 15.3, page 668
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Perfil M y UN
Detalle dimensiones de perfiles M y UN. ht 0.5p
/ tan 30º
Text Reference Figure 15.4, page 668
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Ajuste
Calidad 3(apretado)-9(Suelto)
Equivalencias entre roscas
Text Reference Table 15.1, page 669
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Tornillos de potencia Perfil ACME
Detalle del perfil - Dimensiones. (valores en
pulgadas)
Buscamos mayor ventaja mecánica -
posicionamiento.
Text Reference Figure 15.5, page 670
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Perfil ACME
Datos cortante para una longitud de roscado de 1
pulg
dpdc-0.5p-0.01
Text Reference Table 15.2, page 671
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Tornillo de potencia con collarín
, Ángulo de avanceArcTan l/pdp
Collarín de empuje
Text Reference Figure 15.6, page 672
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Tornillo de potencia con collarín y husillos de
bolas
Text Reference Figure 15.6, page 672
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Fuerzas sobre el tornillo de potencia
?Fv0 ?Fh x r 0
DCOE ?n
Fuerzas actuando sobre. (a) paralelepípedo (b)
sección axial (c) plano tangencial.
Text Reference Figure 15.7, page 673
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Par torsor el tornillo de potencia
?Fv0 ?Fh x r 0
ASCENSO
DESCENSO
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Ejercicios

1. Determine los pares de torsión, de elevación y de
   descenso, así coma la eficiencia del tornillo de
   potencia manufacturado con rosca ACME. es
   autobloqueante? cual es la contribución de la
   fricción del collarín, en comparación con la
   fricción del tornillo, si el collarín tiene, a)
   deslizamiento, m0,15 b) rodamiento, m0,02 ambos
   en aceite. W1000lb. Rosca Acme 1,25-5 y Omedio
   collarín 1,75 in.
2. Mismo ejercicio con W1000lb. Rosca Acme 1-5
   roscado doble y Omc1,5 in. m0,16 rosca y 0,12
   collarín.
3. Igual que el ejercicio dos, pero con roscado
   simple.

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Tipos de sujetadores roscados

• Tornillo y tuerca (c) Tornillo de cabeza (c)
  Birlo.
• NotaArandela o roldana

Text Reference Figure 15.8, page 679
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Equivalencia de la conexión Sistema de resortes
Bolt-and-nut assembly simulated as bolt-and-joint
spring.
Text Reference Figure 15.9, page 680
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Force vs. Deflection of Bolt and Member
Force versus deflection of bolt and member. (s)
Seperated bolt and joint (b) assembled bolt and
joint.
Text Reference Figure 15.10, page 680
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Fueza vs. Deflexión
Text Reference Figure 15.11, page 681
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Bolt and Nut
Figure 15.12 Bolt and nut. (a) Assembled (b)
stepped-shaft representation of shank and
threaded section.
Text Reference Figure 15.12, page 682
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Bolt and Nut Assembly
Figure 15.13 Bolt-and-nut assembly with conical
fustrum stress representation of joint.
Text Reference Figure 15.13, page 683
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Gasketed Joint
Figure 15.17 Threaded fastener with unconfined
gasket and two other members.
Text Reference Figure 15.17, page 694
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Constants for Joint Stiffness Formula
Table 15.3 Constants used in joint stiffness
formula Eq. (15.26) From Wileman et al (1991)
Text Reference Table 15.3, page 684
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Example 15.6
Figure 15.14 Hexagonal bolt-and-nut assembly
used in Example 15.6. (a) Assembly and
dimensions (b) dimensions of frustum cone. (All
dimensions are in millimeters.)
Text Reference Figure 15.14, page 685
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Strength of Bolts (Inches)
Table 15.4 Strength of steel bolts for various
sizes in inches.
Text Reference Table 15.4, page 687
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Strength of Bolts (Millimeters)
Table 15.5 Strength of steel bolts for various
sizes in millimeters.
Text Reference Table 15.5, page 687
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Coarse and Fine Thread Dimensions
Table 15.6 Dimensions and tensile stress areas
for UN coarse and fine threads.
Text Reference Table 15.6, page 687
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Coarse and Fine Thread Dimensions - Metric
Table 15.7 Dimensions and tensile stress areas
for metric coarse and fine threads.
Text Reference Table 15.7, page 69
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Ejercicio Cilindro hidraúlico
Un cilindro hidráulico de do150mm y e2mm
sometido a Pi 250 Kg/cm2 se ha de diseñar con
n1(mínimo). Se embridan las piezas de acero, con
una junta elástica. Determinar tornillo a
colocar, calidad, pretensado considerando un 5
de relajación y espesor de juntas. Atornillos7
At,junta
Roscas finas MF
Métrica Área esfuerzo, mm2 Material disponible calidades
10 61.2 5.8,8.8, 9.8 y 10.9
12 92.1 e juntas0,25mm
16 167 0.5-1-2-3-4
20 272 E2/E11400
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Separation of Joint
Figure 15.15 Separation of joint.
Text Reference Figure 15.15, page 690
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Cyclic Load
Figure 15.16 Forces versus deflection of bolt
and joint as function of time.
Text Reference Figure 15.16, page 691
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Factor Concentración Fatiga
Ka,e
Factor de concentración de esfuerzos, incluye el
factor acabado superficial
SeSeKaKbKcKdKeKgSeKa,eKbKcKdKgSeKa,eKdKg
Kb,axial1
Text Reference Table 15.8, page 692
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Ejercicio Fatiga
Diseñar la junta atornillada que se situaría al
extremo de un recipiente tal que su presión varia
de 75 a 150 kg/cm2. a) Pi y n, tal que a
160kg/cm2 actúe como válvula (suponiendo que no
hay fatiga). b) causa de rotura con el Pi y
tornillo anterior. c) Diámetro de tornillo para
evitar fatiga y n fatiga. Datos
k10,153.Tornillo Calidad 8.8 y 9.8. relajación
5.,Nt(1525)
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Failure Modes of Riveted Fasteners
Figure 15.18 Failure modes due to shear loading
of riveted fasteners. (a) Bending of member (b)
shear of rivet (c) tensile failure of member
(e) bearing of rivet on member or bearing of
member on rivet.
Text Reference Figure 15.18, page 695
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Example 15.9
Group of riveted fasteners used in Example 15.9.
(a) centroid of rivet group Assembly (b) radii
from centroid to center of rivets (c) resulting
triangles (d) direct and torsional shear acting
on each rivet (e) security beding factor (side
view of member). (All dimensions are in inches.)
Text Reference Figure 15.19, page 697
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Text Reference Figure 15.19, page 697
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Cortante debido a la torsión
Text Reference Figure 15.19, page 697
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DATOS Un paso para peatones se remacha a un
puente de acero como se indica en la figura. La
carga máxima sobre el paso es equivalente a una
carga de 3 000 N, localizada a 2 m del costado
del puente de acero por cada par de remaches. Se
supone un factor de seguridad de 5. HALLAR El
diámetro del remache que se necesita si los
remaches estan hechos de acero AISI 1040.
Nota las fuerzas de tensión que actúan sobre los
dos remaches son proporcionales a la distancia
desde el extremo inferior de la ménsula
Text Reference Figure 15.20, page 699
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Fillet Welds
Figure 15.21 Fillet welds. (a) Cross section of
weld showing throat and legs (b) shear planes.
Text Reference Figure 15.21, page 701
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Geometry and Parameters of Welds
Table 15.9 Geometry of welds and parameters used
when considering various types of loading. From
Mott (1992)
Text Reference Table 15.9, page 703-704
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Geometry and Parameters of Welds (cont.)
Table 15.9 Geometry of welds and parameters used
when considering various types of loading. From
Mott (1992)
Text Reference Table 15.9, page 703-704
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Geometry and Parameters of Welds (cont.)
Table 15.9 Geometry of welds and parameters used
when considering various types of loading. From
Mott (1992)
Text Reference Table 15.9, page 703-704
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Electrode Properties
Table 15.10 Minimum strength properties of
electrode classes.
Text Reference Table 15.10, page 705
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Example 15.11
Figure 15.22 Welded bracket used in Example
15.11. (a) Dimensions, load and coordinates (b)
torsional shear stress components at points A and
B. (All dimensions are in millimeters.)
Text Reference Figure 15.22, page 706
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Fatigue Strength Reduction Factors
Table 15.11 Fatigue strength reduction factors
for welds. From Shigley and Mischke (1989)
Text Reference Table 15.11, page 709
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Adhesive Bonded Joints
Figure 15.23 Four methods of applying adhesive
bonding. (a) Lap (b) butt (c) scarf (d)
double lap.
Text Reference Figure 15.23, page 710
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Scarf Joint
Figure 15.24 Scarf joint. (a) Axial loading
(b) bending (c) torsion.
Text Reference Figure 15.24, page 711
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Integrated (Snap) Fasteners
Figure 15.25 Common examples of integrated
fasteners. (a) Module with four cantilever lugs
(b) cover with two cantilever and two rigif
lugs (c) seperable snap joints for chassis
cover.
Text Reference Figure 15.25, page 714
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Cantilever Snap Joint
Figure 15.26 Cantilever snap joint.
Text Reference Figure 15.26, page 714
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Snap Fastener Design
Figure 15.27 Permissible deflection of different
snap fastener cantilever shapes.
Text Reference Figure 15.27, page 715
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Friction Coefficients for Polymers
Table 15.12 Coefficients of friction for common
snap fastener polymers From Bayer Corporation
(1996)
Text Reference Table 15.12, page 716
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Cylinder End Cap Section
Figure 15.28 End cap of hydraulic cylinder for
baler application.
Text Reference Figure 15.28, page 717