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 Mind’s Eye.

Perfile roscado Parámetros empleados para definir un perfil roscado Diámetro mayor, d. Paso por pulgada p=1/n, nº roscas por pulgada Diámetro de cresta, dc Diámetro de paso, dp Diámetro de raiz, dr Text Reference: Figure 15.1, page 667

Roscado AVANCE l = tipo roscado x p (a) Simple, (b) doble, y (c) triple. AVANCE l = tipo roscado x p Text Reference: Figure 15.2, page 667

dc/roscas/pulg/ajuste Perfiles de rosca ACME UN -- M 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

Perfil M y UN Detalle dimensiones de perfiles M y UN. ht= 0.5p / tan 30º Text Reference: Figure 15.4, page 668

Ajuste Equivalencias entre roscas Text Reference: Table 15.1, page 669 Calidad 3(apretado)-9(Suelto) Equivalencias entre roscas Text Reference: Table 15.1, page 669

Tornillos de potencia: Perfil ACME Detalle del perfil - Dimensiones. (valores en pulgadas) Buscamos: mayor ventaja mecánica - posicionamiento. Text Reference: Figure 15.5, page 670

Perfil ACME dp=dc-0.5p-0.01 Text Reference: Table 15.2, page 671 Datos cortante para una longitud de roscado de 1 pulg dp=dc-0.5p-0.01 Text Reference: Table 15.2, page 671

Tornillo de potencia con collarín , Ángulo de avance=ArcTan [l/πdp] Collarín de empuje Text Reference: Figure 15.6, page 672

Tornillo de potencia con collarín y husillos de bolas Text Reference: Figure 15.6, page 672

Fuerzas sobre el tornillo de potencia ∑Fv=0 ∑Fh x r =0 DC=OE θn Fuerzas actuando sobre. (a) paralelepípedo ; (b) sección axial; (c) plano tangencial. Text Reference: Figure 15.7, page 673

Par torsor el tornillo de potencia ∑Fv=0 ∑Fh x r =0 ASCENSO DESCENSO

Ejercicios 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, m=0,15 b) rodamiento, m=0,02 ambos en aceite. W=1000lb. Rosca Acme 1,25-5 y Omedio collarín =1,75 in. Mismo ejercicio con W=1000lb. Rosca Acme 1-5 roscado doble y Omc=1,5 in. m=0,16 rosca y 0,12 collarín. Igual que el ejercicio dos, pero con roscado simple.

Tipos de sujetadores roscados Tornillo y tuerca; (c) Tornillo de cabeza; (c) Birlo. Nota:Arandela o roldana Text Reference: Figure 15.8, page 679

Equivalencia de la conexión: Sistema de resortes Bolt-and-nut assembly simulated as bolt-and-joint spring. Text Reference: Figure 15.9, page 680

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

Fueza vs. Deflexión Text Reference: Figure 15.11, page 681

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

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

Gasketed Joint Figure 15.17 Threaded fastener with unconfined gasket and two other members. Text Reference: Figure 15.17, page 694

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

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

Strength of Bolts (Inches) Table 15.4 Strength of steel bolts for various sizes in inches. Text Reference: Table 15.4, page 687

Strength of Bolts (Millimeters) Table 15.5 Strength of steel bolts for various sizes in millimeters. Text Reference: Table 15.5, page 687

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

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

Ejercicio – Cilindro hidraúlico Un cilindro hidráulico de do=150mm y e=2mm sometido a Pi= 250 Kg/cm2 se ha de diseñar con n=1(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. Atornillos=7% 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 juntas=0,25mm 16 167 0.5-1-2-3-4 20 272 E2/E1=1400

Separation of Joint Figure 15.15 Separation of joint. Text Reference: Figure 15.15, page 690

Cyclic Load Figure 15.16 Forces versus deflection of bolt and joint as function of time. Text Reference: Figure 15.16, page 691

Factor Concentración Fatiga Ka,e Factor de concentración de esfuerzos, incluye el factor acabado superficial Se=Se´KaKbKcKdKeKg=Se´Ka,eKbKcKdKg=Se´Ka,eKdKg Kb,axial=1 Text Reference: Table 15.8, page 692

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: k1=0,153.Tornillo: Calidad 8.8 y 9.8. relajación 5%.,Nt(15:25)

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

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

Text Reference: Figure 15.19, page 697

Cortante debido a la torsión Text Reference: Figure 15.19, page 697

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

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

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

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

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

Electrode Properties Table 15.10 Minimum strength properties of electrode classes. Text Reference: Table 15.10, page 705

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

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

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

Scarf Joint Figure 15.24 Scarf joint. (a) Axial loading; (b) bending; (c) torsion. Text Reference: Figure 15.24, page 711

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

Cantilever Snap Joint Figure 15.26 Cantilever snap joint. Text Reference: Figure 15.26, page 714

Snap Fastener Design Figure 15.27 Permissible deflection of different snap fastener cantilever shapes. Text Reference: Figure 15.27, page 715

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

Cylinder End Cap Section Figure 15.28 End cap of hydraulic cylinder for baler application. Text Reference: Figure 15.28, page 717