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Published byAngelina Ford Modified over 9 years ago
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Machine design 2 Joints 1
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loads mechanical forces, moments… thermal chemical changing in place/ time … static cyclic dynamic 2
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materials metals –ferrous/ non~ cast iron steel – carbon/ alloy plastics ceramics composite density conductivity … elasticity plasticity ductility brittleness toughness (impact) creep 3
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loads & stresses (Mohr, H-M-H) Stress distribution uniforn/linear 4
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general purpose machine elements static elements joints frames springs (mechanical) drive systems bearings shafts couplings & clutches drives vessel systems pipes valves tanks (technical fluids) 5
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function of joints: join elements together:) Kinematic –allowing special freedoms of movement Fixing or orientating no movement at all 6
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Joint types 1. permanent –welded –soldered –brazed –glued –riveted –… detachable (fasteners) –bolted –pin/ cotter pin/ spline –… semi-detachable: press fitted 7
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8 welding glueing mech. joints brazing soldering melting pressing hot cold TmTm 100°C 450°C base material melts permanent detachable © bagyinszky w/wo parts not melts
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Joint types 2. joining by: force shape material 9
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Joint types 2. joining shaft & hub by: force shape material 10 friction positive,we/ so /gl no-slip
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hybrids 11 bolt Split/ groowed pin
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Keys & pins 12 square par. flat ~ tapered Gib-head round Woodruff pin roll-pin keyseat/ keyway
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keyways - stresses 13 milling cutters shearing crushing
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sliding, stress concentration 14 evolvent/ kerb-splines poligon splined shaft
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shaft-hub joints by friction press fit conic rings + locknut clamp
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fit by other means… roll pin groowed pin taper
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other fasteners 1 pin/ bolt double shear loads: bending shearing contact strs. „bearing” stress p = F/vd crushing
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other fasteners 2 (threaded joints next time…) 18 pin: fastening, locating cotter pin (elastic) retaining rings
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welding 19 same material (cohesive forces) melting and/or pressing weldeability (rigidness, oxidation) heat sources: flame, arc, current, beam… butt weld corner weld (fillet seam) filler material MIG, RSW… spot welding
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strength calculations useful length / thickness (faults) 20 allowable stress: σ a = R eh φ /n φ factor of weakening 0,5~0,9 n safety factor
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design rules for welding 21
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welding – pros & cons (almost) the same strength no pretreatment non-series, repair can be automated …. residual stresses oxidation hidden failures …. 22
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molten filler metal soldering T < 450 °C lead, tin, zinc… brazing T > 450 °C silver, brass… 23 adhesive forces less strength surface pretreatment 0.05 -0.2 mm
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rivets 24 shearing rupture of plates crushing solid tubular, blind
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adhesive bonding (glueing) 25 physical bond: solvent, contact, hot-melt… chemical bond: hardening polymers (epoxy resins…)
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adhesives – pros & cons quick, easy no heat insulates repairs pretreatment limited strength limited temps …. 26 honeycomb structure
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Thank you for kindly attention! 27
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