Date post: | 24-Dec-2015 |
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Machine design 2
Joints
1
loads
• mechanical forces, moments…
• thermal • chemical changing in place/ time
• …static cyclic dynamic
2
materials
• metals– ferrous/ non~
• cast iron• steel
– carbon/ alloy
• plastics
• ceramics
• composite
• density• conductivity• …• elasticity• plasticity• ductility• brittleness• toughness (impact)• creep
3
loads & stresses
(Mohr, H-M-H)
Stress distribution uniforn/linear
4
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
function of joints: join elements together:)
• Kinematic –allowing special freedoms of movement
• Fixing or orientating no movement at all
6
Joint types 1.
• permanent– welded– soldered– brazed– glued– riveted– …
• detachable (fasteners)– bolted– pin/ cotter pin/ spline– …
semi-detachable:
press fitted
7
8
welding
glueing
mech.
joints
brazing
soldering
melting
pressing
hot
cold
Tm
100°C 450°C
base material melts
permanent
detachable
© bagyinszky
w/wo parts
not melts
Joint types 2.
• joining by:
force shape material
9
Joint types 2.
• joining shaft & hub by:
force shape material
10
friction positive, we/ so /gl
no-slip
hybrids
11
bolt
Split/ groowed pin
Keys & pins
12
square par.
flat ~
tapered
Gib-head
round
Woodruff
pin
roll-pin
keyseat/ keyway
keyways - stresses
13
milling cutters
shearing
crushing
sliding, stress concentration
14evolvent/ kerb-splines
poligon
splined shaft
shaft-hub joints by friction
press fitconic rings
+ locknutclamp
fit by other means…
roll pin
groowed pintaper
other fasteners 1
pin/ bolt
double shear
loads:bending
shearing
contact strs.
„bearing” stress p = F/vdcrushing
other fasteners 2(threaded joints next time…)
18
pin: fastening, locating
cotter pin
(elastic)
retaining rings
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 materialMIG, RSW…
spot welding
strength calculations
• useful length / thickness (faults)
20
allowable stress:
σa = Reh φ /n
φ factor of weakening 0,5~0,9
n safety factor
design rules for welding
21
welding – pros & cons
•(almost) the same strength
•no pretreatment
•non-series, repair
•can be automated
•….
•residual stresses
•oxidation
•hidden failures
•….
22
molten filler metal
solderingT < 450 °C
lead, tin, zinc…
brazing•T > 450 °C
silver, brass…
23
adhesive forces
less strength
surface pretreatment
0.05 -0.2 mm
rivets
24
shearing
rupture of plates
crushing
solid tubular, blind
adhesive bonding (glueing)
25
physical bond:
solvent, contact, hot-melt…
chemical bond:
hardening polymers
(epoxy resins…)
adhesives – pros & cons
•quick, easy
•no heat
•insulates
•repairs
•pretreatment
•limited strength
•limited temps
•….
26
honeycomb structure
Thank you for kindly attention!
27