Casting Defect

Foundry casting defects.
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  1  Assoc   Prof    Zainal    Abidin    Ahmad Department   of    Manufacturing   &   Ind.   Eng.Universiti   Teknologi   Malaysia METAL   CASTING   PROCESSES   Castin   ualit     Metals   for   Casting   Product   Design   Considerations 6-Aug-08Assoc Prof Zainal Abidin Ahmad2 Casting   Quality   There   are   numerous   o ortunities   for   thin s   to   o    wron   in   a   casting   operation,   resulting   in   quality    defects   in   the   product     The   defects   can   be   classified   as   follows:   Defects   common   to   all   casting   processes   Defects   related   to   sand   casting   process 6-Aug-08Assoc Prof Zainal Abidin Ahmad3 Misrun  A    casting   that   has   solidified   before   completely    filling   mold   cavity    6-Aug-08Assoc Prof Zainal Abidin Ahmad4 Figure 11.22 -Some common defects in castings: (a) misrun  2 Cold   Shut Two   portions   of    metal   flow   together   but   there   is   a   lack   of    fusion   due   to   premature   freezing   6-Aug-08Assoc Prof Zainal Abidin Ahmad5 Figure 11.22 -Some common defects in castings: (b) cold shut Cold   Shot Metal   splatters   during   pouring   and   solid   globules   form   and   become   entrapped   in   casting 6-Aug-08Assoc Prof Zainal Abidin Ahmad6 Figure 11.22 -Some common defects in castings: (c) cold shot Shrinkage   Cavity  Depression   in   surface   or   internal    void   caused   by    solidification   shrinkage   that   restricts   amount   of    molten   metal   available   in   last   region   to   freeze   6-Aug-08Assoc Prof Zainal Abidin Ahmad7 Figure 11.22 -Some common defects in castings: (d) shrinkage cavity Sand   Blow Balloon ‐ shaped   gas   cavity    caused   by    release   of    mold   gases   during   pouring   6-Aug-08Assoc Prof ZainalAbidinAhmad8 Figure 11.23 -Common defects in sand castings: (a) sand blow  3 Pin   Holes Formation   of    many    small   gas   cavities   at   or   slightly    below   surface   of    casting   6-Aug-08Assoc Prof Zainal Abidin Ahmad9 Figure 11.23 -Common defects in sand castings: (b) pin holes Penetration  When   fluidity    of    liquid   metal   is   high,   it   may    penetrate   into   sand   mold   or   sand   core,   causing   casting   surface   to   cons s   o   a   m x ure   o   san   gra ns   an   me a   6-Aug-08Assoc Prof Zainal Abidin Ahmad10 Figure 11.23 -Common defects in sand castings: (e) penetration Mold   Shift  A    step   in   cast   product   at   parting   line   caused   by    sidewise   relative   displacement   of    cope   and   drag 6-Aug-08Assoc Prof Zainal Abidin Ahmad11 Figure 11.23 -Common defects in sand castings: (f) mold shift Metals   for   Casting   Most   commercial   castin s   are   made   of    allo s     rather   than   pure   metals     Alloys   are   generally    easier   to   cast,   and   properties   of    product   are   better     Casting   alloys   can   be   classified   as:     Ferrous     Nonferrous   6-Aug-08Assoc Prof Zainal Abidin Ahmad12  4 Ferrous   Casting   Alloys:   Cast   Iron   Most   important   of    all   casting   alloys     Tonnage   of    cast   iron   castings   is   several   times   that   of    all   other   metals   combined     Several   types:   (1)   gray    cast   iron,   (2)   nodular   iron,   (3)    white   cast   iron,   (4)   malleable   iron,   and   (5)   alloy    cast   irons     T ical   ourin   tem eratures   ∼  1 00 ° C   2 00 ° F   de endin     on   composition   6-Aug-08Assoc Prof Zainal Abidin Ahmad13 Ferrous   Casting   Alloys:   Steel   The   mechanical   ro erties   of    steel   make   it   an   attractive   engineering   material   The   capability    to   create   complex   geometries   makes   casting   an   attractive   shaping   process     Difficulties   faced   by    the   foundry     working    with   steel:   Pouring   temperature   of    steel   is   higher   than   for   most   other   casting   metals   ∼  16 0 ° C   000 ° F     At   these   temperatures,   steel   readily    oxidizes,   so   molten   metal   must   be   isolated   from   air     Molten   steel   has   relatively    poor   fluidity    6-Aug-08Assoc Prof Zainal Abidin Ahmad14 Nonferrous   Casting   Alloys:   Aluminum     enera y    cons ere   to   e    very    casta e   Pouring   temperatures   low   – melting   temperature   of    aluminum   T  m  =   660 ° C   (1220 ° F)     Properties:     Light    weight   Range   of    strength   properties   by    heat   treatment   Ease   of    machining   6-Aug-08Assoc Prof Zainal Abidin Ahmad15 Nonferrous   Casting   Alloys:   Copper   Alloys   Includes   bronze,   brass,   and   aluminum   bronze     Properties:     Corrosion   resistance   Attractive   appearance     Good   bearing   qualities     Limitation:   high   cost   of    copper     Applications:   pipe   fittings,   marine   propeller   blades,   pump   components,   ornamental    jewelry    6-Aug-08Assoc Prof Zainal Abidin Ahmad16


Jul 23, 2017
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