split pattern of green sand molding and hollow casting production
TRANSCRIPT
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Machine Shop (2)
Experiment Report Foundry Workshop
Experiment: Split Pattern of Green Sand
Molding and Hollow Casting Production
Report by:
Jorge Sance!
Student "umber: #$%&$'()
Report *ue *ate: June )%+ ,&))
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1. Introduction
Sand astin!is a metal process caracteri!ed by using sand as te mold material-
.t is ceap and retains its strengt at ig temperature- /e sand is moistened wit
water to de0elop strengt+ plasticity and ma1e it suitable for molding- Sand castings
are produced in speciali!ed factories called foundries- 2unny fact: o0er $&3 of allmetal castings are produced 0ia sand casting process-
2or our process we use "reen Sand- Green Sand is called li1e tis because it is
wet+ not because it is green in color+ and it is a type of molding sand+ or foundry
sand+ and it is not a type of sand per se+ but is actually a mixture of silica+ clay+
water+ inert sludge and antracite+ and terefore must fulfill some conditions#
re$ractoriness% chemica& inertness% permea'i&ity% sur$ace $inish% cohesieness%
$&oa'i&ity% co&&apsi'i&ity% and finallyaai&a'i&ity*cost- "ow we sall define eac of
tese caracteristics-
Re$ractoriness: tis means te sand can witstand 0ery ig temperatures+ tis
would be from te li4uid metal being cast+ and it will not brea1 down- 5ou a0e to
ta1e into consideration tat wen casting+ different types of sand can a0e different
temperature limits- /is is important because if te sand as too low refractoriness+
it will melt and fuse to te casting-
hemica& inertness: te sand mustn6t react wit te metal being cast- /is is
important because some metals are igly reacti0e- Examples are al1ali metals in
te periodic table suc as magnesium and titanium-
+ermea'i&ity: tis refers to te ability of te sand to exaust gases- /is is
important+ because during te casting process+ gasses are produced and tey must
lea0e te mold or else tere will be casting defects+ suc as blow oles and gas
oles-
Sur$ace Finish: tis is defined by te si!e and sape of te sand particles7 finer
particle+ better finis- 8ut you must ta1e into consideration tat permeability
decreases as particles are finer-
ohesieness: tis refers to te ability of te pattern to retain its sape after te
mold is remo0ed-
F&oa'i&ity: tis is te ability of te sand to flow into complex details and corners
witout special processes or e4uipment-
o&&apsi'i&ity: tis means te easiness wit wic a casting can be remo0ed from
te sand mold after it solidifies- Poor collapsibility means tat te sand aderes
strongly to te casting-
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,ai&a'i&ity*cost: tis is important because for e0ery ton of metal poured+ you need
%9 tons of sand- ;nd anoter point to consider is tat most of te sand cannot be
reused+ because it migt be damaged in te process- So to reduce cost+ , types of
sand migt be used+ one type wic will be te facing sand+ wic is te sand in
direct contact wit te casting- ;nd ten te bac1ing sand+ wic can be any type of
normal sand+ wit no special properties-
2. +rincip&es
Casting is a solidification process+ wic means tat most of te properties are
controlled by solidification penomena- ;lso+ most of te casting defects occur in te
solidification process- Solidification occurs in , steps+ wic are nuc&eationand
crysta& !roth- "ucleation is wen solid particles from witin te li4uid material-
/e internal energy of tese particles is lower tan tat of its surrounding medium+
and so tere is an interface between te two- /e formation of te surface at tis
interface re4uires energy+ so as nucleation occurs+ te material undercools+ becauseof te extra energy needed to form te internal surface- .t ten eats up again to te
free!ing temperature+ so tere crysta& !roth- ;ll nucleation represents a crystal+
wic grows as te eat of fusion is extracted from te li4uid until tere6s no li4uid
left- /e direction+ rate and type of growt can be controlled to get te best results-
.n general+ oo&in! urescan be used to control te 4uality of a casting- .n
general+ an area of te casting tat cools rapidly will a0e fine grain structure and if it
cools slowly+ it will a0e coarse grain structure-
/ere are , metods wic are te most widely used today: te "reen Sandand
,ir Setmetods-
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/e "reen Sandmetod consists of ma1ing molds wit wet sand+ ence te name
/e ,ir Setmetod uses dry sand wit no clay but instead fast curing adesi0es- .t
is also 1nown as no ba1e mold casting- .n tis process+ te sand is not rammed to
te flas1+ but ?ust poured in+ and ten because of te resin+ it solidifies at room
temperature- .t gi0es off a better finis tan oter types of sand molds- .t is
considered a cold setting process+ since no eat in in0ol0ed- /is process is mostly
used for brass+ ferric and aluminum alloys-
@en te process is finised+ some irregularities can present- Suc an irregularity is
called a Casting *efect+ wic is any irregularity in te casting process tat is
undesired- Some defects can be tolerated+ wile oters+ if tey can6t be fixed+ te
cast must be disposed of completely- /ere are ( main categories of defects: "as
+orosity+ Shrinka!e+ Mo&d Materia&+ +ourin! Meta&+ and Meta&&ur!ica&defects-
Gas Porosity Srin1age Porosity
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.nclusion Mold Sifting
2las Sort Casting
Hot Tears
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-. +rocedure
Commonly+ te basic process consists of steps:
)A Place a pattern in sand and create a mold- /e facing sand sould be strained
first+ to get finer particles and better finis-
,A Put te pattern and sand in a gating system- if tere are any crac1s andBor oles+
fix tem- ;dd te coating powder- /en place te upper part of te mold- Place
te upper part of te pattern- Redo te process- /en ma1e oles on top- Ma1e
te top smoot-
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%A ;dd water to te sides of te pattern- Remo0e te pattern- .f tere are any crac1s
andBor woles+ fix tem-
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/e next steps would loo1 someting li1e tis:
'A 2ill te mold ca0ity wit molten material
(A ;llow it to cool
A 8rea1 away te sand mold and remo0e te casting- 2or example in te picture+
we can see door andles-