basics of castings

7/25/2019 Basics of Castings

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DEFINITION OF DEFECT:

Imperfection which contribute to a

deviation from the desired qualit level!

Defects can be classified in to three tpes


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Tpe ":

Defects #which can be ascertained durin$ visual inspection or

measurement

Tpe%:

Defects# which can be ascertained onl after &achinin$# 'ectionin$or (adio$raph

Tpe):

Defects# which can be ascertained onl durin$ &echanical testin$#&icro structure e*amination!


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Tpe ": "! E*ternal shrin+a$e ,'urface shrin+a$e-

%! Cross defects

)! Open blow holes

.! /in holes

0! (ou$h surface

1! Cold shuts

2! 'cabbin$


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Tpe%: "! Internal shrin+a$es

%! Core bro+en34loc+a$e3Core warp a$e

)! 4low holes .! Carbon floatation


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Tpe):

"! /oor &icrostructure

%! 5ndesired &etallur$ical properties )! 5ndesired &echanical properties

.! 5ndesired chemical composition


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VARIOUS FOUNDRY DEFECTS (NON-CONFORMITIES):

"! 'hrin+a$e3/orosit

%! Dross

)! 4low holes

.! /in holes0! 'and drops

1! (ou$h 'urface

2! Cold shuts

6! scabbin$

7! Carbon floatation

"8! 'hort pourin$""! &ismatch

"%! Core bro+en

")! Core bloc+ 3 warp a$e

".! Chills ,Carbides-


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SHRINKAGE

It is the discontinuit of the metal!

It is the sa$$ed hole or spon$ area lined with ferrite

crstal called dentrites!

'hrin+a$e defects are more prevalent in ductile iron

than in $ra iron!


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PHENOMENON OF SHRINKAGE:

9hen the molten metal solidifies# the atoms in the

molten metal attract each other and $et a compactedform# which results the volumetric contraction!


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Stages of S!"#$age"!iquid 'hrin+a$e ,/rimar 'hrin+a$e- ; 'hrin+a$e is about

)


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Volume

Practical

Solid contraction

Theoretical

Temperature of the liquid

After pouring

Primary Contraction

Temperature

( Liquid Shrinkage)

Secondary shrinkage

(Solidification shrinkage)

>olumetric Contraction


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TYPES OF SHRINKAGE:"!'urface shrin+a$e

%!Internal shrin+a$e

/orosit;&icro porosit 'pon$ shrin+a$e


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SHRINKAGE PRONE AREAS:

"!?eav sections in the castin$!

%!?ot spots!

)!'harp Corners

.!@rea# which is distant from the feeders ,risers-

0!'ections havin$ abrupt chan$es!

1!(e;entrant corners!

2!@t heav sections after thin sections!


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'?(INA@BE


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ROOT CAUSES:"!Insufficient feeder ,riser-!

%!Insufficient riser nec+!)!&ore in$ate thic+ness!


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METHOD OF RECTIFICATION

%&ROOT CAUSE:-I#s'ff""e#t R"se!&

Ree*"a+ At"o#

"!Increase the riser modulus!%!Increase the feed safet mar$in!

)!(educe the feedin$ distance of the

riser!,%t- t: thic+ness of the plate!

.!/rovidin$ chills!


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,&ROOT CAUSE:- I#s'ff""e#t R"se! #e$&

Ree*"a+ At"o#

"!Correct the nec+ sie , 8!12 transfer modulus- %!Correct the nec+ len$th , ) * &odulus of the

castin$-

)!/addin$


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& ROOT CAUSE:-Mo'+* D"+at"o#

Ree*"a+ At"o#

"!Increase the mold hardness , 60-

%!Improve the clampin$ sstem

)!/lacin$ some wei$hts on the mould or increase the mould wei$ht!

.!(educe the pourin$ temperature to the possible minimum level!


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.&Root Ca'se : - S+o/ Po'!"#g

Ree*"a+ At"o#

"!Increase the rate of pourin$!

%!Increase the in$ate area!3Cho+e area! )!Increase the pourin$ temperature to the ma*imum

possible level!

.!Increase the phosphorus content but it should be 8!"!


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0&Root Ca'se : - 1o/ 2o'!"#g te2e!at'!e

Ree*"a+ At"o#

"!Increase the pourin$ temperature to the ma*imum possible level!

%!(educe the metal holdin$ time in the furnace!

)!(educe the pourin$ distance!,distance between furnace and/ourin$ line-!


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3&Root Ca'se : - H"g4 1o/ a!5o# E6'"7a+e#t

Ree*"a+ At"o#

"!&aintain the CE as nearer as possible to the Eutecticpoint ,.!)


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8&Root Ca'se : - Poo! I#o'+at"o# eto*s

Ree*"a+ At"o#

Improve the inoculation methods! It can be doneonl b trial and errors accordin$ to themechanical 3 metallur$ical requirements of the

castin$!


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9&Root Ca'se : - Poo! I#o'+at"o# eto*s

Ree*"a+ At"o#

Improve the inoculation methods! It can be doneonl b trial and errors accordin$ to themechanical 3 metallur$ical requirements of the

castin$!


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&Root Ca'se : - P!ese#e of +o/ 2os2o!'s

Ree*"a+ At"o#

/hosphorus content is directl related to the fluidit of the moltenmetal! If the /hosphorus content is less than 8!"< then the fluiditof the molten metal is also come down! It will affect the flow ofmolten metal into the mould!

'o maintain the phosphorus level to the possible minimum e*tent!?i$h /hosphorus content will induce the formation of steadite!


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%;&Root Ca'se : - H"g Ca!5o#&

Ree*"a+ At"o#

If presence of carbon is more then late $raphiteprecipitation will also be more! Consequentl thepressure e*erts due to volumetric $rowth of$raphite will also be more! It will create some micro

porosit in the castin$ at the thic+er sections!


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%%&Root Ca'se : - So!t Po'!"#g&

Ree*"a+ At"o#

/our the molten metal to the full level of the

mould!


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'?O(T /O5(INB


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%,&Root Ca'se : - Mo'+* 1ea$

Ree*"a+ At"o#

"!Increase the mould ri$idit b harder rammin$ !

%!Increase the mould ri$idit b usin$ stron$er mouldbindin$ materials!

)!Correct the cope and dra$ sie suitable to the pattern!

.!Improve the clampin$ sstems

0!Increase the mould wei$ht!


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%&Root Ca'se : - Poo! ast"#g *es"g#

Ree*"a+ At"o#

"!(educe the abrupt chan$es of sections as minimum as

possible! %!/rovide ma*imum possible radius at the corners and

the fillets!

)!@void isolated sections as possible as!

.!&inimie the usa$e of cores as possible as!


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GAS DEFECTS:

Bas defects ,blow holes-are $enerated due

to absorption of $ases b the molten metal

durin$ metal pourin$ or the evolution of the$ases from the cores after completion of

pourin$!


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B@' DEFFECT


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PHENOMENON OF GAS DEFECTS:

9hile pourin$ the molten metal into the mould# molten metal will absorb the $asesfrom the moulds ,air aspiration-! This $as will come out of the molten metal because of

low densit!

'ome times core $ases will evolve after completion of pourin$ from the cores !This $aswill come out thru the molten metal and produce small voids on the surface of thecastin$!

Internal defects will also be $enerated due to this core $as! 4ecause the outer surface ofthe metal will start solidif immediatel after pourin$! 'o the entrapped $as will not be

able to come out of the surface! This tpe of defect will be visible onl after machinin$!

ROOT CAUSES :


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"!/oor $atin$ desi$n will induce turbulence in metal flow

%!Insufficient $as outlets

)!Improper sprue and $ate desi$n will allow the air aspiration!

.!?i$h moisture content in the sand

0!ow permeabilit of sand!

1!/resence of more volatile materials

2!/oor mi*in$ of sand! 6!5sa$e of e*cessive coatin$ materials

7!E*cess Nitro$en content in the bindin$ material!

"8!Inadequate curin$ of cores!

""!Bases dissolved in the molten metal!

"%!Breas or rust scraps for meltin$!

")!ow pourin$ temperature

".!/oor pre;treatment of pourin$3treatment ladles! "0!'low /ourin$!


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"!Batin$ sstem should be desi$ned in such a wa that it minimies the airaspiration!

%!@void abrupt chan$es in the $atin$ sstem!

)!/rovide $as out lets wherever possible!

.!&oisture content in the mould to be controlled!

0!If possible# avoid usin$ more fine sand!

1!Content the volatile materials in the mouldin$ sand within )

!'and mi*in$ should be uniform ,homo$eneous- mi* !

6!E*cessive coatin$ materials will evolve the $as when it contacts the

molten metal! 'o e*cessive coatin$ should be avoided!

7!ess cured 3 uncured cores will evolve more $ases after completion ofmolten metal! 'o cores should be cured well!


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"8!Content the nitro$en in the bindin$ material as minimum as possible!/resence of e*cess nitro$en will create pinholes at the surface of thecastin$!

""!@dopt suitable de$assin$ methods to release the e*cess $ases! "%!@void usin$ coated 3$reas scraps for meltin$! It will $enerate more$ases durin$ meltin$!

")!/our the molten metal into the mould at ma*imum possibletemperature in a minimum possible time!

".!Bas absorption will ta+es place from the linin$ sand if ladles are notcured well! 'o Curin$ of treatment3 pourin$ ladles is ver important!


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PIN HO1ES

This defect is often seen in $re iron castin$s but also occurs

in nodular cast irons !

/in holes are normall present ust below the castin$ face!Itwill reveal after shot blastin$!

Nitro$en pinholes are found usuall at the hot spots whereasthe ?dro$en pin holes are found in the areas remote to thein$ate!


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/IN ?OE'


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ROOT CAUSES

"!?i$h residual &a$nesium content!, 8!81


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"!Establish the safer amount of &$!'i J @l content!

%!Ensure the sufficient amount of volatile and moisture content in themouldin$ sand!

)!@void lon$ and comple* runnin$ sstem!

.!Nitri$en content to be contained in the resin bonded cores!

8!8")< ;for thin sectioned castin$s

8!886


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CAR


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C@(4ON FO@T@TION


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(O5B? '5(F@CE:

ac+ness in de$ree of smoothness


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(OOT C@5'E:

"! /attern equipment with in accessible areas for mouldin$ sand!

%! Too small fillet 3ed$e radius!

)! >er hi$h velocit of &olten metal will erode the mould wall!

.! 'and with too hi$h or too low moisture!

0! Too coarse $rain sie of mouldin$ sand!

1! Improper 'and preparation!

2! /oor rammin$ of coarse!

6! Insufficient coatin$ of coarse!

7! Over cured cores!"8! 5neven or insufficient coatin$ or sprain$ of moulds!

""! >er hi$h pourin$ temperature!


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SAND DROP:

It is a defect due to droppin$ of the 'and from

the cope or other area of the mould!


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ROOT CAUSE:

It is due to carelessness of the operator or because of rou$h

handlin$! In adequate mould relievin$ draft induce the mould crac+ and

facilitate sand drops!

9ea+ or lose flas+ bars cause mould distortion will $et crac+durin$ mouldin$!

&isali$nment of moulds!

Inadequate $reen stren$th# impact stren$th# tensile stren$th#shear stren$th and deformation properties of the mouldin$ sand!

Inadequate dr stren$th for dr sand mouldin$!


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MIS RUN

It is a defect which has a lac+ in completeness of

the molten metal durin$ metal fillin$


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CO1D SHUTS

@ Cold shut castin$ is one in which a

definite discontinuit e*ists due toimperfect fusion where two streams ofmetal have conver$ed!

'ometimes these defects are loo+ li+e a $asdefects


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COD '?5T'

ROOT CAUSE:


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ROOT CAUSE:

"! Non uniform castin$ sections resultin$ interrupted metal flow!

%! >er thin In $ates!

)! ow pourin$ temperature!

.! Inadequate $as outlets!0! hi$h volatile matter in the mouldin$ sand!

1! ow permeabilit of sand!

2! ow carbon equivalent;due to low fluidit!

6! >er low phosphorous content!

7! Interrupted pourin$!

"8!Inadequate pressure head!

""!'hort pourin$!

"%!>er slow pourin$!


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"! &ultiple in $ates can be provided for uniform disruptionsof molten metal!

%! Fast pourin$ at ma*imum possible temperature is required!

)! Ensure the qualit of mouldin$ sand for fineness#permeabilit and volatile matters!

.! &aintain ma*imum possible phosphorous content!,8!"0


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DROSS DEFECTS :

It is nothin$ but the inclusions of the

metallic o*ides!

Ductile iron is ver prone for this defect

rather than $ra iron!


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PHENOMENON OF DROSS DEFECTS:

Ductile Iron is produced b treatin$ the molten metal with &a$nesiumallo! 9hile treatment &$ reacts with the molten metal!

&$ has $reater affinit to react with atmospheric o*$en and with the

sulphur present in the molten metal and covert into &a$nesium O*idesand &a$nesium 'ulphides!

The severit is induced when the flow of molten metal $et turbulence!

'ome times presence of @luminium and &an$anese also produces itssulphides and O*ides!

Dross defects are normall found at the top surface of the castin$! To confirm the dross defects# while e*aminin$ the section cut piece under

the microscope we can see the quasi fla+e $raphites around the dross!


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ROOT CAUSES:

"!?i$h &a$nesium 3@luminium and 'ulphurcontent in the molten metal!

%!Turbulence in the flow of metal!

)!/oor de;sulphurisation methods!

.!'ulphur bearin$ materials in the mouldin$materials!

0!ow pourin$ temperature!


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The dross defect cannot be eliminated full but wecan minimie the formation of dross further !To

restrict the further formation of dross within themould # we should ta+e some appropriate actionsin the followin$ areas!


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a&Me+t"#g&

"!&aintain a low sulphur in the base metal!

%!@dd minimum possible &a$nesium 3 &a$nesium allo! )!&aintain carbon equivalent nearer to .!)

equivalent will create se$re$ation of $raphite nodules at theupper surface of castin$ durin$ solidification whicha$$ravates the dross defects!

.!@void use of allos containin$ @luminium in amountshi$her than the requirement to achieve the necessarinoculation properties!

0!Effective de;sulphurisation!


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5&Mo'+*"#g

"!@void use of 'ulphur bearin$ materials!

,e!$ Coal dust-!

%!Ensure adequate volatile content in the

mouldin$ sand to prevent &$ reactionwith atmospheric o*$en!


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*&Meta+ Po'!"#g

"!@void pourin$ of cold metal!

%!inin$ the ladles with frequent intervals!

)!'+im the molten metal effectivel to hold bac+

the sla$!


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SCA


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'C@44INB


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PHENOMENON

9hen the metal enters into the mouldcavit heat is radiated to the top and side

walls of the mould! 'o the mould starts

disinte$rated! 9hen metal touches themould wall it penetrates into the wea+

mould wall


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ROOT CAUSE

"!/oor rammin$ of mould %!?i$h moisture content in the mouldin$ sand

)!/oor qualit of bindin$ material

.!'low pourin$

0!Insufficient;In$ates

1!E*cessive pourin$ temperature


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basics of castings

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