Casting Defect (2)

8/11/2019 Casting Defect (2)

http://slidepdf.com/reader/full/casting-defect-2 1/25

A

SEMINAR REPORT ONCASTING DEFECTS

Guided byDR.ANIL KUMAR SINGHPROFESSOR &(H.O.D)

FOUNDRY TECHNOLOGYNIFFT,HATIA,RANCHI

Submitted by:RAJU KUMAR

A.D.C.(foundry tech.)



INTRODUCTION

CASTING DEFECTS:- The characteristics bywhich castings quality get affected & don’t fulfillthe predetermined design parameter are termed

as casting defects.

It may be classified broadly as:-

1>Major defects:-Not rectified i.e.directrejection.

2>Defects :-very costly if rectified

3>Minor defects:-economically repaired



• WHY DEFECTIVE CASTINGS?

DUE TO 1.Casting & Pattern design2.Pattern equipment3.Flask equipment & rigging

4.Gating & risering5.Moulding sand & core sand6.Core making practice

7.Moulding practice8.Metal composition9.Melting practice



CASTING DEFECTS

BLOW HOLESPIN HOLES

SCAB

RAT TAIL

HOT TEAR

SAND FUSION

BURN ON

METAL PENETRATION

SHRINKAGE DEFECT

COLD SHUT

MISRUNSHIFT & CROSS JOINT

FINS

CRUSH

MOULD WALL MOVEMENT

SWELL

INCLUSIONS

SAND CUTS &WASHERS DROP

SHOT METAL



BLOW HOLE:-The holes found on surface or sub-surface of casting having dia=or>2mm are called

blow holes.

Causes:-

High moisture contentin the sand moulds

Less permeability of

mould or core sand Excess gas generating

binders & additivesused in core making.

Poor venting of mould &core

Rusty & damp chills andchaplets used

Hard ramming of sand

Defective gating system

Remedies:-

Moisture content shouldbe minimized.

Permeability can be

improved by properventing using coarsersand.

Gas generating binders &

additives should beavoided

Chills & chaplets shouldbe dry & clean

Ramming of sand should

not be too hard



PIN HOLES:-The holes found on surface or sub-surface of casting having dia=or<2mm are called

blow holes.

Causes:-

High moisture content in themould.

Wet ladles

Wet refractory lining offurnace

Insufficient degassing ofmelt.

Metal mould reaction

Presence of Al(aluminium

present as impurity forms Al2O3 layer over casting anddoes not the trapped air tocome out).

Remedies:-

Moisture content of mouldshould be minimized

Ladle and lining should bepreheated

Proper degassing melt

To avoid metal mouldreaction, zircon wash isapplied, in cse steel castingand graphite wash in case of

cast irons.



SCAB It is rough & irregular projections on thesurface of casting.SCAB are of two

type<1>expansion scab<2>erosion scab Causes :-

High thermal expansion ofsand

Uneven or hard ramming

High moisture content in themould

Low permeability

Flat surface on cope side ofthe mould

Slow pouring rate

Remedies:-

Sand should be of widedistribution

Ramming of sand should beproper &uniform.

Pouring rate should not betoo slow

Moisture content should beas less as possible

Enforcements can be used onthe cope side where chancesof scabbing in maximum.



RAT TAIL:-It is also an expansion defect,similar to scab but of lower degree.

It causes lurinkles to appear on the top face

of the casting. Causes:-

Prolonged heating of

mould surface Excess moisture

content in the sand

Uneven ramming ofsand

Remedies:-

Moisture content

should beminimized.

Ramming of sand

should be proper Pouring should be

adequately fast.



HOT TEAR :-Irregular cracks occurs on the

casting, during last stages of solidification.

The cracks have very rough surface.

Causes:-

Excess mould hardness

Improper design ofcasting

Insufficient collapsibilityof mould & cores

Long freezing range of

alloy, promotes hot tear Excess shrinkage of

metal

High sulphur contentpromotes hot tear

Remedies:-

Collapsibility of mould &core should be high

Ramming should not betoo hard

If excess sulphur ispresent, then

desulphurization can becarried out



SAND FUSION

It occurs generally in ferrous castings where

pouring temperature is high. Sand particles stickson the surface of the casting, on all sides.

Reasons:-

High pouringtemperature

Low refractoriness

of sand

Remedies:-

Mould can bewashed by highrefractory material

Zircon sand can beused as facing sand,in the mould



BURN ON It occurs in ferrous castings only where

temp. is very high. Metal mould reaction takes

place 2Fe + O2 ® 2FeO2FeO + SiO2 ® FeO. SiO2 (Fayalite)

The whole casting is covered with a layer offayalite.

Reasons:-

High pouringtemperature

Metal mould reaction

Remedies:-

In case of cast irons, coaldust is added in sand mix, itproduces a reducing

atmosphere which does notallow oxygen to react withmetal and form FeO.

Graphite mould wash canalso be done to stop metal

mould reaction



METAL PENETRATION

Molten metal enters the space between sand

grains and thus results in rough surface of the casting.

Reasons:-

Soft ramming Coarse sand grains

High metallostaticpressure

Remedies:-

Proper and uniformramming

Wide distribution ofsand

Washes can beapplied on themould wall.



SHRINKAGE DEFECT :-Irregular cavity formed in

casting due to insufficient metal

Reasons:-

Poor risering

Poor casting design

Lack of directionalsolidification

Remedies:-

Proper gating andrisering

achieve directionalsolidification for thatuse chills,exothermicmaterials, arcing theriser melt, etc.



COLD SHUT When two streams of molten metal meet in

the mould cavity, but do not fuses with each

other perfectly &makes hair like crack is calledcold shut

Reasons:-

Low pouringtemperature

Slow pouring rate Poor gating design

Less fluidity of melt

Remedies:-

sufficient pouringtemp.

higher pouring rate Proper gating design

Increase the fluidityof melt



MISRUN Incompletely filled mould cavities resulting in

incomplete casting is called misrun.

Reasons:-

Very thin sections in

casting Low pouring

temperature

Slow & intermittent

pouring Low permeability

Poor gating design

Insufficient metal

Remedies:-

Proper gating and

risering Proper venting

Sufficient metal shouldbe poured

Thin sections can bepreheated

Pouring should be fastenough

Pouring temperatureshould be correct



SHIFT & CROSS JOINT It is a mismatch of the casting at the parting

line or a variation from specified dimensions of a

cored section due to change in position of core ormisalignment of core in assembling.

Reasons:-

Wrong assembly of mould &core

Incorrect locating pins in themould

Inadequate weighing of thecope part

Loose patterns on the plate

Pattern not properly alignedin the cope & drag part.

Inadequate provisions forcore print or core support

Remedies:-

Core should be properlyassembled. For this purposecore paste and other thingsshould be properly used.

Moulding boxes should beproperly clamped and

weighed. Loose piece of pattern should

be properly aligned withdowel pins

There should be adequatecore prints on pattern for thesupport of core.



FINS They usually occur at the parting line all

along the castings in the form of extra metal

which has to be ground off. These are called fins.

Reasons:-

Incorrect mouldassembly

Insufficient weighing

of the mould Due to high

metallostatic

pressure

Remedies:-

Proper assembly ofcoke & drag

Extra weight should

be provided over themould box

Length of sprue pin

should not be toolon .



CRUSH It is the displacement of sand while closing

or mould thereby deforming mould surface. Due

to this, irregular depressions occur on the surfaceof the casting.

Reasons:-

Excessive weighingof the cope

Careless mould &

core assembly Core print too small

to support the core

Improper ramming

Poor green strength

Remedies:-

Excess weighingshould be avoided

Mould & core should

be assembled,carefully

Proper ramming ofsand should be done



MOULD WALL MOVEMENT The sides of the casting bulge out, due to

mould wall movement. This occurs generally in

gray iron and S.G. Iron castings.

Reasons:-

High moisturecontent in the mould

Less rigid mouldwalls

Remedies:-

Moisture contentshould be as low aspossible

Mould walls can be

made rigid by usingbinders andadditives such asdextrin, molasses

SWELL



SWELL Some portion of the casting may small, due

to poor ramming at that part.

This is called small defect.

Reasons:-

Poor or non uniformramming

Lack of rigidity ofmould walls

High metallostaticpressure

Remedies:-

Ramming should beuniform

Sprue pin should notbe too long

Gating should bedone properly



INCLUSIONS When slag enters the mould cavity, it

solidifies as inclusions. If large amount of slag

enters then it forms smooth depression on theupper surface of the casting.

Reason:-

Slag poured alongwith molten metal.

Remedy:-

Metallic or ceramicnets can be used tofilter the melt.

Skim bob gatingsystem can be used.

Bottom pouringladles can be usedfor slag free, clean

metal.

When molten metal flows over the mould &



When molten metal flows over the mould &core surface it erodes some part of the sand andresults in cuts & washes. The place from where

sand has been eroded there extra metal solidifieson the surface of the casting.

Reasons:- Soft ramming

Insufficient draft on

patterns Improper gating

system

Improper baking of

cores

Remedies:- Ramming properly

Provide Draft

allowance Proper Gating

system

Core baked properly



DROP When portion of sand drops from the cope

part or from other overhanging sections in the

molten metal, then this causes drop defect

Reasons:- Less green strength of

mould

Soft ramming

Improper casting design

Remedies:-

Green strength must beoptimum by havingoptimum moisturecontent & binder level

Ramming should bedone properly

Overhanging sectionscan be strengthened by

using enforcements

SHOT METAL OR COLD SHOT



SHOT METAL OR COLD SHOT Due to sputtering of metal, premature

solidification of metal globules take place. This

premature solidified metal globules do not fusewithin the metal. This is called cold shot.

Reasons:-

Due to gating system which

causes turbulence. Multiple gating

High moisture content in themould creates boiling actionwhich causes metal sputter

Those metal which arereadily oxidized are moreprone to cold shots

Slow, interrupted pouring

Remedies:-

Amount of moisture in the mould

and core sand should be controlledso that it will not create boilingaction.

Gating system should be such thatit will prevent metal shooting intothe mould

Pouring should not be slow



Documents

Casting Defect (2)