05) Gating System in CAsting of Materials

Gating

1. Casting & Welding Engineering
(IE 203)
Second Year,
Industrial Engineering Dept.,
Faculty of Engineering,
Fayoum University
Dr. Ahmed SalahAbouTaleb
1

2. Gating System
2

3. 3
Elements of Gating Systems
•Thetermgatingsystemreferstoallpassageways
throughwhichthemoltenmetalpassestoenterthe
mouldcavity.
•Thegatingsystemiscomposedof
Pouringbasin
Sprue
Runner
Gates
Risers

4. Gating Systems
1-The mould should be completely filled in the smallest time
possible without having to rise metal temperature.
2-The metal should flow smoothly into the mould.
3-Theunwanted material –slag –should not be allowed to enter
the mould cavity.
4-The metal entry into the mould cavity should be controlled.
5-A proper thermal gradient be maintained.
6-Metal flow should be maintained to avoid erosion.
7-Be ensure that enoughmolten metal reaches the mould cavity.
8-Thegating system should be economical and easy to
implement and remove after casting solidification.
9-Thecasting yield should be maximized.
Requirementsneeded in gating system to achieve
a free casting defects:
4

5. Gating Systems
5
Factorscontrollingthefunctioningofgatingsystem:
Typeofpouringequipment,suchasladles,pouringbasinetc.
Temperature/Fluidityofmoltenmetal.
Rateofliquidmetalpouring.
Typeandsizeofsprue.
Typeandsizeofrunner.
Size,numberandlocationofgatesconnectingrunnerand
casting.
Positionofmouldduringpouringandsolidification.

6. Pouring Basin
6
•Apouringbasinmakesiteasierfortheladleorcrucibleoperator
todirecttheflowofmetalfromcrucibletosprue.
•Helpsmaintainingtherequiredrateofliquidmetalflow.
•Reducesturbulenceatthesprueentrance.
•Helpsseparatingdross,slagetc.,frommetalbeforeitentersthe
sprue.

7. Sprue
7
•Aspruefeedsmetaltorunnerwhichinturnreachesthe
castingthroughgates.
•Asprueistaperedwithitsbiggerendattoptoreceive
theliquidmetal.Thesmallerendisconnectedtorunner.

8. Gates
8
•Agateisachannelwhichconnectsrunnerwiththe
mouldcavityandthroughwhichmoltenmetalflows
tofillthemouldcavity.
•Asmallgateisusedforacastingwhichsolidifies
slowlyandviceversa.
•Agateshouldnothavesharpedgesastheymay
breakduringpouringandsandpiecesthusmaybe
carriedwiththemoltenmetalinthemouldcavity.
•Types
•Topgate
•Bottomgate
•Partinglinesidegate

9. Gates
9
TopGate:
•Atopgateismadeinthecopeportionofthemould.
•Inatopgatethemoltenmetalentersthemouldcavity
fromthetop.
•Topgateinvolveshighturbulenceandsanderosion.
•Topgateproducespoorcastingsurfaces.

10. Gates
10
BottomGate:
•Abottomgateismadeinthedragportion.
•Inabottomgatetheliquidmetalfillsrapidlythe
bottomportionofthemouldcavityandrisessteadily
andgentlyupthemouldwalls.
•Ascomparisontotopgate,bottomgateinvolveslittle
turbulenceandsanderosion.
•Bottomgateproducesgoodcastingsurfaces.
•Iffreezingtakesplaceatthebottom,itcouldchoke
offthemetalflowbeforethemouldisfull.
•Createsanunfavourabletemperaturegradientand
makesitdifficulttoachievedirectionalsolidification.

11. Gates
11
PartingLineSideGate:
•Middleorsideorpartinggatingsystemscombine
thecharacteristicsoftopandbottomgatingsystems.
•gateisprovidedalongthepartinglinesuchthat
someportionofthemouldcavitywillbebelowthe
partinglineandsomeportionwillbeaboveit.
•Thecavitybelowthepartinglinewillbefilledby
assumingtopgatingandthecavityabovetheparting
linewillbefilledbyassumingbottomgating.

12. Runner
12
•Itishorizontalplanewhichconnectsthesprueto
gate.
•Therunnershouldbefilledwithmoltenmetalto
avoidslagenteringtocavity.

13. Design of Gating System
13
•Tofillthemouldcavitywithoutbreakingtheflow
ofliquidmetalandwithoutusingveryhighpouring
temperatures.
•Toavoiderosionofmouldcavity.
•Tominimizeturbulenceanddrossformation.
•Topreventaspirationofairormouldgasesinthe
liquidmetalstream.
•Toobtainfavourabletemperaturegradientsto
promotedirectionalsolidification.

14. Improper Gating System Design Defects
14
•Oxidation of metal
•Cold shuts
•Mould erosion
•Shrinkages
•Porosity
•Misruns
•Penetration of liquid metal into mould walls.

15. Gating System Design
1-Pouring time.
2-Choke area.
3-Sprue.
4-Gating ratios.
5-Slag trap system.
15

16. Gating System Design
The time for complete filling of a mould .
Too long pouring time ===== higher pouring temperature.
Too less pouring time ===== turbulent flow in mould.
Optimum time is required
Pouring Time
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17. Gating System Design
The pouring timedepends on:
-Casting materials,
-Casting complexity,
-Casting size, and
-Section thickness.
Pouring Time
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18. Gating System Design
1-Gray cast iron: mass less than 450 kg:
Pouring Time
K:fluidity factor.
T: average section thickness,mm
W: massof the casting, kg
2-Gray cast iron: mass greater than 450 kg:
18W
T
Kt 






59.14
41.1 40
inchesinironoffluidity
K 3
65.16
236.1 W
T
Kt 







19. Gating System Design
3-Steel casting:
Pouring Time
4-Ductile iron:
K
1=2.08 for thinner sections.
K
1= 2.67 for sections of 10 to 25 mm thick.
K
1= 2.97 for heavier sections.
19 WWt log3953.04335.2  WKt
1

20. Gating System Design
5-Copper alloy castings:
Pouring Time
Top gating 1.30
Bottom gating1.8
Brass 1.9
Tin bronze 2.8
203
2WKt

21. Gating System Design
6-Intricately shaped Thin walled castings of mass up to
450 kg:
Pouring Time
W’: mass of the casting with gates and risers, kg
T, (mm) K
3
1.5 up to 2.5 1.62
2.5 up to 3.5 1.68
3.5 up to 8.0 1.85
8.0 up to 15.0 2.20
213
3
WKt 

22. Gating System Design
7-Castings above 450 kg and up to 1000 kg:
Pouring Time
T, (mm) K
4
up to 10 1.00
10 up to 20 1.35
20 up to 40 1.50
40 and above 1.70
223
4
TWKt 

23. Gating System Design
Choke Area
It is themain control area which meters the metal flow
into the mould cavity so that the mould is completely filed
within the calculated pouring time.
A: choke area, mm W: casting mass, kg
t: pouring time, S H: sprueheight, mm
d: mass density of the molten metal, kg/mm
3
C: efficiency of the used gating system.
23gHCtd
W
A
2


24. Gating System Design
Choke Area
Top gate
H = h
Bottom gate
H = h –c/2
Parting gate
H = h –P
2
/2c
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25. Gating System Design
Sprue
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•Astheliquidmetalpassesdownthesprueitlosesits
pressureheadbutgainsvelocity.
•ToreduceturbulenceandpromoteLaminarFlow,from
thePouringBasin,theflowbeginsanear
verticalinclinethatisacteduponbygravityandwithan
accelerativegravityforce

26. Gating System Design
Sprue
26
hc
1
2
3
1 = freesurfaceof metal
2 = spue top
3 = sprue bottom
pouringbasin
sprue
h
t
•Assuming
–entiremouldisatatmosphericpressure(nopoint
belowatmospheric)
–metalinthepouringbasinisatzerovelocity
(reservoirassumption)

27. Gating System Design
Sprue
2732
32
2
2
tt
cc
V gh hA
A V gh h
  
Mass flow rate = A V = constant
Applyingcontinuityequationbetweenpoint2and3weget-2
2
3
t
c
h A
hA



Actual shape of sprue is Parabola
But in order to avoid manufacturing difficulty we use
tapered cylinder shape.