004 gating design

7/21/2019 004 Gating Design

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Design of Risers and Feeding of

Castings A simplified diagram by p

utting inreferences to the equations (1, 2 & !

there is no Equation 3, diagram not changed

"#(1! $ Free%e oint Ratio (FR!

FR'

' (Casting )urface*Casting +olume! *

(Riser )urface*Riser +olume!

"#(2! $ +olume Ratio (+R! ( A-is!

+R''Riser +ol*Casting +ol.Note: The riser volume is the actual poured

volume

References - AFS Text Chapter 16; Chastains Foundr! manual "ol #$ %oo&le

"#(! $ (Free%e oint Ratio! )teel

'/012*y$/0/ 10/.

*The constants are from experiments and

are empirical


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+olumes, )urface Areas, Castings andRisers000

There are relationships between all theseitems and values that will help in designing

a complete mold that controls progressivesolidification, and influences directionalsolidification to produce castings withminimal porosity and shrinkage defects.

This is by ensuring that the risers! are the

last to solidify.


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points about the Riser*CastingRelationship

" # $isers are attached to the

heaviest sections of the casting

% # $isers are the last to solidify

3 # & casting that has more than

one heavy section requires atleast one riser per heavy section

' # (ccasionally the thermalgradient is modified at the mold#metal interface by the introduction

of a )hill) that can better conductthe heat away from the castingand lower the solidification timefor that section.


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3ating * Runner Design

+ow a look at the flow characteristics of themetal as it enters the mold and how it fills thecasting.

(f the flow characteristicsfluidity*4iscosity plays a role0&lso,

velocity,

gravitational acceleration vorte-,

pressure ones,

molten alloy aspiration from the mold and

the momentum or kinetic energy of a fluid.


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The demarcation point is

$e / %000 is considered a 1aminar 2low$e %000 is considered a Turbulent 2low

5b6ecti4e is to maintain Re belo7 2///0


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1&45+&$ 21(6# $E2E$E+E


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T7$871E+T 21(6#

$E2E$E+E


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9E:E$E1; T7$871E+T 21(6


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8asic Components of a 3ating )ystem

The basic components of a gating system areates that feed the casting.

The metal flows through the system in this order.

)ome simple diagrams to be familiar 7ith are9


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)rucible#4old 5nterface) is 7here the metal

from the crucible first contacts the mold

surface0This area is lower than where the4outh of the 9prue is located, by having a pool

of metal from the flow will be less chaotic than

pouring from the crucible down into the sprue.

)?ross#?am) # to skim or hold back any dross

from the crucible or what accumulated through

the act of pouring.&s the lower portion fills and the metal is

skimmed, the clean(er! metal 7ill rise up to

meet the opening of the sprue in a more

controlled fashion0

'ourin& (asin# This is the )rucible #4old 5nterface), & pouring cup and

pouring basin are not equivalents, The pouring cup is simply a larger target

when pouring out of the crucible, a =ouring 8asin has several components

that aid in creating a laminar flow of clean metal into the sprue.

The basin acts as a point for the liquid metal to enter the gating system ina laminar fashion.


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)prue lacement and arts:he sprue is the e-tension of the sprue

mouth into the mold

The choke or narrowest point in the

taper is the point that would sustain a

)@ead) or pressure of molten metal.

To reduce turbulence and promote

1aminar 2low, from the =ouring 8asin,

the flow begins a near vertical inclinethat is acted upon by gravity and with

an accelerative gravity force

2luids in free fall tend to distort from a

columnar shape at their start into anintertwined series of flow lines that

have a rotational vector or vorte- effect

lockwise in the northern hemi#

sphere, and counter clockwise in the

southern hemi#sphere!...


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ressuri%ed $ is a system

7here the gate and runnercross$sectional areas are

either equal or less than

the cho;e cross$sectional

area ' 2nd Runner c*s

Area ' /0?? unit

A ' 1st 3ate ' /0>> unit

A ' 2nd 3ate ' /0>> unit

@npressuri%ed $ :he ;eydistinction is that the

Runner must ha4e a c*s

area greater than the

Cho;e, and it 7ouldappear that the 3ate(s!

7ould equal or be larger

than the Runner(s!0Common Ratio's noted are;

1 : 2 : 4; 1 : 3 : 3

1 : 4 : 4; 1 : 4 : 6


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The rotational effect, though not a strong

force, is causing the cork#screwing effectof the falling fluid. 5f allowed to act on the

fluid over a great enough duration or free

fall the centrifugal force will separate theflow into droplets.

+one of the above promotes 1aminar flow,

plus it aids the formation of dross and gaspick#up in the stream that is going to feed

the casting.


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)ome dimensioning ratios fromChastains Foundry Banual (no02!

"# hoke or sprue base area is "ABth the area of the well.

%# The well depth is twice the runner depth.

3# the $unner is positioned above the midpoint of the

wellCs depth

8y creating a sprue 7ith a taper, the fluid is constrained to

retain its shape, reducing e-cessi4e surface area de4elopment

(dross$forming property! and gas pic;$up0

:he area belo7 the sprue is the ell0 :he 7ell reduces the

4elocity of the fluid flo7 and acts as a reser4oir for the runners

and gates as they fill0


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The runner system is fed by the welland is the path that the gates are fedfrom.

This path should be )8alanced) with the

model of heating or & ductworkserving as a good illustration. The$unner path should promote smoothlaminar flow by a balanced volumetricflow, and avoiding sharp or abruptchanges in direction.

The )$unner E-tension) is a )?ead#End) that is placed after the last gate.The $#E-t acts as a cushion to absorbthe forward momentum or kineticenergy of the fluid flow. The $#E-t alsoacts as a )?rossA>as Trap) for anymaterials generated and picked#upalong the flow of the runner.

&n 5deal $unner is also proportionedsuch that it maintains a constantvolumetric flow through virtually anycross#sectional area. 5n the illustration,notice that the runner becomesproportionally shallower at the pointwhere an in#gate creates an alternatepath for the liquid flow.

:he Runner )ystem


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:he 3ating )ystem

The >ates in this case!accommodate a directionalchange in the fluid flow anddeliver the metal to theasting cavity.

&gain, the design obDective

is to promote laminar flow,the primary causes ofturbulence are sharpcorners, or un#proportionedgateArunner sies.

The % two! dashed blue

areas when added togetherform a relationship to thedashed blue area of the$unner, which forms arelationship to the hoke orbase of the 9prue &rea.


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The issue of sharp corners both innerand outer! create turbulence, low highpressure ones that promote aspiration ofmold gases into the flow, and can drawmold material sand! into the flow. +one of

this is good... 8y providing curved radiuschanges in direction the above effects arestill at play but at a reduced level. 9harpangles impact the solidification processand may inhibit )?irectional 9olidification)with cross#sectional freeing...

The image to the right is Dust too good arepresentation to pass#up..

8y proportioning the gating system, amore uniform flow is promoted with nearequal volumes of metal entering the mold

from all points. 5n an un#proportionedsystem the furthest gates would feed themost metal, while the gates closest to thesprue would feed the least.

this is counter to what one initially thinks!.


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?5$ET5(+&1 9(15?525&T5(+#


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Formulae, Ratios and Design "quations

6hat is covered so far is comprehensive, and intuitive on aconceptual level, but the math below hopefully offers some insightinto quick appro-imations for simple designs, and more in#depthcalculations for comple- systems.

omputeried 2low &nalysis programs are used e-tensively in large2oundry operations.

2rom basic concepts, designing on a state of the art system shall beattempted

004 gating design

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