design of gating systems

DESIGN OF GATING SYSTEMS

MADE BY VAIBHAV PATHAK

MECHANICAL B.TECH 3rd YEAR

The main function of gating system is to lead clean molten metal from ladle to the casting cavity ensuring smooth, uniform and complete filling. The flow of molten metal after being poured is a transient phenomena accompanied by :

• Turbulence,• Separation of the flow from the boundaries,• Dividing and combined flow at the junction,• Simultaneous heat transfer during the flow and

onset of solidification.

INTRODUCTION

• Experimentation through trial and error methods for a given casting geometry.

• Mathematical model.

METHODS TO DESIGN AN OPTIMIZED GATE

BASIC COMPONENTS OF A GATING SYSTEM.

• Pouring Basin.

• Sprue.• Sprue well.• Runner. • Ingate.

POURING BASIN.It is the funnel-shaped opening, made at the top of the mold. The main purpose of the pouring basin is to direct the flow of molten metal from ladle to the sprue.

. SPRUE WELL.It is located at the base of the sprue. It arrests the free fall of molten metal through the sprue and turns it by a right angle towards the runner and also acts as a reservoir for the runners and gates as they fill. 

SPRUE.• Connects the pouring basin

to the runner or ingate. • Generally tapered

downward to avoid aspiration of air.

• The round sprue has a minimal surface area exposed to cooling and offers the lowest resistance to the flow of metal.

• The square or rectangular sprue minimizes the air aspiration and turbulence

RUNNERIn case of large casting, the fluidity length of the molten metal is less than the maximum distance required to be travelled by the molten metal along the flow path. So it is necessary to provide the multiple ingates to reduce the maximum flow distance needed to be travelled by the molten metal.

GATE (INGATES)It is a small passage which connects the runner to the mould cavity. The cross section is square, rectangular and trapezoidal.

GUIDELINES TO DESIGN A GATING SYSTEM

• The size of the sprue fixes the flow rate. • The sprue should be located at certain distance from the

gates so as to minimize velocity of molten metal at ingates.• Rectangular cross-section sprue is better than circular one

with the same cross-sectional area, since critical velocity for turbulence is much less for circular sections.

• In addition, vortex formation tendency in a sprue with circular cross section is higher.

• Sprue should be tapered by approximately 5% minimum to avoid aspiration of the air and free fall of the metal.

• Ingates should be located in thick regions. • Multiple gating is frequently desirable. • Rectangular cross section of runners and ingates are generally

preferred in sand castings.

BERNOULLI’s THEOREM APPLICATION

Bernoulli’s theorem

h+ 𝑝𝜌𝑔 +

𝑣22𝑔=¿constant

h1+𝑝1𝜌𝑔 +

𝑣12

2𝑔=h2+𝑝2𝜌𝑔 +

𝑣22

2𝑔+ 𝑓

Assuming f=0 and system remain at atmospheric pressureNo turbulence and friction.

h1+𝑣12

2𝑔=h2+𝑣22

2𝑔CONTINUTY EQUATION

1 1 2 2Q AV AV

Q=Volumetric flow rateA= Cross section areaV = Velocity

Applying Bernoulli’s Equation at 2 and 3.

h2+𝑣22

2𝑔+𝑝2𝜌𝑔=h3+

𝑣32

2𝑔+𝑝3𝜌𝑔

𝑝2=(𝑣32−𝑣22¿𝜌𝑔

2𝑔 +𝑝3−h2 𝜌𝑔

𝐴2𝑣2=𝐴3𝑣3𝑝2=𝑝3−h2 𝜌𝑔

h2+𝑣22

2𝑔+𝑝2𝜌𝑔=h3+

𝑣32

2𝑔 +𝑝3𝜌𝑔

h3=0𝑝2=𝑝3=𝑎𝑡𝑚 .𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒

h2+𝑣22

2𝑔=𝑣32

2𝑔𝐴2𝑣2=𝐴3𝑣3𝑣2=𝑅𝑣3𝑏𝑢𝑡

𝑣3=√2𝑔h𝑡Then put the values in the equation (1)

(1)

1=h3𝑣32

2𝑔

+𝑣22

𝑣32

𝑅2=1−h2h𝑡

𝑅2=h𝑡−h2h𝑡

=h𝑐h𝑡

𝑅=√ h𝑐h𝑡

But R=𝐴3

𝐴2

3

2

c

t

A hA h

Thus,

The base of the Sprue and Choke are the same. The ratios between the cross-sectional Area can be grouped into either Pressurized or Unpressurized.

Pressurized: A system where the gate and runner cross-sectional areas are either equal or less than the choke cross-sectional area.Unpressurized: The key distinction is that the Runner must have a cross sectional area greater than the Choke, and it would appear that the Gate would equal or be larger than the Runner.

GATING RATIO Areas of Choke : Runner : Gate(s)

THANK YOU

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