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DESIGN OF GATING
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
The flow of molten metal after being poured is a transient
phenomena accompanied by :
• Separation of the flow from the boundaries,
• Dividing and combined flow at the junction,
• Simultaneous heat transfer during the flow and onset of
• Experimentation through trial and error methods for a given casting
• Mathematical model.
METHODS TO DESIGN AN OPTIMIZED
BASIC COMPONENTS OF
A GATING SYSTEM.
• Pouring Basin.
• Sprue well.
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.
• 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
In 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
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
• In addition, vortex formation tendency in a sprue with circular cross section is
• 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
= ℎ2 +
Assuming f=0 and system remain at
No turbulence and friction.
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.
Areas of Choke : Runner : Gate(s)