Design of gating system Chapter 2
CHAPTER 2
DESIGN OF GATING SYSTEM
For Ductile Iron,we use a pressurized gating system of gating ratio 1:2:2 with bottom
gates
1.1 COMPONENT
The component is simple cuboid made of Ductile Iron whose dimensions are 200 mm x
150 mm x 40 mm.
Density of the component, ρ(in kg/mm3) = 7.3 x 10-6 kg/mm3
Volume of the component,V(in m3) =lxbxh
= 200 x 150 x 40
= 12,00,000 mm 3
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Design of gating system Chapter 2
Mass of the component,M(in kg) = Density x volume
= 7.3 x 10 -6 x 12,00,000
= 8.8 kg
Considering a yield of 65% for Ductile Iron
Tho total mass of molten metal poured (in kg) = 8.8 x 100
65
= 13.5 kg
1.2 POURING TIME
Pouring time is the time taken for molten metal to fill the gating system.
Pouring time, T(in seconds) = K1√W
Where K1 - Thickness constant (seconds/(kg)0.5) = 2.97
W - Total mass of molten metal poured(in kg) = 13.5 kg
T = 2.97 x √13.5
T = 10.912 seconds
1.3 EFFICIENCY COEFFICIENT OF GATING SYSTEM
Table 1. Efficiency coefficients, C for various types of gating system
From the table, the efficiency coefficient of Tapered choke sprue with single runner system
is C=0.9
1.4 CHOKE AREA(AC)
Choke area is the cross sectional area which determines the flow of molten metal in
the gating system.For pressurized gating system,the bottom area of the sprue is
considered as the choke area.It is calculated by,
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Design of gating system Chapter 2
Ac = W …(i)
T x C x ρ x √2 x g x H
Where,
W - Total mass of molten metal = 13.5 kg
T - Pouring time = 10.912 seconds
C - Constant efficiency factor of
gating system = 0.9(dimensionless constant)
ρ - density of Ductile Iron = 7.3 x 10 -6 kg/mm3
g - acceleration due to gravity = 9810 mm/s 2
H - effective metal head = H – (c/2) (for bottom gating system)
Where,c – Thickness of component (in mm) = 40
H = 100 – (40/2)
= 80 mm.
Substituting the values in Eqn.(i)
Ac = 13.5 mm 2
0.9 x 7.3 x 10 -6 x 10.912 x √2 x 9810 x 80
= 150.3 mm 2
We know that,for a non pressurized gating system,bottom area of sprue is considered as
choke area.
So, Bottom area of Sprue = 150.3 mm 2
1.5 RUNNER
From the gating ratio 1:2:2.
Area of Runner = 2 x choke area
= 2 x 150.3 mm 2
= 300.6 mm 2
Considering a runner of trapezoidal cross section.
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Design of gating system Chapter 2
We know that
Area of runner = (a + b) x h
2
(a + 2a) 2a = 300.6 mm 2
2
a = 10 mm
b = 20 mm
c = 20 mm
1.6 INGATE CALCULATION
Total ingate area = 2 x choke area (From gating ratio)
= 2 x 150.3 mm 2
= 300.6 mm 2.
Let us consider a 4 gate system.
Area of each gate = Total ingate area/4
= 300.6/4
= 75.15 mm 2
Let us consider a rectangular gate whose length is 4 times its width.
W.k.t Area of rectangle = l x b
= 4b x b.
4b x b = 75.15 mm 2
b = 4.33 mm
h = 17.32 mm
1.7 SPRUE
Let,
Total effective metal head, Hb = 100 mm
Distance between sprue top
and pouring basin = Ht
Area of sprue bottom, Ab = 150.3 mm2
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Design of gating system Chapter 2
Area of sprue top , At = (π/4)(Dt)2
Where,
Dt - Top diameter of the sprue.
We know that,
Ht - 2.5 x Dt
From equation of continuity,we can say that
At/Ab = (Hb/Ht)0.5
(π/4)(Dt)2 = (100)0.5
150.3 (2.5 x D t)0.5
Dt = 17.11 mm
Also,
Ab = (π/4)(Db)2 = 150.3 mm2
Db = 13.86 mm
1.8 POURING BASIN
Depth of pouring basin(in mm), Ht = 2.5 x Dt
= 2.5 x 17.11
= 42.3 mm.
Top diameter of pouring basin(in mm) = 6 x Dt
= 6 x 17.11
= 102.6 mm
Height of dam, Hd = 0.7 x Ht
= 0.7 x 42.3
= 32 mm
Width of dam, Wd = 0.3 x Ht
= 0.3 x 42.3
= 12.69 mm
1.8 RISER AND NECK
1.8.1 Riser
By Naval Research Laboratory Method,
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Design of gating system Chapter 2
Shape factor = L+W
T
Where,
L - Length of Casting(in mm) = 200 mm
W – Width of Casting(in mm) = 150 mm
T – Thicknesss of Casting(in mm) = 40 mm.
Shape factor = 200 + 150
40
= 8.75
From the graph,
Riser Volume = 0.32
Casting Volume
We know that,
Casting Volume, Vc = 12,00,000 mm3
Riser Volume(in mm 3) = 0.32 x Casting Volume
= 0.32 x 12,00,000
= 3,84,000 mm 3
= 384 cm 3
From the graph,
Height of the riser = 1
Diameter of the riser
So, Height of the riser = Diameter of the riser
We know that Volume of the riser(in cm3) = π x r2 x h
= π x (D/2) 2 x D
= (π x D 3 ) /4
(π x D3 )/4 = 384 cm3
D = 7.9 cm
Thus,
Diameter of the riser = 7.9 cm
Height of the riser = 7.9 cm
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Design of gating system Chapter 2
1.8.2 Neck
Height of the neck = 0.8 x t
Where,
T – Thickness of casting(in mm) = 40 mm
Height of the neck(in mm) = 0.8 x 40
= 32 mm.
Length of the neck(in mm) = Dr/3
Where,
Dr – Diameter of the riser = 79 mm
Length of the neck(in mm) = 79/3
= 26 cm
Width of the neck(in mm) = 2.5 x length – (0.18 x diameter)
= 50.8 mm
Depth of notch = Hn/5
Where,
Hn – Height of neck(in mm) = 32 mm
Depth of notch(in mm) = 32/5
= 64 mm
1.9 CALCULATED EFFICIENCY COEFFICIENT OF GATING SYSTEM
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Design of gating system Chapter 2
