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Vol 61 • No. 1 • January 2015
Indian Foundry Journal
19
Design of Gating and Riser System for
Grate Bar Casting
S. Santhi, B. Ramakrishna Surya, S. Jairam, J. Jhansi and P. K. S. Subramanian
Department of Metallurgical and Materials Engineering, Mahatma Gandhi Institute of Technology,
Hyderabad-500075
Corresponding author E-mail: santhi_samave@yahoo.com
The grate bar, used in pallet cars of pallet or sintering plant,
that are used for iron making in blast furnace. Austenitic
stainless steel with low percentage of carbon is considered
for this grate bar casting to prevent sensitisation. A key
element in producing quality castings is the proper design
and sizing of the gating and riser systems. Gating and riser
system are designed with the help of mathematical formulae.
A C programme has been developed to calculate the areas
of sprue, runner and ingates and volume of the riser. Well-
designed gating and riser system improved the quality of
the grate bar casting.
Keywords: Grate bar, Cast stainless steel, Gating system,
Riser, C programme.
Introduction
Metal casting is a manufacturing process where molten or
liquid metal is poured into a mould cavity and allowed to
solidify to acquire the shape of the mould. Metal Casting is
unique among metallurgical processes as complex physics
is involved in it[1]. Any type and shape of an alloy can be
produced using sand casting technique. Sand mould’s
refractoriness helps to retain its shape and size, and shows
a slight expansion when subjected to high temperature
for a long period. Sand casting technique is the most
cost-effective and design-exible in foundry[2]. Innovative
and well-planned management of sand is essential for
maintaining quality of the product and process according
to Ravneet Kakria[3]. The greatest percentage of castings
is produced by sand casting route which is the most
economical with optimum efciency and reclaimability[4].
In sand moulds, the temperature distribution in the molten
metal is uniform and the temperature of the inside surface
of the mould is equal to the temperature of the liquid
metal, because the heat conductivity of the sand is very
low compared to molten metal[5].
The grate bar, used in pallet cars of pallet plant or sintering
plant, that are found in steel industries is shown in Fig.
1. These grate bars are made of cast stainless steel. Since
they undergo repeated heating cycles for a long period of
time, there is always a chance for sensitisation to occur[6].
To prevent this, an austenitic stainless steel is used with low
percentage of carbon (0.2%-0.4%). Nominal Composition
of the cast stainless steel grate bar is 27% Cr-13%Ni as per
ASTM A-297 as given in Table-1[7]. Stainless steel is one of
the most versatile of the common foundry metals. Stainless
steel alloys have special advantages for casting, negligible
solubility for all gases except hydrogen and good surface
nish that is usually achieved with nal products[8].
Table-1: Chemical Composition of Grade
ASTM A297[7]
Elements %wt.
Carbon 0.4
Silicon 2
Manganese 2
Phosphorus 0.04
Sulphur 0.04
Chromium 24-28
Molybdenum 0.50
Nickel 11-14
Fig. 1: Pallet car used in a sintering plant.
A key element in producing quality aluminium castings
is the proper design and sizing of the gating and riser
systems[9]. The soundness of a casting depends upon
how the molten metal enters a mould and solidies. The
assembly of channels which facilitates the molten metal to
Vol 61 • No. 1 • January 2015 Indian Foundry Journal
20
enter into the mould cavity is called the gating system[10].
The major elements of gating system are pouring basin,
sprue, well, runner, and ingate, in the sequence of ow of
molten metal from the ladle to the mould cavity[11] as shown
in Fig. 2. Production costs can be signicantly reduced by
minimising the amount of metal contained in the gating
system[1]. Proper design of an optimised gating system will
be made easier by the application of several fundamental
principles of uid ow. The design of each gating system
depends upon its primary objectives like ease of moulding,
avoiding turbulent ow, erosion of sand from the mould
walls, avoiding inclusion of dross or slag with metal
entering the mould. The main objective of gating system is
The requirements of the riser depend considerably on
the type of the metal being poured and percentage of
volumetric shrinkage for stainless steel is 6.60%.
Gating System
Purpose of the gating system is to direct the ow of the
molten metal into the mould cavity and also prevents
the mould material from entering into the casting, since
pouring the molten metal directly into the mould cavity
can cause the mould to dislodge and cause the material to
get included into the casting. Runner is typically located in
the drag of the casting. Gates are the inlets into the mould
cavity. The gates can be no thicker than the casting section
to which they are attached. It is usually the best practice
to have the gates slightly thinner than the casting section.
Size and dimensions of the present casting are given in Fig.
4 as a schematic diagram. Gating ratio is dened as the
ratio of the area of the sprue to the area of the runner to
the area of the gating system and for the present stainless
steel casting, it is 1:2:1.5.
Fig. 2: Various parts of gating system.
Fig. 3: Pressurised gating system.
to lead clean molten metal keeping in view of the shrinkage
behaviour and the crystal growth morphology[10,11]. There
are primarily two types of gating systems based on the
ratio between sprue, runner and gate area, like pressurised
gating system and unpressurised gating system.
For stainless steel castings, the gating ratio generally
considered is pressurised gating system as shown in Fig. 3
and the value considered is 1:2:1.5. Riser acts as a feeder for
molten metal to the casting as it solidies. A riser must stay
uid and be able to feed the casting during solidication.
Fig. 4: Schematic diagram of
the casting.
Vol 61 • No. 1 • January 2015
Indian Foundry Journal
21
Calculation for Area of Sprue, Area of Runner and Area
of ingates
Area of sprue, area of runner and area of ingates calculated
for present casting are as given below[11,12,13]:
As=[Ra/(d*f* (2*g*H)0.5)] Equation 1
Where, As is area of sprue, Ra is adjusted
pouring rate, g is the acceleration due to
gravity, H is the metallostatic height, d
is density of the alloy, f is Darcy friction
factor for laminar ow
R = [wc/(1.34+t/13.77)] Equation 2
Where, R is pouring rate, t is the critical
thickness of the casting,
wc is weight of the casting
Ce = [C+(0.25*Si)+(0.5*P)] Equation 3
Where, Ce is carbon equivalent, weight
percentages of C, Si and P
K = [(14.9*Ce)+(0.5*Tp)-155] Equation 4
Where, K= uidity of the metal casting, Tp
pouring temperature
Ra = [R/(K*f*0.0254)]
f is the Friction factor Darcy friction factor
for laminar ow
Equation 5
Re is the Reynolds number for laminar ow
Ar=2*As Equation 6
Where, Ar area of runner
Ag=1.5*As Equation 7
Where, Ag area of gate
Calculations for Riser Dimensions
A riser will be added to accommodate the liquid shrinkage
and to supply liquid feed metal to compensate for the
solidication shrinkage within the casting. The riser must
often be larger than the casting it feeds, because it must
supply feed metal for as long as the casting is solidifying.
Therefore, to ensure that the casting solidies before the
riser, the volume of the riser should be greater than that of
the casting[1,14].
Volume of riser > Volume of the casting
Hence, the casting should be designed to produce
directional solidication which sweeps from the extremities
of the mould cavity towards the riser. In this way, the riser
can feed molten metal continuously and will compensate
for the solidication shrinkage of the entire mould cavity.
If this type of solidication is not possible, multiple risers
may be necessary with various sections of the casting
solidifying towards their respective risers.
Chvorinov’s Rule: Chvorinov's Rule is a mathematical
relationship that relates the solidication time for a simple
casting to the volume and surface area of the casting[12].
In simple terms, the rule establishes that under otherwise
identical conditions, the casting with large surface area
and small volume will cool more rapidly than a casting with
small surface area and a large volume. The relationship can
be written as:
Equation 8
Where, t is the solidication time, V is the volume of the
casting, A is the surface area of the casting in contact with
the mould, B is a constant whose value depends upon
the metal and each metal has a unique value and n is a
constant that has a value of 1.5-2.
In the above formula, ratio of the volume of casting to
surface area of the casting is known as the modulus of the
casting. It is seen that there is a direct relationship between
the modulus of casting and the modulus of riser, Modulus
(Mc) method, the simplest method for designing a riser.
Mc = volume of casting
effective cooling surface area Equation 9
Mriser = 1.2 Mcasting Equation 10
Modulus for a cylindrical riser is given by the equation
Mriser= DH
(4H+2D) Equation 11
Where, D = Diameter of the riser, H = Height of the riser
Typical riser height is twice the diameter (H=2D) for body
plate casting
Substitute H=2D in Equation 11
Equation 12
Feeding distance of risers is determined by the alloy being
poured and by the thickness of the section being fed. For
castings, the following formula can be used to approximate
the theoretical feeding distance of a hot riser:
FD = 2T
In the above equation, FD is feeding distance and T is
thickness of casting section.
Table-2: Formulae for Gating and Riser System
Sprue Runner Gate Riser
As=Ra/(2*g*H)0.5 2*As1.5*AsMr=1.2Mc
Vol 61 • No. 1 • January 2015 Indian Foundry Journal
22
Calculation of Gating System
By considering the formulae from Table-2, C programme
has been developed to calculate the dimensions of the
gating and risering system of the present casting[15].
C Programme for Calculation of Gating System
#include<stdio.h>
#include<math.h>
void main()
{
oat Cf,g=9.8,H,Vs,d,w,p=0.5,t,R,Tp,K,Ce,c=0.3,Si=1.75,P=
0.04,b,Ta,T,Ra,As,Ar,Ag; printf("\n enter the value of friction
factor and metallostatic height"); scanf("%f%f",&Cf,&H);
Vs=Cf*(sqrt(2*g*H));
printf(" velocity at the sprue exit is %f",Vs);
printf("\n enter the density of the metal");
scanf("%f",&d);
printf("\n enter the weight of casting, pouring temperature
and wall thickness");
scanf("%f%f%f",&w,&Tp,&t);
R=pow(w,p)/(1.34+(t/13.77));
printf("\n the pouring rate is %f",R);
Ce=(c+(0.25*Si)+(0.5*P));
K=((14.9*Ce)+(0.5*Tp)-155);
printf("\n uidity of the metal casting is %f",K);
Ra=(R/(K*Cf*0.0254));
printf("\n Adjusted pouring Rate is %f",Ra);
As=(Ra/(d*Cf*sqrt(2*g*H)))*10000;
printf("\n correct area of sprue base is %f",As);
Ar=2*As;
printf("\n correct area of runner base is %f",Ar);
Ag=1.5*As;
printf("\n correct area of gate base is %f",Ag);
}
Results for Gating System
Enter the value of friction factor and metallostatic height
0.06 0.21
Velocity at the sprue exit is 0.121728
Enter the density of the metal 7800
Enter the weight of casting, pouring temperature and wall
thickness 4.5 1873 0.06
The pouring rate is 1.577944
Fluidity of the metal casting is 792.786743
Adjusted pouring rate is 1.306021
Correct area of sprue base is 13.755193
Correct area of runner base is 27.510386
Correct area of gate base is 20.632790
C Programme for Calculation of Riser System
#include<stdio.h>
#include<math.h>
void main()
{
oat Wc,H,Mc,D,V,R,Sa;
printf("\n weight of the casting ");
scanf("%f",&Wc);
printf("\n enter the height of the casting in inches");
scanf("%f",&H);
H=H*2.5;
printf("\n enter the diameter of the riser in inches");
scanf("%f",&D);
D=D*2.5;
Mc=(D*H)/((4*H)+(2*D));
R=D/2;
V=3.14*H*pow(R,2);
Sa=V/Mc;
printf("\n the volume of the riser is: %f",V);
printf("\n the surface are of the riser is: %f",Sa);
printf("\n the modulus of riser is: %f",Mc);
}
Results for Riser system
Weight of the casting 4.5
Enter the height of the casting in inches 4
Enter the diameter of the riser in inches 2.5
The volume of the riser is: 306.6406625
The surface area of the riser is: 257.578125
The modulus of the riser is: 1.190476
Dimensions of the Gating and Riser System for
the Present Casting
Table-3 provides details of the gating and resering system
of the present casting.
Table-3: Dimensions for Gating and Risering
System, cm2
Sprue Runner Gate Riser
13.755193 27.510386 20.632790 380.234374
Experimental Studies
Moulding, Melting and Pouring
CO2 moulding is the moulding technique used for the
current experiment. The composition of the moulding sand
considered for the present sand is SiO2 78%, Al2O3 12%,
Na2O(SiO2) 5%, Cr2O3 3% and ZrO2 2% and consistency of
the mixture is achieved by mulled in a 50 kg sand muller.
After ramming into the desired shape by hand hardening,
CO2 gas has been passed into the mould to achieve desired
properties as shown in Fig. 5. Shellac coating is applied on
the mould surfaces of cope and drag and red just before
pouring to ensure non-adherence to surface of the mould
Vol 61 • No. 1 • January 2015
Indian Foundry Journal
23
and to prevent premature solidication. Hardness in excess
of 95 units has been obtained as a result of combination
of ramming and curing by passing CO2. Melting was
carried out in a 250 kg induction furnace with a power
rating of 140 kW and a voltage of 415V. Before pouring,
the chemical composition is analysed using Leco Carbon
Sulphur analyser[16] and composition is in good agreement
with Table-1.
Conclusions
With the help of well-designed gating system, the grate
bar casting is free from inclusions, shrinkage and other
defects. Appropriate riser design removed the undesirable
shrinkage cavity resulting into desirable shape and quality
of the grate bar castings.
Acknowledgements
The authors thank the Managing Director of Sri
Mahalakshmi- Earth Movers Limited, Vishakapatnam and
the Principal, MGIT, Hyderabad for providing support and
permission for carrying out this R&D work.
References
1. ASM Metals Handbook – Volume 15, Casting, ASM
International, The Materials Information Company.
2. Thoguluva Raghavan Vijayaram, Mechanical Property
Investigation of LM6 Alloy Castings Manufactured with the
Aid of Casting Solidication Simulation Technology, Indian
Foundry Journal, Vol.51, No.11, November 2005, p. 30-34.
3. Ravneet Kakria, Chandandeep Singh, Priyavrat Thareja,
Quality Improvement of Aluminium Alloy (LM6) Casting
Using Taguchi Method, Indian Foundry Journal, Vol.53,
No.11, November 2007, p. 33-41.
4. P. J. Tikalsky, H. U. Bahia, A. Deng and T. Snyder, Excess
Foundry Sand Characterization and Experimental
Investigation in Controlled Low-strength Material and Hot-
mixing Asphalt, Contract No. De-fc36-01id13974, October
2004, U.S. Department of Energy, p.13-16.
5. Mollard, F.R., Flemmings M.C. and Nyama E.F., Understanding
Aluminium Fluidity: the Key to Advanced Cast Products, AFS
Trans (1987), Vol. 95, p. 647-652.
6. ASM Metals Handbook Volume 11, Properties and
Selection: Irons, Steels, and High Performance Alloys, ASM
International, The Materials Information Company.
7. ASTM A297 - 14 Standard Specication for Steel Castings,
Iron-Chromium and Iron-Chromium-Nickel, Heat Resistant,
for General Application.
8. Foseco Non-Ferrous Foundryman’s Handbook, Eleventh
Edition, Revised and Edited by, John R. Brown, Butterworth
Heinemann Publisher, 2008.
9. Flemings M.C., Solidication Processing, McGraw-Hill Inc.
London, (1974).
10. Fundamental of Metal Casting Technology by P. C. Mukherjee.
11. R. W. Heine, Carl R. Loper and P. C. Rosenthal, Principles of
Metal Casting.
12. N. Chvorinov, Theory of the Solidication of Castings,
Geisserei, Vol.27, p. 177-255, 1940.
13. Casting Process Design Guidelines, S. Guleyupoglu
Concurrent Technologies Corporation Johnstown,
Pennsylvania, AFS Transactions p. 869-876.
14. Castability Control in Metal Casting via Fluidity Measures:
Application of Error Analysis to Variations in Fluidity Testing
by Brian Albert Dewhirst, Worcester Polytechnic Institute.
15. TURBO C by Akshansh.
17. User Manual of LECO Carbon and Sulphur analyzer.
Fig. 4: Wooden pattern used for preparation of mould.
Fig. 5: Solidied grate bar castings.
Inspection
Figure 6 depicts the solidied stainless steel casting. Non-
destructive testing results show acceptable amount of
pin holes and blow holes in the casting as per standard.
Quality of the casting is meeting requirement of the ASTM
A297 standard.
