Transcript Jayabal-JRE-Valves-P..

Sixth National Foundry Conclave
01-02 March 2013 : Hotel Le Meridien : Coimbatore
Topic : Design & Methoding Of Steel Castings
Presented By : Mr. V.S. Jayabal , M.Tech.,
Managing Director , JRE Valves & Pumps (P) Ltd.,
Designing & Methoding
of Steel Castings
The Birth of the casting
By V.S.J
The Story
My IIT Programme , in the Foundry Technology ,
M.Tech , Started with this story , as told by my
respected Professor in the year of Aug 1970.
By V.S.J
Fundamentals of Casting
Casting processes basically involve the introduction of a molten
metal into a mold cavity, where upon solidification, the metal
takes on the shape of the mold cavity.
Simple and complicated shapes can be made from any
metal that can be melted.
Example of cast parts: frames, structural parts, machine
components, engine blocks, valves, pipes, statues,
ornamental artifacts…..
Casting, one of the oldest manufacturing processes, dates
back to 4000 B.C. when copper arrowheads were made.
By V.S.J
Product Design Considerations

Geometric simplicity:
– Although casting can be used to produce complex part
geometries, simplifying the part design usually improves
castability
– Avoiding unnecessary complexities:
 Simplifies mold-making
 Reduces the need for cores
 Improves the strength of the casting

Corners on the casting:
– Sharp corners and angles should be avoided, since they are
sources of stress concentrations and may cause hot tearing
and cracks
– Generous fillets should be designed on inside corners and
sharp edges should be blended
By V.S.J
Product Design Considerations
 Minor
changes in part design can reduce need
for coring
Design change to eliminate the need for using a core:
(a) original design, and (b) redesign.
By V.S.J
Product Design Considerations
By V.S.J
Gating System
By V.S.J
Pattern design
The Following Points Shall be considered , before selecting the parting line
1.
2.
3.
4.
5.
6.
7.
8.
Dimensional consistency
Padding & Feeder Locations .
Reduce the no. Of cores as much as possible.
The Fettling shop work , must be minimized as much as
possible.
Preferable to go for a aluminum Patterns .
Wherever not possible , wood / Aluminum construction can be
used.
Ex. Ribs , bosses , changeable flanges can be made with
Aluminum.
Multiple patterns depending up – on the quantum
requirements.
By V.S.J
Pattern Shop
1.
2.
3.
4.
5.
It’s Preferable to match plate the patterns with runners ,
risers incl. filters & Integral test bars , wherever reqd.
It’s always a good idea to have the integral test bars for the
castings weighing ex. 700 Kg’s & above.
Chill Pattern need to be made for each & every application.
Suitable Colour coding is Preferable.
Method Drgs must be referred every time.
By V.S.J
Methoding
Primary Considerations
1. Design suitability for the foundry purpose.
2. The Application of the casting
3. Working Medium.
By V.S.J
Casting Processes
 Preparing
a mold cavity of the desired shape
with proper allowance for shrinkage.
 Melting the metal with acceptable quality and
temp.
 Pouring the metal into the cavity and providing
means for the escape of air or gases.
 Solidification process, must be properly
designed and controlled to avoid defects.
 Mold removal.
 Finishing, cleaning and inspection operations.
By V.S.J
Over View of Sand Casting
 Most
widely used casting process, accounting
for a significant majority of total tonnage cast
 Nearly all alloys can be sand casted, including
metals with high melting temperatures, such as
steel, nickel, and titanium
 Castings range in size from small to very large
 Production quantities from one to millions
Buoyancy in Sand Casting Operation


During pouring, buoyancy of the molten metal tends to
displace the core, which can cause casting to be defective
Force tending to lift core = weight of displaced liquid less
the weight of core itself
F b = Wm - Wc
where Fb = buoyancy force;
Wm = weight of molten metal displaced; and
Wc = weight of core
This Buoyancy effect can be avoided , with the proper design of
the Core Print ; In worst cases by Chaplet.
Fluidity of Molten Metal
Fluidity :
The capability of a molten metal to fill mold cavities
Viscosity :
Higher viscosity decreases fluidity
Surface tension :
Decreases fluidity; often caused by oxide film
Inclusions :
Insoluble particles can increase viscosity, reducing fluidity
Solidification pattern :
Fluidity is inversely proportional to the freezing temperature range
By V.S.J
Fluidity of Molten Metal
Mold design :
The design and size of the sprue, runners, and risers affect fluidity
Mold material and surface :
Thermal conductivity and roughness decrease fluidity
Superheating :
The temperature increment above the melting point increases
fluidity
Pouring :
Lower pouring rates decrease fluidity because of faster cooling
Heat transfer :
Affects the viscosity of the metal
Increasing Fluidity :
The fluidity of the Steel can be increased by Micro level
additions of Cerium Mishmetal.
By V.S.J
Types Of Solidification
1. Mushy Formation
2. Directional Solidification
By V.S.J
Solidification contraction for various cast metals
Metal or alloy
Volumetric
solidification
contraction %
Metal or alloy
Volumetric solidification
contraction %
Aluminum
6.6
70% Cu-30% Zn
4.5
Al-4.5% Cu
6.3
90% Cu-10% Al
4
Al-12% Si
3.8
Gray Iron
Expansion to 2.5
Carbon steel
2.5-3.0
Magnesium
4.2
1% Carbon steel
4
White iron
4.0-5.5
Copper
4.9
Zinc
6.5
By V.S.J
Pure Metals / Alloys
Pure metals solidify at a constant temperature;
By V.S.J
Pure Metals / Alloys
Alloys solidify within a temperature range
By V.S.J
Directional Solidification Pattern of Quartz
Growth of Dendrites
By V.S.J
Directional Solidification Pattern of Quartz
Growth of Dendrites
By V.S.J
Directional Solidification Pattern of Quartz
Growth of Dendrites
By V.S.J
Directional Solidification Pattern of Quartz
Growth of Dendrites
By V.S.J
Directional Solidification Pattern of Quartz
Growth of Dendrites
By V.S.J
Directional Solidification Pattern of Quartz
Growth of Dendrites
By V.S.J
Directional Solidification Pattern of Quartz
Growth of Dendrites
By V.S.J
Solidification Time
The solidification time is a function of the volume of a casting and its surface
area.
Solidification time = C ( volume / surface area)2,
(1)
Where C is a constant that reflects mold material, metal properties and
temperature. Thus large sphere solidifies and cools to ambient temperature at
a much slower rate than dose a smaller sphere.
By V.S.J
Solidification Time
Example:
Solidification times for different shapes:
Three pieces being cast have the same volume but different shapes. One is a
sphere; one is a cube, and the other a cylinder with a height equal to its diameter.
Which piece will solidify the fastest and which one the slowest?
The volume is unity, so we have from equation (1):
Solidification time =
The respective surface areas are:
Sphere:
Thus the respective solidification time’s t are
V = (4/3) лr3, r = (3/4 л)1/3,
And A = 4 лr2 =4 л (3/4 л)2/3 = 4.84;
Cube:
V = a3, a = 1,
A = 6a2 = 6;
V = лr2b = 2 лr3, r = (1/2 л)1/3, and
A = 2 лr2 + 2 лrb = 6 лr2 = 6 л(1/2 л)2/3 = 5.54
Cylinder:
1 / surface area
tsphere = 1 / (4.84 2)

0.043 C,

0.028 C,
t cylinder = 1 / ( 5.542)
 0.033
tcube = 1 / (62 )
C.
Hence , For Feeding We are using Cylindrical Feeders , instead of Sphere
feeders ; Because Sphere is having a Slow Solidification Time.
By V.S.J
Types Of Shrinkages
1. Liquid to Liquid shrinkage
Risers
2. Liquid to solid Shrinkage
Risers
3. Solid Shrinkage
Pattern contraction
allowance
By V.S.J
Shrinkage
Shrinkage - Feed Metal requirements :
1.
The Super Heated steel, more than what is reqd can
cause a severe problem.
2. The Most scientific form of Calculating the
solidification time – Modulus method
.
By V.S.J
Calculation of the Feeder Dimensions
1. Identify the Locations – Normally the heavy
junctions.
2. Try to reduce the no. of locations by connecting
them with the pads.
3. The Pads can be either metallic or ins / exo pads.
4. Calculate the solidification time .
5. This is simplified by the Modulus method.
6. Modulus = Volume / Surface Area
By V.S.J
Calculation of the Feeder Dimensions
7. To achieve the directional solidification , the modulus
need to be increased progressively to the neck & to the
feeder.
8. Ex. Casting Modulus is Mc = 1
Neck – 10% More Mn = 1.1
Feeder - another 10% Mf = 1.2
9. Application of Ins/ Exo Sleeves.
10. The Efficiency of the sleeves is governed by the
Modulus Extension Factor ( MEF ).
By V.S.J
Calculation of the Feeder Dimensions
11. Ex. If MEF is 1.2 then , Mf is = 1.2 / 1.2 = 1
1.3
1.2 / 1.3 = 0.92
1.4
1.2 / 1.4 = 0.85
1.5
1.2 / 1.5 = 0.80
The feeder Dimensions can be calculated based on the
– modulus.
Further , depending up – on the contact area available.
The ratio between the diameter & height can be fixed
Thus , smaller & smaller feeders are reqd with efficient
sleeves.
By V.S.J
Calculation of the Feeder Dimensions
12. The No . Of Feeders can also be further reduced
by the effective utilization of the external Chills.
13. The Chill thickness shall be Min 80 % of the
contact area.
14. In the case of the deep pockets in the casting ,
Sand can be superheated & may cause defects.
15.To avoid this Zircon / Chromite sand can be
used , because of their higher density & thermal
conductivity , the problem is minimized.
By V.S.J
Use Of Metal Filters
1. Inspite of the best Practices in the melting & moulding
system , the metal
steel picks up inclusions , as it flows through the pouring
cup & sprues.
2. There are different types of ceramic filters are available.
3. The size of the filters reqd , for particular size of casting
is recommended
by the filter manufacturers.
4. These filters have to be installed in the running system .
5. Our experience shows , remarkable improvement in the
defects caused by inclusions.
6. This is more advantage , if used for expensive stainless
steels .
By V.S.J
By V.S.J
By V.S.J
Typical Methoding
By V.S.J
Typical Methoding
By V.S.J
Casting defects
A.
B.
C.
D.
E.
F.
G.
Metallic Projections
Cavities
Discontinuities
Defective surface
Incomplete Casting
Incorrect dimensions or shape
Inclusions
By V.S.J
By V.S.Jayabal , M.Tech.,
Managing Director , JRE Valves & Pumps (P) Ltd.,