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APPLICATION OF CONCEPT OF MODULUS IN NON-FERROUS FOUNDRIES G.M. RAJENDRA PRASAD
[email protected] 9480504635 ( BANGALORE ) Modulus =
Volume / Surface area
Volume indicates the amount of HEAT HEAT present in the LIQUID METAL & Surface Area refers to the Area through which that Heat can be REMOVED FOR SOLIDIFICATION TO TO TAKE PLACE. On page no 149 ,of DIRECTIONAL SOLIDIFICATION SOLIDIFICATION OF STEEL CASTIINGS by WLODAWER, WLODAWER, you find an equation --Solidification
Time in Minutes Minutes = 2.1(Modulus in Centimeter )²
------for Steel( Green Sand) In FIGURES (last page) in case of 100 Ø X 100 Height(mm) sand casting you have have three Surface Areas 1. Surface Area in contact with Sand Area at the Bottom (Conduction Heat Loss) 2. Surface Area in contact with Sand on the Side (Conduction (Conduction Heat Loss + Convection Heat Loss) 3. Surface Area in contact with Atmosphere at t he Top Top (Radiation Heat Loss)
For Steel---with No Cover on Top Top , You You Get a Solidification Time of 5.0 Minutes.(see FIGURES) If you Calculate Geometrically, you would get a Solidification Time of 5 .8 Minutes. This Difference is because at 1640 C (Pouring Temperature Temperature of Steel) ,because of R adiation Heat Loss , the Top Surface is º
no longer the geometrical area but something more than that. This is called APPARENT APPARENT SURFACE AREA (ASA) .This .This ASA can be Increased (By Chilling in Casting) or Decreased (By Insulating in Feeders). This alters the modulus and it is called MODULUS EXTENTION FACTOR FACTOR (MEF)
For getting a Sound Casting We need to Know 1. % of Shrinkage to be Fed by Feeder 2. % of Shrinkage Required Required for Pattern Pattern 3. Size of Feeder 4. Number of Feeders Required.
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SHRINKAGES V L-L = Loss of Super
Heat for Solidification to Occur. Occur.
V L-S = Loss of Latent L atent Heat for Solidification to V S-S = Contraction
Occur. Occur.
in Solid State from Melting Point to Room Temperature.
V L-L + V L-S
V S-S
6%
8%
6.7%
5.7%
8.3%
8%
STEEL COPPER ALUMINUEM
V S-S
is 8% in Steel on a Volumetric Basis, but on a Linear Scale it became 2% --- this gives you
the Contraction Allowance to be provided on the Pattern
Feeding distance or Range Feeding Distance is Proportional to
X (of the alloy)
=
Density of Alloy x Specific Heat Alloy Thermal Conductivity
In case of Steel Plate (5:1 ) (5 is the Width & 1 is the Thickness) Feeding Distance is 4.5 T (Plain Carbon Steel) In Plain Carbon C arbon Steel = 2.5T (End Effect)+2.0T(Feeder Effect)=4.5T Effect)=4.5T But the Feeding Distance in of Stainless Steel is almost 12T. 12T.
FEEDING DISTANCE = END EFFECT+FEEDER EFFECT FEEDING DISTANCE DISTANCE Steel –Plate—4.5T Aluminum –Plate—11T Copper –Plate—8 T In a bar (1:1) Feeding Distance Reduces (see Wlodawer)
As X increases
feeding distance distance increases. (but data are are not available). You have to pour a plate of the given alloy for copper or aluminum & ascertain the value by radiography (see FIGURES) This gives you the Number of Feeders to be Placed on the C asting.
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In case of Steel
M Feeder = 1.2 M Casting This gives you the Size of Feeder. Similar equation for Copper & Aluminum will have to be established. Now you know , 1. Size of Feeder 2. Number of Feeder 3. Contract Allowance on Pattern to get a Sound Casting. As regards to MEF, you can get it from Figures Wlodawer ‘s
--- Directional Solidification of Steel Castings has a Wealth of Information for Steel Castings.
But no such book is available for Non Ferrous Alloys. With help of Modulus concept in Steel, a good Casting can be made without trials. But it will have have to be established established for Non Ferrous Ferrous Alloys, so that Non Ferrous Castings Castings can also be made without trials. (As of now, it is not possible ,as no data is available) For S.G.Iron foundry foundry men, the books on Gating & Feeding Feeding can be obtained from www.sorelmetal.com . (This is because of Gating & Feeding of Steel Castings & S.G.Iron are totally different.) different.)
Reference 1. Wlodawer—Directional Solidification of Steel Castings. 2. Beeley ------- Foundry technology. 3. Feeding Range ---Cast Metals Research Journal (AFS),June 1975,Volume 11,No 2
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