World Library  
Flag as Inappropriate
Email this Article

Directional solidification

Article Id: WHEBN0012078110
Reproduction Date:

Title: Directional solidification  
Author: World Heritage Encyclopedia
Language: English
Subject: Chill (casting), Centrifugal casting (industrial), Castability, Turbine blade, Full-mold casting
Collection:
Publisher: World Heritage Encyclopedia
Publication
Date:
 

Directional solidification

Directional solidification
Progressive solidification

Directional solidification and progressive solidification describe types of solidification within castings. Directional solidification describes solidification that occurs from farthest end of the casting and works its way towards the sprue. Progressive solidification, also known as parallel solidification,[1] is solidification that starts at the walls of the casting and progresses perpendicularly from that surface.[2]

Theory

Most metals and alloys shrink as the material changes from a liquid state to a solid state. Therefore, if liquid material is not available to compensate for this shrinkage a shrinkage defect forms.[3] When progressive solidification dominates over directional solidification a shrinkage defect will form.[2]

The geometrical shape of the mold cavity has direct effect on progressive and directional solidification. At the end of tunnel type geometries divergent heat flow occurs, which causes that area of the casting to cool faster than surrounding areas; this is called an end effect. Large cavities do not cool as quickly as surrounding areas because there is less heat flow; this is called a riser effect. Also note that corners can create divergent or convergent (also known as hot spots) heat flow areas.[4]

In order to induce directional solidification chills, risers, insulating sleeves, control of pouring rate, and pouring temperature can be utilized.[5]

Directional solidification can be used as a purification process. Since most impurities will be more soluble in the liquid than in the solid phase during solidification, impurities will be "pushed" by the solidification front, causing much of the finished casting to have a lower concentration of impurities than the feedstock material, while the last solidified metal will be enriched with impurities. This last part of the metal can be scrapped or recycled. The suitability of directional solidification in removing a specific impurity from a certain metal depends on the partition coefficient of the impurity in the metal in question, as described by the Scheil equation. Directional solidification is frequently employed as a purification step in the production of multicrystalline silicon for solar cells.

References

  1. ^ Stefanescu 2008, p. 67.
  2. ^ a b Chastain 2004, p. 104.
  3. ^
  4. ^ Stefanescu 2008, p. 68.
  5. ^ Chastain 2004, pp. 104–105,..

Bibliography

  • .
  • .

Further reading

  • .
  • .
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and USA.gov, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for USA.gov and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
 
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
 
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.
 



Copyright © World Library Foundation. All rights reserved. eBooks from World eBook Library are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.