PPT: Solidification & Cooling | Manufacturing Engineering - Mechanical Engineering PDF Download

 Page 1


CONTENTS
? Introduction
? Solidification
? Driving force for solidification
? Nucleation and growth  
? Solidification defects
? Design considerations in casting process
? References
Page 2


CONTENTS
? Introduction
? Solidification
? Driving force for solidification
? Nucleation and growth  
? Solidification defects
? Design considerations in casting process
? References
INTRODUCTION
Solidification ?
?solidification, is a phase transition in which
a liquid turns into a solid when its temperature is
lowered below its freezing point.
Why to study in detail ?
?The solidification of metals and their alloys is
important in various industrial process
? Most of the components produced from metals are
by casting process.
? When a metal is welded a small portion of metal
near the weld melts and resolidifies.
Page 3


CONTENTS
? Introduction
? Solidification
? Driving force for solidification
? Nucleation and growth  
? Solidification defects
? Design considerations in casting process
? References
INTRODUCTION
Solidification ?
?solidification, is a phase transition in which
a liquid turns into a solid when its temperature is
lowered below its freezing point.
Why to study in detail ?
?The solidification of metals and their alloys is
important in various industrial process
? Most of the components produced from metals are
by casting process.
? When a metal is welded a small portion of metal
near the weld melts and resolidifies.
SOLIDIFICATION
?During solidification, the liquid changes in to solid as cooling proceeds.
?The energy of liquid is less than that of the solid above the melting point. Hence 
liquid is stable above the melting point.
?But below the melting point, the energy of liquid becomes more than that of the 
solid.
?Hence below the melting point, the solid becomes more stable than the liquid.
Page 4


CONTENTS
? Introduction
? Solidification
? Driving force for solidification
? Nucleation and growth  
? Solidification defects
? Design considerations in casting process
? References
INTRODUCTION
Solidification ?
?solidification, is a phase transition in which
a liquid turns into a solid when its temperature is
lowered below its freezing point.
Why to study in detail ?
?The solidification of metals and their alloys is
important in various industrial process
? Most of the components produced from metals are
by casting process.
? When a metal is welded a small portion of metal
near the weld melts and resolidifies.
SOLIDIFICATION
?During solidification, the liquid changes in to solid as cooling proceeds.
?The energy of liquid is less than that of the solid above the melting point. Hence 
liquid is stable above the melting point.
?But below the melting point, the energy of liquid becomes more than that of the 
solid.
?Hence below the melting point, the solid becomes more stable than the liquid.
? Thermodynamically, both liquid and solid have equal energy at melting point
and therefore both are equally stable at melting point.
? Freezing is almost always an exothermic process, meaning that as liquid
changes into solid, heat is released.
? This heat must be continually removed from the freezing liquid or the freezing
process will stop.
? The energy released upon freezing is a latent heat and is the entropy part.
? Some under-cooling will be essential for solidification.
? Solidification occurs by two process : nucleation and growth.
SOLIDIFICATION
Page 5


CONTENTS
? Introduction
? Solidification
? Driving force for solidification
? Nucleation and growth  
? Solidification defects
? Design considerations in casting process
? References
INTRODUCTION
Solidification ?
?solidification, is a phase transition in which
a liquid turns into a solid when its temperature is
lowered below its freezing point.
Why to study in detail ?
?The solidification of metals and their alloys is
important in various industrial process
? Most of the components produced from metals are
by casting process.
? When a metal is welded a small portion of metal
near the weld melts and resolidifies.
SOLIDIFICATION
?During solidification, the liquid changes in to solid as cooling proceeds.
?The energy of liquid is less than that of the solid above the melting point. Hence 
liquid is stable above the melting point.
?But below the melting point, the energy of liquid becomes more than that of the 
solid.
?Hence below the melting point, the solid becomes more stable than the liquid.
? Thermodynamically, both liquid and solid have equal energy at melting point
and therefore both are equally stable at melting point.
? Freezing is almost always an exothermic process, meaning that as liquid
changes into solid, heat is released.
? This heat must be continually removed from the freezing liquid or the freezing
process will stop.
? The energy released upon freezing is a latent heat and is the entropy part.
? Some under-cooling will be essential for solidification.
? Solidification occurs by two process : nucleation and growth.
SOLIDIFICATION COOLING CURVES
A  cooling curve is a graphical plot of the changes in temperature with time for a 
material over the entire temperature range through which it cools. 
Total heat to be removed for solidification, Q = m ( SH + LH )
= m (Cp (Tm – Tf ) + L )