Conditioning

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Conditioning
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Conditioning is the

• Operations which alter the internal structure of
  a material to improve the mechanical and physical
  properties.
• The processes fall into three categories thermal,
  mechanical, and chemical.
• The operations include
• Annealing, normalizing, hardening, tempering,
  drying, firing, work harden and catalytic action.

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A materials properties that can be changed by
conditioning include

• Strength ability to resist breaking. Including
  tensile, compressive, shear, torsion.
• Elasticity
• Ductility
• Toughness
• Hardness
• Moisture Content

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Conditioning by Thermal Process

• Annealing
• Normalizing
• Hardening
• Tempering
• Drying
• Firing

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Conditioning by Mechanical Process

• When forming, drawing, and bending the work
  becomes harder and more brittle. This action is
  called work hardening.
• Often this hardening is undesired so it is
  thermal conditioned to reduce the hardness.
• Shot Peening is when shot is thrown at a material
  to improve its surface finish.

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Chemical processes

• This process uses chemical reactions to condition
  material.
• A catalyst are often used with thermosetting
  liquids to generate a chemical reaction to
  polymerize and form long organic chemical chains.
  
• Radiation from gamma rays also can be used to
  polymerize plastic.

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Thermal Conditioning Metals

• Heat treating carefully controls the time,
  temperature, and rate of temperature change.
• Theory of heat treating metals are made of
  roderly three-dimensional arrangements of
  molecules (crystals) heat treating modifies the
  grain structure for one or more reasons
• Relieving internal stress
• Produce a refined or uniform grain size.
• Alter the surface chemistry
• Strengthen the material

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Heat treating metal

• Heat treating takes advantage of the fact that
  metals are allotropic materials, which means they
  can exist in two or more crystal structures.
• Nonallotropic materials can have one one crystal
  structure. This includes all nonferrous metals
  and alloys and some ferrous metals.

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Two-Step Hardening Process

• Often used with steel to increase hardness and
  wear resistance.
• Step 1 Steel is heated above its critical temp
  and cooled rapidly (quenched). This produces a
  martensite a solid solution of iron and carbon
  making an unstable grain structure which is why
  the material is hard, brittle, and unstable.
• Step 2 Tempering- the steel is heated gradually
  to a set temperature. It is then quenched.
  Tempering allows the material return to normal
  lattice structure and stress is removed. Steel
  is less brittle and softer.

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Hardening

• Full Hardening involves hardening the entire
  material. This is done to increase the hardness,
  tensile, and fatigue strength, toughness, and
  wear resistance.
• Includes quench hardening and firing of clays
• Surface Hardening Is used when a fully hardened
  material is not desired. Surface hardening can
  create a ductile part with a hard wear resistant
  surface.
• Precipitation Hardening also called age
  hardening and is used to harden nonferrous
  metals. The metal is held at high temp above
  uniform solid solution and then rapidly cooled to
  room temp. This produces more particles than the
  material can hold and over time these particles
  precipitate out of the solid solution producing
  connectors between crystals of the alloy. What
  this does is reduce slippage between crystals and
  therefore increase hardness.

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Softening

• Includes Normalizing and Annealing
• Annealing heating metal above Ac3 temperature
  and held here for uniform heating and then cooled
  slowly to room temp.
• Normalizing heats above the hardening and
  annealing temps and is cooled in still air,
  produces a finer and uniform grain structure.

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Stress-relieving process

• Used to remove internal stress caused by
  machining, forming, and welding.
• Stress-relieving does not change the grain
  structure.
• It requires heating material to a specific temp.
  and allowed to cool slowly.
• Glass is often stress relieved after forming.

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Drying

• Another thermal conditioning process.
• Kiln drying is a controlled removal of excess
  moisture from wood.

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Bibliography

• Wright, R. T. (1999). Processes of manufacturing
  pp. 316-333Tinley Park, IL Goodheart-Wilcox.