Radiation Heat Transfer

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View Factor Orientation (or View factor or shape factor) plays an important role in radiation heat transfer. View factor is defined as, "fraction of radiation leaving surface 'i' and strike 'j' ". Summation Rule (View Factor) If there is are similar surfaces 'i' and 'j' , then: Blackbody Radiation Exchange Radiation Exchange between Opaque, Diffuse, Gray surfaces in an Enclosure 1. Opaque 2. Surfaces 3. Two surface enclosure Radiation Shield It is used to protect surfaces from radiation act like a reflective surface. References: Material from Class Lectures + Book named Fundamentals of Heat and Mass Transfer by Theodore L. Bergman + My knowledge.  Photoshoped pics  are developed.  Some pics and GIF from Google.   Videos from YouTube ( Engineering Sights ).
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Furnaces For Casting Process

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Furnaces For Casting Process:

Furnaces are used for heating and melting of metals to be poured into the mold for casting.
The most important thing is the selection of furnaces which depends on:
  • Casting alloy melting and pouring temperature.
  • Capacity reqiurement of furnace.
  • Variety of metals or alloys to be melted.
  • Costs of investment.
  • Fuel and maintenance.
  • Environment Pollution.

Types of Furnace Used in Casting:

There are many furnaces among them we are discussing 5 of them:

1. Cupolas:

A type of furnace which is vertical cylinder furnace equipped with tapping spout near base.

Steps involved in this process are as follows:
  • Only used for cast iron.
  • It consist of a steel plate lined with refractory.
  • The charge consisting of iron, coke, flux, and alloying metal is loaded through a charging door located less than halfway up height of cupola.
  • Coke is used as fuel.
  • Forced air is introduced for combustion of coke.
  • Flux (limestone) is used to form slag.

2. Direct Fuel-Fired Furnaces (or Reverberatory Furnace):

  • Charge is heated in a small open-hearth by natural gas fuel burners located on the side of furnace.
  • Flame is reflecting down by the furnace roof.
  • Molten metal is released from the tap hole located at the bottom of hearth.
  • Natural gas is used as fuel.
  • Only for non-ferrous metal like copper-base alloys and aluminium.

3. Crucible Furnaces (or Indirect Fuel-Fired Furnace):

  • Metal is melted without direct contact with burning fuel mixture.
  • Container is made of refractory material pr high temperature steel alloy.
  • Only for non-ferrous metals like bronze, brass and alloy of zinc and aluminium.
  • Oil, gas or powdered coal is use as fuel.
There are three types of Crucible Furnace:
  1. Lift-out Crucible Furnace  ➣  molten metal is transfered by hook.
  2. Stationary Pot Crucible Furnace   ➣  molten metal is transfered by a pot.
  3. Tilting Pot Crucible Furnace  ➣  molten metal is transfered by wheel.

4. Electric-Arc Furnaces:

Furnaces in which heat is generated from an electric arc.
  • High power consumption but having melting capacity 25-40 tons/hr.
  • Only for steel and ferrous alloys.
  • Rapid melting rate.

5. Induction Furnaces:

  • It uses alternating current passing through a coil to develop magnetic field in metal.
  • Induced current causes rapid heating and melting.
  • Only for melting steel, cast iron and aluminium alloys.
  • Fast melting rate and high cost operation.

Ladles:

Molten metal is transfered from furnace to other container by ladles or Crucibles.
There are two types of ladles used in Industries:
  1. Crane Ladle   ➣   For handling large volumes of molten metal using overhead cranes.
  2. Two-man Ladle   ➣   For moving and pouring smaller amounts of molten metal.

Reference:

  • University Notes 
  • Book Fundamental of Modern Manufacturing 6th Edition by Mikell P. Groover
  • Videos from youtube and Google 
  • Images from google images

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