Aluminum Alloys And Foundry Practice

• Casting properties of aluminium alloys:

1)      The alloys should posses minimum solidification shrinkage so that foundry yield is at maximum and the problem of hot tear and micro porosity are minimized.

2)      The alloy should have adequate fluidity in the molten condition.

3)      The should not posses a tendency to hot tear or crack.

4)      The alloy should face minimum problem as regards drossing and gas absorption.

5)      It should possible to produce pressure-tight casting.

• Melting of aluminum alloys:

a)      Crucible furnace

b)      Reverberatory furnace

c)      Pot furnace

d)     Induction heating furnace

• Drossing:

Drossing is the formation of the aluminum oxide and other oxides which are collected on the surface of the molten metal.

Melting with minimum dross-formation occurs when;

a)      Melting is fast

b)      Metal is protected from products of combustion (in the melting furnace).

• Gas absorption:

Aluminium alloys can absorb harmful quantities of hydrogen gas and consequently give rise to gas or pin hole or gas porosity.

• Fluxing and flushing:

Purpose:

a)      To remove dissolved hydrogen from the melt.

b)      To separate dross fro the molten metal

c)      To entrap dross.

Both solid fluxes (containing aluminium and zinc chloride) and gaseous fluxes (i.e. nitrogen, helium, argon, and chlorine) are used to flush the molten metal.

Flushing is carried out by skimming off surface dross and then bubbling gaseous fluxes through the molten metal.

• Grain refinement:

Grain size in cast aluminium alloy can be refined by:

a)      Chilling

b)      Temperature adjustment (i.e. pour at the possible lowest pouring temperature).

c)      Late addition (such as those of boron, titanium, chromium. Columbium and sodium ) to the melt.

• Process of the casting aluminium alloys:

1)      Sand casting

2)      Permanent mold casting(GDC)

3)      Die casting(PDC)

Introduction

Aluminum and its alloy

Characteristic:

1)      Light weight, aluminum weighs one-third that of steel.

2)      Malleability and ductility.

3)      Good electrical conductivity.

4)      High thermal conductivity.

5)      Resistance to corrosion.

6)      Non-magnetic properties.

7)      Affinity to oxygen.

8)      Higher coefficient of expansion as compared to steel.

9)      High tensile strength.

Founding/ casting

            Founding/ casting is the process of producing metal/ alloy component parts of desired shapes by pouring the molten metal / alloy into a prepared mold (of that shape) and then allowing the metal/alloy to cool and solidify. The solidified piece of metal/alloy is known as casting.

Application of metal casting

1)      Transportation vehicle.

2)      Machine tool structures i.e. planner blades (cast iron).

3)      Turbine vanes.

4)      Power generator.

5)      Mill housing .(cats steel)

6)      Railway crossing(Mn steel cast section)

7)      Super charger casing(Mg alloy)

8)      Pump filter and valve (Mg alloy).

9)      Paper mill stock breaker parts (steel casting).

10)  Aircraft jet engine blades.

11)  Agricultural parts.

12)  Sanitary fitting

13)  Communication, construction and atomic energy application.

Types of foundry

a)      Captive foundry:

It makes castings for the same only and all the casting made in a captive foundry is consumed mainly in the product being manufactured by the organization.

b)      A jobbing foundry:

Produces small number of casings of a given types for different customers. Also have facility for mass production.

c)      A production foundry;

Highly mechanized and can produce castings economically on mass scale.

d)     A semi-production foundry:

Combination of  both jobbing and production foundry.

           

Foundry may also classified as:

1)      Ferrous foundry:

a)      Steel foundry (plain carbon steel, low and high ally steel)

b)      Gray iron foundry

c)      Malleable iron foundry

d)     Ductile iron foundry

2)      Non ferrous foundry:

a)      Aluminiaum and magnesium ally foundry(light metal alloy)

b)       Copper, brass and bronze foundry

c)      Lead, tin and zinc based foundry.