Metal Casting Unit 2

METAL CASTING

Dr. Rajesh Ranganathan

C.Manivannan

C.I.T

Die casting

Hot chamber die casting

Cold chamber die casting

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Die Casting

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Die casting machine

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cold chamber die casting

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Die casting product

• In Die casting the molten metal is forced to flow into a permanent metallic mold under moderate to high pressures, and held under pressure during

• Solidification• This high pressure forces the metal into intricate

details, produces smooth surface and excellent dimensional accuracy

• High pressure causes turbulence and air entrapment. In order to minimize this larger in-gates are used and in the beginning, pressure is kept low

• and is increased gradually15

Die casting

• A permanent mold made of metal or ceramic is rotated at high speed (300 to 3000 rpm). The molten metal is then poured into the mold cavity and due to centrifugal action the molten metal conform to the cavity provided in the mould.

• Castings are known for their higher densities in the outer most regions. The impurities and inclusions are closer to the inner diameter

• The process gives good surface finish• Applications: pipes, bushings, gears, flywheels etc. 16

Centrifugal Casting

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Centrifugal casting

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Carbon Dioxide Mould Casting

Suitable proportion of silica sand and sodium silicate binder (3-5% based on sand weight) are mixed together to prepare the sand mixture. Additives like aluminum oxide; molasses etc. are added to impart favorable properties and to improve collapsibility of the sand.

Sodium silicate reacts with carbon dioxide gas to from silica gel that binds the sand particles together. The chemical reaction is given by:

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Assignment - 1

Due date – 31 Dec 10

1. With a neat sketch discuss in detail about the types of pattern and

core making materials

2 Brief about the various types of cores

3 Explain the term pressure die casting, discuss the working principle

of PDC and its applications.

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UNIT- II

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Melting furnaces

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Melting furnaces

A.Cupola furnaceB.Crucible furnace

a.Pit type furnaceb.Tilting furnacec. Oil fired tilting furnace

C.Arc furnacesa.Direct arc furnaceb. Indirect arc furnace

D.Induction furnaces

Types of furnace

Cylindrical type furnace for producing Molten CAST Iron.

Vertical Cylindrical Shell – 6-12mm thick steel plate riveted.Lined inside with refractory bricks

Diameter – 1to 2 mHeight – 3 to 5 m

Whole shell mounted on brickwork foundation or steel columns.

Vertical Cylindrical Shell – 6-12mm thick steel plate riveted.

Carries gases from pre-heating zone to atmosphere.

Iron and Coke are preheated in this zone.Temperature around 1100ºC.

First layer of iron above coke bed.Temperature as high as 1700ºC. Iron is melted in this zone.Molten metal in this zone is collected in well through coke bed.

CO2 produced in combustion Zone comes in contact with hot coke and is reduced to CO.Iron and other elements are protected from oxidizing influence.

Combustion of fuel takes place by oxygen of air blast & produces lot of heat. This heat transferred to other parts of furnace.Silicon & Manganese oxidation develops heat.Temperature : 1540ºC to 1870ºC

The molten metal comes here. Also known as Crucible Zone.

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Cupola furnace

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Crucible furnace

A.Crucible furnacea.Pit type furnaceb.Coke furnacec. Oil fired tilting furnace

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Crucible

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Pit furnace

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Pit furnace

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Applications

a. Gas Carburizingb. Carbo Nitridingc. Nitridingd. Heat Treatmente. Annealingf. Bright Hardeningg. Bright Annealingh. Bright Normalising

Pit furnace

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Crucible gas fired furnace

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Tilting furnace

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• Direct arc furnace• Indirect arc furnace

Arc furnaces

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* The Direct Arc Electric furnace consists of a heavy steel cylindrical shell with a

spherical bottom lined with refractory bricks. The furnace hearth and walls are lined with

magnesite bricks.

* The furnace is built on a tilting platform that facilitates tilting of the furnace forward

for pouring molten metal into ladles. The furnace can also be tilted backwards for

inspection, addition of charge, flux deoxidizers etc. and for removal of slag through the

slag door.

* The roof of the furnace is made of steel shell lined inside with refractory bricks and

can be clamped in position. Metal can also charged from the furnace roof.

* The roof is provided with three circular holes through which non-consumable

graphite electrodes are inserted. The electrodes can be raised and lowered by means of

guides and are usually water cooled to dissipate heat. They are connected to a 3-phase

power supply.

Construction of Direct Arc Electric Furnace

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Direct Arc furnaces

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* The Indirect Arc Electric furnace consists of a cylindrical or barrel shaped steel shell lined with a refractory material. The shell is mounted on rollers and can be tilted through 1800

This facilitates for easy pouring of liquid metal to the ladles. Also, the rollers provide rocking action to the furnace that speeds the melting rate and stirs the molten metal.

* Two carbon electrodes are mounted along the horizontal axis and can be automatically adjusted for maintaining proper arc column.

* A charging door and pouring spout serve their usual purpose.

Construction of Indirect Arc Electric Furnace

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Indirect Arc furnaces

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An Induction Furnace uses induction to heat a metal to its melting

point which is based on the theory of Electro Magnetic Induction. Depending

on their frequency (50 Hz - 250 kHz) these can be divided to three types:

ᴥ High Frequency ᴥ Medium Frequency ᴥLow Frequency

Their capacities range from less than 1kg to 100MT, which are used

for re-melting of iron & steel (steel scrap), copper, aluminium precious metals

and alloys. Even most modern foundries use this type of furnaces and now

more iron foundries are replacing Cupolas with Induction Furnace to

melt cast iron as the former emit lots of dust & other pollutants.

Induction furnaces

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• Channel type induction furnace

• Coreless type induction furnace

Type of Induction furnaces

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Advantages of Induction Furnace

• It has no electrodes and electric arcs which allow productions of steel & alloys low in carbon and occluded gases without any quality problem.

• Low melting losses & alloying elements.

• High power efficiency, therefore, cost-effective.

• Precise control of the operating parameters.

Disadvantages of Induction Furnace

• Refining in Induction Furnace is not as intensive or effective as in Electric Arc Furnace (EAF).

• Life of Refractory lining is low as compared to EAF.

• Removal of S & P is limited, so selection of charges with less impurity is required.

Induction furnaces

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Defects in castings

The general origins of defects lie in three sectors:

• The casting design,

• The technique of manufacture–the method,

• The application of the technique–‘workmanship’.

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Defects are

1. Shaping faults arising in pouring.

2. Inclusions and sand defects.

3. Gas defects.

4. Shrinkage defects due to volume contraction in the liquid state and during solidification.

5. Contraction defects occurring mainly or wholly after solidification.

6. Dimensional errors.

7. Compositional errors and segregation.

Defects in castings

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Shaping faults arising in pouring

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Inclusions and sand defects

The inclusions are

• Indigenous inclusions

• Endogenous inclusions

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Indigenous inclusions

Reactions forming indigenous inclusions involve common

impurities such as oxygen, nitrogen and sulphur, together with

the more reactive metallic constituents of the alloy.

Exogenous inclusions

Individual grains of foreign matter are inevitably dislodged

from furnace ladle and mould, but many exogenous inclusions are

complex aggregates of considerable size. Wide variations in form

and composition are encountered according to origin.

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• Slag or dross or refractories• Moulding material• Oxide films• Lustrous carbon.

Exogenous inclusions

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Slag

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Dross

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Refractories

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Lustrous carbon

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Documents

Metal Casting Unit 2