Open hearth furnace

What is furnace?Equipment to melt metals

Casting

Change shape

Change properties

It is a thermal enclosure used for melting different materials materials such as iron aluminum etc.

Foundry & Casting The place where casting is done is called

foundry.

Casting is defined as:

Casting is a manufacturing process by which

molten/liquid material is poured into a mold

containing a cavity of specific shape, and then

allowed to solidify. The solid casting is then

taken out and cleaned to complete the process

Furnaces Used In Foundry Following some furnaces are used in foundry:

• Blast furnace

• Cupola furnace

• Electric arc furnace

• Pit furnace

• Electric induction furnace

• Direct fuel fired furnace

Direct fuel fired furnace is our concern for presentation today.

Direct Fuel Fired Furnaces Direct fuel Fired furnaces are those in which:

• Fuel is in direct contact with charge material

• Charge is heated by combustions products

• Material is heated by the way of heat transfer through asolid wall.

• Heat transfer takes place through a liquid mediumsurrounding the material.

Types Of Direct Fired Furnaces• Important types are:

• Blast furnace

• Cupola furnace

• Open hearth furnace

• Pit furnace

Open Hearth Furnace

History: William siemens, developed the open hearth

process by preheating the incoming air.

Pierre martin was responsible for dilution of pigiron with scrap.

By combining both siemens-martin open hearthprocess is developed.

Construction Furnace can either tilting or fixed.

The furnace consists of a shallow bath capable ofholding from 60 to 300 tons of metal at a time.

There is back wall, doors in the front wall and a roofover the top.

On each side of bath is a set of two heating chambersone is to pre-heat air and other to pre-heat coalproduced gas.

These chambers are filled with open chequered bricks.

Contnd……. At each end of the hearth openings are provided.

Openings at one end is to allow the passage of heatedgas and air which burns with flame directed down onthe metal.

2nd opening allows the burned gases to escape to thechimney via regenerators.

These regenerators are a series of chequered brickworkheating chambers.

Capacity is 10 to 300 tons.

Diagrams

Lining Of FurnaceLining can be acidic or basic depending

upon the nature of impurities.

If impurities are acidic then acidic lining isused like silica bricks and sand.

If impurities are basic then basic lining isused like magnesite bricks and dolomite.

Charging The Furnace Charging can be in cold and liquid state.

What is mean by cold and liquid state???????

The charge is pig iron, molten or solid iron and scrap.

Limestone and iron ore added as required.

It is charged by mechanical charging machine.

To charge a basic furnace calcined dolomite or sand isthrown over the bottom and side walls.

This operation is called fettling(repairing the lining).

Cntnd……. After fettling hearth is heated about 1500c.

Limestone on bottom is followed by iron ore then ironand scrap.

After about two hours when scrap has begun to meltpig iron is added.

After this melting period begins.

Working Heat is supplied to the furnace by burning the mixture of

gas and air.

Melting may takes place in three hours depending uponthe nature and size of the charge.

During this time some of the carbon and most manganeseand silicon has removed by oxidation.

These impurities are removed by adding limestonemillscale and also by the oxidizing action of the flame.

In boil stage last of carbon is removed.

When melting is completed certain elements are added toremove remaining impurities like, Si, S, and P.

Tapping Tapping is removal of molten product from the

furnace.

When steel is judged for desired carbon content itis than tapped.

At this point slag float on the steel and it isremoved.

De-slagging Slag is removed in two stages;

Some of the slag flows out of the notch duringthe early part of the process.

Remainder is separated by means of specialladle.

When steel is poured into ingot molds retain theslag

Uses Steel produced by open hearth is either of low (0.15-

o.3% carbon) or medium (0.3-o.7% carbon).

Alloy steel is also produced by this process.

Low (0.15-o.3% carbon) steel used in boilers plates,bridge work, structural work etc.

Medium (0.3-o.7% carbon) used in axels, hammers,springs and dies.

Steel Castings Steel casting is a specialized form of casting involving

various types of steel.

Steel castings are used when cast irons cannot deliver enough strength or shock resistance.

Examples of items that are steel castings include: hydroelectric turbine,wheels,gears,railroad,truck,frames, valve bodies, pump casings, mining machinery, marine equipment, and engine parts.