Most use manufacturing process of steel?

The principle of the L. D converter

Name the raw materials used for the charge in L.D process👍

L. D. Process

The name L.D. is derived from the initials of two towns,LINZ & DONAWITZ in Austria where this process was first used.

The L. D. is converter or the basic oxygen converter is designed to produce high quality steel in a relatively shorter time. The basic raw material used in the process are the molten pig iron from the blast furnace and the steel strap. Fluxing agents are used for reacting with impurities and form a slag on the top of the molten metal.

In this process of 👍producing steel, a jet of pure oxygen is blown through a lance which is water cooled.The lance is brought near the molten metal and oxygen is blown at high pressure on the molten metal bath. This leads to the oxidation of carbon and other impurities causing violent agitation which allows all the molten metal to come in contact with the oxygen stream. When the blowing is over,the converter is tipped to remove the slag and again turned the other way to collect the metal into a ladle.

Controlled quantity of carbon and other elements are added to obtain the desired quality of steel.

Electric process

Two types of electric furnace are in use

-electric arc furnace

-high frequency furnace

High grade steels and alloy steels are made by the electric process

No fuel or air is required for burning. Because of this there is no contamination of the charge.

Electric arc  furnace

In this type of furnace, the heat required is generated by electric arcs struck between carbon electrodes and the metal bath. This type of furnace is used for making alloy steels, such as stainless steel, high speed steel etc.

The composition of the steel can be accurately controlled in this process. This process is not influenced by the external conditions and the temparature of the furnace can be maintained to the desired level.

The furnace uses pig iron and selected scrap, and produces high quality steel.

When the metal is molten and the slag is formed on the top surface, the furnace is tilted and the slag is removed. Then the furnace is again tilted in the other way to collect the molten metal. Silicon, manganese and other necessary elements are added in the ladle, and the composition of steel regulated.

The high frequency furnace

This furnace consists of a crucible made of refractory materials, surrounded by an inductor coil which carries the alternating current, and is insulated and water cooled. The outer ring is made of special magnetic iron laminations,, and shields the casting from getting too hot. It also serves as a magnetic sheild to increase the magnetic flux in the coil.

The charge used consists of steel scrap and iron oxide.

The steel is further refined by re melting and addition of the required alloying elements. Steel, produced by these processes, is used for making press tools, cutting tools and precision measuring instruments.

OPEN HEARTH PROCESS

This process eliminates the  disadvantage of the Bessemer process. Most of the steel in our country is produced by SIEMENS MARTIN process using an open hearth furnace.

Open hearth furnace

An open hearth furnace is a reverberatory furnace, having a melting chamber built with refractory materials, bounded at the top the roof, and at the bottom by the hearth. The charging doors are provided at the side walls. The melting area is connected with regenerators through ports.

Fuel for this process is the producer gas generated by a plant which can be fed  to the hearth through two generating Chambers. The air, which forms a combustible mixture, may be fed the same way through the other two chambers

Heating through producer gas and air is the characteristic of the open hearth furnace. For the chemical reaction of the charge, intense heat is required. This can be achieved through regenerating chambers.

The process

The hearth is first prepared and heated  well up to 1500°c. The charge is a mixture of pig iron and steel scrap in different proportions as required according to the class of steel to be manufactured.

The ratio of pig iron to scrap varies from 1:4 to 4:1 A reasonable ratio is 3:2. After the charging is over, the gas is allowed in to the melting champer. During melting, part of  the carbon, most of the silicon and  manganese are removed by oxidation. More carbon will be oxidised away at the  boil stage by adding iron ore to the charge. When the bath reaches the requisite percentage of carbon, the furnace is allowed for tapping. While the metal is flowing into the ladle, a de-oxidiser is added to the steel to remove air, and ensure soundness in the metal.