The process of manufacturing Pencil Ingots from raw materials such as scrap and sponge iron can be broadly classified as:
Selection of Raw-Material
The quality of Raw material required depends upon the type of furnace in use. When induction Furnace is utilized, as is the case, the ideal quality of raw material should be clean shredded scrap of low carbon content and sponge iron.
Charging and Loading of Raw Material into Furnace
The scrap is stored right next to the furnace for easy operation. It is charged into the furnace by using an Electro magnetic device attached to an overhead crane. This ensure~ lifting of sizable amount of scrap which saves time, energy and cost. The crane used is called an E.O.T. Crane. It replaces the need and dependence on manpower. Besides charging of scraps into furnace it also handles other operation like removal of ingots moulds, removal of Pencil Ingots etc.
Selection of Furnace
There are three type of furnaces that are available for melting of scrap into steel. These are - a rotary electric furnace, an electric arc furnace and an induction furnace. A rotary furnace is mostly used for melting pig iron and gray casting. An Electric Arc Furnace is a highly competent equipment for the purpose of steel melting. It not only can melt efficiently but also allows time for analysis of the molten metal and effect adjustment in the constituents of the molten metal. However Electric Arc Furnace is an expensive equipment and unsuitable for small operations. This equipment is there for use in case. of manufacturing special quality steel. It is not economical in case of mini steel plants. An induction furnace is the cheapest and is used in mini 'steel h plants very economically. In an induction furnace, certain. inclusions like carbon and ferroalloys can be added to the molten metal for producing good quality of steel. Induction Furnace An induction furnace is a highly sophisticated equipment consisting of a crucible with a lid. Heat is generated by the induction of medium frequency electricity. The furnace is equipped with the necessary control panel, which receives electrical power at normal 50Hz frequency and converts the same to DC power. The DC power generated is again converted to AC power of medium frequency, which induces the heating effect to the furnace. In addition to the control panel, the entire furnace system is thoroughly cooled for protection. A separate water supply system along with cooling tower is installed to feed the furnace continuously with demineralised cool water. The furnace can also be titled to pour out the molten metal. The inside surface of the crucible is normally coated with castable ceramics and fire clay in intervals of the crucible is normally coated with castable ceramics and fire clay in intervals of 7 days. This practice protects the crucible and gives a longer life to the furnace.
The furnace crucible is charged with the requisite quantity of scrap and sponge iron and the lid are put on. Power introduced and the furnace gets hot and the steel starts to melt. Heating is continued till the entire metal mass melts to liquid 'state. At this stage, a little time is available for adding inclusions like Ferro alloys and carbon, if necessary. A sample of molten metal is sent to the laboratories for analysis. Based on the analysis report, Ferro alloys and other alloys materials are added after proper weightment. The temperature of the metal bath will be adjusted suitably by adjusting power into the furnace to ensure proper mixing of alloys in the bath. After sometime, when the metal bath has reached the appropriate temperature, sample is send to the laboratories and the process is repeated till the desired is quality is obtained. The molten metal is now ready for pouring into the moulds. Casting of Pencil Ingots. The methodology of casting Pencil Ingots is called Uphill Teaming or Bottom Pouring. The advantage is that simultaneously depending on the capacity a number of Pencil Ingots can be cast. Prepared and set moulds will be kept in casting area in proper sequence. The molten metal is poured through a central shaft and is allowed to rise through the ingot moulds through a series of channels. By this method, solid non-porous castings can be achieved and the weight of the molten metal ends any possibility of blowholes. Some of the equipments used in arranging a set of moulds are:¬
Base Plate or Bottom Plate & B.P. Sets Bottom plate is a heavy C.I. Plate, the size of which varies depending on the number of pencil ingots to be cast which on its part depends on the furnace capacity. The Bottom plate has groves to fit in ceramic material made boxed called B.P. Sets. These B.P. Sets are of hollow construction having openings on its faces. These B.P. Sets are so placed inside the grooves of the bottom plate that they are inter connected to one another between the B.P. Sets are filled by ceramic bricks. The entire system is called a B.P. Set Unit. The Ingot bould are kept on the upper opening of the B.P. Sets and the whole system is sealed by means of castable ceramics, fire clay and ramming mass. One central hole of larger dia is kept open to receive the molten metal.
A long pouring pipe with ceramic sleeves inside is kept on the central opening of a B.P. Set and sealed. The molten metal is poured into the system through this central shaft. Molten metal passes through the Central Shaft into the B.P. Sets and next to the ingot moulds. The level of metal rises inside the moulds till the charge is exhausted. The metal is allowed to cool for a few minutes and then the ingot moulds are lifted away by the EOT Crane. Next the entire B.P. Set is also removed with the Pencil Ingots sticking out, to the finishing yard. Now the Ingots, Runners & Risers are removed for sale.