Lecture-6 CUPOLA FURNACE.pptx diagram chemical reaction

zones of cupola

1. CUPOLA FURNACE

2. WHAT IS CUPOLA FURNACE ? The cupola is a most widely used foundry furnace for melting ferrous metals and alloys. Sometimes, it is also used for melting non-ferrous metals and alloys. Cupola furnace is the cheapest means for converting pig iron or scrap metal into gray cast iron. The fuel used is a good quality low sulphur coke. Anthracite coal or carbon briquettes may also be used .

3. STRUCTURE The size of a cupola is expressed in diameters and can range from 0.5 to 4.0 m. The overall shape is cylindrical and the equipment is arranged vertically, usually supported by four legs .   The top of the cupola is fitted with cap to prevent rain entering from the cupola and for avoid harmful gases to the environment. The shell of the cupola, being usually made of steel.

4. PARTS OF CUPOLA Legs : provided for supporting purposes. Slag Hole : used for removing or extracting the slag from the melting iron. Sand Bed : This is in taper form and from this, the melted iron comes out easily. Tuyers : By tuyeres, we enter the gas to the proper burn of fuel. Charging Door :  supply the charge to the furnace. The various charges are Pig Iron, Coke and limestone. Brick lining : made of steel  Spark Arrester : This device used in the system for preventing the emission from the fireplace.

5. OPERATION The  Cupola furnace works on the principle where we generate heat from burning coke and when the temperature of the furnace is above the melting point of the metal then the metal is melt.  The furnace is filled with layers of coke and ignited with torches. When the coke is ignited, air is introduced to the coke bed through ports in the sides called  tuyeres . Wood, charcoal, or biomass may also be used as fuel for the cupola's fire. When the coke is very hot, solid pieces of metal are charged into the furnace through the top. The metal is alternated with additional layers of fresh coke.  Limestone is added as a  flux to prevent the metal from the excessive oxidation. As the heat rises within the stack the metal is melted. It drips down through the coke bed to collect in a pool at the bottom, just above the bottom doors. When metal is melted completely the bottom bar is pulled sharply under  the  plates and bottom is dropped. All remaining  slag,  un-burned coke or molten metal drops from the furnace .

6. ZONES WELL The   space   between   the   bottom   of   the   tuyeres   and   the   sand   bed. M olten metal   collected   in   this   portion. COMBUSTION   ZONE A lso known as oxidizing zone. It is located between the well and melting zone. The height of the zone is normally 15 to 30 cm. A temperature of about 1540°C to 1870°C is achieved in this zone. Exothermic reactions takes place in this   zone .

7. REDUCING ZONE L ocated between the upper level of the combustion zone and the upper level of the coke bed. CO2 is changed to CO through an endothermic reaction CO2  +   C   (coke)      —— >     2CO  temperature to about 1200°C at the top of this zone. MELTING ZONE In this zone melting is done. Located between preheating and combustion zone. Following reaction take place: 3Fe   +   2CO       —— >       Fe3C    +     CO2

8. PREHEATING ZONE This zone starts from the upper end of the melting zone and continues up to  the  bottom level of the charging  door. O bjective of this zone is to preheat the charges from room temperature to about 1090°C before entering the metal charge to the melting zone.  STACK The empty portion of cupola above the preheating zone is called as stack. It provides the passage to hot gases to go to atmosphere from the cupola furnace.

9. ADVANTAGES Simple in Construction. Wide range of material can be melted. Less floor space is reuired . Very skilled operators are not required. Can be easily operated by low skill person. Low cost of operation. Low cost of maintenance. Low cost of construction.

10. DISADVANTAGES I t is very hard to control the temperature in this furnace. Metal elements are converted to their oxide which are not suitable for casting.