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SRI BHAVANI CASTINGS
TWO WEEK INTERNSHIP
PRAGATI ENGINEERING COLLEGE
MANUFACTURING PROCESS OVERVIEW
DESIGN FROM CONSUMER: company that requires casted parts place an order to sri Bhavani castings and sends them the design of the part they require and material to be used in casting and also the required parameters like its tensile strength, elongation and few other important parameters.
He mentions the specifications as ‘FG260/7’. Where FG indicates the material to be used, ‘260’ indicates its tensile strength in MPa and ‘7’ indicates its percentage elongation.
PATTREN MAKING: Pattern is selected by considering the following
Quality of the casting to be produced.
The size and complexity of the shape of the casting to be produced.
Type of the moulding method to be used.
Usually materials like aluminium cast iron or wood is used as pattern material. The patterns are not made to the exact dimensions of the required casting. Certain allowances are made in dimensions.
PREPARATION OF SUITABLE SAND FOR MOULDS: Sand is prepared according to the parameters of castings i.e the size and material of the casting ratio to sand, casting in the mould box and surface finish.
Mainly two types of sands are used for moulds. They are
GREEN SAND: It is the mixer of bentonite, coal dust, fine dust, return sand and water. It is used for small castings. Large ones cannot be done on it because it has relatively low strength when compared to CO2 sand.
Bentonite, coal dust and fine dust are present in three individual containers. These three get mix up in a container into which water flows. The mixer thus obtained enters into the sand mixer. Return sand enters into the sand mixer through separate pipes. Sand mixer mixes these raw materials thoroughly and sends to KOYO machine through conveyors. The ratios of raw materials are controlled through computer
CO2 SAND: it is the mixer of silica sand and sodium silicate and CO2. It is used for larger castings. CO2here acts as catalyst. Initially silica sand and sodium silicate is mixed thoroughly in the mixer. Then it is packed in the mould. After packing, CO2 is passed into the box. Reaction takes place in presence carbon dioxide and the sand gains strength and binding capacity.
TESTING OF SAND: After preparation of sand, tested for its properties. These tests include testing of the capabilities of the sand to withstand the temperature, water vapour content, its ability to blow out these hot gases formed in the cavity.
The tests are made on the sand:
Volatile matter test
Loss on ignition test
Moisture content test
Active clay test
AFS clay test
INPUT (INTO THE FURNANCE): The two main materials used for casting are ‘FG iron (grey cast iron)’ and ‘SG iron (spherodial cast iron)
FG IRON: It is the type of the cast iron that has graphitic microstructure i.e carbon is in the free form (in form of graphite flakes).
C – 3.30-3.50
Si – 1.5-1.7%
Mn – 0.7-1.00%
Easily machinable as carbon is in free form.
High damping capacity.
Have ductile nature
Low tensile strength.
High compressive strength. Its compressive strength is nearly 3-4 times its tensile strength
SG IRON: In this type of cast iron carbon is present in the form of nodules of graphite. Hence it is also called as nodular cast iron. It is obtained by adding ‘Mg’ to ladle containing grey cast iron. This ‘Mg’ converts the flakes of graphite to small graphite spheres.
https://en.wikipedia.org/wiki/CarbonC: 3.2 to 3.60%
https://en.wikipedia.org/wiki/Silicon 2.2 to 2.8%
https://en.wikipedia.org/wiki/Manganese 0.1 to 0.5%
Mg:0.03 to 0.05%
P:0.005 to 0.04%
https://en.wikipedia.org/wiki/Sulfur 0.005 to 0.02%
High fluidity, castability, strength and toughness.
High fatigue and impact resistance.
MELTING: Melting of the metal is done in induction furnace. Main purpose of induction furnace is that when the charge material is molten, the interaction of the magnetic field and the electrical currents flowing in the induction coil produce a stirring action within the molten metal. This stirring action forces the molten metal to rise upwards in the centre causing the characteristic meniscus on the surface of the metal.
WORKING PRINCIPLE: The crucible in the furnace is surrounded by copper wires through which high frequency A.C current is passed. Due to this alternating magnetic field is produced around these wires. By the principle of electromagnetic induction, when a conducting element (metal) is placed in the variable magnetic field, current induces in it. So here current induces in the metal present in the crucible. Heating takes place according to joule’s heating.
TESTING OF SAMPLE: The molten metal is not directly sent for pouring, a test sample called ‘Spectro sample’ is made and is sent for testing on ‘Spectrometer’. The spectrometer is a device which slightly burns the specimen by passing high frequency light rays and gives the percentages of elements present in it by volume. These results are cross checked by required percentages. Necessary changes are made if any and are sent for pouring.
The micro structure is also checked under microscope. This micro scope is connected with the monitor on which we can observe and save the microscopic structure.
POURING INTO MOULDS: The liquid metal is poured into the moulds by ladle. This pouring should be done with certain time limit. Because as the time prolongs solidification of metal begin to take place. Also in SG iron the added Mg begin to react with the oxygen present in the atmosphere and forms MgO. Hence the pouring should be done within ten to fifteen minutes after melting.
COOLING: The poured metal is thus allowed to cool to the room temperature. Usually the molten metal in the risers are more exposed to environment when compared to the inner metal. Hence its cooling takes place earlier. This results to uneven solidification. To prevent this, immediately after pouring some saw dust is added at the runner and riser so that this saw dust burns and gives some heat. This heat prevents the solidification of molten metal in the runner and riser.
BREAKING THE MOULDS: After cooling, these moulds are dropped into the ‘Knock out machine’. The knock out machine is a machine that vibrates (oscillates) with certain amplitude when power is supplied. Due to these vibrations the moulds breaks out. The casting is then removed from the machine and the sand formed is sent for recycling.
PARTIAL MACHINING AND CLEANING THE CASTINGS: The casting taken out from the knock out machine are partially machined i.e cutting out the runners and risers and grinding any excess material. These casting are then cleaned under high pressure air in a closed casing. The cleaned castings are then sent to machining.
FINAL MACHINING: The cleaned parts are machined to accurate dimensions in this stage. Various machined used for this are
Various operations are made by these machines and the dimensions are brought to required sizes.
Usually here the following components are prepared
INSPECTION: After machining the components are sent for inspection. This inspection includes testing of hardness, tensile strength and few other mechanical. Inspection also includes checking of dimensions using gauges.
DISPATCHING: After inspection, the components are packed and finally sent to the costumer. ia.org/wiki/Silicon 2.2 to 2.8%
MELTING: Melting of the metal is done in induction furnace. Main purpose of induc