We know that casting is the process of pouring molten metal in a desired shaped cavity and allowing it to solidify. After the solidification we get the desired shaped object.
Basic Operation of the casting process
- First we have to make a pattern
- Then the we have to melt the metal by applying heat
- pouring the metal into the mold and confirming that the metal gets the desired shape.
What is Pattern in Casting Process
Pattern is the object used to make cavity in the mold. The molten metal is poured into this cavity.
Why a good Pattern is required in casting ?
- To obtain the desired shape and size.
- It is easy to design and manufacture.
- making a pattern is not expensive.
- It is of high strength.
Pattern Materials
- Wood
- Cast Iron / Brass
- Aluminum or White metal
- Plastic gypsum
Pattern Allowances
- Shrinkage allowance (due to cooling)
- Machining allowance (due to machining)
- Shaking allowances (due to rapping)
- Draft allowance (follow the link)
- Distortion allowance (due to irregular shape)
Different Types of Patterns used in Casting
- Split piece pattern
- Match plate pattern
- cope and drag patterns
- sweep patterns
- draw backs
- Loose piece pattern
- Gated pattern
Preparing Mould for the Casting
While preparing mould one should be very careful . Different types of sands and binders are used in mould preparation. These are
Green sand mould: Natural sands , clay and water is used in making green sand mould. It is very cheap with acceptable errors.
Dry Sand Mould: It is natural sand mould with cereal and pitch used binders.
Other materials for mould preparation includes silica sand and binder with additives.
Different Properties of the moulding sand
These are the desired properties of the moulding sand
- Refractoriness
- Cohesiveness
- Permeability
- Co-efficient of expansion
- Adhesiveness
- Collapsibility
- Plasticity
Tests for the different moulding sands
- Moisture Content Test
- Fineness Test
- Testing Amount of Clay
- Permeability Test
- Mould hardness test
- Strength or cohesiveness test
Core Making
What is Core ?
It is a structure made of refractory material . It is prepared before pouring the molten metal on to the cavity. There is another term known as core print which is the projection on a pattern used to make spaces in the mould. It is also known as core seat.
Criteria for selecting a furnace for casting
- Capacity needed to hold the molten metal
- Melting rate
- Quality of the melt
- Temperature needed
- Method of pouring
Operation in Cupola Furnace
Cupola is the most popular furnace for casting non ferrous and ferrous materials . It is known as a shaft furnace. The shell of cupola furnace is made of steel of 8-10 mm thickness. The shell is supported by columns or legs. The inside of the furnace is lined with refractory material to save the furnace from over heating.
Different types of casting processes
- Sand Casting
- Shell Mold Casting
- Expandable Mold Casting
- Plaster Mold
- Ceramic Mold
- Investment Mold or Lost Wax Casting
- Permanent Mold
- Die Casting
- Centrifugal casting
Casting Defects
And lastly comes the casting defects. These defects can occur for different reasons like air trapping in the sand mold, low quality sands, improper ramming , defecting sand mold etc. Go through this link for detailed knowledge of casting defects.
- Different types of casting defects
Original Source: http://mechanicalinventions.blogspot.com/2016/02/steps-involved-in-casting-process.html
September 12, 2018
Categories:
