Introduction of Casting Processes

FLUID FLOW IN CASTING FOR THE SUCCESSFUL CASTING AND

CONTROL OF THE SOLIDIFICATION PROCESS IT REQUIRES ADEQUATE FLUID (MOLTEN METAL AND ENTRAPPED GASES) FLOW IN THE SYSTEM.

Open and Closed Mould

The Gating System A: pouring basin B: Weir C: Sprue D: Sprue well E: Runner F: Ingates G: Runner break up H: Blind J: Riser

Pattern geometry

Pouring basin

DESIGN OF SPURE

DESIGN OF SPURE RELATIONSHIP BETWEEN HEIGHT AND ANY CROSS

SECTIONAL AREA AT ANY POINT IN THE SPURE IS GIVEN BY

A1/A2 = (H2/H1)^(.5)

THE BASIC FUNCTION OF THE GATING SYSTEM IN SAND CASTING IS TO TRAP CONTAMINANTS (SUCH AS OXIDES AND OTHER INCLUSIONS) IN THE MOLTEN METAL BY HAVING THE CONTAMINANTS ADHERE TO THE WALLS OF GATING SYSTEM

DESIGN OF RUNNER

Location of Risers and Open and Closed Risers

•Top riser has the advantage of additional pressure head and smaller feeding distance over the side riser.

•Blind risers are generally bigger in size because of additional area of heat conduction.

Why Riser? The shrinkage occurs in three stages,

1. When temperature of liquid metal drops from pouring to zero temperature

2. When the metal changes from liquid to solid state, and3. When the temperature of solid phase drops from freezing

to room temperature The shrinkage for stage 3 is compensated by providing shrinkage

allowance on pattern, while the shrinkage during stages 1 and 2 are compensated by providing risers.

The riser should solidify in the last otherwise liquid metal will start flowing from casting to riser. It should promote directional solidification. The shape, size and location of the risers are important considerations in casting design

TYPES OF GATE TOP GATE BOTTOM GATE PARTING GATE STEP GATE

TOP GATE

Use of chaplets to avoid shifting of cores

Possible chaplet design and casting with core

Use of chills

The Gating System1. Minimize turbulent flow so that absorption of

gases, oxidation of metal and erosion of mould surfaces are less

2. Regulate the entry of molten metal into the mould cavity

3. Ensure complete filling of mould cavity, and4. Promote a temperature gradient within the casting

so that all sections irrespective of size and shape could solidify properly

PERMEABILITY OF THE WALLS PERMEABILITY OF THE WALLS IS

IMPORTANT BECAUSE OTHERWISE LIQUID WILL PERMEATE THROUGH THE WALLS AND FLOW RATE WILL DECREASE AS THE FLUID WILL FLOW.

Cleaning and Finishing1. Casting is taken out of the mould by shaking and the

Moulding sand is recycled often with suitable additions.2. The remaining sand, some of which may be embedded

in the casting, is removed by means of Shot blasting.3. The excess material in the form of sprue, runners,

gates etc., along with the flashes formed due to flow of molten metal into the gaps is broken manuaaly in case of brittle casting or removed by sawing and grinding in case of ductile grinding.

4. The entire casting is then cleaned by either shot blasting or chemical pickling.

5. Sometimes castings are heat treated to achieve better mechanical properties.