1. Gating system & casting Processes
LECTURE :- 9
UNIT
Gating system & casting Processes
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2. CHAPTER 2:- SYLLABUS Pouring basin, Sprue, choke, runner, ingrate 1
Function
Trap contaminants
Regulate flow of molten metal
Control turbulence
To establish directional solidification . 1 2 3 4 5
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3. CHAPTER- SPECIFIC Objective / course outcome
The student will be able to:
Understand the gating design. 1
furnaces.. 2
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4. Design of gating system
LECTURE :- 9
Design of gating system
Design of gating system
Pouring cup
Cut into cope
Large enough to keep the sprue full
Skim core to provide clean metal
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5. Gating and Riser design
LECTURE :- 10
ELEMENTS
Gating and Riser design
Vena cotracta
Molten metal h1 h2
mold
Aspiration at point 2
Vacuum generation
Pseudo Vena contracta
Prevents vacuum
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6. Rise ring LECTURE :- 9 DTEL Cube Plate
Solidification time for steel castings different shapes in green sand
Cylinder is insulated at ends
Risering a cube and plate
Both castings have equal freezing times yet the riser which is adequate to feed the cube is not adequate to feed the plate
Riser is 4” in dia. Cube is 4” side and plate is 8”x8”x2”
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7. Riser design: Caine’s Method
LECTURE :-9
Riser design: Caine’s Method
Relative riser and casting geometry to obtain sound steel castings
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8. LECTURE :-10 DTEL Riser 1.00 Riser on Plates and large A/V casting
Sound
4.5 t
Vr/Vc t
Defective
0.00
(l+w)/h
4 t t
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9. Furnaces for Casting Processes
LECTURE :-11
Furnaces for Casting Processes
Apart from the type of alloy being produced, selection of equipment for melting and casting must depend upon economic factors. These include the balance between cost and quality requirements for particular classes of casting, and the nature of the demand for molten metal as determined by the pattern of production.
There are numerous types of furnaces used for Casting Processes, however, the most commonly furnaces used in foundries are:
− Cupolas
− Crucible furnaces
− Electric-arc furnaces
− Induction furnaces
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10. Cupola Furnace LECTURE :-
Vertical cylindrical furnace equipped with tapping spout near base
used only for cast irons, and although other furnaces are also used, largest tonnage of cast iron is melted in cupolas
The "charge," consisting of iron, coke, flux, and possible alloying elements, is loaded through a charging door located less than halfway up height of cupola
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11. (c) tilting-pot furnace
LECTURE :- 12
Crucible Furnaces
Metal is melted without direct contact with burning fuel mixture
Sometimes called indirect fuel-fired furnaces
Container (crucible) is made of refractory material or high-temperature steel alloy
Used for nonferrous metals such as bronze, brass, and alloys of zinc and aluminum
Three types used in foundries: (a) lift-out type, (b)
stationary, (c) tilting
Three types of crucible furnaces: (a) lift-out crucible, (b) stationary pot, and
(c) tilting-pot furnace
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12. Electric-Arc Furnaces
LECTURE :- 13
Electric-Arc Furnaces
Charge is melted by heat generated from an electric arc
High power consumption, but electric-arc furnaces can be designed for high melting capacity.
Used primarily for melting steel
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13. Metal Casting Processes
LECTURE :- 14
Casting defects &foundary mechanizing
Metal Casting Processes
Introduction
Sand casting
Shell-Mold Casting
Expendable Pattern Casting
Plaster-Mold Casting
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14. Die Casting Examples LECTURE :- 15 DTEL
A permanent mold casting process in which molten metal is injected into mold cavity under high pressure. Pressure is maintained during solidification, then mold is opened and part is removed Molds in this casting operation are called dies; hence the name die casting Use of high pressure to force metal into die cavity is what distinguishes this from other permanent mold processes
Fig 11.1 (a) The Polaroid PDC-2000 digital camera with AZ91D die-cast, high purity magnesium case. (b) Two-piece Polaroid camera case made by the hot-chamber die casting process
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15. Hot-Chamber Die Casting
LECTURE :-
Hot-Chamber Die Casting
Figure Cycle in hot‑chamber casting: (1) with die closed and plunger withdrawn, molten metal flows into the chamber
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16. Advantages of Hot Chamber Die Casting
LECTURE :-16
Advantages of Hot Chamber Die Casting
Improved productivity
Superior surface finish
High tolerance
Intricate shapes with thin walls can be easily produced
Limitations
Only low melting alloys (such as Zn, Sn, Pb) are cast
Small castings weighing less than 4.5 kg can be cast
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17. Cold‑Chamber Die Casting
LECTURE
Cold‑Chamber Die Casting
Figure Cycle in cold chamber casting: (1) with die closed and ram withdrawn, molten metal is poured into the chamber
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18. LECTURE 1:- NUMBER SYSTEM
Cold chamber die casting suitable for casting of
Aluminum alloy
Mg alloys
Brass etc
Pressure applied in cold chamber die casting method can be
as high as 2000 atmospheres
Advantages
high temperature metals and alloys can be cast
large parts (weighing around 25 kgs) can be cast
high surface finish ( 1 m) and dimensional tolerance
better mechanical properties of the casting because of the fine grains
large cycle time
metal sometimes looses the superheat and cause defects such as
“cold shut”
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19. Shell-Mold Casting LECTURE 1:- 16 Developed in the 1940’s
(b) Pattern and dump box rotated
(c) Pattern dump box in position for the investment
(d) Pattern and shell removed from dump box
Developed in the 1940’s
Produces close dimensional tolerances
Good surface finish
Low cost process
Common methods of making shell molds.
(a) Pattern rotated and clamped
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20. Advantages of Shell Mould Casting
LECTURE :- 16
Advantages of Shell Mould Casting
Good surface finish (Ra 1.25 to 3.75 microns)
High dimensional tolerance
Amenable towards automation
Castings weighing up to 450 kgs can be cast by this process
Thin sections (up to 0.25 mm) can be cast by this process
Limitations
Patterns are expensive
Castings weighing more than 450 kgs cannot be made
Highly complicated shapes cannot be made
Applications
Cast iron, Aluminum and copper alloys are cast by this process
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21. LECTURE 16
Investment Casting
A refractory material (investment) is poured around or built up on a pattern
The investment is hardened by drying or heating
The pattern is removed by melting or burning
Metal is poured into the resulting cavity
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22. LECTURE 16
Investment Casting
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23. Applications of Investment Casting
LECTURE 16
Applications of Investment Casting
Intricate shaped objects like jewelry
Cylinder heads
cam shafts
gas turbine blades
Advantages of Investment Casting Process
Complicated and intricate shaped products can be easily cast
High dimensional tolerance achievable
Surface finish is excellent
Additional machining not required as it is a net shape process
All types of metals and alloys can be cast by this process
Limitations
A relatively expensive process
Size of the casting is limited (max. around 5 kg)
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24. LECTURE 16
Centrifugal Casting
A family of casting processes in which the mold is rotated at high speed so centrifugal force distributes molten metal to outer regions of die cavity
The group includes:
True centrifugal casting
Semicentrifugal casting
Centrifuge casting
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25. True Centrifugal Casting
LECTURE 16
True Centrifugal Casting
Figure Setup for true centrifugal casting.
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26. Semicentrifugal Casting Process
LECTURE 16
Semicentrifugal Casting Process
(a) Schematic illustration of the semicentrifugal casting process.
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27. LECTURE 16
Centrifuge Casting
Mold is designed with part cavities located away from axis of rotation, so that molten metal poured into mold is distributed to these cavities by centrifugal force
Used for smaller parts
Radial symmetry of part is not required as in other centrifugal casting methods
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28. LECTURE 16 blow Surface Defects scar drop scab penetration
Classification of casting defects
blow
scar
drop
scab
penetration
Surface Defects
Internal Defects
blow/gas holes
porosity
pin holes
inclusions and dross
hot tear
shrinkage
mold shift
core shift
Visible Defects
rat tail
swell
misrun
cold shut
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29. DEFECTS IN CASTINGS LECTURE 16 Surface and internal defects DTEL
Molding sand too too fine
or heavily rammed
Sand erosion
Low permeability
Poor venting, high moisture
Hydrogen inclusion
Buoyancy of liq. metal
Inadequate packing
High fluidity
Poor mold strength
Surface and internal defects
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