Post on 28-Dec-2015
transcript
Metal Casting
ISAT 430
Spring 2001 ISAT 430 Dr. Ken Lewis 2Module 5
Metal Casting Casting is an ancient art
More intricate shapes can be made by casting then by hammering
First metals cast were probably gold and copper. Cu melts at 1084° C Au melts at 1064° C
Egyptians were expert at investing or “lost wax” casting Allowed small intricate shapes to be cast.
Spring 2001 ISAT 430 Dr. Ken Lewis 3Module 5
Metal Casting2
Bronze casting
Made when people realized that copper tin alloys cast much easier than copper alone.
The Dark Ages (the fall of Rome {400 CE} until about 1400 CE)
All minds turned to finding and understanding the Spiritual nature of man
Bronze casting of bells became important Over time, they found the purity of the sound came from the
purity of the casting Size, shape, thickness, thinness Chemical composition.
Spring 2001 ISAT 430 Dr. Ken Lewis 4Module 5
Metal Casting3
Cannons First cannon was made by a monk!
Ghent, Belgium 1313 CE Made of bronze
The bore was part of the cast and was rough Very inaccurate Found that accuracy went up in proportion to the
smoothness of the bore Started machining the bore surface
This act today is called “boring” Hmmm.
Spring 2001 ISAT 430 Dr. Ken Lewis 5Module 5
Metal CASTING
Before we can discuss casting
We
Must first digress into
PHASE DIAGRAMS
Spring 2001 ISAT 430 Dr. Ken Lewis 6Module 5
Phase diagrams A phase diagram is a graphical representation of the
phases present and the ranges in composition, temperature, and pressure over which the phases are stable.
Remember: A phase is the part of a system which is chemically
and physically homogeneous throughout and is separable from other portions of the system by bounding surfaces
Spring 2001 ISAT 430 Dr. Ken Lewis 7Module 5
Phase diagrams2 –what is displayed Shows the phases present at difference compositions and
temperature under slow cooling or equilibrium conditions.
Indicates equilibrium solid solubility of one element (or compound) in another.
Indicates the temperature an alloy will start to solidify and the temperature range of solidification.
Indicates the temperature phases start to melt.
Equilibrium Conditions
Spring 2001 ISAT 430 Dr. Ken Lewis 8Module 5
Phase diagrams3 –what is displayed Keep in mind
Equilibrium phase diagrams are determined using slow cooling conditions.
In most cases equilibrium is approached but never fully attained.
Equilibrium Conditions
Spring 2001 ISAT 430 Dr. Ken Lewis 9Module 5
Phase diagram of pure water Water can exist as solid,
liquid or vapor. In the pressure-temperature
(PT) there exists a triple point at a P = 4.65 mm Hg and T = 0.0098°C. Here all three phases
coexist!
Spring 2001 ISAT 430 Dr. Ken Lewis 10Module 5
Phase diagram of pure water2
Liquid and vapor exist along the vaporization line
Solid and liquid exist along the freezing line.
These lines are two phase equilibrium lines.
Spring 2001 ISAT 430 Dr. Ken Lewis 11Module 5
Binary Phase Diagram Cu – Ni is one of the simplest cases. Composition is plotted on the x – axis Temperature is plotted on the y - axis
Spring 2001 ISAT 430 Dr. Ken Lewis 12Module 5
Copper – Nickel Alloy System Solid solution throughout the
entire composition range. Anywhere below the
solidus line the alloy is a solid solution
Anywhere above the liquidus line the alloy is a liquid solution.
Between the liquidus and solidus lines the metal is a mixture of solid and liquid phases.
Spring 2001 ISAT 430 Dr. Ken Lewis 13Module 5
Determination of the Chemical Composition of Phases and Their Relative Amounts in a Mixture
Draw a horizontal tie line. If we start with 60% B
At temperature V The solid will be 80%
B, 20% A The liquid will be
26% B, 74% A When the melt is
complete, the liquid will be all 60% B.
Spring 2001 ISAT 430 Dr. Ken Lewis 14Module 5
Change in the Microstructure of Cu-40 wt.%Ni Alloy During Equilibrium Solidification
Spring 2001 ISAT 430 Dr. Ken Lewis 15Module 5
Amount of a phase present Inverse lever rule
CSL phase present =
CS + CL
CLS phase present =
CS + CL
Spring 2001 ISAT 430 Dr. Ken Lewis 16Module 5
Important Metals Ferrous Non – ferrous
Aluminum & its alloys Magnesium & its alloys Nickel & its alloys Titanium & its alloys Zinc & its alloys Lead & Tin Refractory metals Precious metals
Super alloys
Spring 2001 ISAT 430 Dr. Ken Lewis 17Module 5
Ferrous Metals -based on ironIron
Symbol: Fe
Atomic Number: 26
Specific gravity: 7.87
Crystal structure: BCC
Tm: 2801°F (1539°C)
Modulus of Elasticity E: 30 x 106 lb/in2
Ores: Hematite (Fe2O3)
Applications: Construction, machinery, automotive, railways, etc.
Spring 2001 ISAT 430 Dr. Ken Lewis 18Module 5
Ferrous metals Two major groups
Steel Cast iron
Spring 2001 ISAT 430 Dr. Ken Lewis 19Module 5
Iron - Carbon also called ferrite also called austenite called delta iron Fe3C is called cementite
Not an alloy
Spring 2001 ISAT 430 Dr. Ken Lewis 20Module 5
Iron - Carbon
Percent Carbon Material
<0.008 Iron
0.008 – 1.6 Steels
1.6 – 2.1 Semi steels
2.1 -- ~4 - 5 Cast irons
Spring 2001 ISAT 430 Dr. Ken Lewis 21Module 5
Spring 2001 ISAT 430 Dr. Ken Lewis 22Module 5
Expendable Mold Processes
Sand Casting
Investment (“Lost wax”) Casting
Spring 2001 ISAT 430 Dr. Ken Lewis 23Module 5
Sand Casting Mold is made of green sand (“Green” means that it is
not fired or melted in a furnace) Can withstand the temperatures and pressures of
molten steel. Basic ingredients
SiO2 silica sand A binder clay
Spring 2001 ISAT 430 Dr. Ken Lewis 24Module 5
Sand Casting Mold is made of green sand (“Green” means that it is
not fired or melted in a furnace) Basic properties
Ability to withstand high temperatures Ability to retain shape under the action of metal flow Permeability
Able to pass gases and vapors developed during casting Collapsibility
Allows the mold to be broken up and separated from the casting.
Spring 2001 ISAT 430 Dr. Ken Lewis 25Module 5
Sand Casting Mold Mold is made in a box called a
‘draft’. Bottom part is called the ‘drag’ Top part is called the ‘cope’. The pattern is made of wood,
plastic or metal Sand cores determine the shape
of external cavities Must be stronger than the sand
of the primary mold Must support buoyancy forces
Spring 2001 ISAT 430 Dr. Ken Lewis 26Module 5
The Part The iron casting to be made
in the process Note internal holes
Spring 2001 ISAT 430 Dr. Ken Lewis 27Module 5
The Mold1
Bottom half of the pattern is on the mold board Surrounded by the
bottom or drag half of the flask
May be made by hand or by a jolt machine
Notice the pattern is solid with no holes.
Spring 2001 ISAT 430 Dr. Ken Lewis 28Module 5
The Mold2
Molding Sand is added Tamped or rammed in
multiple layers Need even density so there
is no preferential metal movement.
Tamp
Spring 2001 ISAT 430 Dr. Ken Lewis 29Module 5
The Mold3
After bottom half of mold is filled Top half of pattern is put
in place Top half of the flask is
installed More sand is added and
tamped in place.
Spring 2001 ISAT 430 Dr. Ken Lewis 30Module 5
The Mold4
Section through the mold
The pattern is still in place
The sprue hole has been formed for the entrance of the molten metal.
Spring 2001 ISAT 430 Dr. Ken Lewis 31Module 5
The Mold5
The cope and drag halves of the mold are separated.
The pattern is removed
The gate channel is cut from the sprue to the mold cavity
Spring 2001 ISAT 430 Dr. Ken Lewis 32Module 5
The Mold6 – the core of bonded sand This is the core of the part
It will form the holes in the casting.
This is the core that must withstand the buoyancy forces.
It is carefully placed in the mold.
Spring 2001 ISAT 430 Dr. Ken Lewis 33Module 5
The Mold7 – the finished touch After placing the core in the
mold It is closed and clamped The molten metal is
poured into the mold.
The metal cools The mold is opened and the
part is removed. Finishing means removal
of the channel, etc.
Spring 2001 ISAT 430 Dr. Ken Lewis 34Module 5
Some Impressive Castings
Spring 2001 ISAT 430 Dr. Ken Lewis 35Module 5
V8 cylinder block
Spring 2001 ISAT 430 Dr. Ken Lewis 36Module 5
Six wheel motor truck frame
DieselLocomotive
Spring 2001 ISAT 430 Dr. Ken Lewis 37Module 5
1.5 m Stainless Steel Propeller
MaritimeUse
Spring 2001 ISAT 430 Dr. Ken Lewis 38Module 5
107 m3 Shovel Shoes38 shoes per
assembly
4 assemblies pershovel
Total cast weight333 tons
Spring 2001 ISAT 430 Dr. Ken Lewis 39Module 5
Most Impressive!
BUDDHAat the Po Lin Monastery
on Lantau Island
Spring 2001 ISAT 430 Dr. Ken Lewis 40Module 5
His head isone
piece
Spring 2001 ISAT 430 Dr. Ken Lewis 41Module 5
Spring 2001 ISAT 430 Dr. Ken Lewis 42Module 5
Investment Casting Also known as the “lost wax” process
First used during the period 4000 – 3000 BCE Medieval Italy
Cellini’s golden rings (with miniature sculptures on them)
The pattern (exactly as the part will look) is made of wax or plastic Made by injecting molten wax into a metal die in the
shape of the pattern
Spring 2001 ISAT 430 Dr. Ken Lewis 43Module 5
Investment Casting1
The pattern is first made of Wood Metal Plastic
Material is whatever will allow the craftsman to create the detail desired.
The pattern is made into a mold.
The mold is injected with wax which reproduces the pattern.
Spring 2001 ISAT 430 Dr. Ken Lewis 44Module 5
Investment Casting2
Once the wax cools, the pattern is retrieved.
The pattern is usually both temperature and touch sensitive.
Spring 2001 ISAT 430 Dr. Ken Lewis 45Module 5
Investment Casting3
The master mold makes many patterns.
These are assembled onto a casting “TREE”
The TREE is ready then to receive the outer coatings
Spring 2001 ISAT 430 Dr. Ken Lewis 46Module 5
Investment Casting4
Slurry coating This is a slurry made of
fine silica and binders Water Ethyl silicate
Coating is dried Process is repeated again
and again to build up the mold.
SlurryA watery mixture of insoluble matter
Here: silica, H2O and additives
Spring 2001 ISAT 430 Dr. Ken Lewis 47Module 5
Investment Casting5
The coating is applied again and again The first coatings are
fine grained silica or other refractory material
Almost a powder Provides a smooth
surface to the final casting.
The coating material used is coarser and coarser Building up the strength
of the mold.
Spring 2001 ISAT 430 Dr. Ken Lewis 48Module 5
Investment Casting6
Finally we get the completed mold
There is a common sprue in the middle
The mold is free standing and somewhat delicate
It is still full of wax.
Spring 2001 ISAT 430 Dr. Ken Lewis 49Module 5
Investment Casting7
The one piece mold is held in air and heated to 90° -- 175°C The wax flows out Takes about 12 hours
The wax can be recycled The mold is then fired to
650° -- 1050°C to drive off water Burn off residual wax
Spring 2001 ISAT 430 Dr. Ken Lewis 50Module 5
Investment Casting8
The mold is inverted and placed in a support vessel.
The mold is preheated to a high enough temperature eliminates residual
contaminants. The liquid metal flows
more easily. The liquid metal/alloy is
poured
Spring 2001 ISAT 430 Dr. Ken Lewis 51Module 5
Investment Casting9
Shakeout The system is cooled The mold is broken away
The mold is destroyed.
Spring 2001 ISAT 430 Dr. Ken Lewis 52Module 5
Investment Casting10
The finished product.
Spring 2001 ISAT 430 Dr. Ken Lewis 53Module 5
Investment Casting Example
Spring 2001 ISAT 430 Dr. Ken Lewis 54Module 5
Investment Casting -- Advantages Cast great complexity and intricacy Close dimensional control
Tolerances of ±0.003 in (±0.076 mm) Good surface finish The wax can be recovered This is a net shape process
Spring 2001 ISAT 430 Dr. Ken Lewis 55Module 5
Investment Casting Possibilities - Constraints
Parts are usually small in size Finished products up to around 75 lbs.
Many steps, so relatively expensive. Amenable for most alloy and metal systems
Noble metals Steels Stainless steels Super alloys