1
Q
Casting
A
- process -of casting a Liquid Metal to fill a cavity and solidify into a useful shape
- with few exceptions all materials used in metal manufacture is cast at some point in its processing
- RT typically used for volumetric inspection, but UT used to measure thickness, NR used to detect residual waste
2
Q
Pattern
A
- Pattern chosen to represent the finished product, always the shape of the finished part, with slightly oversized dimensions of the finished part, with slightly oversized dimensions to allow for shrinkage
3
Q
Mold
A
- Some processes mold made to flow into close contact with the pattern
- Pattern may have attachment that serve as channels for flow of materials if not they have to be made. Called channels or runners
- opening outside the mold called a sprue
4
Q
Progressive solidification
A
- freezing of a liquid from the outside towards the center
5
Q
Directional solidification
A
- Frezing from one part of the casting to another such as from one end to the other end
6
Q
Hot spots
A
- highest temp areas after pouring are called hotspots
- located to sources of feed metal
- may disturb good directional solidification with results that shrinks, porosity, cracks, ruptures
- located at spots of greatest sectional dimensions
7
Q
Pouring
A
- usually performed by using ladles to transport the hot metal to the molds
8
Q
Cold shots
A
- Drops of splashing metal lose heat, freeze, and are then entrapped as globules that did not join completely with the metal
9
Q
Cold shut
A
- thin sections that cool too rapidly in contact with the mold may freeze off before the metal travels its complete path or metal flowin in one direction may solidify and then be met by metal flowing through another path
10
Q
gating system
A
- Metal is fed into the cavity that shapes the casting through a gating system consisting of a pouring basin, down sprue, runners and ingates.
11
Q
Risers
A
- Risers, feeders or feed heads serve as wells of materials attached outside the casting, proper to supply Liquid Metal as needed to compensate for shrinkage before solidification is complete
12
Q
Chills
A
- help with directional solidification, chills which are heat absorbing devices inserted in the mold near the cavity
- also improve physical properties
13
Q
Internal chills
A
- become integral part of the casting are occasionally used to speed solidification in areas where external chills cannot be applied
- same material as casting
- RT is used to detect for infused internal chills
14
Q
Shrinkage 3 stages 1. Shrinkage in the liquid
A
- metal is always heated well above the melting temperature called superheat
- superheat allows metal to be transferred and to contact cold equipment without starting to freeze, sufficient time will elapse before freezing occurs
15
Q
- Solidification shrinkage
A
- Transformation from liquid to solid most materials denser as solids than liquids water exception
- metal contracts as they change from liquid to solid
16
Q
- Contraction in the solid state
A
- primary cause of dimensional change to a size different from that of the pattern used to make the cavity in the mold’
- main element of patterns maker shrinkage which must be allowed for by making the pattern oversized
17
Q
Microporosity/ micro shrinkage
A
- Localized shrinkage will develop minute random voids
- can cause a reduction in density and tend to reduce the apparent shrinkage that can be seen on the surface of the casting
18
Q
macroporosity
A
- Porosity of a casting may be amplified by the evolution of the gas before and during solidification
- may form packets or bubbles of its own or may enter the voids of microporosity to enlarge
19
Q
Cupola
A
- special chimney like furnace, similar to the blast furnace used to melt cast iron
20
Q
Crucible furnaces
A
- melting of small quanties 1 to 100 lbs of non ferrous materials is often performed
21
Q
Pot furnaces
A
- quantities of non ferrous materials to several hundred kilograms may be melted in pot furnaces that contain a permanently placed crucible
22
Q
Electric arc furnaces
A
- provides a high intensity heat source that can be used to melt any metal that is commonly cast
- quality of cast metal is high
- arc may be direct between electrode and charged metal or indirect two electrodes above the charge
23
Q
Induction furnace
A
- melts material with the heat dissipated from eddy currents
24
Q
Foundry mechanization
A
- anytime production quantites justify the needed expenditure for equipment, same techniques are subject to almost complete mechanization resulting in higher production rates and improved consistency
25
metal mold and special proceses
* metal patterns and metal core boxes are used in connection s with molding whenever the quantites manufactured justify the additional expense of the longer wearing patterns
26
Continuous casting
* only a small tonnage of castings are produced by continuous casting it is possible to produce 2D shapes in an elongated bar by drawing solidified metal from a water cooled mold
* BAR form cut into billets
27
Sand Molding
* Most commonly used material for construction of molds
28
Procedure for sand molding
* sand: main structural material for the mold
* Pattern: to form a properly shaped and sized cavity
Flask: contain sand around the pattern provide a means to remove the pattern after mold made
* ramming method: compact the sand
* core: to form internal surfaces on the part
* mold gating system: provide means for filling the mold casting with metal at the proper rate and to supply Liquid Metal
29
Green sand
* Green refers to moisture, mixture of sand, clay and moisture
* In the mold, sand particles are bound together by clay
* Clay content can be varied as 2 to 3 percent to 50 %
* water the third component optimum quantity will vary about 2 to 8 percent by weight
30
Patterns
* constructed slightly larger than the expected resulting part to allow for shrinkage of the Liquid Metal
* must be constructed with suitable draft angles to facilitate removal from the mold medium
* flat back: largest 2 dimensions in one pane
* split: separates to form flat back patterns
* Irregular parting: separation along two or more planes for removal of the pattern
31
Flasks
* open faced containers that hold the molten medium as it is packed around the pattern
* constructed of two parts the cope ( upper) and the drag (lower)
* permanent flasks: remain around the sand until pouring is complete
* removable flask: snap flask hinged corners can be unwrapped
Pop off: expanded on two diagonal corners to length and width
Slip Flask: movable sand strips that project inside to obstruct sliding, jackets are placed to maintain alignment
32
Sand compaction manual ramming
* peen and butt rammer used
* peen ramming involves the use of a rib shaped edge to develop high impact pressure and used to pack sand between narrow vertical walls and around the edges of the flask
* butt ramming is done with a brander faced tool for more uniform compaction of the sand
33
Jolt compaction
* Lifting of the table carrying the mold and dropping git against a solid obstruction
* tends to pack the sand more tightly near the parting surface
34
Squeeze compaction
* applied by pushing a squeeze plate against the outside of the sand tends to pack the sand more tightly at the surface
35
Slingers
* Foundaries that manufacture quantities of large castings often use sand slingers to fill and compact the sand in large floor molds
36
Cores
* are batches of mold material, usuallly in the form of inserts that exclude metal flow to form internal surfaces in a casing
* dry strength of a finished core must be sufficient enough to withstand it own weight without sagging the mold and strong enough
* collapsibility important
* RT is frequently used to determine whether or not the core shifter during casting or if all the ore got removed
37
Chaplets
* very large or long, slender cores that might give away under pressure of the flowing metal are given support through chaplets.
* small metal supports with broad surfaced ends usually made from the same metal
* become part of the casting after they serve their function of supporting cores while the material is liquid
* RT is sued to see if it fused or any other internal discontinuity
38
Dry sand mold
* made of green sand modified to favor the dry properties and then dried in an oven
* used mainly when steam formation from the moisture is present would be a serious problem
* skin drying to the depth from a fraction of a centimeter to 25CM
39
Shell Molds
* Dimensions can be held within a few hundredths of a millimeter 1000 of an inch in many cases eliminate or reduce machining
* san bobded with thermosettin plastic
* cured at baking at 300C 572F
* shell thin 3mm
40
Expendable plaster mold casting
* casting cools slowly
* molds made of plaster of Paris with addictives such as talc, asbestos, silica, flour, sand and other materials to vary mold properties used with non ferrous materials
41
Investment (lost wax ) casting
* working pattern is destroyed
* duplicated part starts with a master pattern
* limited to small castings
* high quality but expensive
42
Lost foam casting
*Foam such as polystyrene used instead of wax
* foam cast the polystyrene is fully burned out of the mold before the metal is poured
* should not be used where carbon pickup is not acceptable achieve tolerance .005 to .010 inch
43
Die casting
* similar to that used for permanent molding
* pressure is applied to the Liquid Metal to cause it to flow and uniformly into the cavity of the mold or die
44
Hot chamber die casting
* keeps metal melted in a chamber through which a piston moves into a cylinder ro build up pressure forcing the metal into the die
* machines limited to low pressures
45
Cold chamber die casting
* molten metal is poured into the shot chamber and the piston advances to force the metal into the die
* alu, copper, and magnesium alloys are die cast by this method with liquid pressures as high as 210 MPA
* casting quality is high, but cannot be used for very high strength materials
46
True Centteifrugal casting hallow product
* Shapes the outside of the product with a mold but depends upon centrifugal force developed by spinning the mold to from the inside surface by the liquids metal to assume a cyndrical shape
* principal product was cast iron sewer pipe
* also used for shafts, propellers, columnar grain structure may produce problems
47
Semi centrifugal casting solid products
* density of a casting made this way will vary with dense strong meta around the outside and more porous weaker metal at the center
* wheels , pulleys , gear blanks and other shapes of this kind may be made in this way to obtain max metal properties near the outside periphery
48
Centrifuge casting- multiple
* number of equally spaced mold cavities are arranged in a circle about a central pouring sprue
* may be single or stacked with a number of layers arranged vertically about a common sprue
49
Permanent molds
* may be reused many times, used most fir the shaping of aluminum, copper, magnesium and zinc alloy
* high accuracies and good finishes
* plus or minus 2.5mm
* process is sued to manufacture automobile cylinder heads, pistons, low hp engine connection rods and many more non ferrous castings
50
Single crystal production
* used to produce silicon wafers for semi conductors
* Crystal growth starts at the surface
* with temp gradients being small, growth may occur on the sides of these columns producing structures known as dendrites seals off small pockets of liquid to freeze later
* grain characteristics influenced by cooling rates
51
Eutectic alloy
* One for which solidification takes place at a single temp that is lower than that for the individual component of the alloy
52
Non eutectic alloys
* freeze over a temp range
* dendritic growth is much more evident in the non eutectic alloy than in the pure metal, segregation shows up readily
53
Imperfections in sand casting
* hot tears- cracklike that occur when the material starts to contract during the initial cooling phase just below solidification temp
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