Fundamentals of casting Chapter 13

misruns and cold shuts

When metal begins to freeze before it has completely filled the mold, defects known as ____ and ____ are produced.

inoculation

practice of introducing solid particles

consolidation processes

process developed to facilitate the joining or assembly; examples include welding, brazing, soldering, and the use of discrete fasteners, such as nuts, bolts, screws, and rivets

exothermic material

surrounding the sides or top of the riser with _______ ________ that supplies added heat just to the riser segment of the mold. helps slow the cooling process of the risers. Used to reduce the risers size rather than promote directional solidification.

draft

term used to describe the taper on a pattern of casting that permits it to be withdrawn from the mold.

direct digital manufacturing

3D printing

fillets

A curved surface formed at the intersection of two surface, a rounded edge.

cope

In a horizontally parted two-part mold, it is the top half of the pattern, flask, mold, or core

fluidity

"runniness" of the liquid

dead risers

(also known as cold risers) fill with metal that has already flowed through the mold cavity

live risers

(also known as hot risers) receive the last hot metal that enters the mold and generally do so at a time when the metal in the mold cavity has already begun to cool and solidify

pattern

A physical representation of the object to be cast, modified dimension-ally to reflect both the casting process and the material being cast

single use mold

An economically feasible solution for molding productions of smaller quantities.

sprue

Channel through which molten metal is fed into a mold

turbulent flow

Irregular flow with random variations in pressure. which promotes absorption of gases, oxidation, of the metal, and erosion of the mold

multiple use mold

Made of metal or graphite. Use is generally restricted to products where large quantities are desired for repeated use.

material removal

Part of the casting family. Processes remove selected segments from an initially oversize piece.

cooling rate

Rate at which the liquid or solid is cooling; can be viewed as the slope of the cooling curve at any given point

top riser

Sits on top of a casting and serves as a reservoir for molten metal. The metal in this area will fill in any cracks or space due to shrinkage in the solidifying of the metal.

choke

Smallest cross-sectional area in gating sysem, serves to control the rate of metal flow.

vacuum degassing

Sprays the molten metal through a low-pressure environment and under these conditions the amount of dissolved gas is reduced as the material seeks to establish equilibrium with its new surroundings

solidification

The change of state from a liquid to a solid

undercooling

The difference between the melting point and the actual temperature of nucleation

shrinkage allowance

The dimensional allowance which must be made in molds to compensate for shrinkage of the plastic compound on cooling.

powder metallurgy

The fabrication of metal pieces having intricate and precise shapes by the compaction of metal powders, followed by a densification heat treatment.

parting line

The interface that separates the cope and the drag halves of a mold, flask, pattern, or the halves of a core

parting surface

The interface that separates the cope and the drag halves of a mold, flask, pattern, or the halves of a core (2nd term)

gating system

The network of connected channels used to deliver the molten metal to the mold cavity.

pouring cup

The portion of the gating system that initially receives the molten metal from the pouring vessel

grain refinement

The process of reducing the crystal (grain) size in a solid metal through the action of specific alloying elements or compounds.

mold cavity

The shaped hole into which the molten metal is poured and solidified to produce the desired casting

local solidification time

The time from the start of solidification to the end of solidification.

Chvorinov's Rule

Total solidification time, t, is the time from pouring to the completion of solidification; V is the volume of the casting; A is the surface area; and B is the mold constant. t = B(V I A)"n

stress concentration

a condition in which the maximum normal stress is much greater than the average normal stress due to geometric discontinuity in the structure or concentration of load

core print

a feature that is added to a pattern, core, or mold and is used to locate and support a core within the mold

machining

a form of manufacturing used to create objects by braiding, cutting, drilling, grinding, and/or shaping the material

cooling curves

a line graph that represents the change of phase of matter, typically from a gas to a solid or a liquid to a solid.

equiaxed zone

a region of randomly oriented grains in the center of a casting produced as a result of widespread nucleation

core

a sand (or metal) shape that is inserted into a mold to produce the internal features of a casting, such as holes or passages.

flash

a small amount of fin, or ___, is often present at the parting line, and when the _____ is removed, a line of surface imperfection results.

computer simulation

a type of mathematical model that expresses ideas about mental processes in precise ways

vents

additional channels to provide an escape for the gases that are originally present in the mold or are generated during the pour.

side risers

adjacent to the mold cavity and displaced horizontally along the parting line.

machining allowance

allowances made for additional finishing operations such as machining and grinding

riser

an additional void in the mold that also fills with molten metal.

internal chills

are pieces of metal that are placed within the mold cavity to absorb heat and promote more rapid solidification

drag

bottom half of a two-part mold, the pattern, flask, mold, or core

shrinkage

changes in dimensions as material cools and hardens

core boxes

cores are produced in wood, metal, or plastic tooling, known as...

allowances

dimensional modifications that are incorporated into a pattern

deformation processes

exploit the ductility or plasticity of certain materials, mostly metals, to produce the desired shape by mechanically moving or rearranging the solid

runners

horizontal channels

hot tears

if the mold provides constraint during the time of contraction, tensile forces can be generated within the hot, weak casting, and cracking

blind riser

if the riser is contained entirely within the mold, it is known as ....

open riser

if the risers is open to the atmosphere, it is called an ...

columnar zone

in cast structure, the long, thing solumnar grains that are produced by the favorably oriented crystals that continue to grow

mold constant

incorporates the characteristics of the metal being cast, the mold material, the mold thickness, initial mold temperature, and the amount of superheat

gates

into mold cavity

gas porosity

liquid metals contain sig. amounts of dissolved gas, and after solidifation, the solid structure cannot accomodate that gas and the rejected atoms tend to form bubbles within the casting.

distortion

loss of accuracy

external chills

masses of high-heat-capacity and high-thermal-conductivity materials (such as steel, iron, graphite, or copper) that are placed in the mold adjacent to the casting to absorb heat and accelerate the cooling of various regions

mold filling

mathematics of fluid flow can be applied

shrink rules

measuring devices that are larger than a standard rule by an appropriate shrink allowance

chill zone

narrow band of randomly oriented crystals that forms on the surface of a casting caused by rapid nucleation

growth

occurs as the heat of fusion is extracted from the liquid material

reusable mold

one of the two basic categories of the casting processes ; employ permanent this is _______

molding material

packed around the pattern and the pattern is removed to create all or part of the mold cavity

gas flushing

passing small bubbles of inert or reactive gas through the melt

insulating sleeves

placing _____ around a riser is a technique used to reduce the riser size rather than promote directional solidification.

casting

processes exploit the properties of a liquid as it flows into and assumes the shape of a prepared container and then solidifies on cooling. (both the process and the product when molten metal is poured and solidified in a mold.

solidification shrinkage

shrinkage that occurs when a liquid turns into a solid

expandable-mold casting process

single use molds are used for this

directional solidification

solidification process in which the solidification interface sweeps continuously through the material

superheat

the difference between the pouring temperature and the freezing of the material

nucleation

the first step in a phase transformation. occurs when stable particles of solid form from within the molten liquid.

solidus temperature

the highest temperature where it is all a solid

liquidus temperature

the lowest temperature where the material is all liquid

thermal arrest

the plateau in the cooling curve that occurs during the solidification of a material with fixed melting point

solidification modeling

the principles of heat transfer

additive manufacturing

the production of physical items by adding layer upon layer, much in the same way an inkjet printer lays down ink

freezing range

the region between the liquidus and solidus temperature

slag or dross

the residue or mass of metal left after smelting; worthless matter

flask

the rigid metal or wood frame that holds the molding aggregate

materials processing

the science and technology through which a material is converted into a useful shape with structure and properties that are optimized for the proposed service environment. "whatever must be done to convert stuff into things"

pouring temperature

the temperature of a metal when it is poured into a mold

hot spots

thick sections cool more slowly than other locations and tend to be the sites of localized shrinkage

total solidification time

time from start of pouring to end of solidification

filters

traps any dross, sand, or eroded material and keep it from flowing into the mold cavity

runner extensions

used to catch and trap metal and keep it from entering mold cavities

runner well

used to catch and trap this first metal and keep it from entering the mold cavity (term 2)

sprue well

used to dissipate the kinetic energy of the falling stream and prevent splashing and turbulence as the metal makes he turn into the runner