Fundamentals of casting - Assignment 1

. What are some of the factors that affect the fluidity of a molten metal during pouring into a mold cavity?

Pouring temp relative to melting point, metal comp, viscosity, heat transfer to surroundings

How does solidification of alloys differ from solidification of pure metals?

Pure at constant temp equal to freezing point alloys freeze over a temperature range

Which casting process is the most important commercially?

Sand casting

Identify the three sources of contraction in a metal casting after pouring.

of Liquid during cooling prior to solidification, during phase change, thermal of solidified casting when cooling to room temp

In foundry work, a runner is which one of the following: (a) channel in the mold leading from the downsprue to the main mold cavity, (b) foundryman who moves the molten metal to the mold, or (c) vertical channel into which molten metal is poured into the mold?

(a) channel in the mold leading from the downsprue to the main mold cavity

The upper half of a sand-casting mold is called which of the following: (a) cope or (b) drag?

(a) cope

Sand casting is which of the following types: (a) expendable mold or (b) permanent mold?

(a) expendable mold

Total solidification time is defined as which one of the following: (a) time between pouring and complete solidification, (b) time between pouring and cooling to room temperature, (c) time between solidification and cooling to room temperature, or (d) time to give up the heat of fusion?

(a) time between pouring and complete solidification

In casting, a flask is which one of the following: (a) beverage bottle for foundrymen, (b) box which holds the cope and drag, (c) container for holding liquid metal, or (d) metal which extrudes between the mold halves?

(b) box which holds the cope and drag

Turbulence during pouring of the molten metal is undesirable for which of the following reasons (two best answers): (a) it causes discoloration of the mold surfaces, (b) it dissolves the binder used to hold together the sand mold, (c) it increases erosion of the mold surfaces, (d) it increases the formation of metallic oxides that can become entrapped during solidification, (e) it increases the mold filling time, and (f) it increases total solidification time?

(c) it increases erosion of the mold surfaces (d) it increases the formation of metallic oxides that can become entrapped during solidification

A riser in casting is described by which of the following (three correct answers): (a) an insert in the casting that inhibits buoyancy of the core, (b) gating system in which the sprue feeds directly into the cavity, (c) metal that is not part of the casting, (d) source of molten metal to feed the casting and compensate for shrinkage during solidification, and (e) waste metal that is usually recycled?

(c) metal that is not part of the casting, (d) source of molten metal to feed the casting and compensate for shrinkage during solidification, and (e) waste metal that is usually recycled

In a sand-casting mold, the V/A ratio of the riser should be (a) equal to, (b) greater than, or (c) smaller than the V/A ratio of the casting itself?

(c) smaller than the V/A ratio of the casting itself

During solidification of an alloy when a mixture of solid and liquid metals is present, the solid-liquid mixture is referred to as which one of the following: (a) eutectic composition, (b) ingot segregation, (c) liquidus, (d) mushy zone, or (e) solidus?

(d) mushy zone

Chvorinov's rule states that total solidification time is proportional to which one of the following quantities: (a) (A/V)^n (b) Hf (c) Tm (d) V (e) V/A (f) (V/A)^2 where A = surface area of casting, Hf = heat of fusion, Tm = melting temperature, and V = volume of casting?

(f) (V/A)^2

Why should turbulent flow of molten metal into the mold be avoided?

Accelerates formation of metal oxides, aggravates mold erosion

. Identify some of the important advantages of shape-casting processes.

Complex internal and external shapes, capable of producing net shape parts, very large parts, performed on any liquid metal, mass production

Name the two basic mold types that distinguish casting processes.

Expendable mold and permanent mold

What is a chill in casting?

Internal or external heat sinks that cause rapid freezing in certain regions of the casting

What is the difference between an open mold and a closed mold?

Open- liquid is poured till fills open cavity, closed- permit molten metal to flow from outside into cavity

What is the difference between a pattern and a core in sand molding?

Pattern made of wood metal plastic and has the shape of the part to be cast, core determines the interior geometry of the part

What are some of the limitations and disadvantages of casting?

Porosity, poor dimensional accuracy, poor surface finish, safety hazards, environment

. What is the continuity law as it applies to the flow of molten metal in casting?

Volume flow rate remains the same at the top and bottom of the sprue