Test: Casting Processes - 3 - Mechanical Engineering MCQ

Mercury is not used for making patterns.

• Directional solidification: This is the primary purpose of chills in casting molds. They act as heat sinks, drawing heat away from specific areas of the casting and promoting solidification to start at a specific point and progress in a desired direction. This helps to minimize shrinkage defects and improve the overall quality of the casting.

• Reduce blow holes (B): While achieving directional solidification can indirectly help reduce blow holes by promoting even cooling, chills aren't directly used for this purpose.

• Chills: Chills are heat sinks that promote solidification in a specific direction.

• Padding: This refers to additional sections added to the casting design that solidify last. They act as a reservoir of molten metal to feed the solidifying casting and minimize shrinkage defects in critical areas. Padding works in conjunction with chills to achieve directional solidification.

Therefore, using chills to initiate solidification in a desired direction and padding to provide a reservoir of molten metal for feeding are the key elements for achieving directional solidification.

Chaplets are used to support the core inside the mould cavity, take care of its own weight and overcome the metallostatic forces.

Metal penetration is not caused due to high pouring temperature. It caused due to improper ramming of sand.

Fluidity can be defined as the length of spiral covered by the molten metal before it get solidifies.
Fluidity is the function of temperature, higher the temperature, more will be the fluidity.

Cope and drag are two parts of the casting mould.
Upper part is called cope and lower part is called drag.

If molten metal does not appear in the riser then it means there is either insufficient molten metal or an obstruction between sprue and riser.

Liquid shrinkage and shrinkage during phase change is provided by riser and solid shrinkage can be compensated by providing allowances over the pattern.

In die casting some permanent mould is used which may be made of metal.

• Inoculation is a process used primarily in cast iron production. It involves adding small amounts of specific elements, often alloys containing silicon and other elements, to the molten metal just before pouring.
• The primary purpose of inoculation is to influence the solidification process and microstructure of the cast iron. By introducing these elements, the inoculant provides nucleation sites for graphite precipitation. This can lead to several benefits:
  • Finer and more uniform graphite distribution: This improves the mechanical properties of the cast iron, such as strength and ductility.
  • Reduced formation of iron carbide: This can help prevent brittleness in the casting.

• Improved finish (A): While inoculation can indirectly contribute to a better surface finish by influencing the solidification process, it's not the primary goal.

They create the negative space within the mold that results in a hollow section in the final casting.

Misrun is a casting defect caused due to insufficient fluidity of molten metal.

Scab is sand casting defect caused due to improper ramming of moulding sand.

 An improper riser may give rise to a defect called shrinkage cavity

Sand wash is an irregularity in the surface of the casting resulting from the erosion of the sand mould during pouring and the contour of the erosion is formed in the surface of the final casting.

Gate is the opening through which the molten metal enters the mould cavity. The shape and the cross section of the ingot should be such that it can readily be broken off after casting solidification and also allow the molten metal to enter quietly into the mould cavity.

A riser, also known as a feeder, is a reservoir built into a metal casting mold to prevent cavities due to shrinkage.
Most metals are less dense as a liquid than as a solid so castings shrink upon cooling, which can leave a void at the last point to solidify.

Slush casting is used to produce ornament, small toys etc.

hence sprue is a vertical passage in the parting plane through which molten metal from the pouring basin reaches the mould cavity.

Bottom gating is preferred for reducing splashing and turbulence:

• Reduced falling distance: With the gates at the bottom, the molten metal has a shorter distance to fall before entering the mold cavity. This minimizes splashing and turbulence that can occur when the metal falls from a height.
• Slag and dross settling: Since the gates are at the bottom, any slag or dross (impurities) present in the molten metal tend to settle there before entering the casting cavity. This helps to achieve cleaner metal in the final casting.

Die casting are of two types:
1. Pressure die casting
2. Gravity die casting
In pressure die casting the molten metal is pressurized to enter into the mould while in case of gravity die casting molten metal fined into the mould by means of gravitational force.

Uniform ramming of sand is very necessary for green sand moulding process. Uniform ramming of sand during mould preparation improves mould strength, and makes it dimensionally stable. Uniform ramming done to obtain a smooth and hard casting surface which prevents break out.
Correct answer is D.

Casting acquired high density and are distinguished for their fine grained structure and high mechanical strength

In centrifugal casting mould in rotated about horizontal axis.

Since impurities are lighter than the metal hence they get collected at the inner surface of the casting.

• Dry silica sand: This is the primary base material in shell molding. It provides the structure and strength to the mold.
• Phenol formaldehyde: This is a thermosetting resin binder used in shell molding. When mixed with a catalyst, it reacts and cures to form a strong bond between the sand grains, creating the shell.