MCT Assignment-1 25-02-2025

1. Determination of Permeability of Foundry Sand

Method:

The permeability of foundry sand is determined using a Permeability Meter, which measures the
ability of gases to pass through the sand. This property is crucial in casting to ensure that gases
formed during metal pouring escape easily, preventing defects.

Test Procedure:

1. Preparation of Specimen:

o A standard cylindrical sand specimen is prepared using a sand rammer.

o The specimen typically has a diameter of 50 mm and a height of 50 mm.

2. Mounting the Specimen:

o The sand specimen is placed in a permeability meter, which consists of an air

3. Air Flow Measurement:

o A known volume of air (usually 2000 cm³) is forced through the sand specimen
under a controlled pressure (typically 10 g/cm²).

4. Permeability Number Calculation:

o The permeability number (P) is calculated using the formula:

P=VH/ATP

Where:

▪ P = Permeability number

▪ V = Volume of air (cm³)

▪ H = Height of the specimen (cm)

▪ P = Air pressure (g/cm²)

▪ A = Cross-sectional area of the specimen (cm²)

▪ T = Time in minutes for the air to pass

Sketch of Permeability Apparatus:

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Effect of Moisture and Clay Content on Green Strength of Sand

1. Effect of Moisture Content:

o Low moisture content → Weak bonding, leading to low green strength.

o Optimum moisture content → Maximum bonding strength, leading to high green

o Excess moisture content → Weakens bonding due to excess water film around
sand grains, leading to reduced strength.

2. Effect of Clay Content:

o Low clay content → Poor bonding, leading to low green strength.

o Optimum clay content → Strong bonding, leading to maximum green strength.

o Excess clay content → Causes excessive bonding, making the sand too sticky and
affecting mold collapsibility.

2. Die Casting Process

Short Note on Die Casting

Die casting is a metal casting process where molten metal is forced into a mold cavity under
high pressure. This process is mainly used for producing large quantities of small to medium-
sized metal parts with high precision and excellent surface finish.

Steps Involved:

1. Melting the Metal: The metal (typically aluminum, zinc, or magnesium) is melted in a
furnace.

2. Injection into the Die: The molten metal is injected into a steel die (mold) under high
pressure (ranging from 1000 to 20000 psi).

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3. Cooling and Solidification: The metal cools and solidifies within the die.

4. Ejection of the Casting: The solidified casting is ejected from the mold using ejector pins.

5. Trimming and Finishing: Excess material (flash) is trimmed, and the part is finished as
required.

Types of Die Casting:

• Hot Chamber Die Casting (for low-melting metals like zinc)

• Cold Chamber Die Casting (for high-melting metals like aluminum)

Advantages:

• High production rate

• Excellent dimensional accuracy

• Good surface finish

• Less machining required

Sketch of Die Casting Process:

3. Investment Casting (Lost Wax Process)

Explanation:

Investment casting, also known as the lost wax process, is a precision casting method used to
produce intricate and high-accuracy metal parts. It is widely used in aerospace, medical, and
jewelry industries.

Process Steps:

1. Wax Pattern Creation:

o A wax model of the final casting is created using injection molding or hand
carving.

2. Assembly of Wax Patterns:

o Multiple wax patterns are attached to a central wax sprue to form a tree-like
structure.

3. Ceramic Shell Coating:

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o The wax assembly is repeatedly dipped in ceramic slurry and coated with fine
sand to form a ceramic shell.

4. Wax Removal (Dewaxing):

o The shell is heated to melt and drain out the wax, leaving a hollow ceramic mold.

5. Mold Preheating and Pouring:

o The ceramic mold is preheated, and molten metal is poured into the cavity.

6. Cooling and Shell Removal:

o After solidification, the ceramic shell is broken to retrieve the final casting.

7. Finishing:

o The casting is cleaned, trimmed, and polished as needed.

Sketch of Investment Casting Process:

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Advantages of Investment Casting:

• High dimensional accuracy

• Smooth surface finish

• Can produce complex shapes

• Suitable for various metals (steel, aluminum, titanium)

4. Patterns in Casting

Types of Patterns:

Patterns are the replicas of the final casting, used to create the mold cavity in sand casting.

1. Single Piece Pattern:

• Simplest type, used for simple shapes.

• Made in one solid piece.

• Example: Gear blanks.

2. Split Pattern (Two-Piece Pattern):

• Used for complex shapes.

• Made in two halves, which are aligned using dowel pins.

• Example: Pipe fittings.

3. Match Plate Pattern:

• Two halves of the pattern are mounted on opposite sides of a metal plate.

• Used in mass production for uniformity.

• Example: Automotive parts.

4. Gated Pattern:

• Has integrated gating systems for metal flow.

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• Used in high-volume casting.

• Example: Small machine parts.

5. Loose Piece Pattern:

• Contains removable sections for intricate internal details.

• Example: Engine blocks.

6. Sweep Pattern:

• A rotating wooden section is used to shape large circular molds.

• Example: Large pipes and bells.

7. Skeleton Pattern:

• A framework of the pattern, covered with a sand layer.

• Example: Large turbine castings.

8. Shell Pattern:

• A thin shell of the desired shape used in shell molding.

• Example: Thin-walled castings.

Pattern Materials:

Patterns can be made from different materials depending on cost, durability, and ease of
manufacturing.

1. Wood:

• Lightweight, easy to shape, but wears out quickly.

• Used for small production runs.

2. Metal (Aluminum, Brass, Steel):

• Durable, precise, expensive.

• Used for mass production.

3. Plastic:

• Lightweight, resistant to moisture, but can deform.

• Used in medium production.

4. Wax:

• Used in investment casting for lost wax process.

5. Plaster:

• Used for complex shapes with fine details.

Pattern Allowances in Casting:

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Since metal shrinks and deforms during cooling, allowances are given to patterns.

1. Shrinkage Allowance: Metal contracts on cooling, so the pattern is made slightly larger.

2. Machining Allowance: Extra material is added to allow for final machining.

3. Draft Allowance: Taper is given to allow easy removal from the sand mold.

4. Distortion Allowance: Provided for uneven shrinkage in thin sections.

5. Rapping Allowance: Given to compensate for sand compaction when removing the pattern.

5. Thixocasting and Rheocasting Process

Both Thixocasting and Rheocasting are semi-solid metal (SSM) processing techniques used
for high-precision metal casting, reducing defects like porosity and improving mechanical
properties.

Thixocasting

Working Principle:

• In Thixocasting, the metal alloy is first cast into a preformed billet and then reheated to
a semi-solid state before being injected into a mold.

• The material is partially solid and partially liquid, allowing it to flow like a liquid while
retaining solid characteristics.

• A high-pressure injection system forces the thixotropic (semi-solid) metal into the die
cavity.

Steps in Thixocasting:

1. Billet Preparation: The metal is cast into a billet with a globular grain structure.

2. Heating: The billet is reheated to a semi-solid state (typically 30-50% solid).

3. Injection into the Die: The semi-solid slurry is injected into the mold under high pressure.

4. Solidification and Ejection: The casting solidifies, and the final component is ejected.

Advantages of Thixocasting:

Reduced porosity
Improved mechanical properties
High dimensional accuracy
Suitable for magnesium and aluminum alloys

Rheocasting

Working Principle:

• In Rheocasting, the metal alloy is melted completely first, and then rapidly cooled to
partially solidify before injection.

• Unlike Thixocasting, no pre-cast billet is required.

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• The slurry is prepared directly from the molten metal.

Steps in Rheocasting:

1. Melting: The metal alloy is completely melted.

2. Controlled Cooling: The molten metal is cooled to reach a semi-solid state.

3. Injection into Mold: The semi-solid slurry is injected into a die.

4. Solidification and Ejection: The part cools and solidifies, then is removed from the mold.

Advantages of Rheocasting:

Lower material cost (no billet required)

Comparison of Thixocasting vs Rheocasting

Feature Thixocasting Rheocasting

Billet Requirement Required Not Required

Process Complexity More complex Simpler

Material Cost Higher Lower

Fluidity Good Better

Application High-precision parts Large and complex parts

6. Design of the Gating System

A gating system is a network of channels in a casting mold that guides molten metal from the
pouring basin to the mold cavity.

Components of a Gating System

1. Pouring Basin

o The top part where molten metal is poured.

o Helps in controlling the flow rate.

2. Sprue

o A vertical channel that directs metal into the mold.

o Should be tapered to prevent air entrapment.

3. Runner

o Horizontal channel that carries metal from the sprue to the gate.

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o Designed to prevent turbulence.

4. Gate

o The narrow section where molten metal enters the cavity.

o Controls flow speed and prevents excessive splashing.

5. Riser (Feeder Head)

o Stores extra molten metal to compensate for shrinkage during solidification.

o Ensures defect-free casting.

Types of Gating Systems

1. Pressurized Gating System:

• Smaller cross-sectional area, leading to high metal velocity.

• Reduces air entrapment but may cause turbulence.

• Used in high-speed casting processes.

2. Non-Pressurized Gating System:

• Larger cross-sectional area, allowing metal to flow smoothly.

• Reduces turbulence but may cause slower filling.

• Used in gravity die casting.

The goals for the gating system are:

1. To minimize turbulence to avoid trapping gasses into the mold.

2. To get enough metal into the mold cavity before the metal starts to solidify.

3. To avoid shrinkage.

4. Establish the best possible temperature gradient in the solidifying casting so that the
shrinkage if occurs must be in the gating system not in the required cast part.

5. Incorporates a system for trapping the non-metallic inclusions.