All questions of Metal Casting for UPSC CSE Exam

Shrinkage allowance is the difference in dimensions between the pattern and the final casting due to the shrinkage of the metal during solidification. The amount of shrinkage allowance required is dependent on the material being used for casting.

Explanation:

Steel has the highest shrinkage allowance among the given materials. This is due to the following reasons:

1. High melting point: Steel has a high melting point compared to other materials. This means that it takes longer for the metal to cool and solidify, resulting in more shrinkage.

2. High carbon content: Steel has a higher carbon content than other materials. Carbon is a strong carbide former, which can lead to a reduction in the solidification range of steel, resulting in more shrinkage.

3. Low thermal conductivity: Steel has a lower thermal conductivity than other materials. This means that heat is retained for a longer time, resulting in a longer solidification time and more shrinkage.

4. High density: Steel has a higher density than other materials. This means that it will shrink more during solidification.

Therefore, steel requires the highest shrinkage allowance among the given materials.

Since given machining allowance is 3 mm on each side, add 3 mm on each side of the part shown in figure. The dimensions of pattern after machining will be

For same volume the ratio of surface areas of sphere : cylinder : cube: is 4.84 : 5.54 : 6

To determine the time taken to fill the casting cavity, we need to consider the volume of the cavity and the flow rate of the metal.

1. Calculating the volume of the casting cavity:
The volume of a cylinder is given by the formula V = πr^2h, where r is the radius and h is the height. In this case, the diameter is given as 150 mm, so the radius is 75 mm (or 0.075 m). The height of the cylinder is 200 mm (or 0.2 m). Therefore, the volume of the casting cavity is:
V_cavity = π(0.075)^2(0.2) = 0.00707 m^3

2. Calculating the flow rate of the metal:
The flow rate of the metal depends on the gating ratio and the in-gate area. The gating ratio is not provided in the question, so let's assume it to be 2.

The in-gate area is given as 10 cm^2 (or 0.001 m^2). Therefore, the total gating area is:
A_gating = gating ratio * in-gate area = 2 * 0.001 = 0.002 m^2

3. Calculating the flow rate:
The flow rate of the metal can be calculated using the formula Q = A_gating * V_flow, where Q is the flow rate and V_flow is the velocity of the metal.

Since the height of the metal during pouring is 50 mm above the cope, the total height of the metal column is 200 mm + 50 mm = 250 mm (or 0.25 m).

Using Bernoulli's equation for incompressible flow, the velocity of the metal can be calculated as:
V_flow = √(2gH), where g is the acceleration due to gravity (9.81 m/s^2) and H is the height of the metal column.

V_flow = √(2 * 9.81 * 0.25) = 2.21 m/s

Now, we can calculate the flow rate:
Q = 0.002 * 2.21 = 0.00442 m^3/s

4. Calculating the time taken:
The time taken to fill the casting cavity can be calculated using the formula t = V_cavity / Q, where t is the time taken.

t = 0.00707 / 0.00442 ≈ 1.6 seconds

Since the time needs to be rounded to the nearest whole number, the correct answer is option 'C' - 8 seconds.

Metallic moulds are used in die casting process.

Explanation:

When pouring molten metal into a mould, it is important to ensure that the metal fills the entire cavity without any defects or voids. The use of risers is a common technique to prevent shrinkage defects in castings. A riser is an additional volume of molten metal that is connected to the casting through a channel, and it serves as a reservoir of molten metal that can compensate for the shrinkage during solidification.

If the molten metal does not appear in the riser during pouring, it indicates that a sound casting will be produced. This is because the molten metal has completely filled the cavity without any defects or voids, and there is no need for additional molten metal from the riser. This is a desirable situation, as it indicates that the casting will have good dimensional accuracy and mechanical properties.

If the molten metal does not appear in the riser, it rules out the possibility of the other three options:

- An obstruction between sprue and riser: If there was an obstruction, the molten metal would not have been able to flow freely into the cavity, and there would be defects or voids in the casting.
- Insufficient molten metal to fill the cavity: If there was insufficient molten metal, the cavity would not have been completely filled, and there would be defects or voids in the casting.
- Either insufficient molten metal to fill the cavity or an obstruction between sprue and riser: This is a combination of the previous two options, and it is also ruled out by the absence of molten metal in the riser.

Thus, the absence of molten metal in the riser during pouring is a good sign that a sound casting will be produced.

Shrinkage Allowance in Materials

Introduction
Shrinkage allowance is the amount of additional material that needs to be added to a casting pattern to compensate for the shrinkage that occurs during the solidification and cooling process. The shrinkage allowance ensures that the final casting dimensions are accurate and match the desired specifications. Different materials have different shrinkage rates, which is why different shrinkage allowances are required for different materials.

Explanation
Among the materials mentioned in the options (Cl, Lead, Brass, and Aluminium alloy), the material with the highest shrinkage allowance is Brass.

Shrinkage Allowance Factors
Several factors influence the shrinkage allowance in a material, including:
1. Cooling rate: Faster cooling rates tend to increase shrinkage.
2. Solidification time: Longer solidification times lead to higher shrinkage.
3. Alloy composition: Different alloy compositions can result in varying shrinkage rates.

Shrinkage Allowance Comparison
Let's analyze the shrinkage allowances for each material:

1. Cl (Chlorine)
Chlorine is not a casting material but a chemical element. Therefore, it does not have a shrinkage allowance.

2. Lead
Lead is a soft and malleable material with a relatively low melting point. It exhibits minimal shrinkage during the cooling process. Therefore, the shrinkage allowance for lead is relatively low compared to other materials.

3. Brass
Brass is an alloy composed of copper and zinc. It has a higher melting point compared to lead. Due to the different thermal properties of copper and zinc, brass experiences a significant amount of shrinkage during cooling. Consequently, a larger shrinkage allowance is required for brass castings.

4. Aluminium Alloy
Aluminium alloys are widely used in various industries due to their lightweight and excellent mechanical properties. They have a relatively low shrinkage rate compared to materials like brass. Therefore, the shrinkage allowance for aluminium alloy castings is lower compared to brass.

Conclusion
Among the materials mentioned in the options, brass has the highest shrinkage allowance. This is because brass, being an alloy of copper and zinc, experiences significant shrinkage during the cooling process. It is important to consider the shrinkage allowance when designing casting patterns to ensure accurate final dimensions in the castings.

Shell mould casting uses silica sand and phenal formaldehyde.

Top gate causes turbulence due to high head and velocity

No core is used in centrifugal casting method.

The correct answer is option C: 1, 2, and 4 only.

Shell mould casting, also known as shell molding or shell molding casting, is a casting process that uses a resin-coated sand shell to form the mold. This process offers several advantages over other casting methods. Let's discuss each advantage in detail:

1. Close dimensional tolerance: Shell mould casting provides close dimensional tolerances, meaning that the cast parts can be manufactured with high precision and accuracy. The use of a shell mold allows for greater control over the final dimensions of the cast part, resulting in minimal dimensional variations. This advantage is particularly important in industries where tight tolerances are required, such as aerospace or automotive.

2. Good surface finish: Shell mould casting produces castings with a smooth and consistent surface finish. The resin-coated sand shell used in this process helps to create a mold cavity with excellent surface quality. As a result, the cast parts have a clean and polished appearance, requiring minimal post-processing or finishing operations.

3. Low cost: Shell mould casting is a cost-effective casting method. The process uses readily available materials, such as sand and resin, which are relatively inexpensive compared to other mold materials. Additionally, the use of reusable shell molds reduces the overall production costs as compared to traditional sand casting, where a new mold is required for each casting. The low cost of shell mould casting makes it an attractive option for large-scale production runs.

4. Easier: Shell mould casting is relatively easier compared to other casting methods. The process involves fewer steps and requires less equipment and manpower. The use of pre-coated sand shells simplifies the mold-making process, reducing the time and effort required to produce molds. This advantage makes shell mould casting more efficient and less labor-intensive than some other casting techniques.

In conclusion, shell mould casting offers advantages such as close dimensional tolerance, good surface finish, and ease of use. These advantages make it a preferred choice for many applications where precision, aesthetics, and cost-effectiveness are important factors. Therefore, option C: 1, 2, and 4 only is the correct answer.

Understanding Sand Casting Moulds
Sand casting is a widely used manufacturing process for creating metal parts. The mould used in this process consists of two main parts.
Parts of a Sand Casting Mould
- Cope: This is the upper part of the mould. It is designed to hold the sand and shape of the part being cast. The cope also contains the pouring basin and the sprue through which molten metal is poured.
- Drag: This is the lower part of the mould. It supports the cope and helps in forming the overall shape of the cast part. The drag typically contains the pattern that defines the outer dimensions of the final product.
Why Option 'C' is Correct
- The correct terminology in sand casting is "cope and drag."
- "Cope" refers specifically to the upper section, while "drag" refers to the lower section. This terminology is crucial for understanding how the mould is constructed and how it functions during the casting process.
Significance of Cope and Drag
- The separation of the mould into these two parts allows for easy removal of the pattern after the sand has been compacted.
- It also facilitates the pouring of molten metal, as the cope can be lifted off to access the cavity created by the pattern in the drag.
By understanding the roles of the cope and drag, one gains insight into the fundamental aspects of sand casting, which is essential for effective manufacturing in mechanical engineering.

Centrifugal Casting Method for Symmetrical Shape about Horizontal Axis
Centrifugal casting is a method used for casting articles of symmetrical shape about a horizontal axis. This method involves rotating a mold at high speeds while pouring molten metal into it. The centrifugal force generated by the rotation distributes the molten metal evenly, resulting in a uniform casting with a dense structure.

Advantages of Centrifugal Casting
- Uniform distribution of molten metal: The centrifugal force ensures that the molten metal is distributed evenly throughout the mold, leading to a uniform casting without any defects.
- High density and strength: The centrifugal casting method produces castings with a high density and strength due to the controlled solidification process.
- Enhanced mechanical properties: The rotational motion of the mold helps in aligning the metal grains, resulting in improved mechanical properties of the casting.

Applications of Centrifugal Casting
Centrifugal casting is commonly used for casting articles such as pipes, tubes, and cylindrical components that require a symmetrical shape about a horizontal axis. It is suitable for producing parts with high structural integrity and uniform wall thickness.

Conclusion
In conclusion, the centrifugal casting method is ideal for casting articles of symmetrical shape about a horizontal axis. It offers advantages such as uniform metal distribution, high density, and enhanced mechanical properties, making it a preferred choice for producing high-quality castings for various applications in the mechanical engineering industry.

Statement 1 is wrong because if the velocity is as high as possible the flow will become turbulent which results in sand erosion, respiration effects etc.

Understanding Core Prints in Foundry Processes
In the context of foundry practices, the term "core print" refers to specific features designed to support the placement and stability of cores within a mold. Here's a detailed explanation:
What is a Core Print?
- Core prints are protrusions or recesses integrated into the mold design.
- They facilitate the accurate positioning of sand cores during the mold assembly.
- The primary function is to ensure that the cores remain in place when molten metal is poured into the mold.
Importance of Core Prints
- Alignment: Core prints help align the core with the mold cavity, ensuring that the final casting has the desired internal shape.
- Stability: By providing a secure hold, core prints prevent movement of the cores under the weight of the molten metal.
- Ease of Removal: They also aid in the removal process after casting, allowing for smoother extraction of both the core and the finished part.
Comparison with Other Terms
- Chill: A chill is a device used to control the cooling rate of the metal, not related to core positioning.
- Slinging: This refers to the method of securing or handling molds or cores, which does not pertain to the core's placement.
- Core: While a core is a component used to create internal cavities in castings, it is not the mechanism for its positioning.
In conclusion, core prints are essential for the effective use of cores in metal casting, ensuring that the process yields high-quality and accurately shaped components.

Calculation of Volume of the Cylindrical Riser:

- Given Data:
- Dimensions of the steel slab casting: 30 cm x 30 cm x 6 cm
- Side riser attached to the casting

- Modulus Method:
- In the modulus method, the volume of the riser is calculated based on the volume of the original casting.
- The volume of the riser is assumed to be cylindrical in shape.

- Calculation:
- Volume of the steel slab casting = Length x Breadth x Height
= 30 cm x 30 cm x 6 cm
= 5400 cm3

- As per the modulus method, the volume of the riser is generally assumed to be 1/6th of the total volume of the casting.

- Volume of the cylindrical riser = 1/6 x 5400 cm3
= 900 cm3

- Answer:
- The volume of the cylindrical riser is 900 cm3.

Therefore, the correct answer is not provided in the given options. The correct volume of the cylindrical riser is 900 cm3.

Introduction:
The sand ramming method is used in foundry processes to pack sand around a pattern in order to create a mold cavity. There are various sand ramming methods, and each method produces different results in terms of hardness and density of the mold. The question asks which method results in the hardest layer at the parting plane and around the pattern, while being less dense in the top layers.

Jolting:
Jolting is a sand ramming method where the flask containing the pattern is subjected to a jolting action. This action helps in compacting the sand around the pattern. The jolting action causes the sand particles to rearrange and settle more tightly, resulting in a denser mold. However, this method does not provide uniform compaction throughout the entire mold.

Squeezing:
Squeezing is another sand ramming method where the flask containing the pattern is squeezed by applying pressure. This pressure helps in packing the sand around the pattern. Squeezing provides better uniform compaction compared to jolting and results in a denser mold. However, the hardness of the mold may not be as high as in the case of jolting.

Jolting and Squeezing:
Jolting and squeezing are both used in combination in some sand ramming methods. This combination helps in achieving better compaction and density of the mold. However, the hardness of the mold may still not be as high as in the case of jolting alone.

Slinging:
Slinging is not a sand ramming method. It involves the process of throwing or slinging sand particles onto the pattern to create a mold. This method does not provide proper compaction or density and is not suitable for creating molds with a hard layer at the parting plane and around the pattern.

Conclusion:
Based on the explanations above, it can be concluded that the sand ramming method that results in the hardest layer at the parting plane and around the pattern, while being less dense in the top layers, is jolting (option A). Jolting provides better compaction and hardness compared to squeezing, jolting and squeezing, and slinging.

The correct reasons for the occurrence of hot tear in casting are:

i. Hindered contraction occurring immediately after the metal has solidified:
- When the metal solidifies, it undergoes thermal contraction. However, if there are restrictions in the mold or core, the contraction is hindered, leading to the development of internal stresses in the casting.
- These internal stresses can cause the casting to crack or tear during the cooling and solidification process.
- Hot tear defects are more likely to occur in areas where the metal is thickest, as the contraction is more pronounced in these regions.

ii. Poor collapsibility of the mold and core:
- Collapsibility refers to the ability of the mold and core to collapse or shrink away from the casting as it cools and solidifies.
- If the mold or core has poor collapsibility, it will not shrink away from the casting properly, leading to the development of internal stresses and potential hot tear defects.
- Poor collapsibility can be caused by factors such as improper design of the mold or core, inadequate venting, or insufficient mold or core material.

iii. Too high pouring temperature:
- Pouring temperature refers to the temperature at which the molten metal is poured into the mold.
- If the pouring temperature is too high, it can result in excessive thermal gradients and differential cooling within the casting, leading to the development of internal stresses and hot tear defects.
- High pouring temperatures can also cause the metal to solidify too quickly, reducing its ability to deform and accommodate the thermal contraction, further increasing the likelihood of hot tear formation.

In summary, the occurrence of hot tear defects in casting can be attributed to hindered contraction occurring immediately after metal solidification, poor collapsibility of the mold and core, and too high pouring temperature. These factors contribute to the development of internal stresses in the casting, which can lead to cracking or tearing during the cooling and solidification process.