Casting Processes Overview and Pattern Making

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Questions and Answers

What is the machining allowance for all surfaces as specified?

2 mm

1 mm

5 mm

3 mm (correct)

What is the final dimension at the top after applying the draft allowance of 0.75°?

211.00 mm

210.60 mm

213.80 mm (correct)

212.40 mm

What is a core used for in the casting process?

To enhance the surface finish

To obtain holes or internal cavities (correct)

To make the casting heavier

To provide additional strength to the mould

Which material property must chaplets possess for effective support of large cores?

Ability to conform to molten metal Signup and view all the answers

Which characteristic is NOT required for the cores used in casting?

Improves the color of the casting Signup and view all the answers

What is the purpose of the pouring basin in a gating system?

To act as a reservoir for molten material before it flows. Signup and view all the answers

Which component of the gating system is specifically designed to reduce the momentum of molten metal?

Tapered sprue Signup and view all the answers

What role does the runner play in a gating system?

To connect the sprue to the gate for efficient flow. Signup and view all the answers

Which component functions as the passage for molten metal to enter the mould cavity?

Sprue Signup and view all the answers

What is the purpose of a gate in a gating system?

To control the flow of molten metal into the mould cavity. Signup and view all the answers

What is the primary function of the sprue base in a casting system?

To reduce the momentum of the falling molten metal Signup and view all the answers

Which of the following terms is NOT associated with the characteristics of a sprue?

Pouring temperature Signup and view all the answers

What does the volume flow rate (Q) depend on in the context of a sprue?

The cross-sectional area and velocity of the liquid Signup and view all the answers

What is the effect of a tapered sprue compared to a straight sprue?

It typically avoids turbulence better than a straight sprue Signup and view all the answers

In a casting system, which component directly regulates the flow of molten metal into the mold?

Gate Signup and view all the answers

What is the primary purpose of a pouring basin in metal pouring?

To reduce the eroding force of the liquid metal stream Signup and view all the answers

What role does a ceramic strainer play in the sprue during metal pouring?

It removes dross from the liquid metal Signup and view all the answers

How does a splash core assist in the pouring process?

By reducing the eroding force of the metal stream Signup and view all the answers

What is the main function of a skimmer placed in a horizontal gate?

To prevent lighter impurities from entering the mould Signup and view all the answers

According to Bernoulli’s theorem, what does the term 'head' represent?

The height of the fluid column at a point Signup and view all the answers

If point 2 is used as the reference plane in a pouring system, what is the head at that point?

Zero Signup and view all the answers

What condition is assumed throughout a typical pouring system as highlighted in the content?

Atmospheric pressure at all points Signup and view all the answers

What is the initial velocity of the liquid metal at the top of the sprue?

Zero Signup and view all the answers

What is the purpose of a pattern in the sand casting process?

To form impressions in sand to create a mould for casting Signup and view all the answers

Which of the following statements best describes when casting is most suitable?

For very large parts or designs with internal cavities Signup and view all the answers

What is a significant disadvantage of using wooden patterns?

They absorb moisture, which can alter dimensions Signup and view all the answers

Which metal is commonly used for making patterns due to its advantages in casting?

Aluminum Signup and view all the answers

What is one of the economic advantages of casting compared to other manufacturing processes?

It enables the production of parts in one piece at lower costs Signup and view all the answers

What is a common rationale for selecting metal patterns over wooden patterns?

Metal patterns have higher wear resistance and maintain dimensional tolerances Signup and view all the answers

What are cores used for in the sand casting process?

To create internal voids or shapes in the casting Signup and view all the answers

What is one limitation associated with using metal patterns?

They are heavier and may be subject to corrosion Signup and view all the answers

Study Notes

Casting Processes: Necessity and Overview

Casting is crucial for creating large, single-piece parts and complex shapes with internal cavities.
It's economically advantageous and suitable for materials difficult to process otherwise.
The sand casting process uses a disposable sand mold to create the desired shape. The process is relatable to key duplication.

Sand Casting: Pattern Making

Patterns are replicas of the desired casting, used to create impressions in the sand mold.
They require modifications like allowances for machining and core prints.
Materials include wood (suitable for small quantities and large castings, but susceptible to moisture), metal (for mass production, high wear resistance, and tighter tolerances; aluminum is a common choice), and plastic.

Pattern Making: Material Considerations

Wood: Readily available, lightweight, inexpensive, but absorbs moisture, has a short lifespan, and dimensional changes.
Metal: Durable, maintains tighter dimensional tolerances, longer lifespan, but heavier (copper, steel) and prone to corrosion. Aluminum is frequently used for its balance of properties.
Machining allowance is typically 3 mm per surface. Example: A 100mm dimension requires a 106mm pattern.

Draft Allowance

Draft allowance is included in pattern dimensions to facilitate easy removal from the sand mold.
Example: A 0.75° draft angle applied to a 109mm external detail adds approximately 1.40mm per side.

Cores

Cores create internal cavities or holes that aren't part of the main pattern.
They are produced separately and baked for strength.
They're placed in core prints within the mold; sand, metal, or ceramics are used.
Core properties include strength, erosion resistance, permeability to gases, high refractoriness, and a good surface finish.

Chaplets

Large cores may need additional support provided by chaplets (rigid metal pieces) placed between the core and mold face.
Chaplet material needs to be compatible with the molten metal.

Gating System

The gating system channels molten metal into the mold cavity, preventing erosion of the mold bottom.
Components include: pouring basin, sprue, sprue well, runner, gates, and riser.
A tapered sprue reduces the momentum of molten metal, minimizing turbulence.

Gating System Components and Functions

Pouring Basin: Reduces the force of the molten metal stream.
Sprue: The main vertical channel. A tapered sprue helps regulate flow.
Sprue Base: Reservoir at the bottom of the sprue to moderate the flow.
Runner: Horizontal channel distributing molten metal.
Gate: Smaller channels leading directly into the mold cavity.
Riser: Reservoir supplying molten metal to compensate for shrinkage during solidification.

Preventing Impurities

Pouring basins reduce erosion.
Strainers remove dross (impurities).
Splash cores reduce turbulence.
Skim bobs trap heavier and lighter impurities in horizontal gates.

Engineering Analysis of Pouring: Bernoulli's Theorem

Bernoulli's theorem, considering atmospheric pressure, relates head (height), pressure, and velocity of flowing liquid. The sum of these energies remains constant between two points in the fluid (friction losses are ignored).
In the context of the sprue, the height of the sprue contributes head, while the velocity differences at top and bottom effect the pressure. The initial velocity at the top of the sprue is assumed zero.

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Description

Explore the essential casting processes that enable the creation of complex shapes and large single-piece components. Understand the role of pattern making in sand casting, including material considerations for wood, metal, and plastic. This quiz covers key concepts and advantages of various casting techniques.