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What is the primary function of a mold in casting?
What is the primary function of a mold in casting?
Which statement accurately describes an open mold?
Which statement accurately describes an open mold?
What is the purpose of including a gating system in a closed mold?
What is the purpose of including a gating system in a closed mold?
Which of the following materials is NOT typically used to make molds?
Which of the following materials is NOT typically used to make molds?
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What term is used for the upper half of a mold?
What term is used for the upper half of a mold?
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What is one desirable property of a mold that allows it to withstand high temperatures?
What is one desirable property of a mold that allows it to withstand high temperatures?
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Which of the following describes the 'flask' in the context of molding?
Which of the following describes the 'flask' in the context of molding?
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What happens to the size of the mold cavity during the cooling and solidification of metal?
What happens to the size of the mold cavity during the cooling and solidification of metal?
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What is the primary function of a pouring cup in the gating system?
What is the primary function of a pouring cup in the gating system?
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What are the horizontal channels that liquid metal flows through called in the gating system?
What are the horizontal channels that liquid metal flows through called in the gating system?
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Why are short sprues preferred in a gating system?
Why are short sprues preferred in a gating system?
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What is a key problem caused by turbulent flow in the gating system?
What is a key problem caused by turbulent flow in the gating system?
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Where are gates usually placed in a casting to control shrinkage?
Where are gates usually placed in a casting to control shrinkage?
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How do tapered sprues contribute to the gating system?
How do tapered sprues contribute to the gating system?
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What shape of pouring cups helps in avoiding vortex formation?
What shape of pouring cups helps in avoiding vortex formation?
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Which of the following is NOT an issue caused by turbulent flow during pouring?
Which of the following is NOT an issue caused by turbulent flow during pouring?
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What is the purpose of the choke in a gating system?
What is the purpose of the choke in a gating system?
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Why are runner extensions and runner wells used in a gating system?
Why are runner extensions and runner wells used in a gating system?
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What role does a riser play in the casting process?
What role does a riser play in the casting process?
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How should a riser be designed for optimal functioning?
How should a riser be designed for optimal functioning?
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What characterizes a dead (or cold) riser?
What characterizes a dead (or cold) riser?
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Which type of riser receives the last hot metal entering the mold?
Which type of riser receives the last hot metal entering the mold?
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What is the purpose of a sprue well in the gating system?
What is the purpose of a sprue well in the gating system?
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How does a gating system prevent dross and sand particles from entering the mold cavity?
How does a gating system prevent dross and sand particles from entering the mold cavity?
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What is the primary purpose of a riser in casting?
What is the primary purpose of a riser in casting?
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How does the size and number of risers change with the size of the casting?
How does the size and number of risers change with the size of the casting?
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What influences the location of a riser in a casting?
What influences the location of a riser in a casting?
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What is the role of vent holes in casting?
What is the role of vent holes in casting?
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Why is it important for the connecting channel between the casting and the riser to be sufficiently large?
Why is it important for the connecting channel between the casting and the riser to be sufficiently large?
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What type of casting method permits air and gases to escape naturally?
What type of casting method permits air and gases to escape naturally?
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What happens if the air and gases are not properly evacuated during the casting process?
What happens if the air and gases are not properly evacuated during the casting process?
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How should the heaviest section of a casting be managed during the solidification process?
How should the heaviest section of a casting be managed during the solidification process?
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Study Notes
Manufacturing Processes UES102
- Course offered at Thapar Institute of Engineering & Technology, Patiala.
- Course code: UES102
Mold & Gating System UTA026
- Lecture 20
- Course code: UTA026
The Mold in Casting
- Mold contains a cavity whose shape determines the cast part's shape.
- Molten/hot liquid material (wax or metal) is shaped by a mold cavity and hardens.
- Mold functions as a hollow container.
Open Molds and Closed Molds
- Open mold: simple container shaped like the desired part.
- Closed mold: more complex geometry with a gating system (passageways) leading to the cavity.
Sand Casting Mold (Closed)
- Shows a diagram of a closed sand casting mold with components like pouring cup, riser, core, cope, parting line, and drag.
Sand Casting Mold (Closed)
- The mold cavity's size needs to be oversized to accommodate metal shrinkage during solidification and cooling.
- Molds are composed of various materials, such as sand, plaster, ceramics, and metals.
Mold Terms
- Cope: upper half of the mold.
- Drag: bottom half of the mold.
- Cheek: intermediate molding flask (optional for bigger molds).
- Flask: rigid metal or wood frame supporting the molding sand.
- Parting line: where the two mold halves separate.
Desirable Mold Properties
- Strength: maintains shape and resists erosion.
- Permeability: allows hot air and gases to pass through sand voids.
- Thermal stability: non-reactive with hot molten metal.
- Collapsibility: allows casting shrinkage without cracking.
- Reusability: enables sand from broken molds to be reused.
Gating System
- Channels or networks of channels that guide molten metal into the mold cavity from the exterior.
- Molten metal flows through the system from the pouring cup, to the sprue, runner, & gates, into the mold cavity.
Gating System
- Pouring cup (pouring basin): receives molten metal from the pouring vessel and directs to the rest of the mold.
- Minimizes splash and turbulence as the metal flows into the downsprue.
- Downsprue: vertical portion of the gating system.
Gating System
- Runner: horizontal channels that carry the molten metal.
Gating System
- Gates: controlled entrances into the mold cavity.
- Gates are usually positioned at thickest sections to control shrinkage and towards the bottom to minimize turbulence and splashing.
- Multiple gates and runners are employed for large castings to distribute metal inflow to more than one point in the mold cavity.
Gating System
- Turbulent flow during pouring introduces problems: gas absorption, metal oxidation, and mold erosion.
- Gating systems are designed to minimize turbulent flow.
Gating System
- Short sprues are desirable to minimize the distance the metal falls and the kinetic energy it acquires due to falling.
- Rectangular pouring cups hinder vortex or spiraling funnel formation, which prevents gas and oxides from entering the sprue.
- Tapered sprues also help prevent vortex formation.
Gating System
- Large sprue well dissipates the kinetic energy of the falling stream and prevents splashing and turbulence as the metal flows into the runner.
- Choke: the smallest cross-sectional area in the gating system that regulates the rate of metal flow.
Gating System
- Gating systems can be designed to trap dross (slag) and sand particles from entering the mold cavity.
- Runner extensions and runner wells are used to trap initial molten metal with foreign matter.
Riser
- An additional void in the mold that fills with molten metal.
- Compensates for shrinkage during solidification.
- Designed to freeze after the main casting.
- Larger volume-to-area ratio is critical for a riser's effectiveness in helping main casting to solidify first.
Riser
- Dead risers: fill with metal that previously flowed through the mold cavity.
- Top risers: are almost always dead risers.
Riser
- Live risers (hot risers): receive the last hot metal entering the mold.
- Risers part of the gating system are typically live risers.
- Various types are possible: top, side, etc. depending on casting style.
Riser Location
- Risers should be strategically placed for directional solidification.
- The heaviest section solidifies last—it should be the last to be fed.
- The heaviest section can then act as a riser for adjacent lighter or thinner sections.
- Small castings often need only one riser, while larger ones necessitate multiple risers.
Riser Location
- Number and location of risers depend on the casting configuration.
- Risers are generally located near the casting.
- Adequate channel size between riser and casting is needed to prevent solidification before casting begins
Vent Holes
- Air and hot gases from metal reactions must be evacuated for complete mold filling.
- Sand casting: natural porosity permits air/gas escape.
- Permanent metal molds: vent holes drilled/machined.
References
- Includes numerous books and online resources about manufacturing.
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Description
Explore the concepts of mold and gating systems in manufacturing processes as outlined in the UES102 course at Thapar Institute. This quiz covers different types of molds, casting techniques, and the components of sand casting molds. Test your understanding of how molds influence the shape and quality of cast parts.
