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What is the purpose of the shrinkage allowance when making a pattern?
What is the purpose of the shrinkage allowance when making a pattern?
- To facilitate the removal of the pattern from the mold
- To compensate for expansion during solidification
- To improve the surface finish of the casting
- To compensate for shrinkage during solidification (correct)
What is the purpose of the finish allowance when making a pattern?
What is the purpose of the finish allowance when making a pattern?
- To compensate for shrinkage during solidification
- To improve the surface finish of the casting (correct)
- To compensate for expansion during solidification
- To facilitate the removal of the pattern from the mold
What is the purpose of the rap (shake) allowance when making a pattern?
What is the purpose of the rap (shake) allowance when making a pattern?
- To facilitate the removal of the pattern from the mold (correct)
- To compensate for shrinkage during solidification
- To improve the surface finish of the casting
- To compensate for expansion during solidification
What is the purpose of the draft (taper) allowance when making a pattern?
What is the purpose of the draft (taper) allowance when making a pattern?
Which type of sand mold is typically the cheapest to produce?
Which type of sand mold is typically the cheapest to produce?
Which type of sand mold has the highest strength, making it suitable for larger castings?
Which type of sand mold has the highest strength, making it suitable for larger castings?
What is the typical temperature range used to bake Dry-Sand molds?
What is the typical temperature range used to bake Dry-Sand molds?
Which type of sand mold uses a chemical bonding process to hold the sand together?
Which type of sand mold uses a chemical bonding process to hold the sand together?
What is the typical depth of the dried surface layer in a Skin-Dried sand mold?
What is the typical depth of the dried surface layer in a Skin-Dried sand mold?
According to Chvorinov's Rule, which of the following factors has the greatest influence on the solidification time of a casting?
According to Chvorinov's Rule, which of the following factors has the greatest influence on the solidification time of a casting?
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Study Notes
Pattern Allowances
- Shrinkage allowance: Compensates for the shrinkage that occurs when molten metal cools and solidifies.
- Finish allowance: Accounts for the removal of material during machining or finishing operations.
- Rap (shake) allowance: Facilitates the removal of the pattern from the sand mold.
- Draft (taper) allowance: Allows for the pattern to be easily withdrawn from the mold without damaging the sand.
Sand Mold Types
- Green sand molds: Most cost-effective to produce due to the simplicity of the process.
- Dry-sand molds: Generally have higher strength compared to green sand molds, making them suitable for larger casting applications.
- Skin-Dried molds: Utilize a dried surface layer to improve mold strength and surface finish.
- Chemical bonded molds: Utilize a chemical bonding process to bind the sand particles together.
Dry-Sand Mold Characteristics
- Baking Temperature: Typically baked at temperatures ranging from 200°F to 450°F to enhance mold strength.
- Skin-Dried Layer Depth: The dried surface layer in skin-dried molds is typically around 1/4 inch deep.
Chvorinov's Rule
- Solidification Time Influencer: Chvorinov's Rule states that the volume-to-surface area ratio of a casting has the most significant influence on its solidification time.
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