13637990
Description
Flashcards by Lily Chapman, updated more than 1 year ago
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Created by Lily Chapman
almost 6 years ago
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| Question | Answer |
| Desirable mould properties | -Strength -Permeability -Thermal stability - Collapsibility -Reusability |
| Foundry Sands | SiO2- Silica Sand is held together with water and bonding clay (90% sand, 3% water, 7% clay). |
| Casting defects | -Misrun - Cold shut - Cold shot -Shrinkage cavity |
| What is a misrun? | A casting that has solidified before completely filling the mould. |
| What is a cold shut? | It is where two portions of metal flow together but there is a lack of fusion between them due to premature freezing. |
| What is a cold shot? | It's where metal splatters during pouring and solid globules form and become entrapped |
| What is a shrinkage cavity? | A depression in the surface or a void caused by shrinkage |
| Testing methods | -Visual inspection -Dimensional measurements - Physical tests |
| Product design considerations | Draft- the amount of taper for moulded or cast parts. Draft aids in removal of the part from the mould |
| Types of expendable mould processes | -Shell moulding -Expanded Polystyrene Processes -Investment casting -Plaster mould casting -Ceramic mould casting |
| What is shell moulding? | A process where a thin wall is created by applying a sand-resin mixture around a pattern. |
| Advantages of shell moulding | -Smoother cavity surface gives a better surface finish -Good dimensional accuracy -Fewer cracks in casting -Can be used for mass production |
| Disadvantages of shell moulding | -Expensive mould pattern -Difficult to justify for small quantites |
| What is a Expanded Polystyrene Process? | A process where a mould of sand is packed around a polystyrene foam pattern. The polystyrene vaporises when molten metal is poured on it. |
| What are the advantages of Expanded Polystyrene Process? | -The pattern does not have to be removed from the mould -Speeds up process as two halves of a mould do not have to be used |
| Disadvantaged of Expanded Polystyrene Process | -A new pattern is needed for every casting -May not be economically justifiable, it depends on the cost of producing the pattern |
| What is investment casting? | It's a process where a wax pattern is coated with a refractory material. Once molten metal is poured into the mould the wax melts |
| What is a refractory material? | A refractory mineral is a mineral that is resistant to decomposition by heat, pressure or chemical attack. |
| Advantages of investment casting | -Can create very detailed parts -Good surface finish -Wax can usually be recovered and reused -Additional machining not usually required |
| Disadvantages of investment casting | -Many processing steps are required -Relatively expensive |
| What is plaster mould casting? | A process similar to sand casting, but the mould is made of plaster |
| Advantages of plaster mould casting | -Good surface finish -Captures fine detials |
| Disadvantages of plaster mould casting | -Mould must be baked to remove moisture -Moulds cannot withstand high temperatures |
| What is ceramic mould casting | A similar process to plaster mould casting, however the ceramic can withstand a higher temperature than plaster |
| Applications of permanent mould casting | -High volume production -Makes parts like automotive pistons and pump bodies |
| What is die casting? | A permanent mould process where molten metal is injected into a cavity under high pressure. Pressure is maintined until solidification. |
| Advantages of die casting | -Economical for large volume production -Good accuracy and surface finish -Thin sections are possible -Rapid cooling makes casting strong |
| Disadvantages of die casting | -LImited to metals with low boiling points -Part geometry must allow for removal of the die (mould) |
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