Evaporative-pattern casting is a type of casting process that uses a pattern made from materials that can evaporate when exposed to molten metal. In the process, polystyrene foam is often used which is why this casting technique is also called lost-foam casting.
Evaporative-pattern casting is special because of its ability to create patterns through evaporation. So, the molds used in this casting method are typically made of foam, once the molten metal enters the mold, it vaporizes the form material and then creates a distinct pattern when it cools.
Evaporative pattern casting is used for aluminum casting and other heavy parts like engine blocks, water pipes, etc. This casting is used to produce parts used in aerospace, shipbuilding, automotive, and agricultural equipment. Well, in this reading, we’ll explore what evaporative pattern casting is, its applications, diagrams, advantages, disadvantages, and how it works.
What is Evaporative Pattern Casting?
Evaporative pattern casting is a sand casting process that uses foam to form a replica of an item to evaporate in a sand mold in replacement of molten metal. This casting process is also known as consumable or Eva-foam casting. it is similar to investment casting.
Evaporative pattern casting is of two forms; lost foam and full mold casting. They are widely applicable due to complex designs that can be produced with relative ease. Their difference is that in lost-foam casting, sand is bounded. whilst, in full mold casting the sand is bonded (greensand). As of 2010, the evaporative casting process is predicted to be used for 29% of aluminum and 14% of ferrous casting.
Applications
Evaporative pattern casting is widely used for aluminum casting. It is also used for steel casting, and for iron parts like a water pipe, pump parts and other heavy equipment.
Related: What is Sand Casting? Its Diagram & How it Works
How Does Evaporative Pattern Casting (EPC) Works?
The working of evaporative pattern casting is achieved by producing a foam patter, which is the replica of an item to be cast. This pattern is brushed with refractory substances in order to add extra life to the pattern when molten metal is poured or to make it resistant to high temperatures.
The pattern is then attached with sprues and gates using adhesives. It is placed into a mold surrounded and packed by sand. Another way of doing this is by dipping the pattern into a ceramic slurry, just as investment casting. it forms a shell around it when it dries
The mold is kept at a specific temperature in order to allow the liquid metal to easily flow and reach all parts and cuts of the pattern. After this, molten metal is poured into the mold and the pattern-foaming material vanishes out of the mold as molten metal reaches it.
As the pattern vanishes, the molten metal takes its shape and solidifies. After it solidified, the casting is removed from the mold.
The difference between evaporative casting and sand casting methods is that in evaporative casting the pattern is not removed from the mold. This helps to reduce the need for draft provision.
The evaporative casting method is determined by the grain fineness number, time of vibration, degree of vacuum, and pouring temperature on surface roughness, etc.
Diagram of Evaporative Pattern Casting
Related: What is Centrifugal Casting? Its Diagram & How it Works
Advantages of Evaporative Pattern Casting
Below are the benefits of lost-foam casting:
- Ability to cast lightweight parts
- It is easy to perform when compared with other casting processes
- It offers high dimensional accuracy
- Intricate and complicated shapes can cast without using cores or drafts
- It offers a high surface finish (smoothness) to the casting
Disadvantages of Evaporative Pattern Casting
Below are the limitations of lost-foam casting:
- Pattern are easily distort or damage due to their low strength
- High cost of pattern for low volume applications
- There are better options out there.