Evaporative-pattern casting is a type of casting process that uses a pattern made from materials that can evaporate when exposed to molten metal. Polystyrene foam is often used in the process, 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. In this reading, we’ll explore what evaporative pattern casting is, its applications, diagrams, advantages, disadvantages, and how it works.
Let’s begin!
Related: What is Sand Casting? Its Diagram & 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 that evaporates in a sand mold in place 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. Their wide applicability stems from the relative ease of producing complex designs. The difference lies in the fact that sand in lost-foam casting has a boundary.
In full mold casting, the sand forms a bond, commonly referred to as 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. We also use it for casting steel and iron parts such as water pipes, pump parts, and other heavy equipment.
Therefore, this casting method typically uses foam for the molds. Aerospace, shipbuilding, automotive, and agricultural equipment use this casting to produce parts
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.
Related: What is Investment Casting? Diagram, & How it Works
How Does Evaporative Pattern Casting (EPC) Work?
The working of evaporative pattern casting is achieved by producing a foam pattern, 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, pouring temperature, 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.