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Hybrid Evaporative Pattern Casting System

Hybrid Evaporative Pattern Casting System

Common Challenges

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Introduction

Challenge

Evaporative-pattern casting is a type of casting process that uses a pattern made from a material that will evaporate when the molten metal is poured into the molding cavity. The most common evaporative-pattern material used is polystyrene foam.

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Introduction (contd.)

Challenge

Evaporative casting, consumable or eva-foam casting is a sand casting process where the foam pattern evaporates into the sand mold. A process similar to investmentindustrialmetalcastings.com casting, this expendable casting process is predicted to be used for 29% of aluminum and 14% of ferrous casting.

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Market Trends

Types

1. Lost-foam casting

2. Full-mold casting

Trend

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Lost-foam casting

Lost-foam casting (LFC) is a type of evaporative-pattern casting process that is similar to investment casting except foam is used for the pattern instead of wax. This process takes advantage of the low boiling point of polymer foams to simplify the investment casting process by removing the need to melt the wax out of the mold.

This casting process is advantageous for very complex castings that would regularly require cores. It is also dimensionally accurate, maintains an excellent surface finish, requires no draft, and has no parting lines so no flash is formed.

The two main disadvantages are that pattern costs can be high for low volume applications and the patterns are easily damaged or distorted due to their low strength. If a die is used to create the patterns there is a large initial cost.

Trend

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Full-mold casting

Full-mold casting is an evaporative-pattern casting process which is a combination of sand casting and lost-foam casting. It uses an expanded polystyrene foam pattern which is then surrounded by sand, much like sand casting. The metal is then poured directly into the mold, which vaporizes the foam upon contact.

This casting process is advantageous for very complex castings, that would regularly require cores. It is also dimensionally accurate, requires no draft, and has no parting lines so no flash is formed. As compared to investment casting, it is cheaper because it is a simpler process and the foam is cheaper than the wax.

The two main disadvantages are that pattern costs can be high for low volume applications and the patterns are easily damaged or distorted due to their low strength. If a die is used to create the patterns there is a large initial cost.

Trend

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Difference between Lost-foam and Full-mold

The main difference is that lost-foam casting uses an unbonded sand and full-mold casting uses a bonded sand (or green sand). Because this difference is quite small there is much overlap in the terminology.

Solutions

Process

Solution

In the first step of evaporative casting, a foam pattern is shaped using material like polystyrene. The pattern is attached with sprues, and gates using adhesives and brushed with refractory substances so that the molds are strong and resistant to high temperature. Refractory covered pattern assembly is then surrounded by a sand mixture to form a mold. In some instances the pattern assembly is mixed in ceramic slurry which forms a shell round the pattern when it dries.

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In both cases, the mold in kept at a specific temperature to allow the metal to flow smoothly and enter into every designs and cuts made by the pattern. Molten metal is poured into the mold and the pattern-forming material disappears into the mold. The molten metal takes the shape of the mold and solidifies. When the metal solidifies it is removed from the mold to form the casting.

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Solution

Unlike in the traditional sand casting method, in evaporative sand casting, the pattern does not have to be removed from the mold which reduces the need for draft provisions. Some of the parameter that are used to determine the quality of a eva-foam casting are grain fineness number, time of vibration, degree of vacuum and pouring temperature on surface roughness etc.

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Solution

Applications

Working Together

Evaporative castings is used for steel-casting cast iron parts like water pipe and pump parts, aluminum castings etc..

Advantages

1. High dimensional accuracy and superior casting surface smoothness.

2. Reduced work process unlike other casting methods.

3. Light weight casting can be done.

4. Casting have improved heat resistance and also abrasion resistance and other cast steel properties.

5. Complicated shapes can be cast without using cores or drafts.

Working Together

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