Lost foam casting equipment
Introduction of lost foam casting line
Introduction
The Lost Foam casting process originated in 1958 when H.F. Shroyer was granted a patent for a cavity-less casting method, using a polystyrene foam pattern embedded in traditional green sand. The polystyrene foam pattern left in the sand is decomposed by the poured molten metal. The metal replaces the foam pattern, exactly duplicating all of the features of the original pattern. Like other investment casting methods, this requires that a pattern be produced for every casting poured because it is evaporated ("lost") in the process.
Process Steps
1.Mold foam pattern sections.
2.Age pattern to allow dimensional shrinkage.
3.Assemble pattern if it is a multiple piece pattern.
4.Build cluster (multiple patterns per cluster).
5.Coat cluster.
6.Dry coating.
7.Compact cluster in flask.
8.Pour metal.
9.Extract cluster from flask.
Black area------sand preparation and molding system
1. manipulator
2. winnowing Magnetic separators
3. sanded-up equipment
4. vibrating conveying screen classifier
5. chain elevator
6. water-cooled sand cooling equipment
7. tri-dimensional vibrating table
8. vacuum system
9. dust collector
White area------make the foam mould
1. batch-type pre-foaming machine
2. vertical type mould forming machine
3. bonder machine
4. coating stirring mill
5. hot gas far infra red drying oven
Advantage and disadvantage
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 un-bonded sand of lost foam casting can be much simpler to maintain than green sand and resin bonded sand systems. Lost foam is generally more economical than investment casting because it involves fewer steps. Risers are not usually required due to the nature of the process; because the molten metal vaporizes the foam the first metal into the mold cools more quickly than the rest, which results in natural directional solidification. Foam is easy to manipulate, carve and glue, due to its unique properties. The flexibility of LFC often allows for consolidating the parts into one integral component; other forming processes would require the production of one or more parts to be assembled.
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.
Expandable Pattern Casting (Lost Foam)
Also known as Expanded Polystyrene Molding or Full Mold Process, the EPC or Lost Foam process is an economical method for producing complex, close-tolerance castings using an expandable polystyrene pattern and unbonded sand.
The EPC process involves attaching expandable polystyrene patterns to an expandable polystyrene gating system and applying a refractory coating to the entire assembly. After the coating has dried, the foam pattern assembly is positioned on several inches of loose dry sand in a vented flask. Additional sand is then added while the flask is vibrated until the pattern assembly is completely embedded in sand.
A suitable downsprue is located above the gating system and sand is again added until it is level to the top of the sprue. Molten metal is poured into the sprue, vaporizing the foam polystyrene, perfectly reproducing the pattern. Gases formed from the vaporized pattern permeate through the coating on the pattern, the sand and finally through the flask vents.
In this process, a pattern refers to the expandable polystyrene or foamed polystyrene part that is vaporized by the molten metal. A pattern is required for each casting.
Advantages
No cores are required.
Reduction in capital investment and operating costs.
Closer tolerances and walls as thin as 0.120 in.
No binders or other additives are required for the sand, which is reusable.
Flasks for containing the mold assembly are inexpensive, and shakeout of the castings in unbonded sand is simplified and do not
require the heavy shakeout machinery required for other sand casting methods.
Need for skilled labor is greatly reduced.
Casting cleaning is minimized since there are no parting lines or core fins.
Disadvantages
The pattern coating process is time-consuming, and pattern handling requires great care.
Good process control is required as a scrapped casting means replacement not only of the mold but the pattern as well.
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