The lost foam casting process starts with a polystyrene foam as the mold material which can be carved, machined from a foam block, or created using a process similar to injection molding. A completed polystyrene foam mold is then coated with a ceramic refractory to support the foam’s external form in which the lost foam mold sits. The foam in the casting process is evaporated as molten iron poured into the flask, after then the castings precisely duplicate all of the features of the lost foam pattern.
The pattern is made from molded polystyrene foam. The final foam pattern is approximately 97.5% air and 2.5% polystyrene.
The foam is coated with ceramic refractory by dipping, brushing, spraying, or flow coating. The coating process creates a barrier between the smooth foam surface and the coarse sand surface, which also controls permeability and allows the gas created by the vaporized foam pattern to escape through the coating into the sand. The coating forms a shell so that the molten metal does not penetrate and avoid sand erosion during pouring.
After the ceramic coating dries, the cluster is placed into a flask and baked up with un-bonded green sand. The green sand is then compacted by using a vibration table until it is ready to be poured.
After the sand mould compacted, molten metal is poured into the gating system, in which foam pattern vaporizes and is replaced by metal. Air vents in the side of the flask allow vapor to immediately escape. Pouring will continue until the mold is filled and extreme care is taken to ensure that the correct amount of molten material is poured.
Once the mold has been filled, it is left in sandpit, waiting for the molten material to solidify. Once solidification has taken place, the sand and shell mold are shaken off, and gating system is removed, leaving behind the final lost foam casting parts or products. A cutting process is necessary to separate the castings.
The final lost foam casting parts can then also be heat treated or undergo other finishing operations, which includes cutting away the gates, risers, and runners, sand-blasting or grinding the metal to the required degree of smoothness, and other necessary machining processes.
In China, few foundries involve in lost foam casting. And almost 70% investment casting companies focus their business in lost wax casting process. So only few people have a knowledge on lost foam casting technique. To let you know this casting method better, below we list out the main differences between lost foam casting and lost wax casting:
| Property | Lost Foam Casting | Lost Wax Process |
|---|---|---|
| Composition of Pattern | Expanded Polystyrene (EPS) | Microcrystalline Wax |
| Density of Material used for pattern | Density of Expanded Polystyrene Patterns – 42 kgs./m³ sufficient for strong, sturdy, dimensionally accurate and light patterns | Density of Microcrystalline Wax Patterns – 795 kgs./m³, resulting in heavy delicate patterns |
| Maximum Size of Cast Part | No limitation of size for cast part as EPS Pattern can be molded in sections and finally assembled to form a single pattern | Approx. 200-300mm |
| Maximum Weight of Cast Part | No limitation of weight of cast part | Well Below 125 kgs |
| Rejection of Shell during process | The ceramic shell does not crack during the burn-off process as EPS does not expand but evaporates/melts | The ceramic shell has a tendency to crack during the autoclave process due to the expansion of Wax |
| Pre-Heating of Ceramic Shell | No required, pouring is possible at room temperature of ceramic shell | Required |
| Methoding | Flexible, risers are simply glued on the pattern to suit the methoding. Furthermore the feeding ability of riser is improved with the use of exothermic sleeves | Difficult and has limitations in addition to the problem of riser backfilling |
| Ceramic Shell Thickness | Approx. 5-10mm depending on the size of component | Approx. 10-15mm |
| Pattern/Casting Prototyping | Easily possible as EPS foam can be machined and assembled to form patterns | Difficult |
| Effect of atmospheric heat on patterns | No effect on EPS pattern once cooled in the molding tool | Possibility of Wax pattern to warp or bend |
Precise Cast is recognized as the world leading company in lost foam casting technology. We offer a comprehensive line of lost foam casting equipment, including flask pouring, flask handling and flask compaction. Our production line of foam bead processing equipment is recognized worldwide as the industry standard. For more information or to discuss your particular requirements please contact our technical sales team on telephone number, send us a message or email: [email protected]
