This news article was originally written in Spanish. It has been automatically translated for your convenience. Reasonable efforts have been made to provide an accurate translation, however, no automated translation is perfect nor is it intended to replace a human translator. The original article in Spanish can be viewed at El proceso Lost Foam con modelos de poliestireno expandido

The Lost Foam process with models of expanded polystyrene

15/04/2003

As with many other technologies, the smelting processes they are well in recent years to incorporate to them some of the results of research in engineering. In this way they have only managed to survive the best methods, including the so-called lost foam, and it is based on the use of non-permanent models of expanded polystyrene (EPS).

This process has some similarities with the lost wax process, as both use non-permanent models, but while the wax is melted and therefore does not destroy, the EPS disappears completely by vaporization in the casting stage.

Foundry process

Once obtained models of EPS, and before coating them with sand, these are checked if they had a defect which is reproduced in the final piece.

The initial coating of the model is typically done with a consisting of finely divided siliceous materials refractory porridge and a liquid of transport that is usually water. It is then covered with refractory sand compacted by vibration.

When the sand has reached the adequate height you can proceed to the casting of metal which can be done following the same techniques employed in conventional molding. In this case the key parameters will be the temperature of casting and casting speed. To go adding the casting metal, high temperature, will lead to the destruction of the model leading to gas which run through the coating.

Comparison of the traditional process in sand with the process lost foam

The casting of metals in molds made of sand is still a common practice. Molds are usually made in two parts so that models can retire before casting. Own models are often made in two parts. If the strained parts are empty is required the presence of males.

Advantages of the process lost foam

As in all processes that use non-permanent models, it avoids the problem of storage models.
The accuracy of the strained parts is great, allowing the use of EPS to very tight tolerances.
Simplicity in stages and possibility of recycling that can save some of their materials.
Facilitates the recycling of the sand due to the absence of binder
The amount of used sand is generally lower than in a traditional method.
The use of males and the intervention of specialised personnel in its production is not necessary.
Models may be prepared by combining simpler parts with suitable adhesives.
Ease of automation which is a decrease in costs of operation and defects of models parts and molds.
Better surface finish than with the molding of surface sand, and absence of burrs and lines of partition in the final piece.
Freedom of design, being this practically unlimited.
Possibility to incorporate inserts metal in the piece of cast iron

Different models &quote;lost foam&quote; EPS

Different models "lost foam" EPS

In the process lost foam, the model is made from EPS machined or moulded parts. The mold is usually without dividing and models can be of one piece. The models are simpler and reduces the number of operations needed for its realization.

The absence of partition lines is another advantage resulting from the use of a mould without dividing; reduces the finishing operations and it is easier to make high precision parts.

Applications:

From the very beginning the main field of application was that of the automotive industry. Thus, many manufacturers produce parts with models of EPS being noticeable advantages. Lately there has been the extension from the automotive industry to other sectors requiring parts or components of cast iron.

Another great application is the sculpture that in this case, the lost, and the wax model not only allows the Elimination of the negative mold, but ignores all a repertoire of tedious operations such as the development of a way to motherthe preparation of the mold by piece, the manufacture of the male, the dumping of the wax and the Elimination of the same, the cooking of the mould, etc.

Currently, they are even integrating the mass of heterogeneous material EPS which plastically will be incorporated into the sculptural work