Rheocasting

GISS TECHNOLOGY INCREASES CASTING QUALITY AND SIGNIFICANTLY REDUCES PRODUCTION COSTS OF ALUMINUM CASTING PROCESSES

Rheocasting’s new technology called Superheated Slurry Casting Process allows high-quality castings to be obtained without the need for changes to the mold or press layout. Unlike other semi-solid technologies, the patented model preparation process is extremely simple to implement and opens up new opportunities not only in die casting but also in low pressure and gravity casting.

Technology

The patented Giss technology, of which Mambretti is the exclusive distributor, refers to the preparation of molten metal for foundry processes with  low or zero _Superheat_ temperature.

The difference between the pouring temperature and the _liquidus_ temperature  is called the overheating temperature or _Superheat temperature._  In foundry practice the _Superheat_ temperature  is quite high, generally between 80 ° and 200 ° in relation to the complexity, size and thickness of the casting to be produced.

The technology that refers to the casting of metal at temperatures lower than or equal to those of _liquidus_ is called _Semi-solid casting_ that has existed with different application methods for some decades now. This is the metal casting containing a fraction of solidified stable cores. This fraction reduces the turbulence of the flow and the solidification times and consequently reduces the possibility of porosity from gas and shrinkage with undoubted improvement in the quality of the jet.

However, the semi-solid casting process requires changes to the mould and process in order for the technology to be successfully applied. As a rule, an intermediate metal transfer step (e.g. a prefabricated billet with a non-dendritic structure) is required for the semi-solid to fill the container and the mold cavity

For this reason, the application of semi-solid technology in mass production requires time and considerable investment. The majority of semi-solid processes do not reach high targets in terms of cost/benefit ratio and after a first phase of initial enthusiasm have not been adopted at industrial level.

Giss technology, on the other hand, eliminates the inherent disadvantages of the semi-solid process through a patented metal preparation process that allows to obtain the benefits of the semi-solid without major and expensive changes to the mold and the process.

Process

The Giss process – definable within the category of Rheocasting – exploits the so-called thixotropic  properties of metals prepared with special techniques (in this case the preparation is the object of the patent) which, at temperatures within the solidification range, despite having the consistency of an extremely plastic solid, if mechanically stressed have a viscosity close to that of the liquid.

The thixotropic property is given to the molten metal by the type of solidification structure with which it is produced, of globular type, the result of agitation through the gas to which the metal is subjected during solidification in the cup: the dendritic structure in formation is continuously fragmented by agitation until almost complete solidification, giving the metal a very fine crystalline structure with a rounded appearance.

The desired conditions are achieved by shaking the molten metal through a heat extraction probe inside a container that can be the crucible or pouring cup.

Benefits

From the point of view of the process, the fact of injecting a material at a lower temperature is a great advantage because it greatly lengthens the life of the mold and, given in any case the lower turbulence and reactivity of the melt, allows to drastically lower the porosity of the gas.

From the metallurgical point of view, the lower injection temperature (lower than that of _liquidus_) reduces the solidification shrinkage by limiting the formation of porosity from shrinkage and generates higher solidification speeds to the advantage of the crystalline structure.

In general, however, there are many advantages of the application of this technology and are not only inherent in the quality of the castings. The main ones are as follows:

  • Removal or reduction of squeeze pins with the same cast-part quality

Shorter cycle time:

  • Shorter solidification time
  • Shorter lubrication-drying time
  • Shorter metal pouring time into the shot sleeve

Longer mold life:

  • Second phase speed reduction
  • Lower mould temperature
  • Shorter residence time of the casting in the mold
  • Smaller amount of emulsion per shot

Dimensions:

  • Small footprint
  • Ease of implementation in the die-casting island

Consumption:

  • Reduction of wastewater
  • Reduced energy consumption
  • Ev. smaller press size