For the determination of the * current porosity potential * a measuring system, corresponding to the current state of technology, is developed to take the whole range of possible formation of porosity into consideration.
For this, samples which solidify at atm. pressure respectively at 80 mbar, are analysed. The determined "DENSITY-INDEX" is a reliable indication for the solidification-character of the melt.
Current knowledge shows clearly, that apart from the free hydrogen there is always an unknown quantity of oxides and impurities existing, which is responsible for the development of micro-shrinkage and which contribute a considerable part to the possible formation of porosity in the melt.
Typical solidification defects caused by micro-shrinkage respectively gas porosity are compared in the following picture.
The Knowledge about the currently existing quantity of free hydrogen is only a statement of part of the possible porosity. That means there is an further unknown amount of porosity, because there is no stable relation between free hydrogen and oxides ( combined hydrogen ).
Especially since the application of mechanical melt cleaning systems, the understanding of the relationship hydrogen/oxides has gained significance. With VAC-TEST therefore a measuring method was developed which gives the user a reliable statement of the total porosity potential.
Today the use of these systems is a welcome aid for the assurance of quality. In our efforts to achieve market share we should consequently apply our technological know-how to safeguard and document our high quality standards through the use of reliable quality systems.
Even these systems should receive a regular maintenance, of course proved by certificate and stamp. For the requirements of current quality regulation (e.g. quality-standards, ISO9001 etc.) this is an absolute necessity.