In summary, pinholes are surface pores with a small diameter that are located primarily on the outside of the cast piece or just below the casting skin. There are hydrogen pinholes, hydrogen-nitrogen pinholes and CO-slag reaction pinholes. The blisters that are not connected to the surface often contain a thin graphite film.
In essence, it is possible to successfully fight and prevent pinholes with the mold technology and metallurgical measures mentioned above.
ASK Chemicals offers the following solutions with regard to products and expertise:
- An optimized cold box binder with high reactivity and a low percentage of solvents
- Nitrogen-free no-bake binders
- Water- and alcohol-based coatings for highly stressed cold box, hot box or Croning® (registered trademark of ACTech GmbH) cores in gray iron casting and nodular casting, with coatings that can be flooded, dipped, sprayed and brushed.
- Nitrogen-adsorbing coatings
- Materials that form lustrous carbon during casting and that release a large amount of constituents that can be gasified (= volatile constituents), which in turn contain a sufficient amount of carbon and as little oxygen as possible.
- Inoculants with reduced aluminum content
- Nitrogen-free feeder systems
- Transferring expertise to optimize the gating system in order to give the melt little opportunity for oxidization (short flow paths, avoidance of turbulence), and to thereby achieve a reduction of slag formation.