Aluminium Die Casting: Coating Ladles and Dies with Boron Nitride Coatings

In the die casting and pressure die casting foundries ladles from cast irons or from cast steel are usually used. Due to the large mass these ladles extract large amounts of heat from the melt. In order to avoid this disadvantage, the metal casting working group of the FH Aalen uses cylindrical ladles made out of formed metal sheets. The sheet metal has a wall thickness of 0.8 mm. These ladles have only a small mass and to extract therefore only small amounts of heat the melt.

Usually ladles in the Aluminum foundry industry are protected from an attack of the melt with Boron Nitride Coatings. The more thin-walled however the ladle is, the more important is an appropriate protection by a coating. So consumption of ladles is to be reduced among other things. Still more important is however the avoidance of the iron accommodation of the aluminium melts from the ladles. The metal casting working group of the FH Aalen used ladles coated with the Boron Nitride coating by spraying. It was shown that the coating remains practically unwetted by the aluminium melts, which are poured in the test foundry of the metal working group. Also after numerous castings the non-wetting behaviour of the coating is preserved. This is in as much noteworthy as the non-wetting of the ladle surface prevents a skin formation in the ladle. These skins bring numerous problems with itself. They oxidize at the surface and when reconducting the ladle into the holding furnace then they are usually brought in. Gradually so the oxides in the melt are enriched. Simultaneous their accumulation in the cast parts is to be determined.

Since the Boron Nitride Coating is relatively soft due to the small hardness of the boron nitride, a damage of the coating layer can occur by a mechanical effect. A damage of the coating became apparent with the attempts at the top margin of the ladles. This is caused by hitting the ladles upon outside parts of the holding furnace in order to remove possible remains of the melts from the ladle.

If such a mechanical damage of the coating is avoided, can be operated here with satisfying service lives of the coating.