Wire helix, rinsing, blasting...
The molding material is mechanically removed or rinsed or blasted after the casting process. The tube which remains in the cast piece represents the subsequently needed channel.
There are several possibilities for drawing the pattern. With most applications it is already sufficient to ecologically remove the molding material with high pressure and water. It is generally possible within the cycle times given by the production process (within a few seconds).
Short documentation of the pattern drawing equipment (PDF, 62 KB)
REM surface analysis: No filling leftover detectable (PDF, 496 KB)
As an alternative version there is a wire helix that is put in the tube with the molding material and is used as a later pattern drawing support. The channel is lifted by drawing after the cast.
The molding material can be disposed and recycled without any problems.