In our previous blog on sand core basics, we were dealing with a solid pattern. Wherever possible, patterns with an irregular shape are made in two halves called a SPLIT PATTERN. With a SPLIT PATTERN, we place the bottom part of the pattern face-down in the drag. We then ram green sand around the pattern, flip the drag, pattern, and rammed sand over. We then place the top-half of the pattern on top of the bottom-half, ram green sand around the pattern, insert some risers and sprues. We then lift the cope off of the drag, remove the patterns and complete the rest of the mold (SPRUES, GATES, and RISERS) so that it is ready for pouring.
In the graphic below, we have the SPLIT PATTERN for a hollow pipe with flanges on each end. The pattern can be split in half along a "PARTING LINE". The two halves of the pattern are kept aligned by holes in the bottom half of the pattern and wooden dowels that protrude from the top half. The wooden dowels align with the holes in the bottom half of the pattern. Here's what our pattern would look like.
Now that we have added CORE PRINTS to the PATTERN, we place the bottom half of the pattern face-down in the drag, and ram the drag with green sand.