Hole design for pellet die - Relief / Counterbore

Hole Design is Important for Pelleting

According to Fairfield et al. (2005), relief is a counterbore on the outside diameter of the die. It is necessary when a thick die is required for strength but desired effective thickness is less. Three types of relief are usually used.

1. Two-step relief
   Is a combination of the two straight counterbores with the second stage drilled slightly larger than the first.
   It can be used when a very deep relief is required because of a very short, effective pelleting length on a thick die.
   This reduces the possibility of pelleting in the relief (double pelleting).
2. Straight relief
   The most common pellet die, is simply a counterbore on the outside diameter that is slightly larger than the actual diameter of the pellet hole.
3. Tapered relief
   Can be used to replace straight relief or in combination with a straight relief to provide a two-step relief.
   It removes less metal and improved die strength.