Tip #7: Avoid Mixed Parts/Contaminated Lots
Mixing of fasteners during heat treatment is commonplace. Avoidance and understanding of where fasteners tend to “hang up” in the system is perhaps the best strategy to combat this problem.
1. Leave adequate gaps (10-20 minutes) between different-sized fasteners and different part/lot numbers.
2. Clean out quench tanks after each lot has exited the furnace. Often operators use magnets mounted on poles to retrieve fasteners from quench or rinse tanks.
3. During maintenance shutdowns, drain all tanks (pre- and post-washers, quench and dip tanks) and inspect where parts are accumulating. Not only remove these parts from all areas but implement solutions to keep parts from gathering in these areas.
4. Use separator screens after the quench and after the temper to segregate fasteners by size.
5. Remove stragglers from the system by off-line visual or size-sort means.