Sealing plastic bags.
Anti static bags.
Take your least used (crappiest) soldering iron tip, adjust temperature to 500'C, clean tip.
Lay a bag (to be sealed) on a flat surface with a silicone baking sheet under the bag.
Place a metal ruler at the point of required sealing.
Draw the iron tip at ~1 second per inch along the straight edge.
For zip lock freezer bags, turn the temperature down to ~400'C.
You will have to experiment with speed for your conditions.
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