Shot forms when polymer leaves the die faster than the air can draw it out, or when the melt is too hot and thin, so droplets freeze as beads instead of fibers. It shows as hard specks, and in barrier and filter fabrics each bead is a weak point that lowers hydrohead or opens a pinhole. Cutting throughput per hole and retuning air flow, melt temperature and die settings bring it down.
Lots of shot on the MB layer since the throughput increase, and hydrohead is down ten centimeters.
If shot appears right after a resin lot change, check the melt flow rate before touching the die settings.
Also heard as
- shot defect
- polymer beads
Related terms
Meltblown
Web of very fine fibers made by blasting molten polymer from a row of tiny die holes with hot, high-speed air.
Hydrohead
Shop and spec clip for hydrostatic head: the water pressure a fabric holds before water comes through.
Pinhole
Tiny hole in a barrier fabric or film that lets liquid or particles through.
Melt flow rate
Grams of molten polymer pushed through a standard die in 10 minutes, the basic measure of how easily a resin flows.
Same word, different worlds
One full stroke of a manual grease gun, the everyday unit for how much grease goes in.
Welding, Brazing & NDEShop word for a radiograph of a weld, or the act of X-raying it, as in the weld got shot.
Nuclear Safety & Radiation ProtectionA single industrial radiography exposure, used to x-ray a weld with a gamma source or X-ray tube.
Photonics & LasersA single laser pulse, especially from a high-energy or low-repetition-rate system.