A swab soaked in MEK is rubbed back and forth across the cured film, usually 50 double rubs, and the surface is rated for softening, dulling and color transfer to the cloth. A fully cured thermoset barely changes; an undercured one smears and rubs through. It is the most common quick cure check on the line, although some chemistries naturally show slight rub-off even when properly cured.
Did a 50 double-rub MEK on the first rack, slight dulling, no color on the rag, we're good.
Run the rub test on a known good part next to the suspect one, because some chemistries always show a little color on the rag.
Also heard as
- MEK rub
- solvent rub
- double rubs
Related terms
Undercure
A film that did not get enough time at temperature to crosslink fully, so it looks fine but performs poorly.
Fingernail test
The rough floor check of cure: dig a thumbnail into a cooled part and see if it marks.
Pencil hardness
A scratch test that rates film hardness by the hardest pencil lead that will not gouge it.
Cure schedule
The time at temperature a powder needs to cure fully, measured at the part's metal, not the oven air.