что-то вроде "время (шлифования) без искр", "время шлифования без подачи" -
"Spark out is a term used when precision values are sought and literally means "until the sparks are out (no more)". It involves passing the workpiece under the wheel, without resetting the depth of cut, more than once and generally multiple times. This ensures that any inconsistencies in the machine or workpiece are eliminated." - https://en.wikipedia.org/wiki/Surface_grinding

https://www.eng-tips.com/viewthread.cfm?qid=80602

https://books.google.co.uk/books?id=GQgJAwAAQBAJ&pg=PA281&lpg=PA281&dq=%D0%B2%D1%80%D0%B5%D0%BC%D1%8F+(%D1%88%D0%BB%D0%B8%D1%84%D0%BE%D0%B2%D0%B0%D0%BD%D0%B8%D1%8F)+%D0%B1%D0%B5%D0%B7+%D0%B8%D1%81%D0%BA%D1%80&source=bl&ots=WTWMQg7evN&sig=ACfU3U1u_3MKPcIcu5mX6AEpQAojswmPhg&hl=en&sa=X&ved=2ahUKEwjx38_x5tviAhWhqHEKHT4dBEQQ6AEwAHoECAgQAQ#v=onepage&q=%D0%B2%D1%80%D0%B5%D0%BC%D1%8F%20(%D1%88%D0%BB%D0%B8%D1%84%D0%BE%D0%B2%D0%B0%D0%BD%D0%B8%D1%8F)%20%D0%B1%D0%B5%D0%B7%20%D0%B8%D1%81%D0%BA%D1%80&f=false

"число оборотов для вывода искры (шлифование без подачи)"
-здесь деталь вращаетеся и число оборотов - это то же время.