Impact wrench opening torque?

Captain Slow IRL

Hi all,
Hoping someone can help me understand something a little better! An impact wrench (here) states that it's bolt break away torque is 840Nm. Does this mean that if something has been tightened to 830Nm, it will open it?
Thanks in advance!

mathew

Dont know if you can tighten something to a specific torque.. but ye, it'll provide up to 840Nm of torque, so if 830Nm is required to open a bolt, that wrench will do the job...

milltown

Not quite that simple in practice as it depends on a great many factors, probably most importantly how recently the bolt was tightened to 830NM. Also will depend on the material in the bolt and the substrate, how clean it was when tightened, temperature then and now etc. etc. etc.

Really, it matters not what torque it was tightened to as that could have little bearing on what's required to break it loose. From experience, bolts tightened to 330NM on HP water pumps could take almost twice that to loosen after a few months in service. That example is purely subjective btw. I never used a torque wrench to loosen a bolt but I'm basing my guesstimate on the amount of leverage and sweat required to loosen vs. tighten.

Captain Slow IRL

I'm assuming fresh, clean threads (unlubricated)

I bought one of these guns, recently and have had trouble removing, admitedly, rusty studs. When I tried to loosen them with a breaker bar and socket, they take very little effort - an awful lot less than 840Nm!