Broken blade.

[Ktrim]

So while mowing Saturday on zero turn, cruising along suddenly it sounded like the entire deck was self imploding. I immediately turned off deck drove to the garage and found right outer blade was missing half its blade. I did not hit anything in recent memory and blades had been wire wheeled and sharpened around 3 or 4 mowings ago. At that time blades were visually inspected and no obvious defects were spotted. Has anyone ever had this happen??
The big dings in the half still there I believe are from the piece getting hit when it came off.

 

[NCL4701]

Hard to tell without seeing the broken edge but hard to imagine it wasn’t stress fractured from a prior impact. With something as hard as a mower blade fractures can be difficult to see on visual inspection prior to catastrophic failure such as you experienced.

If you look at the broken edge and see anything other than bright, shiny metal that would support a prior fracture that finally let go.

And no, I’ve bent blades, knocked chunks out of blades, but never had one break a huge chunk off like that. Seen a LOT of catastrophic metallurgical failures due to previously unknown fractures but not specifically on a mower blade. Can imagine that was a quite jarring experience.

 

[Flintknapper]

Never experienced a 'broken' blade on any mowing device in over 50 years of mowing.

Bent some, had large chips taken out, hit some pretty significant objects (enough to shear a crank/flywheel key). But have never had a blade actually break.

I can imagine the horrendous imbalance that would have resulted. Bet that was 'special'.

 

[Ktrim]

Never experienced a 'broken' blade on any mowing device in over 50 years of mowing.

Bent some, had large chips taken out, hit some pretty significant objects (enough to shear a crank/flywheel key). But have never had a blade actually break.

I can imagine the horrendous imbalance that would have resulted. Bet that was 'special'.

Special it was.🫨Luckily didn't damage anything else. All new blades. All is good again.

 

[GrizBota]

Never experienced a 'broken' blade on any mowing device in over 50 years of mowing.

Bent some, had large chips taken out, hit some pretty significant objects (enough to shear a crank/flywheel key). But have never had a blade actually break.

I can imagine the horrendous imbalance that would have resulted. Bet that was 'special'.

Had one of the blades on my brush hog break at the pivot point. But I’ve hit more stumps and large brush than I can say. Things got pretty wobbly until I turned off the PTO.

 

[lynnmor]

Hard to tell without seeing the broken edge but hard to imagine it wasn’t stress fractured from a prior impact.

If we could see the broken edge straight on then we might be able to determine the cause. Vibration and imbalance can cause fatigue cracks over time, it doesn't have to be a violent collision.

 

[Ktrim]

If we could see the broken edge straight on then we might be able to determine the cause. Vibration and imbalance can cause fatigue cracks over time, it doesn't have to be a violent collision.

Blades are always balanced when sharpening. However I did have a bad hub a while back. Bearings were shot. That blade may have been on it and fatigued it. ????

 

[Ktrim]

Straight on pic

 

[Flintknapper]

Had one of the blades on my brush hog break at the pivot point. But I’ve hit more stumps and large brush than I can say. Things got pretty wobbly until I turned off the PTO.

Yep, with a rotary cutter (Brush Hog) one blade can get knocked over the top of the other and become wedged there. It will nearly shake you out of the seat before you can disengage the PTO.

 

[GrizBota]

Yep, with a rotary cutter (Brush Hog) one blade can get knocked over the top of the other and become wedged there. It will nearly shake you out of the seat before you can disengage the PTO.

Yes Sir. Been there, done that, got the T shirt.

 

[NCL4701]

Straight on pic

Not the most glaringly obvious example, but IMO the coloration strongly suggests that was cracked prior to the final failure.

Lynnmor is certainly correct that vibration can cause stress cracking so it could have been from excessive vibration over time. Also could be from a prior impact, or possibly from damage caused in manufacturing or shipping.

If it was vibrating enough to cause fracturing from fatigue, I would expect the operator to pick up on that as it would have to be pretty significant vibration. Can’t totally rule it out, though.

Manufacturing defect isn’t totally excluded either, but unlikely based on the extreme rarity of this type event. The glaring weakness of that argument for exclusion is it’s basis in anecdotal evidence rather than real research.

Impact starting a crack that may have progressed due to normal stresses of use until it failed: given the normal use of a mower blade, that would still be my strongest suspect. Potential fractures that are undetectable without testing that isn’t cost effective on a mower blade is the reason if you ever hit something hard enough to bend a blade it should be replaced rather than bent back and put back in service. Argument against prior impact would likely be it wasn’t bent and didn’t have other indication of severe impact when it was recently serviced.

That’s my opinion which isn’t worth much.

 

[GreensvilleJay]

so the 64K$ question...
did you FIND the missing half ?????
Knowing Mr. Murphy, if you haven't, you will ,in a rather bad way........
When you do, take both pieces to dealer, ask the parts person what glue to they sell to put them back together...... after the laughs, maybe,just maybe, they'l cut you a deal for a new blade.

I'm just happy nobody got hurt when '1 became 2' !!!!

 

[lynnmor]

Straight on pic

We can see that the break originated right next to the mounting surface or washer. Make sure that the surfaces contacting the blade are flat to minimize a stress point.

 

[Ktrim]

so the 64K$ question...
did you FIND the missing half ?????
Knowing Mr. Murphy, if you haven't, you will ,in a rather bad way........
When you do, take both pieces to dealer, ask the parts person what glue to they sell to put them back together...... after the laughs, maybe,just maybe, they'l cut you a deal for a new blade.

I'm just happy nobody got hurt when '1 became 2' !!!!

Actually in corn field somewhere. Maybe find it the fall. 30 seconds earlier it would have hit, or gone through the side of the house.

 

[jimh406]

So while mowing Saturday on zero turn, cruising along suddenly it sounded like the entire deck was self imploding. I immediately turned off deck drove to the garage and found right outer blade was missing half its blade.

What brand/model is your mower?

 

[Ktrim]

What brand/model is your mower?

Kubota z122

 

[CGMKCM]

Not a metalurgist so FWIW. Based on picture in post #8. I wonder if that blade was a little loose and the compression washers spun creating heat in that area. It looks like a color change in the metal where the washer would contact the blade.

 

[Ktrim]

Not a metalurgist so FWIW. Based on picture in post #8. I wonder if that blade was a little loose and the compression washers spun creating heat in that area. It looks like a color change in the metal where the washer would contact the blade.

I see what you're talking about but all was set and tight. Rechecked torque before removing bolts. ?????