Oh Snap!

[Cigalert]

I'm having a bit of an issue with a main ingredient to my production...a large spiral mixer has been acting like a cat. When it's moving it snaps and outside that it's been laying around not doing shit.

First off, 2 weeks ago the main shaft that turns the "hook" snapped. This is a 2' x 3" shaft....snapped. WTF...I've never seen anything like it. It's belt driven by 9 v-belts but I would think the belts would slip before this thing snaps. Either way, got a new way turned out of 304 and replaced all the bearings as a precaution.

2 days after the install 3 M20x55mm socket head bolts snapped. So this time, instead of the main drive shaft giving up the bolts that attach to it are the weak link. The bolts hogged out the holes pretty good so I laid, upside down re-tapping the blind holes in an attempt to save me half a day.

In the last week all 3 of the "hook" bolts snapped again. So I'm reading a little about these bolts. "They have a Class 5g6g thread fit, a minimum Rockwell hardness of C39, and minimum tensile strength of 174,000 psi. " 174k psi and these things are shearing like a fireball cap at riverland.

The bolts are seated properly, the threads are clean, the surfaces are faced....I'm running out of patience and if this shit goes down tonight I can kiss my next few days off cause I'll be pulling a 30 hour shift trying to get holiday orders out for tomorrow.

Below is a pic of the hook. 3 bolts install at the top of the hook into the shaft.

If someone can tell me how dough can snap 3 M20 bolts without throwing a 6' pry bar inside while It's running gets to be the first subscriber of my "loaves for life" repayment program.

[WESTERNAERO]

Is the thread bottoming out before the bolt shoulder is making contact? I don't see any marks or scoring from the auger flange or a washer on the shoulder area of the bolt.

[Cigalert]

Is the thread bottoming out before the bolt shoulder is making contact? I don't see any marks or scoring from the auger flange or a washer on the shoulder area of the bolt.

There is about 1/4" to the bottom. The bolts pictured were only in about an hour before snapping.

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[CampbellCarl]

....."When its moving it snaps".....Are you saying that you can hear a snapping noise while it's operating? I'm thinking a binding or alignment issue is causing the hook then bolts to give up. Are there any kind of alignment adjustments on the gear box (or whatever drives the hook)?

[WESTERNAERO]

Are there drive dogs or pins from the shaft to the auger? Or are the bolts acting as the torsional(twisting) load?

[HB Vic]

Lighten the load on the poor old girl

[Cigalert]

....."When its moving it snaps".....Are you saying that you can hear a snapping noise while it's operating? I'm thinking a binding or alignment issue is causing the hook then bolts to give up. Are there any kind of alignment adjustments on the gear box (or whatever drives the hook)?

Zero alignment. The only potential for slop was in the bearings on the shaft. Plus, there isn't anything that puts pressure on the hook outside of dough.

Are there drive dogs or pins from the shaft to the auger? Or are the bolts acting as the torsional(twisting) load?

The bolts are the only acting device against a load. Unless the bowl goes through a catastrophic failure (which is has) there's no real "load" outside of a 60% moisture content of dough.

Lighten the load on the poor old girl

Obviously over-loading can cause this, over time....but I am running at or under manufacturers specs for load handling. These bolts are shearing clean like its getting jarred and not worn. But I don't think purposely tossing a forklift into the bowl would shear the bolts....the belts would give up first. The bolts have snapped in the past but they looked worn....threads flattened..slightly backed out. That was a one time event 4 years ago...this is different. This keeps happening.


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[HB Vic]

Did you know slamming a 500hp motor in gear at high rpm's will shear a 1 1/4" prop shaft clean in half like it was cut with a saw?

[HB Vic]

Lighten the load and use softer hardware

[Stainless]

Hey Cig, is it possible the bolts are loosening under load and then shearing?