Re: Emerg Repair Of Drive Drum
You just have to gouge out down to the edge of the disc; provide a decent weld prep; fill it up and grind smooth.
This crack probably started life over a void left by inadequate weld penetration or deliberately entrained slag. Deliberately; because some slag entrainment is allowed for in most weld strength assessments. That void or SE presented a loss of support to the shell and the shell has cracked over time. So; if you fill the void you will get a better drum than was originally supplied. The weld prep must extend over the diaphragm whereas the crack does not.
What surprises me is how you managed to spot the crack. I didn't know Vegamite produced X-Ray vision!
As a precaution the rest of the perimeter could be US checked for voids etc. I'll dig out a crack propogation programe for you later today. You will know when you have gouged out enough when you come to the void, etc..shell thickness & all that. The rapid growth indicates that the void was quite large; so we are thinking about the old chestnut of entrained electrode used to fill up a large weld zone. With all the hype about shell/diaphragm connections over the last thirty years one would think that the weld inspectors would be up to the job. ■
John Gateley johngateley@hotmail.com www.the-credible-bulk.com
Welding Help
I agree with everything john has stated previously. The one thing I would ad is to use
ispropyl alcohol to clean out the crack and bring it out to the naked eye. I also know of another welding helper- drill ahole in the end of the crack to stop it from spreading further. ■
Re: Emerg Repair Of Drive Drum
Thanks John etc
The crack was spotted when the lagged segments - replacable - were changed. No Vegemite was used in the process.
Much better to find this out rather than endure the consequences.
Trying to lift up 30T of belt/buckets and material will not be nice.
We will be doing a weld repair in 2 days and new pulley (aussie built and made) will be here in 2 weeks.
The crack has grown 150mm in 2 weeks and the shaft is obv. flexing and deflecting more as it rotates . can see the movement/run out at the driuve unit torque arm.
The crack would have intiated at the root....suggest undercut or overroll. Cold comfort for us, have to check a few others now.
Cheers
James ■
Emerg Repair of Drive Drum
HI All,
We have a bucket elevator and have found the drive drum shell to be cracked on the outside.
The crack lines up with the end disc/sheel weldment - connection.
There is no cracking evident on the outside surface of the dis or weld. So we beleive that the crack originates from the root of the weldment.
The crack extends for about 1/6th of the shell circumference.
The pulley design is taped end disc with welded connection to the shell and Bikon 3 part locking elements.
The crack is on the NDE of the pulley ie does not carry much torque.
We need to ensure that the pulley does not fail drastically until a new unit has been fabricated and delivered - not the right time of year.
To do so, we are thinking of repair welding up of the crack - full depth - in situ style.
Has anyone:
Performed successful repairs with welding of pulley shells.
Any idea on what the critical crack lenght would be - it has grown 150mm over the past 2 weeks...speed is 39rpm and carryies a lot of load.
Many thanks
James ■