Looking for a method to recognise...

[Halla26]

Hello all

Basically we have a large oven in work that has a large rotating slat conveyor inside, each slat held by 2xM24 hexagonal bolts either side onto a chain conveyor. Currently conscientious employee's watch the conveyor going round occasionally to see if any of the bolts have fell out or worked loose, quite easy to tell if one is missing due, however depending on speed/person not always picked up causing a lose slat to fall out and boom disaster!

Now I'm looking everywhere i.e. internet to see if any simple object recognition methods to use to simply scan now and then from the outside to the conveyor to detect missing bolts. Like what is used on a train track to detect missing fasteners. Anyone used such a system or ideas where i should be heading to?

Thanks in advance

[RWOLFEJR]

Without seeing this I'll just toss this out there...
Would seem a better train of thought to keep the bolts from coming out rather than detecting one of four missing? If the conveyor is designed for "x" load, I'm guessing one bolt missing on one side might be risking failure instantly before the eyeball would have a chance to have a look at an empty hole?

Maybe switch to an alloy pin with a head and put it in the hole... then drill through your slat and pin... then counter bore through the top side of the slat and through the pin stopping short of going through the bottom of the slat. Then smack a rolled pin into the counterbore to keep it in place... then ding the edge of the rolled pins hole so it can't back out. The through hole is so you can put a smaller punch in from the bottom to drive the pin back out if you need to change the slat.

Or if it's a bolt and nut through your slat maybe a locknut (I really like the steel insert locknuts) or a jam nut... or a different fastener altogether. Like the pin with a washer and e-clip...?

Far as seeing if the bolt is missing I'm sure somebody on here is well versed in those sorts of sensors and will chime in.

Good luck and pass out some hard hats... !!
Bob

[Halla26]

Thanks for the input!
It rarely happens if honest, maybe twice this year, but its one of them you don't want to grow comfortable with it case it does eventually happen again. Luckily one bolt coming out doesn't cause the fault instantly, its more when one bolt comes out and the other works loose then the problem starts to arise. So if can monitor somehow the bolts coming round i.e. the hexagonal head with some sort of monitoring would be ideal from a maintenance point of view instead of holding a torch watching for 40 mins :-)

Yes it is a bolt and lock nut with the steel insert, i think with the heat of the oven (hot then cooling) and vibration over the time the occasional nut will work loose

Cheers bob! Sound advise ;-)

[jboggs]

I share Dave's opinion. Change the design so that loosening bolts are not possible. For example, replace the threaded connections with pinned connections.

Or, screw threaded studs into the mounting holes instead of bolts. Weld the studs in place so they cannot back out. Then put the conveyor slats in place and hold them down with slotted nuts that can be pinned to drilled holes in the studs. Like this:

91853a029p1l.png

[Halla26]

Totally agree with you both, I have mentioned this myself but the idea was shrugged off... We have another oven (one a lot older) and two other similar conveyors, one has welded nuts on and the other was drilled with pins through. Not sure why this oven is different but unfortunately not up to me how it runs.. Being the maintenance on this oven in particular i wanted a detection method for the conveyor to stop the issue of loose bolts, similar basically to what they use on railway tracks

[jboggs]

Halla - I would bet that those older ovens were probably originally built the same way as the new one - with bolted slats. Someone took the initiative to solve the problem of falling slats by eliminating threaded connections. Can you follow their example and just do it?

While detection of missing bolts may seem like a good idea, I think it would be costly, difficult to execute properly, and probably wouldn't be very reliable. In other words you would probably still have some missing bolts.

[RWOLFEJR]

We use the steel insert locknuts on wearplates inside of a rotary forging machine that delivers about 2,400 blows per minute or 40 blows a second. The machine is beating on parts ranging from 1,400 to 2,000 degrees and the machine gets pretty hot... especially in the area where these bolt / nuts are. Then the machine shuts down and cools. (unfortunately we aren't running three shifts...) With the thermal cycling and the wicked vibration the only time we've had a nut fail was during installation. Occasionally the steel insert will pop out and then you've lost your locking mechanism.

All that to say... could be that the system you have in place is fine but maybe just need to ensure that each nut did indeed keep its insert at assembly?

I still vote fix the issue over watching out for it. But I can relate to the difficulty that one can have making any changes in a plant...