Fluid Coupling Blasted
Mr. Heilmann,
Our conclusion is merely by deduction. We know what happened, the backstops did not engage (as they suffered no internal damage or indication of any attempt at stopping the load) when they should have. We don't exactly know why but here is why the elastic shock wave may make sense.
1.) Even without the shock wave idea, by rigid body dynamic analysis of the entire conveyor we determined a time window of only 0.6 seconds from the +90 to -90 RPM, the rotational speed at which the back stop pins became centripetally released.
2.) It is worth noting that the conveyors total coasting inertia is held together by the fluid couplings and this connection drops out at about 400 RPM (when the working vortices are lost), losing about 50% of the coasting inertia (that is the motor and the outer half of the fluid coupling). So the deceleration rate is significantly increased at the time when the back stops must engage. Loss of this inertia could be the stimulant of the shock wave. The shock wave could be through the belt but it also could be through the high speed reducer input, as this is where the torsional inertial load is lost when the transmitting vortices drop out
2.) The high speed backstops, by Bibby, had a far too long arc of engagement, up to 28 degrees (which is only .78 degrees at the drive pulley) according to their sales rep. Because of this both backstops were sized to independently stop the entire load. These were not of the sprague type with nearly zero backlash
3.) Our working model simulation of the backstop required a seven fold deceleration rate (compared to what our rigid body dynamics simulated for the whole conveyor) in order to deny them time to drop
4.) All of this is very pure and idealistic
5.) Your point about slip of the belt, in case of an elastic shock wave through the belt is valid depending on the location of the shock wave at the critical time. The tension may also be instantaneously increased around the drive pulley depending on timing
I welcome the comments of others that have had this experience or that can offer additional insight.
Joe Dos Santos ■
Which Hold Back Is Better ? Slow Speed Or High Speed ?
Dear experts,
Location wise, which hold back is better ? Slow speed ( fixed on pulleys ) or High speed ( fixed on gearboxes first stage shafts ) ? What are their advantages and disadvantages ? I have seen many high speed hold backs, which are normally , the integral part of gearboxes, but have seen only very few slow speed hold backs.
The slow speed hold back is found fixed with the pulley, which is at the highest elevated pulley in the conveyor's profile ? Is it necessary that, it should be fixed at top most located pulley ? Cannot it be fixed at other locations ?
Regards, ■
Fluid Couplings Blasted
I have done both. The low speed hold backs when specified but the high speed back stops when I get to choose. For sure the low speed backstops are much more expensive. The high speed backstops have always been reliable for me and they cost much less.
Joe Dos Santos ■
Re: Fluid Couplings Blasted
Gentlemen,
This has been kicked to death many times , just to refresh the holdback device in the original post had failed 2DAYS earlier BEFORE the incident . Despite this , the conveyor was ran loaded . Of course there was an accident !!!!! ■
Robert 90& Co
Dear Mr. Robert90,
pls. allow me to express my bewilderment seeing your above post. What exactly is your point in copying 3 sentences out of the original post? Please explain your intentions, or please anyone explain me what happens not only in this place. Does anyone collect points or stars at higher authorities? Or is an avatar made more solid by having posted posts, as such?
Thank you in advance for your kind interest
R. ■
Robert 90& Co
Hello Roland Heilmann,
Thank you. This guy does SEO = search engine optimzation and he is probably being paid by his client.
I am confronted with these people every morning, and often I kill them but sometimes I let them go. This is often a mistake.
I guess I will delete Robert 90 the next time. I am sure he does not read this.
We have a Bulk Video section, see http://videos.bulk-online.com/ and we have to delete some 20-30 videos each day because they are pure spam. Same with the Bulk-Blog. The good news is that there are now filters available which block the spam, but it still takes much time to delete all this from the databanks.
I appreciate your involvement. Keep up the good work!
Reinhard Wöhlbier ■
Re: Fluid Couplings Blasted
Dear All,
I am just adding some information about fluid couplings. Fluid couplings have lot of application in marine and industrial machine drives; in this system variable speed operation and start-up control is possible without shock loading of the power transmission. ■
Fluid Couplings Blasted
Dear experts,
Today there was a serious problem. One of the conveyors was running with three drives. All three drive arrangements were having three fluid couplings. All the specifications of the components of these drives are same.
This conveyor was having external hold back at a very higher elevation. It had been mounted on the dicharge ( Head ) pulley . The hold back had failed two days back. Shutdown was awaited for replacing the hold back.
Early this morning, it was reported that the fluid couplings were broken. All the fluid couplings were found like "blasted" from inside. Though I am not sure, the conveyor was tried to be started from the control room when it was tripped. The load made the conveyor to rotatae in reverse. The starting command tried to rotate in forward direction. This would have caused the couplings blasted. Luckily no one was at the site , when this had happened.
Have you ever come across such problems ? Why fusible plugs or the seals not failed?
Thanks & regards, ■