Re: Life Of Slew Bearings
Originally Posted by NarayananNalinakshan
Dear Friends,
I remember to have seen some documents,where the life of the slew bearings
was given to be 1.25 million cycles.
Some documents stipulated 50,000 working hrs.
Recently I have been informed that the life can be 100,000 working hrs.
The life reduces if the rail is supported by rails/stone ballast system due to
chances of uneven settlement of track.
Opinion of experts is requested on the above.
With Regards,
Narayanan Nalinakshan.
Namaskar,
Good Afternoon,
You have pretty much answered your own inquiry as you
have done your homeworks.
If your lucky enought to have bedrock it negates the need for
pilings UNLESS the bedrock is extremely fractured like shallow
sedimentary shale or basalt etc. requiring concrete with
in situ mono piles with drilled foundation holes and rebar cages.
The next thing is the rail foundation and as mentioned above....
If you are not using an airport runway grade concrete or greater strength concrete with
a long curing time.......
The other issue is whether you want a slab between the rails of the system.
A slab between the rails poured and key connected to the rail pours at the base will add strength
to to the entire slab as you will have huge forces multiplied against the superstructure of the reclaimer stacker
as the wind will simply push agains the entire mass and them transmit the force against the carriage,rails, rail anchors,
the rail support slab and then into the ground.
A floating slab is out of the question because of these stresses.
DONT FORGET that every kilogram, Kilo, Metric Ton is going to be riding on those little wheels on the undercarriages.
ADDED to this is the quality of the slew bearing AND its lubrication method and oil viscosity which is directly affected
by the temperature the unit operates in.
AND every wheel is only contacting an area the size of an American DIME and trying to gain adhesion at all times when moving.
I personally am unaware as to whether these units have sand boxes for creating traction on the rails but they should have them. ■
Who's Who
Dear Mr. Narayanan Nalinakshan,
one needs to be most exact when it is coming to life cycle definition of slew bearings.
Main point: These bearings are all the time under load (vertical weight load, tilting torque, wind in different forces etc.). However they will not all the time rotate. So, 100.000 hs "under load" might mean ~ 11 years @ 7/7 24/24 and this might not satisfy some. However, if slew occurs, say, during 1000 h a year and said number relates to rotation time, we would then look perhaps at a huge oversizing.
Inclination of rail underground will, or should, rather affect the Long Travel system and the slew drives, than the slew bearing itself. The supporting structure re machined support surface for the slew bearing must be sufficiently stiff in order not to deflect / bend and cause additional strain / load onto the slew bearing. There's however the requirement to consider such load components for design.
Along the lines of Izaharis: Money spent on good rail foundations is money saved in later stage refurbishments & repair.
Regards
R. ■
Re: Life Of Slew Bearings
Originally Posted by Roland Heilmannone needs to be most exact when it is coming to life cycle definition of slew bearings.
Main point: These bearings are all the time under load (vertical weight load, tilting torque, wind in different forces etc.). However they will not all the time rotate. So, 100.000 hs "under load" might mean ~ 11 years @ 7/7 24/24 and this might not satisfy some. However, if slew occurs, say, during 1000 h a year and said number relates to rotation time, we would then look perhaps at a huge oversizing.
Inclination of rail underground will, or should, rather affect the Long Travel system and the slew drives, than the slew bearing itself. The supporting structure re machined support surface for the slew bearing must be sufficiently stiff in order not to deflect / bend and cause additional strain / load onto the slew bearing. There's however the requirement to consider such load components for design.
Along the lines of Izaharis: Money spent on good rail foundations is money saved in later stage refurbishments & repair.
Regards
R.
Dear Sirs,
Nowadays the Stacker Reclaimer operates up to 5000 hrs annually,and most of the time it is also slewing.
If we consider 50,000hrs the life shall be 10 years,20 years if it is 100,000hrs. But these timing definitely require a good track and Good maintenance system.
But still I feel the cycle is a better way to explain life of slew bearing.
In India most of the high rate of material handling takes place in Ports,Where the sub soil is very weak.
I have posted this query for the benefit of several Engineers who asked me about life.
Hence the valued reply given by both of you will definitely benefit them.
Thanks and Regards,
Narayanan Nalinakshan. ■
Spinning Around.
As pointed out, the slewing activity is rather divorced from ground conditions. A boom is supposed to be 'balanced' and slight tilting is not significant and might not be much more detrimental than the torque imposed within the slew drive or even the end of travel reversing etc.
I imagine this post originated in the possibility to rotate the slewing ring after some 10 years and thus present the less worn sector of the slewing ring to the travel arc. There was a Canadian and/or Australian outfit who used to specialise in this work. They ought to be still around (search these forums) just because they should be booming. Depending on your slew arc they can double your life. Mind you, jacking the rotating superstructure clear of the base and re-grouting is not going to be cheap...but you have to do that for replacing a dodgy bearing anyway.
Since this remedy has not appeared in your original text it seems that the jacking points were not fitted during manufacture and it would be necessary to have any new welding certified if you are considering standing about 250t atop it. Incidentally, the stiffness of the turntable in general should be adequate for the conditions encountered in the rail tolerance etc. If the track degenerates and the documentation supports the design as specified then the further considerations of operational life are irrelevant. ■
John Gateley johngateley@hotmail.com www.the-credible-bulk.com
Life of Slew Bearings
Dear Friends,
I remember to have seen some documents,where the life of the Slew bearings was given to be 1.25 million cycles.
Some documents stipulated 50,000 working hrs.
Recently I have been informed that the life can be 100,000 working hrs.
The life reduces if the rail is supported by rails/stone ballast system due to chances of uneven settlement of track.
Opinion of experts is requested on the above.
With Regards,
Narayanan Nalinakshan. ■