A possible source for the ball bearings that resist thrust in this part of the engine is New Hampshire Ball Bearing, HiTech Division. Airbus notes their product as being in the A380. The bearings "Inch Series, Thin Section - Radial and Gothic Arch" are available in 1/2" bore steps up to 10" bore. I have to check Airbus' other bearing suppliers for the A380 before I can be more certain, assuming I can get equally good data (experience teaches this will not be true with every supplier). Their link is at nhbb.com and p29 in the catalog (p30 in the pdf) is wanted, in case of trouble with the link:
I'm not sure these are big enough for this job, as 13754 lbs thrust is the highest capacity listed, using chrome steel (52100). You can find special products on the site, which mentions that spent oil pickup extensions can be placed on the inner races, and that puller grooves can be put in the outer races, dogs to prevent rotation in the outer housing, etc. NHBB makes custom bearings also; the largest cataloged standard bearings are 1/2" cross-section with 1/4" balls.
One thing to note is that thrust capacity increases with diameter, and is hard to come by. Taken with the fact that machinery is usually designed with only two bearings per shaft, and a flexible coupling is used with more than two, we immediately know where the center bearing is on the LP shaft. It has to be on the larger forward shaft; on, adjacent or near to the boss housing the interior splines. These splines have to accomodate angular deflection between the two sections of the shaft, more at some times than other times.
I have been wondering for some time if the helical twist to the splines is also put to use providing a clamping force for the inner race of this bearing. Given that thrust resistance is so hard to come by in this bearing, I have no doubt that the primary purpose of the twist is to transmit the tension load, created by the aft gas forces on the LPT blades, directly forward to the fan. This reduces the force on this bearing.
Parts of this reasoning can be applied to the IP shaft, which also has a set of splines.
What I am thinking is that if we have an oil fire, we have to look for a source of ignition. Talk about oil flash point (tech board) is all well and good, but the fire point is another, where a pool of oil under an ignited flash will burn without self-extinguishing. That's a bit higher, but the auto-ignition point is substantially higher--404 degrees C in the recommended Mobil Jet Oil II (as shipped from the factory, a highly-inhibited ester synthetic). There seems to be some discussion as to a change in oil in some of the QF32 engines.
Where was the source of energy to ignite this oil fire? Even an explosive mixture of gasoline fumes will not be ignited by just any spark. I think even 15 mA circuit contacts are permitted now in such atmospheres. I used to use a bowl of gasoline to quench the stream of sparks coming off my grinding wheel (the same leaded gas I washed my hands in). Well, definitely don't try this at home
One thing that seems worth a look is the effect of the unrestricted ops for oil temp up in the 190s-C, as compared to the more common 160-165-C in some other jet turbines. I'd say the 160-165 considers a limit to viscosity reduction to maintain adequate bearing lubrication and cooler running, although it may consider use (military?) of the Dow non-varnishing synthetic (glycol). The higher temp in the 190s seems to push the 3% evaporation limit in 6.5 hrs (a regulation?), here at 204-C for the supplied oil, on the cutting edge upstream of the measurement. Oil also has the advantage of being someone else's oil, and maybe not the oil type shipped in the engine. Just observations. I could not locate any lubrication recommendations on the NHBB site, except possibly in referenced industry standards (typically costly to obtain now).