Oil whirl within Journal Bearings

Oil whirl is probably the most common cause of subsynchronous instability in hydrodynamic journal bearings. Typically, the oil film itself flows around the journal to lubricate and cool the bearing. This develops an average speed slightly less than 50 percent of the journal surface speed (Figure 1).

Normally, the shaft rides on the crest of an oil pressure gradient, rising slightly up the side of the bearing somewhat off vertical at a given, stable attitude angle and eccentricity. The amount of rise depends on the rotor speed, rotor weight and oil pressure. With the shaft operating eccentrically relative to the bearing center, it draws the oil into a wedge to produce this pressurized load-carrying film.

Figure 1. Oil Film Within a Journal ¹

If the shaft receives a disturbing force such as a sudden surge or external shock, it can momentarily increase the eccentricity from its equilibrium position. When this occurs, additional oil is immediately pumped into the space vacated by the shaft. This results in an increased pressure of the load-carrying film, creating additional force between the oil film and shaft. In this case, the oil film can actually drive the shaft ahead of it in a forward circular motion and into a whirling path around the bearing within the bearing clearance. If there is sufficient damping within the system, the shaft can be returned to its normal position and stability. Otherwise, the shaft will continue in its whirling motion, which may become violent depending on several parameters.

- James E. Berry, Technical Associates of Charlotte, PC

Oil Whip Instability

Oil whip occurs on those machines subject to oil whirl when the oil whirl frequency coincides with and becomes locked into a system’s natural frequency (often a rotor balance or critical speed frequency). If we take an example, when the rotor speed increased to just above 9,200 RPM, its speed increased to 2X its first balance natural frequency. At this time the oil whirl which was approximately 43 percent of RPM, was brought into coincidence with this critical speed. The oil whirl was suddenly replaced by oil whip - a lateral forward precessional subharmonic vibration of the rotor. At this point, the oil whip frequency remains the same, independent of the rotor RPM. Note that the oil whip frequency never changed even though the machine continued up in speed to 12,000 RPM. When a shaft goes into oil whip, it's dominant dynamic factors become mass and stiffness in particular; and its amplitude is limited only by the bearing clearance. If it's not being corrected, oil whip may cause destructive vibration resulting catastrophic failure – often in a relatively short period of time.

So make sure:

1. check your bearings (i.e clearance etc)
2. oil specs, viscosity-wise and type
   
3. oil pressure and temperature
4. leakage
5. internal damping

A slight mistake will cause you thousands of dollars. Sometimes 30 seconds mistake will cost you 100k (if it involves compressors) and it will be your most expensive lesson ever. Common mistake is temperature, so watch your temp!!

Knowledge is power.

Early days... less work offcoz compared to now

Showing a happy face (pretending)


After a hard day full of work


Adakah lakonan semata-mata?


"fill up castable kat atas tu nanti tak stable"


"Danny wuz ere". Applying knowledge yg dipelajari di hi-skool


Did some troublesome castable mixing. "Am I static or rotary, why hv 2 do this?"


A "refreshing" night view (malam pun kene kejer nie)


wt Abg Azhan, Leading Technician. I said, "Been there, done that"


The very back end of our plant, flare tower

Umm... I think the pics ain't cool enough, don't have too many pics in my thumbdrive rite now unfortunately, plus it's hard to take pictures in the plant, u need a permit! I guess next time will surely upload super cool ones.

ARGGGGHHHH BOSAN NYER DUK KERTEH!!!!!...

Knowledge is power, and Happy CNY!

I like the smell of ...

MasyaAllah begitu cepat masa berlalu. Sudah hampir 3 bulan sudah saya bekerja di "perkampungan chemical" di Terengganu ini. Sukar untuk saya gambarkan perbezaan hidup sebagai pelajar dan hidup sebagai seorang perkerja makan gaji. Jurang yang besar memisahkan 2 kehidupan ini menyebabkan ada di kalangan rakan2 saya mengaku kalah gara-gara tidak dapat "cope" dgn perubahan ini.

"Fear of newness does trigger your stress. But stress is good, use it to optimize your performance rather than worrying about it" - chewah, words of wisdom nie ciptaan sendiri LOL

Saya pada mulanya agak ter-culture shock sikit bekerja dengan company melayu ni. Sehingga sekarang saya masih lagi menyesuaikan diri dgn suasana kerja lasak saya ni. Untuk pengetahuan semua, I'm working in a petchem plant where life can be 'shorten' just by hearing the should-wear-double-hearing-protection noise from the compressors and the sharp tangy-like smell of innocent looking ammonia. I'm a mechanical maintenance guy, more on rotating equipments though (i.e rotary engineer). The day I stepped my right foot into the ammonia plant, was the day they decided to shut down the plant. Teng-teng-teng (Action-like backround music starting to roar, pretty much like the medical checkup story) Meaning I got a hell lotsa works to do. But this is the best time to learn. Haha you'll never know how tough it was unless you work in a plant. Correction, not was but is. It is TOUGH! Yeah you rite there, thank you for asking, I mostly do work 7 days a week!

Tetapi saya masuk di Ammonia sebagai engineer, bukan sebagai pelajar praktikal. Maka my learning curve is spiking high way harder than the practical students because, I'm paid to do work and at the same to learn as well. It's not an easy job. I remember going to work a couple of weeks ago at 8 in the morning and I got back home 4.30 am the next day. Then I woke up at 8, went to work at 9 am the same day & got back at 2 am the next day. This is my life. Which is takde life LOL. I'm not working for the money (though it's partially true LOL), it's responsibility and you gots to finish what you have started.

"Bukan senang nak cari duit"

Now I know the meaning behind it. The more you get the more you will spend it and the more you want it. But don't get me wrong, I do spent my money on things that I like. If I don't then, there's no meaning risking my life everyday in the plant, I could die instantly here. Tapi berpada-padalah dalam spending tue lol.

"If not, then who's going to"

Kadang-kadang saya berfikir, kenapa saya memilih kerja ini sedangkan kerja di pejabat jauh lebih selesa, lebih macho (yer ker?), lebih selamat etc. ?? (Plus tinggal kat area sini memang bosan) and I can't find the answer for it. But one thing for sure, I like what I'm doing and believe me not everybody want's to do what I'm doing (I actually did ask the interviewer to put me in a plant though, and here I am LOL). It's risky, it's dirty, it's nasty (hyperbola lak ayat aku nie), and very challenging. I do this job because it's fun and if I don't do it, who is going to?

Guys, frens, & everybody, stay sharp & good luck in life!

*yeah I'll upload some pics later. Cool ones. Sangat busy at the moment (I can't believe myself writing this blogpost at cybercafe, sedey sungguh... rumah pun xde streamyx lagi, jauh kene gi Dungun cari TM point!!! bila masa nk pergi tue?? LOL)

Knowledge is power