One alternative is to have the lowest rolling element partially submerged in oil. That causes friction from chruning in high speed applicaitons.
Another alternative is to use some kind of oil ring or flinger ring. These are trying to do roughly the same thing as the oil mist (ensure that some minimum quantity of oil is available) but the oil mist does it more effectively and reliably.
In other applications oil such as journal bearings, oil functions to remove heat from the bearing. I wouldn't hink this is much of a factor in rolling bearings. I would think if the bearing was in contact with enough oil to be removing significant heat it would also be increasing friction.
=====================================
Eng-tips forums: The best place on the web for engineering discussions.
I just looked in Neale's Lub handbook and saw that mist is indeed used for some journal bearings, chains, gears etc. I was assuming you meant rolling bearings. Please clarify the application.
=====================================
Eng-tips forums: The best place on the web for engineering discussions.
Could be the vapour pressure of the type of oil. The seal and contact element heat up quickly at high speed, and the oil will change in phase and the seals can be damaged.
Opinion only
Thank U psafety. In that case , for the refinery plant,equipments, is it advisable NOT to go for Mist Lubrication? What precautions we need to take if the client prefers it . Pl advise.
I work in a large oil refinery. We use pure lube oil mist on approximately 500 pumps. Oil mist is not flammable. It is too lean to burn. I have seen a demonstration where pure mist is directed into an open flame. It will not light off. Now, if there is stray mist that is allowed to accumulate as liquid oil, then that can be a fire hazard. We use collection boxes at each pump to catch the stray mist and condense it to liquid. We have never had a fire associated with mist.
Back to the original question, I have never applied pure oil mist to a "high speed" machine. The highest speed we have is probably 3600 rpm. But, I have never seen any prohibition against pure mist at higher speeds. A bearing lubed with pure mist will run cooler, run cleaner and last longer. This suggests that higher speed would be a better application for pure mist than lower speed. Contact the manufacturer of the mist system to get their recommended application limits for speed. The two systems I am familiar with were made by Alemite and Lubrication Systems.
Mr Pellin,
I personally have taken mineral oil CCFP 350-degF + and turned it into a viscous flame thrower by adjusting the air/oil ratio. The closer to an aerosol type mist the more flammable. I increased the oil/decreased the air till the droplets were larger and had the small flames stairstep right up to nozzle. All ignition was with the use of a torch striker (sparker).
I did not watch someone else, I performed the tests. It will and does happen!!
Don Coffman
I believe we are talking about something different. The mist that we are discussing is lube oil mist from a generator designed for system wide lubrication of bearings. It is generated at a precise concentration with a precise droplet size. The generator that produces it is instrumented to monitor the mist header pressure and mist density. If the mist density changes higher or lower, an alarm is produced. The mist generated by this system cannot burn. It is too lean to combust. It represents no fire hazard at all. I believe you are referring to some other form of mist of varying droplet size and varying density. The original question is regarding the type of oil mist system that I am speaking of.
John,
The system I refer is in fact an oil mist unit that was to be used on low-speed line shaft bearings in a paper converting operation. Static electricity in this area/part of the country is extreme in the winter. This unit was not monitored.
In process safety; if it can happen it will. I refused to allow this unit to be installed. I only relay my own experience. Mists of any combustible is a hazard. NFPA has chapters on this (or did). I have researched and this is a well documented flammability concern (in the correct concentrations).
I do NOT want to get into an argument, but IF a material will burn, flammability should be a concern. I have been involved in the design of combustible dust & gas/vapor explosion protection systems for many years and speak from that experience.
Maybe your monitoring will control the hazard to the satisfaction of all.
In reply to the original question, I highly recommend the use of oil mist. In our particular conversion, we documented a reduction in bearing failures of about 80 percent. Bearing failures often result in seal leaks and many of our products are extremely hazardous. For process streams that include light ends that pose a risk of vapor cloud or hot oil streams above their auto-ignition temperature, avoiding bearing failures and seal leaks represents an extreme improvement in reliability and safety. However, as Mr. Coffman points out, nothing is without risk. I would only consider a well engineered lube oil mist system with full instrumentation, controls and alarms suitable to guarantee consistent mist delivery. Systems of this type are readily available and would be considered standard for an oil refinery or petro-chemical plant. In fact, I am not aware of any major US oil refineries that do not currently use oil mist in at least a portion of their plant.
Thanks a lot JJ and Psafety for your valuable time to discuss the issue threadbare. As finally said , running a system with proper design and control , we can avoid risks and this is what is required for greater reliability of the equipments and availability of the plant. Thanks onceagain .
I agree with JJPellin. I have worked in several oil refineries and all of them were using pure oil mist lubrication on hundreds of pumps. The reliability benefits from this technology far outweigh any safety issues.
Just to back up the safety of a well-engineered system. A large percentage (I believe ~40%) of the refining capacity in the U.S. is operating with the pumps on pure oil mist lubrication. I am not aware of a single incident where the oil mist ignited. As Mr. Pellin says, it is too lean to support combustion.
I also do not believe there is a prohibition against the use of pure mist lubrication in high speed applications, but as with any change, an engineered review is certainly recommended.
