CHAPTER 30 Lubrication Flashcards
What are the purposes of lubrication?
Friction, wear reduction, corrosion reduction, temperature control, shock absorption, sealing. of the six functions of a lubricant. The first two listed are the most important in the majority of applications to separate bearing surfaces, in order to reduce friction and where.
Things to remember, with friction reduction, wear reduction and corrosion reduction
Even when two surfaces are machined, smooth, there are still microscopic, hills and valleys. These hills and valleys will try to line up, which creates extra friction. Lubrication is used to separate the hills and valleys, and reduce friction and wear. As far as corrosion reduction goes, chemical compounds are often added to the lubricant to prevent the formation of acids due to oxidization.
Three general classes of lubricants
Solid, semi solid and liquid
Solid lubricants
Suitable for use under high load and or extreme temperature conditions good for lubricating idle equipment in storage and bearings that are very difficult to service materials that are used as solid lubricants include graphite, soapstone Mollybee denim
Semi solid lubricant
Semi solid, lubricants or greases, are produced by combining liquid lubricant usually petroleum oil with a thickening agent or soap, because it does not drip or splash. It finds a wide application in the textile and food industry serves to seal out dirt and water from the bearing and gives the working surface of permanent protective coating to avoid rusting during idle periods. Grease is not suitable for large amounts of heat must be continually carried away from the bearing liquid lubricant is used for that can have different additives put into them to meet different service requirements.
Three general classes of liquid lubricant
Mineral oils, fixed oils and synthetic oils
Mineral oils
Most commonly used class of liquid lubricant is processed in a fraction in tower, where various grades of lubricating oil are drawn off of different levels from the tower
Fixed oils
Also called fatty oils and are made of animal or vegetable origin and include lard whale oil, castor oil, and canola oil. They are rarely used by themselves as lubricants, but are incorporated into greases or mixed with mineral oils for special applications.
Synthetic oils
Include poly glycol’s, and silicones suitable for high temperature service are resistant to sludge and oxidation main disadvantage to synthetic oil’s. Is there a high cost?
To general categories of lubrication
Boundary lubrication, and fluid film lubrication
Boundary lubrication -surfaces, or separated by only a microscopic film of lubricant certain amount of metal to metal contact will exist between the surfaces
Fluid film, lubrication - also called flooded lubrication lubricating film between surfaces, thick enough to completely separate the surfaces, and it can only exist if the bearing clearance space is flooded with oil and moving service in the bearing is in continual motion
Shell (sleeve), or journal bearing
Are usually constructed with a white metal alloy lining commonly called Babbitt. The Babbitt is suitable because it yields or deforms slightly to conform to load conditions particles can become in bedded in it rather than scoring the shaft. It is fairly corrosion resistant easily replaced bearings are termed shell type And larger more difficult to replace bearings are poured. Tape journal bearings are common when the rotating mass or weight is high, such as turbines and large pumps forced lubrication with some type of positive displacement pump is very common a ring oiled bearing uses a ring that picks up oil from the reservoir beneath the bearing end, drags it up through the bearing slot, where it is distributed between the shaft and bearing.
Antifriction bearing
These are your ball and needle bearings or tapered roller bearing. These barons consist of moving components which role between two surfaces called races.
Thrust bearing
The purpose of a thrust bearing is to prevent a rotating shaft from moving in an axial direction. The lubrication therefore is of the boundary type. The load that this bearing can carry is limited they can be in a form of a pad. These pads are free to tilt, and thus allow the formation of an oil wedge to separate the bearing pad from the shaft collar tilting pad thrust bearings are the Michel’le and the Kingsbury tape
General classes of lubricants
Solid semi solid and liquid 
How viscosity works
The thicker, something is the more viscous it gets meaning it won’t flow as easy
