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45 Cards in this Set
- Front
- Back
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What is the purpose of lubrication |
Reduces friction between components and increases component life by reducing wear |
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Name and describe the types of friction |
Sliding friction - occurs when two surfaces slide over each other Rolling friction - takes place when spherical or cylindrical body rolls over a surface Fluid friction- when lubricating oil is applied to two surface in contact. A film of oil is formed, because there is no metal to metal contact sliding occurs between the layers of oil within the film, called fluid friction |
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How is oil attracted to a surface to be lubricated? |
Oil forms in layer of globules and cohesive forces occur between layers of globules, adhesive forces occur between the oil and metal surfaces |
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Describe how oil will separate two metal surfaces sliding over one another |
Theory of adhesion causes unlike materials to stick together, polar attraction |
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How is air (foam) controlled in oil? |
-by using a foam depressant or foam inhibitors during refining |
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How is water controlled in lubricating oils |
(water gets into the lubricating system due to faulty seals and condensation inside the metal housing and condensation inside the metal housing or tank. This happens when the machine cools to ambient temperature from an operating temperature of 40C to 60C) -demulsibility is the ability of a petroleum oil to separate from water upon standing, it can be increased by additives Emulsibility - is the ability of a petroleum oil to mix with water using a special emulsifying agent. A common example is the cutting fluid used in a machine shop -rust inhibitors are added to the oil to reduce the rusting of ferrous parts, which occur if there is water in the system |
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How is wear and load capacity enhanced in lubricating oils |
-by adding chemicals to oil, load and capacity additives can be separated into 2 groups -anti wear additives- minimizes wear -extreme pressure - used in heavy load or shock loading |
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Why are extreme pressure oils never mixed with other oils |
-there may be chemical reactions -do not mix different brands |
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What is the purpose of detergents in oils and what oils are they used in |
-detergents cleans surface of components - dispersants - keeps contaminants in suspension **detergent motor oils are not added to industrial oils because of the following complications -contamination of the oil, causing excessive foaming -deposits in critical clearance spaces -filter problems |
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Describe the following wasted oil or once through systems |
A) squirt can - oldest method of applying oil, this method leads to extremes of over or under lubrication B) wick feed oilers - uses capillary action of a strand or strands of wool to transfer the oil from the reservoir to the shaft, flow depends on number and length of wool strands and on height of the oil in reservoir C) drip feed oiler - provides a visual check and a means of controlling flow of oil by adjusting a needle valve |
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What quality of oil is used in the following systems: |
A) once through systems - low grade (low cost) oil, must meet viscosity and film strength requirements B)enclosed lubricating sytstems- one which the oil is circulated over and over, must use a highly stable oil with additives |
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Describe the following enclosed lubrication systems |
A) ring oiler - mechanical means of oiling a shaft, consists of a ring that rotates around a shaft with bottom sitting in a pool of oil at bottom of housing |
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How does overfilling the lubricating system affect its operation |
Results in excessive foaming and a temperature rise in the unit, it decreases the viscosity of the oil, reduces service life of the oil |
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Describe both accurate and approximate methods of quality checks on used lubricating oil |
Accurate oil check - in plant lab test or send samples to an approved testing lab Approx oil quality check - comparing 1 used sample to one new one compare - smell, touch, sight, using a magnet to check for particles |
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Describe oiliness |
Because of their chemical composition some molecules are attracted and held more strongly to metal than others, oils rich in these molecules are said to be high in oiliness or lubricity |
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What is grease composed of |
Usually made by Thickening lubricating oils with soap. The thickener controls water resistance, resistance to machine breakdown from constant use, temperature range, and the ability of the grease to stay in place. Soap content for general use grease us usually from 7-18 percent, but can be as low as 3 percent or as high as 50 percent for special greases. |
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What properties of grease can be attributed to the thickener |
The thickener controls water resistance. Resistance to machine breakdown from constant use, temperature range and the ability of grease to stay in place |
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Describe the following |
Complex soap grease - made from special soaps and are multi-purpose Non-soap greases - used to suit special conditions of temperature, environment or service life, common thickeners are carbon black, silica gel, and special clays Multi purpose grease - designed to allow one grease to be used instead of 3 or 4 separate grades, cuts down on inventory, time of application, and lubrication errors Extreme pressure greases - designed for shock loading or high local pressure areas, usually contain compounds of chlorine phosphorus or sulphur as additives. Molybdenum sulphide is a common additive to improve the anti-wear capacity |
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How does the National Lubricating Grease Institute grade grease? |
NLGI grades range from 000 for softest grease through 00, 0, 1, 2,3,4,5 and 6 for the hardest |
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Describe the following |
A) Dropping point - the temperature at which a grease becomes fluid enough to drip, common greases in general industrial use have dropping points that range from 135C(275F) - 182C(360F) |
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What factors are considered when choosing a grease for a certain application |
-company requirements for choice of lubricants, means of application and frequency of application -type, speed, temp, pressure and environment of the bearing or machine unit -manufacturers recommendation |
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Describe how viscosity affects the lubricating qualities of oil |
-viscosity is the resistance to flow -oils with high viscosity are thicker and pour more slowly than those with low viscosity -viscosity is most important property of lubricating oil -viscosity affect the generation of heat in bearings, the ease with which machines start in the cold, sealing effects of oil and the rate of consumption in oil |
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How is minimum power loss achieved through lubrication? |
The oil should have the lowest viscosity able to carry the load on the bearing |
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How does temperature affect viscosity |
-when oil is heated the molecules move with increasing violence, this causes them to move further apart and the oil expands. Because the molecules are more active and have more room to flow past one another, the oil “thins out” - the viscosity drops |
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Describe how viscosity is measured using the saybolt viscosimeter |
-heat a 60 ml sample of oil to 40C (100F) -allow oil to flow through a calibrated orifice 1.765 mm in diameter and 12.25 mm long -measure the time it takes in seconds for 60 ml to drain off |
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Which oil will change viscosity more sure to temperature change? |
An oil with a VI of 20 or An oil with a VI of 100 (An oil with a VI of 20 changes more) **the higher the VI number, the smaller the change in viscosity due to temperature |
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Describe the oil wedge theory |
-when the shaft is at rest most of the oil is squeezed out of the contact area -as the shaft begins to rotate slowly, oil climbs up the side of the bearing (moves opposite direction to rotation) -eventually oil surrounds the shaft lifting it hydraulically -at full speed, oil enters at the area of lowest pressure -the shaft now carries the oil in the direction of rotation toward the area of max pressure -the oil wedge forms and forces the shaft up and toward the center of the bearing. It does this until pressure is equalized and shaft position is maintained |
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Describe the following |
A) Dropping point - the temperature at which a grease becomes fluid enough to drip, common greases in general industrial use have dropping points that range from 135C(275F) - 182C(360F) B) directional fluidity- when moving in a bearing, grease tends to shear into thin layers that move in the direction of rotation, under shearing stress the apparent viscosity of grease falls rapidly until it approaches the viscosity of the oil used in its manufacture. |
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How is oxidation of oil controlled |
-by adding oxidation inhibitors or anti - corrosion additives during refining |
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Describe how to handpack a bearing |
1- fill the spaces between the rings with grease after assembly 2-pack the housing 1/3 full for high speed, 1/2 full for slow speeds 3- do not overpack, causes grease to churn increasing temps |
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Compare oil to grease as a lubricant |
Grease advantages -good lubricant for heavy loads at low or medium speeds -requires relatively simple seals -provides better startup protection after short periods of downtime -gives better rust protection during periods of downtime -tends to stay put Oil advantages -good lubricant for high to very high speeds -develops less fluid friction than grease -has a flushing action that washes dirt and solid contaminants to the bottom of the housing -can be used as a heat exchange medium -can be easily removed from the housing |
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What are the functions of the lubricant during machining operations |
-cool the work piece -cool the cutting tool -protect against rust -prevent welding of metal chips with the tool -wash away metal chips -allow high speed cutting for better productivity and surface finish |
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What types of oil are used for machining operations |
Straight cutting oil Emulsifiable oils Chemical oils ***these are also called cutting fluids (all of the above) |
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What procedures should be followed when using cutting fluids |
-use protective clothing and splash guards, avoid prolonged contact -use oils at room temperature for best performance -apply the oil in a continuous stream covering all the work -use soft water - hard water leaves a residue of minerals or salts -always add oil to water, never add water to oil -after cutting empty and clean the sump if it is to be left for some time |
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What safety precautions should be followed while handling lubricants |
Avoid prolonged contact with skin Avoid inhaling fumes, prolonged exposure can be toxic |
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What body or bodies regulate the handling, storage and disposal of lubricants |
Local, provincial and federal legislation |
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How are grease guns advantageous over handpacking |
-doesn’t depend on gravity for flow conditions - grease guns produce 10000 psi of pressure |
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How is metering achieved on a spring-compression grease cup |
-pressure is applied to the grease by screwing the cap down by hand, or by an automatic compressor. There is a screw near the attachment point to allow for flow adjustment |
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Describe the operating principles of automatic lubricators |
-similar to spring compression cups -triggered mechanically or electronically |
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What conditions should be considered for the lubrication of open gears |
Temperature, method of application, environment, gear materials and choice of lubricant |
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What factors should be considered for the lubrication of enclosed gears |
Load, operating speed, operating temps, lubrication method, type of gear, environment |
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What type of lubricant should be considered for worm wheel and hypoid gears |
Must use an oil with special additives because the gears generate high pressure and considerable friction |
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What should be watched on a trial run with a new lubricant |
Extreme temperature rise or other indicators of trouble **when grease is first introduced the temp will go up until it settles in |
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what lubricant should be used for high speed operation and extreme temps |
Oil |
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What is the recommended oil level for oil lubricated ball bearings and why is it so important |
-normally covers the bottom of the outer race, but does not cover the center point of the lowest ball or roller -over oiling causes churning which results in a temperature rise |
