The correct lubricant – ANSWERS
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Questions 1.0:
1. What are the three groups of base oils? ► Paraffinic, naphthenic, synthetic
2. Which two groups of base oils are called mineral and why? ►
Paraffinic and naphthenic – they come from the ground, from crude oil
3. What are R&O oils? ► Oils that have only rust and oxidation inhibitor additives
4. What do you achieve by having the right viscosity? ► Ability to lubricate
5. How does viscosity change with temperature? ► It drops with increasing temperature
Questions 1.1:
1. What is a 'heavy' oil? ► Oil having a high viscosity, also called 'thick'
2. In measuring what viscosity is gravity involved? ► Kinematic because we measure how fast the oil flows down
3. At what temperature do we measure the viscosity of industrial lubricating oils? ► 40 degrees Centigrade (Celsius)
4. At what temperature do we measure the viscosity of automotive oils? ► 100 °C
5. Is ISO VG 68 a typical viscosity for industrial gear oils? ► No, it's too light, typical grades are ISO VG 220 or 320
6. What are the viscosity limits of an ISO VG 220 oil? ► 220 ± 10% = 198 to 242 cSt
Questions 1.2:
1. How many engine oil SAE viscosity grades are there? ► 14
2. Are there maximum kinematic viscosity limits for SAE grades with W? ► No
3. Which SAE grades are recently introduced? ► SAE 8, 12, 16
4. What is a multi-grade oil? ► An oil that complies with two SAE viscosity grades (one with W and one without W)
5. Could we have an SAE 30-40 multi-grade? ► No
Why? ► a) There is no W grade; b) SAE 30 and 40 limits do not overlap
6. Is CCS relevant to SAE 40? ► No, it is specified only for W grades
Questions 1.3:
1. How many automotive gear oil SAE viscosity grades are there? ► 11
2. Are there gaps or overlaps in KV limits in SAE 80 through 250? ► No
3. The test not shown in the table is... ► Shear stability test – oil must stay in grade
4. Which grades are tested for temperature at which the oil is 150000 mPa.s? ► W grades
5. What are the SAE viscosity grades without W of both engine and gear oils having viscosities at 100 °C:
(a) 15 mm
2/s ► SAE 40 and 90
(b) 25 mm
2/s? ► SAE 60 and 140
Questions 1.5:
1. What is the name of the additive used to improve pour points? ► Pour point depressant
2. Do synthetic and naphthenic base oils have good (low) pour points? ► Yes
1.7 EXERCISE
Completed dual purpose viscosity-temperature chart
Viscosity-temperature chart with added viscosity grades
| Lubricant |
Kinematic viscosity (KV), mm2/s |
VI |
KV |
| at 40 °C |
at 100 °C |
at 0 °C |
at 70 °C |
| Synthetic gear oil |
230 |
27.6 |
155 |
1500 |
70 |
| SAE 20W-50 engine oil |
135 |
17.2 |
139 |
850 |
43 |
| Synthetic engine oil |
125 |
22.9 |
214 |
520 |
50 |
| SAE 30 engine oil |
100 |
11.4 |
102 |
750 |
30 |
| Refrigeration compressor oil |
55 |
6.5 |
65 |
450 |
16.6 |
| Hydraulic oil ISO VG 32 |
30 |
5.2 |
102 |
160 |
11.5 |
NOTES:
a) The viscosity at 40 °C of SAE 20W-50 engine oil will be of interest later.
b) Comparing VI of Synthetic gear oil and Synthetic engine oil (both PAO based), you can see that it is generally more difficult to get a better (higher) VI with heavier (higher viscosity) hydrocarbons. For this reason, SAE 20W-50 engine oil's viscosity at 100 °C is close to the low limit of 16.3 cSt.
c) Refrigeration compressor oil is naphthenic (see 1.9.7). This oil's viscosity is on low side, it should be closer to ISO VG 68. However, in refrigeration it is more important to have a straight cut base oil (just one base oil, not a mixture of two base oils) than the exact viscosity. In refrigeration, the base oil type and quality is the most important aspect (9.4).
Questions 1.7:
1. What does a low viscosity index mean? ► The oil's viscosity changes a lot with changing temperature
2. Does a low viscosity index oil have a steep or not so steep line in the chart? ► The line of a low VI oil in the viscosity-temperature chart is steep
3. What is the unit of measurement of VI? ► There is no unit of measurement
4. You have added values at 70 °C in the above table. Are the values at 70 °C averages of the values at 40 °C and 100 °C (that means exactly in the middle between the values at 40 °C and 100 °C)? ► No. E.g. average of 30 and 5.2 (the last example) is 17.6 cSt but the viscosity at 70 °C is 11.5. Look at the chart how far 11.5 is from 17.6. cSt
Why? ► Because of the log-log scale for viscosity
Questions 1.8:
1. When should you start worrying about foam on the top of the oil surface ► When it spills out of the reservoir or is sucked into circulation
2. What are defoamants and what could they spoil? ► Additives that reduce foaming, they can spoil the air release
3. What is a good air release result for ISO VG 46 hydraulic oil? ► 7 minutes
4. Two oils (a) and (b) have been tested. Which foam results are better and why?
(a) Foam 180/10;
(b) Foam tendency 190/0/120, foam stability 20/0/0. ►
This is a trick question: (a) is better because tendency in Sequence I in a was 180 (vs. 190 in b) and stability 10 in a while 20 in b. However, test results are technically superior in b because Sequences II and III were also run.
Questions 1.9:
1. What requirements must be satisfied to qualify for Group III? ► Sulphur 0.03% maximum, saturates at least 90% and VI at least 120
Questions 1.9.2:
1. Are PAO hydrocarbons like mineral oils? ► Yes
Why? ► They are hydrocarbons
2. List all advantages of PAO ► High and low temperature performance, excellent response to oxidation inhibitors, energy savings, food-grade suitability, excellent in screw-type air compressors
3. List all disadvantages of PAO ► Price. See also switching to PAO on the next page and warning in the section about Refrigeration compressors
4. What is the API base stock category for PAO? ► Group IV
Questions 1.9.5:
1. List all advantages of PAG ► High and low temperature performance, considerable energy savings, anti-wear in worm gears with phosphor-bronze bull gears, clean evaporation and burning, superior performance in air compressors
2. List all disadvantages of PAG ► Price. Switching to PAG complicated (until the mixable technology prevails). Hygroscopic. Seals. Concern about aluminium.
3. What synthetics are used in compressors? ► PAO in screw type air compressors, PAG in car air-conditioners and air compressors, diesters in reciprocating air compressors, polyolesters in refrigeration compressors
4. What base oils are biodegradable? ► Vegetable oils and esters
Questions 1.10:
1. List some characteristics of naphthenics ► Low VI (bad), low pour point (good), more natural lubricity, more readily emulsify with water and better solubility of additives, availability in lower viscosities
2. List basic requirements needed in most lubricating oils ►
The correct viscosity, low enough pour point, oxidation stability and rust protection (R&O), low foam and air release as well as good water separability
3. What are the performance requirements for automotive engine oils? ►
The main requirements are a) keeping the engine clean and b) preventing wear....
4. When there is a demulsibility requirement, would the result of 39-37-4 (45) be acceptable? ► No
Why (2 reasons)? ► Too much emulsion (4, usually 3 maximum) and it took too long (45 minutes, usually 30 max.)
REVISION 1:
1. What are the three aspects of every lubricating oil that are good to consider first? ► Base oil quality (e.g. synthetic or not), performance that is specific for each application, and the most important characteristic of a lubricating oil - viscosity
2. How do we achieve the required performance of a lubricating oil? ►
In some applications, the right base oil is essential, otherwise it is the right additive(s) for each application
3. What does “multi-grade 20W-50” tell us about the oil's
(a) base oils ► Nothing
(b) performance ► Nothing
(c) viscosity? ► The oil meets all requirements of both SAE 20W and SAE 50
4. List the names of 12 additives mentioned so far. ►
Anti-rust, oxidation inhibitor, viscosity modifier, pour point depressant, defoamant, anti-wear, detergent, dispersant, EP, lubricity, tackiness, demulsifier
5. What can be spoilt by a defoamant? ► Air release
6. What are the old, still commonly used names for mm
2/s and mPa.s? ►
Centistoke (cSt), centipoise (cP)
7. What is the relationship between dynamic and kinematic viscosity? ►
Dynamic = Kinematic x Density
8. What are the viscosity limits of an ISO VG 460 oil? ► 460 – 46 = 414 cSt minimum, 460 + 46 = 506 cSt maximum, at 40 °C
9. What are the SAE viscosity grades of engine and gear oils that have viscosities at 100 °C:
(a) 10 mm
2/s ► SAE 30 and SAE 80
(b) 18 mm
2/s ► SAE 50 and SAE 90
10. Which ISO VG grade is close to SAE 90? Hint: Use the viscosity-temperature chart.
Use the chart on the last page and mark the middle value of the new SAE 90, 16 cSt, above 100 °C – you will see that you are close to the line of ISO VG 150 that you drew earlier; you are assuming that the VI of the SAE 90 oil is normal, around 100, so its line will be parallel to the lines drawn in the chart.
Note: The middle of the old SAE 90 was close to ISO VG 220.
11. You need an oil that is 30 mm
2/s at 50 °C. Which ISO VG will you choose? ►
In the same chart, find the point 30 cSt at 50 °C (above 50 °C) – you will see that the point is very close to ISO VG 46
12. You have an ISO VG 100 gear oil. The equipment manufacturer's (OEM's) requirement is "minimum 40 cSt at the operating temperature". The operating temperature is 80 °C. Can you use the oil? ►
In the same chart, find the point 40 cSt at 80 °C (above 80 °C) – you will see that the point is very far from ISO VG 100, you need much heavier oil
13. What does a low viscosity index do to the oil? ► It makes the oil's viscosity change a lot with changing temperature
14. How do we achieve a high VI? (Mention both methods.) ►
Use viscosity modifier additive (previously called VI improver) or a base oil that has a higher VI
15. Is an engine oil which has a Noack of 22% good? ► No, but it is a tricky question: in some engines, the oil might be good enough, but in modern engines, 15 % is the usual maximum limit, 13% for API CI-4 Plus
16. (a) What does Foam Tendency 150/60/140 mean? ►
Bubbling air through a column of oil heated to 25 °C, the foam level reached the 150 millilitre mark (Sequence I), then the oil was heated to 75 °C and the foam reached 60 ml (Sequence II) and when cooled to 25 °C it was 140 ml (Sequence III)
(b) What does Foam Stability 10/10/10 mean? ►
After Sequence I, the foam dropped to 10 ml after 10 minutes, it also dropped to 10 ml after 10 minutes after Sequences II and III
17. Is a hydraulic oil which has an air release of 28 minutes good enough? ► No, a good figure is 7 minutes for ISO VG 46 hydraulic oil
18. What requirements must be satisfied to qualify for Group II base stock? ► Sulphur 0.03% maximum, saturates at least 90% and VI 'normal' that means around 100 or up to 119 (when it would be considered Group II+); note that the VI minimum of 80 is nonsense
19. What are good and bad aspects of PAO? ► Well, what are they?
20. What are good and bad aspects of PAG? ► Dtto
21. Which lubricants are (a) often approved as 'food-grade' lubricants ► PAO
and which are (b) biodegradable? ► Esters
Questions 3.1:
1. What must an engine oil do in internal combustion engines? ►
(a) Lubricate, which includes protection against rust and corrosion and reducing noise and vibration
(b) Cool
(c) Clean
(d) Seal
2. Who decides what oil viscosity should be used? ► OEMs
3. What are the differences between detergent and dispersant additives? ► Detergent protects parts against deposits and dispersant keeps contaminants in suspension
4. What are the functions of ZDDP? ► Anti-wear and oxidation inhibitor
5. When is Group I base oil suitable in automotive engine oils? ►
When there is no Noack limit and the base oil meets low temperature viscosity requirements and the OEM allows it or the vehicle guarantee has lapsed
Questions 3.2:
1. Compare the new API categories with regard to backward compatibility; fuel economy; and Ford's acceptance:
(a) API CK-4 ► yes, backward compatible; no; yes if also meets Ford's new specification WSS-M2C171-F1
(b) API FA-4 ► no; yes – improved economy; not acceptable to Ford
2. If phosphorus content is limited, which additive is limited? ► ZDDP
3. What is 'SAPS'? ► Sulphated ash, phosphorus and sulphur content that is often limited in automotive engine oils for environmental reasons
4. What is the sulphated ash limit for Detroit Diesel big 2-stroke engines? ► 1.000%
5. What TBN was specified for Cummins engines? ► 10 minimum
Questions 3.5:
1. How many ILSAC standards are current (in force)? ► Only one (unlike API) plus the previous for one year
2. Which API category is on the level with ILSAC GF-5? ► API SN
3. Give one example each of cleanliness and wear protection requirements ►
Cleanliness: piston deposits and stuck rings in Sequence IIIG, sludge and varnish in Sequence VG
Wear: cam plus lifter wear in Sequence IIIG, also bearing, piston ring, cam and cam follower wear
4. Can SAE 15W-40 and 20W-50 oils satisfy ILSAC requirements? ► No, only SAE 0W-xx, SAE 5W-xx or SAE 10W-xx are allowed
Questions 3.16:
1. How do you decide what viscosity (what SAE) you should select? ► Equipment manufacturer (OEM) tells you – check the manual
2. How do you decide what performance level (what API GL) you should select? ► Equipment manufacturer (OEM) tells you – check the manual
3. Should you go for a higher performance level than specified? ► No, not with gear oils (with engine oils: yes)
4. Where do you use heavier oils, in synchromesh gearboxes or in rear axles? ► Rear axles
5. What API GL level is usually used in limited-slip differential oils? ► API GL-5
6. What is added to the oil to make it suitable for limited-slip differentials ► Friction modifiers
7. What letter is used in product names to show that they have the right formulation for ZF? ► A, Shell has started using Z
REVISION 2:
1. Which oil is heavier, SAE 50 or ISO VG 68? ► SAE 50
2. If a lubricant has a VI of 50, what base oil does it contain? ► Naphthenic
3. In which applications is anti-wear the key performance additive? ► Automotive engine oils and hydraulics
4. Is 25 a typical result for (a) pour point ► No, should be a multiple of 3
(b) flash point ► No, far too low, typical could be 220 °C
(c) Noack ► No, for applications where it is specified, it is too high (12-15% max.)
(d) air release ► Perhaps but not in hydraulic oils (7 minutes there)
(e) sulphated ash ► Never. In automotive oils around 1, in marine up to 9
(f) TBN ► Not in automotive but in marine oils yes.
5. Which of the engine oil specifications, API, ILSAC and ACEA:
(a) caters for both petrol (gasoline) and diesel engines ► API and ACEA
(b) has specific categories for various designs of vehicles ► ACEA
(c) allows only one valid specification ► ILSAC
(d) introduces new categories, leaving some old ones valid and unchanged ► API
(e) cancels some and revises all remaining categories ► ACEA
(f) is the most common world-wide ► API
(g) is the result of American-Japanese co-operation ► ILSAC
6. Is API SE/CC a good oil for modern car engines? ► No
and modern truck engines? ► No
7. Was API CI-4 a success? ► No, it was introduced too hastily
8. What is a good automotive engine oil viscosity in moderate climates? ► SAE 15W-40
9. When should you use a synthetic engine oil? ► If you are rich or when you are forced by the manufacturer
10. Use key word(s) to describe API GL-4 ► synchromesh
and API GL-5 ► differential, final drive, hypoid
11. Is it a good idea to use an API GL-5 oil where API GL-4 is specified? ► Bad idea
12. Which manufacturers of heavy equipment do not specify API GL-4 and GL-5? ► Eaton and ZF for their FreedomLine, Caterpillar, and Allison
13. Which viscosity grades are used to describe gear oils in question 11? ► Engine oil SAE numbers
14. What could be a moisture (water) limit in an used ATF? ► 0.2% maximum but preferably much less
15. Why do we test TAN? ► To see if the oil oxidized
16. What is the latest Dexron and what kind of lubricant does it require? ► Synthetic Dexron-VI (VI means 'six')
17. How many ATFs does Castrol have? ► 12 plus a power steering fluid
18. Can UTTO and STOU be used in (a) engines ► Yes – of farm equipment
(b) hydraulics ► Yes – of farm equipment
(c) transmissions ► Yes – of farm equipment
(d) hypoid gears? ► No
Questions 5.0:
1. What are the 3 conditions for the formation of an oil wedge? ►
Enough oil of the right viscosity in a well-designed plain bearing with a shaft turning at a sufficient speed
2. Describe all three lubrication conditions ►
Hydrodynamic: an oil wedge is formed in a well designed plain bearing provided there is enough oil of sufficient viscosity and the speed of rotation is also sufficient
Boundary: there is some metal-to-metal contact
EHL: the oil is pressurized so much that it turns almost solid deforming metal surfaces
3. Under what lubrication conditions do rolling element bearings operate? ► EHL
4. Under what lubrication conditions do plain bearings operate? ► Hydrodynamic or boundary, mixed during a start up
5. Under what lubrication conditions do gears operate? ► Hypoid: boundary (severe rubbing). Spur and helical gears: EHL for a fraction of a second, otherwise boundary. Worm gears: boundary (sliding)
6. Mention four different types of additives that help to reduce wear and friction under boundary conditions ► Lubricity, anti-wear, EP, solid additives
Questions 6.0:
1. What base oils are used in industrial EP gear oils? ► Mineral (paraffinic Group I) unless the operating temperature is more than 90 °C
2. List all additives commonly used in industrial EP gear oils ►
R&O, EP, defoamant, demulsifier, corrosion inhibitor (metal deactivator), friction modifier, pour point depressant
3. Name the most common industrial EP gear oil specification used internationally ► DIN 51517 Part 3 (CLP)
4. What is the best EP test for gears and why? ► FZG because it tests wear on gears
5. What happens when the operating temperature in a gearbox increases from 90 to 100 °C? ►
The service life of mineral-based lubricants is reduced by half
6. You have two similar well-designed spur gearboxes driven by an electric motor at 1500 rpm. One (a) runs at 60 °C and the other (b) at 75 °C. What oil grades should you use? ► (a) ISO VG 100 (b) ISO VG 220.
Hint: In the chart for Tellus S oils in Hydraulics, determine which viscosity grades are close to the points where the 40 cSt line crosses 60 °C and 75 °C lines. (You need the extra lines that you have been instructed to draw on p. 12)
Questions 6.1:
1. What makes worm gearboxes different from other gears? ►
Metals used and the geometry of contact: they do not have steel-on-steel combination and they require lubricity because of the sliding action
2. What is the best lubricant for worm gearboxes? ► PAG
Questions 7.0:
1. Name the 5 main aspects that should be considered first regarding greases ►
The same three as for liquid lubricants: base oil quality, performance (additives) and the oil viscosity; PLUS the nature of the thickener, and consistency (softness)
2. Grease descriptions/types are based on what? ►
The nature of the thickener, if it's a soap then the metal(s), e.g. 'calcium grease'
3. What does NLGI 2 mean? ►
It means consistency of a soft grease: in the worked penetration test, the result was between 265 and 295 tenths of millimetre
4. What does “clay thickener, NLGI 1½, oil ISO VG 150, no EP” tell you about a grease and could it be a multi-purpose grease? ►
A grease designed to stand high temperatures (clay), very soft (NLGI), suitable for speeds that would depend on the operating temperature (ISO VG 150), not fortified for heavy and shock loads. It's not a MP grease, because the thickener is wrong, it is too soft and it does not have the required EP additive
5. Does the oil ever separate from grease? ►
It must – to be able to lubricate, it's called bleeding, you'll find a puddle of oil on the top of grease in storage = no problem but you can't mix it back into the grease
6. On what kind of gears do we sometimes use grease? ► Open (big) gears and small leaky gearboxes
7. You have a cylindrical roller bearing on a 55 mm shaft running at 1500 rpm. What could the re-lubrication interval be? ►
55 is close to 60, if it was a radial ball bearing, the interval would be say 11 000 hours; for a cylindrical roller bearing, it is one half thus 5500 hours
8. What conditions must be satisfied to be sure about the answer to question 7? ► There is no vibration, shock loading and environmental extremes
9. If you were to replenish the bearing in question 7, how much grease should you pump into it? (Use your technical feel to estimate your answer.) ►
To make the calculation simple, let's assume that the bearing's outside diameter is 100 mm and the width 25 mm, then 0.005 x 100 x 25 = 12 grams
10. Is the re-lubrication interval longer or shorter with bigger bearings? ► Shorter
11. Is the re-lubrication interval longer or shorter with higher speed? ► Shorter
12. What is the highest and the lowest oil viscosity in greases given as examples in this manual? Give the figures, name the greases and mention the thickeners ► 30 cSt at 40 °C in clay-based Mobilgrease 28, 4100 cSt at 40 °C in aluminium complex open-gear grease Shell Malleus GL 3500
13. What is still the most popular grease thickener? ► Lithium
14. What does ' thixotropic' mean? ► The grease is harder when undisturbed (e.g. when it is sealing) and softer when stirred (when lubricating)
15. What is better, grease or oil? Why? ► Oil is definitely better for lubrication and it is necessary for extreme conditions, but grease is needed when the equipment is not designed for oil lubrication and when the lubricant must stay on the job and instead of falling off
Questions 8.0:
1. What is a circulating oil? ► An oil for bearings and other suitable lubricated parts included in the circulation, "general purpose" oil
2. What viscosities of circulating oils have been mentioned in this manual (both by numbers and in words)? ►
Spindle oils ISO VG 10, turbine oils ISO VG 46, paper machine oils ISO VG 320, extremely heavy oils (much more than 1000 cSt at 40 °C) for plain bearings in sugar mills. Recommended viscosities, e.g. 13 cSt minimum at the operating temperature
3. What is a turbine oil? ► A very high quality R&O oil
4. What does water in oil do to rolling element bearings? ► Destroys them
5. Is it a good idea to use oils with viscosity modifiers in bearings and gears? ► No
Questions 9.0:
1. For what application is DIN 51506 VDL relevant? ► Cylinder lubrication of reciprocating (piston) air compressors with very high air temperatures
2. What is the best air compressor cylinder lubricant type? ► Diester
3. What must you watch with reciprocating compressors to ensure safety of operation? ►
Valves need to be regularly inspected and cleaned if necessary
4. What is the recommended viscosity for cylinder lubrication? ► ISO VG 100 or 150
5. What is the common viscosity for bearing lubrication in piston compressors? ► ISO VG 68
6. Mention some materials of seals suitable for diesters ►
Viton, Teflon, fluorinated hydrocarbons, silicone, fluorosilicone, polysulphide and Buna-N with more than 36% acrylonitrile groups
7. At what operating temperature has ISO VG 46 oil viscosity of 10 mm
2/s? ► 85 °C
Hint: Go to the viscosity-temperature chart on p. xx and follow the line for '46'
8. What are the two basic types of screw compressors? ► Oil-flooded and oil-free
9. What is the typical oil viscosity grade for oil-flooded screw compressors? ► ISO VG 46
10. What do coalescer filters do? ► Separate the remaining small droplets of oil from the air (after the large droplets were separated in the reclaimer)
11. What are different oil suppliers striving to achieve? ►
(a) outstanding resistance to oxidation;
(b) high FZG rating;
(c) low tendency to form carbonaceous deposits on valves;
(d) the ability to prevent the blockage of coalescer filters
12. What will happen if you lubricate a high vacuum pump with an ordinary mineral oil? ►
It won't work because the the oil vapour will fill the vacuum
13. What will happen if you lubricate a compressor that compresses oxygen with a mineral oil or PAO? ► It will explode
Questions 9.4:
1. For which refrigerants are the following lubricants recommended?
(a) naphthenic oils ► Freons, ammonia
(b) alkyl benzene ► Freons, ammonia
(c) polyol ester ► HFC (R-134a) and 'drop-in' mixtures
(d) PAG ► Hydrocarbons, ammonia and CO2 in some equipment, HFC
(e) PAO ► CFC, carbon dioxide, ammonia (pure PAO only)
Questions 10.0:
1. Which two different types of anti-wear additives are used in hydraulic fluids? ► Zinc (ZDDP) and non-zinc which can be ashless
CHALLENGE Hint No. 2:
So what is wrong? What Vic is doing obviously does not work and the lubricants are to blame. What correct lubricants should he use and why?
Make a table listing all the problems (1st column). With what does Vic lubricate everything? What do we know about those lubricants? Put the lubricants into a 2nd column in the table next to the problems. Continue with the table (3 or 4 more columns), e.g. what is Vic's outcome when he is using his current lubricants and what's the reason for the bad outcome. Consider VISCOSITY - BASE OILS – PERFORMANCE!
Then check the
solutionor go to
Hint No. 3.
REVISION 3:
1. Is EHL relevant to worm gears; why? ► No, there is no rolling (that would extremely pressurize the oil), only sliding
2. Which gear oils have more EP – automotive or industrial and which type of gears requires the highest EP content? ► Automotive (GL-5 6%, GL-4 3%, industrial 2% of the same EP package in rough figures), hypoid gears require GL-5 unless lightly loaded
3. What might be the reasons for the instruction: "Never use EP oils in industrial gearboxes which have an internal backstop"? ► It's not clear. The first guess would be that there are some bronze parts that would get damaged. That does not seem to be the case. The correct answer probably is that good EP oils contain some lubricity for friction reduction (thus power saving) which causes the backstop to slip. See:
EP gear oils should never be used in industrial gear drives that use internal backstops
The EP additive can prevent the backstop from working correctly
4. What are the two common viscosity grades for industrial gearboxes and at what operating temperatures do these grades reach the optimum viscosity in a gearbox described in the text? ► ISO VG 220 gets down to 40 mm
2/s at 75 °C and VG 320 at 82 °C
5. What alternatives for lubricating open gears do you know? ► Black lube containing bitumen (asphalt) with or without diluent; grease with an extremely heavy oil; and heavy synthetic that is circulated (thus the gears need to be enclosed – are they still “open gears”?)
6. In which aspect(s) are the open gear lubricants unusual? ►
Base oil: if bitumen or synthetic, viscosity always extremely high (similar to plain bearings in sugar mills)
7. Describe a multi-purpose grease considering all 5 main aspects and explain the significance of each ►
(a) Base oil mineral (usually nothing better is needed, partially naphthenic which is needed during the production of the grease);
(b) ISO VG 150 to 200 mm
2/s at 40 °C (for slow to moderate speeds, high loads);
(c) EP for high loads;
(d) lithium soap which has no bad properties;
(e) NLGI 2 = soft for easy application
8. Describe paper machine oils ► Circulating oils with added anti-wear (ZDDP), they have a higher viscosity either ISO VG 220 or 320 and must have good demulsibility and air release; synthetic versions used in Scandinavia
9. What oils are needed for plain bearings, what is the best quality oil of this type, what is this oil's usual viscosity grade and at what operating temperature does this oil reach the optimum viscosity? ► R&O oils, turbine oils are top quality – they are ISO VG 46 so they reach 30 mm
2/s at 50 °C
10. Give three or four typical oil viscosities for various compressors and their parts ► ISO VG 46 for rotary screw air compressors; ISO VG 68 for small reciprocating air compressors and most refrigeration compressors; ISO VG 100 to 150 for cylinders of reciprocating air compressors
11. What is alkyl benzene, where is it used and with what is it compatible and miscible? ► Synthetic hydrocarbon that has a low pour point; used in refrigeration compressors with Freons and ammonia; it is compatible with all commonly used sealing materials and miscible with mineral oils
12. What must be done because polyol ester is hygroscopic (readily absorbs moisture)? ► After opening the container, close it tightly and use the lubricant within a few days
13. Who is the most important hydraulic pump manufacturer – considering its specification which effectively determines if a hydraulic fluid is 'premium quality'? ► Parker Hannifin (Denison)
14. What are the highest and lowest viscosity of hydraulic fluids and why? ►
In rounded figures: 1000 cSt to be able to suck it in to the pump and 10 cSt to lubricate the pump and prevent excessive leakage
15. What is the main advantage of using high VI hydraulic fluids? ► Power saving
16. Is it a good idea (Yes/No) to use synthetics base stocks in the following applications? If so, exactly in what applications and what synthetics? Can you save energy?
-- Automotive engines ► No, unless you must or costs are not a consideration. But this might change in future when lighter and lighter oils will be used to save fuel and those oils will have to be synthetic to meet the specifications
-- Two stroke engines ► Only if you need to meet certain specifications or want to have a biodegradable lubricant
-- Automotive gears ► No, not normally, only in extreme conditions
-- Automotive transmissions ► There is a clear shift to synthetics in these applications
-- Brake fluids for cars ► Yes, they are synthetic
-- Industrial gears, excluding worm gears ► No, only at high temperatures
-- Worm gears ► Yes, definitely, PAG! Well proven energy savings.
-- Open gears and big enclosed gears ► Yes, but not too common as yet
-- Grease applications ► No, only in special applications
-- Bearings, excluding turbines and paper machines ► No (perhaps not yet)
-- Steam turbines ► No, except two things:
(1) there is a hydraulic system to control the turbine, in some designs, it uses the same oil from the same tank; it would be good, in some cases, to have a fire-resistant fluid in hydraulics, so the idea is to use it in the whole turbine.
(2) PAG is promoted in this application.
-- Paper machine oils ► Exceptions (Scandinavia)
-- Air compressors ► Yes, except where the oil lubricates only bearings and gears
-- Refrigeration compressors ► Yes
-- Hydraulics ► No, only in special applications (or perhaps not yet)
-- Machine tools ► No
-- Transformers ► No
-- Metal cutting and grinding ► Yes, in “High-Water Base Fluid” for grinding
CHALLENGE Hint No. 3:
Vic uses only one oil and one grease in all applications.
The oil is an old specification SAE 20W-50, 135 cSt at 40 °C (p. 12).
The grease has a very heavy base oil, perhaps 1000 cSt at 40 °C (p. 42) or even more.
Did you list all the problems and lubricants?
Grease-lubricated bearings on electric motors fail and need replacing: Grease
Lathe: surfaces of the cut pieces are not smooth: 20W-50 (2 reasons)
Lathe: parts do not move smoothly: 20W-50
Lathe: had to replace some worn gears: 20W-50
Lathe: noise and smoke when cutting: 20W-50
Hydraulic press too slow: 20W-50
Hydraulic press does not want to start: Grease
Hydraulic press: bearings get hot: Grease
Piston compressor: has to clean the valves (explosion): 20W-50
Piston compressor: air pressure low: 20W-50 (at a reduced feed)
Old car's differential loud: 20W-50 and grease
Old car: must flush the engine: 20W-50
Old car: must add a special additive: 20W-50
Worm gearbox gears: 20W-50
Wind pump sluggish: 20W-50
Why do Vic's oil and grease cause problems in those applications? Which correct lubricants will eliminate the problems?
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