SynLube™
Lube-4-Life®
|
|
|
|
VISCOSITY
CHECK BACK IN FEW DAYS!
INTRODUCTIONViscosity is the measure of the internal friction in a liquid or the resistance to a flow. Low viscosity fluids flow easily
(water, alcohol); There are number of different techniques by which fluid's resistance to flow is measured. Because Viscosity changes with temperature and sometimes also with pressure, it is also important that when different fluids are compared that the measurements were conducted under the same temperature and pressure conditions. The common metric unit of absolute viscosity is the poise. For convenience, the CentiPoise (cP) — one one-hundredth of a poise — is the unit customarily used. Laboratory measurements of viscosity normally use the force of gravity to produce flow through a capillary tube (viscometer) at a controlled temperature. This measurement is called kinematic viscosity. The more customary unit is the centistoke (cSt) — one one-hundredth of a stoke.
VISCOSITY - GeneralWe are accustomed to the notion of friction as a force that is exerted opposite to that which brings about motion when one solid moves in contact with another. Such friction force tends to slow and eventually stop movement, unless the propulsive force is maintained so that the friction force is equalized. There is also a friction where solid moves through liquid, as when ship plows through water. The ship once set in motion will come to halt; unless the propulsive force is maintained here too. Although water seems so smooth and lacking any projection to catch the ship, water nevertheless absorbs enough energy when it is pushed apart by the ship to eventually stop it. This friction arises from the fact that it is necessary to expend energy (power) to pull the water apart against its own cohesive forces in order to make room for the ship to pass through it. The energy expanded varies greatly with the shape of the object that passes through the fluid. If the fluid is pulled apart gently and gradually, and then brought back even more gently and gradually, then the energy needed to be expanded is minimal. Such action is possible only by object that is of "teardrop" shape. By contrast if the fluid is pulled apart abruptly in such a way as to force it into eddies and other turbulence, such as by cube, the maximum energy will have to be expanded to move the cube through the fluid. The friction between a moving solid and a surrounding liquid increases with velocity, so no matter how streamlined the object may be, eventually a terminal velocity will be reached and thus and object falling through the water accelerated by gravitational pull, will eventually fall at a constant speed. Any object will sink faster in fluid of low viscosity such as water, and will sink much slower in a high viscosity fluid such as glycerin. Viscosity of a fluid can thus be "measured" by the time it takes for object, such as a steel ball bearing, fall through a test tube with oil, for example. The friction makes itself evident even when the liquid itself is the only substance involved. When any liquid moves, or pours, it does not move all-in-one as a solid does. Instead, a given portion of the liquid will move relative to a neighboring portion and "internal friction" between these two portions will counter the motion. Where the cohesive forces that impose this internal friction are low, as in water, we are not ordinarily very aware of this. When the cohesive forces are high such as in cold honey, the fluid pours very slowly. The internal friction for any fluid is higher at low temperature, and much lower at higher temperatures. So honey that was in refrigerator, will barely flow, but once warmed to room temperature will pour easily. The difference in flow between freezing cold and boiling hot water however is so small as not being perceivable by human senses. However, very sophisticated laboratory equipment can detect the difference. Where the difference in flow between hot and cold fluid is very small, such fluid is said to have HIGH VISCOSITY INDEX. (High VI) By contrast honey will be solid at freezing and water like at boiling temperatures, such fluid is said to have LOW VISCOSITY INDEX. (Low VI) At room temperature water has viscosity of just about ONE CentiPoise, while the common anesthetic - diethyl ether has viscosity of 0.23 CentiPoise or 23 MilliPoise, and glycerol is about 1,500 CentiPoise or 15 Poises. The unit of viscosity the Poise has been named in honor of French physician Jean Louis Poiseuille (1799-1869), who in 1843 was the first to take time to study viscosity in quantitative manner. As a physician he was interested in the manner in which blood moved through blood vessels. But his observations proved to be valid for ALL liquids. For the purpose of lubrication, viscosity has been since the beginnings of Lubrication Engineering held as the most important quality of the Lubricant. The reason for this is that if the lubricant is too thin, it gets forced out from bearing surface under pressure and poor lubrication occurs, this leads to bearing surface damage. If the lubricant is too viscous, it either does not flow into the bearing surface, causing lube starvation, and thus certain bearing damage. Or it consumes too much energy, which is then converted to heat and the bearing may be overheated, at which point it can seize due to loss of running clearance. Therefore oil that is either too viscous or too thin, will cause premature failure of any bearing surface. The proper viscosity for given application is therefore extremely important. That is why the first lubricant standard J300 that was developed by SAE in 1911 was Viscosity Classification of Motor Oils, and although this standard was revised and updated many times it is still used today world-wide for Motor Oil applications. However unlike the exact scientific value of Poise for Absolute Viscosity, the SAE viscosity numbers are "staircase" approximations for KINEMATIC Viscosity. For example Motor Oil that is measured to have viscosity of 9.5 cSt @ 100 C will be rated as SAE 30, while another Motor Oil that is measured to have viscosity of 12 cSt ( or 26% more viscous ) will also be rated as SAE 30 Motor Oil. Yet in real life operation 26% difference in viscosity may make difference between engine that will run forever and one that will wear out prematurely. That is why "stay in grade" over the service life of the Motor Oil is so important! The SAE J300 measurement is only relating to a FRESH UNUSED MOTOR OIL. As few as 20 hours of operation will change viscosity of pure petroleum oil. Some oils will shear and thin out to SAE 20 or below, while some oils will oxidize and sludge up to become much more viscous like SAE 40 or even SAE 60! The "best" motor oil will be SAE 30 when fresh and SAE 30 when drained out after its use. Motorists make the common mistake that every SAE 30 oil is the same in performance, but the reality, however, is quite different. Even more drastic differences in viscosity for fresh and used oils can be observed in multi-viscosity or multi-grade oils such as SAE 5W-30. The SAE J300 viscosity classification therefore should not be confused with any level of quality or long term performance. API Service Classifications are used to distinguish Motor Oil performance levels and are based on specific engine and laboratory tests. No matter what oil you use for any purpose the ideal viscosity that provides the ultimate lubrication, that is TOTAL bearing surface separation, and at MINIMUM power that is consumed by the lubricants viscosity (MINIMUM TEMPERATURE RISE) occurs ONLY at ONE combination of:
Under ALL other combinations of the three factors, the lubricant is NOT IDEAL. Some lubricants, due to much higher than normal viscosity index, can have more advantageous performance over much wider range of TEMPERATURE, SPEED and LOAD, than others and therefore can be used more universally in wide range of applications. That is why some lubricants such as single grade SAE 30, must be changed to SAE 20 when operating temperature is reduced or to SAE 40 or SAE 50 when the operating temperature is increased. So thicker more viscous oil is needed when engine is operated at higher temperature such as high summer heat. Similarly the proper viscosity depends on LOAD, the higher the load the thicker or higher SAE number is required. So on highly loaded engine designed to used SAE 30 oil under normal operation SAE 40 or SAE 50 should be utilized. Speed however has the opposite effect, when engine designed to run at 2,000 RPM is constantly run at 6,000 RPM but at the same load, the SAE 30 oil should be substituted with SAE 20 oil. Higher operating speed requires thinner or lower viscosity lubricant. It is possible in some applications that the increase in load can be just offset by the increase in speed and then the same oil such as SAE 30 that is just right for NORMAL operation will be also JUST RIGHT for the new HIGH LOAD and HIGH SPEED regime. "Old" truckers are well aware of this from experience, they get much better and longer engine life when running in lower gear up-hill. Extra LOAD is imposed on the engine by climbing uphill (lifting cargo weight against the pull of gravity requires more power therefore the engine LOAD is increased), this can be balanced by running engine at much higher RPM (this requires thinner lubricant). The alternative of running uphill in low gear, that is at slow engine speed and increased load would surely require increase in motor oil viscosity or else almost certain engine damage would result. It would be rather inconvenient to change motor oil before and after every major hill on the Interstate. Therefore changing gears is much more feasible. Thinner motor oils such as 5W-20 or even 0W-20 are becoming more popular these days and are even specified by some OEM's (FORD & HONDA) on new 2001 cars. Although these oils are promoted as "energy conserving" they generally trade a gain of less than 0.1 MPG in Corporate Average Fuel Economy (CAFE) for shorter useful engine life. FORD which has previously designed cars to have 10 year or 150,000 miles life has reduced the mileage life expectation to "beyond 100,000 miles" on vehicles that are operated on SAE 5W-20 Motor Oil. HONDA only claims "useful life" as 7-years or 70,000 miles in EPA certifications for their CIVIC which uses SAE 5W-20 Motor Oil, while the previous model that utilized SAE 5W-30 Motor Oil was certified for 10 year or 100,000 mile durability. Since both HONDA and FORD Warranty their NEW cars for ONLY 3-years or 36,000-miles the reduction in engine life expectancy is not a factor. By contrast Mercedes-Benz recommends use of ONLY Synthetic Motor Oil that is at least SAE 5W-40! This is a recent increase in recommended viscosity from SAE 5W-30. Apparently customer research indicated that engine longevity is more important to typical MB customer than fuel economy. Even more important is the High-Shear High-Temperature MINIMUM specification in SAE J300. In tables below you will notice that there are "two" SAE 40 specifications, one with minimum HSHT value of 2.9 cP for Automotive Oils (SAE 0W-40; 5W-40; 10W-40) and the other for Heavy Duty Oils (HDO) (SAE 15W-40; 20W-40; 25W-40; 40). This double specification is at insistence of heavy duty engine manufacturers who have required HSHT viscosity limits consistent with good engine durability in high-load, severe service operation. HSHT value of 3.7 cP or 27% more viscous oil at 150ºC (300ºF). Yes, a 27% increase in viscosity makes a difference between Automotive engine that lasts 100,000 miles and Truck engine that lasts 1,000,000 miles! When you consider that most Automotive Motor Oils are ONLY 3 cP, while our If you wish to learn more about viscosity, following definitions which are also mirrored in our GLOSSARY should give you more technical know-how than you ever dreamed possible!
The measure of the internal
friction or the resistance to flow a liquid. Measurement of a fluid’s resistance to flow. The common metric unit of absolute viscosity is the poise, which is defined as the force in dynes required to move a surface one square centimeter in area past a parallel surface at a speed of one centimeter per second, with the surfaces separated by a fluid film one centimeter thick. For convenience, the CentiPoise (cP) — one one-hundredth of a poise — is the unit customarily used. Laboratory measurements of viscosity normally use the force of gravity to produce flow through a capillary tube (viscometer) at a controlled temperature. This measurement is called kinematic viscosity. The unit of kinematic viscosity is the stoke, expressed in square centimeters per second. The more customary unit is the centistoke (cSt) — one one-hundredth of a stoke. Kinematic viscosity can be related to absolute viscosity by the equation:
In addition to kinematic viscosity, there are other methods for determining viscosity, including:
Since viscosity varies inversely with temperature, its value is meaningless unless the temperature at which it is determined is reported.
Absolute Viscositythe ratio of shear
stress to shear rate. The common unit of absolute viscosity is the poise and CentiPoise cP (see viscosity). Absolute viscosity divided by the fluid’s density equals kinematic viscosity. Absolute viscosity is typically measured by a rotary viscometers to determine the torque on rotating spindle and so measure the fluid's shear resistance. Changing the rotor (spindle) dimensions and the gap between the rotor and stator wall (container) and the speed of rotation can change the rate of shear. Examples of rotary viscometers that are used for Absolute Viscosity measurements:
In relation to oils for Automotive applications such as Motor Oil or Gear Oil, the CCS and MRV test equipment at low temperatures is used to determine if the test lubricant does not get too thick to prevent safe engine or transmission operation at low temperatures. If Motor Oil is too viscous to flow, even if engine can be started, certain mechanical damage will result due to localized oil starvation. In transmissions both manual and automatic, proper shifting may be impaired, affecting safe vehicle operation once vehicle is put in motion.
Apparent ViscosityThe ratio of shear stress to rate of shear of a non-Newtonian fluid such as lubricating grease, or a multi-grade oil, calculated from Poiseuille’s equation and measured in poises. The apparent viscosity changes with changing rates of shear and temperature and must, therefore, be reported as the value at a given shear rate and temperature (ASTM Method D 1092).
Kinematic Viscosityabsolute viscosity of a fluid divided by its density at the same temperature of measurement. It is the measure of a fluid’s resistance to flow under gravity, as determined by test method ASTM D 445. To determine kinematic viscosity, a fixed volume of the test fluid is allowed to flow through a calibrated capillary tube (viscometer) that is held at a closely controlled temperature. The kinematic viscosity, in centistokes (cSt), is the product of the measured flow time in seconds and the calibration constant of the viscometer.
An arbitrary scale used to show the magnitude of viscosity changes in lubricating oils with changes in temperature. Oils with low VI number such as VI=0 ("zero") have high dependence of viscosity change on temperature. They thicken quickly with decreasing temperature, and thin out quickly with increasing temperature. Oils with high VI number such as VI=200, will still thicken with decreasing temperature but not as rapidly, and also will thin out with increasing temperature, but again not as much as low VI oil. VI number can also be "negative" Tables found in ASTM Method D 2270 are widely used to determine VI number. However, VI does not tell the whole story -- it only reflects the viscosity/temperature relationship between temperatures of 40°C and 100°C. Two lubricants or base oils with the same VI number may perform dramatically different at low temperatures in the -5°C to - 50°C range.
Chemical additive that is added to finished lubricants to improve the viscosity index. lubricant additive, usually a high-molecular-weight polymer, that reduces the tendency of an oil to change viscosity with temperature. Multi-grade oils, which provide effective lubrication over a broad temperature range, usually contain V.I. improvers. While Viscosity Index Improvers can enhance viscosity index (VI), they can break down under shear or over time, resulting in diminished performance.
the manner in which the viscosity of a given fluid varies inversely with temperature. Because of the mathematical relationship that exists between these two variables, it is possible to predict graphically the viscosity of a petroleum fluid at any temperature within a limited range if the viscosities at two other temperatures are known. The charts used for this purpose are the ASTM Standard Viscosity-Temperature Charts for Liquid Petroleum Products, available in 6 ranges. If two known viscosity-temperature points of a fluid are located on the chart and a straight line drawn through them, other viscosity-temperature values of the fluid will fall on this line; however, values near or below the cloud point of the oil may deviate from the straight-line relationship.
Possessing viscosity. From the Latin word for a sticky species of birdlime that
is a slowly-pouring liquid.
device for measuring viscosity; commonly in the form of a calibrated capillary tube through which a liquid is allowed to pass at a controlled temperature in a specified time period.
SAE J300 Viscosity Classification (April 1997)
*The SAE 5W-50 rating shown above is for SynLube™ Lube-4-Life™ Motor Oil.
However, the previous specification has been revised by SAE in December 1999 to one tabulated below. According to "new" J300 our existing version of SynLube™ Lube-4-Life™
Motor Oil should have been classified as SAE 0W-50,
however our customer research has shown that this unusual classification was "too
radical" and "too scary", so we have decided to retain our
existing rating of SAE 5W-50 that was
originated in 1985. This required slight "thickening"
of the lubricant at low temperatures, achieved by only 2% increase of one of our existing
ingredients. By "missing" the target SAE 0W low
temperature viscosity by SAE J300 Viscosity Classification (Current)
*The SAE 5W-50 rating shown above is for SynLube™ Lube-4-Life™ Motor Oil.
ISO International Standards Organization This organization which is worldwide in scope sets standards and classifications for lubricants. An example is the ISO viscosity grade system.
for classifying industrial lubricants according to viscosity.
For example: lubricant with an ISO grade of 32 has a viscosity within the range of 28.8 — 35.2 cSt, the mid-point of which is 32. (see Table below) ISO viscosity grade number Table: viscosity range expressed in centistokes (cSt) at 40°C
*The SAE 5W-50 SynLube™ Lube-4-Life™ Motor Oil is rated ISO VG 100.
Due to the fact that there are number of differing Viscosity measuring standards it is sometimes confusing to determine what is the viscosity of fluid in a viscosity system of interest if the viscosity is quoted in units used in another viscosity system. The chart below gives approximate equivalence of values for a typical conventional fluids.
Which SAE rating is the best ?A:SAE 0W-60 but it is not available, yet ! Theoretically the best possible SAE Viscosity rating is 0W-60, but only small experimental quantities of such lubricants were ever produced. The NASA SynLube™ is rated SAE 0W-60, but it sells for $90.00 per Liter, therefore it is not economical or practical for average automotive use. SynLube™ Lube-4-Life™ is rated SAE 5W-50 (ISO 100) Below is the list of SAE Viscosity Ratings in order of preference from Best to Worst:The Best Possible SAE 0W-60 (Very Expensive)The Best Available SAE 5W-50 (Possible only with Fully Synthetic Motor Oil)SAE 5W-40 for Colder Climates (Synthetic or Blend) SAE 10W-50 for Warmer Climates (Synthetic or Blend) 3rd Best SAE 5W-30 for Colder Climates SAE 10W-40 for Normal Climates SAE 20W-50 for Hot Climates** Average SAE 10W-30 SAE 15W-40 for Heavy Duty Diesel Applications Acceptable SAE 30 for Normal Climates, but not in Winter SAE 40 for Warmer Climates, but not in Winter SAE 50 for Hot Climates, but not in Winter SAE 5W-20 for sub-zero temperatures, Winter use only** Legend: ** = unless use is prohibited by the engine manufacturer To make sense of the above recommendations we must define what all those climatic conditions mean. The definitions can be found in the table below:
*The SAE 5W-50 rating shown above is for SynLube™ Lube-4-Life™ Motor Oil.
|
|
Send mail to synlube@aol.com with questions or comments about this web site.
Lube-4-Life®
is a Registered Trademark of SynLube, Inc.
|
This page is still under construction!
