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About oil > Terms of Use > Quality indicators > Additives
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To facilitate the study of the oil several group all indicators according to operational significance. The first group comprises all parameters of the lubricating properties of the oil, the second group - indicators characterizing the stability of the oil, the third - the corrosion properties and the fourth group will include all benchmarks.
View the properties of lubricants in the same sequence.
Viscosity — the most important property of a lubricating oil.
When selected engine oil, machinery or equipment, first of all pay attention to the viscosity of the oil. Recall that according to the hydrodynamic theory of lubrication can not resolve the question of the suitability of oil for the car, not knowing its viscosity.
The viscosity value is not limited to the fact that it affects the creation of liquid lubricant in friction. Depends on the viscosity, and cooling friction parts, piston rings and seal in the cylinder, and ease of starting.
That is why the study of the properties of oils with viscosity begins. As already mentioned, viscosity is called the friction generated within the liquid, i.e. the friction generated between the molecules of the liquid moving under influence of the external force.
The most common way to determine the viscosity of the oil is based on measuring the time during which a defined volume of the oil flows from an instrument called a viscosimeter. Oil with high viscosity, flow out of the viscometer slowly than oil with low viscosity.
There are other methods for determining the viscosity.
Viscosity, specific viscometer Ostwald - Pinkevich called kinematic viscosity is expressed in Stokes (St) or centistokes (cSt). Currently, this method is used in most cases.
Viscosity was determined at a temperature of strictly defined, since it greatly varies with the oil temperature. The higher the temperature, the lower the viscosity, the temperature decreases the viscosity increases sharply.
Talk about the viscosity of the oil, without specifying the temperature at which it is defined, it would be pointless. In fact, light oil at a low temperature becomes more dense than the most viscous oil at high temperature. That's why when it comes to the viscosity of the oil, be sure to indicate the temperature at which it was determined.
Different oils are raziomu change in viscosity with temperature changes due: some more slowly, others more rapidly. Rate of change of viscosity with changes in temperature is important because it expresses a property performance oils. The lower the viscosity of the oil varies with changes in its temperature or, in other words, is flatter than the curve of the viscosity, the higher the quality of the oil.
The rate of change of viscosity depending on the temperature sometimes express the so-called viscosity index, which is calculated according to the formulas. The higher the viscosity index, the flatter is its temperature-viscosity curve
This is because the oil viscosity at a gentle curve maintains a high temperature viscosity sufficient to ensure reliable lubrication of the rubbing of the hottest parts of the engine, i.e. the piston, cylinder, connecting rod head; at low temperature viscosity is not so high that during the cold season ignition problems and provide much resistance when pumping through tubes and channels lubrication system.
Oil has a higher viscosity index, ie flatter temperature curve viscosity are considered the best and in preference to oil with low viscosity index, ie a steep viscosity curve. What is better to use the same viscosity oil - with large or small?
On such a general question can not be answered. For the same engine, but working in different conditions may require different oil viscosity. For example, for an engine mounted on the tractor is required oil viscosity greater than for the same engine installed in the bus, plying on asphalt roads, or on the excavator. To operate the engine at low temperatures require oil lower viscosity than for use in hot conditions.
In the selection of oil viscosity is taken into account a number of conditions associated with both the features of the engine, and the peculiarities of its operation.
The viscosity value for the engine oil is very high. The viscosity of the dependent: the power loss due to friction, wear of friction parts, piston ring seal, oil consumption *, fuel consumption, ease and speed of the engine is started, the temperature of rubbing parts.
Let us consider the basic conditions under which are clearly visible positive and negative characteristics of low viscosity and high viscosity oils.
Oxidation of compounds refers to the process of oxygen with other substances. Changes in the quality of oil in the engine is running caused primarily by oxidation of the oil. The oxygen reacts with the molecules of the oil, destroys them, thereby forming a completely new products: acids, resins, asphaltenes, carbenes and car-boyd. The accumulation of oxidation products in the oil entails a change in the appearance of oil and its physico-chemical properties: Color changing oil - Oil darkens the oil viscosity increases, the acidity increases, oily substances appear that fall as sludge. Oil oxidation is the main reason that in its details the engine lubrication system and various kinds of carbonaceous contaminated sediments.
Bottom of the piston, the wall of the combustion chamber and valves are covered by a layer of rough solid coke-like substance. The piston skirt, the inner part of the piston and connecting rods are covered by a thin film of lacquering. On the walls of the crankcase, at various parts in the crankcase on the filters, oil lines laid in a black pasty products.
Carbonaceous deposits formed in the engine, can be divided into three fundamentally different types: lacquer, varnish and gum.
Lacquer or varnish deposits, called carbonaceous material in the form of a thin layer of durable lakopodobnogo brown or black, is deposited in the area of the piston rings (on the skirt of the piston, the piston rings in the grooves on the inner walls of the piston) and the connecting rod.
Nagar called solid carbonaceous material is deposited in the combustion chamber at the bottom of the piston at the top of the piston skirt girdle, on the walls of the combustion chamber, on the valves and candlelight.
Sediments called substance is deposited in the form of black pasty clots on the walls of the crankcase, on the details, located in the crankcase, in the 'valve box, a crankshaft on filters in the oil line and others. All these three types of carbon deposits (lacquer, varnish and precipitation) known since the inception of the internal combustion engine. .
Reliability, efficiency and service life of the powerful engine is largely dependent on the burning of piston rings from carbon deposits in the combustion chamber of the pile precipitation crank crankshaft journals, filters and oil lines. Therefore, to ensure the reliability and efficiency of the engine, it is necessary to eliminate or minimize the number of different carbonaceous deposits accumulated inside the engine as its operation. This is a very important task can be accomplished by further improving the design of the engine, the proper organization of its operation, improve the quality of used fuel and oil.
The oil's ability to maintain their properties in adverse conditions unchanged is called stability, that is resistance.
Speaking about the stability of the oil, be sure to indicate against what and under what conditions it should be sustained, for example, oxidation stability, thermal stability, and so on.
Thermal stability shows the conversion rate of the oil film in the lacquer film. Sedimentation of the engine in all its forms is largely dependent on the quality of the oil. With the increase in viscosity of the oil decreases the possibility of formation of sludge in the engine. Oils, not resistant to oxidation, sediment yield faster and more stable than oil.
Oil with special additives is less prone to sedimentation than pure oil as an additive oils help keep the insoluble impurities and harder to resist oxidation.
Corrosion properties of oils
Currently, assemblies of modern engines are made of different materials.
Bearings with inserts of non-ferrous metals, such as lead-Babbit and so on., Having good mechanical properties, have become insufficient corrosion resistant. Under the influence of the oxidation products of the oil they are easily broken. There are several methods for assessing the corrosion properties of oils.
One of them is determined by the corrosion weight loss of the plates during their immersion in the extraction and oil heated to 140 ° C. The speed of immersion of the plate 15 times per minute. Test duration of 50 hours is determined by the degree of corrosion weight loss of the plate; calculate weight loss in grams per square meter. The more reduced the weight of the plate, the more corrosive properties of the oil.
On the second acid number is determined by the oil. Mineral oil may contain naphthenic acids. Although the acidic properties of the naphthenic acids is not great, nevertheless, in contact with metals, especially colored, they cause corrosion to form metal soaps. Metal soaps may be in oil or in a dissolved form, or fall out of solution as a precipitate. The amount of naphthenic acids contained in the oil is determined by acid number. The acid number referred to milligrams of KOH (read: potassium of Al) required to neutralize the naphthenic acids are in one gram of oil. KOH - is the chemical symbol of alkali - caustic potash. Mineral oil usually contain some naphthenic acids, and therefore, an acid number, expressed in milligrams of KOH per 1 gram of oil, various grades in the range from 0.05 to 0.42.
At present, the rate of acid number for the motor oil has lost its significance and can only be a reference.
Flash Point and Fire.
When heating the oil to evaporate. Couples, mixing with air to form an explosive mixture. The lowest temperature to which the oil should be heated to the vapors formed an explosive mixture with air, flammable when held close to the flame it is called a flash.
Heating oil temperature at which not only the oil vapors erupt when brought near to them fire, but lights up and the oil is called ignition temperature of oil.
For the first time began to define a flashpoint in kerosene to detect harmful impurities impurity gasoline, since the content of gasoline leads to an explosion. Subsequently, this figure was useful and - assessing the quality of oils. Between the volatility of oil and a flash point there is a certain relationship. Light oil fractional composition, that is, low viscosity oils have a lower flash point than high. Low flash point and fire characterize flammability oil.
Pour point.
Oils not solidify when cooled as soon as the water and become progressively more and more viscous until completely lose their mobility. If oil contains hydrocarbons vysokozastyvayuschie - paraffins, then the temperature is lowered, they are allocated in the form of crystals and thus contribute to more rapid hardening of the oil. The temperature at which the oil loses mobility called pour point.
Pour point of the title is a very important indicator properties of the oil. Many operating staff mistakenly believe that it is for them, this figure is given in the data sheet to know at what the lowest temperature possible to apply this oil. By solidification temperature can not be set at exactly what temperature the oil will still be pumped and will provide the starting of the engine. Typically the temperature at which the mobility of the oil is sufficient to start a cold engine, and pumping the oil is always higher than the pour point of the oil to approximately 10-20 ° C.
Why is such a discrepancy between the freezing point and the actual behavior of oil in service? The thing is that the laboratory method for determining the freezing temperature is very imperfect.
Sometimes when determining the pour point of the same oil sample obtained by different persons very different data.
Ash content.
The residue obtained by combustion in a platinum crucible, a porcelain cup or a certain amount of oil, expressed as a percentage of oil is called ash content. Method for determination of ash downtime. Oil slowly evaporated and then formed after evaporation of carbon residue calcined at dark red-hot to complete digestion. The ash content in the pure oil should be minimal. A significant amount of ash indicates a poor cleaning of the oil on the oil content of mineral salts and various impurities.
In oils containing additives permitted increased ash content.
Color.
All methods of determining the color of lubricating oils are reduced compared to the color of the test sample with color glass or reference standard solution. Previously, color is an indicator of the degree of purification of oil. Currently, only the color definition is important for manufacturers. Operatives for color lost value as an indicator of the quality of the oil.
Mechanical impurities and water.
By the mechanical impurities are all foreign bodies in oil in suspension. Sometimes fresh oil during storage and transport fall dust, sand and water.
Waste oil also polluted coke, metal particles and so on. The oil containing mechanical impurities, not suitable for the lubrication of engines, as impurities increase wear, sooth and clog filters. Corollary pres-mechanical impurities in the oil such constants distort readings as coke, ash, and they increase the mechanical impurities, usually increase. Not less dangerous water content in the oil. In the presence of water in the oil can make a pretty simple way: it is necessary to heat the oil in a glass tube over 100 ° C (but not higher than 150 ° C). If the oil contains water, even in small quantities, the oil will foam, you will hear the characteristic crackling and the tube will flinch. When it is required to determine the amount of water
in oil, the test was carried out in a special device consisting of a metal flask, glass refrigerator and glass traps. 100 milliliters of test oil was mixed with 100 ml ligroin. This mixture was heated in a metal flask. Evaporate-schiesya wherein naptha and water condensed in the cooler and flows down: ligroin back into the flask, and the water stays in the trap. Heating was stopped when the amount of water trapped stops increasing. The amount of water distilled from the oil expressed as a percentage.
Consumption of oil in the engine.
It is known that the oil flow in automotive and aircraft engines, internal combustion is approximately 3-5% of the fuel consumption. At first glance it may seem that such a relatively small percentage of oil consumption is not worth paying attention. I have to say that such an opinion would be deeply flawed. Consumption of oil in the engine is one of the most important performance. Inadequate lighting in the literature of this indicator is explained by the difficulties in establishing a precise flow of oil in the engine. These difficulties arise from the fact that the oil consumption in the engine has a complex dependence on many factors.
Oil consumption depends on the constructive characteristics of the engine from the lubrication system of the degree of wear of the engine, the state of the piston rings on the mode and operating conditions, the quality of the used oils and combustible and so. D. Even in the same engine without having no defects, oil consumption is not constant but changes all the time with a change in the mode of engine operation and durability.
Oil consumption - is a certain degree of a technical condition of the engine. Many oil consumption - hence the engine in poor condition: he or badly worn or there are any faults. Little oil consumption - hence the engine in good condition.
Consumption of oil in the engine is in four directions.
The first direction (most importantly) -sgoranie oil in the engine cylinders. The more oil enters from the crankcase into the combustion chamber, the more oil is combusted, the more oil is ejected together with the exhaust gases in the air and, consequently, the greater the consumption of oil.
Loss of oil from the combustion of the most inevitable. You can dramatically reduce losses from oil combustion, reduce them to a minimum, but it is impossible to eliminate completely.
All that facilitates the penetration of oil into the combustion chamber will affect the increase in oil consumption.
The oil penetrates into the combustion chamber through the piston rings, like that of the oil is pumped, entering at the cylinder wall and the piston in the combustion chamber. Therefore, the amount of oil entering the combustion chamber, depends primarily on the technical condition of the cylinder group.
With an increase in the clearances between the piston and the cylinder walls, between the rings and the walls of grooves which are arranged in a ring, more oil will enter the combustion chamber will flow more oil. Oil consumption is also increased in the following cases: loss of elasticity piston rings, pile of sludge and varnish slots on the oil ring and oil holes in the pistons, piston rings sticking and alignment gaps in the joint locks in the piston rings on the piston. In other words, the more frayed knot friction piston - cylinder, the worse its technical condition, the
more oil enters the combustion chamber where it is burned.
The second direction - oil evaporation. The faster the oil evaporates, getting on the hot parts of the engine, the more oil consumption. Engine oil consumption associated with evaporating oil depends on the fractional composition of the oil and the heat from the engine Vågå mode. The lighter oil on the fractional composition, the faster it evaporates and the more, consequently, oil consumption due to evaporation. The higher the temperature of the cylinders and pistons in the engine, the
favorable conditions for the evaporation of the oil and the higher its consumption.
Conventional automotive engines that have relatively low thermal conditions, volatility of oil does not really matter, because it does not have a significant effect on consumption.
At high temperatures, the cylinder and piston, for example, aircraft engines, highly oil evaporates, resulting in greatly improved consumption. For such engines is usually selected oils having low volatility.
The third area - the periodic replacement of used oil with fresh oil. As is known, in car engines - a few thousand kilometers, and in the air - after a certain number of hours the engine has completely drained from the oil system the so-called waste oil and pour in fresh oil. The more frequently changes the oil, the more oil consumption.
As the consumption of oil in the engine crankcase automobile or aircraft engine oil tank periodically add fresh oil to stay there the waste oil. But topping of fresh oil continues to a certain limit. After a certain number of hours the engine completely replace oil; All waste oil is drained and the lubricating system is filled with fresh oil.
Clearly, the less frequent oil is replaced, the less it is spent, and, conversely, when the changes are more frequent consumption increases. To conserve oil would rarely need to change the oil. But then the engine will run on a contaminated oil, and it is fraught with grave consequences - the engine can fail prematurely.
It turns out that to save the motor and prolong the life of better oil change often.
The fourth direction - oil leak through loose connections in the crankcase lubrication system, through bearing seals and the release of oil through the engine breather. Lack of tightness seals crankshaft, crankcase gasket, valve boxes lids, covers timing gear and other faults can cause excessive oil consumption.
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