MINERAL BASE OILS

Mineral oils can be divided into two distinct groups: PARAFFINIC and NAPHTHENIC oils.

What is better for a specific application, naphthenic or paraffinic oils? There is no hard and fast answer. In some applications naphthenic base oils will be more cost-effective, in others paraffinic oils might have the edge under certain conditions.

 For a base oil, many requirements have to be fulfilled in various applications.

1.  VISCOSITY
The viscosity of an oil is important for its cooling and lubricity properties. The lower the viscosity, the better the cooling. An increase in temperature reduces the viscosity.  The rate of change in viscosity with temperature can be expressed in terms of viscosity index (VI). A small reduction in viscosity coupled with a large temperature changes indicates a high viscosity index.

Paraffinic oils have a higher VI than naphthenic oils. A high VI is required in certain applications. Automotive lubricants is one example where lubrication is needed at both high and low temperatures. However, for cooling applications, such as metal working or quenching, a low VI is better because of the lower viscosity (better heat transfer) at operating temperatures. Viscosity (kinematic) is measured according to ASTM D 445.
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2.  VISCOSITY VS BOILING RANGE
An oil is a mixture of many different kinds of molecules, each with its own boiling point. Therefore, an oil will boil over a range of temperatures, hence boiling range. The higher the boiling range temperatures (i.e. the higher molecular weight), the higher the viscosity. It has been found that the point of 50% distillation in the boiling range relates to the viscosity of an oil. Paraffinic oils give lower viscosity at a given boiling range, due to the higher mobility of the paraffinic molecules. This means that the boiling range for a paraffinic oil will lie at a higher level than for a naphthenic oil of the same viscosity.

3.  FLASH POINT
The flash point of an oil is specified for safety reasons, but also because it indicates how volatile the oil is. Light parts of the oil determine the flash point which is extremely sensitive to contaminants from lighter oils, such as gas oil or gasoline. The flash point is reached when the oil releases enough gases to make the gas mixture above the oil ignitable in the presence of an open flame. The PM (Pensky Marten) closed cup method (ASTM D 93) gives the best repeatability. Another method is the COC (Cleveland Open Cup) ASTM D 92, which, generally, gives 510°C higher flash point values. This method is often used in the USA and elsewhere for formulated products.

4. FLASH POINT VS BOILING RANGE
It is at the low temperature area of the boiling range that flash point is determined. A correlation exists between the 5% point in the boiling range and the flashpoint. The  lighter the products, the lower the flashpoint. Thus, two oils with the same viscosity (50% point) may have different flash points depending on the shape of the distillation curve at low temperatures

5.  LOW TEMPERATURE PROPERTIES
Low temperature properties are important in a cold climate. The N-alkanes in paraffinic oils crystallise upon cooling which impedes the free flow of the oil. A differential scanning calorimeter (DSC) can be used for measuring the amount of N-alkanes. When the cloud point occurs (i.e. the crystallisation point), the oil is no longer a Newtonian fluid, but has become a two-phase system. Naphthenic oils are virtually free from N-alkanes. This means that no yield stress is needed to start moving the oil at low temperatures, which is important in many applications. Pour point, the lowest temperature at which an oil flows, is measured according to ASTM D 97.

6. VOLATILITY
As mentioned earlier, volatility is related to the flash point. Low volatility is important for high temperature applications, e.g some metalworking operations, like drawing and stamping and high-temperature greases. A method for measuring the volatility is ASTM D 972. The loss in mass after 22 hours evaporation at a certain temperature (often 107°C) is determined.

7.  DENSITY
Density increases with the aromatic and naphthenic content. A standard coefficient, 0.00065/°C, can be used in most cases for calculating the density at other temperatures than those already measured. Density is measured according to ASTM D 4052

8.  SOLUBILITY
The solubility properties of an oil are important in areas such as grease manufacturing. It is also important for keeping oxidation products in solution and for seal swell.
Viscosity Gravity Constant (VGC) is an indication of solubility. A high VGC value means good ability to dissolve polymers, additives and oxidation products. VGC can be calculated from density and kinematic viscosity (ASTM D 2501).
Aniline point is also a property that indicates the solubility of an oil. It is defined as the lowest temperature at which a mineral oil is completely miscible with an equal volume of aniline (ASTM D 611). The lower the aniline point, the better the solubility.
In the past, low refined oils, such as aromatic oils or distillates, were used where high solubility was needed. Due to health and safety reasons, these products are now banned in most countries. Due to sophisticated refining techniques, Nynas naphthenic oils are label-free, and yet retain low aniline scores i.e. good solubility. Nynas T-grades have the best solubility properties


If you are looking PARAFFINIC OIL please feel free to contact us.