Is the lubricant conductive? Pure lubricants are basically non-conductive.
Then the problem came - static electricity. Because of the relatively poor conductivity of the insulator, friction prone to static electricity.
During the transportation, the oil will friction with the container and the parts to generate static electricity. If the static electricity is not released in time, the static electricity spark may be generated to cause the combustion explosion.
For the generation of static electricity, the better the insulation of the material, the more likely it is to generate static electricity. Insulator conductivity is much smaller than the conductor.
01 What is the conductivity of lubricating oil?
For the practical application, the conductivity of the lubricating oil to us what is the guideline? The conductivity of the lubricating oil shows the ease of static electricity produced by the oil, lubricating oil in the transport, flow, use and material friction, may Electrostatic discharge can occur, but static electricity can cause harm.
Conductivity of lubricating oil in pS / m. The lower the conductivity of the lubricant, the better the insulation of the lubricant and the easier it is to generate static electricity. The factors that affect the electrical conductivity of lubricants are: the type of base oil used to formulate lubricants, the type of additives, oil contained in the water, impurities, mechanical impurities, metal powders, etc., will affect the conductivity of lubricating oil. For example, pure water itself has very low conductivity and therefore is not electrically conductive. However, tap water is conductive because it contains some metallic mineral salts, acids and alkalis, so tap water conductivity is increased.
02 lubricant will be conductive?
Under normal circumstances, the conductivity of lubricating oil is very low, so it can be used as insulating oil or transformer oil, although the role of transformer oil is not lubrication. However, there are cases where the lubricant may also be electrically conductive, depending on the composition of the lubricant (base oil, additives) and impurities contained in the lubricant.
03 What factors affect the conductivity of lubricating oil?
1) the conductivity of base oil and lubricating oil:
Lubricating oil is formulated with base oil plus additives. The lower the degree of refining of the base oil, the stronger the polarity and the greater the conductivity of the oil. Depending on how the base oil is refined and refined, the American Petroleum Institute API divides the base oils into five categories: API Class I, API Class II, API Group III, API Group IV, and API Class V oils:
Base oil types
API Class I oils: Relatively polar, conductivity less than 10pS / m (very low)
API Class II oils: Polarity is weaker than a class of oils with conductivity less than 10pS / m (very low)
API Group III oils: Class III oils have almost no polarity without additives and have very low conductivity below 10 pS / m.
API Class IV oil: very low, less than 10pS / m.
API V class oil: Strong polarity, conductivity is generally higher than 2000pS / m.
In the past, API Class I oils were commonly used in the production of lubricants. Over the past few years, lubricants have gradually shifted from API Class I oils to API Class II, API Group III base oils, and synthetic oils. Compared to API Group I oils, Group II oils and Group III oils offer many advantages, such as better oxidation resistance and longer pot life. However, these oils are relatively more prone to static electricity than API class I oils. The main hazards of static electricity are three aspects: oil storage and transportation safety issues, electrostatic discharge may be partially burning oil or parts, there is a film is causing the problem.
Lubricating oil type: Conductivity of oil (part of oil) at 23 ° C
2) additives on the conductivity of lubricating oil:
In addition to the type of base oil, additives also affect the conductivity of the lubricant. Organometallic additives increase the electrical conductivity of lubricants. Common organic metal additives such as ZnDTP antiwear agent are widely used in engine oil and hydraulic oil. They are multifunctional additives that can be anti-wear, anti-oxidation and anti-metal corrosion. Because ZnDTP contains zinc, it has environmental impact and is therefore limited. The use of zinc-free anti-wear agent, the corresponding reduction of the conductivity of lubricating oil, is relatively more likely to produce static electricity.
3) Temperature on the conductivity of lubricants:
In addition to the base oil and additives, the temperature also affects the conductivity of the lubricant. For the same lubricant, the temperature increases, the conductivity of the lubricant increases. However, the relationship between conductivity and temperature of lubricating oil is not purely proportional, different lubricants, increasing the temperature, the increasing trend of conductivity is different. In the case of constant temperature, the conductivity of lubricating oil is not necessarily constant, the water contained in the lubricating oil, whether it contains impurities, contact with metal debris, depletion of additives, the use of lubricating oil (oxidized Degree) will change the conductivity of lubricating oil.
4) Impurities on the conductivity of lubricating oil:
Pure oil conductivity is very low, so it is insulated at room temperature. Lubricants need to add some additives to the base oil in production to change the conductivity of finished lubricants. The type of additive, the amount of metal ions in the finished product results in a difference in the electrical conductivity of the finished product.
Lubricants should be kept clean during use. If the oil contains water or contains some metal powder, it will significantly change the conductivity of the lubricating oil.
04 Why does the lubricant generate static electricity?
Lubricants in the storage and transportation, circulating flow, as the oil and the surrounding parts of the friction, it may produce static electricity. The resulting electrostatic voltage intensity is related to the conductivity and flow of the lubricant. The lower the electrical conductivity of the lubricant (the better the insulation of the lubricant), the more oil the oil is in circulation, and the more friction the fluid flows with the tube wall, the more static electricity is generated.
Specifically, lubricants and lubrication systems are more prone to static electricity under these conditions:
· API Class II oils and Group III oils are more prone to static electricity than lubricants formulated with API Class I oils.
· The additive formulation used does not contain polar additives, such as zinc-free.
• Conductivity of finished lubricant (fresh oil or used oil) is less than 400pS / m.
Lubricants flow from narrow spaces or thin tubes.
· High flow rate of lubricant.
· Filter design issues that cause severe friction with the filter material in the flow of lubricant.
Hose, oil is not grounded.
· The oil level drops too low.
· There is a lot of bubbles in the oil.
05 Lubricants electrostatic discharge hazards
Electrostatic discharge may occur if more charge is accumulated in the lubricant. In some cases, static sparks may even cause safety problems or even burn and explode. Under normal circumstances, electrostatic discharge can occur in the filter or tank, discharge a slight crackle. If the electrostatic voltage is high, static electricity may rapidly occur several times in a row. When a large area where different materials meet, it is more prone to electrostatic discharge. Lube oil filter due to the use of more plastic, and oil contact, prone to static electricity.
Electrostatic discharge caused by sparks instantaneous high temperature may be close to 1000 ℃, if the oil itself flammable, then such a high temperature is very dangerous. In addition, the vapor of the hydrocarbon mixture volatilized from the oil may cause spontaneous combustion if it reaches a certain concentration near the fuel tank. Turbine oil and hydraulic oil may also generate static electricity and discharge electricity in a circulating flow, but will generally extinguish quickly.
06 Hydraulic Oil Static and Turbine Oil Electrostatic
In recent years, there are more problems with static electricity generated by hydraulic systems and turbine oils than before. The main reasons include the following:
• Today's hydraulic and turbine oils, gas turbine oils, are starting to use more API Class II oils and Class III oils that perform better than API Class I oils but with lower conductivity than Class I oils. Coupled with the turbine oil containing organic metal additives rarely, so low conductivity, easy to accumulate static electricity, may lead to film problems.
· As equipment requirements increase, the same tank needs more flow and the oil creates more friction in the flow.
· Cleanliness requirements of lubricating oil are more and more strict, especially hydraulic oil, which requires that the lubricating oil is filtered very cleanly, the filtration strength is increased, and the static electricity is more likely to be generated.
· The current equipment is very demanding on the cleanliness of lubricating oil, the oil filter is very clean and the impurity is less.
07 lubricant conductivity testing
In some cases, the conductivity of the oil needs to be tested to avoid the hazards associated with electrostatic discharge, especially when used in large volumes of oil. If static electricity poses a safety hazard or, in some cases, it is found that unexplained fuel oil is charred and oil of unknown origin is found in the oil, the electrical conductivity of the oil can be tested. Lubricating oil conductivity testing standards with reference to ASTM D2624.
As mentioned earlier, the conductivity of a lubricant increases with increasing temperature. If the conductivity of a lubricant is greater than 400 pS / m at 20 ° C, the oil or lubrication system is less prone to electrostatic problems. If the conductivity of lubricating oil is lower than 400pS / m, it is relatively easy to generate static electricity.
08 How to prevent static electricity lubricant?
If the lubrication system is prone to electrostatic problems, grounding is a common method of eliminating static electricity, but in some cases grounding may not necessarily solve the problem. If grounding does not solve the problem of static electricity, here are four other ways to eliminate static electricity:
1. The use of anti-static filter, the filter material used to guide the static in time to prevent static discharge.
2. In the oil under the premise of the use of higher conductivity instead of lubricating oil. However, it is important to fully assess and avoid the risk of oil diversion.
3. The components of the lubrication system components and the combination of transformation, use less prone to static electricity materials, or to avoid the accumulation of static electricity materials.
4. Adjust the flow rate and tank size to reduce the oil friction in the circulating flow.