Analysis of Extreme Pressure and Anti-Wear Performance of Industrial Gear Oil Compound Additive

Analysis of Extreme Pressure and Anti-Wear Performance of Industrial Gear Oil Compound Additive

What is Industrial Gear Oil Additive Package?

Industrial Gear Oil Additive Package is a multi-functional additive combination made from various single additives such as extreme pressure agents, anti-wear agents, antioxidants, detergent dispersants, and rust inhibitors through scientific compounding and synergistic optimization. Its core function is to endow industrial gear oil with excellent extreme pressure anti-wear, anti-oxidation, anti-rust and anti-corrosion, anti-emulsification and other properties, adapt to complex working conditions such as heavy load, high speed, high temperature, and high dust during the gear transmission process, avoid failure problems such as wear, scuffing, pitting, and rusting of gears, extend the service life of gearboxes and the oil change cycle of lubricating oil, and reduce the equipment operation and maintenance costs of industrial production.

As the core component of mechanical transmission, industrial gears are widely used in various industries such as mining, metallurgy, wind power, cement, shipping, and chemical engineering. During operation, the contact pressure on the tooth surface is extremely high (up to 1000 - 3000 MPa under heavy load conditions), accompanied by instantaneous high temperature and metal friction. Simple base oil cannot meet the requirements of lubrication and protection, and performance upgrades must be achieved by adding compound additives. High-quality industrial gear oil compound additives need to balance formulation compatibility and working condition adaptability, not only avoiding side reactions between different additives but also optimizing the ratio according to the load characteristics and temperature ranges of different industries, which is also the core technical difficulty in the research, development, and production of compound additives. 

UNPChemicals is a professional supplier of high-quality and high-performance industrial gear oil additive packages.Mechanism of Action of Sulfur-Phosphorus Extreme Pressure Additives

Sulfur-phosphorus extreme pressure additives are the core components of industrial gear oil compound additives and also the key to achieving extreme pressure and anti-wear performance. Their mechanism of action is based on the chemical activity of sulfur and phosphorus elements. During the friction process on the gear tooth surface, they form multi-layer protective films through physical adsorption and chemical reactions, isolating direct metal contact, resisting the wear and scuffing risks caused by heavy loads and high temperatures. Moreover, the synergistic effect of sulfur and phosphorus elements can make up for the performance shortcomings of single-element additives, achieving stable protection under all operating conditions. This is also the most widely used extreme pressure and anti-wear system in the current industry. 

(1) Anti-wear and initial extreme pressure effects of phosphorus element

The phosphorus-based components (mainly phosphate esters, alkyl phosphites, thiophosphate amine salts, etc.) in the sulfur-phosphorus composite additive preferentially exert anti-wear effects under medium to low load and medium to low temperature conditions. Their molecules adsorb onto the metal active sites on the gear tooth surface through polar groups, forming a dense physically adsorbed film that reduces frictional collisions at uneven areas on the tooth surface and decreases the amount of wear. Meanwhile, the phosphorus-based components have a certain degree of oiliness, which can reduce the friction coefficient of the tooth surface, decrease frictional heat generation, and delay the aging of the lubricating oil. 

When the working condition load increases and the tooth surface temperature reaches 100 - 150°C, the phosphorus-based components undergo a hydrolysis reaction to form acidic phosphate esters, which react chemically with the tooth surface metal (mainly iron) to form a thin and dense inorganic phosphate passivation film (the main component being Fe₃(PO₄)₂). This film has moderate hardness and low shear strength, which can effectively disperse the contact pressure on the tooth surface, prevent minor scratches on the tooth surface, achieve initial extreme pressure protection, and lay the foundation for the sulfur-based components to function. This process is a "mild reaction" that does not corrode the tooth surface, and the film can be repeatedly formed to ensure continuous protection, making it suitable for medium-load gear transmission working conditions. 

(2) Extreme Pressure and Anti-Scuffing Effects of Sulfur Element

Sulfur-based components (mainly sulfurized olefins, sulfurized fatty acid esters, polysulfides, etc.) are the core extreme pressure components under heavy load conditions, and their function depends on chemical reactions triggered by high temperatures. When gears are operating under heavy load and high speed, the instantaneous temperature of the tooth surface can rise above 200°C. At this time, the oil film is prone to rupture, and the sulfur-based components rapidly decompose, releasing active sulfur atoms, which undergo intense chemical reactions with the tooth surface metal to form a layer of sulfide reaction film (mainly composed of FeS and FeS₂) with high melting point and high hardness. The melting point of this film can reach 1193°C, far higher than the instantaneous high temperature during gear operation, and it has excellent anti-shear properties, which can effectively resist heavy load impact and prevent serious failure problems such as scuffing and sintering caused by direct contact between tooth surface metals. 

Different from the phosphorous-based film layer, the formation of the sulfide film layer has "self-healing" properties. When the film layer is damaged by friction, the sulfur-based components can quickly replenish and react with the tooth surface metal again to form a new protective film, ensuring the continuity of extreme pressure protection. In addition, the reaction rate of the sulfur-based components can be optimized through formula adjustment to avoid tooth surface corrosion caused by overly intense reactions, taking into account both extreme pressure performance and tooth surface protection effects, and adapting to heavy-duty and extreme working conditions such as mining and metallurgy. 

(3) Synergistic mechanism of sulfur and phosphorus

The core advantage of sulfur-phosphorus extreme pressure additives lies in the synergistic effect of sulfur and phosphorus components, rather than the individual action of single components. The two can complement each other's weaknesses and improve the overall extreme pressure and anti-wear performance. On the one hand, the passivation film formed by the phosphorus-based component can preferentially isolate partial metal contact, reduce the reaction intensity of the sulfur-based component, avoid excessive corrosion of the tooth surface, and at the same time provide a uniform reaction substrate for the formation of the sulfur-based film layer, ensuring that the sulfide film layer is evenly distributed and has strong adhesion; on the other hand, the high-hardness sulfide film layer formed by the sulfur-based component can enhance the load-bearing capacity of the overall protective film, make up for the shortcoming of insufficient hardness of the phosphorus-based film layer, and resist heavy load impact. 

In addition, the synergy between sulfur and phosphorus can also inhibit the side effects of single components: the phosphorus-based component can alleviate the damage to the tooth surface caused by corrosive substances generated from the high-temperature decomposition of the sulfur-based component, while the sulfur-based component can enhance the wear resistance and high-temperature resistance of the phosphorus-based film layer. The combination of the two can adapt to the full range of working conditions from low load to heavy load and from low temperature to high temperature, which is also one of the core formulation advantages of UNPChemicals industrial gear oil compound additives - by precisely adjusting the sulfur-phosphorus ratio, achieving a balance between extreme pressure anti-wear performance and tooth surface protection, and adapting to the different working condition requirements of different industries. 

Load-carrying capacity test of compound agents in heavy-duty gearboxes

Heavy-duty gearboxes (such as those in mining crushers, wind turbine main gearboxes, and metallurgical rolling mill gearboxes) have extremely high requirements for the load-carrying capacity of compound additives. The load-carrying capacity directly determines whether gears will experience failure problems such as scuffing and pitting. Therefore, it is necessary to verify the extreme pressure and anti-wear performance of compound additives through standardized tests to provide a scientific basis for industrial applications. Currently, the mainstream load-carrying capacity testing methods in the industry include the four-ball test and the Timken test. These two types of tests evaluate the extreme pressure performance and anti-wear performance of compound additives from different dimensions respectively, and the test results can directly guide the selection of compound additives and the optimization of formulations.

(1) Core testing methods and standards

(2) Interpretation of Test Results and Their Association with Practical Applications

1. Interpretation of Four-Ball Test Results: The PB value reflects the anti-wear load-carrying capacity of the compound agent. A higher PB value indicates better anti-wear performance of the compound agent under medium and low loads, which can prevent slight wear of gears; the PD value reflects the extreme pressure load-carrying capacity of the compound agent. A higher PD value indicates stronger ability of the compound agent to withstand heavy loads and prevent metal sintering, making it suitable for heavy-duty gearbox operating conditions; the smaller the wear scar diameter (WSD, under the conditions of a load of 400N and a temperature of 80°C), the more excellent the anti-wear performance, which can reduce the amount of gear wear and extend the oil change interval.

2. Interpretation of Timken Test Results: The OK value is a key indicator for the selection of compound additives for heavy-duty gearboxes. The higher the OK value, the stronger the anti-scuffing and anti-seizure capabilities of the compound additive under high-speed, line contact conditions, which can prevent serious failure problems such as scratches and seizure on the gear tooth surface; the lower the tooth surface scuffing grade (grades 1-5, with grade 1 being the best), the more stable the protective effect of the compound additive.

The compound designed for heavy-duty gearboxes requires an OK value of ≥600N to meet the stringent operating conditions of industries such as mining and metallurgy. 

(3) Correlation between Test Precautions and Formula Optimization

The bearing capacity test must strictly control the test conditions (temperature, load, rotational speed, test time) to avoid result distortion caused by condition deviations; meanwhile, the test needs to be combined with the type of base oil, as different base oils (mineral oil, synthetic hydrocarbon oil, ester oil) have different compatibilities with compound additives, which will directly affect the test results. Therefore, when optimizing the formulation, it is necessary to first match the type of base oil, and then adjust the sulfur-phosphorus ratio and additive compounding scheme through testing. 

In addition, under heavy load conditions, the load-carrying capacity of the compound additive must also cooperate with components such as antioxidants and dispersants to prevent the failure of the protective film caused by lubricant oxidation and metal abrasive particle deposition. In the formulation development, UNPChemicals combines ashless antioxidants with high-efficiency dispersants, enabling the compound additive to not only meet the load-carrying capacity standard but also inhibit the oxidation and aging of the oil, disperse metal abrasive particles, and further enhance the long-term lubrication performance of heavy-duty gearboxes. 

4. Micropitting Protection and Compound Formulation Design

Micro-pitting is one of the common failure modes in heavy-duty gearboxes, mainly manifested by the appearance of a large number of tiny corrosion pits (with diameters ranging from a few micrometers to dozens of micrometers) on the gear tooth surface. In the initial stage, it does not affect the operation of the gears, but long-term development can lead to tooth surface spalling and gear failure. Especially in wind power and precision gear transmission equipment, the harm of micro-pitting is more prominent. The occurrence of micro-pitting is closely related to tooth surface contact stress, oil film thickness, and lubricating oil performance. Among them, the formulation design of the compound additive is the core means to inhibit micro-pitting, which needs to balance extreme pressure anti-wear performance and micro-pitting protection performance to avoid conflicts between the two.

(1) Generation mechanism of micropitting

The essence of micropitting is the result of the synergistic action of fatigue corrosion and wear on the tooth surface: under heavy load conditions, the alternating contact stress on the gear tooth surface leads to the generation of fatigue cracks on the tooth surface; meanwhile, acidic substances (oxidation products, additive decomposition products) in the lubricating oil react with the tooth surface metal, accelerating crack propagation; in addition, when the oil film thickness is insufficient, local metal contact occurs on the tooth surface, and frictional heat accelerates corrosion and crack development, ultimately forming tiny pitting pits, and the pitting pits will continue to expand, leading to tooth surface failure. 

In response to the generation mechanism of micropitting, the formulation design of the compound agent needs to achieve three major objectives: enhancing oil film strength, inhibiting acid corrosion, and alleviating tooth surface fatigue stress. 

(2) Key Points in Formulation Design of Micro-Pitting Protection Type Compound Agent

1. Optimize the sulfur-to-phosphorus ratio to balance extreme pressure anti-wear and micropitting protection: The ratio of sulfur and phosphorus components directly affects the micropitting protection effect. Excessive sulfur content can exacerbate tooth surface corrosion and increase the risk of micropitting; excessive phosphorus content can lead to an overly thick film layer, affecting the fluidity of the oil film and reducing the lubrication effect. Therefore, in the formulation design, the sulfur content needs to be controlled within 2.0%-3.5% and the phosphorus content within 0.5%-1.2%, forming a thin and dense protective film through synergistic action, which not only resists heavy-load wear but also reduces the risk of corrosion.

2. Compound antioxidants to inhibit acid corrosion: The acidic substances produced by the oxidation of lubricating oil are a key factor exacerbating micro-pitting. Therefore, it is necessary to compound high-efficiency antioxidants to inhibit oil oxidation and reduce the generation of acidic substances. Amine antioxidants such as alkyl diphenylamine and phenyl-α-naphthylamine should be preferentially selected, which can synergize with sulfur-phosphorus components to neutralize acidic substances, enhance the thermal oxidation stability of lubricating oil, prevent additives from decomposing to produce corrosive substances, and at the same time, amine antioxidants can also relieve tooth surface fatigue stress and reduce crack generation.

3. Adding extreme pressure anti-wear auxiliary components to enhance oil film strength: By compounding auxiliary components such as borate and organic molybdenum, which work synergistically with sulfur-phosphorus components, the strength and toughness of the oil film are enhanced, preventing local metal contact caused by oil film rupture. Meanwhile, the organic molybdenum component can reduce the friction coefficient, decrease frictional heat generation, alleviate tooth surface fatigue, and further improve the micro-pitting protection effect.

4. Adapt base oils to improve formulation compatibility: The viscosity and fluidity of base oils affect the oil film thickness, so it is necessary to select appropriate base oils according to the operating conditions and use them in combination with compound additives. For operating conditions with extremely high requirements for micropitting protection, such as wind power and precision gears, synthetic hydrocarbon oils or ester-based base oils should be preferentially selected and used in combination with UNPChemicals' special compound additives, which can improve the stability of the oil film and further optimize the micropitting protection effect.

(3) Evaluation Criteria for the Micro-pitting Protection Effect

Currently, the industry uses the ISO 14635-1 standard to evaluate the micropitting protection performance of compound additives. The FZG gear testing machine is used to simulate the operating conditions of gears, and the proportion of micropitting area on the tooth surface is tested, which is divided into 5 grades (Grade 1 is the best, with the micropitting area proportion ≤ 1%; Grade 5 is the worst, with the micropitting area proportion > 25%). High-quality micropitting protection compound additives need to meet the standard of Grade 2 or above, that is, the micropitting area proportion ≤ 5%.

5. Evaluation Method for the Performance of Compounding Agents in FZG Gear Testing Machine

The FZG gear testing machine is an authoritative evaluation device for the extreme pressure anti-wear performance and micropitting protection performance of industrial gear oil additives. By simulating the actual meshing conditions of gears (load, speed, temperature, lubrication method), it comprehensively evaluates the comprehensive performance of additives. Its test results are highly consistent with industrial practical application scenarios, serving as the core basis for additive research and development, product verification, and customer selection. The standards it adheres to include international and domestic standards such as DIN 51354, ASTM D4998, and GB/T 13672-2021.

(1) Testing Principle and Equipment Parameters of FZG Gear Testing Machine

The FZG gear testing machine uses standard spur gears (module 2.5, number of teeth 20/40) to simulate the meshing, friction, and load transfer during the gear transmission process. By adjusting the load level, rotational speed, and oil temperature, it simulates different industrial working conditions. During the testing process, the tooth surface wear amount, friction coefficient, and oil temperature changes are monitored in real time. After the test, the tooth surface damage conditions (pitting, scoring, scuffing) are observed through a surface profilometer and microscope to comprehensively evaluate the protective performance of the compound agent.

Core equipment parameters: speed range 500 - 3000 rpm, load level 1 - 12 (Level 1 being the lowest, Level 12 the highest, corresponding to tooth surface contact pressure 500 - 3500 MPa), oil temperature control range 40 - 150°C (accuracy ±1°C), capable of continuous load increment or stepwise loading tests, suitable for evaluation requirements of different working conditions such as medium load and heavy load, and highly matching the testing requirements of all series of UNPChemicals compound additives. 

(2) Core Test Items and Evaluation Indicators

(3) Test Process and Industrial Application Value

The standard procedure of the FZG gear test is divided into four stages: 1. Pretreatment: Mix the compound to be tested with the base oil in the specified ratio, heat it to the test oil temperature, and circulate to lubricate the gears to ensure the uniform formation of the oil film; 2. Running-in stage: Operate at a low load (Level 2-3) and rated speed to run in the gear tooth surfaces and reduce initial wear; 3. Testing stage: Increase the load incrementally according to the preset load levels (or apply stepwise loading), continuously operate for the specified time, and monitor various parameters in real time; 4. Post-treatment: Disassemble the gears, observe the damage on the tooth surfaces, detect changes in the performance of the oil, and issue a test report. 

The industrial application value of this test is mainly reflected in three aspects: First, it provides data support for the research and development of compound agents, optimizing the formulation ratio through testing and enhancing performance adaptability; Second, it provides a scientific basis for customer selection, allowing customers to make choices based on their own working conditions (load level, temperature); Third, it verifies the reliability of the actual application of compound agents. The FZG test simulates real gear operating conditions, and the test results can directly reflect the effectiveness of compound agents in industrial equipment, reducing the risk of customer selection. 

Conclusion

Extreme pressure anti-wear performance is the core competitiveness of industrial gear oil compound additives, directly determining the service life of gearboxes and the stability of industrial production. Especially in heavy-duty and precision gear transmission conditions, extremely high requirements are placed on the load-carrying capacity and micropitting protection performance of compound additives. Sulfur-phosphorus extreme pressure additives form multi-layer protective films through the synergistic effect of sulfur and phosphorus, effectively resisting heavy-duty wear and corrosion, and are currently the mainstream extreme pressure anti-wear system in the industry; standardized tests such as FZG gear test, four-ball test, and Timken test provide a scientific basis for the performance evaluation of compound additives, ensuring that products are suitable for actual working conditions. 

The Price of Industrial Gear Oil Additive Packages

The price of Industrial Gear Oil Additive Packages varies depending on factors such as brand, specification, composition, and sales channels. If you are interested in Additive Packages, please feel free to contact us.

Supplier of Industrial Gear Oil Additive Packages

UNPChemicals is a professional supplier of high-quality and effective Industrial Gear Oil Additive Packages. We offer several remarkable products, namely Industrial Gear Oil Additives UNP IG402A,High extreme pressure (EP) type industrial gear oil additive packages UNP IG402B,Low-Odor Type Industrial Gear Oil Additive Package UNP IG402C,etc.

Industrial Gear Oil Additives UNP IG402Aare a specialized class of compounds designed to enhance the performance of gear oils in various industrial applications.These additives are carefully formulated to provide a combination of properties that improve the efficiency,longevity,and reliability of gear systems.

High extreme pressure (EP) type industrial gear oil additive packages, like UNP IG402B, are specialized blends of chemical compounds designed to enhance the performance of base oils used in industrial gear lubricants. These packages are formulated to provide exceptional protection under conditions where gears experience heavy loads, high pressures, and potential metal-to-metal contact.

The Low-Odor Type Industrial Gear Oil Additive Package UNP IG402C is a specialized blend of chemical additives designed to enhance the performance of industrial gear oils while minimizing the strong odors typically associated with traditional gear oil additives, particularly those containing sulfur-based extreme pressure (EP) agents. This additive package is mixed with base oils (mineral or synthetic) to create gear lubricants that protect industrial gearboxes under demanding conditions, such as high loads and temperatures, while being more user-friendly in terms of smell—ideal for environments where odor control is a priority.

Professional Lubricant Additive Manufacturer

UNPChemicals,aka Luoyang Pacific United Petrochemical Co., Ltd., focuses on the application and development of special lubricating grease additives such as MODTC, MODTP, molybdenum amide, thiadiazole metal deactivators, and phosphate esters. With nearly 30 products in seven series, including extreme pressure anti-wear additives and special grease additives, it is a global manufacturer of special lubricating grease additives and a national high-tech enterprise with great influence and leading role in the industry. If you are looking for Lubricant Additive or technical information, feel free to contact UNPChemicals.