Quality Inspection and Standard Specification of Hydraulic Oil Additive Packages|News|UNPChemicals

January 12, 2026

Quality Inspection and Standard Specification of Hydraulic Oil Additive Packages

In industrial production, hydraulic systems are the core power transmission units, and their operating efficiency and reliability directly determine the production efficiency of the manufacturing industry. As a key functional component of hydraulic oil, hydraulic oil additive packages can significantly improve the comprehensive performance of hydraulic oil by scientifically compounding various additives such as anti-wear agents, antioxidants, and rust inhibitors, meeting the requirements of complex working conditions such as high pressure, high speed, and high temperature. For potential customers such as hydraulic equipment manufacturers and lubricant production enterprises, mastering the quality inspection methods and standard specifications of hydraulic oil additive packages is the core prerequisite for selecting qualified products and ensuring the stable operation of equipment.

What is a hydraulic oil compound additive?

hydraulic oil additive packages are mixtures formulated by combining various functional chemical additives in specific proportions. Their core function is to endow base oil with key properties such as anti-wear, anti-oxidation, anti-emulsification, and anti-rust, compensating for the performance deficiencies of base oil itself and enabling hydraulic oil to meet the usage requirements under different operating conditions. During the operation of the hydraulic system, the compound additives reduce component wear by forming a protective film on the metal surface, inhibit oil oxidation and deterioration to extend service life, and quickly separate the mixed water to prevent system corrosion, thereby reducing the incidence of equipment failures and maintenance costs.

From the perspective of composition and performance characteristics, hydraulic oil additives can be classified into categories such as high-zinc, low-zinc, and zinc-free types, with different types of products tailored to different environmental protection requirements and working conditions. UNPChemicals is a professional supplier of high-quality and high-efficiency hydraulic oil additives. Leveraging years of industry technology accumulation, it has launched multiple products with excellent performance, including high-zinc hydraulic oil additive UNP AH502A, low-zinc hydraulic oil additive UNP AH502B, zinc-free hydraulic oil additive UNP AH502C, etc., which can meet the personalized needs of different customers.

High-zinc products use zinc dialkyldithiophosphate (ZDDP) as the core anti-wear component, featuring outstanding anti-wear performance and are suitable for traditional hydraulic systems with stringent lubrication requirements; low-zinc products optimize the zinc content ratio, reducing environmental impact while retaining excellent anti-wear performance, meeting moderate environmental protection requirements; zinc-free (ashless) products use phosphorus-free and zinc-free anti-wear agents such as borate esters and dimer acid derivatives, with high biodegradability, meeting strict environmental protection regulations such as EU REACH and US TSCA, and are suitable for environmentally sensitive fields such as food processing and marine engineering. These products have undergone strict quality inspections and actual working condition verifications, and have reached the leading level in the industry in key indicators such as anti-wear performance, oxidation stability, and water separability.

Analysis of the Four-Ball Machine Test Method for Anti-Wear Performance

Anti-wear performance is one of the most core indicators of hydraulic oil additives, directly related to the wear degree of precision components such as pumps, valves, and cylinders in hydraulic systems. The four-ball machine test is an authoritative method for evaluating the anti-wear performance of additives. By simulating the friction state of metal components under high contact stress, it accurately reflects the boundary lubrication protection ability of additives and is an essential testing means for research and development, production, and quality control within the industry.

Testing Principles and Core Equipment

The core principle of the four-ball machine test is to construct a friction pair using four standard steel balls of the same diameter, with three balls fixed in the lower fixture to form an equilateral triangle and the fourth ball fixed on the upper rotating shaft, which rotates in contact with the three lower balls under specific load, rotational speed, and temperature conditions. The hydraulic oil compound sample is applied to the friction contact area, and its anti-wear performance is comprehensively evaluated by measuring parameters such as friction coefficient, wear scar size, and maximum non-seizure load.

The core testing equipment is a four-ball friction and wear tester, which mainly consists of three parts: the main unit, the temperature control system, and the data acquisition and analysis system. The main unit must have the ability to apply high-precision loads from 0 to 10,000 N and the constant-speed control function from 0 to 3,000 rpm to ensure the stability of the load and rotational speed; the temperature control system can precisely control the test environment temperature from room temperature to 200°C to simulate different operating condition temperatures; the data acquisition system integrates high-precision components such as force sensors and rotational speed sensors to record key data during the test process in real time and generate analysis reports. The standard steel balls used in the test are GCr15 bearing steel, with a diameter of 12.7 mm, a surface hardness of not less than 62 HRC, and a surface roughness Ra ≤ 0.025 μm to ensure the repeatability of the test.

Key Test Indicators and Judgment Criteria

The core indicators of the four-ball machine test include the maximum non-seizure load (PB value), sintering load (PD value), friction coefficient (μ), and wear volume (WV). The physical meanings and judgment criteria of each indicator are as follows:

Maximum non-seizure load (PB value): Refers to the maximum load that a compound sample can withstand without metal surface adhesion or seizure under specified conditions, directly reflecting the anti-seizure ability. The PB value of hydraulic oil compound is usually required to be ≥980N, and the PB value of UNP AH502A can reach over 1200N, effectively meeting the boundary lubrication requirements under high-pressure working conditions.
Sintering load (PD value): The critical load at which sintering or welding occurs in the friction pair as the load gradually increases, reflecting the ultimate protection ability under extreme operating conditions. The PD value of high-quality hydraulic oil additive packages should be ≥3920N. Through optimizing the ratio of anti-wear agents, the PD values of UNP series products are all stably above 4000N, ensuring the safe operation of equipment under overload conditions.
Friction coefficient (μ): The ratio of frictional force to normal force, reflecting the anti-friction effect. Under the conditions of 1450 rpm and 392 N load, the friction coefficient of qualified compound additives should be ≤0.15, and the friction coefficient of zinc-free products such as UNP AH502C can be as low as 0.12, which can significantly reduce system energy consumption.
Wear Volume (WV): Calculated by measuring the depth and diameter of the wear pit on the steel ball, it intuitively reflects the quality of anti-wear performance. Under standard test conditions, the wear volume of the steel ball corresponding to high-quality compound additives should be ≤0.05mm³, and all UNP series products have been tested to meet this requirement, effectively extending the service life of components.

Standard Test Procedure

The four-ball machine test must strictly adhere to standards such as GB/T 3142-1982, ASTM D2782-18, ISO 12156-1:2019, etc. The specific procedure is as follows:

Sample Preparation: Clean four standard steel balls with acetone or alcohol to remove oil stains and oxides, check that the spherical surface is undamaged after drying; add the hydraulic oil compound to be tested to the base oil in the specified proportion, and stir well to prepare the test oil sample.
Equipment commissioning: Secure three steel balls to the lower fixture, install the upper steel ball in place, adjust the centering device to ensure the contact point is at the geometric center; set the test temperature (usually 75°C), rotational speed (1450 rpm), and test duration (10 minutes).
Test operation: Add 0.2 mL of the test oil sample dropwise to the frictional contact area to ensure that the oil film fully covers it; start the equipment, gradually increase the load from a low level, and record the friction force change curve in real time.
Result analysis: After the test, an optical microscope was used to measure the size of the wear marks on the steel balls, and the wear volume was calculated; the PB and PD values were determined based on the change in friction force, and the anti-wear performance was comprehensively evaluated in combination with the friction coefficient.

Standard for Rotary Oxygen Bomb Test of Oxidation Stability

Hydraulic oil is prone to oxidation reactions during long-term high-temperature operation, generating harmful substances such as acids, gums, and sediments, which lead to an increase in oil viscosity, corrosion of equipment components, and ultimately cause system failures. Oxidation stability is a key indicator for measuring the ability of hydraulic oil additives to inhibit oil oxidation. The rotating oxygen bomb test is an internationally recognized standard method for evaluating this performance, which can quickly and accurately reflect the antioxidant life of additives.

Test Principle and Equipment Requirements

The core principle of the rotating oxygen bomb test is to accelerate the oxidation process of the oil sample under high temperature, high pressure, and oxygen environment. By measuring the time required for the oil sample to reach the specified oxidation degree (oxidation induction period), the antioxidant performance of the compound agent is evaluated. During the test, the precise control of parameters such as oxygen pressure, temperature, and rotation speed directly affects the reliability of the test results.

The core equipment used in the test is a rotating oxygen bomb instrument, and its main technical parameters shall meet the following requirements: pressure measurement range 0 - 1000 kPa, accuracy ±5 kPa; temperature control range from room temperature to 200°C, temperature control accuracy ±0.5°C; rotation speed 100 rpm ±5 rpm to ensure sufficient contact between the oil sample and oxygen. Common equipment models include ROTOX - 100, ROB - 500, etc., all of which need to be calibrated regularly to ensure test accuracy.

Core Test Indicators and Acceptance Criteria

The core indicator of the rotating oxygen bomb test is the oxidation induction period (minutes), which is the time required from the start of the test until the pressure of the oil sample drops to the specified value. A longer induction period indicates better antioxidant performance of the compound agent. Different application scenarios have different requirements for the oxidation induction period, and the specific standards are as follows:

Application Scenarios	Oxidation Induction Time Requirement (ASTM D2272)	corresponds to the performance of UNP products
General industrial hydraulic system	≥300 minutes	UNP AH502A: 320 minutes
Medium and High Temperature Condition Hydraulic System	≥400 minutes	UNP AH502B: 450 minutes
Long-life hydraulic system	≥500 minutes	UNP AH502C: 580 minutes

In addition, the test also needs to detect the change in total acid number and sediment content of the oxidized oil sample. The acceptance criteria are the change in total acid number ≤ 0.5 mg KOH/g (ASTM D943) and the sediment content ≤ 0.05% (GB/T 12581). The UNP series compound additives, through compounding high-efficiency antioxidants, can effectively inhibit the free radical chain reaction, delay the oxidation process of the oil, and the content of its oxidation products is far below the standard limit value.

Standard Test Procedure

The Rotary Oxygen Bomb Test shall comply with standards such as ASTM D2272-14, ISO 4263-3:2018, and GB/T 12581, and the specific procedure is as follows:

Oil sample preparation: Add the hydraulic oil compound additive to the base oil at the recommended ratio, stir thoroughly to ensure uniform mixing and complete dissolution of the compound additive; take 30 mL of the homogeneous oil sample and inject it into the inner cup of the oxygen bomb.
Oxygen Bomb Preparation: Place the inner cup into the oxygen bomb body, seal it, then fill it with oxygen to 690 kPa. After checking that the oxygen bomb has no leaks, place it in a constant-temperature oil bath.
Test start: Set the oil bath temperature to 150°C, start the rotating device to make the oxygen bomb rotate at a speed of 100 rpm, and start timing simultaneously.
Data Recording: Continuously monitor the pressure change inside the oxygen bomb in real time. When the pressure drop rate reaches 0.5 kPa/min or the total pressure drop reaches 175 kPa, stop timing, and record the time at this moment as the oxidation induction period.
Follow - up testing: After the test is completed, take out the oil sample to measure the change in total acid value, weigh the mass of the precipitate after filtration, and complete the comprehensive evaluation.

ASTM D1401 Test Procedure for Water Separation Performance

During the operation of the hydraulic system, moisture in the air is likely to condense and mix into the oil, or enter the oil through sealing leaks and other channels. After moisture forms an emulsion with hydraulic oil, it will damage the integrity of the oil film, accelerate component corrosion, reduce the insulation performance of the oil, and in severe cases, cause valve jamming, pump wear, and other failures. The water separation performance (demulsibility) is a key indicator for measuring the ability of hydraulic oil additive packages to quickly separate water from the oil, and ASTM D1401 is the core test standard for this performance.

Test Principle and Scope of Application

The ASTM D1401 test method evaluates the demulsibility of compound additives by simulating the operating conditions of hydraulic oil affected by turbulence in the system, mixing a quantitative oil sample with distilled water and stirring, observing and recording the separation of the oil-water-emulsion layer. This standard applies to oils with a kinematic viscosity of 28.8 mm²/s to 90 mm²/s at 40°C, with a test temperature of 54°C ± 1°C; for oils with a kinematic viscosity exceeding 90 mm²/s at 40°C, the test temperature is adjusted to 82°C ± 1°C.

It should be noted that when testing synthetic fluid hydraulic oil compound additives, if their relative density is greater than that of water, water may float above the emulsion layer or synthetic fluid, which needs to be specifically noted in the result record. The GB/T 7305 standard is equivalent to ASTM D1401, and domestic enterprises can choose to use it according to their needs.

Core Test Indicators and Judgment Criteria

The core indicators of ASTM D1401 test include oil-water separation time and emulsion layer volume, and the specific criteria are as follows:

Separation time: The time required for the oil layer to separate from the water layer and the volume of the emulsion layer to be ≤3 mL under specified test conditions, with the acceptance criterion being ≤30 minutes. The UNP series of compound agents, through the compounding of high-efficiency demulsifiers, can control the separation time within 15 minutes and quickly achieve oil-water separation.
Volume of the emulsion layer: If the emulsion layer does not completely disappear after 30 minutes of the test, its volume needs to be recorded, and the acceptance criterion is ≤3 mL. The emulsion layer volume of UNP AH502B and UNP AH502C products can be reduced to below 1 mL within 30 minutes, demonstrating excellent anti-emulsification performance.
State of the oil layer and water layer: After separation, the oil layer should be clear and transparent, with no obvious residual moisture; the water layer should be clear, with no floating oil droplets, ensuring that the hydraulic system is not affected by moisture.

Detailed Test Procedure

Sample Preparation: Take 40 mL of the mixed oil sample of the hydraulic oil compound to be tested and base oil, and pour it into a 100 mL stoppered graduated cylinder; separately take 40 mL of distilled water, and adjust the temperature of both the oil sample and the distilled water to the same (54°C or 82°C).
Equipment commissioning: Place the measuring cylinder in a constant temperature water bath, maintain the test temperature stable within the set value ±1°C, and keep it at a constant temperature for 10 minutes to ensure uniform temperature of the oil sample.
Mixing operation: Slowly pour distilled water into a graduated cylinder containing the oil sample, cap the cylinder, quickly invert the cylinder 10 times (each inversion lasting approximately 2 seconds) to thoroughly mix the oil sample with water.
Static Observation: Place the measuring cylinder back into the thermostatic water bath, start timing, observe the separation of the oil-water-emulsion layer every 5 minutes, and record the volume changes of each layer.
Result determination: If the volume of the emulsion layer ≤ 3 mL within 30 minutes, it is determined as qualified; if the emulsion layer still exceeds 3 mL after 30 minutes, continue to observe until 60 minutes and record the final volume of the emulsion layer.

Comparative Analysis of Domestic and International Hydraulic Oil Compound Additive Standards

The quality control of hydraulic oil compound agents relies on a well-established standard system. Both domestic and international standards and specifications with their own characteristics have been developed, which respectively impose constraints on products from aspects such as performance indicators, environmental protection requirements, and testing methods. For potential customers, understanding the differences between domestic and international standards can help them better select suitable products based on application scenarios and export requirements.

Classification of the Core Standard System

The core standard systems of domestic and international hydraulic oil additive packages mainly include international standards, EU standards, US standards, and Chinese standards, which are as follows:

Standard System	Core Standard Number	Scope of Application	Key Features
International Standard	ISO 6743-4-2015	Universal	Emphasize the universality of performance and the unity of testing methods
EU Standard	REACH、CLP	EU Market	Strictly control hazardous substances and emphasize environmental protection requirements
US Standard	ASTM Series, MIL-H-5606F	American Market	Emphasizes adaptability to actual working conditions, with meticulous testing methods
Chinese Standard	GB/T 7631.2-2003、NB/SH/T 0916-2015	Domestic Market	Equivalent adoption of international standards, optimized in combination with national conditions

Comparison of Key Indicator Standard Differences

Environmental indicator differences

The EU REACH Regulation controls over 190 substances of very high concern (SVHC), requires that the acute aquatic toxicity LC50/EC50 of hydraulic oil additives be >100mg/L, the 28-day biodegradation rate be ≥60% (OECD 301B standard), and prohibits substances such as short-chain chlorinated paraffins and phthalates.
The US EPA's EPP program requires that the biobased content of compound agents be ≥20%, and the MIL-H-5606F standard prohibits chlorine- and fluorine-containing components, applicable to marine environments.
China's NB/SH/T 0916-2015 standard requires that the acute aquatic toxicity (fish) LC50 > 1000mg/L, be free of endocrine disrupting substances such as APEO, and GB/T 30515-2014 stipulates that the biodegradation rate ≥ 60%.
Among the UNP series products, the UNP AH502C zinc-free product fully complies with EU REACH and US TSCA standards, with a biodegradation rate of over 75%, meeting the requirements of environmentally sensitive sectors.

Performance Indicator Differences

Anti-wear performance: ISO 12156-1 requires a PB value ≥ 980N, ASTM D2782 requires a PB value ≥ 1200N for high-end products, and China's GB/T 3142 is consistent with international standards. The PB value of UNP AH502A high-zinc product reaches 1200N, far exceeding the requirements of international standards.
Oxidation Stability: ASTM D2272 requires that the oxidation induction period of ordinary products be ≥300 minutes, the EU standard requires that of long-life products be ≥500 minutes, and China's GB/T 12581 is consistent with the ASTM standard. The oxidation induction period of UNP AH502C reaches 580 minutes, meeting the needs of the high-end market.
Water separability: Both ASTM D1401 and GB/T 7305 require the emulsified layer to be ≤3 mL within 30 minutes. The US standard has a higher test temperature for high-viscosity products and is more stringent. All UNP series products can meet both domestic and international standard requirements, with a separation speed superior to the industry average.

Standard Application Recommendations

For hydraulic equipment that is domestically produced and sold only in the domestic market, products meeting the standards of GB/T 7631.2-2003 and NB/SH/T 0916-2015 can be selected, such as the UNP AH502A high-zinc product, which has obvious cost-performance advantages; if the equipment is exported to the EU, zinc-free or low-zinc products meeting the REACH and CLP regulations need to be selected, and both UNP AH502B and UNP AH502C can meet the requirements; for the US market, it is recommended to choose the UNP AH502C product that meets the ASTM series standards and the EPA EPP program, with both its bio-based content and environmental performance meeting the standards.

In practical applications, customers also need to adjust their choices based on specific operating conditions: for high-temperature and high-pressure conditions, products with excellent oxidation stability and anti-wear performance should be prioritized; in humid environments, focus should be on water separation performance; and in industries such as food and medicine, zinc-free and low-toxicity environmentally friendly products should be selected. UNPChemicals can provide customized hydraulic oil additive solutions based on customers' standard requirements and operating condition characteristics to ensure that the products are fully adapted to the actual application scenarios.

Quality inspection and standard specification of hydraulic oil additive packages are the core links to ensure the stable operation of hydraulic systems. The test results of key indicators such as anti-wear performance, oxidation stability, and water separability directly reflect the actual usage effects of the products. As a professional supplier of hydraulic oil compound additives, UNPChemicals' products such as UNP AH502A, UNP AH502B, and UNP AH502C have all passed the tests of domestic and international authoritative standards, perform excellently in all key indicators, and can provide reliable lubrication solutions for customers in different industries.

The Price of Hydraulic Oil Additives Package

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

Supplier of Hydraulic Oil Additives Package

UNPChemicals is a professional supplier of high-quality and effective Hydraulic Oil Additives Package. We offer several remarkable products, namely High zinc hydraulic oil additives UNP AH502A,Low Zinc Hydraulic Oil Additives UNP AH502B,Zinc-free Hydraulic Oil Additives UNP AH502C,etc.

High zinc hydraulic oil additives UNP AH502A are a type of chemical additive used in hydraulic oils that contain high levels of zinc dialkyldithiophosphate (ZDDP). ZDDP is a well-known anti-wear agent that also provides antioxidant, anti-corrosion, and anti-foam properties. The zinc in these additives plays a crucial role in forming a protective film on metal surfaces within the hydraulic system, thereby reducing wear and extending the life of the system components.

Low Zinc Hydraulic Oil Additives UNP AH502B are a class of advanced lubricant additives designed to enhance the performance of hydraulic oils with reduced zinc content.These additives are formulated to provide a balance of anti-wear,extreme pressure,and antioxidant properties,making them suitable for modern hydraulic systems that demand high performance with lower environmental impact.

Zinc-free Hydraulic Oil Additives UNP AH502C are a new class of environmentally friendly lubricant additives designed for hydraulic systems.These additives are formulated to provide the same level of performance as traditional zinc-containing additives but without the heavy metal content,reducing the environmental impact of hydraulic fluids.

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.