1. What are the requirements of hydraulic system for hydraulic oil?
A viscosity: it is the primary factor in selecting hydraulic oil. The viscosity is too high, which increases the movement resistance, reduces the self-priming performance of the pump, increases the loss along the way and increases the power loss. The viscosity is too low, the internal and external leakage increases, and the volumetric efficiency is low, which reduces the lubricity of the hydraulic components and reduces the service life of the components. Therefore, the appropriate viscosity range must be selected according to the working conditions of the hydraulic system, generally between 12-100mm2 / S (40 ¡æ), and the oil is required to have a high viscosity index, generally greater than 90, so as to maintain the temperature change and the viscosity change of the oil is relatively small.
B lubricity: because the hydraulic components are in the boundary lubrication state under the conditions of starting, stopping, high load and high impact. In order to prevent wear and tear and prolong the service life of components (especially pumps and motors), hydraulic oil is required to have good oiliness, extreme pressure and wear resistance.
C oxidation stability: hydraulic oil is easy to oxidize and deteriorate under high temperature and high pressure. After oxidation, the acid value increases, corrodes the components and forms colloid, which is easy to block the filter and block the components. Therefore, it is required to have good oxidation stability and thermal stability.
D shear stability: when the working medium passes through the throttling gap or damping hole at high speed, the polymer chain of the viscosity index improver is easy to break, resulting in the decrease of the viscosity index. At high temperature, the viscosity decreases greatly, so it is required to have good shear stability.
E rust prevention and corrosion resistance: when water and air are mixed into the hydraulic oil, it is easy to cause rust on the finished surface of components. The oil is required to have rust prevention and corrosion resistance.
F anti emulsifying property: water is generated when hydraulic oil is mixed with water or air for condensation. Under long-term stirring, it is easy to generate emulsion and hydrolyze its additives. Therefore, the oil is required to have good water separation performance and good hydrolysis stability.
G. anti foam property: the hydraulic oil pressure changes and contacts with air, so that bubbles are mixed in the oil, so that the pressure and energy transmission are unstable, and the pump and motor produce cavitation, vibration, noise, oil cylinder jitter, etc. Therefore, hydraulic oil must have good foam resistance and air release ability.
H compatibility with sealing materials: improper selection of hydraulic oil will soften or harden the sealing materials, resulting in sealing failure. Therefore, it is required that the compatibility between hydraulic oil and sealing materials be good.
2. How to classify hydraulic oil? What are the varieties and specifications?
1) There are seven types of mineral oil: l-hh oil, also known as mechanical oil; L-HL oil is the general machine tool hydraulic oil; L-hr oil; L-HM precision machine tool guide oil; L-hg oil, i.e. hydraulic guide oil or precision machine tool guide oil; L-HV oil, also known as low temperature or low pour point hydraulic oil, engineering hydraulic oil, high viscosity index oil and thickened hydraulic oil; L-hs oil, namely synthetic low temperature hydraulic oil.
2) There are five types of flame retardant hydraulic oil: l-hfa hydraulic oil (oil in water emulsion, high water-based hydraulic fluid), l-hfb hydraulic fluid (water in oil emulsion), l-hfc hydraulic fluid (water glycol flame retardant fluid), l-hfdr hydraulic fluid (phosphate flame retardant fluid), l-hees hydraulic fluid (synthetic ester flame retardant fluid)
3) Special hydraulic oil: aviation hydraulic oil, aviation flame retardant hydraulic oil, marine and artillery hydraulic oil, etc.
In metallurgical production, due to the large pressure and flow of most hydraulic systems and high control accuracy, there are high requirements for the performance of hydraulic oil. L-HM anti-wear hydraulic oil is most used, and the flame retardant fluid is mainly l-hfc water glycol hydraulic fluid.
3.What are the performance characteristics and application scope of various mineral hydraulic oils?
See attached table:
Application range of mineral oil hydraulic oil
Machine oilLow temperature hydraulic oil
Oil product name | main performance | Scope of application |
Antioxidant stability and foam resistance are general | The hydraulic system is generally not applicable | |
General machine tool industrial lubricating oil | Good oxidation safety, rust prevention and foam resistance | It is applicable to general-purpose machine tools below 7MPa |
Anti wear hydraulic oil | It has excellent anti-oxidation, anti rust, anti-wear, thermal safety and anti foaming properties | It is suitable for precision machine tools above 7MPa and hydraulic systems without silver and bronze components above 14MPa |
Hydraulic guide oil | It has anti creep property, and other properties are the same as those of anti-wear hydraulic oil | Suitable for hydraulic guide rail system |
Low pour point, high viscosity index and good shear stability. Other properties are the same as those of anti-wear hydraulic oil | It is applicable to the hydraulic system of outdoor engineering machinery in cold areas above - 15 ¡æ |
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4.What is the performance and scope of application of various fire-resistant hydraulic oils?
See attached table:
Application scope of fire-resistant hydraulic oil
Oil product name | main performance | Scope of application |
Oil in water emulsion | It has certain rust resistance and foam resistance | It is used for hydraulic systems below 7MPa that require flame resistance, economy and large leakage |
High water base solution | It has certain lubricity, rust resistance and foam resistance, and has good stability | It is used for hydraulic systems below 7MPa that require flame resistance, economy and large leakage |
Water in oil emulsion | It has good lubricity, rust resistance and foam resistance | It is used for 14MPa hydraulic system requiring good flame resistance, lubricity and rust prevention |
Water glycol solution | It has good lubricity, rust resistance, flame resistance and stability, and low freezing point | It is used for hydraulic systems below 21MPa requiring fire resistance, lubrication and rust prevention, and can also be used for low temperature systems |
Phospholipid | Excellent lubricity and flame resistance, strict sealing materials and certain environmental protection restrictions | It is suitable for high temperature, high pressure and fire-resistant precision hydraulic system |
Synthetic ester | Excellent lubricity, flame resistance, high and low temperature stability, good biodegradability, meeting the requirements of environmental protection | It is suitable for high temperature, high pressure and fire-resistant precision hydraulic system |
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5.How to select mineral hydraulic oil according to hydraulic pump type and working temperature?
See attached table:
Hydraulic oil selected for various hydraulic pumps
Vane pumpScrew pumpRadial Piston Pump
Pump type | ³Õ¾±²õ³¦´Ç²õ¾±³Ù²â(50¡æ)£¯³¾³¾2*²õ-1 | Applicable hydraulic oil | ||
5-40¡æ | 40-80¡æ | 5-40¡æ | 40-80¡æ | |
¡Ü7²Ñ±Ê²¹ | 19-29 | 25-44 | N32, n46hh oil or HL oil | N46, n68hh oil or HL oil |
¡Ý7²Ñ±Ê²¹ | 31-42 | 35-55 | N46, n68hm oil | N68, n100hm oil |
19-29 | 25-49 | N32, n46hl oil or HM oil | N46, n68hl oil or HM oil | |
Gear pump | 19-42 | 58-98 | N32, N46, n68hl oil or HM oil | N100hl oil or HM oil |
19-29 | 38-135 | N32, N46, n68hl oil or HM oil | N68, n100hl oil or HM oil | |
Axial piston pump | 26-42 | 42-93 | N32, N46, n68hl oil or HM oil | N68, n100hl oil or HM oil |
Note£º¢Ù HH refers to mechanical oil
¢Ú HL is a general machine tool industrial lubricant
¢Û HM is anti-wear hydraulic oil
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6.How to select fire-resistant hydraulic fluid according to service temperature and pressure?
See attached table:
Select the fire-resistant hydraulic fluid according to the service temperature and pressure
Oil in water emulsion
±Ê°ù±ð²õ²õ³Ü°ù±ð£¯²Ñ±Ê²¹ °Õ±ð³¾±è±ð°ù²¹³Ù³Ü°ù±ð¡æ | ¡Ü7 ¡Ü50 | 7-14 ¡Ü60 | 7-14 50-80 | ¡Ý14 80-100 |
¡Ì | ||||
High water base solution | ¡Ì | |||
Water in oil emulsion | ¡Ì | |||
Water glycol solution | ¡Ì | ¡Ì | ¡Ì | |
Phosphate liquid | ¡Ì | ¡Ì | ||
Synthetic ester solution | ¡Ì |
7. What are the types of anti-wear hydraulic oil? What are the characteristics?
1) High zinc type (known as "conventional zinc type" abroad): zinc content in oil ¡Ý 0.07%. This type is the main oil of HM oil at home and abroad. For steel steel friction pairs, such as high and medium pressure vane pumps, the wear resistance is the best. High zinc type is divided into high zinc and neutral high zinc. Neutral high zinc has better extreme pressure and wear resistance, while alkaline high zinc has good oxidation resistance and thermal stability due to high pH value and high alkalinity.
2) Low zinc type (known as "stable zinc type" abroad): the zinc content in the oil is less than 0.07%, generally 0.03% - 0.04%. It has good adaptability to materials. It is suitable for medium and high pressure vane pumps and plunger pumps with copper and copper alloy.
3) Zinc free type (known as "non zinc type" abroad): the oil does not contain zinc and other metal salts. It is mainly suitable for plunger pump. In addition to its high cost and inferior wear resistance to zinc type, it is not easy to corrode the hydraulic system with copper and silver components, and its water separation, hydrolysis stability, filterability and thermal oxidation stability are better.
8. What are the requirements of hydraulic oil for oil pollution?
According to statistics, 70% of the faults of the hydraulic system are caused by the oil pollution that does not meet the requirements, so the oil cleanliness is very important to the normal operation of the hydraulic system. At present, there are two standards for the cleanliness of oil, which are widely used in China, namely ISO4406 and nasl638. Different components and pressures have different requirements for oil cleanliness. According to the recommendations of Vickers, ISO4406 is used to measure the cleanliness. The requirements for oil cleanliness corresponding to various components and pressure levels are as follows:
Component name | Pressure MPa | ||||
<13.8 | 13.8-20.7 | >20.7 | |||
Quantitative gear pump | 18£¯15 | 17£¯15 | 16£¯13 | ||
Quantitative vane pump | 18£¯15 | 17£¯14 | 16£¯13 | ||
Pump | Quantitative piston pump | 17£¯15 | 16£¯14 | 15£¯13 | |
Variable vane pump | 16£¯14 | 15£¯13 | 15£¯13 | ||
Variable displacement piston pump | 16£¯14 | 15£¯13 | 14£¯12 | ||
<13.5 | 13.8-20 7 | >20 | |||
Directional valve (solenoid valve) | 18£¯15 | 17£¯14 | |||
Pressure control valve (pressure regulating valve) | 17£¯14 | 17£¯14 | |||
Flow control valve (standard) | 18£¯15 | 18£¯15 | |||
Check valve | 18£¯15 | 18£¯15 | |||
Cartridge valve | 18£¯15 | 17£¯14 | |||
Threaded cartridge valve | 16£¯13 | 15£¯12 | |||
valve | Filling valve | 18£¯15 | 17£¯14 | ||
Load sensing directional valve | 16£¯14 | 15£¯13 | |||
Hydraulic remote control valve | 16£¯13 | 15£¯12 | |||
Proportional directional valve (throttle valve) | 16£¯13 | 15£¯12 | |||
Proportional pressure control valve | 16£¯13 | 15£¯12 | |||
Proportional cartridge valve | 16£¯13 | 15£¯12 | |||
Proportional threaded cartridge valve | 16£¯13 | 15£¯12 | |||
Servo valve | 14£¯11 | 13£¯10 | |||
Cylinder | 18£¯15 | 18£¯15 | 18£¯15 | ||
Gear motor | 19£¯17 | 18£¯15 | 17£¯14 | ||
Hold | Vane motor | 18£¯15 | 17£¯14 | 16£¯13 | |
Axial piston motor | 17£¯14 | 16£¯13 | 15£¯12 | ||
radial piston motor | 18£¯14 | 17£¯13 | 16£¯13 | ||
Swashplate structure motor | 16£¯14 | 15£¯13 | 14£¯12 | ||
Ball bearing system | 13£¯11 | ||||
Bearing | Roller bearing system | 14£¯12 | |||
Plain bearing (high speed) | 15£¯13 | ||||
Plain bearing (low speed) | 16£¯14 | ||||
General industrial reducer | 15£¯13 | ||||
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9. How to compare the pollution levels of ISO4406 and nasl638?
Comparison table between ISO4406 and other pollution levels:
ISO4006 | NASl638 | SAE749D | Granules of greater than 10 ¦Ì in each ml of oil | ACFTD mass concentration/mg/L |
26£¯23 | ¡ª | ¡ª | 140000 | 1000 |
25£¯23 | ¡ª | ¡ª | 85000 | ¡ª |
23£¯20 | ¡ª | ¡ª | 14000 | 100 |
21£¯18 | 12 | ¡ª | 4500 | ¡ª |
20£¯18 | ¡ª | ¡ª | 2400 | ¡ª |
20£¯17 | 11 | ¡ª | 2300 | ¡ª |
20£¯16 | ¡ª | ¡ª | 1400 | 10 |
19£¯16 | 10 | ¡ª | 1200 | ¡ª |
18£¯15 | 9 | 6 | 580 | ¡ª |
17£¯14 | 8 | 5 | 280 | ¡ª |
16£¯13 | 7 | 4 | 140 | 1 |
15£¯12 | 6 | 3 | 70 | ¡ª |
14£¯12 | ¡ª | ¡ª | 40 | ¡ª |
14£¯11 | 5 | 2 | 35 | ¡ª |
13£¯10 | 4 | 1 | 14 | 0.1 |
12£¯9 | 3 | 0 | 9 | ¡ª |
11£¯8 | 2 | ¡ª | 5 | ¡ª |
10£¯8 | ¡ª | ¡ª | 3 | ¡ª |
10£¯7 | 1 | ¡ª | 2.3 | ¡ª |
10£¯6 | ¡ª | ¡ª | 1.4 | 0.01 |
9£¯6 | 0 | ¡ª | 1.2 | ¡ª |
8£¯5 | 00 | ¡ª | 0.6 | ¡ª |
7£¯5 | ¡ª | ¡ª | 0.3 | ¡ª |
6£¯3 | ¡ª | ¡ª | 0.14 | 0.001 |
Note: ¢Ù sae7490 is the oil pollution level proposed by the American Society of automotive engineers in 1963.
¢Ú ACFTD is fine test dust of air filter.
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10. How to specify the particle size and quantity of nasl638 pollution level particles?
Nasl638 oil contamination level (number of particles in 100ml)
Pollution level | Particle size range ¦Ìm | ||||
5-15 | 15-25 | 25-50 | 50-100 | >100 | |
00 | 125 | 22 | 4 | 1 | 0 |
0 | 250 | 44 | 8 | 2 | 0 |
1 | 500 | 88 | 16 | 3 | 1 |
2 | 1000 | 178 | 32 | 6 | 1 |
3 | 2000 | 356 | 63 | 11 | 2 |
4 | 4000 | 712 | 126 | 22 | 4 |
5 | 8000 | 1425 | 253 | 45 | 8 |
6 | 16000 | 2850 | 506 | 90 | 16 |
7 | 32000 | 5700 | 1012 | 180 | 32 |
8 | 64000 | 11400 | 2025 | 360 | 64 |
9 | 128000 | 22800 | 4050 | 720 | 128 |
10 | 256000 | 45600 | 8100 | 1440 | 258 |
11 | 512000 | 91200 | 16200 | 2880 | 512 |
12 | 1024000 | 182400 | 32400 | 5760 | 1024 |
