Knowledge of particle counter-oil pollution degree

2021-05-06 16:57

Oil pollution degree

Oil pollution degree refers to the content of solid particle pollutants per unit volume of oil, and the concentration of solid particle pollution in the oil. For other pollutants, such as water and air, the water content and air content are expressed. The degree of oil contamination is an important indicator for evaluating the degree of oil contamination.

At present, the oil pollution degree mainly adopts the following two expression methods:

l Quality pollution degree: the quality of the pollution degree of solid particles contained in the unit volume of oil, generally expressed in ml/L

l Particle pollution degree: the number of particles of various sizes per unit volume of oil. The range of particle size can be expressed in intervals, such as 5-15μm, 15-25μm, etc.; it can also be expressed by a size greater than a certain size, such as >5μm, >15μm, etc.

In addition, the oil pollution degree can also be expressed in parts per million (ppm), mass ppm or volume ppm.

Although the quality pollution degree expression method is relatively simple, it cannot reflect the size and distribution of particle pollutants. The harmful effects of particle pollutants on components and systems are closely related to their particle size distribution and quantity. Therefore, with the development of particle counting technology, the current The expression method of particle contamination has been generally adopted.

In order to quantitatively assess the degree of oil pollution, all major industrial countries in the world have formulated their own oil pollution degree. In recent years, they have tended to adopt uniform international standards. The following introduces the United States NAS 1638 oil pollution level and ISO 4406 oil pollution level international standards.

A NAS 1638 solid particle pollutant level

NAS 1638 was proposed by the U.S. Aerospace Industry Department in 1964, and is still widely used in the United States and other countries around the world. It is based on the particle concentration, and is divided into 14 pollutant levels according to the maximum allowable particle number in the 5-15, 15-25, 25-50, 50-100 and >100μm 5 size intervals in the oil, as shown in Table 1. .

It can be seen from the table that the particle concentration ratio of two adjacent grades is 2. Therefore, when the oil pollution concentration exceeds the maximum 12 levels in the table, the pollution level can be determined by extrapolation.

The measured particles in each size range are often not of the same level, and the highest level is generally taken as the oil pollution level. But this treatment method is sometimes unreasonable. For example, if the pollution degree of each size segment of 5-15, 15-25, 25-50, 50-100 and >100μm is 7, 7, 6, 10 and 8, if the maximum is taken, the oil pollution degree should be It is level 10. However, considering the hazard size that may enter the clearance of the moving pair and cause abrasion, the pollution degree of 7 is more realistic.

B ISO 4406 International Standard for Pollution Degree of Solid Particles

The ISO 4406 oil pollution degree international standard uses two numbers to indicate the pollution degree of the oil. The first number represents the number of particles larger than 5μm in 1mL oil, and the back number represents the particles larger than 15μm in 1mL oil. The level of the number, separated by a slash between two numbers. For example, pollution level 18/13 means that the number of particles larger than 5μm in the oil is rated as 18, and the number of particles per milliliter is between 130,000 and 250,000; the number of particles larger than 15μm is rated as 13, and the number of particles per ml is between 4,000 and 4,000. Between 8000.

Table 2 shows the ISO 4406 pollution level and the corresponding particle concentration. According to the size of the particle concentration, there are 26 levels.

The ISO 4406 pollution degree standard selects two characteristic sizes: 5μm and 15μm. They basically reflect the harmful effects of blockage and siltation caused by smaller particles in the oil and abrasion caused by larger particles.

At present, the ISO 4406 pollution degree standard has been widely adopted by countries all over the world. The national standard GB/T 14039-93 "Code for the pollution degree of solid particles of hydraulic system working medium" formulated by my country is equivalent to ISO 4406.

The approximate correspondence between ISO 4406 and several other pollution levels is shown in Table 3.

①The pollution level proposed by the American Society of Automotive Engineers in 1963

②Fine test dust of air filter

At present, the minimum particle size of NAS 1638 and ISO 4406 pollution degree standards are both 5μm. With the development of modern hydraulic technology and the further improvement of the development of oil pollution control, high-precision oil filters with an absolute accuracy of 1 to 3 μm have been used in hydraulic systems with high cleanliness requirements. Therefore, amendments to ISO 4406 have been proposed. It is recommended to add a number that reflects the pollution degree of particles larger than 2μm, and use 3 numbers to indicate the degree of oil pollution. For example, 22/18/13, the above numbers indicate particle concentrations >2μm, >5μm and >15μm, respectively.

Recently, ISO 4402 "Calibration of Liquid Particle Counters" has been revised, and a new calibration method ISO 11171 has been developed. The use of a new calibration method improves the accuracy of particle analysis, but at the same time brings about the problem of redefining particle size. In the past, the particle sizes measured by the ISO 4402 calibration method were 2μm, 5μm and 15μm, but with the new calibration method they were 4.6μm, 6.4μm and 13.6μm. For this reason, ISO 4406 has recently been revised and improved. The revised ISO 4406:1999 stipulates that: for the pollution level counted by an automatic particle counter, the particle concentration levels in the three size ranges of >4μm, >6μm and >14μm Said. For counting with a microscope, the particle concentration levels >5μm and >15μm are still used.