GB/T 4797.6-1995 Natural environmental conditions for electrical and electronic products Dust, sand and salt spray
Some standard content:
National Standard of the People's Republic of China
Natural environmental conditions for electric and electronic products
Dust, sand, salt mist
Environmental conditions appearing in naturefor electric and electronic productsDust, sand, salt mist
GB/T 4797.6-1995
This standard refers to the international standard IEC721-2-5 "Classification of environmental conditions Part 2: Environmental conditions occurring in nature Group 5: Dust, sand, salt mist" (1991, first edition). 1 Subject content and scope of application
This standard explains the characteristics, distribution and impact of dust, sand and salt mist environments occurring in nature on products, as well as the factors affecting these environmental conditions.
This standard is applicable to natural conditions and their impacts that products may suffer when exposed to dust, sand and salt mist during storage, transportation and use. The impact of these environmental factors is often closely related to wind and increases several times with the increase of wind force. For environmental factors and conditions related to wind, refer to GB/T4797.5\Precipitation and wind". 2 Reference standards
GB4796 Classification of environmental parameters for electrical and electronic products and their severity classification GB4797.5 Natural environmental conditions for electrical and electronic products Precipitation and wind 3 Effects of dust, sand and salt spray on products
3.1 Dust, sand, salt spray and related wind can affect products in various aspects, the most important of which are: a.
Dust enters sealed containers and enclosures;
Degrades electrical performance, such as contact failure, change in contact resistance, change in track resistance (potentiometer); causes wear or failure of moving bearings, axles, knobs and other moving parts; causes surface erosion (erosion, corrosion); causes optical surface blur;
Contaminates grease;
Reduces thermal conductivity,
Causes blockage of working vents, sleeves, ducts, filters, holes, etc.; generates static electricity during high-speed movement (such as sandstorms), affecting communication systems. 3.2 Accumulated dust and sand combined with other environmental factors (such as water vapor) may have serious effects on products, such as corrosion and mold growth. When hot and humid atmosphere combines with chemically aggressive dust, it will cause corrosion. Similar effects will occur when there is salt mist in the atmosphere. 3.3 The effects of ion conduction and corrosive dust (such as deicing salt, etc.) must also be considered. Approved by the State Bureau of Technical Supervision on June 2, 1995 78
Implemented on June 1, 1996
4 Natural dust and sand environment
4.1 Dust and sand Classification
GB/T4797.6—1995
Based on different aerodynamic characteristics, dust and sand are distinguished as follows: Dust: It can be determined as material particles with no specified source or composition, and the particle size is between 1μm and 150μm. Due to natural air a.
air end flow, particles with a diameter of less than 75μm can remain in the atmosphere for a long time. b. Sand: It is represented by the non-compacted accumulation of condensed rock debris sediments, and its basic composition is round quartz particles. When this term is applied in sedimentary petrology, it refers to particles between 100um and 1000μm in size. Unless it is constantly subjected to strong natural or induced airflow or end flow. Particles with a diameter greater than 150μm cannot stay in the air and spread. c.
Dust and smoke: It is a dispersed system composed of particles smaller than 1um in the air. 4.2 Types and characteristics of dust
4.2.1 Types of dust
Most dust in nature is mainly composed of quartz. In deserts and similar dusty areas, dust can cause damage to products. The main feature of quartz is its hardness, which can cause rapid wear or damage to products, especially moving parts. However, material abrasion usually occurs when dust is combined with high-speed airflow or dust with a long action period. 4.2.2 Characteristics of dust
4.2.2.1 The important characteristics of natural dust are its non-absorption and chemical inertness, but when the atmosphere contains moisture or other gases, it may cause corrosion to metals.
4.2.2.2 The most notable characteristics of fine dust are usually its non-abrasiveness and hygroscopicity. 4.2.3 Characteristics of Dust
4.2.3.1 Particle Size
The approximate range of dust and sand particle sizes is: Fine Dust
Coarse Dust
Below 75 μm
75~~150 μm
150~1000 μm
The approximate distribution of dust and sand particle sizes is shown in Figure 1. 100
Figure 1 Cumulative distribution of dust particle sizes
Particle size, μm
4.2.3.2 Particle Hardness
GB/T 4797.6-1995
The hardness of an individual particle can be used to determine its ability to scratch objects it contacts. Sand, which is composed of tiny fragments of crystalline quartz or other minerals, is usually slightly harder than most fused silica glasses. Therefore, sand can scratch the surface of most optical glass devices. Applying pressure to the captured sand particles can cause them to break. The hardness levels of several common substances (according to the Mohs hardness) are shown in Table 1. Substances with a higher hardness level can scratch any substance with a lower hardness level. Table 1 Hardness levels of several common substances
Mohs hardness level and representative substances
1 Talc
2 Gypsum
3 Calcite
4 Fluorite
5 Apatite
6 Orthoclase
7 Quartz
8 Citrine
9 Corundum
10 Diamond
4.2.4 Concentration
Alabaster, diatomaceous earth
Kaolinite
Galena, mica, (nail ）
Si-Mg-Ni ore, marble, serpentine
knockstone, dolomite
asbestos, opal
window glass
magnetite, feldspar
agate, ferromagnetic ore, (knife steel) flint, fused quartz, olivine
andalusite, calcium carbide
emery
sapphire, silicon carbide
tungsten carbide
4.2.4.1 From the mass, the degree can be calculated, that is, the mass of particles per unit volume of air. The concentration of dust in the atmosphere varies greatly with geographical location, regional climate type and conditions, and the degree of human activities. Under certain conditions, a large amount of dust is locally and temporarily separated from the floating dust on the surface and blown away by the wind. 4.2.4.2 In mild climate areas, the typical concentrations of dust encountered in various areas are shown in Table 2. Table 2 Typical dust concentrations
Rural and suburban areas
Industrial areas
Dust concentrations, mg/m2
0.04~0.11
0.10~0.45
0.50~2.00
4.2.4.3 Higher dust concentrations occur under induced conditions, such as those caused by helicopters and tracked vehicles. Appendix A shows approximate values of dust concentrations induced by helicopters and vehicles. 4.2.4.4 Typical dust concentrations at different altitudes in the desert are shown in Table 3. The movement of dust near the ground in the desert in the air flow is shown in Appendix B.
Visibility conditions
Clear, visibility 130 km
GB/T 4797. 6--1995
Table 3 Variation of dust concentration in desert with increasing altitudeHigh
Dust storm, visibility 300 m, air speed 10~15 m/s150
Dust concentration
4.2.4.5 Dust concentration and the chance of large particles appearing increase with increasing wind speed. Figure 2 shows the general relationship. However, it varies with factors such as temperature, humidity, and particle composition. Particles larger than 150 μm are generally confined to an air layer 1 m near the ground. In this layer, about half of the sand particles (by mass) move within 10 mm above the ground surface, while the other half, mostly, move within 100 mm near the ground surface.
The measured results of the relationship between the dust content (pieces/cm\) and wind speed in the air in Northwest my country are shown in Figure 3. 1000
Wind speed, m/s
Figure 2 Dependence of the maximum particle size on the wind speed Note: Curve 3H of the near-ground conditions (less than 1m) that affect the maximum particle size
Wind speed, m/s
Figure 3 Relationship between the dust content and wind speed in the outdoor atmosphere (Huoyan Mountain Gobi Desert, Xinjiang, 1m above the ground) 81
4.3 Factors affecting the dust environment
GB/T 4797.6—1995
4.3.1 The dust environment is influenced and controlled by factors such as topography, wind, temperature, humidity and precipitation. None of these factors can independently determine whether a region is dusty or dust-free. Usually, two or more factors must be combined to work. In the most severe situations in nature, such as in desert areas, all factors generally and strongly lead to high concentrations of dust. The structural characteristics of the terrain can cause high-speed strong winds and cause sandstorms. For example, when air passes through col-type landform structures with great force, it will significantly increase wind speed. 4.3.2 Sand is widely distributed on the land surface of the earth. Deserts are the original source of naturally occurring wind-blown dust. The area of the world's major deserts is about one-fifth of the total area of ancient land. Table 4 lists the main deserts in my country, which are the original source of naturally occurring wind-blown dust in my country. The total area of deserts (including Gobi and desertified land) in the country is 130.8×104km2, accounting for about 13.6% of the total land area of my country. Table 4 Main deserts in my country and their geographical locations and areas Desert name
Taklimakan Desert
Gurbantunggut Desert
Kumtag Desert
Qaidam Basin Sand
(including wind erosion land)
Badain Jaran Desert
Tengger Desert
Ulan Buh Desert
Kubqi Desert
Mao Us Sandy Land
Hunjingdake (Little Tengger) Sandy Land
Korqin Sandy Land
Hulunbuir Sandy Land
Geographic location
Tarim Basin in Xinjiang
Huaigar Basin in Xinjiang
Eastern Xinjiang, western Gansu; Luoyang Southern Bu Nur Lowland, northern Altun Mountains
Qaidam Basin in Qinghai
Western Alxa Plateau in Inner Mongolia
Southeastern Alxa Plateau in Inner Mongolia
Northeastern Alxa Plateau in Inner Mongolia, southwestern Houtao Plain of the Yellow River
Northern Ordos Plateau in Inner Mongolia, south of Hetao Plain of the Yellow River
Central and southern Ordos Plateau in Inner Mongolia and northern ShaanxiWww.bzxZ.net
Southern Xilin Gol League and northwestern Zhaowuda League in the eastern Inner Mongolia Plateau
The lower reaches of the Xiliao River in the west of the Northeast Plain
Hulunbuir Plateau in northeastern Inner Mongolia
B40～1200
300~600
1 000~1 200
2 600~3 400
1300~1800
1 400～~1 600
1000～1200
1 300～1600
100～~300
X103 km2
4.3.3 Compared with sand, dust particles have a very low settling velocity, can remain suspended in the air for a long time, and can stay on the surface of any place. Under dry conditions, soils with at least 9% dust particles (by mass) become medium powdery, and soils with more than 14% dust particles may be completely dusty. Except for Antarctica, 40% of the world's land surface is classified as dry areas, and another 40% is seasonally dry areas. Dust is expected to occur over most of the world's land surface during most of the year. Even in areas with heavy rain, where the protective cover is destroyed, dust will still be produced. Many wet areas have good drainage, so that most of the unprotected soil will turn into dust in a very short time after heavy rain. 4.3.4 Figure 4 shows the occurrence of wind in areas with moderate inland winds. Figure 5 shows the relationship between the number of occurrences of sand-raising winds (wind speed 5m/s) and the frequency of wind speed in northwest my country. 4.3.5 Figure 6 shows the settling speed of particles of different sizes. From this figure, the settling time can be estimated. For small particles, the effects of thermal changes and other vapor flows on the settling time should be considered.
Clean room area
GB/T4797.6—1995
Wind speed, m/s
Figure 4 Percentage of moderate-intensity wind in inland areas 20 H
Percentage of sand-raising wind in the total wind speed throughout the year, %5Relationship between the number of occurrences of sand-raising wind (≥5m/s) and wind speed frequencyFigure 5
(Taklimakan area, Xinjiang)
GB/T 4797.6—1995
Coarse dust
Fine dust
Particle size, μm
Figure 6 Settling velocity of particles retained in the air Note: The curve refers to the case of particles with a concentration of 1g/cm when the temperature is 0℃ and the pressure is 101.3kPa. 5 Dust in venetian blinds and enclosures
5.1 Characteristics of dust
5.1.1 Types of dust
In venetian blinds and enclosures, dust of various materials can be found, such as quartz, cement, powders, organic fibers, etc. 5.1.2 Distribution of particle sizes
The distribution of particle sizes varies significantly depending on whether the location is outdoors, loaded on a vehicle or in a venetian blind. Due to the filtering effect of the shelter, the maximum particle size in venetian blinds and enclosures is smaller than in unweathered locations. The maximum particle size in venetian blinds and enclosures is about 100 μm.
·5.1.3 Dust deposition density
Typical values of dust deposition density in different regions are shown in Table 5. The dust deposition values are samples of dust flowing into the measuring device from the outdoor atmosphere. They cannot be taken into account for local dust in enclosed places, for example, in mines, cement plants, sawmills and similar places, where deposition occurs throughout the entire production process.
Rural and suburban areas
Industrial areas
5.2 Factors affecting the dust environment
5.2.1 Regions and locations
GB/T 4797.6—1995
Table 5 Typical dust deposition density
Dust deposition, mg/(m·h)
5.2.1.1 The impact of dust in shuttered or enclosed places is significantly different from that in outdoor places, such as dust storms in desert areas, the local environment around vehicles driving on dusty roads, etc. 5.2.1.2 Dust in enclosed and shuttered places is caused by many sources. Dust may be quartz, deicing salt, fertilizers, etc., which can penetrate such places through ventilation holes or damaged windows. 5.2.1.3 Dust may also be composed of small fibers of natural or artificial materials, for example, from clothing or carpets used in daily life in living rooms or offices.
5.2.1.4 Other sources of dust are found in garages, such as seeds and machine wheel grinding dust. 5.2.1.5 The distribution of material particle sizes varies with different types of dust. The only thing they have in common is that they have approximately the same maximum particle size. See 5.1.2.
5.2.2 Effects of dust
In louvers or closed spaces, there are also small air movements. The basis for identifying this air flow effect is: a. Deposition of dust on deposition products may be caused by four different mechanisms: 1) Deposition in stagnant air;
2) Deposition on the protected surface;
3) Attraction by electrostatic forces;
4) Capture in narrow channels, such as in filters with forced air circulation. The movement of air tends to delay or hinder the deposition of sand and dust. b. The process of sand and dust entering the product may occur as follows: 1) brought into the interior by forced air circulation,
2) brought into the interior by the thermal movement of air,
3) entering the interior by the thermal expansion and condensation of air or the change of atmospheric pressure. 6 Salt spray
6.1 Formation process of salt spray
6.1.1 Salt spray refers to a dispersion system composed of tiny droplets of salt in the atmosphere. Its cause is mainly due to the violent disturbance of seawater in the ocean, the breaking of wind and waves, and the waves hitting the shore, which produce a large amount of foam and bubbles. When the bubbles burst, tiny water droplets will be generated. Most of the seawater droplets fall due to gravity, and some are in a state of equilibrium with eddy diffusion and are distributed on the sea surface. They rise into the air with the air flow, and evolve into a dispersion system through processes such as cracking, evaporation, and mixing, forming atmospheric salt nuclei. These salt nuclei can reach an altitude of more than 2,000 meters with the rising air flow. 6.1.2 The sea salt particles or salt mist distributed on the sea surface are transported to the land by wind and advection, and can be blown to many kilometers inland from the ocean. In typhoons, it can penetrate hundreds of kilometers inland. 6.2 Characteristics of salt mist
6.2.1 Composition
6.2.1.1 The atmosphere in the ocean and coastal areas contains a large amount of salt, including salt formed by solid particles or droplets like salt solution, and also contains various other components.
6.2.1.2 The salt content of seawater is determined by the total amount of solid matter contained in 1 kg of seawater (expressed in grams). At this time, all bromine and iodine are 85
GB/T 4797.6--1995
Equal amounts of chlorine are substituted, all carbonates are converted into oxides, and all organic matter is oxidized. Table 6 shows the composition of the main salt ions in seawater, because most of the salts in seawater are electrolyzed into ionic states. The salt content calculated after appropriate combination according to Table 6 is shown in Table 7. Table 6 Main composition of seawater
Cations
Sodium Na+
Magnesium Mg2+
Calcium Ca2+
Strontium Sr2+
Anions
Sulfate SO,\
Bicarbonate HCO),
Br-
Borate BO),
Percentage of salt content
Note: Natural seawater is often polluted by various wastes discharged from ships and industrial production sites, and these pollutants themselves can increase the activity of bacteria. Table? Amount of salt contained in 1kg of seawater
Types of salt
Sodium sulfate
Calcium chloride CaCl2
Potassium fluoride KCI
Sodium bicarbonate NaHCO;
Potassium bromide KBr
Boric acid H,BO
Strontium chloride SrCl2
Sodium fluoride NaF
6.2.1.3 The composition of the salty atmosphere is approximately equivalent to that of seawater. The salt content of natural seawater can be taken as 3.4%, which varies with geographical regions and climatic factors. For example, the value in the Red Sea is about 4%. The salt content of the surface seawater in the coastal areas of China in winter is shown in Table 8. In summer, due to the large amount of river fresh water entering the sea and mixing with seawater, the average salt content of each sea area is slightly reduced, especially near the Yangtze River Estuary and the Pearl River Estuary, when the salt content is only about 0.5%. 86
6.2.2 Particle size
GB/T4797.6—1995
Table 8 Salt content of surface seawater in China's coastal waters (winter)Sea
Yangtze River Estuary
Salt content, %
3.15~3.25
6.2.2.1 The diameter of salt spray particles is generally small, with few larger than 40μm, most of them are below 2um, and more than 90% are less than 5μm. The salt nuclei of the primary ecology in the ocean are larger, with the maximum nucleus diameter reaching 300pm. As the water evaporates, concentrates, and spreads to the inland air, it becomes smaller, and few are larger than 20μm.
6.2.2.2 The mass of salt spray particles is between 10-11 and 10-5 mg. Its composition is mainly chloride, sodium and sulfate ions. The ratio of sodium to fluoride ions contained in the primary ecological salt core of large particles is about the same as that of seawater, but the proportion of sulfate ions in small particles is slightly larger. 6.2.3 Concentration and sedimentation
6.2.3.1 The concentration of a specific suspended particulate matter can be determined by the mass of the pollutant in a known volume of air or water sample. Then divide the mass by the volume of the sample to obtain the mass value per unit volume, which can be expressed in grams, milligrams or micrograms per cubic meter or liter. For suspended particles that only remain for a relatively short time, their mass can be expressed by the average sedimentation value within a specified time. For salt spray, the sedimentation value is accurately measured by a standardized method (such as the "wet candle method" specified in ISO9225 standard or the "wet gauze method" specified in GB10593.2 standard) to express the salt content in the air. 6.2.3.2 Salt spray concentration
a. The maximum salt content in the air appears over the ocean, especially in the subtropical areas with high evaporation, reaching 5 mg/m. During strong winds, the salt spray content can increase many times. The salt content of 99 mg/m2 was recorded on the deck of a ship sailing in the waves of level 3 wind (wind speed 3.4~~~5.4 m/s) in the South China Sea. The value measured by the "Polar" scientific research ship in the waves of level 4 wind (wind speed 5.5~~7.9 m/s) in the South Pacific was 113 mg/m. The chloride content measured in the tropical air mist water in the Atlantic Ocean of the United States is about 35 mg/L. b. The concentration of salt spray over land is often affected by atmospheric conditions, the degree of evaporation of seawater, wind direction, wind speed diffusion factors, and is also related to precipitation conditions, distance from the sea, coastal landforms, etc. Generally, the salt spray content in coastal and harbor areas is lower than that in the open sea. Salt spray particles caused by waves hitting the shore and splashing waves are directed to The distance of land transportation often depends on the particle size, wind direction and speed, so that the atmospheric salt spray content decreases rapidly with the increase of the distance from the coast to the inland. At an altitude of 2 to 3 km below the troposphere, the concentration of salt particles is initially the highest in the lowest layer. When the marine air mass moves inland, it dilutes the salt particles, forming rain and large salt particles falling. The remaining small salt particles are evenly distributed in the troposphere. Figure 7 is an example obtained by actual measurement along the southeast coast of my country. For the transportation process of salt spray particles from the sea to the land, see Appendix C. 87
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GB/T4797.6—1995
1-Salt spray content in the air·area/m
2-Salt spray deposition, mg/. m·d
Distance from the coast, km
Figure 7 Relationship between salt fog content in the air, salt fog deposition and distance from the coast (measured values along the southeast coast of my country) The salt fog concentration above the ground is highest above the salt field, which can be 10 times higher than the concentration above the general coastal land. At Ximen Port in the Panama Canal area, the highest fluoride concentration in the air pollution record data was 0.15 mg/m: The sodium chloride content in the air in Haikou and Zhanjiang in my country reached 0.28 mg/m and 0.36 mg/m. 6.2.3.3 Salt fog deposition
a, Salt fog mainly settles in coastal areas near the coast. Generally, the deposition is larger within 300 to 500 m from the coast. It decreases with the increase of distance from the coast within about 80 to 1600 km inland, and reaches a constant value of about 0.35 mg/m2·a . However, in inland saline-alkali areas, the pollution caused by the dust on the ground containing salt and being blown up by the wind and floating into the air should be considered (see Chapter 7). The amount of salt fog deposition is related to the salinity, temperature, air mass characteristics and thickness of the seawater in the adjacent sea area, wind direction and speed, precipitation, air humidity, coastal terrain, forest coverage, etc., and there are large differences. Generally, areas with large waves and heavy fog will have large salt fog deposition. In coastal areas, the amount of salt fog deposition can be as high as 122.8mg/(m2·d)(44.83t/(km2·a)). Under normal circumstances, it is 12.3~60.0mg/(m2·d). According to the records of West Gate Port in the Panama Canal Zone, the total amount of salt deposition during one year reached 1400mg/(m2·d) (daily average), and the daily average recorded at the same station in March 1964 exceeded 5200mg/m2. c. During 1962-1965, the results of the actual measurement of salt fog deposition in some southeastern coastal cities in my country showed that the average value was between 10 and 33 mg/(m2·d), the maximum value was between 15 and 54 mg/(m2·d); the minimum value was between 5 and 20 mg/m2·d). Between 1959 and 1962, the highest value recorded on the British coast was 136 mg/(m2·d). During the same period, the values in Mumbai and Cochin, India were 20 mg/(m2·d) and 65 mg/(m2·d), respectively. In July 1967, the average deposition measured at the docks of Shantou, Zhanjiang, Yulin and other places in my country was 195 mg/(m2·d).
The approximate distribution of the annual average daily deposition values of salt in various regions is shown in Table 9. Table 9 Typical distribution of annual average daily salt deposition values
Islands and coastal areas in the ocean
Humid coastal and inland areas
Severity
Severe
Moderate
Deposition
mg/(m2. d)
Above 8~90
Above 0.8~~8
Reference distance
Within 50~100km from the sea
About 80~1600km from the sea
Moderately semi-humid to humid inland areas
Dry areas
6.3 Factors affecting salt spray environment
GB/T 4797.6—1995
Continued Table 9
Severity
Sedimentation
mg/(m2·d)
Mild
Slight and negligible
0.8～1.6 or above
Reference distance
More than 500km from the sea
Excluding saline-alkali areas
The concentration level of salty atmosphere is affected by many factors such as seawater wave disturbance, atmospheric evaporation, air flow movement and wind diffusion. The environmental factors affecting the level of salt fog content in the land surface atmosphere and the amount and distribution of salt fog deposition are mainly: wind direction and wind speed
When the wind blows from the ocean to the land, it is conducive to bringing the salt fog on the sea surface into the inland, increasing the salt fog content in the ground air, and the salt content increases with the increase of wind force. The amount of salt fog over the ocean increases with the increase of wind force and waves, so that the salt content in the air also increases. For example, in the South China Sea, when there is no wind, the air salt content is 1.0~～~1.65mg/m2, and when the wind force is 1~~3 (1~～5m/s), it reaches 6.2mg/m2. Inland areas far from the coast, the salt content in the air is below 0.01 mg/m2. When there is a 10m/s level 5 wind, it can reach 0.1-0.5 mg/m2. In tropical storms (typhoons), it can rise to more than 30 mg/m2.
b. Relative humidity of air
When the air humidity is high, it is easy for salt nuclei to adsorb and condense, making the diameter larger, heavier, and easier to land. On the contrary, when the air is dry, the water in the salt spray particles will evaporate, the particle size will become smaller, and dry salt nuclei will be generated, which is conducive to spreading with the wind. For example, in dry tropical areas, where there is little rainfall and low temperatures, fine-grained salt may be formed and mixed with sand and dust, and carried hundreds of kilometers inland by moderate winds. Distance from the sea
The distance that salt spray generated in the ocean is transported to the land generally depends on the particle size and wind speed. The salt content of the atmosphere often decreases rapidly with the distance from the coast to the inland. Figure 7 shows the relationship between the amount of salt spray deposition and the distance from the coast observed in the southeastern coastal areas of my country from 1962 to 1965. The relationship between the amount of sodium chloride deposition and the distance from the coast measured in Africa is given in Figure 8. 1000
(p,u)/u*2
Distance from the sea, km
Figure 8 Variation of sodium chloride deposition with distance from the coast (measured in Africa) d
Coastal landforms
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