Basic measures to prevent electrostatic hazards
To prevent static electricity, first try to prevent static electricity from being generated. The static electricity generated should be limited as much as possible to the extent that it is not dangerous. Secondly, the generated electric charge is leaked or neutralized as soon as possible, thereby eliminating the accumulation of large amounts of electric charge.
1, reduce friction and electrification
In the transmission, the slip on the belt and other transmission parts should be reduced. If the belt is to be tight, maintain a certain tension and avoid overload operation. The belts to be used should be made of conductive tape or conductive triangle tape with high transmission efficiency. In the equipment for conveying flammable gas, flammable liquid and flammable and explosive objects, direct shaft (or coupling) transmission should be adopted. Generally, belt drive should not be adopted; if belt drive is required, effective anti-static measures must be taken. Limiting the flow rate of flammable and flammable liquids can greatly reduce the generation and accumulation of static electricity. When the liquid is advected, the amount of static electricity generated is proportional to the flow rate, and the cut is independent of the inner diameter of the pipe; the amount of static electricity generated when the liquid is turbulent is proportional to the flow rate of 1.75, and is proportional to the inner diameter of the pipe of 0.75. . At present, the standards for controlling the flow rate in various countries in the world are not uniform. In short, when determining the flow rate, not only the inner diameter of the pipe, but also the nature of the fluid, the composition and quantity of the impurities contained, and the material of the pipe, etc., should be considered. The flammable liquid flowing in the pipeline, even if it has a high average charge density, often has a large capacitance in the pipeline and does not show a high voltage. It is cut in the pipeline and there is no air, so it does not cause Burning and exploding. In this case, although static electricity does not pose a danger inside the pipeline, its serious hazard is mainly at the exit of the pipeline, which must be taken seriously.
2, electrostatic grounding
The role of electrostatic grounding is to discharge the charge that may accumulate on the conductor, so that the conductor is equipotential to the earth, so that the potential difference between the conductors is zero.
A. Static grounding
Electrostatic grounding is a way to provide a static charge leakage path. In fact, the generation and leakage of static electricity are parallel, and it is a process of inputting and outputting electric charges to a charged body. The electrostatic potential accumulated on the object, when the capacitance to the ground is constant, depends entirely on the difference between the amount of electricity generated by the object and the amount of leakage. The electrostatic electrification rate is a random variable. Changes over time can increase slowly or dramatically. In order to ensure the electrostatic safety of the object, it is solved by leakage (grounding). The application range of electrostatic grounding is conditional. Not all objects can be charged by means of grounding. In general, metal conductors and equipment that may cause fires, explosions, and safety hazards, non-metallic materials that are electrostatic conductors, and the human body must be grounded today. At the same time, it is also necessary to consider the problem of grounding of the whole system. Otherwise, the grounding will cause electrostatic discharge. For example, when a charged human body (or object) in an insulated state approaches or comes into contact with a grounding body, a discharge spark is generated. Conversely, when a grounded human body (or object) approaches a lively encouraged conductor, a spark discharge is also generated.
B. Static grounding method
(a) Direct grounding: Direct grounding is electrical grounding, that is, using a metal wire to connect the charged body directly to the grounding trunk.
(b) Indirect grounding: Indirect grounding is a grounding method in which an object other than metal is electrostatically grounded, and all or part of its surface is closely connected to the grounding body. In other words, the charged body and the grounding body are connected by an electrostatic conductor having a certain resistance value.
3, reduce the resistivity
When the resistivity of the substance is less than 106 Ω·cm, the accumulation of static charges can be prevented.
A. Add conductive filler
The resistivity is lowered by incorporating a substance having good electrical conductivity. For example, in the rubber refining process, a certain amount of graphite powder is blended to make it a conductive rubber; in rubber production, a small amount of metal powder and graphite powder are added to make it a low-resistance plastic; in industrial oil, Mix a small amount of alcohol or a small amount of acetic acid; inject some metal soap such as magnesium oleate into benzene to reduce its electrical resistivity.
B. Using antistatic agent
The antistatic agent uses fat and oil as raw materials, and its main component is quaternary ammonium salt. Its function is to adsorb the moisture in the air on the surface of chemical fiber, rubber, plastic and other objects, and increase the electrical conductivity. Such as SN cationic antistatic oil agent also has a certain effect. In the chemical fiber, the propylene oxide hydrophilic gene is added; the ASA3 antistatic additive is added to the liquid such as aviation kerosene; and the electrostatic agent is applied on the photographic film, so that the surface resistivity or volume resistivity can be greatly reduced and reduced. The accumulation of static electricity.
4, increase the air humidity
When the relative humidity of the air is above 65-70%, the surface of the object tends to form a very thin film of water. The water film can dissolve carbon dioxide in the air, so that the surface resistivity is greatly reduced, and the static charge is less likely to accumulate. If the relative humidity of the surrounding air drops to 40-50%, the static electricity is not easily dissipated, and it is possible to form a high potential. A common method of increasing the humidity of the air is to spray water mist into the air. Rotary fan sprayers are generally used, but the machine is not explosion-proof and must be blown from outside the wall.
5, air ionization method
By using a static eliminator to ionize oxygen and nitrogen ions in the air and turn the air into a conductor, the static charge on the surface of the object can be effectively eliminated. Commonly used static eliminators are:
(a) Inductive static eliminator
It can also be divided into steel grounding induction, brush induction, needle tip induction and so on. Mainly used in the production and processing industries of paper, rubber, textile, plastics.
(b) High voltage static eliminator
She mainly has external, power frequency AC, thyristor, AC high frequency and high voltage. In the chemical, textile and other industries, it can be selected according to different requirements. In addition, there are high-pressure ion currents, radioactive radiation, etc., which are suitable for other special places.