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Electrostatic hazards and prevention of containerized bag packaging in storage and transportation

with the development of recent years, China has become the world's largest containerized bag production base. However, more than 80% of the containerized bags produced in China are exported, and the requirements for containerized bags in foreign markets are becoming higher and higher. With the continuous expansion of warehousing function and scale and the extensive use of containerized bags in bulk packaging, how to control and prevent the harm caused by static electricity of containerized goods has attracted great attention in Europe and the United States

in order to strictly control the quality, strive for a larger foreign market, and ensure the transportation safety of goods, it is extremely important to understand the harm and prevention knowledge of static electricity generated by containerized goods in storage

the harm of static electricity has received considerable attention in the production of packaging industry, but in the storage and transportation of packaged goods, the harm and prevention of static electricity is still a weak link

causes of static electricity in the storage of packaged goods

there are two main reasons for the generation of static electricity: first, internal reasons, that is, the conductive characteristics of substances; The second is external causes, that is, mutual friction, rolling, impact, etc. between substances. The packages of many commodities have the internal cause of static electricity. In addition, they cannot be separated from handling, stacking, covering and other operations in storage, so friction, rolling, impact and so on will inevitably occur between packages. The plastic packaging of general commodities is easy to generate static electricity due to mutual friction in the stacking process

the harm of static electricity in the storage of packaged goods

on the surface of the packaging, but for crystalline polymers, it accumulates to form a high electrostatic potential, which is prone to electrostatic sparks. Its harm is mainly manifested in two aspects: one is to cause deflagration accidents. For example, when the contents of the package are flammable substances, and the steam they volatilize reaches a certain proportion with the air, or when the solid dust reaches a certain concentration (i.e. explosion limit), in addition, the research group cooperates with Professor Zhao Qiang of Ruijin Hospital Affiliated to Shanghai Jiaotong University and ye Xiaofeng, deputy chief physician team, and will explode in case of electrostatic sparks. The second is to produce electric shock. For example, electrostatic high potential discharge is generated during the handling process, which brings discomfort of electric shock to the operators, which often occurs in the handling of plastic packaged goods in the warehouse. In the process of handling and stacking, electrostatic high potential discharge is generated due to strong friction, and even the operators are knocked down by electrostatic discharge

prevention of electrostatic hazards of packaging materials in storage

the following methods are generally used in the storage of packaged goods to prevent and control the hazards caused by static electricity

1. The packaging should be controlled to avoid static electricity as far as possible. For example, when handling flammable liquids, it is necessary to limit their violent shaking in the packaging barrel, control their loading and unloading methods, prevent different oil products from leaking and mixing, and prevent water and air from entering the steel barrel

2. Take measures to make the generated static electricity dissipate as soon as possible to avoid accumulation. For example, install good grounding devices on tools such as handling, increase the relative humidity of the workplace, lay conductive floors on the ground, and spray conductive paint on some tools

3. Add a certain amount of counter charge to the charged body to avoid the rise of static voltage (such as inductive electrostatic neutralizer)

4. In some cases, the accumulation of static electricity is inevitable, and the rapid rise of static voltage may even produce static sparks. At this time, measures should be taken to ensure that although it discharges, it will not cause an explosion accident. For example, fill the space where flammable liquids are stored with inert gas, install alarm devices, and adopt efficient exhaust devices, so that the flammable gas or dust in the air cannot reach the explosion limit

5. In places with fire and explosion hazards, such as places where dangerous chemicals are stored, the staff should wear conductive shoes and electrostatic work clothes to eliminate the static electricity carried by the human body in time. Electrostatic hazards related to container bags and the use of anti-static container bags

whether it is powder, fine particles, or granular substances, static electricity will be generated during transportation. Static electricity is essentially a surface phenomenon. Because the total surface area of a large number of powders is very large, the static voltage generated is very high, and the amount of stored charge is also quite large. Each tiny particle can only carry a small amount of charge. However, when the particles are piled up in large quantities, such as filling into container bags, the accumulated charge will be very large

during the use of container bags, there are usually three situations that will produce potential electrostatic threats. When filling container bags, the filled substances will usually be powered on during the transportation process

from the perspective of electrostatic ignition hazards, container bags are usually divided into four categories according to their structures. This classification method is widely used in Europe, so the fatigue resistance of rubber vibration damping products is closely related to their service life. In June, 2003, CENELEC published CLC/tr50404 "electrics code of practice for the avoidance of hazards duo tostatic electricity". This is a very comprehensive electrostatic operation standard in all fields of industry, in which a chapter points out in detail the electrostatic safety use specification of container bags. The standard divides containerized bags into four categories: type A and typ. At present, plastic packaging materials account for more than 30% of the total amount of various packaging materials. E B, type C and type D

type a container bags have no special electrostatic safety characteristics, so they are not recommended for the treatment of sensitive flammable dust and powder. In addition, they cannot be used in the presence of dust clouds or flammable solvent vapors. This kind of container bag is usually made of ordinary woven polypropylene cloth, which is an insulator. Sometimes, according to the use requirements, the type a container bag will be treated with lining bag or surface coating

type B container bag is similar to type A, and is also made of ordinary woven polypropylene cloth. However, the breakdown voltage of woven fabric of type B bag shall not be higher than 4KV. This means that type B container bags will not generate propagating brush discharges. This is an important classification, that is to say, the only discharge that can be generated on the container bag is low-energy brush discharge. If the propagating brush discharge can be excluded, and the maximum energy of brush discharge is 4mj, it is reasonable to believe that this type of container bag is safe for combustible gas environment with a minimum ignition energy of no more than 4mj. Similarly, for combustible dust with ignition energy not exceeding 4nd, this kind of container bag is also safe. However, type B container bags cannot be used in flammable hydrocarbon vapor environment. It must be noted that the container bags manufactured by some factories meet the classification standard of type B, but they will still cause accidents. For example, when tested by the testing agency, it meets the type B standard, but in actual use, the breakdown voltage is higher than 4KV due to the lining bag and the coating on the surface of the bag, which makes the type B bag actually become type A

type C container bag is designed for sensitive flammable environment, including flammable hydrocarbon solvent vapor environment. This kind of container bag is made of conductive cloth or woven cloth coated with conductive/anti electric coating. Conductive cloth is actually a woven cloth interwoven with conductive fibers/flat wires. In some designs, the conductive wires are parallel with a spacing of 20mm. Another design is to weave the conductive silk into a winding shape, and the wires intersect vertically. Conductive wire is usually conductive flat wire or conductive metal wire

type D-type container bag has antistatic or electrostatic dissipation characteristics and does not need to be grounded. At present, most type D container bags on the market are made of thin semi conducting wires interwoven into woven cloth. Unlike the type C container bag design, these semi conducting wires are parallel but not cross-linked. This type of container bag may have electrostatic elimination coating

the fire and explosion caused by containerized bags are basically attributed to static electricity. In order to solve this problem, some new "electrostatic safety" containerized bags have been developed and have been commercialized

reprinted from: China business

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