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Prevention of electrostatic in paint production 2

Prevention of electrostatic in paint production 2

Issue Time:2020-08-22

In the paint production process, the biggest hazards caused by static electricity are explosions and fires. Although the amount of static electricity is not large, because of its high voltage, it is prone to discharge and electrostatic sparks. Therefore, in workplaces with flammable liquids, static sparks may cause fires;

In places with explosive gas mixtures or explosive fiber mixtures, an explosion may be caused by static sparks.

There are the following situations in places prone to static electricity fire accidents during the paint production process.

1.When using pipes to transport solvents and resins with resistivity in 1011-1015 ohm·cm, especially when using plastic pipes such as polyethylene, static electricity is more likely to occur. Experiments show that when using polyethylene plastic pipe to transport toluene, the static voltage can be measured as high as 25,000 volts.

For example, a paint factory used a plastic tube to pump toluene from a 53-gallon iron bucket to a storage tank. The first bucket was pumped smoothly. Then, about two-thirds of the second bucket was pumped, an explosion occurred and caused a fire. An operator died. The reason is that when the plastic pipe transports toluene, it rubs with toluene to generate static electricity, and the discharge spark ignites the toluene vapor and causes a fire.

2.When pouring a solvent with a resistivity of 107-1011 ohm·cm, if the solvent has a strong impact with the container, or the scouring splash will generate static electricity.

For example, a paint factory uses an oil tank truck to load and unload the fuel oil for the boiler. The tank truck stops at the entrance of the oil storage tank, inserts the oil drain hose into the oil inlet of the oil storage tank, opens the cut-off door and the upper cover of the tank truck tank, and starts unloading. After working for about a minute, there was a sudden explosion with a loud noise, which caused a fire. The reason is that the position of the oil pipeline is too high, as much as 3 meters from the oil surface, and the oil directly impacts the liquid surface in the tank to generate static electricity. The tank car body, the tank and the oil discharge hose and other oil unloading facilities have no conductive grounding device, and the static charge cannot release, generated electrostatic discharge sparks causing oil vapor deflagration.

3.Static electricity may be generated during the resin dilution process and the mixing process of paint mixing. Also in the filtration process of solvents, resins and varnishes, static electricity will also be generated due to the friction between the material, the container and the filter.

A paint factory used a 20-mesh wire mesh nailed on a wooden frame as a filter, and the iron red paint slurry was pumped by a gear pump through the filter into a storage tank, and a fire accident occurred. The reason is that the wooden frame barbed wire filter rests on the storage tank and is in an insulated state. The static electricity generated by the friction between the iron red paint paste (phenol alcohol paint paste) and the filter screen cannot leak and gradually accumulates. Finally, the discharge spark causes combustion.

4.When the resin is smelted, sampling with a metal sampler can also generate static electricity.

For example, when a paint factory is refining phenolic resin, a small iron spoon is used as a sampler to take samples. Burning occurred when the iron spoon left the resin surface after sampling. The reason is that when the sampler quickly leaves the resin, it rubs against the resin to generate electrostatic discharge sparks, which ignite the solvent vapor in the pot and burn.

When organic powders such as phthalic anhydride, pentaerythritol and rosin are fed, static electricity will be generated when the powder rubs and collides with the container wall or other appliances.

For example, during the production process of alkyd resin in a paint factory, when the operator put the whole package of powdered phthalic anhydride (packed in plastic bags) from the feeding port of the reactor, it suddenly burned. The reason may be that static electricity is generated when the whole package of phthalic anhydride is dumped from the plastic bag, or the feeding rate of phthalic anhydride may be too fast, causing the phthalic anhydride dust to rub against the wall of the kettle to generate static, and it will burn when released.

6.When using solvents or alkaline washing to clean containers or utensils, beware of static electricity.

A paint factory injected 20 kg of caustic soda with water into the reactor to clean the aluminum powder defloating liquid on the walls of the kettle. When the stirrer was turned on for about half a minute, the operator heard a violent reaction sound like a pot boiling in the kettle, and immediately stopped stirring. However, the aluminum powder slurry and lye were sprayed violently from the feeding port of the reactor, and went straight to the roof. After a few seconds, an explosion and burning occurred. The reason is that the caustic soda reacts violently with the aluminum powder to generate hydrogen gas, and strong friction occurs when it is sprayed from the mouth of the kettle, generating high-potential static electricity, which causes an explosion after discharge.

The hazards of static electricity to paint production, in addition to causing explosions and fire accidents, can also cause electric shock injuries.

When using a rubber mixing machine to produce various types of tablets, the rollers of the rubber mixing machine and the paint flakes are violently rubbed and squeezed, which will generate a higher potential. When the operator approaches the charged rolls and paint flakes, they will receive electric shocks. The degree is not directly fatal, but it may cause panic due to inductance, causing accidental secondary accidents such as falling and solid fall. A paint factory once conducted an electrostatic test on the vinyl chloride paint sheet rolled by a rubber mill in winter, and the highest electrostatic potential measured was up to 50 kV.