Gravure workshop fire and explosion conditions
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The damage caused by the fire in the gravure workshop is devastating. Under what circumstances will this happen? How to avoid?
Condition of fire and explosion
The gravure coating workshop is a fire and explosion. It is a chemical reaction between organic solvents and oxygen. It must have three conditions at the same time:
1. The VOC concentration is greater than 100% of the LEL, that is, exceeding the lower explosion limit.
2. There is a source of ignition, that is, the local temperature exceeds the ignition point of the solvent.
3. There is sufficient oxygen near the burning point.
All fire accidents are the result of the simultaneous occurrence of these three necessary conditions. Precautionary measures are nothing more than avoiding the three necessary conditions at the same time. Because the oxygen in the air is generally sufficient, it is normal to avoid the simultaneous occurrence of the first two conditions, preferably one does not appear.
What are the higher concentrations of VOC in the gravure coating workshop?
1. Inside and top of the ink tank or glue bucket. Therefore, if you use an electric ink pump, you must use an explosion-proof motor or an air pump.
2. Near the coat head. Due to the constant stirring of the coating roller, the surrounding concentration of the ink glue tank and the plate roller is high, and if there is electrostatic discharge, it is easy to ignite and burn.
3. The inside of the oven where the printing coater is closer to the feed port. In particular, most of the solvents are now fast-drying solvents, and the heating temperature is high. Most of the solvents are evaporated inside the oven near the feed port. The concentration is the highest here. If the amount of air is insufficient, the coating is thick. Larger, it is possible to exceed the lower explosion limit.
Precautions
1. Eliminate the source of fire. The printing house does not allow smoking and other open fires in the workshop. The most prone to occur are sparks caused by static electricity and sparks caused by collision or friction. Especially in the above three places, there should be no sparks. Therefore, the inside of the oven or the glue bucket, the applicator head, and the printing applicator should be cleaned from the inside of the oven.
Static elimination is to eliminate the local high voltage on the surface of the material. At present, there is a method of grounding through the conductor and an electrostatic generator elimination method. The electrostatic generator elimination method is to generate positive and negative ions through the generator to neutralize the voltage on the material, and the electrostatic generator is a discharge process in the work itself, so it cannot be too close to the place where the VOC concentration is high, and there is a hidden danger in itself. Advocate adoption. The method of grounding the conductor is economical and practical, generally using copper wire, copper wire, aluminum foil close to the material, or adding an electrostatic brush and then grounding the copper wire or the electrostatic brush. The problem that is easy to occur is that the copper wire or the electrostatic brush is connected to the ground wire through the frame or the guide roller. In the middle, the insulation may be caused by the corrosion of the frame contact surface, oil, or the like, or the machine itself may be disconnected due to the ground wire and the joint is broken. . It is recommended to connect copper wire or electrostatic brush and ground wire directly with special wiring.
Friction and fire are caused by collisions or frictions. In the past, accidents occurred when the above metal fell and hit the ink tank to generate sparks and ignite the solvent.
When the air humidity is high, the static electricity on the film or paper is easily leaked through the air. Therefore, maintaining proper humidity in the workshop also plays a role in eliminating static electricity.
2. A VOC concentration alarm is installed in the oven. Once the concentration is too high, the VOC concentration alarm will automatically alarm.
3. Install carbon dioxide fire extinguishing device, once the fire will automatically spray carbon dioxide fire.
4. Do not put glue, solvent and ink in the vicinity of the gravure press, it is best to be isolated from the machine, in order to prevent the surrounding solvent from igniting and exploding when a fire occurs together, resulting in a major accident. It is best to keep the spare material away from the more dangerous places, and not too much.
5. Ensure that the air intake of the oven cannot be lower than a minimum value. The minimum air volume should ensure that the VOC concentration is less than 25% of the LEL.
Gravure printing machine, coating machine, and compound machine oven will not cause fire and explosion under normal conditions due to the large amount of air in and out. The occurrence of a fire explosion is often caused by insufficient oven temperature, the operator shuts the intake and exhaust damper too small, or the exhaust fan does not work due to line failure or belt breakage, and the VOC content of the material is large.
6. There is a pressure relief port on the oven. Once the pressure of the oven rises to a certain extent, the pressure relief port automatically opens, so that the oven cannot burst.