1 combustible substance powder
The most serious accident in electrostatic powder spraying operation is the combustion and explosion caused by powder spraying, for three reasons: first, powder coating is flammable, which may cause combustion and explosion; Second, during normal spraying, if the distance between the sprayer electrode and the workpiece (or other objects) is improper, sparks may occur, and if the constant current source control fails, the spark energy may exceed the minimum ignition energy of suspended powder explosion; The third is the mixing of powder and air in the powder spraying bin. If the recovered air volume is not enough to reduce the mixed concentration of powder and air to the allowable concentration, it is easy to reach the lower limit of explosion concentration. When the electrostatic ignition energy exceeds the minimum ignition energy of powder, it may cause an explosion accident.
2 electrical fault
There are many electrical accidents in electrostatic powder spraying, among which the failure rate of spraying room, spray gun device, electric furnace, drying channel and other equipment is high. The electric shock caused by electrostatic high voltage of spraying device is often caused by short circuit fault of electrical circuit; Aging of electric heating elements of electric heating furnace, confusion between static electricity and electrical grounding, wrong connection or poor grounding will all cause electrical appliances to be electrified and hurt people; Accidents caused by abrasion and leakage of power cable insulation layer of mobile equipment.
3 Mechanical accident
The harm of mechanical accidents in electrostatic powder spraying can not be ignored, especially degreasing, derusting, phosphating and water washing in wet pretreatment process, spraying equipment or tank immersion equipment, preheating furnace of shot blasting and sand blasting equipment, powder spraying bin, curing furnace and cooling device in dry pretreatment process are prone to accidents. Workpieces or catenary, hook parts and falling parts may cause serious damage to equipment and even explosion accidents.
4 spraying process
From the process analysis, the accident factors of electrostatic powder spraying include many aspects, such as process rationality, parameter suitability, equipment connection between processes and so on. Whether the interlocking design of power system control device is reasonable; Whether the setting of safety warning signs is reasonable and whether the explosion-proof measures are effective; Whether the safety alarm system and fire fighting system equipment are appropriate, especially the speed of information perception and processing mode. From the perspective of operation and management, the improvement of labor protection measures is mainly considered; The implementation level of safety operation procedures and standards; Technical training for operators before taking up their posts, including safety education; Effectiveness of safety technical inspection; Equipment maintenance, maintenance cycle and quality; Safety accident emergency equipment, including emergency repair equipment, article preparation and other factors.
Accident prevention countermeasures
1 general layout of painting workshop
The painting workplace should be arranged on the windward side of the minimum frequency wind direction all the year round in the factory area, leaving a sufficient safe distance from the factory front area, crowded places and factories with high cleanliness requirements. In principle, it should be set up as an independent factory building, and at the same time, it should be set up with fire exits according to the relevant provisions of GB500 16-2006 Code for Fire Protection in Building Design to ensure more than two unblocked entrances and exits. The emergency evacuation distance between the painting operation station and the entrance and exit safety door in a super-large factory building is generally not more than 25m. When the painting operation adopts a closed painting process and keeps the negative pressure in the closed painting space, and a combustible gas concentration alarm system or an automatic explosion suppression system (including qualified explosion relief devices) is provided, and the fire protection zone of the painting section accounts for less than 20% of the painting workshop area, the workshop can determine the fire protection requirements according to the D and E production workshops in the production fire risk classification.
2 operator safety management
Operators must be familiar with equipment systems, including emergency rescue facilities, fire fighting facilities and alarm devices, and be skilled in operation. Operators should receive training before taking up their posts, understand the safety performance of the equipment, and consciously abide by the safety operation procedures. Operators must be familiar with and abide by personal labor protection knowledge, and require dust collection measures when cleaning dust. Check and maintain the equipment regularly to ensure that the equipment is in good condition. Full-time security officers must conduct inspections and regular inspections on the production site.
3 Safety of painting equipment
The design of painting equipment should meet the national general safety requirements and the professional safety requirements of painting operation safety regulations. Coating equipment and instruments shall have the following technical data: instruction manual (including safety instructions); Complete product nameplate (name, model, main parameters, manufacturer's name and address, manufacturing time).
Spraying equipment and other mobile electrical equipment should be equipped with dust covers, and their power cables should be supported by brackets; Slack laying to prevent abrasion of insulation protection layer and looseness of plug-in port. Lighting equipment and switches used in powder coating operation area must meet explosion-proof and dust-proof requirements. The electrical interlocking system between power supply, powder supply system and ventilator must be tested regularly. Equipment conductors located in the painting operation area, including transmission chain, powder spraying bin, air duct, recovery device, etc. It must be firmly grounded to prevent the electric charge generated by arc discharge from accumulating on the grounded insulated conductor near electrostatic spray gun.
Strictly carry out routine inspection of pipelines, pumps and valves in the pretreatment equipment system, set pressure reducing valves and stop valves on the steam pipeline in sections, and monitor whether the heater, heat exchanger and steam pipeline are overpressure. Curing furnace must be equipped with air circulation duct or exhaust duct to prevent the accumulation of irritating volatile atmosphere or combustible gas caused by long-term operation. Pipes, pumps and valves of oil and gas drying and curing equipment should be regularly overhauled, and no leakage is allowed. The pretreatment of painting includes mechanical pretreatment such as shot peening, power tool polishing and high-pressure water cleaning, chemical pretreatment such as degreasing, pickling, neutralization, surface adjustment, phosphating, passivation and cleaning, as well as organic solvent treatment of workpieces and removal of old paint. The process equipment involved in the pretreatment part of painting shall meet the requirements. Except for oversized workpieces, any paint spraying process should be carried out in the painting (powder) room. The ventilation of painting (powder) room should be organized airflow, and its ventilation must meet the requirements of explosion-proof safety and industrial hygiene at the same time. All kinds of coating equipment, spraying equipment and auxiliary devices entering the coating (powder) room shall meet the safety technical conditions for use in dangerous areas with explosive gas environment.
The workshop specially set up for painting operation or the designated space with burning possibility should be classified as a mild danger zone, but all open flames must be prohibited to prevent foreign fire from entering. Painting engineering design should meet the requirements of relevant fire resistance rating and explosion-proof and safe evacuation of factory buildings. Building structures, components and materials should be selected according to the requirements of fire and explosion prevention; The minimum width of the evacuation door should not be less than 0.8m, and it should be opened in the evacuation direction; The clear width of the evacuation walkway should not be less than1.4m; ; Evacuation facilities should be equipped with emergency lighting and safety evacuation signs. The painting workshop should correctly arrange the process routes of different areas, take necessary partition and isolation facilities from the design elements conducive to safety, hygiene, fire protection, energy saving and environmental protection, and pay attention to the fire prevention spacing and fire prevention zoning. The central air conditioning pipeline in the painting workshop should be equipped with fire dampers when entering the fire danger zone.
Choose a spray gun with excellent performance. Safe low-voltage gun feeding and circuit feedback technology should be controlled by constant current source output. When the spray gun electrode is close to the grounded workpiece, the high voltage generator can reduce the output voltage accordingly, and the power supply can be automatically turned off when it is short-circuited with the ground. Choose reasonable process parameters, use low voltage as far as possible for electrostatic spraying, and the voltage output is 30 ~ 70 kV.
The ventilation rate of the powder spraying bin must be adjusted according to the opening section to ensure that the powder does not escape at the opening of the powder spraying bin. At the same time, the total recovered air volume during spraying should ensure that the concentration of overspray powder is at the lower explosion limit.
The recovery and purification device connected with the powder spraying cabin should be provided with a quick pressure relief port facing the outdoor space to prevent explosion accidents. Grid or magnetic separation device should be installed at the entrance of the dust suction pipeline with high wind speed in the powder spraying bin to prevent metal or hard objects from entering the pipeline to generate sparks due to friction and collision. A powder cleaning mechanism should be set in the powder spraying cabin, and it is best to clean powder continuously to keep no powder accumulated in the cabin. Recover the wind speed in air ducts, horizontal pipes, bends, etc. The powder suction device must be large enough (≥ 15m/s) to ensure that there is no powder accumulated in the pipeline and prevent the dust explosion in the spraying space from causing a more destructive secondary explosion. A flame detector and a linkage fire extinguishing device are adopted in the powder spraying bin, and a partition valve is arranged on the communication air duct between the powder spraying bin and the recovery device.
Repair and correct the hook regularly to prevent the hook accident of the transmission chain caused by the looseness and skew of the hook; It is also necessary to prevent the hanger from swinging and falling off, causing collision sparks between electrodes of electrostatic circuit and insufficient distance to cause critical discharge or short-circuit discharge.
4 electrical safety
The electrical safety of the painting workshop must meet the overall explosion-proof requirements, that is, the motors, electrical appliances, lighting, lines, switches and connectors meet the explosion-proof safety requirements, and it is forbidden to connect temporary wires indiscriminately. In addition, most of the accidents in electrostatic coating are due to the ungrounded grounding, resulting in an isolated state. Conductive objects in the paint spraying room must clearly distinguish between high voltage potential and grounding potential, and they must be grounded except those or parts where high voltage is to be applied.
According to the grounding mode, the safety countermeasures are as follows: the operator must wear conductive shoes; Thoroughly clean the soles; Conductive objects in the painting room must be grounded; Cleaning with solvent tank fixed and grounded; Operators using electrostatic portable paint spray gun must operate the paint spray gun by hand; The hanger for hanging the coated object shall be sufficiently cleaned to keep the coated object at ground potential; The floor of the spray booth should always be conductive. For the coating machine or coating tank that may be charged, fully ventilate before grounding, and then use it after removing the residual charge. Key points of operation: the high pressure must be turned off at the end of painting, and the high pressure must be confirmed before cleaning. When conductive paint is used and the paint supply system is insulated from the ground, the paint tank is grounded first. If solvent is used to clean the insulating material, apply high pressure after confirming that the solvent is dry; Regularly clean the coating dust pollution of the coating machine; Do not use a coating machine that will retain solvent vapor to prevent pollution; Tighten loose or fallen high-voltage cables or coated hoses; In order to prevent discharge, an interlocking device is provided for high-voltage equipment. The key points of safety control of coating machine system and its auxiliary equipment are: setting necessary interlocking devices; If sequential actions are required, operations outside the sequence cannot be specified; Appropriate interlocking devices shall be provided for conveyors, entrance and exit doors, air supply and exhaust, fire fighting devices and coating machines; Set up safety fences or devices to prevent operators from entering; Use a longer hanger to reduce the contact point between the conveyor and the hanger; Adopt automatic cleaning system; Set automatic fire extinguishing device.
In addition, high-rise workshops should have facilities for preventing direct lightning, and precision electrical equipment and control systems should have facilities for preventing induced lightning. It is forbidden to set up or enter electromagnetic radiation equipment, facilities, tools and articles that are prone to electrostatic discharge in fire and explosion danger areas. In explosive dangerous places, when anti-static grounding and lightning protection grounding are difficult to separate, grounding resistance should be selected according to lightning protection grounding resistance.
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