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In recent years, with the continuous improvement of China's manufacturing industry, CNC plasma cutting machines have been widely used in industrial enterprises, which has improved the overall level of China's machinery manufacturing industry. The large amount of smoke generated by the CNC plasma cutting machine in the process of use diffuses the entire manufacturing workshop, which not only endangers the health of employees, but also pollutes the atmosphere. More and more enterprises pay attention to and pay attention to the treatment of dust and dust of modern industrial enterprises.
1. Dust and hazards generated by the survival workshops of modern industrial enterprises
Welding equipment used in industrial production workshops, such as manual arc welding, CO2 gas shielded welding machine, argon arc welding machine, submerged arc welding machine and other welding equipment will produce a large amount of welding fumes; in the metal cutting process, some enterprises due to For the processing precision, a numerically controlled plasma cutting machine is used. During the plasma cutting process, a large amount of soot is generated instantaneously due to metal melting and high-speed gas collision; in the metal grinding process, a large amount of metal dust is also generated.
Metals produce various harmful gases and fumes during welding , grinding and cutting. These harmful gases and soots are characterized by very small particle sizes, accounting for about 70% below 0.5 microns and about 30% above 0.5 microns. The ability to suspend is strong. The harmful effects of these harmful gases and smoke can be summarized into three aspects: 1. damage to the central nervous system of the human body; 2. damage to the human body; 3. damage to human skin and respiratory tract. The operator welding one hour is equivalent to the danger of him smoking 58 boxes of 20 cigarettes.
Scientific research and health queries indicate that there are many inhalable substances (such as manganese oxide and potassium and sodium oxides) in cutting dust, and once these substances enter the human body, they will cause great damage to the human body. The cutting operation of the portable CNC cutting machine in the case of smoke and dust for a long time has a higher proportion of respiratory diseases such as chronic bronchitis than other people, and the inhalable substances will accumulate in the bones and blood of the human body, causing the function. Decline and even stimulate cancer, especially in recent years, with the use of many cutting materials containing chemical components such as Cr, Mn, Ni, etc., the impact of cutting soot on occupational well-being is increasingly severe.
(Figure 1: The light generated by the light gantry during plasma cutting fills the entire workshop)
It can be seen that these dusts are very harmful to the human body. We must adopt effective treatment methods to improve the working environment of workers and control the pollution of the atmospheric environment.
Second, the main way of numerical control plasma cutting machine dust control
Because plasma generates a large amount of harmful and toxic gases during the cutting process, most domestic enterprises use wet dust removal method and dry dust removal method.
1. Wet dust removal method.
With the wet dust removal method, the usual practice in China is before the CNC plasma cutting.
Make a water cutting platform and place the cut material on the surface of the sink or in water for cutting. If the cutting material is placed on the top of the water tank, the smoke generated by the cutting process will be significantly reduced, but due to the impact of the compressed air, there is still some smoke and dust overflowing, and the treatment effect is not ideal; if the cutting material is placed under the water tank, the plasma The cutting torch cuts the material under water. This method can eliminate the harm of harmful toxic gas to the operator and the workshop environment, but it will affect the cutting efficiency, that is, the cutting speed will decrease, the loading and unloading auxiliary time will be lengthened, and the aluminum cutting and cutting Metal materials such as magnesium also need to be explosion-proof, to prevent the position of the workpiece from moving, and more importantly, to cause water pollution. Due to the complicated chemical composition of the dust generated by cutting, the treatment is quite difficult and the cost is very high.
(Figure 2: Wet cutting platform with sink)
2, dry dust removal method
The dry dust removal method is to add a set of soot trapping device for the CNC cutting platform, and directly transport the collected soot to the soot filter purification equipment, and then discharge after the treatment reaches the standard. The smoke generated by plasma cutting is basically formed below the workpiece slit, so the suction negative pressure cutting platform becomes the most common smoke trapping device.
In order to save investment and improve the efficiency of exhausting, the maximum amount of soot collected can be achieved with the minimum air supply volume. Generally, only the area being cut is vacuumed, so the cutting platform is divided into several uniforms along the main guide rail of the cutting machine. The enclosed small area has an air outlet on the side. The dry dust removal method is widely used because of its simple structure, reliable operation and good dust removal effect. As shown below:
(Figure 3: Single-side lower exhaust filter type dry dust removal)
Third, the filter cartridge type dust collector to clean the dust of the plasma cutting dust
Plasma cutting dust removal and cleaning methods are generally common in two ways, namely direct suction and blowing.
Suction type.
(1) Direct suction dust removal system.
The direct suction type generally has three methods according to the size of the plasma cutting work surface, namely, a single-side direct suction type dust removal system, a double-side lower suction damper type dust removal system, and a four-side lower suction damper type dust removal system.
1. Single side direct suction dust removal system. That is, a plurality of air-venting chambers of equal width are installed on one side of the lower part of the cutting machine platform, and each of the air-venting chambers is designed and installed with a mechanism for opening the damper, and the switch is triggered as the cutting gantry moves, and the smoke generated by the cutting machine is sucked in time correspondingly. The air duct directly enters the dust collector to purify. This method is mainly adapted to the cutting work platform within 3m.
(Figure 4: Single-side lower draft cutting structure diagram)
(Figure 5: Structure diagram of the damper type ventilating workbench)
2. Double-side lower damper type dust removal system. The dust removal system is provided with a ventilating duct on each side of the cutting platform. This form of dust removal is suitable for platforms with a cutting platform width between 3 and 5.5 meters.
(Figure 6: Double-sided lower exhaust cutting structure diagram)
(Figure 7: Legend for double-sided lower draft cutting application)
3. Four-side lower damper type dust removal system. When the effective width of the cutting platform is relatively large, the method of exhausting and dusting by the four air ducts is adopted, that is, two air ducts with dampers are added in the middle of the cutting platform, which is equivalent to equally dividing the cutting platform into two sides in the width direction. The lower ventilating workbench is together.
(2) Double suction dust removal system.
The dust removal method is mainly on one side of the cutting platform and a sliding suction channel, which moves the suction port. On the other side of the cutting platform is a blower with a small axial fan, and the air outlet is fixed to the cutter at the same time and is kept in line with the cutting head. The lower part of the cutting platform is a drafting duct with a vertical plate, which is always kept in a limited width of the cutting, that is, a portion where smoke is generated. This type of dust removal method not only has a simple structure for cutting the platform, but also uses less air volume. Classification of blow suction dust removal system: Due to its structural characteristics, this dust removal method is not suitable for platforms with a cutting platform width of less than 2.5 meters. According to the width of the platform, it can be divided into a single sliding air duct blowing and dust removing system, a double sliding air duct blowing and dust removing system; and an airborne blowing and dust removing system.
(Blowing suction sliding duct diagram)
1. Single sliding air duct suction and dust removal system. According to the structural characteristics of the platform and the airflow structure characteristics, in order to achieve a good dust removal effect, there is a certain requirement for the width of the cutting platform. Generally, this type of dust removal method is not applicable to platforms with a cutting platform width of less than 2.5 meters. For the effective width of the cutting platform between 3 and 4.5 meters, the dust removal effect is ideal. The dust removal method has certain requirements on the coverage of the steel plate on the cutting platform. When the coverage of the steel plate reaches 80% or more, the dust removal effect is obtained. optimal.
(Single sliding air duct suction and dust removal system schematic)
2. Double sliding air duct suction and dust removal system. This type of dust removal method is mainly for the width of the cutting platform.
In the working platform of more than 5 meters, the wider the working platform, the greater the air volume makes the dust removal effect less and less ideal. In order to make this large-span cutting machine also have a good dust removal effect, we design the cutting platform. The workbench is divided into two rafts on average in the width direction, and there is a sliding suction channel on each side of the workbench. The schematic diagram is as shown in the figure below, which is equivalent to two blowdown type dust removal systems.
(Double sliding duct blowing suction dust removal diagram)
3. Airborne dust removal system. This kind of dust removal method is also the evolution of the blow-up type dust removal system. The biggest advantage is that there is no space for the pipeline to stand in the workshop. The whole set of dust removal equipment is placed on the gantry to move with the cutting machine. This kind of dust removal method is more suitable for platforms with a small cutting platform width. The larger the air volume used, the larger the volume of the dust removal equipment unit, which makes the manufacture of the cutting machine gantry difficult. The structure is as follows:
(Airborne dust removal system legend)
4. Comparison of plasma cutting and dust removal before and after opening.
(Before dust removal is turned on) (after dust removal is turned on)
Fourth, the main features of the filter cartridge dust collector
1. Selection of filter cartridges. At present, the main use of film polyester filter cartridge and flame retardant nano filter cartridge.
The fiber gap of the membrane polyester filter cartridge (such as cotton cloth, cotton satin, paper and other traditional cellulose) is 5~60um. When the smoke passes, some dust particles in the dust will enter the filter and block. The filter element; when the blocking condition is gradually deteriorated and the effective cleaning can not be performed, the gas resistance of the filter element will rise, and the gas flow rate that can pass will also decrease. If there is no automatic cleaning, the filtering effect will drop rapidly.
The surface of the filter material used in the flame-retardant nano filter cartridge is attached with a layer of polytetrafluoroethylene film, and the smallest mesh hole can be
Blocks most submicron dust particles; submicron dust particles accumulate on the surface of the filter material and form a permeable dust cake. Most of the dust particles are blocked on the outer surface of the filter material and cannot enter the filter material inside. Sweeping can be cleared in a timely and effective manner. The filter material has a relatively high filtration efficiency, and is at least 3 to 5 times higher than the conventional filter material; and the service life is more than 2 times higher than the conventional filter material, and the filtration efficiency can reach 99.9% or more. In addition to the greatly improved filtration accuracy, it also enhances the cleaning effect, prolongs the service life and reduces the operation and maintenance costs.
2. Automatic cleaning device. The dust collector must be equipped with a PLC automatic pulse jet cleaning device. When the purifier is operated for a period of time, fine soot is adsorbed on the surface of the filter material, so that the permeability of the filter material is lowered. When the system pressure difference exceeds a certain set value, the differential pressure signal outputted by the differential pressure sensor will activate the pulse generator. The pulse generator starts the pulse injection valve, and the clean compressed air is ejected from the valve port, and the ejector airflow is applied to the filter cartridge. The pulse is sprayed; the fine dust adsorbed on the surface of the filter material falls off from the surface of the filter drum under the action of the air stream, and falls into the dust collector of the lower part. In order to improve the anti-blowing and cleaning effect, the series of dust collectors are designed to be combined with online and offline cleaning methods. Due to the high filtration precision, the filtered air dust content is far below the national emission standard, and can be directly discharged through the system air outlet, and the purified air can be directly circulated indoors.
The above is the application and summary of the author in numerical control plasma cutting and dust removal for many years. With the government attaches great importance to environmental protection, the environmental awareness of enterprises is continuously enhanced, and the requirements of environmental protection for laborers are becoming stronger and stronger. The pollution sources generated by cutting, welding , grinding, painting and other aspects will be treated. The environmental pollution in China will certainly be improved, and the application of pollution sources such as CNC plasma cutting and dust removal will gradually become popular.
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