Effect of painter skills and methods on paint utilization
Abstract: The effects of spraying method, spraying process and painting skill on coating utilization rate are expounded. It is pointed out that the use of advanced spraying methods, improved spraying process, improving the quality of painting workers and standard coating management are the key to improving coating utilization.
Air spraying method is the simplest and most basic spraying method. It is also a widely used spraying method. Its main principle is to use compressed air (pressure of 0.3 to 0.5 MPa) to flow through the nozzle. A negative pressure is generated around the paint to be sucked out, and is atomized by the rapid diffusion of compressed air. Its spray utilization rate is the lowest among all spray methods, generally in the range of 30% to 60%, and the environmental pollution is the most serious. With the air spray method, a considerable part of the paint is wasted due to atomization and scattering during spraying. This not only increases the manufacturing cost, but also increases the blockage of the filter cotton in the spray booth, polluting the environment and equipment. In order to improve the utilization rate of paints, the author believes that it is necessary to start with the coating method, painting process and painting management, and implement the whole process control in order to achieve good results.
1 Factors affecting the utilization rate of paint Spray paint
1. 1 Effect of spraying method
The air spray method, the high pressure airless spray method, the high pressure auxiliary gas spray method (also known as the mixed gas spray method) and the electrostatic spray method are used for comparative analysis.
Different spraying methods have obvious differences in coating utilization rate due to different principles. Under the same conditions, high-pressure auxiliary gas spraying (mixed air spray gun) is 10% to 20% more efficient than air spray coating; Spraying is 30% to 40% more efficient than air spray coatings.
1. 2 The impact of operational skills
The painter's operating skills affect the entire process of spraying: Before spraying, it is expressed by the operator's preparation of the paint, and the knobs of the PQ-2 gun are adjusted, such as paint control valve, air control valve and fan control valve. When spraying, it is expressed in the distance between the spray gun and the workpiece. The speed of the gun, the uniformity of the gun and the overlap of the front and rear spray frames are reflected in the timely cleaning and maintenance of the spray gun. The air pressure is generally controlled at about 0.5 MPa, the paint output is controlled at about 200 mL / min, the gun speed is controlled at 300 to 450 mm / s, the spray width is controlled at about 150 mm, and the spray distance is controlled at 200 to 250 mm. It is ideal to spray the lap of about 1 / 3 or so. The ability to master these skills will directly affect the utilization of the paint and the life of the spray gun.
At present, many companies have low operating skills for paint sprayers. There are two main reasons: (1) Some companies have centralized the production process by product, and implemented the â€œone person multi-energyâ€ production mode, which greatly reduced the spraying operation. Degree of specialization (2) Painting work is dirty, tired, toxic and harmful. Many people are reluctant to engage in this type of work, or they are converted to other types of work. For the above reasons, the technical quality of the painter is not high, the skill of the spray operation is not enough, the paint mist is excessively scattered, and the rework is often caused by the leakage, sag, and excessive thickness of the paint film, and the operator saves consciousness. Light and thin, greatly reducing the utilization of paint. Vibrating plate spraying
1. 3 Influence of dispersion of painting site
The annual usage of a company's coatings is more than 30 tons. However, due to the dispersion of the three-point coating operation, the one-time spraying operation has a small batch size, which reduces the utilization rate of the coating. Because of each spraying operation, the loss of paint in the paint tube, paint bucket and spray gun is certain. The smaller the batch size of one-time jobs, the more times you need to work, so the more you waste. In addition, the dispersion of painting sites has also affected the popularization and application of some new high-efficiency coating methods.
1. 4 Influence of other factors No pump water curtain spray booth
The wind speed in the spray booth has an effect on the utilization rate of the paint. The wind speed range when the paint utilization rate is maximum is 0.3 to 0.5 m / s. From the actual situation, the wind speed in the spray booth is mostly around 0.3 m / s, so the impact is small. In addition, the type of coating used, the shape and size of the workpiece also have a certain effect on the utilization of the coating. 2 Improvement measures
2. 1 Improved spraying method
Improving the spraying method is actually improving the spray gun and its ancillary facilities. Considering the high utilization rate of various spray guns, only the primer is applied to the inner surface of the workpiece, and the thickness is greater than 50 Î¼m; the outer surface is sprayed with primer and topcoat, and the total thickness is greater than 90 Î¼m. In order to ensure the quality of the product, a high-pressure auxiliary gas spray gun (mixed air spray gun) was used instead of the current air spray gun spray primer electrostatic spray gun instead of the current air spray gun spray paint. In the case of other factors, not only the utilization rate of the paint It can increase the quality of the top coat by more than 20%, and the amount of paint mist, dust and compressed air is significantly reduced, so that both economic and environmental benefits can be achieved. In addition, the use of high-pressure auxiliary gas spray gun can not only improve the utilization of paint, but also improve work efficiency. However, the following points should be noted during the operation: (1) The preparation and end time are relatively increased. Due to the use of high-pressure paint buckets and high-pressure paint tubes to transport the paint liquid, the preparation and end time are relatively increased, generally around 20 min. However, for the high-pressure auxiliary gas spray gun, because the working efficiency is 1.5 times of the air spray gun, and the spraying time is more than 1 h, that is, spraying more than 12 kg of paint can save about 20 minutes of painting time. (2) Remaining in the paint tube The treatment of the paint, the amount of paint left in the pipeline (about 0.5 kg) and the thinner used in each cleaning, should be as continuous as possible, that is, use as much as possible in large batches, reducing the number of cleanings. In actual operation, it is also possible to spray the paint in the pipeline by adding the diluent in time, and the diluent can be reused after being filtered. (3) The electrostatic spray gun has a certain range of resistance requirements for the paint liquid, and the workpiece is well grounded: The resistance value of the paint liquid is mainly adjusted by the thinner. The grounding is realized by the hook or the special grounding wire, but the good or bad of the two can be judged in time from the adsorption of the paint mist, so the problem can be found in time. Generally, the hook or grounding wire should be cleaned once every 20 days. (4) The general solvent-based electrostatic spray guns mostly use the external power supply, so there is a fire hazard in electrostatic spraying. A new built-in electrostatic spray gun from GRACO, USA, requires no external power supply, generates static electricity from compressed air, and is extremely safe. According to the manufacturer's introduction, even if the workpiece is well grounded, even if the gun is short-circuited with the workpiece, the release energy is extremely small, and only arc light is generated without sparking, and there is no possibility of fire.
2. 2 Improve the painting process No pump water curtain spray booth
In order to give full play to the high utilization rate of the high-pressure auxiliary gas spray gun (mixed air spray gun) or electrostatic spray gun coating, it is the key to the success of the application whether the batch can be increased in one-time spraying operation. The relatively concentrated implementation of the â€œpainting operation pointâ€ and the specialization of â€œspraying operationâ€ are effective methods to increase the batch size of the spraying operation.
An electric locomotive production company refers to the manufacturing experience of European electric locomotive parts, and changes the coating process of the electrical parts of the electrical branch to the electrical cabinet, from the original "first assembly, back lacquer" to "first lacquer, After assembly". In this way, the coating points of the electrical branch can be revoked, the painting operation point is more centralized, the utilization rate of the coating is improved, and the manufacturing process and quality of the product are improved.
2. 3 Standard coating management
If the new type of spray gun is used, it is estimated that a total investment of about 250,000 yuan is required. According to the annual consumption of 2 million yuan of paint, if you save 20%, you can recover all the investment within one year. However, improving the utilization of the coating, it is not enough to simply improve the spraying method from the hardware. From air spray guns to high-pressure auxiliary gas spray guns (mixed air spray guns) to electrostatic spray guns, while the hardware performance has been greatly improved, the software environment, the quality and management of employees, has been put forward accordingly.
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