Steel pipe in the use and transportation, the inevitable use of the environment and the impact of the transmission medium, prone to chemical or electrochemical reaction and then corrosion, so the use of anti-corrosion coating steel pipe can effectively prevent corrosion of steel.
Analysis of Corrosion Protection Technology of Steel Pipe
At present, domestic and foreign commonly used welded pipe, oil casing and other seamless steel pipe factory automatic painting process mainly has the following four:
Steel pipe anti-corrosion coating process one: the use of leaching coating, coating before and after the middle roller conveyor line to form a coating. And then fork and fork transfer, hook-like chain rolling conveyor, steel pipe into the steam oven, heating and drying;
Steel pipe anti-corrosion coating process two: the use of electrostatic coating method, before and after the application of the application of inclined roller roller conveyor to form a coating. And then lift the elevator lift to the shelf cooler, the natural drying;
Steel pipe anti-corrosion coating process three: steel pipe transport, the use of UV coating system, vacuum coating method, coupled with the air erosion to form a coating. Immediately after coating UV radiation curing coating. Is characterized by the formation and curing of the coating are completed between the two rollers;
Steel pipe anti-corrosion coating process four: coating by heating no air spray method, the application of roller conveyor before application, after application of sub-synchronous V-shaped tooth chain conveyor to form a coating. After coating the steel pipe from the stepper into the horizontal V-shaped chain conveyor into the steam drying box, heating and drying.
Comparison of various coating processes
Steel pipe anti-corrosion coating process one: As a result of the use of leaching coating, coating hanging serious. And because the roller and chain design is unreasonable, the coating there are two longitudinal and multiple ring scratches. This process is being eliminated. The only merit of this process is that it is heated and dried after coating;
Steel pipe anti-corrosion coating process two: the existence of hanging film coating, the whole body spiral scratches and whitening quality defects. In particular, the thickness of the coating at the screw abrasion is only one-fifth of the specified thickness and the appearance is poorly felt. At the same time the process of electrostatic ignition process of fire hazards, in recent years has occurred several fire accidents, posing a threat to safe production. No drying process is also an important flaw in the process. Because of this process there are many difficult to overcome and mutually restrictive contradictions, making it increasingly obsolete, has been unable to adapt to the requirements of modern factory automatic painting, will gradually withdraw from the field of steel coating;
Steel pipe anti-corrosion coating process three: is a technologically advanced but not very mature technology. In the two rollers between the moment to complete the spraying and curing, the advantages of self-evident. But there are also difficult to overcome the weaknesses, such as: steel pipe surface pretreatment requirements are extremely strict, slightly inadvertently, adhesion decreased significantly; UV coatings and equipment expensive, technical management requirements; coating crisp, Bump, easy to fall off, and difficult to make up. Due to the existence of such a number of problems so that the promotion of this process is subject to constraints;
Steel pipe anti-corrosion coating process four: is a technology developed in recent years more advanced and relatively mature technology. It overcomes the other process of the existence of a serious sagging film, abrasions, whitening, fragile and other ills. The resulting coating adhesion strong, flexible, rust-proof effect is very good, very few sagging, beautiful and complete. The process also has a simple, complete, technical management requirements of low and safe features. As a result of technical improvement called steel pipe heating without gas spraying complete sets of technology.
Treatment technology of airless spray of steel pipe
Process one to the process of three embodies the traditional process of the prevalence of painting defects, that is, serious sagging film, abrasions, whitening and so on. The latest technology four to solve this series of problems, and formed a perfect steel pipe heating airless spray sets of technology. The technology has the following technical advantages.
1. Avoid strip or spiral abrasions
In the late 1990s, Chinese experts analyzed the abrasion of steel pipe coating. At that time the abrasions mainly for the steel surface width of 40 mm two longitudinal full-length abrasions. For the introduction of foreign steel pipe coating production line before and after the use of painting before and after the roller conveyor, and the middle of the shower box is also installed roller design, the two sides put forward the front of the front roller conveyor belt conveyor transmission mode for airless spray Of the technical program. This program in the early 21st century, by the Beijing Polonus Painting Equipment Co., Ltd. in Daqing General Machinery Plant tubing plant to achieve and put into production applications. It is proved that this process can effectively prevent the longitudinal abrasion of the steel pipe. After the coating, there are only two small dotted teeth with a spacing of 600 mm, and the self-healing property of the coating itself is adopted. Reflected well. The process of further improvement (taking the process of segmented conveyor belt before and after spraying), so that the steel pipe is always in contact with the V-shaped teeth of the chain, and the front and rear chain synchronous movement, to ensure that the spray between the surface and the fulcrum The minimum contact, to avoid the roller conveyor strip scratches the ills, beautiful and complete coating. At present, the technical level both in the international and domestic in the current is more advanced. The technology is not only advanced and mature, has been in the domestic 13 automatic oil line to be verified. As for the spiral band abrasions to prevent very simple, remove the screw conveyor to this method can be.
2. To overcome the problem of sagging
Hanging can be divided into five types: specific gravity, too thick, low viscosity type, special shape type, contact type. Steel pipe anti-rust coating is relatively small proportion of the impact of the sag can be ignored. The main types of steel pipe sag are too thick and low viscosity type, the secondary type is special shape and contact type. As the steel pipe section is round, close to the streamline, so the paint is more easy to flow, easy to hang, it is inevitable, but can overcome. Only by spraying the original viscosity of the higher viscosity but after the viscosity reduction of the coating, with the temperature to reduce the higher viscosity of the way to reduce the flow of paint on the surface of the pipe to overcome the sagging. The contact type sagging is due to the contact surface of the steel pipe after contact with the steel pipe surface, forming a contact surface near the surface of the steel pipe, guiding the coating to leave the coating film to form a sagging. This is inevitable. But can be reduced by film thickness control. Fortunately, the number and size is very small, the appearance of little impact.
As for the thick type of sagging due to the formation of a lot of reasons, it is necessary to pay attention to the problem is a lot of this is the need to control the key, must ensure that the following: steel pipe anti-corrosion coating steel pipe must ensure a certain speed, and can in a certain range Within the adjustment.
Steel pipe corrosion coating steel pipe transport must be uniform motion;
Corrosion-resistant coating of steel pipe with no gas heating spray method, the working pressure of the paint can be adjusted, while the pressure must be stable. The heating temperature of the coating can be adjusted;
Steel pipe anti-corrosion coating nozzle model through the correct selection of the experiment, including the flow, spray width and other parameters;
Steel pipe anti-corrosion coating airless automatic gun for the steel pipe circular cross-section of the uniform distribution of the angle for the steel pipe surface and the steel pipe surface distance can be adjusted;
Steel pipe anti-corrosion coating must ensure that the center of the gun group and steel pipe center;
Steel pipe anti-corrosion coating exhaust air volume wind speed and spray state must match;
The corrosion resistance of the pipe is good.
If for each type of steel pipe are carefully adjusted above points, too thick sag is completely overcome. The problem is to establish a complete coating process management system to ensure that the variety of replacement, the technical adjustment work in an orderly manner.
3. To prevent the coating whitening
The formation mechanism of the whitening defects in the coating film is the result of the condensation of the moisture into the coating to produce a translucent white film. There are many reasons for its production, such as the air humidity of the construction environment, excessive dispersion of the coating, the temperature of the dispersion process, the local temperature of the coating surface, the water content in the coating, the surface temperature of the workpiece is too low, the boiling point of the solvent or the ratio is improper, Wait. For steel pipe coating, the first three are the main reason. These manifestations are a forming process under certain conditions. As an electrostatic coating, the main reason for the formation of whitening of the coating can be described as follows: After the air humidity in the environment is relatively large and the temperature is relatively low, the coating is dispersed from the slotted electrostatic atomizer and then dispersed Steel pipe surface. In this process, due to the excessive dispersion of the coating into an extremely large quantity and extremely fine coating droplets, the specific surface area of the coating is large, the area of the contact with the wet air is large, and the water molecules can be attracted to the surface of the water and mixed with the coating liquid The stream eventually enters the interior of the coating, resulting in a whitening defect in the coating.
As can be seen from the above discussion, the ambient air humidity is only the conditions, the real reason is the excessive dispersion of paint. In order to prevent the appearance of the coating whitening defects can be in the ambient air humidity under the same conditions, through the control of excessive dispersion approach to achieve. The use of heated airless spray method is considered to be the best way to control the above two reasons. The so-called heating airless spray, as the name suggests, heating is the coating heated to a temperature after spraying. The general temperature is between 40 and 80 ° C. Airless spray means that the air is not compressed when the paint is atomized. The atomization principle is: the liquid coating with a pressurized pump to a certain pressure, through the pipeline into the spray gun, sprayed through the nozzle after the formation of high-speed liquid film; high-speed liquid film and air friction after the dispersion is small Droplets and atomization. Its atomization effect is moderate, will not occur excessive dispersion, suitable for pipeline coating. Airless spray can reduce the amount of solvent, spray coating high viscosity, spray paint than air-saving, slightly larger than the amount of electrostatic spraying paint. But through the recovery device can make up for this weakness. As the heating airless spray with temperature and atomization advantages, as the best choice for steel coating. And this choice process effect is obvious, a number of manufacturers and a number of coating lines to use the results, always found no white phenomenon. Even far from the ocean coating can also ensure good anti-rust effect. In addition, the effect of heating and drying after the heating of the airless coating to prevent the occurrence of whitening defects can not be ignored.
Through the above description, anti-corrosion coating steel pipe can effectively avoid corrosion problems such as steel pipe, making the use of steel pipe can play a greater role.
Source: China Stainless Steel Pipe Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)