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    Home > Coatings News > Paints and Coatings Market > An analysis of the causes of coating losses and conservation measures

    An analysis of the causes of coating losses and conservation measures

    • Last Update: 2020-11-28
    • Source: Internet
    • Author: User
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    1 Introduction
    The marine platform is a large-scale engineering structure at sea, its steel structure has long been in the salt spray, moisture and sea water environment, by the sea water and sea life erosion, and produce severe electrochemical corrosion. Corrosion seriously affects the metalic properties of the structural materials of marine platforms, thus affecting the safety of the use of marine platforms. The construction of marine platforms requires the use of a large number of coatings, and due to weather, technology and construction reasons, will cause the waste of coatings
    China
    . This paper focuses on the causes of coating losses and related savings measures.
    2 Factors of coating loss
    2.1 Environmental factors
    there are many environmental factors that affect coating usage, such as temperature, humidity, dust concentration, etc., but the most important environmental factors are wind. Spraying operations in high wind environments can easily cause the paint to disperse resulting in increased waste, which can lead to dry spraying and a significant decrease in spray quality, so construction is not allowed when the wind speed is too high. Therefore, the general spraying construction as far as possible to use indoor spraying, outdoor spraying to choose to work in a less wind speed environment, or will be coated around canvas and other objects, to minimize the impact of wind speed on spraying.
    In outdoor wind environment construction, paint loss is inevitable, the usual coating loss relationship is as follows: "well ventilated but relatively closed places" less than "almost windless outdoor places" less than "windy outdoor places." Figure 1 is the film and loss when coating is sprayed, where the dotted part is the film and loss of the coating when spraying under windy conditions, and the solid line is the spraying effect under the ideal condition of no wind.
    2.2 Construction factors
    during the construction process caused by the loss of paint, the main factors include the paintman's business level, the selection of gun nozzles, the geometry of the components to be coated and so on.
    2.2.1 Paintman's business level
    Because the marine engineering steel structure is characterized by large volume, heavy mass, irregular, so in addition to a small number of profiles can be flowing projectile spray primer, everything else is artificial paint, paint hand's level has a direct impact on the loss of paint.
    (1) paint hand experience will directly affect the thickness of the paint film, paint film is too thick is the performance of paint waste, and need to continue to invest in artificial to polish off the thick coating;
    (2) paint hand if the upper coating film is not dry in the case of the next job, will produce pinholes and other paint diseases, resulting in unnecessary repair work.
    (3) when the sprayer is working at different temperatures, the distance between the spray gun and the structural parts is uncertain, for example, when the temperature is high, the spray gun is too far away from the component to be coated will produce dry spray phenomenon; The repair of paint disease causes waste of paint and can lead to quality problems of paint film.
    (4) Paint hand if the operation is not correct, for example, the spray gun should be perpendicular to the spray surface, and when the spray gun and spray surface is 45 degrees, there will be about 65% of the paint loss.
    2.2.2 The selection of the
    nozzle has a great impact on the construction of the coating, the viscosity of the coating, the thickness of the coating film, the geometry and area of the coated components are the factors to be considered in the selection of the nozzle. Responsible and skilled sprayers will choose the right nozzle for painting according to these factors, if the area of the coated component is small, and the spray width of the nozzle is larger, the loss of paint will occur. Figure 2 is the intention of spraying small area components to produce paint loss in the case of large diameter nozzles.
    , nozzle wear has a greater impact on spraying operations. Usually after spraying 500 to 1000 L, the nozzle will be severely worn, after the nozzle wear, the nozzle will become large and round, which makes the fan surface of the spray paint become smaller, when the fan surface becomes 25% smaller, the nozzle needs to be replaced. If the nozzle is not replaced in time, the nozzle spray beam graphics will be very irregular, and flow rate will exceed the theoretical flow rate, in such a case even if a qualified operator completely according to the requirements of operation, it is difficult to control the amount of paint and ensure spray quality, resulting in waste of paint and further repair work.
    table 1 is a change in the spray and flow of a nozzle with the degree of wear.
    2.2.3 Geometry of the components to be applied
    the vast majority of small components, grilles, and large components with special structures inevitably result in coating losses due to their small coating acceptance area.
    table 2 is based on the paint loss of different components counted on numerous items.
    2.3 Losses caused by other causes
    (1) Because most of the marine structures are large structures, so in the segment construction, coating after the group pair, in the process of components or large areas of transport will inevitably produce bumps, squeezes and other phenomena, after the coating of the components or large areas after the completion of the group will be these bumps, squeezes and other paint damage repair. If the repair is not timely, corrosion will occur at the coating damage, the repair workload will increase.
    (2) scaffolding is indispensable on the construction site, scaffolding and removal is also at any time, in the process will have completed the coating of the structure caused bump damage, and this damage is random, unpredictable, the damage needs to be repaired in time to prevent corrosion and expansion.
    (3) in the process of platform construction, due to professional communication and coordination work is not in place leading to unreasonable process arrangements, treatment of the finished surface re-welding, cutting and other fire operations, this part of the burn repair amount accounted for a larger proportion of the total amount of paint.
    3 Measures to Save Coatings
    3.1 Reducing environmental factors
    (1) temperature: Each coating has temperature requirements at the time of construction. According to ISO 8502-4, the substrate temperature is at least 3 degrees C above the dew point during construction. At the same time, we should pay attention to the temperature difference during construction and curing, if the temperature difference is too large, the phenomenon of coating cracking is inevitable. Therefore, in the construction process needs to monitor the temperature changes at any time, especially in winter, outdoor operation if the temperature does not meet the requirements, should be set up insulation sheds and other auxiliary space, and thermal ventilation, to ensure a suitable working environment and good paint film curing.
    (2) humidity: Ambient humidity is also a factor affecting the coating construction and curing process, according to ISO 8502-4: the relative humidity of the air is not greater than 85%. Therefore, coating operations are not permitted in foggy, rainy and snowy weather with relatively high humidity. But on the other hand, at all times to try to complete the work in accordance with the requirements of the duration, so in the humidity is large, must be in accordance with the reality, the use of matching dehumidification equipment, at the same time can pass into the appropriate amount of heating, so that the humidity reduced to less than 85%.
    (3) wind: reducing the impact of wind on coating operations can greatly save paint. Try not to do outdoor spraying in windy environments, it is necessary to carry out necessary protection when spraying outdoors, such as the establishment of shelters to reduce the impact of the wind.
    3.2 Reduce the impact of the construction process
    (1) paint hand selection: enterprises to project-driven, cost-leading direction, in order to meet the project's construction schedule, control costs, ensure quality, choose excellent paint hand in the coating operation is the first. Of course, the mood of the paint hand operation and other subjective factors, the spraying results also have a great impact, so enterprises in the selection of personnel to carry out operations, especially important construction work, as far as possible to consider the quality of personnel.
    (2) Gun nozzle selection: according to the geometry of the components to be coated to choose the appropriate nozzle, such as the small structure of the components to choose the spray fan size of the gun, the larger viscosity of the paint to choose a larger aperture of the nozzle.
    (3) component placement: for small components such as brackets, grilles, railings, pipelines and feet, due to its complex structure will lead to a large amount of waste of paint, recommended measures: (1) for complex shaped components to choose a better level paint paint; The thickness and the quality of the coating; (3) for railings, brackets and other components to be arranged together for overall spraying, (4) for some difficult to spray and film thickness is difficult to guarantee the part, such as a variety of small holes (fan holes, flowing water holes, human holes, etc.) cutting edges, profiles, welds, free edges, etc. must be pre-coated, Figure 3 for the need to pre-coat the site diagram.
    3.3 Other aspects
    (1) For projects with a longer project cycle and a larger post-spray area, you can spray workshop primers on all individual components in the early stages, and carry out the overall sand sweep and coating work after the completion of the main structure, which can not only guarantee the overall quality of the coating, but also greatly save the amount of paint.
    (2) strengthen process control, the need to spray components for a relatively accurate area calculation, according to the coating packaging volume, solid content, the required dry film thickness, component type and paint hand business level, in advance to estimate the required paint dosing.
    4 Conclusion
    Paint quantity control is an important part of enterprise cost control, reducing the loss of coating materials is also the embodiment of energy conservation and emission reduction, scientific formulation and strict implementation of relevant conservation measures, in order to fundamentally reduce the loss and waste of coating materials.
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