Discussion on Low Dust Sand Blasting Technology with Liangshi Sponge Abrasive
With the increasingly fierce competition in the shipbuilding industry today, the increasing promotion of the concept of "green shipbuilding", and many variables facing the industry itself, major shipyards around the world have upgraded or innovated their original processes based on the construction connotation of "shell", "outfitting", and "painting" in order to better adapt to the development of the future shipbuilding industry.
The painting field represented by "painting" includes rust removal operations. According to statistics, 70% of coating defects are related to the surface treatment status of the substrate. Most shipyards in China use sandblasting as a surface treatment process for sectional rust removal and cabin special coating. This traditional process can meet quality requirements, but it ignores environmental pollution and the health impact on operators. At the same time, with the mandatory implementation of the PSPC (Coating Protection Standard) specification, all shipyards are faced with the new problem of how to solve the problem of excessive coating damage in ballast tanks.
Under the background of not affecting the engineering quality, but also implementing the company's "green shipbuilding" policy, and also responding to the PSPC specifications, improving the sandblasting process has become a key issue that needs urgent consideration. Based on the actual situation of Waigaoqiao Shipyard, a new process, sponge abrasive low dust sand blasting, is studied and discussed in depth.
2.Implementation of sand blasting process
2.1 Introduction to sand blasting process
Sand blasting (shot blasting) is a method of surface rust removal. It uses compressed air as the power to spray metal or non-metallic particles as abrasive at high speed onto the surface to be treated, removing rust and cleaning the surface by impact and grinding. It can thoroughly clean the oxide skin and rust on the steel surface, achieve whitening treatment on the old coating surface, and also achieve a light sanding treatment on the coating surface [I]. Sand blasting can not only achieve high-quality rust removal on the surface of steel plates, but also provide a certain degree of roughness to meet the surface treatment requirements of applying high-performance coatings.
2.2 Problems in sand blasting process
Conventional abrasives (copper ore, ceramics, steel sand, steel shot, etc.), due to the hardness and brittleness of their own materials and the pressure of compressed air, become powder sand dust after being washed onto the surface of the steel plate. The resulting powder sand dust has brought many inconvenience to construction and the environment.
2.2.1 Environmental issues
After sandblasting, most conventional abrasives have become powder and cannot be reused, so they have to be treated as scrap. Even for a ship with a small deadweight tonnage, it is necessary to treat at least hundreds of tons of waste sand after sandblasting. Using metal abrasives with a saving rate of up to 80% can also generate a certain amount of mineral dust and dust after surface treatment.
This makes the workload of sand cleaning, cleaning, and waste sand treatment after sand blasting heavy, and it is also necessary to arrange a waste storage yard. If the cleaning process is slightly careless, sand and dust can also be mixed into the air, affecting atmospheric quality.
2.2.2 Labor protection issues
Sand blasting is the largest factor in the formation of fugitive emissions. After the abrasive becomes powder, it directly flies away in the cabin. The sand dust that floats in the cabin contains a variety of heavy metal components and extremely fine particles, which can even penetrate the protective clothing and masks of workers, causing great harm to the construction personnel in the cabin. Working in such an environment for a long time can cause toxic pneumonia or sand lung, which can lead to lung cancer in severe cases. In addition, after metal abrasives impact the substrate, the flying debris will rebound onto the construction personnel, causing a strong sense of pain, and also causing eye discomfort, injury, and other eye injuries.
2.2.3 Construction period issues
The use of conventional abrasive sand blasting during the general assembly, dock, and dock stages takes a long time to clean, which has a significant impact on the environment and other construction. Therefore, most shipyards use power tools to polish, but power polishing not only has poor rust removal quality, but also has low efficiency, affecting the overall assembly, dock, and dock turnover rate. With the implementation of the thousands of PSPC specifications, there are new regulations on the surface treatment of damaged ballast tank coatings after closure. If the damaged ballast tank coatings exceed the standard, only using power tools to polish them is far from meeting the requirements of the specifications, and using conventional abrasive sand blasting can easily lead to delays in construction plans.
In response to the above adverse factors, the industry has conducted a lot of detailed discussions and research, and introduced a new rust removal process - sponge abrasive low dust sandblasting process. This process uses an advanced flexible sandblasting and recycling combination kit, and upgrades conventional abrasives to sponge abrasives.
3.Basic principles and construction procedures of sponge abrasive low dust sand blasting process
3.1 Construction principle of sponge abrasive
The core of sponge abrasive low dust sandblasting system is sponge abrasive, which has low dust and low ejection performance. This patented technology combines the absorption capacity of a polyurethane sponge with the cleaning and grinding capabilities of traditional sandblasting processes. The flexibility of the sponge abrasive makes it flatten when impacting the treated surface, instantly expanding to three times the actual size and forming a vacuum, which will capture the vast majority of airborne particles, debris, and other substances that leave the surface after impact, exposing the substrate.
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3.2 Composition of sponge abrasive low dust sandblasting equipment
Sponge abrasive low dust sandblasting equipment is equipped with sponge abrasive, mainly used for internal and external rust removal. This equipment mainly consists of an abrasive supply unit and an abrasive circulation unit. The abrasive supply unit consists of a material storage cylinder and a central control panel, with a one-time storage capacity of 60Kg, which can supplement abrasive during the sandblasting process. The abrasive circulation unit is composed of a separation bucket, an abrasive circulator, a waste reclaimer, and an abrasive reclaimer.
Sponge abrasive low dust sandblasting equipment is equipped with sponge abrasive, mainly used for internal and external rust removal. This equipment mainly consists of an abrasive supply unit and an abrasive circulation unit. The abrasive supply unit consists of a material storage cylinder and a central control panel, with a one-time storage capacity of 60Kg, which can supplement abrasive during the sandblasting process. The abrasive circulation unit is composed of a separation bucket, an abrasive circulator, a waste reclaimer, and an abrasive reclaimer.
3.3 Workflow of sponge abrasive low dust sandblasting equipment
When the equipment is in use, the central control panel can accurately adjust the injection pressure and the feed speed of the sponge abrasive based on the specific fluidity of the sponge abrasive. The abrasive supply unit sprays the sponge abrasive onto the treated surface through a nozzle. After construction, the abrasive used in the abrasive separation bucket is transferred to the abrasive circulator for classification and purification under the action of vacuum air flow and pneumatic force. After being processed by the classification device of the abrasive circulator, reusable sponge abrasives are separated from oversized debris and used waste materials (ineffective abrasives and pollutants) for recycling. In the entire process flow, sandblasting, abrasive replenishment in the sandblasting cylinder, abrasive recovery, and impurity separation all operate independently.
4. Construction effect of sponge abrasive low dust sand blasting process
4.1 Improving construction quality
The use of sponge abrasives makes the surface roughness of the steel plate uniform after treatment, further improving the adhesion between the coating and the steel plate, enhancing the anti-corrosion effectiveness of the coating, extending the durability of the coating film, and also conducive to the leveling and decoration of the coating.
4.2 Equipment is lightweight and easy to operate
The equipment has a compact structure, and the total weight of the sandblasting and recycling combination kit is about 150Kg. The steel frame with rollers can be dragged to the required work area at any time. The closer the device is moved to the work area, the shorter the length of the skin tube used, and the better the treatment effect. Due to its low dust and low ejection performance, the difficulty of collecting abrasive in the cabin is reduced, the collection time is shortened, and the work efficiency is improved. At the same time, it has little impact on other construction in the operation area and can achieve cross operation.
4.3 Application of sponge abrasive low dust sandblasting process in PSPC specifications
At present, the damage rate of the coating in the ballast tank after the entire ship is closed in major domestic shipyards is between 4o/o-8%, or even higher. Power tool polishing is used to surface treat the damaged coating. According to the PSPC specification, the surface treatment after the closure of the ballast tank requires that the total area of the connected damaged area exceed 25m2 or 2% of the total area of the tank, and the surface treatment should reach Sa2 ½ Level. After the formal implementation of the PSPC, if the coating damage in the ballast tank area during the closure stage cannot meet the above requirements, it must be sandblasted to Sa2 ½。
If conventional abrasive sand blasting is used, it will inevitably lead to dust flying in the enclosed cabin, which will have a negative impact on subsequent abrasive recovery, cleaning, paint spraying, surrounding work, and many other situations, and even directly threaten the entire ship's construction process.
The sponge abrasive low dust sandblasting process can be used as an emergency response plan for coating damage exceeding the standard after the ballast tank is closed. It not only improves the response ability of the PSPC specification, but also has high rust removal efficiency and convenient cleaning, solving the problem of extending the dock cycle.
5. Characteristics of sponge abrasive low dust sandblasting process
5.1 Reducing environmental pollution
The sand and dust pollution caused by conventional abrasive materials in the outfield is extremely serious and difficult to control, which simply cannot meet environmental requirements. The metal abrasive commonly used in the infield also produces a certain amount of sand dust. Once handled carelessly, sand and dust can mix into the air, forming atmospheric pollution. Sponge abrasives can capture up to 99% of air pollutants, thereby protecting the environment and public health.
5.2 Improving work efficiency
The steel debris generated after impact on the surface is basically captured by sponge abrasive, which does not cause significant dust raising in the work area, reducing the time to wait for sand and dust to settle, and subsequently greatly reducing the workload of surface cleaning. Due to the low resiliency of sponge abrasives, the distribution of abrasives dropped after sandblasting is relatively regular, facilitating recovery, and the recovery process will not cause secondary dust flying. Compared with traditional processes, sand blasting and cleaning processes have lower construction difficulties, shorter construction time, and greatly improved overall efficiency.
5.3 Ensuring the health of construction personnel
The sand dust generated in the work area after conventional abrasive construction is extremely numerous and fine, which contains a variety of heavy metal elements. When harmful particles enter the human body, they can cause upper respiratory tract infections, seriously affecting the health of workers. Sponge abrasives capture the vast majority of harmful pollutants, reducing the risk of workers' exposure to hazardous substances, and reducing the responsibilities and costs associated with factory labor protection equipment updates, treatment, recuperation, and even litigation, compensation, and other related costs. In addition, unlike traditional processes, sponge abrasive low dust sandblasting has low dust and low ejection performance, which can reduce the likelihood of eye injury and other occupational injuries.
5.4 Reduce equipment failures
Nowadays, various types of equipment play a crucial role in the process of ship construction. Instruments, electronic instruments, and rotating equipment that are exposed to sand and dust for a long time are prone to interference or premature failure. The sponge abrasive low dust sandblasting process can reduce the vast majority of sand dust compared to traditional processes, improving the overall stability of equipment and factories. Not only does it reduce the frequency of equipment maintenance, but also mechanics, welders, electricians, and other operators can work in areas adjacent to sandblasting construction, reducing downtime caused by surface treatment.
5.5 Improving the recycling rate of abrasive resources
The recycling of resources is an important link in energy conservation and emission reduction. At present, conventional abrasives other than steel grit (shot) become powder during the sanding process and cannot be reused. Although steel grit (shot) abrasives can be recycled, their recovery rate only reaches about 80%, but as a new type of green abrasive, sponge abrasives have a recovery rate of up to 96%, which improves the efficiency of abrasive cycle utilization again, effectively saving abrasive resources for enterprises.
Guided by the concept of "green shipbuilding", modern shipbuilding advocates people-oriented, environmental protection, energy conservation, and emission reduction. In ship rust removal operations, the use of conventional abrasives is bound to be limited by environmental regulations, while the application of sponge abrasives, known as "green abrasives" in the industry, can solve problems such as environmental pollution, health hazards, and low utilization of abrasives in traditional processes, Complying with the international development trend of "green shipbuilding". With the acceleration of the production rhythm of shipbuilding enterprises, improving traditional processes, making resource planning, and introducing effective advanced processes can achieve the goals of reducing environmental pollution, ensuring the health of construction personnel, and improving production efficiency, and also laying a solid foundation for "green shipbuilding".