The cleanliness of the metal surface is critical prior to the liner process. This is mainly achieved through two steps: one is to use the heating method to remove oil stains from the metal surface in the temperature range of 110°C to 150°C; The second is to remove various impurities on the metal surface. There are two approaches that are usually taken:
Manual method: Ideal for small equipment or when other methods are not suitable. Knives, abrasive cloths, wire brushes, and grinding wheels or portable grinding wheels are first used to remove oxide from the metal surface. Subsequently, organic solvents are used to remove floating rust or oil from the surface. Although this method is simple and easy, it is less efficient and not suitable for large equipment. Mechanical method: It is more widely used, covering dry sandblasting, wet sandblasting, closed sandblasting, shot blasting, tumbling and high-pressure water flow rust removal and other means. Among them, the closed sandblasting method is widely used by professional factories. Its advantages lie in continuous operation and good dust prevention effect, but the equipment is relatively complex, so it is not suitable for the construction of power plants to improve water treatment equipment. For sporadic improvements or the manufacture of metal finishes for rubber-lined corrosion-resistant equipment, the dry blasting method is an ideal choice. The main advantages of this method are the simplicity of the equipment, the high efficiency of the work, and the high quality. Although there is a problem of silica dust diffusion affecting the environment, it is still a suitable choice in terms of the overall effect. The dry sandblasting method can effectively remove rust, oxide and other dirt on the surface of the object, so that the metal surface forms a uniform and rough texture, so as to enhance the adhesion between the rubber and the metal surface. In the sandblasting method, angular, hard grit grains, such as quartz sand (or iron sand), are usually used. In some cases, river sand can also be used as an alternative, but it is more consumed, produces more silica dust, and requires frequent screening of excessively fine particles. The particle size of quartz sand is usually between 2 4mm and iron sand is 12~1.5mm, while river sand is 3 6mm. All these sand grains must be free of impurities and well dried before use. In rainy weather, work should be suspended. The compressed air used for abrasive blasting needs to be cooled, filtered, dewatered, and degreased. The amount of compressed air should be controlled at 8 12m min, and the pressure should be maintained at 5 6kgf cm.
Before starting the blasting work, check and make sure that all the lines are securely connected (since most of the work is temporary, the pipes are mostly pressure-resistant hoses, especially for the moving part of the work). In addition, it is necessary to check whether there is any air leakage, whether the opening and closing of each valve is flexible, and whether the air pressure and air volume are normal.
Staff must wear well-fitting overalls, high-waisted rubber boots, and long-sleeved canvas or leather gloves. At the same time, they are also required to wear gas masks (the inhaled air should be filtered through a cotton filter and the volume adjusted according to the comfort of the staff) and dust caps. After entering the work area, the staff should first check the condition of the working face, and then notify the guardian to open the exit door of the air-water separation tank and start working. Due to the large dust in the container, which may affect the line of sight, it should be prepared with a running light wrapped in iron gauze for lighting, and the sand particles also need to be self-sufficient. The distance between the blast gun and the working surface is usually controlled within 15 to 30 mm until the metal surface is sprayed gray and free of any rust. For ease of inspection, chalk can be used to divide the work surface into strips or blocks. If the work is going well, an area of 5 7m can be sprayed every 8 hours. When blasting is done on the outside of the vessel, measures should be taken to reduce the loss of sand particles. During the sandblasting process, the following points should be noted: water should be released from the separation tank regularly to prevent wet air from being fed into the spray gun; If the sight glass (two to three layers, a thin layer of plexiglass can be sandwiched in the middle) on the gas mask should be replaced in time if it is damaged to prevent injury; When the casing in the blasting gun is worn, it should be replaced in time to prevent damage to the gun body. Due to the harsh working conditions, it is usually recommended to work in continuous operation at 05 After 2 hours the operator is replaced.