Anti-corrosion technology of forklift and its application

In the 1980s, forklift anti-corrosion technology did not receive enough attention in China. As the forklift market continues to expand, forklift competition is increasingly fierce. The application of innovative anti-corrosion technology can not only improve the appearance quality of the forklift, but also increase the internal quality of the forklift, extend the service life of the forklift, improve the grade of the forklift, and even become a growth point for the sales of the products.
1 The main factors causing corrosion of forklifts are the environmental factors and their own structural factors.
Forklift trucks can be divided into internal combustion forklifts and battery forklifts. Most internal combustion forklifts are used in ports, docks and industrial and mining sites. The use environment is rather harsh, especially in the port and chemical industries. Due to the combined effects of subtropical, wet tropical, maritime climatic environment and industrial waste gas and dust, the forklift parts are corroded and damaged. Corrosion is more serious; battery forklifts are mostly used in indoor places such as warehouses, where environmental changes are small, and corrosion caused by environmental factors is relatively light.
The corrosive environment generated inside the forklift, such as the high temperature generated by the engine and the combustion exhaust gas containing sulfur and chloride ions, the acid mist generated by the battery, the liquid leakage, the vibration caused by vibration during work, the local damage caused by friction and collision, etc. The main cause of corrosion damage to forklift components.
The main mechanism of metal corrosion is the conversion of raw metals into metal oxides, causing structural parts or components to rust, damage or even repair and scrap. The aging of non-metallic materials such as paint, rubber and fiberglass fiber is mainly caused by physical and chemical changes such as cracking, degradation and dissolution of the polymer structure after the environmental comprehensive action, resulting in a decrease in appearance and performance. It can be seen that the design structure, application materials, technology and protective measures of the forklift directly determine the corrosion resistance of the forklift.
2 Application status of corrosion resistance and anti-corrosion technology of domestic forklifts The protection design and application of anti-corrosion technology and process level of domestic forklifts are relatively low. Most domestic forklift paint layers have low fullness, flatness, gloss and adhesion; the quality of coatings and conversion coatings is not good, especially in heavy corrosive environments (acid mist, high temperature, etc.). Directly after using for a period of time, rust stains appear, the paint layer is foaming, peeling, discoloration, loss of light, the cleanliness of the fuel tank is reduced, and the non-metallic parts are deformed. Compared with foreign or domestic joint-made brand forklifts, the shape, materials and processes of domestic forklifts directly affect the grade of the products.
At present, it is a large share of the domestic forklift market, and the leading domestic technology is Heli forklift and Hangzhou forklift. The appearance quality of these two brands of forklifts has improved significantly in the past two years, and the anti-corrosion technology and application status adopted have certain representativeness. According to its improvement status and implementation effect, we conclude that improving the anti-corrosion performance of the forklift requires comprehensive measures from the structural design and manufacturing processes to achieve the best results.
2.1 Avoid corrosion from the structural design of the forklift (1) Consider preventing the accumulation of corrosive media in the overall arrangement of the forklift. Try to avoid enclosed areas, or keep the closed system ventilated and well drained, such as ventilation and heat dissipation of the internal combustion forklift. The exhaust gas generated by the engine is discharged from the lower part of the counterweight as much as possible or from the upper part of the counterweight by purging and cooling. For battery forklifts such as reach trucks, ventilation windows can be provided to keep the motor cool and ventilated, and the bottom of the battery box has a leak hole and a liquid trap.
(2) Pay attention to protection in shape design and avoid accumulation of water vapor and dust. Foreign advanced forklifts pay great attention to the design of the brand, such as Linde, HYSTER, TOYOTA, JUNGHEINRICH and other brand forklifts, the shape is smooth, not only reflects the beauty and functional design, but also is not easy to accumulate water and scale, it is worth learning.
(3) Pay attention to the protection of exposed parts. The electrical device and the connector are arranged on the inside or with a protective cover. A dust cover is provided on the part of the vehicle that is exposed to corrosion and easy to enter. For example, the tilting hydraulic cylinder and the exposed section of the steering cylinder of the steering hydraulic cylinder are provided with a dustproof cover; and the exposed process holes or function holes of the vehicle body are provided with waterproof plugs.
(4) Consider uniform corrosion when designing parts, and choose one or several combined anti-corrosion methods. Commonly used protection methods for forklifts include coating, electroplating, conversion coating and anti-rust oil and grease. Different processes have different corrosion resistance. For example, Hangzhou H series forklifts, many of the previous pins, shafts, bolts, bracket surfaces are blackened, hydraulic cylinder heads and many other exposed processing surfaces are not treated, so that the forklift has been rusted before leaving the factory. By improving the surface treatment requirements, improving the rationality of part design, and effectively standardizing the surface treatment process, the appearance quality and corrosion resistance of the product are improved.
The coating is used for corrosion protection, and the characteristics and quality indicators of the paint coating need to be clarified. For example, the coating of the body structure emphasizes the decorative and corrosion resistance; the coating of the front and rear bridges emphasizes the protection; the coating of the battery case emphasizes the acid resistance; the coating of the exhaust pipe emphasizes the heat resistance and the like. The use of metal plating shall be expressed in accordance with GB/T13911-1992 "Methods for Metal Plating and Chemical Treatment". Threaded fasteners refer to GB 5267-1985 "Threaded fastener plating" standard to determine coating requirements. Generally, a galvanized layer of 7 to 10 μm is used to obtain a better protective effect. For parts in a heavily corroded environment, a galvanized layer of 20 to 25 μm is used. Pay attention to the color of the post-treatment and post-treatment of the metal coating to avoid color mixing and affect the appearance of the whole machine.
(5) Pay attention to avoid crevice corrosion, electrochemical corrosion, stress corrosion cracking. The inevitable gap structure, such as the hood weld seam, is sealed with a sealant. For the dissimilar metal connection, the metal with the potential should be selected as much as possible, or the insulation should be taken to avoid electrochemical corrosion.
(6) The structure of the parts should facilitate the implementation of the protective process and, if necessary, the process holes. For example, the position of the opening in the fuel tank is to facilitate the shot blasting of the entire surface of the nozzle. Process holes are required for chemically pre-processed workpieces such as overhead guards to prevent build-up.
(7) Consider the selection of corrosion-resistant materials with excellent properties, such as galvanized sheets, color coil boards, composite materials and engineering plastics. FRP has the characteristics of good manufacturability, high specific strength and low cost. It can achieve certain heat insulation and noise reduction effects with the insulation pad. It has been applied to forklift hood, battery cover and general shield. At present, the FRP parts are generally made of unsaturated polyester resin and alkali-free glass fiber as the main raw materials, combined with steel plate reinforced laminated pressure, which can obtain good appearance quality, and the welding edges and paints caused by welding are difficult to cover up. Spot welding scars, but poor durability, easy to age, suitable for trial production and small batch products. For large-sized shell-type shaped parts, engineering plastics (such as ABS engineering plastics) can be used instead of FRP for better decorative and durability. The hood is greatly affected by the environment, and it is more reasonable to use a thin steel plate or a galvanized plate to protect the coating. Forklifts will learn more about the application of new materials in the automotive industry.
2.2 New anti-corrosion technology and new materials with less investment and quick effect (1) Improve the coating production process and improve the appearance quality and corrosion resistance of forklifts. The coating of domestic forklifts generally adopts white dry paint which can be dried at low temperature. The topcoat used is transitioning from a low solids solvent to a high solids solvent and powder coating, from an acrylic engineering enamel to a highly decorative, corrosion resistant polyurethane or acrylic enamel; primer and intermediate The materials of the layer are not good, some are still using alkyd primer and perchloroethylene iron red primer and perchloroethylene putty, two coats, etc., and some have used phosphating primer and iron red with good corrosion resistance. Epoxy ester primer, unsaturated polyester putty (atom). Due to the need of mass production, the forklift painting has been changed from the grounding type to the assembly line production. After the assembly and commissioning, the production process of the whole machine topcoat is changed to the partial paint, that is, the parts are completely painted, then assembled, commissioned and refined. The whole library is equipped; the imported air-assisted spray gun and the high-pressure airless spray gun are used instead of the ordinary air spray gun to improve the utilization rate and coating efficiency of the paint material; the paint film is naturally dried to be dried to improve the adhesion of the paint. And hardness, speeding up production. It not only meets the needs of mass production, but also avoids the pollution caused by the paint of the whole machine, the incomplete paint film, the low adhesion and low hardness. Due to the relationship between paint raw materials and domestic and foreign similar paint products, there are great differences in quality. Hangzhou Forklift Factory adopts internationally famous brand paints, and its paint layer's fullness and gloss are obviously better than those of domestic similar paints.
(2) Improve the pre-treatment process to improve the corrosion resistance and the adhesion of the coating. The pre-treatment of domestic forklift parts is mainly shot peening and chemical pretreatment.
At present, shot peening is mainly applied to thick plate structural parts and castings, such as inner and outer gantry, frame, counterweight, hydraulic cylinder and so on. For the main purpose of derusting and descaling, the surface of the material does not form a protective film, and the corrosion resistance of the part depends on the surface coating. The workpiece after shot peening needs to be painted as soon as possible. As far as the frame is concerned, its structure is special: it has a working oil tank and a fuel tank (the battery forklift has only a working oil tank). The cleanliness of the fuel tank has always been the focus of quality control. Using shot peening, the inner surface corners of the fuel tank, corners are easy to stick to fine pills, dust, and the method of vacuum cleaner and manual wiping has certain effect, but the surface of the material is still easy to return to rust, and the cleanliness of the oil during the use of the forklift have a great impact. Foreign forklifts such as NISSAN forklift frame pre-weld panels are pre-treated, and pre-coating treatment mainly uses chemical pretreatment.
Chemical pretreatment is mainly applied to thin-plate structural parts with less scale, such as engine covers and instrument frames. The thin plate parts are easily deformed by shot peening; the simple pickling-washing-neutralizing-washing-drying-(coating) process does not give good adhesion and is easy to return to rust. At present, the main application of more mature medium temperature phosphating technology: degreasing and degreasing - derusting - washing - medium temperature phosphating - washing - medium temperature passivation - drying - (painting). After phosphating and passivation, the phosphating film formed on the surface has good corrosion resistance in the atmosphere and can effectively improve the adhesion of the coating. Since phosphating process control is much more complicated than shot peening, it is a good idea to work with a professional pre-treatment or coating plant. Some of the thin-plate structural parts of the Hangzhou forklift adopt the medium temperature phosphating pretreatment and the powder coating-spraying process.
3 Development direction of anti-corrosion technology for forklift application (1) Application of cathodic electrophoresis primer to improve the anti-corrosion ability of forklift structural parts In the current various paint construction processes, cathodic electrophoresis primer has the strongest anti-corrosion ability, which is at the Swedish Corrosion Research Institute. The investigation was confirmed. Cathodic electrophoretic coating production can achieve full automation, safe construction and high efficiency; water can be used as solvent, no discharge and almost no pollution; uniform paint film and excellent corrosion resistance, electrophoresis after phosphating Salt spray capacity can reach 800-1200h; paint film bonding strength and toughness and hardness indicators have advantages. This anti-corrosion technology has been widely used in automotive and light industrial products and is increasingly mature. Although there is no introduction to this production process in the domestic forklift industry, it has already been applied in foreign forklifts, such as NISSAN forklift hoods, overhead guards, instrument racks and other small structural parts such as rims and battery brackets. . Application in domestic forklift products only needs to improve the existing process: substrate pretreatment (including phosphating) - cleaning - deionization washing - cathodic electrophoresis primer - deionized water washing - cleaning - curing - (top coat coating) It can be realized by adding electrophoretic coating equipment to the existing phosphating pretreatment processing line, or using the electrophoresis coating line of a professional collaborative factory. At present, cathodic electrophoretic paints are mostly made of acrylic resin, epoxy resin and polyurethane. They have good compatibility with the topcoats (acrylic or polyurethane enamel) used in forklifts, and the production is simple.
(2) Application of Dacromet technology to improve the corrosion resistance of forklift parts in the environment of heavy corrosion. Dacromet is a sheet-like zinc-based chromate protective coating, also known as zinc-chromium film, which is a high-tech of international surface treatment. Excellent performance of Dacromet-treated metal products: high corrosion resistance, generally 6-8μm thick coating can ensure red rust in 480~1 000h in salt spray test, 5-7 times of electrogalvanizing; high Heat resistance (heat resistant to 300 ° C), the surface film will not be corroded even after being exposed to high temperature for a long time, and the electroplating method (colored chromate treatment), at 100 ° C, the surface chromate The film begins to change, and the corrosion resistance drops sharply. It has no hydrogen embrittlement and is suitable for high-strength parts. It has been widely used in automobiles, motorcycle parts, electric power, marine engineering, etc., and has received extremely high evaluation. This technology has not been applied to domestic forklifts, but some parts of the power system, such as engine coupling bolts and tubing hoops, can be seen on the drawings of the NISSAN forklift. Zinc-chromium membrane protection has been adopted. With the development of domestic Dacromet technology and the reduction of production costs, it is believed that domestic forklifts may also apply zinc-chromium membrane protection to parts in the environment of heavy corrosion (high temperature, high corrosive environment).
4 Conclusion To improve the corrosion resistance and appearance quality of forklifts, the emphasis is on improving the rationality of the design and applying advanced anti-corrosion processes and materials. These comprehensive measures are equally applicable to other types of construction vehicles and storage vehicles.

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