Huicong Surface Treatment Network: “China’s official vehicle reform has been underway for 19 years, yet year after year, the reform seems to remain stuck in neutral. The trend of overstaffed vehicle allocations and the private use of official vehicles remains strong.” Li Weihua, a member of the National Committee of the Chinese People's Political Consultative Conference and Vice Chairman of the Anhui Provincial CPPCC, pointed out that waste and corruption on wheels cannot be delayed or postponed. He suggested institutionalizing the reform and adopting a “coordinated, holistic approach” to tackle the persistent problem of official vehicles being used for personal purposes. Once this solution—“strictly defining the scope and standards for official vehicle allocation, adopting a ‘zero-tolerance’ policy toward private use of official vehicles, dealing with each case as it arises, taking tough measures, and drawing on practices from Hong Kong and Macao by standardizing official vehicle models, uniform livery, and unified colors to facilitate public oversight”—was proposed, it immediately sparked heated debate. From a technical perspective, unifying vehicle livery is not particularly difficult to implement; the real challenge lies in whether uniform livery can truly prevent violations. At present, this remains an open question. Nevertheless, we can still explore the automotive painting processes we are already familiar with. From the standpoint of automotive painting technology, vehicle painting generally consists of two main parts: first, surface treatment of metal substrates prior to painting, also known as pretreatment techniques; second, the actual painting application process. Surface treatment primarily involves removing oil stains, dust, rust, and old paint layers during repair work from the substrate surface, thereby improving the surface condition of the workpiece. This includes mechanical and chemical treatments tailored to specific conditions, such as phosphating, oxidation, and passivation. Meanwhile, automotive painting processes vary significantly depending on the type of vehicle. For heavy-duty trucks, the primary painted components are the front cab, which has higher painting requirements; other parts, such as the cargo bed and frame, have lower painting demands than the cab. The painting of passenger buses differs considerably from that of freight trucks. The body of a passenger bus comprises the chassis, frame, interior cabin, and exterior surfaces, with the exterior surfaces having the highest requirements. Exterior surfaces must not only provide excellent protection and aesthetics but also feature large painting areas, multiple flat surfaces, and often incorporate two or more colors, sometimes even including decorative stripes. As a result, the painting cycle is longer, the construction standards are higher, and the painting process is more complex than for freight trucks. Passenger cars and small station wagons have higher requirements than large buses and freight trucks, both in terms of surface decoration and underlying protective layers. Their surface coatings must meet Class I decorative precision standards, boasting a beautiful appearance with mirror-like gloss or smooth surfaces free of fine impurities, scratches, cracks, wrinkles, blisters, or any defects visible to the naked eye, and they must also possess sufficient mechanical strength. The underlying coating must serve as an excellent protective layer, offering superior rust resistance and corrosion protection, along with strong adhesion. Local or full-area applications of putty with good adhesion and high mechanical strength should ensure that, even after several years of use, no rusting or peeling occurs.

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Huicong Surface Treatment Network: I. What is Dip Coating? The coating flows from the coating reservoir above the dip-coating machine through a dip-coating knife, forming a continuous and uniform coating film. The workpieces are fed onto a conveyor belt and pass beneath the dip-coating knife, where they are evenly coated with a layer of paint. Any coating that does not adhere to the workpiece is collected by a return trough and returned to the coating reservoir, then pumped back into the system for reuse. II. What are the different drying methods used in dip coating? Dip coating can be dried using four methods: ambient temperature drying, oven drying, microwave drying, and UV curing. III. What types of coatings can be used in dip coating? Dip coating can apply PU coatings, PE coatings, NC coatings, UV coatings, and water-based coatings. IV. What components make up a dip-coating application system? The first type: intermittent PU dip-coating line design—includes a double-sided vacuum dust removal machine, a 7-meter Class 100,000 clean dip-coating booth, a Class 100,000 dip-coating flash-drying room, and a dust-free curing room (which can also be designed as a 15-meter strong-microwave drying tunnel for final curing). The second type: fast-drying PU dip-coating line design—includes a double-sided vacuum dust removal machine, a 7-meter Class 100,000 clean dip-coating booth, a 45-meter defoaming and leveling tunnel, a 45-meter solvent-evaporation flash-drying tunnel with weak microwave assistance, a 15-meter strong-microwave drying tunnel for final curing, and a 5-meter cold-air cooling and packaging section. The third type: fast-drying water-based coating dip-coating line design—includes a double-sided vacuum dust removal machine, a 7-meter Class 100,000 clean dip-coating booth, a 45-meter moisture-evaporation flash-drying tunnel with weak microwave assistance, a 15-meter strong-microwave drying tunnel for final curing, and a 5-meter cold-air cooling and packaging section. The fourth type: fast-drying UV coating dip-coating line design—includes a double-sided vacuum dust removal machine, a 7-meter Class 100,000 clean dip-coating booth, a 45-meter weak-microwave defoaming and leveling tunnel, a 3-meter UV curing machine, and a packaging section. The Class 100,000 dip-coating booth is equipped with a volatile solvent extraction tower, positive-pressure ventilation, a dip-coating machine, and a paint-mixing area. The air particle standard required is below 10 microns. V. Where can dip coating be applied? Dip coating is suitable for coating flat workpieces up to 10 cm high. It is widely used in industries such as door manufacturing, panel furniture, kitchen cabinets, flooring, moldings, decorative glass, new environmentally friendly building materials, printing, blinds, inkjet printing, handicrafts, calcium silicate boards, ecological wood panels, and integrated exterior wall insulation and decoration systems. VI. What are the advantages of dip coating? Coating methods include dip coating, spray coating, brush coating, roller coating, and immersion coating. Dip coating is an environmentally friendly method that saves labor, reduces paint consumption, is fast, produces excellent mirror-like finishes, and achieves good pore-filling effects. However, dip coating can only be used on flat workpieces, which is its main limitation. Dip coating is developing very rapidly. Table 1: Comparison of Advantages and Disadvantages between PU Dip Coating and PU Spray Coating Feature | PU Dip Coating | PU Spray Coating --- | --- | --- Mirror-like finish | Good | General, with spray-induced orange-peel effect; good pore-filling, easy to stack pores | Pore-filling effect | Good, uniform and easy to stack pores | Requires operator handling, saves 3 times more labor than professional spray painters | Paint consumption | Saves paint, no waste—about 50% less waste | Faster—5 times faster than spray coating | Space-saving—occupies less space | Power consumption | Saves 10 times more power than spray coating | Wastewater | No wastewater—no water curtain cabinet, no wastewater or paint mist, no PM2.5 | High toxicity in working environment | No waste residue | Exhaust gas | Less—1 time less | Investment | 280,000 yuan (dust collector + dip-coating booth + dip-coating machine) | 450,000 yuan (one dip-coating booth = 9 spray booths) | Spraying gun + water curtain cabinet + flash-drying room + air pump | Recruitment | Easy to recruit workers—oil painters are hard to find | Can handle irregular-shaped parts | Yes | VII. What factors determine the surface effect of dip-coated coatings? a. Quality of the dip-coating paint; b. Precision of the dip-coating knife on the dip-coating machine; c. Operational control of process parameters such as paint viscosity, conveyor speed, and the width of the bottom gap at the dip-coating machine’s outlet during dip coating; d. Dust-free level of the dip-coating booth; e. Dust removal efficiency of the double-sided vacuum dust removal machine. VIII. What conditions must be met for constructing a dip-coating production line, and what types of coatings can be applied? 1. The furniture must be made of flat-panel materials. 2. The dip-coating capacity must be substantial—a dip-coating team of 6 people can coat over 1,000 square meters, and the total area requiring dip-coating for primer and topcoat each month must exceed 10,000 square meters. 3. The dip-coating machine can apply PU primers, PU topcoats, PE white primers, PE transparent primers, NC primers, NC topcoats, color touch-ups, UV coatings, and water-based coatings. It can achieve open-matte effects, fully enclosed matte effects, and glossy mirror-like finishes.

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