Application of basic coating process in automobile sheet metal parts maintenance

2020-08-11 15:48:27

1、 Basic coating of ferrous metal sheet

Black metal plate is easy to be exposed to the air or contaminated with harmful substances and other factors, and gradually occur oxidation and corrosion, resulting in yellow rust spots, damage to the original coating layer. Especially in the process of sheet metal work, after hammering, welding and other processing parts, the original coating protection layer is more likely to be damaged, accelerate corrosion, even if the paint film is sprayed, the paint film will quickly fall off with the base coating. At this time, it is necessary to conduct a thorough coating treatment.

Clean the surface of black metal plate with wire brush or iron sand paper. The metal surface of automobile sheet metal parts can be thoroughly polished and cleaned by nylon grinding disc, which has been widely used at present. When the car body is disassembled and repaired (especially the accident vehicle), the spray fluid specially used for rust removal, paint removal, oxidation slag and dirt removal before and after metal welding shall be sprayed on the folded edge and lap joint of the sheet metal, or the antirust primer with good anti rust ability shall be used instead.

2、 Basic coating of sheet metal joint surface

If the repaired automobile body is not treated with anti rust treatment, the joint of sheet metal parts will be oxidized and rusted due to the existence of various impurities and water vapor within one or two years, which will affect the strength of the welding point. Therefore, it is necessary to spray welding zinc in time.

Welding zinc flux (zinc rich coating) is a new material specially used to prevent oxidation and corrosion on the joint surface of sheet metal parts. It has good conductivity, high temperature resistance and electrochemical cathodic protection. It can form a layer of anti rust protection layer between the welding joint surfaces of sheet metal parts, improve the ability of not being rusted around the solder joint, protect the solder joint, and ensure that the strength of the repaired body is not inferior to that of the original body.

3、 Foundation coating of shaping welding joint

Although the welding seam, solder joint and repaired steel plate surface have been polished and cleaned, there are still countless micro invasive and irregular small bumps which can not be seen by naked eyes, which are mixed with countless oxides, impurities, water vapor, etc. Although ordinary putty or antirust paint has antirust function, it can only prevent the invasion of external rust and play a temporary sealing role. As long as it is affected by humidity and other harsh environment, defects will appear quickly. If epoxy primer is used, it can play an effective protective role.

Epoxy primer is suitable for coating on the joints of panel or lap joint surface after welding, grinding, heating and rapid cooling shrinkage. It is a good rust inhibitor. Generally, the feather edge (i.e. the groove of the paint film) on the edge of the repair part is well done, and then the epoxy primer is applied after the surface is cleaned, which can ensure that the panel after various treatments will not rust for a long time, even if it is originally rusty, it will also prevent the expansion of the rust range.

4、 Foundation painting at joints

For the metal plate directly coated without special sealing treatment of sheet metal, the joints of automobile parts outside the welding or overlapping joint surface will be deformed and cracked due to the erosion of various sundries, such as oil, coolant, sewage, etc., and the vibration of uneven road surface. The anti rust sealing defense line of the interface is broken through and its function is lost. It is necessary to apply special sheet metal sealant at the joints of plates.

Sheet metal sealant is a non corrosive polyurethane structural adhesive, which can be used to fill, cover, bond and seal. Sometimes it can replace welding without damaging the paint. It has strong adhesion, high strength after curing, strong and reliable, can enhance the strength of single component and thin shell body, and can maintain the anti-corrosion function of welding or overlapping joints, especially in the inside and outside of wheel arch, chassis, rear compartment, cabin inner bottom plate and engine compartment.

5、 Foundation painting in cavity of box section member

During the car body overhaul, it will be found that the original factory sheet metal parts in the box section member cavity have been repaired due to accident reshaping before, and the steel plate has become thinner and penetrated. This is due to the neglect of internal anti rust, so that the rust is leaking out and expanding. These box cross-section members are often the main load components of the integral body, which will have an important impact on the crashworthiness and durability of the vehicle. Therefore, the anti rust treatment must be done well in the chamber of box section or bag type components.

The anti rust wax inside the car body is a good assistant for cavity protection. It has excellent permeability and can easily penetrate into all corners and joints. The automobile stamping parts have moisture resistance and drainage property, which can prevent the cavity that can not be sprayed with paint from rusting and wear out, and prevent the internal rust of the welding part of the body plate. In addition, special spray rods and nozzles can also be used to coat the inner surface of these plates. Ensure the final maintenance quality.

6、 Other functions of body foundation coating

1. Shockproof treatment at the joint of framework and skin

After the engine hood and luggage compartment cover are disassembled, the body sealant must be filled between the skin and the lining before closing. In this way, the closed skin will be close to the lining, otherwise the skin will be loose, there will be abnormal noise when opening or closing the engine hood or luggage compartment cover, and resonance sound may also occur during driving.

2. Heat insulation, moisture-proof and noise proof treatment of body bottom plate

On the upper surface of the body bottom plate, the metal surface of the sheet metal components and welding parts must be polished and sprayed with anti rust primer. After drying, the sound insulation lining or pad of the same type of body of the original factory shall be pasted to absorb the vibration and noise generated by vehicle movement.

For the lower surface of the underbody panel (the outer side of the body), the