Grinding and polishing to repair car scratches

Car beauty, car "face" project - grinding and polishing to repair car scratches, after the car is used for a long time, the phenomenon of aging of the paint surface often occurs, even scratches, it must be polished and polished for repair, even lacquering repair.

 

After the car is used for a long time, the aging of the paint surface often occurs. Especially in the midsummer season, the sun exposure and rain erosion every day are easy to damage the paint surface. It is difficult to avoid accidentally scraping when driving. Once these problems occur, the owner must consider scratch repairing the vehicle (Figure 1). Generally, small areas of paint scratches and shallow scratches can be repaired by grinding and polishing (Fig. 2), while moderate scratches and deep scratches cannot be treated by grinding. Repair by lacquering. When the vehicle is moderately and deeply scratched, the surface of the car body will be deformed to different degrees. The small area concavity shall not exceed 5mm, and the putty shall be leveled by filling the putty and then the touch up treatment. When the deformation is more serious, it needs to be treated with sheet metal.

 

For a car to be repainted, first determine the type of original paint. Only when the type of the original paint is clearly known can the repaired car paint surface be consistent with the paint surface before repair.

 

 

 

First, the identification of the old paint of the car

 

 

 

Solvent method

 

Wipe the paint film with a white cloth dipped in lacquer thinner and observe the degree of dissolution of the paint film (Table 1).

 

 

 

2. Crude wax wiping method

 

The paint film was wiped with a white cloth dipped in crude wax to observe the degree of dissolution of the paint film (Table 2).

 

 

 

3. Sandpaper grinding method

 

Polish the paint surface with P500 ~ P1200 sandpaper (Table 3).

 

 

 

4. Hardness test method

 

The hardness of various paints after drying is different. Generally speaking, the paint hardness of two-component paint and baking paint is higher than that of self-drying paint. The usual method for determining the hardness and thickness of the film is to measure it with an electromagnetic thickness gauge or a mechanical thickness gauge. Use it according to the manufacturer's instructions.

 

 

 

Second, the treatment of moderate scratches

 

 

 

Polishing

 

(1) Check if the primer is properly attached.

 

(2) Use P320～P800 water sandpaper to polish the scratched part of the middle coating and the topcoat layer to make it smooth and smooth.

 

(3) The edge of the damaged part is trimmed so that the edge is not scratched, and the sanding area can be appropriately enlarged if necessary. The surface of the object to be sprayed is polished to a matt state with a sandpaper of P1500 or higher.

 

 

 

2. Cleaning and drying

 

(1) Use special cleaning agents to remove oil, paraffin and other foreign matter from the polished surface (Figure 3)

 

(2) Dry the cleaning surface with a drying device, or blow dry with compressed air.

 

 

 

3. Stickers

 

Paste paper is extremely important for repair, and proficiency can improve the quality of repairs and reduce unnecessary troubles. The method of pasting the topcoat paper used in different locations is also different (Figure 4).

 

(1) Anti-Paste: Applicable to dark line slot and open line slot.

 

(2) Positive stickers: Applicable to the decorative strip interface.

 

(3) Compaction sticker: suitable for large-area spraying and repairing at the edge of the gap.

 

(4) Cover: Applicable to tires, headlights and two parts at the same time.

 

(5) Cut: used for car logo.

 

 

 

4. Medium coating (spraying primer)

 

(1) Spray the adjusted primer evenly in the grinding position, and the virtual spray area is as large as the sanding position below P600. This is sprayed 2 to 3 times, and dried for 3 to 5 minutes each time.

 

(2) Drying of the medium-coated paint film, if the repaired area is not large, it can be naturally dried at room temperature, but the time is long; generally, the far-infrared drying lamp or the far-infrared drying box (reflective type) is used for local drying. The distance should be about 500mm, the baking distance is too close, and the local overheating will cause the primer or paint surface to foam.

 

(3) After the medium-coated paint film is dried, the make-up paint film is lightly ground with P600-P800 water-sand paper to make it smooth and flat, and the touch is not rough. If there are sand holes, fill the eye ash and polish it repeatedly. There are two types of grinding methods: dry grinding and wet grinding. When dry grinding, blow the sanding part with compressed air (Fig. 5), and then clean the floating ash with a clean sticky cloth. When wet grinding, polish the surface of the repaired medium with P600~P800 water sanding paper. Also, polish until touched by hand without roughness, rinse with water, dry or blow dry with compressed air, preferably with a far-infrared light box.

 

 

 

Third, deep scratches

 

 

 

1. Remove the paint film and putty from the damaged part, and polish the edges with water sandpaper (P60 ~ P180) to make it slope.

 

 

 

2. Clean the scratches with a dewaxing cleaner and allow to dry.

 

 

 

3. Mix the atomic ash with a hardener at a certain ratio, stir evenly, and then apply it. To stratify the scraping, the first layer can be scraped with alloy or fiber ash, and then the ordinary quick-drying putty can be scraped on top of the layer until the recess is filled.

 

 

 

4. After the atomic ash is dried, use the P60~P400 water sandpaper to level the atomic ash. If it is not flat, continue to fill until it is flat.

 

 

 

5. Check that the polished surface is smooth and smooth.

 

(1) Hand touch check

 

Repeatedly repairing the paint surface with the palm of your hand, the quality requirements are met without the feeling of blocking the hand.

 

(2) Visual inspection

 

Pour water on the surface to be repaired and then observe it on the side. If it is not flat, you can see a wave.

 

 

 

6. Clean again with dewaxing car wash solution, dry and spray the primer, and polish. When grinding, use the water sandpaper of P1500 or higher to polish the area around the sprayed part.

 

 

 

7. Cover the unpainted area with tape and cover paper. Then use a degreaser to wipe the parts that need to be sprayed 1 or 2 times. After the degreaser is dried, use a dusting cloth to remove dust. It should be noted that it is absolutely impossible to wipe with the degreaser not dry.

 

 

 

8. Select the appropriate primer to spray and polish.

 

At this point, the repair operation of the car scratch has been introduced. In the actual repair work, we must be proficient in the repair method of car scratches, so that we become a qualified car beautician.