The surface treatment process
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The surface treatment process
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The first anti-corrosion steps are taken in the body shop. Galvanized sheet steel is used for those parts of the body that are most exposed to corrosion. See also “Body repairs”, Technical description, Galvanized body parts.
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1.
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Cleaning of bodies from the body shop.
When the body arrives at the paint shop it goes through an initial cleaning process. This is where all the mechanical machining remnants and a large proportion of the grease and oil remaining on the body after assembly are removed.
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2.
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Degreasing
To attain as good a base as possible for the continued surface treatment, the rest of the grease deposits are removed from the body with an alkali degreasing agent.
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3.
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Phosphatising
Phosphatising gives the metal a good basic protection and base for the primer.
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4.
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Washing
The body is washed to remove residue from phosphatising.
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5.
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Passivation
A solution containing chromium compounds is flushed over the bodywork. This makes the phosphate coating denser and further increases the corrosion protection.
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6.
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Washing
The body is flushed with desalinised water.
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7.
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Electrocoating (ED)
The body is lowered into a bath containing anti-corrosion paint and a negative electric current is led to the body. The positively charged paint particles are drawn to the body in the same way as iron filings to a magnet. In this way, a layer of anti-corrosion paint covers the entire body, cavities, joints, etc.
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8.
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Washing
After the ED bath, the body is immersed and flushed clean from surplus paint.
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9.
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Oven hardening
The paint from the ED bath is hardened for 17 minutes once the body has reached a temperature of +182°C.
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10.
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Inspection and grinding
Any dust particles and paint run are removed.
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11.
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Sealing
Seams and joints over the whole body are sealed with PVC sealant. This is mainly to prevent moisture from entering but it also acts as a sound insulator.
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12.
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Noise suppression mats
Noise suppression mats are placed in strategic points in the body to reduce resonance.
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13.
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Cleaning
Dust is removed from the body.
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14.
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Underbody treatment
Stone chip protection and underbody compound are applied all over the bottom plate and in the wheel housings.
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15.
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Oven hardening
The body passes through an IR oven so that the sealant hardens. The sound insulation batts also soften slightly at the same time and take the form of the body panel contours.
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16.
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Intermediate coat
The intermediate coat forms a good base for the top coat, for both its adhesion and its appearance. The intermediate coat also contributes to the corrosion protection by withstanding stone chipping. The paint is applied by a robot with rotation cups. When the cups rotate, a fine spray is formed which migrates to the body and gives it an even coat. Interior surfaces that are difficult to reach are painted manually.
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17.
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Oven hardening
The intermediate coat hardens for 32 minutes at a temperature of +155°C.
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18.
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Grinding
Any dust particles and paint runs are levelled off.
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19.
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Cleaning
Grinding dust and other foreign particles are removed from the body so that it is absolutely clean before the top coat is applied.
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20.
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Top coat
The top coat is applied in the same way as the intermediate coat with robots fitted with rotation cups. Metallic paint is applied in two coats. First a thin coat with a high pigment content and then a thick coat of clear enamel to protect the pigment and give it a high gloss.
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21.
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Oven hardening
The top coat hardens for 30 minutes at a temperature of +140°C.
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22.
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Final inspection
After painting, the body is inspected rigorously. If any paint runs, scratches or dust particles are found in the paint or if there is any damage in the coating, the body is returned for paint repair before going on to the next station.
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23.
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Anti-corrosive treatment
Penetrating wax is injected into cavities in the sills, members, etc.
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24.
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Oven hardening
The body is heated to +80°C for approx. 2 minutes so that the wax can spread maximally in the cavities and dry.
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