Body Pre-Treatment, Painting and Sealing
The body is pre-treated to ensure high resistance to corrosion and stone chip damage. Prior to the first major pre-treatment process, the body shell is high-pressure washed to remove any metal dust and residual oil.
The first major pre-treatment process consists of phosphate and electro-paint deposition, which together with zinc coating, forms the basis of the corrosion protection. This process includes high pressure knock-off, alkali de-greasing, zinc phosphate conversion of body steel (dissolving iron and coating with zinc phosphate crystals), trivalent chrome rinsing and demineralized water rinsing, sealing all chemicals and impurities.
Both dip and spray techniques are employed and the bodies are submerged to the waistline during the first and third rinses of the main phosphate clean. Chemical strengths and solution temperatures are continuously monitored and accurately controlled throughout the process.
An 80% water primer is then cathodic electro-deposition applied to the thoroughly cleansed bodies in a uniform "sag-free" film 18 to 32 micron thick. Optimum durability of the electroprimer is achieved by finally curing in a stoving oven at 165 °C for a period of 20 minutes.
All underbody seams of the fully primed bodies are then manually sealed, to prevent water and dust ingress into the vehicle and to enhance corrosion protection.
A semi-automatic airless spray application of a PVC coating 800 to 1000 g/sq.m, is applied to the underside of the main floor panels, trunk floor and rear wheel arches.
The upper panels of primed and externally sealed body shells are next lightly scuffed to remove imperfections and a PVC coating is applied to all internal seams by an airless spray technique. A PVC bead seal is also applied to the doors, hood and trunk clinch joints.
Following anti-corrosion, sealing and priming treatment, the bodies enter the first stage of cosmetic painting. This consists of the application of two coats of a highly chip resistant polyester surfacer, employing high voltage electrostatic spinning bells, to achieve a final film thickness of 35 to 50 micron. Between surfacer coats, a polyurethane coat is automatically applied to the sills to impart even greater resistance to stone chipping.
All interior panels are then painted using a color keyed sealer, wet-on-wet with a surfacer material, after which the body shells are stoved at 160 °C for a period of 20 minutes. Further protection against corrosion is provided by a medium solids black pigmented wax which is airless spray applied to vehicle undersides.
Critical body box-sections are similarly protected by spray injecting a high solids wax. This is then re-flowed at 70 to 90 °C to achieve optimum seam/joint penetration and form a resilient and durable internal coating.
After Full wet sanding, rinsing and drying to provide a good substrate, a color-keyed semi-matt sealer coat is applied using electrostatic bells to achieve a film build of 25 to 35 micron. The bodies are then stoved for a further 20 minutes at a temperature of 145 °C and subjected to a local "seek-and-find" de-nib operation prior to the final two coat process. The final top coat finish is achieved by using polyester base coat colors and an acrylic sag resistant clear coat. This clear over base (COB) process produces a high gloss, durable paint finish with a film thickness of 50 to 65 micron, which is finally cured at a temperature of 135 °C for 20 minutes.
The Munsell three dimensional system of color management is employed to achieve highly accurate control of vehicle colors. This system ensures that paint pigmentations are accurately maintained and facilitates vigorous final checking of finished vehicles for color match. The hue of individual panels such as trunk lids, doors and hoods is in some instances adjusted to offset the effects of differing light angles. Where applicable, coachlines are manually applied and radiant heat cured on the completed and valeted vehicle prior to hand spray application of a protective wax coat.