C4AJ01F1 - 307
OVERHAUL, ALUMINIUM BONNET
The rework operations require tooling used only on aluminium (risk of corrosion by contact if using tooling meant for steel panels) .
1 - SPECIFIC FEATURES OF ALUMINIUM
1 - 1 - BRITTLENESS OF THE SURFACE
The high-level sensitivity to knocks and scratches requires care in all handling operations and in storing .
A very clean condition is also indispensable to avoid scratches from various waste from all sources .
In all cases, reworking with abrasive materials is to be considered as tricky and must be carried out judiciously .
1 - 2 - THREAD CORROSION
The aluminium protects itself by creating a coating of alumina; there is therefore no corrosion which causes perforation as there is with steel .
On the other hand, so-called thread corrosion, started by damage to the paint film, can develop by cell effect on aluminium .
Since sanding is a factor which makes this type of corrosion worse, sanding of stripped metal should be kept to a strict minimum .
This corrosion shows itself as a thread which goes under the paint film and which can in the long term cause blistering of the paint; this particularly applies to stone chips on the front of the bonnet .
Sandpapering aluminium with sandpaper which has previously been used for steel causes particles of steel to become encrusted on the surface of the aluminium .
It is therefore essential to separate sandpapering of aluminium from sandpapering of steel to prevent any risk of thread corrosion .
2 - EQUIPMENT USED FOR REWORKING ALUMINIUM
Kit (workshop part no. (-).1527) comprising :
WARNING : the tools have an aluminium-coloured identification in addition to their marking .
IMPERATIVE : use only abrasive paper P150, P320, P500 .
3 - PROCEDURES FOR DEALING WITH FAULTS
3 - 1 - DENT
Note results using a spoon .
Pass the panel beater's block, 150 paper .
Pass the body-builder block without going onto the paper 320 .
3 - 2 - SPLINTER
Use a wooden tapered needle .
If necessary, give a few blows at an angle with the bumping hammer .
Pass the panel beater's block, 150 paper .
Pass the body-builder block without going onto the paper 320 .
3 - 3 - DOWEL PIN
Use a wooden tapered needle .
If the fault is significant, work with the wooden mallet, supported by the wooden dolly .
If the dowel pin is still noticeable to the touch, use the bumping hammer at an angle .
Pass the panel beater's block, 150 paper .
Pass the body-builder block without going onto the paper 320 .
3 - 4 - SCRATCHES
Pass the panel beater's block, 150 paper .
Pass the body-builder block without going onto the paper 320 .
IMPERATIVE : discontinuation of the grooved file, the orbital sander. restrict to an absolute minimum the sanded surfaces; remove dust and swarf .
4 - SCRATCHES DOWN TO THE BRACKET
IMPERATIVE : reconstitution of original base on stripped backing: apply a layer of zinc chromate with etch primer (guarantee of satisfactory adhesion for the following products) .
Application to the area concerned of a twin-component surface or finisher primer (guarantee of long life and quality of repair) .
Carry out stoving for 30 minutes at 60 °c .
Sanding down of the surface to P500 .
Continue the process by applying the paint finish .
5 - REPAIR OF PANELS WITH FLATNESS FAULTS
WARNING : use of any kind of polyester mastic is prohibited on aluminium .
Flatness defects will be rectified by successive applications of primer followed by suitable sanding .
NOTE : if the repair cannot be undertaken, the part must be replaced .
Traditional stages of re-painting :
WARNING : specify finer granules (go down one level), in fact aluminium is more fragile than steel and the abrasive graules may cause deep scratches which are difficult to conceal .
6 - UNDERCOATS; FINISHING
IMPERATIVE : observe the repair procedure recommended by service technical departments, the paint products offered have successfully complied with an extremely strict specification sheet, which offers the optimum end result .
IMPERATIVE : adhere to the technical data sheets of the suppliers .