204 Section 2 Nonstructural Repairs Copyright Goodheart-Willcox Co., Inc. area. At the same time, the lead stick must be heated enough to soften it. Hold the torch at an angle so it can heat both the lead stick and the fill area as the lead is applied to the panel. Lay out enough softened lead to overfill the fill area. After applying the lead, the repair must be smoothed. During this step, the lead filler on the panel is softened with heat. The softened lead filler is then spread out and smoothed with a wooden paddle. The face of the paddle is coated with a layer of tallow or paddle lubricant to prevent the lead from sticking to the paddle. To coat the paddle with tallow, heat the face of the paddle with the torch and touch the face of the paddle to the surface of the tallow. The hot paddle face will melt the tallow. Once the lead filler cools, it can be filed in the same way as filing high areas when metal finishing. The lead can be finished by block sanding in the same way as body filler. Reapplication of lead filler is not recommended because the existing lead on the panel will need to be heated and may melt off unless extreme care is taken. Lead filler can be covered with body filler, if needed. The lead dust created when filing and sanding can be hazardous to your health. Always wear an approved respirator when working with lead products. Aluminum Panel Repair Operations Some vehicles are made entirely of aluminum. Other vehicles may have one or more aluminum panels, such as a deck lid or hood. Aluminum is lighter than steel. Additionally, aluminum is easier to recycle than steel. It is anticipated that the use of aluminum body panels will increase in the future. Low-crown aluminum panels are the easiest aluminum panel to repair. Dents are the most commonly repaired type of damage in an aluminum panel. When repairing a dent in a low-crown panel, care must be taken to prevent stretching the panel. Aluminum is softer than steel. Therefore, hammer-on- dolly straightening will easily stretch aluminum. Do not use hammer-on-dolly techniques when straightening aluminum. All metal panels are work hardened by folds and body lines during manufacture. Damage adds additional work hardening. Aluminum can crack due to work hardening straightening it may cause cracks. Heating the panel during straightening will minimize the possibility of cracking. When buckles are released from WARNING a damaged steel panel, the metal tends to return to the undamaged location. Aluminum panels do not have this memory. Steel particles left over on grinder disks, sandpaper, and files will contaminate bare aluminum. Use dedicated tools and sandpaper when working on an aluminum panel. Make the repairs in an area of the shop that is isolated from the steel repair area. Use a dust extraction system designed for removing aluminum dust. Aluminum is much more sensitive to heat than steel heat spreads faster through an aluminum panel than a steel panel. To prevent warpage, power sanders used on aluminum panels should be equipped with a foam backing pad. The use of 80-grit (or finer) sand- paper and disks will prevent excessive removal of aluminum while sanding. Aluminum does not change color when heated as steel does. Controlled heat is very beneficial in repairing aluminum. Do not heat an aluminum panel to more than 400° F. The adhesive that binds aluminum parts is weakened by tempera- tures above 400° F. Therefore, always check the back side of a panel for adhesives before heating. Avoid heating panels that contain adhesive. Monitor the temperature of the repair area with an infared ther- mometer as the panel is heated. Due to the shiny surface of bare aluminum, an infared thermometer cannot make an accurate reading of bare aluminum. Leave the paint on the panel while heating. If the paint must be removed, apply a piece of masking tape to the bare area and point the infared thermometer beam at the masking tape. Heating aluminum above 600° F, called annealing, permanently weakens the metal by removing work hardening. Aluminum melts at 1200° F. When performing shrinking, leveling, or raising operations on an aluminum panel, the hammer blows must be softer than those used on steel. Tap lightly. The faces of hammers and dollies used for aluminum repair must be free from nicks and gouges. Any irregularities on the faces of the straightening tools will be transferred to the aluminum. Some technicians use plastic- or rawhide-faced hammers to straighten aluminum. Most body fillers used on steel can also be used on aluminum. The aluminum panel should be coated with epoxy primer before applying the filler. Edge Alignment Figure 9-64 shows an aluminum hood with a bent edge. The edge is three layers thick and has work hardening from the bend in the hem. To mini- mize the chance of cracking, the lip is heated to less than 400° F with a heat gun. The heating starts at the perimeter of the bend and works toward the center. Immediately after the panel is warmed, a wood block is used as a dolly to support the undamaged areas and the bend is straightened with a C-clamp.