Aluminum is a silver-white, soft, nonmagnetic, ductile metal called bauxite, and is the most abundant metal on Earth. Aluminum is used extensively in the aerospace, transportation, packaging, and building industries. As with any non-ferrous metal, aluminum objects can be manipulated and repaired with a torch. Aluminum melts at 1220º Fahrenheit (660º Celsius). In order to braze or solder aluminum, you will need to use an appropriate brazing material that melts at a lower temperature than the aluminum. One of those materials is an alumite brazing rod that melts at 700º - 750º Fahrenheit (400º Celsius). Here is the process to repair an aluminum object by brazing:
Prepare the Aluminum - Aluminum must be thoroughly cleaned in order to be brazed. To prepare and clean the aluminum object, do the following:
- Hammer the Aluminum - With a steel hammer, get rid of any dents or bumps in the aluminum by pounding it on a steel anvil. Continue to hammer the aluminum by pounding it on a wooden block that is softer than the steel anvil until all flaws are removed.
- Brush the Aluminum - With a coarse stainless steel brush, scrub the area to be braised thoroughly to rid the metal of any and all corrosion, oxidation, or impurities present on the metal. If any oxidation remains on the aluminum object, it cannot be joined to another piece of aluminum or repaired with an aluminum braising rod. Widen the area that you are brushing to include the area surrounding the repair site.
- File the Aluminum - File all areas to be joined with a series of steel files that range from coarse to fine. The action of filing roughs up the aluminum surface and exposes the pure element of aluminum underneath. Continue to file the area to be braised with finer and finer steel files until you have a smooth surface.
Braze the Aluminum - This step involves the introduction of a propane, or oxygen acetylene brazing torch and an alumite brazing rod:
- Light the Torch - Turn on the gas on the top of the fuel tank and point the tip of the torch at a flint spark torch igniter. Create a spark with the igniter and light the flame of the torch. Turn the flame up to its maximum setting to clean out the fuel hoses and then down to the size flame you wish to use.
- Heat the Aluminum - Heat the entire aluminum object's surface with a large, bushy flame on the torch. Work in a circular motion and continue to heat a large area of the aluminum object until it glows with intense red-orange heat. Once you have the entire area glowing, turn down your torch to create a smaller, more pointed flame and concentrate the torch heat on just the area that you want to repair. Keep the torch in this area to maintain the red-orange glow of intense heat from the torch.
- Heat the Alumite Brazing Rod - With the torch in your non-dominant hand, keep it moving in a circular motion to maintain heating the aluminum object. With your dominant hand, bring in the alumite brazing rod and heat it along with the aluminum object until they are both glowing with intense red-orange heat. Once both the rod and the object are glowing together, they are both just under their melt temperatures. Immediately bring the rod into contact with the aluminum object and melt the tip of the rod onto the object. Completely cover the area to be repaired with the molten alumite brazing rod. The molten metal rod will continue to melt and cover the aluminum object until you pull the flame away.
Finish the Aluminum - After you have completely covered the aluminum object's repair site with melted alumite brazing rod, pull the flame away and turn off the torch. Allow the aluminum object to air cool.
- Pickle the Aluminum Object - When cool, plunge the aluminum object into a solution of heated, sodium-bisulfate liquid pickle. This will clean off any oxides created during the brazing operation. Allow the aluminum object to remain in the pickle solution for 10 - 15 minutes. After you have pickled the object, remove it from the pickle and rinse with plain water.
- File, Sand, and Polish the Aluminum Object - Once the freshly pickled and rinsed object is dry, file the repaired area with steel files followed by several grades of aluminum oxide sandpaper to completely smooth and refine the surface. When you have achieved the finish that you want, wipe the entire area with a soft dry cloth to remove any filing and sanding dust particles. Your final step is to hand or mechanically polish your aluminum object.
Once you have repaired and polished your aluminum object, you can examine it and make changes by starting this process again to refine its shape and surface texture with steel tools. This is a slow process that allows you to get the exact effect that you want with steel shaping and smoothing tools. When you have achieved the effect that you want, polish as desired. For further assistance, contact local professionals, such as those from Exoticar Paintworks Inc.