Aluminum Polishing Part V - Compounding
Posted by Jay Schneider. Filed under Aviation.
May 5, 2011
GOING TO WORK - COMPOUNDING
Now that we have covered the types of surface conditions, defects and the different machines used to polish aluminum, it is now time to put your skills to work. I like to group aluminum polishing into three distinct stages 1) Compounding: 2) Polishing and 3) Finishing.
Definition: Preparing the surface for restoration. Compounding is a process whereby the surface is taken down to a level to which a total restoration can be built upon.
It is imperative and must always be remembered that the polish you choose is only 50% of what is needed to do the job correctly. The pad you choose is the other 50%. Depending on the severity of the surface condition, Compounding may be accomplished in several ways. One way may be as simple as using a conventional 7.5” X 1.5” 100% wool pad cutting pad and your favorite aluminum polish. This may be all that is necessary but some aluminum surfaces may be harder to bring back due to the metallurgy of the aluminum, outside forces and just plain oxidation. More drastic measures may be taken to expedite the compounding process. For a faster cut, simply change the pad to a 100% Wool 7.5” X 1” pile and the same polish. The shorter pile height of the wool pad will act as a stiffer bristle like action giving the operator a more aggressive cutting action. As general rule, the shorter the pile height of the wool, the more aggressive the pad. Several manufactures like, Rolite Company for example, offer a Pre Polish which is generally 50% more aggressive than their regular metal polish. This is certainly the way to go should you have to level the surface completely, or just want to speed up the process. For heavier corrosion issues, I have successfully used an abrasive loaded non-woven pad in addition to the polish. The scouring pads usually come in 6”X9” pads and are green, grey or maroon in color depending on their level of aggression. Here is how it works: purchase a 51/2” hook backing plate, attach the 6”X9” pad the plate, cut it down by following the outside diameter of the plate and you have yourself a nice, aggressive cutting disc safe for aluminum. Do not run this pad dry – use a little bit of the polish to help lubricate as you polish. Simply place a teaspoon amount on the surface and run the buffer half speed, (500RPM on a rotary), or #3 on an orbital machine. You’ll be amazed at the speed and quality of this cutting action.
I recommend working an area of about 1.5 sq ft. This area is very manageable and easy to learn the art of aluminum polishing if one has never tried to polish aluminum before. Make sure the area you will be focusing on is clean prior to polishing. Set the machine up with your pad, and place some of the polish on the surface. Place the pad down onto the surface and slowly bring up the RPM’s on the machine. Note: It is very important to move the machine in a north to south & east to west movement as you work the surface. This pattern will help minimize swirls and keep surface temps down as overheating can cause an oil canning effect of the sheet aluminum stretching it to the point where it cannot be brought back to its original state.
As you move along from area to area, occasionally inspect the surface of the wool pad for aluminum oxide build up which can be easily detected by the appearance of a dark greasy or black grease matting down the wool fibers. These tell tale signs indicate that you are on the right track and compounding correctly. However, aluminum oxides are detrimental to us in several ways: 1) the pad is becoming too aggressive which will create swirl marks, and 2) create excessive heat. This is now the best time to change or wash the pad.
Remember – consistent pad pressure and pattern as well as clean pads will yield the best results. Don’t become frustrated – aluminum polishing is truly an art form and takes time to become proficient and good at it. Next up? Aluminum Polishing Part VI – Polishing.
Keep the Blue Skies Up and Happy Motoring!
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