topic 22096
Polishing Cast Aluminum
adv.
A discussion started in 2003 but continuing through 2019
2003Q. If I have a course Aluminum Intake Manifold (cast molded) and was wondering if there was a certain technique to getting this to a smoothed polished finish?
Chris Hoglund- Auburn Hills, Michigan
A. Big job for you. Takes me usually 5___8 hours, going flat out. Always use a lubricant, I alternate between kerosene and vegetable fat. Use grit rolls of 80_120_240_320. You need about 15 of each grit. These rolls go on a tapered spindle in an electric die grinder, no faster than 3000 rpm. That was the easy part! Next, use hard felt cones and grey cutting compound all over. Don't forget the detail in nooks and crannies -- the hard part! Wash off with degreaser. Finish with a stitched cotton buff and tripoli all over. You must use a fast __3850, rpm and powerful machine for this. Forget adapting bench grinders or old washer motors, they don't cut it! To really brighten it up, use a spiral stitched cotton mop of two sections by 10 inch dia., plus hyfin compound sparingly. Good luck!
Mark Gunn- NSW, Australia
How to finish aluminium small castings?
2003adv.
Q. I need some technical advice on the following:
1. What is the best method to get excellent surface luster and finish on cast aluminium curio items such as statuettes? I have seen some with excellent finish but I don't have an idea to produce the item myself.
2. What is the type of tank to be used for electropolishing solution (mixture of heated acids)? Our stainless steel tank doesn't last long.
Alex Abraham- Ernakulam, Kerala, India
2003
A. Vibratory tumblers work quite well, you will however round off the detail the longer it is tumbled for. With our castings (small lightweight high detail) we run them for several days in 3 stages of silicon carbide imbedded plastics, followed by a full day cycle in saw dust imbedded jeweler's rouge [paid link to product info at Amazon]. They come out with a great finish!
As for bright dip-electropolish tank, try a ceramic lined vessel. If you're like me and do this is in small quantities you can find the tumbler setups through jewelry suppliers, and you can even get ceramic lined containers in various sizes at your local grocery store.
Good luck!
Jason Aube- Flint, Michigan
Polishing of aluminum sand castings
2005 -- this entry appended to this thread by editor in lieu of spawning a duplicative threadWE ARE DOING SAND CASTING OF ALUMINUM GRADE BS 1400 LM4 AFTER MACHINING ON LATHE MACHINES WE HAVE TO DO POLISH WANT GLASS SURFACE FINISH KINDLE SUGGEST ANY PROCESS AO CHEMICAL
SHAPES ARE COMPLICATED OF OUR ITEMS or SUGGEST ME MATERIAL TO BE USED WITH CHEMICAL ANALYSIS
DEEPAK INDUSTRIES - INDIA
adv.
Q. Hi Pros,
How to get a good high mirror surface on cast ADC 12 aluminum without black marks? We are producing some 10-20 cm high solid aluminum items that are meant for indoor use.
We currently have 2 problems with this surface.
- Some items have black dots in the surface; can anybody tell how to get rid of them?
My guess is that after the casting process, when the items cool, there are particles in the air that contaminate the items.
- We get oxidation so the surface turns white-ish after 6 months; is there any way to close the surface of aluminum better? (I don't want to give the items any form of coating).
Thank you very much for you reply.
Product development - Denmark
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October 17, 2012
A. #1 If it is not in the cast metal then it has to be the environment  AF Kenton Hatboro, Pennsylvania October 17, 2012 A. Finn, 
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October 19, 2012
Q. Hi AF Kenton
Thanks for reply. I also suspect the environment to be the bad guy!
Could you please give me some more info about how to slow the oxidation down, by gas, and liquid?
(Maybe with links or other)
Hi Anna B.
Thanks for reply. I am currently trying to get the spec. of the AD12, I will let you know ASAP.
- Denmark
A. I would be reluctant to suggest a protective coating until you correct the problem of the spots. Gases are not very economical protective systems, so I'd look into liquids. Any petroleum base product offers some protection. Again you need to define your needs in the way of protection and use.
AF Kenton
Hatboro, Pennsylvania
July 4, 2016 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread
Q. I recently purchased a large box of aluminum castings used for jewelry and other items. Some is rough cast and need sprues removed, all the way to polished but uncoated pieces. I know how to remove casting marks with a grinder, but the castings are rough (sand cast). Will a tumbler or vibratory tumbler polish out these pieces? (What type media?) And do I need to seal the finished (shiny) pieces as they still will leave dark aluminum residue on skin, etc. Any ideas? Thank you!
Teresa Wallaceartist - Okla City, Oklahoma USA
July 7, 2016
A. If your castings are rougher than 35 RMS you can try a fast cut (rough) ceramic media in a vibe.The larger the better for speed or a time period 4-8 hrs or more. After that you, you may want to go to a coarse plastic media for a couple of hours or until smooth. A third step brightening can be done wet or dry.
All metals will oxidize over a period of time. The sooner you can protect them the better.
AF Kenton
Hatboro, Pennsylvania
January 21, 2019
Q. Hello hope you all are doing well over there.
We are making some cast aluminum products but we are not getting the desired surface finish while turning. There are some people in Agra city of India who are doing the same thing. They are getting the finish like chrome while turning ... but the problem is they are not telling is their technique. What should we do to get chrome like surface finish on lathe?
Do we need some kind of special bit metal or lathe hand made tool? Please suggest something and helps us to reach our goals.
Thanking you.
Aluminum utensils - Moradabad,U.P,India
January 2019
A. Hi Mohd. Please fully read this thread then search the site for "polishing aluminum". How do you know they are doing it on a lathe? If they are doing it on a lathe, I would be virtually convinced that they are doing a multi-step polishing sequence as described here, not turning to a chrome-like finish. If you are attempting to reverse engineer someone else's process, you should get some of their parts and do a full inspection and metal analysis so you are 100% confident that their material is absolutely identical to yours. Good luck.
Regards,
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Striving to live Aloha