View Full Version : Mold polishing

12-17-2004, 09:43 PM
I need to polish a small mold for a silicone rubber part, my efforts so far with a little buff wheel and dremel have been pretty poor, as the buff marks are showing up in the rubber after molding as a sheen, and dullness. I'm using a fine aluminum polish, some green stuff I picked up at Lowes.

The mold is 6061, the cavity is full of little nooks and crannies like an english muffin.

If anyone knows how to tackle this I'd love to hear it.

12-17-2004, 11:54 PM
Put baking soda into a sand blaster and be VERY gentle. I'd go and buy a small cheap hand held unit to keep things simple. The mould would then at least be consistant.

12-18-2004, 12:11 AM
I have a bead blast cabinet, I can just change out the bead for some baking soda. That will leave a smooth surface?

12-18-2004, 12:25 AM
Hi, I use vibratory tumblers to polish my prosthetic parts. I can achieve almost a mirror finish in 2 steps even down to the nooks and crannies. It usually takes about 9 hours or more depending on the amount of polish within the bowl. Send me a picture of what you are trying to polish. MechMan

12-18-2004, 12:33 AM
I have a 10 gallon vib polisher too....for those big .50 BMG rifle casings I reload. You use corn cob / walnut? I'll try that (why I never thought of it I'll never know).


12-18-2004, 01:46 PM
Hi, Corn cob with aluminum polish. It usually takes about a quart of polish for the amount of parts I do. My tumblers hold about 5 gallons of media and a gallon of parts. I plan to post pictures soon of this process. The results are extremely good and require hardly any labor at all. MechMan

01-02-2005, 11:28 PM
If the issue is marks, then only a mechanical method or very skilled polisher will do. Otherwise, the silicone should have no release issues. I would recommned you use the method which best suits the geometry and size of the part.

Depending on how agressive the buff marks are, you may not be able to get rid of them with baking soda or any other blast media as it will not address the height tranisition you are seeing in the parts. Not knowing how you machined the features, I would suggest the following for a milled part.

1. If possible remachine the feature using the smallest step over and two profile paths in different directions (this should reduce or elininate the scallops).
2. Use scotsh brite (green in color) this will eliminate the tool marks and prevent agressive metal removal.
3. Abrasive blast if you want. This will not give you a high polish, and my experience in PDMS is that it adds a surface energy to the mold which makes demolding tough. I have not used it on silicone I only add the PDMS excerpt as a disclaimer. Unless you absolutely need a high polish I would think the scotch brite finish would do you fine.
4. If the high polish is absolutely necessary, then do yourself a favor and hand polish. Mechanial systems are just too agressive and aluminum is too soft to tolerate polishing screwups.

Shoot me a PM or email if you need more alumium mold polishing info.


Jim Estes
03-01-2005, 11:27 PM
Most of the molds that I have built for rubber parts, have had a bead blasted surface. This helps with release of the part, and it hides flow lines and imperfections in the part. ALuminum is very hard to polish correctly because material can be removed very quickly with aggressive techniques. Patients is the key to polishing aluminum. Don't be in a hurry to grab that coarse grit, you may be doing more harm than good.


03-02-2005, 12:35 AM
Try a bag of white rice in your vibe machine.(dry no liquid !!!) low intensity, long time(24 hrs). i use this to polish 6061 t6 . also try bright dip with nickel from any good plater after the rice treatment.