Finishing aluminum castings?

[SED]

The 80 year old sand cast aluminum crankcase on the bacon slicer grabs dirt like a magnet.  It seems to have surface porosity that holds an oil film. 

I've heard that bead blasting peens the surface closing pores and that the surface stays cleaner after.  Any experience with this?

Are there other techniques?  (I've been told "tumbling" has a similar effect, but can't find any that do a very small number of parts locally.)

BTW don't want polished cases - the original surface should be preserved as much as possible.

Thanks!
Shawn

[Antietam Classic Cycle]

Bead blasting done correctly (high volume, low pressure) will leave a surface that's smooth and easy to keep clean. Same with vapor blasting. Vapor blasting seems to leave a more shiny surface than HVLP bead blasting though.

[SED]

Bead blasting down correctly (high volume, low pressure) will leave a surface that's smooth and easy to keep clean. Same with vapor blasting. Vapor blasting seems to leave a more shiny surface than HVLP bead blasting though.

Great info.  Thanks Charlie!

[cliffrod]

In a recent thread on another forum, a trusted acquaintance discussed use of zinc shot (approx $5/lb) to blast certain things like aluminum intakes.  It weighs less than steel shot (like I keep here for occasional stone use) so it can be used in a typical suction rig or cabinet for reuse.   It would likely peen a surface better than glass bead without being as aggressive as steel shot on something soft like aluminum.   I haven't tried it yet but probably will. 

This is an old factory aluminum Ford intake after he blasted it with zinc shot-

[SED]

In a recent thread on another forum, a trusted acquaintance discussed use of zinc shot (approx $5/lb) to blast certain things like aluminum intakes.  It weighs less than steel shot (like I keep here for occasional stone use) so it can be used in a typical suction rig or cabinet for reuse.   It would likely peen a surface better than glass bead without being as aggressive as steel shot on something soft like aluminum.   I haven't tried it yet but probably will. 

This is an old factory aluminum Ford intake after he blasted it with zinc shot-

Thanks Cliff.  Something to ask about. 

[injundave]

I have had success in the past using Pledge furniture polish. Spray it liberally on the castings then go for a ride (20 minutes or so). The wax in the polish gets into the pores of the alloy and dirt can be wiped off. Repeat as often as needed.

[Canuck750]

Vapor blasting will hone the surface smooth and close some of the porosity, once cleaned a liberal coat of ACF-50 will prevent corrosion and make clean up very easy. My 72 Eldo was cleaned and treated to ACF-50 over 5 years ago and grime just rinsed off. I think you will be very pleased with Vapor blasting, you can control the sheen by limiting the blast time.

[SED]

Thanks Guys!  Sounds like the pledge and ACF-50 may act similarly.  Have to try the ACF-50.

[SED]

Charlie, I may get the opportunity to blast my own castings.  Do you know the approx. pressure used in HVLP bead blasting?

[harry h]

I just got a vapor honing cabinet and LOVE IT!.  As Jim/canuck750 says, you can control the amount of shine.  Here is a manifold I did, the other one wasn't touched.  Started out pretty rough.  Used #13 glass bead.

[SED]

I just got a vapor honing cabinet and LOVE IT!.  As Charlie says, you can control the amount of shine.  Here is a manifold I did, the other one wasn't touched.  Started out pretty rough.  Used #13 glass bead.

That looks great.  What vapor honing setup do you have?

[harry h]

That looks great.  What vapor honing setup do you have?

Vapor Honing Technologies VH3630, I added a closed loop system.

[Ryan]

If the goal is to stop the seep without altering the look, can't you blast the inside? It won't make it easier to wipe off, but could slow or stop the oil from making its way to the surface.

[Antietam Classic Cycle]

Charlie, I may get the opportunity to blast my own castings.  Do you know the approx. pressure used in HVLP bead blasting?

15 psi. It takes a cabinet purpose made for it and large compressors with lots of volume. The shop that does it for me has two huge compressors in tandem to deliver enough volume.

I just got a vapor honing cabinet and LOVE IT!.  As Charlie says, you can control the amount of shine. 

Actually, that was Jim/canuck750.

A friend bought this vapor blasting setup and it does a great job, but is limited in what size parts you can do.
http://vaporhoningtechnologies.com/micro-vapor-hone/

[SED]

15 psi. It takes a cabinet purpose made for it and large compressors with lots of volume. The shop that does it for me has two huge compressors in tandem to deliver enough volume.

That is a direct pressure set-up rather than siphon?

[John Ulrich]

After cleaning.  Sodium Silicate brushed on the block, washed off then baked in the oven will provide a protective barrier in the pores against oil staining.

[Frenchfrog]

Interesting John...I use Sodium Silicate for waterproofing masonry and rendering...it's got unusual properties and not well know.

[Antietam Classic Cycle]

That is a direct pressure set-up rather than siphon?

Yes, it's a pressure system. 

[SED]

After cleaning.  Sodium Silicate brushed on the block, washed off then baked in the oven will provide a protective barrier in the pores against oil staining.

John, Interesting.  What flavor of sodium silicate?  And where do you get it?  There are several chemical versions for cleaning decks, sealing concrete, painting prep...  Some reportedly have impurities that could discolor the aluminum.

Thanks,
Shawn

[Antietam Classic Cycle]

I *think* this was the product recommended to me by Charley Cole:

https://www.aircraftspruce.com/pages/me/metalprep/alodine1001.php

[John Ulrich]

John, Interesting.  What flavor of sodium silicate?  And where do you get it?  There are several chemical versions for cleaning decks, sealing concrete, painting prep...  Some reportedly have impurities that could discolor the aluminum.

Thanks,
Shawn

I purchased mine at a science store that sold chemicals.  I googled the name and found multiple sources in various sizes from 4 oz. to gallons.  The stuff I used was in liquid form.  No idea what "version."  I see a clear version is listed.

[SED]

Thank you John and Charlie!  I'll let you know how it goes.

[Frenchfrog]

Over here Sodium Silicate is available at DIY stores....it seems to come in various thicknesses...In English it is also known as water glass , some times it is really runny, other times rather gloopy but always clear here.