Material Selection - Interference Fit into Aluminum Housing

T

tb123_

Plastic

Joined

Nov 23, 2020

• Nov 23, 2020

• #1

I'm making (designing) some bearing cups to hold bearings that will press into aluminum housing (bearing presses into cup and then bearing cup assembly presses into aluminum hole). I could use some recommendations on material selection for the bearing cups.

Goals: 1. prevent aluminum galling, good machinability/low cost, corrosion resistance is desired but not necessary

So far I am considering 4130 (will rust but the cost is lower than SS), 304SS, 416SS, or 7075-T6 type III anodized.

Any input would be greatly appreciated!

 

M

Milland

Diamond

Joined

Jul 6, 2006

Location

Hillsboro, New Hampshire

• Nov 23, 2020

• #2

Check out galvanic corrosion - using stainless steels, unless properly passivated, may cause corrosion from electrochemical actions.

Of your choices, I'd probably use 7075, but that means good control of diameters and interferences to minimize excess press and risk of deformation during assembly.

 

M

Milland

Diamond

Joined

Jul 6, 2006

Location

Hillsboro, New Hampshire

• Nov 23, 2020

• #3

But it begs the obvious questions - why not size the main part for the bearing press? And if you need isolation, perhaps a hard plastic cup is the way to go? Even a chemical retainer might work and save costs due to less precision needed for the mate.

 

T

tb123_

Plastic

Joined

Nov 23, 2020

• Nov 23, 2020

• #4

Milland said:

But it begs the obvious questions - why not size the main part for the bearing press? And if you need isolation, perhaps a hard plastic cup is the way to go? Even a chemical retainer might work and save costs due to less precision needed for the mate.

Click to expand...

The "main part" is already produced. This is an automotive suspension part (OEM material is aluminum - no changing this) that I am making replacement bearings for the no-longer-available OEM bearings.

Thanks for the heads up on the corrosion issues I might run across with touching dissimilar metals. I had not really considered this. The OEM bearing housings are some type of steel (magnetic so I don't think they are stainless). This car uses many steel bearings pressed into aluminum all over the place including wheel bearings. There are no signs of corrosion issues with the OEM parts after decades of use... I would like to match the material that the OEM used if I can determine what it is...

 

jim rozen

Diamond

Joined

Feb 26, 2004

Location

peekskill, NY

• Nov 23, 2020

• #5

If you have the ability to heat the aluminum housing you can make your steel part an interference fit. This is a common approach to fitting steel ball bearings into aluminum housings.

Will not work well if you use 7075 however.

 

T

tb123_

Plastic

Joined

Nov 23, 2020

• Nov 23, 2020

• #6

jim rozen said:

If you have the ability to heat the aluminum housing you can make your steel part an interference fit. This is a common approach to fitting steel ball bearings into aluminum housings.

Will not work well if you use 7075 however.

Click to expand...

I'd prefer not to need heat. The factory parts are some type of alloy steel and press in easily with about 0.0025 interference and approximately 1" diameter.

 

L

Limy Sami

Diamond

Joined

Jan 7, 2007

Location

Norfolk, UK

• Nov 23, 2020

• #7

If you're considering anodized Alu, I'd go for 12L14 chemi blacked and call it good.

 

J

jz79

Stainless

Joined

Mar 21, 2017

Location

Latvia

• Nov 23, 2020

• #8

zinc plated low carbon steel would be my choice (that is what the oem bearing housing is basically), next would be any aluminum apart from 2xxx or 7xxx, these 2 have lower corrosion resistance and the suspension part itself usually is some "gum" alloy casting, meant to bend before braking, way way before braking, so using a high strength al alloy makes no sense, hard anodizing is fine, but regular will do the same thing for less money

zinc plating is basically next to aluminum on galvanic compatibility chart, stainless is very far from al - so - not recommended here, it will most likely cold weld/gall and come out together with chunks of al casting

 

T

tb123_

Plastic

Joined

Nov 23, 2020

• Nov 23, 2020

• #9

My thought to use 7075 was that it appears to be one of the hardest aluminum alloys. The hardcoating was to further increase hardness, not necessarily to increase corrosion resistance. I am under the impression that aluminum galling mostly occurs when both sliding surfaces are soft... that's why I was thinking it would be best to use something harder for the pressed in part.

 

M

Milland

Diamond

Joined

Jul 6, 2006

Location

Hillsboro, New Hampshire

• Nov 23, 2020

• #10

I'd like to check on something - when you say "bearings", what type of bearings are you using? Do they have any cushioning aspect, or are they a rigid plastic bushing, or a rolling element type?

 

T

tb123_

Plastic

Joined

Nov 23, 2020

• Nov 23, 2020

• #11

spherical bearings

 

M

Milland

Diamond

Joined

Jul 6, 2006

Location

Hillsboro, New Hampshire

• Nov 23, 2020

• #12

tb123_ said:

spherical bearings

Click to expand...

You're probably better off with a plated steel rather than the 7075 then. With a metal/metal bearing you get high instantaneous loads when impact occurs (no rubber cushion), and 7075 doesn't have the cracking resistance that a mild steel would have.

But you would want the steel to be zinc plated, as suggested previously.