Coating to prevent carbon and stainless steel to corrode togehter

[Grettir]

Good day!

Introduction:

We produce a lifting device with a load bearing pin which is made of W 1.4418 a stainless steel with 15% Cr - 5% Ni - 1% Mo (moderete corrosion resistance).
This load bearing pin is placed in a bushing. The only fuction this bushing has is to assure that we have the right "distance" between 2 plates. Today we produce this bushing in W 1.4418 to prevent that it corrodes together with the stainless pin.

We however have no need for the stainless bushing. The only reason it is stainless is due to the fact the the pin is stainless. Since we produce this bushing with an outer diameter of �150 - �260 - �350 - and �440!! You can imagine that this is a rahter costly solution (we are talking about heavy section tube with a thickness of 15 up to 40 mm thick!!)

Solution:

A standard carbon steel bushing with a surface treatment which prevents the steels from corroding together.
Painting is not an option since we talk about small tolerances.

Demands:

- Some impact resistance. Bushing is not subjected to any point loading but will suffer some rough handling during assembly.
- Resistant to a surface pressure of 80 N/mm2

[MichiganMan]

(11-30-2009 01:44 PM)Grettir Wrote:  Good day!

Introduction:

We produce a lifting device with a load bearing pin which is made of W 1.4418 a stainless steel with 15% Cr - 5% Ni - 1% Mo (moderete corrosion resistance).
This load bearing pin is placed in a bushing. The only fuction this bushing has is to assure that we have the right "distance" between 2 plates. Today we produce this bushing in W 1.4418 to prevent that it corrodes together with the stainless pin.

We however have no need for the stainless bushing. The only reason it is stainless is due to the fact the the pin is stainless. Since we produce this bushing with an outer diameter of �150 - �260 - �350 - and �440!! You can imagine that this is a rahter costly solution (we are talking about heavy section tube with a thickness of 15 up to 40 mm thick!!)

Solution:

A standard carbon steel bushing with a surface treatment which prevents the steels from corroding together.
Painting is not an option since we talk about small tolerances.

Demands:

- Some impact resistance. Bushing is not subjected to any point loading but will suffer some rough handling during assembly.
- Resistant to a surface pressure of 80 N/mm2

Seems pretty simple. Manufacture the bushing from the carbon steel slightly oversized on the I.D., then sandblast and thermal spray (probably arc spay based on the surface area, but depends on the finish you need to hold) with stainless and grind to the desired finish. Since your coating is actual metal there should be sufficient impact resistance, and the pressure shouldn't be problematic. You may want to consider the amount of relative motion bushing-to-pin in order to determine the thickness of the stainless used.

[Gordon]

Hi MichiganMan

to the Surface Engineering Forum.

Thanks for your input. Sounds like a reasonable suggestion.

Nit picking mode: Don't like term "sandblast" prefer grit blast as I would not recommend using silica sand as the abrasive on health and safety grounds as well as quality. I know you did not mean to use sand.

[MichiganMan]

Gordon,

A point well taken. I should have been more specific. "Sandblast" is used in the US more loosely than elsewhere and I did mean to indicate "grit". Angular abrasive (steel grit, aluminum oxide, etc.) should be used with the mesh size dependent on the method of blasting used and the profile requirements of the thermal spray used.

[djewell]

To make it even cheaper, you could coat the inside with bronze instead of stainless steel. This would give you some additional interesting properties such as making it easier to remove the pin.