Galling 2

[Erkamal]

Hi friends,

I have worked in valve industry . i am facing many times galling issue.

now i have faced one new issue. i have to make two matching parts with UNS N0 8825 material. will they gall?

Is there any material combination chart to prevent galling.or wht shd i take care for material selection to prevent galling.

Regards
Kamlesh

 

[boo1]

Alloy 825 (UNS designation N08825) is a nickel-chromium alloy with additions of molybdenum and copper.

The most common way to reduce galling is have a hardness difference of atleast 50 BHN. You can obtain this differeence through coating one surface, weld overlay, or cold working/anneal combo. Any coating system must resist the enviroment.

 

[boo1]

For coating consider a high velocity oxygen fuel (HVOF) process. With HVOF, coatings are projected on the substrate in the semi-molted condition at high velocities—resulting in high hardness, strong bond strength and high durability. Common coatings applied using HVOF include 88WC-12Co, 83WC-17Co. We use Metco powders they can help identify what system to use.

 

[EdStainless]

Are both parts wetted?
If not then you could change alloy on one of them, or use one in the cold worked condition to provide higher hardness.

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Plymouth Tube

 

[OGMetEngr]

For many FCC alloys (i.e. - Ni-base alloys) a hardness difference does not eliminate galling, and sometimes doesn't help at all. It really depends on the couple, but I'd be willing to bet alloy 825 doesn't do so good. Almost all couples with Ni-alloys as one material gall at low stress levels. There are some BeCu alloys and stainless alloys used specifically for their galling resistance against many materials. May want to look at those depending on other requirements. Another option is hardfacing via thermal spray.

 

[Erkamal]

HI frd,
thx a lot.

My both parts are wetted like trim. so they are movable one inside other. so will coating work? Little worried for that.

 

[boo1]

we have had very good sucess with HVOF wear coarings

 

[OGMetEngr]

The hardface thermal spray coatings boo1 mentioned are good. Many years success with those here too.

 

[johnchrc]

I worked at Downhole wireline compnany that used 718 as primary material and found that using 825 made a big diffence in falling.

I think applying TDC or XADC to one of parts will reduce galling. Key is to keep hardness difference as large as possible and to have very fine finish. Peen other part for galling resistance. It work hardens surface and knocks down asperities.

BeCu is an option but doesn't always agree with strength and certain environmental concerns.

TDC has 78 Rc
XADC is TDC with diamond substrate = 98 Rc
It is applied in anodic bath.
I use TDC and it is the best anti galling thread coating
Coating is ~ .0006 thick
Molycoate 4300 is good dry film option.
Copper coating is typical coating called
out by premium thread vendors.
I would be interested in your choice and results.














I

- CJ

 

[johnchrc]

I should add that it was 718 made up to 825. For
Some reason that combination performed well. still cold worked pin and copper
Coated box.

- CJ