Little help with ground finish for oil seal

V

viper

Titanium

Joined

May 18, 2007

Location

nowhereville

• Dec 28, 2009

• #1

My other engineers are out for the week and I am trying to get some quotes in to mfg and grind some small shafts. they have an oil seal that rides on them on the OD so finish will be important for proper seal life. All the data I have reflects a surface finish of .5-.8Ra but that seems rather extreme in my opinion. Right now I am quoting with a finish of 5-10Ra but curious what is typically done in the industry for this type of work?

We will also be applying a dry lube coating to the parts so they must be Al oxide blasted lightly before coating. I do not want to pay for extra finishing that I will screw up in coating. Is the .5-.8Ra in the micro finishing area? I am doubting this is obtainable with grinding alone but could be wrong.. Tolerance is +/- .0003

 

V

vesa_

Plastic

Joined

Mar 13, 2008

Location

Vaasa, Finland

• Dec 29, 2009

• #2

Do not mess around with shaft finishes, if seal manufacturer is known, then they have set limits. If you don't know what to use, try parker, they do every kind of seals and state limits for those.
Thumb of rule surface finish for axle of this kind is Ra 0.8. This is in millimeters. If there is coating, then it should cover surface roughnesses, so Ra 0.8 sounds fine. Rough enough for coating to stick on it.
Could it be that surface finish is stated in millimeters and you are thinking about it inches?

 

G

Glenn Wegman

Hot Rolled

Joined

Jan 6, 2007

Location

Florida

• Dec 29, 2009

• #3

Just looked at the CR Seal handbook under "Shaft Requirements" and it states :

Seals perform best on medium carbon steel (SAE 1035, 1045) or stainless steel shafts. Good chrome or nickel plated surfaces, properly finished, are acceptable.

Now under "Bore Requirements" it states:

A bore finish of approx 125 microinches or smoother should be maintained to assure proper sealing.



Don't you just love it?

 

G

Glenn Wegman

Hot Rolled

Joined

Jan 6, 2007

Location

Florida

• Dec 29, 2009

• #4

Pissed me off, so I went to the National Oil Seal Handbook.

The only mention I quickly saw is in reference to their Redi-Sleeve repair sleeves for seal surfaces:

The surface provided by a Redi-Sleeve is the best possible sealing surface ground to a 10-20 Microinch Ra (.25-.50 Micrometer Ra) finish....

 

PixMan

Diamond

Joined

Jan 30, 2007

Location

Central MA USA

• Dec 29, 2009

• #5

viper said:

...All the data I have reflects a surface finish of .5-.8Ra but that seems rather extreme in my opinion. Right now I am quoting with a finish of 5-10Ra...

Click to expand...

Seems to me there's a mix of Ra finishes specified in both microinch (your "5-10Ra") and micrometer.

The ".5-.8Ra" if a metric designation (which I really think it is), that would be 20-32 microinch.

 

V

viper

Titanium

Joined

May 18, 2007

Location

nowhereville

• Dec 29, 2009

• #6

The specs that I have read for the seals do not have units so rather useless info but I am lead to believe the .5-.8Ra is micrometers because the seals are metric.. I have specified 5-10Ra microinches which sounds like it is smoother than is really required.

 

B

Brian@VersaMil

Stainless

Joined

Mar 18, 2001

Location

Gaston, Oregon USA

• Dec 29, 2009

• #7

TOLERANCE of .0003 for the seal dimensions on a shaft??? Get real- 3 TENTHS?? Surface finish for grinding is important- PLUNGE grinding the sealing surface, but your SIZE tolerance is absurd. Typical seals don't require a size tolerance that precise.

 

charlie gary

Stainless

Joined

Oct 4, 2009

Location

near Seattle, Washington, USA

• Dec 29, 2009

• #8

Maybe the tight tolerance is for a bearing next to the seal? Just my guess.......

 

V

viper

Titanium

Joined

May 18, 2007

Location

nowhereville

• Dec 29, 2009

• #9

Charlie is a winner! Yes, the 3 tenths is a bearing fit with a seal next to it. diam tolerance is the the bearing, surface finish is for the seal.

 

A

adama

Diamond

Joined

Dec 28, 2004

Location

uk

• Jan 2, 2010

• #10

It can also vary depending on matirial of seal and weather its sliding or rotory. The liquid can play a key factor in it too. Scratch direction can also be a very important factor. Seals need to weep idealy ever so slightly to lubricate them selves. To fine will destroy them as quick as to corse.