Premature Wear Out of SAE 52100 Rings 7

[Prasham]

We are manufacturing spinning rings used in Textile Industry. They are made from SAE 52100 or equivalent grade of steel pipes. After machining they are heat treated (marquenching) to 62-63 HRc. Later they are polished using vibratory and centrifugal machines.

We have enclosed a pic which shows cross section of the ring and the traveller ("c" shaped small component) which runs on it at around 30 meter/sec speed. Usual life of the ring is around 2-3 years. There is no lubrication between ring & traveller which please note.

At times we have received complaints from out customers that the rings get worn out prematurely in say 2-6 months. We have found that most of these worn out rings have 62 HRc or higher hardness which is as per the requirement. The traveller that runs on rings have hardness of 55-57 HRc. What could be triggering the wear out ?

 

[EdStainless]

I believe that you need to looking at microstructures. Changes in the grain size, size and distribution of carbides, and steel cleanliness could all be factors.

I presume that you have ruled out any variations in the products that your customers run as being an issue?

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P.E. Metallurgy, Plymouth Tube

 

[Compositepro]

Pipe as a starting material might not have the most consistent metallurgy and cleanliness that you want for for your application. Also, ring spinners process cotton from fields and there can be a wide variation the amount and type of abrasive particles in the fiber.

 

[metengr]

Hardness does not always equate to improved wear resistance. Other factors come into play that can wear a hardened surface, as mentioned by Compositepro.

 

[Prasham]

Thanks for the prompt replies.

We use 2nd grade tubes and hence I believe that there could be more impurities or other problems that you guys have mentioned. What can I do to ensure that the same doesn't happen again ?

 

[metengr]

First, before you jump off the cliff and condemn material you need to evaluate the failures using a metallurgical lab to determine if the material is not suitable or you need to have some type of modified surface done to enhance wear resistance(abrasion or other).

If the material is of lower quality for your service condition, the easy fix is to develop an engineering specification that details the material specification so that your procurement folks order the material you specify.

 

[tbuelna]

The type of 52100 bearing steel tube stock you describe often comes in a heat treat condition that is optimized for machining, but it also leaves a decarburized surface layer that must be removed during machining.

If you can get a copy of ASTM A295 I believe it gives some limits for the depth of the decarburized layer.

 

[mrfailure]

You should also evaluate carbide microstructure using ASTM A892, including using the photomicrographs that are part of the standard (they used to be in the standard, but now ASTM sells the plates separately). These ratings are referenced in ASTM A295.

 

[tbuelna]

Prasham-

Can you provide a definition of what you mean by a "worn out" ring? Is it a certain dimensional condition that the ring surface has eroded to?

 

[Prasham]

Pls check the image that I had attached in the opening post. You shall notice that there is very small contact area between the two components.

When I say worn out, I mean that the contact area that I mentioned above gets uneven and hence the small component that runs over the ring can't run smoothly anymore.

I hope I have explained it clearly.

 

[Maui]

Prasham, is the wear that you described on the traveler or is it on the 52100 ring? Can you provide a photo that shows a typical worn out component that this customer has been complaining about?

 

[Prasham]

There is wear on traveller as well as ring. Traveller have lower hardness of around 55 HRc while rings have hardness of 62-63 HRc. Thus travellers gets worn out in normal cycle while life of ring is much higher. But in this case while the traveller life is normal, life of the ring is shortened to great extent.

I've enclosed a pic to show the abnormal wear. Hope it will clarify the matter a bit.

 

[tbuelna]

Thanks for the last picture. From what I can tell the surface damage on the inner corner of the ring rim appears to be localized, and more like galling/brinelling than abrasive wear.

Comparing the picture in the OP of a generic ring/follower and the picture of your own ring design in the last post, the one big difference I see is how much smaller the corner radius is of your ring rim where the traveler bears against it. The picture of the generic ring shows a cross-section with very generous radius at the inner rim corner where the traveler bears against it. With your ring design it seems possible that a high radial load applied to the traveler could produce local brinelling damage to the sharp radius ring rim edge, due to the minimal surface area at this contact. After the initial brinelling to the local surface, every time a traveler passes over that spot the damage would progressively get worse. So one suggestion I would offer is consider modifying the profile of your ring and travelers so that they have a much lower contact stress level. From what I can see, ring surface hardness is not the main problem you have.

 

[Prasham]

@tbuelna, thanks for the exhaustive post.

Firstly little about the images that I have attached in my previous post. The first image of cross section of Ring is a photograph used for marketing purpose it doesn't show the actual dimensions. The second pic was of actual ring that has faced the "brinelling / wear out".

To have a clearer idea I am attaching a dimensional drawing of the ring to understand that there is very small contact area between Ring & Traveller. Also you may note that we check the same on a 50X magnification projector to make sure that our product is as per the standard profile. So the deviation would be pretty small and wouldn't really make difference.

Now considering that its local Brinelling, what precautions can we take to make sure that it doesn't happen again in our future lots ?

 

[tbuelna]

Have you done a calculation to determine the max contact stress produced at the interface between the traveller and the ring edge radius? With that tiny corner radius of 0.8mm on the ring it wouldn't take much radial force on the narrow section traveller to brinnell the ring surface. Try doing a calculation for the elastic contact stress limit of a convex section traveller body bearing against a 0.8mm radius convex section ring surface.

The only other thing I could suggest is making sure the metallurgy of your ring is what you specified. As I noted above, with the type of raw material you used for this part, there can be an issue with de-carburization in the outer surface layers. And from your picture of the ring, it looks possible that you might not have removed enough of the inner stock surface to fully remove the de-carburized layer.

 

[Prasham]

As far as the profile goes, its standard across all manufacturers in the world. Moreover if there is a design flaw it should affect all the rings but that's not the case here.

How much layer should be removed to De-carb the rings properly ?

 

[Maui]

Prasham, decarburization is the loss of carbon from the surface of the part during heat treatment. It usually results from the presence of oxygen in the furnace atmosphere during austenitizing. Decarburization can be partial (which can be bad) or complete (which is worse). Examination of the microstructure of the a failed 52100 ring will allow you to determine if the part had been decarburized.

It is also possible that there is retained austenite in the microstructure. This could also lead to the premature failure that you described. An examination of the failed part should also allow you to determine if this is the source of the problem as well. Do the rings undergo a cryogenic treatment as part of the normal heat treating cycle?

Maui