HSLA RB-80 Used in Radial Ball Bearings 1

[dougs1967]

Has anyone ever heard over unground bearings using outer raceways manufactured from HSLA steel. Any input appreciated. I have put forth alot of effort into actual life/load dynamic testing and comparing to standard bearings using low carbon grade steel stamped outer races that have been case hardened with basically no success even at 1/2 load rating applied to HSLA outer races. Bearings are running at 60 surface feet a minute for comparative testing, both grease and oil have been run still no success on HSLA. Heavy ball paths are worn into the HSLA. Thoughts anyone?

 

[tbuelna]

dougs1967-

HSLA steels were intended primarily to be used in the as-rolled condition. I don't recall having seen an instance of HSLA steel being carburized. From your description, it sounds like there is insufficient hardness in the raceway surface, or that the finished race surface geometry may lack adequate conformal contact (osculation curvature) with the balls, causing excessive contact stress.

While I have seen low-cost, low-performance ball bearings with outer races formed from sheet metal, I don't recall what material was used or the heat treatment. I think you would be better off sticking with a case hardened race made from a cold-rolled carbon steel. Cold-rolled material actually has pretty good grain structure and the surface is much smoother & clean than hot-rolled material. While it appears that cost is an issue for your application, if possible it would also be a good idea to give the race surface a low-cost finish process to improve smoothness (ie. honing, tumble & roller burnish, etc). If you are heat treating the race after forming, I would also recommend doing some tests to develop an "as-formed" part shape that compensates for any heat treat distortion.

Hope that helps.
Terry

 

[TVP]

HSLA steel at ~ 80 HRB is grossly inadequate for bearing races. Typical materials used are alloy steels like 52100 (SAE J404) at > 60 HRC.

 

[CoryPad]

In addition to through hardened 52100 steel, races for tapered roller and ball bearings commonly use 5120 steel that has been case carburized. These parts usually use forging not stamping. Some thin needle roller bearings use stamped housings/retainers that are carburized, with basic 1010 low-carbon steel as the material.

 

[dougs1967]

To: tbuelna (Aerospace) I agree insuficiemnt hardness of the HSLA at the raceway surface. Sheet metal races use Cold Rolled Draw Quality Steel to manufacture parts. They are then carburized to obtain the hardened surface. Typicalll metal stamped bearings have been around for many years and are an economical in most cases. They are used in powered roller conveyorsat RPM's up to 400. They are used in gravity roller conveyors as well.

Cost is a major issue, and driving cost out of commodity stamped bearings is one of my main jobs, yet having a product that meets required test revolutions. Bearing and raceways I am working with have a proven design for nearly 50 years, I am seeking alternative materials that may alleviate heat treatment particulary for gravity applications where either the Chinese have beat us up on pricing or plastic products suffice.

 

[dougs1967]

To: TVP (Materials) The bearings I am dealing with are low carbon steel using carburized races. These are known in material handling industry as commercial grade or unground bearings. My company has been manufactruing them in the USA for over 50 years. Driving cost out with HSLA is an attempt to have a product that suffices for low speed gravity applications, where heat is not an issue and loads are minimal.

 

[dougs1967]

To : CoryPad (Materials)

I am talking about metal stamped unground bearings using low carbon steels, well known to many roller conveyor manufacturers. These are not precisions bearings that are made of chrome steels. Driving out cost is the goal, please see some of my other posts with.

 

[TVP]

Doug,

Thanks for the additional information. HSLA steels, with their predominantly ferritic microstructure, will not have sufficient resistance to contact stress to be used for ball bearing races. Low carbon steel + case carburizing is probably the lowest cost method to obtain adequate resistance to contact stress. Maybe substituting ferritic nitrocarburizing for case carburizing could provide enough case hardness & depth for very low load applications. Salt bath nitriding of low carbon steels can attain a case depth of ~ 0.2 mm in 90-120 minutes at a temperature of < 600 C, which means that the process costs can be less than traditional carburizing operations that take several hours at temperatures > 900 C. White layer formation provides wear resistance but may be too brittle for the contact conditions. I would contact Kolene/Nitromet to discuss this type of application. Ferritic nitrocarburizing also can be done in conventional gas furnaces or using plasma, which allow more tailoring of the surface conditions, but generally are not as productive as the other methods including case carburizing.

 

[dougs1967]

To: TVP (Materials)

Thanks for the imformation.....Stay tuned