Shaft material for bearing application 2

[prdave00]

I have a bearing application. The bearing is press fit into a housing per bearing mfg recommendation. The inner race is E51200 steel and am trying to decide the best material for the rotating shaft (slip fit inside bore per mfg recommendation). The shafts will be rotating at 140 rpm with a varying 100 lb load (estimate). I've narrowed it down to the following, but welcome other suggestions:

- AISI 1045 Steel, Chrome Plated, 68-72 HRC
- E52100
- General purpose tool steel such as D2
- High performance tool steel: M2, M2/M7 (?), or M4
- the bearing manufacturer also recommended 4100 series alloy steel, but my research has shown this has lower wear resistance than some of the others

I assume I can harden and temper for optimal wear resistance or purchase it in the final condition.

I'm hoping to find stock ground to size, but will need to add some grooves for retaining rings and possibly add a key way.

 

[blacksmith37]

I don't understand why you are considering such very high hardness/low toughness shaft materials. The shaft will fit tightly inside the rolling element brg- no wear here. What is happening at the other end of the shaft ? What diameter is the shaft ?

 

[tbuelna]

prdave00,

Unless you're concerned with fretting between the shaft and inner race ID, then you don't need a super-hard shaft material. The shaft material only needs to have sufficient strength to accommodate your anticipated bending/torsional/shear loads. A quenched & tempered alloy steel like 4140 would likely work very well.

Regards,
Terry

 

[prdave00]

The bearing manufacturer recommends a line to line to slight clearance fit with the shaft and a slight press fit into the housing. The problem I'm seeing is the inner ring of the bearings wearing grooves into the shaft. The bearings are installed at each end of a link arm connecting a crank arm to a rocker arm so neither shaft or bearings are stationary. The wear is predominantly occurring along the shaft is keyed into the crank arm. The problem went away when I switched to a shaft made out of a high-carbon CoCrMo alloy that we fortunately had on hand (and a metallurgist at Carpenter suggested). This material doesn't have a high hardness but is rich in finely dispersed carbides. The downside is that the material is not cheap and difficult to machine. I wanted a reasonable substitute. There is a good possibility I'm over thinking this. After all the former shaft material was 304 so I was probably asking for it.

 

[arunmrao]

If 304 stainless steel was the original shaft material,it implies that there must be some form of aqueous corrosion environment. You could then try some of the precipitation hardened stainless steels like 17/4 PH etc.

 

[TVP]

prdave00,

Either 1045 that has been induction hardened (with or without chrome plating) or 4140 quenched and tempered (or induction hardened) should be suitable for your application. I would not even consider the tool steel options.

 

[prdave00]

arunmrao: Thanks for the suggestion. 17-4 was actually an interim solution before switching to the CoCr material and, while wear improved, it still didn't buy me as many cycles as I wanted in between maintenance.

TVP: Thank you also for the suggestion. I'll stay away from tool steel for now. Do you know how 4140 would perform in terms of corrosion? Splashing of water onto the shaft is possible. I know from experience that E52100 oxides pretty quickly when exposed to water and not properly dried.

 

[arunmrao]

Suggest,if you could consider a stainless steel sleeve over the shaft please.

 

[tbuelna]

prdave00,

Since the shaft/inner race is rotating with respect to load, then this should be an interference fit or be clamped axially with something like a bearing locknut. The grooves you see on your shaft are due to relative motion at the inner race/shaft interface, and will likely continue to occur regardless of how hard the shaft surface is made.

If you use interference fits on both inner and outer races, make sure that the installed bearing still has running clearance.

Hope that helps.
Terry

 

[ERT]

I would agree with Terry, I think the key question is that if the inner race is experiencing reversing or rotating load relative to the shaft, then a free floating inner race with clearance is the root issue.

It is difficult to guess the best mounting option without understanding the entire assembly, but typical options are:
1) Axial clamping - bearing locknut, end caps, or "Superbolt"
2) Thermal interference fit (dry ice shaft, or heat inner race - induction heater are commonly used for this)
3) Taper lock bushing - Ringfeder, Trantorque, etc.
4) Adhesive - Loctite "Bearing Mount" product or similar, but think carefully about how to get bearing off again.
5) Convert to sleeve bearing?

ERT