Shaft material for 841 impregnated bearings. 1

[sboutin]

Hello, First post here.

I having trouble deciding what material to use for a shaft on an assembly, semi exposed to the elements. It is a truck mounted roll off dumpster frame side roller.

The bearings are 841 30W oil impregnated for a 1.125 shaft. This is currently in design phase only an not in use. Max RPMs this will see are maybe 30-35, with max 4k lb load for only a few mins a day. Bearing manufacturer recommends a .4% carbon shaft or hardened 400 series stainless and to avoid 300 series. We currently use a 1045, non hardened shaft, but it is grease-able with .015 clearance. This is my first time utilizing bronze bearings in a repetitive production use. The shaft is also welded to a 304 tang for retention. I do NOT have access to reheating for tempering after welding and preheating, and would be difficult at this time without a vendor to supply me the welded shaft.

1. If 410 or 416HT is chosen, will the small amount of heat put into the end on the shaft after welding cause any cracking using MIG solid core 308 or 309. OR would TIG be more viable for less heat transfer?

2. If 4140 TGP is used, which just happens to have the right surface finish (no trouble welding) I'm concerned if the unit sits for periods of time that moisture will penetrate the bearing surface clearance of only .002-.003 (especially with the side to side clearance total of .100) and cause lock up, especially in our eastern region with road salts, calcium chlorides and general surface rust of the shaft.

 

[nsoller]

I would keep with the 1045 shaft with a zerk added like your doing currently. I understand your looking for something that wont rust, but anything that is made for lifting needs to be maintained. If there is a required greasing schedule, then there will always be eyes on this and it will not wither away and kill someone. If it were stainless then it might get neglected for maintenance because it does not get any attention. I would also surly stay away from 4140 especially if you are not planning on post treatment after welding to it. 4140 is very brittle if not annealed, and welding to that can cause some hardening/tempering. No brittle materials should ever be used to lift anything around people. Brittle failures kill people. Always go with ductile lifting materials and just over design for a factor of safety of 4 or more. Would it be fine using a hardened shaft, likely. But human lives are worth over doing it.

 

[TugboatEng]

If 1045 is working in a soft condition, your application is not challenging. 17-4 PH would likely be a big improvement and tolerates welding of small components. You may find 400 series SS to be less expensive but also more likely to crack after welding.

Consider brazing for attachment of fittings. Brazing allows you to attach fittings to hardened steels without the need for additional heat treatment. I have had good success brazing 1144 steel with silicon bronze to make T handle wrenches. Also, cadmium alloyed silver wire has very low melting temperature with very high strength.

 

[sboutin]

The purpose of this project is to eliminate greasing, so a grease-able shaft overrides the design. This isn't being used for lifting around people, or overhead lifting. Its a set of 6 of these rollers helping roll on and off a dumpster, no overhead lifting. Picture a roller on your boat trailer with a plain bearing, no grease or maintenance. As far as using a hardened shaft, it is recommended for the function and life of the bearing and to avoid galling. We currently weld 4140, no preheat, BUT, it is cast, non hardened parts.

1045 is working due to being greased and having lots of tolerance between the steel roller (no bearing) I will look into 17-4 Stainless, it does have more shear strength and higher thermal shock resistance than 4140 or 416, and also come in CG, perfect for the bearing. I also see it can be welded with 309L. Google: Oxyacetylene welding is not recommended since carbon pick up may occur in the weld. Now, with the amount of weld on the tang perimeter, and the hardness already above 416, (required for bearing) should I go with the annealed condition, especially since I'm welding with no preheat?

 

[TugboatEng]

I can only give information based on experience. Load pins are ubiquitously 17-4PH. The strain gauges are installed internally and stainless steel caps welded on. From that observation, you should be fine to weld a tang on a 17-4 pin in the precipitation hardened condition.

In your application, hardness is your primary goal as that is what will prevent galling and wear. If you can't find a hard alloy that supports welding also consider bolting on the tang. Hardnesses up to R 45C-50C are still machinable.

 

[nsoller]

knowing the application better, I am in agreeance with Tug.

 

[sboutin]

Appreciate the feedback!

Now I also have a primary roller supported by one end, that the dumpster bodies ride up to get off the ground. Those will utilize a 1.50" shaft with 841 bearings as well and due to the current cost of that diameter in stainless, its unfeasible to use the same 17-4 (finance dept would have a fit). I will have to go with the 4140 QT TGP for this application. Does anyone have experience with Black Oxide or other conversion coatings of this nature with bearing shafts or other uses where the Oxide will see friction wear? I hate to go through the process just to have the bearing remove the finish with friction on start up. As stated in my first question, I'm concerned with the unit sitting and the shaft surface rusting and causing binding or contaminating the bearings. Keep in mind, only conversion coatings will work, for plating will gall plain bearings.

Nov. 2021 4140 QT TPG = $17 per ft
17-4 PH = $66 per ft
plus machining costs

 

[TugboatEng]

Oxides are abrasive, not good for bearing applications. A nitrided surface will both improve wear resistance and corrosion resistance.