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stainless or not
2

stainless or not

stainless or not

(OP)
I am currently looking for materials to produce some 3mm and 4mm shafts from.  These will range from 50 to 80 mm in length.  The shafts will be exposed to the elements, mostly dirt and water.  I am afraid that the stainless will not have enough strenth compared to say a grade 5 steel bolt.  But I have not found a steel alloy with enough corrosion resistance other than stainless.  Currently 303 stainless is being considered becouse it is free machining.  The shaft will experiance shock loads of up to 50lbs over a 25 mm area that is in double shear.

Any Ideas if the SS will hold up or is there a better steel to use that would be somewhat corrosion resistant.  

RE: stainless or not

There are quite a few Stainless alloys that will equal the strength of a Grade 5 bolt.
I'm not a my desk but alloys like Nitronic 60, 17/4 Ph, 17/7 PH alloys will meet your design parameters as to strength.
Comeback with a little more information as to actual conditions of use or how what are the condition creating the double shear.  
Also will any movement or wear be involved?

RE: stainless or not

You might have more choices than you thought.
The PH grades will have great strength in the aged condition.
You might also look at a duplex grade like 2205.  Without any cold working it will have a yield strength of about 75ksi.

If you need more strength than that then look at a 300 series or 200 series alloy that has been cold drawn.  You have no trouble getting 100ksi yield with good ductility.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.
http://www.trenttube.com/Trent/tech_form.htm

RE: stainless or not

(OP)
The part is basically a double ended bolt with only 5 mm of thread on each end.  The shaft is suspended in two 10 mm wide bearing surfaces.  Between that the load is equally distributed along the shaft.  The load will also rotate about 60 degrees perpendicular to the axis of the shaft.  It is bassically a suspension point for a small car.  

The main problem I expect is not that the shaft will shear is that it will bend.  The bearing surfaces are nylon and will be able to flex some.  

EdStainless  I have been looking at the 303 ss but I am not sure if I can get it cold drawn.  But all of my vendors tell me they would prefer to use 303 becouse if machines better.  

I am new to making shafts of this size.  In a mounting that flexes.  So I am not sure if i need something with a higher yield strenth or a higher hardness so it wont bend.

Thanks
00dawg
puzzled engineer.

RE: stainless or not

You need high elastic modulus, section area, and second area moment to avoid elastic deformation during bending.  You need high yield strength to avoid plastic deformation during bending.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

RE: stainless or not

If you use a cold-worked 300 or 200 series you will get better machinability because the cold working improves the chip-breaking aspect, just as it does in carbon steel.
If machinability is really dominant (it seems like a minor cost compared to materials)then go to a cold worked stainless 304 like the ones Ugine makes with controlled oxides, the Ugima series.
2205 will have good machinability, too compared to annealed 300 series.

RE: stainless or not

(OP)
Thanks guys for all the tips.  As far as machinging goes The hard part so far is to find a vendor willing to do a small quantity. But I have some interested in doing it on some sweedish screw machines. My first order will only be 1000 pcs.  So in relation to the material cost the machining is still cost prohibative.  I will check on cold worked material to start with.  

This is a great place I am glad I found it.  After only doing manufactuing for a few years I think I have forgot most of my "real engineering" skills.


Thanks
Sammy C. Cornelius

RE: stainless or not

People that do small size thread rolling might be able to do the job.  There are several people around that do this.  
Checkout the bottom of the page at following site.

http://www.morris01550.com/thrdrd.htm

RE: stainless or not

Thread rolling is the way to go.  I have a couple of local guys here that do a lot of it.  Cutting threads in stainless is a loosing battle.
Cold drawn stainless bar will roll OK also.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.
http://www.trenttube.com/Trent/tech_form.htm

RE: stainless or not

50 lbf does not seem like a large load even for 3mm dia but it depends on the unsupported span.

What is the distance between the two 10mm bearings?

303 might have adequate strength.  You can look at your strength of materials text or machinery's handbook or mechinical engineering handbook and do the calcuation for stress.

RE: stainless or not

Thread rolling is a good option,but you need to premachine the material to a close dia before offering for rolling. Since you have both ends threaded,head preparation is not an issue.

RE: stainless or not

arunmrao,
All the people that roll threads have the proper size wire on hand.  The only problem I see is his quanity of 1000 pcs.   

RE: stainless or not

The practice is different in India. Thread rollers who do jobbing work do only that operation and nothing else. I but the stock, forge the heads, trim the flash,premachine to the required dia and then offer it to the thread roller. Quantity is not a major issue. The preoperations are time consuming and expensive. If the stock is alloy steel ,then next a suitable heattreatment is done followed by blackening.

RE: stainless or not

Could you use a hardened bolt and a SS sleeve?

RE: stainless or not

(OP)
That is a pretty good idea IFRs.  I will have to check into that.  That would be really cheap and also probably stronger than just a stainless rod.  

Later
00dawg

RE: stainless or not

(OP)
Well I have finally found a suplier for the steel atleast.

I will contact them tomorrow but they seem to have a huge selection of metric size material.

Here is the link.

http://www.metricmetal.com/round.htm

Atleast now I can tell my vendors where to purchase instead machining down 1/8 and 3/16 rod.

RE: stainless or not

I am assuming that the load is applied through a sleeve or some other close fitting 'tunnel'; What clearance is there between the bearings and the distributed load?

If you have an evenly distributed load and no clearance, there will be just shear at the bearing surface interface.

Truck

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