304 vs 316 stainless steel for shafts. 1

[eski1]

Hi
Just been asked to quote on some conveyor shafts in both Duplex 31803 & 316 stainless steel .
The shafts are mostly 25 Ø and 600mm long they are in a food factory but not in contact with product or caustic acids .
Typical conveyor situation lots of quick start stops etc but as for weight on conveyor that is just milk bottles .
As the shafts are supported on both ends in bearings ,they mostly fail at the moment in the middle because of breaking in 2 halves. So i wish to know if pricing in 304 & duplex would be better as there is no strenght benifit by using 316 . I believe at present they are made in 303 grade st/st.

many thanks in advance

Jeff

 

[arunmrao]

If there is no contact you might use 410 grade shafts or alternately 17/4 grade material. They would last long without any problem.

_____________________________________
"It's better to die standing than live your whole life on the knees" by Peter Mayle in his book A Good Year

 

[metengr]

Honestly, I don’t think you have provided anywhere near the information needed to justify a material recommendation from my view. Have you or someone carefully examined the conveyor roll failures to confirm the failure mechanism? This is first and foremost to decide on corrective actions. Simply stating the conveyor roll failures are located in the mid span means nothing without confirmation of the failure mechanism. Are the roll failures caused by fatigue or torsional overload or failing from 20 years of service life , etc? Are these rolls direct coupled to a drive system or simply carry weight by a belt? Sorry, but I would not support any material change with only this limited information.

 

[Zinov]

I will use 17-4PH or SS455 both heat-treatable.
Unless your application needs non-magnetic grade than you should stay in the 300 series.
another reason may be the room operating temperature
if you have risk of brittle-ductile transition you should stay with 300 series.
Finally in term of corrosion resistance the 300 series
have generally a high corrosion resistance to the 400 series.

303 is a low cost grade but has low resistance also.
316 can be found stronger than both 303 and 304 , but little more expensive.

 

[eski1]

Hi

metengr more info as requested below
Shafts are failing due to Torsional overload
They last approx a year then fail .
The shafts that are failing are direct coupled to a drive mechanism.
Operate in room temperature atmosphere.

because of the speed the conveyors need to start /stop the motors don't soft starts on them
As well as knowing the best material for these to be in the main question i would like answering is , is 316 better in this application than 304 .

many thanks in advance
Jeff

 

[metengr]

eski1;

As well as knowing the best material for these to be in the main question i would like answering is , is 316 better in this application than 304 .

No, no advantage.

I believe given your recent information you have low cycle fatigue failures in drive conveyor rollers from excessive starting torque. Thus, you will need to upgrade the conveyor drive rollers to a heat treated low alloy steel or as recommended earlier consider 410 stainless steel. Either case, a quench and temper heat treatment will be necessary to provide needed strength requirements to overcome torsional and bending loads from starting torque.

You realize one can calculate the torsional and bending strength of a given roll diameter needed for starting torque. Once this is known, throw in a design factor and now you can select a suitable material.

Enough consulting........

 

[EdStainless]

If you are looking for more strength and similar corrosion resistance then look at lean duplex alloys such as 2101, 2202 and such. They will cost less than 2205 or 316.
Be as strong as 2205, and much stronger than 304 or 316.
And have similar corrosion resistance to 316.


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Plymouth Tube

 

[mfgenggear]

I don't understand why so cheap of material is used, then there is question why it fails?
It seems if you build it right in the first place then this type issue would be non existing.
where is all the training for the calculations being used. I totally agree with meteng.

or am I missing something here?

Mfgenggear

 

[KENAT]

This is a build to print type job right, not your actual design?

So quote in the materials they ask, then if you want to quote in some additional materials and share any 'cost savings' with them feel free. Maybe even quote in one of the other materials mentioned saying how it may improve the life etc.

At the end of the day seems the choice isn't up to you, your 'customer' can pick any of the options you quote.

I like it when machine shops come back with suggestions to cut costs or improve lead times etc., however I sometimes say no - especially when I know something they don't that affects the choice.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[stanweld]

eskil,
Are the shafts cold drawn/cold finished or solution treated? How have you concluded torsional overload as the sole failure mechanism? If the shafts are simply under designed, that can readily be rectified even if 304/316 is required for some strange reason. Whereas these fracture events have apparently been long ongoing, redesign should have long ago been accomplished long ago. Or does your company' management have the attitude that the design is infallible and the status quo must prevail?

 

[prostocktom]

I use 2205 in an application of pump shafts on 1000-1500 HP engines with great success.

You might call Scott @ Best Stainless

http://www.beststainless.com/

and see what they think about your problem.

Tom

 

[Guest102023]

One of the Nitronic alloys would be suitable; they have excellent strength at small diameters. I have seen Nitronic 30 used for a marine drive shaft.

 

[Izzyix]

Is the conveyor manufacturer still in business - get recommendation? What material did he install originally to meet the operating criteria?
If no-go, then as suggested, 2101 lean duplex, 31803 Duplex or ZERON 100 Super Duplex, depending on how much you want to pay and strength / fatigue resistance required. 2101 least expensive to ZERON 100 most expensive but highest strength / fatigue resistance. Often used in high strength pump shafts.

Bear in mind that surface finish plays a very important part in fatigue fracture control, material should be fine ground or polished, not peeled.