How to order 4.5"X4.5"X10' steel

[Shotout]

Sorry if this is the wrong forum, it was the closest I could find to what I needed to ask.

I have a job that requires a shaft with a 4.5in sq body 39.25in long, OAL 9.5ft, for use in a hammer mill and the print specifies 1045 C.S. We have called everyone we can think of and it seems this doesn't exist outside of 5in 1018 hot rolled. We contacted the plant eng and he said no to the 1018 but said we can substitute a superior material for the 1045 but still can't find anything close. We asked about machining a body out of another material which we could find and ordering oversized round stock for the journals but that is out too. If anyone has ordered material that would be suitable can you clue me in on what to call and ask for. Our steel sales reps aren't able to help so I figured someone here would probably know.

Thanks
Scott

[DareBee]

I would be looking for 4140 or 4340.

[big_mak]

If they are picky, have it cut from plate!!!!!

What other options do you have?

[Shotout]

I ended calling the steel mill that supplies our supplier. They faxed me a nice little sheet explaining it was a special order product with an ungodly req minimal order and faxed the customer this with a note and sketch showing the 3 piece construction I had suggested earlier. Seems either they misunderstood the salesman (he's new) or just decided to go with reality. Needless to say my life just got whole lot easier I'm going to mill the body from cut plate as suggested and then bore it to accept oversized stock for the journals to be turned after welding.

Thanks Mak and Darebee
Scott

[Geof]

Originally Posted by Shotout ......Needless to say my life just got whole lot easier I'm going to mill the body from cut plate as suggested and then bore it to accept oversized stock for the journals to be turned after welding. Thanks Mak and Darebee Scott

You mention 'plant eng'; is this guy really an engineer?

For a hammer mill shaft I would not go near this fabricated solution with a ten foot pole. I suggest you make sure you have it in writing from the customer that this is fully approved by them and is an acceptable method of manufacturer. My opinion/prediction is that you are making an item that is a prime candidate for fatigue failure and this is based on having worked at a place that did use this type of fabrication for heavy duty sawmill equipment and did get this type of failure.

[Shotout]

Originally Posted by Geof You mention 'plant eng'; is this guy really an engineer? For a hammer mill shaft I would not go near this fabricated solution with a ten foot pole. I suggest you make sure you have it in writing from the customer that this is fully approved by them and is an acceptable method of manufacturer. My opinion/prediction is that you are making an item that is a prime candidate for fatigue failure and this is based on having worked at a place that did use this type of fabrication for heavy duty sawmill equipment and did get this type of failure.

We did get it by fax but he is a maintance engineer as you said. I'll take it up with the owner and see what he says. The only other solution I can think of is to turn it from 6.5in stock and mill the flats on the body, but our mills aren't up to the wt, doubly so with the overhang from the mill table. The fatiuge issue, is from structural changes in the steel from the heat of welding coupled with the impact shock loading on those changed molecular structures? Something else?

Thanks
Scott

[Geof]

Originally Posted by Shotout .....The fatiuge issue, is from structural changes in the steel from the heat of welding coupled with the impact shock loading on those changed molecular structures? Something else? Thanks Scott

The answer to your questions is yes, but before giving you a lecture on metal fatigue, stress concentration, etc, let me suggest some books that are a worthwhile read; I checked amazon.com and they do have them.

The New Science of Strong Materials or Why You Don't Fall through the Floor (Princeton Science Library) by J. E. Gordon and Philip Ball (Paperback - Jan 30, 2006)
Buy new: $19.95 $14.96 28 Used & new from $12.15

2.
Structures: Or Why Things Don't Fall Down by J. E. Gordon (Paperback - Jul 8, 2003)
Buy new: $18.95 44 Used & new from $3.94
In Stock

Metals In The Service Of Man by W Alexander And A Street (Paperback - 1956)
3 Used & new from $7.00

These are not new books (obviously....1956, probably well before you were born) but they are the best I have come across for a low pressure introduction to material science.

Metal fatigue is something most people, even most Machinists I have encountered, do not really understand. The common idea when a fatigue failure is encountered is that the metal has "crystallized" and become brittle and that is why it has broken. This is a wrong idea because all metals are crystalline, that is their normal structure, and a part that has experienced a fatigue failure is no more brittle when it fails than when it was made. All metals are susceptible to fatigue failure when they are used in an application that applies a cyclic load and particularly when the load reverses cyclically. Some metals such as plain carbon steels can be very fatigue resistant and when the load is very small they are fatigue proof, but some such as aluminum and aluminum alloys will always experience fatigue failure when used with a cyclic load no matter how small the load is; with a small load it may take a long time but it will happen. Many alloy steels and particularly stainless steels will also experience fatigue failure eventually no matter how small the applied load.

Fatigue failure can (will) occur even when the load is a small fraction of that needed to break the part and even a small fraction of the load needed to deform a part plastically. Loads that are well within the elastic limit; in other words, loads that are so small the part returns completely back to the unloaded state with absolutely no permanent distortion, will cause fatigue failure when they are applied in a cyclic or reversing manner. It just takes longer when the load is only cyclic in one direction and does not reverse direction. An example of a cyclic load is the compression of a spring and anyone familiar with die springs knows they fail due to fatigue cracks. A reversing load is experienced by any rotating shaft and fatigue failure on axles and drive shafts on machinery is a common type of failure.

The reason that fatigue failure happens is because every metal part contains what are called 'stress raisers' or 'stress concentrators' and these exist both at the structural or large scale level and the atomic/molecular/crystal or small scale level.

Structural Stress Raisers:

Any shaft, or a beam, that has a bending load applied does not experience the same type of stress throughout its cross section; one side has a tensile stress and the other a compressive stress while in the middle there is a 'neutral zone' that has no stress. The amount of stress and also the way in which the stress changes across the shaft depends on the load and on the diameter of the shaft and this is where large scale stress raisers can arise. Shafts very often have different diameters, smaller through the bearing supports and larger in the part between the bearings so the load is carried by different cross sections; because the cross section is different along the shaft the way in which the stress changes and the distance out from the centerline that a particular stress occurs is different. This means that at a change in diameter there is a mismatch because one part of the shaft has to have a very different stress distribution to the part immediately beside it. This cannot happen and the result is that the stress distribution becomes bunched up right at the step between the two diameters and the most highly stressed part of the shaft is right at the corner. The step or corner between two diameters is a very effective stress raiser and even though the maximum stress in other parts of the shaft may be well below the limit that the material can handle at the step it may be above the elastic limit and even a good fraction of the ultimate tensile strength. The amount of 'bunching up', or stress concentration, depends on how sharp the corner is and this is the reason changes in diameter on shafts should have a fillet that is as large as possible and should have a good surface finish because around the fillet the tool marks can act as a lot of individual stress raisers.

By itself the concentrating of stress at a change in diameter might not lead to fatigue failure but the effect of small scale stress raisers adds to the problem and brings in an additional stress concentration.

Crystal Stress Raisers:

Metals have a crystalline structure in which the atoms are nicely aligned but not perfectly aligned because all metals have impurities or have cooled in an uneven manner which causes crystal defects. A good way to visualize crystal defects in two dimensions is to lay out a few dollars worth of pennies on a flat surface and line them up perfectly regularly so every penny is touching six others; this is a flawless crystal or it is within the area you have lined up. Now take out a penny and replace it with a dime or nickel and it is not possible to get everything touching because the different sized coin doesn't fit. It might be possible to choose a combination of pennies, nickels and dimes so that an even repeating pattern can be constructed using the three coins in specific ratios; this is how alloys of different metals crystallize and often the structure can be stronger than the pure metals. The different sized atoms mean that the long arrays of atoms cannot slide past each other as easily; when the atoms (coins) are all the same size if one row slips past another it does not alter the overall pattern, however, when two or more sizes are in the pattern moving one row may totally disturb the overall pattern so it is much more difficult for this to happen. Impurities are like sticking in a silver dollar; it is so big it doesn't fit at all and wedges the rows apart weakening the bonds between atoms. Shrinkage stresses from uneven cooling do the same thing, some rows are pulled apart some bunched up leading to weak spots on an atomic level.

Initiation of Fatigue Cracks:

The combination of large and small scale stress raisers is what allows fatigue failure to start. The large stress raiser gives a region of concentration that is still below the ultimate bulk strength of the material but the small scale stress raisers within this region may further concentrate the stress so that an atomic scale crack starts. This crack then acts as its own stress raiser and every time the load cycles the crack gets bigger and bigger until eventually many hundreds of thousands of cycles later, or millions of cycles, it has grown to such as size that at some point the remaining uncracked material cannot carry the load and the part fracture rapidly all the way through.


Fabricated/Welded Structures/Shafts and Fatigue Failure:

Welded shafts can be very prone to fatigue failure particularly when the welded joint as at a change in diameter and the reasons for this are more or less obvious from the description above: The change in diameter gives the initial stress concentration. The heat affected zone around the area of the weld gives the regions of uneven cooling. Inclusions of slag (oxidized metal) from the welding increase the level of impurities.

Coupled to these three factors is the probability (almost a certainty) that the area of solid material under load in the region of the weld is considerably smaller than the full shaft diameter. Rarely does the welding go to the center of the shaft, nearly always it is simply a deep fillet weld that goes somewhat below the smaller diameter and up into the larger diameter. Because the weld area is less than the total shaft area even in the absence of any stress concentrators the weld has a higher stress than the parent material off the shaft. The combination of smaller area and stress concentrators means this type of fabrication is not desirable for structures subject to cyclic loads.

It is possible to make a shaft joint with welding that can be acceptable: The weld has to penetrate the full diameter of the shaft, must not have any inclusions and has to be normalized or stress relieved before and after machining.

[Shotout]

Geof

That is probably the clearest explaination I've read. Our school text was essintially "Hey there is such a thing as metalurgy and if you learn it you'll be exposed to these concepts". TBO I learned more when I read my text during horseshoeing school. Forging, heat ranges; grain refinement; heat treatments are as you know critical when making tools, often out out of S ans O series tool steels in that trade. I'll check out the references you provided. I'm looking at 32yrs until I'm old enough to retire so anything I learn now ought to serve me quite awhile.
Thanks
Scott

[Geof]

Originally Posted by Shotout ..... during horseshoeing school. Forging, heat ranges; grain refinement; heat treatments....Scott

I had forgotten you are a Farrier, sorry. Of course you have the background to understand it.

[Shotout]

Originally Posted by Geof I had forgotten you are a Farrier, sorry. Of course you have the background to understand it.

Don't apologize, it was informative and the references will serve me well in the future I am sure. I'm currently trying to digest a couple of other books but I've added those to my reading list. I look at the purchase of good texts just like the purchase of good tools and I always appreciate someone willing to share their knowledge and experiance.

Scott