How to salvage core portion out of a bar stock for expensive material? 10

[salmon2]

Experts: we buy large diameter nickel based alloys and we really prefer material in tube format, but you know often times we end up with getting bar stocks. What is the best way to get the core portion out and save it for small parts?

 

[unclesyd]

I would give a call to the following and discuss your problem and possible solutions. There have been some progress using diamond core drill for this. Everything thing depends on your application. There are numerous shops that can do this.

http://www.americanheller.com/trepanning-main.html

http://www.amhollow.com/main/whatwedo.php

 

[MikeHalloran]

You can use trepanning tools, which are kind of a specialized tubular boring bar that leaves a core. Chip removal can be tricky, so you might be happier with the pre-developed commercial versions than with rolling your own.



Mike Halloran
Pembroke Pines, FL, USA

 

[salmon2]

Thanks learned a new process.

 

[tbuelna]

salmon2,

You mention your preferred stock requirement is a large diameter tube. Depending upon your actual length/diameter/wall thickness requirements, rolled rings may be more cost effective. With a rolled ring there is a cost involved with the rolling process, but there is also no material selvage like there is with trepanning. Ring rolling can be cost effective where the material cost is very high. The ring rolling process is relatively inexpensive, since it is largely automated and requires no tooling.

Terry

 

[salmon2]

Thank you Terry, I see it is a upsetting, piercing/punching, rolling process, similar or close to forging.

 

[arunmrao]

In applications under discussion ,requiring digging out large materials to produce a center hollow is laborious and material consuming. Can easier methods like plate rolling and welding not be adopted.? Is welding prohibited,

The material under discussion is high Ni alloy,and often one might find it difficult to source in other forms.

But, I have seen similar methods being adopted for 316 grades,which is a waste.



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

 

[unclesyd]

I hardily endorse the use or rolled rings. We have a lot of parts made from these rings.
You might also want to look at these process if your part is amenable to them. Wisconsin Centrifugal is very good and has several ways to get to the end product. Dynamic though limited in sizes makes a very good product.

http://www.metaltek.com/product-applications/castings/centrifugal-castings.html

http://www.flowform.com/flowforming/cap_sizes_tolerances.php

 

[salmon2]

To arunmrao, I know welding can be as good as seamless if done right. But welding is a big deal in subsea application, basically it opens a totally new can of worms we try to stay away from it.

To unclesyd, thank you for the pointers. Will check them out. Conern I have they may have long lead time. Our qty is very low and time is tight as we are in prototype. Definitely will consider them for production.

 

[Wrenchbender]

If you have low quantities, little time, and bar stock on hand, trepanning is probably the most feasible. We needed various lengths of 16-inch Dia X 3-inch wall specialty steel tubing (all > 5 ft). Rotary piercing worked fine, but trepanning was quicker and less costly than piercing, centrif casting or even hogging out. In our case, makes a 7/8 inch annulus of chips the full length. Search 'trepanning' and 'deep hole drilling' for your next stop.

 

[moltenmetal]

This of course implies that you're after through holes, in which case the trepanning is worth considering for sure. If you're after single-ended holes, you're screwed.

Some bar operations will give you a core charge for your chips, provided they're segregated by material. That can be better than hauling them off to a scrap dealer who will need to find a market for them.

 

[redpicker]

If you are expecting the core of a large bar to have the same properties the bar has at mid-radius, you will be mistaken. I've worked for companies that trepanned bars and had several folks ask to buy the cores. We always told them they were only scrap. A few wanted us to certify them, we would refuse.

I wouldn't use a treapnned core for anything that scrap wasn't a suitable raw material for.

rp

 

[ornerynorsk]

Years ago while working on one of the naval gun projects, shell loading mechanisms specifically, we rolled large tubes from ~10mm HY100 plate, welded the seam, machined about 50% of it away, and sent it onward for thermal treatment, further welding as part of a larger weldment, and finish machining.

Huge, huge savings at the end of the day rather than trying to use solid material, and actually ended up with better mechanical props as a result.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[salmon2]

Everyone, excellent discussion and I learned quite a lot from every input.

To redpicker, we are talking about aging or precipitation hardening steel, so I personally feel dimension is not that critical, right? How about a re-heat treatment to the core?

To ornerynorsk, that is a cool job. I agree flat rolled and welded plates got superior straightness, concentricity, consistent wall thickness. Sadly, a lot of people don't even consider welded tube at all. Our case is corrosion is obstacle.

 

[salmon2]

Correction: it isnot aging or precipitation steel. It is aging or precipitation metal like Monel or inconel.

 

[unclesyd]

I have to take an exception to redpicker's post about the cores of large bar stock. We have always used cores of the Nickel or Chrome Alloys without any downgrading due to location. On low alloy steels if you start with good quality material you can use the core if you are going to heat treat it to get rid of the mass effect of the larger bar.

 

[redpicker]

Yes, one of the issues with the core from a large low-alloy steel bar is the quality of heat treatment. Another, however, is the grain size, which is generally larger nearer the center than closer to the surface. Also, the center is likely to contain more inclusions and differ somewhat in chemistry, since the ingot or bloom the bar was rolled/forged from will solidify from the surface to the center and impurities and alloying elements are concentrated there. Finally, there are more shrinkage imperfections at the center of the ingot/bloom, and while the rolling/forging operations improve the soundness, the material quality of the core will be less than that closer to the surface. The quality may be suitable for some applications, but I stand by my original statememt that if you expect to have the same properties in the core as you have at mid-radius, you will be mistaken.

rp

 

[unclesyd]

Not to contest your the last post, I will agree that there is a very small difference in physical properties of large diameter bar stock especially the low alloy steels. There is a lot that goes into making steel bar today to achieve a uniform cross section both in structure and chemistry. Of course you pay extra for this. Normally any difference is insignificant and that it isn't considered in such things as large diameter shafts with a taper, a small steam turbine shafts where there are several steps in the shafts, or anything that has large machined steps. I agree that are very critical applications where you might not want to use the complete wrought bar where on would want to use a forged bar. We would normally do an analysis on any failed part and if possible do a macro etch of a cross section to ascertain if there were any underlying problems with the microstructure.
Over the years I've never seen any measurable problem with large diameter high alloy bar. In some case we have used wrought bar for high speed impellers that equal forged blanks.

We use a lot of tool steels and PH steels in components where the highest operational stresses would be at the center of the starting bar stock in some cases a 10" diameter bar.

I will also agree that if you have any reservations about the application you may not want to use the core unless you do a through analysis of the material.

 

[moltenmetal]

Take the cores and do full UT and even a few pull samples or etches if you really care- they'd still be worth a fortune relative to a pile of chips!

 

[arunmrao]

A better way to salvage the chips is giving to a renowned remelter and having them cast as pigs or ingots. These could then be rerolled or forged and used. (sorry could not resist from making this suggestion. )

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