On Wed, 24 Apr 2013 09:46:33 -0700 (PDT), "Denis G."
wrote:

On Apr 24, 11:17*am, Ed Huntress wrote:
On Wed, 24 Apr 2013 09:06:13 -0700 (PDT), "Denis G."









wrote:
On Apr 24, 10:47*am, Ed Huntress wrote:
On Wed, 24 Apr 2013 08:31:23 -0700 (PDT), "Denis G."

wrote:
On Apr 24, 9:34 am, Ed Huntress wrote:
On Wed, 24 Apr 2013 07:28:47 -0700 (PDT), "Denis G."

wrote:
On Apr 23, 12:57 pm, Richard wrote:
On 4/24/2013 12:48 AM, Gunner Asch wrote:

On Tue, 23 Apr 2013 08:41:46 -0500,
wrote:

On 4/23/2013 7:57 PM, Gunner Asch wrote:
Fella brought over a gun part for a Marlin lever action..he was
missing a pin..so I made one up for him and installed it..and as I was
inspecting it..I noticed a rather serious crack starting to develop at
one end of the sintered metal part. I fixed it by using my tig torch
and silver bearing flux..I packed the crack full of the heavy green
flux and zapped it with the tig..sealed it up well enough and I put a
slight layer over the area of the crack. After polishing it up with a
fine wire wheel, it looked good. But...is it?

How well does this sort of thing work with sintered metal parts?

Should I warn the guy to buy a new Widget? (Marlin just closed their
doors...so parts may become hard to find)

Any suggestions for other similar fixs with sintered metal parts?

Gunner

Which part?

Better link

http://www.urban-armory.com/diagrams/mar1894.gif

Part #8, 9, and 10 (and 11)

He was missing the #10 pin..and I turned, annealed, replaced it and
peened it into place gently.

Gunner

Why do I get the impression that the rifle has been overstressed?
Repeatedly.

http://en.wikipedia.org/wiki/Metal_fatigue

Sintered metal parts start out with a bazillion "cracks" (voids) when
they go into the furnace (or hot isostatic press) and hopefully come
out with none. Everything is controlled (temperature, pressure,
atmosphere) to get near net shape and avoid having to machine the
part. Not to say that it can't be repaired, but I'd rather go to the
dentist.

Dollars to donuts, though, they ain't HIPping those gun parts. At
most, they're post-pressed and copper-infiltrated.

This part, though, looks like it wouldn't be practical to post-press.
And it's probably not infiltrated.

--
Ed Huntress

I was guessing that it was HIPped with the holes and final features
drilled and machined. *(Certainly you can't pull apart the mold with
those sideways holes. *The HIPped parts I've seen have copper powder
mixed in and with 30-50 ksi pressing you get pretty good part strength
and compaction and it's more state-of-the-art.
On the other hand, my experience is more with R&D and I don't know how
much throughput you'd get from HIPping vs. more conventional belt-
driven open air sintering furnaces, so maybe you're right.

Unless there's some advance in HIPping since I was covering PM, it's
done in strippable metal cans -- one for each part. That drives costs
'way up. It's used mostly in aerospace, or it was.

HIPping of cast parts doesn't require cans, but PM does, or it did.

Ferrous parts that require some toughness and a bit of ductility often
are pressed, sintered, possibly hot post-pressed, and then
infiltrated, usually with copper. As an example, that's how they make
the bevel driven gears on DeWalt angle-head grinders. It's not cheap
compared to plain press-and-sinter, but it's a heck of a lot cheapter
than HIP. You get 100% density with infiltration, as you can with HIP.

--
Ed Huntress

You're right about the cans. They're crushed and disposable and the
HIPped material had to undergo final machining. It is more
expensive. * I've been away from that business for a while and don't
remember everything. *I pulled out one of my PM books and saw the
process that you describe. *The PM that I'm familiar with had the all
powders premixed before pressing.

What you're describing is by far the most common way it's done.

PM can be fascinating. By mixing powders and sintering at full
diffusion temperatures, you can produce alloys that are not possible
any other way.

For example, the most exotic of the high-speed-steels: Crucible CPM
REX 121. You can't make it by melting. That stuff is HIPped, BTW.

Regarding memory, I can empathize with that. d8-)

--
Ed Huntress

PM is a neat subject. Although it get a lot of bad press for cheap
parts, I wonder how many people would sleep at night knowing that most
jet turbine blades are made with it.

Right. And the connecting rods in a lot of automobile engines. PM is
all over the place, and it's often hard to identify, particularly when
it's been post-pressed. It looks like a high-quality forging. And it
often performs as well or even better than one.

It's come a long way from the days when it was used for cheap parts
that often were brittle and weak.

--
Ed Huntress