I don't know why I was thinking about this. You know, all the forging processes we are familiar with are done by compressing the material. I once saw a production process that used tension to forge the part. The company was making SS meat hooks. They put a bar in a fixture that clamped both ends, then the middle was heated by induction and the bar was streached like in a tensile test machine. Formed two nice points before it parted in the middle. I imagine this has a bad effect on the integrity of the steel, but it worked great for them.

Oh I don't know how bad for the steel it'd be wouldn't it be about the same as drawing wire? No die but how much does the drawing die actually do towards compressing the metal anyway? Some of course but it's mostly a tensile forging process.

Frosty

Good Point, Frosty. (why do I hate saying that)? (grin)

But.........Now you're talking about cold process too.

Edited June 18, 200917 yr by nakedanvil

Spent a year one summer in cold draw of seamless steel tube part of the mill.. Normaly the tube is pulled through a die and over a mandrill. That mill could they did Id and od size and even pulled rifleing in some caliber of naval gun liner. One bench I was told could generate a million lbs pull. The tubeing the worked with was bettween 2 inches and like 18 inches normally. Most of it was for bearing races.

Draw tends to concentrate defects etc, toward the rear of the piece.

Hot streaching would tend to aline and grain boundries along the major axis of strain

PS unlike glass and and so forth, cold draw happens at the die or not at all. You get a massive realignment of the size distribution and and direction of of grain in the steel.

Edited June 18, 200917 yr by Charlotte
ps.

Oow, oow, I just thought of another one. I used to have a book from Atlas Steel in Canada. They were a large producer of hollow drill steel for jack-hammer bits. They showed step-by-step how the hollow steel was made, absolutely fascinating!

They started with a large billet of steel and they punched a hole in the center. The billet was maybe 18” diameter and the hole was about 4”. They then inserted a piece of pure iron that just fit in the hole. Then the billet went through the rolling process to become, what, a mile of 1” hex bar? The bars were cut to length and a small part of the end was broken off.

Here’s where the stretch forging came in. They would get hold of the soft iron in the middle and start pulling. Now of course they couldn’t just pull it out, but as they pulled it would stretch out and get skinnier and this would progress all the way down the bar until the entire core came out! It’s kinda like the plastic they use to hold a six-pack together. You ever pull on that stuff? One part stretches and before it breaks another adjacent area starts stretching. In iron this happens because as it stretches it becomes work-hardened and even though smaller has more tensile strength than the adjacent part. Cool stuff!

That is kink of cool. I've heard of that process but never seen it.
The mill i worked in used the piercing process for seamless tubing. It was kind of neat to watch them grab a billet from the rotating hearth, put it in the pierce and watch as the billet would begin to spin and throw off scale as the piercing rod attached to big massively counter weighted wheel you slam into and tubing would squirt back along the piercing rod. 8 inch tube with 2 inch wall in like 30 seconds.

For some reason that I never could get explained to me they did all their their stainless tube by extrusion.

They use a similar process to make fiber optic cable. The take a optically doped glass billet, roll an outer layer of reflective glass around it. Then they take it to the top of a tower heat it and it literally creates a continuous drop. By the time it reaches the bottom of the tower is is the right size and cooled enough for adding the plastic coating and then rolling onto large spools

I was in a Dana axle factory some years ago. Their process for making axles started with induction heating and upsetting to create the flange. Next the shaft portion was cold stretched to increase length and decrease diameter. It was interesting to see. I am not certain why they used this process, but I think it may have had to do with the volume of steel needed to create the flange vs. the OD needed in the finished shaft. I suspect that the finished shaft diameter would have been to small to allow for an upset of sufficient length to create the flange. (3:1 aspect ratio would have been exceeded).

Charlotte- The tube mill you were in didn't happen to be one of the Timken facilities? I worked for Timken for a couple of years on the bearing side and had a chance to tour their piercing mill in Canton OH. It was just as you described.

Patrick

Spent a year one summer in cold draw of seamless steel tube part of the mill.

I've had jobs like that - where one summer = a year!

Note too that a meat hook is probably not a very high performance part! Smoothness and sterilizablity were probably the driving requirements.