Recycling chips

[JMC]

I have often wondered what happens to the chips that get sent out to recycling. We recycle all of our stuff anymore....Alum goes into the aluminum bin...but different alloys get mixed together. Are they somehow able to reprocess it into a specific alloy again?

Steels are another story. A couple of years ago we were turning in 500lbs of 17-4 chips a week. Does the stuff get made back into 17-4? We kept everything as "pure" as possible, but contaminates (ie other types of steel) were bound to get in there.

As far as "regular" carbon steels....all of that stuff gets mixed together. I am pretty sure that that stuff gets made into re-bar or something. I remember on time back in school I was making somethign out of re-bar....and kept breaking tools. After fighting & grinding the crap out of the thing...you could see the shape of a 3/8" wrench start to appear.

So....just wondering how they do reprocess different materials?

 

[Motomoron]

From what I've seen on "How it's made" it all goes in the furnace with the train rail and beer cars and old toaster ovens and get melted. Samples are taken and the appropriate additional metals and chemicals are added to make whatever alloy they're aiming for.

 

[Perry Harrington]

Train rail is directly turned into metal fence posts by heating and running through a rolling mill.

 

[starbolin]

What happens to the scrap depends on what part of the country you are in and thus what mill it goes to. Here most the scrap is either made into pipe or goes to Japan. Pipe being tightly specified, the mills are somewhat picky about the quality of the scrap. Your location will be different.

Some mills can tolerate more contaminants than others. It depends on their customers. Your recycler gets a weekly list of requirements from the mill and can chose whether to do the separation or to take a lower price.

In general, copper in the steel is bad, as is carbon in the stainless. Some special steel grades can tolerate a little copper and so again it depends on the mill's customers. Steel mixed in the aluminum results in hard carbides that are bad for the grain structure but steel would be the easiest to sort out of non-ferrous.

One always hears stories of various items found 'embeded' in a piece of steel. It stretches credulity to imagine anything surviving the melting process but rather easy to imagine items such as misplaced wrenches falling into the rolling line. The heat and pressure of which would instantly weld the item into the structure nicely.

 

[bryan_machine]

Yup.

On a tour of the local Nucor plant, got basically that story. They only take scrap from large aggregators. They have zero tolerance for some things (radioactivity for example), and do indeed melt it and add things to it to make it meet the specs required.

Recyclers of brass, bronz, aluminum, etc, would have different rules.

Note that making steel from scrap requires much less energy and is therefore much cheaper. It's one of the earliest forms of large scale recycling - the seattle nucor plant was apparently built from scratch as a remelt plant. In 1910.

Similar wins for other metals.

It is easy to add stuff to the melt (inject it with lance, pour it in, etc.) but can be hyper difficult to remove things.

 

[recoilless]

I second on the above post. I did a job at the Nucor plant over in central Illinois and watched w/ some amazement while load after load of swarf, some of it much much larger than the swarf I see get dumped. One of the higher ups gave me a short tour and explanation of how they sort different grade/alloys as they supposedly have a special in house process for determination. Very interesting

 

[John in CA]

I was under the impression that it didn't much matter what was what when it came to chips; I thought I remembered reading that 80-90% or so turned into slag anyway, due to the high surface area/mass ratio. Is this innaccurate?

 

[surplusjohn]

I know that there are various fluxes for pulling out unwanted elements in a melt, comes to the top as slag. The Nucor mill in Auburn was orginally built as a re rolling mill that used old rr rail and re rolled it directly into rebar. This was the early 70s when there was probably lots of old rail coming up. I have seen photos of rolling mills in Pakistan and Bangladesh that had guys hand torching long pieces off of plate from old ships and then rolling that directly into re bar.