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Annealing small bearing balls

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cidrontmg:
Itīs the season to heat the house/shop (in the northern hemisphere, that is. On the other side, wait 6 months before trying this...), and for me, also the season to anneal bearing balls. I use (and have used) them for things such as machine ball handles, governor weights, Newtonīs cradles (where I usually harden them again after drilling and tapping a hole in them), and for "ornaments" in bar ends. Contrary to some beliefs, it is quite possible to anneal bearing balls so that they can be drilled (or otherwise machined on) with "usual" HSS tools. The important thing is to maintain the (red) heat for quite some time, and then let them cool very slowly. Slowly meaning at least some hours before you can pick a 20 mm ball up without burning your fingers.
You can put the balls in a metal box (so they wonīt roll all over the place. An empty sardine or corned beef tin, for example), and heat the box to red. Then you cover the box with hot sand, or ashes, or make an enclosure around it of firebricks so that it is all encased, and will not cool in a snap. I usually put the box in a (wood) fireplace, let the fire burn to embers, and after a few hours, try to drill one ball, or use a file on it. If it isnīt soft enough, it has cooled too quickly, and you have to renew the process, and make the cooling time longer. The balls are air hardening.
This works usually fine with largish balls, meaning some 10 mm and up. But small balls (~6 mm and smaller) have a tendency to cool a lot faster, because of their smaller heat capacity, and relatively larger surface area in comparison to their mass. And they are likely to remain hard (or rather, harden again). One way to prevent this from happening is, to get a biggish metal block (something like 25x25x25 mm at least, of steel, cast iron, brass, copper, but NOT aluminium, tin or lead, obviously...), then drill some deep holes on the block, over halfway down, slightly bigger than the balls, and put the balls in there. The metal block will not cool too readily, neither will the balls near the center inside it.
The balls emerge from this treatment quite black and covered with scale. They can be polished again to a high lustre, but not quite as bright as they were before annealing, so donīt even try.  :poke:
 :wave:

Jonny:
Many thanks for the how to, its answered a few of my questions over the years.

Know what i am doing with most spring steels forging, hardening, tempering and annealing.
http://pic20.picturetrail.com/VOL15/728921/3960275/49395040.jpg
http://pic20.picturetrail.com/VOL15/728921/3960275/49395578.jpg
Its then reheated up and buried in the coke but far quicker 20 to 120 mins until coke and heat goes out, maybe 1 in 200 one breaks.

doubleboost:
I used the same method to soften some large lathe tools so that i could machine them

left them in the furnace to cool very slowly

Machinable but still very tough


Not much flex now

JimM:
Doubleboost that's exactly what I want to do with some large tools - unfortunately I knackered 3 cutters before I realised it was the material rather than my technique which was causing me issues  :doh:

How long do you need to keep the tools at temperature before allowing them to cool and do you think a charcoal BBQ would get them hot enough (I've got no open fire and the wife would murder me if I incinerated the lawn !)

Thanks

Jim

Lew_Merrick_PE:

--- Quote from: JimM on January 04, 2011, 11:36:52 AM ---Doubleboost that's exactly what I want to do with some large tools - unfortunately I knackered 3 cutters before I realised it was the material rather than my technique which was causing me issues

How long do you need to keep the tools at temperature before allowing them to cool and do you think a charcoal BBQ would get them hot enough (I've got no open fire and the wife would murder me if I incinerated the lawn !)
--- End quote ---

Jim -- with proper air feed and flow, you can smelt steel with the proper charcoal.  Charcoal fired smelters were not uncommon as late as the 1840's in many parts of the U.S.  There was one I toured as a child somewhere in southern Missouri and the one that gave "Irondale" (Washington) it's name was charcoal fired well into the 1860's.  It's the "BBQ" part that will give you problems for anything of size (mass).

Building up a proper tuyere and getting the airflow right is neither hard nor trivial.  Many of the "designs" floating around force all the air into the center of the furnace leaving you with "cold" edges.  Uneven heat is a killer for any large part (say more than 1/2 inch X 1/2 inch X 3 inches).  You need to think through and "see" the airflow you need to get a bed of coals sufficient to your task.

My main forge/founding furnace is a 24 inch ID truck brake drum.  I got it from a truck repair shop many years ago as scrap (in those days, that was $0.10/lb).  I lined the inside with (about) 1.5 inches of fire clay (mixed 2:1 with sand) with all my "air grooves" molded into it.  I have to replace the "lining" about every 50 uses.  The tuyere attaches to the wheel studs (using lots of high-temp anti-seize compound) and is 2 IPS pipe welded to a "wheel lug plate."  The outside gets wrapped with high temp insulation (Kaowool or equivalent).  I made a cover for it similar to the one you see in many "charcoal foundry" books (sheetmetal OD woven with wire and filled with fire clay & sand mixture).  I typically use a salad plate as the tuyere cover.

This gives me numerous options.  As a furnace, I have a (roughly) 20 inch diameter X 3 inch tall part space.  It also makes a decent forge for parts up to 18 inches long.  It will work with charcoal for many things, but it will handle coke as well.  The whole thing is (roughly) 35 inches X 30 inches (base frame with casters) X 32 inches tall.  Unfortunately, it is still in storage as my shop, which fits really nicely in 2500 sq ft, is currently crammed into 880 sq ft.

The blower is four DC muffin fans.  The box said that they were 16 cfm units (which I doubt).  I arranged them in a 2X2 array and power them using an LM317 adjustable voltage regulator which lets me control their output reasonably well.  A sheetmetal (square-to-round) transition gets the air into the 2 inch pipe.  The pipe feeding the tuyere has a gooseneck bend in it.  I milled out an area at the bottom of the gooseneck and cast a zinc filler such that any "charge" flowing down the tuyere will melt the zinc and end up in a catch basin (a large ceramic flower pot with the watering hole plugged up).  If you have any chance of having molten metal in your unit, this is an essential part of the set-up!

The basis here can be scaled according to your needs.  Brake drums that can no longer be turned are usually very inexpensive.

On the other hand, I cannot tell you how many times I have done heat treating and annealing in a glorified "hobo stove."  The main problem with this these days is finding a coffee tin that has a real "top" on it.  The "fuel shelf" only needs to be high enough to feed in air from your tuyere (which is for the little set-up I have just two muffin fans).  I wrap my unit in fiberfrax (an alternative to "Kaowool") and figure that if I get three uses out of it, I have won.  I just, as in early last month, drew the temper from a MT3 dead center and then re-heat treated and tempered it using such a beast.  I do not think I would try anything much larger in that set-up.

Does this help?

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