Rolling Bearings Manufacturing: Rings And Rollers Of Steel!

Two of my readers have out-and-out asked me recently to write something on bearings (and two other readers had bearing related matters for me), so OK, here we go.

Today I received the below from Peru re a sale we made recently (and so was the catalyst to get me to write this now):

Tax ID	Doc	Doc No.	Salesman	Cash/Credit	Codigo	Qty	Price	Dsct	Amount
1006xxxxxx	F	0061997	OF	C	B5-1/2	28698	0.03	0	$860.94

Allow me to explain.  On September 6 (not listed above, to save horizontal space), we sold 28,698 pcs of steel ball "B5-1/2" (B5 being a Chinese brand of steel ball, the 1/2 is a one half inch size steel ball).  That "Qty" of 28,698 pcs is the FIRST TIME (newer readers may want to track down my article "Ameru Trading del Peru S.A." in my June (I believe, perhaps May) archives) we have ever sold anything over 20,000 pieces at one pop.  OK, the unit price is just $0.03, but still.  Hey, it is a good excuse to start my bearing article...

To begin with, rolling bearings are in almost all cases made with "52100" steel, its properties are here.  52100 steel is fairly hard, and has about 1% Carbon (for hardness) and about 1% Chromium.  FYI  and a bit O/T, stainless steel has up to 20% chromium.  Some bearings are made with stainless steel, particularly for harsh chemical environments, but stainless is not as good (because it is not hard) as 52100 for typical applications like wheels of cars.

Most rolling bearings (at least the ones we buy and sell) consist mainly of the three below components:

-- rolling elements (balls or rollers)
-- inner and outer rings
-- cage (to hold the rolling elements in place inside the bearing

The rolling elements are typically made from 52100 steel that is supplied in wire form, wire approximately of the diameter of the rolling element.  The wire is snipped off, and the steel chunks then go into a series of machines that grind them into balls and later polished.  There are various grades of precision and other  specifications (roundness, roughness, etc.) that the bearing manufacturers ask for.  In some cases, the bearing manufacturers "farm out" the rolling element manufacturing to specialists, a great example is NN, Inc., ticker NNBR on NASDAQ.  NNBR has a spectacular price chart (for devotees of stock trading), having fallen to 1 from about 20 in 2008/9 and back up to 16 or so, and now down again.  Of interest is the fact that "tapered rollers" (going into tapered roller bearings, "Timken" type bearings, "TRBs") are hardly ever farmed out, in that the technology is more difficult and the TRB manufacturers want this proprietary.

The inner and outer rings are made two different ways (depending on the size, how many are to be produced in that production run, etc.):

-- they can be made by hot-forging
-- or machined from precision tubing (supplied by steel companies)

I myself had the great pleasure of twice visiting a bearing plant in Spain some 12 and 15 years ago.  This was a small (and using OLD technology)  manufacturer of rolling bearings.  For the rings, they made them both ways mentioned above.  Both times they were forging pieces.  And while in their offices talking with their Export Director we could hear & feel the *poom* sound of the forge pounding the steel pieces into shape.  I believe they used their forge for the high production pieces as well as their large size bearings (say with an outer diameter of over 4 inches).  After forging, the steel pieces went on to be precision ground and polished (and later assembled with the rolling elements into completed bearings).

They used other machines to cut and grind steel tubing (tubing fairly precise in its ID and OD to save them work) for bearings they machined only.  IIRC, they machined rings only in their shorter production runs.

The steel cages are usually supplied by outsiders, the steel quality is not as important nor are other specs, as long as they fit OK and are softer than the other bearing components, that is all that is needed.

The various components are then assembled by other machines.  After assembly, the bearings then go on to get heat treated.  There are two schools of thought (or at least there were):

Case Hardened (in which the heat treatment is somewhat shorter and hotter to make the steel harder on and near the surface, while the interior is left more malleable).

Through Hardened (in which the whole bearing's steel is hardened all the way through).

There are (were) long running arguments about which was "better".  Some material science guys said case hardening was better, in that the bearing would not crack as easily (eg, when a wheel bearing hits a nasty pothole), but the through hardening guys said the bearing was tougher if the whole piece was hardened.  I am not an engineer nor do I know enough about steel to say who might be correct.

After heat treatment, the bearings are allowed to cool, they are then sent on to be packaged and shipped.  In some cases, however, the bearings will often get a rubber seal or steel shield (to help keep out dirt), the seals or shields are usually bought from outside companies as well.

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In the near future, I will write about some of the world's bearing companies.  What they produce, how they compete and what their niches are.