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Steel Making

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Making Steel Balls






Category: THE FORGING OF STEEL

Steel balls are made from rods or coils according to size, stock
less than 9/16-in. comes in coils. Stock 5/8-in. and larger comes
in rods. Ball stock is designated in thousandths so that 5/8-in.
rods are known as 0.625-in. stock.

Steel for making balls of average size is made up of:

Carbon 0.95 to 1.05 per cent
Silicon 0.20 to 0.35 per cent
Manganese 0.30 to 0.45 per cent
Chromium 0.35 to 0.45 per cent
Sulphur and phosphorus not to exceed 0.025 per cent

For the larger sizes a typical analysis is:

Carbon 1.02 per cent
Silicon 0.21 per cent
Manganese 0.40 per cent
Chromium 0.65 per cent
Sulphur 0.026 per cent
Phosphorus 0.014 per cent

Balls 5/8 in. and below are formed cold on upsetting or heading
machines, the stock use is as follows:

TABLE 14.--SIZES OF STOCK FOR FORMING BALLS ON HEADER
-------------------------------------------------------
Diameter of Diameter of Diameter of Diameter of
ball, inch stock inch ball, inch stock, inch
----------------------------------------------------
1/8 0.100 5/16 0.235
5/32 0.120 3/8 0.275
3/16 0.145 7/16 0.320
7/32 0.170 1/2 0.365
1/4 0.190 9/16 0.395
9/32 0.220 5/8 0.440
-------------------------------------------------------

For larger balls the blanks are hot-forged from straight bars.
They are usually forged in multiples of four under a spring hammer
and then separated by a suitable punching or shearing die in a
press adjoining the hammer. The dimensions are:

-----------------------------------------------------------
Diameter of ball, Diameter of die, Diameter of stock,
inch inch inch
---------------------------------------------------------
3/4 0.775 0.625
7/8 0.905 0.729
1 1.035 0.823
-----------------------------------------------------------

Before hardening, the balls are annealed to relieve the stresses
of forging and grinding, this being done by passing them through a
revolving retort made of nichrome or other heat-resisting substance.
The annealing temperature is 1,300 deg.F.

The hardening temperature is from 1,425 to 1,475 deg.F. according to
size and composition of steel. Small balls, 5/16 and under, are
quenched in oil, the larger sizes in water. In some special cases
brine is used. Quenching small balls in water is too great a shock
as the small volume is cooled clear through almost instantly. The
larger balls have metal enough to cool more slowly.

Balls which are cooled in either water or brine are boiled in water
for 2 hr. to relieve internal stresses, after which the balls are
finished by dry-grinding and oil-grinding.

The ball makers have an interesting method of testing stock for
seams which do not show in the rod or wire. The Hoover Steel Ball
Company cut off pieces of rod or wire 7/16 in. long and subject
them to an end pressure of from 20,000 to 50,000 lb. A pressure
of 20,000 lb. compresses the piece to 3/16 in. and the 50,000 lb.
pressure to 3/32 in. This opens any seam which may exist but a
solid bar shows no seam.

Another method which has proved very successful is to pass the
bar or rod to be tested through a solenoid electro-magnet. With
suitable instruments it is claimed that this is an almost infallible
test as the instruments show at once when a seam or flaw is present
in the bar.





Next: The Forging Of Steel

Previous: Heat Treatment Of Axles



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