THE ROLLING OF RODS
Steel rods and what we will call large wires are rolled from billets
which are long, and approximately square blocks of steel. The size and
shape of the billets used vary, depending upon the process and the size
of the rod to be rolled. Much of the finished rod is sold as such for
various purposes for which round steel is desired and an immense tonnage
of one of the smaller sizes is used as the intermediate raw material
from which wire is drawn.
Rod mills have a very interesting history, which, by the way, is but one
of several histories of the development of the iron and steel processes
and products which should make us proud of the genius of man in the way
of metallurgical, mechanical and business development.
The Belgian Mill
The first bars and rods were rolled in the old two-high mill, where,
after each pass they were pulled back over the top roll and inserted
into the next groove by the roller as is usual with the two-high mill.
Then along came the three-high mill which probably resulted in greater
advantage to rod rolling than to other lines, important, even, as it was
to them.
But long, thin bars or rods are quite pliable when at white or rolling
heat and the “catcher” soon discovered a way by which he could save time
and push up his tonnage. He skillfully caught the forward end of the bar
as it came through, and, giving it a quarter twist, he inserted it in
the proper return groove without waiting for the whole bar to run
through to his side before starting it on its return journey. This, of
course, was easily possible with the slow speeds then used.
Naturally the rod coming through from one side and going back to the
other formed a loop.
The roller, at the front, was not slow in discovering that on long rods
he could do the same thing, so rods were soon regularly going through
three or more passes at the same time.
[Illustration:
WIRE DRAWING OF 350 YEARS AGO
]
It was soon found out that it was better to use a second set of rolls
placed end to end with the first for the third and subsequent passes as
the roller had hardly room or time to loop the rod on the return and
start his next one. This second set of rolls was connected on the same
shaft and therefore made to run at the same speed as the first. It
worked out that by use of such extra sets of rolls and an additional
helper or two the same long rods could be running through as many as six
or seven passes at once with a great saving in time.
As it came from the final pass the forward end of the finished rod was
seized in a pair of tongs by a boy who ran with it away from the rolls,
stretching it out along the floor to cool. As the various sets of rolls
were connected on the same driving shaft and revolved at the same speed,
the loops which were formed between passes continually grew longer.
Here, too, boys with iron hooks were useful in controlling the loops.
Later it was found advisable to have each succeeding mill speeded enough
to take the rod as the preceding pair of rolls delivered it; then the
loops remained of approximately constant length.
[Illustration:
PLAN OF A MODERN LOOPING MILL (THE GARRETT MILL)
]
To push production the mill was run faster and faster. As longer rods
were rolled, a hand-operated reel was devised to which the boy attached
the forward end of the rod while another turned the reel. But the speed
of the mill was limited mainly because of the slow reel and the awkward
method of getting the rod attached to it.
The Bedson Continuous Mill
About 1867 George Bedson of England, invented the first “continuous”
mill.
Instead of looping the rod around and back through the rolls he put
several sets of rolls each in front of the other with every other pair
vertical. This alternate horizontal and vertical roll arrangement was
necessary because the reduction of the billet or rod in any pass can be
only in a direction perpendicular to the axis of the rolls. The roller
and catcher had given it a quarter-turn twist each time they started it
into the two-high rolls. Bedson’s successive pairs of rolls were set
close together, each pair being speeded enough that it took the rod
exactly as fast as the preceding pair delivered it. The billet or rod,
therefore, traveled through them in a straight line.
This continuous process was, of course, of great advantage in that
considerable speed could be attained and there was not the rapid cooling
nor the opportunity for loss by scaling from exposure to the air which
occurred with the long loops of the Belgian Mill. It was a great
advance, but the speed was yet held down by the finishing pass and the
inability of the reel to coil the rod fast enough.
The greatest development came through the inventive genius of two men,
Charles Morgan and George Garrett, who developed the two separate types
of mill which have made the rod rolling industry what it is to-day. The
work of both was done in this country.
The Morgan Continuous Mill
Morgan’s also was a continuous process. The billet was put in at one end
of a new type of heating furnace which Morgan devised, and was gradually
pushed along to the other end. From this second or outgoing end, the
long, narrow, white-hot billet went through several pairs of two-high
rolls set close together, each successive pair having smaller grooves
than the one preceding it, so that, after traversing these several pairs
of rolls, the rods emerged from the last pair finished, having traveled
in a straight line through them.
Hand reeling was much too slow for Morgan who invented two different
types of high-speed automatic reel which, in the highly speeded mills of
to-day, receive and coil wire coming from the finishing passes at speeds
of over one-half mile per minute. It is stated that the billets and rods
therefrom traverse the rolls so fast and the pressure is applied so
quickly and so hard that the rods emerging from the finishing passes are
hotter than were the billets when they went into the rolls.
[Illustration:
THE BILLET TRAVERSES THE MORGAN CONTINUOUS MILL AT HIGH SPEED EMERGING
FROM THE LAST ROLL AS FINISHED ROD
]
As was explained, no reduction in thickness is brought about by the
sides of the grooves in the rolls. Therefore, a bar or rod must be
turned after each pass unless Bedson’s alternating horizontal and
vertical rolls are used. This turning Morgan did in spiral tubes
inserted between the successive sets of rolls, all of which were
horizontal. These tubes operate as does the “rifling” in a gun barrel,
in turning the rod.
In Bedson’s mill, with its alternating horizontal and vertical pairs of
rolls, it was possible to roll only one rod at a time. With Morgan’s
system, in which all rolls were horizontal, several rods could be
traversing the mill side by side.
With the high-speed reels and what are known as “flying shears” in which
billets or rods can be cut to any length while going at full speed,
Morgan’s mill had come to a high stage of development. It was
practically automatic.
The Garrett Mill
While Morgan was developing his continuous mill, William Garrett was
improving the old Belgian mill. Garrett believed and insisted that with
proper working, rods could be rolled from billets of much larger
diameter and greater weight than the long narrow billets which had been
used. He eventually did away with an intermediate rolling operation by
using larger billets.
You remember that in the Belgian mill the “catchers” looped the rods
back into the rolls. To do this work automatically Garrett inserted
between the sets of rolls looping troughs which guided the forward ends
of the rods around and into the next groove in the rolls. These troughs
are called “repeaters.” It was found that while they worked very well
for looping the cross-sections known as the squares, they were less
suitable for looping the oval sections which were produced with every
other pass. These were better and more safely done in the old way, i.e.,
by manual labor. They are generally so done to-day. With the Morgan
high-speed reel, sloping floors to better take care of the loops, and
with successive pairs of rolls each running at higher speed than the
preceding pair, the Garrett mill has apparently kept pace with the
Morgan.
Each has its advantages and each is used for certain classes of work.
For long continued runs on rod of one size the Morgan mill can produce
more cheaply, its product is more uniform in temper and the loss from
scaling is less as little of the rod is exposed while in the mill. As
the first pair of rolls in the Morgan mill is set close to the furnace,
less than one-quarter of the billet is in the mill at any one time and
the forward end of the billet is on the reel as finished rod before the
last of the billet leaves the furnace. With any process something
occasionally goes wrong so that the rod does not follow the path
intended. In such cases misshapen or tangled rod results. Such spoiled
billets or rods are called “cobbles.” With what is known as the “flying
shears,” which in the Morgan mill cuts the billet or rod while it is
traveling at high speed, the rear part of the piece can be cut off and
saved in case of cobbling. On this account the Morgan mill is said to
give less scrap than the Garrett.
The Garrett mill, on the other hand, gives rod which is more uniform all
along in shape and diameter and it has the considerable advantage that
it is quickly adaptable to change of product; it does not require such
complicated and nice adjustment as does the Morgan mill. So, despite the
greater danger to the rollers from the circling loops about them, which
occasionally become unmanageable, the Garrett mill is largely used.