Non-technical chats on iron and steel, and their application to modern industry

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.

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.

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.

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.