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.
CHAPTER XIX
WIRE AND WIRE DRAWING
It may be rather disconcerting to some enthusiastic ones who assume that we Moderns have made all the progress that is worth while to learn that so many of our supposedly new products were far antedated. In the case of wire, again, we were antedated as much as 30 centuries. The wires which were produced by the Ancients, however, were usually of the noble metals, gold and silver. They were not drawn through dies as are the wires that we know, but were hammered into shape from long, thin strips of metal. The earliest use of our “drawplate” method of which we find authentic mention was in the 14th century in Germany. The wire was hand-drawn. Machine-drawn wire was being produced in England as early as 1565.
In the United States the wire drawing industry had become pretty well established by the middle of the 17th century. As Cort had not at this time invented the rolling process for bars and rods, very uneven strips of metal only were available from which to draw the wires. But, even so, with our highly developed rod mills and our present very satisfactory No. 5 wire rod to begin with, our wire drawing methods are yet seemingly crude and show small advance compared with the very great progress which has been made in other lines of the iron and steel industry.
Unlike the processes of forging, rolling, etc., drawing of wire is done cold. In this condition steel has its highest strength to stand the strain. The rod or wire is pulled through very hard cast iron or steel dies, the general process being well likened to pulling a rope through a small knot hole.