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.
As was seen in the rolling of plates, “cold working” raises the strength, lowers the ductility and embrittles steel more than does the regular “hot working” at the cherry-red or white heats which are usual in the forging and rolling processes. If the so-called “cold finishing” at very low red or black temperatures affects the physical properties of plates, it can be readily understood that cold-drawing of wire and of seamless tubes at ordinary temperatures of 70 to 100° F., must considerably accentuate the effects noted. So much is this so that drawn wires and tubes have to be frequently annealed, i.e., heated to a good red heat for a time between successive trips through the dies, annealing having the effect of off-setting the lowered ductility and increased brittleness which would cause the wire to break. In some cases the wire has to be annealed after each pass or draft, but oftener several passes are possible before annealing is necessary. This depends largely upon the quality of the steel used and the amount of “reduction” attempted in each pass.
The raw material, No. 5 soft wire rod, which is about one-fifth of an inch in thickness, comes to the wire-drawing plant from the rod mill. This No. 5 rod is the thinnest which the mills have found it economical to roll, so further pulling down in size can best be done by “drawing.”
Before Drawing into Wire the Scale Must Be Removed from the Rods by “Pickling” in Acid
As all iron and steel materials which have cooled in air from a red heat are covered with a hard, brittle scale of iron oxide, the rod must first be “pickled,” i.e., digested in hot, weak sulphuric acid, which, in 10 or 15 minutes so dissolves and loosens the hard surface that it can be readily jarred loose and washed off. By immersion in a vat of boiling milk of lime, the pickled rod is given a lime coating which neutralizes any acid which remains, and, when dry materially aids in the lubrication of the wire while it is going through the dies. Thorough drying, called “baking,” is accomplished in the dry house at 300 or 400° F., from which the rod with soft, scaleless, lime-coated surface goes to the “drawing” benches. After rinsing free from the pickling acid, the wire is often allowed to acquire a soft film of rust by spraying it with water and keeping it wet in the air for a short time before going to the lime vat. This rust or “sull” coat itself assists in the lubrication. However, the color of the product is not as good as when the “sull” coat is not used, and such wire usually goes into articles for which darker color is no drawback.
Single Wire-Drawing Block
A Wire-Drawing Die
The dies with more or less funnel-shaped holes of accurate diameter are set vertically. They are of extremely hard material in order to stand as long as possible the severe service without excessive wear, which sooner or later so enlarges the holes that the dies become useless. Then they must be removed and either discarded, or, in the case of steel dies, the holes reduced by hammering and redrilled. Often the holes of worn cast iron and steel dies are enlarged to the next larger size and so used.
The Drawing of Wire
The loose end of each coil of rod of wire is hammered or otherwise made smaller for a length long enough to be threaded through the hole in the die and firmly grasped by tongs or “pliers.” The die being firmly fastened, the draw head, of which the pliers are a part, is drawn away until a sufficient length has come through that it can be attached to a revolving block or drum which thereafter continuously pulls the rod through the die and winds it into a coil about the block as it comes, at speeds as high as 400 feet a minute.
As the rod passes through the box in which the die is fastened, besides its lime or sull coating it is sometimes provided and takes up other lubricants, such as soap, grease, or tallow.
The coil of wire is lifted off the drum and tied, or is redrawn to wire of a smaller size.
After from one to several drafts, depending upon conditions, the wire must be annealed for several hours, and again pickled to remove the scale formed, washed, lime-coated and dried. For wire which must undergo many reductions or passes, as must all small wires, several drawings, annealings and cleanings must be gone through with before it is down to the desired size.
In order to work properly and not cut the die too fast, which would rapidly enlarge the hole and cause the rear end of the wire to be of different thickness than the forward end, the rod or wire must be of maximum softness. Either under-cleaning or over-cleaning will make the metal harsh, as, also, will under-baking in the dry ovens. These they endeavor to avoid in preparing the rod.
Other lubricants may be used and certain finishes or colors given to the wires. Such are the various white to red coatings which come from using tin and copper sulphate solutions instead of lime coatings. This is more often done with fine wire than with thicker. Certain “patenting” processes make use of various methods of tempering wires by cooling in air after a last annealing.
Not only are wires ordered to size but many times also of certain temper or grades of hardness and stiffness. These various tempers are determined largely by the chemical analysis of the steel and the number of drafts after the last annealing.
Piano wire is well known to have a very high strength, sometimes as high as 400,000 pounds per square inch. Spring wire is rolled and drawn from higher carbon steel than is ordinary wire, and, through heat treatment, the best properties are imparted to it.
Besides being in this form used for miscellaneous purposes, thousands of tons of wire are annually made into wire nails, staples, wire fence, barbed wire, etc., all of which products are of American derivation, with the possible exception of wire nails. Even this, however, if not originally ours we have made ours through our great production. All are very speedily turned out by automatic machines into which the wire or wires feed. The product drops out into boxes below or is rolled into coils as is the case of the wire fence and barbed wire. The speed of the machines is so great that the eye cannot begin to follow the operation.
Wire being so well known it is not necessary to speak of its uses, but it will be interesting to call attention to the very extensive production of this steel product. Of the 32,000,000 tons of steel produced in 1915, for instance, over 3,000,000 tons were rods and wire, and when we think of the length of small or even average sized wire that it takes to make a pound, a hundred weight, or a ton, some slight conception of the amount of wire produced and used comes to us. As the material for wire gauze and cloth, wire rope, cable, piano strings, springs of all sorts, pins, needles, nails, fence, barbed wire, and the myriad of other things, wire really is one of our great products.
It was mentioned that piano wire had been made which had a tensile strength as high as 400,000 pounds per square inch, which is six or seven times the strength of an equivalent cross-section of steel rail or plate. Wire is undoubtedly the strongest product which is made from steel. This is why wire rope or cable is so strong. It is made by twisting together many small wires.
Though extremely recent from the standpoint of our world’s history, the building of the famous Brooklyn Bridge by the Roeblings was far enough back that we likely have forgotten that each of the four big 15¾–inch cables is made up of 5,296 separate wires tied into a bundle.
Undoubtedly the best preservative against corrosion for iron and steel is what is known as “hot galvanizing.” Much wire is hot galvanized. In this process the wire is “pickled” in weak acid to remove scale, given a soft red coating by dipping in weak muriatic acid and drying. The strands of wire 20 or 30 abreast are run through a kettle of molten zinc. The wires are wiped smooth and free from excess zinc by pulling them through asbestos pads. A continuous coating of zinc is thus permanently left upon the surfaces of the wires which very effectively keeps them from rusting. Wires which have to stand severe weather conditions may not have the excess zinc wiped from them. Telegraph and telephone wires often have the thicker or unwiped coating.
Very naturally the drawing of wire requires use of much greater power than the rolling of rod and the speed of drawing is nowhere near as great. Therefore the cost of wire is comparatively much greater than the cost of rolled products. In the case of watch springs it was once computed that the product had to bring 50,000 times the cost of the steel from which the wire was drawn.
“Continuous” wire drawing has not been so successful nor advantageous as was the continuous rolling of rods. It has been possible in a small way and with certain grades of the product to apply the continuous process, but, mainly on account of mechanical difficulties, continuous drawing of wire seems to be comparatively unimportant.
CHAPTER XX
THE MANUFACTURE OF PIPE AND TUBES
Tubes of some sort have been in use by man since very early times. Nature provided the first ones in the way of hollow stems of shrubs, such as alder and bamboo. Some of these we saw in use by the early smiths conveying the blast of air from their goat-skin bellows into the crude clay furnaces built in the hillside.
Tubes made of clay, stone, lead and bored logs were also used. Much later pipes made of cast iron came into rather extended use for the conveyance of water. The general use of gunpowder greatly accelerated the manufacture of small tubes which the smiths produced for gun barrels by hammering and welding together long, red-hot strips of wrought iron about round rods or “mandrels.” About 1815 illuminating gas came to be used in England for house lighting. This brought a demand for tubes of considerably greater length, which were first made by screwing or otherwise fastening together old gun barrels which were very plentiful at that period.
The first patents for the making of welded pipe as we know it were taken out in 1824 and 1825, the latter for the butt-welding method of pulling a narrow iron plate, called “skelp,” through a bell-shaped orifice which curled it and welded the edges together very much as is done to-day by this process.
Our modern pipe of both butt-weld and lap-weld varieties is manufactured either from wrought iron or from soft steel.