US2696378A

US2696378A - Method of heating steel slugs for forging or extrusion

Info

Publication number: US2696378A
Application number: US241619A
Authority: US
Inventors: Andrew F Krischer
Original assignee: United States Steel Corp
Current assignee: United States Steel Corp
Priority date: 1951-08-13
Filing date: 1951-08-13
Publication date: 1954-12-07
Anticipated expiration: 1971-12-07

Description

Dec. 7, 1954 A. F. KRlTscHER 2,696,373

ME'rHoD OF HEATING STEEL sLUGs FOR FORGING OR zEx'rRUsIoN l Filed Aug. 13 1951 FIE United States Patent" O METI-IOD OF HEATING'STEELSLUGS FOR FORGING OR EXTRUSION Application August 13,. 19511, .Serial No. 241,619 7 Claims. (Cl. 263-62) This invention relates to the heating of masses of metal and, in particular, to the heatingV of billets ,or slu'gs* of steel for hot-working by extrusion or' forging.

The extrusion of steel through formin'g'dies accomplished but requires a special technique andis still beset with numerous difficul'ties. For example, the heating of the billets or Slugs has usually been eifected in conventional furnaces at relatively low rates. `The heavy Scale resulting is abrasive in Character and causes rapid wear of the dies, besides reducing the product yield per pound' of billet weight. Such scale is not fully removed by conventional descaling practice and' the port-ion left' on the billets impairs' the surface' finish'k of the extruded product, In addfhas been besides damagin'g the d'ies. tion, the power required for the extrusion operation has been very high. Experience has shown, furthermore, that stainless-steel;,billets heated by conventi'onalf; methods and equipment, i. e., involving long heating times suchas several hours, occasionally willl not "push" when' placed in the press, al'though heated to the proper temperature.

' I have inventeda novel method of heating steel. billets or' slugs for extrusionwhichV overcomes these difficulties and is characteri'zed by further important advantages. The invention is also useful in' heating billets for ordinary forgi-ng Operations. My invention. is based on'the fact that ordinary steel, while losing most of its* tensile strength at temperatures in 'the n'eighborhood. of those required for forging or extrusion', still retains sufficient strength at such te'mperat'uresV to' sustain substantial loads. Recent investigations show, for example, that low-carbon steel'has a short-time tensile strengt of about. 2500 p. s. i. at 2000 F. and about l5001p'. s`. i. at 2`3'00' F'. I take advantage of this fact to provide a novel method of supporting and handling billets or Slugs while .being heated for working by forgingor' extr'us'i'on. I' 'also u-tilize an irnproved type of 'heating' furnace. andneifect the heating at a rate much greater than has beerr thought possible heretofore. I am thereby enabled to utilize fully the short-time strength at high temperatures.

In a preferred practice, I weld a steel Stud to one end of a billet or slug and, by means of the welded-on Stud, I support the slug while conveying it through a continuous, panel-type furnace which heats it rapidly to extrusion or forging temperature. After the billet has been heated and while still suspended by the Stud, I subject it on emerging from the furnace to a descaling treatment and also immerse it in a fused Salt bath heated to about the desired final temperature of the billet. After a short time, I remove the billet from the bath, shear off the stud and then deliver the billet immediately to the extrusion press.

A complete understanding of the invention may be obtained from the following detailed description and explanation which refer to the accompanying drawings ill ustrating the present preferred practice. In the drawmgs,

Figure 1 is a diagrammatic elevation illustrating the welding of a Stud to one end of a billet;

Figure 2 is an elevation partly broken away showing the heating furnace with a billet traveling therethrough;

Figure 3 is a partial cross-section through the furnace;

Figure 4 is a Vertical section through a water-spray descaler;

Figure 5 is a longitudinal Vertical section through the salt-bath container;

Figure 6 is a diagram the stud;

illustrating the shearing oif of 2,6%,378 Patented Dec. 7, 1954 ICC VFigure. 7 is an-el'evatio'n of ltheupper end of the billet showing the hook for suspending it and the Shield for protectin'g theV supporting Stud; and I Figure S is a set of curves showing ther progress of the heating of both stainless and low-carbon steel' billetsv by my' invention.

Referring now in detail to the draw-mgs, a billet or sliuig 10- of the desired composition and having the size and' Shape appropriate for the intended extrusion, has a stud 11 of low-carbon steel flaslr-welded. to one end thereoIf normal to thesurface thereof as shown in Figure 1. TheZ billet will usually be a cylinder several inches in diameter having a length twoor three times the diameter and weighing several. hundred pounds. The Stud is preferably headed and its shank has such diameter as to. provide a section sufficient to carry the billet suspended thereby without substantial elongation when heated to the maximum billet temperature required for extrusion.

The stud .Welding may conveniently be effected by a conventional device 12 designed for such purpose and available` commercially. This device operates first to strike an electric arc between the stud and-billet and then, after fusing a pool of metal in the surface of the latter, to thrust the Stud forcibly thereinto and hold it there until the' molten metal solidifies. Such a weld, When cold,`has a; strength greater than that of the` Stud proper. Even at elevat'ed temperatur-es, say 2.300`L` F., the weld Strength is a-pp'roximately equal to that of the Stud.V A plurality of studs may be used, depending on the weight to be Supported Since the latter determines the total sectional area of studs' needed for a given billet.

' When the stud has been welde'd to the billet, the latter is hungon a supporting-hook 13 depending from a conveyor trolley (not shown). The hook is slotted or bifur- -catedto receive the sha'nk of the stud and engage the undersid'e' of its'l head. The trolley from which the hook dep'endsr travels above a furnace 14' of the panel type having. a longitu'dinal slot in the top thereof through which the shank of the hook passes. The billet is thus quickliy heated' by burners 15 mountedin the spaced side walls or panelsof the. furnace, as it travels along the length thereof. `While only one billet is shown in the furnace, it will usually be preferable to pass a continuous succession of billets therethrough in close order.

Instead of a headed Stud and a bifurcated hook, I may use headless studs and engage them with gripping j'aws carried by a travelingtrol-ley.

Thefiringv rate of the burners, the speed of travel of thebillets and the length of the furnace are correlated so that the billets are rapidly heated to a temperature of-about 2300`o VF. The total heating time should be .not more than about six minutes per inch of diameter of the billet and is preferably less, i. e., from three to five minutes per inch of diameter. By reason of the rapid heating, the studs which Will carry the load stated for thirty minutes, may be relied on to suspend the billets safely. The heating of the billets according to the invention is shown graphically in Figure 8 for both stainless steel and carbon steel. As there shown, the latter heats more rapidly at first but, because of the dip in the curve, is soon overtaken by the stainless-steel billet. In both cases, the heating curve is steep and smoot The heating rate shown far exceeds the maximum rate heretofore thought feasible for stainless steel. An important result of the rapid heating is that only a thin layer of Scale is formed on the billets, which is light and flaky in Character. Such Scale can be easily and thoroughly removed thus saving die wear and insuring a good surface on the finished product.

In order to reduce the loss of strength by the stud supporting the billet as they are both heated during travel through the furnace, I may employ a cylindrical shield 16 of thermal insulation surrounding the Stud and resting on the top of the billet, as shown in Figure 7. Such a shield utilizes the so-called Stack effect." That is to say, the ascent of hot gases through the central region of the Shield will induce a downfiow of cool air along the inner surface of the wall thereof, which keeps the stud at a temperature somewhat lower than that of the billet. In addition, the Shield serves as a radiation barrier and the weld as a conduction barrier. The combined effect is aided by the 'za a cooling effect of the hook which keeps the stud several hundred degrees below the temperature of the billet.-

The billets may be rotated as they pass through the furnace, if desired, as by rotating the hooks on which they are suspended, for greater uniformity of heating.

On reaching the exit end of the furnace after being heated to a forging temperature of from 1950 to 2300 F., the billets are subjected to a descaling operation as by being lowered into a tank 17 fitted with a plurality of nozzles 18 discharging water sprays at high Velocity. Because of the light, flaky Character of the scale resulting from the rapid heating of the billets, it is etfectively dislodged by such sprays so quicldy that no substantial cooling of the billet occurs.

The heated billets are next immersed in an elongated tank 19 containing a bath of fused salt such as barium Chloride, heated to a temperature approximating the desired final temperature of the billets, and caused to travel therethrough, thus continuing the immersion for a short time. The salt bath serves several purposes. first place, it exerts a descaling action so that the descaling by water sprays may be omitted if desired. The salt bath also equalizes the temperature in various portions of the billet. Finally it forms a film on the surface of the billet which acts as a lubricant during the extrusion. O

On reaching the exit end of tank 19, the billet is raised therefrom, and suspended over the charging chute 20 leading to the inlet to the extrusion press. Then the stud 11 is cut off by shears 21. The billet is thus immediately delivered to the extrusion press for hot working therein.

It is to be noted that the invention is characterized by numerous advantages some of which have already been mentioned. Outstanding among these is the reduction in the power required by the extrusion press for working billets heated according to the invention. In fact, the extrusion ratio of a given press may thereby be increased by as much as 10 or 15%. Rapid heating is facilitated by the method of supporting the billets on a suspending stud and by the use of a panel-type furnace. The thin scale formed during the quick heating is easily removable and so permits avoidance of the destructive effect thereof on the forming dies. In additon, the yield of product per billet is increased by reducing the amount of scale. By using a suitable conveyor, the billets may be conveyed through the furnace, descaler and salt bath without disengagement from the supporting hooks 13, thus expediting the overall heating cycle and eliminating conveying baskets or carriers which are very expensive and have but a linlited life.

Although I have disclosed herein the preferred embodiment of my invention, I intend to cover as Well any change or modification therein which may be made without departing from the spirit and scope of the invention.

I claim:

1. In a method of heating billets to temperatures suitable for extrusion,

forging or the like, the steps including In the weld providing a billet having a metal suspending attachment ed to one end thereof, engaging the attachment with a traveling support to suspend the billet, then passing the suspended billet and at least a portion of the attachment through an elongated heating chamber, thereby subjecting substantially the entire surface of the suspended billet uniformly to the heat of the chamber and heating the billet at a rate such that it reaches a forging temperature exceeding 2000 F. before the strength of the attachment falls below the weight of the billet.

2. The method defined by claim 1 characterized by shearing said attachment while the billet remains suspended from said support and delivering the billet by gravity to hot-working means.

3. The method defined by claim 1 characterized by said attachment having a head and said support engaging the under side thereof.

4. The method defined by claim 1 characterized by supplying heat to the billet as it traverses the chamber at a rate such as to heat the billet to forging temperature in a time of from three to five minutes per inch of transverse dimension.

5. The method defined by claim 1 characterized by shielding the attachment throughout its entire length while the billet is passing through the chamber.

6. The method defined by claim 1 characterized by descaling the billet as it emerges from the heating chamber and then immersing the billet in a bath of fused salt heated to about the same temperature as the billet.

7. The method defined by claim 1 characterized by subjecting the heated billet to a water-spray descaling as it emerges from the heating chamber.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REF ERENCES "High Speed Heating of Steel by Mawhinney in Industrial Heating, January 1951, vol. XVIII, No. 1, pages 40-44, inclusive.