US3156043A - Process for warm extrusion of metal - Google Patents

Description

INVENTORS, Charles Ilrazinsn 'E er' at` cf M/-TIIu'ldar and A- n/y Filed March 9, 1956 C. G. GRAZIOSO ETAL PROCESS FOR WARM EXTRUSION 0F METAL Nov. 10, 1964 P/"zof 6r? exzrasz'on ai' room temperature Cf/,az slug "0 engi/z [aims/2f Pfc/W@ and mdf/[36 H6321 .slug OZOOVe/aw /lql United States Patent C 3,156,043 PROCESS FOR WARM EXTRUSlN OF METAL Charles G. Grazioso, 2116 Hartel Ave., Philadelphia 15, Pa., and Gerard W. Mulder, RR. 2, Delavan, Wis. Filed Mar. 9, 1956, Ser. No. 570,645 1 Claim. (Cl. 29--552.3) (Granted under Title 35, U.S. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalty therein.

This invention relates to a method of extruding metals and more particularly to the extrusion of a billet at a temperature in the Vicinity of the critical point, Acl, of the metal to be worked.

Heretofore metal has been extruded cold, at room temperature, and hot wherein the metal to be worked is heated to a temperature substantially at the melting point thereof where the properties of the metal are thixatropic.

We have discovered that a number of important advantages can be gained in the extrusion of high or low carbon ferrous ,metals and alloys, or non-ferrous metals and alloys, if a billet to be extruded is changed in its physical properties and particularly in its response to physical forces by being heated to a temperature below the critical point, Acl of the metal and then extruded.

Our process is to be distinguished from pre-heating in that the temperatures used cause substantial physical changes in the metal over and above changes normally associated with pre-heating. However the temperatures utilized are substantially below the temperature at the melting point of the metal to be worked as in hot forging or hot extrusion.

Our studies have shown that the property of flowability f metal is not directly proportional to temperature of the metal being extruded. Little advantage over cold extrusion, is noted in increasing the temperature of a billet to be extruded above room temperature in the range of 400 F. In fact, little advantage has been noted in increasing the temperature of a billet to a point below 750 F. At temperatures above 75 0 F. the fiowability increases rapidly and this increase in flowability carries on as the temperature is further increased. We prefer to heat the metal to within 200 F. of the critical point of the metal of the billet.

A metal billet extruded at a temperature in the range between 750 F. and within 200 F. of the critical point can be shaped in one extrusion an amount equal to three separate and distinct cold extrusions and many small products may be extruded at vthe low end of the temperature range.

A billet heated to a temperature in this range requires but one half to one third the press tonnage required in cold extrusion to cause the metal to ow; the number of unit extrusionsrequired will be decreased; in many cases the need for auxiliary heat treatment or annealing is obviated, or at least materially reduced, thereby reducing capital investment and fabrication costs.

An object of this invention, therefore, is to change the physical properties of a metal to be extruded by heating the metal above room temperature and below the critical point AC1.

3,156,043 Patented Nov. 10, 1964 ice critical point AC1 to completely cup the billet in one extrusion.

A further object of our invention is to heat a ferrous or non-ferrous billet to a temperature within the range of 750 F. to within 200 F. of the critical point AC1 and vextrude the billet at a temperature within said range.

A further object of this invention is to heat a low or high carbon steel billet, or alloy thereof, to within 200 F. ofthe critical point AC1 of the billet and extrude the billet at that temperature.

A more specic object of our invention isv to heat a steel, or steel alloy billet to within 200 F. of the billet In the drawing,

FIGURE 1 shows a typical mill schedule for prior art cold extrusion cupping of an artillery shell;

FIGURE 2 shows a typical mill schedule for warm extrusion cupping of an artillery shell and FIGURE 3 shows an iron-carbon phase diagram illus'- trating the lower critical temperature and phase changes of steel on heating and cooling.

The following example is given by way of illustrating the method, and further advantages, of our invention.

A three inch round bar of W.D. 1018 steel is cut t0 a length equivalent to the weight of a finished mm. artillery shell which weighs approximately 26 pounds. This billet was heated to 1250 F. in a controlled atmosphere furnace. It was then placed in a 3000 ton hydraulic press. The die used was substantially equivalent to dies used on the third successive cold extrusion when this shell is fabricated by cold extrusion. Hydraulic pressure was applied and the actual dial reading of the press reached a maximum of 890 tons. The iinal piece had size and shape substantially equivalent to that obtained on the third extrusion under cold extrusion methods.

To accomplish this same degree of metal ow under cold extrusion, three individual extrusions are required with press tonnages approximating 2000 ton-s of the first press, 1500 tons on the second press, and 1200 tons on the third press. Coupled with this it is necessary under cold extrusion methods to anneal the piece being Worked after each extrusion in order to permit reestablishment of grain size prior to additional extrusion.

We have found that die life is substantially increased over the die life of cold extrusion methods. And since the temperatures are lower than the temperatures used in hot extrusion we have found these dies to last longer than. Y

those used in hot extrusion methods. Further, in our process only one third the number of dies, hydraulic or mechanical presses, and annealing equipment will be necessary on a production line making this process far more economical as to first costs as Well as operating costs.

Studies have been made as to the most economical temperature at which to Warm Extrude metal. At temperatures above 750 F. the flowability increases rapidly and this increase in owability carries on as the temperature is further increased. We prefer to heat metal to within 200 F. of the critical point of the metal, but in this range we find it necessary to use controlled atmosphere furnaces to prevent oxide formations on the surface of the billet. Lower temperatures reduce the tendency to form oxides but require more press tonnage and result in more operations to perform the same degree of Work.

The optimum temperature will vary depending upon the chemical composition, size, shape and weight of the t end product. Many small products may be extruded in one operation at the low end of the temperature range, whereas the economy on large pieces requiring considerable extrusion may lie in the upper zone of our temperature range even though controlled atmosphere heating is required to prevent oxide formations on the metal surfaces.

It is understood that the particular method above described is given by way of example only and that our invention may be variously practiced within the scope of the following claim.

We claim:

A process of forming high or low carbon steel or its alloys consisting of heating in a controlled atmosphere a 3 inch diameter billet of WD. 1018 steel 0f a weight approximately the Weight of a finished product to 1250" F.,

3 placing said billet in a fully cupped die, and fully cupping 2,667,390 said billet in a single extrusion. 2,756,876 2,767,835 References Cited in the le of this patent 2,767,837 UNITED STATES PATENTS 5 2,767,838

1,968,442 Clark et al. July 31, 1934 2,183,358 Six Dec. 12, 1939 2,400,866 Kronwall May 21, 1946 page 349.

4 Watson et al Ian. 26, 1954 Watson etal July 31, 1956 Nachtman et al Oct. 23, 1956 Nachtman Oct. 23, 1956 Nachtman Oct. 23, 1956 OTHER REFERENCES Metals Handbook, 1948 ed., A.S.M., page 7 and

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