US2955709A

US2955709A - Hot extrusion of metals

Info

Publication number: US2955709A
Application number: US360708A
Authority: US
Inventors: Sejournet Jacques
Original assignee: Cefilac SA
Current assignee: Cefilac SA
Priority date: 1952-07-01
Filing date: 1953-06-10
Publication date: 1960-10-11
Anticipated expiration: 1977-10-11

Description

Oct. 11, 1960 y J. sEJouRNET 2,955,709

Hoz' ExTRUsIoN oF METALS Filed June 10, 1953 "E presses comprising Vessentially a container in which the States Patent tice 1,955,709 -0 nor XTRUsIo'oFimTALs i Jacques Sejournet, Paris; France,`a`ssignor to Compagnie du Filage des Metaux et des Joints Curty :"'Fiifi'rii 10, 1953, SerINO. 360,708 Claimspriority, application France July'l, 1952 -6 claims.' (Cl. 207-10) The "present invention concernsY the hot extrusion of 'metal`s,;Which i's generally effected by means of hydraulic Srnetal billet'toibe transformedis placed, a die which tits "at on'e end ofthisv cont-ainsiA and the oriiiceof 'which rep- 'resents the cross section of the part which it is desired to' obtain by extrusion, and a punch which enters the containerandpresseson the end'of the billet opposite `thatfacing `'the dieand` `tnansfrnitsto said billet theforce :developed by 'the'. press, so Kas to force the metal Vof the billet through the die. j

s The great-number of the `metals. and alloys submitted to such a press extrusion process'doV not in `general pre- 'sentf surfaceifaults. Metals andalloys, however, of poorly rduictilej nature 'or f'badV homogeneity and 'more particulanly diiiioult to extrude, provide such fault-s after `extrusion." x m One of these faults is constituted vby cnacksglocalized at thehont end Iof the extruded Iliar,-whicl1 may be circular cracks,`off ktlie'solcalledV palm -"1:reetype, or spreading cracks, the latter occurring generallyin products. ex-

, 'truded from-cast billets.

Cb=4, Fe=4);'Siliconbronze (copper 97,` silicon 3).

The presence Vof these yfau-ltsrrnakes it necessary to pare olf the fronttendsof theextnded a`rs,"wlich constitutes iafserious economic-disadvantage 'ias inf general the `metals or alloys dealt with are costly. f l j A -"obj"e`c`t 'ofthe-present Iinvention is to provide a p'rbcess which makes `-it-possibleto"avoid in alpactically mann the -formation I'the'fa'ult's above referred t'; 'and lto 'decrease 4ina-11 important proportion the length of the portion tobe pared olf at the front ends of the exi 4 truded bars. l

Said 'Aprfdess--consistg essentillyjinplacing, between the billet of metal to be extruded and the bottom off the extrusion press container, an auxiliary part, for instance a disc of a simple metal or of an alloy different from that constituting the billet and covering substantially the entire area of the end of the billet, lthe nature and propl erties of the metal forming said part being selected by experience, as being capable of preventing the formation of undesirable faults.

The thickness of the metal disc thus placed in front of the billet should be fairly high, for instance on the order of 5 to 50% of its diameter. It may be either secured by any known means, such as welding, for instance, on the front of the billet, before extrusion, or previously placed in the bottom of the container.

When extrusion takes place under such conditions, the disc is deformed at the beginning of the extrusion Vand covers the rst portion of the extruded bar, thus preventing the formation of the above mentioned cracks. After extrusion it is then suiiicient to separate said vportion of Patented Oct: l1-1, 1960 the bar, which is rthus covered, and which is very substantiallysho'rter thanthat on which the cracks would -have 'occuied in the case of' a direct extrusion of the billet,.witl`1out interposing of the disc according to the process of the'piesent invention. s

The explanationof this result, @as well as more precise detailsas to the manner of carrying out the invention are givenv hereinafter -with reference to the appended drawing wherein:

Figlre lis a-pespective view Vof Vthe end of an extruded "cylindrical bar having so-called palm ltree cracks: j

Figure '2' isiasiinilar view of a bar having spreading or flaring cracks.

Figure 3 is a 'diagrammatic view, showing a billet 1 and a container 6 'forthe billet, before the billet has been placed in the container, the billet being shown as divided into 'imaginary slices' 1a-1e.

Figure 4 is -a` diagrammatic view, showing the billet l partially extruded intothe bar 2.V

Figure 5 is a view in diametral section of a billet pro vided with a' disc according to the invention.

' Figure 6 is 'a 'similar view of theV front end Aof'an eX- truded bar, acordingto the invention,` made from the billet offFi'gure 5.

As indicatedfabove,-during the extruding of som inetalswand; alloys .which have poor ductility or which are lackingin homogeneity, there may occur, at the front end Athrough thedie'7 into aba'r 2 (Figure 4), the imaginary parallel slices*1;1e'ofth billet 1 are deformed into -slr'apesfZ'a-le which nest linto one another as shown in VFigureY 4.' Thec'eitna'l portion a .(Figure 3) 'ofthe vfruit face ofthe billet, v"corresponding tothe cross section of the `die is punched'by the latter and becomes, after extrusion, a slightly bulging surace A (Figure 4). The remainder bf the front face of the billet, or annular surface by (Figure '3)"c`overs the lirst portion of the extruded bar wat B (Figure 21). The/'cylindrical surface c (Figure 3) of the billet becomes, vafter extrusion, the remainder C (Figuref'4) of fthe'extrude'dv bar. TheV surface a undergoespnactically no 'superficial deformation, the surface 'c undergoes ifa practically constant deformation from one to 'the other "end of the billet, and the surface b undergoes very' 'important increasing superficial deformation,

YThese 'differences' in deformation and the Vswaging of' the various slices on one another, entail the'productionfin :the headportionofithe extruded bar, of tensions which, infextrtfding metals :or alloys, fsteels, for instance;'poo1"ly duotile or not suciently homogeneous, cause the formation of the above mentioned faults, and the entire portion of the bar which offers such faults has to be cut-off and rejected.

To prevent the economic icon-sequences of this phenomenon of cracks., according to the invention a disc 4 is placed in front of the billet 1 (Figure 5). This disc is made of a metal or alloy which, during extrusion, does not cause the formation of said faults, said disc being attached'to the billet, by welding for instance.

i During extrusion, the disc 4 is subjected to a deformation similar to that undergone, in the case of Figures 3 and 4, by the slice 1a of the billet 1 and covers at 4a (Figure 6), the frontend of the bar 5 extruded from the billet 1, preventing the formation of faults. It is then suicient to cut-off the portion of the bar 5 which is covered by the defonrned disc 4a, while inthe case of Figure 4, it is often necessary to reject the whole end of the extruded bar, up to the slice 2e.

-Insteadrof being connected with the billet 1 before extrusion, and therefore heated to the same temperature as the billet, the disc 4 may be placed at the bottom of the extrusion press container, before introducing the billet. It is then possible to heat the disc either 5to the Vsame temperature as the billet, or to a different temperature, which makes it possible if necessary, to adjust the re-l sistance to deformation of the metal constituting the disc to that of the metal constituting the billet. i

VA metal is generally used, for the disc, offering a lower resistance to deformation than that of the .billet at the same temperature. results in a new advantage, i.e. decreasingthe extrusion pressure at the start, and there- 'fore increasing thevpossibilities of deformation.

Thus for extruding a high speed steel such as above referred to, a car-bon steel disc may be used, and for extruding silicon bronze, an ordinary bronze disc.

Experience has shown that the process according to the Vinvention gives all Vthe better results as the tool lubrication is itself more thorough in operation. It is therefore recommended to lapply this process with a'suitable lubrication, and more particularly by using as lubricant, a product which can melt in Contact with the billet or the tool at the operation temperature, while remaining viscous, and especially glass.

When the disc 'and billet are at different temperatures, it maybe suitable to adjust the lubricant tothe temperature, therefore to use a juxtaposition of glasses having substantially the same viscosity, one at the temperature of the disc land the other o'ne at the temperature of the metal to be extruded. The amountsof these two lubricants should, of course, be adjusted to the relative sizes of the two surfaces of different natures to be lubricated.

The lfollowing examples illustrate various practical embodiments of the process of the invention.

Example 1 -T-he extrusion was effected, in a container having a diameter of 140 mm., with a 1500 ton press, on billets of S.816 steel, 130 mm. in diameter and 300 `mm.long, into round bars 35 mm. in diameter.

extruded bars, reaching 0.50 rn.

When on the contrary and according to the invention, a steel disc (0.1 canbon) and 30 mm. thick was welded in front of the billet, by operating under the same conditions otf .temperature and lubrication, faultless bars were obtained, a 50 mm. length of which merely was covered by the deformed disc, as shown in Figure 6. 4The metal of the disc was easily separated from that of the bar. Y

Example 2.-In a container 148 mm. in diameter, with a 1500 ton press, billets` of pure'molybdenum, 140 mm. in diameter and 450 mm. long, were extruded into round bars 80 mm. in diameter.

Proceeding with the extrusion inv the 'usual manner, after raising the billet to a temperature of 1350 C., and

vlubricating by means of Pyrex glass, the formation of ared cracks was found over an extruded length reaching to 0.10 m.

If, on the contrary, a few seconds before introducing the billet, a steel disc (0.1 carbon) was introduced into the container, mm. thick and raised to a temperature of 1100 C. using as a lubricant glass wool placed between the Pyrex glass and the disc, faultless bars were obtained on which -a length of a few centimeters only was covered by the deformed disc.

What I claim is:

1. In a method of extruding a heated solid metal billet through a die to form a solid bar, the steps comprising interposing between the leading end face of the billet and the die, prior to extrusion, an auxiliary metal part covering substantially the entire area of said leading end face, the auxiliary metal part and the billet, at the temperature employed for each of them, being such that the lauxiliary metal part offers a lower resistance to deformation than the billet, said auxiliary metal part being of such thickness that it forms only a short cap on the front l end of the bar extruded Vfrom the billet, extruding all of lsaid auxiliary metal part land all but a small portion of the billet through the die, the billet having such poor ductility at the extrusion temperature employed that the front end of the extruded bar would crack if said auxiliary metal part were not employed, and severing the front end portion of the extruded bar covered by said cap from the remainder of said extruded bar.

2'. A method according to claim 1, wherein the metal of the billet is high speed steel.

3. A method according to claim 1, wherein the metal of the billet is high speed steel and said auxiliary metal part is low carbon steel.

4. A method according to claim 1, wherein the metal of the billet is refractory steel.

5. A method according to claim 1, wherein the metal of the billet is refractory steel and said auxiliary metal part is low carbon steel.

v 6. A method according to claim 1, wherein the metal of the billet is silicon bronze and wherein said auxiliary metal part is bronze of a character which offers a lower resistance to deformation than the silicon bronze at the temperatures of the billet and auxiliary metal part.