US3116834A

US3116834A - Extrusion of metal tubing

Info

Publication number: US3116834A
Application number: US77619A
Authority: US
Inventors: Hoffmann Leo
Original assignee: Baldwin Lima Hamilton Corp
Current assignee: Baldwin Lima Hamilton Corp
Priority date: 1960-12-22
Filing date: 1960-12-22
Publication date: 1964-01-07
Anticipated expiration: 1981-01-07

Description

Jan. 7, i964 l.. HOFFMANN ExTRUsVoN oF METAL TUBING 2 .Sheets-Sheet l Filed Dec. 22, 1960 INVENTOR LEO HOFFMANN AGENT.

Jan. 7, 1964 L. HFFMANN EXTRUSION OF METAL TUBING Filed Dec. 2.2, 1960 2 Sheets-Sheet 2 E wm mv United States lPatent 3,116,834 EXTEUSHN Gli METAL TUBHNG Leo Heitmann, New York. NAZ., assigner to Baldwin- Lirnadlamilton Corporation, Philadelphia, Pa., a corporation of Pennsylvania Filed Elec. 22, weil, Ser. No. '77,619 6 Claims. 1{(Ii. 207-10) This invention relates to the hot extrusion of metal tubing over a mandrel, and particularly to the extrusion of tubinfJ at relatively high temperatures.

When producing tubes in the above manner, a heated billet is inserted in a container and the metal is then forced through an annular or similarly shaped orifice formed by an apertured die in conjunction with a mandrel. In one conventional method the mandrel is stationary during extrusion and only the front part thereof projects into the opening of the die. Removal of the extruded tube from the front tip of such mandrel is relatively easy, but the stationary tip is subject to high pressure and friction at elevated temperatures for an extended period of time, which resul-ts in pronounced wear. A necliing effect may occur and cause destruction of the tool.

in another conventional procedure the mandrel has a relatively long effective portion and is gradually advanced in the die opening during extrusion so that any wear will be distributed over a surface area of substantial size and there is not much danger of localized overheating.v How ever, it is difficult to strip such mandrel from the end of the tube after extrusion. This is due to the fact that during extrusion the temperature of the tube material is considerably higher than that of the mandrel and upon comple ion of the operation the tube shrinks quickly upon the cooler tool. Sometimes, mandrels of this type have been tapered to facilitate the ow of metal over the mandrel during extrusion. This would also tend to assist in the stripping operation but is generally not sufficient alone to prevent freezing of the tube on the mandrel. Besides, the extruded tube will have a tapered inner wall and thus a varying Wall thickness throughout its length. This is not acceptable in cases in which the inner wall of the tube must be cylindrical at least over a major portion of its length.

lt is an object of the invention to avoid the aforesaid difficulties in the hot extrusion of metal tubing in a simple and effective manner.

lt is also an object of the invention to provide means for minimizing the shrinkage of extruded metal tubing upon a mandrel.

it is another object of the invention to facilitate stripping of a mandrel after hot extrusion by varying the intercontour of extruded tubing at the rear end thereof and to keep such variation small so that the entire length of the tubing may be used for the ultimate purpose for which the product is intended.

it is a further object of the invention to facilitate stripping of a mandrel after hot extrusion by varying the internal contour of extruded tubing amply at the rear end thereof and severing such rear end from the major portion of the tubing after extrusion.

lt is also an object of the invention to provide an improved mandrel for hot extrusion, which is adapted to be gradually advanced in a die opening at least during the maior portion of the operation but may be stripped easily from metal tubing extruded thereover.

One aspect of the invention involves the arrangement of an auxiliary portion or relief shoulder on the mandrel. Shoulders have been provided on extrusion mandrels for various purposes in past but have not been dimenioned and arranged to minimize the freezing of tubing on mandrels.

alienati Further objects, features and advantages of the invention will become apparent as the description proceeds.

In the drawings which illustrate certain embodiments of the invention by way of example,

FIG. l is a diagrammatic, fragmentary section through an improved metal tube extrusion press showing the parts in an initial stage of the operation, certain dimensions being exaggerated for better illustration;

FlG. 2 is a section similar to FlG. 1 but showing the parts at the end of the extrusion;

FIG. 3 is a section showing the rear end of an extruded tube and illustrates a modified procedure;

FIG. 4 is a section similar to FIG. 2 but shows a further modification.

Referring to FlG. l of the drawings, the extrusion apparatus illustrated therein comprises a container lil adapted to receive a heated billet or charge 12 to which pressure is applied by a stem or plunger ld with the aid of a dummy block 16. rThe stern la has a bore i3 therethrough to receive and guide a movable mandrel holder Ztl.

A movable mandrel generally indicated at 3@ comprises a relatively long main or front portion 32 and a normally shorter auxiliary portion in the form of an auxiliary or relief shoulder or collar 34 positioned adjacent the rear end of the main portion 32. The cross section of shoulder 34 is similar' to, but slightly lmger than, the cross section of portion 32. Mandrel Sil passes through a bore 36 of dummy block lo and is attached to its holder Ztl at 3S. The main mandrel portion 32 is sufficiently long to extend at least through the major portion of billet l2.

A die dil is mounted on a support d2 and has an opening, the narrowest portion 44 of which forms an annular extrusion orifice in conjunction with mandrel 30.

The billet l2 when loaded in the container may either be hollow to accommodate the mandrel 3th, or it may be solid and then pierced in the container by applying pressure to the mandrel holder 2li, the mandrel 3d being in each case advanced through the billet until the tip of its front portion 32 is positioned in portion i4 of the die opening, at which time the shoulder 3d has entered the rear portion of the billet. Upon application of pressure to stem 14, the billet will first be caused to bear against the wall of the container as well as against both

mandrel portions

32, 34 and will then be forced to flow through the extrusion orifice between mandrel portion 32 and die d@ to form a tube generally indicated at Sii. The mandrel is gradually advanced together with stem i4 by means of the holder 2@ so that successive parts of the main mandrel portion 32 will cooperate with the die. lt will be clear that during this stage of the operation which is illustrated in PEG. 1, the inner contour of tube 5d will correspond to the cross section of the main mandrel portion 32 while the outer contour of the tube will be determined by the inner contour of the die opening at its narrowest portion 44. The opening of die @il and the main portion 32 of the mandrel are dimensioned so that at room ternperature the extruded tube will have a prescribed or selected or nominal cross sectional size.

ln the past the operation has normsdly been con in the manner described until completion of ex As indicated hereinbefore, this would result in the hot material of the tube shrinking upon the cooler mandrel 3@ along the entire length of the mandrel portion 32 which is cylindrical in the embodiment describe. to obthe maior tain a substant .ny uniform wall thickness i' portion of tube 5d, and it would be very difficult to withdraw the mandrel by means of its holder at the end of the extrusion for stript the mandrel from the tube. The temperature difference e'twcen the tube and mandrel and the corresponding shrinkage effect will be oarticuiarly pronounced if the mandrel is of the type eelt pped with internal passages for the circulation of a cooling mediun According to the intention, shrinkage of the tube upon *the mandrel is minimized in a simple and effective manner. After the major portion of the tube has been extruded, tl e inner contour of the extrusion orice is enlarged to an extent sulieient to compensate for a predetermined amount of shrinkage which will occur in the area of the rear end of the tube after extrusion, and the :remainder of the tube is then extruded through the modi- `fied orifice. The change in the orifice occurs when the yshoulder 34 of mandrel Sti enters the narrowest portion of the die aperture. To obtain the desired elect, the ldiarnetrical size of shoulder 34 should be generally on the order determined by the equation d=d (1-i-c delta) 'wherein d represents the diameter of shoulder 34, d the diameter of the main portion 32 of the mandrel, c the `Coc'jicien ol linear expansion (and contraction) of the m rial of the tube per unit of length and temperature, .and delta a predetermined average drop in temperature `of the tube upon completion of the extrusion or more 'precisely in the period of time extending from extrusion 'to stripping. It in the saine interval the temperature of `the mandrel likewise changes considerably, this should be taken into consideration and the shrinkage of the tube :should then be detemined relative to the mandrel. For example, if the mandrel cools down somewhat after extrusion and before stripping and thus contracts to a cerztain extent, this may be deducted from the expected ab- :solute shrinkage of the tube, but in case the temperature of the mandrel increases due to absorption of heat from t he tube and the mandrel thus expands, this will be equiv- .aient to an increase in shrinkage of the tube so that the .amount to be compensated for should be augmented afcordingly. The change in the diametrical dimension of 'the mandrel, of course, follows from its coetiicient of linear expansion and the expected change in its tempera- *.ture.

As the coeilcient of linear expansion of a material norimally varies somewhat in dilerent temperature ranges, it 'may be found expedient for exact calculations to use an :average value when handling metals such as copper, v.copper alloys, and steel which are extruded at high tem- ,peratures With the mandrel shaped in the manner described the last end of the tube will be extruded with an enlarged inside diameter to compensate for expected shinkage relative to the mandrel in the area of the tube end as ;shown in FIG. 2. ln the drawings a lirst, prescribed hole Aor bore of tube 5d extending through the major portion thereof is indicated at 52 while a second, slightly larger hole or bore at the rear end of the tube is indicated at :54. It will be clear that the size of bore 54 is such that .after a predetermined shrinkage the tube end will still clear, or barely touch, the relatively long main portion 32 of the mandrel. lt may also be said that the bores S2, .5d are dimensioned so that the LD. of bore measured lduring stripping will generally be on the order of the LD. oi bore 52 measured during extrusion.

'\Viien, `lor example, tubing of 3 LD. is extruded from Vbrass having a linear coefficient of expansion (and contraction) per unit of length and per degree F. of about 00601 and the temperature differential delta amounts to '1GCO F., the diameter of shoulder will be determined approximately by the equation (1+.ccoo1x1eom in zsns in.

Thus, bore 5d will be only ab ut .03 larger in diameter than bore 52 and the complete length of the extruded tube including the slightly modilied rear end thereof will often be found acceptable for practical use, in particular if a drawing operation is carried out after extrusion.

Preferably, the diameter d' of shoulder 34 exceeds the calculated amount slightly but if it is desired to keep ,changes in Vthe inner contour of the tube to a minimum,

dialnet r d may closely correspond to the calculated dimension. a

The diterencc in size of holes 52 and 56 is shown cxaggerated in the drawings for better illustration.

The length of tube extruded over shoulder 3:2., i.e., the length of bore 54, should be such that the smaller bore 52 no longer surrounds the main mandrel portion 32 when the extrusion is completed. At this time, firm contact between tube and mandrel will occur only aY the shoulder 34 over a short distance resulting in a very limited amount of friction so that stripping of the mandrel from the tube will be easy. lf desired, the shoulder 34 proper may be slightly tapered to additionally facilitate stripping and this will in no way atleet uniformity of wall thickness obtained in the major portion of the tube along its bore S2.

in the embodiment of FIGS. l and 2 mandrel 3d is arranged for movement in unison with stem throughout the extrusion, including the last stage of the operation when the auxiliary shoulder 34 has entered the die opening and cooperates therewith. Keeping in mind that bore 52 of t xe tube should clear mandrel portion 3?. at the end of the extrusion, the larger bore S4 should then extend along the length L of mandrel portion 32 and further along the relatively short distance L by which shoulder 34 will protrude from the narrowest portion 44 of the die Opening in the position of the parts shown in FIG. 2, i.e., the length of bore 54 should substantially equal L-l-L. Since, as stated, mandrel 30 travels in unison with stem lf2', the extruded length of bore 54 will also be equal to Lr, wherein r is the extrusion ratio in the region of bore 54, that is, the relation of the cross sectional area of the billet to the cross sectional area of the tube at the rear end thereof. t follows that the distance L should be on the order determined by the equation Preferably the distance L will be made slightly greater than calculated so that the bore 54 will be somewhat longer than required to make sure Contact between thc wall of bore 5?. and mandrel portion 32 will be avoided at the end of the extrusion.

For example, when extruding the aforementioned brass tubes of 3 I.D. at an extrusion ratio of 2l with the portion 32 of the mandrel being 2G long, the length L will be on the order determined by the equation Instead of continuing to move the mandrel forward after shoulder 34 has entered the narrowest portion 44 of the die opening, the mandrel may be stopped at this instant. This will reduce the area of contact between the extruded tube and shoulder 34 at the time stripping is carried out. It is true that wear will be increased somewhat at the shoulder 34 when the latter is stationary during extrusion, but this will not have severe consequences since only a limited amount of material passes over shoulder 34. The length of the portion of billet l2 to be extruded over the auxiliary shoulder under these conditions, i.e., with the shoulder in a stationary position, will be approximately equal to L/ r. This is analogous to the foregoing equation lor L when neglecting any small distance through which, in a stationary position, the shoulder 34 may project from the narrowest portion 44 of the die opening.

FIG. 3 illustrates an extruded tube after it has been severed, at the terminal face shown at the right in FIG. 3, from remnant S6 (FIG. 2) of the billet in any suitable conventional manner and removed from the press. As indicated hereinbefore, in accordance with one aspect of the invention the portion having the enlarged bore 54 therein inf-1 in.

is retained as an integral part of the tube since frequently a slight variation in internal diameter will be found acceptable for practical purposes. However, a modified procedure may be used under certain conditions. If the requirements are exacting and the tube must have a uniform internal diameter throughout its length, or if the use of the full length extruded is not planned for other reasons, the end of the tube hhaving the enlarged bore 54 may be cut off approximately in the plane indicated at 58. When using this procedure, of course, the size of bore 54 need not be held within close limits and the diameter of shoulder 34 may then be determined in a somewhat liberal manner so that during stripping there will be ample play between the wall of bore 54 and the circumference of the main mandrel portion 32.

Another modification of the invention is shown in FIG. 4 in which various elements retained from FIGS. l and 2 without change are designated by like reference characters. T he modified mandrel generally indicated at 7 ti which includes a main portion 72 and an auxiliary or relief shoulder 74 is equipped with a cutting shoulder or collar 76, the latter fitting snugly in the narrowest portion 44 of the die opening as well known in the art. The parts are illustrated in the position at the end of the extrusion in which mandrels of this type and their holders are normally locked in the forward direction to prevent entrance of the cutting shoulder in the die opening prematurely during extrusion. After the mandrel 70 and its holder 2t) have been released, they are advanced by applying pressure to holder 2% so that the cutting shoulder 76 will enter the die opening to push the extruded tube out of the die and thereby sever it from the remainder Se of the billet. The use of the relief shoulder 74 is of particular significance in combination with the cutting shoulder 76 since here stripping of the mandrel will be delayed by releasing the mandrel from its locked position and advancing it during the shearing step. Due to this delay the tendency of the tube to shrink will be more pronounced when the cutting shoulder is used and the tube may contract to a degree making stripping extremely difiicult or impo-ssible if the relief shoulder 74 is not employed.

As shown in FIG. 4, the main portion 72 may include a short conical portion 78 to provide for a smooth connection with the auxiliary shoulder 74. The tube generally indicated at 8@ will then have a tapered portion between the bores 82 and 84 thereof as shown at 86.

In cases where the wall thickness need not be entirely uniform even in the major portion of the tube, the invention may be used in combination with a slight taper of the main portion of the mandrel to facilitate extrusion. Ease in stripping will be insured by means of the auxiliary shoulder 34, and the taper of the main portion 32 will be very limited.

Wherever the expression tubing is used in the description and claims, it should be interpreted as including hollow shapes of circular or non-circular cross section.

While certain preferred embodiments of the invention have been described, it will be understood that various modifications and changes may be made without departing from the scope and spirit of the invention as defined in the appended claims.

Having described my invention, what I claim and desire to secure by Letters Patent is:

1. In a method of extruding metal tubingfrom a heated billet, the steps of extruding the major portion of said tubing through an orifice of annular type having original o-uter and inner contours corresponding to a selected outer and a first inner contour of said tubing, then enlarging the inner contour of the orifice, and extruding the remainder of said tubing with a second inner contour determined by said enlarged inner contour of the orifice, the difference between the original and enlarged inner contours of said orifice and the corresponding difference between the first and second inner contours of said tubing being such that upon a predetermined shrinkage at the end of the extrusion the size of said second inner contour of the tubing will generally be on the order of the size of said first inner contour measured during extrusion.

2. In a method of producing metal tubing over a mandrel from a heated billet, the steps of extruding the major portion of said tubing through an orifice of annular type having outer and inner contours corresponding to a selected shape of said tubing, then enlarging the inner contour of the orifice to an extent at least sufficient to compensate for a predetermined amount of shrinkage of the tubing after extrusion, and extruding the last portion of said tubing with an inner contour determined by said enlarged inner contour of the orifice over a length at least suiiicient to completely clear said mandrel outside said orifice.

3. A method as specified in claim 2, including the step of severing said last extruded portion of the tubing from said major extruded portion thereof.

4. In a press for the extrusion of metal tubing from a heated billet, a die having an opening therethrough, a mandrel movable into said opening of the die to form an extrusion orifice between said die and mandrel; said mandrel having a main portion adapted to extend at least through the major portion of the length of said billet and shaped to produce a prescribed inner contour of said tubing, and a relatively short effective auxiliary portion adjacent the rear end of said main portion, the cross section of the auxiliary portion exceeding the cross section of said main portion to an extent suiiicient to compensate for a predetermined amount of shrinkage of said tubing relative to said main portion of the mandrel; and means for advancing said mandrel through said die during extrusion, whereby the tubing will first be formed over successive parts of said main portion of the mandrel to receive said prescribed inner contour but the rear end of the tubing will be formed over said auxiliary portion of the mandrel to receive an inner contour enlarged in accordance with the size of said auxiliary portion to minimize shrinkage of the tubing upon the mandrel after extrusion.

5. A press as specified in claim 4, wherein said mandrel i includes a cutting shoulder for severing extruded metal tubing from residue of said heated billet, said cutting shoulder being located adjacent the rear end of said relatively short eective auxiliary portion of said mandrel.

6. A press as specified in claim 4, in which the die opening has a narrowest portion, and the length of the auxiliary portion of the mandrel projecting from said narrowest portion of the die opening at the end of the extrusion is on the order of wherein L is the length of the main mandrel portion, and r the extrusion ratio prevailing during formation of the rear end of the tubing and representing the relation of the cross sectional area of the billet to the cross sectional area of said rear end of the tubing.

References Cited in the file of this patent UNITED STATES PATENTS 1,664,990 Oehmig et al Apr. 3, 1928 1,854,411 Leighton Apr. 19, 1932 FOREIGN PATENTS 898,884 Germany Dec. 7, 1953

Claims

1. IN A METHOD OF EXTRUDING METAL TUBING FROM A HEATED BILLET, THE STEPS OF EXTRUDING THE MAJOR PORTION OF SAID TUBING THROUGH AN ORIFICE OF ANNULAR TYPE HAVING ORIGINAL OUTER AND INNER CONTOURS CORRESPONDING TO A SELECTED OUTER AND A FIRST INNER CONTOUR OF SAID TUBING, THEN ENLARGING THE INNER CONTOUR OF THE ORIFICE, AND EXTRUDING THE REMAINDER OF SAID TUBING WITH A SECOND INNER CONTOUR DETERMINED BY SAID ENLARGED INNER CONTOUR OF THE ORIFICE, THE DIFFERENCE BETWEEN THE ORIGINAL AND ENLARGED INNER CONTOURS OF SAID ORFICE AND THE OCRRESPONDING DIFFERENCE BETWEEN THE FIRST AND SECOND INNER CONTOURS OF SAID TUBING BEING SUCH THAT UPON A PREDETERMINED SHRINKAGE AT THE END OF THE EXTRUSION THE SIZE OF SAID SECOND INNER CONTOUR OF THE TUBING WILL GENERALLY BE ON THE ORDER OF THE SIZE OF SAID FIRST INNER CONTOUR MEASURED DURING EXTRUSION.