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Publication numberUS3826122 A
Publication typeGrant
Publication dateJul 30, 1974
Filing dateMar 24, 1972
Priority dateJun 16, 1970
Publication numberUS 3826122 A, US 3826122A, US-A-3826122, US3826122 A, US3826122A
InventorsBraeuninger K
Original AssigneeBraeuninger K
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Mandrel for extruding tubing
US 3826122 A
Abstract
A mandrel and mandrel-dummy block assembly for extrusion of tubing is disclosed wherein the mandrel has a shaft cross sectional area so related to the working section cross sectional area that the mandrel will stay in place without attachment to the dummy block. Such mandrel reduces the problems of mandrel necking down and breakage.
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United States Patent [191 Braeuninger MANDREL FOR EXTRUDING TUBING [76] Inventor: Karl F. Braeuninger, 535 Plantmore Dr., Ferguson, Mo. 63135 [22] Filed: Mar. 24, 1972 [21] Appl. No.: 237,690

Related US. Application Data [62] Division of Ser. No. 55,531, July 16, 1970.

[52] US. Cl. 72/264, 72/370, 72/482 [51] Int. Cl. B21c 23/04 [58] Field of Search 72/264, 370, 266, 479,

[56] References Cited UNITED STATES PATENTS 1/1964 Hoffman 72/266 [111 3,826,122 [45 July 30,1974

3,526,119 9/1970 Wassen 72/264 Primary ExaminerCharles W. Lanham Assistant Examiner-Robert M. Rogers Attorney, Agent, or Firm-Stephen S. Grace; Robert W. Selby 57 ABSTRACT A mandrel and mandrel-dummy block assembly for extrusion of tubing is disclosed wherein the mandrel has a shaft cross sectional area so related to the working section cross sectional area that the mandrel will stay in place without attachment to the dummy block. Such mandrel reduces the problems of mandrel necking down and breakage.

6 Claims, 6 Drawing Figures PATENTED O 3. 826. l 22 INVENTOR. {2y 4 Kar/F Braeum'nger PAnsmmmown 3.826.122

SHEEI 2 OF 2 Con fa/her Ram Bil/e7 I o 5 Uummy b/OCA Con {Oi/vet Ram 71,56 Mano re/ Dummy /ock INVENTOR.

Kar/E Braeun/nyer IQTTORNEY BACKGROUND OF THE INVENTION I-Iollow tubing of metal or plastic materials is commonly made by extruding a solid billet around a short mandrel held in position in a surrounding female die member by a supporting bridge or porthole" element which extends a short distance into the container of the extrusion press. Such structures require that the extruding material must be separated into two or more streams" which must be joined together again in the die. Sometimes the resulting weld zones are undesirable.

If truly seamless tubing is desired, it is extruded from hollow billets around a mandrel passing through the entire billet and secured to the ram or a dummy block ahead of the ram. Such mandrels are commonly secured to the ram by threaded joints, bolted retainer plates, T-belts, or a hammer head enlargement behind a flange on the ram. The latter provides a floating mandrel which seeks its own position centered in the female die.

It is known that mandrels thus retained on the ram frequently break because the frictional forces in the die exceed the tensile strength of the mandrel. This may happen for various reasons. For example, the billet may be pushed to an excessively small butt left inside the container, the metal temperature may be too low (requiring excessively high extrusion pressure), the mandrel temperature may be too high (lowering its tensile strength), the mandrel size must be so small that it has intrinsically low strength, or the mandrel may be subjected to bending stresses as well as tensile stresses due to improper mounting or eccentrically positioned hole in the billet. Naturally, broken mandrels are an expensive problem because of costly down time on the press, loss of metal scrapped, and the cost of new mandrels.

An object of the present invention is to provide a mandrel and mandrel-dummy block assembly which reduces or overcomes the breakage and other problems presently encountered.

THE INVENTION The present invention relates to a mandrel having a working section and an enlarged shaft wherein the shaft average cross-sectional, area (A,) is about equal to where A is the average cross sectional area of the working section, P is the maximum fluostatic pressure in the container of the extrusion machine, and S is the frictional stress on the working section during extrusion. The working section is that portion of the mandrel which is in contact with the hollow billet as it is formed into tubing through an extrusion die.

Such a mandrel can be held secure in a plain socket or hole on a ram or dummy block by the fluid pressure of the material being extruded acting against an enlarged shaft of the mandrel where it enters the socket, i.e., the mandrel need not be attached to the ram or dummy block. The size of the enlargement can be calculated such that product of the enlargement of the cross section of the mandrel shaft (A, A,) multi plied by the fluid pressure in the container (P) about equals the frictional forces (A 8) normally tending to pull the mandrel through the die but is slightly lower than the tensile strength of the mandrel. The result of this proper balance of forces is that during normal extrusion the mandrel is retained in its socket by the back" pressure on its shaft. This also permits the mandrel to move forward a short distance and then back without necking or breakage. However, if unexpected conditions arise to increase the forces tending to pull the mandrel through the die, such forces will be resisted only until the tensile strength of the mandrel is approached. Then the unexpected forces will pull the mandrel from its socket rather than fracturing it or necking .it down smaller than dimensional tolerances.

The enlargement of the mandrel shaft required for proper retaining in its socket according to my invention is usually small enough that if the mandrel is pulled from its socket completely by excessive tensile stresses it will simply pass through the die without damaging the die or causing sudden destructive extrusion pressures to be built up. If calculations show that the enlargement of cross section must exceed the size of the opening in the female die member and such a mandrel is pulled from its socket by excessive tensile stresses it will simply lodge against the inner die face to plug it off. This mayv cause an increase in pressure in the container but this pressure is under rather constant control and can be relieved by the press operator before it is harmful to other press equipment, the mandrel or the die.

The applicant has furthermore found that if the socket for the mandrel shaft tapers slightly outwardly from the face bearing against the billet or slightly in back of said face to the face bearing against the ram, the mandrel can have a gyro pendulum motion, i.e., can adjust itself in any direction into the center point of metal flow. Alternatively, the shaft section can be tapered inwardly from front to back to permit such pendulum motion.

The enlargement of the mandrel shaft can be stepwise but is preferably a gradual straight or curved taper. The retaining pressure depends only upon the difference in area between the working section and its shaft. A curved taper is best because it avoids stress concentrations associated with abrupt changes in diameter.

In order to facilitate removal of the mandrel from the butt end of the billet after tubing has been extruded, the mandrel preferably has a short, raised shoulder portion of the working section next to the shaft. The shoulder cross sectional area is intermediate between the working section area and the shaft area.

FIG. 1 is a drawing of one embodiment of the mandrel of the present invention.

FIG. 2 is a drawing of a back face of block which can be used in combination with the mandrel of the present invention.

FIG. 3 is the cross section of the dummy block of FIG. 2 taken along line 3-3.

FIG. 4 is a drawing of another embodiment of the mandrel of the present invention.

FIG. 5 is a schematic diagram of the extrusion equipment including an embodiment of the mandrel of the present invention and billet at the start of a push.

FIG. 6 is a schematic diagram of the extrusion equipment including an embodiment of the mandrel of the present invention and billet at the end of a push.

a loose dummy Referring to FIG. 1, the mandrel comprises a working section, denoted generally as 1, and a shaft, 2. The working section has a nose portion 3 and raised shoulder 4. The working section is normally tapered outward slightly from nose to tail. An actual mandrel of this design made for extruding magnesium alloy tubing had the following dimensions. 0.785 inch diameter at the nose of the working section, 0.793 inch diameter at just below the shoulder section, 0.805 inch shoulder diameter, 1.250 inch shaft diameter, 3 inch long shaft, l2 inch long working section.

Such a mandrel can be used in an extrusion machine in combination with an attached dummy block (not shown) or loose dummy block such as shown in FIGS. 2-3. The dummy block 5 has a socket concentric with the center of the dummy block cross section. Such socket is tapered outwardly from slightly in back of the face bearing against the billet 7 (this gives less wear on the socket surface than if the taper were complete) to the face bearing against the ram 8. Such taper permits the end of the nose of the mandrel to move in any direction perpendicular to the direction of the extrusion (gyro-pendulum motion) and prevents flexing of the mandrel in case of off center billets or erratic metal flow through the die. This avoids the combined effect of friction and bending stresses.

Another embodiment of the mandrel of the present invention is shan in FIG. 4. In tis embodiment the shaft 2 is tapered from front to rear and contains a threaded hole 9.

The mandrel of the present invention can be utilized in the following manner to extrude tubes of metal, plastic or similar materials. The extrusion is carried out on a conventional extrusion machine having an extrusion container, tubing die and movable ram. Where a loose dummy block is used, the hollow billet and dummy block are loaded into the extrusion container. The working section of the mandrel, normally lubricated and heated, is inserted through the socket of the dummy block into the billet. The ram is advanced and the tube extruded. The relative position of the extrusion equipment and billet at the start of the push is shown in FIG. 5. The mandrel is not attached to the ram or dummy block but merely seated in the dummy block socket. As the ram is moved forward the mandrel, having the prescribed shaft to working section area relationship, is held in position by the fluid pressure in the container acting on the shaft. FIG. 6 shows the position of the extrusion equipment and billet at the end of the push. The billet is reduced to a small butt end. The shoulder of te working section is wedged in the butt. The die and ram are pulled away. The mandrel is removed by e.g., screwing a ring into the threaded hole 9 in the mandrel shaft (FIG. 4) and attaching a chain to the ring and the movable extrusion frame which moves the ram. The frame is then moved back pulling the mandrel out of the butt through the dummy block.

Where an attached dummy block is used, the procedure is similar. The hollow billet is loaded into the extrusion container and the nose of the mandrel inserted into the billet. The ram having the dummy block attached thereto is moved into place such that the mandrel shaft is positioned in the dummy block socket. The ram is then further advanced to extrude the. tube.

The mandrel of the present invention is particularly suited for extruding small inside diameter metal tubing which cannot practicallybe extruded by conventional techniques due to the-tendency of the mandrel to neck down and break. Especially difficult extrusions of tubes with either extremely thin-or extremely heavy walls are successfully made using the present mandrel.

The basic equation for the area of the shaft which will permit the mandrel to begin to move forward'out of the dummy block due to the frictional force of the material flowing forward over the mandrel is where A area of mandrel shaft A average cross sectional area of working section of mandrel P maximum fluostatic pressure in the container, dependent on the press capacity and container diameter.

S stress on the working section developed by friction.

The shaft diameter may be readily calculated from A in Equation (1). Too large a shaft diameter will restrict the mandrel movement and permit the necking'typical of the conventional die mandrel process, whereas too small a shaft diameter will permit the mandrel to be sucked through the die at the end of the push. A shaft diameter slightly smaller than optimum is to be preferred to one too large, since the undamaged mandrel can be retrieved from the inside of the die if it is sucked through the die.

S=F/A where F =force exerted on mandrel by friction. At any given instant during extrusion F P 2 1TD1 where P, fluostatic pressure in the container at the time in question D diameter of working section of mandrel L billet length at the time in question p. coefficient of friction between the extruded material and mandrel. Also at any instant during extrusion P2 ug. LID2) where P, pressure on the die D container diameter e naperian logarithm base. Therefore, letting x 4p.L/D

F P 6 LID2)7TD1LI.L P,,(e")'rrD, X D u/4p.

= P,1rD,D (e)x/4 In order to determine F throughout the push, it is necessary to set up the following differential equation.

Solving the differential equation between limits where x, 4p.L,/D,, L being the length of the billet at the end of the push (butt).

x 4uL /D L being the length of the billet at the start of the push. Integrating and rearranging terms,

F: POWDIIL w: L2/D2 up L1ID2).]

The generally accepted formula for the pressure at the die is P BY log R where Y tensile yield strength of the material being extruded (in the present example, alumina), at the temperature of extrusion; assumed to be percent of the room temperature yield strength for these calculations.

R extrusion reduction ratio. B a constant dependent on the extrusion die parameters.

where K a constant established as 4 for all light alloys.

8, bearing length of the die for the tube being extruded. (The multiplier 5.5 takes into consideration the bearing effect of the mandrel.)

B bearing length for a round rod having the same cross sectional area as the tube being extruded.

C, O.D. circumference of tube being extruded.

C [.D. circumference of tube being extruded.

C circumference of round rod having the same cross sectional area as the tube being extruded.

In order to calculate the actual diameter of a mandrel shaft, it is necessary, of course, to utilize the above equations in reverse order. Considering the case of aluminum tubing having 3.812 inches O.D. X 1.547 inches 1.D., where B 0.5 inch, B 1.0 inch, C 11.98 inches, C 4.86 inches and C 10.93 inches.

B =4 X 5.5 X 0.5(ll.98 4.86)/l.0 X 10.93 16.93

For a tube area of 9.53 sq. in. and a 16 inches diameter container area of 201 sq. in. (billet 1.D. ignored), the reduction ratio would be 21.1. Assuming Y 0.15 X 3500 psi 525 psi.

P 16.93 X 525 Xlog 21.l 27,100 psi For a 25 inches long billet and 4 inches butt, assuming The value of 0.04 for p. assumes good lubrication. 1f the lubrication on the mandrel were to break down, t could easily increase to a value of 0.10, in hich case F would be 424,000 pounds and S would be 225,000 psi. However the working temperature of the mandrel could easily exceed 1,000, at which temperature the yield strength of H11 or H13 tool steel is only about 120,000 psi. Therefore, to avoid breaking the mandrel, a maximum value of 100,000 psi should be assumed for S. The fluostatic pressure P in the 16 inches container on the 5,500T press could reach 5,500 X 2,000/201 55,000 psi, so

Shaft diameter V 4A V 6.76 2.60 inches To add further safety and insure that the mandrel would move forward rather than neck down, the shaft diameter was made 2.500 inches.

What is claimed is:

1. A method of extruding tubes from an extrusion press having a movable ram which comprises 7 a. providing a mandrel which has a working section having a nose and a tail, and a shaft abutting the tail of the working section wherein the shaft cross sectional area is about equal to A S/P A where A is the average cross sectional area of the working section,

I, is the maximum fluostatic pressure in the container of the extrusion machine, and

S is the frictional stress on the working section during extrusion b. positioning the nose of the mandrel-working section in hole of a hollow billet and the shaft in the socket of a dummy block 0. extruding the billet through a die to form a tube.

. 2. The method of claim 1 wherein the extruded tubes are metal.

3. The method of claim 2 wherein the metal is selected from the group consisting of aluminum alloys and magnesium alloys.

4. A method of extruding a tube from an extrusion press having a movable ram, an extrusion chamber, and a die which comprises:

a. providing 1. a dummy block having a socket concentric with the center of the dummy block cross section, the socket being tapered outwardly from front to rear;

2. a mandrel having a working section, a shaft section tapered inwardly away from the working section, and a raised shoulder portion of the working section between the shaft and the nose of the mandrel, wherein the average shaft cross sectional area is about equal to A SlP A where A is the average cross sectional area of the working section,

P is the maximum fluostatic pressure in the container of the extrusion machine, and

S is the frictional stress on the working section during extrusion;

b. positioning in the extrusion chamber a hollow metal billet wherein the metal is selected from the group consisting of aluminum alloys and magnesium alloys; c. positioning 1. the nose of the mandrel working section in the hole of the hollow metal billet in the extrusion chamber and 2. the shaft of the mandrel in the socket of the dummy block;

d. and continuously advancing the ram and mandrel, thereby extruding the billet through the die to form a tube.

5. The method of claim 4 wherein the dummy block is attached to the ram.

6. A method of extruding a tube, formed of aluminum alloy or magnesium alloy, from an extrusion press having a movable rarn carrying a dummy block with an axially centered socket formed therein and an extrusion container receiving the ram and dummy block, the extrusion container being positioned against and aligned with a die plate having a die orifice therein, which comprises:

a. providing a mandrel having a working section and a shaft section and placing the shaft section in said socket in the dummy block, the shaft section being frictionally held in said socket, the shaft cross sectional area being equal to A S/P A where A is the average cross sectional area of the working section,

P is the maximum fluostatic pressure in the container of the extrusion machine, and

S is the frictional stress on the working section during extrusion, whereby the frictional stress on the working section during extrusion does not ordinarily exceed the .stress necessary to move the shaft section out of said frictional engagement, the shaft section being smaller in diameter than the die orifice;

b. placing a hollow billet of aluminum alloy or magnesium alloy in the extrusion container,

c. advancing the ram and mandrel and positioning I the nose of the mandrel working section in the hole of the hollow billet; and

d. continuously advancing the ram and mandrel throughout extrusion of the hollow billet through the die to form a tube.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US3116834 *Dec 22, 1960Jan 7, 1964Baldwin Lima Hamilton CorpExtrusion of metal tubing
US3526119 *Jul 17, 1967Sep 1, 1970Reisholz Stahl & RoehrenwerkMethod and apparatus for extruding metallic tubes
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3994149 *May 22, 1975Nov 30, 1976Allmanna Svenska Elektriska AktiebolagetPress for hydrostatic extrusion of tubes
US4761866 *Nov 25, 1986Aug 9, 1988Sundstrand CorporationMethod of working in situ the end of a heat exchanger tube
US5208435 *Nov 25, 1991May 4, 1993Sequa CorporationLightweight ram for bodymaker
US5272900 *Sep 18, 1992Dec 28, 1993Exco Technologies, LimitedBayonet style connector for metal extrusion dummy block
US5311761 *Sep 18, 1992May 17, 1994Exco Technologies, LimitedMetal extrusion dummy block having a spring loaded valve
US5918498 *May 23, 1997Jul 6, 1999Robbins; Paul H.Dummy block construction
US20150174630 *Jul 24, 2013Jun 25, 2015Sms Meer GmbhDirect or indirect metal pipe extrusion process, mandrel for extruding metal pipes, metal pipe extruder and extruded metal pipe
WO1993010934A1 *Nov 13, 1992Jun 10, 1993Sequa CorporationLightweight ram for bodymaker
Classifications
U.S. Classification72/264, 72/482.94
International ClassificationB21C26/00, B21C25/04, B29C47/54, B21C25/00, B29C47/36
Cooperative ClassificationB29C47/54, B21C25/04, B21C26/00
European ClassificationB21C25/04, B29C47/54, B21C26/00