GB2169231A - Apparatus and methods for extruding tubes with off-centre bores - Google Patents

Abstract

Tubes having a longitudinal off-center passage therein are extruded from billets having off-center bores. The apparatus includes a die 30 for forming the outer shape of the tube and a mandrel 71 for forming its passage, both being located off-center, so that flow of the material through the die will not push the mandrel to one side and cause the passage in the tube to be incorrectly located. The mandrel may be non-circular in cross-section. <IMAGE>

Description

SPECIFICATION Apparatus and methods for extruding tubes with off-center bores This invention relates to metal working and more particularly to apparatus and methods for extruding metal to form tubular members having off-center passages or bores therein.

Metal tubes have been extruded for many years.

For the most part, these have been tubes of regular cross-section, such as conventional tubes with concentric inside and outside surfaces. Extruding tubes of this type does not present a great problem.

There has developed a need to extrude tubes in which the bore is off center with respect to the tube's outer surface. The outer wall of such tube might be round, non-circular, substantially oval, or other desired shape, for instance, with the bore being positioned so far off center that the thickest portion of the wall might be three or more times as thick as the thinnest portion of the wall.

It is desirable that the bore of the extrusion be formed to finish size during the extrusion process so that subsequent machining of the bore will not be necessary.

In extruding tubes, a die having an aperture of suitable size and shape forms the outer wall of the tube while a mandrel of suitable size and shape and having a portion thereof extending into or through the die aperture forms the bore or passage of the tube.

Typically, the mandrel extends through the die aperture and forms therewith an annular die opening through which metal or other extrudible material is extruded to produce the tube. Tubes of uniform section, such as a hollow cylinder, are readily extruded and present no problem since a round billet with a round bore is extruded through a round annular opening formed between a round die aperture and a concentrically located round mandrel. When the billet, the die aperture and the mandrel are concentric, the extrudible material, as it is being extruded, flows into and through the die aperture about the mandrel uniformly and does not tend to push the mandrel to one side.Ideally, the flow of the extruding material is as nearly axial or linear as possible with uniform velocity distribution in the flow stream and, at the same time, creating uniform pressure forces acting about that portion of the mandrel which is disposed near and within the die aperture.

It is readily seen that unless these pressure forces about the mandrel are substantially equal, the mandrel may be forced off center or from its engineered position, and the extruded tube will have a wall which is too thick on one side of the bore and too thin on the opposite side. This problem becomes more real when consideration is given the fact that the mandrel is usually long and slender, hence more readily deflected from its engineered position. It must be sufficiently long to extend through both the billet and the die aperture.

In the cases discussed hereinbelow, the billet was about 36 inches long by about 12 inches in diameter and the mandrel about 2.5 inches in diameter by about 42 inches long.

The problem of displacing or deflecting the mandrel to one side in the extrusion process is greatly multiplied as the extrudible material becomes stronger, harder, and/or more resistant to flow.

This is true in the stronger metals, and particularly so in the case of premium grades of steel, such as, for instance, Type 4140 steel. Such materials require much greater forces to extrude them through a die, other things being equal and can result in tremendous side loads acting upon the mandrel which could easily bend or break it.

U.S. Patent 1,916,645, which issued to J.H. Taylor on July 4, 1933, teaches extruding curved pipe fittings, the extrusion being caused to crook because the extruded material issued faster from one side of the die aperture than from the opposite side as a result of the mandrel being eccentrically located with respect to the billet. In some instances, Taylor's tubes have a thicker wall on one side than on the opposite side. This he appears to accomplish by moving his mandrel toward one side. Taylor does not teach extruding such tubes which are straight. Taylor extrudes short pieces with a large bore and thin wall. His mandrel is large in diameter and may have sufficient stiffness to resist the imbalance of the side loads.Taylor does not teach how to locate the off-center bore in a billet and the off-center mandrel is a die opening for extruding a straight tube having an off-center bore while having uniform flow velocities through all parts of the annular die aperture. Neither does Taylor teach how to provide uniform flow velocities, nor how to compensate when moving the mandrel laterally to a new position in the die aperture.

U.S. Patent 3,241,346 issued to J. H. Doss on March 22, 1966. This patent teaches the extrusion of tubes with off-center bores using apparatus wherein a mandrel is suspended from fins in the containing vessel with its lower end portion extending downwardly through the die opening. The mandrel may be located off-center to produce tubes with eccentric bores. Since the fins, when supporting the mandrel, forms several ports upstream of the die opening, Doss teaches that the area of these ports is eccentric in proportion to the degree of off-centering desired in the extrusion.

The fins in Doss split the extruding material into separate streams upstream of the die and these streams must come together again to form a single homogeneous stream, which cannot be accomplished with metals because they are extruded at temperatures below their melting temperatures.

Doss does not teach how to locate the off- centeredness of the mandrel relative to the billet in order to produce a tube with eccentric bore while having uniform linear flow through the die aperture.

U.S. Patent 3,242,531 issued to E. Nohl on March 29, 1966; Russian Patent 129138 which issued to Marti Frederek on 6 October, 1959; Russian Patent 627883; French patent 2 314 781, which issued to B. Kazimierzak on 18 February, 1977; German Patentschrift 842188 which issued 23 June 1952; and German Offenlegungschrift, which issued 3 July, 1980, all appear to be not pertinent relative to the present application.

U.S. Patent 4,333,527 which issued on June 8, 1982 to Robert S. Higgins, et al. for SIDE POCKET MANDREL AND METHOD OF CONSTRUCTION shows a tubular structure, a portion of which could be extruded as a tube having an off-center longitudinal passage.

U.S. Patent Application, Serial No. 06/350,283, filed February 19, 1982 by David T. Merritt, et al.

and entitled SIDE POCKET MANDREL, now U.S.

Patent No. 4,416,330, shows a similar structure, a portion of which could be extruded as an irregular tube.

U.S. Patent Application, Serial No. 06/503,728, filed June 13, 1983 by Olen R. Long for APPARA TUS AND METHODS FOR EXTRUDING IRREGULAR TUBES, now U.S. Patent No. ,teaches the extrusion of irregular tubes including an irregular tube suitable for use in constructing side pocket mandrels such as that illustrated and described in the just-mentioned application, Serial No. 06/350,283, of David T. Merritt, et al., of which Olen R. Long is a coinventor. In this sole application of Olen R.

Long, the irregular tube has a wall that varies in thickness about the irregular bore. However, the variation in wall thickness about the bore, while presenting problems, was extrudible using a centered die aperture and centered mandrel, even though the extrusions were of Type 4140 Steel which is hard and strong and is forced through the die only with great force.

The present invention makes it possible to extrude tubes of almost any desired section having off-center passages therein of almost any section.

It is particularly useful in extruding tubes for use in making the receptacle portion of side pocket mandrels such as those taught in U.S. Patent 4,333,527 mentioned above, or for other uses. Such extrusions may be of high strength material, such as Type 4140 Steel, for instance.

None of the prior art of which applicants are aware discloses methods and apparatus for extruding tubes having off-center longitudinal passages therein wherein the extrudible material flows through the die uniformly and linearly. U.S. Patent 4,333,527 and U.S. Applications, Serial No. 06/ 503,728 and 06/350,283, all three of which are mentioned hereinabove, and incorporated herein for all purposes by reference thereto.

The present invention is directed to apparatus and methods for extruding a tube of desired section having an off-center longitudinal passage of desired section therein using, for instance, an extrusion press having a containing vessel for containing a billet of extrudible material; a die closing one end of the containing vessel and having an aperture of suitable shape through which the billet material may be extruded; means movable into the opposite end of the containing vessel for forcing the extrudible material through the die aperture; and a mandrel extending through the billet and having at least a portion thereof disposed in the die aperture and forming with the die aperture an annular die opening through which the extrudible material is extruded to produce a tube of desired cross-section, the relationship of the containing vessel and the die aperture to the mandrel being predeterminable with considerable precision.

It is therefore one object of this invention to provide methods for extruding tubes having off-center passages therein, the relationship of the mandrel to the containing vessel and to the die aperture being predetermined with great accuracy so that the lines of flow of the extrudible material through the annular die opening will be substantially linear having a mandrel of any desired section for forming the inner shape of the extruded tube.

A further object is to provide apparatus for extruding tubes with off-center bores wherein the mandrel is located off-center relative to the containing vessel for containing the billet by a predetermined amount and the mandrel is also located off-center relative to the die aperture by a predetermined amount, the off-centeredness of the mandrel with respect to the containing vessel and the off-centeredness of the mandrel with respect to the die aperture being determined by a first dividing line passing transversely through the center of the area of the mandrel dividing the annular area of the transverse section of said containing vessel into a large area and a small area and a second dividing line passing through the center of area of the mandrel section at said die dividing the annular die opening into a large area and a small area, the dividing line in both instances being perpendic ular to the direction of the off-centeredness, the ratio of the large area of the containing vessel section to the small area thereof being substantially equal to the ratio of the large area of the annular die opening to the small area thereof.

Other objects and advantages will become apparent from reading the description which follows and from studying the accompanying drawings wherein: Figure 1 is a fragmentary schematical view of an extrusion press in the act of extruding a tube in accordance with the present invention; Figure 2 is a cross-sectional view of the extruded tube taken along line 2-2 of Figure 1; Figure 3 is an isometrical view of a tubular billet of extrudible material; Figure 4 is a longitudinal view of a side pocket mandrel having at least one portion thereof formed from a short length of tube extruded in accordance with the present invention; Figure 5 is a cross-sectional view taken along line 5-5 of Figure 4; Figure 6 is a view similar to Figure 2 but showing a cross-section of a round tube having an offcenter bore; ; Figure 7 is a diagrammatical view showing pressure forces acting inwardly about the outer surface of the mandrel of the extrusion press during the extrusion operation; Figure 8 is a cross-sectional view of a conventional prior art die for extruding tubes having an off-center bore; Figure 9 is a diagrammatical view showing the relationship of mandrel, die, and and containing vessel, with the mandrel centrally located relative to such vessel; Figure 10 is a diagrammatical view similar to Figure 9 but showing the die aperture centered with respect to the containing vessel and the mandrel positioned off center with respect to both;; Figure 11 is a cross-sectional view of a tube which may be like the tube of Figure 2 but showing a vertical line running through the center of the tube bore and representing the axis of symmetry and a horizontal line running through the center of the tube bore and perpendicular to the axis of symmetry; Figure 12 is a cross-sectional view taken through a tubular billet such as the billet of Figure 3 and showing the off-center bore thereof; Figure 13 is a view showing the cross-section of a mandrel having a non-circular section; Figure 14 is a fragmentary cross-sectional view as it would appear when taken through the die means while the mandrel is in position extending through the die aperture; and Figure 15 is a fragmentary cross-sectional view as it would appear when taken through the containing vessel, billet and mandrel during the extruding operation.

Referring now to Figures 1 and 2, it will be seen that an extrusion press or apparatus is schematically shown and is indicated generally by the reference numeral 20. The press 20 has a body 22 having a cylindrical portion 24 and a fixture support portion 26, as shown.

Extrusion die means 30 is held by fixture 32 mounted on the support portions 26 of the press.

The die means 30 has an extrusion aperture 38 of the desired cross-section, and its entrance end is flared to provide a suitable guide which may be in the form of rounded corners as at 40. In some instances, it may be desirable to form the guide with a taper, chamfer, or other desired shape.

Protective means such as that indicated by reference numeral 44 may be mounted adjacent the exit end of the die. The protective means 44 includes a flange 46 adjacent the die means and having a protective tubular sleeve 48 with a bore 49 attached to its rearward side as shown and extending in a direction away from the die means.

Protective means 44 will offer some protection to the expensive die 30 and perhaps other parts of the apparatus should there be an explosion or other catastrophe.

A containing vessel 50 having a bore 56 is supported upon the support portion 26 of the press, and the rearward end 52 of the vessel 50 is preferably held against the face side 54 of the die means 30. Thus, the die means closes the rearward end of the bore 56 of the vessel 50.

Ram means 60 is provided which includes a ram 61 which is telescopable into the containing vessel, as shown, and its forward end 62 is movable thereinto by main piston 66 to which the ram 60 is attached as by retaining ring 68 and bolts 69. The main piston 66 is slidable in bore 24a of cylinder portion 24 of the press. The forward end of ram 61 carries a pusher plate 70 having an aperture 76, and various such pusher plates may be had and interchanged as needed depending upon the sizes and shapes of the extrusions to be made.

A mandrel such as mandrel 71 is used to form or shape the off-center bore or passage 72 in the extrusion while the die aperture 38 forms or shapes the exterior surface 73, seen in Figure 2. The mandrel 71 preferably extends through the die aperture 38 as shown to form annular or annulus-like die opening 74 between the die and the mandrel, and it is through this annular die opening that hot metal is extruded to form the tubular extrusion 75.

The term "annular die opening" or "annulus-like die opening" as used herein each indicate that ring-like opening or orifice formed between the mandrel and the die as the mandrel extends into or through the die aperture. See annular die opening 74 of Figure 1 and annular die opening 158 of Figure 14. The annular die opening can take various shapes since the shape of the die aperture as well as the shape of the mandrel can be varied as desired.

The mandrel 71 could, for small tubes, be attached to a pusher plate having no aperture. In such case, it is difficult to insert billets into the containing vessel unless they are quite short. For long billets, the mandrel is preferably carried by the ram means as seen in Figure 1 so that it projects through the aperture 76 of the pusher plate 70 at all times. The aperture 76 in the pusher plate 70 provides lateral supportforthe mandrel 71 to help maintain it in proper position in the aperture 38 of the die 30. Even so, uneven flow of the extruding metal through the die might force the mandrel from its engineered position, causing the passage through the extrusion to be displaced too far from its intended location. This is especially true if high strength material such as Type 4140 Steel is extruded.

The mandrel 71 has its inner end attached to base member 80 (shown in dotted lines), and the base member 80 is attached to auxiliary piston 81 slidably mounted in auxiliary bore 82 of main piston 66 as shown.

Since the auxiliary piston 81 is slidable in bore 82 of the main piston 66, the mandrel is extensible and retractable as the auxiliary piston moves forward and back relative to the main piston. When the mandrel 71 is retracted, it extends outward of the pusher plate 70 only a few inches. By moving the auxiliary piston forward, the mandrel is extended. The limit of extension for the mandrel is reached when the forward side of base member 80 engages the inner side of the pusher plate 70.

When both mandrel 71 and the main piston 66 are retracted, a hot tubular billet such as billet 86 (see Figure 3) of suitable extrudible material is placed before the vessel 50 and oriented to align its bore or passage 87 with mandrel 71 and die aperture 38. It is then moved into vessel bore 56. This billet preferably is of a size to fit closely but freely in the vessel 50, and its bore 87 freely accommo dates mandrel 71. The billet does not have to be round, neither does its bore, but economy dictates that they, both the billet and its bore be round principally because the containing vessel on the extrusion press is cylindrical and because bores can be formed in billets economically by drilling. If soft materials are to be extruded, the billet may not need to be bored, but instead, may be pierced by the mandrel.Hydraulic pressure from a suitable source is applied to the main and auxiliary pistons 66 and 81. The auxiliary piston, being much less massive than the main piston, moves first and extends the mandrel 71. The mandrel extends through the bore or passage 87 of the billet 86 and also through the die aperture 38. Hydrauiic pressure is built up in cylinder 24a, and the ram begins to move toward the die means and the pusher plate 70 engages the billet, pushing the billet ahead of it until its forward end engages the die means. The ram is moved yet farther into the ves sel to apply an axial force to the billet.When sufficient ram force is applied to the billet in the containing vessel, the billet begins to upset and fill the available space within the vessel between the pusher plate and the die means and between the outer surface of the mandrel and the inner well of the containing vessel. The extrudible material then commences flowing through the annular die opening 74 between the exterior of the mandrel 71 and the inner wall of the die aperture 38 as the ram advances slowly toward the die. The extrudible material of the billet is extruded rather rapidly, the extrusion being much smaller in section than the billet. If the velocity of the extrusion becomes excessive, the heat in the area of the die becomes excessive and metal begins to wipe off at the die and the extrusion is diminished in cross-section and poorly shaped, usually with unwanted longitudinal grooves.It, therefore, is poor in quality and very likely unfit for its intended purpose.

Figure 2 shows a cross-section of the extrusion 75. This cross-section may be exactly like that disclosed in previously mentioned Application Serial No. 350,283 (now U.S. Patent 4,416,330) incorporated herein by reference. It should be clear that the outer shape 73 of the extrusion 75 is determined by the shape of the die aperture 38, while the opening or inner shape 72 of the extrusion is determined by the cross-sectional shape of the mandrel 71. The configuration of the cross-section of extrusion 75 as shown in Figure 2 is presented by way of explanation and it is understood that the shape of the die aperture and the section of the mandrel can be varied as desired to produce extrusions of desired configurations.

Understandably, the aperture 76 in the pusher plate, like the shape of mandrel 71, need not be round, but is shaped to conform to the shape of the mandrel with sufficient clearance to allow free movement of the mandrel therethrough. The clearance about the mandrel should be minimal, perhaps on the order of 0.008 to 0.010 inch (0.020 to 0.25 millimeter) depending upon size. Preferably a portion of the free end of the mandrel is tapered slightly so that the clearance increases a little toward the forward end of the mandrel to prevent excessive friction between the mandrel and the extrusion.

The ram stroke is limited and ends before the pusher plate strikes the die in order to avoid damage to either the die or the pusher plate. Upon retraction of main piston 66, the ram and the mandrel must be retracted from the extrusion. In so doing, the extrusion is dragged rearwardly through the die for a short distance before the mandrel pulls free thereof. The containing vessel is then withdrawn from around the extrusion and gotten out of the way. At this time, it will be seen that the rearward end of the extrusion has a large malformed head about one inch (25.4 millimeters) thick and as large as vessel bore 56 and now spaced several inches from the die. This head is cut off and discarded as scrap.

The extrusion is then removed from the die and is laid aside to cool slowly. The extrusion is preferably allowed to lie straight as it is allowed to cool down below the transition temperature (the temperature below which the metal will now flow or become distorted because of its own weight).

The extrusion 75 may be cut into lengths suitable for use in constructing desired products, for instance, side pocket mandrels such as the side pocket mandrel illustrated and described in Application Serial No. 350,283, supra, or that indicated by the reference numeral 90 in Figures 4 and 5. It is seen that the side pocket mandrel 90 is provided with lower body section 92 having a cross-section as seen in Figure 5. The cross-section seen in Figure 5 corresponds to that seen in Figure 2 and discussed earlier. A valve receptacle 94 and flow ports 95 have been formed in this body member 92 before welding it into the side pocket mandrel as at 97 and 98 as shown.

In the manufacture of side pocket mandrels, such as the side pocket mandrel 90 illustrated in Figure 4, it is sometimes desirable to make than with circular exterior walls particularly in the large sizes for use in high pressure wells since the circular side pocket mandrels have superior collapse strength, other things being equal. A circular tube 100 having an off-center bore 101 is seen in Figure 6. Tube 100 would be suitable for use in the construction of round side pocket mandrels similar to oval mandrel 90 of Figure 4.

As was stated earlier, extruding such tubes having off-center bores, such as the tubes 75 and 100, presents a problem, especially if such tubes are to be formed of high strength material such as Type 4140 Steel which is a very suitable material for high strength side pocket mandrels.

The problem, as mentioned earlier, relates to the need to maintain a balance of forces acting inwardly about the mandrel. The diagram of Figure 7 shows a tube 114 being extruded. The dotted circle 115 represents the upset diameter of the billet or the inner wall of the containing vessel which confines it. The billet material is being crowded through the annular die opening between the exterior of the mandrel 116 and the inner wall of the die aperture 117. The inward flow of the material applies inward forces to the mandrel. These forces are represented by the inwardly directed arrows.

Ideally, these forces should be equal. If these forces are unbalanced, lateral displacement of the mandrel relative to the die aperture is likely to result, and this would cause the passage in the extruded tube to be laterally displaced from its engineered location. If such disclocation is beyond tolerance, such tubes would be unfit for use. This would be costly in time, materials, and money.

Actual attempts were made to produce tubes such as tube 75 from Type 4140 steel, using prior art apparatus and methods. The accepted procedure called for use of die means having a crosssection like that seen in Figure 8.

In Figure 8, the die means 110 has a substantially qval aperture 111 through which a mandrel (not shown) would extend and form with aperture 111 an annular die opening through which a substantially oval tube, such as tube 75 (Figure 2), could be extruded. In order to substantially equalize the forces tending to displace the mandrel laterally and distort the annular opening just mentioned, and at the same time keep the mandrel in its conventional central location relative to the billet, it was necessary to provide a second aperture in the die 110. This second aperture is indicated by reference numeral 112. As a tube is extruded through aperture 111, material simultaneously extrudes through aperture 112 also. The second extrusion thus formed is called a sacrificial extrusion. It is considered a necessary evil. It is expensive.Type 4140 Steel is expensive, although it is one of the more economical grades of premium high strength materials suitable for mandrels such as mandrel 90. This sacrificial extrusion wastes, in this case, about 30 percent of the material.

Experimental extrusions were made using a die such as that shown in Figure 8. In a very short time the web between the two die openings began to deteriorate or melt, beginning at the entrance end of the die. This experiment was made using a small die and producing a tube much too small for use in side pocket mandrels. In larger sizes, the problem would have been foreseeably worse, so this prior art die design was abandoned and experiments then pursued using arrangements in accordance with the illustrations of Figures 9 and 10.

Figure 9 shows diagrammatically the relationship between the mandrel, the die aperture, and the billet if the sacrificial strip is not resorted to. The mandrel 120 is centered with respect to the container vessel bore 122 and is properly positioned with respect to the die aperture 124. The annular die opening 126 between the aperture and the mandrel is the opening through which the billet material would be extruded to form a tube of the shape of opening 126. The flow of the extrudible material will not be balanced about the mandrel because the thick material in the region A of the billet will only be partially used to form the thin part of the tube. The excess material from region A must flow around the mandrel 120 to help form the thick portion of the tube.Extruding Type 4140 Steel in this case is considered impossible because of the extreme pressure required to extrude the material and because of the extreme imbalance of side loads on the mandrel as the material flows from region A toward the opposite side of the mandrel would in all likelihood destroy the mandrel.

Figure 10 presents a similar case. It shows aperture 124 centered with respect to container vessel bore 122 while mandrel 120 is properly positioned with respect to aperture 124 to provide an annular die opening 126 of proper shape. The mandrel in this case is off center while the aperture is centered. This case is better than the case presented in Figure 9 but is still not good enough especially if high strength material is to be extruded.

In accordance with the present invention, the relationship between the containing vessel and the mandrel for any shape extrusion with a bore or cavity of any shape therein can be predetermined with a high degree of precision in a manner which will now be described.

In Figure 11, there is shown a cross-section of a tube to be extruded. This tube could have any desired configuration of inner and outer shape but, for the sake of simplicity, is shown to have the same shape as does the tube 75 illustrated in Figure 2 and is therefore indicated by reference numeral 75. A horizontal line 77 is drawn through the center of area or center of the bore 72, dividing the cross-section of the tube into two portions, a large area and a small area, which are indicated by the letters A and B, respectively. It is readily seen that this horizontal line 77 is perpendicular to the direction of the off-centeredness of the bore 72. The offcenteredness of the bore 72 is obviously in a downward direction along the axis of symmetry, indicated by the vertical line 78 (which also passes through the center of area or center of the bore 72). Thus line 77 is horizontal.

The areas of the portions A and B are determined and compared to obtain their ratio. For the sake of illustration, assume that portion A has 2.5 times the area of portion B, that is, the ratio of A to B is 2.5 to 1. This same ratio must be established between the mandrel and the containing vessel which then determines the location for the bore in the billet.

Referring now to Figure 12, it will be seen that an upset billet 86 in the process of being extruded is provided with a passage or bore 87 now closed about mandrel 116 and has a horizontal line 88 drawn through the center of area of the mandrel.

The upset billet fills the annular space between the mandrel and the containing vessel. This annular space is sometimes referred to herein as the "mandrel-containing vessel annulus". Line 88 divides the cross-section into two portions, a large area and a small area, which are indicated by the letters C and D, respectively. The ratio of the large area C to the small area D should substantially equal the ratio of A to B as before determined with respect to the tube 75 of Figure 11. In the case at hand, C:D must equal A:B which equals 2.5 to 1.

Since these ratios are 2.5 to 1, it is readily seen that the upper portion, C, of the billet will go to make the upper portion, A, of the tube and that the lower portion, D, of the billet will go to make the lower portion, B, of the tube. In this manner, the lines of flow of the extruding material extruding through the die will be substantially straight.

Thus, since the ratio in each case is 2.5 to 1, the area of the containing vessel bore minus the area of the mandrel section is divided by 3.5, that is, 2.5 plus one, to obtain the area of the lower portion D of the billet. The remainder of the area, of course, constitutes the upper portion C of the containing vessel. The areas of such portions of figures, and, indeed, the area of any plane figure of any shape may be determined through use of a well known engineering instrument known as a Compensating Polar Planimeter. The dividing line, such as dividing line 88, may be adjusted until the desired ratio is obtained.

Having A:B::C:D, the lines of flow of the extruding material through the die should be as straight and uniform as possible and the mandrel should not deflect from its engineered position.

It is readily understood that the ratio of A to B of the selected tube is determined first. Next, the mandrel is located with respect to the containing vessel bore so that after upsetting the billet the ratio of its region C to its region D will equal the ratio of region A to region B just determined for the tube. Then, the die aperture is located about the mandrel in accordance with the section of the tube to be extruded.

In actual experiments, tubes shaped virtually like that represented in Figure 2 were extruded from Type 4140 Steel in accordance with this invention without using excessive pressures in the main cylinder of the extrusion press. The extrusions produced were of excellent quality and the bore remained in its engineered position throughout the length of the long extrusion. As anticipated, the bores of the tubes were formed to finished size by the mandrel as the tubes were extruded, and further work on the bore was not required.

As was mentioned hereinabove, Type 4140 steel and other high strength materials are very resistant to flow even at extruding temperatures. So, unless the mandrel is rightly located relative to the containing vessel and the die aperture, the lines of flow of the extrudibie material as it flows through the annular die opening will not be substantially straight, and the resulting imbalance of side loads on the mandrel will cause it to be deflected from its engineered position (and may even cause breakage of the mandrel). As a result, all or considerable portions of the expensive extrusions may necessarily be scrapped.

Figure 13 shows a cross-section of an extrusion 130 similar to the extrusion shown in previously filed Application for Patent, Serial No. 06/503,728 incorporated by reference hereinabove. Such an extrusion is useful in the manufacture of side pocket mandrels such as the side pocket mandrel 90 seen in Figure 4 of the present application. Such extrusion goes to make the upper body section 99 of such side pocket mandrel. The off-centeredness in the extrusion 130 is not nearly so great as that in extrusion 75 (Figure 2), nevertheless, it is enough to be a real problem, it has been found.

Referring to Figure 13, it is seen that extrusion 130 has a substantially oval outer surface 132 and has an irregularly shaped passage 133 providing an inner surface 134. The wall 136 is not of uniform thickness, but is much thicker in the region indicated by the reference numeral 138 than in the region 140 or 142. As viewed in Figure 13, it is readily seen that more metal will be required to form that portion above centerline 143 than will be required to form that portion below the centerline.

Thus, the lateral forces acting upon the mandrel as the material is extruded through the die will not be balanced if the mandrel or die is centrally located with respect to the containing vessel. Actual practice confirms this. The mandrel must be located off center with respect to the containing vessel in order to bring such lateral forces into balance. The amount of this off-centeredness can be determined with great accuracy. Figure 14 will help in making this determination.

Figure 14 shows a die 150 having an aperture 152 for forming the outer surface of the extrusion 130 of Figure 13. This die aperture shown is substantially oval in shape. A mandrel 156 is positioned in the die aperture and forms an annular die opening 158 therewith. Mandrel 156 will form the cavity or passage 133 in the extrusion 130 (Figure 13). In order for the lateral forces on the mandrel to be balanced, the mandrel must be correctly related to the containing vessel, as before explained.

Otherwise, the lateral forces acting upon the mandrel will be unbalanced, and poor to disastrous results will be obtained. To balance these forces, the mandrel must be located off center with respect to the containing vessel (and, therefore, the upset billet), then the annular die opening must be located with respect to the off-center mandrel to provide the proper annular die opening 150 and thus assure that passage 133 will be located at its true engineered position in the extruded tube.

A horizontal line is drawn across the mandrel section as at 160 and the area of the mandrel section on each side of this line is measured by suitable means, as through use of a Compensating Polar Planimeter. The line 160, if it is not correctly positioned, must be moved up or down untii the mandrel section areas above and below it are equal. Line 160 then will pass through the center of area of the mandrel section. The intersection of line 160 with the axis of symmetry 162 of the mandrel section locates the center of area 164 for the mandrel section.

The line 160, which now passes through the center of area of the mandrel section, as seen in Figure 14, divides the annular die opening 158 into two areas, a large area A' and a small area B'.

Areas A' and B' are than measured, as with the aforementioned planimeter, and area A' is divided by the area of B' to obtain the ratio of A' to B'.

Suppose that the areas A' and B' measure 5.60 to 4.0 square inches, respectively. This would be a ratio of 5.60 to 4.0, or 1.40 to 1.0. The mandrel must be located with respect to the containing vessel ac cording to this ratio, as was explained with respect to Figure 12.

Referring now to Figure 15, it will be seen that the containing vessel is indicated by the numeral 175 and that it has a bore 176 for containing a billet 178 which surrounds the mandrel 156 which passes longitudinally through the containing vessel. The cross-sectional view shows the billet in its upset condition. Thus, the billet fills completely the annular space in the containing vessel surrounding the mandrel. Horizontal line 182 passes through the center of area 164 of the mandrel 156 as did line 160 in Figure 14. Clearly, both line 160 and line 182 lie in a common place. (Vertical line 162 also passes through the center of area 164.) Line 182 divides the billet into two areas, a large area C' and smaller area D', respectively. The ratio of C' or D' should be equal to the ratio of A to B or 1.4 to 1 established aforetime as explained with respect to Figure 14.Of course, the billet, if it is of hard material and cannot be pierced with the mandrel, must be provided with a bore which is formed therein beforehand as by drilling, casting, or other suitable operation. The bore of the billet must be of sufficient size to readily receive the mandrel which must pass therethrough. And, it must be located such that when the billet is placed in the containing vessel the billet bore will be satisfactorily aligned with the mandrel so that the mandrel will not be deflected as it enters and passes therethrough. It is understood that close tolerances on the inside and outside diameters of the billet only serve to minimize the void spaces which must be filled as the billet is upset and, at the same time permits using a billet of greater volume to make more economical use of the expensive extrusion operation.

It is understood that although the mandrel may be non-circular, for instance the non-circular man drel 156 of Figure 14, the bore formed in the billet will usually be conveniently round, as shown in Figure 12, because billets can be drilled or bored readily and ahead of time and because the bore is preferably correctly located and sized for each size and configuration of piece to be extruded with an off-center passage therein. The billet bore can, however, be any suitable size or shape.

In locating the billet bore, the temperatures and the thermal coefficients of the billet, mandrel, and the containing vessel as well as desired clearances should be carefully taken into account and suitably allowed for consistent with good engineering practices.

Thus, it has been shown that apparatus and methods have been provided for extruding tubes having off-center bores; that such tubes may be extruded of high strength materials such as Type 4140 Steel; that the mandrel can be precisely lo cated with respect to the containing vessel accord ing to the annular die opening to be used so that the lines of flow of the extruding material through the die will be as straight as possible, thus avoid ing unbalanced side loads on the mandrel at the aperture area; that tubes of any desired exterior shape (circular, non-circular, oval, rectangular, polygonal with any desired number of sides, or other shapes) may be extruded, each with an off-center bore and that the off-center bore may be of any desired shape (circular, non-circular, oval, et cetera), and that extrusions produced by the methods and apparatus of this invention are of high quality and are useful as material for the manufacture or fabrication of tools such as side pocket mandrels or other desired structures.

While the extrusion of high strength materials has been discussed hereinabove, and particularly Type 4140 Steel, the apparatus and methods of this invention are applicable to the extrusion of other materials also.

While tubes suitable for use in constructing side pocket mandrels have been illustrated and described hereinabove, tubes of the type disclosed herein may find utility in many other places.

The foregoing description and drawings of the invention are explanatory and illustrative thereof, and various changes in sizes, shapes, materials, and arrangements of parts, as well as certain details of the illustrated construction, may be made within the scope of the appended claims without departing from the true spirit of the invention.

Claims (6)

1. A method of extruding a tube having an offcenter passage therein, said method comprising the steps of: (a) providing a containing vessel having an inner wall; (b) providing a die having an aperture therethrough; (c) closing one end of said containing vessel with said die; (d) providing a billet of extrudible material and placing it in said containing vessel; (e) providing a mandrel with a noncircular cross-section and disposing said mandrel eccentrically through said containing vessel, said mandrel passing through said billet and into said die aperture to form an annular die opening therebetween; (f) applying an axial force to said billet directed toward said die to upset said billet and causing it to expand laterally to fill the annular space between said mandrel and the inner wall of said containing vessel, the mandrel being so located with respect to said containing vessel and said die aperture that the ratio of the greater area of the billet section on one side of a line passing through the center of area of the mandrel section to the lesser area of the billet section on the opposite side of that line is equal to the ratio of the greater area of said annular die opening on one side of a line passing through this center of area of the mandrel section to the lesser area of said an nular die opening on the opposite side of that line, both such lines lying in a common place; and continuing to apply said axial force to said billet to cause said extrudible material to be extruded through said annular die opening.

2. The method of claim 1 wherein the step of providing said mandrel includes the step of form ing the mandrel with a cross-section which will cause the extrudible material to issue from the an nular die opening as an extrusion having a longitu dinal passage therein which constitutes a circular bore with a keyway-like channel in one side thereof.

3. Apparatus for extruding a tube having an offcenter longitudinal passage therein, comprising: (a) a containing vessel for containing a billet of extrudible material, said billet having an off-center bore therethrough whose centerline is parallel to but displaced from the centerline of the billet by a predetermined amount; (b) die means closing one end of said containing vessel and having a die aperture therethrough of desired shape and size; (c) a mandrel with a non-circular cross-section and size extending through said containing vessel and through said bore of said billet when said billet is present in said containing vessel, a portion of said mandrel extending into said aperture of said die and forming therewith an annular die opening through which the extrudible material is extrudible, said mandrel being located off-center relative to said die aperture by a predetermined amount, the off-centeredness of said mandrel with respect to said containing vessel being determined by a first dividing line passing transversely through the center of area of said mandrel dividing the transverse section of said mandrel-containing vessel annulus into a large area and a small area and a second dividing line passing through the center of area of the mandrel section at said die dividing said annular die opening into a large area and a small area, said first and second dividing lines lying in a common place, the ratio of the large area of the mandrel-containing vessel annulus section to the small area thereof being substantially equal to the ratio of the large area of the annular die opening to the small area thereof; and (d) means movable into said containing vessel and toward said die means for forcing the extrudible metal through said annular die opening.

4. The apparatus of claim 3 wherein the section of said mandrel is shaped such that the extrusion will have a passage therethrough which is essentially circular with a keyway-like channel in one side thereof.

5. A method of extruding a tube having an offcentre passage therein substantially as hereinbefore described.

6. Apparatus for extruding a tube having an offcentre passage therein substantially as hereinbefore described with reference to and as shown in the accompanying drawings.