DE2846658C2 - Metallic shell for the production of extrusion billets for the powder metallurgical production of pipes - Google Patents

Description

8. Case according to claim 7, characterized in that at least the end face (34; 134) of the front insert (30, 130 ) is beveled or rounded at its outer edge (35, 135).

9. Cover according to claim 7 or 8, characterized in that a funnel-shaped insert (30) is provided on the front end face of the cover (1), in which the angle {y) between the wall of the central bore (32) and the conical outer surface (36) of the funnel-shaped insert (30) about 40 ° ^c to 50, is preferably 45 °.

10. Case according to claim 7 or 8, characterized in that a substantially semi-spherical insert (130) is provided at least on the front end side of the sheath (1), having a an approximately circular arc-shaped cross-sectional profile (136) having boundary surface (136) between the Wall of the central bore (132) and its largest outer diameter, the center points (138) of the circular arc profile (136 ) lying approximately in the area of the intersection between the flat end face (134) and the central bore (132).

11. Case according to one or more of the claims 1 to 10, characterized in that at least the outer jacket (2) is spiral-welded.

12. Cover according to claim 11, characterized in that the slope (λ) of the spiral formed by the weld seam (5) in relation to the length (L, L) of the cover (1) is dimensioned so that the weld seam

(5) forms one, two or more complete turns

13. Case according to claim 11 or 12, characterized in that the spiral weld seam has been smoothed by means of rolling and / or grinding

14. Case according to one or more of claims 1 to 10, characterized in that at least the outer jacket (2) consists of an extruded tube

The present invention relates to a metallic shell of annular cross-section from an outer and an inner jacket made of thin, preferably 1 to 2 mm thick, ductile sheet metal to accommodate isostatic metal or alloy powders to be pre-pressed in the manufacture of extrusion billets for powder metallurgy Production of pipes.

The DE-PS 24 19 014 already describes a method for producing pipes made of stainless steel, the Uniform structure as well as uniform physical and chemical properties and good processing properties have, wherein powder of such steel is filled into metallic shells and the sealed shells are compressed by means of pressure acting on all sides and the extrusion billet thus obtained is extruded into tubes, and by atomizing steel powder made of predominantly spherical particles, produced by melt in inert gas, thin-walled sheaths made of a ductile metal are used, the thickness of which is 0.1 to 5 mm, but a maximum is about 5% of the outer diameter of the shell, the density of the steel powder filled into the shell through Vibration and / or ultrasound is increased to about 60 to 70% of the theoretical density and the density of the Steel powder by cold isostatic pressing of the shell using a pressure of at least 1500 bar to at least 80% of the theoretical density is increased, the extrusion billet is heated and then hot to the Pipe is pressed into place.

It has now been shown that with the extruder: Surface flaws received in the front part of the extruded product, which is why had that at the transition between the cover and the jacket there was a strong disturbance of the flow, which was due to the disturbing effect of the weld. This caused a significant loss of yield on the finished product.

The object of the present invention is to provide an envelope by which the yield of flawless pipes increased, d. H. The percentage of defective pipes is reduced after extrusion can be obtained.

According to the invention, this object is given by what is stated in the characterizing part of the main claim Features solved. The inventive design of the shell has the advantage that the flow properties can be improved during extrusion and the yield of defect-free tubes is increased.

In the case of the casing according to the invention, the inserts are preferably made of electrically conductive metal, in particular Soft iron or some other cheap metal.

Since when extruding the extrusion billets into tubes, glass is normally used as a lubricant and great demands on lubrication when

Extrusion presses, especially of stainless steel grades, are to be placed at higher temperatures, it is advantageous to have a front insert with a substantially flat end face to use.! to make an extrusion bolt with an essentially flat to get the front face, so that in the form of a glass washer on the front face of the Extruded bolt given lubricant is really exploited.

Advantageously, the inserts can be used as the shell be formed at the end closing cover, the inserts with the shell outer jacket and the Inner casing jacket can be welded tightly. Advantageously, between the inserts and the interior of the shell and sheet metal inserts are arranged, which are designed as a cover and with the Outer jacket and the inner jacket are tightly connected by welding.

In a preferred embodiment of the invention, an insert is provided on the front end face of the casing, which is funnel-shaped and has a central bore, the angle γ between the wall of the central bore for the inner casing of the casing and the conical surface of the funnel-shaped insert about 40 ° to 50 °, in particular 45 °.

In a further advantageous embodiment of the invention, at least on the front end face an annular insert provided with a central bore, the one substantially has flat end face, and its boundary surface between the wall of the central Bore and its largest outer diameter has an approximately circular arc-shaped cross-sectional profile, wherein the center points of the circular arc profile approximately in the area of the line of intersection between the flat end face and the central hole.

Another significant improvement of the casings and the extruded billets made therefrom and the Extruded tubes can be used in combination with the inserts described above or independently can be achieved by these inserts that at least the jacket of the shell over the entire circumference has approximately the same strength properties in the axial direction. Preferably at least the outer jacket is the casing according to the invention from a thin-walled, spiral-welded or extruded one Tube formed, iiine such a design of the outer jacket the sheath has the advantage that extruded tubes are obtained in which the failure rate and thus the rejects are noticeably reduced.

The pitch of the spiral formed by the weld seam is preferably in relation to the length dimension the shell so that the weld seam forms approximately a complete turn. One with such a The outer jacket provided for a weld seam points at each point along its circumference in the axial direction only one weld seam and approximately the same strength properties in the axial direction. Alternatively can the weld seam forms two, three or more complete turns.

The casings of the present invention are used to manufacture extrusion billets for extrusion of pipes made of stainless steel or high-alloy nickel steels, especially heat-resistant steels for Heat exchangers, e.g. B. high-alloy nickel steels with 80% nickel and 20% chromium, with the invention Sheath powders made of metal or metal alloys or mixtures thereof or mixtures of powders made of metals and / or metal alloys is filled with ceramic powders. As a powder is preferred spherical or predominantly spherical powder used with a medium diameter preferably below about 1 mm. Spherical powder is preferably used, which is in a protective gas, preferably an argon atmosphere, from the desired starting material, d. H. the desired metal and / or metal alloy has been produced by atomization. Powder particles are preferably used with a diameter greater than 1 mm, at least for the most part, screened off as there is a risk of that argon is enclosed in powder particles with a diameter greater than 1 mm. Such an inclusion of argon can be used during sputtering z. B. be done by turbulence. An argon inclusion would occur during extrusion cause unfavorable properties of the extruded pipes and lead to inclusion lines.

According to the invention, the shell for producing the bolts for the extrusion pipes is filled with the powder, the density of the powder filled in the casing being vibrated to about 60 to 71% of the theoretical Density is increased and the frequency of the vibration is preferably at least about 70 Hz, advantageously 80 to 100 Hz is selected. By vibrating at 80 to 100 Hz, a density of around 68 to 71% the theoretical density can be obtained.

After the powder has been filled in and compacted by means of vibration, the casing is closed, preferably after evacuation and / or filling with inert gas. After that, the density of the powder is determined by cold isostatic pressing with a pressure of at least 4000 bar, preferably 4200 to 6000 bar, especially 4500 to 5000 bar at least 80 to 93% of the theoretical density increased.

It has been shown that shells made of thin sheet metal, in particular sheet metal approximately 1.5 mm thick, are particularly are beneficial. The material used for the casing is preferably iron that is low in carbon, in particular with a carbon content less than 0.015%, especially less than 0.004%, is used to carburize the powder during heating and to prevent extrusion.

Through the aiiseiiigeii pressure in the Kalisosiai Pressing the casing is compressed and uniformly in both the longitudinal direction and in the radial direction then forms an extrusion bolt. This extrusion bolt should not have any irregularities as far as possible have, as these lead to difficulties in the extrusion of pipes.

In order to produce a bolt for extrusion of a pipe, a sleeve is used, which acts as an annular body is designed and the outer jacket is formed by a spiral-welded pipe section, the z. B. is made of an approximately 1.5 mm thick sheet metal.

Inside this outer jacket, there is an inner jacket, e.g. in the form of a longitudinally welded pipe section used, which has a smaller diameter, but the same wall thickness as the outer jacket. On one side, an annular cover is attached between the outer and inner casing and the Annular space between the two tubes closed on one side. Then spherical powder is in the ring roughness filled and by vibrating with z. B. 80 Hz compressed to about 68% of the theoretical density. then is evacuated and the other end face of the annular body through a corresponding second cover sealed. This is followed by a cold isostatic

Pressing in a liquid, e.g. B. water, with a Pressure of z. B. 4700 bar. The pressure on all sides results in an extrusion bolt with one density from Z. B. 88% of the theoretical density.

In the case of the casing according to the invention, the aim is for the spiral weld seam to be as smooth as possible and if possible, the properties of the sheet are not significantly changed. Therefore, the weld becomes preferable smoothed by rolling and / or by grinding. The smoothing of the weld seam by means of rollers can be done immediately after the welding process.

In the case of casings for the production of pipes, it can be useful not only to use the outer casing, but also also to manufacture the inner jacket from a tube that has roughly the same strength properties along its circumference in the axial direction Here, the inner jacket can either consist of a spiral-welded one Pipe or consist of an extruded pipe. The use of such a tube for the inner jacket is particularly useful for large dimensions. With smaller dimensions it is generally sufficient if the outer jacket of the shell is made from a pipe section running along its Has approximately the same strength properties in the axial direction.

In the following, the invention is explained in more detail using a schematic drawing of an exemplary embodiment explained

F i g. Fig. 1 shows an open-topped cover in elevation;

F i g. 2 shows a modified embodiment of the casing in longitudinal section; and

F i g. 3 shows a partial section of a further embodiment.

The shell is shown in FIG. 1 generally denoted by 1. The shell has an outer jacket 2 and an inner jacket 4. The outer jacket 2 consists of a spiral-welded pipe section with the length L. The weld seam 5 runs spirally over the circumference of the outer jacket 2, the spiral having a pitch angle λ which is dimensioned so that the spiral forms approximately one complete turn. It has been shown that it is expedient to arrange the weld seam 5 in such a way that it is between the weld seam 16, by means of which the in FIG. 1 cover of the shell, not shown, is welded to the outer shell 2, and the weld seam indicated at 16, by means of which the bottom of the shell is attached to the outer shell, forms a complete turn L ' denotes This length L' can be referred to as the effective length of the shell. It is useful to choose the helix angle ac of the spiral weld so that

tg * ^;

η ■ π · D

where D is the diameter of the shell and π is the number of desired turns which the spiral weld seam 5 should have. It has proven to be useful to choose η − 1. However, it can also be advantageous to choose η = 2, 3, 4 or equal to a larger whole number.

The outer jacket 2 and also the inner jacket 4 of the sheath 1 consisted of a practical example Sheet metal with a thickness of 1.5 mm and a carbon content of less than 0.004%. The in F i g. 1 not shown The cover was welded in along the weld seam 16 Powder, which for the most part consists of spherical particles with a mean diameter of less than 1 mm and which was produced from the desired starting material by sputtering in an argon atmosphere was filled into the envelope. After filling, the powder was vibrated at a frequency from 80 Hz to a density of about 68% of the theoretical density. It was then evacuated and the envelope closed by means of a lid. The lid was welded approximately along line 16 in F i g. 1 connected to the outer wall 2 of the shell. In the embodiment mentioned, the sheath had a Length of 600 mm and an outer diameter of 150 mm. The inner diameter of the inner jacket 4 was about 55 mm. The inner jacket 4 consisted of a longitudinally welded pipe section with a Longitudinal weld seam 6. The density of the powder was then determined by cold isostatic pressing with a pressure increased from 4700 bar to about 88% of the theoretical density. The extrusion billet thus obtained was, as described in DE-PS 24 19 014, extruded into a pipe

In the embodiment according to FIG. 2, an insert 30 and 40 are arranged both in the area of the lid 10 and of the base 20, which form the front and rear end faces of the shell. The front insert 30 is conical and has a central bore 32 for receiving the inner jacket 4 of the casing. The conical surface 36 of the conical or funnel-shaped insert 30 forms an angle γ with the wall of the bore 32 which is between approximately 40 ° and 50 ° and in particular 45 °. The insert 30 has an essentially flat end face 34. However, it is beveled or rounded at its outer edge at 35 and then initially has a cylindrical section 37 which merges into the conical surface 36. At 39, the transition from the conical surface 36 to the wall of the central bore 32 is rounded. The cover 10, which is designed as a sheet metal insert, corresponds in its contour exactly to that of the adjacent parts of the insert 30. In particular, the cover 10 has a cylindrical section 17 on the outer edge, which ensures that the cover 10 rests well on the outer casing 2, The outer edge of this cylindrical section 17 is connected to the outer casing 2 by means of a weld 16 is tightly welded to the inner jacket 4 Also, the ceiling! 10 has a rounding-off corresponding to the connection 39 of the insert 30.

In the area of the rear end face of the casing 1, an insert 40 forming an approximately flat plate is arranged which has a central bore 42 and an outwardly facing end face 44. This plate-shaped Insert 40 is also beveled or rounded at the edge at 45 and has an outer cylindrical section 47 on. The shell base 20 corresponds in its shape to the shape of the insert 40 and also has a outer cylindrical section 27 and an inner cylindrical section 29. The bottom 20 is means Weld seams 26 and 28 are tightly welded to the outer jacket 2 and the inner jacket 4. The inserts 30 and 40 are preferably made of soft iron.

In Fig. 3 is a modified embodiment of FIG Sheath shown, with one on the front face

the insert 130 provided for the shell has a substantially circular arc-shaped cross-sectional profile 136 and a flat end face 134 and a central bore 132. The centers of the circular arc-shaped Cross-sectional profiles 136 preferably lie approximately in the region of the line of intersection between the planar end face 134 and the wall of the bore 132, d. H. in the area of the front boundary line of the bore 132, and these center points are indicated at 138 and 138 '. The approximately circular arc-shaped cross-sectional profile 136 has the advantage that when the bolt is extruded, it is made of soft iron or a similar metal Insert 130 together with the cover UO, the welds 116, 118 and the adjacent parts of the outer jacket 102 and the inner jacket 104 form the first part of the tube, which is after extrusion is cut off or even falls off by itself if the connection to the preferably stainless steel Steel, made from the powder filling of the shell, no or insufficient subsequent pipe Has strength. Due to the approximately circular arc-shaped design of the boundary line 136 of the Insert 130 is achieved that the dividing line between the front, as waste section the extruded pipe and the actual pipe made of high quality stainless material sharp and formed as a separating surface extending essentially perpendicular to the pipe's longitudinal axis is. The cover 110 also has an approximately cylindrical section 117, which at 116 with the outer jacket 102 of the shell is welded, as well as an approximately cylindrical inner section 119, which is attached to the inner jacket 104 and tightly connected to the inner jacket at 118 by means of a circumferential weld seam is the transition from the wall of the central bore 132 to the circular cross-sectional profile 136 is rounded off at 139.

It can also be advantageous to connect the inserts 30 and 40 directly to the outer jacket 2 or the inner jacket 4 to be welded tightly. In this case, cover 10 and base 20 can be omitted. In an analogous way the insert 130 according to FIG. 3 directly welded tightly to the outer jacket 102 and the inner jacket 104 will.

When using sheet metal inserts as a cover or base, it can be useful to place the inserts on them 30, 40, 130 to be attached by spot welding. In many cases, however, it is also sufficient to use inserts 30, 40 and 130 through the crimped ends 15, 25 and 115 of the outer jacket 2 and 102 respectively.

The use in the area of the front face of the shell leads to a kind of tunnel effect during extrusion, if this insert is made of ductile material, e.g. B. ductile iron, soft iron, low-alloy carbon steel or cast iron, there is the pressure that is required in the recipient of the extrusion press for pressing is lowered if the front insert is made of ductile material and this material is easier to use Flow can be brought about as the powder filling of the extrusion bolt. Is the flow process that occurs during extrusion takes place, once initiated, it also affects the powder filling, even if the flow limit the powder filling is higher than the yield point of the ductile material of the insert; so it finds a species Tunnel effect instead

For this purpose 3 sheets of drawings

Claims (7)

Patent claims: 1. Metallfsche envelope of annular cross-section made of an outer and an inner jacket made of thin, preferably 1 to 2 mm thick, ductile sheet metal for receiving isostatically pre-pressed metal or alloy powders in the manufacture of extrusion bolts for the powder-metallurgical production of pipes, characterized in that on the front and / or rear end face of the casing (1) a substantially plate, cone, hemispherical or funnel-shaped insert (30, 130; 40) made of solid material is provided, which has a central bore (32, 132; 42) is provided for the inner jacket (4; 104) 2. Hüile according to claim 1, characterized in that the inserts (30, 40) are designed as the cover (1) at the end closing cover. 3. Case according to claim 2, characterized in that the inserts (30, 40) are welded to the outer jacket (2) and to the inner jacket (4). 4. Cover according to claim 1, characterized in that sheet metal inserts (10, 20) are arranged between the inserts (30, 40) and the interior (8) of the cover (1). 5. Case according to claim 4, characterized in that the sheet metal inserts (10, 20) are designed as a cover and are connected to the outer jacket (2) and to the inner jacket (4) by welds (16, 18, 26, 28). 6. Case according to one or more of claims 1 to 5, characterized in that the inserts (30, 40) are made of soft iron. 7. Cover according to one or more of claims 1 to 6, characterized in that at least the insert (30; 130) on the front end face of the cover (1) has a substantially planar end face (34; 134) .