DE2846659A1 - Powder filled capsule for use as extrusion blank - for making stainless steel or nickel-chromium alloy tubes, is isostatically pressed after filling - Google Patents

Abstract

The blanks are extruded into tubes or bars made of stainless steel or alloy steel with high Ni content, and esp. heat resisting tubes contg. 80% Ni, 20% Cr, and used in heat exchangers. The capsules are made of sheet metal, 1-2mm thick, contg. 0.015% C, esp. 0.004% C, and have a peripheral bulge. The capsule is filled withspherical grains of metal or alloy powder made by shotting, esp. in Ar atmos and the powder may include ceramics. The filled capsule is vibrated at 80-100 Hz, so that powder has 60-71% of the theoretical density, and is then sealed and cold isostatically pressed at >=4000 bars, pref. 4500-5000 bars, to attain min. 80-93% density. The bulge on the capsule disappears during the pressing operation. Defects are reduced due to the use of a bulge-free blank and the tubes have precise dimensions.

Description

description

Capsules and pellets for extruding objects, esp.

Tubes, and Methods of Making the Capsules and Compacts Additive to P 24 19 014.5-24 The present invention relates to a development of the main patent ................ (patent application P 24 19 014.5-24).

The main patent ............. (patent application P 24 19 014.5-24) concerns a method of making stainless steel pipes that are uniform Structure as well as uniform physical and chemical properties and good Have further processability, with powder from such steel in metallic Capsules filled and the closed capsules by means of pressure acting on all sides are compressed and the compact thus obtained is extruded into tubes, and steel powder produced by atomizing melt in inert gas from predominantly spherical particles is used. thin-walled capsules made from a ductile metal are used whose wall thickness a maximum of about 5% of the outer diameter of the capsule is the density of the steel powder filled in the capsule Vibration and / or ultrasound increased to about 60 to 70% of the theoretical density and the density of the steel powder by cold isostatic pressing of the capsule by means of a pressure of at least 1500 bar to at least 80%, preferably 80% to 93% of the theoretical density is increased, the compact is heated and then hot, preferably at temperatures of at least about 12000C to the desired one Semi-finished product is extruded.

According to the main patent (patent application P 24 19 014.5) it can be advantageous be that you have the metallic capsules, which are filled with the steel powder, before after closing evacuated and / or with a gas, in particular an inert gas, e.g. argon. Furthermore, according to the main patent ...........

(Patent application P 24 19 014.5-24) preferably metallic capsules used whose wall thickness is less than 3%, in particular less than 1% of the outer diameter the capsule is and in particular metallic capsules used, their wall thickness is between about 0.1 to 5 mm, preferably between about 0.2 and 3 mm.

According to the procedure according to the main patent ....................

(Patent application P 24 19 014.5-24) composite pipes can also be produced, where one uses thin-walled metallic capsules, which by one or more concentric partitions in two or more areas are separated and one the predominantly spherical powder particles of the various steel grades filled in one of these areas while vibrating at the same time, then the partitions removed and the capsules sealed, followed by cold isostatic pressing and the extrusion is carried out at an elevated temperature. When extruding the compacts glass is usually used as a lubricant for pipes.

It has now been shown that the compacts often deviate from show the ideal shape and therefore to difficulties and rejects when extruding to lead.

It is the object of the present invention to provide a capsule and a compact to create in which these difficulties of the known designs avoided and in which the rejects and defective products are as low as possible are.

This object is achieved in that at least the The shell of the capsule has approximately the same strength properties over the entire circumference having axial direction.

Preferably at least the outer jacket of the capsule is according to the invention formed by a thin-walled, spiral-welded or extruded pipe. One Such a design of the outer shell of the capsule offers the advantage that extruded Products, especially pipes, are obtained in which the error rate and thus the rejects are noticeably reduced.

The slope is preferably that formed by the weld seam Measure the spiral in relation to the length of the capsule so that the weld seam is approximately forms a complete turn. One provided with such a weld seam Outer jacket has only one at each point along its circumference in the axial direction Weld seam and in the axial direction approximately the same strength properties. Alternatively, the weld seam can form two, three or more complete turns.

The present invention is applicable to capsules and compacts for extruding objects, especially pipes, rods or similarly profiled, elongated, dense, metallic objects, in particular made of stainless Steel or high-alloy nickel steels, especially heat-resistant steels for heat exchangers, E.g. high-alloy nickel steels with 80% nickel and 20% chromium, whereby in the invention Capsule powder made of metal or metal alloys or mixtures thereof or mixtures of powders made of metals and / or metal alloys filled with ceramic powders will. The powder used is preferably spherical or predominantly spherical Powder used, with an average diameter preferably below about 1 mm. According to the invention, spherical powder is used, which is in a protective gas, preferably Argon atmosphere, from the desired starting material, i.e. the desired metal and / or metal alloy has been made by atomizing. Powder grains are preferably used here with a diameter greater than 1 mm, at least for the most part, screened, because there is a risk that in powder grains with a diameter greater than 1 mm Argon is included. Such inclusion of argon can occur during atomization e.g. caused by turbulence. An inclusion of argon would be unfavorable during extrusion Induce properties of the extruded articles and lead to inclusion lines.

According to the invention, the capsule for producing the compacts for the tubes to be extruded filled with the powder, the density of the in the capsule filled powder by vibration to about 60 to 71% of the theoretical density is increased and wherein the frequency of the vibration is preferably at least about 70% Hz, advantageously 80 to 100 Hz is chosen. By vibrating at 80 to 100 Hz, a density of about 68 to 71% of the theoretical density can be obtained.

After filling and compacting the powder by means of vibration the capsule closed, preferably after evacuation and / or filling with inert gas. After that, the Density of the powder by cold isostatic pressing with a pressure of at least 4000 bar, preferably 4200 to 6000 bar, especially 4500 up to 5000 bar, with at least 80 to 93% of the theoretical density increased.

It has been shown that capsules, which are generally made of thin sheet metal, preferably about 1 to 2 mm thick sheet metal, especially about 1.5 mm thick sheet metal, especially are beneficial.

The material used for this capsule is preferably low-carbon iron, especially with a carbon content of less than 0.015%, especially less than 0.004 t, to prevent carburization of the powder during heating and extrusion.

Due to the pressure on all sides during cold isostatic pressing, the Capsule compressed uniformly both longitudinally and radially and then forms a compact. This compact should not have any irregularities have, since these lead to difficulties during extrusion, especially during extrusion of pipes, lead.

In order to produce a compact for extruding a pipe, a capsule is used, which is designed as an annular body, the outer jacket this ring body is formed by a spiral-welded pipe section which e.g.

is made of an approximately 1.5 mm thick sheet.

Inside this outer jacket, an inner jacket, e.g.

used in the form of a longitudinally welded pipe section, the one smaller diameter, but the same wall thickness as the outer jacket. An annular cover is attached to one side between the outer and inner casing and the annular space between the two tubes is closed on one side. Then it will be spherical powder is filled into the annular space and vibrated at e.g. 80 Hz compressed to about 68% of the theoretical density. Then it is evacuated and the other one End face of the annular body sealed by a corresponding second cover. This is followed by cold isostatic pressing in a liquid, e.g. water, with a pressure of e.g. 4700 bar. The all-round pressure gives you one Compact with a density of e.g. 85 t of the theoretical density.

In the case of the capsule according to the invention, the aim is that the spiral-shaped The weld seam is as smooth as possible and, if possible, the properties of the sheet metal changed significantly.

Therefore, the weld seam is preferably by means of rolling and / or by means of Loops smoothed. The smoothing of the weld seam by means of rollers can be carried out immediately to the welding process.

In the case of capsules for making tubes, it may not be useful only the outer jacket, but also the inner jacket from a pipe to manufacture that along its circumference approximately the same strength properties in the axial direction Has direction. The inner jacket can either consist of a spiral-welded one Pipe or consist of an extruded pipe. Applying an extruded or spiral-welded pipe for the inner jacket is particularly important for large dimensions expedient. For smaller dimensions, it is generally sufficient if the According to the invention, the outer casing of the capsule is made from a pipe section, which along its circumference has roughly the same strength properties in the axial direction Has direction.

In the following the invention is based on a schematic drawing explained in more detail using an exemplary embodiment: FIG. 1 shows a capsule for production of pellets for extruding pipes in a perspective view, the Capsule is open at the top.

The capsule is denoted generally by 1 in FIG. 1. The capsule 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 in a spiral over the circumference of the outer jacket 2, the spiral having a pitch angle Oc, which is dimensioned so that the spiral forms approximately one complete turn.

It has been shown that it is useful to arrange the weld 5 so that they are between the weld 16, by means of the one not shown in FIG Lid of the capsule is welded to the outer shell 2, and the weld seam indicated at 16, by means of which the bottom of the capsule is attached to the outer shell, a complete Forms turn. The distance between the weld seams 16 and 26 is shown in FIG L 'denotes. This length L 'can be referred to as the effective length of the capsule. It is advisable to select the helix weld angleoC so that tg X = L 'n ff' D, where D is the diameter of the capsule and n is the number of desired Turns that the spiral weld seam 5 should have. It has been found to be functional proven to choose n = 1. But it can also be advantageous, n = 2, 3, 4 or to be chosen equal to a larger whole number.

The outer shell 2 and also the inner shell 4 of the capsule 1 passed in a practical example made of sheet metal with a thickness of 1.5 mm and a carbon content less than 0.004%. The cover not shown in Fig. 1 was along the weld seam 16 welded in. To produce the compact was powder, which was predominantly Part made of spherical Grains with a medium diameter under 1 mm and that by atomization in an argon atmosphere from the desired starting material made of stainless steel, for example, was filled into the capsule. To the powder was filled with vibration at a frequency of 80 Hz densified a density of about 68% of the theoretical density. It was then evacuated and the capsule closed by means of a lid. The lid was made by welding connected approximately along the line 16 in FIG. 1 to the outer wall 2 of the capsule. the Capsule had a length of 600 mm and a length in the embodiment mentioned Outside diameter of 150 mm. The inner diameter of the inner jacket 4 was approximately 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 increased with a pressure of 4700 bar to about 85 t of the theoretical density. Of the The compact obtained in this way was, as described in the main patent, extruded to form a tube.

All information and characteristics disclosed in the documents, in particular the disclosed spatial arrangement, insofar as they are used individually or in combination are new compared to the prior art, claimed as essential to the invention.

Claims (9)

Claims 1. Capsules for compacts for extruding objects, esp. of pipes, rods or similarly profiled, elongated, dense, metallic Objects, especially made of stainless steel or high-alloy nickel steels, especially heat-resistant steels for heat exchangers, e.g. high-alloy nickel steels with 80% nickel and 20% chromium, the capsule made of thin, preferably 1 to 2 mm thick and preferably low in carbon, a carbon content less than 0.015%, preferably less than 0.004%, comprising sheet and in the Capsule powder made of metal or metal alloys or mixtures thereof or mixtures of powders made of metals and / or metal alloys filled with ceramic powders is, which is preferably made of spherical or predominantly spherical Grains consists in a protective gas, preferably argon atmosphere, from the desired starting material are produced by atomization and where the density of the powder filled in the capsule by vibration with preferably 80 to 100 Hz is increased to about 60 to 71 t of the theoretical density and after Seal the capsule with the density of the powder by cold isostatic pressing a pressure of at least 4000 bar, preferably 4200 to 6000 bar, in particular 4500 to 5000 bar, further increased to at least 80 to 93% of the theoretical density is, in that at least the outer jacket (2) of the Capsule (1) along its circumference approximately the same strength properties in the axial direction Has direction. 2. Capsules according to claim 1, characterized in that g e k e n n -z e i c h n e t, that at least the outer jacket (2) is spiral welded. 3. Capsules according to claim 1, characterized in that g e k e n n -z e i c h n e t, that at least the outer jacket (2) is extruded. 4. Capsules according to claim 1 or 2, characterized in that g e k e n n -z e i c h n e t that the pitch (oil) of the spiral formed by the weld seam (5) in the The relation to the length (L) of the capsule (1) is dimensioned so that the weld seam (5) forms about one, two or more complete turns. 5. Capsules according to one or more of claims 1, 2 and 4, characterized it is not noted that the spiral weld seam is made by means of rolling and / or Grinding is smoothed. 6. Compact for extruding objects, especially pipes, rods or similarly profiled, elongated, dense, metallic objects, in particular stainless steel or high-alloy nickel steels, in particular heat-resistant steels for heat exchangers, e.g. high-alloy nickel steels with 80% Nickel and 20% chromium, in that it is a capsule (1) according to one or more of claims 1 to 5. 7. A method for producing capsules according to one or more of Claims 1 to 5, characterized in that at least -the outer jacket the capsule is made from a spiral-welded or extruded pipe section will. 8. The method according to claim 7, characterized in that g e k e n n -z e i c h n e t that the pitch of the spiral weld seam in relation to the length of the pipe section is chosen so that the weld seam of the pipe section is about one, two or more forms complete turns. 9. A method for producing compacts according to claim 6, characterized It is noted that the capsules are produced according to claim 7 or 8 will.