EP1294501A1

EP1294501A1 - Method and device for producing steel, especially stainless steel press fittings.

Info

Publication number: EP1294501A1
Application number: EP01933971A
Authority: EP
Inventors: Walter Bauer; Jürgen NÄGELER; Walter Viegener
Original assignee: Witzig and Frank Turmatic GmbH
Current assignee: Witzig and Frank GmbH
Priority date: 2000-06-30
Filing date: 2001-05-16
Publication date: 2003-03-26
Anticipated expiration: 2021-05-16
Also published as: US20040003645A1; WO2002002255A1; CZ20024128A3; DK1294501T3; DE50107057D1; CN1438923A; DE10031989B4; US6843096B2; ATE301513T1; BR0111978A; BR0111978B1; EP1294501B1; SK286457B6; PT1294501E; CN1208145C; SK18012002A3; JP2004501773A; ES2247111T3; DE10031989A1

Abstract

Special steel press fittings are produced in two process steps, which can be performed simultaneously, or also one after the other. The cut to size blank is widened in a die is upset in order to form the desired pipe connection areas.

Description

Method and device for producing press fittings made of steel, in particular stainless steel

For pipe installation, both for heating pipes and for drinking water installation or for gas pipes, press fittings have increasingly come into use as connection technology, which are used to connect pipe ends to one another and to produce pipe branches. 'Press fittings are pushed onto the respective pipe ends in order to produce the pipe connection, an O-ring held in an annular bead of the press fitting producing a fluid-tight connection. The press fitting is then plastically deformed radially inwards on a correspondingly provided press area, as a result of which it is mechanically secured at the pipe end. The compounds thus obtained can be produced reliably and are stable over the long term.

Depending on the pipe material, press fittings made of the same material are required. Copper press fittings are used to install copper pipes. EP 0649689 B1 deals with the manufacture. Longitudinally or transversely divided dies are used to manufacture these copper press fittings, into which a correspondingly preformed blank with a widened tube end is to be inserted. The inner shape of the die has an annular groove which defines the outer shape of an annular bead to be formed on the press fitting. To form this ring bead, an upsetting device with a support mandrel is used, which is inserted for support into the open tube end of the blank lying in the die. In order to make the wall material of the blank flow into the annular groove, the upsetting device has a trailing or upsetting sleeve with which the tube end is axially compressed in the die. The wall material of the press fitting flows plastically into the ring groove. In order to then reliably design the seat for the 0-ring with the required precision, the support mandrel and the follower sleeve are removed from the tool and a rolling process is carried out. For this purpose, a rotatably mounted roller held on a finger is used, which is inserted into the pipe end and pressed radially outwards against the ring bead to be formed. The roll now runs a number of times, rolling the corresponding ring bead. This process is specially designed and suitable for the production of copper press fittings. It requires a blank whose outer dimensions match the receiving space of the die so that it fits snugly in the die. The blank must therefore first have the corresponding rough shape before upsetting to form the ring bead. To do this, it must be expanded at its end areas. This step must be carried out beforehand. After inserting the pre-expanded blank into the die, it is cut to size. A compression and rolling step is then carried out in the die on the pre-expanded and calibrated (cut to length) blank in order to produce the desired ring bead. Copper press fittings are obtained which have a ring bead set back against the pipe mouth. A pressing of the press fittings is possible with appropriate pressing tools or pressing tongs, which at the same time capture the parts of the fitting on both sides of the O-ring, which means that a very good mechanical connection between the pipe end and the press fitting is obtained even when using copper as the fitting material.

The tools for pressing the press fittings are specifically designed for the special shape of the press fittings. When using other shaped press fittings, the installer must purchase new tools.

Stainless steel press fittings for stainless steel pipe installation are generally designed so that an 0-ring seat is formed directly at their free end. A typical representative of such press fittings can be found in EP 0361630 B1. This press fitting has one Connection section, the inside diameter of the

Outside diameter of a pipe to be connected is expanded. At the end of the press fitting, the wall of the press fitting is first bent radially outwards and then flanged inwards to form an annular bead. Such press fittings cannot be pressed with the same tools as are already used for copper press fittings that have a pressing area on both sides of the O-ring.

The production of press fittings requires machines and processes with which press fittings can be reliably produced in very large numbers. In order to achieve reliable pipe connections, the press fittings have to be manufactured with small tolerances. This must be possible at the lowest possible manufacturing costs. Accordingly, the machine or device for producing the press fittings should be of simple and robust construction and still be able to reliably produce press fittings of the desired quality.

Based on this, it is an object of the invention to provide a device and a method for producing press fittings, in particular made of stainless steel, with which press fittings of the desired quality and with the required process reliability can be produced in a simple manner. In addition, it is an object of the invention to provide press fittings made of stainless steel, which can be produced inexpensively and used in practice.

This object is achieved by a method for producing press fittings according to claim 1 and by a Device for producing press fittings according to claim 6 solved.

Steel tubing is used to manufacture the press fittings, from which pieces are cut to length. The cut-to-length pipe sections are formed into a press fitting in an integrated process step with two sub-steps, the two process sub-steps being designed in such a way that they can be carried out directly in succession in one tool without an intermediate step.

To manufacture the press fittings, the pipe sections that have been cut to length are expanded and provided with an annular bead that serves as an O-ring seat. The widening and beading (ie the formation of the bead) thus takes place in one go. Between the two partial steps of the process, the press fitting does not have to be transported to another tool, nor does it have to be processed, for example recalibrated or cut to length. The sequence of steps is accordingly cutting to length, widening, beading. Because the processing and beading can be combined to form a forming stage that can be carried out in a single processing station, the processing machine manages with a reduced number of processing stages. The combination of the expansion and the beading on the machine for producing the press fittings allows a very considerable reduction in the design and construction work, which ultimately results in a considerable reduction in the cost of the stainless steel press fittings. On the other hand, it has been shown that in spite of the absence of an intermediate calibration between the expanding and the crimping, ie despite the combination of the two individual steps to form an integrated process step, have the desired press fittings manufactured in the required dimensional accuracy and quality, so that fault-free pipe connections can be made with the press fittings manufactured in mass production.

In the method, the diameter of the pipe end of the blank is preferably widened by more than twice the wall thickness. This creates the possibility of starting from a blank that has been cut to length from the pipe material of the type that is to be connected to the press fittings in the later installation. No special pipe material is therefore required for the production of the press fittings, which in turn lowers costs and simplifies production. The widening of the pipe ends also has the effect that an insertion end is formed on the press fitting to be produced, which limits the axial insertion depth of the pipe to be connected. This creates defined conditions, so that the crimp connection to be produced receives the required axial tensile strength.

To carry out the method, a mandrel for expanding the pipe end of the blank is first inserted into the same axially under pressure. The conical front end of the mandrel expands the tube end, which is stretched in the circumferential direction and thus abuts the outer cylindrical lateral surface of the mandrel with a radially inward force. The outside diameter of the mandrel and the inside diameter of a corresponding section of a form receiving the blank are coordinated with one another in such a way that the wall of the expanded blank now also, at least almost, lies against the inside wall of the form. In the now following Process step which can overlap with the expansion step, ie can begin before this has ended, the tube end is subjected to a compressive axial force, for example by means of an annular shoulder provided on the mandrel or a separate pressure sleeve. Surprisingly, the material of the wall of the pipe end bulges outward in a ring area provided in the form of an annular groove despite the radially inward bias due to the axial compressive force, the stainless steel material expanding in the circumferential direction even further than in the expansion step happen. To do this in the illustrated form, a stainless steel material with high compressive strength and toughness is required. The stainless steel material often used in the water pipe installation meets these requirements.

The method is suitable for producing the press fittings from a welded pipe material. In the area of the weld produced, for example, by the laser welding process, there may be a surface texture that is not suitable for the tight fit of a 0 • ring. This can be the case in particular if the pipe material has been welded from the outside. This can be remedied by reworking the upsetting step, especially the weld. This can be done, for example, in a rolling process by repeatedly rolling from the inside, in particular the weld seam area. As a rolling process, for example, a so-called roller burnishing can be carried out, in which a roller carried by a finger and rotatably mounted is inserted into the tube end and rolled along an orbital path in the formed bead. Preferably several thousand, preferably more than ten thousand repetitions are carried out in which the roller is pressed radially outwards. In particular, the weld area is smoothed here. Alternatively, the ring groove can be ground. In some cases, it may be sufficient to only grind the weld area. While roller burnishing has the advantage of closing pores and craters by closing them, particularly short cycle cycles and particularly good bead geometries can be obtained in the grinding process.

The press fittings to be produced can have one, two, three or more pipe ends - depending on the application. The simplest application is a straight pipe connector with two pipe ends. End caps have only one pipe end. Branch pieces can have three or more pipe ends, the blanks of such branches being produced in a preparatory work step in such a way that corresponding straight pipe ends are present in the desired number. If elbow fittings are to be produced, a piece of pipe cut to length is first bent in a corresponding shape, after which the process steps discussed above are then carried out.

The device suitable for producing the press fittings has a combined expansion and compression Station to which at least one multi-part tool, a processing mandrel and a compression element belong. The expansion mandrel and the compression element can be combined with one another in one part or formed separately. Both elements, the expansion mandrel and the compression element, are used on the same tool (shape) simultaneously or in succession. The combined expansion and compression station is therefore a single processing station in which both expansion and beading are carried out without an intermediate step. The upsetting and crimping in only one processing station enables a particularly cost-effective, yet precise manufacture of press fittings, ie the manufacture of the press fittings as a mass-produced product in a quality that permits reliable production of long-term tight press connections.

The tool preferably has a receiving space which has a plurality of sections, ie at least a first and a second section, which have a different diameter and merge into one another at an annular shoulder. The diameter of the first section preferably corresponds to the outside diameter of the unexpanded blank, while the blank of the second section should correspond approximately to the outside diameter of the blank after the expansion step has been carried out. The annular shoulder formed between the first and the second cutout serves to fix the outer shape of the press fitting in the transition from its non-expanded to its expanded area. In addition, the annular shoulder can serve as a stroke limiter for the expansion mandrel, in particular if its drive device does not determine the stroke depth. The tool can be divided parallel to the longitudinal direction of the pipe end or transversely to it. In the case of parallel division, the tool (the mold) is formed by two mold halves, the dividing line of which is essentially at the same level as the center line of the blank. The annular groove formed in the mold halves for fixing the outer shape of the bead to be formed is present in both mold halves and is unchangeable in its axial extent. In contrast, the transverse division of the mold half permits the creation of a dividing line in the center of the annular groove, so that the axial extent of the annular groove can be varied. It is particularly advantageous here to move the mold during the expansion and / or compression process in such a way that the annular groove gradually closes, ie reduces its axial extent from a larger dimension to the target dimension. This makes it possible to first cry out a larger area of the tube wall, which may make the bulging wall better conform to the shape of the annular groove. It is essential, however, that the annular groove is closed before wall material has penetrated too far outwards, ie into the gap between the mold halves.

It is possible to combine the expanding mandrel and the compression element by forming an annular shoulder on the expanding mandrel. Here the upsetting element and the expanding mandrel always run synchronously, which results in high process reliability and a simple tool. If necessary, the compression element can, however, be a separately driven pressure sleeve which is displaceably mounted on the mandrel, which rests on the tube end and compresses it after the tube end has been fully expanded. Here it is possible to use the pressure sleeve, e.g. actuated by way of control or force-controlled to achieve optimal production results. In any case, the stroke of the pressure element is dimensioned such that the material of the pipe end bulges outwards in the area of the annular groove, but is not pushed together to form a flat disk flange. This is preferably achieved by controlling the pressure element. In contrast, the expanding mandrel can be connected to its drive device, for example with the interposition of a relatively hard spring, so that it runs resiliently against the annular shoulder between the first section and the second section of the tool.

The device can additionally be provided with a roller station. This can be arranged in a separate processing station if a very fast work cycle is desired. However, it is preferred to also integrate the roller station into the expanding and upsetting station. The roller station includes a roller rotatably mounted on a finger and a drive device with which the finger is inserted into the flared and beaded tube end and moved there in a circular motion until the bead formed, in particular in the area of a possible weld seam of the tube wall, has the desired shape Has. Instead of the roller station, a grinding device can also be provided.

With the method and the device, press fittings made of stainless steel can be produced, which have a widened pipe end and in this a ring bead for receiving an O-ring as a sealing element. The special feature of these stainless steel press fittings is that on both sides of the O-ring, ie the ring bead, there are tubular squeeze areas of the same diameter and approximately the same axial length that can serve as the squeeze area. The stainless steel press fitting is pressed on both sides of the O-ring with a pipe end to be connected. This not only increases the assembly security and the strength of the connection, but also the acceptance in the market and also allows the use of crimping tools, as they have been used for copper press fittings.

Advantageous embodiments of the invention are the subject of the drawing, the description or the subclaims.

Exemplary embodiments of the invention are illustrated in the drawing. Show it:

1 shows a device for producing press fittings, with a tool, a mandrel and a compression element, during the expansion step, before compression, in a schematic sectional illustration,

2 shows the tool according to FIG. 1, after completion of the expanding step and the upsetting step, in a schematic sectional illustration,

3 shows the tool according to FIG. 1 during a rolling process,

4 shows a modified embodiment of a device for producing press fittings during the expansion step, in a schematic sectional illustration development,

5 shows the device according to FIG. 4, after completion of the expansion and compression step, in a simplified and schematic sectional illustration,

6 shows a further embodiment of a device for producing press fittings, during the expansion step, in a schematic sectional illustration,

Fig. 7 shows the device. FIG. 6, after expansion and compression, in a schematic sectional illustration,

8 shows a further embodiment of the device according to the invention, with a movable die, during the upsetting process, in a schematic sectional illustration,

FIG. 9 shows the device according to FIG. 8, at the end of the two processing operations (expansion and compression) in a schematic sectional illustration, and

10 shows a finished stainless steel press fitting for connecting two stainless steel pipes, in a schematic sectional illustration.

FIG. 1 illustrates a device 1 for producing press fittings, as can be seen, for example, as a straight press fitting 2 from FIG. 10. The device 1 according to FIG. 1 is used for the production of curved press fittings, for which purpose pre-bent, cut and tubular blanks 3 with constant inside and outside diameters are assumed.

The device 1 has a mold or die 5 held and divisible on a base 4, which encloses a receiving space 6 with a first section 7 and a second section 8. The first section 7 of the receiving space 6 has an inner diameter which corresponds to the outer diameter of the blank 3. The second section 8 serves to receive a pipe end 9 of the blank 3, which will form the later squeezing area of the press fitting to be formed. The inside diameter of the essentially cylindrical second section 8 of the receiving space 7 is larger than the outside diameter of the non-deformed pipe end 9. The inside diameter of the second section 8 is preferably larger by approximately twice the wall thickness of the pipe end 9 than the outside diameter of the undeformed pipe end 9. In the transition between a conical ring shoulder 11 is provided in both sections 7, 8 of the interior 6. At a certain distance from the ring shoulder 11 and preferably at a still greater distance from the open end 12 of the receiving space 7, an annular groove 14 is formed in the tool 5, which defines the outer contour of an annular bead 15 to be formed on the press fitting 2. The annular groove 14 forms a closed ring of constant, approximately semicircular, cross section. The tool 5 illustrated in FIG. 1 is divided parallel to a longitudinal direction 16 of the receiving space 6. The longitudinal direction 16 coincides with the two axial directions of the open tube ends of the blank 3.

The tool 5 includes an expansion mandrel 18, a compression element 19 and a drive device 21 for this. The expansion mandrel 18, the compression element 19, the drive device 21 and the tool 5 form a combined expansion and compression station 22 of the device 1.

The expanding mandrel 18 is a cylindrical element provided on its end face with a chamfer 23, the outside diameter of which is slightly larger than the outside diameter of the pipe end 9 which has not yet been expanded. The chamfer 23 defines a conical annular surface, the diameter of which is immediately following the end face of the Expansion mandrel 18 is smaller than the inner diameter of the unexpanded tube end 9. The chamfer 23 includes an acute cone angle, which is dimensioned such that the expansion mandrel 18 can be pushed into the tube end 9 without widening the tube end 9 in front of it. The length of the expanding mandrel 18 is greater than the distance between the annular shoulder 11 and the annular groove 14.

The expanding mandrel 18 is rigid and possibly integrally connected to the upsetting element 19, which in the embodiment of the device 1 according to FIG. 1 is formed by a cylinder body which merges into the cylindrical expanding mandrel 18 with a stepped or annular shoulder-like transition 25. The cylinder body has one Outer diameter that exceeds the inner diameter of the expanded pipe end 9. The outer diameter of the cylinder body is preferably smaller than the inner diameter of the second section 8 of the interior 6, so that the mandrel or body formed from the expansion mandrel 18 and the cylinder body can move into the second section 8 of the receiving space 6 of the tool 5.

The drive device 21, which in the present exemplary embodiment is formed by a hydraulic drive, serves to actuate and move this combined expansion and compression mandrel. This includes a piston 26, which divides a working space 28a and a further working space 28b into a cylinder space 27. The piston 26 is connected, for example, via a piston rod 29 to the expansion mandrel 18 and the compression element 19. Fluid channels, not further illustrated, serve to selectively apply pressurized hydraulic fluid to the working spaces 28a, 28b. As a result, the piston rod 29 can be moved in a targeted manner in both axial directions in the direction of the arrows 31, 32.

The device 1 described so far operates as follows:

It is assumed that tubular blanks 3 with a constant diameter are cut to length and pre-bent; This is inserted into the tool 5, after which the tool is closed. The blank 3 protrudes with its pipe end 9 into the section 8 of the receiving space 6, whereby it does not abut the tool 5 here. Due to the curvature of the blank 3, it is axial in the tool 5 fixed. The mandrel 18 is in its rightmost position in FIG. 1 and is not yet in contact with the pipe end 9. Fluid is now applied to the working space 28b, as a result of which the piston 26 and with it the piston rod 29, the compression element 19 and the Expanding mandrel 18 can be moved towards the tool 5, as indicated by the direction of the arrow 31. The expansion mandrel 18 rests with its chamfer 23 on the end surface of the pipe end 9, which is preferably deburred and optionally provided with a small internal and external chamfer. Due to the continued axial movement of the expansion mandrel 18, this penetrates into the tube end 9, without essentially pushing it together. Due to the now occurring expansion of the wall of the pipe end 9 in the circumferential direction, a certain shortening of the pipe end 9 can occur. The widened tube end 9 lies under tension on the lateral surface of the expansion mandrel 18. This slides further and further into the interior of the pipe end and expands longer and longer sections of the pipe end. Even before the chamfer 23 reaches the ring shoulder 11, the compression element 19, ie the corresponding step 25 (ring shoulder), is placed on the end face 9a of the pipe end 9. As the piston 26 moves further, the pipe end 9 is now compressed, as a result of which the wall of the pipe end 9 spontaneously bulges outwards against its own radially inward bias in the region of the annular groove 14. This is done on the entire scale. The length of the upsetting stroke is dimensioned such that the upsetting process is ended when the wall of the tube end 9 lies completely in the annular groove 14. This is illustrated in Figure 2. The compression stroke is approximately as long as the difference between the wall length of the ring bead and the axial length of the same. The length of the stroke can be dimensioned by appropriate design of the drive device 21, for example by limiting the piston stroke accordingly. Once the working stroke has been completed, that is to say the pipe end 9 has been expanded and compressed, as illustrated in FIG Extend from tool 5 and release the press fitting. This can now be removed from the mold 5 by opening it and inserting a new blank 3, after which the work cycle explained above is repeated. Only a single piston stroke of the piston 26 is therefore required to produce the press fitting. The manufacture is effective and precise.

Particularly in the event that the blank 3 has been cut to length from a welded tube, it is advisable to connect a further work step, which can be carried out in the same tool 5 or in a separate tool. In the example illustrated in FIG. 3, use is made of the former possibility. The blank 3 is already compressed and remains in the form 5 for the rolling step. A rolling device 34 is used to carry out the rolling step. This includes a finger-like carrier, on the free end of which a roller 36 is rotatably mounted, the diameter of which is significantly smaller than the inner diameter of the widened pipe end 9. The carrier 35 is connected to a drive and positioning device 37, which is set up to rest the roller 36 against the wall. Then the carrier is moved so that the roller 36 move into the interior of the tube end 9 and then move in the radial direction so that the roller 36 executes a circular movement in the formed ring bead 15. For example. the roller burnishing process is carried out for 2 to 4 seconds at a speed of more than 5000 rpm. This results in more than 10,000 revolutions, which ensure sufficient smoothing of the ring bead on its inside, in particular in the area of any weld seam. Alternatively, a driven grinding wheel can be provided instead of the roller 36, which grinds over the entire ring bead 15 or only the area of the weld seam.

A modified embodiment of the device 1 is illustrated in FIG. 4. Insofar as the device 1 corresponds to the device 1 according to FIG. 1, the same reference symbols are used and reference is made to the above description.

In contrast to the device 1 described above, the device 1 according to FIG. 4 has a drive device 21 with separate drives 21a, 21b for the expansion mandrel 18 and the compression element 19. The expansion mandrel 18 is provided on its side remote from the chamfer 23 with a blind bore 40, from which a compression spring 41 is received. This is supported on the bottom of the blind bore 40. A piston rod 42 of a hydraulic piston 43 plunges into the blind bore 40. The hydraulic piston 43 is arranged in a hydraulic cylinder 44 and divides two working spaces 45a, 45b there. The expansion mandrel 18 can be moved in both directions 31, 32 by targeted application of pressure to the working spaces 45a, 45b. The stroke of the piston 43 is so great that the expanding mandrel 18 can run against the annular shoulder 11. This serves as a stroke limiter for the piston 18. The spring 41 is so hard that it is not compressed or is not compressed significantly when the expansion mandrel 8 is inserted into the pipe end 9. This causes a precise shaping of the diameter transition of the blank 3 from the expanded pipe connection area 9 to the non-expanded area. In addition, the device 1 becomes insensitive to positioning tolerances between the tool 5 and the drive device 21.

A further special feature of the embodiment of the device 1 illustrated in FIG. 4 lies in the compression element 19. This is designed as a sleeve which is slidably mounted on the expansion mandrel 18. The sleeve is provided with its own drive device 21a, which includes a piston 47 mounted in a cylinder 46. This divides two working spaces 48a, 48b, which can be selectively and selectively acted upon by hydraulic fluid. In this way, the sleeve can be moved in a targeted manner in the direction of the arrows 31, 32 in order to attach its end face to the end face 9a of the pipe end 9 and to compress the pipe end 9. Both drive devices 21a, 21b can be controlled independently of one another, as a result of which the widening and upsetting of the pipe end 9 can be optimized. In particular, this embodiment has its meaning if the tools 5 have to be changed frequently on one machine in order to be able to produce different press fittings.

While FIG. 4 illustrates the widening of the pipe end 9, FIG. 5 shows the state of the device 1 after the end of the upsetting step. The widening mandrel 18 has pressed the tube wall firmly against the inner shoulder 11. The tube end 9 is fully expanded and the sleeve is immersed so far in the tool 5 and has compressed the tube end 9 so far that the tube wall just fills the annular groove 14 and thus the desired bead 15 is formed.

A further embodiment of the device 1 is illustrated in FIG. Insofar as there is agreement with the above embodiments, reference is made to the above description based on the same reference numerals.

In contrast to the embodiments described above, the tool 5 of the device 1 is not only divided into two, but into three parts. In addition to its division parallel to the longitudinal central axis 16, it is divided in a plane that lies in the annular groove 14. A tool part 5a is thus present, which can be attached to the remaining tool 5 before, during or after upsetting. A corresponding cylindrical seat 50 is used for centering. The tool part 5a is preferably attached to the seat 50 on the tool 5 before the upsetting step begins. For this purpose, the tool part 5a is moved towards the tool 5 in the direction of arrow 31 by means of a corresponding positioning device. The positioning device also carries the drive device 21 for actuating the expansion mandrel 18 and the compression element 19. If both processing steps, ie expansion and compression, have been carried out, the device 1 has the state illustrated in FIG. The piston 26 is now withdrawn from the pipe end 9 by pressurizing the working space 28a. After that the tool part 5a is moved away from the tool 5 in the direction of the arrow 32. The pipe end 9 is thereby partially released. After opening the remaining tool 5, the press fitting 3 can now be removed. The advantage of this embodiment is that the tool part 5a holds the other two parts of the tool 5 together on the seat 50 and that a precisely working tool can be built up in a simple manner, in particular in the region of the annular groove 14.

A modified embodiment of the device 1 illustrated in FIGS. 6 and 7 is shown in FIGS. 8 and 9. While in the embodiment described above (FIGS. 6 and 7) the expansion mandrel 18 and the compression element 19 were movably guided and driven relative to the tool part 5, the expansion mandrel 18 in the embodiment of the device 1 according to FIGS. 8 and 9 is rigid on the tool part 5a held and the compression element 19 is designed as an annular pressure surface 25 'on the tool part 5a. Overall, this is connected to a drive device (not illustrated further) and can be specifically moved in the direction of the arrows 31, 32.

Following its half 14b of the annular groove 14, the other half 14a of which is accommodated in the rest of the tool 5, the tool part 5a has a bore 52 which is reduced to the diameter of the expansion mandrel 18 at a certain distance from the annular groove half 14b. This passes through the rest of the bore 52. At its end it is provided with an end plate 18 'which is clamped against an abutment 53 by the tool part 5a. The unit formed from abutment 53, Tool part 5a and expansion mandrel 18 can be moved as a whole towards and away from tool 5 by means of the drive device. The distance between the annular surface 25 'and the annular groove 14 is in turn dimensioned such that when the molds 5, 5a are closed, the widened tube end 9 is compressed to such an extent that the bulging tube wall just fills the closing annular groove 14. This is illustrated in Figure 9. A three-part shape and a single drive device are used here both for the expansion mandrel 18 and the compression element 25 '.

Press fittings 2 can be produced with the above-described devices and the corresponding method, as illustrated by way of example in FIG. 10. Such a stainless steel press fitting is produced from a welded piece of pipe, the weld seam 60 of which is illustrated schematically in FIG. 10. It has one, two or more pipe connection areas 61, 62 which are hollow-cylindrical in total. Each pipe connection area 61, 62 has two hollow cylindrical sections 61a, 61b; 62a, 62b, between each of which the annular bead 15 is arranged. The two cylindrical sections 61a, 61b; 62a, 62b have the same inner diameter. They form squeeze areas for connecting pipes. The pipes to be connected are then mechanically connected to the press fitting 2 on both sides of the respective O-ring 63.

The method presented allows the production of stainless steel press fittings practically in a single operation, which comprises two process steps that can take place simultaneously or in succession. From the- elongated blank is expanded and compressed in a tool in order to form the desired pipe connection regions 61, 62. The process has proven to be reliable for stainless steel press fittings. Other pressure-resistant and tough metals can also be used. The method is particularly suitable in connection with a subsequent rolling or grinding step for the production of press fittings from welded stainless steel pipe.

Claims

Claims:

1. Method for producing press fittings, in particular press fittings made of steel, in particular stainless steel, starting from blanks with at least one pipe end in each case,

with a first method step, in which at least the pipe end is picked up by a tool and expanded with a mandrel whose outside diameter exceeds the inside diameter of the end, by pushing the mandrel axially into the pipe end, and

with a second method step, in which the tube end is compressed axially in the same tool immediately following the first method step in order to bend an annular region of the tube end radially outward into an annular groove formed in the tool.

2. Process for the production of press fittings, characterized in that in the first process step the diameter of the pipe end is widened by more than twice the wall thickness of the pipe end.

3. A process for the production of press fittings, characterized in that the mandrel inserted into the pipe end in the first step remains in the pipe end during the implementation of the second step.

4. Process for the production of press fittings, characterized in that the blank is made from a welded stainless steel pipe.

5. A process for the production of press fittings, characterized in that a cut piece of welded stainless steel pipe is used as a blank.

6. Device (1) for producing press fittings, in particular press fittings made of steel, in particular stainless steel, starting from blanks (3), each with at least one pipe end (9),

with a combined expansion and compression station (22), which includes at least the following elements:

a multi-part tool (5) which has a receiving space (6) for the blank (3), the receiving space (5) for receiving the pipe end (9) of the blank (3) at least a first section (7) with the same diameter as the blank (3) and a second section (8) with an inner diameter that is larger than the outer diameter of the pipe end (9), the second section (8) having an annular groove (14) on its inner surface, in order to determine the outer shape of an annular bead to be formed on the pipe end (9),

an expansion mandrel (18) which is axially movable into and out of the section (8) of the receiving space (6) and connected to a drive device (21) and whose outside diameter exceeds the inside diameter of the pipe end (9) and is less than the inside diameter of the section (8) into which the expansion mandrel (18) is to be inserted, so that between see the expansion mandrel (18) and the inner surface of the section (8) an annular space is defined, the radial thickness of which corresponds approximately to the wall thickness of the press fitting (3), and

a compression element (19) which is axially movable towards and away from the annular groove (14) of the tool (5) and is connected to a drive device (21) and which has an annular pressure surface (25) which is set up to to be brought into contact with the pipe end (9) and to compress the pipe end (9).

7. The device according to claim 5, characterized in that the interior (6) of the tool (5) between the first section (7) and the second section (8) has an annular shoulder (11).

8. The device according to claim 5, characterized in that the tool (5) is formed in two parts and divided along a surface which is arranged parallel to the pipe longitudinal direction (16) of the press fitting (9).

9. The device according to claim 5, characterized in that the tool (5) transverse to the longitudinal direction of the tube

(16) of the blank (3) is divided.

10. The device according to claim 5, characterized in that the expansion mandrel (18) via a spring means (41) is connected to its drive device (21b).

11. The device according to claim 5, characterized in that the expansion mandrel (18) with its Drive device (21) is rigidly connected.

12. The apparatus according to claim 5, characterized in that the expansion mandrel (18) is rigidly connected to the compression element (19) and the drive device (21) for the expansion mandrel (18) also forms the drive device (21) for the compression element (19) ,

13. The apparatus according to claim 5, characterized in that the compression element (19) and the expansion mandrel (18) have mutually independent drive devices (21a, 21b).

14. The device according to claim 9, characterized in that a part (5a) of the tool (5) is rigidly connected both to the expansion mandrel (18) and to the compression element (19).

15. The device according to claim 5, characterized in that the device (1) additionally has a rolling device (34).

16. The device according to claim 5, characterized in that the device additionally has a grinding station with a grinding wheel which can be moved into the pipe end (9) and is transferred in a radial movement into the ring bead (15) in order to carry out a grinding operation in this.

17, press fitting of stainless steel, with a designed as a pipe end (9) connection area in which an annular bead is formed (15) for receiving an O-ring (63), to which ^'on both sides for pressing with connect hollow cylindrical regions (61a, 61b; 62a, 62b) serving a tube.