DEVICE FOR THE MANUFACTURING OF CLOSED PROFILE SEMI-FINISHES BY MEANS OF A SOFT MAGNET POLYMER COMPOSITE IMPEDER

Description

[0001] The invention relates to a device for the production of closed profile semi-finished products according to the first claim and is used for inductive longitudinal seam welding.

[0002] The majority of steel pipes manufactured in Germany are longitudinally welded during the manufacturing process. Pipes produced in large quantities are generally manufactured continuously.

[0003] The processing chain essentially consists of coil feeding, sheet forming, sheet edge processing, longitudinal seam welding, calibration, heat treatment (if necessary), straightening, and cutting. In such a process with numerous processing steps, the processing speed is generally limited by the welding process.

[0004] Since high-frequency induction welding (HFI welding) allows for high welding speeds (up to 200 m / min) with good energy efficiency, it is the most widely used welding process in terms of output. A continuous pipe production line, consisting of an uncoiling unit, strip welding unit, strip storage unit, roll forming units, strip edge processing unit, longitudinal seam welding unit, heat treatment unit, straightening stands, and a flying band saw, involves high investment costs. Significant cost savings for pipe manufacturers can therefore be achieved, in particular, by increasing processing speed and reducing downtime. The process is especially well-suited for the production of small and medium-sized pipes up to a diameter of approximately 60 mm and / or thick-walled pipes.

[0005] The past two decades have seen significant improvements primarily in energy transformation. Advances in power electronics, such as IGBTs (Insulated-Gate Bipolar Transistors – up to approximately 400 kHz) and MOSFET-based converters (Metal Oxide Semiconductor Field-Effect Transistors – up to approximately 2 MHz), have enabled the efficient generation of increasingly higher-frequency currents. High-frequency currents generate high-frequency electromagnetic fields in an inductor. These fields induce eddy currents of the same frequency f in electrically conductive materials, leading to a local concentration of the current density distribution and, consequently, to local heating of the electrically conductive material through resistance heating. Examples of such conductive materials include metallic steel pipes.Locally confined heating of the pipe is particularly necessary with modern steel materials such as multiphase or low-alloy fine-grained steels to prevent softening of the area outside the weld. For many safety-relevant applications, a frequency of f = 100 kHz is therefore considered the lower limit. A high frequency increases the efficiency of energy transfer from the inductor to the pipe preform, and the local heating of the joining zone further reduces heat losses. Additionally, due to the so-called skin effect, a higher frequency must be selected for thin walls to limit heat input to the joining zone. High-frequency currents, however, reduce the effectiveness of conventional ferrite impeder cores. Since ferrites are currently the dominant material for impeders in the pipe industry, there is room for improvement in this area.

[0006] Another crucial factor influencing efficiency and the feasibility of high processing speeds is reducing leakage current, as leakage leads to undesirable heating of the pipe circumference. Impeder cores are used for this purpose. They increase the resistance of the current path along the pipe's back, resulting in an increase in the usable gap current. Small-diameter pipes have a small internal volume, so the volume of the impeder cores must also be small. This increases the demands on the impeder core's efficiency, particularly its saturation flux density. Current pipe welding systems operate at the performance limit of conventional ferrite impeders. Further increasing the processing speed is not possible, as this would require an increase in electrical power.This would primarily increase the leakage current, leading to heating of the pipe back and damaging the microstructure of modern metallic materials there, as well as complicating the processing of the overheated pipe body in the subsequent processing stages of upsetting and calibration. Therefore, high welding speeds of ≥ 70 m / min are currently only achieved with larger pipe diameters ≥ 50 mm.

[0007] In industrial settings, flow impeder systems are primarily used for high-temperature arc welding (HFI) of steel pipes and profiles. The achievable diameter range (D) is from D min = 10 mm to D max = 660 mm, with possible wall thicknesses from s min = 0.12 mm to s max = 25 mm. Applications with materials such as aluminum, zinc, or brass are also possible, although impeder systems are not suitable for every material.

[0008] Achievable profile shapes range from simple round or rectangular profiles to complex geometries.

[0009] To fully utilize material properties and ensure high process efficiency, a high operating frequency is particularly desirable in HFI longitudinal seam welding of thin-walled tubes. However, a high operating frequency limits the effectiveness of conventional impeder systems. Another process limitation is the usable impeder volume. New impeder materials with improved electromagnetic properties can further contribute to increased processing speeds and efficiency.

[0010] Impeder cores for HFI pipe welding are commercially available in a limited variety of geometric shapes, but from a material perspective, they are always soft magnetic ferrites. These are poorly or non-conductive ceramic materials made of iron oxide (FeₓO₅ and derivatives) that are sintered into the desired shape. Ferrites are very brittle and extremely difficult to machine using conventional methods. Therefore, they must be held in place by clamping systems.

[0011] Due to their poor machinability, geometries deviating from a circular cross-section are problematic. Equipment manufacturers and end users currently attempt to overcome this by bonding several smaller round impeder cores together. However, the uncooled and electromagnetically ineffective filler and bonding area represents a significant weak point. Such impeders therefore typically achieve very short service lives of only a few hours. The limited shape variety and machinability of ferrites also negatively impact the service life of circular impeder cores: The edges of the tube preform between the inductor and the weld point emit high levels of radiant heat. Weld spatter and arcing can also occur in this area, and scorch marks can detach. The ferrite core is usually protected from these undesirable sources of defects by a casing for a period ranging from two hours to one week.If the casing is worn, conductive pipe material residues are deposited on the electrically non-conductive impeder core. These are heated by eddy currents and thus destroy the ferrite. Increasing the thickness of the protective casing in the case of circular impeder cores can maintain protection for a longer period. However, this also reduces the electromagnetically effective volume of the impeder core along its entire length, thereby worsening the process.

[0012] The following properties of ferrites as impedance core materials are accepted due to a lack of alternatives in the current state of the art: 2. The saturation flux density is relatively low ∘ Limitation of the magnetic energy density ∘ Limitation of the welding speed 2. The permeability is very high ∘ High concentration of magnetic flux density in the edge regions of the impeder core ∘ Temperature increase in near-edge layers of the ferrite core ∘ Increase in the thermal losses of the impeder core ∘ Cascade-like deterioration of the volumetric power of the impeder core ∘ Increase in the leakage current ∘ Deterioration of the overall process efficiency ∘ Limitation of the welding speed 2. Brittle material character of ferrites ∘ Mechanical machinability of ferrites is severely limited ∘ Use of internal metallic (CuZr,austenitic steels) Tension rods for fixing ∘ metallic tension rods are heated by the EM field ∘ additional heating of the impeder core ∘ deterioration of the overall process efficiency 2 strong temperature dependence of the magnetic properties ∘ near-surface cooling channels difficult to manufacture + partial protective elements cannot be placed ∘ use of outer shells for water cooling of the surface of ferrite cores ∘ increase in distance impeder core - pipe inner wall ∘ increase in leakage current ∘ deterioration of the overall process efficiency ,

[0013] The current state of the art shows that the impeder core is a critical component in a pipe manufacturing line. Ferrites are currently the dominant impeder core materials. However, they have significant disadvantages with regard to saturation flux density, permeability, machinability, and the temperature sensitivity of their electromagnetic properties. These properties have a particularly negative impact on small and medium pipe diameters, where the impeder core volume is limited.

[0014] From an economic perspective, impeder systems are highly relevant plant components in HFI pipe welding lines.

[0015] The internal ferrite impeder, which is still state of the art and a reference solution, is known from US 3,037,105 A. The design of the impeder core from dynamo sheets as an alternative material variant is described in US 4,596,913 A. Cooling an impeder core by means of backflow is known from US 4,443,677 A.

[0016] An external impeder made of soft magnetic composites is known from publication US 2008 / 0308550 A1.

[0017] For industrial applications such as induction hardening, soft magnet polymer composites have been developed for field guidance and focusing of electromagnetic fields. These composite materials consist of electrically insulated soft magnet particles and temperature-resistant polymers such as PTFE as the matrix material. During the manufacturing process, the particles are pressed together with the polymers, resulting in a high particle packing density and a homogeneous particle distribution. Primary applications include induction hardening and heating tasks in the packaging and automotive industries.

[0018] The polymer matrix material thus improves the mechanical properties of the composite compared to ceramic ferrite, enabling the material to be machined by milling, turning, and drilling. Polymers like PTFE are very good electrical insulators. This is advantageous because the formation of eddy currents must be avoided in field guide elements such as impedance cores. These would lead to the destruction of the component through direct Joule heating. Furthermore, polymers like PTFE possess excellent chemical resistance. This is necessary because cooling lubricants as well as various lubricating oils and greases are used continuously in the process. Figure 1As a temperature-stable plastic, it can be used at temperatures up to 250 °C, and briefly even up to 300 °C. However, these temperature limits are significantly lower than those of ceramic ferrites. Furthermore, the low thermal conductivity of PTFE (0.24 W / (m·K)) and WMPK (0.04–0.06 W / (m·K)) as well as the high power dissipation of WMPK (PV ∼ 50–65 W / cm³) are thermal disadvantages. Therefore, impeder cores made of WMPK must be specially protected against weld spatter, melt pools, or electric arcs. The thermal decomposition of the impeder core represents a significant technical risk for the development of an impeder system with an industrially usable service life.

[0019] The use of soft magnet polymer composites for inductive longitudinal pipe welding is known from the publications by MS Milicevic and VM Milicevic, "Impeder for HF inductive welding of steel tubes", IEE Proceedings-Science, Meas. Technol., vol. 149, no. 3, pp. 113-116, 2002" and "Quality Improvement of Steel Pipes Produced by Seam Welding with New Magneto-Dielectric Impeder", Mater. Trans., vol. 47, no. 6, pp. 1464-1468, 2006, doi: 10.2320 / matertrans.47.1464". Energy savings of [amount missing] were achieved through the use of composites available at that time. 45% of pipes with diameters of 21.3 mm (wall thickness s = 2.65 mm) and 26.9 mm (wall thickness s = 2.5 mm) were welded, and a potential increase in processing speed of 90% was predicted. Furthermore, the use of a WMPK impeder resulted in a comparatively very fine-grained microstructure in the weld seam. Commercial applications for WMPK impeders are not yet known.This has several causes. Firstly, the geometries of the ferrite impeders were adopted for the WMPK impeders without any modifications. Secondly, specific solutions for cooling and protecting the poorly thermally conductive composites were lacking. This can lead to a short service life due to overheating or destruction of the impeder cores. Since Milicevic's research, further optimized materials have become available, exhibiting improved material properties with regard to their suitability as impeder cores.

[0020] The object of the invention is to develop a device for the production of closed profile semi-finished products, whereby the use of an impeder core, for example made of composites of soft magnets and polymers, as the impeder core material in HFI tube welding aims to improve the process from an economic and technical perspective. A reduction in manufacturing costs can be achieved by increasing the welding speed and the associated improved plant utilization. A further objective is to reduce energy consumption in the overall process, thereby simultaneously lowering manufacturing costs and improving the process's environmental footprint. Concentrated energy input into the weld seam also reduces weld bead thickness and the volume of the weld swell. This can eliminate the need for subsequent seam processing, such as weld removal or seam rolling, in some applications.Furthermore, the quality of the weld seam and the mechanical properties of the pipe, in particular with regard to maximum hardening, ductility, and defects arising from process discontinuities, are to be improved. An additional objective of the invention is to increase the service life of the impeder system, which, due to necessary tool changes, results in a reduction in the downtime of the entire pipe manufacturing plant and a reduction in the overall process costs.

[0021] This problem is solved using the features of the first patent claim.

[0022] Advantageous embodiments result from the dependent claims.

[0023] The invention relates to a device for manufacturing closed profile semi-finished products by means of inductive longitudinal seam welding, comprising an impeder core and an inductor that can be inserted into a profile semi-finished product and wherein the inductor envelops the profile semi-finished product at least partially during the joining process and forms a joining zone on the profile semi-finished product, wherein, according to the invention, the impeder core consists of a soft magnet polymer composite and does not have a protective covering enveloping the impeder core, wherein a protective component is arranged on the top side of the impeder core pointing towards the joining zone.

[0024] According to the invention, the protective component is therefore only partially arranged on the impeder core in the area or region of the joining zone.

[0025] The protective component does not enclose or surround the impeder core.

[0026] This saves material for the protective component and makes the tool - the impeder - consisting of impeder core and protective component easier and cheaper to manufacture.

[0027] It is still possible to extend the dwell times and thereby make the entire process more cost-effective.

[0028] To protect the impeder from spatter and the resulting overheating, industrial pipe welding systems use protective covers that completely enclose the impeder. However, these reduce the usable impeder volume and therefore also the efficiency of the process. According to the invention, protective components are selectively attached to the critical points of the impeder, thus protecting the impeder with only a minimal reduction in effective volume.

[0029] The protective component is preferably designed in the form of a plate or as a segment of a hollow cylinder.

[0030] The protective component is particularly preferably arranged in or on a corresponding shaped element of the impeder core. The shaped element can be designed as a groove or a flat.

[0031] In an advantageous embodiment, the protective component is positioned directly at an outer end of the impeder core and extends at least partially along the impeder core and parallel to its longitudinal axis.

[0032] In a preferred embodiment, the protective component is only attached to the upper surface of the impeder and in a further embodiment can consist of one or more components.

[0033] The protective component has a high temperature resistance (melting temperature > 800 °C) and can be made of, for example, aluminum oxide Al 2 O 3, which is characterized above all by good wear resistance and a relatively low cost level.

[0034] Furthermore, one or more protective components can be designed as flat semi-finished products or as profile components.

[0035] The length of the protective component depends on the specific application, whereby the protective component may, for example, be located only directly at the welding point or extend to the entire length of the impeder core.

[0036] The impeder core can consist of a single impeder core element or a segmented multi-part impeder core and at least partially of a composite of soft magnetic materials in the form of particles or platelets and one or more polymers.

[0037] A preferred variant of the impeder core has at least one continuous cooling bore through which a liquid or gaseous cooling medium can flow.

[0038] The impeder core is preferably cooled by means of a cooling medium arranged between the pipe and the impeder core.

[0039] The impeder core can be designed as a flow impeder or as a backflow impeder such that, as a flow impeder, a cooling medium is guided outside and / or inside along the impeder core in the process direction.

[0040] In a reflux impedance system configuration, the cooling medium is guided along the outside in the process direction and returned through the interior of the impedance core. Alternatively, the cooling medium is guided through the interior of the impedance core in the process direction and returned along the outside.

[0041] By utilizing cooling via the cooling medium located outside the impeder core, heat dissipation preferably occurs primarily into this cooling medium, with the cooling medium particularly preferably extending to the height of the protective component.

[0042] In an advantageous embodiment, the device has means for adjusting the inclination angle α of the impeder core axis with respect to the longitudinal axis of the profile semi-finished product.

[0043] Particularly preferred are the essential external dimensions of the impeder core designed such that the impeder core has a distance of s ≤ 2 mm, preferably s ≤ 1 mm, to the internal dimensions of the profile semi-finished products for profile semi-finished products with internal dimensions below 30 mm, and a distance of s ≤ 3 mm, preferably s ≤ 2 mm, to the internal dimensions of the profile semi-finished products for profile semi-finished products with internal dimensions above 30 mm in the area of ​​a weld point on the profile semi-finished product.

[0044] The term internal dimension corresponds to the average internal diameter d for profile semi-finished products, especially tubes and profiles with the distance dx between the respective opposite sides of the internal geometry.

[0045] Semi-finished profile products include tubes or closed profiles. Closed profiles can be, for example, rectangular box profiles or complex profile geometries.

[0046] The profile semi-finished products are preferably made of steels, aluminium and aluminium alloys, nickel and nickel alloys, copper and copper alloys or other metallic materials as well as combinations thereof.

[0047] The device according to the invention, for the first time, does not have a circumferential protective shell. The elimination of the circumferential impedance protection shell allows for an increase in the diameter of the impedance core, thereby increasing the efficiency.

[0048] For the protection of the impeder core, a preferably ceramic protective component is used for the first time, instead of a circumferential protective shell.

[0049] Replacing an impedance protection sleeve with a ceramic protective component allows for an increase in impedance volume. This results in improved efficiency, which can lead to increased welding speed and / or a reduction in welding power.

[0050] The use of soft magnet polymer composites allows for an increase in the saturation flux density in the impeder to more than B sat ≥ 900 mT, thereby increasing the system's efficiency. Comparable competing methods have a saturation flux density of B sat ≥ 500 mT.

[0051] The desired reduction in energy consumption can also be attributed to the material properties of the soft magnet polymer composites and the associated improvement in efficiency. The electrical power Pel at the generator at a constant feed rate has resulted in a reduction of the electrical power Pel compared to the electrical power Pel* required by competing processes.

[0052] In one embodiment, when welding ferritic steel tubes with an outer diameter x wall thickness of D12 x 1.15 mm at a production speed of 75 m / min, the distance between the impeder core and the inner tube wall can be reduced to approximately 1 mm. Compared to the required generator power of Pel = 58 kW in a conventional, state-of-the-art setup, this can be reduced to as low as Pel = 33 kW by using the optimized impeder. This corresponds to an energy saving of approximately 43%.

[0053] The service life can also be increased with the solution according to the invention, whereby the service life of the impeder of the device according to the invention should reach ts ≥ 24 h. Competing methods generally achieve service lives of ts * = 4 - 24 h.

[0054] Inductive high-frequency, medium-frequency or multi-frequency longitudinal seam welding is used.

[0055] The invention is explained in more detail below using an exemplary embodiment and accompanying drawings.

[0056] They show: Figure 1 shows a sectional view of the pipe cross-section through a device according to the invention, Figure 2 shows a sectional view of the side view of the device according to the invention. Figure 1 The device shown, Figure 3 the ratio of the dimensions of an impeder core without a protective component and a profile semi-finished product, Figure 4 an inclination angle adjustment of the impeder core without a protective component in the profile semi-finished product, Figure 5 an inclination of the protective component in relation to the impeder core axis.

[0057] The Figures 1 and 2Figure 1 shows an embodiment of a device for welding tubular profile semi-finished products R, wherein this is carried out by means of inductive high-frequency, medium-frequency, or multi-frequency longitudinal seam welding and is constructed with the components described according to the invention. The device has an impedance core 1 and an inductor 2. The profile semi-finished products / tubes R shown in the embodiment preferably consist of conventional carbon steel. The inductor 2 is positioned in front of the upsetting roller center point (not shown).

[0058] The impeder system lacks a surrounding protective casing. The elimination of the surrounding impeder protective casing allows for an increase in the diameter of the impeder core.

[0059] Instead of a circumferential protective shell, a ceramic protective component 3 is used to protect the impedance core. This protective component 3 is designed as a ceramic plate, so that it covers the entire area under the inductor 2 up to the weld point SP (see Figure 2The ceramic protective component 3 protects against spatter. In the exemplary embodiment, it has a length of Iceramic = 80 mm and a thickness of sceramic = 1 mm. In this application example, a groove is milled into the impeder core, and the ceramic component is bonded into it. The ceramic component is positioned directly at the impeder outlet, i.e., the end where the welding process takes place. This ensures that the critical area of ​​the inductor is completely traversed. This critical area is exposed to high flux density and, consequently, to the risk of supersaturation, as well as particularly intense impeder heating. Furthermore, the impeder core in the critical area is exposed to the risk of weld spatter. The ceramic component protects the impeder core in the critical area from direct contact with weld spatter by dissipating heat and by reducing the material volume in the area particularly exposed to intrinsic heating.

[0060] The impedance core is designed as a cylinder, for example with or without cooling fins or cooling grooves on the outer shell (cooling fins or cooling grooves are not shown) and can have a continuous internal bore 4 for supplying cooling water. This reduces manufacturing effort and increases the impedance core volume in the particularly relevant edge region. Alternatively, internal cooling can be achieved through multiple cooling bores in a configuration not shown. However, it is also possible to construct an impedance core with cooling fins and / or cooling grooves (not shown) on the outer shell.

[0061] In the application example, this internal bore has a diameter of, for example, 3 mm. A cooling medium flows through the cooling bore. The cooling bore allows for the defined supply of cooling media and thus effective and monitorable cooling inside the impeder core. There, the materials according to the invention are at risk of overheating due to their relatively low thermal conductivity.

[0062] Such a design can be advantageous for larger impeder diameters. Furthermore, the cooling of the outside of the impeder core 1 is achieved by a cooling medium SW between the impeder core 1 and the profile semi-finished product R, which is supplied by additionally "flooding" the profile semi-finished product R, according to [reference to relevant document]. Figures 1 and 2 This is guaranteed. Such flooding is carried out by means of added swath water.

[0063] Figure 3Figure 1 shows the relationship between the dimensions of the impedance core 1 and the profile blank R. The essential outer dimensions of the impedance core 1 have a distance of s to the inner diameter d of a round profile blank R, here a tube with a round cross-section. A distance s ≤ 2 mm applies to inner dimensions less than 30 mm. A distance s ≤ 3 mm to the inner diameter of the profile blank R applies to profile blanks R with inner dimensions greater than 30 mm.

[0064] In the case of a rectangular design of the profile semi-finished product R with an inner length d 1 and d 2, the corresponding distance s 1 , s 2 between impeder core 1 and inner wall of the profile semi-finished product R is to be selected according to the distance s.

[0065] A tilt adjustment is included in the Figure 4 The device has means to deflect the longitudinal axis 5 of the impedance core 1 relative to the longitudinal axis 6 of the profile semi-finished product R by the angle α.

[0066] An inclined arrangement of an impedance protection component 3 at the angle β relative to the impedance core axis 5 is in the Figure 5 depicted.

[0067] The invention enables the realization of highly economical inductive longitudinal seam welding of single-layer sheets or metallurgically clad sheets for the production of single- or multi-layer steel tubes. Reference symbol list

[0068] 1 Impeder core 2 Inductor 3 Protective component 4 Bore 5 Longitudinal axis of the impeder core 6 Longitudinal axis of the profile semi-finished product RProfile semi-finished product / pipe SWCooling medium / trailing water I Ceramic length s Ceramic thickness sDistance dInner diameter d1, d2Inner length s1, s2Distance at inner length d1, d2 αAngle βAngle

Claims

1. Device for manufacturing closed semi-finished profile products by means of inductive longitudinal seam welding, comprising an impeder core (1) which can be inserted into a semi-finished profile product (R), and an inductor (2) which surrounds the semi-finished profile product (R) at least in some regions during the joining process and forms a joining zone on the semi-finished profile product (R), wherein the impeder core (1) consists of a soft magnetic polymer composite, characterized in that the device has no protective cover surrounding the impeder core (1), wherein a protective component (3) is arranged at least on the side of the impeder core (1) facing the joining zone.

2. Device according to claim 1, characterized in that the protective component (3) is plate-shaped, designed as at least one plate-shaped segment and / or as at least one segment of a hollow cylinder.

3. Device according to claim 1 or 2, characterized in that the protective component (3) is arranged in or on a corresponding form element of the impeder core (1).

4. Device according to one of the preceding claims, characterized in that the protective component (3) is positioned directly at an outer end of the impeder core (1) and extends at least in some regions along the impeder core (1) and parallel or at an angle (ß) to its longitudinal axis (5).

5. Device according to one of the preceding claims, characterized in that the impeder core (1) consists of a single impeder core element or a segmented multi-part impeder core (1).

6. Device according to one of the preceding claims, characterized in that the protective component (3) consists of one or more components.

7. Device according to one of the preceding claims, characterized in that the impeder core (1) consists at least partially of a composite of soft magnetic materials in the form of particles or platelets and one or more polymers.

8. Device according to one of the preceding claims, characterized in that the impeder core (1) has at least one continuous cooling bore (4) through which a liquid or gaseous cooling medium can flow.

9. Device according to claim 7, characterized in that the impeder core (1) can be cooled by means of a cooling medium arranged between the semi-finished profile product (R) and the impeder core (1), wherein the impeder core (1) is designed as a flow impeder or as a return flow impeder in such a way that, as a flow impeder, a cooling medium is guided on the outside and / or inside along the impeder core (1) in the process direction, and, in the form of the backflow impeder system, a cooling medium is guided along the outside in the process direction and returned through the interior of the impeder core (1) or guided through the interior of the impeder core (1) in the process direction and returned along the outside.

10. Device according to one of the preceding claims, characterized in that the device has means for adjusting the angle of inclination α of the impeder core (1) relative to the longitudinal axis (6) of the semi-finished profile product (R).

11. Device according to one of the preceding claims, characterized in that the absence of the protective cover increases the impeder core volume, wherein the essential outer dimensions of the impeder core (1) have a distance of s ≤ 2 mm from the internal dimensions of the semi-finished profile product (R) for semi-finished profile products (R) with internal dimensions of less than 30 mm and a distance of s ≤ 3 mm from the internal dimensions of the semi-finished profile product (R) for semi-finished profile products (R) with internal dimensions of more than 30 mm (R).