APPARATUS AND METHOD FOR PREFORMING A METAL STRIP FOR THE MANUFACTURE OF ROLLED AND WELDED TUBES

Abstract

An apparatus and method for preforming a metal strip (40) for manufacturing welded and rolled tubes, comprising an engraving tool (20) and a strip edge chamfering tool (30), wherein the engraving tool comprises an engraving roller (1) having a cylindrical surface (2) with a central engraving portion (3, 3'), and the strip edge chamfering tool comprises an edge chamfering roller (31) comprising a recessed central section (34) and side sections (35) on each side of the central section, and an anvil roller (32), wherein the edge chamfering roller (31) and the anvil roller (32) are configured to receive and pass the metal strip in a clearance (33) formed between the rollers, wherein the clearance (33) has a reduced height in the side sections, which are positioned through which the longitudinal side edges of the metal strip will pass.so that the longitudinal side edges on each side of the metal strip, and on the engraved side of the metal strip, are beveled when it passes between the pair of rollers (31, 32).

Description

APPARATUS AND METHOD FOR PREFORMING A METAL STRIP FOR THE MANUFACTURE OF ROLLED AND WELDED TUBES TECHNICAL FIELD The present invention relates to an apparatus for preforming a metal strip for the manufacture of rolled and welded tubes and a method for preforming a metal strip. BACKGROUND OF THE TECHNIQUE Welded tubes and pipes are typically manufactured by longitudinally forming flat strips of metal into a nearly complete tube and then welding the two ends together. There are many application areas for rolled tubes, for example, in the HVAC&R (Heating, Ventilation, Air Conditioning, and Refrigeration) market. Within this technical field, environmental demands are driving the development of more efficient air conditioning and refrigeration equipment. In response, efforts have been made to supply smaller diameter tubes with a wide range of internal surface improvements, capable of increasing their heat transfer coefficient compared to standard solutions. Manufacturing methods for advanced products, such as small-diameter welded tubes with an internal surface pattern for heat exchange applications, should yield... Gana Ln / zznz / E / YiAi results in products with minimal unwanted internal irregularities to achieve optimal flow and heat transfer properties. With increasing demands for cost reduction, there has been interest in providing an alternative to copper tubing, which has traditionally dominated use in air conditioning and refrigeration equipment, in the form of aluminum tubing. Therefore, it is desirable to find a way to manufacture aluminum tubing with characteristics that are competitive for applications such as those in the HVAC&R field. SUMMARY OF THE INVENTION This description relates to an apparatus for preforming a metal strip for the manufacture of welded and rolled tubes, comprising an engraving tool and a strip edge chamfering tool. The engraving tool comprises an engraving roller having a cylindrical surface with a central engraving portion. The strip edge chamfering tool comprises an edge chamfering roller with a recessed central section and side sections on each side of the central section, and an anvil roller, configured to receive and pass the metal strip in a clearance formed between the rollers. The clearance has a reduced height in the side sections, which are located in Γΐ?ηα Ln / zznz / E / YiAi a position through which the longitudinal side edges of the metal strip will pass, so that the longitudinal side edges on each side of the metal strip, and on the engraved side of the metal strip, are beveled as they pass between the pair of rollers. Preferably, the engraving tool comprises the cylindrical surface of the engraving roller, and said surface comprises the central engraving portion and the side portions arranged on each side of the central portion, said central portion being provided with an engraving pattern and said side portions being free of the engraving pattern, and the central section of the strip edge chamfering tool is dimensioned such that an engraving pattern on a metal strip passing between the pair of rollers through the edge chamfering space is not affected by the rollers. The strip edge chamfering tool (30) is preferably separate from the engraving tool and arranged downstream of the engraving tool in a direction of travel (T) of the strip to be preformed. Alternatively, the engraving tool and the strip edge chamfering tool can be integrated to comprise a combined engraving and edge chamfering roller, so that the central engraving part is Γΐ?ηα Ln / zznz / E / YiAi included in the central section of the free space for edge beveling. The first and second rollers are shaped such that the clearance includes a central section sized so that an etched pattern on a metal strip passing between the rollers is unaffected. The clearance also includes side sections on either side of the central section, where the clearance height is reduced. These side sections are positioned so that the longitudinal edges of the metal strip pass through them, such that the longitudinal edges on each side of the strip, on the side facing the etching roller, are beveled as they pass between the rollers. This minimizes the weld bead height of the finished rolled and welded tube. Advantageously, when the strip edge chamfering tool is arranged downstream of the engraving tool in a direction of displacement (T) of the strip to be preformed, the engraving pattern in the central portion of the engraving roller preferably comprises a plurality of grooves arranged on the cylindrical surface of the central portion, and the cylindrical surface of each side portion is preferably level with the cylindrical surface of the central portion between the grooves, which further contributes to Γΐ?ηα ίη / ζζηζ / Ε / γίΛΐ reduce the inside height of the weld bead. The engraving roller may consist of a pack of rollers with a central engraving pattern and side rollers, where the side rollers are arranged on each side of the pack of rollers with the central engraving pattern, and where the pack of rollers with the central engraving pattern has a cylindrical surface forming the central part and the side rollers have cylindrical surfaces forming the side parts. This allows flexibility in the choice of the engraving pattern. The cylindrical surface of the engraving roller preferably has a total width of 15 mm or more, and the central part of a suitable engraving roller has a width that is 85 to 99% of the total width. The central section of the clearance between the first and second rollers of the strip edge chamfering tool has a width equal to or greater than the width of the central portion of the engraving roller to ensure that the engraved pattern in the central portion of the strip is not affected by passing through the edge chamfering tool. The first roller of the edge chamfering tool roller pair is preferably designed to include a recess with outward-sloping side edges on each side of the recess, running along the circumference of the cylindrical surface of the first roller. The sloping side edges are Γΐ?ηα Ln / zznz / E / YiAi conveniently inclined at an angle of 30 to 60°, preferably 43 to 47°, to provide sufficient edge beveling. The side sections of the clearance between the first and second rollers may suitably have a width such that for each of the side sections is equal to or greater than half the difference between the total width of the engraving tool (Wl) and the width of the central part of the engraving tool (W2). The present description further relates to a method for preforming a metal strip comprising engraving a pattern on the strip in a central portion along its longitudinal direction, while the side portions on each side of the central portion of the strip are rolled without an engraved pattern, and chamfering the longitudinal side edges of the strip on the side bearing the engraved pattern. During chamfering, the strip material at the longitudinal side edges is pressed down to 20-60% of the strip thickness, preferably 35-40%, thereby forming a beveled edge surface along the longitudinal side edges of the strip to minimize the internal weld bead of the finished welded tube. The engraved pattern provided on the strip comprises protrusions, and the side portions of the strip are appropriately rolled during the engraving step to a strip thickness that is Γΐ?ηα Ln / zznz / E / YiAi approximately at the same level as the thickness of the strip between the protrusions of the engraved pattern. In this way, the side portions of the strip will have a lesser thickness compared to the thickness of the original metal strip, leading to a smaller internal weld bead on the tube. Beveling of the side edges preferably follows in a subsequent step. The present invention will become apparent from the detailed description provided below. The detailed description and specific examples describe preferred embodiments of the invention for illustrative purposes only. Those skilled in the art will understand from the guidance provided in the detailed description that changes and modifications may be made within the scope of the invention. Γΐ?ηα Ln / zznz / E / YiAi BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic illustration of a preferred preforming configuration; Fig. 2 is an exploded perspective view of an example of an engraving roller according to a preferred embodiment of the present invention; Fig. 3a is a cross-sectional view of the engraving roller of Fig. 2; Ln / zznz / E / YiAi Fig. 3b is a cross-sectional view of the circled detail shown in Fig. 3a; Fig. 3c is a cross-sectional view of a detail of an alternative modality; Fig. 4 schematically illustrates a detail of an engraving part of an engraving roller of an example in accordance with the present invention; Fig. 5 schematically illustrates a detail of an engraving part of an engraving roller of another example according to the present invention; Fig. 6 shows a partial cross-sectional view of a tube that has a design engraved on the inside; Fig. 7 schematically illustrates the edge of a strip that is preformed by an engraving roller according to the present invention. Fig. 8a shows a part of an edge beveling roller; Fig. 8b shows a part of an edge chamfering tool with a strip entering the tool; Figs. 9a, 9b and 9c schematically show the seam section of a rolled strip during welding of its longitudinal side edges. DETAILED DESCRIPTION The present invention relates to an apparatus for preforming a metal strip for the manufacture of welded and rolled tubes, comprising an engraving tool and a strip edge chamfering tool. The strip edge chamfering tool may preferably be arranged downstream of the engraving tool in the direction of advance of the strip to be preformed. However, alternatively, the strip edges may be chamfered before engraving, or the engraving and edge chamfering operations may be integrated into a single tool comprising a combined engraving, edge chamfering, and anvil cylinder.In an apparatus with the edge chamfering tool arranged before the engraving tool in the strip's travel direction, the engraving roller and the edge chamfering roller may include the same features and configuration as described below for the embodiment in which the edge chamfering tool is arranged after the engraving tool in the strip's travel direction. In an apparatus comprising a combined engraving and edge chamfering tool with a single combined engraving and edge chamfering roller, the engraving and edge chamfering are performed simultaneously, meaning that the engraving pattern is arranged within the recess of the strip's receiving space, which is dimensioned accordingly. Γΐ?ηα Ln / zznz / E / YiAi that the central part of the strip receives the engraving pattern on its surface and the longitudinal side edges are beveled, and preferably an unengraved part is provided on each side of the engraved central part of the strip. Regardless of the configuration of the strip-forming apparatus, the intended result is the production of a preformed metal strip with a surface-etched pattern in its central portion and beveled longitudinal side edge portions. This enables the efficient manufacture of small-diameter tubes by profiling and welding the preformed strip. The apparatus is described below primarily based on the preferred embodiment in which the etching tool and the edge-beveling tool are separate tools, each comprising a strip-forming roll and an anvil. However, it should be understood that the details described below apply to all embodiments unless otherwise stated. By performing the engraving and edge beveling in separate subsequent stages, the strip pre-forming process is more flexible and the properties of the resulting preformed strip are easier to control. In this embodiment, the engraving tool comprises an engraving roller having a cylindrical surface with a central portion and lateral portions arranged on each side of the The tool for chamfering the edges of strips comprises a first and second roller pair, wherein the first roller is an edge chamfering roller comprising a recessed central section and side sections on each side of the central section, and the second roller is an anvil roller. The edge chamfering roller and the anvil are configured to receive and pass the metal strip in a clearance formed between the rollers. The first and second rollers are shaped such that the clearance includes a central section dimensioned so that an engraving pattern on a metal strip passing between the roller pair is unaffected by the rollers.The clearance also includes side sections positioned on either side of the central section, where the clearance height is reduced. These side sections are located where the longitudinal edges of the metal strip will pass, so that the longitudinal edges on each side of the metal strip, on the side facing the engraving roller, become beveled as they pass between the pair of rollers. In this way, the height of the weld bead on the finished tube formed by rolling and welding can be minimized, as will be described in more detail below. Γΐ?ηα Ln / zznz / E / YiAi Consequently, the device can preform a metal strip to facilitate welding and result in a final tube product with improved weld quality. The finished tubular products may be suitable as advanced, small-diameter tubular products made of aluminum or aluminum alloys, with a diameter of 20 mm or less, preferably 5 to 10 mm. The tubular products are preferably manufactured as continuous tubular coils with a length exceeding 500 m, preferably exceeding 1000 m. Such tubular products are used, for example, in the fields of heating, ventilation, air conditioning, and refrigeration. The process of rolling welded tubes involves rolling a preformed strip into a tubular shape and welding the longitudinal edges of the strip to obtain the tube using high-frequency welding on an induction-heated welding coil. To achieve this, the strip is fed into a mill or forming apparatus that shapes the strip through several consecutive forming steps, performed by multiple forming rollers. As the strip passes through the welding coil, an electromagnetic field is induced around the coil, causing a current to flow in the strip, primarily concentrated at the edges to be joined. The resistance of The electric current in the metals generates the necessary heat at these edges, which quickly reach their melting point. While the edges are still molten, they are forged together by interaction with the lateral pressure rollers, which apply force to the strips and thus generate the required pressure at the interface of the two edges. As they pass through the welding rollers, the oxidized and molten metal are extruded from the joint, and the clean underlying metal is bonded. After welding, the sizing rollers complete the process, giving the tube its final, desired geometry. The production of advanced tube products, such as small diameter welded tubes with an inner surface pattern for heat exchange applications from metal strips, involves a two-stage process, which includes the strip preforming stage, and the roll forming stage that shapes the strip into a tubular form and welds it to a tube. In the manufacture of welded and rolled tubing from aluminum strips, it is important to mitigate problems that may arise due to the characteristics of the aluminum material. To achieve the desired heat transfer properties, the tubes have an internal embossed surface pattern. Preferably, the variation in strip width should be kept to a minimum to improve stability in the welding process and the quality of the finished tube product. Γΐ?ηα ίη / ζζηζ / Ε / γίΛΐ The strip is typically supplied as a blank roll to the preforming stage, where it is prepared for tube forming and welding in the next stage. The preforming stage involves stamping the strip onto the surface that will form the inside of the tube, creating the embossed pattern that will form the internal grooves. After preforming, the strip can be stored on a roll until it is rolled and welded into a tube. The engraving process performed at an engraving station involves a cold forming process applied to the strips to create the surface pattern. The engraving pattern on the central portion of the engraving roller preferably comprises a plurality of elongated grooves of a certain depth, arranged at an angle to the direction of rotation of the engraving roller. The groove depth of the engraving roller pattern is preferably less than 0.35 mm. Various engraving patterns can be applied; for example, a helical pattern improves performance in evaporation applications, and a herringbone pattern improves performance in condensation applications. Applying the desired pattern to the surface of the strip by engraving is a cold roll forming process, in which the blank strip is fed into a system A rolling mill of coupled rollers, comprising an engraving roller and an anvil roller, applies the necessary forming pressure. The engraving roller has a cylindrical surface comprising a central portion with an engraving pattern and side portions arranged on each side of the central portion. The side portions are unengraved. The central portion of the engraving roller is provided with a negative of the desired strip pattern and is pressed onto the strip, which is held by the anvil roller, thereby cold-rolling and engraving the strip. The engraving pattern provided on the engraving roller causes the impression of a corresponding engraving pattern on the surface of the strip, where the grooves of the engraving roller pattern correspond to protruding fins on the strip, thus creating a fin pattern on the surface of the strip.The height of the fin corresponds to the maximum depth of the groove in the engraving roller pattern. The anvil roller can be fixed in a horizontal position, while the engraving roller can be freely adjusted vertically, varying the space between the rollers, which allows for optimal adaptation and distribution of the forming pressure on the strip. The central part of the engraving roller may consist of a pack of central engraving pattern rollers, and the side parts may consist of The engraving rollers are arranged on either side of the central engraving roller pack. The central roller pack with the engraving pattern has a cylindrical surface that forms the central part of the engraving roller, and the side rollers have cylindrical surfaces that form the side parts of the engraving roller. This provides flexibility in the engraving pattern. Alternatively, the engraving roller can be made from a single piece. The core roller assembly with the engraved pattern may consist of a single engraved pattern disc, or two or more engraved pattern discs with or without spacer discs between them. The engraved pattern discs and the optionally included smooth spacer rings may preferably have chamfered edges at the interface between them, so that the chamfered edges form circumferential channels at these interfaces. This minimizes local stress on the material and thus reduces the risk of tool breakage. The central set of engraved rollers is responsible for pattern formation, while the side rollers create the unpatterned side sections of the strip, as described below, by pressing against the outer edges. The two side rollers can be screwed onto the central engraving ring, which can be attached to a central shaft and secured in position at the engraving station. Yi?na Ln / zznz / E / YiAi As mentioned, the side portions of the engraving roll have no engraving pattern. Therefore, the outer side portions along the engraved and cold-rolled strip have no engraved pattern but a smooth surface. By providing these patternless side portions along the strip during the preforming stage, the risk of variations in strip edge thickness can be minimized, the risk of irregular geometries at the strip edge at the welding point can be reduced, and the risk of the engraved fins welding together, resulting in a large internal weld bead, can be avoided.Consequently, the arrangement of the patternless side sections on the engraved strip allows for optimal control of the strip edge geometry, which is essential to ensure optimal welding conditions, to improve process stability and tube quality after welding. The cylindrical surface of the engraving roll can have a suitable overall width of 15 mm or more, with the central portion being 85 to 99% of the overall width. A strip width of 15 mm or more is suitable for manufacturing heat exchanger tubes for HVAC&R applications, for example, up to 64 mm. The width of the unpatterned side portions of the engraving roller is determined based on considerations The GΓΐ?ηα Ln / zznz / E / YiAi relates to the ease of welding and heat transfer performance of the finished tube. Wider unpatterned side portions will be easier to weld, as this will more closely approximate a standard plain strip welding procedure. However, excessively wide unpatterned side portions can negatively affect the final heat transfer performance, since ideally a continuous pattern around the entire inner circumference of the tube would be desirable. Consequently, the width of the unpatterned side portions should preferably be as small as possible, while ensuring that no engraved fins are included in the inner weld bead. It has been found that the combined width of both unpatterned side portions of the strip should preferably be 1 to 15% of the total strip width when the strip has a total width of 15 mm or more. The cylindrical surfaces of the side portions of the engraving roller are preferably level with the cylindrical surface of the central portion between the grooves of the engraving roller pattern. This is particularly beneficial in combination with the beveling of the strip edge that takes place in the subsequent preforming step, described below, as it can further reduce the height of the inner weld bead of the finished welded tube. Consequently, the strip in the area of ​​the side portions The patternless side portion is preferably rolled downwards to the nominal thickness of the strip's bottom wall during the etching stages, i.e., so that it is flush with the bottom of the grooves between the pattern fins on the etched surface. Therefore, the side portions remain smooth but are still rolled to a thickness less than the original blank. This improves the performance of the final tube, as the height of the inner weld bead can be reduced, resulting in less disturbance to the fluid dynamics within the final tube. The desired thickness of the patternless side portions can be achieved by selecting the outer diameter of the etching roll for the side portions to be the same as the outer diameter of the etching roll for the center portion. During high-frequency welding of rolled tubes on an induction-heated welding coil, a weld bead typically forms inside the tube. The high-frequency welding process is essentially a hot forging process, during which molten material from the tube edges is ejected from the weld area both inside and outside the tube. This internal ejection, after solidification, forms the inner bead. For larger diameter tubes, the weld bead rarely presents a problem. However, internally enhanced tubes suitable for HVAC&R applications often have The pipe has a small diameter of 20 mm or less, and therefore it is important that the inner weld bead be as small as possible. To ensure the minimum height of the inner bead, while maintaining the burst pressure of the pipe at the required levels, the shape of the edges of the incoming etched strip is modified. The edges of the strip are beveled on the side that will form the inside of the pipe, in a cold roll forming process. By adjusting the bevel angle and length, which defines the slope and dimension of the bevel, the height of the inner flange can be kept low enough to be contained within the depth of the etched surface pattern. As mentioned, according to the preferred embodiment, the strip edge chamfering tool comprises a first and second pair of rollers, configured to receive and pass the metal strip in a clearance formed between the rollers. The first and second rollers are shaped such that the clearance includes a central section dimensioned so that an engraved pattern on a metal strip passing between the pair of rollers is unaffected by the rollers. This ensures that the engraved pattern remains intact on a strip that has been engraved before entering the edge chamfering tool. The clearance further comprises side sections arranged on each side of the central section, wherein the clearance has a height Reduced Ga?a Ln / zznz / E / YiAi. The side sections are positioned where the longitudinal side edges of the metal strip will pass, so that the longitudinal side edges on each side of the metal strip, on the side that was facing the engraving roller, become beveled as they pass between the pair of rollers. After rolling the strip into a nearly finished tube shape, the edges of the strip will be welded together. Due to the beveling of the edges, there is less material present at the longitudinal edges of the strip. This is particularly pronounced when the undesigned side portions of the strip have been rolled to be level with the bottom of the embossed design as described above. In this way, the internal weld bead begins to build up on the inner surface of the tube from a lower wall thickness level, rather than the higher original strip thickness.Less material is expelled from the weld area, and the beveled edges create a space where some of the molten material can be contained. This allows the weld bead height of the finished tube, formed by rolling and welding, to be minimized while maintaining the mechanical properties of the finished product. The rollers of the edge beveling tool can be designed in various ways. Preferably, the first roller of the pair of rollers in the beveling tool The edges are arranged so that the engraved side of the strip faces the first roller and are designed to comprise a recess having outward-sloping side edges on each side of the recess, running along the circumference of the cylindrical surface of the first roller. The sloping side edges are suitably inclined at an angle of 30 to 60°, preferably 43 to 47°, to provide sufficient edge chamfering. The side sections of the clearance between the first and second rollers may suitably have a width such that, for each side section, it is equal to or greater than half the difference between the total width of the engraving tool (W1) and the width of the central portion of the engraving tool (W2).Since the clearance between the edge chamfering tool rollers is sized so as not to affect the engraving pattern, having a height that exceeds the maximum thickness of the strip, an outer edge of the strip is chamfered by the inclined sides of the side sections of the chamfering roller, as illustrated schematically in Fig. 7, which shows an edge chamfering operation in a step subsequent to the engraving step. The present invention further relates to a method for preforming a metal strip comprising engraving a pattern on the strip in a central portion along its longitudinal axis, while the lateral portions on each side of the The central portion of the strip is rolled without an engraved pattern, and the longitudinal side edges of the strip are beveled on the side with the engraved pattern. As mentioned previously, the engraving is preferably done separately before beveling the edges, but if desired, it can be done afterward or simultaneously with the beveling. During beveling, the strip material at the longitudinal side edges is pressed down to 20–60% of the strip thickness, preferably 35–40%, thus forming a beveled edge surface along the longitudinal side edges of the strip to minimize the internal weld bead of the finished welded tube.The etching pattern provided on the strip comprises protrusions, and the side portions of the strip are appropriately rolled during the etching process to a strip thickness that is approximately the same as the thickness between the protrusions of the etching pattern. This is particularly advantageous when etching is performed before beveling the edges. Therefore, the side portions of the strip will be thinner, resulting in a smaller internal weld bead on the tube. Γΐ?ηα Ln / zznz / E / YiAi DESCRIPTION OF EXAMPLE MODALITIES The present invention will now be described with reference to the accompanying drawings, which show preferred embodiments of the invention. However, the invention can be implemented in other ways and should not be interpreted as being limited to the embodiments presented herein. The embodiments presented are provided to fully convey the scope of the invention to a person skilled in the art. Fig. 1 is a schematic illustration of a setup 20 for preforming a metal strip 40. The setup includes an engraving station with an engraving roller 1 and an anvil 22, and an edge chamfering tool 30 comprising a pair of rollers 31, 32. The strip 40 is moved through the preforming tools in a displacement direction T. Figure 2 is an exploded perspective view of an example of an engraving roller, and Figure 3a is a cross-sectional view of the same roller, with Figure 3b showing details. The engraving roller 1 has a cylindrical surface 2, comprising a central portion 3 having an engraving pattern 10 and side portions 4a, 4b arranged on either side of the central portion 3. The side portions 4a, 4b are free of an engraving pattern as shown in Figure 3b. The cylindrical surface of the engraving roller has a total width Wl, and the central portion has a width W2, which is 85 to 99% of the total width Wl. Γΐ?ηα Ln / zznz / E / YiAi In the example shown, the central part 3 of the engraving roller 1 comprises a central engraving pattern roller 6, and the side parts 4a, 4b comprise side rollers 7a, 7b. The side rollers are arranged on either side of the central engraving roller. The engraving pattern 10 on the central part of the engraving roller comprises a plurality of elongated grooves 11 having a depth DI and arranged at an angle to the direction of rotation of the engraving roller, said groove depth DI of the engraving pattern preferably being less than 0.35 mm. As shown in Figs. 3a-3b, the cylindrical surfaces of the side parts 4a, 4b are flush with the cylindrical surface of the central part 3 between the grooves. Figure 3c is a schematic cross-sectional view of a detail of a combined engraving and edge-beveling roller. In this case, the engraving portion 3' is arranged in the central section 34' of the recess 37'. The unpatterned side portion 4a' is also included in the central section 34'. The side section 35' includes the angled edge that bevels the side edges 36'. The central engraving roller may take the form of an engraving pattern roller bundle, comprising multiple rollers with an engraving design. Thus, the central part 3 of engraving roller 1 may consist of a bundle An engraving pattern roller assembly comprising one or more engraving pattern discs 13a, 13b with cylindrical engraving surfaces having the same or different engraving patterns. Fig. 4 illustrates a detail of an engraving pattern roller assembly comprising two pattern rollers, the metal strip 40 to be engraved, and the anvil 22. In this case, the engraving pattern roller assembly comprises two engraving pattern discs 13a, 13b, each with an engraving pattern consisting of grooves arranged at an angle, but with mirror patterns, which together form a herringbone pattern on the engraved strip. Fig. 5 illustrates a detail of an engraving pattern roller assembly comprising a smooth spacer ring 15 between the engraving pattern disc 13a, 13b. In this case, the cylindrical surface of each spacer ring is level with the cylindrical surface of the central portion 3 between the grooves. As shown in Fig.5, the etched pattern discs 13a, 13b and the plain spacer ring 15 have chamfered edges 16, 17 at the interface between them. Fig. 6 shows a partial cross-sectional view of a tube 18 having an internal etched herringbone pattern 19. Figure 7 shows a cross-section of a portion of a finished preformed strip, which has been preformed by an engraving roller according to the present invention in a step subsequent to engraving. The contour of the recess provided in The beveling cylinder 31 is indicated by a dashed line. The recess comprising the central section 34 and the side sections 35 (only one of which is shown in Fig. 7) forms the receiving space for the strip 33 together with the anvil (not shown). The clearance 33 is dimensioned so that the tabs 44 of the engraving pattern in the central portion 41 of the strip are unaffected, and in this example, the side section 35 comprising the outwardly angled edge that bevels the side edge 36 has a width greater than the unpatterned side portion 42 of the strip. The outermost edge of the strip is beveled to a thickness represented by the dashed line 43.The drawing also shows how the surface of the side portion 42 is level with the bottom of the grooves created between the fins 44 of the central portion 41, in which an engraving pattern is provided comprising a plurality of protruding fins 44 (only one fin is shown in this drawing). The fins 44 correspond to the grooves 11 of the engraving pattern 10 on the engraving roller (Fig. 3b). Fig. 8a shows a portion of an edge beveling roller 31 comprising a central section 34 dimensioned such that an engraving pattern on a metal strip passing between the pair of rollers is unaffected by the rollers 31, 32. The side sections 35 are arranged on each side of the central section, wherein the clearance 33 has a Reduced height. The center section 34 and the side sections 35 together form a recess 37 that runs along the circumference of the cylindrical surface of the first roller. The recess has outwardly sloping side edges 36 on each side formed by the side sections 35. Fig. 8b shows a portion of an edge chamfering tool configured to receive and pass the metal strip 40 in a gap 33 formed between the rollers 31, 32. In this drawing, the upper roller 31 corresponds to the roller shown in Fig. 8a. The upper roller forms the edge chamfer on the side of the strip that is to be the inside of the finished tube. The roller 32 acts as an anvil. Figures 9a, 9b, and 9c illustrate the welding principle and show the seam cross-section of a rolled strip during the welding of its longitudinal side edges. After preforming in the apparatus comprising the etching tool and the edge-beveling tool, the strip is rolled until the beveled edges are close together (Fig. 9a). The nearly closed tube is then subjected to high-frequency welding by passing it through a welding coil, where the strip material begins to melt due to the energy induced by the high-frequency coil (Fig. 9b). During welding, the molten material fills the space formed between the beveled edges of the strip and forms the weld bead (Fig. 9c). Due to this space Γΐ?ηα ίη / ζζηζ / Ε / γίΛΐ and the low thickness of the strip in the welding area, the height of the inner weld bead can be kept to a minimum. A person skilled in the art will realize that the present description is not limited to the preferred embodiments described above. A person skilled in the art further realizes that modifications and variations within the scope of the appended claims are possible. Moreover, variations of the described embodiments can be understood and implemented by a person skilled in the practice of the claimed invention from a study of the drawings, the description, and the appended claims.

Claims

1. An apparatus for preforming a metal strip (40) for manufacturing rolled and welded tubes, comprising an engraving tool (20) and a strip edge chamfering tool (30), wherein the engraving tool comprises an engraving roller (1) having a cylindrical surface (2) with a central engraving portion (3, 3'), and the strip edge chamfering tool comprises an edge chamfering roller (31) comprising a recessed central section (34) and side sections (35) on each side of the central section, and an anvil roller (32), wherein the edge chamfering roller (31) and the anvil roller (32) are configured to receive and pass the metal strip in a clearance (33) formed between the rollers, wherein the clearance (33) has a reduced height in the side sections, which are in a position through which the longitudinal side edges of the metal strip will pass.so that the longitudinal side edges on each side of the metal strip, and on the engraved side of the metal strip, are beveled as they pass between the pair of rollers (31, 32), 2. The apparatus according to claim 1, wherein the engraving tool comprises the cylindrical surface (2) of the engraving roller (1), said cylindrical surface comprising the central engraving portion (3) and the side portions (4a, 4b) arranged on each side of the central portion, said central portion being provided with an engraving pattern (10) and said side portions being free of an engraving pattern, and - the central section (34) of the tool for chamfering the edge of the strip (30) is dimensioned such that an engraving pattern of a metal strip passing between the pair of rollers through the space for chamfering the edge (33) is unaffected by the rollers (31, 32).

3. The apparatus according to claim 1, wherein the engraving tool and the strip edge chamfering tool are integrated to comprise a combined engraving and edge chamfering roller, wherein the central engraving portion (3') is comprised in the central section (34') of the edge chamfering clearance (33).

4. The apparatus according to any of claims 1-3, wherein the engraving pattern (10) in the central engraving portion comprises a plurality of grooves (11) arranged on the cylindrical surface of the central portion (3), and wherein the cylindrical surface of each side portion (4a, 4b) is level with the cylindrical surface of the central portion (3) between the grooves, and wherein the strip edge chamfering tool (30) is arranged downstream of the engraving tool in a displacement direction (T) of the strip to be preformed.

5. The apparatus according to claim 4, wherein the engraving roller (1) comprises a central engraving roller pack (6) and side rollers (7a, 7b), said side rollers being arranged on each side of the central engraving pattern roller pack, and wherein the central engraving pattern roller pack has a cylindrical surface forming the central part (3) and the side rollers have cylindrical surfaces forming the side parts (4a, 4b).

6. The apparatus according to any of claims 1-5, wherein the cylindrical surface of the engraving roller has a total width (Wl) of 15 mm or more, and the central part of the engraving roller has a width (W2), which is 85-99% of the total width (Wl).

7. The apparatus according to any of claims 1-6, wherein the central section (34) of the clearance (33) between the first and second rollers (31, 32) of the strip edge chamfering tool (30) has a width (W3) that is equal to or greater than the width (W2) of the central part (3) of the engraving roller (1).

8. The apparatus according to any of claims 1-7, wherein the first roller (31) of the pair of rollers in the edge chamfering tool comprises a recess (37) having outwardly inclined side edges (36) on each side of the recess, running along the circumference of the cylindrical surface of the first roller.

9. The apparatus according to claim 8, wherein the inclined side edges (36) are inclined at an angle of 30-60°, preferably 43-47°.

10. The apparatus according to any of claims 1-9, wherein the side sections (35) of the clearance (33) between the first and second rollers (31, 32) each have a width that is equal to or greater than half the difference between the total width of the engraving tool (Wl) and the width of the central part of the engraving tool (W2).

11. A method for preforming a metal strip (40) comprising - engraving a pattern on a central part (41) of the strip, in a longitudinal direction thereof, while the side parts (42) on each side of the central part of the strip are rolled without an engraving pattern and - chamfering the longitudinal side edges (43) of the strip on the side of the strip that is provided with the engraving pattern.

12. The method according to claim 11, wherein, during beveling, the strip material at the longitudinal side edges (43) of the strip is pressed down to 20-60% of the strip thickness, preferably 35-40%, thereby forming an inclined edge surface along the longitudinal side edges of the strip.

13. The method according to claim 11 or 12, wherein the engraving pattern comprises protrusions (44), and the side portions of the strip are rolled during the engraving step to a strip thickness that is approximately at the same level as the strip thickness between the protrusions of the engraving pattern, followed by beveling of the side edges in a subsequent step.

14. The method according to any of claims 11-13, wherein the engraving and edge beveling are performed simultaneously on an integrated Γΐ?ηα Ln / zznz / E / YiAi edge engraving and beveling tool.

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