Apparatus and method for preforming a metal strip for roll forming and for manufacturing welded tubes

Abstract

An apparatus and method for preforming a metal strip (40) for the production of roll-formed and welded tubing, comprising an embossing tool (20) and a strip edge chamfering tool (30), wherein the embossing tool comprises an embossing roll (1) having a cylindrical surface (2) with a central embossing portion (3, 3'), and the strip edge chamfering tool comprises an edge chamfering roll (31) having a recessed central section (34) and side sections (35) on each side of the central section, and an anvil roll (32), wherein the edge chamfering roll (31) and the anvil roll (32) are configured to receive and pass the metal strip in a gap (33) formed between the rolls, the gap (33) having a reduced height at the side sections where the longitudinal side edges of the metal strip pass, whereby the longitudinal side edges on each side of the metal strip and on the embossed side of the metal strip are chamfered as the metal strip is passed between the pair of rolls (31, 32).

Description

Technical Field

[0001] The present disclosure relates to an apparatus for preforming a metal strip for the manufacture of roll formed and welded tubes, and a method for preforming a metal strip.

Background Art

[0002] Welded pipes and tubes are typically manufactured by longitudinally forming a flat metal strip into a substantially complete tube and then welding two edges together. Roll formed tubes have many applications such as in the field of the HVAC&R market (heating, ventilation, air conditioning and refrigeration). In this technical field, environmental requirements have motivated the development of more efficient air conditioning and refrigeration appliances. Accordingly, efforts have been made to supply tubes with a smaller diameter with extensive internal reinforcement that can increase its heat transfer coefficient relative to standard smooth solutions. The manufacturing methods of advanced products, such as welded tubes with a small diameter with internal patterning for heat exchange applications, must result in products with minimal undesirable internal non-uniformities in order to obtain optimal flow characteristics and heat transfer. As the demand for cost reduction has increased, there has conventionally been interest in providing alternatives in the form of aluminum tubes to copper tubes, which have accounted for the majority of use in air conditioning and refrigeration appliances. Therefore, it is desirable to find a method for manufacturing aluminum tubes with competitive characteristics for applications in the field of HVAC&R and the like.

Summary of the Invention

Means for Solving the Problems

[0003] The present disclosure relates to an apparatus for preforming a metal strip for the manufacture of roll formed and welded tubes, including an embossing tool and a strip edge chamfering tool. The embossing tool includes an embossing roll having a cylindrical surface with an embossed central portion. The strip edge chamfering tool includes an edge chamfering roll having a recessed central section and side sections on each side of the central section, and an anvil roll, the edge chamfering roll and the anvil roll being configured to receive and pass a metal strip in a gap formed between the rolls. The gap has a reduced height in the side sections where the longitudinal side edges of the metal strip pass through, whereby the longitudinal side edges on each side of the metal strip and on the embossed side of the metal strip are chamfered when passed through the roll pair.

[0004] Preferably, the embossing tool includes the cylindrical surface of the embossing roll, the surface including a central embossed portion and side portions disposed on each side of the central portion, the central portion being provided with an embossing pattern and the side portions being free of an embossing pattern, and the central section of the strip edge chamfering tool being dimensioned such that the embossing pattern of the metal strip passing through the roll pair through the edge chamfering gap is not affected by the roll. The strip edge chamfering tool (30) is preferably separated from the embossing tool and disposed downstream of the embossing tool in the moving direction (T) of the strip to be preformed.

[0005] Alternatively, the embossing tool and the strip edge chamfering tool may be integrated to include one combined embossing and edge chamfering roll, whereby the central embossed portion is included in the central section of the edge chamfering gap.

[0006] The first and second rolls are shaped such that a central section sized so that the embossing pattern of the metal strip passing between the pair of rolls is not affected by the rolls includes a gap. The gap further includes side sections disposed on each side of the central section, and in the side sections, the gap has a reduced height. The side sections are located at positions through which the longitudinal side edges of the metal strip pass, whereby the longitudinal side edges of the metal strip on each side of the metal strip, on the side facing the embossing roll, are chamfered when passing between the pair of rolls. Thereby, the height of the weld bead of the finished roll formed and welded tube can be minimized.

[0007] Advantageously, when a strip edge chamfering tool is disposed downstream of the embossing tool in the moving direction (T) of the strip to be preformed, the embossing pattern of the central portion of the embossing roll preferably includes a plurality of grooves disposed on the cylindrical surface of the central portion, and the cylindrical surface of each side portion is preferably at the same height as the cylindrical surface of the central portion between the grooves. This further contributes to reducing the internal weld bead height. The embossing roll can be composed of a central embossing pattern roll pack and side rolls, the side rolls are disposed on each side of the central embossing pattern roll pack, the central embossing pattern roll pack has a cylindrical surface forming a central portion, and the side rolls have a cylindrical surface forming a side portion. Thereby, the embossing pattern can be selected flexibly. The cylindrical surface of the embossing roll preferably has a total width of 15 mm or more, and the central portion of the embossing roll preferably has a width that is 85 to 99% of the total width.

[0008] The central section of the gap between the first and second rolls of the strip edge chamfering tool has a width greater than or equal to the width of the central portion of the embossing roll to ensure that the embossing pattern in the central portion of the strip is not affected by the passage of the edge chamfering tool. The first roll of the pair of rolls in the edge chamfering tool is preferably a recess and is designed to include a recess having outwardly inclined side edges on each side of the recess that extend along the circumference of the cylindrical surface of the first roll. The inclined side edges are preferably inclined at an angle of 30 to 60°, preferably 43 to 47°, to provide sufficient edge chamfering.

[0009] The side sections of the gap between the first and second rolls may each preferably have a width that is at least half the difference between the total width (Wl) of the embossing tool and the width (W2) of the central portion of the embossing tool for each of the side sections.

[0010] The present disclosure further relates to a method of preforming a metal strip, the method comprising embossing a pattern in the longitudinal direction in the central portion of the strip while the side portions on each side of the central portion of the strip are rolled without an embossing pattern, and chamfering the longitudinal side edges of the strip on the side where the embossing pattern is provided. During chamfering, the strip material of the longitudinal side edges of the strip is pressed to 20 to 60%, preferably 35 to 40% of the strip thickness, thereby forming an inclined edge surface along the longitudinal side edges of the strip to minimize the internal weld bead of the finished welded tube. The embossing pattern provided on the strip includes protrusions, and the side portions of the strip are preferably rolled to a strip thickness that is substantially the same as the strip thickness between the protrusions of the embossing pattern during the embossing step. Thereby, the side portions of the strip have a thickness that is thinner than the thickness of the original metal strip. This results in a smaller internal weld bead in the tube. Preferably, chamfering of the side edges continues in a subsequent step.

[0011] The present disclosure will become apparent from the detailed description given below. The detailed description and specific examples disclose only the preferred embodiments of the present disclosure as an example. Those skilled in the art will understand that changes and modifications can be made within the scope of the present disclosure from the guidance in the detailed description.

Brief Description of the Drawings

[0012]

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Figure 9c

DETAILED DESCRIPTION OF THE INVENTION

[0013] The present disclosure relates to an apparatus for preforming a metal strip for the manufacture of roll-formed and welded tubes, including an embossing tool and a strip edge chamfering tool. The strip edge chamfering tool can preferably be arranged downstream of the embossing tool in the moving direction of the strip to be preformed. However, as an alternative, chamfering of the strip edge before embossing or integration of the embossing and edge chamfering operations in one tool including a single combined embossing and edge chamfering roll and an anvil can be envisioned. In an apparatus where the edge chamfering tool is arranged in front of the embossing tool in the strip moving direction, the embossing roll and the edge chamfering roll can include the same features and configurations as those described for embodiments where the edge chamfering tool is arranged behind the embossing tool in the strip moving direction. In an apparatus including a combined embossing and edge chamfering tool with a single combined embossing and edge chamfering roll, the embossing and edge chamfering are performed simultaneously. This means that the embossing pattern is arranged within the recess of the strip receiving gap. The strip receiving gap is dimensioned such that the central portion of the strip receives the embossing pattern on its surface, the longitudinal side edges are chamfered, and preferably non-patterned portions are provided on each side of the embossed central portion of the strip.

[0014] Regardless of how the strip preforming apparatus is set up, the intended result is the production of a preformed metal strip having an embossed surface pattern in its central portion and chamfered longitudinal side edge portions. This enables the efficient production of small-diameter tubes by roll forming and welding the preformed strips. In the following, the apparatus will be described based on a preferred embodiment in which the embossing tool and the edge chamfering tool are separate tools each including a strip preforming roll and an anvil. However, it should be understood that all of the details described below apply to all of these embodiments unless otherwise specified.

[0015] By performing embossing and edge chamfering in separate subsequent steps, the strip preforming process becomes more flexible, and the characteristics of the resulting preformed strip are easier to control. In this embodiment, the embossing tool includes an embossing roll having a cylindrical surface with a central portion and side portions disposed on each side of the central portion. The central portion is provided with an embossing pattern. The side portions do not have an embossing pattern. The strip edge chamfering tool includes a pair of first and second rolls. The first roll is an edge chamfering roll including a recessed central section and side sections on each side of the central section. The second roll is an anvil roll. The edge chamfering roll and the anvil are configured to receive and pass a metal strip roll in a gap formed between the rolls. The first and second rolls are shaped such that the gap includes a central section dimensioned so that the embossing pattern of the metal strip passing between the pair of rolls is not affected by the rolls. The gap further includes side sections disposed on each side of the central section. The gap has a reduced height. The side sections are located where the longitudinal side edges of the metal strip pass. Thereby, the longitudinal side edges of the metal strip on each side of the metal strip, on the side directed toward the embossing roll, are chamfered when passing between the pair of rolls. Thereby, as will be described in more detail below, the height of the weld bead of the finished roll formed and welded tube can be minimized. Thus, with this apparatus, the metal strip can be preformed to smooth the welding, and a final tube product with improved welding quality can be provided.

[0016] The final tube product can preferably be an advanced small-diameter tube product made of aluminum or an alloy thereof having a diameter of 20 mm or less, preferably 5 - 10 mm. The tube product is preferably manufactured as a continuous tube coil having a length exceeding 500 m, preferably exceeding 1000 m. The use of such a tube product is found, for example, in the fields of heating, ventilation, air conditioning or refrigeration.

[0017] The process of welded tube roll forming involves roll forming a preformed strip into a tubular shape and welding the longitudinal edges of the strip together to obtain a tube by high-frequency welding in an induction heating welding coil. To achieve this, the strip is fed to a forming mill or apparatus that forms the strip through different successive forming steps carried out by the same number of forming rolls. As the strip passes through the welding coil, an electromagnetic field is induced around the welding coil. The electromagnetic field induces a current that mostly concentrates and flows in the edges to be joined in the strip. The resistance of the metal to the current causes the generation of the heat required at these edges to quickly reach the melting point. When the edges are still in a molten state, they are forged together due to the interaction with the side squeezing rolls, applying force to the strip and thus generating the pressure required at the interface of the two edges. As it passes through the welding roll, oxidized metal and molten metal are extruded from the joint, and the clean metal below is joined. Following welding, sizing rolls complete the process and give the tube the required final shape.

[0018] The manufacture of advanced tube products, such as small-diameter welded tubes with inner surface patterning for heat exchange applications from metal strips, involves a two-step process that includes the step of preforming the strip and the step of roll forming the strip into a tube and welding it to make a tube.

[0019] In the manufacture of roll-formed and welded tubes made from aluminum strips, it is important to mitigate the problems arising from the characteristics of the aluminum material. To achieve the required heat transfer characteristics, the tubes have an internal embossed surface pattern. Variations in strip width should preferably be kept to a minimum in order to improve the stability in the welding process and the quality of the finished tube product.

[0020] The strip is typically provided in the form of a blank strip coil at the preforming stage. At the preforming stage, the strip is prepared so that the tube forming and welding in the next stage are ready. The preforming stage includes the step of embossing the strip on the surface that forms the inside of the tube to obtain an embossing pattern that forms the internal grooves of the tube. After the preforming stage, the strip can preferably be stored in the form of a coil until it is roll formed and welded in the form of a tube.

[0021] The embossing procedure carried out at the embossing station includes a cold deformation process carried out on the strip for the purpose of obtaining a surface pattern. The embossing pattern in the central part of the embossing roll preferably includes a plurality of elongated grooves having a specific depth and arranged at an angle with respect to the direction of rotation of the embossing roll. The groove depth of the embossing roll pattern is preferably less than 0.35 mm. Various embossing patterns can be applied. For example, a helical pattern improves the performance in evaporation applications. A herringbone pattern improves the performance in condensation applications.

[0022] Applying the required pattern to the strip surface by embossing is a cold roll forming process in which the blank strip is sent to a combined roll system including an embossing roll and an anvil roll, and the required forming pressure is applied. The embossing roll has a cylindrical surface including a central portion having an embossing pattern and side portions disposed on each side of the central portion. The side portions do not have an embossing pattern. The central portion of the embossing roll is provided with a negative of the required strip pattern and pressed against the strip supported by the anvil roll, thereby cold roll forming and embossing the strip. The embossing pattern provided on the embossing roll results in a trace of the embossing pattern corresponding to the strip surface. The grooves of the embossing roll pattern correspond to the protruding fins of the strip. Thereby, a pattern of fins is created on the strip surface. The fin height corresponds to the maximum value of the groove depth of the embossing roll pattern.

[0023] The anvil roll can be fixed in a horizontal position. On the other hand, the embossing roll can be freely adjusted in the vertical direction, changing the roll gap, and thus enabling adjustment and optimal distribution of the forming pressure on the strip.

[0024] The central portion of the embossing roll can be composed of a central embossing pattern roll pack. The side portions can be composed of side rolls disposed on each side of the central embossing roll pack. The central embossing pattern roll pack has a cylindrical surface forming the central portion of the embossing roll. The side rolls have a cylindrical surface forming the side portions of the embossing roll. In this way, flexibility regarding the embossing pattern is obtained. Alternatively, the embossing roll can be made as an integral unit.

[0025] The central embossing pattern roll pack can be composed of a single embossing pattern disk or two or more embossing pattern disks with or without spacer disks therebetween. The embossing pattern disks and optionally included smooth spacing can preferably have inclined edges at their interface therebetween. Thereby, the circumferential channels are formed in the interface by the inclined edges. This minimizes the local stress in the material and thus reduces the risk of tool breakage.

[0026] The central embossing pattern roll pack performs the pattern forming process. The side rolls serve to provide the non-patterned side portions described below by pressing on the outer portions of the strip. The two side rolls can be bolted to the central embossing ring. The central embossing ring can be clamped to the central shaft and can be fixed in place at the embossing station.

[0027] As described, the side portions of the embossing roll are without an embossing pattern. Thereby, the cold roll forming and the outer portions along the embossing strip have a smooth surface without any embossing pattern. By providing these non-patterned side portions along the length of the strip during the preforming stage, the risk of strip edge thickness variation can be minimized, the risk of non-uniform geometric shapes of the strip edges existing at the weld points can be reduced, and the risk of embossing fins being welded together to cause the formation of large internal weld beads can be avoided. Thus, providing the non-patterned side portions on the embossing strip enables optimal control of the strip edge shape. This is extremely important in ensuring optimal welding conditions for improving process stability and tube quality after welding.

[0028] The cylindrical surface of the embossing roll can preferably have a total width of 15 mm or more. The central portion has a width that is 85 - 99% of the total width. A strip width of 15 mm or more, such as up to 64 mm at most, is suitable for the manufacture of heat exchanger tubes for HVAC&R applications.

[0029] The width of the side portion of the unpatterned embossing roll is determined based on considerations related to the ease of welding of the finished tube and heat transfer performance. The wider the width of the unpatterned side portion, the easier it is to weld in order to approach the standard procedure for smooth strip welding. However, if the width of the unpatterned side portion is too wide, in an ideal case, a continuous pattern over the entire inner circumference of the tube may be required, which can have an adverse effect on the final heat transfer performance. Therefore, while ensuring that the embossed fins are not included in the internal weld bead, the width of the unpatterned side portion should be as small as possible. When the strip has a total width of 15 mm or more, it has been found that the combined width of both unpatterned strip side portions should preferably be 1 - 15% of the total strip width.

[0030] The cylindrical surface of the side portion of the embossing roll is preferably at the same height as the cylindrical surface at the center between the grooves of the embossing roll pattern. This can further reduce the height of the internal weld bead of the finished welded tube and is particularly beneficial in combination with the edge chamfering of the strip performed in the subsequent steps of the preforming described below. Therefore, the strip in the area of the unpatterned side portion is preferably rolled during the embossing step to the nominal bottom wall thickness of the strip, i.e., the same height as the bottom of the groove between the fins of the embossed surface pattern. Thus, the side portion is kept smooth but is still rolled to a thickness thinner than the original in the blank form. This can reduce the internal weld bead height, improve the performance of the final tube, and as a result, there is less disturbance to the hydrodynamics within the final tube. The required thickness of the unpatterned side portion can be obtained by selecting the outer diameter of the embossing roll at the side portion to be the same as the outer diameter of the embossing roll.

[0031] During high-frequency welding of a roll-formed tube in an induction heating welding coil, the weld bead is usually formed inside the tube. The high-frequency welding process is an accurate hot forging process. During the accurate hot forging process, the molten part of the tube edge is discharged from both the inner and outer welding areas of the tube. The internal discharge forms an internal bead after solidification. For tubes with a larger diameter, the weld bead rarely causes problems. However, internally reinforced tubes suitable for HVAC&R applications typically preferably have a small diameter of 20 mm or less. Therefore, it is important that the internal weld bead is as small as possible. To ensure the minimum internal bead height while maintaining the required level of tube burst pressure, the strip edge of the incoming embossing strip is modified in shape. The strip edge is chamfered on the side that forms the inside of the tube in the cold roll forming process. By adjusting the chamfer angle and the length that defines the slope and dimensions of the chamfer, the height of the internal bead can be kept low enough to be included in the depth of the embossed surface pattern.

[0032] As described, according to a preferred embodiment, the strip edge chamfering tool includes a pair of first and second rolls configured to receive and pass a metal strip in a gap formed between the rolls. The first and second rolls are shaped such that the gap includes a central section dimensioned so that the embossing pattern of the metal strip passing between the pair of rolls is not affected by the rolls. This ensures that the embossing pattern remains undamaged on the strip that has been embossed prior to entering the edge chamfering tool. The gap further includes side sections disposed on each side of the central section. In the side sections, the gap has a reduced height. The side sections are located where the longitudinal side edges of the metal strip pass. Thereby, the longitudinal side edges of the metal strip on each side of the metal strip, on the side directed towards the embossing roll, are chamfered when passed between the pair of rolls. After roll forming the strip into an almost completed tube form, the edges of the strip are welded together. Due to the edge chamfering, there is less material present at the longitudinal edges of the strip. This is particularly pronounced when the side portions of the non-patterned strip are rolled to the same height as the bottom of the embossing pattern as described above. In such a way, the internal weld bead begins to accumulate on the inner surface of the tube from the bottom wall thickness level instead of the larger original strip thickness. Less material is removed from the weld area. The chamfered edges form a space that may contain a portion of the molten material. Thereby, the height of the weld bead of the completed roll formed and welded tube can be minimized while maintaining the performance of the completed product to meet mechanical requirements.

[0033] The rolls of the edge chamfering tool can be designed in various ways. Preferably, the first roll of a pair of rolls in the edge chamfering tool is arranged such that the embossing side of the strip faces the first roll and is designed to include a recess. The recess has outwardly inclined side edges on each side of the recess that extend along the circumference of the cylindrical surface of the first roll. The inclined side edges are preferably inclined at an angle of 30 to 60°, preferably 43 to 47°, in order to provide sufficient edge chamfering. The side sections of the gap between the first and second rolls can preferably each have a width that is at least half of the difference between the total width (Wl) of the embossing tool and the width (W2) of the central part of the embossing tool for each of the side sections. The gap between the rolls of the edge chamfering tool is dimensioned so as not to affect the embossing pattern by having a height that exceeds the maximum strip thickness. The outer edge of the strip is chamfered by the inclined side of the chamfering roller side section as schematically shown in FIG. 7 showing the edge chamfering operation in the step following the embossing step.

[0034] The present disclosure relates to a method of preforming a metal strip, comprising embossing a pattern in the longitudinal direction of the strip at a central portion thereof while side portions on each side of the central portion of the strip are rolled without an embossing pattern, and chamfering longitudinal side edges of the strip on the side where the embossing pattern is provided. As mentioned above, the embossing is preferably carried out separately before the edge chamfering, but may be carried out after the edge chamfering or simultaneously with the edge chamfering if necessary. During the chamfering, the strip material of the longitudinal side edges of the strip is pressed to 20% - 60%, preferably 35% - 40% of the strip thickness, thereby forming an inclined edge surface along the longitudinal side edges of the strip to minimize internal weld beads in the finished welded tube. The embossing pattern provided on the strip includes protrusions. The side portions of the strip are preferably rolled to a strip thickness substantially the same as the strip thickness between the protrusions of the embossing pattern during the embossing step. This is particularly advantageous when the embossing is carried out before the edge chamfering. Thereby, the side portions of the strip have a thinner thickness which causes smaller internal weld beads in the tube.

[0035] The present disclosure will now be described with reference to the accompanying drawings in which preferred exemplary embodiments of the disclosure are shown. However, the disclosure may be practiced in other forms and should not be construed as limited to the embodiments disclosed herein. The disclosed embodiments are provided to fully convey the scope of the disclosure to those skilled in the art.

[0036] FIG. 1 is a schematic view of a setup 20 for preforming a metal strip 40. The setup includes an embossing station with an embossing roll 1 and an anvil 22, and an edge chamfering tool 30 including a pair of rolls 31, 32. The strip 40 moves through the preforming tool in the moving direction T.

[0037] Figure 2 is an exploded perspective view of an example of an embossing roll. Figure 3a is a cross-sectional view of the same roll. Figure 3b shows the details. The embossing roll 1 has a cylindrical surface 2 including a central portion 3 having an embossing pattern 10 and side portions 4a, 4b disposed on each side of the central portion 3. The side portions 4a, 4b have no embossing pattern as shown in Figure 3b. The cylindrical surface of the embossing roll has an overall width Wl. The central portion has a width W2 that is 85 to 99% of the overall width W1.

[0038] In the illustrated example, the central portion 3 of the embossing roll 1 is composed of a central embossing pattern roll 6. The side portions 4a, 4b are composed of side rolls 7a, 7b. The side rolls are disposed on each side of the central embossing roll. The embossing pattern 10 of the central portion of the embossing roll has a depth Dl and includes a plurality of elongated grooves 11 disposed at an angle with respect to the direction of rotation of the embossing roll. The groove depth Dl of the embossing pattern is preferably less than 0.35 mm. As shown in Figures 3a - b, the cylindrical surfaces of the side portions 4a, 4b are at the same height as the cylindrical surface of the central portion 3 between the grooves.

[0039] Figure 3c is a schematic cross-sectional view of the details of a combined embossing and edge chamfering roll. In this case, the embossing portion 3’ is disposed in the central section 34’ of the recess 37’. The non-patterned side portion 4a’ is also included in the central section 34’. The side section 35’ includes an inclined edge chamfering side edge 36’.

[0040] The central embossing roll can be in the form of an embossing pattern roll pack including a plurality of embossing pattern rolls. Thus, the central portion 3 of the embossing roll 1 can be composed of an embossing pattern roll pack including one or more embossing pattern disks 13a, 13b having a cylindrical embossing surface provided with the same or different embossing patterns thereon. FIG. 4 shows details of an embossing roll pack including two pattern rolls, a metal strip 40 to be embossed, and an anvil 22. In this case, the embossing pattern roll pack includes two embossing pattern disks 13a, 13b. The two embossing pattern disks 13a, 13b are arranged at an angle to form a herringbone pattern on the embossing strip together, and each has an embossing pattern consisting of grooves with a mirroring pattern. FIG. 5 shows details of an embossing roll pack including a smooth spacing 15 between the embossing pattern disks 13a, 13b. In this case, the cylindrical surface of each spacing is at the same height as the cylindrical surface of the central portion 3 between the grooves. As shown in FIG. 5, the embossing pattern disks 13a, 13b and the smooth spacing 15 have inclined edges 16, 17 at their interface. FIG. 6 shows a partial cross-sectional view of a tube 18 having an internal embossing herringbone pattern 19.

[0041] FIG. 7 shows a cross-section of a part of a finished preformed strip preformed by an embossing roll according to the present disclosure in a step following embossing. The contour of the recess provided in the edge chamfering roll 31 is indicated by a dashed line. The recess including the central section 34 and the side section 35 (only one of which is shown in FIG. 7) forms a strip receiving gap 33 together with an anvil (not shown). The gap 33 is dimensioned so that the fins 44 of the embossing pattern in the central portion 41 of the strip are not affected. In this example, the side section 35 including the outwardly inclined edge chamfering side edge 36 has a greater width than the non-patterned side portion 42 of the strip. The outermost edge of the strip is chamfered down to the thickness represented by the dashed line 43. The drawing also shows how the surface of the side portion 42 is at the same height as the bottom of the groove created between the fins 44 of the central portion 41 provided with an embossing pattern including a plurality of protruding fins 44 (only one fin is shown in this drawing). The fins 44 correspond to the grooves 11 of the embossing pattern 10 of the embossing roll (FIG. 3b).

[0042] FIG. 8a shows a part of the edge chamfering roll 31 including a central section 34 dimensioned so that the embossing pattern of the metal strip passing through the nip of the rolls is not affected by the rolls 31, 32. The side sections 35 are disposed on each side of the central section. The gap 33 has a reduced height. The central section 34 and the side sections 35 together form a recess 37 extending along the circumference of the cylindrical surface of the first roll. The recess has outwardly inclined side edges 36 on each side formed in the side section 35. FIG. 8b shows a part of an edge chamfering tool configured to receive and pass through the metal strip 40 in the gap 33 formed between the rolls 31, 32. In this drawing, the upper roll 31 corresponds to the roll in FIG. 8a. The upper roll forms an edge chamfer on the side of the strip that will be inside the finished tube. The roll 32 functions as an anvil.

[0043] Figures 9a - c show the welding principle and show the seam of a roll - formed strip during welding of its longitudinal side edges. After pre - forming in an apparatus including an embossing tool and an edge chamfering tool, the strip is roll - formed until the chamfered edges are brought close to each other (Figure 9a). The almost - closed tube is subjected to high - frequency welding by passing it through a welding coil. The strip material begins to melt due to the energy induced by the high - frequency coil (Figure 9b). During welding, the molten material fills the space formed between the edges of the chamfered strip and forms a weld bead (Figure 9c). Due to the thin thickness of the strip in this space and the welding area, the internal weld bead height can be kept to a minimum.

[0044] Those skilled in the art will understand that the present disclosure is not limited to the above - described preferred embodiments. Those skilled in the art will further understand that modifications and variations are possible within the scope of the appended claims. Additionally, modifications to the disclosed embodiments can be understood and realized by those skilled in the art who practice the claimed present disclosure from a consideration of the drawings, the present disclosure, and the appended claims.

Claims

1. An apparatus for preforming a metal strip (40) for the manufacture of a tube having internal grooves, roll formed and high frequency welded, comprising an embossing tool (20) and a strip edge chamfering tool (30), - The embossing tool includes an embossing roll (1) having a cylindrical surface (2) with a central embossing portion (3, 3') and side portions (4a, 4b) arranged on each side of the central portion, wherein an embossing pattern (10) is provided in the central portion and the side portions have no embossing pattern, - The strip edge chamfering tool includes an edge chamfering roll (31) having a recessed central section (34, 34') and side sections (35, 35') on each side of the central section, and an anvil roll (32), The edge chamfering roll (31) and the anvil roll (32) are configured to receive and pass the metal strip in a gap (33) formed between the rolls during use, The gap (33) has a reduced height in the side sections where the longitudinal side edges of the metal strip pass, whereby the longitudinal side edges on each side of the metal strip and on the embossed side of the metal strip are chamfered when passing between the pair of rolls (31, 32), The embossing pattern (10) of the central embossing portion includes a plurality of grooves (11) arranged on the cylindrical surface of the central portion (3), The cylindrical surfaces of each side portion (4a, 4b) are of the same height as the cylindrical surface of the central portion (3) between the grooves. An apparatus.

2. - The strip edge chamfering tool (30) is arranged downstream of the embossing tool in the moving direction (T) of the strip to be preformed, - The embossing tool includes the cylindrical surface (2) of the embossing roll (1), the cylindrical surface including the central embossing portion (3) and side portions (4a, 4b) arranged on each side of the central portion, wherein an embossing pattern (10) is provided in the central portion and the side portions have no embossing pattern, and - The central section (34) of the strip edge chamfering tool (30) is dimensioned so that an embossing pattern of a metal strip passing between the pair of rolls through the edge chamfering gap (33) is not affected by the rolls (31, 32), the apparatus according to claim 1.

3. The embossing tool and the strip edge chamfering tool are integrated to include a single combined embossing and edge chamfering roll, whereby the central embossing portion (3') is included in the central section (34') of the edge chamfering gap (33), the apparatus according to claim 1.

4. The embossing roll (1) is composed of a central embossing pattern roll pack (6) and side rolls (7a, 7b), The side rolls are arranged on each side of the central embossing pattern roll pack, The central embossing pattern roll pack has a cylindrical surface forming the central portion (3), and the side rolls have cylindrical surfaces forming the side portions (4a, 4b), the apparatus according to any one of claims 1 to 3.

5. The cylindrical surface of the embossing roll has a total width (Wl) of 15 mm or more, The central portion of the embossing roll has a width (W2) that is 85 to 99% of the total width (Wl), the apparatus according to any one of claims 1 to 4.

6. The central section (34) of the gap (33) between the first and second rolls (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 portion (3) of the embossing roll (1), the apparatus according to claim 5.

7. The side sections (35) of the gap (33) between the first and second rolls (31, 32) each have a width that is at least half of the difference between the total width (Wl) of the embossing tool and the width (W2) of the central portion of the embossing tool, the apparatus according to claim 5 or 6.

8. The first roll (31) of the pair of rolls in the edge chamfering tool includes a recess (37), The recess (37) has outwardly inclined side edges (36) on each side of the recess and extends along the circumference of the cylindrical surface of the first roll, the apparatus according to any one of claims 1 to 7.

9. The device according to claim 8, wherein the inclined side edge (36) is inclined at an angle of 30 to 60°, preferably 43 to 47°.

10. A method for preforming a metal strip (40) for the manufacture of a tube having internal grooves, roll formed and high frequency welded, using the device according to any one of claims 1 to 9, comprising: - embossing a pattern in the longitudinal direction in the central portion of the strip while the side portions (42) on each side of the central portion (41) of the strip are rolled without an embossing pattern, the embossing pattern including protrusions (44), and the side portions of the strip being rolled to a strip thickness substantially the same height as the strip thickness between the protrusions of the embossing pattern during the embossing step; - chamfering the longitudinal side edges (43) of the strip on the side where the embossing pattern is provided; The method comprising.

11. During the chamfering, the strip material of the longitudinal side edges (43) of the strip is pressed to 20 to 60%, preferably 35 to 40% of the strip thickness, thereby forming an inclined edge surface along the longitudinal side edges of the strip. The method according to claim 10.

12. The method according to claim 10 or 11, using the device according to claim 2 or, when dependent on claim 2, any one of claims 4 to 9, followed by the step of chamfering the side edges.

13. The method according to claim 10 or 11, using the device according to claim 3 or, when dependent on claim 3, any one of claims 4 to 9, wherein the embossing and edge chamfering are carried out simultaneously in an integrated embossing and edge chamfering tool.

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