Method for correcting eccentricity in a tube

Abstract

The invention relates to a device for correcting eccentricity in a tube, enabled to be installed in a drawing machine and in continuity with a die of the same drawing machine, and comprising a bench, a rotating rotor and a tilt, wherein the bench and the die of the drawing machine have coincident axial axes; the rotor being inserted in the bench with the same axial axis as the bench, and with capacity for free rotation inside the bench; the tilt being inserted and fixed in the rotor wherein the axial axis thereof is coincident with the rotor axis, wherein the tilt also has the same capacity for rotation as the rotor and is concentrical about the axial axis thereof; the tilt having a hole in a direction parallel to the axial axis thereof, said hole being in an off-centre position in relation to the axial axis of the same tilt.

Description

OBJECT OF THE INVENTION

[0001] The object of the present invention application is to register a method for correcting eccentricity in a tube, which incorporates notable innovations and advantages compared to techniques used hitherto.

[0002] More specifically, the invention proposes the development of a method for correcting eccentricity in a tube which, due to the particular arrangement thereof, makes it possible to correct the eccentricity of a tube more effectively during the manufacturing process thereof.

[0003] In document US 3 167 176 A, the drawing mandrel itself is configured to tilt during the drawing operation in order to reduce eccentricity. In document US 3 131 803 A, the drawing die itself is configured to tilt during the drawing operation in order to reduce eccentricity. FR 1 059 136 A shows the drawing and straightening of tubes. The tilt is driven in rotation by a motor. JP S62 212012 A shows a process of drawing a straight pipe. For this purpose the tilt is driven in rotation by a motor.BACKGROUND OF THE INVENTION

[0004] In the current state of the art, quality requirements of copper tubes for industrial use are known, given that such tubes are usually subsequently subjected to new deformation processes, such as re-drawing to smaller sizes, to large expansions and / or demanding curvatures, and ultimately, much more aggressive working conditions.

[0005] This means that it is extremely important to maintain the uniformity of the properties of the tube both with regard to thickness and at a microstructural level._It is known in the state of the art that a minimum thickness must be maintained to withstand the pressure of the fluid transported by the tube, and it is also well known that there is a need to reduce the thickness of the copper tube to a minimum to reduce the cost of the necessary metal.

[0006] A good part of these features in the tubes are established during the drawing process thereof.

[0007] In line with the aforementioned points, one of the main parameters that determines the quality of a copper tube is the eccentricity thereof. Eccentricity is an indicative value of the concentricity of a tube.

[0008] Errors in eccentricity can lead to structural failures of the tube (reduction of the minimum thickness) or a waste of material (increase in the minimum thickness), among others.

[0009] One process that has a major impact on the eccentricity of a tube is the drawing process thereof.

[0010] The present invention contributes to solving this problem, since it allows the eccentricity of a tube to be corrected in a very effective manner during the manufacturing process thereof, and above all with the notable added advantage that previous measuring and knowing the prior eccentricity of the tube itself is not required.DESCRIPTION OF THE INVENTION

[0011] The present invention has been developed with the aim of providing a method for correcting eccentricity in a tube, being drawn along a tube path in a drawing machine equipped with a drawing die, wherein said tube has an eccentricity between the outer perimeter and inner perimeter thereof so that said tube has a maximum thickness and a minimum thickness along a circumferential path due to said eccentricity, is characterised in that it comprises the following steps: a first passage of the tube through a through hole of a tilt, said through hole having an axial axis parallel to the axis of the die of the drawing machine, said hole being laterally shifted in relation to said axial axis of the die, wherein said through hole has a capacity for free and concentrical rotation in relation to said axial axis of the die of the drawing machine, a subsequent passage of said tube , through the inside of said die of the drawing machine, the axis of the tube therefore in the subsequent passage through the die being shifted and substantially parallel in relation to the axis of said tube in the first passage thereof through the through hole, a free movement of the tube, which is simultaneous to the first passage of the tube through the through hole and simultaneous to the subsequent passage of said tube through the die, wherein said free movement is generated in the subsequent passage of the tube through the die acting on and affecting the difference in tube thickness due to the eccentricity of the tube itself; wherein the free movement is allowed by the capacity for free rotation of the through hole of the tilt, and said free movement involves a tilt of the section of the tube that is prior to _the subsequent passage though the die thereby generating a free rotation of said tilt and said through hole around said axial axis of the die.

[0012] The method for correcting eccentricity in a tube, wherein initially, prior to the first passage, the tilt is placed around the tube by means of the through hole, and subsequently the tube is placed in the drawing machine such that the tilt is inserted in and coupled to a rotor inserted in a bench installed in said drawing machine, said rotor enabling said rotation of the tilt and the through hole.

[0013] The present invention corrects the eccentricity of a tube effectively during the manufacturing process thereof and, above all, has the notable added advantage that previous measuring and knowing the prior eccentricity of the tube itself is not required.

[0014] Other features and advantages of the method for correcting eccentricity in a tube will become apparent from the description of a preferred yet non-exclusive embodiment, which is illustrated by way of non-limiting example in the accompanying drawings, wherein:BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is a schematic view indicative and explanatory of the eccentricity that can be present in a tube. Figure 2 is a schematic and cross-sectional view of a device for correcting eccentricity in a tube. Figure 3 is a schematic view indicative of a rotation or tilt of the tube in a preferred embodiment of the method for correcting eccentricity in a tube of the present invention. Figure 4 is a schematic view of a preferred embodiment of the method for correcting eccentricity in a tube of the present invention. Figure 5 is a schematic view indicative of an evolution of the rotation or tilt of the tube in a preferred embodiment of the method for correcting eccentricity in a tube of the present invention. Figure 6 is a representation of tests carried out by the applicant with advantageous outcomes with regard to the resulting eccentricity using the method for correcting eccentricity in a tube of the present invention. DESCRIPTION OF A PREFERRED EMBODIMENT

[0016] As can be seen in figure 1, it is known in the state of the art that a tube can have an eccentricity between the outer diameter thereof and the inner diameter thereof and therefore the same tube can also have a maximum or greater thickness and a minimum or lesser thickness due to said eccentricity.

[0017] In the state of the art, eccentricity is usually calculated as a percentage:

[0018] In the same figure 1, a tube ideally without eccentricity is represented on the left, wherein the perimeter and external diameter thereof compared to the perimeter and internal diameter thereof turn out to be concentrical circumferences, and wherein, accordingly, no differences in thickness are seen along the circumferential path thereof.

[0019] In contrast, in the same figure 1, another tube that has a clear eccentricity is represented on the right, wherein the outer perimeter and inner perimeter thereof are no longer mutually concentrical circumferences, and therefore, as a result, it can be seen that said the tube has different thicknesses along the circumferential path thereof, as indicated by a circle and arrows in the same figure 1.

[0020] In accordance with the previously mentioned points, the method for correcting eccentricity in a tube of the present invention is designed to correct the eccentricity of a tube effectively during the manufacturing process thereof.

[0021] As schematically and preliminarily shown in the cross-sectional view in figure 2, a device for correcting eccentricity in a tube not forming part of the present invention is intended to be installed in a drawing machine 1 for the tube 2 itself, and in continuity with a die 3 of the same drawing machine 1 during the operation thereof.

[0022] As can be seen in figure 3, after numerous tests carried out on tube drawing machines and processes, through 3D simulations, the applicant has observed that the difference in eccentricity along the length of a tube 2 has a tendency towards a natural rotation or tilt of the tube 2 in the usual drawing process of the tube 2 itself, originating at the entry of the tube 2 into a die 3 of a drawing machine 1. Said tilt observed in the section of the tube 2 prior to the passage thereof through the die 3 is aimed towards the perimeter or thickest wall of the same tube 2 with eccentricity, if there is freedom to do so, as indicated by the curved arrow in figure 3.

[0023] In said figure 3 it can be seen how the tube 2 passes through a die 3 of a drawing machine 1, moving to the left in the direction indicated by the arrow in figure 3 as a consequence of the drawing process thereof. The passage of the tube 2 through the die 3 means that the same tube 2 experiences a tilt originating in the same die 3 and in the section thereof that has not yet passed through the die 3. Said tilt, indicated by the curved arrow of figure 3, is aimed towards the perimeter or thickest wall of the same tube 2, and is therefore a rotation with respect to an axis Z that is perpendicular to axes X and Y, as indicated in figure 3.

[0024] The same applicant has also observed that allowing the aforementioned rotation and tilt of the tube 2 around the Z axis and towards the perimeter or thickest wall of the same tube 2 with eccentricity leads to a notable improvement of the final eccentricity resulting from the same drawing process of the same tube 2.

[0025] With the intention of allowing said rotation or tilt of the tube 2, and as can be seen in figure 2, a device for correcting eccentricity in a tube not forming part of the invention may comprise a bench 4, a rotating rotor 5 and a tilt 6, the bench 4, rotor 5 and tilt 6 having a general circular geometry.

[0026] The bench 4 is integral with the drawing machine 1, and is arranged so that the axial axis of the bench 4 is coincident with the axial axis of the die 3 of the drawing machine 1, as can be seen in the figure 2.

[0027] The rotor 5 is inserted in the bench 4, and has the same axial axis as the bench 4 and the capacity for free rotation inside the bench 4 and concentrically around the same axial axis thereof, in this preferred embodiment by means of bearings 41 installed between the bench 4 and the rotor 5.

[0028] On the other hand, the tilt 6 is inserted in the rotor 5 in a fixed position in relation to the same rotor 5 and in such a way that the axial axis thereof is also coincident with the axial axis of the rotor 5, as can be seen in figure 2, and as a result, the tilt 6 also has the same capacity for rotation as the rotor 5 and concentrically about the same axial axis thereof.

[0029] In addition to all of the previously described points, in this device for correcting eccentricity in a tube, the tilt 6 has a through hole 61 in a direction parallel to the axial axis thereof, with the particular feature in that said through hole 61 is in an off-centre position in relation to the axial and rotational axis of the tilt 6 itself, and therefore said through hole 61 is also able to freely rotate concentrically in relation to the rotational axis of the tilt 6 itself, as also indicated by the rotating arrow in figure 2.

[0030] Thanks to this device for correcting eccentricity in a tube, and in particular to the explained capacity for rotation of the tilt 6 thereof and the through hole 61 thereof, in a drawing machine 1 the aforementioned rotation can be allowed, and the explained tilt of the tube 2 around the Z axis and towards the perimeter or thickest wall of the same tube 2 with eccentricity can be enhanced, as represented in figure 3, which implies a notable improvement of the final eccentricity of the tube 2 in the same drawing machine 1 that incorporates this device for correcting eccentricity in a tube, as experimentally verified by this applicant.

[0031] Such as it is represented in figure 2, the tilt 6 and the rotor 5 are coupled and fixed by means of a mutually complementary conical geometry between them. This fixing allows the tube 2 to be directed into the drawing machine 1 and in the device described.

[0032] In other words, initially prior to the end of the tube 2 entering the drawing machine 1 and this device, the tilt 6 is placed at the beginning of the tube 2 by means of the through hole 61 thereof. The tube 2 is then directed into the drawing machine 1, such that the tilt 6 makes contact with, is inserted in and coupled to the rotor 5, aided by the mutually complementary conical geometry between the tilt 6 and the rotor 5. This conical coupling between the tilt 6 and the rotor 5 makes it possible to achieve a final fixing and positioning, as shown in figure 2.

[0033] This invention includes a method for correcting eccentricity in a tube, being drawn along a tube path in a drawing machine 1 provided with a drawing die 3.

[0034] In one embodiment, said method of the invention can also be carried out by using the device for correcting eccentricity in a tube described above.

[0035] As was previously described in figure 1, it is known in the state of the art that a tube 2 has an eccentricity between the outer diameter thereof and the inner diameter thereof, so that said tube has a maximum or greater thickness and a minimum or lesser thickness along a circumferential path due to said eccentricity.

[0036] The method for correcting eccentricity in a tube of the present invention comprises several steps, as schematically described below in figure 4 and with the help of figure 2.

[0037] Firstly, in the path of the tube 2, there is a first passage 10 of the tube 2 through a through hole 61 of a tilt 6, in the direction indicated by the straight arrow in figure 2 from right to left.

[0038] Said through hole 61 has an axial axis parallel to the axis of the die 3 of the drawing machine 1, said hole 61 being laterally shifted in relation to said axial axis of the die 3, wherein said through hole 61 has a capacity for free and concentrical rotation in relation to said axial axis of the die 3 of the drawing machine 1, as indicated by the rotating arrow of the same figure 2.

[0039] Following the path of the tube 2 indicated by the straight arrow in figure 2 from right to left, the same tube 2 continues with a subsequent passage 20 inside said die 3 of the drawing machine 1, the axis of the tube 2 in the subsequent passage 20 through the die 3 thus being shifted in relation to the axis of said tube 2 in the first passage 10 thereof through the through hole 61, as can be seen and deduced in figure 2.

[0040] As previously mentioned and explained, the initial eccentricity of the tube 2 itself generates free rotation around the Z axis and a natural tilt of the tube 2 at the entrance of the die 3, which is represented and indicated by the curved arrow in figure 3.

[0041] This free rotation around the Z axis and the tilt experienced by the tube 2 is possible due to the possibility of free rotation or rotation of the tilt 6 and the through hole 61 thereof as indicated by the rotating arrow in figure 2, such that the tilt 6 and the through hole 61 thereof turn or rotate to the position thereof depending on the location of the perimeter or thick wall of the tube 2, according to the previous eccentricity of the same tube 2.

[0042] This means that simultaneously with the first passage 10 through the through hole 61 and the subsequent passage 20 of said tube 2 through the die 3 along the path of the tube 2, indicated by the straight arrow in figure 2 from right to left, there is a free movement 30 of the same tube 2.

[0043] Said free movement 30 is generated in the subsequent passage 20 of the tube 2 through die 3, and specifically by acting on and affecting the difference in thickness of the tube 2 due to the eccentricity of the tube 2 itself that is represented in figure 1.

[0044] Figure 5 shows the free rotation that the tube 2 can experience around the Z axis, measured at different points along the length thereof according to the advance and subsequent passage 20 of the same tube 2 through the machine 3.

[0045] In accordance with all that has been previously explained, the capacity for free rotation of the tilt 6 and the through hole 61 thereof allows the tube 2 to enter the die 3 with a certain tilt, which is the tilt the tube 2 itself tends to freely, which could not be achieved without using the method of the present invention, also taking into account that the orientation of the specific tilt is free, such that the tilt 6 and the through hole 61 thereof end up turning or rotating towards the side of the perimeter or thick wall of the tube 2, according to the previous eccentricity of the same tube 2.

[0046] In short, the present invention takes advantage of the natural tilt of the tube 2 that initially occurs as a consequence of the previous eccentricity of the tube 2 itself in order to turn or rotate the tilt 6 and the through hole 61 thereof, thus allowing the tilt of the tube 2 to have a value greater than that which the tube 2 itself freely tends to have. In this way, a tilt of the tube 2 is allowed in the general drawing procedure, and a lower output eccentricity is achieved in the drawing of the tube 2 without the need to previously measure the incoming eccentricity of the same tube 2.

[0047] In addition, said free movement 30 is allowed by the capacity of free rotational movement of the through hole 61 of the tilt 6 indicated by the rotating arrow of figure 2, and also involves a tilt of the section of the tube 2 that is prior to the subsequent passage 20 though the die 3 thereby generating a free rotation of said tilt 6 and said through hole 61 around said axial axis of the die 3, as can also be deduced from the rotating arrow in figure 2.

[0048] As previously mentioned, in a preferred embodiment of the method for correcting eccentricity in a tube of the present invention, initially prior to starting the general drawing procedure of the same tube 2 in a drawing machine 1, the tilt 6 is placed at the beginning of the tube 2 by means of the through hole 61 thereof. The tube 2 is then directed into the drawing machine 1 so that the tilt 6 makes contact with, is inserted in and coupled to the rotor 5. A conical coupling between the tilt 6 and the rotor 5 helps make it possible to achieve a definitive fixing and positioning, as shown in figure 2. Subsequently, the first passage 10 of the tube 2 through the through hole 61 of the tilt 6 is carried out, as previously described, as well as all the rest of the method for correcting eccentricity in a tube described in the present invention.

[0049] Figure 6 shows the best results obtained by the applicant in the resulting eccentricity in a tube 2 after the drawing thereof and using the method for correcting eccentricity in a tube of the proposed invention.

[0050] The top image of figure 6 represents the plastic deformation observed by means of 3D simulations that the tube 2 experiences after passing through the die 3 of a drawing machine 1, in using the method for correcting eccentricity in a tube of the proposed invention.

[0051] The Y axis of the coordinates of the two graphs in figure 6 corresponds to the axis of the die 3, and the origin of coordinates is the centre of the outlet face of the die 3.

[0052] The tube 2 therefore moves from right to left, as indicated by the horizontal straight arrow in figure 6.

[0053] The X axis of the coordinates of the top graph of figure 6 dimensions the cross section of the tube 2 at different points of the length thereof after having experienced a drawing throughout 225 mm, and shows how the geometry of the tube 2 changes in the first 225 mm of drawing as a result of the plastic deformation indicated in the top image of the same figure 6.

[0054] Point A of the Y axis coordinate of the two graphs in figure 6 corresponds to the value Y=-225mm and corresponds to the first point of the tube 2 that has passed through drawing die 3 using the proposed invention, without seeing the results yet.

[0055] Point B of the Y axis coordinate of the two graphs in figure 6 corresponds to the Y=0 coordinate value, and therefore corresponds to the point of the tube 2 just at the exit of the die 3, and after a previous path of 225mm from right to left of the same tube 2 through the die 3 using the proposed invention.

[0056] Point C of the Y axis coordinate of the two graphs of figure 6 corresponds to the part of the same tube 2 not yet processed by the die 3, but which nevertheless already experiences the tilt of the tube 2, which has been previously explained, represented and indicated in figures 3 and 5.

[0057] In the bottom graph of figure 6, the evolution of the thicknesses of the thick wall and the thin wall of the tube 2 can be seen, as well as the evolution of the resulting eccentricity in the same tube 2 during the path of the first 225 mm of drawing, meaning between the values -225mm and 0mm of the Y coordinate.

[0058] On the Y coordinate more than 50 mm to the right of the bottom graph of figure 6, obviously neither the thickness of the thick wall nor of the thin wall nor the eccentricity in tube 2 vary, since they have not yet passed through the die 3, and therefore they show the thicknesses of the thick wall and the thin wall and the value of the eccentricity of the tube 2 with constant values, prior to being subjected to drawing.

[0059] The thicknesses of the thick wall and the thin wall and the eccentricity values of the tube 2 appear between the values -200mm and -100mm of the Y coordinate of the bottom graph of figure 6, and they are still not too different from the values greater than 50 mm on the Y coordinate to the right of the graph prior to being subjected to drawing, since they correspond to the initial sections of the tube 2 and only at the beginning of the drawing process using the proposed invention.

[0060] It is between the values -50mm and 0mm of the Y coordinate, in other words when the use of the method for correcting eccentricity in a tube of the proposed invention is already effective, when the notable drop and improvement in eccentricity of the tube 2 is appreciated, specifically noting and comparing the value of the eccentricity on the 0 coordinate mm at point B of the Y axis of the last processed section of the tube 2, which is almost equal to 2%. This value is much lower and better than the constant eccentricity value of approximately 6% on the Y coordinate, greater than 50 mm from point C, which marks the eccentricity of the tube 2 prior to the drawing thereof, as can be seen in the graph at the bottom of figure 6.

[0061] In other words, as indicated in the bottom graph of figure 6, using the method of the present invention, the resulting eccentricity in a tube 2 during the drawing process thereof is lower and better by a value D than the initial eccentricity in the same tube 2 prior to the drawing thereof.

[0062] In this preferred embodiment of the present invention, the tube 2 is made of copper or a copper alloy.

[0063] A resulting tube according to the method described above, and which in this preferred embodiment is metal, made of copper or a copper alloy.

[0064] In short, the method for correcting eccentricity in a tube of the present invention allows the tube 2 itself to rotate freely along the path thereof, depending on how it freely acts on the difference in thicknesses due to its own eccentricity in the subsequent passage 20 thereof through the die 3, as represented in figure 1.

[0065] The method for correcting eccentricity in a tube of the present invention is intended to correct the eccentricity a tube 2 can have in a more effective way than what has been known up to now in the state of the art, and above all, with the added advantage of not requiring to previously measure or know the prior eccentricity existing in the tube itself 2.

[0066] The applicant has verified that by means of this particular technique described in the present invention, the resulting tube has a significantly lower and better final eccentricity than the results normally obtained in the known state of the art, and also with the significant added advantage of not requiring previous measuring or knowing the prior eccentricity existing in the tube 2 itself.

[0067] The details, shapes, dimensions and other accessory elements, as well as the materials used to manufacture the method for correcting eccentricity in a tube of the invention, may be suitably substituted for others which are technically equivalent without departing from the scope defined by the claims included below.

Claims

1. A method for correcting eccentricity in a tube, being drawn along a tube path in a drawing machine (1) equipped with a drawing die (3), wherein said tube (2) has an eccentricity between the outer perimeter and the inner perimeter thereof so that said tube has a greater thickness and a lesser thickness along a circumferential path due to said eccentricity, characterised in that it comprises the following steps: - a first passage (10) of the tube (2) through a through hole (61) of a tilt (6), said through hole (61) having an axial axis parallel to the axis of the die (3) of the drawing machine (1), said hole (61) being laterally shifted in relation to said axial axis of the die (3), wherein said through hole (61) has a capacity for free and concentrical rotation in relation to said axial axis of the die (3) of the drawing machine (1), - a subsequent passage (20) of said tube (2), through the inside of said die (3) of the drawing machine (1), the axis of the tube (2) therefore in the subsequent passage (20) through the die (3) being shifted and substantially parallel in relation to the axis of said tube (2) in the first passage (10) thereof through the through hole (61), - a free movement (30) of the tube (2), which is simultaneous to the first passage (10) of the tube (2) through the through hole (61) and simultaneous to the subsequent passage (20) of said tube (2) through the die (3),wherein said free movement (30) is generated in the subsequent passage (20) of the tube (2) through the die (3) acting on and affecting the difference in tube (2) thickness due to the eccentricity of the tube (2) itself; wherein the free movement (30) is allowed by the capacity for free rotation of the through hole (61) of the tilt (6), and said free movement (30) involves a tilt of the section of the tube (2) that is prior to _the subsequent passage (20) though the die (3) thereby generating a free rotation of said tilt (6) and said through hole (61) around said axial axis of the die (3).

2. The method for correcting eccentricity in a tube according to claim 1, wherein initially, prior to the first passage (10), the tilt (6) is placed around the tube (2) by means of the through hole (61), and subsequently the tube (2) is placed in the drawing machine (1) such that the tilt (6) is inserted in and coupled to a rotor (5) inserted in a bench installed in said drawing machine, said rotor (5) enabling said rotation of the tilt (6) and the through hole (61).

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