ES2382399B1 - EXCENTRICITY MEASUREMENT SYSTEM FOR NON-PHERROMAGNETIC METAL TUBES AND CORRESPONDING METHOD - Google Patents

Abstract

Eccentricity measuring system for non-ferromagnetic metal tubes by using induced currents, comprising # at least three coils separated equidistant from each other and radially from the axis of a metal tube to be measured and arranged externally to said metal tube, said coils being linked at least to a variable frequency alternating current power supply, each of said coils being associated with a measuring device and with data processing means configured to determine an eccentricity value of the metallic tube to be measured, in wherein said data processing means are associated with a data storage device, # each of said coils being linked to an electrical signal filtering system and an electrical signal amplifier system.

Description

Eccentricity measurement system for non-ferromagnetic metal tubes and corresponding method

OBJECT OF THE INVENTION

The purpose of this patent application is to register an eccentricity measurement system for non-ferromagnetic metal tubes that incorporates notable innovations and advantages.

More specifically, the invention proposes the development of an eccentricity measurement system for non-ferromagnetic metal tubes, based on the use of induced currents, comprising at least three coils located radially with respect to the axis of a tube to be measured and processing means to determine the eccentricity of the tube to be measured.

The present invention also relates to an eccentricity measurement method for non-ferromagnetic metal tubes based on the use of induced currents.

BACKGROUND OF THE INVENTION

The eccentricity is an indicative value of the concentricity of a tube and is calculated by measuring the thicknesses of the tube along its entire circumference.

There is no regulation that regulates the eccentricity but the minimum wall thicknesses of the copper tube. Currently, the UNE-EN 1057 and UNE-EN 12735-1 regulations regulate the minimum wall thickness that the sanitary pipe and the ACR tube must meet, respectively, so that they can withstand the pressure of the fluids circulating inside.

In the manufacturing process of the tubes, after extrusion, several stretching processes are usually performed. Experimentally it has been shown that the eccentricity of the final tube is marked by the eccentricity in the original tube, that is, the tube at the exit of the extrusion press, as can be seen in the graph of figure 4. In said figure 4 represents the eccentricity of the original tube or press tube against the eccentricity of the final tube as a percentage, and it can be verified that said eccentricity moves in the different processes. A 4% reference value for eccentricity in the final tube is also shown in the graph with a dashed line. Said value has been found as an empirical reference to limit said eccentricity in the final tube and thus avoid producing tubes with an excess of material and therefore of weight.

It is vitally important to measure and correct eccentricity at the point of origin. As can be seen in the graph in figure 4, if we start with press tube eccentricity values below the 8-10% interval, it is possible to obtain a final tube with an eccentricity <4%, thus achieving a better use of the raw material.

On the other hand, for the production of copper tube there are two types of technology:

Presses of low extrusion ratio (thicker tube), accompanied by a rolling mill. This is a solution that requires a greater investment due to the cost of the mill, as well as having more space for its location and greater maintenance requirements. However, this type of presses, combined with the laminator, ensures an eccentricity of less than 8% since the rolling process has the advantage that greatly improves the eccentricity of the original tube coming out of the press.

Presses of high extrusion ratio (smaller thickness of the tube, does not need a back laminate and can be directly stretched). This system is technically simpler, requires less maintenance for its operation and takes up less space, which results in lower costs than low extrusion ratio presses. However, in this case the guaranteed eccentricity on average is 8% (it can be in the range of 2 to 15%), which requires greater control of the tubes to avoid excessive deviations from the standards; also as a counterpart the number of rejections increases with respect to the presses of low extrusion ratio. If greater control is not carried out, the eccentricity greater than 8% must be compensated with the use of a greater quantity of raw material to guarantee the minimum thickness of the metal tube.

It is therefore necessary to know the exact value of the eccentricity of the tube at the exit of the press, since this value can be related to the variables that can produce it, and consequently correct and / or adjust them.

Examples in the state of the art are known as the American document US 3693075 A in which a system for measuring the eccentricity of a tube made of non-ferromagnetic material by the use of induced currents is disclosed. This system employs a pair of coils, a main and a secondary, and is based on the known fundamentals of electromagnetism.

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According to said known fundamentals, by circulating electric current through a coil a magnetic field is generated. If said coil is located in the vicinity of an electrical conductive material, said magnetic field induces electrical currents in the material. The characteristics of the induced electric current depend on the characteristics of the inductive magnetic field and the material. In turn, these induced currents, in turn, induce a magnetic reaction field that opposes the first and, in the coil, the corresponding variation in potential difference due to the presence of this conductive material can be measured.

The measurement of the potential difference induced in the presence of the conductive material, provides information on the properties of this material as well as its geometric characteristics.

Continuing with the previous American document, in a condition of use, the wall of the tube to be measured is located between both coils. This feature limits the versatility of the system since it cannot be used for example for sealed pipes. Another drawback of the invention of the previous American document is that it requires rotating the tube to be measured in a condition of use in order to have several measurements in a segment of the tube. In addition, high accuracy cannot be obtained in the measurements obtained by using a two-coil configuration as illustrated by the American document.

There is therefore a need to obtain an eccentricity measurement system for non-ferromagnetic metal tubes by induced currents as well as a measurement method that solves the above inconveniences while also providing additional advantages.

DESCRIPTION OF THE INVENTION

The present invention has been developed in order to provide an eccentricity measurement system for non-ferromagnetic metal tubes that solves the aforementioned drawbacks, also providing additional advantages that will be apparent from the description that follows.

It is therefore an object of the present invention to provide an eccentricity measurement system for non-ferromagnetic metal tubes, based on the use of induced currents, which is characterized by comprising at least three coils separated equidistant from each other and located radially with respect to to the axis of a metal tube to be measured. All coils keep the same separation distance from the metal tube and are arranged externally to said metal tube.

Said coils are linked to at least one alternating current power supply of variable frequency, so that in a condition of use, the power supply supplies an alternating electric current to each of the coils, which in turn generate a magnetic field inductor variable with time, which induces an electric current in the metal tube to be measured, said current of the metal tube creating a magnetic field of reaction opposite to the magnetic field inductor, in which said magnetic field of reaction partially demagnetizes the coils, which produces a variation of the voltage in each of the coils.

Each of said coils is associated with a measuring device configured to measure said voltage variation. Additionally, each of said coils is associated with data processing means configured to compare the difference in voltage variation for each combination of two coils and determine an eccentricity value of the tube to be measured, in which said data processing means They are associated with a data storage device.

In addition, each of said coils is linked to an electrical signal filtering system and an electrical signal amplifier system.

Thanks to these characteristics, an eccentricity measurement system is obtained that does not require rotating the metal tube to be measured and which can be applied to sealed tubes, in a static position or in longitudinal movement, thereby increasing the productivity in the manufacturing of said tube metal.

According to a preferred aspect of the invention said processing means have a programmable controller of the PLC type; and said measuring device is preferably an electrical resistance voltage divider bridge.

In a preferred embodiment, the eccentricity measurement system of the invention may have a signal filtering system, a signal amplifier system and a data storage device.

Preferably, said power supply supplies an alternating current with a frequency between 200 and 1000 Hz.

On the other hand, each coil is housed in a cylindrical protective body.

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The metal tube to be measured preferably has an outer diameter greater than 30mm, and a thickness between 0.5 and 3.5mm.

It is also another object of the invention to provide an eccentricity measurement method for non-ferromagnetic metal tubes, which is characterized by comprising the steps of:

position at least three coils equidistant from each other and radially from the axis of a metal tube to be measured,

measure the voltage variation in each coil,

filter the electrical signals from each of the coils,

amplify the electrical signals obtained after filtration,

determine differences in voltage variations for each combination of two coils,

store and process the electrical signals obtained after amplification.

The eccentricity measurement method described above can be carried out continuously in an extrusion metal tube manufacturing process.

Other features and advantages of the eccentricity measurement system of the present invention will be apparent from the description of a preferred but not exclusive embodiment, which is illustrated by way of non-limiting example in the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1.- It is a schematic and partial view of the system according to the invention applied on a cross section of a metallic tube to be measured;

Figure 2.- It is a schematic and perspective view of the system according to the invention applied on a segment of the metallic tube to be measured;

Figure 3- It is a block diagram showing the method according to the invention; Y

Figure 4- It is a graph that relates the eccentricity of the press tube with that of the final tube as a percentage.

DESCRIPTION OF A PREFERRED EMBODIMENT

As shown in the accompanying figures, a preferred embodiment of an eccentricity measurement system for non-ferromagnetic metal tubes is seen, based on the use of induced currents.

In Figure 1 three coils (1) can be seen schematically separated equidistant from each other and located radially with respect to the axis of a metal tube (4) to be measured, and the coils (1) are arranged externally to the tube metallic (4). The coil (1) is made of an electrically conductive material such as copper although it will be possible to use any other material that has similar technical characteristics.

Preferably, the three coils (1) are located equidistant at 120 ° from each other and keeping approximately a distance between 0 and 3 mm with respect to the outer face of the metal tube (4) to be measured, depending on whether said metal tube (4) is at rest, where it can make contact, or moving in the longitudinal direction, where it does not make contact. It can also be seen that each coil (1) is housed in a cylindrical protective body (2) to prevent damage to the winding of the coils (1). In the attached figures, said cylindrical protective body (2) is schematically represented, so that the coils (1) are visible for a better understanding of the invention.

In Figure 2 it can be seen that the coils (1) are linked to an alternating current power supply (5) of variable frequency, which supplies an alternating current with a frequency between 200 and 1000 Hz. The alternating current is conducted from the power supply (5) to each coil (1) by means of a cable (3a), which can be any available in the market and that is suitable for this purpose.

Continuing with Figure 2, it can be seen that each of said coils (1) is linked to an electrical resistance voltage divider bridge (17), an electrical signal filtering system (6) and an amplifier system (7) of Electrical signal.

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In addition, each of said coils (1) is linked to data processing means such as a programmable controller (8) of the PLC type. In turn, said controller (8) is associated with a data storage device (9).

Preferably, each coil (1) will be linked to its own electrical resistance voltage divider bridge (17), an electrical signal filtering system (6) and an electrical signal amplifier system (7). Instead, the coil set (1) will be linked to the same controller (8) and the same data storage device (9) that they will share.

The coils (1) and the previous systems and elements are linked through a cable (3b), which can be any available in the market and that is suitable for this purpose.

When measuring the eccentricity of the metal tube (4), a method comprising a series of steps represented in the block diagram of Figure 3 can be followed.

The three coils (1) are positioned equidistant from each other (11) and positioned radially with respect to the axis of the metal tube (4) to be measured. At this time and in a condition of use, the power supply (5) supplies an alternating electric current to each of the coils (1), which in turn generate a magnetic field variable inductor with time, which induces a electric current in the metal tube (4) to be measured, said metal tube current (4) creating a magnetic reaction field opposite to the inductive magnetic field. This magnetic reaction field partially demagnetizes the coils (1), which produces a variation of their autoinductance (hereinafter L). This variation of L is proportional to the thickness of the metal tube (4) to be measured. The variation of L translates into a voltage variation of the coils (1) that is measured (12) by means of the electrical resistance voltage divider bridge (17).

The electrical signals from each of the coils (1) are then filtered (13), and amplified

(14) the signals obtained after filtration (13).

Subsequently (15) possible differences in voltage variations are determined for each combination of two coils (1). It is based on the fact that, according to the known fundamentals of electromagnetism discussed above, as they are metal tubes (4), the only geometric variable that will influence the voltage variation will be the thickness of the metal tube (4). Thus, if when comparisons of voltage variations are made for each combination of two coils (1), there is no difference between a pair of coils (1), it will mean that there is no difference in thickness between the positions of The two coils. This determination (15) of possible differences is made as many times as possible pairs of coils (1) may exist. In the present embodiment by presenting three coils (3) three different combinations would be possible, and if in the three possible combinations no difference appears, it will therefore be a suitable metal tube (4), substantially without eccentricity.

Additionally, the electrical signals obtained after the determination (15) are stored and processed (16).

The programmable controller (8) is configured to compare the difference in voltage variation for each combination of two coils (1) and determine an eccentricity value of the metal tube (4) to be measured, according to the calibration of said controller (8 ).

One of the advantages of the present method is that it can be carried out continuously in a manufacturing process of metal tubes (4) by extrusion.

Although three coils (1) are used in the present embodiment, it should be noted that an even or even greater number will be possible, depending on the needs detected by the person skilled in the art. The fact of using three coils (1) responds to the fact that if a metal tube (4) is eccentric, never three points located approximately 120º will have the same thickness, and on the contrary, a metal tube (4) always has two points with the same thickness (there is always a plane of symmetry in any type of tubes, whether concentric or eccentric). With a configuration of three coils (1), the maximum error in the eccentricity measurement will be at most 5%, according to the Montecarlo numerical analysis method.

As for the metal tube (4) to be measured, the above described method will be applicable for non-ferromagnetic metal tubes (4) of outside diameter preferably greater than 30 mm and of thicknesses preferably in a range between 0.3 and 3.5 mm ; by varying the frequency of the alternating current of the power supply (5) it will be possible to adjust the precision of the eccentricity measurement to the desired thickness. As the thickness decreases, the frequency must be raised to avoid loss of measurement sensitivity.

Finally, Figure 4 shows a graph that demonstrates the relationship between the eccentricity of the press tube and the eccentricity of the final tube, according to tests carried out. The data represented have been obtained experimentally using a high extrusion ratio press.

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A target eccentricity value of the final tube of 4% has been marked with a dashed line.

The details, shapes, dimensions and other accessory elements, as well as the materials used in the manufacture of the measuring system of the invention may be conveniently substituted by others that are technically equivalent and do not depart from the essentiality of the invention or the scope defined by the

5 claims included below.

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Claims (10)

1. Eccentricity measurement system for non-ferromagnetic metal tubes, based on the use of induced currents, characterized by the fact that it comprises at least three coils (1) separated equidistant from each other and located radially with respect to the axis of a metal tube (4) to be measured, in which all coils (1) keep the same separation distance from the metal tube (4) and are arranged externally to said metal tube (4), said coils (1) being linked to at least one alternating current power supply (5) of variable frequency, so that in a condition of use, the power supply (5) supplies an alternating electric current to each of the coils (1), which in turn generate a magnetic field variable inductor with time, which induces an electric current in the metal tube (4) to be measured, creating said current of the metal tube (4) a magnetic reaction field opposite to the inductive magnetic field, in which said magnetic reaction field partially demagnetizes the coils (1), which produces a variation of the voltage in each of the coils (1), each of said coils (1) being associated with a measuring device configured to measure said voltage variation, each of said coils (1) being associated with data processing means configured to compare the difference in voltage variation for each combination of two coils (1) and determine an eccentricity value of the metallic tube (4) to be measured, wherein said data processing means are associated with a data storage device (9), each of said coils (1) being linked to an electrical signal filtering system (6) and an electrical signal amplifier system (7).

2.

 Eccentricity measuring system for non-ferromagnetic metal tubes according to claim 1, characterized in that said processing means have a programmable controller (8) of the PLC type.

3.

 Eccentricity measuring system for non-ferromagnetic metal tubes according to claim 1, characterized in that said power supply (5) supplies an alternating current with a frequency between 200 and 1000 Hz.

Four.

 Eccentricity measuring system for non-ferromagnetic metal tubes according to claim 1, characterized in that each coil (1) is housed in a protective cylindrical body (2).

5.

 Eccentricity measuring system for non-ferromagnetic metal tubes according to claim 1, characterized in that said measuring device comprises an electrical resistance voltage divider bridge (17).

6.

 Eccentricity measuring system for non-ferromagnetic metal tubes according to claim 1, characterized in that the metal tube (4) to be measured has an outer diameter greater than 30mm.

7.

 Eccentricity measuring system for non-ferromagnetic metal tubes according to claim 1, characterized in that the metal tube (4) to be measured has a thickness between 0.5 and 3.5 mm.

8.

 Eccentricity measurement method for non-ferromagnetic metal tubes, characterized by the fact that it comprises the steps of:

position (11) at least three coils (1) equidistant from each other and radially with respect to the axis of a metal tube (4) to be measured, measure (12) the voltage variation in each coil (1), filter (13) the electrical signals from each of the coils (1), amplify (14) the electrical signals obtained after filtration, determine (15) differences in voltage variations for each combination of two coils (1), store and process (16) the electrical signals obtained after the determination. ES 2 382 399 Al 9. The eccentricity measurement method for non-ferromagnetic metal tubes according to claim 8, characterized in that it is carried out continuously in a metal tube manufacturing process (4) by extrusion. ES 2 382 399 Al ES 2 382 399 Al ES 2 382 399 Al ES 2 382 399 Al SPANISH OFFICE OF THE PATENTS AND BRAND Application no .: 201230095 SPAIN Date of submission of the application: 24.01.2012 Priority Date: REPORT ON THE STATE OF THE TECHNIQUE 51 Int. Cl.: G01B7 / 312 (2006.01) G01B7 / 06 (2006.01) RELEVANT DOCUMENTS

Category

56 Documents cited Claims Affected

X

US 4099418 A (ALUMINUM CO OF AMERICA) 07/11/1978, summary; column 8, line 16 column 10, line 10; column 1, line 30 - column 2, line 30; Figures 5-6. 1-9

TO

US 3850026 A (ATOMENERGIKOMMISSIONEN ET AL.) 11/26/1974, summary; column 5, line 64-column 6, line 6; figure 2. 1,8,9

TO

US 5914596 A (WEINBAUM HILLEL) 06/22/1999, column 3, line 66 column 11, line 24; figures. 1-3.5

TO

US 5963031 A (BEKAERT SA NV) 10/05/1999, column 1, line 1-column 2, line 56; 1.8

Category of the documents cited X: of particular relevance Y: of particular relevance combined with other / s of the same category A: reflects the state of the art O: refers to unwritten disclosure P: published between the priority date and the date of priority submission of the application E: previous document, but published after the date of submission of the application

This report has been prepared • for all claims • for claims no:

Date of realization of the report 24.05.2012

Examiner E. P. Pina Martínez Page 1/5

REPORT OF THE STATE OF THE TECHNIQUE Application number: 201230095 Minimum documentation sought (classification system followed by classification symbols) G01B Electronic databases consulted during the search (name of the database and, if possible, terms of search used) INVENES, EPODOC, WPI State of the Art Report Page 2/5  WRITTEN OPINION Application number: 201230095 Date of the Written Opinion: 24.05.2012 Statement

Novelty (Art. 6.1 LP 11/1986)

Claims Claims 1-9 IF NOT

Inventive activity (Art. 8.1 LP11 / 1986)

Claims Claims 1-9 IF NOT

The application is considered to comply with the industrial application requirement. This requirement was evaluated during the formal and technical examination phase of the application (Article 31.2 Law 11/1986).  Opinion Base.- This opinion has been made on the basis of the patent application as published. State of the Art Report Page 3/5  WRITTEN OPINION Application number: 201230095  1. Documents considered.- The documents belonging to the state of the art taken into consideration for the realization of this opinion are listed below.

Document

Publication or Identification Number publication date

D01

US 4099418 A (ALUMINUM CO OF AMERICA) 11.07.1978

D02

US 3850026 A (ATOMENERGIKOMMISSIONEN et al.) 11/26/1974

D03

US 5914596 A (WEINBAUM HILLEL) 06/22/1999

D04

US 5963031 A (BEKAERT SA NV) 05.10.1999

 2. Statement motivated according to articles 29.6 and 29.7 of the Regulations for the execution of Law 11/1986, of March 20, on Patents on novelty and inventive activity; quotes and explanations in support of this statement D01 is considered the prior art prior to the object of the request. This document affects the inventive activity of all claims, as will be explained below. Claim 1 Following the terminology used in claim 1, document D01 describes the following system (references in brackets correspond to D01): Eccentricity measuring system for tubes comprising at least three sensors (100-102) separated equidistant from each other and located radially with respect to the axis of a tube (T) to be measured, in which all the sensors store the same separation distance from the tube and are arranged externally to said metal tube (see figure 5), each sensor being associated with a meter (75-78) and with processing means (112) configured to compare the signals from each combination of sensors and determine a tube eccentricity value. The difference between this device and the object of claim 1 lies in the type of sensor used which, while in the claimed device are inductive sensors (coils) in document D01, are ultrasonic sensors. On the other hand, the use of inductive sensors for measuring thicknesses in tubes based on the detection of so-called "eddy currents" or induction currents in metallic materials is known. Thus, document D02 shows a device for measuring wall thicknesses in metal tubes, which uses a plurality of sensors arranged externally to the tube (see D02, figure 2). Among the possible alternatives to ultrasonic-based sensors, this document describes the use of sensors based on induction currents (see D02 col. 5, lin. 64, col. 6, lin. 6). Thus, to the extent that these types of sensors and associated electronics are widely known in the related art sector (see for example D03 and D04) and used interchangeably, it is considered that the use of one type of sensor or another is a mere alternative of selection of techniques sufficiently known and within the reach of an expert in the field, who would choose one or the other to achieve its objective without the exercise of an inventive effort. Therefore, in view of the prior art, it is considered that claim 1 does not satisfy the requirement of inventive activity as set forth in article 8.1 of Patent Law 11/86. Claims 2-7 The dependent claims do not comprise additional technical characteristics or alternative embodiments that confer on the claimed system the requirement of inventive activity (Art. 8.1 LP) against the prior art. Claims 8-9 As for the method claimed in claim 8, as in the case of the system it is considered that the method described in document D01 only differs in the type of sensors used, but that the essential steps thereof are described analogously in D02, this is:

-

place at least three sensors (100-102) equidistant from each other and radially from the axis of a metal tube to be measured (fig. 5).

-

measure the variation of the output signal on each sensor (71-75)

-

determine (17, 112) differences in the variations of the output signal for each combination of two sensors (col. 8, lin 63 -col. 10, lin. 10)

-

process (120) the electrical signals obtained after the determination.

State of the Art Report Page 4/5  WRITTEN OPINION Application number: 201230095 Thus, the differences between the claimed method and the one described in D01 again reside in the particular characteristics of use of the induced currents technique, and which are usual and known steps in the sectors of the technique related to signal processing (filtering , amplification, storage, etc.). As for the application of the method in the continuous measurement in the process of manufacturing metal tubes by extrusion, it is the same application described in D01. Accordingly, claims 8 and 9 lack the requirement of inventive activity (Art. 8.1 LP). In conclusion, in view of the prior art, the application does not satisfy the patentability requirements set forth in Art. 4.1 of Patent Law 11/86. State of the Art Report Page 5/5