Method for classifying metal tubes

Abstract

A method or classifying metal tubes in which the measuring of the eccentricity over the entire length of the tube is provided, and in which the classification occurs on the basis of the length of the tube portions which have eccentricity either higher or lower than one or more eccentricity thresholds.

Claims

1. A method for classifying a metal tube having a total length, comprising: providing a detection system for detecting an eccentricity of a tube, including a first detection head and a second detection head, both the first detection head and the second detection head including at least three transducers, the first detection head being placed on an opposite side of a traction device from the second detection head, a relative movement being provided between the tube and the detection system; providing a processor adapted to process data obtained from said detection system, the data including a first eccentricity threshold; a first reference length correlated to said first eccentricity threshold; the method comprising the steps of: measuring the eccentricity of the tube along the entire total length by means of the detection system, during said relative movement; execrating a first sum of lengths of tube portions having eccentricity either higher than or equal to the first eccentricity threshold by means of the processor; assigning a first class to the tube if a value of said first sum is lower than said first reference length, otherwise assigning a second class to the tube.

2. The method according to claim 1, wherein a second eccentricity threshold, higher than the first eccentricity threshold, and a second reference length, correlated to said second eccentricity threshold, are defined, wherein in step b) a second sum of lengths of tube portions having eccentricity either higher than or equal to the second eccentricity threshold is also executed, and in step c) a third class is assigned to the tube if a value of said second sum is either higher than or equal to said second reference length, otherwise said second class is assigned to the tube if the value of said first sum is either higher than or equal to said first reference length, otherwise the first class is assigned to the tube.

3. The method according to claim 2, wherein a third eccentricity threshold, higher than the second eccentricity threshold, and a third reference length, correlated to said third eccentricity threshold, are defined, whereby in step b) a third sum of lengths of tube portions having eccentricity either higher than or equal to the third eccentricity threshold is also executed, and in step c) a fourth class is assigned to the tube if a value of said third sum is either higher than or equal to said third reference length, otherwise, said third class is assigned to the tube if the value of said second sum is either higher than or equal to said second reference length, otherwise said second class is assigned to the tube if the value of said first sum is either higher than or equal to said first reference length, otherwise the first class is assigned to the tube.

4. The method according to claim 3, wherein a fourth eccentricity threshold S4, higher than the third eccentricity threshold, and a fourth reference length, correlated to said fourth eccentricity threshold, are defined, whereby in step b) a fourth sum of lengths of tube portions having eccentricity either higher than or equal to the fourth eccentricity threshold is also executed, and in step c) a fifth class is assigned to the tube if a value of said fourth sum is either higher than or equal to said fourth reference length, otherwise a fourth class is assigned to the tube if the value of said third sum is either higher than or equal to said third reference length, otherwise said third class is assigned to the tube if the value of said second sum is either higher than or equal to said second reference length, otherwise said second class is assigned to the tube if the value of said first sum is either higher than or equal to said first reference length, otherwise the first class is assigned to the tube.

5. The method according, to claim 4, wherein said first eccentricity threshold is equal to 2%, said second eccentricity threshold is equal to 4%, said third eccentricity threshold is equal to 6%, and said fourth eccentricity threshold is equal to 8%.

6. The method according to claim 1, wherein the eccentricity of the tube along its entire total length is detected in a drawing machine.

7. The method according to claim 6, wherein the eccentricity is detected by the second detection head, the second detection head arranged downstream of the traction device of said drawing machine.

8. The method according to claim 7, wherein said first detection head and second detection head are provided with ultrasound transducers, equally angularly spaced apart from one another.

9. The method according to claim 1, wherein there is provided a detection of the length of the tube as a function of time by means of said detection system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further features and advantages of the invention will become more apparent in light of the detailed description of preferred, but not exclusive, embodiments of a method for classifying tubes, disclosed by way of a non-limiting example, with the aid of the accompanying drawings, in which:

(2) FIG. 1 shows the graph of a first in-line eccentricity measurement of a first tube,

(3) FIG. 2 shows the graph of a second inline eccentricity measurement of a second tube,

(4) FIG. 3 shows the graph of a third in-line eccentricity measurement of a third tube,

(5) FIG. 4 shows a diagrammatic view of a drawing machine for tubes on which the method of the invention can be applied.

(6) The same numbers and the same reference letters in the figures identify the same elements or components.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

(7) In order to achieve the method for classifying tubes of the present invention, there are provided: a detection system for detecting the eccentricity of the tube, adapted to measure the eccentricity of the tube along its entire length Ltot, a relative movement being provided between the tube and the detection system, and a processor adapted to process data obtained from the detection system.

(8) The detection system is capable of detecting both the eccentricity and the length of the tube as a function of time, that means capable of detecting both the eccentricity and the length of the tube during said relative movement.

(9) A first embodiment of the method for classifying metal tubes provides the definition of a first eccentricity threshold S1 and of a first reference length L1 correlated to said first threshold S1, and comprises the steps of:

(10) a) measuring the eccentricity of the tube along the entire overall length Ltot, by means of the detection system, during the relative movement between tube and detection system,

(11) b) executing a first sum of lengths of tube portions having eccentricity either higher than or equal to the first threshold S1 by means of the processor,

(12) c) assigning a first class (Class 1) to the tube if the value of said first sum is lower than the first reference length L1, otherwise assigning a second class (Class 2) to the tube.

(13) A second embodiment of the method for classifying metal tubes provides the definition of a first eccentricity threshold S1, a second eccentricity threshold S2, higher than the first threshold S1, a first reference length L1 correlated to said first threshold S1, and a second reference length L2 correlated to said second threshold S2, and comprises the steps of:

(14) a) measuring the eccentricity of the tube along the entire overall length Ltot, by means of the detection system, during the relative movement between tube and detection system,

(15) b) executing, by means of the processor, a first sum of lengths of tube portions having eccentricity either higher than or equal to the first threshold S1 and a second sum of lengths of tube portions having eccentricity either higher than or equal to the second threshold S2,

(16) c) assigning a third class (Class 3) to the tube if the value of the second sum is either higher than or equal to said second reference length L2, otherwise assigning the second class (Class 2) to the tube if the value of the first sum is either higher than or equal to the first reference length L1, otherwise assigning the first class (Class 1) to the tube.

(17) A third embodiment of the method for classifying metal tubes provides the definition of a first eccentricity threshold S1, a second eccentricity threshold S2, higher than the first threshold S1, a third eccentricity threshold S3, higher than the second threshold S2, a first reference length L1 correlated to said first threshold S1, a second reference length L2 correlated to said second threshold S2, a third reference length L3 correlated to said third threshold S3, and comprises the steps of:

(18) a) measuring the eccentricity of the tube along the entire overall length Ltot, by means of the detection system, during the relative movement between tube and detection system,

(19) b) executing, by means of the processor, a first sum of lengths of tube portions having eccentricity either higher than or equal to the first threshold S1, a second sum of lengths of tube portions having eccentricity either higher than or equal to the second threshold S2, and a third sum of lengths of tube portions having eccentricity higher than the third threshold S3,

(20) c) assigning a fourth class (Class 4) to the tube if the value of the third suns is either higher than or equal to the third reference length L3, otherwise assigning a third class (Class 3) to the tube if the value of the second sum is either higher than or equal to the second reference length L2, otherwise assigning the second class (Class 2) to the tube if the value of the first suns is either higher than or equal to the first reference length L1, otherwise assigning the first class (Class 1) to the tube.

(21) A fourth embodiment of the method for classifying metal tubes provides the definition of a first eccentricity threshold S1, a second eccentricity threshold S2, higher than the first threshold S1, third eccentricity threshold S3, higher than the second threshold S2, a fourth eccentricity threshold S4, higher than the third threshold S3, a first reference length L1 correlated to said first threshold S1, a second reference length L2 correlated to said second threshold S2, a third reference length L3 correlated to said third threshold S3, and a fourth reference length L4 correlated to said fourth threshold S4, and comprises the steps of:

(22) a) measuring the eccentricity of the tube along the entire overall length Ltot, by means of the detection system during the relative movement between tube and detection system,

(23) b) executing, by means of the processor, a first sum of lengths of tube portions having eccentricity either higher than or equal to the first threshold S1, a second sum of lengths of tube portions having eccentricity either high than or equal to the second threshold S2, a third sum of lengths of tube portions having eccentricity higher than the third threshold S3, and a fourth sum of lengths of tube portions having eccentricity higher that the fourth threshold S4,

(24) c) assigning a fifth class (Class 5) to the tube if the value of the fourth sum is either higher than or equal to the fourth reference length L4, otherwise assigning a fourth class (Class 4) to the tube if the value of the third sum is either higher than or equal to the third reference length L3, otherwise assigning a third class (Class 3) to the tube if the value of the second sum is either higher than or equal to the second reference length L2, otherwise assigning the second class (Class 2) to the tube if the value of the first sum is either higher than or equal to the fast reference length L1, otherwise assigning the first class (Class 1) to the tube.

(25) In the following examples, the method of the invention provides dividing the tubes into five classes. Only one of the five classes is assigned to each tube. Starting from the first class, Class 1, which is assigned to tubes of the best quality in terms of eccentricity, the quality of the tube increasingly decreases, until arriving at the last class, Class 5, assigned to tubes of the worst quality.

(26) For the purposes of assigning the classes, there are defined four threshold values, or eccentricity thresholds, expressed in percentage value (e %). In particular, the first threshold S1 can be selected equal to 2%; the second threshold S2 can be selected equal to 4%; the third threshold S3 can be selected equal to 6%, the fourth threshold S4, or last threshold, can be selected equal to 8%.

(27) On the basis of the eccentricity measured in-line, one or more tube portions can have an eccentricity lower than the first threshold or ranging between two close thresholds, or higher than the last threshold. In other terms, one or more tube portions have an eccentricity which can be either higher than or equal to one or more of one of the four thresholds.

(28) For the purposes of assigning the class, it is also calculated the sum of the lengths of tube portions which have eccentricity either higher than or equal to the first threshold S1, the sum of the lengths of tube portions which have eccentricity either higher than or equal to the second threshold S2, the sum of the lengths of tube portions which have eccentricity either higher than or equal to the third threshold S3, and the sum of the lengths of tube portions which have eccentricity either higher than or equal to the fourth threshold S4.

(29) It is apparent that the sum of the lengths of tube portions which have eccentricity either higher than or equal to threshold S1 comprises also the sum of the lengths of tube portions which have eccentricity either higher than or equal to threshold S2, to threshold S3 and to threshold S4, respectively. In the same way, the sum of the lengths of tube portions which have eccentricity either higher than or equal to threshold S2 comprises also the sum of the lengths of tube portions which have eccentricity either higher than or equal to threshold S3 and to threshold S4, respectively. And again, the sum of the lengths of tube portions which base eccentricity either higher than or equal to threshold S3 comprises also the sum of the lengths of tube portions which have eccentricity either higher than or equal to threshold S4.

(30) Each sum is compared with predetermined reference length values, or reference lengths indicated by L1, L2, L3 and L4, and associated with the eccentricity threshold S1, S2, S3 and S4, respectively, thus defining conditions for assigning classes.

(31) If several conditions are met at the same time, according to a predefined criterion, the class associated with the tube is the highest class met, i.e. the class that identifies a tube of worst quality according to the convention used.

(32) The conditions for assigning classes are the following:

(33) The tube is in Class 1 if the sum of the lengths of tube portions which have eccentricity either higher than or equal to threshold S1 is lower than a first reference length L1, for example equal to 30 m.

(34) The tube is in Class 2 if the sum of the lengths of tube portions which have eccentricity either higher than or equal to threshold S1 is either higher than or equal to the first reference length L1.

(35) The tube is in Class 3 if the sum of the lengths of tube portions which have eccentricity either higher than or equal to threshold S2 is either higher than or equal to a second reference length L2, for example equal to 20 m.

(36) The tube is in Class 4 if the sum of the lengths of tube portions which have eccentricity either higher than or equal to threshold S3 is either higher than or equal to a third reference length L3, for example equal to 15 m.

(37) The tube is in Class 5 if the sum of the lengths of tube portions which have eccentricity either higher than or equal to threshold S4 is either higher than or equal to a fourth reference length L4, for example equal to 10 m.

(38) FIGS. 1, 2, 3 illustrate, respectively, the graphs obtained from the eccentricity measurements of three different tubes. The measurement was taken along the entire length of each tube, which is equal to 86 m. The eccentricity of the tubes of each example is different, as is further described, below.

(39) The axis of abscissas in the graphs illustrated in FIGS. 1, 2, 3 depicts a time t.

(40) The axis of ordinates depicts the eccentricity values. The selected eccentricity thresholds S1, S2, S3 and S4 are indicated with a solid line.

(41) Alternatively, the axis of abscissas can depict a length.

Example 1

(42) From the eccentricity measured on a first tube having a length of 86 m, and from the graph depicting it (FIG. 1), the following emerges:

(43) the sum of the lengths of tube portions which have eccentricity between threshold S1 and threshold S2 is equal to 27 m,

(44) the sum of the lengths of tube portions which have eccentricity between threshold S2 and threshold S3 is equal to 54 m,

(45) the sum of the lengths of tube portions which have eccentricity between threshold S3 and threshold S4 is equal to 5 m,

(46) and, considering the conditions for assigning classes described above, the following emerges:

(47) the sum of the lengths of tube portions which have eccentricity either higher than or equal to threshold S1 is equal to 86 m, that is equal to the entire length of the tube (given by the sum of 27 m+54 m+5 m),

(48) the sum of the lengths of tube portions which have eccentricity either higher than or equal to threshold S2 is equal to 59 m (given by the sum of 54 m+5 m),

(49) the sum of the lengths of tube portions which have eccentricity either higher than or equal to threshold S3 is equal to 5 m.

(50) Therefore, two of the conditions for assigning classes defined above are met, i.e. the eccentricity of the tube is higher than threshold S1 for a length (86 m) higher than L1=30 m, which is the condition for assigning Class 2, and the eccentricity of the tube is higher than threshold S2 for a length (59 m) higher than L2=20 m, which is the condition for assigning Class 3. According to the predefined criterion defined above, the highest class possible is assigned, and in this case Class 3 is assigned to the tube.

Example 2

(51) From the eccentricity measured on a second tube having a length of 86 m, and from the graph depicting it (FIG. 2), the following emerges:

(52) the sum of the lengths of tube portions which have eccentricity lower than threshold S1, is equal to 51 m,

(53) the sum of the lengths of tube portions which have eccentricity between threshold S1 and threshold S2 is equal to 23 m,

(54) the sum of the lengths of tube portions which have eccentricity between threshold S2 and threshold S3 is equal to 12 m,

(55) and, considering the conditions for assigning classes described above, the following emerges:

(56) the sum of the lengths of tube portions which have eccentricity either higher than or equal to threshold S1 is equal to 35 m (given by the sum of 23 m+12 m),

(57) the sum of the lengths of tube portions which have eccentricity either higher than or equal to threshold S2 is equal to 12 m.

(58) Therefore, one of the conditions for assigning classes defined above is met, i.e. the eccentricity of the tube is higher than threshold S1 for a length (35 m) higher than L1=30 m.

(59) This is the condition for assigning Class 2, which is the class assigned to the tube.

Example 3

(60) From the eccentricity measured on a third tube having a length of 86 m, and from the graph depicting it (FIG. 3), the following emerges:

(61) the sum of the lengths of tube portions which have eccentricity between threshold S2 and threshold S3 is equal to 5 m,

(62) the sum of the lengths of tube portions which have eccentricity between threshold S3 and threshold S4 is equal to 37.5 m,

(63) the sum of the lengths of tube portions which have eccentricity higher than threshold S4, is equal to 43.5 m,

(64) and, considering the conditions for assigning classes described above, the following emerges:

(65) the sum of the lengths of tube portions which have eccentricity either higher than or equal to threshold S1 is equal to 86 m, that is equal to the entire length of the tube (given by the sum of 5 m+37.5 m+43.5 m),

(66) the sum of the lengths of tube portions which have eccentricity either higher than or equal to threshold S2 is also equal to 86 m, that is equal to the entire length of the tube (given by the sum of 5 m+37.5 m+43.5 m),

(67) the sum of the lengths of tube portions which have eccentricity either higher than or equal to threshold S3 is equal to 81 m (given by the sum of 37.5 m+43.5 m),

(68) the sum of the lengths of tube portions which have eccentricity either higher than or equal to threshold S4 is equal to 43.5 m.

(69) Therefore, four of the conditions for assigning classes defined above are met, i.e.: the eccentricity of the tube is either higher than or equal to threshold S1 the length (86 m) higher than L1=30 m, which is the condition for assigning Class 2, the eccentricity of the tube is either higher than or equal to threshold S2 for a length (86 m) higher than L2=20 m, which is the condition for assigning Class 3, the eccentricity of the tube is either higher than or equal to threshold S3 for a length (81 m) higher than L3=15 m, which is the condition for assigning Class 4, and the eccentricity of the tube is either higher than or equal to threshold S4 for a length (43.5 m) higher than L4=10 m, which is the condition for assigning Class 5,

(70) According to the predefined criterion defined above, the highest class possible is assigned, and in this case Class 5 is assigned to the tube.

(71) The method of the invention can for example be used in association with a drawing machine for tubes of the type shown in FIG. 4. Such a drawing machine 1, defining a longitudinal axis Y, comprises: a first die 3, or working die, flit executing the drawing of a tube 2 by the use of a mandrel; a device 5 the varying the inclination of the tube entering into said first die 3; a second die 6, or skin pass die, for executing a skin pass operation on the tube, arranged downstream of said first die 3; an in-line detecting system for detecting the eccentricity of the tube; a data processing system 7 for processing signals coming from said detection system and sending input data to said device 5 for varying the inclination of the tube so as to correct the eccentricity of the tube in-line.

(72) In a first variant of the drawing machine, the in-line system for detecting the eccentricity of the tube comprises a first detection head provided with at least transducers 8, preferably four transducers, arranged in the die holder of the second die 6. Providing these transducers in structure of the skin pass die, and not in the structure of the working die, allows increased duration of the useful life of the transducers. Indeed, the second die 6 performs only one pass on the outer surface of the tube (skin pass) to ensure contact with the tube itself, the thickness of which needs to be measured. Therefore, the second die 6 will undergo beating Which, although is high, is significantly lower than that undergone by the first die 3.

(73) The in-line eccentricity detection system also comprises a second detection head 9, arranged downstream of said second die 6 and provided with at least three transducers 8, preferably but not necessarily four in number. This second detection head allows the eccentricity obtained to be measured and checked, thus ensuring the system is correcting and not creating further eccentricity.

(74) Advantageously, this second detection head 9 is configured to certify the tubes according to the method of the invention, by assigning to each of them a profile of the variation of the eccentricity thereof along the entire length thereof. Such a certification allows the manufacturer direct the tube to one type of production rather than to another.

(75) Said second detection had 9 provided preferably downstream of a caterpillar 10, or a traction device, on which both the first die 3 and the second die 6 are arranged.

(76) The transducers 8, 8 are preferably of the ultrasound type and are arranged equally angularly spaced apart from one another. Other types of transducers can in any case be used.

(77) The number of transducers in each detection head can also be greater than four, for example equal to six or eight. The greater the number of transducers, the more accurate the eccentricity measurement, therefore the sensitivity of the device 5 for varying the inclination of the tube is to be designed so as to maximize the accuracy of the eccentricity measurement.

(78) A chamber 13 is provided, coaxial to the longitudinal axis Y, between the first die 3 and the second die 6.

(79) Alternatively, in a second variant of the drawing machine, the aforesaid first detection head can be provided in the chamber 13, arranged between the die holder of the first die 3 and the die holder of the second die 6, and comprises at least three transducers, preferably of the ultrasound type and equally angularly spaced apart from one another. Also in this case, the number of the transducers 8 is preferably four or greater than four. The structure of chamber 13 provides a channel 23 for the passage of a coupling means, preferably drawing oil, in contact with the ends of the transducers and with tube 2 itself. This detection head will detect the eccentricity of tube 2 immediately after the drawing in the first die 3 and before the skin pass operation in the second die 6. Taking the measurement in this chamber between working die and skin pass die allows a more precise measurement to be obtained because, at the chamber 13, the tube is stationary in transverse direction with respect to axis Y, therefore the transducers can be positioned closer to tube 2. Furthermore, the ultrasound signal must not cross different materials such as those of which the dies are made, as there is only oil between the transducer and tube 2 to be measured. Finally, the higher quantity of oil and the non-direct contact of the transducer with the hot die for the deformation machining makes such an area better the protecting the transducers from overheating.

(80) In a third variant of the drawing machine, there are provided two first detection heads: one provided in chamber 13, arranged between the die holder of the first die 3 and the die holder of the second die 6, and comprising at least three transducers; the other provided in the die holder of the second die 6 and provided with at least three transducers 8, as described for the first variant.

(81) Both in the second and in the third variant, the second detection head 9, which is arranged downstream of caterpillar 10, is configured to certify the tubes according to the method of the invention and, preferably, sends signals with the eccentricity measurement to the data processing system 7 for the subsequent sending of input data to the device 5 for varying the inclination of the tube so as to vary the inclination of the tube and correct the eccentricity of the tube in-line.

(82) Preferably, the second detection head 9 is arranged at a distance of 12-16 meters from the working die 3.