Method for producing a steel tube including cleaning of the inner tube wall

Abstract

A method for producing a steel tube including the step of the manufacturing a steel tube having an inner tube wall, an outer tube wall, and a free tube cross-section enclosed by the inner tube wall, wherein after the manufacturing, the steel tube includes at least one contaminant on the inner tube wall. After the manufacturing of the steel tube, the inner tube wall is cleaned by introducing liquid or solid CO.sub.2 into the free tube cross-section, and of applying the liquid or solid CO.sub.2 onto the inner tube wall to remove the contaminant therefrom.

Claims

1. A method for producing a steel tube comprising the steps of: manufacturing said steel tube having an inner tube wall, an outer tube wall, and a free tube cross-section enclosed by the inner tube wall, wherein after the manufacturing, the steel tube includes at least one contaminant on the inner tube wall; cleaning the inner tube wall by introducing liquid or solid CO.sub.2 into the free tube crosssection and applying the liquid or solid CO.sub.2 onto the inner tube wall to remove the at least one contaminant from the inner tube wall, wherein the liquid or solid CO.sub.2 is introduced from a first end of the steel tube into the free tube cross section, measuring the temperature of the steel tube during the application of the liquid or solid CO.sub.2 onto the inner tube wall, and interrupting cleaning if the temperature of the steel tube falls below a predetermined temperature threshold.

2. A method according to claim 1, wherein the manufacturing of the steel tube includes forming a hollow shell in a form of a finished dimensioned steel tube.

3. A method according to claim 2, wherein the forming is performed by cold pilgering the hollow shell to the form of the finished steel tube.

4. A method according to claim 3, wherein, during the cold pilgering, a mandrel bar lubricant is transferred from a mandrel bar to the inner tube wall and removed again from the inner tube wall by applying the liquid or solid CO.sub.2.

5. A method according to claim 2, wherein the forming is performed by cold drawing the hollow shell into the form of the finished steel tube.

6. A method according to claim 5, wherein during the cold drawing, a drawing oil is transferred from a drawing core to the inner tube wall and removed again from the inner wall by applying the liquid or solid CO.sub.2.

7. A method according to claim 1, wherein measuring the temperature during the application of the liquid or solid CO.sub.2 onto the inner tube wall includes measuring the temperature at a second end of the steel tube.

8. A method according to claim 7, wherein the predetermined temperature correlates to a state of cleanliness of a surface of the steel tube.

9. A method according to claim 1, wherein the cleaning of the inner tube wall occurs by CO.sub.2 snow blasting or by dry ice blasting.

10. A method according to claim 1, wherein introducing the liquid or solid CO.sub.2 includes feeding pressurized air into the free tube cross-section.

11. A method according to claim 1, wherein introducing liquid or solid CO.sub.2 into the free tube cross-section includes inserting a lance into the free tube cross-section, wherein measuring the temperature of the steel tube includes measuring a temperature of the outer tube wall with a temperature sensor, and wherein the method further comprises simultaneously moving the cleaning lance and the temperature sensor in a longitudinal direction along the tube.

12. A method according to claim 11, wherein the method further comprises maintaining the temperature sensor and an outlet nozzle of the cleaning lance at the same longitudinal position while moving in the longitudinal direction along the tube.

13. A method according to claim 11, wherein the predetermined temperature correlates to a state of cleanliness of a surface of the steel tube.

14. A method according to claim 1, wherein the predetermined temperature correlates to a state of cleanliness of a surface of the steel tube.

Description

(1) Additional advantages, features and application possibilities of the present invention become apparent on the basis of the following description of an embodiment and the associated figures.

(2) FIG. 1 shows the cold pilger rolling mill from the prior art in a schematically side view.

(3) FIG. 2 shows a schematically cross-sectional view of an embodiment for carrying out the cleaning steps according to the invention.

(4) FIG. 3 shows a schematically cross-sectional view of an alternative embodiment for carrying out the cleaning steps.

(5) In the represented embodiments, identical or similar elements are marked with identical reference numerals.

(6) In FIG. 1, the structure of a cold pilger rolling mill is represented schematically in a side view. The rolling mill consists of a roll stand 101 with rolls 102, 103, a calibrated rolling mandrel 104 as well as a feeding clamping carriage 105. In the represented embodiment, the cold pilger rolling mill has a linear motor 106 as direct drive for the feeding clamping carriage 105. The linear motor 106 is constructed from a rotor 116 and a stator 117.

(7) During the cold pilgering in the rolling mill shown in FIG. 1, the hollow shell 111 is fed step-wise in the direction of the rolling mandrel 104 and over and past the latter, while the rolls 102, 103 as they rotate are moved horizontally back and forth over the mandrel 104 and thus over the hollow shell 111. In the process, the horizontal movement of the rolls 102, 103 is predetermined by a roll stand 101 on which the rolls 102, 103 are rotatably mounted. The roll stand 101 is moved back and forth by means of a crank drive 121 in a direction parallel to the rolling mandrel 104, while the rolls 102, 103 themselves are set in rotation by a rack which is stationary relative to the roll stand 101, and with which toothed wheels that are firmly connected to the roll axles engage.

(8) The feeding of the hollow shell 111 over the mandrel 104 is performed by means of the feeding clamping carriage 105, which allows a translational movement in a direction parallel to the axis of the rolling mandrel. The conically calibrated rolls 102, 103 arranged one above the other in the roll stand 101 rotate in opposite direction to the feeding direction of the feeding clamping carriage 105. The so-called pilger mouth formed by the rolls grips the hollow shell 111 and the rolls 102, 103 push off a small wave of material from outside, which is stretched by a smoothing pass of the rolls 102, 103 and by the rolling mandrel 104 to the predetermined wall thickness, until an idle pass of the rolls 102, 103 releases the finished tube. During the rolling, the roll stand 101 with the rolls 102, 103 attached to it moves against the feeding direction of the hollow shell 111. By means of the feeding clamping carriage 105, the hollow shell 111 is fed by an additional step onto the rolling mandrel 104, after the idle pass of the rolls 102, 103 has been reached, while the rolls 102, 103 with the roll stand 101 return to their horizontal starting position. At the same time, the hollow shell 111 undergoes a rotation about its axis, in order to obtain a uniform shape of the finished tube. As a result of multiple rollings of each tube section, a uniform wall thickness and roundness of the tube as well as uniform inner and outer diameters are achieved.

(9) In order to reduce the friction between rolling mandrel 104 and the mandrel bar supporting the rolling mandrel 104, respectively, and the hollow shell 111, a mandrel bar lubricant, for example, a graphite-containing lubricant, is applied onto the rolling mandrel 104. This mandrel bar lubricant forms residues on the inner tube surface of the finished reduced tube. The aim is to remove this residue from the inner tube wall over the entire length of the tube by means of the process steps according to the invention which are described below.

(10) In the embodiment of the invention described here as an example, the cold pilger rolling mill is used in order to manufacture the steel tube, i.e., in order to form the hollow shell to the form of the finished tube. However, this forming step of the method according to the invention could also occur alternatively by cold drawing the hollow shell, for example.

(11) FIG. 2 shows a dry snow blasting of the inner tube wall of a finished reduced tube 1 obtained by cold pilgering, for example. In this dry snow blasting, the tube 1 contaminated on its inner tube wall during the cold pilgering is cleaned to remove the mandrel bar lubricant. For this purpose, a cleaning lance 3 is introduced into the tube 1, so that its outlet nozzle 4 is located in the free tube cross section 5 of the tube 1.

(12) Through the cleaning lance 3, dry snow 6 is fed by means of pressurized air 7 into the tube, and it is blasted through the outlet nozzle 4 onto the inner tube wall 2 so that the latter is cleaned by means of the dry snow. Here, the dry snow is used, on the one hand, as a cleaning agent, i.e., for dissolving the contaminant, and, on the other hand, also as an abrasive which, in a manner similar to sandblasting, detaches the contaminant from the inner tube wall. The contaminant detached from the inner tube wall 2 is removed from the tube 1 by means of the pressurized air jet.

(13) In the embodiment of FIG. 2, the temperature of the tube 1 is measured by means of a temperature sensor 8. Here, the temperature sensor 8 is moved simultaneously with the cleaning lance 3 along the tube 1, wherein the temperature sensor 8 is always located approximately at the level of the outlet nozzle 4 of the cleaning lance 3.

(14) If one assumes that, at the time when the dry snow 6 strikes a contaminant on the inner tube wall 2, the contaminant first undergoes cooling, and is subsequently removed from the inner tube wall 2, then an appreciable cooling of the tube 1 itself occurs only when the contaminant is removed from the inner tube wall 2. If therefore the temperature of the tube 1 measured by the temperature sensor 8 falls below a predetermined temperature threshold, then it is assumed that the inner tube wall has been completely cleaned at the site where the temperature sensor 8 is currently located. In order to clean the tube 1 over its entire length, the cleaning nozzle 4 at the tip of the cleaning lance 3 and the temperature sensor 8 are moved slowly in the longitudinal direction along the tube, as indicated by the arrows 9.

(15) FIG. 3 shows an alternative arrangement for blasting the inner tube wall 2 of a steel tube 1 using dry snow 6. In this alternative embodiment, the dry snow is injected by means of pressurized air 7 into the tube 1. However, the injection occurs from the first end 10 of the tube 1, wherein the feed line 11 for the dry ice snow 6 is attached by means of a flange 12 to the first end 10 of the tube 1. Therefore, this embodiment does not require any parts that are moved along the tube during the cleaning process.

(16) In this embodiment, the temperature of the tube 1 is measured by means of a temperature sensor 8 at the second end 13 of the tube. When the cleaning process is started, the tube first undergoes cooling at the first end 10 where the dry snow 6 enters first into the free cross section 5 of the tube 1. This cooling of the tube 1 then spreads, as the cleaning is continued, in the longitudinal direction of the tube 1, until the second end 13 of the tube is also cooled. This cooling at the second end 13 of the tube 1 is detected by means of the temperature sensor 8.

(17) In the represented embodiment, it is assumed that, when the temperature sensor 8 at the second end 13 of the tube 1 reaches a cooling of 3° C., in comparison to the initial temperature of the tube 1 before the introduction of the dry snow 6, the tube 1 has been cleaned over its entire length.

(18) For the purpose of the original disclosure, reference is made to the fact that all the features, as they are disclosed to a person skilled in the art from the present description, the drawings and the claims, even if they have been described in concrete terms only in connection with certain additional features, can be combined both individually and also in any desired combinations with other features or groups of features disclosed here, to the extent that this is not explicitly excluded, or to the extent that technical circumstances make such combinations impossible or unreasonable. A comprehensive, explicit description of all the conceivable combinations of features is omitted here only for the sake of the brevity and readability of the description.

(19) While the invention has been represented and described in detail in the drawings and in the above description, this representation and this description occur only by way of example and are not intended to limit the scope of protection as defined by the claims. The invention is not limited to the embodiments that have been disclosed.

(20) Variant forms of the disclosed embodiments are evident to the person skilled in the art from the drawings, the description and the appended claims. In the claims, the word “comprise” does not exclude other elements or steps, and the indefinite article “an” or “a” does not exclude a plural. The mere fact that certain features are claimed in different claims does not rule out their combination. Reference numerals in the claims are not intended to limit the scope of protection.

REFERENCE NUMERALS

(21) 1 Tube 2 Inner tube wall 3 Cleaning lance 4 Outlet nozzle 5 Free tube cross section 6 Dry ice snow 7 Pressurized air 8 Temperature sensor 9 Direction of movement 10 First end of the tube 11 Feed line 12 Flange 13 Second end of the tube 101 Roll stand 102, 103 Roll 104 Rolling mandrel 105 Feeding clamping carriage 106 Linear motor 111 Hollow shell 112 Chuck 116 Rotor 117 Stator