Apparatus and method for anodizing inner surface of tube

Abstract

The invention relates to an apparatus and a method for anodizing an inner surface of a tube. An anodizing apparatus is disclosed that includes an anode holder adapted to hold a tube such that the tube is adapted to receive an electrolyte, and the tube has a first surface profile formed on an inner surface of the tube. The anodizing apparatus further includes a cathode holder adapted to concentrically hold the cathode in the tube such that the cathode has a second surface profile formed on an outer surface of the cathode and the outer surface faces the inner surface of the tube. The cathode holder and the anode holder are adapted to supply electrical potentials of a predetermined current density to the cathode and the tube, respectively, and the surface area ratio between the first surface profile and the second surface profile is maintained within a predetermined range so as to form a uniform anodized coating on the second surface profile.

Description

Technical Field

[0001] The present disclosure relates to aspects of forming an anodized coating on an interior surface of a tube. Background Art

[0002] Metal tubes, such as aluminum tubes, are used to transfer heat from a fluid flowing therein to the outer surface of the tube. One of the fields of application of such tubes is as cooler tubes in air conditioning units to discharge heat from the refrigerant flowing therethrough. The tubes may have reinforcements formed on the inner surface of the tube to increase the surface area, which increases the heat transfer capacity of the tube. In one example, the reinforcements may be rifling or any other structure formed on the inner surface to increase the surface area in contact with the fluid flowing through the tube, thereby increasing heat transfer. Typically, the tubes are anodized to form a corrosion-resistant coating to prevent galvanic corrosion caused by the fluid flowing through the tube.

[0003] The coating is currently formed by an anodizing process. However, due to the reinforcements on the inner surface, the coating may not have a uniform thickness across the inner surface of the tube. In one example, a reinforcement on the inner surface, such as a valley, may have a layer of coating that is less thick than the layer of coating at other areas in the reinforcement. As a result, the coating in the valley is more susceptible to erosion and, therefore, may be a starting point for corrosion. Summary of the invention

[0004] This summary is provided to introduce a selection of concepts in a simplified format that are further described in the detailed description of the invention. This summary is neither intended to identify key or fundamental inventive concepts of the invention nor is it intended to be used to determine the scope of the invention.

[0005] A method for anodizing the inner surface of a tube is disclosed herein. The method includes mounting the tube on an anode holder, wherein the tube has a first surface profile formed on the inner surface of the tube. In addition, the method includes mounting a cathode on a cathode holder to concentrically place the cathode inside the tube, wherein the cathode has a second surface profile formed on the outer surface of the cathode, and the outer surface faces the inner surface of the tube. The method also includes pumping an electrolyte through an annular space between the outer surface and the inner surface. In addition, the method includes applying an electric potential across the tube and the cathode via the anode holder and the cathode holder, respectively. In addition, the surface area ratio between the first surface profile and the second surface profile is maintained within a predetermined range so as to form a uniform anodized coating on the second surface profile.

[0006] In one or more embodiments, the method includes linearly oscillating the cathode at a predetermined rate along the length of the tube via a linear drive unit of the cathode holder.

[0007] In one or more embodiments, the method includes rotating the cathode at a predetermined rotation speed inside the tube by a rotation drive unit of the cathode holder.

[0008] In one or more embodiments, moving the cathode includes maintaining a predetermined distance between the cathode and a surface contour of the tube.

[0009] In one or more embodiments, the predetermined range of the surface area ratio is 9:1 to 1.5:1.

[0010] In one or more embodiments, a tube is disclosed having a first surface profile formed on an inner surface and an anodized coating formed on the first surface profile by the method of one or more embodiments.

[0011] In one or more embodiments, an anodizing apparatus is disclosed, comprising an anode holder adapted to hold a tube such that the tube is adapted to receive an electrolyte and the tube has a first surface profile formed on an inner surface of the tube. The anodizing apparatus also comprises a cathode holder adapted to concentrically hold a cathode in the tube such that the cathode has a second surface profile formed on an outer surface of the cathode and the outer surface faces the inner surface of the tube. The cathode holder and the anode holder are adapted to supply a potential of a predetermined current density to the cathode and the tube, respectively, and a surface area ratio between the first surface profile and the second surface profile is maintained within a predetermined range so as to form a uniform anodized coating on the second surface profile.

[0012] In one or more embodiments, the power source is adapted to apply a potential of a predetermined current density across the cathode holder and the anode holder.

[0013] In one or more embodiments, the pumping unit is adapted to pump the electrolyte through the tube.

[0014] In one or more embodiments, the cathode holder includes: a pair of clamping contacts configured to supply an electrical potential to the cathode; a linear drive unit configured to linearly oscillate the cathode at a predetermined rate along the length of the tube; and a rotational drive unit configured to rotate the cathode inside the tube at a predetermined rotational speed.

[0015] In one or more embodiments, the anode holder includes a pair of clamping contacts configured to supply an electrical potential to the cathode.

[0016] In one or more embodiments, the magnitude of the predetermined current density is in the range of 4 to 20 amps per square foot.

[0017] In one or more embodiments, the first surface contour and the second surface are rifling.

[0018] In one or more embodiments, the predetermined rate is in the range of <>, and the predetermined rotational speed is in the range of 1 to 50 revolutions per minute (RPM).

[0019] In one or more embodiments, the cathode is made of an aluminum alloy.

[0020] In one or more embodiments, the predetermined range of the surface area ratio is 9:1 to 1.5:1.

[0021] In order to further illustrate the advantages and features of the present disclosure, a more particular description of the present invention will be provided by reference to specific embodiments of the present invention, which are illustrated in the accompanying drawings. It is recognized that these drawings depict only typical embodiments of the present invention and are therefore not to be considered as limiting the scope of the present invention. The present invention will be described and explained in the accompanying drawings with additional specificity and detail. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] These and other features, aspects and advantages of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings, in which like characters refer to like parts throughout the drawings, and in which:

[0023] Figure 1 A schematic diagram of anodizing equipment is shown;

[0024] Figure 2 shows a cross section of a tube in which the cathode of an anodizing apparatus rotates inside the tube;

[0025] Figure 3 illustrates a cross section of a tube with the cathode of an anodizing apparatus oscillating inside the tube; and

[0026] Figure 4 A flowchart diagram depicting a method for anodizing a tube is shown;

[0027] Furthermore, the skilled person will appreciate that the elements in the drawings are illustrated for simplicity and may not necessarily be drawn to scale. Furthermore, in terms of the construction of the device, one or more components of the device may have been represented by conventional symbols in the drawings, and the drawings may show only those specific details relevant to understanding the embodiments of the present disclosure so as not to obscure the drawings with details that would be readily apparent to one of ordinary skill in the art having the benefit of the description herein. DETAILED DESCRIPTION

[0028] For the purpose of promoting an understanding of the principles of the present disclosure, reference will now be made to various embodiments, and specific language will be used to describe these embodiments. It will be understood, however, that no limitation of the scope of the present disclosure is intended thereby, and such changes and further modifications in the illustrated system and such further applications of the principles of the present disclosure as illustrated therein are contemplated as would normally occur to one skilled in the art to which the present disclosure relates.

[0029] It will be understood by those skilled in the art that the foregoing general description and the following detailed description are illustrative of the present disclosure and are not intended to limit the present disclosure.

[0030] References throughout this specification to "aspect," "another aspect," or similar language mean that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the present disclosure. Thus, appearances of the phrases "in an embodiment," "in another embodiment," "some embodiments," "one or more embodiments," and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

[0031] The term "comprises, comprising" or any other variation thereof is intended to cover a non-exclusive inclusion, such that a process or method that includes a list of steps includes not only those steps, but may also include other steps not expressly listed or inherent to such process or method. Similarly, without more constraints, one or more devices or subsystems or elements or structures or components preceded by "comprises ..." do not exclude the presence of other devices or other subsystems or other elements or other structures or other components or additional devices or additional subsystems or additional elements or additional structures or additional components.

[0032] Embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings.

[0033] Figure 1 An anodizing apparatus 100 is shown, which can be used to form a uniform coating on a tube 102. The anodizing apparatus 100 is adapted to perform an electrochemical process, known as an anodizing process, to form a non-reactive anodized coating on the inner surface of the tube 102. During the anodizing process, the inner surface 102A of the tube 102 undergoes controlled corrosion. The non-reactive anodized coating may be a metal oxide layer that protects the inner surface 102A of the tube 102 from the fluid flowing through the tube 102. Based on the application area of ​​the tube 102, the tube 102 may have a reinforcement on the inner surface 102A. For example, the tube 102 may have a reinforcement to increase the area of ​​the inner surface 102A of the tube 102. In one example, the reinforcement may be a rifling.

[0034] In one example, the anodizing apparatus 100 can employ an electrolyte and a cathode 104 to form a metal oxide. In one example, the anodizing apparatus 100 can be used to coat a tube 102 made of an aluminum alloy, such as a 6061 or 6063 alloy. In addition, by changing the parameters of the anodizing apparatus 100, such as the applied voltage, current, and type of electrolyte, the anodizing apparatus 100 can be used to form a coating on any type of aluminum alloy. The anodizing apparatus 100 is designed in such a way that the inner surface is completely covered with an oxide layer, regardless of the surface profile of the inner surface 102A.

[0035] The anodizing apparatus 100 may employ a variety of apparatuses that enable the anodizing apparatus 100 to form an anodized coating of uniform thickness. For example, the anodizing apparatus 100 uses a cathode 104 that may have a surface profile, which is different from the cathode having a smooth surface currently used. In addition, the surface area ratio between the cathode 104 and the tube 102 is maintained within a predetermined range to form an anodized coating of uniform thickness. In addition, the anodizing apparatus 100 may actuate the cathode 104 relative to the tube 102 to further enhance the formation of the anodized coating. The details of each of the aforementioned apparatuses will be discussed later.

[0036] The anodizing apparatus 100 may include, but is not limited to, a power unit 106, an anode holder 108, a cathode holder 110, and a pumping unit 112, details of which will be provided later. The power unit 106 is adapted to provide an electric potential across the anode holder 108 and the cathode holder 110. The power unit 106 may be configured to provide direct current (DC). In addition, the power unit 106 may receive power from an alternating current (AC) source, such as a mains supply source. In order to convert the AC supply source into a DC supply source, the power unit 106 may employ a rectifier 114. The rectifier 114 may be a half-bridge rectifier or a full-bridge rectifier. Although not shown, the power unit 106 may include additional electrical components, such as a voltage booster and a DC-DC converter, to provide an electric potential of a predetermined current density to the cathode 104 and the tube 102 via the cathode holder 110 and the anode holder 108, respectively. In one example, the power unit 106 may provide an electric potential with a predetermined current density. Furthermore, the magnitude of the predetermined current density may be in the range of 4 to 20 amperes per square foot.

[0037] In one example, the anode holder 108 can be configured to hold the tube 102 in a predefined configuration and can serve as a positive terminal for the power cell 106. The anode holder 108 can also include a pair of clamping contacts that perform two tasks. First, the clamping contacts hold the tube 102 in a pre-set configuration, and second, the clamping contacts can ensure contact so that the potential is applied to the tube 102. The anode holder 108 can be made of graphite or any other material suitable for holding the tube 102. Although not shown, the anodizing apparatus 100 can include multiple anode holders 108, which can be used to supply the potential of multiple tubes 102 in parallel.

[0038] In this example, the anode holder 108 is shown as making contact with the outer surface 102B at the end of the tube 102. In another example, the anode holder 108 may be connected to the central area of ​​the tube 102. In yet another example, the anode holder 108 may have a greater width to connect with a larger area of ​​the outer surface 102B. The increased contact points or contact area and distribution of current over a larger area of ​​the outer surface 102B of the tube 102 allow for uniform distribution of current.

[0039] For example, cathode holder 110 may be configured to receive cathode 104. Cathode holder 110 may be adapted to perform two tasks. First, cathode holder 110 may provide negative potential to cathode 104, and second, cathode holder 110 may move cathode 104 relative to tube 102 to achieve an anodized coating of uniform thickness. For example, cathode holder 110 may include a pair of clamping contacts configured to supply negative potential. In addition, cathode holder 110 may include a linear drive unit 118, which may be coupled to the end of cathode 104. Linear drive unit 118 may be configured to oscillate cathode 104 inside tube 102 along the length of tube 102. Such oscillation may change the effective gap between cathode 104 and tube 102. The effective distance may be defined as the shortest distance between two closest points on outer surface 104A and inner surface 102A, respectively. In one example, linear drive unit 118 may be a reciprocating type machine, and cathode 104 may be oscillated at a predetermined rate. The predetermined rate may be 0.5 to 1000 revolutions per minute.

[0040] In addition, the cathode holder 110 may include a rotation drive unit 120 coupled to the end of the cathode 104. The rotation drive unit 120 is configured to rotate the cathode 104 inside the tube 102. The rotation drive unit 120 may be designed to rotate the cathode 104 at a predetermined rotation speed. In one example, the predetermined rotation speed is in the range of 1 to 50 revolutions per minute (RPM). In addition, in order to support the rotation of the cathode 104, the cathode holder 110 may include a pair of bearings 122 attached to either end of the cathode 104 to support the rotation of the cathode 104. The cathode holder 110 is configured in a manner such that the cathode 104 can rotate and translate back and forth at the same time.

[0041] In one example, the pumping unit 112 may be configured to pump electrolyte through the tube 102. The pumping unit 112 may be part of a fluid circuit that supplies electrolyte to the tube 102. Although not shown, the pumping unit 112 may be connected to a first end of the tube 102 via a hose so that the electrolyte flows into the tube 102 represented by the inlet path 124. In addition, the second end of the tube 102 is represented by the outlet path 126. In one example, the fluid circuit may be a closed loop circuit so that the fluid returns to the pumping unit 112 after leaving the tube 102. In another example, the fluid circuit is an open loop circuit so that the pumping unit 112 pumps fresh electrolyte to the tube 102. The pumping of the electrolyte by the pumping unit 112 not only ensures the presence of the electrolyte in the tube 102 to ensure a constant anodizing process, but also removes hydrogen gas generated at the outer surface of the cathode 104 during the anodizing process. The removal of the gas ensures that the surface of the cathode 104 is exposed for the anodizing process.

[0042] The anodizing apparatus 100 may also include additional apparatus that can assist in the movement of the cathode 104. For example, the anodizing apparatus 100 may include one or more spacers 128 that support the cathode 104 inside the tube 102. The spacer 128 is essentially non-conductive and can be configured to hold the cathode 104 at the center of the tube 102 so that the cathode 104 does not contact the tube 102 to prevent short circuits and / or arcing in the anodizing apparatus 100. In one example, the number of spacers 128 may depend on the length and thickness of the cathode 104. Each spacer 128 may include a hole at its center to receive the cathode 104. In addition, the spacer 128 may include a plurality of cutout portions that allow the electrolyte to pass through. The spacer 128 may have a diameter slightly smaller than the orifice of the tube 102 so that the spacer 128 can be easily inserted and removed while being installed orthogonal to the length of the tube 102.

[0043] According to the present disclosure, the cathode 104 used in the anodizing apparatus 100 may have a surface profile such that the ratio of the area of ​​the surface profile of the inner surface 102A of the tube 102 is within a predetermined range so that a uniform anodized coating is formed. Figure 2 and Figure 3 The details of the surface profiles of both the cathode 104 and tube 102 as well as the motion imparted by the cathode holder 110 are discussed.

[0044] Figure 2 A cross section of a portion of the tube 102 is shown, wherein the cathode 104 is rotated inside the tube 102 so that the outer surface 104A of the cathode 104 faces the inner surface 102A of the tube 102. In addition, the tube 102 may have a first surface profile formed on the inner surface 102A of the tube 102, and the cathode 104 may include a second surface profile formed on the outer surface 104A of the cathode 104. In one example, the first surface profile and the second surface profile may be rifling on their respective surfaces. In one example, the first surface profile may include a set of peaks 202 and valleys 204 formed between adjacent peaks 202. Similarly, the second surface profile may include peaks 206 and valleys 206. The collection of the surface areas of the peaks 202 and valleys 206 may define the surface area of ​​the first surface profile, and the collection of the surface areas of the peaks 206 and valleys 208 may define the surface area of ​​the second surface profile. In addition, the surface area ratio of the first surface profile and the second surface profile is maintained within a predetermined range. Within this range, the transfer of ions through the electrolyte is maintained at a predetermined rate, which enables the anodizing process on the inner surface 102A to occur at a uniform rate on the inner surface 102A. Therefore, the anodized coating 210 thus formed may have the same thickness at the peak 202 and at the valley 206.

[0045] In order to further enhance the formation of a uniform coating, the cathode 104 is rotated at a predetermined rotational speed inside the tube 102. The predetermined rotational speed is in the range of 1 to 50 revolutions per minute (RPM). In addition, the predetermined rotational speed may depend on a variety of factors. For example, the predetermined rotational speed depends on the surface area ratio, the length of the second surface profile extending at most. Rotating the cathode 104 at the predetermined rotational speed ensures that a predetermined distance is maintained between the outer surface 104A and the inner surface 102A, so as to maintain a stable transfer of ions via the electrolyte to form an anodized coating.

[0046] Figure 2 A cross section of a portion of the tube 102 is shown with the cathode 104 oscillating inside the tube 102. The cathode holder 110 ( Figure 1 ) causes the cathode 104 to oscillate at a predetermined rate to change its position along the length of the tube 102, as shown by the dashed line. In addition, the cathode 104 is oscillated so that the distance between the peaks 206 on the cathode 104 and the valleys 204 in the inner surface 102A can be reduced to maintain a predetermined rate of ion transfer through the electrolyte. The predetermined rate of oscillation can depend on a variety of factors, such as the size of the peaks 202 and valleys 204, the surface area ratio, and the area at most that the first surface profile and the second surface profile extend on the tube 102 and the cathode 104, respectively, as well as other examples.

[0047] In one example, the cathode holder 110 may apply both oscillating motion and rotational motion. In such a case, Figure 2 and Figure 3 The movements depicted in will be performed simultaneously.

[0048] Now about Figure 4 A method for forming an anodized coating on the inner surface 102A of the tube 102 is described, Figure 4 A method for anodizing a tube is illustrated. The order in which the method steps are described below is not intended to be construed as a limitation, and any number of the described method steps may be combined in any suitable order to perform the method or an alternative method. Additionally, individual steps may be deleted from the method without departing from the spirit and scope of the subject matter described herein.

[0049] In one example, method 400 may be performed in part or in whole by Figure 1 The method is performed by the anodizing apparatus 100 shown in FIG. The method starts at step 402, where a tube 102 having a first surface profile on its inner surface 102A is mounted on an anode holder 108. Thereafter, at step 404, a cathode having a second surface profile on its outer surface 104A is mounted on a cathode holder 110 such that the outer surface 104A faces the inner surface 102A of the tube 102.

[0050] In addition, at step 406, the pumping unit 112 pumps electrolyte through the annular space between the outer surface 104A and the inner surface 102A. Finally, at step 408, an electric potential is applied across the tube 102 and the cathode 104 by the power unit 106 via the anode holder 108 and the cathode holder 110, respectively. The application of the electric potential and the maintenance of the surface area ratio between the first surface profile and the second surface profile facilitate the formation of a uniform anodized coating on the first surface profile. The method 400 may also include the steps described above with respect to Figure 2 and Figure 3 The cathode 104 is rotated at step 408 and the cathode 104 is oscillated at step 410 in an explained manner.

[0051] According to the present disclosure, maintaining the surface area ratio between the first surface profile and the second surface profile facilitates forming a uniform anodized coating on the first surface profile. In addition, the oscillating and rotating motions ensure a stable transfer of ions to ensure a uniform thickness of the anodized coating across the entire surface of the inner surface 102A of the tube 102.

[0052] Although specific language has been used to describe the present disclosure, it is not intended that any limitation be created thereby. As will be apparent to those skilled in the art, a variety of work modifications may be made to the method in order to implement the inventive concept as taught herein. The accompanying drawings and the foregoing description give examples of embodiments. Those skilled in the art will appreciate that one or more of the elements described may be well combined into a single functional element. Alternatively, certain elements may be divided into a plurality of functional elements. Elements from one embodiment may be added to another embodiment.

Claims

1. A method for anodizing the inner surface of a tube, comprising: mounting the tube on an anode holder, wherein the tube has a first surface profile formed on an interior surface of the tube; mounting a cathode on a cathode holder to concentrically position the cathode inside the tube, wherein the cathode has a second surface profile formed on an outer surface of the cathode and the outer surface faces the inner surface of the tube; pumping electrolyte through the annular space between the outer surface and the inner surface; and applying a potential across the tube and the cathode via the anode holder and the cathode holder, respectively, Wherein, a surface area ratio between the first surface profile and the second surface profile is maintained within a predetermined range to facilitate forming a uniform anodized coating on the first surface profile.

2. The method according to claim 1, comprising: The cathode is linearly oscillated along the length of the tube at a predetermined rate by a linear drive unit of the cathode holder.

3. A method according to any one of the preceding claims, comprising: The cathode is rotated at a predetermined rotation speed inside the tube by a rotation drive unit of the cathode holder.

4. A method according to any one of the preceding claims, wherein: Moving the cathode includes maintaining a predetermined distance between the cathode and a surface contour of the tube.

5. A method according to any one of the preceding claims, wherein: The predetermined range of surface area ratio is 9:1 to 1.5:

1.

6. A pipe having a first surface profile formed on an inner surface and an anodized coating formed on the first surface profile by the method according to claims 1 to 5.

7. An anodizing device comprising: an anode holder adapted to hold a tube, wherein the tube is adapted to receive an electrolyte and the tube has a first surface profile formed on an inner surface of the tube; and a cathode holder adapted to hold a cathode concentrically in the tube, wherein the cathode has a second surface profile formed on an outer surface of the cathode and the outer surface faces the inner surface of the tube, wherein the cathode holder and the anode holder are adapted to supply a potential of a predetermined current density to the cathode and the tube, respectively, and The surface area ratio between the first surface profile and the second surface profile is maintained within a predetermined range to facilitate forming a uniform anodized coating on the second surface profile.

8. Anodizing apparatus according to claim 7, comprising a power source adapted to apply the potential of the predetermined current density across the cathode holder and the anode holder.

9. Anodizing apparatus according to claim 7, comprising a pumping unit adapted to pump the electrolyte through the tube.

10. Anodizing apparatus according to any one of the preceding claims, wherein: The cathode holder comprises: a pair of clamping contacts configured to supply the potential to the cathode; a linear drive unit configured to linearly oscillate the cathode at a predetermined rate along the length of the tube; and A rotation drive unit is configured to rotate the cathode inside the tube at a predetermined rotation speed.

11. Anodizing apparatus according to any one of the preceding claims, wherein: The anode holder includes a pair of clamping contacts configured to supply the electrical potential to the cathode.

12. Anodizing apparatus according to any one of the preceding claims, wherein: The magnitude of the predetermined current density is in the range of 4 to 20 amperes per square foot.

13. Anodizing apparatus according to any one of the preceding claims, wherein: The first surface contour and the second surface are rifling.

14. Anodizing apparatus according to any one of the preceding claims, wherein The predetermined rate is within the range of <>, The predetermined rotational speed is in the range of 1 to 50 revolutions per minute (RPM).

15. Anodizing apparatus according to any one of the preceding claims, wherein The cathode is made of aluminum alloy.

16. Anodizing apparatus according to any one of the preceding claims, wherein: The predetermined range of the surface area ratio is 9:1 to 1.5:1.

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