JPS5919188B2 - Metal tube protective coating processing method and equipment for carrying out this method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for protecting metal against corrosion, and more particularly to a method and apparatus for applying a protective coating to a metal tube.

In the production of heat exchangers, if the tube wall is used as a partition between media with different chemical/physical properties, e.g. in the thermal energy sector, it may be necessary to The invention is particularly suitable when the internal medium is water and steam.

Producing tubes from metals that exhibit sufficient corrosion resistance in two media with different chemical/physical properties often requires the use of special high alloys, which is not economically viable. .

Besides, it is necessary. In some cases, alloy selection is practically impossible. Therefore, bimetallic tubes and protective coating tubes that can be corrosion resistant can replace special high alloy tubes.

The first case involves considerable technical problems, 9 and the manufacturing technique is economically disadvantageous.

Regarding the manufacture of the second coated tube, since the protective coating applied to the tube is often a low cost, low alloy/low carbon steel, the tube is placed in two different corrosive media. In this case, care must be taken that the corrosion resistance is not sufficiently high.

Previously known methods of applying protective coatings to metal tubes include applying coatings of the same or substantially the same composition to the interior and exterior surfaces of the metal tube.

Among the many known types of coatings applied to pipes, diffusion coatings have the best technical properties.

In industry, zinc-clad tubes are most widely used, followed by aluminum-clad tubes.

The production volumes of tubes with diffusion coatings of refractory metals such as chromium, manganese, silicon, etc. are extremely limited. The reason for this is that the currently used metal coating techniques are low-productive and at the same time labor-intensive and cannot always guarantee the required quality of the metal to be protected. For example, the currently widely used diffusion metal coating method involves a metal diffusion mixture containing a powder of the metal used, an inert additive, and a halide or ceramic powder saturated with a halide compound of the metal used. Place the tube inside. The production process includes the following steps: That is, the steps of preparing the tubes to be subjected to metal diffusion treatment, loading the tubes into a container, filling the gaps between the tubes and inside the tubes with a mixture for metal diffusion (filling step), and sealing the container. heating the container in a heat treatment furnace, isothermally holding the container at a predetermined temperature, cooling the container in the furnace, cooling the container outside the furnace, sealing the container, and removing metal diffusion mixture particles from the surface of the tube. When carrying out the diffusion chromium coating with a thickness of up to 0.2n on low carbon steel pipes, the isothermal holding time reaches 10-15 hours, including the heating period and cooling period, the metal coating process The total time will be 30 to 50 hours. When metal is exposed to high temperatures (1000-1150) for such long periods of time, the structure and physical properties of the metal undergo changes that cannot necessarily be recovered by subsequent heat treatment of the tube. The chemical composition of the metal also tends to change in areas adjacent to the protective diffusion layer (subject to decarburization). Due to the problems described above, techniques for applying protective coatings to tubes are limited. Protective coatings have limited use in protecting tubes made of high strength/refractory low alloy steels due to the deterioration of the strength properties of the tube base metal. Diffusion metal coating processes are generally carried out in intermittent action, single chamber heat treatment equipment.

The disadvantage of this type of device is that it is not suitable for a significant increase in productivity. This is because increasing the power used and increasing the number of tubes loaded increases the heating and cooling periods and causes uneven heating of the tubes. The known chromium scattering coating technique is carried out in a three-chamber heat treatment furnace, the first chamber containing tubes and chromium (metallic diffusion agent).
and in the second chamber,
The tube to be coated is saturated with chromium and the tube and metal diffuser are cooled in the third chamber. These chambers are arranged sequentially and separated from each other by vacuum gates. Including. To implement the diffusion chrome coating method,
The tubes are placed in a box-like open container and coated with chromium or ferrochrome powder. The container is then placed on a movable trolley and the trolley is placed inside the first chamber. The productivity of these furnaces is not improved, and the metal of the tubes receiving this diffusion chromium coating is susceptible to strong decarburization. I do not yet hear of vacuum direct current type equipment or other continuously operating type equipment for diffusion metal coating of tubes being used. However, similar types of equipment are used for diffusion coating steel strips. Inside this type of device, metal diffusion occurs as the strip is passed over a metal diffusion agent that has been heated to its active vaporization temperature. This type of equipment consists of a chamber in which the strip is unwound from the roll, a metal diffusion chamber with a metal evaporator therein for carrying out the metal diffusion treatment of the strip, and a chamber for winding the strip into a roll after the metal diffusion treatment. Two types of conveying means are known for use in conveying tubes through heating chambers.

That is, six-roller type conveyance means and wheel type conveyance means are known. Both types of means are capable of carrying out simultaneous transport of a plurality of tubes, which can be advanced while rotating about their respective axes. If heating of one side of the tube is required, a wheel-type transport mechanism is the preferred type because it allows for an increased number of rotations of the tube over a given length along the tube path. This results in more uniform heating of the tube surface. Using this same type of tube transport in a vacuum metal coating system does not provide uniform heating and metal diffusion of the tube. This is different from the case of a grate-type heat transfer furnace, where heat transfer is performed by radiant heat and hot gas return, whereas in a vacuum furnace, heat transfer from the heat source (the heat source that evaporates steam from the metal) is carried out. This is also carried out by means of beam radiation, so that when simultaneously transporting several tubes arranged in a row, the tubes in the center of this row have a lower Even if they are equidistant from the heat source,
This is because it is heated to a high temperature. Due to heat exchange, the heat source itself has a slightly lower temperature at the outer edge of the furnace than at its center. It is therefore an object of the invention to prevent the above-mentioned disadvantages.

The gist of the present invention is that after metal diffusion treatment and heat treatment of the tube,
It is an object of the present invention to provide a method and apparatus for providing a protective coating on a tube that provides the same tissue and mechanical properties as a tube without the protective coating.

In a metal tube protective coating process in which a diffusion metal coating of the tube is carried out in a vacuum chamber containing the metal to be evaporated, the present invention provides that, before carrying out the coating of the tube, the melting point is significantly lower than that of the tube metal. A metal having a melting point or higher than the melting point of the metal charged into the tube is charged into each tube and continuously rotates around the axis while advancing vertically above the metal that evaporates inside the vacuum chamber. The object of the invention is achieved by means of a method for carrying out the metal coating of tubes at high temperatures. The method of applying a protective coating to a metal tube according to the present invention is capable of forming a protective diffusion coating on the exterior and interior surfaces of the tube, consisting of a variety of metals that are resistant to the corrosive media in which the tube is used.

The present method of vaporization also makes it possible to significantly reduce the time required for heating, metal diffusion and cooling of the tube being treated.

According to the invention, this is achieved by directly heating the tube or tubes, in contrast to the known methods in which the tubes to be coated are heated by means of a container and a powdered metal diffusion agent. I decided that it was possible. When carrying out diffusion coatings, the tube temperature is selected taking into account the metal quality and its effect on the coating speed. Upon completion of the coating operation, cooling of the tube is also carried out at high speed. This is because, after the metal diffusion process, it is transferred to a water-cooled discharge chamber. For example, when performing a diffusion chromium coating on the outer surface of a tube, 0.15 to 0.2
A 01ri11 thick chromium layer is formed on a tube made of low carbon steel in a time of 5 to 6 minutes, compared to 10 to 15 hours for metal coating by known methods. It should also be noted that the process time of the method of the invention is limited only by the time required to form the diffusion layer on the tube being treated. The reason why the metal surface layer adjacent to the diffusion layer is prevented from being decarburized is that the protective diffusion layer 6 is formed at a high speed.

Furthermore, by applying a protective coating to the tube at high speed,
It has become possible to expedite the production process and reduce the cost of tubes with protective coatings.

Tubes coated on the inside and outside with protective coatings of various compositions are most often used in various heat exchange devices. The selection of coatings for the inner and outer surfaces of the tube is based on the corrosion resistance of these coatings in the medium used. : will be implemented. An important factor that must be observed in this case is that the metal deposited on the inside surface of the tube has a melting point lower than the melting point of the tube base metal, and that when applying the diffusion coating, this diffused metal enters the tube metal. It has to melt and dissolve. The outer surface of the tube has a variable melting point (higher than the melting point of the tube metal,
The temperature and time at which the coating step is carried out are selected corresponding to the required thickness of the coating to be deposited. If the coating process temperature does not have a detrimental effect on the properties of the tube metal, the process is carried out at the maximum temperature possible for transporting the coated tube. However, if the heating temperature during the metal diffusion treatment affects the structure and properties of the tube metal and cannot be recovered during the next heat treatment, the metal diffusion treatment temperature should be selected to minimize the negative effect on the properties of the tube metal. be done. According to one embodiment of the invention, the melting point of the metal to be evaporated is greater than or equal to the melting point of the metal placed inside each tube.

This makes it possible to expand the selection range of protective coatings used in various corrosive media, including the melting point of the metal placed inside the tube as well as refractory metals with a melting point higher than the melting point of the tube metal. It is possible to apply the coating to the outer surface of the tube.

According to another embodiment of the invention, the metal diffusion treatment of the tube is carried out at a temperature above the melting point of the metal to be vaporized.

As a result, the overall production process can be accelerated by significantly increasing the temperature of the diffusion coating process.

This also makes it possible to increase the production efficiency of metal diffusion treatment and reduce the cost of the cladding tube.

According to another embodiment of the invention, during the coating process,
The head portion of each tube is raised relative to its distal portion such that the longitudinal axis of each tube makes an angle of up to 15 tubes in the direction of tube travel with the horizontal plane. This embodiment of the invention is effective when coating long tubes. As a result, metal masses of various shapes can be used as metal diffusion agents for coating the inner surface of the tube, and these metal masses can preferably be placed in the head section of the tube.

During the coating process, the metal placed in this head part melts due to the heating action and moves towards the end part of the tube, as the end part is gradually heated to a high temperature. Penetrate inside it. By changing the angle of inclination of this tube, we can vary the time during which the tube is in contact with the molten metal and also vary the various parameters of the deposited layer (thickness of the layer and concentration of the element lead to be saturated). The gist of the invention is to provide a vacuum chamber containing a metal evaporator, a tube inlet chamber, a tube outlet chamber;
The latter two chambers are each equipped with a vacuum gate and a tube storage device, arranged on either side of the vacuum chamber and fixed in stands spaced apart from each other along the tube run. Equipped with multiple identical wheels,
Means are provided for conveying the tubes to be coated through all the above-mentioned chains, the axes of rotation of the wheels in each stand being parallel to each other, and the similarly arranged wheels in the other stands According to the present invention, the rotational axis of the wheel is arranged on a virtual arc having its highest point on the vertical axis of the stand. achieved in

The tube diffusion metal coating apparatus according to the present invention is capable of simultaneously depositing coatings of different chemical compositions on the exterior and interior surfaces of the tube being treated. Uniformity in the thickness of the deposited layers is achieved by maintaining the same temperature conditions during the coating process. This is achieved by the arc-like structure of the wheels in each stand and thus the arc-like arrangement of the pipes on the wheels. Since the temperature of the evaporator is highest at its center and lower along its outer edges, the tubes passing above the center of the evaporator will be further spaced from the evaporator than other tubes. According to one embodiment of the invention, each stand is provided with a mechanism for allowing rotation about its vertical axis.

As a result, it is possible to vary the relationship between the rotational speed and the translational speed of the tubes, and also to vary the mutual spacing of the tubes depending on their diameter, thus achieving an effective coating. things become possible.

Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings.

The metal pipe protective coating device according to the present invention has a first
As shown in the figure, chambers 1, 2, and 3 are provided for metal diffusion, feeding, and discharge of metal tubes 4, respectively.

These chambers 1, 2, 3 are arranged in series and are separated from each other by vacuum gates 5, 5, respectively. A plurality of metal evaporators 6 are placed inside the metal diffusion chamber 1 . The metal evaporator 6 is basically a closed container made of a refractory material and provided with a hole through which the metal tube 4 is inserted. A heating element 7 and a lid plate 8 having an opening are arranged inside the evaporator 6 . Chambers 2 and 3 are each metal tube 4
The metal tubes 4 have a storage grid-like device 9 of mutually similar construction and each vertically movable by an actuator 10.
This device 9 holds a plurality of rows of tubes in the width direction and a plurality of tubes in the vertical direction, and before the coating device is operated, the chamber 2 is opened and the tubes 4 are installed in this device 9. The tube 4 is carried into the chamber 2 by, for example, opening the lid at the left end of the chamber 2 in FIG. At this time, each vacuum gate 5 is normally closed. In order to pass the metal tube 4 through the interiors of the chambers 1, 2, and 3, the apparatus of the present invention uses a plurality of conveying devices 11 (first
4). This conveyance device has the shape of a stand 12 in which a plurality of wheels 13 having the same diameter are arranged in an arc shape and are spaced apart from each other along the running path of the pipe 4. The rotational axes of the wheels 13 in each stand 12 are parallel to each other and coincide with the rotational axes of other wheels 1-3 similarly mounted on other stands 12. The center of rotation of the wheel 13 in each stand 12 is located on an imaginary arc with its highest point on the vertical axis of the stand (FIG. 2). In this way, wheel 1
3 are arranged in an arc shape, on the metal evaporator 6, the tube 4 corresponding to the center will be away from the evaporator 6, and the lateral ends of the array of tubes 4 will be closer to the evaporator 6. On average, tubes 4 are coated. These wheels 13 are connected to a drive device 14 via a bevel gear 15 and an idler gear 16.
Rotationally driven by. A frame 17 supported on a support mechanism 18 to hold the device of the invention in an inclined position.
Chambers 1, 2, and 3 are placed on top of the chamber.

The metal diffusion chamber 1 includes one or more metal evaporators 6
It can be manufactured to accommodate.

Furthermore, in order to vary the rotational speed of the metal tube 4, each stand is equipped with a mechanism for rotating it around its vertical axis. The device of the invention operates as follows.

Into the tube storage device 9 accommodated in the supply chamber 2 the metal tube 4 prepared for coating and filled with metal diffusion agent is introduced as described above.

Tube 4 located at the bottom row among the tubes held in device 9
are arranged on the wheels 13 of the transport device. Next, chambers 1, 2, and 3 are sealed, and then the inside thereof is vented to a residual pressure of 10-1 to 1011111Hg using a vacuum pipe. The metal diffusing agent placed inside the evaporator 6 is
It is heated by the heating element 7 to a temperature at which active evaporation occurs. When the metal treatment agent is heated to the required temperature, the vacuum gate 5 is opened and the drive device 14 of the conveying device 11 is activated. At this time, the metal tube 4 placed on the wheel 13 is rotated and simultaneously transferred from the chamber 2 to the chamber 1.The metal tube 4 is heated as it passes through the evaporator 6. The metal diffusing agent inside the metal tube is heated and melted by the heat emitted from the metal tube 4, and its outer surface is coated with the evaporated metal diffusing agent. The temperature of the metal tube 4 is adjusted by adjusting the size of the opening in the cover plate 8.
After passing through the metal diffusion chamber 1, these metal tubes pass into the discharge chamber 3, where they are removed from the wheel 13 by a grid-like storage device similar to the device 9 described above. The storage device 9 provided in the inlet chamber 2 is lowered one step to enable the coating of the metal tubes 4 held in the next step. After all of these metal tubes 4 held in the device 9 are coated,
Both vacuum gates 5 are closed and the group of metal tubes to be coated is then introduced into the supply chamber 2, while at the same time the metal tubes 4 already coated and held in the storage device of the discharge chamber are introduced. It is removed from the discharge chamber 3, which is optionally water-cooled, for example by opening the end plate of the chamber 3. Note that the storage device in the discharge chamber also accommodates a group of coated tubes 4 one after another while moving upward one step at a time. When it is desired to vary the rotational speed of the metal tubes 4 while keeping the forward speed constant, or when it is desired to vary the distance between the axes between the variable diameter metal tubes 4, the stand 12 is rotated around its vertical rotation axis. In this way, the angle α between the arrangement direction of the wheels 13 and the axis perpendicular to the axis of the tube 4 is varied (FIG. 4).

When a metal diffuser in the form of a metal block is used for the coating process or when it is necessary to adjust the thickness of the inner coating layer of the metal tube 4, the device of the present invention is operated by the mechanism 18 at 15.
The angle of inclination of the metal tube 4 is varied to vary the time that the tube is in contact with the molten metal. The present invention
In various heat exchangers used for sulfuric acid production, it is most suitable for flowing sulfuric acid inside metal tubes and flowing water outside metal tubes.

A sulfuric acid resistant silicon diffusion coating is applied to the inner surface of the metal tube, and a chromium diffusion coating is applied to the outer surface of the metal tube. To obtain this type of coating, a 45 (fl) silicon-containing iron alloy is charged inside the metal tube and the outer coating of the metal tube is carried out above the chromium-filled evaporator. This coating step is carried out at a temperature of 1350°C. Within 5 minutes, a 0.15-0.2011t11 thick chromium layer is formed on the outer surface,6 with a chromium concentration of the order of 40-47%, and 0.25-0.301r1 on the inner surface.
The silicon concentration in which the first diffusion layer is formed is 17-25%.

The present invention is also applied to the manufacture of boiler tubes for heating surfaces.

In this case, a diffusion chrome coating is carried out on the outer surface of the tube. Around the coating process 1250-135
It is carried out at a temperature of 0° C. for 6-7 minutes.

During this time, a 0.15-0.20 thick chromium layer is formed on the outer surface. After undergoing this heat treatment, the coated tube has similar textural properties and mechanical customization as the uncoated tube.

[Brief explanation of the drawing]

1 is a longitudinal sectional view of an apparatus for carrying out the method of the invention; FIG. 2 is a front view of the tube conveying means seen from the side into which the tubes to be coated are charged; FIG. A sectional view taken along the - line in the figure, and FIG. 4 a plan view of the conveying means for the metal tube to be coated. 1... Vacuum chamber, 4... Metal tube, 6...
...Metal evaporator, 12...Stand, 13
······wheel.

Claims (1)

[Claims] 1. In a metal tube protective coating method in which vaporized metal is attached to a metal tube in a vacuum chamber to form a diffusion metal coating, the melting point of the tube metal is A metal having a significantly lower melting point is introduced into each tube 4, and the tubes 4 are placed in a metal evaporator 6 inside the vacuum chamber 1.
These tubes 4 are subjected to metal coating processing at a temperature higher than the melting point of the metal disposed inside these tubes 4 while advancing them in the axial direction and continuously rotating them around their respective axes. Characteristic metal tube protective coating processing method. 2. Claim 1, characterized in that the melting point of the metal to be evaporated is higher than the melting point of the metal fed into each tube 4.
The method described in section. 3. The method according to claim 1, wherein the metal coating of the tube 4 is carried out at a temperature higher than the melting point of the metal to be evaporated. 4. During the metal coating process, the head portion of each tube 4 is raised relative to its distal end such that the longitudinal axis of each tube 4 forms an angle of less than 15° with respect to the horizontal plane and with respect to the direction of tube travel. A method according to claim 1, characterized in that: 5 a vacuum chamber equipped with a metal evaporator, a tube inlet chamber and a tube outlet chamber arranged on either side of said vacuum chamber and each equipped with a vacuum gate and a tube storage device, spaced apart from each other along the path of the tube; and a device for transporting pipes within the chamber by having a plurality of wheels of the same diameter attached to the arranged stands, and the rotation axes of the wheels of each stand are parallel to each other and the rotational axes of the wheels of the other stands are parallel to each other. A device 6 characterized in that the center of rotation of each wheel 13 of each stand 12 is arranged on a circular arc when viewed from the running direction of the pipe. Device according to claim 5, characterized in that it is provided with a mechanism that allows rotation about a vertical axis.