Thermothermite formula for coating ceramic layer in steel pipe and preparation method of formula

Abstract

The invention discloses a thermite formula for coating a ceramic layer in a steel pipe and a preparation method of the thermite formula, and relates to the technical field of steel pipe lining metal ceramic, the formula comprises aluminum powder, ferric oxide, silicon dioxide and oxygen, and further comprises copper oxide and diboron trioxide, the content of oxygen is smaller than the amount of oxygen consumed when the aluminum powder is completely oxidized, and the content of silicon dioxide is smaller than the amount of copper oxide consumed when the aluminum powder is completely oxidized. When the oxygen participating in the reaction is exhausted, aluminum which does not participate in the oxidation reaction exists. According to the invention, by adding the diboron trioxide and the copper oxide, a traditional metal ceramic lining steel pipe combined in a mechanical mode can be improved into a metal ceramic inner covering steel pipe combined in a brazing mode, so that the binding force of the inner covering layer and the base pipe is improved, and the surface flatness of the inner covering layer is improved so as to reduce the fluid conveying resistance; the metal ceramic internally-coated steel pipe manufactured through the formula and the specific implementation method has the advantages of being high in bonding force between the internally-coated layer and the base pipe, smooth in surface, resistant to high temperature and high pressure and resistant to corrosion.

Description

Technical Field

[0001] The present invention relates to the technical field of metal-ceramic lined steel pipes, and particularly to a thermite formula for coating a ceramic layer on the inner wall of a steel pipe and a preparation method of the formula. Background Art

[0002] The metal-ceramic lined steel pipe is manufactured by the self-propagating high-temperature synthesis (SHS) method. Specifically, the powdered mixed thermite is filled into the steel pipe, and the steel pipe is horizontally placed on a centrifuge and rotated at a high speed. While the steel pipe is rotating, the thermite is ignited to cause a thermite reaction (oxidation-reduction reaction) of the powder. Among them, the heavier, reduced metal melts and deposits and solidifies on the inner wall of the steel pipe under the action of centrifugal force to form a metal layer, and the lighter, oxidized aluminum generates aluminum oxide and adheres to the surface of the reduced metal to form a ceramic layer. This method can be used to obtain an abrasion-resistant and corrosion-resistant surface layer on the inner wall of the steel pipe. The reduced metal layer generated by this method is mechanically combined with the inner wall of the steel pipe. The steel pipe manufactured by this method is called a metal-ceramic "lined" steel pipe. As shown in the attached specification Figure 1 From the outside to the inside, it includes a carbon steel base pipe 1, a reduced ferroalloy layer 2, and an aluminum oxide corundum layer 3.

[0003] The combustion synthesis of metal-ceramic lined steel pipes is generally achieved through a thermite reaction. The main raw materials are generally aluminum powder and iron oxide. The basic thermite oxidation-reduction reaction equation is: 2Al + Fe2O3 = Al2O3 + 2Fe + 836 KJ / mol (836 kilojoules per mole).

[0004] In order to control the reaction rate, prevent the carbon steel base pipe from melting, and increase the fluidity of the reactants in the molten state, about 4% of SiO2 (silicon dioxide) is usually added to the formula. The basic reaction formula is: Al + Fe2O3 + SiO2 = Al2O3 + Fe + Si + 836 KJ / mol (836 kilojoules per mole). The weight ratio of the formula is generally: Al:Fe2O3 = about 1:2.8, and about 4% of SiO2 is added.

[0005] The above method has the following deficiencies:

[0006] 1. In order to prevent the carbon steel base pipe from melting, the thermite energy in this formula can be controlled at 836 kilojoules per mole. Although the iron in this reaction reaches the molten flow temperature, the inner surface of the carbon steel base pipe does not melt, and the reduced iron layer does not metallurgically fuse with the inner surface of the carbon steel base pipe. Under the action of high temperature, high pressure or strong impact force, the iron layer is prone to cracking and falling off.

[0007] 2. Due to the relatively fast combustion synthesis reaction rate and the mechanical limitation of the steel pipe rotation speed, the solidification of the iron liquid is relatively fast, resulting in a poor flatness of the inner lining layer.

[0008] To this end, we propose a thermite formulation for the inner ceramic coating of steel pipes and a preparation method of the formulation to solve the above problems. Summary of the Invention

[0009] In the present invention, copper oxide (CuO) material is added to the above thermite formulation to replace part of silicon dioxide, and the reduced copper is used to braze the reduced iron layer to the inner wall of the carbon steel base pipe, improving the bonding force between the iron layer and the carbon steel base pipe; boron trioxide (B2O3) is added to replace part of iron oxide, increasing the fluidity of the liquid reduced metal, meeting the condition of 836 kJ / mol, and can be appropriately adjusted according to the heat energy required for the wall thickness of the steel pipe.

[0010] To solve the above technical problems, a thermite formulation for the inner ceramic coating of steel pipes provided by the present invention includes: aluminum powder, iron oxide, silicon dioxide, oxygen, and further includes copper oxide and boron trioxide. The content of oxygen is less than the amount of oxygen consumed when the aluminum powder is completely oxidized, and there is unreacted aluminum after the oxygen participating in the reaction is exhausted.

[0011] Preferably, the content of the copper oxide is less than 4%.

[0012] Preferably, the weight ratio of the aluminum powder to the iron oxide in the formulation is 1:2.5 - 3.

[0013] The present invention also provides a method for preparing the above thermite formulation for the inner ceramic coating of steel pipes, including the following steps:

[0014] S1. Load the dry thermite powder prepared according to the above formulation into the steel pipe;

[0015] S2. Place the carbon steel base pipe filled with the thermite powder on a rotary centrifuge;

[0016] S3. Start the centrifuge to rotate the carbon steel base pipe. After reaching the set rotation speed, ignite the thermite powder at one end of the carbon steel base pipe. The thermite powder burns rapidly from one end of the carbon steel base pipe and spreads to the other end. Under the action of thermite, iron, copper, boron, and silicon in the powder are reduced and melted, and aluminum is oxidized and deposited and solidified on the inner surface of the carbon steel base pipe under the action of centrifugal force;

[0017] S4. After the carbon steel base pipe is cooled, take out the carbon steel base pipe, and the inner metal ceramic coating of the carbon steel base pipe is completed.

[0018] Preferably, the set rotation speed at which the centrifuge rotates the carbon steel base pipe in S3 is greater than 800 r / min.

[0019] Preferably, in S4, the carbon steel base pipe is taken out after it is cooled to below 600 °C.

[0020] Compared with the related technology, the present invention has the following beneficial effects:

[0021] 1. In the present invention, the addition of boron trioxide and copper oxide can upgrade the traditional metal-ceramic lined steel pipe combined by mechanical means to a metal-ceramic clad steel pipe combined by brazing, improving the bonding strength between the clad layer and the base pipe and enhancing the flatness of the surface of the clad layer to reduce the fluid transportation resistance.

[0022] 2. In the present invention, the metal-ceramic clad steel pipe manufactured using this formula and specific implementation method has the characteristics of strong bonding strength between the clad layer and the base pipe, a flat surface, high temperature and high pressure resistance, and corrosion resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a schematic structural diagram of a metal-ceramic lined steel pipe in the prior art;

[0024] Figure 2 is a state diagram of a carbon steel base pipe filled with thermite powder in the present invention;

[0025] Figure 3 is a state diagram of the carbon steel base pipe after igniting the thermite powder and reaching the designed rotation speed in the present invention;

[0026] Figure 4 is a schematic structural diagram of a metal-ceramic lined steel pipe manufactured according to the present invention.

[0027] Reference numerals in the figures: 1. Carbon steel base pipe; 2. Reduced iron alloy layer; 3. Aluminum oxide corundum layer; 4. Thermite powder; 5. Reduced iron alloy layer; 6. Corundum layer; 7. Reduced copper brazing layer. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0028] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0029] The combustion synthesis of traditional steel pipes lined with metal ceramics is generally achieved through the thermite reaction. The main raw materials are generally aluminum powder and iron(III) oxide, and its basic thermite redox reaction equation is:

[0030] 2Al + Fe2O3 = Al2O3 + 2Fe + 836 KJ / mol (836 kilojoules per mole).

[0031] In order to control the reaction rate, prevent the carbon steel base pipe 1 from being melted, and increase the fluidity of the reactants in the molten state, about 4% of SiO2 (silicon dioxide) is usually added to the formula, and its basic reaction formula is:

[0032] Al + Fe2O3 + SiO2 = Al2O3 + Fe + Si + 836 KJ / mol (836 kilojoules per mole), and its preferred formula weight ratio is: (Al): iron(III) oxide (Fe2O3) = about 1:2.8, and about 4% of silicon dioxide (SiO2) is added.

[0033] The present invention discloses a thermite formula for inner ceramic coating of steel pipes, and its formula includes: aluminum powder, iron(III) oxide, silicon dioxide, oxygen, and also includes copper oxide and boron trioxide. The formula weight ratio of aluminum powder to iron(III) oxide is 1:2.5 or 1:3, preferably 1:2.8. The content of the oxygen is less than the amount of oxygen consumed for complete oxidation of the aluminum powder, and there is unreacted aluminum that has not participated in the oxidation reaction after the oxygen participating in the reaction is exhausted.

[0034] The present invention adds copper oxide (CuO) material to replace part of the silicon dioxide in the above-mentioned prior art thermite formula. The content of copper oxide is less than 4%. The reduced copper is used to braze the reduced iron layer and the inner wall of the carbon steel base pipe together to improve the bonding force between the iron layer and the carbon steel base pipe; add boron trioxide (B2O3) to replace part of the iron(III) oxide to increase the fluidity of the liquid reduced metal, meet the condition of 836 kilojoules per mole, and the required heat energy can be appropriately adjusted according to the actual wall thickness of the carbon steel base pipe 1. Its basic reaction formula is:

[0035] Al + CuO + Fe2O3 + SiO2 + B2O3 = Al2O3 + Fe + Si + B + Cu + 836 KJ / mol.

[0036] The redox reaction formula of this formula is not a completely balanced equation. This reaction requires controlling the reaction heat to ensure that the base pipe is not melted, and enabling the iron, copper, silicon, and boron in the powder to be completely reduced to a liquid state and have excellent fluidity; the aluminum in this formula is more than the oxygen participating in the reaction. After the oxygen completely participates in the reaction, there is unoxidized aluminum distributed on the surface of the inner coating layer to play a role in enhancing the corrosion resistance.

[0037] A method for preparing the thermite formula for inner ceramic coating of the above-mentioned steel pipe, comprising the following steps:

[0038] S1. Refer to Figure 2 , and fill the dried thermite powder prepared according to the above formula into the carbon steel base pipe 1;

[0039] S2. Place the carbon steel base pipe 1 filled with the thermite powder 4 on a rotating centrifuge;

[0040] S3. Start the centrifuge to rotate the carbon steel base pipe 1. The set rotation speed is greater than 800 r / min. After reaching the set rotation speed, ignite the thermite powder 4 at one end of the carbon steel base pipe 1. The thermite powder 4 burns rapidly from one end of the carbon steel base pipe 1 and spreads to the other end. At this time, refer toFigure 3 , under the thermite action, iron, copper, boron, and silicon in the powder are reduced and melted, aluminum is oxidized and deposited and solidified on the inner surface of the carbon steel base pipe 1 under the action of centrifugal force;

[0041] S4. After the carbon steel base pipe 1 is cooled to below 600 °C, the carbon steel base pipe 1 is taken out, and the cermet inner lining of the carbon steel base pipe 1 is completed. Refer to Figure 4 , the cermet-lined steel pipe made by the present invention is as Figure 4 shown, and includes a carbon steel base pipe 1, a reduced copper brazing layer 7, a reduced iron alloy layer 5, and a corundum layer 6 arranged in sequence from outside to inside.

[0042] The principle of the present invention is as follows:

[0043] 1. The melting point of copper (1083.4 °C) is lower than that of iron (1538 °C), and the specific gravity (8.96 g / cm 3 is greater than that of iron (7.86 g / cm 3 ). The specific gravities of copper and iron are both greater than that of aluminum oxide (3.97 g / cm 3 ). Under the action of melting state and centrifugal force, they will be distributed in layers, from the inside to the outside in sequence as corundum layer - reduced iron layer - reduced copper brazing layer; when the thermite redox reaction makes the temperature of the base pipe higher than the melting point of copper (about 1100 °C), the outer reduced copper layer will play a role in brazing the reduced iron layers on the inner wall of the carbon steel base pipe together;

[0044] 2. Boron trioxide has a relatively low melting point (450 °C). In addition to increasing the fluidity of the molten metal and improving the surface flatness of the metal layer, it can also act as a brazing wetting agent;

[0045] 3. When transporting conductive liquid media, the unreacted aluminum distributed on the surface of the inner lining layer becomes the anode and is sacrificed, playing a role in protecting the iron alloy layer from corrosion and enhancing the corrosion resistance of the inner lining layer;

[0046] 4. The aluminum oxide corundum ceramic layer deposited on the surface of the inner lining layer has extremely strong wear resistance and can improve the service life of the steel pipe when transporting abrasive media.

[0047] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or also includes elements inherent to this process, method, article or device.

[0048] Although embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A thermite formula for inner ceramic coating of steel pipes, the formula includes: Aluminum powder; Iron(III) oxide; Silicon dioxide; Oxygen; It is characterized in that it further comprises: Copper oxide and boron trioxide; The content of the oxygen is less than the amount of oxygen required for the complete oxidation of the aluminum powder, and there is unreacted aluminum after the oxygen participating in the reaction is exhausted.

2. The thermite formula for inner ceramic coating of steel pipes according to claim 1, characterized in that, The content of the copper oxide is less than 4%.

3. The thermite formula for inner ceramic coating of steel pipes according to claim 1, characterized in that, The formula weight ratio of the aluminum powder to the iron(III) oxide is 1:2.5 - 3.

4. A method for preparing the thermite formula for inner ceramic coating of steel pipes according to any one of claims 1 to 3, characterized in that, It includes the following steps: S1. Fill the dry thermite powder prepared according to the above formula into the steel pipe; S2. Place the carbon steel-based pipe (1) filled with the thermite powder (4) on a rotary centrifuge; S3. Start the centrifuge to rotate the carbon steel-based pipe (1). After reaching the set rotation speed, ignite the thermite powder (4) at one end of the carbon steel-based pipe (1). The thermite powder (4) burns rapidly from one end of the carbon steel-based pipe (1) and spreads to the other end. Under the action of aluminothermy, iron, copper, boron, and silicon in the powder are reduced and melted, and aluminum is oxidized and deposited and solidified in layers on the inner surface of the carbon steel-based pipe (1) under the action of centrifugal force; S4. After the carbon steel-based pipe (1) is cooled, take out the carbon steel-based pipe (1), and the metal-ceramic inner coating of the carbon steel-based pipe (1) is completed.

5. The thermite formula for inner ceramic coating of steel pipes and the preparation method of the formula according to claim 4, characterized in that, In the step S3, the set rotation speed at which the centrifuge rotates the carbon steel-based pipe (1) is greater than 800 r / min.

6. The thermite formula for inner ceramic coating of steel pipes and the preparation method of the formula according to claim 5, characterized in that, In the step S4, take out the carbon steel-based pipe (1) after it is cooled to below 600 °C.

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