JPS6286173A - Production of composite pipe - Google Patents

Abstract

PURPOSE:To decrease FeO in ceramics by using a thermit mixture added with a specific ratio each of Si3N4 and SiC in the stage of coating the ceramic layer in a steel pipe by utilizing a thermit reaction. CONSTITUTION:The Si3N4 or SiC is added to the chief thermit mixture composed of the theoretically compounded iron oxide and Al at 1.5-4.0wt% by the Si-component in the chief mixture. Such thermit mixture is packed in the base pipe 1 to form the thermit layer 2. The thermit layer is ignited in a centrifugal field generated by a high speed rotation to induce the thermit reaction. The molten metal formed by the exothermic reaction and the molten ceramics are subjected to gravity sepn. to coat and formed the desired ceramic layer 4 formed via the metallic layer 3 formed on the inside surface of the pipe 1. The formed ceramics is made denser and the composite pipe having the improved strength, hardness and corrosion resistance of the ceramics is obtd. by the above-mentioned method.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to an improvement in a method of coating the inner surface of a main tube with a ceramic layer using a thermite reaction, and improves the performance of ceramics while promoting the thermite reaction. Regarding how to improve.

(Prior art) Composite pipes made by coating the mother pipe with a ceramic layer are used as transportation pipes for various fluids and industrial piping because the ceramic layer exhibits good properties such as heat resistance, abrasion resistance, and corrosion resistance. It has common uses as a member.

Various methods have been used to manufacture this type of composite tube, but recently, so-called centrifugal thermite rt-, which utilizes centrifugal force and thermite reaction, has been proposed as a suitable manufacturing method. That is, in this method, as shown in FIG.
A thermite agent made of a mixture of a metal reducing agent and a metal oxide at a certain ratio such as No. 201 is loaded to form a thermite agent layer 2, and this is ignited in a centrifugal force field due to high speed rotation.
A thermite reaction as exemplified in equation (1) is carried out, and the molten metal and molten ceramic produced by this exothermic reaction are separated by specific gravity to form a produced metal layer 3 on the inner surface of the main tube 1 as shown in FIG. A desired ceramic layer 4 is formed thereon.

Fez O1+2A6- 89. -Ch →-2Fe
+199 Kcal/1 mole to 8 R-C (11 The mixing ratio of the metal oxide and metal reducing agent is usually adjusted to the theoretical mixing ratio. For example, in the example of Fe20) and i, The molar ratio is Fe20i:A6=1:2, and the weight ratio is Fe20y;^ff=2.9641.

However, if only the thermite main agent is used in which the metal oxide and metal reducing agent are in a stoichiometric mixing ratio, the resulting ceramic layer will become porous. is added in an amount of 5 to 15% by weight based on the base material to make the ceramic densified.

(Problems to be Solved by the Invention) However, when SiO□ is added, a glass phase of 5i02 and a compound of SiO□ and FeO (Fez 5i04 ) phase is formed, and the ratio of corundum in the ceramic decreases, resulting in a decrease in strength and hardness. In addition, in acidic liquids (especially at high temperatures), Fe
Since the Fe content in the 2SiO4 phase is eluted, there is a drawback that sufficient corrosion resistance cannot be obtained. By the way, 7%5iC
When h is added, FeO is 14% in the produced ceramics.
Contains to some extent.

In view of the above-mentioned problems, the present invention was made with the aim of reducing FeO in ceramics without impairing the densification of ceramics in the centrifugal thermite method, and thereby improving strength, hardness, and corrosion resistance. be.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a method of adding Si3 N4 or/and SiC to a thermite main agent consisting of theoretically blended iron oxide and ^l. The point is that an added thermite agent containing 1.5 to 4.0% by weight of Si added to the base material is used as a thermite agent in the centrifugal thermite method.

(Example) The present inventor believes that the reason why a large amount of PeO remains in the produced ceramic is that the reducing power of the metal reducing agent in the thermite agent is weak, and furthermore, the thermite reaction is carried out in the atmosphere, so the metal oxide is It was thought that this was because it was not effectively reduced by the metal reducing agent.

As a result of intensive research based on this idea, we have discovered a method that allows the thermite reaction to be carried out in isolation from the atmosphere, increases the reducing power of the metal reducing agent in the thermite agent, and further contributes to the densification of the resulting ceramics. Ta.

That is, an additive thermite agent in which Si3 N4 or SiC is added to a thermite main agent consisting of theoretically mixed iron oxide and ^β is used as a thermite agent in the centrifugal thermite method.

The heat generated by the thermite reaction reaches up to 3000°C in the case of Fe2Ch and hen-based materials, for example. On the other hand, Si3
Since the decomposition temperature of N4 and SiC is 3000°C or less, Si3N4 and SiC easily decompose into Si and gas components during the thermite reaction, and each performs a suitable action.

By the way, the decomposition temperature of Si3N4 is 1900°C, and the decomposition temperature of SiC
It is 2600°C.

Si3N4 is made of Si and N due to the high temperature of thermite reaction.
It is broken down into. Si acts as an excess reducing agent and reduces the amount of unreacted iron oxide remaining in the ceramic, and also forms 5tCh (glass phase) during the solidification process, filling the corundum grain boundaries and contributing to the densification of the ceramic. On the other hand, N becomes N2 gas and encapsulates the reaction system as an inert gas, blocking 02 in the atmosphere and ^l in the added thermite agent, allowing the thermite reaction to proceed as theoretically, and eliminating unreacted oxidation. Reduce iron production as much as possible.

On the other hand, SiC decomposes into St and C, and Si acts as described above. C oxidizes and burns to become CO2 and CO gas, which isolates the entire reaction system from the atmosphere and forms a more favorable reducing atmosphere to reduce the amount of unreacted iron oxide remaining.

In order to isolate the reaction system from the atmosphere, attempts were made to conduct the reaction in an N2 gas or static gas atmosphere, but it was not possible to simply form a gas flow on the surface layer of the thermite agent with both ends of the main tube open. , sufficient isolation was difficult. In addition, by placing the entire main tube in a chamber and filling it with the inert gas after vacuum degassing, it is possible to completely isolate it from the atmosphere, but in such a case, special equipment is required. , resulting in a decline in productivity.

5i311j4 In order to find a suitable addition amount of SiC, the present inventor added metal St to the thermite main agent in various proportions, and determined that the addition amount of Si was determined by adjusting the porosity of the ceramic and the adhesion shear force between the ceramic and the produced iron. We investigated what kind of influence G has. The results are shown in Figures 3 and 4.
As shown in the figure.

FIG. 3 is a graph showing the relationship between the amount of S1 added and the ceramic porosity. In the case of no Si addition, the ceramic porosity is extremely porous at about 25%;
When the illumination is ~5%, it becomes dense, and when it exceeds 5%, it becomes porous.

FIG. 4 is a graph showing the relationship between the amount of Si added and the adhesion shear force between the produced iron and the produced ceraminox. As shown in Fig. 5, the contact shear force is measured by using a composite tube (using a steel pipe as the mother tube) manufactured by the centrifugal thermite method, placing the mother tube 1 and the produced iron layer 3 on a punching table 5, and Calculations were made based on the pressing force when only the ceramic layer 4 was pressed through the punch 6 and the resulting ceramic layer 4 was pushed away. According to the figure, it can be seen that when Si exceeds 4%, the adhesion shear force is considerably lower than when no Si is added (approximately 120 kg/a+I). At this time, as a result of cross-sectional observation of the composite tube, it was observed that a considerable number of voids were generated at the boundary between the produced ceramic layer 4 and the produced iron 1ii3'.

The above is thermite main agent (Fe20t 1,2A
12), but substantially the same results were obtained when FeO was used as the metal iron oxide.

Based on these facts, when Si is added in a weight ratio of 1.5 to 4% to the theoretically mixed iron oxide and AI thermite main ingredients, ■ Ceramic porosity 2 to 3% ■ Between produced iron and produced ceraminox Adhesive shear force of 250
~100 kg/cd can be shown to obtain a good ceramic lined tube.

Note that when 1.5 to 4% of St was added, FeO in the produced ceramic was about 5%.

From the above, Si3N4 or/and SiC has a Si content of 1.5 to 4% (Si 3
2.5-6.7% for N4 only, 2.1-5 for SjC only
．． 7%), it is possible to obtain a composite pipe that is dense and has a good lining condition.

In addition, methods for loading the thermite agent into the main tube include spraying a mixture of 5J3N4 and/or SiC to the thermite main agent, or spraying Si3N4, etc. onto the main tube, and then spraying the upper surface of the main tube. A thermite base agent may be sprayed on the surface. Further, the mother pipe is not limited to a metal base such as a steel pipe, but may be an inorganic base pipe such as a concrete pipe or a ceramic pipe.

Next, other specific examples will be described together with conventional examples, comparative examples, and comparative examples. The conventional example is one in which SiO□l is added, and the comparative example is one in which metallic Si is added.

(1) Mix and prepare the additive thermite agent shown in Table 1, load it into the main pipe (steel pipe) listed in the table so that it has an approximately uniform thickness, and rotate it at high speed (1400 to 1500 rpm). It ignited and caused a thermite reaction.

(2) After the thermite reaction was completed, the tube was sufficiently cooled to obtain a composite tube. A ceramic layer of about 4 as thick was formed on the inner surface of each of the composite tubes.

(3) Table 2 shows the results of examining the composition and physical properties of the produced ceramics. The corrosion resistance is expressed as an index based on the conventional example, and was calculated by immersing it in a 10% H2S04 (sulfuric acid) solution and measuring the corrosion loss.

Next (Effects of the Invention) As explained above, according to the present invention, in the centrifugal thermite method, S
Since we use an additive thermite agent in which i3N4 or/and SiC is added in an Si content of 1.5 to 4.2% by weight based on the base material, the thermite reaction decomposes Si3N4 and SiC, resulting in 7Si, N2 gas, CO2 gas, CO gas is generated, and St acts as an excess reducing agent, reducing the residual amount of unreacted iron oxide in the ceramics, and also forms SiO□ during the solidification process, filling the corundum grain boundaries and making the ceramics densified. Make it familiar. On the other hand, N2 gas etc. encapsulate the reaction system, and the ^β in the added thermite agent and 0 in the atmosphere
By blocking □, it is possible to allow the thermite reaction to proceed according to theory, and to reduce the production of unreacted iron oxide as much as possible. This not only densifies the produced ceramics, but also makes F
The e2SiO4 phase can be reduced as much as possible, the strength, hardness and corrosion resistance of the ceramic can all be improved, and a composite tube with a produced ceramic layer of extremely high quality can be obtained.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of the mother tube showing the loading state of thermite agent in the centrifugal thermite method, Figure 2 is a cross-sectional view of the mother tube (i.e., composite tube) after the thermite reaction, and Figure 3 is the amount of Si added and pores. FIG. 4 is a graph showing the relationship between the amount of Si added and adhesion shearing force, and FIG. 5 is a cross-sectional explanatory diagram showing the adhesion shearing force test method. DESCRIPTION OF SYMBOLS 1... Mother pipe, 2... Thermite agent layer, 3... Generated metal layer, 3'... Generated iron layer, 4... Generated ceramic layer.

Claims (1)

[Claims] 1. In a method of loading a thermite agent on the inner surface of the mother tube and causing a thermite reaction in a centrifugal force field to coat the inner surface of the mother tube with a generated ceramic layer via a generated metal layer, the theory Thermite agent is characterized in that an additive thermite agent is used as the thermite agent, in which Si_3N_4 or/and SiC is added in an amount of 1.5 to 4.0% by weight based on the base agent to the thermite base agent consisting of iron oxide and Al. A method for manufacturing a composite pipe.