JPH0363457B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for forming an alloy layer having desired material characteristics on the inner surface of a metal main tube. (Prior Art and Its Problems) Composite pipes in which the inner surface of a metal pipe is coated with an alloy layer having excellent wear resistance, corrosion resistance, etc. are used in various fields. Various methods have been used to manufacture this type of composite tube, but recently a method using the so-called centrifugal thermite method, which utilizes centrifugal force and thermite reaction, has been proposed as a suitable manufacturing method. ing. In this method, as shown in Fig. 1, a metal main pipe 1
Thermite agent 2, which is made of a mixture of a metal reducing agent Al and metal oxides such as Fe, Cr, and Ni at a certain ratio, is loaded on the inner surface, and is ignited in a centrifugal force field due to high speed rotation. Various thermite reactions are carried out as shown in the table, and the molten alloy and molten ceramic produced by this exothermic reaction are separated by specific gravity to form a desired alloy layer 3 on the inner surface of the main tube 1 as shown in FIG. After coating the ceramic layer 4 through the tube, as shown in FIG. 3, the ceramic layer 4 is removed to obtain a composite tube 5 whose inner surface is coated with only the desired alloy layer 3.

[Table] In this case, the mixing ratio of various metal oxides and Al is usually calculated theoretically based on the chemical reaction formula shown in Table 1. However, some types of metal oxides have weak reducing properties, so Al cannot be completely oxidized.
Al remains in the produced alloy, and not only does the produced alloy not have the desired composition, but it often contains 1% or more of Al. In this case, the melt flowability and corrosion resistance of the produced alloy are significantly reduced. The deterioration of the material properties has become a problem. The present invention has been made in view of such problems, and is a method for manufacturing composite pipes using the centrifugal thermite method, which reduces the residual amount of Al in the coating alloy layer and produces an alloy that does not cause deterioration of the material quality. It is an object of the present invention to provide a method for coating the inner surface of a main tube with a layer. (Means for Solving the Problem) In order to achieve the above-mentioned purpose, in a method of forming a desired alloy layer on the inner surface of the main tube using the centrifugal thermite method, the Al content in the alloy layer is In order to reduce this, the weight ratio W/Wo of the amount W of Al added in the thermite agent to the theoretical amount Wo of Al added for reducing the metal oxide in the thermite agent is set to 0.9 or less. (Example) Next, the weight ratio W/ of the Al addition amount W in the thermite agent according to the present invention and the Al addition amount Wo theoretically calculated for reducing the metal oxide in the thermite agent
The reason why Wo (hereinafter referred to as Al addition ratio) is set to 0.9 or less will be explained, and specific examples will be mentioned. As shown in Table 2, the present inventor prepared thermite agents in which the addition rate k of the metal oxide was kept constant and the value of the Al addition ratio was varied, and the thermite agent was loaded into the main tube to produce thermite. A reaction was caused and the composition of the resulting alloy layer was investigated. The results are shown in Table 3 and Figure 4.

【table】

[Table] According to Figure 4, the Al content in the produced alloy is
When the Al addition ratio exceeds 0.9, it increases rapidly;
It was found that the Al content was extremely low at 0.5% or less. In addition, as the Al addition ratio is reduced, Fe and Ni in the resulting alloy increase,
It can be seen that Cr, which has weak reducing properties, decreases. The metal main pipe used in the present invention is as follows:
Any material can be used as long as it can withstand thermite reaction, such as ductile cast iron pipes and steel pipes. Next, based on Table 3 and Figure 4, the target composition of the final alloy to be produced is determined in weight percent: Fe: 74%, Ni:
An example of manufacturing a composite pipe in which the inner surface is coated with an alloy layer containing Cr: 8% and Cr: 18% will be described.
It should be noted that all percentages shown below mean percentages by weight. (1) Calculating the compounding ratio k'% of metal oxide to obtain the target alloy composition Example 1 (Target Al: 0.24%) In Figure 4, when the Al addition ratio = 0.9, the formation If the content of alloying element X in the alloy is x%, and the addition rate (compounding ratio) of metal oxide Mixing ratio k′x of X′ in
(%) is expressed as k′x=y/x×kx(%), where y is the content (%) of X in the target alloy to be manufactured. Therefore, k′ _Cr2O3 = 18/14.6×21≒26% k′ _NiO = 8/10.7×9≒7% k′ _Fe2O3 = 100−26−7=67% Example 2 (Target Al: 0.02% case) In Figure 4, based on the values when the Al addition ratio = 0.8, k' _Cr2O3 = 42% k' _NiO = 6% k' _Fe2O3 = 52% (2) Calculate (1) in the same way as Based on the blending ratios determined, thermite agents were prepared by blending each metal oxide as shown in Table 4. Internal diameter 113mm, length 490mm, wall thickness as main pipe
Using a 7.5 mm ductile cast iron pipe, the thermite agent was sprayed while rotating the main pipe at a low speed, and then the rotation was increased to a G _NO. of 90, at which time the thermite agent was ignited to cause a thermite reaction.

[Table] In Table 4, in Example 2, Fe ₂ O ₃ = 75 g, Al =
A total of 25g (theoretical blend) of 100g of thermite agent for ignition was sprayed to facilitate the occurrence of thermite reaction, whereas in the comparative example, this thermite agent for ignition was not sprayed. (3) Table 5 shows the results of examining the composition of the obtained alloy layer.

[Table] In the alloy composition produced in Example 1, Fe and Cr are slightly lower than the target, and Ni is slightly higher, but the key point, Al, is in the case of Sample 1 (Al: 2.48%) in Table 3. When compared, it was definitely reduced to less than 0.1%. In Example 2, the ratio of Cr ₂ O ₃ in the thermite agent is large, k' _Cr2O3 ≒ 42%, but the thermite reaction occurs easily by using the ignition thermite agent, and the Al content in the alloy is also good at 0.1%. It was hot. On the other hand, in the comparative example, no reaction occurred even though ignition was attempted several times because no thermite agent for ignition was used. (Effects of the Invention) As explained above, according to the present invention, when coating the inner surface of the metal main tube with a desired alloy layer,
Since the centrifugal thermite method is applied and the Al addition ratio in the thermite agent is 0.9 or less, the residual amount of Al in the produced alloy can be kept to 0.5% or less, effectively reducing the flowability and corrosion resistance of the produced alloy. can be prevented.

[Brief explanation of drawings]

Figures 1 to 3 are cross-sectional views of the main pipe showing the manufacturing process of the composite pipe of the present invention. Fig. 1 shows the state in which the thermite agent has been sprayed on the inner surface of the main pipe, and Fig. 2 shows the state after the thermite reaction. FIG. 3 shows the state after the ceramic layer has been removed, and FIG. 4 shows the relationship between the Al addition ratio, the produced alloy composition, and the amount of residual Al. 1... Mother pipe, 2... Thermite agent, 3... Alloy layer, 4... Ceramics layer, 5... Composite tube.

Claims (1)

[Claims] 1. A thermite agent made of a mixture of Al and multiple metal oxides is loaded on the inner surface of the metal mother tube, and the thermite agent is ignited in a centrifugal force field to cause a thermite reaction, thereby forming an alloy layer on the inner surface of the mother tube. In this method, the ceramic layer is removed and only the alloy layer is formed on the inner surface of the main tube.
In order to reduce the content, the weight ratio W/Wo of the amount W of Al added in the thermite agent to the theoretical amount Wo of Al added to reduce the metal oxide in the thermite agent was determined.
A method for manufacturing a composite pipe having an alloy layer coated on the inner surface, characterized in that the inner surface of the composite pipe is 0.9 or less.