JPS58132296A - Manufacture of sound absorbing material - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a sound absorbing material having a ceramic skeleton used in an exhaust silencing device interposed in the exhaust gas flow path of an internal combustion engine or other various combustion devices. So there are 9.

Traditionally, sound absorbing materials used for this type of application include:
Fibrous materials made of glass wool, ceramics, metals, etc.
There are foamed and particle layered porous materials. However, if these materials are used as sound-absorbing materials as they are, components that form tar and soot contained in the exhaust gas will adhere to the surfaces and internal pore walls and turn into tar, which will continue to grow over a relatively short period of time. Over time, sound-absorbing materials become clogged, significantly reducing their initial sound-absorbing performance, leading to intensified noise and reduced operating efficiency.

Therefore, the inventors of this application conducted various investigations into the causes of the above-mentioned clogging, and the following findings were found. In other words, due to the moisture contained in the exhaust gas and the moisture retained on the wall surface of the sound-absorbing material, tar-forming components and soot accompanying the exhaust gas are likely to adhere to the surface of the sound-absorbing material. Due to the large roughness of the exhaust gas flow in the vicinity, the tar-forming components enter the sound-absorbing material together with the exhaust gas and adhere to the surface of the sound-absorbing material and the pore walls. is polymerized and turned into tar at the exhaust gas temperature, and the generated tar-like substance further promotes the above-mentioned adhesion phenomenon, resulting in tar and soot being densely adhered to the entire surface and inside of the sound absorbing material.

Therefore, in order to maintain the initial characteristics of sound absorption performance over a long period of time, it is necessary to reduce the surface energy of the sound absorption material to suppress the adhesion of tar-forming components, and to reduce the roughness of the surface of the Jf material to improve the exhaust gas flow. It is effective to reduce the disturbance of In this case, in order to reduce the surface energy of the sound absorbing material, the surface layer of the sound absorbing material may be formed of a conductive material, and the surface roughness of the sound absorbing material may be increased by increasing the smoothness of the surface of the surface layer. Bye.

From this point of view, we conducted further research based on the idea of solving the above m= by coating the surface of the porous base material with a substance having low surface energy. As a result, when organic materials such as fluororesins, which are generally considered to have low surface energy, or inorganic solid lubricants such as graphite and molybdenum dioxide are used as coating materials for porous substrates, exhaust gas There are inconveniences such as the surface temperature rising to 150-500℃ when immersed in gas and losing its low surface energy properties, and the coating material itself decomposing, but due to the covalent bond between fluorine and carbon. It has been found that the above-mentioned disadvantages do not occur when the compound hydrogen fluoride (graphite fluoride) is used.

However, on the other hand, since the viscosity of the above organic substances can be easily adjusted, it is easy to form a film on the surface of a porous substrate. It has the advantage of not causing organic matter to enter the interior of the material. This means that from the viewpoint of not causing a decrease in sound deadening performance due to film formation,
It's hard to throw away.

Therefore, the inventors conducted various investigations in order to take advantage of the inherent advantages of high-molecular organic substances and abutted graphite, and were able to complete this invention.

That is, the present invention uses a base material made by carbonizing the surface of a polymeric organic coating applied to a porous ceramic framework, in which fluorinated graphite and tar from combustion residue of fuel are discharged from a combustion device. This method involves plating a reducing agent that is inhibited at exhaust gas temperature and an alkaline earth metal element at the same time.

Hereinafter, the present invention will be described in detail based on examples.

〔Example〕

As a porous skeleton, T io, -A I , O, -M
A gO-based ceramic porous body was used. Polyacrylonitrile dissolved in a solvent and made into a paste was applied to this surface, and the solvent was volatilized at 100°C. After preheating at 850°C in argon gas, the ceramic was fired at 800"C. A base material having a carbonaceous film on the surface was obtained.

Then, the base material and the Cu electrode were inserted into an electrolytic solution containing fluorinated graphite, potassium silicate and Ag powder, and a surfactant as a dispersant, and O was placed on the anode.

The carbonaceous coating of the base material was connected both in the dark and in the dark, and the surface of this carbon coating V was simultaneously plated with brominated graphite and O to form a composite coating thereof.

An enlarged sectional view of the sound absorbing material thus obtained is shown in FIG. In Figure 1, (1) is a ceramic porous skeleton particle, and (2) is a polyacrylonitrile coating.
The polymeric organic layer adhering and penetrating the surface and inside of the porous substrate, (3) is a carbonized coating 11, and (4) is a composite coating of fluorinated graphite, potassium silicate, Ag powder, and On. be.

Next, the sound absorbing material manufactured by the method of this invention and 8i0
．． - With respect to a conventional sound absorbing material made of an AI, O, ceramic porous body, the sound absorption coefficient, soot adhesion, and the associated changes in sound deadening performance over time were investigated.

Figure 2 shows the in-tub method (JI8A140s).
- Normal incidence sound absorption coefficient measured under - condition is shown.

The curve B of the sound absorbing material according to the present invention is a characteristic of a conventional sound absorbing material made of a ceramic porous body.

From FIG. 2, it can be seen that the sound absorbing material produced by the method of the present invention has a higher sound absorption coefficient and better sound absorption characteristics than the conventional material.

Next, the above two types of sound absorbing materials are formed into a cylindrical shape to construct an exhaust silencing device as shown in Fig. 8.
The engine was installed in a vehicle with a displacement of 200,000 mm, and after approximately 10,000 km of actual driving, the silencing performance was measured using JI8D1616 and compared with the initial value before actual driving.

In FIG. 8, (5) is a casing constituting the exhaust silencer, (6) is an exhaust gas inlet pipe, (7) is an exhaust gas passage,
(8) is a sound absorbing material, and (9) is an exhaust gas outlet pipe. Figure 4 shows the frequency characteristics of the silencing performance. Curves C and C'
are the characteristics at the initial stage and after actual running when using the sound absorbing material according to the method of this invention, and curve and D'
are the initial and actual characteristics when using a conventional sound absorbing material made of porous ceramic material. As can be seen from Figure 4, the sound-absorbing material manufactured by the method of the present invention not only has good initial sound-absorbing performance, but also exhibits almost no decline in initial performance after 10,000 actual runs. However, after actual driving, the noise-absorbing performance of the sound-absorbing material made of porous ceramic material deteriorated significantly in all frequency bands. In addition, when we took out both sound absorbing materials and visually observed them while measuring their noise-absorbing performance, we found that the sound absorbing material of this invention was almost as clean as the initial one, whereas the conventional sound absorbing material made of porous ceramic material was almost clean. A large amount of black soot had adhered to the entire surface, causing severe clogging.

Regarding this point, in the sound absorbing material manufactured by the manufacturing method of the present invention, although the porous skeleton is made of non-conductive ceramic, the surface of the polymeric organic coating applied to this skeleton is carbonized. Because it is conductive, it does not carry static electricity, and since the fluorinated graphite that is attached to the surface of this carbonaceous coating by plating inherently has an extremely small surface energy, it is the main cause of soot adhesion. This makes it difficult for liquid combustion residues such as water (steam) and tar to adhere to the surface of the sound-absorbing material, so soot does not adhere to the surface, or even if soot does, the flow of exhaust gas is reduced. It is thought that it was easily blown away.

By the way, in this invention, as the organic polymer material to be applied to the porous substrate, in addition to the polyacrylonitrile in the example, organic polymer materials mainly including pitch, cellulose (rayon), polyvinyl alcohol, and other resins are used. can be used alone, and in order to carbonize them, in an inert gas, at 200 to 500° coii
700 to 1200 degrees or after this
Experiments have confirmed that when fired at a temperature of 0, the material becomes carbonaceous with some residual organic matter. tit, use of silver powder, sodium sulfite, metal powder, carbon powder, sulfite, ferrous salt, tin salt, sootous nitrate, sootous sulfate, oxalate, and other reducing agents. I can do it. Sara Ct. As the alkali agent, potassium silica, sodium alginate, sodium silicate, lithium silicate, sodium carbonate, alkali metal oxide, alkali metal silicate, hydroxide, basic oxide and other alkali agents can be used. can. The above reducing agent suppresses polymerization due to oxidative polymerization of the tar generated, and the alkaline agent
It acts to prevent the formation and precipitation of tar by neutralizing or saponifying the substances produced by polymerization of tar products and inhibiting the progress of the polymerization reaction.

In this invention, the graphite fluoride, the reducing agent, and the alkali agent mentioned in 1 above originally have a not so strong adhesion force to the porous substrate of %/-h4; Since they are plated on the porous substrate together with other types of simple metals that have strong adhesion, they are strongly bonded to the porous substrate. Therefore, it has excellent mechanical strength, that is, vibration resistance and impact resistance. It was.

Bubbly graphite itself has a microscopic layered structure.

In addition, since the reducing agent and alkaline agent are themselves porous, the resulting sound absorbing material exhibits excellent sound absorbing performance, especially in the low frequency band. The content weight percentage - can be changed in the range of %5 to 95% depending on the application and usage conditions, and the frequency band showing the maximum sound absorption coefficient can be adjusted by adjusting the weight and adjusting the plating time. can. The reason why each weight percentage is set to 5 to 95% is because if each weight percentage is 5% or less, the purpose of addition cannot be practically achieved.

As is clear from the above description, according to the present invention, a sound absorbing material that is extremely smooth and has a small surface energy can be obtained, so that the sound absorbing material has good sound damping performance. Even when used in the #l'9IC gas flow path of an exhaust silencing device for an internal combustion engine, clogging with soot does not occur over a long period of time, and the silencing performance does not deteriorate. Therefore, since the sound absorbing material produced by the manufacturing method of the present invention has high performance and long life, it can be widely applied in manufacturing exhaust silencing devices for internal combustion engines such as automobiles.

[Brief explanation of the drawing]

Figure 1 jd is an enlarged sectional view showing the structure of the sound absorbing material produced by the manufacturing method of this invention, Figure 2.4 is a characteristic diagram showing the performance of the sound absorbing material produced by the manufacturing method of this invention, and Figure 3 is the manufacturing method of this invention. FIG. Note that the same reference numerals in the figures indicate the same or corresponding parts. (1)... Selantsk porous skeleton %C2)...117
II & molecular organic layer% (3)...carbonaceous film, (4)
--- Composite coating, (8) --- Sound absorbing material. Agent Shin Kuzuno - (1 other person) Figure 1 Figure 2

Claims (1)

[Claims] (1) A base material made by carbonizing the surface of a polymeric organic coating applied to a porous ceramic skeleton,
A method for producing a sound absorbing material that simultaneously plates a reducing agent and an alkaline earth metal element that prevents tar combustion residue of fuel from turning into tar at the temperature of exhaust gas discharged from a combustion device.