JPS58129490A - 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 sound absorbing material used in an exhaust silencing device for an internal combustion engine.

Conventionally, sound absorbing materials used in exhaust silencers for internal combustion engines include glass wool, ceramic porous materials, and metal porous materials. However, when these materials are used as sound-absorbing materials, when an internal combustion engine is operated, tar and soot, which are combustion residues of fuel such as gasoline, adhere to the surface and cause clogging in a relatively short period of time, reducing sound-absorbing performance. This often resulted in intensified noise and adversely affected the fuel efficiency of the internal combustion engine. In addition, when glass wool or porous ceramic materials are used as sound absorbing materials in exhaust silencers for internal combustion applications, the high pressure of exhaust gas and large vibrations may cause the sound absorbing materials to become powdered or damaged. Sometimes I ended up doing something like that and it became completely useless. and,
When a porous metal body is used, the temperature of the exhaust gas inside the silencer is as high as 400 to 800°C, and the exhaust gas contains corrosive sulfur oxides and nitrogen oxides, so unless a special heat-resistant alloy is used, As corrosion deterioration due to high-temperature oxidation becomes significant, corrosion products may cause clogging, and the skeleton of the porous material will corrode and disappear, making it useless as a sound absorbing material. Since the pore size is relatively large as a basic characteristic of the body, there are often disadvantages such as the absence of any material with good sound absorption performance. Conventional sound absorbing materials have major drawbacks as mentioned above.
None of them could be put to practical use as an exhaust muffler for internal combustion engines.

To overcome these drawbacks, the inventors have already proposed a sound absorbing material that utilizes the tactile effect of substances.

This invention does not utilize the catalytic action of substances;
As a result of considering the mechanism of tar generation from fuel combustion residue and attempting various studies, we found that reducing substances inhibit the polymerization due to oxidative polymerization of tar generated substances, or that alkaline substances inhibit polymerization due to the polymerization of tar generated substances. These substances can prevent tar formation and precipitation by blocking the progress of the polymerization reaction by neutralizing or saponifying the produced storage, and also act as a deterrent to the adhesion of graphite gas. This is based on the discovery that it is possible to make a sound absorbing material by incorporating it into a binder and applying it to a porous metal body to improve sound absorption properties and heat resistance.

Hereinafter, this invention will be described in detail according to examples.

[Example 1. ] A sintered metal made by Mitsubishi Metals (trade name: Diamond Knot Filter, thickness: 6) was used as the metal porous sound-absorbing base material, and the following composition example 1. The composition was uniformly applied using a ball coater, dried at 80°C for 80 minutes, and then baked at 650°C for 80 minutes to harden it.

(Composition example 1.) Reducing agent 2 Ag powder 48tt% Alkaline agent; Potassium silicate 1011% Binder Niga 2 quality frit 19 Heavy B additives: alumina, bentonite, water 171 Low surface energy substance: graphite fluoride 611 %Additives have the effect of improving the adhesion and film performance of the coated product, increasing the strength and adhesion performance to the underlying porous material after the coating film is formed, and making the film porous. The sound absorbing material of this invention manufactured in this manner has the following properties.

An enlarged cross-section is shown in FIG. 1, which shows a nice configuration. That is, (1) is a particle of a metal porous body, and (2) is a reducing agent particle.

(3) is a binder that contains and disperses reducing agent particles (2), an alkali agent, and fluorinated graphite (6) and penetrates into the spaces between particles (1) of the porous metal body; Binder (3
) is applied to the surface of the porous coating. In this case, the mixed alkali agent of composition example 1° is not particularly drawn in FIG. 1 because it dissolves during the mixing operation. In this way, soluble substances are
It is also present in the reducing agent used in this invention. In addition, additives such as alumina are equivalent to or larger than the reducing agent in terms of particle size, but they are not included in Figure 1 because they do not play a major role. Not yet. Create a composition using the sound absorbing material of this invention configured as shown in Figure 1! <Comparing the performance with that of a porous metal material without any coating.

Figure 2 shows sulfur dioxide (sulfur dioxide gas) in air containing 6 ppm at a temperature of 400 to 800°C using an electric furnace. The figure shows the weight change rate due to corrosion when left for 2 hours. As is clear from Fig. 2, curve a shows the weight change rate of the sound absorbing material of the present invention manufactured as described above, the #4 wire made of the same material, and the sound absorbing material consisting only of metal porous bodies. , the sound absorbing material of the present invention has an exhaust gas temperature of 400 to 80, which is the exhaust gas temperature in an exhaust silencer for an internal combustion engine.
Even at 0°C in air containing sulfur dioxide, corrosion hardly progresses and it has good corrosion resistance. In comparison, in the case of the conventional metal with only one porous body, the weight change due to corrosion became more severe as the temperature increased, and visual observation showed that yellow-green corrosion products were attached to the surface.

It can be said that the corrosion resistance of the sound absorbing material of the present invention is 10 times or more better than that of a metal porous material alone at a temperature of 700° C. or higher.

FIG. 8 shows the normal incidence sound absorption coefficient measured under the same conditions by the in-pipe method (JISA1405).

Curve C is the characteristic of the sound absorbing material of the present invention, and curve d is the characteristic of the sound absorbing material consisting only of metal porous bodies. From FIG. 8, it can be seen that the sound absorbing material of the present invention has a considerably higher sound absorption coefficient than that of a material made only of porous metal. This is the result of Composition Example 1 from the surface of the metal porous body. By applying and curing the composition of
This is due to the fact that the structure shown in the figure is also essentially porous, allowing air to flow through it.

That is, composition example 1. The coated cured product itself forms part of the sound absorber, and the sound absorption coefficient can be adjusted depending on the method of application. However, in the experiments conducted by the inventors, care must be taken because if the amount of coating is too large, the sound absorption coefficient will actually decrease.

Next, the two types of sound absorbing materials mentioned above were molded into a cylindrical shape and incorporated into the exhaust silencing system of a commercially available domestically produced passenger car (displacement 1,600 cc), and after about 10,000 actual trips, the J I 5
The noise reduction performance was measured using D1616, and FIG. 4 shows a comparison diagram with the initial value before actual driving.

Curves c1 and CI are the initial and actual % performance when using the sound absorbing material of the present invention, respectively.
f 1 and f: are the initial characteristics and the characteristics after actual running, respectively, when a conventional sound absorbing material consisting of only a metal porous body is used. As can be seen from Figure 4, the sound-absorbing material of this invention not only has good initial sound-absorbing performance, but also has almost no deterioration in initial performance after 10,000 miles of actual driving. Actual driving 1 for those using only porous sound absorbing material
It decreases after heating, and the decrease is particularly significant in the high frequency range. Furthermore, after measuring the silencing performance, both sound absorbing materials were taken out and visually observed, and it was found that the sound absorbing material of this invention was almost as clean as the initial one, but the one with only a metal porous material was A large amount of black tar-like and soot-like combustion residue and yellow-green corrosion products had adhered to the entire surface, causing severe clogging. In other words, as can be seen from this result, even if tar-forming components in the exhaust gas are scattered and attached to the surface of the sound-absorbing material, the reducing agent and alkaline agent dispersed in the sound-absorbing material of the present invention are This action prevented oxidative polymerization (increasing the boiling point) and caused it to automatically vaporize (purify) at the temperature of the exhaust gas without turning into tar. It is thought that the initial sound deadening performance did not deteriorate much because the soot adhesion prevention effect and soot adhesion dispersion effect were effectively exerted. In addition,
The Ag powder used as a reducing agent in this example works as an oxidation catalyst depending on the application, but it works as a good reducing agent in cases where there is a lack of oxygen at high temperatures, such as in an exhaust gas atmosphere. It is.

The above-mentioned buttomized graphite and other components can effectively exhibit their respective functions at 6 to 95 weight, but preferably both are 50! i[deoru.

[Example]

As a porous sound-absorbing base material, a foamed metal manufactured by Sumitomo Electric (trade name: Cell Knot, thickness 5) was used. Second half composition/Example 2. and 8. Example 1. After mixing the wires in the same manner as in the case of , the mixture was sprayed onto the sintered metal and cured by firing to obtain the sound absorbing material of the present invention.

(Composition Example 2.) Reducing agent: Sulfite) Lithium 55 Strong binder Nialuminum phosphate) 2511% (Composition Example 8.) Alkaline agent: Sodium aluminate 5811% Binder: Methylphenyl silicone 2211% Additives :
Silica stone, organic bentonite, thinner 50% by weight Low surface energy material: graphite fluoride 10'i [fl] Using this sound absorbing material and the same porous metal material as above, composition examples B and 8. For those that do not have any composition applied,
Example 1. Various performances were investigated in exactly the same way as in the case of . Results 1 Composition Example 2. and 8. The sound absorbing material of the present invention coated and cured with the composition of the present invention has excellent corrosion resistance, sound absorption coefficient, and odor in any of the temporal changes in sound deadening performance due to clogging prevention. It was found that the case had almost the same addictive characteristics as the case shown in the figure. In other words, in this invention, it is more important to create a sound absorbing material that is not clogged with tar and whose initial sound absorbing performance hardly deteriorates than by using FC using at least one of a reducing agent and an alkaline agent. I can do it.

Let us now consider the good corrosion resistance of the sound absorbing material of this invention. Corrosion caused by combustion exhaust gas is mainly caused by high-temperature oxidation and condensed water, and these are accelerated by sulfur oxides such as S (h) and N0% contained in the exhaust gas.
These are substances such as NOx.

These substances usually become corrosive through oxidation and dissolve in water to form even more corrosive acidic substances such as sulfuric acid and nitric acid, thereby accelerating corrosion. The reducing agent used in this invention suppresses the above-mentioned oxidation, and the alkaline agent neutralizes highly corrosive acidic substances and eliminates the corrosive properties. It is considered that the sound absorbing material of this invention exhibits good corrosion resistance.

Next, let us consider a salt mine in which the sound absorbing material of the present invention has the effect of preventing tar from adhering to it. At the beginning of the process in which combustion residues in exhaust gas are oxidized and tar is formed, a similar reaction starts from hydrocarbons and progresses gradually, resulting in polymerization ( It is thought that the substance is converted into a high-boiling point substance.

R1 (-R+H・・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・■R・+0. →RO
O-・・・・・・・・・・・・・・・・・・・・・
・・・・・・・■ROO・+H→ROOH+ R・ ・
・・・・・・・・・・・・・・・・・・・・・■2ROO
H-4RO・+ROO+ H＊0 River・・・・・・・・・
・・・・・・・・・■R・＋R・→R−R・・・・
・・・・・・・・・・・・・・・・・・ Old・・・・・・■R
O@+ RH-+ROH+ R・・・・・・・・・・・・
・・・・・・・・・・・・・・・(6)2ROO・→
Non-radical products ・・・・・・・・・・・・ ・・・
('D However, in the above formula, RH: Hydrocarbon %R・: Hydrocarbon radical H・:
Hydrogen radical, RO・Nioxy radical ROO・:
Peroxy radical, ROH: hydride, ROOH
: Hydroperoxide, R-R: Polymer, i.e.
Due to heat action, some hydrocarbons are activated and a reaction begins as shown in equation (2). And ROH, ROOH, R-
R etc. are generated. Non-radical substances produced in the formula are alcohols, aldehydes, ketones, etc. These are further oxidized to acids, oxyacids, acid anhydrides, esters, etc., and are then oxidatively polymerized to have even higher molecular weight. It becomes a thing. The reducing agent used in this invention serves to suppress these successive oxidation reactions. Similarly, the alkaline agent used in this invention is used to neutralize acidic substances such as acids (carboxylic acids) and oxyacids produced as the reaction progresses, and to prevent the reaction from proceeding any further, as well as to neutralize the produced ester g. Due to the two effects of hydrolysis (saponification) into alcohol and acid,
It serves to prevent the reaction from proceeding any further.

By the way, the reducing agent used in this invention may be one that is thermally stable among the general reducing agents such as metal powder, carbon powder, sulfite, ferrous salt, and tin salt. I can do it. As the alkaline agent, common alkali (basic) substances such as potassium silicate, sodium aluminate, sodium silicate, lithium silicate, sodium carbonate, and alkali metal oxides can be used.

In addition to foamed metals and sintered metals as in the examples, examples of porous metal bodies used as base materials in this invention include metal fibers,
Commercially available general-purpose materials such as inorganic fiber-reinforced metals can be used.

The heat-resistant binder used in this invention includes:

Examples include wax (vitreous frits), alkali metal silicates, colloidal silica, colloidal alumina, metal silicate, cements, silicone resins (faces), and mixtures thereof.

The fluorinated graphite used in this invention is a chemically very stable white to gray fine powder in which one fluorine atom is strongly bonded to each carbon atom through a covalent bond, and is industrially available. Generally, it is produced by directly reacting fluorine generated by electrolyzing fluoric anhydride with carbon. Its properties include low surface energy and a small coefficient of friction.
It has been put into practical use as a solid lubricant. In this invention, as a method for dispersing and adhering the fluorinated graphite to the surface of a porous material, as described in the examples, a method of dispersing it in a resin binder or an inorganic binder and applying and baking it in a round shape is suitable. In addition to the present invention, metals may be used as porous materials, such as Nl? Another effective method was to eutectoid plate the surface of a porous metal body with oxidized graphite dispersed in a plating solution together with Cr or the like.

It was also effective to use commercially available spray sets and face-shaped sprays in which fused graphite was dispersed in a resin binder.

The sound absorbing material of the present invention is intended to be used in an exhaust silencing device for an internal combustion engine, but depending on how it is used, it may also be used as a sound absorbing material in other equipment such as a combustor.

As explained above, a metal porous body is used as a base material.

If the sound absorbing material of the present invention contains at least one of a reducing agent and an alkaline agent and fluorinated graphite in the heat-resistant binder that is applied and cured on the porous metal body,
It has excellent high-temperature oxidation resistance and corrosion resistance, and has good sound absorption performance, and when used as a sound absorption material in an exhaust silencer for an internal combustion engine, it can effectively prevent the adhesion of tar and soot, and it also has noise reduction performance that can occur due to clogging9. It is possible to prevent the deterioration of the noise and maintain the initial good silencing performance. Therefore, since it has high performance and long life, it can be widely used in exhaust silencing devices for internal combustion engines such as automobiles.

[Brief explanation of the drawing]

FIG. 1 is an enlarged view showing an example of the configuration of a metal porous body and the sound absorbing material of the present invention, and FIGS. 2 to 4 are characteristic diagrams showing the performance of the sound absorbing material of the present invention. In the figure, the same reference numerals indicate the same or corresponding parts, (1) is the particle of the metal porous body, (2) is the reducing agent particle, (3) is the binder, (4) is the porous coating, and (5) is the It is fused graphite. Agent Makoto Kuzuno (1 other person) Fig. 1 Fig. 2 Zhang skin (ν Fig. 3 11 [1 h CHz)

Claims (1)

[Claims] (1) The heat-resistant binder, which is made of a porous metal body and is coated and cured on the porous metal body, contains at least one of a reducing agent and an alkali agent, and graphite fluoride. A sound-absorbing material featuring