JPS6312814A - Exhaust pipe for heat insulation and noise insulation - Google Patents

Abstract

PURPOSE:To improve heat insulation and noise insulation performance of an exhaust pipe by inserting sealant inflated by heat of exhaust gas into a gap between an inner tube in which exhaust passes through and an outer tube or a mesh sleeve loosely fitted along the circumference of the inner tube. CONSTITUTION:In an exhaust pipe for discharging exhaust gas, connected to an engine for automobiles, an inner tube in which exhaust gas passes through and an outer tube or a mesh sleeve loosely fitted along the circumference of the inner tube are provided. And sealant inflated by heat of exhaust gas is inserted into a gap between the inner tube and the outer tube or the mesh sleeve. The main components of the sealant are 60-85wt% of heat-resisting inorganic fiber and 10-30wt% of material inflated by heating, and the sealant is formed in a sheet-like shape by adding a proper quantity of organic or inorganic bonding agent to said main components and applying a paper making process thereto. As the material inflated by heating, inflation type black lad having a layer crystal structure or the like is used.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an exhaust pipe that discharges exhaust gas from an engine of an automobile, etc., and more specifically relates to an exhaust pipe that has heat insulation and sound insulation performance for exhaust gas. be.

[Conventional technology]

Conventionally, pipes made of heat-resistant metals such as stainless steel have been used for exhaust pipes that discharge exhaust gas from automobile engines, etc., but in recent years, as engine performance has improved, exhaust gas temperatures have risen and insulation has become necessary. There are also strong demands for noise reduction, and quieter cars are required. As a measure for the heat insulation, a hollow double-tube structure or a double-tube structure using glass fiber or ceramic fiber as an intermediate material has been proposed. In addition, a protector made of glass fiber, ceramic fiber, or a blend of both mats is attached around the exhaust pipe to insulate it.6 Also, as measures against noise, hollow double pipes, stainless steel mesh wire moldings, and glass The sound insulation effect is achieved by double pipes that use fibers and ceramic fibers as intermediate materials.

[Problem that the invention seeks to solve]

Among the conventional techniques mentioned above, hollow double pipes have little heat insulation effect and exhaust gas leaks from the flange connecting the double pipes. Double pipes in which glass fiber or ceramic fiber is used as the intermediate material of the double pipe have the disadvantage that the intermediate material is scattered due to engine vibration and exhaust gas pressure, and its effectiveness gradually decreases. Furthermore, since various important parts such as a flexible tube, a catalytic converter, and a muffler are connected to the exhaust pipe, a connecting part is required to connect the parts. Moreover, since it is a double tube, there is a temperature difference between the inner tube and the outer tube, which causes a difference in thermal expansion between the tubes, so the inner tube and outer tube cannot be integrated by methods such as welding, and there is always a joint part. must be free. Currently, molded stainless steel wire is commonly used as a sealant for joints. However, since molded products made by compressing stainless steel wire are metal, they not only have no insulation effect, but also gradually lose their elasticity due to repeated heating and cooling, and eventually become loose, making it impossible to use them as a sealing material. There were drawbacks.

On the other hand, although double-pipe pipes are effective as a noise countermeasure, single-type protectors intended for heat insulation not only have a complicated shape, but also pose a new problem: wind noise. The present invention aims to solve these conventional problems.

[Means and operations for solving the problems] In order to solve the above problems, as a result of repeated experiments using various model exhaust pipes, the exhaust pipe of the present invention was conceived and the invention was completed. That is, an exhaust pipe for discharging exhaust gas connected to an engine of an automobile or the like is composed of an inner pipe through which the exhaust gas passes and an outer pipe or a mensch sleeve loosely fitted around the outer periphery of the inner pipe. This is an exhaust pipe in which a sealing material that expands at the temperature of exhaust gas is inserted into the gap between the inner pipe and the outer pipe or mesh sleeve.

The present invention will be explained in detail below.

By the way, exhaust gas discharged from engines of automobiles and the like tends to be hotter and moreover, its discharge speed also tends to be faster. Therefore, an effective exhaust pipe for discharging exhaust gas is a triple pipe, which is composed of an inner pipe and an outer pipe or a mesh sleeve, with a heat insulating material inserted in the middle. The sealing material that expands at the temperature of the exhaust gas used here includes 60 to 85% by weight of heat-resistant inorganic fibers such as ceramic fibers and silica fibers, and materials that expand when heated, such as expandable graphite, vermiculite, and expandable mica. The main component is 10 to 30% by weight of an expanding material,
A suitable amount of an organic or inorganic binder is added to this sheet-like material and formed by a conventional paper-forming method.By inserting this sheet-like material, the above-mentioned problems can be solved. The heat-resistant inorganic fiber used here is selected to have an amount of 60 to 85% by weight, but if it is less than 60% by weight, the bulk density becomes high, and if it is more than 85% by weight, the expansion performance decreases. Among these, 65 to 75% by weight is preferably selected. The bulk density is selected in the range of 0.3 to 0.6 g/cII, among which 0
．． 35 to 0.50 g/cd is suitably selected. The reason for this limitation is that at 0.3 g/cJ or less, the inorganic fibers constituting the sealing material move easily due to vibration, become easily broken, and are scattered by exhaust gas. If it exceeds 0.6 g/cd, the thermal conductivity becomes high, which not only deteriorates the heat insulation effect but also causes high compressive stress when inserting into the gap, making the work difficult. In addition, the free expansion coefficient at 700°C is 50 to 15
A range of 0% is used, and a range of 80 to 120% is preferably selected.

The reason for this limitation is that if it is less than 50%, it is not effective enough to alleviate the gap caused by shrinkage of the sealing material due to heating.
If it exceeds 150%, the expansion pressure of the sealing material itself becomes high, and there is a risk of deforming the outer tube such as a mensch sleeve.

By the way, conventional sheet-like materials that expand when heated are widely known, and can absorb the difference in thermal expansion between ceramics and metals, provide cushioning properties against the brittleness of ceramics and metals, and absorb shocks such as vibrations. It is used for the purpose of alleviating the

Therefore, the expansion coefficient of these thermally expandable sheets is at least 200% or more at 700°C to absorb the difference in thermal expansion between ceramics with a small coefficient of thermal expansion and metals with a large coefficient of thermal expansion. was necessary. For this purpose, the bulk density was also required to be 0.6 g/c+J or more.The sealing material that expands at the temperature of exhaust gas in the present invention has the purpose of absorbing the difference in thermal expansion between metals, so the sealing material itself It is sufficient to absorb the contraction of the air and keep it in place without moving due to force such as vibration, and not only does it not require a high expansion rate, but also because its main purpose is heat insulation and exhaust gas sound insulation. Sheet materials that expand when heated cannot be used.

The present invention will be explained below with reference to Examples.

〔Example〕

65 parts by weight of ceramic fiber (trade name Ibiwool), 25 parts by weight of unexpanded vermiculite from South Africa, 5 parts by weight of starch, and 3 parts of bentonite are sequentially put into a large plastic container along with 211 parts of water, and a propeller is prepared. Thoroughly mixed using a mechanical stirrer. Next, 2 parts of a polyacrylamide-based flocculant was gradually added to form a floc, and a 3-inch sheet was formed by a conventional paper-forming method, and after drying, it was 0.35 g/a
A sheet with a bulk density of
An exhaust pipe with an outer diameter of 55-amφ was prepared by wrapping it around the outer circumference of a stainless steel pipe with a diameter of φ and fitting an outer tube made of iron. Hot air heated to 800° C. was continuously sent into the pipe, and after approximately one hour, the pipe was cooled to obtain a test specimen. This test specimen had a vibration acceleration of 7G, an amplitude of 1.5, and a frequency of 2930C.
Vibration was applied for 1 hour using a model testing machine under the conditions of /S. As a result, there was no scattering of the sealing material in this exhaust pipe, and no changes were observed. In addition, 50t
As a result of continuously blowing air at a rate of a/sec and observing the scattering situation, no scattering was observed although fuzzing was observed on the surface.

Moreover, when the temperature of the outer tube was measured while the hot air heated to 800°C was continuously sent, it was 385°C.

The temperature was 515°C when a hollow double tube without a sealing material was used as a blank. In addition, when we measured the amount of sound attenuation using a Rion sound level meter, we found that there was an attenuation of 28 dB compared to when there was no sealant.

70 parts by weight of silica-alumina ceramic fiber (product name: Ibiwool), 20 parts by weight of expandable graphite processed from natural graphite, 8 parts by weight of acrylonitrile butadiene latex
Parts by weight were sequentially charged into a large plastic container along with 201 parts of water, and thoroughly mixed using a propeller type stirrer. Next, 2 parts by weight of sulfuric acid band was added and coagulated into flocs.
A sheet of approximately 3.0 mm was made using a conventional paper making method, and after drying, a sheet having a bulk density of 0.4 g/- was obtained. The physical properties of this sheet were as shown in Table 1. An exhaust pipe was created in the same manner as in Example 1. Furthermore, when the same test as in Example I was conducted, neither deformation nor scattering was observed. Further, the temperature of the outer tube was 420°C.

(Comparative Example 1) Silica-alumina ceramic fiber (trade name: Ibiwool) blanket (bulk density 0.13g/aJ)
), an exhaust pipe was created in the same manner as in Example 1. This exhaust pipe was tested using the same test method as in Example 1, and although there was no change in vibration resistance, it was observed that the air caused scattering from the surface up to 5 dragons. Also, the temperature of the outer tube is 410
It was ℃. The physical properties of this blanket were as shown in Table 1.

(Comparative Example 2) 25 parts by weight of ceramic fiber (silica fiber), 60 parts by weight of unexpanded mica, 12 parts by weight of montmorillonite, and 2 parts of acrylamide resin were sequentially charged into a large polyethylene container along with 201 parts of water, and the mixture was placed in a large plastic container using a stirrer attached to the second propeller. Mix thoroughly. Next, 1 part by weight of sulfuric acid band was added, the mixture was coagulated into a floc, and a sheet having a size of approximately 3.0 mm was formed by a conventional paper forming method, and after drying, a sheet having a bulk density of 0.65 g/cd was obtained. The physical properties of this sheet were as shown in Table 1. An exhaust pipe was made using stainless steel for the inner pipe and a mensch sleeve made of stainless steel wire for the outer pipe, and vibration and wind speed tests similar to those in Example 1 were conducted.
In the process of making the test specimen at 00°C, the sheet was wedged into the mesh sleeve, and deformation of the mesh sleeve was observed. Furthermore, during the vibration test, some pieces were found to have fallen off. Furthermore, in the wind speed test, about 10 Iu fell off. Further, the temperature of the outer tube was 495°C.

Table 1 Table of physical properties of sealing material [Effects of the invention] As described above, the exhaust pipes obtained in Examples 1 and 2 of the present invention have a free expansion rate at 700°C compared to Comparative Examples 1 and 2. It was found that the exhaust pipe was controlled and had better vibration resistance and wind speed resistance than Comparative Example 1, which is an example of a conventional exhaust pipe, and that stable performance over a long period of time could be obtained even in actual equipment. In addition, in Comparative Example 2, which has high expansion performance, it was found that the expansion of the sheet caused deformation of the mesh sleeve and deteriorated vibration resistance, and the amount of sound attenuation was also lower than that of a hollow double pipe. It turned out to be effective.

Claims (1)

[Claims] 1) In an exhaust pipe for discharging exhaust gas connected to an engine of an automobile, etc., an inner pipe through which the exhaust gas passes, and an outer pipe or a mesh sleeve loosely fitted around the outer periphery of the inner pipe. An exhaust pipe for heat and sound insulation, characterized in that a sealing material that expands at the temperature of exhaust gas is inserted into the gap between the inner pipe and the outer pipe or mesh sleeve. 2) The expandable sealing material is mainly composed of 60 to 85% by weight of heat-resistant inorganic fibers and 10 to 30% by weight of a material that expands upon heating, and an appropriate amount of an organic or inorganic binder is added thereto to form a sheet using a papermaking method. 2. The heat-insulating/sound-insulating exhaust pipe according to claim 1, wherein the exhaust pipe is a sealing material molded into. 3) The heat-resistant inorganic fiber is selected from at least one of silica-alumina, siliceous amorphous fiber, alumina, mullite, and zirconia crystal fiber. Exhaust pipe for heat insulation and sound insulation as described in section. 4) Claims 1 to 4, wherein the material that expands upon heating is selected from one or more of expandable graphite, vermiculite, and expandable mica each having a layered crystal structure. The heat-insulating/sound-insulating exhaust pipe described in item 3. 5) The expanding sealing material has a bulk density of 0.3 to 0.6.
g/cm^3, and the free expansion coefficient at 700℃ is 5.
The heat-insulating/sound-insulating exhaust pipe according to any one of claims 1 to 4, characterized in that the exhaust pipe has a characteristic of 0 to 150%.