Abstract:
A structure and construction method of sintered porous frame. The structure of present invention can be applied as a soot filter and catalyst converter to treat exhaust gas from internal combustion engines by coating a layer of catalyst material such as platinum. The inventor use the combustible material foam as a porous substrate to coat a metallic layer. Further the procedure is to apply a sintering process to form a sintered porous frame. Thus the user can use the sintered porous frame to proceed catalyst coating or photo-catalyst coating.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of The Invention  
         [0002]     Present invention relates to a structure and construction method of sintered porous frame. The structure of present invention can be applied as a soot filter and catalyst converter to treat exhaust gas from internal combustion engines by coating a layer of catalyst material such as platinum. Also the sintered porous frame can be applied as an air-cleaning filter to be applied in the air venting system by coating a layer of anti-microbe material such as photo catalyst.  
         [0003]     2. Description of the Related  
         [0004]     A metallic honeycomb body has passages through which exhaust gas can pass from one end to the other. The honeycomb is obtained from a flat metal sheet and corrugated metal sheet, and which are welded together. The combined sheet is rolled and coated with desired catalysts, and then wrapped with a metal case to form a catalyst converter. Detailed production process is described in U.S. Pat. No. 5,306,890.  
         [0005]     The above prior art can only provide the primary structure with the ability to establish a large surface area to enhance the effect of catalyst in the exhausting pipe of a combustion engine. But the skill is constrained on the welding process being high cost for working. Also the surface area is constrained on the skill level of metal working.  
         [0006]     Some methods to improve the structure of the above skill include, U.S. Pat. No. 5,481,084 describes a method to treat metal sheet surface with electric arc to increase surface area. U.S. Pat. No. 5,567,395 describes a method to provide a turbulence generating section within the honeycomb to improve efficiency. U.S. Pat. No. 6,036,926 &amp; WO9715393 describes a method to use bent-over re-enforced metal sheet to produce a honeycomb with reinforced structure and to improve efficiency. The contact surfaces from above are still within a limited improvement. Because the surface-extra structure usually suffers from insufficient adhesion to the metal surface and has adhesion durability problem after several thermal shock cycle.  
         [0007]     Owing to its coarse passages, the honeycomb can not be used to filter soot (particles) from diesel engine exhaust. An extra, finer filter (or called “soot trap”) is usually required to be installed either before the honeycomb converter (U.S. Pat. No. 4,719,571), or parallel to the converter and control exhaust flow pass through selected chamber mechanically, to capture the soot (U.S. Pat. No. 5,264,186). It can prevent the poisoning of catalyst by such soot, and reduce soot emission. However, it is a complicate process and need to install an extra filter unit, which increase cost and weight for a vehicle.  
         [0008]     Converter will be heated up while engine starts, and quenched while the engine stops. The repeated cycle usually causes thermal shock to the converter structure. There are methods to improve its strength by special welding (U.S. Pat. No. 5,316,997), or to provide a buffer zone to accommodate metal thermal- expansion mechanically (U.S. Pat. No. 5,403,558, U.S. Pat. No. 6,467,169, U.S. Pat. No. 6,458,329, U.S. Pat. No. 5,846,495). However, such buffer section will require extra space for thermal expansion need, which either reduce usable surface area, or increase total volume of the converter. If the diameter of the converter is increased then there will be a problem to have exhaust gas passes through evenly through all the passages. If the length of the converter is increased, then, there will be an increase of back-pressure to the engine.  
         [0009]     80% of current air pollutant is from the emission while engine &amp; converter has not yet reached its working temperature. Therefore, there are methods to provide a solution, e.g. zeolite or molecular sieve absorbent chamber (U.S. Pat. No. 5,051,244, U.S. Pat. No. 5,108,716) or a separate preheating device (U.S. Pat. No. 5,296,198, U.S. Pat. No. 5,465,573, etc.) are described. However, such device either increase back pressure or reduce fuel efficiency.  
         [0010]     Ceramic is strong in compression, and can be coated with catalyst and wrapped with a metal case for catalyst converter application. A detail description of the process can be found in U.S. Pat. No. 4,556,543. Ceramic honeycomb with 400 channels per square inch can be produced from either extrusion or extrusion molded (U.S. Pat. No. 6,680,101).  
         [0011]     Ceramic is strong with compression, but however, has only poor thermal shock resistance. It can be cracked with limit cycle of heating/quenching, which leads to performance loss. There are methods to reinforce the thermal shock resistance by applying thicker walls to certain channels (US 2004/0101654), or trying to improve the thermal shock problem with specified L/D of the converter (US) or specified shape (semi-oval) of the converter (U.S. Pat. No. 5,304,351). But such methods can not satisfy the need for a light-weight, effective catalyst carrier.  
         [0012]     Due to the heat capacity and low thermal conductivity of ceramic, the ceramic honeycomb takes longer time to reach its operational temperature after engine starts. As already describe in metal honeycomb, such low performance has create problem and need extra filter or another pre-heater to treat the exhaust gas while engine/converter are still below its operation temperature. It increases cost and weight, hence reduce fuel efficiency for a vehicle.  
         [0013]     A ceramic foam structure as described in U.S. Pat. No. 4,451,441 includes the use of a fine cell (15 to 50 ppi, pores per inch) ceramic foam as filter, and a coarse cell (2 to 20 ppi) as catalyst carrier for catalyst converter system. It is claimed to provide a light weight, high surface area, and much less back-pressure solution for catalyst application. The ceramic foam is produced by coating a reticulated polyurethane foam with ceramic slurry and then sintered it in about 750° C. to form a ceramic foam. Polyurethane polymer is in fact, burn-out in the sintering. However, due to the weak mechanical strength of such tiny ceramic foam strut, it can not satisfy the need to pass thermal shock and provide sufficient strength, during service life.  
         [0014]     U.S. Pat. No. 5,422,085 describes a method to reduce nitrogen oxide (NOx) emissions in diesel engine exhaust gases. The NOx laden stream is treated with a silver catalyst supported on a nickel coated foam, which is made by chemical coating of nickel on a polyurethane foam substrate. Owing to the high activity of silver with sulfide in an internal combustion engine exhaust atmosphere, and the insufficient corrosion- and oxidation resistance of nickel in oxidizing atmosphere, this device has not been actually produced commercially.  
         [0015]     The ceramic structure is still with a new requirement on manufacturing and transportation. The manufacturing process for ceramic honeycomb requires precise tooling for molding. Also the tooling has its life cycle and maintenance duty. Also the ceramic material needs god protection on transportation to prevention impact damage. Thus the production cost is high and new structure for catalyst converter is still required.  
         [0016]     Present invention provides a convenience structure and construction method on a low production cost to meet the many requirements. Present invention inherits traditional advantages can provide property on large area for catalyst efficiency, efficient to filter diesel soot (particle), thermal shock resistance and short warm-up time.  
       SUMMARY OF THE INVENTION  
       [0017]     The major purpose of present invention is to provide a structure and construction method on sintered porous frame to handle massive production in low cost and high quality which can be used on gas exhausting of a vehicle or the air venting system for air cleaning.  
         [0018]     To achieve the above purpose, the core structure of present invention is still similar to the traditional porous structure of the prior art. The inventor use the combustible material foam as a porous substrate to coat a metallic layer. Further the procedure is to apply a sintering process to form a sintered porous frame. Thus the user can use the sintered porous frame to proceed catalyst coating or photo-catalyst coating.  
         [0019]     The structure of the present invention comprises a porous structure with metallic-bond or covalent bond inside the structure to connect the whole-body, and the material of the porous structure have the bearing ability for a sintering process with certain temperature range; wherein the material of porous structure is at least half part formed by metallic material.  
         [0020]     The method of the present invention comprises the following steps: to get the porous substrate by a kind of combustible material; to proceed the coating process by a metallic material being able to bearing the combustion temperature of the combustible material; to put the coated porous substrate into sintering process to remove the combustible substrate and to generate the porous structure by metallic material through metallic-bond or covalent bond inside the structure to connect the whole-body to produce the sintered porous frame.  
         [0021]     Drawings and the tables only form a part of present specification without any restrictions to present invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]     The various objects and advantages of the present invention will be more readily understood from the following detailed description when read in conjunction with the appended drawing, in which:  
         [0023]      FIG. 1  is a flow-chart diagram of current manufacturing method of sintered porous frame; and  
         [0024]      FIG. 2  is a shape of the cave inside the sintered porous frame. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0025]     What is invented is a method to produce a metallic foam with high tensile strength, high surface area with low back-pressure, low thermal expansion coefficient, high thermal shock resistance, low weight, and design flexibility to provide a proactively heating metallic foam to reduce complexity and improve fuel economic to satisfy the need in catalyst converter application, and at the same time, increase surface area to provide a more effective exhaust gas treatment while reducing converter weight.  
         [0026]     Polyurethane foam materials (or similar polymer structure) are first treated by electrochemical deposition. For ensuring the electro-conductivity, copper sulfide electroconductive (94 wt % of copper sulfide and 6 wt % of epoxy binder) layer is precoated on the surface of the polyurethane foam. There are other electroconductive layers, e.g. graphite, carbon black, etc., can also be used. There are other methods to provide an electroconductive layer on the polyurethane substrate, like PVD, CVD, chemical plating, etc. The resulted polyurethane foam material is then plated electrically with any desired metal, or a special metal composition. The later can be achieved by adjusting electrode and plating bath composition. After the electrical plating with a certain thickness (usually from 60 to 150 microns) of metal on top of the polyurethane foam and electroconductive layer, the resulted foam is then sintered in a hydrogen-ammonia atmosphere at 350° C. to 500° C. for 30˜45 minutes in a furnace, and then the temperature is increased to 650° C. to 900° C. gradually in about  30  minutes. The foam is reducible in the furnace of 650° C. to 900° C. with hydrogen-ammonia atmosphere for another 60˜90 minutes. The sintering temperature need to be controlled carefully in order not to melt the metal composition, but need to allow the metal compositions to be reduced. Polyurethane polymer within the foam material is then burn-out, leaving a hollow triangular cave (maybe other kind of cave shape), covered by the metal. Please also refer to the  FIG. 2  The cave can reduce the thermal expansion of the whole structure.  
         [0027]     The resulted metallic foam can then be coated with catalyst composition from previous coating technologies for catalyst converter applications. The resulted foam is an ideal carrier body not only can be used as a carrier for such catalysts, but a foam with finer cell structure (90 to 120 ppi) also can be used as a diesel soot trap (or called “filter). The cell structure is only limited by the original polyurethane foam morphology. Therefore, a cell size from 5 to 150 ppi can be produced.  
         [0028]     The hollow cave under the metal strut can provide the metallic foam with excellent strength and thermal shock resistance. Owing to the shape of the metal walls, the linear thermal expansion of such foam is very low, which provides good dimensional and thermal shock stability. The hollow cave also provides a maximum surface area with less material weight. The reduced weight requires less heat to warm-up the foam, hence a converter made from the foam can be heated-up to operational temperature faster.  
         [0029]     Another benefit from this invention is the metallic foam can be coated with a nickel-chromium alloy on the out surface. It can then be heated with adequate electric current from an automobile electricity generator or batterer. It provide a proactively heating carrier, which can be used to replaced any carrier material described in prior art for both catalyst converter or filter/trap. It simplify current requirement to have dual chambers, and reduce manufacturing cost with fuel efficiency improvement.  
         [0030]      FIG. 1  is the flow-chart diagram of current manufacturing method of sintered porous frame. The sintered porous frame can be widely used in the fluid transferring machine for some treatment of chemical reaction. The manufacturing method comprises: to get the porous substrate by a kind of combustible material (such as the polymer foam); to proceed the coating process by a metallic material being able to bearing the combustion temperature of the combustible material; to put the coated porous substrate into sintering process to remove the combustible substrate and to generate the porous structure by metallic material through metallic-bond or covalent bond inside the structure to connect the whole-body to produce the sintered porous frame. Wherein the metallic bond is easy to be recognized as common bond in the metal or alloy and the covalent bond is for the little non-metal material inside the metal base generated form sintering or for property improvement of metal base.  
         [0031]     The steps of the present invention also contains the below variations: Wherein the coating process can contains two sub-processes for ease to attach the metal material on the combustible material, the pre-coating process and the enhanced-coating process, the pre-coating process for binding a layer of metal-plating-allowable material on the porous substrate, the enhanced-coating process for plating a thick layer of metallic material to construct the main porous structure of the sintered porous frame. Wherein the pre-coating process can be to sputter metal or metal-plating-allowable material on the porous substrate. Wherein the pre-coating process can be to spread the conductive glue on the porous substrate. Wherein the spreading method for conductive glue is by spraying. Wherein the pre-coating process can be to put the porous substrate into the specified chemical solution, the specified chemical solution being contained the metal-plating-allowable material. Wherein the metallic material comprise nickel or chromium to have the ability to heat the porous structure with electrical power for industrial application. (such as pre heating in the exhausting pipe of the vehicle) Wherein the metallic material comprises copper, aluminum or their alloy that the metal can have the flexibility for installation and heat durability in sintering process. Wherein the sintering process can contain the process to generate the metal deoxidation in the gas contained ammonia.  
         [0032]     The structure of the sintered porous frame comprises: a porous structure with metallic-bond or covalent bond inside the structure to connect the whole-body, and the material of the porous structure have the bearing ability for a sintering process with certain temperature range; wherein the material of porous structure is at least 90 percent to whole body formed by metallic material.  
         [0033]     The variations of the structure of the sintered porous frame are described in the bellow: Wherein the porous structure has little holes inside and the wall of little hole have the residual carbon compound generated by the heating process of sintering. Wherein the porous structure can be bended allowable to form a special shape to fit the predetermined space in the flowing-fluid device. (such as ventilation pipe or gas exhausting pipe) Wherein the certain temperature range can be from 150-900 Centigrade. Wherein the porous structure can be coated with a catalyst material or anti-microbe material. Wherein the metallic material can comprise copper, aluminum or their alloy. Wherein the metallic material can comprise nickel or chromium to have the ability to heat the porous structure with electrical power for industrial application.  
         [0034]     The present invention can provide many benefits then the prior art. Such as the no-welding point structure, high catalyst efficiency from non uniform porous structure, efficient to filter diesel soot (particle), thermal shock resistance and short warm-up time. Also the cost is reasonable for mass production.  
         [0035]     In addition the structure of the present invention can be applied as a base frame to coat the material of photo catalyst because of the property of the sintered porous frame having the above described many benefits. Nearly 40 years after the publication of the photo-catalyst theory on 1972 Nature magazine, TiO2 has only been studying in recently two decades under the environmental protection against pollution. Previously, the photo-TiO2-catalyst only works under ultraviolet, nowadays, practical TiO2 products work under visible light come into the market in succession.  
         [0036]     Also the application area of the sintered porous frame can be extended to the chemical engineering industry for example to coat a layer of catalyst for function of De-NOx or De-SOx.  
         [0037]     Above is the optimal implementation of present invention, it will be apparent that various changes and modifications can be made without departing from the scope of the invention as defined in the claims.