EP1951637A2 - Systeme d'extrusion de substrat poreux - Google Patents

Systeme d'extrusion de substrat poreux

Info

Publication number
EP1951637A2
EP1951637A2 EP06788219A EP06788219A EP1951637A2 EP 1951637 A2 EP1951637 A2 EP 1951637A2 EP 06788219 A EP06788219 A EP 06788219A EP 06788219 A EP06788219 A EP 06788219A EP 1951637 A2 EP1951637 A2 EP 1951637A2
Authority
EP
European Patent Office
Prior art keywords
fibers
substrate
ceramic
extrudable mixture
fiber
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP06788219A
Other languages
German (de)
English (en)
Other versions
EP1951637A4 (fr
Inventor
Bilal Zuberi
Robert G. Lachenauer
Sunilkumar C. Pillai
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
GEO2 Technologies Inc
Original Assignee
GEO2 Technologies Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US11/322,777 external-priority patent/US20070152364A1/en
Application filed by GEO2 Technologies Inc filed Critical GEO2 Technologies Inc
Publication of EP1951637A2 publication Critical patent/EP1951637A2/fr
Publication of EP1951637A4 publication Critical patent/EP1951637A4/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C67/00—Shaping techniques not covered by groups B29C39/00 - B29C65/00, B29C70/00 or B29C73/00
    • B29C67/20—Shaping techniques not covered by groups B29C39/00 - B29C65/00, B29C70/00 or B29C73/00 for porous or cellular articles, e.g. of foam plastics, coarse-pored
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/71—Ceramic products containing macroscopic reinforcing agents
    • C04B35/78—Ceramic products containing macroscopic reinforcing agents containing non-metallic materials
    • C04B35/80—Fibres, filaments, whiskers, platelets, or the like
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D39/00—Filtering material for liquid or gaseous fluids
    • B01D39/14—Other self-supporting filtering material ; Other filtering material
    • B01D39/20—Other self-supporting filtering material ; Other filtering material of inorganic material, e.g. asbestos paper, metallic filtering material of non-woven wires
    • B01D39/2068—Other inorganic materials, e.g. ceramics
    • B01D39/2082—Other inorganic materials, e.g. ceramics the material being filamentary or fibrous
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/0009—Use of binding agents; Moulding; Pressing; Powdering; Granulating; Addition of materials ameliorating the mechanical properties of the product catalyst
    • B01J37/0018—Addition of a binding agent or of material, later completely removed among others as result of heat treatment, leaching or washing,(e.g. forming of pores; protective layer, desintegrating by heat)
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B28—WORKING CEMENT, CLAY, OR STONE
    • B28B—SHAPING CLAY OR OTHER CERAMIC COMPOSITIONS; SHAPING SLAG; SHAPING MIXTURES CONTAINING CEMENTITIOUS MATERIAL, e.g. PLASTER
    • B28B1/00—Producing shaped prefabricated articles from the material
    • B28B1/52—Producing shaped prefabricated articles from the material specially adapted for producing articles from mixtures containing fibres, e.g. asbestos cement
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B28—WORKING CEMENT, CLAY, OR STONE
    • B28B—SHAPING CLAY OR OTHER CERAMIC COMPOSITIONS; SHAPING SLAG; SHAPING MIXTURES CONTAINING CEMENTITIOUS MATERIAL, e.g. PLASTER
    • B28B3/00—Producing shaped articles from the material by using presses; Presses specially adapted therefor
    • B28B3/20—Producing shaped articles from the material by using presses; Presses specially adapted therefor wherein the material is extruded
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B28—WORKING CEMENT, CLAY, OR STONE
    • B28B—SHAPING CLAY OR OTHER CERAMIC COMPOSITIONS; SHAPING SLAG; SHAPING MIXTURES CONTAINING CEMENTITIOUS MATERIAL, e.g. PLASTER
    • B28B3/00—Producing shaped articles from the material by using presses; Presses specially adapted therefor
    • B28B3/20—Producing shaped articles from the material by using presses; Presses specially adapted therefor wherein the material is extruded
    • B28B3/26—Extrusion dies
    • B28B3/2636—Extrusion dies using means for co-extruding different materials
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B28—WORKING CEMENT, CLAY, OR STONE
    • B28C—PREPARING CLAY; PRODUCING MIXTURES CONTAINING CLAY OR CEMENTITIOUS MATERIAL, e.g. PLASTER
    • B28C5/00—Apparatus or methods for producing mixtures of cement with other substances, e.g. slurries, mortars, porous or fibrous compositions
    • B28C5/40—Mixing specially adapted for preparing mixtures containing fibres
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B28—WORKING CEMENT, CLAY, OR STONE
    • B28C—PREPARING CLAY; PRODUCING MIXTURES CONTAINING CLAY OR CEMENTITIOUS MATERIAL, e.g. PLASTER
    • B28C5/00—Apparatus or methods for producing mixtures of cement with other substances, e.g. slurries, mortars, porous or fibrous compositions
    • B28C5/40—Mixing specially adapted for preparing mixtures containing fibres
    • B28C5/404—Pre-treatment of fibres
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
    • B29C48/03—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor characterised by the shape of the extruded material at extrusion
    • B29C48/05—Filamentary, e.g. strands
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
    • B29C48/03—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor characterised by the shape of the extruded material at extrusion
    • B29C48/09—Articles with cross-sections having partially or fully enclosed cavities, e.g. pipes or channels
    • B29C48/11—Articles with cross-sections having partially or fully enclosed cavities, e.g. pipes or channels comprising two or more partially or fully enclosed cavities, e.g. honeycomb-shaped
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B18/00—Layered products essentially comprising ceramics, e.g. refractory products
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
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    • C04B14/00—Use of inorganic materials as fillers, e.g. pigments, for mortars, concrete or artificial stone; Treatment of inorganic materials specially adapted to enhance their filling properties in mortars, concrete or artificial stone
    • C04B14/02—Granular materials, e.g. microballoons
    • C04B14/04—Silica-rich materials; Silicates
    • C04B14/10—Clay
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B33/00—Clay-wares
    • C04B33/36—Reinforced clay-wares
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
    • C04B35/16—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on silicates other than clay
    • C04B35/18—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on silicates other than clay rich in aluminium oxide
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/626—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B
    • C04B35/62605—Treating the starting powders individually or as mixtures
    • C04B35/62625—Wet mixtures
    • C04B35/6263—Wet mixtures characterised by their solids loadings, i.e. the percentage of solids
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/626—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B
    • C04B35/63—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B using additives specially adapted for forming the products, e.g.. binder binders
    • C04B35/6303—Inorganic additives
    • C04B35/6316—Binders based on silicon compounds
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B38/00—Porous mortars, concrete, artificial stone or ceramic ware; Preparation thereof
    • C04B38/0006—Honeycomb structures
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B38/00—Porous mortars, concrete, artificial stone or ceramic ware; Preparation thereof
    • C04B38/007—Porous mortars, concrete, artificial stone or ceramic ware; Preparation thereof characterised by the pore distribution, e.g. inhomogeneous distribution of pores
    • C04B38/0074—Porous mortars, concrete, artificial stone or ceramic ware; Preparation thereof characterised by the pore distribution, e.g. inhomogeneous distribution of pores expressed as porosity percentage
    • E—FIXED CONSTRUCTIONS
    • E04—BUILDING
    • E04C—STRUCTURAL ELEMENTS; BUILDING MATERIALS
    • E04C5/00—Reinforcing elements, e.g. for concrete; Auxiliary elements therefor
    • E04C5/07—Reinforcing elements of material other than metal, e.g. of glass, of plastics, or not exclusively made of metal
    • E04C5/073—Discrete reinforcing elements, e.g. fibres
    • E04C5/076—Specially adapted packagings therefor, e.g. for dosing
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/02—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust
    • F01N3/021—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters
    • F01N3/022—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters characterised by specially adapted filtering structure, e.g. honeycomb, mesh or fibrous
    • F01N3/0222—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters characterised by specially adapted filtering structure, e.g. honeycomb, mesh or fibrous the structure being monolithic, e.g. honeycombs
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B28—WORKING CEMENT, CLAY, OR STONE
    • B28B—SHAPING CLAY OR OTHER CERAMIC COMPOSITIONS; SHAPING SLAG; SHAPING MIXTURES CONTAINING CEMENTITIOUS MATERIAL, e.g. PLASTER
    • B28B3/00—Producing shaped articles from the material by using presses; Presses specially adapted therefor
    • B28B3/20—Producing shaped articles from the material by using presses; Presses specially adapted therefor wherein the material is extruded
    • B28B2003/203—Producing shaped articles from the material by using presses; Presses specially adapted therefor wherein the material is extruded for multi-channelled structures, e.g. honeycomb structures
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29L—INDEXING SCHEME ASSOCIATED WITH SUBCLASS B29C, RELATING TO PARTICULAR ARTICLES
    • B29L2031/00—Other particular articles
    • B29L2031/60—Multitubular or multicompartmented articles, e.g. honeycomb
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
    • C04B2111/00474—Uses not provided for elsewhere in C04B2111/00
    • C04B2111/00793—Uses not provided for elsewhere in C04B2111/00 as filters or diaphragms
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
    • C04B2235/30—Constituents and secondary phases not being of a fibrous nature
    • C04B2235/34—Non-metal oxides, non-metal mixed oxides, or salts thereof that form the non-metal oxides upon heating, e.g. carbonates, nitrates, (oxy)hydroxides, chlorides
    • C04B2235/349—Clays, e.g. bentonites, smectites such as montmorillonite, vermiculites or kaolines, e.g. illite, talc or sepiolite
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
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    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
    • C04B2235/50—Constituents or additives of the starting mixture chosen for their shape or used because of their shape or their physical appearance
    • C04B2235/52—Constituents or additives characterised by their shapes
    • C04B2235/5208—Fibers
    • C04B2235/5216—Inorganic
    • C04B2235/522—Oxidic
    • C04B2235/5228—Silica and alumina, including aluminosilicates, e.g. mullite
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    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
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    • C04B2235/52—Constituents or additives characterised by their shapes
    • C04B2235/5296—Constituents or additives characterised by their shapes with a defined aspect ratio, e.g. indicating sphericity
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    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/60—Aspects relating to the preparation, properties or mechanical treatment of green bodies or pre-forms
    • C04B2235/602—Making the green bodies or pre-forms by moulding
    • C04B2235/6021—Extrusion moulding
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
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    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/70—Aspects relating to sintered or melt-casted ceramic products
    • C04B2235/74—Physical characteristics
    • C04B2235/75—Products with a concentration gradient
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    • C04B2237/00—Aspects relating to ceramic laminates or to joining of ceramic articles with other articles by heating
    • C04B2237/30—Composition of layers of ceramic laminates or of ceramic or metallic articles to be joined by heating, e.g. Si substrates
    • C04B2237/32—Ceramic
    • C04B2237/34—Oxidic
    • C04B2237/341—Silica or silicates
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    • C04B2237/00—Aspects relating to ceramic laminates or to joining of ceramic articles with other articles by heating
    • C04B2237/30—Composition of layers of ceramic laminates or of ceramic or metallic articles to be joined by heating, e.g. Si substrates
    • C04B2237/32—Ceramic
    • C04B2237/38—Fiber or whisker reinforced
    • C—CHEMISTRY; METALLURGY
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    • C04B2237/00—Aspects relating to ceramic laminates or to joining of ceramic articles with other articles by heating
    • C04B2237/50—Processing aspects relating to ceramic laminates or to the joining of ceramic articles with other articles by heating
    • C04B2237/58—Forming a gradient in composition or in properties across the laminate or the joined articles
    • C04B2237/586—Forming a gradient in composition or in properties across the laminate or the joined articles by joining layers or articles of the same composition but having different densities

Definitions

  • the present invention relates generally to an extrusion processes for extruding a porous substrate, and in one particular implementation to an extrusion process for extruding a porous ceramic substrate.
  • substrates are used in filtering applications to filter particulate matter, separate different substances, or remove bacteria or germs from air. These substrates may be constructed to operate in air, exhaust gases or liquids, and may be manufactured to endure substantial environmental or chemical stresses.
  • catalytic materials are deposited on the substrate for facilitating chemical reactions. For example, a precious metal may be deposited on an appropriate substrate, and the substrate may then act to catalytically convert dangerous exhaust gases into less noxious gases.
  • these rigid substrates operate more effectively with a higher porosity.
  • Porosity is generally defined as the property of a solid material defining the percentage of the total volume of that material which is occupied by open space. For example, a substrate with 50% porosity has half the volume of the substrate occupied by open spaces. In this way, a substrate with a higher porosity has less mass per volume than a substrate with a lower porosity.
  • Some applications benefit from a lower mass substrate. For example, if a substrate is used to support a catalytic process, and the catalytic process operates at an elevated temperature, a substrate with a lower thermal mass will more quickly heat to its operational temperature. In this way, the time for the catalyst to be heated to its operational temperature, i.e., light off time, is reduced by using a more porous and less thermally massive substrate.
  • Permeability is also an important characteristic for substrates, particularly filtering and catalytic substrates. Permeability is related to porosity, in that permeability is a measure of how easily a fluid, such as a liquid or gas, may flow through the substrate. Most applications benefit from a highly permeable substrate. For example, an internal combustion engine operates more efficiently when the after- treatment filter provides lower back pressure to the engine. Low back pressure is created by using a more highly permeable substrate. Since permeability is more difficult to measure than porosity, porosity is often used as a substitute guide to the permeability of a substrate.
  • a Styrofoam drinking cup is formed of a highly porous foam material, but is not permeable to the flow of liquid. Therefore, in considering the importance of porosity and permeability, the pore structure of the substrate must also be examined.
  • the Styrofoam material has a closed pore network. This means that the foam contains many non connected and/ or closed-ended pores. In this way, there are many voids and open spaces within the foam, but since the pores are not connected, the fluid or gas cannot flow from one side of the foam to the other.
  • the material is said to possess more open pore network.
  • the more connected channels formed through the material the higher the permeability becomes for the substance.
  • the substrate would be defined as having a completely open pore network. It is important to note the difference between cells and pores.
  • Cells refer to the channels that run (generally parallel to each other but not necessarily) through the honeycomb substrate. Often, the honeycomb substrates are referred to in the context of how many cells they have per square inch.
  • a substrate with 200 cells per square inch has 200 channels along the principle axis of the substrate.
  • Pores refer to the gaps inside the material itself, such as in the material that constitutes the wall separating two parallel channels or cells.
  • Completely or mostly open pore network substrates are not known in the filtering or catalytic industries. Instead, even the most porous available extruded substrates are a hybrid of opened pore and closed pore porosity.
  • substrates be formed with high porosity, and with an internal pore structure that enables a similarly high permeability.
  • the substrates have to be formed with a sufficiently rigid structure to support the structural and environmental requirements for particular applications.
  • a filter or catalytic converter that is to be attached to internal combustion engine must be able to withstand the likely environmental shock, thermal requirements, and manufacturing and use stresses.
  • the substrate needs to be produced at a cost low enough to allow for widespread use.
  • a filtering substrate must be affordable and usable in developed as well as developing countries. Accordingly, the overall cost structure to filters and catalytic converter substrates is a substantial consideration in the substrate's design and selected process.
  • Extrusion has proven to be an efficient and cost-effective process to manufacture rigid substrates of constant cross section. More particularly, extrusion of ceramic powder material is the most widely used process for making filter and catalytic substrates for internal combustion engines. Over the years, the process of extruding powdered ceramics has advanced such that substrates may now be extruded having porosities approaching 60%. These extruded porous substrates have had good strength characteristics, may be flexibly manufactured, may be manufactured at scale, maintain high quality levels, and are very cost-effective. However, extrusion of powdered ceramic material has reached a practical upper limit of porosity, and further increases in porosity appear to result in an unacceptably low strength.
  • the extruded ceramic powder substrate has not proven strong enough to operate in the harsh environment of a diesel particulate filter.
  • extruded ceramic powder substrates have tried to increase cell density, but the increase in cell density has resulted in an unacceptable back pressure to the engine.
  • the extruded ceramic powder substrate does not have sufficient strength at very high porosities, and also produces unacceptable back pressure when there is a need for increased surface area. Accordingly, the extrusion of ceramic powder appears to have reached its practical utility limits.
  • the industry has a need for a rigid substrate that has high porosity and an associated high permeability.
  • the substrate would be formed as a highly desirable open cell network, would be cost-effective to manufacture, and could be manufactured with flexible physical, chemical, and reaction properties.
  • the present invention provides an extrudable mixture for producing a highly porous substrate using an extrusion process. More particularly, the present invention enables fibers, such as organic, inorganic, glass, ceramic or metal fibers, to be mixed into a mass that when extruded and cured, forms a highly porous substrate. Depending on the particular mixture, the present invention enables substrate porosities of about 60% to about 90%, and enables process advantages at other porosities, as well.
  • the extrudable mixture may use a wide variety of fibers and additives, and is adaptable to a wide variety of operating environments and applications.
  • Fibers which have an aspect ratio greater than 1, are selected according to substrate requirements, and are mixed with binders, pore-formers, extrusion aids, and fluid to form a homogeneous extrudable mass.
  • the homogeneous mass is extruded into a green substrate.
  • the more volatile material is preferentially removed from the green substrate, which allows the fibers to interconnect and contact.
  • fiber to fiber bonds are formed to produce a structure having a substantially open pore network.
  • the resulting porous substrate is useful in many applications, for example, as a substrate for a filter or catalyst host, or catalytic converter.
  • ceramic fibers are selected with an aspect ratio distribution between about 3 and about 1000, although more typically will be in the range of about 3 to about 500.
  • the aspect ratio is the ratio of the length of the fiber divided by the diameter of the fiber.
  • the ceramic fibers are mixed with binder, pore former, and a fluid into a homogeneous mass.
  • a shear mixing process is employed to more fully distribute the fibers evenly in the mass.
  • the ceramic material may be about 8% to about 40% by volume of the mass, which results in a substrate having between about 92% and about 60% porosity.
  • the homogeneous mass is extruded into a green substrate.
  • the binder material is removed from the green substrate, which allows the fibers to overlap and contact.
  • a porous substrate may be produced without the use of pore formers.
  • the ceramic material may be about 40% to about 60% or more by volume of the mass, which results in a substrate having between about 60% and about 40% porosity. Since no pore former is used, the extrusion process is simplified, and is more cost effective. Also, the resulting structure is a highly desirable substantially open pore network.
  • the disclosed fiber extrusion system produces a substrate having high porosity, and having an open pore network that enables an associated high permeability, as well as having sufficient strength according to application needs.
  • the fiber extrusion system also produces a substrate with sufficient cost effectiveness to enable widespread use of the resulting filters and catalytic converters.
  • the extrusion system is easily scalable to mass production, and allows for flexible chemistries and constructions to support multitudes of applications.
  • the present invention represents a pioneering use of fiber material in an extrudable mixture. This fibrous extrudable mixture enables extrusion of substrates with very high porosities, at a scalable production, and in a cost-effective manner.
  • the present invention enables mass production of filters and catalytic substrates for wide use throughout the world.
  • FIG. 1 is a block diagram of a system for extruding a porous substrate in accordance with the present invention.
  • FIG 2 is an illustration of a fibrous extrudable mixture in accordance with the present invention.
  • FIGs. 3A and 3B are illustrations of an open pore network in accordance with the present invention.
  • FIG. 4 is an electron microscope picture of an open pore network in accordance with the present invention and a close pore network of the prior art.
  • FIG. 5 is an illustration of a filter block using a porous substrate in accordance with the present invention.
  • FIG. 6 are tables of fibers, binders, pore formers, fluids, and rheologies useful with the present invention.
  • FIG. 7 is a block diagram of a system for extruding a porous substrate in accordance with the present invention.
  • FIG. 8 is a block diagram of a system for curing a porous substrate in accordance with the present invention.
  • FIG. 9 is a block diagram of a system for processing fibers for a porous substrate in accordance with the present invention.
  • FIG. 10 is a diagram for extruding a gradient porous substrate in accordance with the present invention.
  • FIG. 11 is a diagram for extruding a gradient porous substrate in accordance with the present invention.
  • FIG. 12 is a diagram for extruding a gradient porous substrate in accordance with the present invention.
  • system 10 uses an extrusion process to extrude a green substrate that can be cured into the final highly porous substrate product.
  • System 10 advantageously produces a substrate having high porosity, having a substantially open pore network enabling an associated high permeability, as well as having sufficient strength according to application needs.
  • the system 10 also produces a substrate with sufficient cost effectiveness to enable widespread use of the resulting filters and catalytic converters.
  • the system 10 is easily scalable to mass production, and allows for flexible chemistries and constructions to support multitudes of applications.
  • System 10 enables a highly flexible extrusion process, so is able to accommodate a wide range of specific applications.
  • the substrate designer first establishes the requirements for the substrate. These requirements may include, for example, size, fluid permeability, desired porosity, pore size, mechanical strength and shock characteristics, thermal stability, and chemical reactivity limitations. According to these and other requirements, the designer selects materials to use in forming an extrudable mixture.
  • system 10 enables the use of fibers 12 in the formation of an extruded substrate.
  • fibers 12 may be, for example, ceramic fibers, organic fibers, inorganic fibers, polymeric fibers, oxide fibers, vitreous fibers, glass fibers, amorphous fibers, crystalline fibers, non-oxide fibers, carbide fibers, metal P u C T / U S O 6 / 5 S Ei 3 Qf fibers, other inorganic fiber structures, or a combination of these.
  • ceramic fibers will be described, although it will be appreciated that other fibers may be used.
  • the substrate will often be described as a filtering substrate or a catalytic substrate, although other uses are contemplated and within the scope of this teaching.
  • the designer selects the particular type of fiber based upon application specific needs.
  • the ceramic fiber may be selected as a mullite fiber, an aluminum silicate fiber, or other commonly available ceramic fiber material.
  • the fibers typically need to be processed 14 to cut the fibers to a usable length, which may include a chopping process prior to mixing the fibers with additives. Also, the various mixing and forming steps in the extrusion process will further cut the fibers.
  • additives 16 are added. These additives 16 may include binders, dispersants, pore formers, plasticizers, processing aids, and strengthening materials.
  • fluid 18, which is typically water, is combined with the additives 16 and the fibers 12.
  • the fibers, additives, and fluid are mixed to an extrudable rheology 21. This mixing may include dry mixing, wet mixing, and shear mixing.
  • the fibers, additives, and fluid are mixed until a homogeneous mass is produced, which evenly distributes and arranges fibers within the mass.
  • the fibrous and homogenous mass is then extruded to form a green substrate 23.
  • the green substrate has sufficient strength to hold together through the remaining processes. [00034]
  • the green substrate is then cured 25.
  • curing is defined to include two important process steps: 1) binder removal and 2) bond formation.
  • the binder removal process removes free water, removes most of the additives, and enables fiber to fiber contact. Often the binder is removed using a heating process that burns off the binder, but it will be understood that other removal processes may be used dependent on the specific binder used. For example, some binder may be removed using an evaporation or sublimation process. Some binders and or other organic components may melt before degrading into a vapor phase. As the curing process continues, fiber to fiber bonds are formed. These bonds facilitate overall structural rigidity, as well as create the desirable porosity and permeability for the substrate. Accordingly, the cured substrate 30 is a highly porous substrate of mostly fibers bonded into an open pore network 30.
  • the substrate may then be used as a substrate for many applications, including as a substrate for filtering applications and catalytic conversion applications.
  • system 10 has enabled a desirable extrusion process to produce substrates having porosities of up to about 90%.
  • an extrudable material 50 is illustrated.
  • the extrudable material 50 is ready for extrusion from an extruder, such as a piston or screw extruder.
  • the extrudable mixture 52 is a homogeneous mass including fibers, plasticizers, and other additives as required by the specific application.
  • Figure 2 illustrates an enlarged portion 54 of the homogeneous mass. It will be appreciated that the enlarged portion 54 may not be drawn to scale, but is provided as an aid to this description.
  • the extrudable mixture 52 contains fibers, such as fibers 56, 57, and 58. These fibers have been selected to produce a highly porous and rigid final substrate with desired thermal, chemical, mechanical, and filtration characteristics. As will be appreciated, substantially fibrous bodies have not been considered to be extrudable, since they have no plasticity of their own. However, it has been found that through proper selection of plasticizers and process control, an extrudable mixture 52 comprising fibers may be extruded. In this way, the cost, scale, and flexibility advantages of extrusion may be extended to include the benefits available from using fibrous material.
  • a fiber is considered to be a material with a relatively small diameter having an aspect ratio greater than one.
  • the aspect ratio is the ratio of the length of the fiber divided by the diameter of the fiber.
  • the 'diameter' of the fiber assumes for simplicity that the sectional shape of the fiber is a circle; this simplifying assumption is applied to fibers regardless of their true sectional shape.
  • a fiber with an aspect ratio of 10 has a length that is 10 times the diameter of the fiber.
  • the diameter of the fiber may be 6 micron, although diameters in the range of about 1 micron to about 25 microns are readily available. It will be understood that fibers of many different diameters and aspect ratios may be successfully used in system 10. As will be described in more detail with reference to later figures, several alternatives exist for selecting aspect ratios for the fibers. It will also be appreciated that the shape of fibers is in sharp contrast to the typical ceramic powder, where the aspect ratio of each ceramic particle is approximately 1.
  • the fibers for the extrudable mixture 52 may be metallic (some times also referred to as thin-diameter metallic wires), although Figure 2 will be discussed with reference to ceramic fibers.
  • the ceramic fibers may be in an amorphous state, a vitreous state, a crystalline state, a poly-crystalline state, a mono-crystalline state, or in a glass- ceramic state.
  • a relatively low volume of ceramic fiber is used to create the porous substrate.
  • the extrudable mixture 52 may have only about 10% to 40% ceramic fiber material by volume. In this way, after curing, the resulting porous substrate will have a porosity of about 90% to about 60%. It will be appreciated that other amounts of ceramic fiber material may be selected to produce other porosity values.
  • the fibers are typically combined with a plasticizer. In this way, the fibers are combined with other selected organic or inorganic additives.
  • these additives provide three key properties for the extrudate. First, the additives allow the extrudable mixture to have a rheology proper for extruding. Second, the additives provide the extruded substrate, which is typically called a green substrate, sufficient strength to hold its form and position the fibers until these additives are removed during the curing process. And third, the additives are selected so that they burn off in the curing process in a way that facilitates arranging the fibers into an overlapping construction, and in a way that does not weaken the forming rigid structure.
  • the additives will include a binder, such as binder 61.
  • the binder 61 acts as a medium to hold the fibers into position and provide strength to the green substrate.
  • the fibers and binder(s) may be used to produce a porous substrate having a relatively high porosity.
  • additional pore formers such as pore former 63, may be added.
  • Pore formers are added to increase open space in the final cured substrate.
  • Pore formers may be spherical, elongated, fibrous, or irregular in shape. Pore formers are selected not only for their ability to create open space and based upon their thermal degradation behavior, but also for assisting in orienting the fibers.
  • the pore formers assist in arranging fibers into an overlapping pattern to facilitate proper bonding between fibers during later stage of the curing. Additionally, pore-formers also play a role in the alignment of the fibers in preferred directions, which affects the thermal expansion of the extruded material and the strength along different axes.
  • extrudable mixture 52 may use one or more fibers selected from many types of available fibers. Further, the selected fiber may be combined with one or more binders selected from a wide variety of binders. Also, one or more pore formers may be added selected from a wide variety of pore formers.
  • the extrudable mixture may use water or other fluid as its plasticizing agent, and may have other additives added. This flexibility in formation chemistry enables the extrudable mixture 52 to be advantageously used in many different types of applications. For example, mixture combinations may be selected according to required environmental, temperature, chemical, physical, or other requirement needs. Further, since extrudable mixture 52 is prepared for extrusion, the final extruded product may be flexibly and economically formed. Although not illustrated in Figure 2, extrudable mixture 52 is extruded through a screw or piston extruder to form a green substrate, which is then cured into the final porous substrate product.
  • the present invention represents a pioneering use of fiber material in a plastic batch or mixture for extrusion.
  • This fibrous extrudable mixture enables extrusion of substrates with very high porosities, at a scalable production, and in a cost-effective manner.
  • the present invention enables mass production of filters and catalytic substrates for wide use throughout the world.
  • FIG. 3A an enlarged cured area of a porous substrate is illustrated.
  • the substrate portion 100 is illustrated after binder removal 102 and after the curing process 110.
  • fibers such as fiber 103 and 104 are initially held into position with binder material, and as the binder material burns off, the fibers are exposed to be in an overlapping, but loose, structure.
  • a pore former 105 may be positioned to produce additional open space, as well as to align or arrange fibers. Since the fibers only comprise a relatively small volume of the extrudable mixture, many open spaces 107 exist between the fibers. As the binder and pore former is burned off, the fibers may adjust slightly to further contact each other.
  • the binder and pore formers are selected to burn off in a controlled manner so as not to disrupt the arrangement of the fibers or have the substrate collapse in burn off.
  • the binder and pore formers are selected to degrade or burn off prior to forming bonds between the fibers.
  • the bonds may be formed in several ways.
  • the fibers may be heated to allow the formation of a liquid assisted sintered bond at the intersection or node of the fibers. This liquid state sintering may result from the particular fibers selected, or may result from additional additives added to the mixture or coated on the fibers. In other cases, it may be desirable to form a solid state sintered bond.
  • the intersecting bonds form a grain structure connecting overlapping fibers.
  • the fibers In the green state, the fibers have not yet formed physical bonds to one another, but may still exhibit some degree of green strength due to tangling of the fibers with one another.
  • the particular type of bond selected will be dependent on selection of base materials, desired strength, and operating chemistries and environments.
  • the bonds are caused by the presence of inorganic binders presenting the mixture that hold the fibers together in a connected network. And do not burn off during the curing process.
  • bonds such as bonds 112 facilitates forming a substantially rigid structure with the fibers.
  • the bonds also enable the formation of an open pore network having very high porosity.
  • open- space 116 is created naturally by the space between fibers.
  • Open space 114 is created as pore former 105 degrades or burns off.
  • the fiber bond formation process creates an open pore network with no or virtually no terminated channels.
  • This open pore network generates high permeability, high filtration efficiency, and allows high surface area for addition of catalyst, for example.
  • the formation of bonds can depend upon the type of bond desired, such as solid-state or liquid-assisted/ liquid-state sintering, and additives present during the curing process.
  • the additives, particular fiber selection, the time of heat, the level of heat, and the reaction environment may all be adjusted to create a particular type of bond.
  • FIG. 3B another enlarged cured area of a porous substrate is illustrated.
  • the substrate portion 120 is illustrated after binder removal 122 and after the curing process 124.
  • the substrate portion 120 is similar to the substrate portion 100 described with reference to Figure 3A, so will not be described in detail.
  • Substrate 120 has been formed without the use of specific pore formers, so the entire open pore network 124 has resulted from the positioning of the fibers with a binder material. In this way, moderately high porosity substrates may be formed without the use of any specific pore formers, thereby reducing the cost and complexity for manufacturing such moderate porosity substrates. It has been found that substrates having a porosity in the range of about 40% to about 60% may be produced in this way.
  • Picture set 150 first illustrates an open pore network 152 desirably created using a fibrous extrudable mixture. As can be seen, fibers have formed bonds at intersecting fiber nodes, and pore former and binders have been burned off, leaving a porous open pore network.
  • picture 154 illustrates a typical closed cell network made using known processes. The partially closed pore network has a relatively high porosity, but at least some of the porosity is derived from closed channels. These closed channels do not contribute to permeability. In this way, an open pore network and a closed pore network having the same porosity, the open pore network will have a more desirable permeability characteristic.
  • the porous substrate may be extruded in to a filter block substrate 175 as illustrated in Figure 5.
  • Substrate block 175 has been extruded using a piston or screw extruder.
  • the extruder could be conditioned to operate at room temperature, slightly elevated temperature or in a controlled temperature window. Additionally, several parts of the extruder could be heated to different temperatures to affect the slow characteristics, shear history, and gellation characteristics of the extrusion mix. Additionally, the size of the extrusion dies may also be sized accordingly to adjust the expected shrinkage in the substrate during the heating and sintering process.
  • the extrudable mixture was a fibrous extrudable mixture having sufficient plasticizer and other additives to allow extrusion of fibrous material.
  • the extruded green state block was cured to remove free water, burn off additives, and form structural bonds between fibers.
  • the resulting block 175 has highly desirable porosity characteristics, as well as excellent permeability and high usable surface area. Also, depending on the particular fibers and additives selected, the block 175 may be constructed for advantageous depth filtering.
  • the block 176 has channels 179 that extend longitudinally through the block.
  • the inlets to the block 178 may be left open for a flow-through process, or every other opening may be plugged to produce a wall flow effect.
  • the channels may be formed with an evenly sized square, rectangular, or triangular channel pattern; a square/ rectangular or octagon/ square channel pattern having larger inlet channels; or in another symmetrical or asymmetrical channel pattern.
  • the precise shapes and sizes of the channels or cells can be adjusted by adjusting the design of the die. For example, a square channel can be made to have curved corners by using EDM (Electronic Discharge Machining) to shape the pins in the die. Such rounded corners are expected to increase the strength of the final product, despite a slightly higher backpressure.
  • EDM Electro Discharge Machining
  • die design can be modified to extrude honeycomb substrates where the walls have different thicknesses and the skin has a different thickness than the rest of the walls.
  • an external skin may be applied to the extruded substrate for final definition of the size, shape, contour and strength.
  • the high permeability of the substrate walls enable relatively low back pressures, while facilitating depth filtration. This depth filtration enables efficient particulate removal, as well as facilitates more effective regeneration.
  • the fluid flowing through the substrate is forced to move through the walls of the substrate, hence enabling a more direct contact with the fibers making up the wall. Those fibers present a high surface area for potential reactions to take place, such as if a catalyst is present. Since the extrudable mixture may be formed from a wide variety of fibers, additives, and fluids, the chemistry of the extrudable mixture may be adjusted to generate a block having specific characteristics.
  • the fibers are selected to account for safe operation even at the extreme temperature of an uncontrolled regeneration.
  • the fiber and bonds are selected so as not to react with the exhaust gas across the expected operational temperature range.
  • a first step in designing a porous substrate is to understand the final application for the substrate. Based on these requirements, particular fibers, binders, pore formers, fluids, and other materials may be selected. It will also be appreciated that the process applied to the selected materials may affect the final substrate product. Since the fiber is the primary structural material in the final substrate product, the selection of the fiber material is critical for enabling the final substrate to operate in its intended application. Accordingly, the fibers are selected according to the required bonding requirements, and a particular type of bonding process is selected.
  • the bonding process may be a liquid state sintering, solid-state sintering, or a bonding requiring a bonding agent, such as glass-former, glass, clays, ceramics, ceramic precursors or colloidal sols.
  • the bonding agent may be part of one of the fiber constructions, a coating on the fiber, or a component in one of the additives. It will also be appreciated that more than one type of fiber may be selected. It will also be appreciated that some fibers may be consumed during the curing and bonding process. In selecting the fiber composition, the final operating temperature is an important consideration, so that thermal stability of the fiber may be maintained.
  • the fiber is selected so that it remains chemically inert and unreactive in the presence of expected gases, liquids, or solid particulate matter.
  • the fiber may also be selected according to its cost, and some fibers may present health concerns due to their small sizes, and therefore their use may be avoided.
  • the fibers are selected according to their ability to form a strong rigid structure, as well as maintain the required mechanical integrity. It will be appreciated that the selection of an appropriate fiber or set of fibers may involve performance and application trade-offs.
  • Figure 6, Table 1 shows several types of fibers that may be used to form a fibrous extrudable mixture.
  • the fibers may be oxide or non-oxide ceramic, glass, organic, inorganic, or they may be metallic.
  • the fibers may be in different states, such as amorphous, vitreous, poly-crystalline or mono- crystalline.
  • Table 1 illustrates many available fibers, it will be appreciated that other types of fibers may be used.
  • Binders and pore formers may then be selected according to the type of fibers selected, as well as other desired characteristics.
  • the binder is selected to facilitate a particular type of liquid state bonding between the selected fibers. More particularly, the binder has a component, which at a bonding temperature, reacts to facilitate the flow of a liquid bond to the nodes of intersecting fibers.
  • the binder is selected for its ability to plasticize the selected fiber, as well as to maintain its green state strength.
  • the binder is also selected according to the type of extrusion being used, and the required temperature for the extrusion. For example, some binders form a gelatinous mass when heated too much, and therefore may only be used in lower temperature extrusion processes.
  • the binder may be selected according to its impact on shear mixing characteristics. In this way, the binder may facilitate chopping fibers to the desired aspect ratio during the mixing process.
  • the binder may also be selected according to its degradation or burnoff characteristics. The binder needs to be able to hold the fibers generally into place, and not disrupt the forming fiber structure during burnoff. For example, if the binder burns off too rapidly or violently, the escaping gases may disrupt the forming structure.
  • the binder may be selected according to the amount of residue the binder leaves behind after burnout. Some applications may be highly sensitive to such residue. [00049] Pore formers may not be needed for the formation of relatively moderate porosities.
  • the natural arrangement and packing of the fibers within the binder may cooperate to enable a porosity of about 40% to about 60%.
  • a moderate porosity substrate may be generated using an extrusion process without the use of pore formers.
  • the elimination of pore formers enables a more economical porous substrate to be manufactured as compared to known processes.
  • pore formers may be used to cause, additional airspace within the substrate after curing.
  • the pore formers also may be selected according to their degradation or burnoff characteristics, and also may be selected according to their size and shape. Pore size may be important, for example, for trapping particular types of particulate matter, or for enabling particularly high permeability.
  • the shape of the pores may also be adjusted, for example, to assist in proper alignment of the fibers.
  • a relatively elongated pore shape may arrange fibers into a more aligned pattern, while a more irregular or spherical shape may arrange the fibers into a more random pattern.
  • the fiber may be provided from a manufacturer as a chopped fiber, and used directly in the process, or a fiber may be provided in a bulk format, which is typically processed prior to use. Either way, process considerations should take into account how the fiber is to be processed into its final desirable aspect ratio distribution.
  • the fiber is initially chopped prior to mixing with other additives, and then is further chopped during the mixing, shearing, and extrusion steps.
  • extrusion can also be carried out with unchopped fibers by setting the rheology to make the extrusion mix extrudable at reasonable extrusion pressures and without causing dilatency flows in the extrusion mix when placed under pressure at the extrusion die face.
  • the chopping of fibers to the proper aspect ratio distribution may be done at various points in the overall process.
  • the fiber Once the fiber has been selected and chopped to a usable length, it is mixed with the binder and pore former. This mixing may first be done in a dry form to initiate the mixing process, or may be done as a wet mix process. Fluid, which is typically water, is added to the mixture. In order to obtain the required level of homogeneous distribution, the mixture is shear mixed through one or more stages. The shear mixing or dispersive mixing provides a highly desirable homogeneous mixing process for evenly distributing the fibers in the mixture, as well as further cutting fibers to the desired aspect ratio. [00051]
  • Figure 6 Table 2 shows several binders available for selection.
  • binders are generally divided into organic and inorganic classifications.
  • the organic binders generally will burn off at a lower temperature during curing, while the inorganic binders will typically form a part of the final structure at a higher temperature.
  • Figure 6 Table 3 shows a list of pore formers available. Pore formers may be generally defined as organic or inorganic, with the organic typically burning off at a lower temperature than the inorganic. Although several pore formers are listed in Table 3, it will be appreciated that other pore formers may be used.
  • Figure 6 Table 4 shows different fluids that may be used. Although it will be appreciated that water may be the most economical and often used fluid, some applications may require other fluids. Although Table 4 shows several fluids that may be used, it will be appreciated that other fluids may be selected according to specific application and process requirements.
  • the mixture may be adjusted to have a rheology appropriate for advantageous extrusion.
  • proper rheology results from the proper selection and mixing of fibers, binders, dispersants, plasticizers, pore formers, and fluids. A high degree of mixing is needed to adequately provide plasticity to the fibers.
  • the amount of fluid is typically finally adjusted to meet the proper rheology.
  • a proper rheology may be indicated, such as by one of two tests. The first test is a subjective, informal test where a bead of mixture is removed and formed between the fingers of a skilled extrusion operator.
  • a second more objective test relies on measuring physical characteristics of the mixture.
  • the shear strength versus compaction pressure can be measured using a confined (i.e. high pressure ) annular rheometer. Measurements are taken and plotted according to a comparison of cohesion strength versus pressure dependence.
  • a rheology chart identifying rheology points may be created. For example, Table 5 Figure 6 illustrates a rheology chart for a fibrous ceramic mixture.
  • Axis 232 represents cohesion strength and axis 234 represents pressure dependence.
  • the extrudable area 236 represents an area where fibrous extrusion is highly likely to occur. Therefore, a mixture characterized by any measurement falling within area 236 is likely to successfully extrude.
  • the rheology chart is subject to many variations, and so some variation in the positioning of area 236 is to be expected. Additionally, several other direct and indirect tests for measuring rheology and plasticity do exist, and it is appreciated that any number of them can be deployed to check if the mixture has the right rheology for it to be extruded into the final shape of the product desired. [00053] Once the proper rheology has been reached, the mixture is extruded through an extruder.
  • the extruder may be a piston extruder, a single screw extruder, or a twin screw extruder.
  • the extruding process may be highly automated, or may require human intervention.
  • the mixture is extruded through a die having the desired cross sectional shape for the substrate block.
  • the die has been selected to sufficiently form the green substrate. In this way, a stable green substrate is created that may be handled through the curing process, while maintaining its shape and fiber alignment.
  • the green substrate is then dried and cured. The drying can take place in room conditions, in controlled temperature and humidity conditions (such as in controlled ovens), in microwave ovens, RF ovens, and convection ovens. Curing generally requires the removal of free water to dry the green substrate.
  • the temperature may then be raised to burn off additives, such as binders and pore formers.
  • the temperature is controlled to assure the additives are burnt off in a controlled manner. It will be appreciated that additive burn off may require cycling of temperatures through various timed cycles and various levels of heat.
  • the substrate is heated to the required temperature to form structural bonds at fiber intersection points or nodes.
  • the required temperature is selected according to the type of bond required and the chemistry of the fibers. For example, liquid-assisted sintered bonds are typically formed at a temperature lower than solid state bonds. It will also be appreciated that the amount of time at the bonding temperature may be adjusted according to the specific type of bond being produced.
  • the entire thermal cycle can be performed in the same furnace, in different furnaces, in batch or continuous processes and in air or controlled atmosphere conditions.
  • the substrate is slowly cooled down to room temperature. It will be appreciated that the curing process may be accomplished in one oven or multiple ovens/ furnaces, and may be automated in a production ovens/furnaces, such as tunnel kilns.
  • System 250 is a highly flexible process for producing a porous substrate.
  • the substrate requirements are defined as shown in block 252.
  • the final use of the substrate generally defines the substrate requirements, which may include size constraints, temperature constraints, strength constraints, and chemical reaction constraints.
  • the cost and mass manufacturability of the substrate may determine and drive certain selections. For example, a high production rate may entail the generation of relatively high temperatures in the extrusion die, and therefore binders are selected that operate at an elevated temperature without hardening or gelling.
  • the dies and barrel may need to be maintained at a relatively higher temperature such as 60 to 180C.
  • the binder may melt, reducing or eliminating the need for additional fluid.
  • a filter may be designed to trap particulate matter, so the fiber is selected to remain unreactive with the particulate matter even at elevated temperatures.
  • a fiber is selected from Table 1 of Figure 6 as shown in block 253.
  • the fiber may be of a single type, or may be a combination of two or more types. It will also be appreciated that some fibers may be selected to be consumed during the curing process.
  • additives may be added to the fibers, such as coatings on the fibers, to introduce other materials into the mixture.
  • dispersant agents may be applied to fibers to facilitate separation and arrangement of fibers, or bonding aids may be coated onto the fibers. In the case of bonding aids, when the fibers reach curing temperatures, the bonding aids assist the formation and flowing of liquid state bonds.
  • Binder methylcellulose 0.5 140.0 280.0 23.1
  • Pore former methacrylate 1.19 500.0 420.2 34.7
  • a binder is then selected from Table 2 of Figure 6 as shown in block 255.
  • the binder is selected to facilitate green state strength, as well as controlled burn off. Also, the binder is selected to produce sufficient plasticity in the mixture.
  • a pore former is selected from Table 3 of Figure 6 as shown in block 256. In some cases, sufficient porosity may be obtained through the use of fibers and binders only. The porosity is achieved not only by the natural packing characteristics of the fibers, but also by the space occupied by the binders, solvents and other volatile components which are released during the de-binding and curing stages. To achieve higher porosities, additional pore formers may be added.
  • Pore formers are also selected according to their controlled burn off capabilities, and may also assist in plasticizing the mixture.
  • Fluid which is typically water, is selected from Table 4 Figure 6 as shown in block 257.
  • Other liquid materials may be added, such as a dispersant, for assisting in separation and arrangement of fibers, and plasticizers and extrusion aids for improving flow behavior of the mixture.
  • This dispersant may be used to adjust the surface electronic charges on the fibers. In this way, fibers may have their charge controlled to cause individual fibers to repel each other. This facilitates a more homogeneous and random distribution of fibers.
  • a typical composition for mixture intended to create a substrate with > 80% porosity is shown below. It will be appreciated that the mixture may be adjusted according to target porosity, the specific application, and process considerations.
  • the fibers selected in block 252 should be processed to have a proper aspect ratio distribution.
  • This aspect ratio is preferred to be in the range of about 3 to about 500 and may have one or more modes of distribution. It will be appreciated that other ranges may be selected, for example, to about an aspect ratio of 1000.
  • the distribution of aspect ratios may be randomly distributed throughout the desired range, and in other examples the aspect ratios may be selected at more discrete mode values. It has been found that the aspect ratio is an important factor in defining the packing characteristics for the fibers. Accordingly, the aspect ratio and distribution of aspect ratios is selected to implement a particular strength and porosity requirement.
  • fibers into their preferred aspect ratio distribution may be performed at various points in the process.
  • fibers may be chopped by a third-party processor and delivered at a predetermined aspect ratio distribution.
  • the fibers may be provided in a bulk form, and processed into an appropriate aspect ratio as a preliminary step in the extrusion process.
  • the mixing, shear mixing or dispersive mixing, and extrusion aspects of process 250 may also contribute to cutting and chopping of the fibers. Accordingly, the aspect ratio of the fibers introduced originally into the mixture will be different than the aspect ratio in the final cured substrate. Accordingly, the chopping and cutting effect of the mixing, shear mixing, and extrusion should be taken into consideration when selecting the proper aspect ratio distribution 254 introduced into the process.
  • the fibers processed to the appropriate aspect ratio distribution are mixed to a homogeneous mass as shown in block 262.
  • This mixing process may include a drying mix aspect, a wet mix aspect, and a shear mixing aspect. It has been found that shear or dispersive mixing is desirable to produce a highly homogeneous distribution of fibers within the mass. This distribution is particularly important due to the relatively low concentration of ceramic material in the mixture.
  • the rheology of the mixture may be adjusted as shown in block 264. As the mixture is mixed, its rheology continues to change.
  • the rheology may be subjectively tested, or may be measured to comply with the desirable area as illustrated in Table 5 of Figure 6. Mixture falling within this desired area has a high likelihood of properly extruding.
  • the mixture is then extruded into a green substrate as shown in block 268. In the case of screw extruders, the mixing may also happen inside the extruder itself, and not in a separate mixer. In such cases, the shear history of the mixture has to be carefully managed and controlled.
  • the green substrate has sufficient green strength to hold its shape and fiber arrangement during the curing process.
  • the green substrate is then cured as shown the block 270.
  • the curing process includes removal of any remaining water, controlled burn off of most additives, and the forming of fiber to fiber bonds.
  • bonds are formed at the intersecting points or nodes. It will be appreciated that the bonds may result from a liquid state or a solid-state bonding process. Also, it will be understood that some of the bonds may be due to reactions with additives provided in the binder, pore formers, as coatings on the fibers, or in the fibers themselves. After bonds have been formed, the substrate is slowly cooled to room temperature.
  • Method 275 has a green substrate having a fibrous ceramic content.
  • the curing process first slowly removes remaining water from the substrate as shown in block 277. Typically, the removal of water may be done at a relatively low temperature in an oven. After the remaining water has been removed, the organic additives may be burnt off as shown in block 279. These additives are burnt off in a controlled manner to facilitate proper arrangement of the fibers, and to ensure that escaping gases and residues do not interfere with the fiber, structure. As the additives burn off, the fibers maintain their overlapping arrangement, and may further contact at intersecting points or nodes as shown in block 281.
  • the fibers have been positioned into these overlapping arrangements using the binder, and may have particular patterns formed through the use of pore formers.
  • inorganic additives may have been used, which may combine with the fibers, be consumed during the bond forming process, or remain as a part of the final substrate structure.
  • the curing process proceeds to form fiber to fiber bonds as shown in block 285.
  • the specific timing and temperature required to create the bonds depends on the type of fibers used, type of bonding aides or agents used, and the type of desired bond.
  • the bond may be a liquid state sintered bond generated between fibers as shown in block 286. Such bonds are assisted by glass-formers, glasses, ceramic pre-cursors or inorganic fluxes present in the system.
  • a liquid state sintered bond may be created using sintering aides or agents as shown in block 288.
  • the sintering aides may be provided as a coating on the fibers, as additives, from binders, from pore formers, or from the chemistry of the fibers themselves.
  • the fiber to fiber bond may be formed by a solid-state sintering between fibers as shown in block 291.
  • the intersecting fibers exhibit grain growth and mass transfer, leading to the formation of chemical bonds at the nodes and an overall rigid structure.
  • a mass of bonding material accumulates at intersecting nodes of the fibers, and forms the rigid structure. It will be appreciated that the curing process may be done in one or more ovens, and may be automated in an industrial tunnel or kiln type furnace.
  • Process 300 shows that bulk fibers are received as shown in block 305.
  • the bulk fibers typically have very long fibers in a clumped and interwoven arrangement. Such bulk fibers must be processed to sufficiently separate and cut the fibers for use in the mixing process. Accordingly, the bulk fibers are mixed with water 307 and possibly a dispersant agent 309 to form a slurry 311.
  • the dispersant 309 may be, for example, a pH adjuster or a charge adjuster to assist the fibers in repelling each other. It will be appreciated that several different types of dispersants may be used.
  • the bulk fibers are coated with a dispersant prior to introduction into the slurry.
  • the dispersant is simply added to the slurry mixture 311.
  • the slurry mixture is violently mixed as shown in block 314. This violent mixing acts to chop and separate the bulk fibers into a usable aspect ratio distribution. As described earlier, the aspect ratio for the initial use of the fibers will be different than the distribution in the final substrate, as the mixing and extrusion process further chops the fibers.
  • the water is mostly removed using a filter press 316 or by pressing against a filter in another equipment. It will be appreciated that other water removal processes may be used, such as freeze drying.
  • the filter press may use pressure, vacuum or other means to remove water.
  • the chopped fibers are further dried to a complete dry state as shown in block 318.
  • These dried fibers may then be used in a dry mix process 323 where they are mixed with other binders and dry pore formers as shown in block 327.
  • This initial dry mixing assists in generating a homogeneous mass.
  • the water content of the filtered fibers is adjusted for proper moisture content as shown in block 321. More particularly, enough water is left in the chopped fiber cake to facilitate wet mixing as shown in block 325. It has been found that by leaving some of the slurry water with the fibers, additional separation and distribution of the fibers may be obtained. Binders and pore formers may also be added at the wet mix stage, and water 329 may be added to obtain the correct rheology.
  • the mass is also shear mixed as shown in block 332.
  • the shear mixing may also be done by passing the mixture through spaghetti shaped dies using a screw extruder, a double screw extruder, or a shear mixer (such as sigma blade-type mixer).
  • the sear mixing can also take place in a sigma mixer, a high shear mixer, and inside the screw extruder.
  • the shear mixing process is desirable for creating a more homogeneous mass 335 that has desirable plasticity and extrudable rheology for extrusion to work.
  • the homogeneous mass 335 has an even distribution of fibers, with the fibers positioned into an overlapping matrix. In this way, as the homogeneous mass is extruded into a substrate block and cured, the fibers are allowed to bond into a rigid structure.
  • Process 350 is designed to enable the manufacture and extrusion of a substrate block having a gradient characteristic.
  • a substrate may be produced having a first material towards the center of the block, and a different material towards the outside of the block.
  • a material having a lower coefficient of thermal expansion is used towards the center of the block where particularly high heat is expected, while a material with relatively high coefficient of thermal expansion is used on the outer areas where less heat is expected. In this way, a more unified expansion property may be maintained for the overall block.
  • selected areas of a block may have higher density ceramic material for providing increased structural support.
  • These structural support members may be concentrically arranged or axially arranged in the block.
  • the specific materials may be selected according to desired gradients in porosity, pore size, or chemistry according to the application requirements. Further, the gradient may entail the use of more than two materials.
  • the gradient structure may be produced by providing a cylinder of a first material 351.
  • a sheet of a second material 353 is wrapped around the cylinder 351 as shown by illustration 355.
  • layer B 353 becomes a concentric tube around the inner cylinder 351.
  • the layered cylinder 355 is then placed in a piston extruder, air evacuated, and the mass extruded through a die.
  • material will mix at the interface between material A and material B, facilitating a seamless interface.
  • Such an interface enables the overlapping and bonding of fibers between the two different kinds of materials, thereby facilitating a stronger overall structure.
  • the material Once the material has been extruded, cured, and packaged, it produces a filter or catalytic converter package 357 having a gradient substrate. More particularly, the A material forms at the center of the substrate, while the B material 361 forms at the outer portions. It will be appreciated that more than two materials may be used, and that pore size, porosity, and chemical characteristics may be gradiently adjusted.
  • a first cylinder 379 is provided at about the size of the piston extrusion barrel.
  • the outer cylinder 379 is the actual barrel used in the piston extruder.
  • An inner tube 377 having a smaller diameter than the outer tube 379 is provided.
  • the tubes are concentrically arranged so that the inner tube 377 is concentrically positioned inside of tube 379.
  • Pellets of a first extrudable mixture material 383 are deposited inside tube 377, while pellets of a second extrudable mixture material 381 are deposited in the ring between tube 377 and tube 379.
  • the inner tube is carefully removed, so that material A is concentrically surrounded by material 381.
  • Method 400 has a column of extrudable mixture 402 having alternating disks of two extrudable materials.
  • Extrudable mixture 402 has a first material 403 adjacent to a second material 404.
  • material A is relatively porous, while material B is less porous.
  • the material will flow through the extrusion die causing fibers from the A portion and the B portion to mingle in an overlapping arrangement. In this way, each A and B portion are bonded together to become a fibrous substrate block.
  • a filter 406 is created.
  • Filter 406 has a first part 407 having relatively high porosity and a second portion 408 having less porosity. In this way, gas flowing through filter 406 is first filtered through a high porosity area having large pore size, and then filtered through a less porous area having smaller pore size. In this way, large particles are trapped in area 407, while smaller particles or trapped in area 408. It will be appreciated that the size and number of material disks may be adjusted according to application needs. [00067]
  • the fiber extrusion system offers great flexibility in implementation. For example, a wide range of fibers and additives, may be selected to form the mixture. Several mixing and extrusion options exist, as well as options related to curing method, time, and temperature. With the disclosed teachings, one skilled in the extrusion arts will understand that many variations may be used. Honeycomb substrate sis a common design to be produced using the technique described in the present invention, but other shapes, sizes, contours, designs can be extruded for various applications.
  • the channels in an extruded substrate may need to be plugged.
  • Material of composition similar to the extruded substrate is used to plug the substrate.
  • the plugging can be done in the green state or on a sintered substrate. Most plugging compositions require heat treatment for curing and bonding to the extruded substrate.

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Abstract

La présente invention concerne un mélange extrudable destiné à la production par extrusion d'un substrat hautement poreux. L'invention concerne plus particulièrement la possibilité de prendre des fibres (organiques, inorganiques, en verre, en céramique, ou en métal) et de les mélanger en une masse qui à l'extrusion et au durcissage, forme un substrat hautement poreux. L'invention permet d'obtenir, selon le mélange, des porosités de substrat d'environ 60 % à environ 90 %, et des avantages de traitement à d'autres possibilités également. Le mélange extrudable, qui peut utiliser une grande diversité de fibres et additifs, s'adapte à une large plage d'applications et d'environnements d'exploitation. Les fibres, d'un rapport d'aspect supérieur à 1, sont choisies en fonction des spécificités du substrat, et sont mélangées à des liants, des porogènes, des adjuvants d'extrusion, et du fluide de façon à former une masse extrudable homogène. L'extrusion de cette masse homogène donne un substrat vert. La matière la plus volatile est éliminée de façon préférentielle du substrat vert, ce qui permet aux fibres de s'interconnecter et de se toucher. Pendant le traitement de durcissage, des liaisons de fibre à fibre se forme de façon à produire une structure en réseau à pores sensiblement ouverts. Le substrat poreux obtenu convient à de nombreuses applications, et notamment en tant que substrat pour filtre ou hôte catalytique, ou comme convertisseur catalytique.
EP06788219A 2005-11-16 2006-07-21 Systeme d'extrusion de substrat poreux Withdrawn EP1951637A4 (fr)

Applications Claiming Priority (5)

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US73723705P 2005-11-16 2005-11-16
US11/322,777 US20070152364A1 (en) 2005-11-16 2005-12-30 Process for extruding a porous substrate
US11/323,429 US20070107395A1 (en) 2005-11-16 2005-12-30 Extruded porous substrate and products using the same
US11/323,430 US20070111878A1 (en) 2005-11-16 2005-12-30 Extrudable mixture for forming a porous block
PCT/US2006/028530 WO2007061457A2 (fr) 2005-11-16 2006-07-21 Systeme d'extrusion de substrat poreux

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EP1951637A4 EP1951637A4 (fr) 2009-10-28

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WO2007061457A2 (fr) 2007-05-31
AU2006317688A1 (en) 2007-05-31
KR20080068114A (ko) 2008-07-22
DE202006017355U1 (de) 2007-04-05
EP1951637A4 (fr) 2009-10-28
DE202006017357U1 (de) 2007-04-26
WO2007061457A3 (fr) 2007-11-01

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