WO2005097446A1

WO2005097446A1 - Method for forming organic bonded bodies using ultrasonic energy

Info

Publication number: WO2005097446A1
Application number: PCT/DK2005/000238
Authority: WO
Inventors: Per Stobbe
Original assignee: Liqtech A/S
Priority date: 2004-04-07
Filing date: 2005-04-07
Publication date: 2005-10-20

Abstract

The present invention discloses the practical forming of green stage, non-fired bodies with a tool supplied with ultrasonic energy. The method is applicable in industrializing the production of capped Diesel Particulate Filter Channel bodies, which hereby proves that the otherwise standard liquid based-pre-softening method can be eliminated fully.

Description

Method of forming organic bonded bodies using ultrasonic energy

Field of the invention

The invention relates to a method of shaping dried green bodies based on metal or metal oxide particles bonded with an organic binder into desired shapes not easily formed otherwise.

In particular the present invention relates to a method, by which an extruded organic polymer bonded dry body is converted into a low cost different shaped body such as a dried honeycomb body with a multiplum of parallel channels in a Wall Flow Filter (WFF) body or cross-flow-filter body before sintering it into a final product. The WFF principle is suitable for filtering off particles in a fluid such as particles in hot gas streams or particles in liquid streams.

In operation, such WFF bodies will be exposed to hot and particulate loaded exhaust gas from combustion engines. The WFF should be able to withstand the high temperatures, thermal stresses and corrosiveness of the exhaust gas. Solid particles emitted by combustion engines typically have sizes from nanometre until few microns (μm). Therefore the pore structure of the filter body should have good porosity for obtaining high permeability and very controlled pores designed to mechanically retain the particles in the filter bodies.

Background of the invention

Diesel Particle Filters (DPF) are produced by extruding bodies based on a composite material of metal oxide particles and an organic binder into a multi cell honeycomb body. The organic binder is typically a cellulose ester, but could also be based on paraffin, wax, plastics or combination thereof. The honeycomb body is converted to a WFF (Wall Flow Filter) when each channel are blocked off alternating at each end face of the extruded green stage body. Typically one half of the channels at the one end face are blocked like in a chessboard pattern and the other part of the channels closed in the opposite end. The density of channels is within the industry referred to as CPSI (Cells Per Square Inch) and typically ranges from 50 to 300 for DPF.

Originally two different methods were developed for closing alternate channels in a multi channel honeycomb body, viz.: o The closing method of Corning Glass Works, Corning, N.Y., USA, disclosed in US 4,752,516, and o the capping method of NGK Insulators, Ltd., Nagoya, Japan, disclosed in US 4,283,210.

These two basic methods are still used worldwide for producing Wall Flow Filters (WFF's) from honeycomb bodies: o The Corning method use extra plastical paste material introduced by force through a rubber mask into every second channel in each body end face. o The NGK method forms and shapes each second pair of channel walls into a roof without adding further material just after the extrusion of the honeycomb structural body when it is still in a soft and plastic state.

The NGK method was later modified in EP 0692995 having priority date of April 5, 1993.

EP 0692995 discloses dry-deformation with a special designed tool in order to obtain the capping of open passage ends. Furthermore transducers are mentioned for measuring the deformation force, the motion distance, etc., but no information about additional added energy such as ultrasonic energy or ultrasonic transducers or added heat is mentioned.

However, EP 0692995 never takes into account the issue of actual performing the bending or deformation of the dry and solid walls without breakage or the issue of making the closing tight. It is of outmost importance that the capping (or plugging) of the channels in a WFF does not produce or leave any holes larger than the body wall pore sizes, which typically range from 1 to 50 μm. Dry- deformation or breakage of the dry walls create craters or cracks, which after firing of the body reveal holes typically 100 times larger than the filtering pores. For a filter body this will change the filtration performance dramatically and is not acceptable. The filtration efficiency for soot particles from Diesel engines will drop from the required more than 95% to typically less than 75% efficiency.

In the EP 0692995 patent this issue was solved by thorough softening the honeycomb ends with water before the capping procedure so no breakage or craters were formed, but this requires high accuracy and can only practically be done by human hand. The human wafer softening and operation of a hand operated capping tool with typically 2-6 parallel mounted identical tools bonding shaping the body end walls together insure satisfactory closing of the channels, but the method is extremely time consuming.

Therefore using softened honeycomb ends in order to avoid craters and wall breakage is only a method practicable for small-scale production. Large-scale production requiring very accurate pre-softening is not practical.

The present invention has revealed that the pre-softening step can be fully eliminated without any risk for producing craters or cracks.

Summary of the invention

Polymers and elastomers are usually highly sound-absorbing or attenuative. Reinforced plastics and other types of multi-phase and composite materials are generally attenuative and produce scattering of an emitted soundfield. Most ceramics or metallic oxide are likewise attenuative. The combination of an organic binder and ceramic or metallic oxide particles in a desired ratio (typical 85%o particles and 15% binder) gives the dried green bodies the necessary attenuative properties for being formable by the application of ultrasonic energy stress. To introduce ultrasonic energy into a forming system requires an ultrasonic transducer and an ultrasonic power supply or "generator." The generator supplies electrical energy at the desired ultrasonic frequency typically from 5 Hz - 500 kHz. The ultrasonic transducer based on typically ceramic piezoelectric elements converts the electrical energy from the ultrasonic generator into mechanical vibrations.

The ultrasonic generator converts electrical energy from the line, typically alternating current at 50 or 60 Hz, into electrical energy at the ultrasonic frequency. Various manufacturers produces different such generators. Nearly all current ultrasonic generators use solid-state technology. There have been several relatively recent innovations in ultrasonic generator technology, which may enhance the effectiveness of ultrasonic cleaning equipment. These include square wave outputs, slowly or rapidly pulsing the ultrasonic energy on and off, and modulating or "sweeping" the frequency of the generator output around a central operating frequency. The most advanced ultrasonic generators have provisions for adjusting a variety of output parameters to customize the ultrasonic energy output for the task.

The present inventor has now discovered a novel capping principle based on supplying ultrasonic energy to the capping tool.

Thus, the present invention provides a method of shaping the structures of a body made of a composite material comprising ceramic, metallic and/or metal oxide particles and an organic binder with a mechanical tool, characterised in that said mechanical tool is provided with at least one contacting surface capable of effecting ultrasonic vibrational or oscilating motion and contacting the surface(s) of said body structures in a dry and solid state with the contacting surface of the mechanical tool and causing it to perform ultrasonic vibrational or oscilating motion so as to deliver ultrasonic energy to the body structures thereby making them plastic and deformable and shaping them to the desired shape. With the invention method a time reduction from 30 to 4 minutes is obtainable so the product will reach a price more suitable for marked penetration.

Sonic motion applied to the forming tool with frequencies ranging from 5 Hz -500 kHz (Infra-sonic to Ultra-sonic) and displacement ranging from 0.5 μm until 50 μm allow dry-forming within seconds for a most beautiful result.

The Tylose MH300 type of plasticizer product from Clariant or similar Methyl- hydroxy-ethyl-cellulose is an exemplary organic binder in extruded bodies of ceramic or metal oxide particles. After drying the extruded bodies application of ultrasonic energy shortly makes the dry walls plastical and deformable. After termination of the ultrasonic energy the walls stiffen instantaneously and the process is finished within about one second.

Preferred embodiments of the method according to the present invention are defined in the dependent claims.

Short description of the drawings

Fig. 1 illustrates a cross-sectional view of an extruded filter body plug according to the prior art disclosed in the corning patent US 4,752,516,

Fig. 2 is a partial cut-away perspective view of the prior art filter body illustrated in Fig. 1 ,

Fig. 3 is a cross-sectional view of a filter body manufactured by the prior art water softening method disclosed in EP 0 692 995 and a tool for use in this method,

Fig. 4 is a cross-sectional view of a filter body produced by the dry capping method disclosed in EP 0 692 995 and a tool for use in this method, Fig. 5 is a cross-sectional view illustrating the same type capping method as that in Fig. 5, but further illustrating how a shape-preserving body has to be inserted in the channels for deforming the side walls thereof, and Fig. 6 is skits illustrating an operators provided with a tool which can be used for performing the method according to the present invention.

Detailed part of the description Figs. 1 - 5 are only included for illustrating the background of the present invention. Therefore, they will not be further explained herein, but a detailed explanation can be found in EP 0 692 995.

Preferring to Fig. 6 illustrating an operators to be used in the method of the present invention, 100 is an ultrasonic generator, which converts electrical energy from line, typically alternating current at 50 or 60 Hz, into electrical energy of the ultrasonic frequency. The ultrasonic generator also includes an ultrasonic transducer, which performs the ultrasonic electric energy into vibrational or oscilating motion.

101 is an interconnecting member for fixing the shaping tool 102 and transmitting the ultrasonic energy from the transducer to the shaping tool 102.

In use the tool 102 is positioned in the appropriate open ends of the channels in a dry and solid green body which are to be closed. The transducer is then activated for a few seconds and then stopped and removed leaving perfectly closed channels without any cracks or craters. The tool is then inserted to other appropriate open ends of channels which are to be closed and so on.

Examples

A plastic paste material was prepared with the following composition:

Compound Grams

Coarse SiC F180 (50 - 100 particle diameter) 15.000

Fine SiC FCP15 (submicron) 3.000

MH 300 1.200

Stearic acid 400

Ethanol 1.000

Ethandiol 200

PVA solution 300

Water 2.800

The ingredients are mixed by first mixing the particular materials and then adding the liquid materials. After follow mixing the material is ready for extrusion. The extrusion process was effected using a standard single auger extruder. In this way an extruded string of a multi channel body was produced which was cut into appropriate size and then dried until non sticky and stiff. The dried items was subjected to a closing method according to the invention with satisfactory properties.

1. With water as softening medium and DPF wall capping one body with 90 CPSI being 87 x 87 mm in cross section with 37 x 37 = 1369 individual 2 x 2 mm cells with 0.8 mm walls thickness of which every second channel must be closed in each body end face. This takes for a very skilled person manually app 30 minutes including the water softening, forming of the walls, powder drying, extra capping, channel cleaning, inspection and possible repair. A technique described very detailed over a >5 year period and production of more than 25 tons and DPF. This is one of the drawbacks of the Silicon Carbide based DPF (Diesel particulate Filter) technologies developed by Stobbe Engineering A/S in the period from 1988 until 1996 in Denmark. In practise this channel capping process turned out to be a very time consuming and costly technique.

The fully sonic dry-capping method has shown recently that time required can be reduced to 4 minutes. Which is a factor of 30 : 4= 7.5 times faster. None of the previous stages is now needed. The tool with a suitable number of teeth and design is gently put in place above of the body and forced with less that 5 kilo into place and one second energy added.

2. Practical results have been obtained with one second applied force from a constant 35 kHz power supply (equipment supplied by Rinco Ultrasonics in Denmark) connected to a 2 or 3 layer piezoelectric disc element transducer for 5 μm amplitude coupled acoustic to the amplification horn for mechanical to the tool.

3. Further automatization of the vastly simplified dry-capping method potentially offer further time reduction for even further unit price reduction. Involving a robot for no human hand operation.

4. Forming of complicated non honeycomb filter bodies based on pre-extruded and dried blocks into filter elements of design, shape not possible to mass produce otherwise. Dry-forming of cut to desired volume blocks into discs with a tapered ring in the circumference.

5. Forming of close to full density pre-extruded bodies cut into desired volumes and mounted into the forming tool consisting of parts mounted in an uni-axial press followed by adding ultrasonic energy for increased fluidability of the soft or dried bodies.

The above procedure may be altered according to usual practice for the person skilled in the art without extending beyond the scope of the invention. Other uses of the present invention though cost effective extrusion of particle and polymer based bodies followed by drying and fast further forming with ultrasonic tolls and energy.

Claims

1. A method of shaping the structure(s) of a body made of a composite material comprising ceramic, metallic and/or metal oxide particles and an organic binder with a mechanical tool, characterised in that said mechanical tool is provided with at least one contacting surface capable of effecting ultrasonic vibrational or oscilating motion and contacting the surface(s) of said body structure(s) in a dry and solid state with the contacting surface of the mechanical tool and causing it to perform ultrasonic vibrational or oscilating motion so as to deliver ultrasonic energy to the body structures thereby making them plastic and deformable and shaping them to the desired shape.

2. A method according to claim 1 , characterised in that the body has an internal multichannel structure and the method is used for closing selected open ends of the channels.

3. A method according to claim 2, characterised in that the multichannel structure is that of a honeycomb and that just one end of each channel is closed by performing the method.

4. A method according to claim 3, characterised in that the open end of the each second channels is closed at the one end of the body so as to produce a chess-board pattern at that end and the open ends of the remaining channels are closed at another end of the body so as also to produce a chess-board pattern in that end of the body.

5. A method according to any of claims 2 - 4, characterised in that each channel in cross section is substantially polygonal, in particular quadratic or rectangular.

6. A method according to any of the preceding claims, characterised that the body is an extruded body in the green, but dried and solid state.

7. A method according to claim 6, characterised in that the body is a cylinder the cross section of which has a circular, oval, quadratic, rectangular or other desired outer circumference.

8. A method according to any of the preceding claims, characterised in that the body is made of a material comprising silicium carbide particles as the main component.

9. A method according to any of the preceding claims, characterised in that the body produced after subsequent calcination and/or firing constitutes an appropriate filter body.

10. A method according to any of the preceding claims, wherein the body to be formed is a filter body in the green state comprising a plurality of coextending throughgoing passages separated by common passage walls, the method comprises deforming and bending each second pairs of adjacent passage walls together so as to close each second passage at that end.

11. A Diesel engine soot particulate Wall Flow Filter manufactured with channels closed by the method as described in any of the preceding claims.