DE19750964A1 - Combustion chamber production method for vehicle heating unit - Google Patents

Abstract

The combustion chamber (2) or at least a part (A) consisting of the circumferential cover wall (8) and face cover wall (4), is produced as a single piece by metal powder die-casting process. An Independent claim is also included for the combustion chamber formed as a single piece, sintered metal die casing.

Description

The invention relates to a method for producing a Combustion chamber of a burner for a heater, in particular Vehicle heater, or for thermal regeneration exhaust particle filter, as well as one using this method manufactured combustion chamber, with a peripheral boundary wall, a forehead boundary wall and possibly a coax len air supply nozzle for the supply of combustion air that protrudes into the combustion chamber, as well as given if a side connector to accommodate a Ignition device.

Such combustion chambers of burners for the aforementioned one fields of application are known. You have the well-known combustion chambers made of stamped and then bent sheet metal parts sets what a considerable effort for connecting the individual parts, usually by welding or soldering, means. These connection techniques usually pull a heat distortion of the combustion chamber, so that the The combustion chamber must be adjusted before installation.

For a more efficient production according to DE 44 42 425 A1 suggested the combustion chamber or parts thereof as fine Form casting, especially after the well-known wax melting process. In this process, a  Manufacturing mold for a wax model, which the shape of the investment casting to be ultimately manufactured, gefer does. A larger number of these wax models are then connected to a common pouring channel, in a - often consist of ceramic particles with binders des - molded material. During the subsequent pouring the wax models melt and they become when they are out melt the resulting mold cavities with liquid metal filled out. This is then used to demould the investment castings Mold material destroyed.

The object of the invention is, while maintaining the principle the production of castings in the combustion chambers chambers or parts thereof to be further improved.

The object on which the invention is based is achieved by a manufacturing process specified in claim 1 a kind.

The manufacturing process is advantageously further developed according to the features of claims 2 to 7.

A distillery produced by the method according to the invention Chamber is characterized by the features of claim 8.

The combustion chamber according to the notes is advantageously further developed paint claims 9 to 18.

So it becomes a method of making a combustion chamber a burner for a heater or for a thermal re generation of an exhaust gas particle filter, with a circumferential loading boundary wall, a forehead boundary wall and given if a coaxial air supply nozzle for the supply tion of combustion air, which into the combustion chamber protrudes, as well as, if necessary, a side connector for the  Housing an ignition device, proposed that Combustion chamber or at least that from the perimeter limitation wall and the forehead boundary wall existing part of the Combustion chamber as a one-piece injection molded part after the metal Powder injection molding process.

In particular, sinterable metal powder particles are divided into one prefabricated negative form of the combustion chamber or part of the Combustion chamber injected using a spray device. Then the injection molded body is made from the negative mold removed and finally the injection molded body sintered.

It is particularly useful if the sinterable metal powder ver particles before being injected into the negative form in egg thermoplastic that serves as a binding and flow aid embedded and after injection and after removal from the negative mold and before sintering from the thermoplastic be freed or released again.

The sintered injection molded body of the combustion chamber or the part of the combustion chamber can after the actual Ferti be subjected to a quality assurance process.

Preferred as metal for the metal powder particles Steel or a steel alloy use, especially au stenitic or ferritic stainless steel, nickel alloyed Steel, case hardening steel or tempering steel.

Polar long-chain polyace is preferred as the thermoplastic tal used with additives.

The metal powder particles are preferably 35% to 50% Volume fraction with the thermoplastic ("binder"). to a granu lat compounded or mixed.  

A combustion chamber manufactured according to the invention provides, at least least the perimeter boundary wall and the forehead boundary wall as a one-piece, injection-molded, sintered metal form injection molded part.

The combustion chamber can be an evaporator combustion chamber or a Air atomizing combustion chamber.

Also in the one-piece, injection-molded, sintered Me tall injection molded part a preferably coaxial air supply trim integrated be formed, which in the focal protrudes into the chamber and on the inside of the combustion chamber Has air passage openings.

Furthermore, one-piece, injection-molded, sintered Metal injection molded part, preferably a side receptacle Mutzutzen for receiving an ignition device, in particular Glow plug, be integrated.

A combustion chamber is particularly complex if in one-piece, injection molded, sintered metal injection molding partly also a flame holder is integrated.

The combustion chamber can be completed if in one lumpy, injection molded, sintered metal injection molded part at least partially also a swirl device for the off formation of a swirl flow of the supplied combustion air is integrated.

Is an air supply nozzle an integral part of the Metal injection molded part, so can the air through openings through the nozzle wall right through the Injection molding with finished, with the openings preferred circumferentially evenly distributed, in particular sieve-like ver  are divided. So the openings are not separated by a sepa advise subsequent drilling.

If the combustion chamber is designed as an evaporator combustion chamber, can preferably be a porous evaporator body in the form of a Sintered molding can be provided, which is preferably on the inside circumference of the circumferential boundary wall is arranged.

The porous evaporator body can also consist of several individual molded parts or from several layers of material with under different porosity exist.

The porous evaporator body can also be a separate one be injection molded part, which after the metal powder spray casting process is made.

The porous evaporator body can preferably with the rest of the Sintered combustion chamber or with other combustion chamber parts and therefore be firmly connected, especially on the inner circumference the perimeter wall.

The metal powder injection molding process is generally known (see, for example, company lettering CM-Pulverspritzguß GmbH, D-88427 Bad Schussenried, title: "Everyone is talking about MIM - we do it!"). The process is known to be economically sensible and applicable for the production of complex small parts that weigh less than 20 g (see in particular sheet 5 , last paragraph, to sheet 6, first paragraph, the aforementioned company publication), if only because of the high raw material costs and the expensive tools required (see in particular chapter "Disadvantages of the MIM process" on page 6, with te, ff of the company publication) and because of the long tool manufacturing times (repeated changes to the tool required), and the fact that prototypes only can be produced from final tools.

For larger parts, size is already in the 100g range and shape of the component during sintering, in which shrinkage of the component takes place by 18 to 25%, through which effective gravity to deform the component.

Generic combustion chambers are components, which in Investment casting method weigh about 200g, which is why experts Brenn have not yet chambered according to the metal powder injection molding process manufactured.

The inventor / applicant is the only one who is concerned about the mentioned concerns and the feasibility of gat tional combustion chambers in metal injection molding, the so-called MIM process (Metal Injection Molding) signa has identified and proven.

It has been shown that the aforementioned MIM method is nevertheless applicable to generic combustion chambers and despite the material shrinkage during sintering, no rework processing in combustion chambers is necessary. Leave the components now produce with a significantly smaller wall thickness than with for example when investment casting. Another advantage of the invention according process for the production of combustion chambers (in Ver same as investment casting) is that the process time is significantly lower ten (1 day) (for investment casting the pro is time more than 10 days).

Compared to investment casting, the following advantages result in particular:

• - higher process reliability
• - tighter tolerances  
• - lower manufacturing costs
• - less weight and reduced wall thickness.

The invention is illustrated below with the aid of an embodiment game with reference to the attached one existing figure explained in more detail, in which an evaporator combustion chamber manufactured according to the invention is shown mathematically in an axial section.

The combustion chamber 2 shown in the drawing consists essentially of a flat end boundary wall 4 , which merges radially outside into a mounting flange 6 , a cylindrical circumferential boundary wall 8 , which carries away from the end boundary wall 4 at right angles, one centrally from the end wall 4 perpendicular to the right carrying cylindrical air supply stubs 10 and a receiving connector 12 for receiving a Zündein direction, preferably a glow plug.

The mounting flange 6 has a circular outer circumference. The Luftzuführungsstuzten 10 is concentric, so that between the air-supplying pipe 10 and the circumferential limiting wall 8, an annular space is formed at the circumferential boundary wall. 8

The longitudinal central axis of the combustion chamber 2 is designated 14 with net. Measured in the axial direction, the air supply connector 10 is approximately half as long as the circumferential boundary wall 8. When viewed in the cross section, not shown, the receiving connector 12 has a part-circular inner contour which extends over approximately 240 °. The partial circumferential wall of the receptacle connector 12 represents, as it were, a bulge in the circumferential boundary wall 8 , the circumferential boundary wall 8 being interrupted where the receptacle connector 12 connects. The Aufnah mestutzen 12 does not extend to the right up to the end of the circumferential boundary wall 8. The longitudinal central axis 16 of the receiving socket 12 is somewhat outside the circumference limitation wall 8 and is parallel to the axis 14. The wall of the air supply nozzle 10 has a circumferential distribution and in two rows axially next to each other radial, round air through openings 18 for the combustion air.

At the downstream right end of the air supply pipe 10 in the drawing, several webs are provided in an axial continuation distributed over the circumference, so that longitudinal slits are formed between the webs, through which air can be deflected radially into the annular space.

At the upstream in the drawing left end and at the downstream in the drawing right end (ie Be the beginning of the webs), the air supply nozzle 10 is open.

All previously mentioned parts of the combustion chamber 2 are out together forms an integral metal powder injection molded part.

The air supply nozzle 10 can also be made separately and then be united with the metal powder injection molded part.

To the left of the end boundary wall 4 , a substantially cylindrical air supply housing 20 is connected, which can contain a diffuser for generating a swirl flow entering the air supply duct 10 . A fan, not shown, is connected to the air supply housing 20 and supplies the combustion air with the required excess pressure, which can enter the schematically drawn air supply housing 20 axially or radially.

At the downstream end of the air supply nozzle 10 , a plate which is convexly curved towards the left is arranged as a flame holder 22 , which is braced against the left end face of the air supply housing 20 by means of a central, axially extending, small rod 24 . At the left end, the small rod 24 leads through the end face of the air supply housing 20 and is fastened there by a screwed nut 26 .

The curved flame holder is made of sheet metal. However, it can also be integrated integrally into the metal powder injection molded part. In this case there is no fastening rod 24 .

Furthermore, one can see in the drawing a porous evaporator body 28 to the right of the end boundary wall 4 and radially inside on the circumferential boundary wall 8. The porous evaporator body 28 is preferably made of sintered metal and has been sintered there in particular. In the axial direction, the evaporator body 28 in the illustrated embodiment is somewhat shorter than the circumferential boundary wall 8 , but could also be the same length or longer than the circumferential boundary wall 8 .

In the area where the interior of the receptacle connector 12 for the ignition device merges into the interior of the combustion chamber 2 , ie the annular space between the circumferential boundary wall 8 and the air supply connector 10 , the porous evaporator body 28 has an opening 30 which is only one in size Fraction of the interruption of the circumferential loading boundary wall 8 there, but can also have virtually the entire size of the interruption.

Finally, one can see in the drawing a guide and protective ring 32 , the wall at right angles from the forehead limiting wall 4 to the right into the annular space between the circumferential loading boundary wall 18 and the air supply nozzle 10 protrudes. The axial length of the ring 32 is 5% to 30% of the axial length of the air supply connector 10. The ring 32 is preferably also formed in one piece with the metal powder injection molding.

At the top left of the drawing, a bore 34, which is inclined at 45 °, is also provided for the supply of fuel, wherein a bore (not shown) with a press fit can be inserted into bore 34 . In reality, the bore 34 is rotated by 150 ° relative to the position shown next to the receptacle 12 for the Zündein direction.

As mentioned above, the combustion chamber 2 is manufactured in whole or in part as a one-piece metal powder injection molded part by the metal powder injection process.

In summary, the production is characterized by

• - Injection of sinterable metal powder particles into a prefabricated negative form of the combustion chamber 2 or the part of the combustion chamber 2 , in particular with the aid of a plastic injection machine,
• - sintering the injection molded body in the negative form, and
• - Remove the sintered injection molded body the one- or multi-part negative form, the so-called Injection mold.

According to the MIM process, two well-known manufacturers are  technologies, injection molding and sintering, combi kidney. In contrast to conventional sintering, MIM process without external force, d. H. without pres by molecular binding of the very fine metal powder particle made of compact body. The manufactured one Body has a density of more than 95% and is everyone conventional sintered part far superior in strength.

It has been shown that it is particularly useful before the injection molding of the sinterable metal powder particles a thermoplastic serving as a binding and flow aid embed and after the injection molding again from the thermoplastic to liberate or relieve.

The thermoplastic preferably consists of a polar, long chain polyacetal and various additives.

The metal powder, preferably steel or a steel alloy tion, especially austenitic or ferritic noble steel, nickel alloy steel, case hardening steel or tempering steel, is preferred with 35% to 50% by volume with the Thermoplastic, the so-called "binder", to form a granulate, the so-called feedstock, compounded or mixed.

As with plastic injection molding, the feedstock can be on normal extrusion injection molding machines at approx. 150 ° to process. For dimensional accuracy and surface quality here is the injection mold or the negative form of the body of vital importance. The highly crystalline polyacetal stabilizes the injection molded Body in such a way that also automatic handling Robots is possible.

While the part is now finished with plastic injection, injection molding is only the first in the MIM process  Step in the part production, the so-called "green body" represents.

In the subsequent debinding process, the green body is removed from the Polyacetal, which is used only for shaping during the injection process is released. Here, the well-known acid instability of the polyacetal exploited. The green body becomes (together with other green compacts) in a so-called debinding oven in which there is a nitrogen atmosphere det. At an oven temperature of approx. 140 ° then Salpe tersäure pumped into the furnace and evaporated immediately. The This creates an acidic atmosphere in the furnace chamber attacks the part inside and splits the poly Acetal catalyzed to formaldehyde. The Depoli Merisation or debinding runs from the outside to the inside a speed of 1 mm / h to 3 mm / h in the parts hi no from After debinding, the green compacts are porous become so-called "brownies", d. H. Parts that are not bin which have more shares. The in this step The gases formed will belong to the furnace system burned the two-stage torch without residue.

In the next process step, sintering, the parts compacted into compact bodies. The sintering takes place in Va vacuum furnaces lined with molybdenum. Depending sintering takes place due to the alloy used different temperatures and in different atmospheres spheres (hydrogen or nitrogen) instead. Usually the sintering temperatures for metal parts are between 1250 ° C and 1450 ° C. The porosities created during debinding are filled during the sintering, and the powder particles ver bake to a solid, homogeneous and compact body. The This compression is based on diffusion processes between run off the individual powder particles. Through this condensation The brownies shrink to their final finished part  size. The shrinkage during sintering is depending on the Le Gierpulver between 18% and 25% and must by corre Larger design of the injection molding tools or Nega tive form are taken into account.

After sintering, the MIM-manufactured parts are finished tig. The dimensions can then still be measured or the parts of a specific quality assurance be drawn.

It should also be noted that contained in the subclaims independently protectable features despite the made formal reference to the main claim should have independent protection. Otherwise, all fall all inventions contained in the entire application derischen features in the scope of the invention.

Claims (18)

1. A method for producing a combustion chamber ( 2 ) of a burner for a heater or for thermal regeneration of an exhaust gas particle filter, with a peripheral boundary wall ( 8 ), an end boundary wall ( 4 ) and optionally a coaxial air supply nozzle ( 10 ) for the supply of combustion air, which protrudes into the combustion chamber ( 2 ), and optionally a lateral connection piece ( 12 ) for accommodating an ignition device, characterized in that the combustion chamber ( 2 ) or at least the one from the peripheral wall ( 8 ) and the end boundary wall ( 6 ) existing part of the combustion chamber is produced as a one-piece injection molded part according to the metal powder injection molding process. 2. The method according to claim 1, characterized, that sinterable metal powder particles in a prefabricated te negative form of the combustion chamber or part of the combustion chamber injected using a sprayer be that then the injection molded body the negative form is removed, and that finally the injection molded body is sintered. 3. The method according to claim 2, characterized, that the sinterable metal powder particles before Ein inject into the negative form in one as a binding and Flow aid serving thermoplastic embedded and after injection and after removal from the  Negative form as well as before sintering the thermoplastic again be freed or released. 4. The method according to any one of claims 1 to 3, characterized, that the sintered injection molded body of the Brennam mer or part of the combustion chamber a quality assurance process is subjected. 5. The method according to any one of claims 1 to 4, characterized, that as the metal of the metal powder particles steel or a Steel alloy is used, especially austeniti shear or ferritic stainless steel, nickel alloy Steel, case hardening steel or tempering steel. 6. The method according to any one of claims 3 to 5, characterized, that as a thermoplastic polar long-chain polyacetal with Additives is used. 7. The method according to any one of claims 3 to 6, characterized, that the metal powder particles at 35% to 50% by volume part with the thermoplastic ("binder") to a granulate be compounded or mixed. 8. Combustion chamber, at least partially manufactured according to one of the methods according to one of claims 1-7, characterized in that at least the circumferential boundary wall ( 6 ) and the end boundary wall ( 4 ) is designed as a one-piece, injection molded, sintered metal injection molded part. 9. combustion chamber according to claim 8, characterized, that the combustion chamber is an evaporator combustion chamber or a Air atomizer combustion chamber is. 10. Combustion chamber according to claim 8 or 9, characterized in that in the one-piece, injection-molded, sintered Me tall injection molded part also a preferably coaxial air supply nozzle ( 10 ) is integrated, wel cher protrudes into the combustion chamber ( 2 ) and inside the combustion chamber shell side air passage openings ( 18 ). 11. Combustion chamber according to one of claims 8 to 10, characterized in that in the one-piece, injection-molded, sintered Me tall injection molded part also a preferably lateral receiving socket ( 12 ) for receiving an ignition device, in particular glow plug, is integrally formed. 12. Combustion chamber according to one of claims 8 to 11, characterized in that in the one-piece, injection-molded, sintered Me tall injection molded part also a flame holder ( 22 ) is integrally formed. 13. combustion chamber according to one of claims 8 to 12, characterized, that in the one-piece, injection-molded, sintered Me tall injection molding at least partially also a swirl device for the formation of a swirl flow of the supplied combustion air is integrated.   14. Combustion chamber according to one of claims 10 to 13, characterized in that the air passage openings ( 18 ) are evenly distributed over the circumference, in particular are distributed in a sieve shape. 15. Combustion chamber according to one of claims 8 to 14, characterized in that a porous evaporator body ( 28 ) is provided in the form of a Sin terformteile, which is preferably arranged on the inner circumference of the circumferential boundary wall ( 8 ). 16. Combustion chamber according to one of claims 1 to 15, characterized in that the porous evaporator body ( 28 ) consists of several single molded parts or of several layers of material with different porosity. 17. Combustion chamber according to one of claims 8 to 14, characterized in that the porous evaporator body ( 28 ) is designed in the form of a separate injection molded part produced by the metal powder injection molding process. 18. Combustion chamber according to one of claims 15 to 17, characterized in that the porous evaporator body ( 28 ) is versin tert with the rest of the combustion chamber or with other combustion chamber parts.