WO2002092881A2

WO2002092881A2 - Method for producing at least partially coated bodies with a coating consisting of a sinterable material

Info

Publication number: WO2002092881A2
Application number: PCT/EP2002/003786
Authority: WO
Inventors: Alfred Mattern
Original assignee: Gkn Sinter Metals Gmbh
Priority date: 2001-05-12
Filing date: 2002-04-05
Publication date: 2002-11-21
Also published as: DE10123199B4; DE10123199A1; WO2002092881A3

Abstract

The invention relates to a method for producing at least partially coated bodies with a coating consisting of a sinterable material. According to said method, in a first step a support body is brought at least partially into contact with a suspension, whereby the suspension contains the sinterable material; in a second step, the support body is rotated, the rotational speed lying in the range of approximately 80 to approximately 1,500 U/min, preferably in the range of approximately 100 to approximately 1,000 U/min; in a third step, the support body is removed from the suspension; in a fourth step, the support body, which is now at least partially coated, is dried; and in a fifth step, the coated support body is sintered.

Description

Process for producing at least partially coated bodies with a coating made of a sinterable material

The present invention relates to a method for producing at least partially coated bodies with a coating made of a sinterable material and to at least partially coated bodies themselves and their use.

DE 197 16 595 C1 discloses a process for producing a metal layer with open porosity, in which a suspension, which has metal powder, dispersant and substances for adjusting the viscosity, is placed on a carrier

Is applied in layers, dried on the carrier and then sintered, the layer thickness of the suspension applied to the carrier being selected so that the layer thickness of the metal layer after sintering is at least three times as thick as the mean powder diameter of the metal powder, and in which Carrier is used the inner wall of a pipe. The tube can rotate during the application and drying of the suspension. DE 197 16 595 C1 proposes that the suspension metered into a rotating, depending on the application purpose porous

Pipe is fed by means of, for example, a tube or a spray head. When using a spray head, the spray head or the pipe can rotate. The tube is rotated at about 60 rpm.

A disadvantage of the method described in DE 197 16 595 C1 is in particular that the internally coated tubes produced by means of the method described therein have a coating on the surface of which there is a line in the form of a screw. The main reason for this is that the

Suspension is fed into the tube via a tube or a spray head, the tube necessarily having to be kept horizontal. Due to the in DE 197 16 595 The method described in C1 is therefore only obtained with internally coated pipes which have a non-uniformly formed coating surface. This is extremely disadvantageous since it increases the flow resistance, for example, when using such tubes as filters.

The object of the present invention is to provide a method by means of which sintered coatings can be produced on carrier bodies which have a uniform surface.

This object is achieved according to the invention by a method for producing at least partially coated bodies with a coating made of a sinterable material, whereby

in a first step, a carrier body is at least partially brought into contact with a suspension, the suspension comprising the sinterable material;

in a second step, the carrier body is set in rotation, the rotational speed of the rotation being in a range from approximately 80 to approximately 1500 rpm, preferably in a range from approximately 100 to approximately 1000 rpm;

in a third step the carrier body is removed from the suspension;

in a fourth step, the now at least partially coated carrier body is dried; and

in a fifth step the coated carrier body is sintered.

In addition to the sinterable material, the suspension preferably comprises solvents, binders, stabilizers and / or dispersants. The individual components of the suspension are mixed together, for example by agitators, until a homogeneous distribution of the individual components of the suspension is achieved. Subsequently, the support body, possibly rotating, is immersed in the suspension. Here, the rotational speed of the rotation when the carrier body is introduced into the suspension is in a range from approximately 0 rpm to 100 rpm. After the support body has been introduced into the suspension, the speed is regulated to a range from about 80 to about 1,500 rpm. The rotation of the body sets the suspension in motion, the particles of sinterable material contained in it, in particular, preferably being deposited on the carrier body due to their high density. If a tube is inserted into the suspension as a carrier body, centrifugal forces act on the particles of sinterable material contained in the suspension, in particular when the tube rotates about its longitudinal axis, so that these particles settle on the inside of the tube in a very short time deposit.

After a treatment time in a range from about 0.5 to 20 seconds, preferably in a range from about 3 to 10 seconds, the carrier body is removed from the suspension. This removal is preferably carried out with rotation of the carrier body in a range from 0 rpm to 100 rpm, preferably 10 rpm to about 30 rpm. The rotation maintains the green layer forming on the carrier body in this phase, and the drying process is accelerated.

The drying in the fourth step can also be carried out while rotating the carrier body in an area which corresponds approximately to that when the carrier body is removed from the suspension in the third step.

Then, in the fifth step, depending on the type and size of the sinterable material used, the carrier body is included the green coating formed on this sintered at conventional sintering temperatures, in particular for metallic materials, at temperatures in a range between 800 and 2,000 ° C., preferably 850 ° C. to 1,400 ° C.

The process according to the invention advantageously gives coatings on support bodies which have a very uniform surface. Screw lines or similar on the surface of the coating layer are avoided. In addition, the method according to the invention can be carried out extremely inexpensively, since in particular the coating time is drastically reduced in contrast to methods known in the prior art, in particular also that known from DE 197 16 595 C1.

Sinterable materials in the sense of the present invention, which can be used for the coating layer arranged on the carrier body, but also for the carrier body itself, are understood to mean powders and / or fibers and / or wires, produced from metals, ceramics, metal oxides, silicates and / or plastics and / or mixtures thereof. Usable metallic materials are not only powders made of pure metals, but also powders made of metal alloys and / or powder mixtures made of different metals and metal alloys. These include in particular steels, preferably chromium-nickel steels, bronzes, nickel-based alloys such as Hastalloy, Inconel or the like, it being possible for powder mixtures to also contain high-melting constituents such as platinum or the like. The metal powder used and its particle size depend on the respective application. The preferred powders are the alloys 316 L, 304 L, Inconel 600, Inconel 625, Monel and Hastalloy B, X and C. Ceramic materials such as Ti0 ₂ , Al ₂ 0 ₃ and / or Zr0 ₂ can also be used as sinterable materials. The powders used for the coating, but also for the carrier body, have particle sizes which range from about 0.05 μm to 150 μm, preferably in a range from 0.5 μm to 60 μm, even more preferably in a range from approximately 0.5 μm to approximately 20 μm. The amount of powder in the suspension ranges from about 10% to about 60% by weight based on the total amount of the suspension.

If metal oxides or mixtures of such materials are used as sinterable materials or in mixtures with other sinterable materials, these are in particular selected from a group comprising metal oxides which can be reduced and / or not reduced. Reducible oxides for the purposes of the present invention are metal oxides which can be reduced to the respective metal in a reducing hydrogen atmosphere, preference being given to those selected from a group comprising AgO, CuO, Cu ₂ 0, Fe ₂ 0 ₃ , Fe ₃ 0 ₄ and / or NiO. In contrast, reducible oxides for the purposes of the present invention are oxides which cannot be reduced in industrial atmospheres, in particular hydrogen. Oxides are preferably selected from a group comprising Ti0 ₂ , A1 ₂ 0 ₃ , Zr0 ₂ , Cr ₂ 0 ₃ , MgO, CaO and / or Si0 ₂ .

Solvents preferably included in the suspension are selected from a group comprising water, alcohols, in particular methanol, ethanol, isopropanol, and also terpenes, C ₂ -C ₅ -alkenes, toluene, trichlorethylene, diethyl ether and / or C 1 -C 6 -gdehydes and / or ketones. Solvents which can be evaporated at temperatures below 100 ° C. are preferred. The amount of solvent used is in a range from about 20 to about 90% by weight, based on the total amount of the suspension. Mixtures of solvents are preferably used.

Mixtures of alcohols such as ethanol and methanol with water are particularly preferred.

The binder included in the suspension is preferably selected from a group comprising polyvinyl acetates, waxes, shellac, amide waxes, polyethylene oxides and / or polyglycols. Polyalkylene oxides and glycols are preferably used as Polymers and / or copolymers with average molecular weights in a range from about 100 to 500,000 g / mol, preferably 1,000 to 350,000 g / mol, more preferably 5,000 to 6,500 g / mol, are used. The binders are preferably used in an amount in a range from about 0.5 to about 10% by weight, based on the total amount of the suspension. Particularly preferred binders are polyvinyl acetates with an average molecular weight in a range from about 5 × 10 ³ to 50 × 10 ³ g / mol, preferably 15 × 10 ³ to 30 × 10 ³ g / mol.

The suspension containing the sinterable material preferably has a stabilizer selected from a group comprising organic and / or inorganic acids, inorganic bases, polyacrylamines, polyacrylic acid and / or amines. Acetic acid, citric acid, hydrochloric acid, oxalic acid, lithium hydroxide, ammonium hydroxide, triethandiamine and tetramethylammonium hydroxide are particularly preferred. The amount of stabilizer used is in a range from about 3 to 13% by weight, based on the total amount of the suspension. The addition of stabilizers weakens the tendency of the sinterable particles, particularly when using metal oxides, to agglomerate, as a result of which a more uniform surface and, in the case of porous coatings, a more uniform pore distribution is achieved.

Furthermore, the suspension containing the sinterable material preferably comprises dispersants selected from a group comprising polyamines, phthalic acid esters and / or polyethyleneimines. The viscosity of the suspension used can be optimally adjusted by adding dispersants, in particular polyethlenimines.

The materials which are also provided for the coating can be used for the carrier body. However, it is not necessary here for the material of the coating to match that of the carrier body. The carrier body can be made from powders, fibers, ceramics and / or wire mesh. In the production of an at least partially coated tubular body, it is preferably rotated about its longitudinal axis and perpendicularly in relation to the bottom of the container holding the suspension in the second step of the method according to the invention. In such a process, centrifugal forces act uniformly in the interior of the tube, which arise from the rotation of the tubular body, so that a very uniform coating is obtained extremely quickly on the inside of the tubular body.

If it is intended to produce a body that is only partially coated using the method according to the invention, the carrier body to be coated is preferably partially provided with a protective cover. This protective cover can consist, for example, of a protective tube which is attached to the outside of a tube which is only to be coated on the inside, for example by means of silicone, rubber, polyurethane or other deformable plastics.

This makes it possible to carry out a coating on a carrier body in a targeted manner in narrowly defined areas.

The present invention further relates to an at least partially coated body with at least one carrier body and at least one coating of a sinterable material which is at least partially arranged thereon, the coating having an average roughness depth R _{z in} accordance with DIN EN ISO 4768 which is less than or equal to approximately 60%. is the maximum grain diameter of the sinterable material used to produce the coating.

According to DIN 4768: 1990, the average roughness depth R _{z is} defined as the arithmetic mean of the individual roughness depths of five adjacent individual measuring sections. The at least partially coated bodies according to the invention have a coating which has an extremely uniform surface. The average roughness depth R _z is preferably less than or equal to approximately 50% of the maximum grain diameter of the sinterable material used to produce the coating.

The coating and / or the carrier body is preferably porous. If both the coating and the carrier body are porous, it is preferably provided that the coated body according to the invention has a pore size that decreases in the direction of flow, i.e. that, for example, in the case of a tubular filter element, the coating is arranged on the inflow side on the inside thereof. On account of the markedly uniform formation of the surface of the coating, the bodies according to the invention have significantly reduced flow resistances compared to those known in the prior art, as a result of which energy and thus also costs are saved when using the bodies according to the invention. Furthermore, when the bodies are used, in particular as filter elements, their backwashing properties are significantly improved since the filter cake formed on a smooth surface can be removed more easily.

The coating preferably has a thickness in a range from approximately 5 μm to approximately 500 μm, more preferably approximately 20 μm to approximately 100 μm. The at least partially coated body according to the invention is preferably tubular. Here, the coating is preferably only arranged on the inside and / or the end faces of the tubular body.

Finally, the present invention relates to the use of at least partially coated bodies according to the invention as a filter element, catalyst, membrane reactor and / or friction material. If, for example, the body according to the invention consists of a porous coating and a solid support body or a support body without continuous pores, put together, the coating can serve as a catalyst, for example. When the body according to the invention is used as a filter element, both the support body and the coating are porous. The markedly uniform surface of the coating saves energy and, particularly when used as a filter element in cross-flow filtration, improves the backwashing properties.

This and other advantages of the present invention are explained in more detail with reference to drawings. Show it:

Fig. 1 is a schematic representation of the method according to the invention;

2 shows a micrograph of an internally coated tubular body in cross section; and

3 shows a tactile diagram of an individual measuring section of the inner coating of the tube shown in FIG. 2.

1 clarifies the method according to the invention and shows a body 1 according to the invention shown in cross section, which comprises a carrier body 2 and a coating 3. The body 1 is designed as a tube, the coating 3 is arranged on the inside of the tube. On the outside of the body 1, a cover 9 is provided, which can be a protective tube, for example. This protective tube is firmly connected to the outside of the body 1 at least at its ends by means of silicone or a rubber seal. The tubular body 1 is arranged in a container 5 which is filled with a suspension 4. Here, the tubular body 1 is arranged in such a way that it is arranged perpendicular to the bottom 6 of the container 5 in the latter. At the bottom of the container 5, a rear mechanism, for example a paddle stirrer, is preferably arranged (not shown). This agitates the suspension 4 to ensure homogeneous mixing. The agitator is at rest when the carrier body 2 is set in rotation after being introduced into the container 5.

The agitator is only switched on again after the (rotating) removal of the carrier body 2 from the container 5. If a paddle stirrer is used, suspension 4 is removed from the agitator below the paddle to facilitate stirring and is added again just above the paddle. This makes stirring much easier. In addition, the container 5 together with the agitator can be pivoted in order to simplify detachment of the particles settling on the bottom of the container 5.

In the first step of the method according to the invention, the tubular carrier body 2, provided with a cover 9 arranged on the outside thereof and fastened by means of silicone, is moved into the container 5 which contains the suspension 4. The carrier body 2 together with the cover 9 is then set in rotation along a longitudinal axis 7 of the carrier body 2 in the direction of an arrow 8. Here, the suspension 4 in the tube interior 10 is also set in rotation by the rotation of the carrier body 2 together with the cover 9, the centrifugal forces acting in the suspension 4 in the tube interior 10 of the carrier body 2 causing the particles contained in the suspension 4, in particular the sinterable material and binders, increasingly deposit on the inner wall of the carrier body 2. As a result, the coating 3 is formed. The suspension 4 in the tube interior 10 of the carrier body 2 is depleted of particles, in particular the sinterable material and binder contained therein, which only partially flow back into the tube interior 10 of the carrier body 2 from the bottom 6 of the container 5. Alternatively, it can also be provided that, in addition to the movement of the tubular support body 2, the container 5 is also rotated with the suspension 4. Will both the Carrier body 2 together with cover 9 and the container 5 with the suspension 4 contained therein in rotation, so the rotation takes place in the ratio of the container 5 to the carrier body 2 with cover 9 defined.

The duration of the rotation of the carrier body 2 including the cover 9 depends on the one hand on the type of suspension 4 used and on the other hand on the desired thickness of the coating 3. After the desired thickness of the coating 3 has been reached, the coated body 1 including the cover 9 is aligned removed from the container 5, wherein the coated body 1 including cover 9 can continue to rotate during removal. The cover 9 is then removed from the coated body 1 and the coated body 1 is dried. Drying can take place, for example, at room temperature, but it can also be provided, depending on the dependency of the suspension used, that the drying is carried out at slightly elevated temperatures in a range from about 40 ° C. to about 80 ° C. For this purpose, the coated body 1 can be dried over a drying section equipped, for example, with a continuous oven.

Finally, in the last step, the coated body 1 is sintered. The sintering conditions are selected depending on the materials used for the carrier body 2 and the coating 3. Through the sintering, the coating 3 is firmly connected to the carrier body 2. If both the carrier body 2 and the coating 3 are made of metal, the coated body 1 is sintered metallically via the coating 3 and the carrier body 2.

The sintering process carried out in the last step of the method according to the invention essentially comprises two steps, firstly the debinding of the binder used in a first step and the actual sintering process in a further step. The debinding process itself is not limited to specific time-temperature programs limits. Typically, in a debinding process, the green body is gradually heated to a temperature in a range from 280 ° C to 420 ° C at a rate of 3 - 10 ° C / min and depending on the size of the body to be sintered for a certain period of time kept at this temperature until the binder is completely removed. The coated body is then gradually heated further until the necessary sintering temperatures are reached, which depend on the material used and its grain size.

Both the debinding process and the actual sintering process can be carried out under protective gas (such as H ₂ , N ₂ , Ar) and / or mixtures thereof or in vacuo.

A coated body 1 according to the invention was produced in the form of a tube according to the method according to the invention. A porous tube with an inner diameter of 10 mm and an outer diameter of 14.5 mm diameter and a length of 1,000 mm was used as the carrier body, which is made of Cr-Ni steel powder by isostatic pressing and subsequent sintering.

The Cr-Ni steel powder Anval 316 L with a maximum grain size of less than / equal to 18 μm was used as the sinterable material in suspension 4. A mixture of 90% by weight of ethanol and 6% by weight of deionized water was also used as the solvent for suspension 4. In this 4% by weight, based on the amount of solvent and binder, polyvinyl acetate (manufacturer: Wacker-Chemie) with a molecular weight in a range from 15 × 10 ³ to 30 × 10 ³ g / mol as binder in granular form for the suspension 4 used. The mixture of the sinterable steel powder used and the solvent / binder mixture consisted of one volume of sinterable steel powder and three volumes of solvent / binder mixture. The suspension was obtained by homogenizing the individual components in a tumble mixer over a period of 4 hours.

The tube used as carrier body 2 and described above was provided on its outside with a protective tube made of steel, which was attached to the outside of the tube by means of silicone. The tube provided with the protective tube was now introduced into the container 5 without causing the tube to rotate in such a way that it is arranged perpendicularly in relation to the bottom 6 of the container 5 therein. The tube with the cover 9 was then set in rotation about its longitudinal axis at a speed of 530 rpm. After a coating time of 6 seconds, the body 1 now provided with a coating on the inside of the tube, including the cover 9, was removed from the container 5 with the suspension 4 with an export speed of 1.5 / sec while rotating at 20 rpm removed and the coating dried in a rotating manner. The cover 9 was then removed from the coated body 1 and this was dried for 30 minutes without rotation. In a final step, the body 1 thus obtained was sintered with the green compact coating at a temperature of 1,000 ° C. for 3 hours under vacuum. A partial section from a cross section through the coated body 1 obtained is shown in FIG. 2. The high uniformity of the coating 3 can be clearly seen, in particular the very uniform surface facing the tube interior 10.

3 shows a scanning step diagram from the surface of the coating 3 facing the inside 10 of the body 1 produced as described above. A Mahr Perthometer S3P was used as the measuring device with a T5 RHT 3-50 50 CAL button. The measurement was carried out in accordance with DIN EN ISO 3274. The length of the evaluated scanning distance L was 4 mm, the entire scanning distance including the lead and follow-up distances was 5.6 mm. The width of a box indicated in FIG. 3 in the horizontal direction corresponds to 250 μm, that in the vertical direction 10 μm. The surface roughness is measured in the longitudinal direction of the cut tube as produced above.

The determined average roughness value R _a corresponding to the arithmetic mean of the amounts of all profile values of the roughness profile in accordance with DIN EN ISO 4287 was determined to be 1.69 μm, the average roughness depth R _{z in} accordance with DIN 4768: 1990 and DIN EN ISO 4287 was 8.71 μm, the maximum roughness depth R_, _a -. corresponding to the greatest single roughness depth within the total measuring distance according to DIN EN ISO 4287 was 9 μm, the core roughness depth R _κ according to the depth of the roughness core profile according to DIN EN ISO 13565-1 and -2 corresponded to 6.23 μm, and the basic _{roughness depth} R _3z according to the mean value the individual roughness depths according to works standard DB N 31007 (1983) was found to be 7.92 μm.

The values for R, _-ax are preferably in a range from 30 to 70%, preferably 45 to 60%, for R _κ in a range from 10 to 50%, preferably 25 to 40%, for R _3z in a range from 40 up to 60% and for R _a in a range from 5 to 30%, preferably 8 to 20%, in each case based on the maximum grain size of the sinterable material used.

The average roughness depth R _z was thus less than 60% of the maximum grain diameter of the sinterable material used to produce the coating. The obtained porous tubular body coated on the inside was used as a filter. This resulted in an improved backwashing ability and cleanability of the filter due to the excellent surface quality. In addition, the flow resistance of the same was reduced.

Claims

Expectations

1. A method for producing at least partially coated bodies (1) with a coating (3) made of a sinterable material, wherein

in a first step, a carrier body (2) is at least partially brought into contact with a suspension (4), the suspension (4) comprising the sinterable material;

in a second step the carrier body (2) is set in rotation, the rotational speed of the rotation being in a range from approximately 80 to approximately 1,500 rpm, preferably in a range from approximately 100 to 1,000 rpm;

in a third step the carrier body (2) is removed from the suspension (4);

in a fourth step, the now at least partially coated carrier body (2) is dried; and

- In a fifth step, the coated carrier body (2) is sintered.

2. The method according to claim 1, characterized in that the body (1) is removed in the third step rotating from the suspension (4).

3. The method according to any one of claims 1 or 2, characterized in that the suspension (4) further comprises solvents, binders, stabilizers and / or dispersants.

4. The method according to any one of the preceding claims, characterized in that in a tubular body (1) this is rotated in the second step about its longitudinal axis and perpendicular to the bottom (6) of the suspension (4) receiving container (5).

5. The method according to any one of the preceding claims, characterized in that the carrier body (2) to be coated is at least partially provided with a protective cover.

6. At least partially coated body (1), produced in particular by the method according to one of claims 1 to 5, with at least one carrier body (2) and at least one coating (3) of a sintered material arranged thereon, wherein the coating (3) has an average roughness depth R _{z in} accordance with DIN EN ISO 4768, which is less than or equal to approximately 60% of the maximum grain diameter of the sinterable material used to produce the coating (3).

7. body (1) according to claim 6, characterized in that the average roughness R _{z is} preferably less than or equal to about 50% of the maximum grain diameter of the sinterable material used to produce the coating (3).

8. body (1) according to one of claims 6 or 7, characterized in that the coating (3) and / or the

Carrier body (2) is porous.

9. body (1) according to any one of claims 6 to 8, characterized in that the coating (3) has a thickness in a range from about 5 microns to about 500 microns, preferably about 20 microns to about 100 microns.

10. body (1) according to any one of claims 6 to 9, characterized in that the body (1) is tubular.

11. Body (1) according to one of claims 6 to 10, characterized in that the coating (3) is arranged only on the inside and / or the end faces of the tubular body (1).

12. Use of coated bodies (1) according to one of claims 6 to 11 as a filter element, catalyst, membrane reactor and / or friction material.