EP0977909B1 - Thin, fine pored metal layer - Google Patents

Abstract

The invention relates to a metal layer with open porosity and with a maximum thickness of 500 mu m, whereby the diameter of the through pores is at most a twelfth of the thickness of the layer. In order to produce a metal layer with open porosity, a suspension containing metal powder, dispersant as well as substances for adjusting the viscosity is deposited in layers on a support, dried and then sintered. The thickness of the suspension layer deposited on the support must be such that the thickness of the metal layer after sintering is at least three times the diameter of the metal powder.

Description

The invention relates to an open metal layer Porosity.

Porous metal layers consisting of fabric and nonwoven are known of the type mentioned, in particular can be used as a filter.

In the case of filters, small layer thicknesses should be aimed at to minimize unwanted flow resistance. It are about 100 µm thin, metallic fabric Filters, which are then disadvantageously proportionate have large pores. Also need to manufacture accordingly thin and therefore expensive wires used become. The fabrics made from it are consequently also correspondingly expensive.

If a metallic fleece is used, it can small pore sizes in the micrometer range can be achieved. Then the fleece thickness is at least one half a millimeter. The layer thicknesses of the aforementioned Furthermore, nonwovens cannot be manufactured very precisely. Relatively large tolerances have to be accepted become.

As an alternative to metal, a. Ceramics and plastics used as filter materials. Ceramic filter are also relatively thick, however, and it occurs a correspondingly large flow resistance. Also ductility is not guaranteed. For many purposes further represents the brittleness of the ceramic Material is a disadvantage.

If plastic is used as filter material, so are no increased operating temperatures possible. For some Plastic is not a suitable filter material for application purposes because it does not meet the requirements can be sterilized, e.g. B. in medical or required in the food sector are. The filter can be used again Cases not possible.

EP 570 889 67 describes a process for the production a porous layer on a metal surface, where a mixture of binder, metallic Powder and brazing filler made of metal powder with specific grain size as a suspension on the metal surface is applied. This will then heated and sintered.

DE-A 2 323 878 describes a method for coating described a metal substance. This will start with a binder solution with volatile and low volatility Components applied to the metal substrate. Subsequently we applied metal powder to this layer. First, the volatile components evaporated. Then, by heating too the volatile components evaporate. Another Heating leads to the formation of one with the metal substrate connected porous metal layer.

From US-A 3 855 638 is a surgical metallic Known prosthesis with a porous metallic layer. The pores forming the space are included larger than 20 µm, but advantageously a maximum of 50 µm in size. The layer thickness varies from 100 µm to 1000 µm. For the preparation will contain an aqueous slurry Metal powder and binder, on the metallic Prosthesis applied, heated to remove the water, and then sintered, the organic Binder is driven out.

A method is also known from FR-A 2 520 265 for the production of a particle-bound heat pipe wick on inner walls of a heat pipe. In doing so the particles, e.g. B. +325 stainless steel microspheres up to -100 mesh (44 - 149 µm) in a suitable diameter Binder solution suspended and on the heat pipe wall painted. The binder is at 400 ° C evaporated under reduced pressure. Subsequently the green layer thus obtained is at 1250 ± 50 ° C for Sintered for 2 hours.

The object of the invention is to produce a temperature-resistant, sterilizable, simple and reproducible metal layer to be produced with continuous Porosity that is ductile, mechanically stable and elastic is and at - if they are used as a filter will occur - low flow pressure losses. Microfiltration tasks with the metal layer are also intended can be perceived.

The object of the invention is achieved by a maximum 500 µm thick metal layer, in other words through solved a metal foil that has an effective pore diameter has up to a twelfth, preferably up to a fifteenth of the layer thickness of the Metal layer. The channels are here as pores to understand who is going through the layer Create open porosity. Occasional "cavities" due to inhomogeneities there are no pores in the The meaning of the claim.

The aforementioned cavities due to inhomogeneities Experience has shown that it does not matter if the layer thickness one according to the invention from particles or from powder produced porous layer at least three times is larger than the average particle diameter. Becomes the sophisticated layer of particles or powders produced according to the invention, the effective Pore diameter in particular up to a quarter, preferably up to a fifth of the average particle or powder grain diameter of the used Powder.

For example, there is a 500 µm thick metal layer before, the effective size of the pores is the cause continuous (open) porosity, up to 500/12 mm, i.e. up to approx. 40 µm. Expressed differently this means that substances smaller than approx. 40 µm to be able to pass through the metal layer.

Was a metal layer from powders size 50 microns Made according to the invention, the layer thickness should at least three times as thick as the powder diameter, So be at least 150 µm to inhomogeneities cavity problems due to the material are reliable to avoid. The effective pore diameter of the The layer is then regularly up to 50/4 µm (3 * 50/12 µm), preferably up to 50/5 µm (3 * 50/15 µm).

In an advantageous embodiment of the invention the layer thickness of the metal foil maximum 100 µm, preferably not more than 50 µm. The effective pore size in the aforementioned sense is maximum in all cases 1/12 of the layer thickness.

The metal allows elevated temperatures, behaves ductile, mechanically stable and elastic. About that the material can also be easily sterilized. The Layer thickness of the layer or film can be compared to a fleece or a fabric within narrow tolerance limits getting produced. The manufacture is also special inexpensive compared to a fabric.

The layer consists of metals that are sinterable are. Metals that have this property in mind of the claim, form during a sintering process Sintered bridges between individual metallic Powder grains. Steel, stainless steel, bronze and Nickel form sintered bridges in the aforementioned sense. These are better than reactive metals like aluminum and titanium sinter.

The sophisticated metal layer can be characterized by film casting known in the ceramic field become. For this, a pouring slurry is first in other words, a suspension is provided. The Slurry has metal powder. The average diameter of the metal powder is less than a third the layer thickness to be produced.

The ratio of metal powder to layer thickness ensures that the layer consists of several layers There are powder grains. So are going through the layer Avoided "holes" that are significantly larger than the desired effective pore size. The more Layers of powder are possible, the more reliable kicking no "holes going through".

Disadvantageously increases with the number of powder layers Flow resistance too. According to the current state of knowledge a metal layer should therefore preferably consist of 5 to 10 Powder layers should be built up.

In addition to the powder, the slip consists of a solvent, Dispersant, binder and if necessary from a substance to adjust the viscosity of the slip to an applied pouring or spraying device.

For example, the thinner the pouring slot in one pouring device used, the thinner must be the slip. This adjustment is made if necessary through the substance to adjust the viscosity.

Isopropanol is particularly suitable as solvent, but also toluene, water etc. Can be used as a dispersant Phthalic acid bis (2 ethylhexyl ester) can be used. For example, polyvinyl butyral is suitable as a binder. As a substance to adjust the viscosity to equipment Conditions can be used fish oil.

When selecting the slip, make sure that that the subsequent sintering interferes as little as possible becomes. Carbon, oxygen or nitrogen are allowed in the sintered product therefore in not too high concentrations occur. Are oxide, carbide, nitride formations to avoid during sintering. The slip should therefore consist of substances that are used for compliance of the above requirements thermally light are decomposable.

If a self-supporting layer is to be produced, then the slip preferably also contains a release agent like polyethylene glycol. The release agent causes a dried one made from the slip Layer of a carrier sufficiently uncomplicated can be solved.

The slip is applied in layers on a carrier. As a carrier z. B. a plastic or metal foil.

The slip is dried and removed from the carrier, or detached if a self-supporting metal layer to be manufactured. Then this green compact sintered.

Alternatively, the sophisticated, porous metal foil by means of the spray process known from DE 41 20 706 made from the suspension, i.e. from the slip become.

The layer can in an advantageous further process step be calibrated by rolling. On in this way, for example, a 117 µm thick film rolled to exactly 100 µm thickness. The metal layer can be produced reproducibly in terms of its thickness become.

Alternatively, the pore size can be rolled defined shrink. It can have a defined pore size be produced reproducibly. The flow resistance or the flow rate is consequently at the layer produced according to the method can be calibrated.

The demanding layer can be used as a filter, for sound insulation purposes or used with flame arrestors become.

In a further embodiment of the invention Layer firmly connected to the inner wall of a pipe. The tube is continuously porous and can, for example can be used as a filter. The effective pore size in the tube is then preferably larger than that of the metallic Layer to low flow resistance to get. The tube then acts as a carrier.

To manufacture such a tube with a porous inner layer z. B. first a suspension (slip) as produced in DE 41 20 706. This suspension will dosed in a rotating, depending on the application Porous tube fed. By rotating the pipe becomes the suspension evenly and in layers on the Separated inside wall. During the rotation process dries the suspension. Is the desired layer thickness reached, the supply of the suspension is stopped. As soon as the drying process is finished the rotation ends. Then the pipe with the dried suspension, i.e. with the green body sintered.

In an advantageous embodiment of the above Manufacturing process is in the case of a porous tube this sealed from the outside. This prevents that excess suspension penetrate into the pores of the tube can if this is larger than the powder diameter are.

In a further advantageous embodiment of the The suspension is processed using a tube fed into the tube with the open porosity. The The tube is moved in a defined manner in the tube. To this Wise is an even distribution of the suspension ensured in the pipe.

In an alternative embodiment of the method a spray head is inserted into the pipe. The spray head or the pipe rotates. In this way, the Sprayed inside walls of the pipe. This procedure corresponds the spray process known from DE 41 20 706. It is particularly useful for pipes with an inner diameter of more than 50 mm.

In the figure, a pipe wall 2 is shown in sections open porosity shown in cross section, on the according to the process a metal layer 1 as an inner coating has been applied. The inside coating is in in the manner shown in the figure, a maximum of 500 µm thick.

The invention is illustrated by the following examples explained in more detail.

For the production type "film casting" is a slick manufactured with the following components:

Weigh in 100 g of stainless steel powder, average powder diameter ≤ 16 µm 14.4 g toluene 26% by weight isopropanol 3% by weight methyl ethyl ketone 1% by weight 0.56 g Polyvinyl butyral - 98 1.0 g Polyethylene glycol - 400 1.0 g Phthalic acid bis - (2 ethylhexyl ester)

The sample is mixed for 2-2.5 hours, e.g. in the tumble mixer and then immediately on a film casting bench poured to thicknesses of e.g. 60 µm, 120 µm or thicker (tested up to 400 µm).

After drying (approx. 3 h) and stripping the layer, the sintering process follows. Here, sintering was carried out at 950 ° C for 1-3 hours in a vacuum (<10 ^-2 mbar), argon or argon + 4% by volume hydrogen in a tube furnace. The product is a flexible, porous metal foil with a relative density between 55% and 69%. The pore maximum for the powder mentioned is about 5-7 µm in diameter.

For a production by means of that known from DE 41 20 706 The spray process is first the spray suspension by mixing binder solution and powder in Ratio 2: 1 (vol. Shares) produced. As a binder solution became a 9% (wt%) shellac ethanol solution used and as a metal powder a gas atomized 316 L stainless steel powder with a grain diameter <16 microns.

After about 8 hours of homogenization in the tumble mixer, the The suspension is sprayed directly into a suitable system become.

This is done by spraying 50 - 200 µm thick Layers on polyethylene foils (PE-HD 0.2 mm).

After drying (5-10 min) the desired film shape cut out with a punching or cutting tool: here Ø 93 mm with punching tool. After 1-2 Hours of drying time (here 2 hours) is the PE film from peeled off the green sheet. The sintering was carried out at 950 ° C, Carried out in vacuo for 1 hour. The product has one relative density of 63% and a pore maximum at approx. 6 microns.

For an inner coating of porous carrier tubes, stainless steel 316 L, Ø _{powder grains} <5 µm was used as the powder material. The binder solution is a 9% shellac solution (shellac ethanol). The spray suspension consists of a mixture of powder and binder solution in a ratio of 1: 2.

Powder and binder solution are homogenized in a tumble mixer for 8 hours. For the internal coating, the pipe to be coated (here Ø _i = 15 mm, length = 400 mm) is set in rotation (here approx. 60 revolutions / min) and suspension is metered into the pipe via a dosing head (Ø 3 mm) that can be moved at constant speed , After a drying time of approx. 5 minutes, the tube is inserted into the sintering furnace and sintered at 950 ° C. for 1 hour in a vacuum. Inner coatings with porosities between 30 and 50% were produced in a thickness range between 20 and 300 µm.

Claims (5)

1. Method for producing a sintered metal layer with open porosity, with the following steps:

   a suspension comprising metal powder, dispersant and substances for adjusting viscosity is applied in the form of a layer to a substrate,

   the thickness of the layer of suspension applied to the substrate is chosen so that the thickness of the metal layer after sintering is at least three times the mean powder diameter of the metal powder,

   the suspension is dried on the substrate,

   the dried metal layer is stripped from the substrate prior to sintering,

   the metal layer is sintered.
2. Method for producing a metal layer with open porosity on the internal wall of a tube which has through-going porosity, with the following steps:

   a suspension comprising metal powder, dispersant and substances for adjusting viscosity is applied in the form of a layer to the internal wall of a tube,

   the thickness of the layer of suspension applied to the internal wall of the tube is chosen so that the thickness of the metal layer after sintering is at least three times the mean powder diameter of the metal powder,

   the suspension is dried and then sintered.
3. Method according to the preceding Claim wherein the tube rotates during application and drying of the suspension.
4. Method according to either of the preceding Claims 2 and 3 wherein the external wall of the porous tube is sealed with a sealing medium until the suspension is dried.
5. Metal layer with open porosity, obtained in accordance with any one of Claims 2 to 4, and with a maximum layer-thickness of 500 µm, wherein the effective diameter of the through-going pores is not more than one twelfth of the layer-thickness, the metal layer being formed as the internal wall of a tube with through-going porosity.

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