EP1689545A2

EP1689545A2 - Initial product and method for producing baked bodies for lightweight building elements

Info

Publication number: EP1689545A2
Application number: EP04819200A
Authority: EP
Inventors: Hans Schneidereit; Ralf Kretzschmar; Matthias Reinfried; Chris Kostmann; Ulf Waag; Günter Stephani; Kurt Zobel; Frank Schulze; Jörg FÄRBER
Original assignee: Glatt Systemtechnik GmbH
Current assignee: Glatt Systemtechnik GmbH
Priority date: 2003-11-21
Filing date: 2004-11-21
Publication date: 2006-08-16
Also published as: WO2005051575A2; WO2005051575A3; DE10355298B4; DE10355298A1

Abstract

The invention relates to an initial product and method for producing baked bodies for lightweight building elements, in particular metal and metal alloy elements. The aim of said invention is to produce low-cost baked lightweight building elements ensuring the resistance thereof in a reproducible form. For this purpose, the initial product for producing the inventive baked bodies is embodied in such a way that a first layer consisting of a sintered powder and a first organic binder/binder mixture is formed directly on a core. A second layer consisting of a sintered powder and of a second organic binder is applied to said first layer, said organic binder being activated and/or plastically/elastically shaped in such a way that at least a temporary integral joint is formed between the initial products.

Description

Preliminary product for and process for the production of green bodies for ^* sintered lightweight components

The invention relates to precursors for green bodies from which sintered lightweight components can in turn be produced, and to a method for producing green bodies. It is particularly suitable for lightweight components made of metals or metal alloys.

From EP 0 300 543 AI it is known to produce metallic or ceramic hollow spheres. A coating is applied to particles of foamed polymer. The coating should be formed from a suspension in which a binder and metallic and / or ceramic particles are contained.

The binder can also be contained in the suspension in dissolved and / or colloidal form. It should only take into account the respective powder material and the resulting requirements for a subsequent one Pyrolysis and sintering can be selected.

The coated and dried particles are then pyrolyzed at temperatures between 200 and 600 ° C. in order to drive off the organic components. Subsequently, the green solid spherical particles can be further processed into hollow spheres by sintering.

In this prior art, however, it was also pointed out by way of example that foam balls coated with an iron or aluminum oxide powder and binder mixture can be introduced into a plate-like shape. The filled form should then be in boiling water for you

Period of about 2 minutes. Water can get into the mold through holes. The foam balls should be re-foamed by the heating. After the mold has cooled, a body should be able to be removed, which after a

Drying can be pyrolyzed and sintered. After sintering, an iron or aluminum oxide sponge body is said to have been produced, which has good strength and is light.

However, it has been shown that sintered lightweight components cannot be manufactured with sufficient strength and economically cheap.

This means that lightweight components can also be made from sintered ones

Hollow balls are produced, which have been integrally connected. Here, however, the hollow spheres, which are in themselves manufactured, must be brought into the desired shape of the respective component. Thereafter, additional measures, which usually result in energy consumption, must be carried out the, which leads to increased manufacturing costs and expenses.

This also applies to the manufacture of lightweight components from coated polymer cores, which are shaped and subsequently debindered and sintered as a whole. This increases the time required for production. Immersion in water leads to a major change in the shell composition and a change in shell thickness and shell homogeneity. In concrete terms, this means that in the connection areas of hollow balls sintered together, different strengths within a lightweight component produced in this way have to be accepted. Furthermore, the drying of the water-soaked samples requires very long process times due to the poor flow, especially with balls with a diameter <3mm.

It is therefore an object of the invention to make the production of sintered lightweight components more cost-effective and to ensure the strength of such lightweight components in a reproducible form.

According to the invention, this object is achieved with preliminary products according to claim 1, from which green bodies can be made available for lightweight components which can be produced by sintering, and the method for producing green bodies according to claim 9. Advantageous refinements and developments of the indication can be achieved with the features specified in the subordinate claims.

The precursors according to the invention for the production of green bodies, from which they are then removed by sintering. term lightweight components can be made from a core. There is a first layer on the core. This first layer is formed from a sinterable powder and a first organic binder / binder mixture. This layer can be applied to a core, which is preferably formed from a foamable polymer, such as polystyrene, using conventional techniques. The application can be done, for example, by spraying. Sinterable powders can be suitable metals, metal alloys and ceramics.

Possibly . after drying, a second layer is then applied to the first layer as an overcoat. The overcoat is also formed from sinterable powder and a second organic binder. The second organic binder differs from the binder / binder mixture of the first layer and is characterized by an energy input, e.g. activated by the influence of a heated fluid and / or deformed plastically / elastically. With this property, the preliminary products according to the invention can be cohesively connected to one another and form green bodies. The energy input can also be achieved using a microwave.

An activatable binder can, for example, polymerize or further polymerize with appropriate heating, or crosslink a binder formed from several components.

In the case of plastic / elastic deformation of such a binder, a cohesive adhesive connection of preliminary products can be formed.

The binders for the overcoat should be be chosen so that they can be effective with a low energy input.

Binders suitable for the first layer, which can be used alone or as a mixture, are polyvinyl alcohol, binders based on cellulose (e.g. Tylose), polyvinyl pyrolidone (PVP) or polyvinyl butyral (PVB).

Acrylates, waxes, multiple alcohols or a polyglycol can advantageously be used to form the overcoat.

The consistency of the overcoating of preliminary products according to the invention has an advantageous effect on the strength in the formation of lightweight components during their sintering. The consistency of the overcoating of preliminary products according to the invention has an advantageous effect on the formation of lightweight structural elements in the green state and on their sintering

Strength. The overcoating runs off into the contact points and menisci are formed, regardless of any previous deformation of the green balls. This process can also occur during debinding and leads to the same effects. Since the overcoating contains sinterable powder, the menisci formed in the green state or during debinding after sintering form meniscus-shaped transition regions between the now sintered spheres, regardless of the previous degree of deformation of the green spheres, which make a significant contribution to strength. Compared to the known state of the art, the processing of the green spheres into shaped bodies only results in a change in the overcoating, which has a positive effect on the shaped body properties. The same layer of sinterable powder can be contained in the first layer and in the overcoating, wherein the same grain sizes or different grain sizes can also be selected in the first layer and overcoating.

Suitable metals or metal alloys can be used as powder. In particular, the first layer can also be used for the respective sinterable ones

Powder suitable sintering additives and possibly alloying elements may be included.

However, a sinterable powder other than that contained in the overcoat can also be contained in the first layer. With the different starting powders, metal alloys or intermediate metals (e.g. aluminides or suicides) can then form the supporting structure of a lightweight component during sintering for the completion of lightweight components.

However, lightweight components made of iron or iron alloys can also be produced if suitable starting powders are used in the first layer and in the overcoat.

The preliminary products can also be designed in such a way that the core has a cavity which is enclosed by a polymer or the core itself is designed as a cavity which is enclosed by the first layer.

The proportion of sinterable powder which is contained in the overcoating in relation to the binder should advantageously not be greater, but preferably less, than the proportion of sinterable powder contained in the first th layer is included.

Advantageously, the preliminary products according to the invention have a spherical surface and spherical to ellipsoidal shape, which is used in the production of the

Grünkδrpers and a finished lightweight component can also be maintained. However, deformation of the hollow spheres is also possible. A lightweight component formed from such hollow spherical particles connected by sintering has, in particular, mechanically favorable properties for many applications.

However, there is also the possibility of producing a lightweight component from preliminary products which, at least in some areas, has cells which deviate from the spherical shape and which can be formed by plastic deformation of preliminary products in the production of green bodies, which will be discussed in more detail below.

Such cells of a lightweight component deviating from the spherical shape can be arranged, for example, on surfaces or in the area of lightweight components close to the surface, so that a corresponding one

Surface formation of lightweight components can be achieved.

For the manufacture of green cores, the procedure is such that the preliminary products described are filled into a mold. Subsequently, a heated gas, preferably air or steam, preferably water vapor (increased heat capacity) is passed through openings formed on the mold, so that it flows through the cavities between the preliminary products. This involves heating, which vation and / or the plastic / elastic deformation of the binder of the overcoat. Hot gas or steam flows directly along the surface of the overcoat, so that the required temperature increase can be achieved very quickly.

The temperature should be between 40 and 200 ° C, preferably between 80 and 120 ° C.

After a specific temperature for the binder of the overcoating has been set over a correspondingly long period of time (usually a few minutes), during activation and / or deformation, cooling takes place, which results in a cohesive connection of the parts in contact Contact leading intermediate products.

Now the green body formed from the interconnected intermediate products can be removed from the mold and, if necessary, sintered after drying to form a finished lightweight component, whereby conventional sintering technology can be used, taking into account the respective sinterable powders.

It is advantageous to arrange the one or more molding tools in a chamber. The hot gas or steam can be so easily compared to that

Ambient pressure, increased pressure, for example 0.5 to 2 bar, flow into the mold so that the entire mold volume flows through and all surface areas are safely reached. The gas or steam flow should at least from two sides in counterflow through appropriately arranged openings inflow at the mold.

A chamber for receiving molds can also have an advantageous effect on accelerated cooling of the green body. Thus the chamber can be operated with negative pressure, for example at 0.7 bar.

To accelerate the cooling, a coolant can also be introduced into the chamber alone or in addition, or the mold can be flowed or sprayed on from the outside.

The molds can be made from a suitable metal with one or more negative mold (s) for green bodies. They should be made up of at least two parts for opening and closing the molding tool. Options for the use and / or the attachment of core elements to the molding tools should advantageously be available in order to be able to form different geometries on green bodies.

However, the molding tools can also be designed such that a compressive force can be exerted on the preliminary products contained therein, which leads to a plastic deformation of preliminary products during the production of green bodies, which is then also retained in the finished sintered lightweight components, as previously has already been addressed.

However, the same effect can also be achieved on its own or in addition by means of preliminary products, the polymeric core of which still contains a proportion of a propellant gas, which leads to post-foaming with an accompanying increase in volume of the cores in the mold when heated. This creates a plastic deformation of the preliminary products, which is retained after the green bodies have cooled and also after the sintering. In this form, compressive forces also act on the substances and powders forming the first layer and the overcoating.

Since the first layer and the overcoating have a minimum degree of viscosity at the temperatures in question, the powder components also flow, which leads to an equalization of the

Wall thickness also leads to plastically deformed areas of primary products, which is also retained in the finished sintered lightweight components.

The invention will be explained in more detail below with the aid of examples.

example 1

One liter of styrofoam balls with an average diameter of 3.82 mm were coated with a metal powder suspension consisting of 200 g of carbonyl-Fe powder and a binder content of 8 g of polyvinyl alcohol and 2 g of tylose. Then an overcoating consisting of 100 g carbonyl-Fe powder and

20 g of acrylate sprayed onto the already coated balls.

The balls coated in this way are filled into a two-part shaping tool by means of a filling injector, a gap width, set by means of a closing plate, of 3 mm remaining between the mold halves. The filled tool was then subjected to saturated steam with an autoclave steam pressure of 1 bar for 5 s and the 3 mm wide gap between the

Tool halves were closed and the tool then steamed for 1 s. After cooling the tool to approx. 30 ° C, the tool was opened and the molded part removed.

In a subsequent heat treatment at 1120 ° C / 60min / H2, the molded part was debindered and sintered.

Example 2

One liter of styrofoam balls with an average diameter of 1.97 mm were coated with a ceramic powder suspension consisting of 100 g of Al ₂ O ₃ powder and a binder content of 4 g of polyvinyl alcohol and 1 g of tylose. An overcoating consisting of 40 g of Al ₂ O ₃ powder and 5 g of acrylate was then sprayed onto the balls which had already been coated.

The balls coated in this way are filled into a two-part shaping tool by means of a filling injector, a gap width of 1 mm, set via a closure plate, remaining between the mold halves. The filled tool was then subjected to saturated steam with an autoclave steam pressure of 1 bar for 8 s and the 1 mm wide gap between the tool halves was closed and the tool was then steamed for 0.5 s. After cooling the tool to approx. 30 ° C, the tool was opened and the molded part removed.

During a subsequent heat treatment at 1900 ° C / 60min / air, the molded part was debindered and sintered.

Claims

claims

1. Preproduct for the production of green cores for sintered lightweight components, in which a first layer, which is formed from a sinterable powder and a first organic binder / binder mixture, is formed on a core; a second overcoat formed from a sinterable powder and a second organic binder is formed on the first layer; wherein the second organic binder can be activated and / or plastically / elastically deformed by an energy input for the formation of an at least temporary integral connection of preliminary products.

2. Preproduct according to claim 1, characterized in that the core is formed from polystyrene.

3. intermediate product according to claim 1 or 2, characterized in that the core has a cavity.

4. Pre-product according to one of the preceding claims, characterized in that the sinterable powder (s) is / are a metal or a metal alloy.

5. Pre-product according to one of the preceding claims, characterized in that the proportion of the sinterable powder in relation to the proportion of binder in the overcoating is ≤ the proportion of sinterable powder in the first layer.

6. Pre-product according to one of the preceding claims, characterized in that the organic binder mixture, the first layer, is formed from polyvinyl alcohol, a binder based on cellulose, polyvinyl pyrolidine and / or polyvinyl butyral.

7. Pre-product according to one of the preceding claims, characterized in that the binder for the overcoating is an acrylate, a wax, or a polyglycol.

8. intermediate product according to one of the preceding claims, characterized in that the intermediate product has a spherical surface.

9. A process for the production of green cores for sintered lightweight components using preliminary products according to one of claims 1 to 8, characterized in that preliminary products are filled into a molding tool, energy is introduced into the filled molding tool, the binder of the overcoating being activated and / or plastically / becomes elastically deformable; and by subsequent cooling, a cohesive connection of the preliminary products forms a green body of interconnected preliminary products, which is removed from the mold.

10. The method according to claim 9, characterized in that the energy input with heated gas or steam, the / through openings formed in the mold in the mold and flows through cavities between intermediate products.

11. The method according to claim 9, characterized in that the energy input takes place with the energy of microwaves.

12. The method according to claim 10, characterized in that the gas or the steam is introduced into the mold with a pressure which is higher than the ambient pressure.

13. The method according to any one of claims 9 to 12, characterized in that the pressure within a chamber in which the mold is accommodated is reduced during cooling.

14. The method according to claim 13, characterized in that the pressure is reduced to below the ambient pressure.

15. The method according to any one of claims 9 to 14, characterized in that hot air or steam with a temperature between 40 and 200 ° C is introduced into the mold.

16. The method according to any one of claims 9 to 15, characterized in that hot air or steam is introduced into the mold from at least two sides in countercurrent.

17. The method according to any one of claims 9 to 16, characterized in that a pressure force is exerted on the preliminary products in the mold during the heating.

18. The method according to claim 17, characterized in that the preliminary products are plastically deformed.

19. The method according to claim 16 or 17, characterized in that by means of polystyrene contained in preliminary products, which still contains a proportion of propellant gas, a post-expansion of the core and a plastic deformation of preliminary products in the mold is achieved.

20. The method according to any one of claims 9 to 19, characterized in that the demolded green body is dried.