DE1817588A1 - Aluminium oxide rich powder composition for - die casting process - Google Patents

Abstract

The powder mixture containing a plasticiser is suitable for the production of dies which are sintered at high temp. The powder grains are first coated with a polar substance, e.g., aliphatic carboxylic acids, aldehydes or alcohols to which the plasticiser is added. Suitable plasticisers may be oils, greases, waxes and/or synthetic resins, which on drying, may be hardened by the action of a gaseous compd.

Description

Process for the manufacture of materials suitable for the injection molding process powder metallurgical masses.

The invention relates to a method for producing for the injection molding process suitable powder metallurgical masses.

Powder metallurgical masses are understood in a broader sense the following masses: 1. masses of metal powders 2. masses of hard materials 5. masses from a mixture of both groups of substances.

These powdery starting materials are used to make it under Applying high temperatures to sintering moldings, which to a large extent and for the most varied of applications have found their way into technology. Of the The intended use is largely dependent on the material composition of the starting powder certainly.

Metals resistant to high temperatures belong to the masses of the first group such as molybdenum and tungsten, metals of the iron group for the production of sintered iron or sintered steel or copper or aluminum powder.

The second group, the hard materials, mainly includes the high-melting point Carbides and nitrides, but especially oxides, especially high-purity aluminum oxide. Moldings are made from starting powders such as tungsten carbide, boron nitride and aluminum oxide made of great hardness and density, because of their high wear resistance for example as materials for cutting tools, drawing cones for wire drawing, Thread guides in the textile industry, mechanical seals, etc. increasing use Find. Moldings made from sintered aluminum oxide find their additional good insulation properties and their resistance to chemically aggressive substances in particular also used in electronics and pump construction.

The third group is mainly known as cermets and made possible by the most varied combinations of materials the first two groups also have a combination in the properties of the finished sintered molded body and thus enables extensive adaptation to the respective Intended use. For example, the thermal shock resistance of moldings can be determined made of high-purity aluminum oxide by adding metals, which is of considerable importance for turbine blades, for example.

The disadvantage of these very high quality materials is that they are in are complex and therefore expensive to manufacture. With moldings of simpler geometric shape is generally the powdery starting material, optionally with the addition of lubricants, pressed into moldings, which are then added after the fire high temperatures, depending on the used starting material can be up to 20000C, can be ground to the desired shape and size. But this grinding work in particular is very complex, since it is especially important for very hard and dense sintered products because of the great hardness of the shaped body diamond tools must be used. In the case of moldings with a very complex geometric shape is the process of pressing and subsequent grinding to the desired shape not feasible anyway.

So you have to be proportionate. tried this powder metallurgy early on Masses, similar to what is known from injection molding technology for plastics, to deform after the injection molding process, so that after the fire only one more little grinding or polishing work, for example for deburring or other purposes Eliminating bumps is required.

In order to be able to spray these powder metallurgical masses at all, they become plasticizing substances such as oils, waxes and more recently in particular synthetic resins added and the mixture under pressure and heating in injected into the cavity of the corresponding matrices. It shows, however, - that the even distribution between the plasticizing substance and the powder very difficult, especially when very finely divided powder with a grain size Bt for example below 2 P should be sprayed. Just However, these fine-grained powders result in the highest quality sintered products with one microcrystalline grain base, which is crucial for optimal mechanical strength Influence is.

The disadvantage of such an uneven distribution of the platifying agent, which cannot be completely avoided even by kneading Bo for a long time, lies in that in many cases the moldings obtained have larger pores and gaps and then the high stresses they are subjected to for the purposes mentioned above are exposed, do not withstand.

The object of the invention is therefore to provide a method for manufacturing to find powder metallurgical masses suitable for the injection molding process, that does not have these disadvantages and as evenly as possible for each individual grain supplies necessary proportion of plasticizer.

According to the invention, this object is achieved in a method of manufacture of powder metallurgical masses suitable for the injection molding process, in particular Alumina-rich masses with plasticizing additives for the production of moldings, which are sintered to moldings at high temperatures, thereby dissolved and the Above mentioned disadvantages avoided that the powder grains on their surface first of all, it is coated with polar substances and then the plasticizing substance is admixed.

With the inventive addition of polar substances to the powdery Starting material is achieved that the powder grains with a layer of this coating polar substances, which are generally only the thickness of a molecule, and that the powder grains so coated then probably interact with the plasticizers step and so an extremely even and fine distribution is achieved. The function is that used according to the invention polar Fabrics are twofold: First of all, they ensure a very even division the mass into individual powder grains and then for a uniform Distribution of the powder grains so coated in the plasticizer. The thus obtained very uniform mass is ideal for injection molding and results in very uniform briquettes that are free of pores and hairline cracks after sintering etc. Mistakes are.

For the coating of the powder grains, organic ones are preferred Compounds, in particular aliphatic carboxylic acids, aldehydes or alcohols use, such as palmitic or stearic acid and the lower types of polymerization of vinyl alcohol. Bifunctional polar substances that plasticize with the active substances can interact and thus act as a mediator cause between the inorganic starting material and the plasticizer. Such bifunctional substances are, for example, dicarboxylic acids, such as Fumaric acid, the half-esters of such dicarboxylic acids or oxycarboxylic acids. The wrapping the powder grains are expediently in liquid suspension. With higher fatty acids As a coating agent, these are dissolved in benzene, for example, the powder grains suspended in this solution and shaken for as long, expediently several hours, until the powder grains are provided with a molecular layer of the coating agent are. The amount of coating agent is approximately 1 percent by weight of that used Powder.

As plasticizing substances, oils, fats, Waxes or synthetic resins, expediently the first-mentioned substances also in a mixture used with synthetic resins. Quantity and selection of the plasticizing substances depend largely on the conditions under which the injection molding process is carried out , but in particular also on the nature of the powder, such as its specific Surface. By weight it becomes about 8 to 15 weight based on the weight of the powder added to plasticizer. In general, such molded articles are so manufactured that after shaping by the injection molding process and drying at temperatures up to 300 ° C the moldings at relatively low temperatures first be subjected to a pre-firing, for example in the case of noses rich in aluminum oxide a fire at 800 - 12000C in an oxidizing atmosphere. That way before the dense sintering process, the last traces of organic matter, which for the most part Part has already escaped during the drying of the molding, removed so that imperfections can be avoided in the sintered product. Then the briquettes are subjected to the final sealing firing subject, which in the case of aluminum oxide powders at temperatures above 1400 C, in in some cases at 1800 to 20000C.

With metallic powders, such a fire would understandably- lead to the oxidation of the finely divided powder and the enveloping substance becomes therefore expelled under another suitable atmosphere, for example by water substance or cracked gas (mixture of hydrogen and nitrogen), these -e gases can be used in excess and thereby safely remove the organic substances.

The plasticizing agents should be selected so that they do not become so soft with increasing heating that the molding collapses in itself.

A particularly advantageous embodiment of the method according to the invention is therefore that the plasticizing substances during drying of the molding are hardened by gaseous compounds.

For example, when using phenoplasts as plasticizers Hydrogen chloride or ammonia, formaldehyde or mixtures of the last two mentioned Gases are used, especially in compounds that contain these substances when heated separate in gaseous form, so that the hardening process takes place over a longer period of time extends and with a temperature-related increasing softening of the plasticizing agent the hardening process goes hand in hand, i.e. a collapse of the molding is avoided will.

The inventive method is for all powder metallurgy rule Wet materials such as metals, carbides, nitrides, silicides and oxides are particularly suitable but for masses based on alumina, because alumina especially too thixotropic processes and thus a uniform distribution and compression Opposes considerable resistance during the spraying process. The invention therefore becomes described in more detail below using an example made of aluminum oxide masses.

Example: 100 g Aluniiniumx> iidpu1ver with an A12D3 content of 99.4% with 300 ml of a 3% solution of stearic acid in benzene for 5 hours shaken at room temperature, the suspension thus obtained then dried by spray drying and 10% by weight of a plasticizer Base of a phenol-formaldehyde precondensate mixed in a kneader and at a At a temperature of 150 ° C. and under a pressure of 1000 kgf / cm², it was injected into an injection mold.

The molding obtained in this way is dried at a temperature of 300.degree and then at a temperature of 1200 ° C. in an oxidizing atmosphere pre-burned.

This pre-firing is followed by the sharp firing at one temperature from 18u00C and a burning time of 50 minutes.

Claims (1)

Claims S Process for the manufacture of materials suitable for injection molding powder metallurgical masses, in particular masses rich in aluminum oxide with plasticizing Additives for the production of moldings, which are molded at high temperatures are sintered, characterized in that the powder grains on their surface first covered with polar substances and then the plasticizing substance is admixed. 2. The method according to claim 1, characterized in that for the Coating of the powder grains aliphastic carboxylic acids, aldehydes or alcohols use Find. 5. The method according to any one of claims 1 or 2, characterized in that that bifunctional polar substances are used with the plasticizing acting substances can interact. 4. The method according to any one of claims 1 to 5, characterized in, that as plasticizing substances oils, fats, waxes and / or synthetic resins Find use. 5. The method according to one of claims 1 to 4, characterized in that that the plasticizing substances when drying the molding by gaseous Connections are hardened.