DE3608095A1 - Process for the production of sintered shaped parts - Google Patents

Abstract

Process for the production of components with a complex shape, such as turbine blades or wheels made of metal or ceramics by pressure diecasting using especially suitable binders.

Description

Process for the production of sintered molded parts

Technical Field: The invention relates to a method of manufacturing of sintered metal or ceramic parts by injection molding a mass that contains a strippable binder and optionally a lubricant.

State of the art: Known methods comprise the following steps: - Mixing the sinterable metal or ceramic powder with a binder, see above that an injection-mouldable mass is created.

- Injection molding of the mass to form the molded part - Driving the binder out of the molded part by means of a first heat treatment - Sintering of the resulting blank to the finished part - If a density close to 100% of the theoretical density is required in the finished part, hot iso- Static recompression The following binders are used: a) Thermoplastics (e.g. polyethylene, polyethylene waxes, paraffin waxes, cellulose and their derivatives, polyamides, polyaeryls, styrenes) b) Duroplasts, epoxies, polyimides, polyesters, phenol-melamine-resorcinol resins c) Mixtures from groups a) and b) The following properties of the binder are particularly important for the production of molded parts by injection molding: - Good flowability even with small proportions of the binder in the mass - Achieving good dimensional stability in the molded part during heating - Complete The binder can be removed by baking, leaving an adjustable amount of free carbon behind. Disadvantages of the known binders: Group a) These binders have the advantage of good flowability and are usually completely removable. The disadvantage of this group is that only a low degree of dimensional stability can be achieved because thermoplastics pass into the liquid phase when they are heated.

Usually, therefore, mixtures of thermoplastics with different Melting points chosen. Nevertheless, the temperature control is during the bakeout of Binders very critical and the bakeout process must be very careful, take place over a long period of time (3 to 10 days), otherwise there is a risk that the parts deform or cracks appear.

The binders of group b) give a good dimensional stability of the Injection molded parts. Since hardened thermosets do not melt when the binder is expelled, the risk of undesired deformations or soot formation is much smaller than with thermoplastics.

The disadvantages of these binders are that only one is essential less fluidity can be achieved and that after heating always much more freely Carbon (about 15% to 50% related) remains.

In the prior art, there is therefore a targeted adjustment of what is left behind Carbon is only possible to a very limited extent.

By mixing binders from group a) and b) to group c) the advantages of both groups can be combined to a certain extent, but then the disadvantages of both groups occur, albeit to a lesser extent, on.

Description of the invention: The object of the invention is to provide a binder that is characterized by the following properties: - Achieving good flowability - Good dimensional stability of the parts and improved heating behavior and, if desired: - Share of carbon left behind adjustable from 0.001% to 10%.

Solution: According to the invention, a method is now proposed for the production of sintered molded parts made of metal or ceramic by injection molding a Composition that contains an expellable binder and a lubricant, which is characterized is through a binder with - a thermoplastic, the degree of crosslinking according to the Processing in the injection molding compound can be increased and with advantage - a lubricant, this lubricant itself in turn advantageously consists of various components and is of low viscosity (less than 100 poise), so that it has good sliding properties can be achieved.

The proportion of the binder is advantageously between 2 and 20%, based on the spray mass.

After shaping and crosslinking, the thermoplastic has a high Molecular weight and thus a high melting point. This achieves that the lubricant mixed with the binder when driving out the binder at a Temperature can be removed at which the post-crosslinked thermoplastic is still does not melt and that therefore a certain strength remains in the molded part.

The lubricant can be removed relatively easily without the vapor pressure leads to damage (deformation, cracks) of the molded part when it is baked out.

If then at a higher temperature (60 to 90% of the melting temperature) the post-crosslinked thermoplastic is driven out because of the previously removed Lubricant already has pores and channels through which the thermoplastic is now also escapes without damaging the part.

Thus, a binder is created that has very good sliding properties and can be removed easily (i.e. relatively quickly). With help of a Thermoset Part of the remaining carbon can be targeted adjust, d. H.

a thermoset is only used if it is desired that after a certain amount of carbon remains after baking.

In the production of sintered parts made of metal or ceramic with This new binder is proceeded as follows: a) Preparation of a mass, consisting from the powder to be processed and the binder; if necessary, to the To increase homogeneity, a solvent is used after mixing the ingredients the mass is evaporated.

b) processing the mass by injection molding to form the molded part c) increasing the Degree of crosslinking of the crosslinkable thermoplastic contained in the binder with for it suitable methods, such as thermal or radiation crosslinking.

d) Driving out the binder by suitable heat treatment.

e) Sintering and, if necessary, redensification by hot isostoric pressing of the molded parts to almost complete, theoretical density.

By increasing the degree of crosslinking in the thermoplastic after injection molding two advantages are achieved: - During injection molding, the thermoplastic is relative low molecular weight and low viscosity (less than 100 poise).

- The thermoplastic can be crosslinked afterwards.

Ways of carrying out the invention: a) For binders: crosslinkable Thermoplastic: polyethylene, post-crosslinkable by heat in the presence of water (e.g.

humid atmosphere in the treatment chamber) Type: HDPEX CG 71210: 10 Manufacturer ASEA Kerbel Stockholm b) for lubricants: A mixture of zinc stearate and stearic acid in equal parts c) Mixable thermoset: phenolic resin type SW 433 Manufacturer: Bakelite Company Embodiment 1: Composition of a sprayable Mass for SiC: Powder to be processed: sinterable - SiC (melting temperature 2700 ° C), mixed with 0.6% amorphous boron.

2 grain size 1? m, BET spec. Surface 15 m / g.

78% SiC powder, 6% crosslinkable thermoplastic, 12% lubricant, 4 % Thermoset.

With this approach, 1.6% remains free after the binder has been baked out Carbon back in the SiC molding, which act as a sintering additive.

Working example 2: Composition of a sprayable mass for Ni-based alloy molded parts: Powder to be processed: Udimet 700 (Ni-based alloy), grain size less than 45 µm, mean grain size 30 µm Composition of the mass: 95.5% U-700 powder 2% cross-linkable thermoplastic 2.5% lubricant With this composition, less than 0.001 remains z back free carbon in the Ni-based molding. This is desirable because carbon deteriorates the mechanical properties of the molded part.

Modifications of the examples described can of course be made perform without departing from the scope of the invention. In particular, can also other injection-moldable, injection-moldable, extrudable, extrudable metals or ceramics are processed.

Baking out or driving out binding agents and possibly lubricants can im.Aus Ausführungsbeispiel 1 either continuously for a few hours or in stages in partial steps from room temperature to over a few hundred OC (1st stage) up to about Sintering temperature (75 - 95% of the melting temperature) in an inert atmosphere (Ar). A molded part sintered in this way had a density of 3.14 g / cm and 650 N / = 2 flexural strength.

For the embodiment 2 known bakeout and Sintering conditions are applied.

It is important in the invention that the additives of the injection molding compound very different temperatures are removed and that a thermoplastic is part of it, whose disposition Degree of wetting after injection molding increased very much so that the (green) parts are sufficiently dimensionally stable even before sintering.

Commercial use: For complex molded parts such as B. turbine blades or wheels manufactured according to the invention from metal or ceramic by injection molding can be.

The invention also includes all combinations of the features claimed and those explained in the description to illustrate the invention are.

Claims (6)

Claims 1. A method for producing sintered molded parts Made of metal or ceramic by injection molding a mass that is an expulsible binder and contains a lubricant, characterized by the use of a binder, which contains a thermoplastic, its degree of crosslinking after processing of the mass is increased to a molding. 2. A method for producing sintered molded parts according to claim 1, characterized by using a binder content of about 2 to 20%, preferably 4 to 12% based on the mass that can be injection molded. 3. The method according to claim 1 or 2, characterized in that the Share of carbon left behind in the molded part between 0 and 10% is adjusted to the total mass by adding a thermoset. 4. The method according to claim 1 to 3, characterized in that the the binder used contains a low-viscosity (low-molecular) lubricant, that with one Temperature that is between 60 and 90% of the melting temperature of the post-crosslinked thermoplastic is driven out. 5. Process for the production of sintered molded parts made of metal or ceramic characterized by: a) preparation of a mass consisting of the material to be processed Powder and the binder by mixing, where appropriate, to ensure homogeneity to increase, a solvent is added and after mixing the ingredients of the Mass is evaporated, b) processing of the mass by injection molding to form a molded part, c) Increasing the degree of crosslinking of the crosslinkable thermoplastic contained in the binder with particularly suitable methods, such as thermal or radiation crosslinking, d) driving out the binder by suitable heat treatment, e) sintering and optionally by hot isostatic pressing, recompaction of the molded parts to almost complete, theoretical density. 6. Application of the process for components as complex as Turbine blades or wheels made of metal or. Ceramics.