EP0215074A1

EP0215074A1 - Production process for sintered compacts

Info

Publication number: EP0215074A1
Application number: EP86901792A
Authority: EP
Inventors: Werner Hüther
Original assignee: MTU Motoren und Turbinen Union Muenchen GmbH
Current assignee: MTU Aero Engines GmbH
Priority date: 1985-03-15
Filing date: 1986-03-12
Publication date: 1987-03-25
Also published as: WO1986005424A1

Abstract

Procédé de pièces complexes faconnées, comme des aubes ou des roues de turbines en métal ou en céramique par moulage par injection, utilisant un liant approprié à cet effet.Process of complex shaped parts, such as blades or impellers of metal or ceramic turbines by injection molding, using a suitable binder for this purpose.

Description

Process for producing sintered molded parts

Technical field:

The invention relates to a method for the manufacture of ^'sintered components made of metal or ceramic by Spritz¬ casting a composition containing a austreibbares binder and optionally a lubricant.

State of the art:

Known methods include the following steps:

- Mixing the sinterable metal or ceramic powder with a binder, so that an injection moldable

Mass arises.

- Injection molding of the mass into the molded part

- Expelling the binder from the molded part by a first heat treatment

- Sintering 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 re-compaction

The following are used as binders: a) thermoplastics (e.g. polyethylene, polyethylene waxes, paraffin waxes, cellulose and their derivatives, polyamides, polyaeryls, styrenes)

b) thermosets, epoxies, polyimide 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 fluidity even with small proportions of the binder in the mass

- Achieve good dimensional stability in the molded part during baking

Complete removal of the binder by heating, leaving behind an adjustable amount of free carbon

Disadvantages of the known binders:

Group a) These binders have the advantage of good fluidity and are usually also completely removable. The disadvantage of this group is that only a low dimensional stability can be achieved because thermoplastics pass into the liquid phase when baked out. Mixtures of thermoplastics with different melting points are therefore usually chosen. Nevertheless, the temperature control during the heating of the Binders are very critical and the heating process must be carried out very carefully over a long period of time (3 to 10 days), otherwise there is a risk that the parts will deform or crack.

The binders of group b) give the injection molded parts good dimensional stability. Since hardened thermosets do not melt when the binder is driven out, the risk of undesired deformation or soot formation is significantly lower than with thermoplastics.

The disadvantages of these binders are that only a much lower fluidity can be achieved and that there is always a lot of free carbon (about 15% to 50% based) after baking.

In the prior art, therefore, a targeted setting of the remaining carbon is only possible to a very limited extent.

By mixing binders of 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 also appear, albeit to a lesser extent.

Presentation of the invention:

The object of the invention is to provide a binder which is distinguished by the following properties:

- Achieve good fluidity

- good dimensional stability of the parts and improved heating behavior and if desired:

- The amount of carbon left is adjustable from 0.001% to 10%. Solution:

According to the invention, a method is now proposed for producing sintered molded parts made of metal or ceramic by injection molding a composition which contains an expellable binder and a lubricant which is characterized by a binder

a thermoplastic, the degree of crosslinking of which can be increased after processing in the injection molding compound, and advantageously

- A lubricant, which lubricant itself advantageously consists of various components and is low-viscosity (less than 100 poise), so that good sliding properties are achieved.

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

After shaping and cross-linking, the thermoplastic has a high molecular weight and thus a high melting point. It is thereby achieved that the lubricants mixed with the binder can be removed when the binder is driven out at a temperature at which the post-crosslinked thermoplastic does not yet melt and that the molded part therefore has a certain strength. The lubricant can be removed relatively easily without the vapor pressure leading to damage (deformation, cracks) in the molded part during heating.

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

This creates a binder that has very good sliding properties and can be removed easily (ie relatively quickly). With the help of a thermoset Part of the remaining carbon can be adjusted in a targeted manner, ie

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

In the production of sintered components made of metal or ceramic with ^this' new binder is as follows drive ver¬ a) treating a composition consisting of the ver¬ to working powder and the binder; if necessary, in order to increase the homogeneity, a solvent is used which is evaporated after the constituents of the mass have been mixed.

b) Processing the mass by injection molding to give the molded part

c) Increasing the degree of crosslinking of the crosslinkable thermoplastic contained in the binder using suitable methods, such as thermal or radiation crosslinking.

d) driving out the binder by suitable heat treatment.

e) sintering and, if necessary, hot compression 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 relatively low molecular weight and low viscosity (less than 100 poise)

- The thermoplastic can be cross-linked subsequently. 1 ways of carrying out the invention:

a) For binders: crosslinkable thermoplastic: polyethylene, postcrosslinkable - 5 bar by heat in the presence of water (e.g. moist atmosphere in the treatment chamber)

Type: HDPEX CG 71210: 10 Manufacturer ASEA Chervil Stockholm 10 b) for lubricants:

A mixture of zinc stearate and stearic acid in equal parts

- * 5 c) Mixable thermoset: phenolic resin type SW 433 Manufacturer: Bakelite

Embodiment 1

20th

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 u m, BET spec. Surface 15 / g.

25 78% SiC powder, 6% cross-linkable thermoplastic,

12% lubricant, 4% thermoset.

With this approach, 1.6% of free carbon remains in the SiC molded part after the binder has been heated, which 3 act as a sintering additive.

Design example 2:

Composition of a sprayable composition for Ni-based 35 alloy molded parts: Powder to be processed: Udimet 700 (Ni-based alloy), grain size less than 45 µm, average 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% free carbon remains in the Ni-based molded part. This is desirable because carbon deteriorates the mechanical properties of the molded part.

Modifications to the examples described can of course be carried out without departing from the scope of the invention. In particular, other injection-moldable, extrusion-capable, extrudable, extrudable metals or ceramics can also be processed.

In example 1, the heating or expelling of binders and, where appropriate, lubricants can either be continuous for a few hours or in stages in steps from room temperature to over a few hundred C (1st stage) to about sintering temperature (75-95% of the melting temperature) temperature) in an inert atmosphere (Ar). Such a

3 sintered molding had a density of 3.14 g / cm and

2 650 N / mm bending strength.

Known baking and sintering conditions can be used for embodiment 2.

It is important in the invention that the additives of the spray compound are removed at very different temperatures and that this includes a thermoplastic, the use of which degree of wetting is very strongly increased after the injection molding, so that the (green) parts are sufficiently dimensionally stable even before sintering.

Commercial application:

For complicated molded parts, e.g. Turbine blades or wheels, which according to the invention can be produced from metal or ceramic by injection molding.

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

Claims

Patent claims

1. Process for producing sintered molded parts from

Metal or ceramic by injection molding a mass which contains an expulsible binder and a lubricant, characterized by the use of a binder which contains a thermoplastic, the degree of crosslinking of which is increased after the processing of the mass into a molded part.

2. A method for producing sintered moldings according to claim 1, characterized by the use of a binder content of about 2 to 20%, preferably 4 to 12%, based on the injection-moldable mass.

3. The method according to claim 1 or 2, characterized gekennzeich¬ net that the proportion of carbon left in the molded part between 0 and 10% based on the total mass is adjusted by the addition of a thermoset.

4. The method according to claim 1 to 3, characterized in that the binder used is a low-viscosity

Contains (low molecular weight) lubricant, which in a Temperature that is between 60 and 90% of the melting temperature of the post-crosslinked thermoplastic is driven out.

_5> Process for manufacturing sintered metal or ceramic parts characterized by:

a) preparation of a mass, consisting of the powder to be processed and the binder, by _Q mixing, where appropriate, in order to increase the homogeneity, a solvent is added and, after mixing the constituents of the mass, is evaporated,

₅ b) processing the mass by injection molding to give the molded part,

c) increasing the degree of crosslinking of the crosslinkable thermoplastic contained in the binder using methods which are particularly suitable for this purpose, such as thermal crosslinking or radiation crosslinking,

d) driving out the binder by means of suitable heat treatment,

5 e) sintering and optionally by hot isostatic pressing, post-compression of the molded parts to almost complete, theoretical density.

6. Application of the method for so complicated shaped components such as turbine blades or impellers made of metal or ceramic.

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