PROCESS FOR THE PRODUCTION OF COMPONENTS FOR COMBUSTION ENGINES OR TURBINES

Abstract

The present invention relates to a process for the production of components for combustion engines or turbines, in particular for the production of hollow-valve components, with which for the first time powdery titanium-based alloys, in addition to conventional materials, can be processed into these components. In the process, metal powder and/or metal alloy powder are mixed in a compounder with a binding agent and optionally a flux, the mixture is shaped by injection moulding, the shaped compound is chemically debound, the chemically debound compound is thermally debound at a temperature of less than 450° C. and the chemically and thermally debound compound sintered at a temperature below the melting temperature of the metal and/or metal alloy for the production of the component. The components can be combined with each other in conventional manner by form- and force-locking and also molten joining processes.

Description

The present invention relates to a process for the production of components for combustion engines or turbines, in particular for the production of hollow-valve components.

Today, combustion engines are expected to combine high performance and low fuel consumption. Gas-exchange valves as used in combustion engines must be able to withstand very high operating temperatures and mechanical stresses. Inlet valves, which are cooled with each intake stroke by cool make-up gases flowing around them, reach valve disk temperatures of over 500° C. Outlet valves reach temperatures of over 800° C.

As valves are mobile components, the driving power to be applied increases exponentially with the weight of the oscillating masses, i.e. the valves. Thus there is a requirement to further optimize valves in respect of weight without losses in mechanical and thermal strength.

Hollow valves with a stem, a valve cone and a valve disk, wherein valve cone and valve disk together form a cavity, are known for example from DE 198 04 053 A1. Such hollow valves or hollow valve parts are currently moulded either by hot extrusion or upsetting and forging. Heat-resistant steels such as material nos. 1.4882 (X 50 CrMnNiNbN 21 9), 1.4871 (X 53 CrMnNiN 21 9) or 2.4955 (NiFe 25 Cr 20 NbTi) are predominantly used for the valve cone and valve disk. Other materials, in particular lightweight materials based on titanium in powder form cannot, due to the high reactivity of titanium vis-à-vis oxygen, nitrogen and carbon and the concomitant embrittlement of the material, be processed, or not profitably, into hollow-valve components using the named processes.

The object of the invention is therefore to provide a process for the production of components for combustion engines or turbines, in particular for the production of hollow-valve components such as valve cones or valve disks with which other materials can also be processed profitably.

The object is achieved by a process for the production of components for combustion engines or turbines, in which:

• • (a) metal powder and/or metal alloy powder are mixed in a compounder with a binding agent and optionally an aggregate material,
  • (b) the mixture is shaped by injection moulding,
  • (c) the shaped compound is chemically debound,
  • (d) the chemically debound compound is thermally debound at a temperature of less than 450° C.,
  • (e) the chemically and thermally debound compound is sintered at a temperature below the melting temperature of the metal and/or the metal alloy to produce the component.

With the process according to the invention, in addition to the martensitic-ferritic and austenitic steels or nickel-based alloys, titanium-based materials in particular can also be processed profitably into hollow-valve components, whereby a further weight saving compared with the known hollow valves can be achieved. Titanium alloys which contain aluminium and/or vanadium as additional constituents are preferably used. These additional alloy constituents are each preferably contained in a quantity of 2 to 10 wt.-% based on the overall weight of the alloy.

The binding agent is preferably selected from the group composed of: polyamides, polyoxymethylene, polycarbonate, styrene-acrylonitrile-copolymerisate, polyimide, natural waxes and oils, thermosetting plastics, cyanates, polypropylene, polyacetate, polyethylene, ethylene vinyl acetate, polyvinyl alcohol, polyvinyl chloride, polystyrene, polymethyl methacylate, anilines, mineral oils, water, agar, glycerol, polyvinyl butyryl, polybutyl methacrylate, cellulose, oleic acid, phthalates, paraffin waxes, carnauba wax, ammonium polyacrylate, digylceride stearate and oleate, glyceryl monostearate, isopropyl titanate, lithium stearate, monoglycerides, formaldehyde, octanoic acid phosphate, olefin sulphonates, phosphate esters, stearic acid and mixtures of same. The proportion by volume of the binding agent is preferably less than 60%, more preferably 20 to 50%.

The mixing in the compounder is preferably carried out at a temperature of 50 to 250° C., most preferably 90 to 150° C.

The injection moulding is also preferably carried out at a temperature of the mixture of 90 to 150° C. and preferably at a pressure of 400 to 800 bar.

The chemical debinding is preferably carried out in a paraffin bath, preferably in a hexane bath. The chemical debinding is carried out at a temperature of preferably 10 to 65° C., more preferably 30 to 50° C.

The thermal debinding is carried out at a temperature of less than 450° C., preferably 200 to 350° C. and preferably under vacuum at a pressure of preferably 2 to 20 mbar.

The sintering is preferably carried out at 80 to 90% of the melting temperature of metal or metal alloy and more preferably under an inert gas atmosphere. The inert gas is preferably argon. Alternatively, the sintering can also be carried out under vacuum. In this case, the pressure is preferably 10-3 to 10-5 mbar.

Hollow-valve components produced in this way can be combined with each other in conventional manner by form- and force-locking and also molten joining processes. For example, valve disk and valve cone can be combined by a shrink fit. Valve cone and valve stem can be combined by a molten joining process.

PREFERRED EMBODIMENT

Using the process described above a titanium alloy with 6 wt.-% aluminium and 4 wt.-% vanadium was processed into a valve disk and a valve cone. Valve cone and disk were combined by a shrink fit.

FIG. 1 is an illustration of the combined valve disk and cone in top view and in section along the line A-A.

FIG. 2 shows a produced hollow-valve component according to the preferred embodiment as a whole component (right) and split (left).

Claims

1. Process for the production of components for combustion engines or turbines, in which

(a) metal powder and/or metal alloy powder are mixed in a compounder with a binding agent and optionally an aggregate material,

(b) the mixture is shaped by injection moulding,

(c) the shaped compound is chemically debound,

(d) the chemically debound compound is thermally debound at a temperature of less than 450° C.,

(e) the chemically and thermally debound compound is sintered at a temperature below the melting temperature of the metal and/or the metal alloy to produce the component.

2. Process according to claim 1, characterized in that the component is a hollow-valve component.

3. Process according to claim 2, wherein the hollow-valve component is a valve cone.

4. Process according to claim 2, wherein the hollow-valve component is a valve disk.

5. Process according to claim 1, characterized in that a titanium alloy is used as metal-alloy powder.

6. Process according to claim 5, characterized in that the titanium alloy contains aluminium and/or vanadium as additional constituents.

7. Process according to claim 6, characterized in that the titanium alloy contains 2 to 10 wt.-% aluminium and/or 2 to 10 wt.-% vanadium based on the overall weight of the alloy.

8. Process according to claim 1, characterized in that the binding agent is selected from the group consisting of: polyamides, polyoxymethylene, polycarbonate, styrene-acrylonitrile-copolymerisate, polyimide, natural waxes and oils, thermosetting plastics, cyanates, polypropylene, polyacetate, polyethylene, ethylene vinyl acetate, polyvinyl alcohol, polyvinyl chloride, polystyrene, polymethyl methacylate, anilines, mineral oils, water, agar, glycerol, polyvinyl butyryl, polybutyl methacrylate, cellulose, oleic acid, phthalates, paraffin waxes, carnauba wax, ammonium polyacrylate, digylceride stearate and oleate, glyceryl monostearate, isopropyl titanate, lithium stearate, monoglycerides, formaldehyde, octanoic acid phosphate, olefin sulphonates, phosphate esters, stearic acid and mixtures of same.

9. Process according to claim 1, characterized in that the proportion by volume of the binder in the mixture is less than 60%.

10. Process according to claim 9, characterized in that the proportion by volume of the binding agent in the mixture is 20% to 50%.

11. Process according to claim 1, characterized in that the mixing in the compounder is carried out at a temperature in the range from 50 to 250° C.

12. Process according to claim 1, characterized in that the injection moulding is carried out at a temperature of the mixture of 90 to 150° C.

13. Process according to claim 1, characterized in that the injection moulding is carried out at a temperature of 400 to 800 bar.

14. Process according to claim 1, characterized in that the chemical debinding is carried out in a hexane bath.

15. Process according to claim 1, characterized in that the chemical debinding is carried out at a temperature of 10 to 65° C.

16. Process according to claim 15, characterized in that the chemical debinding is carried out at a temperature of 30 to 50° C.

17. Process according to claim 1, characterized in that the thermal debinding is carried out at a pressure of 2 to 20 mbar.

18. Process according to claim 1, characterized in that the sintering is carried out at 80% to 90% of the melting temperature of the metal or metal alloy.

19. Process according to claim 1, characterized in that the sintering is carried out under an inert gas atmosphere.

20. Process according to claim 19, characterized in that the inert gas is argon.

21. Process according to claim 1, characterized in that the sintering is carried out under vacuum.

22. Hollow-valve component which is produced by a process according to claim 1, characterized in that it is composed of a titanium-based alloy.

23. Hollow-valve component according to claim 22, characterized in that in addition to titanium the titanium-based alloy contains 2 to 10 wt.-% aluminium and/or 2 to 10 wt.-% vanadium.