Metal Component and Method for the Production Thereof

Abstract

A metal component which has a face which during use is thermally or mechanically more highly loaded than the environment thereof and which is at least partially covered with a glaze or enamel layer and a method for the production thereof. The metal component requires no specific limitations during the thermal processing operation and nonetheless ensures optimum protection for the surfaces which are highly loaded during use. The glaze or enamel layer contains, with respect to the enamel frit used to produce the enamel coating, from 2 to 35% by weight of an admixture of particles which consist of at least one material from glass, organic plastics materials, and synthetic oxide mixtures or melts, which each have a thermal expansion coefficient of a maximum of 5010.sup.7 K.sup.1 and a melting temperature of at least 500 C.

Claims

1.-15. (canceled)

16. A metal component comprising a face at least partially covered with a glaze or enamel layer, wherein during use, the face is thermally or mechanically more highly loaded than the remainder of the component and wherein the glaze or enamel layer comprises an admixture of particles of at least one material selected from the group consisting of glass, organic plastics materials, synthetically produced oxides and admixtures of such oxides, and the particles have a maximum thermal expansion coefficient of 5010.sup.7 K.sup.1 and a melting temperature of at least 500 C., and wherein, the glaze or enamel layer comprises, with respect to the frit used to produce the glaze or enamel layer, 2 to 35% by weight of the admixture.

17. The metal component according to claim 16, wherein the glaze or enamel layer comprises, with respect to the frit used to produce the glaze or enamel layer, 10 to 30% by weight of the admixture.

18. The metal component according to claim 16, wherein the admixture comprises pre-ground ceramic particles.

19. The metal component according to claim 18, wherein the particle size of the ceramic particles is from 5 to 150 m.

20. The metal component according to claim 16, wherein the admixture contains magnesium aluminium silicate particles.

21. The metal component according to claim 16, wherein the admixture contains lithium glass ceramic particles.

22. The metal component according to claim 16, wherein the admixture contains quartz glass particles.

23. The metal component according to claim 16, wherein the admixture contains zirconium aluminium silicate particles.

24. The metal component according to claim 16, wherein the admixture contains aluminosilicate particles.

25. The metal component according to claim 16, wherein the enamel or glaze layer is 50 to 1000 m thick.

26. The metal component according to claim 16, wherein the enamel or glaze layer has a thermal conductivity of less than 2510.sup.7 K.sup.1.

27. The metal component according to claim 16, wherein the face which is at least partially coated with the enamel or glaze layer surrounds a space or channel of the metal component which is thermally loaded during use by a gas which is formed therein or which flows therethrough.

28. The metal component according to claim 16, wherein the metal component is a cast component which is cast from a cast metal.

29. A method for producing a metal component comprising a face at least partially covered with a glaze or enamel layer, wherein during use, the face is thermally or mechanically more highly loaded than the remainder of the component, the method comprising: providing the metal component; providing an enamel or glaze slurry comprising a frit and, with respect to the frit, 2.0 to 35% by weight of an admixture of particles of at least one material selected from the group consisting of glass, organic plastics materials, synthetically produced oxides and admixtures of such oxides, wherein the particles have a maximum thermal expansion coefficient of 5010.sup.7 K.sup.1 and a melting temperature of at least 500 C.; applying the enamel or glaze slurry to at least a portion of the face of the metal component; drying and burning-in the applied enamel or glaze slurry; thermally processing the metal component.

30. The method according to claim 29, wherein burning-in of the enamel or glaze slurry which has been applied to the metal component comprises locally heating the metal component in the region where the enamel or glaze slurry has been applied at a first temperature and keeping the portions of the metal component outside of this region at a second temperature, wherein the second temperature is lower than the first temperature.

31. The method of claim 29, wherein the thermal processing comprises cooling at a cooling rate that is higher than a cooling rate achieved by cooling in static air.

32. The method of claim 31, wherein in the thermal processing comprises cooling in moving air.

33. The method of claim 29, wherein after thermal processing, the enamel or glaze layer formed from the enamel or glaze slurry is mechanically processed.

Description

EXAMPLE 1

[0056] A cylinder head which is cast from a conventional Al-cast alloy for a highly compressed diesel engine is annealed at 500 C. for a time of 30 minutes and subsequently cooled to ambient temperature.

[0057] Subsequently, on the surface portions which are intended to be provided with an enamel coating, the oxidic reaction products, in particular Al.sub.2O.sub.3 and the other impurities which have been produced during the annealing operation, are eliminated. To this end, the respective surfaces are pickled with dilute nitric acid HNO.sub.3. Subsequently, the cylinder head is flushed in order to neutralise the previously pickled surface first with dilute alkali lye and then with water. After the drying, there is applied a slurry which has been mixed in accordance with the following recipe:

100 parts of enamel frit
3 parts of boric acid
3 parts of caustic potash
3 parts of water glass
55 parts of water

[0058] In order to measure the parts mentioned, the same hollow measure was used in each case. That is to say, 100 hollow measure units of enamel frit are mixed in each case with three hollow measure units of boric acid, caustic potash and water glass and with 55 hollow measure units of water. In this instance, the overall weight of the added enamel frit was established.

[0059] This admixture was ground in a porcelain mill.

[0060] After the grinding operation, there was added to the admixture obtained with respect to the weight of the enamel frit contained in the admixture 20% by weight of cordierite in powder form which has a thermal expansion coefficient of typically 10-30 10.sup.7 K.sup.1. The admixture formed in this manner was then ground again, until an admixture with uniform grain size was obtained.

[0061] The channels of the cylinder head whose surfaces are intended to be coated with the enamel layer were then flushed with the slurry in order to wet the relevant surface portions with the slurry.

[0062] Drying was followed by a burning-in operation, in which the cylinder head was maintained for a time of 50 minutes at a temperature of 510 C.

[0063] The enamel layer obtained in this manner had, even with extreme temperature changes, a good adhesion to the Al-cast substrate and a high level of insensitivity with respect to the formation of cracks.

EXAMPLE 2

[0064] A turbocharger housing which has also been cast from an Al-cast alloy for an internal combustion engine was annealed at a temperature of 500 C. for 30 minutes and subsequently cooled to ambient temperature. The inner surfaces of the turbocharger housing which are intended to be coated with an enamel layer were subsequently freed from oxidic adhesions and other impurities by means of sandblasting.

[0065] For the coating, a slurry was prepared which was mixed from:

100 parts of enamel frit
4 parts of boric acid
4 parts of caustic potash
4 parts of water glass
55 parts of water.

[0066] For the measurement of the parts mentioned, the procedure is as explained in relation to Example 1. The overall weight of the enamel frit added to the slurry admixture was also established in this instance.

[0067] The slurry admixture formed from the components mentioned was also ground in a porcelain mill to the desired grain fineness.

[0068] After the grinding operation, there were added to the admixture with respect to the weight of the enamel frit contained in the admixture 17.5% by weight of quartz glass powder with a thermal expansion coefficient of typically 5.4 10.sup.7 K.sup.1. The admixture formed in this manner was then ground again until an admixture with uniform grain size was obtained.

[0069] The slurry obtained was then poured into the turbocharger housing and by means of rotation of the housing distributed in a uniform manner on the surfaces which are intended to be coated.

[0070] Drying was followed by a burning-in operation, in which the turbocharger housing was maintained for a time of 45 minutes at a temperature of 525 C.

[0071] The enamel layer obtained in this manner had, even with extreme temperature changes, a good adhesion to the Al-cast substrate and a high level of insensitivity with respect to the formation of cracks.