EP3292087A1

EP3292087A1 - Metal part and method for producing same

Info

Publication number: EP3292087A1
Application number: EP16724697.4A
Authority: EP
Inventors: Wolfgang KÜHN; Annett Bretschneider; Rolf Gosch; Bernhard Stauder; Jurij GONTAREV
Original assignee: Nemak SAB de CV
Current assignee: Nemak SAB de CV
Priority date: 2015-05-07
Filing date: 2016-05-06
Publication date: 2018-03-14
Also published as: WO2016178079A1; DE102015107171A1; TW201702204A; TWI703106B; US20180148845A1; CN107635938A

Abstract

The invention relates to a metal part that has a surface which is thermally or mechanically loaded to a greater degree than its surroundings when the metal part is being used and which is at least partly covered with a glaze or enamel layer. The invention also relates to a method for producing same. The metal part according to the invention allows the heat treatment to be carried out without any particular restrictions while still ensuring an optimal protection of the respective surfaces which are subjected to high loads when the metal part is used. This is achieved in that the glaze or enamel layer contains 2 - 35 wt.% of an addition of particles with respect to the enamel frits used to form the enamel layer, and the addition of particles is made of at least one material of the group consisting of glass, organic plastics, synthetic oxide mixtures, or melts, in each case having a thermal expansion coefficient of maximally 50 x 10^-7 K^-1 and a melting temperature of at least 500 °C.

Description

Metal part and method for its production

The invention relates to a metal part, which has a surface which is thermally or mechanically higher in use than its environment is charged, said surface at least in sections with a glaze or to protect against thermal or mechanical stresses

Enamel layer is occupied. In particular, the metal part is a cast part cast from a metallic cast material.

Likewise, the invention relates to a method for producing a metal part, in particular casting, with a

Area that is at least one place where they are in use of a high thermal cycling

is exposed, is covered with an enamel or glaze layer.

As detailed in the article "Possibilities and Limitations of Enameling of Light Metals" by Dr.-Ing. Wolfgang Kühn, published in Surfaces Polysurfaces No 2/09,

Pages 6 - 9, explains, wins the enameling of

Components made of lightweight materials, such as aluminum,

Magnesium and titanium materials are increasingly important. From a technical point of view, the protection of the component surfaces from corrosive attacks has been the focus of attention. As explained further in the cited article, enamel coatings are glass layers which, above all with regard to the melting temperature and the coefficients of thermal expansion, are provided for them

Carrier materials were adjusted. They connect the

Properties of a glass surface with the material and processing properties of metals. In contrast to other coatings, the bonding of the respective enamel coating combines a glass-metal composite, in which intermediate layers, so-called intermetallic phases, form between the glass material and the metal substrate. These ensure a particularly intense adhesion of the coating on the metal. For this purpose, modern enamels are today multicomponent mixtures which, using their eutectic at low stoving temperatures, have very good mechanical hardness and chemical resistance

to reach. For example, enameled workpieces can be machined by bending, sawing or drilling and can additionally be provided with functional nanoscale sol-gel layers, for example to supplement the hard, scratch-resistant enamel layer with a temperature-resistant non-stick effect.

From DE 10 2010 025 286 AI it is further known that the inner surfaces of exhaust ducts of

Light metal castings, such as cylinder heads, for internal combustion engines thereby effectively against a

Protect thermal overload that they are at least partially covered with a coating that is formed from a glass material. In the practical use of this proposal, there is a particular challenge in that the coating on the one hand must safely withstand the mechanical and thermal stresses occurring during operation and

on the other hand, a mechanical processing of adjacent to the coated surface portion sections of the respective component without the risk of spalling of the coating must allow.

One regarding their mechanical and thermal

Resilience further optimized enamel coating can be with the in DE 10 2013 108 428 AI and

Produce WO 2015/018795 AI presented enamel powder. Its constituents are composed in such a way that the enamel coating formed therefrom generally has a higher compressive strength than other coatings of this type known from the prior art. Therefore, this known enamel powder is particularly suitable for producing an enamel coating on one

Metal casting made of light metal or a

Alloy alloy exists.

Practical experiments have shown that in the

previously explained manner assembled and obtained enamel or glaze coatings meet the expectations set in principle. It turns out, however, that in the heat treatment of metal parts, which are provided with such coatings, a

particularly careful and careful temperature control is required.

Against this background, the task arose

To propose metal part of the type specified, in which no particular restrictions in the Heat treatment exist and in which, however, an optimal protection of each heavily used in use areas is guaranteed.

Likewise, a procedure should be mentioned which is for

Production of such metal parts is suitable.

With respect to the metal part, the invention has this object _ by a with the features mentioned in claim 1

solved metal part solved.

The reliable production of metal parts of the

According to the invention can be accomplished by the method specified in claim 14 according to the invention.

Advantageous embodiments of the invention are specified in the dependent claims and are explained below as the general inventive concept in detail.

An inventive metal part for a

Accordingly, the internal combustion engine has one in use

thermally or mechanically higher than their environment charged area, which is at least partially covered with a glaze or enamel layer. According to the invention, the glaze or enamel layer contains, based on the enamel frit used to form the enamel layer, 2 to 35% by weight of an admixture of particles which consist of at least one material from the group "glass, organic plastics,

Synthetically generated oxides and mixtures of such oxides, wherein the production of the oxides is optionally carried out via a melt consist ", each having a thermal

Expansion coefficients of at most 50 x 10 ^{~ 7} K ^"1 and has a melting temperature of at least 500 ° C.

By the term "glaze or enamel layer", according to the understanding of the invention, layers consisting of

inorganic compounds are formed, which consist of fused together oxides of alkali and

Erdalkaligruppe exist. These include Si0 ₂ , A1 ₂ 0 ₃ , B ₂ 0 ₃ , Li ₂ 0, Na ₂ 0, CaO, MgO and K ₂ 0. The layers may additionally inorganic or organic compounds in the form of fibers, such as. As SiC or C fibers, and other enamel typical, known in the art additives. In the production of the glaze or

Enamel layers are ground the premelted compounds used as frit with water.

Subsequently, the fibers are optionally added.

According to the present invention, particles are additionally added to the slip, preferably after its production, which contribute a minimized coefficient of thermal expansion

have maximized melting temperature. Die_s_e._Par-tike.l- consist of materials belonging to the group "glass, organic plastics, synthetically produced oxides and mixtures of such oxides, wherein the production of the oxides has optionally taken place via a melt" belong. The materials in question are characterized by having a very low maximum coefficient of thermal expansion of not more than 50 x 10 ^-7 K ^-1 and a high melting temperature of not less than 500 ° C

Particulate addition provided according to the invention is particularly suitable for materials which have a

Expansion coefficients of at most 25 x 10 ^-7 K ^-1 , in particular at most 10 x 10 ^-7 K ^-1 Blending powder suitable materials of the type in question is the coefficient of expansion in the

Practice typically at least 0.5 x 10 ^{~ 7} K ^-1 , wherein also minimum expansion coefficients of at least 2 x 10 ^" ⁷ K ^{" 1} or at least 4 x 10 ^{~ 7} K ^{"1 are} regularly encountered.

Powders for the purposes of the invention must also have a high melting temperature.

Melting temperatures of at least 900 ° C have proven to be particularly suitable here, the

Melting temperature optimally in the range of

1000 - 1400 ° C is located.

The amount of admixture added according to the invention is determined by the weight of the enamel frit provided to form the enamel layer. That is, should the enamel or glaze coating of 100 grams

Enamel frit according to the invention the slip

2 - added 35 grams of powdered admixture of materials which are determined in accordance with the invention.

The slip thus obtained is added to the

applied protective portion of the respective surface, dried there and to the respective glaze or

Enamel layer burned. The drying and the

Baking can be carried out in a conventional manner by bringing the metal part in total to the required temperature. If this results in the course of processing of the metal part, can be used for drying and baking a process in the respective metal part due to existing heat for drying become. This is suitable, for example, for castings in which the cast part, which is still cast, is coated in accordance with the invention. Similar possibilities arise when the metal part is a thermoformed, in particular hot-forged, component. Also, the drying and baking can be completed in the course of a heat treatment, which passes through the metal part to adjust its mechanical and other properties.

Surprisingly, metal parts according to the invention have shown that the enamel or enamel there provided

Glaze layer as a result of addition according to the invention additionally admixtures of particles of materials, in which a particularly low coefficient of thermal expansion is combined with a high melting temperature, is also insensitive to temperature changes, if this

Temperature changes take place at high speed. Such extreme temperature changes occur, for example, when quenching metal parts after a

Heat treatment, when the metal parts by means of a

Quenchant, e.g. Water, spray or liquid nitrogen, be quenched. Here, cooling rates of more than 2 K / s, typically at least 5 K / s

achieved, with a typical upper limit of

Achieved water quenching or water spray

Cooling rates at 30 K / s is. It turns out that even with such a fast deterrent

accompanying thermal shock secure adhesion of the coating on the respective metal substrate

is guaranteed.

Cracks resulting in a fast and extreme Temperature change in an inventive

Coating inevitably arise, heal after reheating, so that even with repeated temperature changes no deterioration of the protective and adhesive properties of the coating over the

Initial state occurs. Practical experiments have shown here that components coated according to the invention can be cooled beyond the quenching to room temperature, for example with liquid nitrogen, to a temperature of up to -196 ° C. without a

Damage is caused by the protective effect of

Coating is permanently impaired.

The recipe according to the invention of an enamel or

Glaze layer thus allows on different

Metal materials such coatings to produce and permanently secure. Accordingly, the invention is suitable for coating metal parts,

in particular castings, from one

Ferrous material as well as for_dle_es_chi.cht.ung_von-T-ei-len -, - which are made of a light metal casting material, in particular an Al-casting material. The adhesion of the coating to the respective metal substrate is ensured by the reactivity between the base material and the enamel. The additional addition according to the invention then ensures the required

Thermal shock resistance.

Particularly favorable affects the invention

provided admixture, if their content based on the added to the slip weight of enamel frit

at least 8% by weight, in particular at least 10% by weight is. An optimal utilization of the properties of the particulate powder admixed according to the invention results when the content of powder particles based on the weight of the enamel frit is at most 30% by weight, in particular at most 20% by weight.

It has been found that an optimal distribution of the particles of admixture in the applied to the surface area to be protected slip and a correspondingly optimal distribution and effect in the metal part produced enamel or glaze coating then sets if the enamel or glaze layer or The slip applied to the area to be protected in the context of the method according to the invention

contains pre-ground ceramic particles as an admixture. In particular, here particles have a positive effect with respect to the thermal shock resistance of the enamel or

Glaze coating consisting of a fineness of

5 - 150 μπι in the coating or the applied

Slip are present.

Their protective effect unfolds an enamel or

Glaze layer then particularly effective if it is 50-1000 μπι thick, with an optimal effect at the same time optimized durability of the layer at a

Layer thickness of 300 - 500 μηα results.

Excessive heating of each to be protected

Surface section can be ensured that the invention applied enamel or

Glaze layer has a thermal conductivity of less than

10 x 10 ^{~ 7} K ^-1 , where coatings with a Thermal conductivity of less than ^{4.times.10.sup.-7} K.sup.- ^{1 have} been found to be particularly advantageous in this respect, in particular if the layer thicknesses of the coating according to the invention are in the range explained above.

The particles added according to the invention as admixtures can, but do not have to consist of a material of pure sort. Rather, mixtures can also be used

use such materials as admixtures, if these materials each according to the invention

prescribed requirements for her

Meet thermal expansion coefficients and melting temperatures.

In principle, refractory materials and in particular material particles from the group of magnesium aluminum silicates are suitable as material for the particles added as admixture of the coating according to the invention.

Lithium glass ceramics, Quar_zgläs_er _, _ _. ZirkojLaluminLums-ili-ka-te or alumo-silicates.

Among the candidate materials of the system MgO Al ₂ 0 ₃ -Si02 (magnesium aluminum silicates) include in particular cordierite (M2A2S5), to the alumino-silicates in particular mullite (A ₃ S ₂ ). Also, particles consist of components of these systems are used, in particular particles of Si0 ₂ in amorphous or crystalline structure or A1 ₂ 0 ₃ in Korundmodifikation.

Of the zirconium aluminum silicates (Zr0 ₂ -Al ₂ 0 ₃ -Si0 ₂ ) are in particular zirconium mullite (ZSA ₃ ) or zirconia (ZS) as for to call the purposes of the invention particularly suitable materials.

Lithium ceramics or technical glasses, such as quartz glass, also have minimized expansion coefficients at high melting temperatures and can be in

sufficiently chopped form for the purposes of the invention add the enamel.

Of course, mixtures of the

above-mentioned materials are used with other materials for the purposes of the invention, if they meet the formulated in terms of their expansion coefficient and their melting temperature of the invention requirements. These include, for example

Porcelain materials, which is a typical

Thermal expansion coefficient of at most 0.5 x 10 ^"7 K ^{" 1} and have a particularly high melting temperature of more than 1600 ° C.

Known oxide ceramics have a typical

Expansion coefficients of 8 x 10 ^{~ 7} K ^"1 at lying in the range of 900 ° C melting temperatures.

The admixtures provided according to the invention can be added in commercially available form. The materials used to prepare the admixture which are suitable here are known to the person skilled in the art, as are the methods for suitable comminution of the relevant materials (see, for example, Gerald Routschka, Hartmut Wuthnow [Ed.] "Practical Guide Refractory Materials"), 5th edition , Vulkan Verlag, ISBN 13: 978-3802731617). The organic plastics which are suitable for the purposes according to the invention are described, for example, in the AVK - Industrievereinigung Reinforced Plastics Association "Handbuch Faserverbundkunststoffe: Grundlagen, Verarbeitung,

Applications ", Vieweg + Teubner Verlag, Edition: 3rd, Completely revised edition 2010 (October 27, 2009).

The coating according to the invention is particularly suitable for protecting those surfaces of a metal part which are thermally stressed thermally during use by a gas forming or flowing through it. Such surfaces may be present in a space or channel of the metal part in which, in use, correspondingly hot gas forms or is flowed through in use of hot gas. Such conditions arise for example in metal parts, in particular castings, for

Internal combustion engines in the field of combustion chambers and the exhaust ducts, but also in the range of turbocharger housings, pistons and other exposed to the heat of an exhaust gas stream

Parts of a Verbrennungs.smq.to_r.s_ Dab..e.i_könn.en- example, the exhaust gas-carrying manifolds of the exhaust system of an internal combustion engine be formed from a sheet metal material. There, too, proves to be an invention

obtained enamel or glaze layer with regard to the protection against excessive local heating very low.

But it may just be appropriate for such components, not only the loaded by hot gas inner surfaces by a coating according to the invention

protect. So it may also be appropriate outer surface portions of the respective metal part in

coating according to the invention, if there special mechanical or thermal loads occur. Also, the glaze or enamel layer according to the invention can be a corrosion protection that protects the insert against a chemically aggressive liquid or gaseous medium.

The typical application for the invention is a cylinder head produced as a casting for a

Combustion engine. Likewise, the invention is also suitable for a housing for a turbocharger, which is arranged in the exhaust gas stream of an internal combustion engine and whose exhaust gas flowed through channel in accordance with the invention is coated.

The coating according to the invention makes it possible to decisively increase the power of an internal combustion engine. For this purpose, the areas surrounding the combustion chamber, such as pistons, block running surface and cylinder head combustion chamber roof surfaces can be coated in accordance with the invention.

Through the achieved in this way reduction of

Heat losses are one step closer to the goal of an "adiabatic engine." Furthermore, it may be expedient to have the intake ports of the internal combustion engine at least

to be coated according to the invention so that the incoming air is shielded from the high temperature of the casting material respectively surrounding the inlet duct in the case of highly charged engines, thus achieving a higher degree of charge and concomitantly increased engine efficiency. Also, one can

coating according to the invention for the reduction of

Radiation losses of engines and other thermal systems by the low heat conduction contribute. Finally, can be by the invention in the

Combustion process resulting reaction gases with higher thermal efficiency in the subsequent processes.

If the coating according to the invention is to be embodied as an enamel layer, then it is suitable as the basis for this

in particular an enamel, as described in DE 10 2013 108 429 AI, the content of which is hereby incorporated into the disclosure of the present application. The specified in the relevant German patent application

Enamel powder is particularly suitable for covering in operation thermally and mechanically highly loaded metallic surfaces and is present as a mixture containing 100 parts of a glass powder, optionally 10 - 22 parts of coarse glass grains, which are larger than the particles of the glass powder, 0.1 -. 7 , 5 parts of ceramic fibers, glass fibers or carbon fibers, and alternatively to each other or in combination with each other, 10-2 parts of a powdery oxidic compound of a light metal or 1-5 parts of a powder of a

Contains heavy metal. By means of the slip formed from this mixture, the slip provided according to the invention

Added admixture, a coating is obtained, which also meets the highest requirements for their protective effect and durability safely.

If here "parts" as Dosiermaß is mentioned, it is understood that the amount of the enamel powder added to the respective component is measured by means of a unit for all the same unit size and inventively provided for each component "parts" the respective Multiple this

Denote unit size. In accordance with the above explanations, an inventive method for producing a

Metal part, which has a surface in use thermally or mechanically higher than its surroundings, the

at least in sections with a glaze or

Enamel layer ^'is occupied, following steps:

- Providing the metal part;

- Providing an enamel or Glasurschiickers containing based on the enamel frit used to form the enamel or glaze 2.0 - 35 wt .-% of an admixture of particles consisting of at least one material of the group "glass, synthetic oxide mixtures or

Melting, organic plastics ", each having a thermal expansion coefficient of at most

50 x Ϊ0 ^"7 K ^{" 1} and a melting temperature of at least

500 ° C;

- applying the enamel or glaze slip on the

Section of the respective surface of the metal part;

- drying and baking the applied enamel or glaze slip;

Heat treating the metal part, wherein the heat treatment optionally comprises cooling at a cooling rate higher than the cooling rate achieved by cooling in still air, in particular cooling on agitated air;

optional mechanical processing of the enamel or glaze slip formed from the enamel or glaze slip

Glaze layer. The insensitivity of the invention applied

Coating allows a wide margin

Heat treatment and other processes associated with

Manufacture of a component with optimal properties are required. For example, the metal part for baking the applied enamel or

Heat glaze loops locally in the area of the applied enamel or glaze slurry coating and keep them outside of this range at a lower temperature so that the metal sub-substrate is not affected by the burn-in treatment. Also, the

Coating of the invention mechanically, for example by grinding, be post-processed.

The invention is suitable for any metal parts that are exposed to the conditions of use discussed above. These include on metal base by forming produce metal parts as well as metal parts that are made by applying a primary molding process, such as casting or forging.

The invention thus provides a metal part and a

Processes for its production are available, which allow a precise production, and in particular allow the coating of internal cavities. A particular advantage of the coating according to the invention consists in the fact that it protects highly effectively against thermal, corrosive or mechanical loads without the need for additional components. Tolerance problems, as would be the case with molded parts are avoided in this way. The possible by the invention minimized layer thickness while optimized protection function allow optimized in terms of weight savings interpretation and

Design of the metal part also in the areas where high loads are expected.

The baking of the coating can be particularly

economic way in the course of a

Heat treatment process, in particular a

Solution annealing process to be completed, as it is usually passed through in the production of castings for internal combustion engines.

As a result of the coating according to the invention

guaranteed protection, less stringent requirements can be placed on the thermal, corrosive or mechanical resistance of the metal material. This allows

lower cost and lower overall load capacity

To use materials.

The invention is based on

Embodiments explained in more detail.

example 1

A cylinder head cast from a conventional Al casting alloy for a high compression diesel engine is annealed at 500 ° C for 30 minutes and then cooled to room temperature.

Subsequently, at the surface portions to be provided with an enamel coating, the oxide reaction products, in particular Α1 ₂ 0 ₃ , and the other incurred in the course of annealing

Eliminated impurities. For this purpose, the surfaces concerned are stained with dilute nitric acid HN0 ₃ .

Subsequently, the cylinder head to neutralize the previously pickled surface first with dilute

Alaklilauge and then rinsed with water. After drying, a slip is applied, which has been mixed according to the following recipe:

100 parts of enamel frit

3 parts of boric acid

3 parts potassium hydroxide solution

3 parts of water glass

55 parts water

For dimensioning of said "parts" each have the same amount of hollow used. That there are 100

Hollow units of enamel frit, each with three

Boron acid, potassium hydroxide and water glass and mixed with 55 units of water. The total weight of the added enamel frit has been recorded.

This mixture has been ground in a porcelain mill.

After grinding, the resulting mixture, based on the weight of those contained in the mixture

Enamel frit 20 wt .-% Codierit been added in powder form, which has a thermal expansion coefficient of

typically 10 - 30 10 ^"7 K ^{" 1} . The thus formed Mixture was then ground again until a mixture with uniform grain was present.

Then, the channels of the cylinder head, whose surfaces should be covered with the enamel layer, have been flushed with the slurry to wet the respective surface sections with the slurry.

After drying, a burn-in, in which the cylinder head over a period of 50 minutes at a

Temperature of 510 ° C has been maintained.

The enamel layer thus obtained showed good adhesion to the Al casting substrate and high insensitivity even under extreme temperature changes

RissbildüngV

Example 2

A cast also from an Al casting alloy

Turbocharger housing for an internal combustion engine has been annealed at a temperature of 500 ° C for 30 minutes and then cooled to room temperature. The one with

Enamel layer to be coated inner surfaces of the turbocharger housing are then oxidic

Buildup and other contaminants by means of

Sandblasting has been released.

For the coating, a slip has been provided which is made

100 parts enamel frit,

4 parts of boric acid, 4 parts potassium hydroxide solution,

4 parts of water glass,

55 parts of water has been mixed.

When dimensioning the said "parts" is as in

Explained in connection with Example 1 explained. The total weight of the enamel frit added to the slip mixture has also been recorded here.

The formed from said components

Slip mixture has also been ground in a porcelain mill to the desired grinding fineness.

After grinding, the mixture is based on the weight of the enamel frit contained in the mixture 17.5 wt .-% quartz glass powder with a

Coefficient of thermal expansion of typically 5.4 was added 10 ^"7 K ^_1. The resulting mixture was then ground again until a mixture of uniform grain size was present.

Thereafter, the slip obtained is filled in the turbocharger housing and distributed by rotating the housing evenly on the surfaces to be coated.

After drying, a burn-in, in which the turbocharger housing has been held over a period of 45 minutes at a temperature of 525 ° C.

The enamel layer thus obtained showed a good adhesion to the AI even under extreme temperature changes. Cast substrate and a high insensitivity to cracking.

Claims

P AT ENT TO SPRU

1. Metal part which is thermal or in use

has mechanically higher than their area exposed area, which is at least partially covered with a glaze or enamel layer, d a d u r c h

The glaze or enamel layer is related to those used to form the

Enamel layer used enamel frit contains 2 - 35 wt .-% of an admixture of particles, the

at least one material of the group "glass, organic plastics, synthetically produced oxides and mixtures of such oxides, wherein the production of the oxides is optionally carried out via a melt", each having a thermal expansion coefficient of at most 50 x 10 ^"7 K ^{" 1} and a Melting temperature of at least 500 ° C.

2. Metällteil according to claim 1, d a d u r c h

The glaze or enamel layer is related to those used to form the

Enamel layer used enamel frit 10 - 30 wt .-% of the admixture contains.

3. The metal part according to claim 1, wherein the enamel or glaze layer contains pre-milled ceramic particles as an admixture.

4. metal part according to one of the preceding claims,

d a d u r c h g e k e n e c i n e t, d a s s is the fineness of the ceramic particles 5 - 150 μπι.

5. Metal part according to one of the preceding claims,

The additive contains magnesium aluminum silicate particles.

6. Metal part according to one of the preceding claims,

The additive contains lithium glass ceramic particles.

7. Metal part according to one of the preceding claims,

d a d u r c h e c e n c i n e s, the s of the admixture contains quartz glass particles.

8. Metal part according to one of the preceding claims,

characterized in that the admixture contains zirconium aluminum silicate particles.

9. The metal part according to one of the preceding claims, characterized in that the admixture contains alumino-silicate particles.

10. The metal part according to one of the preceding claims, wherein the enamel or glaze layer is 50-1000 μπι thick.

11. Metal part according to one of the preceding claims, characterized in that the enamel or glaze layer has a thermal conductivity of less than 25 x 10 ^{~ 7} K ^"1 has.

12. Metal part according to one of the preceding claims, characterized in that the at least partially coated with the enamel or glaze layer surface surrounds a space or channel of the metal part, _ is thermally loaded in use by .ein- in him forming or him flowing gas ,

13. Metal part according to one of the preceding claims, characterized in that it is cast from a cast metal casting. A method of making a metal part that is thermally or mechanically higher in use than its

Environment has polluted area, at least

Sectionally covered with a glaze or enamel layer, comprising the following steps:

- Providing the metal part;

- Providing an enamel or Glasurschiickers containing based on the enamel frit used to form the enamel or glaze 2.0 - 35 wt .-% of an admixture of particles consisting of at least one material of the group "glass, organic plastics, synthetic produced oxides and mixtures of such oxides, wherein the production of the oxides is optionally carried out via a melt "consist, each having a coefficient of thermal expansion of

at most 50 x 10 ^-7 K ^-1 and a melting temperature of at least 500 ° C;

- Applying the enamel or Glasurschiickers on the respective portion of the surface of the metal part;

- drying and baking the applied enamel or glaze slip;

- Heat treating the metal part, wherein the

Heat treatment optionally comprises a cooling at a cooling rate which is higher than the cooling rate, which is achieved in a cooling in still air, in particular in a cooling on moving air; - Optional mechanical processing of the

Enamel or glaze chip formed enamel or glaze layer.

The method of claim 14, d a d u r c h

The metal part for baking the applied enamel or

Glaze slip in the area of the applied enamel or glaze slip coating is locally heated and outside this area at a lower

Temperature is maintained.