OXIDATION PROTECTION LAYER FOR ENGINE PISTONS MADE OF STEEL OR AN IRON-BASED ALLOY

Abstract

A coating for reducing high-temperature oxidation of a piston for an internal combustion engine is provided. This coating is obtained by means of a composition containing titanate or zirconate, wherein at least one metal pigment is introduced into the coating.

Claims

1. A piston, for an internal combustion engine, which at least in part has a layer, wherein the layer can be obtained by means of a composition comprising at least one titanate or zirconate of the general formula (I); and wherein the layer contains at least one metal pigment, ##STR00002## wherein R1, R2, R3 and R4 each independently represent H or an organic residue; preferably H, a phenyl group or a C1-C6 alkyl group; and particularly preferably a phenyl group or a C1-C4 alkyl group; M represents Ti or Zr; and n represents an integer.

2. The piston according to claim 1, wherein the composition comprises a titanate, preferably tetramethyl titanate, tetraisopropyl titanate, tetrabutyl titanate and/or tetraphenyl titanate.

3. The piston according to claim 1, wherein at least one metal pigment based on a zinc, magnesium or aluminum alloy, preferably an aluminum-magnesium alloy or a zinc-magnesium alloy, is used.

4. The piston according to claim 1, wherein the layer can be obtained by applying the composition, partially or completely dissociating the titanate of the general formula (I), and curing the composition.

5. An internal combustion engine comprising a piston according to claim 1.

6. A method for manufacturing a piston, comprising the following steps: a) applying a composition comprising at least one titanate or zirconate of the general formula (I) onto the piston; b) applying at least one metal pigment onto the piston; c) partially or completely dissociating the titanate or zirconate; and d) curing the composition.

7. The method according to claim 6, wherein the dissociation of the titanate of the general formula (I) is initiated by exposure to moisture, heating or irradiation.

8. The method according to claim 6, wherein the titanate and the metal pigment are applied by means of the same composition.

9. The method according to claim 6, wherein in step b) at least one metal pigment based on a zinc, magnesium or aluminum alloy, preferably an aluminum-magnesium alloy or a zinc-magnesium alloy, is applied onto the piston.

10. (canceled)

Description

BRIEF DESCRIPTION OF THE FIGURES

[0008] FIG. 1 shows micrographs of a coated and an uncoated piston after an engine running test.

DETAILED DESCRIPTION OF THE INVENTION

[0009] Consequently, the invention relates to a piston, in particular a piston for an internal combustion engine, which is made of steel or another iron-based alloy, wherein a layer is applied onto at least a part of the piston, which layer can be obtained from a composition containing titanate or zirconate and contains at least one metal pigment. Furthermore, the present invention relates to a method for producing this layer and its use for preventing high-temperature oxidation or bot gas oxidation of the piston.

[0010] Within the scope of the invention, a layer that can be obtained from a composition containing titanate is preferred.

[0011] In the production of the layer according to the invention, the titanate or zirconate contained in the composition is used as a precursor. A layer based on TiO or ZrO units is formed by partial or complete dissociation of the organic residues.

[0012] This dissociation process can be initiated after the application of a suitable composition by exposure to moisture, including atmospheric moisture, or introduction of energy, for example by irradiation or heating. This dissociation process leads to curing of the layer.

[0013] Preferably, the layer that can be obtained from the composition containing titanate or zirconate contains 20 to 40% by weight of titanium oxide or 20 to 40% by weight of zirconium oxide, based on the entire layer, in the fully cured state. In this regard, the expression in the fully cured state relates to a layer obtained by application by means of a spray gun and subsequent heating in an oven at approximately 250 C. for 30 minutes.

[0014] The partial or complete dissociation of the organic residues causes the titanate or zirconate molecules to shrink, so that the produced layer can exhibit cracks and pores. This leads to problems with the cohesion of the layer.

[0015] It has now been shown that cohesion is significantly improved if at least one metal pigment is added to the coating. In this way, a coating can be obtained that leads to improved protection of the piston against oxidation, so that the problem underlying the invention is solved.

[0016] According to the invention, a compound of the following general formula (I) is used as the titanate or zirconate:

##STR00001##

[0017] wherein R1, R2, R3 and R4 each independently represent H or an organic residue; preferably H, a phenyl group or a C1-C6 alkyl group; and particularly preferably a phenyl group or a C1-C4 alkyl group. R1, R2, R3 and R4 may optionally have substituents, but are preferably unsubstituted groups. M represents Ti or Zr, preferably Ti, n represents a natural number, preferably 1 to 4.

[0018] In a particularly advantageous embodiment of the invention, a titanate is used which is selected from the group consisting of tetramethyl titanate, tetraisopropyl titanate, tetrabutyl titanate and tetraphenyl titanate. The zirconate is preferably selected from the group consisting of tetramethyl zirconate, tetraisopropyl zirconate, tetrabutyl zirconate and tetraphenyl zirconate.

[0019] Within the scope of the invention, the titanates and zirconates can also be used in the form of chelate complexes.

[0020] The layer that can be obtained by means of the composition containing titanate or zirconate contains at least one metal pigment.

[0021] Alloys based on zinc, magnesium or aluminum are particularly suitable as metal pigments. Aluminum-magnesium and zinc-magnesium alloys are preferred.

[0022] Within the scope of the invention, the metal pigment is used, for example, in the form of a powder, preferably a powder with a particle diameter of 50 m or less.

[0023] Preferably, the layer according to the invention has a thickness in the range of 5 to 100 m, more preferably 10 to 50 m, in particular 10 to 30 m.

[0024] The layer according to the invention can also be part of a multilayer system. This means that other layers can be applied onto the piston in addition to the layer according to the invention in order to influence different properties of the piston. These layers can be applied under or on top of the layer according to the invention.

[0025] The layer according to the invention is suitable for all steels and iron-based alloys that are conventionally used in pistons for internal combustion engines.

[0026] A piston with the layer according to the invention can be manufactured by means of a method comprising the following steps: [0027] a) applying a composition comprising at least one titanate or zirconate of the general formula (I) onto the piston; [0028] b) applying at least one metal pigment onto the piston; [0029] c) partially or completely dissociating the titanate or zirconate; and [0030] d) curing the composition.

[0031] In the method according to the invention, steps a) and b) can be carried out individually or together. Preferably, the composition containing titanate or zirconate and the metal pigment are applied together. Particularly preferably, the metal pigment is added to the composition containing titanate or zirconate before it is applied onto the piston. For this purpose, the metal pigment can be used in the form of a powder or a paste, for example.

[0032] Subsequently, the titanate or zirconate is dissociated as described and the layer is cured.

[0033] By using the layer according to the invention, high-temperature oxidation or hot gas corrosion of the piston can be reduced.

Effect of the Invention

[0034] A composition containing a titanate and a zinc-magnesium alloy pigment was applied by spraying onto a piston made of 42CrMo4. Subsequently, the composition was cured by heating in an oven at approximately 250 C. for 30 minutes.

[0035] The coated piston and an uncoated piston were subjected to an engine running test for 516 hours, wherein the engine was operated alternately for 30 minutes under full load and 2 minutes at idling speed.

[0036] Micrographs of the two pistons after completion of the test are shown in FIG. 1. As apparent from FIG. 1, an oxidation layer with a thickness of approximately 43 m has formed on the uncoated piston. In contrast, high-temperature oxidation (hot gas corrosion) was prevented by the titanate-containing layer according to the invention.