DE102009056875B4 - Bearing housing, charging device and method for surface treatment of a bearing housing - Google Patents

Abstract

Process for the surface treatment of a bearing housing (1) for a charging device, in particular in a motor vehicle, - in which a surface of the bearing housing (1) is at least partially enriched with nitrogen and / or carbon, - in which the surface is subsequently at least partially passivated.

Description

The present invention relates to a method for surface treatment of a bearing housing for a charging device, such a surface-treated bearing housing and a charging device equipped with such a bearing housing.

Currently, inter alia, for charging facilities, such. As exhaust gas turbocharger, bearing housing used without aftertreatment. Due to a better visual complacency and to improve corrosion protection, the bearing housings are usually painted. Since the bearing housings have unfavorable material properties, especially wear-intensive areas, such. B. a bearing bore or a support surface for a variable turbine geometry in the turbine-side region of the bearing housing, subjected to increased wear. To counteract this increased wear, it is currently common, for. B. equip the bearing for an adjustment of a variable turbine geometry with a hardened bush in which the adjusting shaft of the variable turbine geometry is rotatably mounted. Through this hardened bush, the wear in the region of the variable turbine geometry adjusting shaft is reduced, which leads to an increased service life of the charging device. However, the production of such a bearing housing is much more expensive by painting when using a high-quality corrosion protection.

Various charging devices with bearing housings are for example from the DE 197 32 478 B4 , of the DE 103 14 209 B3 , of the DE 100 80 396 B4 , of the DE 103 25 985 A1 , of the DE 100 61 846 A1 , of the EP 1 394 451 B1 , of the EP 1 830 071 A2 and the WO 2009/092635 A2 known.

The present invention is concerned with the problem of providing, for methods of manufacturing a bearing housing and an associated loading device with such a bearing housing, an improved or at least another embodiment with which a bearing housing improved with regard to its wear and corrosion resistance can be produced.

According to the invention, this problem is solved by the subject matters of the independent claims. Advantageous embodiments are the subject of the dependent claims.

The invention is based on the general idea, in a method for surface treatment of a bearing housing for a charging device, which can be used in particular in a motor vehicle to enrich the surface of the bearing housing at least partially with nitrogen and / or carbon and subsequently to passivate the surface at least partially. By enriching the surface of the bearing housing at least partially with nitrogen and / or carbon, optionally under thermal action in a medium temperature segment, the surface of the bearing housing can be hardened. Subsequent passivation also improves corrosion protection and, in the case of corresponding alloys, makes the bearing housing black or matt black. As a result, on the one hand, the bearing housing is designed visually appealing and further improves the heat output due to the formation of a black body via infrared radiation.

As the material for such a bearing housing, an iron alloy is usually used. But it is also conceivable to use titanium-aluminum alloys, or alloys which are temperature-resistant in a temperature range of up to about 1100 ° C. In the case of ferroalloys or hard steels, passivation of the surface will result in a dark or black or matte black surface. In the case of z. As a titanium-aluminum alloy is the formation of such a matte black surface, if any, by admixing of corresponding alloying components approximately possible. Otherwise, titanium-aluminum alloys show rather light or gray or matt gray surfaces as a result of passivation. Usually casting material is used, but also an application of the method to forged material is possible.

The enrichment of the surface of the bearing housing with carbon and / or nitrogen can be carried out by means of nitriding, nitrocarburizing or teniferization. An enrichment with carbon alone can also be carried out during the production of the bearing housing material, in which case as a material for the bearing housing z. As carbon-hardened steels can be used.

In the case of nitriding, the surface of the corresponding workpiece is treated so that nitrogen diffuses into the workpiece surface and forms iron nitrides in a surface layer. Depending on the process and the time of treatment, this surface layer may become several tens of microns thick during nitriding. A distinction is made between salt bath nitriding, gas nitriding and plasma nitriding. In gas nitriding, the workpiece is exposed to a nitrogen-releasing atmosphere at temperatures around 500 ° C and treatment times of several tens of hours. The nitrogen-releasing atmosphere may include nitrogen itself or nitrogen compounds such as ammonia. When Salzbadnitrieren is the Workpiece of a salt bath melt at a temperature of around 500 ° C and also exposed for several hours treatment time. As salts of Salzbadschmelze various nitrogen-containing salt compounds can be used. Finally, in plasma nitriding, the surface of the workpiece is also heated in a temperature range around 500 ° C with ionized, nitrogen-emitting gas, such. As nitrogen or ammonia treated. Due to the nitration, a surface layer is formed which is temperature-resistant up to about 500 ° C and which exhibits a significantly higher hardness than the core hardness of the workpiece.

In nitrocarburizing, the surface layer of a workpiece is simultaneously enriched with nitrogen and carbon. A distinction is made between gas nitrocarburizing, salt bath nitrocarburizing and plasma nitrocarburizing. In gas nitrocarburizing, the workpiece is also exposed to a temperature around 500 ° C, being disposed in a gas mixture capable of delivering both nitrogen and carbon. Usually, nitrogen is used as the nitrogen-releasing gas or nitrogen and used as carbon-releasing gas z. B. carbon dioxide. In salt bath nitrocarburizing, the workpieces are exposed to molten salt at temperatures around 500 ° C. The salt bath components used are alkali metal cyanates and alkali metal carbonates. The spent salts can each be post-dosed after the reaction. In plasma nitrocarburization, the workpiece is also exposed to a temperature around 500 ° C, using similar gas mixtures as in gas nitrocarburizing, but these gas mixtures are ionized.

A special form of nitration is teniferization, in which the workpieces are placed in a nitriding bath with controlled cyanide-cyanate content at a temperature around 500 ° C. During teniferization, mainly nitrogen is stored in the surface layer, so that teniferization can essentially be regarded as salt bath nitration.

All previously described enrichment processes can be used alone or in any desired sequence to enrich the surface of the bearing housing at least partially with nitrogen and / or carbon. Due to the incorporation of carbon and / or nitrogen in the surface of the workpiece by z. B. at least one of the above enrichment process, occurs a dimensional change or volume change of a few micrometers of the workpiece, but which is limited essentially to the edge zones. If the dimensions of the workpiece are tightly tolerated, the workpiece may have to be reworked after the incorporation of carbon and / or nitrogen or after the subsequent passivation.

In a further embodiment of the method, it is also possible to glass bead the workpiece. In this case, the glass bead blasting before the enrichment of the surface with nitrogen and / or carbon or before the passivation of the surface can take place. By the glass bead blasting it is also possible to increase the corrosion protection. It is advantageous if in the production of the non-surface-treated workpiece, the increase in volume of the workpiece due to the surface treatment is taken into account, since thereby at least partial removal of the finished surfaces can be prevented or reduced. After the enrichment of the surface of the bearing housing at least partially with nitrogen and / or carbon, it is advantageous to at least partially passivate the surface. For this purpose, usually the still hot workpiece is quenched in an oxidizing medium. This can be done in the case of a gas process by blowing with oxygen or air or in the case of a salt bath process by immersing the still hot workpiece in an oxidizing medium, such as oxidizing Salzbadschmelzen and oxidizing salt solutions. In the case of a plasma process, as in the case of a gas process, the blowing of the workpiece with an oxidizing gas atmosphere may also be ionized. The subsequent passivation process is not necessarily linked to a corresponding enrichment process. So you can passivate the enriched with a gas process workpiece in a salt bath and the enriched in a salt bath workpiece by blowing with oxygen or air.

By oxidizing or passivating the workpiece surface, an oxide layer is formed, which is similar to such. As in the anodizing process, by their formation on the surface of an in-diffusion of oxidizing media such. As oxygen, at least reduced in the workpiece during use. Thus, after passivation, the workpiece has on the surface an oxide layer which protects the workpiece from subsequent oxidation.

Furthermore, due to the temperature treatment associated with the surface treatment, the bearing housing is stress-relieved, whereby internal stresses are eliminated and no distortion occurs after or at a temperature load. Furthermore, due to the formed surface, the workpiece is provided with a higher hardness at least on the surface and, in addition, the tribological properties, and thus the friction, the wear and the lubrication, are improved. Furthermore, the fatigue strength of a improved such bearing housing as a result of compressive stresses on the surface. In addition, there is a lower tendency to seize in press dressings with such bearing housings. Finally, a Feinstbearbeitung is possible by z. As honing, rag or finishing.

In nitriding or nitrocarburizing, a surface layer is formed which has an external connection layer and a diffusion layer arranged below it. The entire at least partially nitrogen and / or carbon enriched surface layer can be up to 900 microns thick, depending on the process and duration of application of the process. As a rule, the connecting layer is made thinner than the diffusion layer and as a rule up to 10 micrometers thick. However, depending on the method, thicker tie layers or even no tie coat are possible. In general, the bonding layer has a high hardness, a low adhesion tendency and the possibility of receiving lubricant due to pores arranged in the bonding layer. In addition, the connection layer is passivated by z. B. oxidation and is also described by a low toughness. In addition to low toughness, the diffusion layer also has high strength, improved residual compressive stresses and increased heat resistance.

Such a surface treatment is advantageous on a bearing housing, especially for. B. in the region of a through hole, in which the adjusting shaft is mounted for a variable turbine geometry. Thus, due to the improved tribological properties, the usual, arranged at this point bushing omitted, since the surface hardened by the surface treatment method surface of the through hole has sufficiently good tribological properties for mounting the adjusting shaft for a variable turbine geometry. As a result, bearing housing with a hardened surface are easier to produce and the design effort is reduced in such bearing housings.

Other important features and advantages of the invention will become apparent from the dependent claims, from the drawings and from the associated figure description with reference to the drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination given, but also in other combinations or in isolation, without departing from the scope of the present invention.

Preferred embodiments of the invention are illustrated in the drawings and will be described in more detail in the following description, wherein like reference numerals refer to the same or similar or functionally identical components.

It show, each schematically:

1 a bearing housing for a charging device that can be equipped with a variable turbine geometry,

2 a section through a surface layer of the bearing housing after a surface treatment by nitriding or nitrocarburizing.

Like in the 1 is shown, has a bearing housing 1 a compressor side 2 and a turbine side 3 on. On the turbine side 3 can be a support surface 4 be arranged for a variable turbine geometry. As with such a bearing housing 1 with a variable turbine geometry, not shown, the variable turbine geometry must be adjustable from the outside, is such a bearing housing 1 with an adjusting lever arranged outside thereof 5 equipped, the rotationally fixed with an adjusting shaft 6 is connected and the over the adjusting shaft 6 can control the variable turbine geometry. The 1 shows the current state of the art due to the non-hardened surfaces of the bearing housing 1 in the range of the adjusting shaft 6 a bearing bush 7 needed, so that the wear in the range of the adjusting shaft 6 can be reduced. If the surface is hardened by a surface treatment process, this bearing bush can 7 omitted and the adjusting shaft 6 directly in one in the bearing housing 1 arranged passage opening 8th without bearing bush 7 be stored. Furthermore, between the compressor side 2 and the turbine side 3 in the bearing housing 1 a warehouse 9 arranged for a shaft of a rotor, also not shown.

In the 2 is a cross section through a surface layer 10 a bearing housing 1 represented after enrichment with nitrogen and / or carbon. Here were used as starting material cast iron 11 with laminar embedded graphite 12 used. A connection layer 13 is on the outside of the surface layer 10 arranged while a diffusion layer 14 between the bearing housing 1 and the tie layer 13 is positioned. The under the connection layer 13 located diffusion layer 14 is mainly enriched with nitrogen, where the nitrogen may be chemically bound in the form of iron nitrides in the case of ferrous alloys. In the connection layer 13 Due to the increased incorporation of carbon carbonitrides occur, so that the connecting layer 13 has different material properties than the diffusion layer 14 , The interaction of both layers 13 . 14 allows high resistance to wear, increased corrosion resistance due to the passivation of the bonding layer 13 and due to the high strength of the diffusion layer 14 and improved compressive residual stresses, increased resistance to contact fatigue and increased fatigue strength. In addition, due to the increased heat resistance of the diffusion layer 14 given a better dimensional stability, a reduced heat wear and increased resistance to thermal fatigue.

Claims (14)

Process for the surface treatment of a bearing housing ( 1 ) for a charging device, in particular in a motor vehicle, - in which a surface of the bearing housing ( 1 ) is at least partially enriched with nitrogen and / or carbon, - in which the surface is subsequently at least partially passivated. A method according to claim 1, characterized in that the surface is at least partially enriched by nitriding, in particular gas nitriding, with nitrogen. Method according to one of the preceding claims, characterized in that the surface is at least partially enriched by nitrocarburizing with nitrogen and carbon. Method according to one of the preceding claims, characterized in that the surface is passivated by oxidation. Method according to one of the preceding claims, characterized in that the bearing housing ( 1 ) is at least partially glass bead blasted after enrichment with nitrogen and / or carbon and before passivation. Method according to one of the preceding claims, characterized in that the method in the region of a passage opening ( 8th ) for an adjusting shaft ( 6 ) of a variable turbine geometry on the bearing housing ( 1 ) is carried out. Method according to one of the preceding claims, characterized in that the method in the region of a bearing ( 9 ) for a shaft of a rotor on the bearing housing ( 1 ) is carried out. Method according to one of the preceding claims, characterized in that the method in the region of a support surface ( 4 ) of a variable turbine geometry on the bearing housing ( 1 ) is carried out. Bearing housing ( 1 ) for a charging device, in particular in a motor vehicle, wherein the bearing housing ( 1 ) one, a diffusion layer ( 14 ) and a connection layer ( 13 ) comprehensive surface layer ( 10 ), which at least partially compared to the rest of the bearing housing ( 1 ) is enriched with nitrogen and / or carbon. Bearing housing according to claim 9, characterized in that the surface layer ( 10 ) in the region of a passage opening ( 8th ) for an adjusting shaft ( 6 ) of a variable turbine geometry on the bearing housing ( 1 ) is trained. Bearing housing according to claim 9 or 10, characterized in that the surface layer ( 10 ) in the area of a warehouse ( 9 ) for a shaft of a rotor on the bearing housing ( 1 ) is trained. Bearing housing according to one of claims 9 to 11, characterized in that the surface layer ( 10 ) in the region of a support surface ( 4 ) of a variable turbine geometry on the bearing housing ( 1 ) is trained. Bearing housing according to one of claims 9 to 12, characterized in that the surface layer ( 10 ) is dark, in particular black, by subsequent oxidation, so that heat radiation due to infrared radiation is improved. Charging device, in particular for a motor vehicle, with a bearing housing ( 1 ) according to one of claims 9 to 13.

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