DE1929602A1 - Process for the production of gray cast iron parts with internal plain bearing surfaces - Google Patents

Description

Dr.-lng. H. c. F. PORSCHE KG 7 STUTTGART-ZUFFENHAUSEN PORSCHESTRASSE 42

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Process for the production of gray cast iron parts with internal sliding bearing surfaces.

The invention relates to a method of manufacture of gray cast parts with internal sliding bearing surfaces, in particular of rocker arms for internal combustion engines, which are provided with a bearing bore formed by a core inserted into the casting mold will.

The invention aims to produce a ledeborite watch Rush sliding layer in holes or recesses of Giiaugußt.

It is known to locally create surface zones of greater hardness on gray cast iron parts by influencing the cooling rate. In the case of gray cast iron parts produced by sand casting, quenching bodies, which are highly thermally conductive, are placed in the casting mold in order to influence the cooling rate of the cast iron in the surface zone, whereby the depth of the surface zone influenced by the increased cooling rate can be adjusted by appropriately dimensioning the body. '' Depending on the composition, in particular with regard to the alloy components G and Si of the cast iron, various microstructures with different mechanical properties can also be achieved in the surface zone by varying the cooling rate, whereby the achievable microstructure for a given cast iron composition is essentially dependent on the strength of the supercooling . For the mass production of gray cast parts with a certain microstructure in the surface zone , permanent molds made of steel are used, which, because their wall thickness cannot be increased at will for reasons of strength.

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can be wrestled to reduce their thermal conductivity with a coating of poor or no thermal conductivity; em Material are provided. This means for influencing the structure formation in the surface zone by means of Cooling speed, have so far only been used for the outer surfaces of gray cast iron parts. (E. Piwowarsky, high quality cast iron, Springer Verlag Berlin, 1951) · This is due, among other things, to this. Ren that a distortion-free solution for internal sliding surfaces was not considered possible. So far for internal If the surfaces of gray castings required a special surface hardness, the castings were regular post-treatment, such as hardening and subsequent tempering or nitriding, chrome plating (chrome hardening) and the like, subjected. In particular in the case of rocker arms of internal combustion engines, the "interacting with the rocker arm shaft Sliding bearing surface mostly formed by sockets subsequently inserted into the bearing eye of the rocker arm. That Inserting a bushing into the bearing eye of the rocker arm is complex, however, since the bearing eye is pressed before the Bushing must be turned out.

In contrast, the invention is based on the object of creating a method by which in gray cast iron parts of the type mentioned above, in particular in the case of rocker arms of internal combustion engines provided with bearing bores simple means a favorable microstructure is obtained, which is suitable as a plain bearing surface without major aftertreatment is.

This object is achieved according to the invention in that the core is formed by a thin-walled steel bushing is inserted into the mold and removed from the bore after the casting has been removed from the mold, and finally at least that portion of the bore that forms the sliding bearing surface is ground to conform to the fit. After demolding the steel bushing can be removed from the hole by unscrewing

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will. The steel bushing can also be pushed out, especially in the case of through bores or recesses. By dimensioning the wall thickness of the steel bushing, the depth of the surface zone influenced by the increased cooling rate can be set in a known manner. According to the invention it can also be provided that the steel bushing is heated prior to the casting process in order to their setting to obtain a certain structure formation in the surface zone. When using a cast iron with about J5 to 4 % C and less than 2.5 ^ Si, the bush is heated so that a cooling rate of about 500 ° C / min. is achieved, whereby a Ledeboritisches structure ™ in the surface zone

is formed, which has satisfactory running properties with sufficient hardness. By increasing the cooling rate and, if necessary, simultaneously reducing the alloy content of Si, the decomposition of carbide can be reduced, so that a harder microstructure is created in the surface zone, while conversely a decrease in the cooling rate and possibly a simultaneous increase in the alloy content Si leads to increased decomposition of carbide and thus leads to a less hard microstructure in the surface zone. To increase the heat dissipation capacity of the steel sleeve may be according to the invention additionally provided that a coolant flow passes through the bushing overall Λ, which then reaches a over arbitrarily long time constant heat dissipation through the steel bushing and thereby varying the depth of the influenced by the increased cooling surface zone arbitrarily can be. In a further expedient individual embodiment of the process according to the invention, it is also proposed that when producing smaller, continuous bores or recesses having cast parts, several cast parts are molded together and instead of individual steel bushings for each cast part, a common, continuous steel tube is used for several cast parts. As a result, in addition to the molding, a flow of coolant is also passed through the "steel bushings of several GuQtell & föaau & £ ffi®uht. Finally, as a further

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Measure to influence the cooling rate be provided that the steel bushings or a steel pipe are covered with a layer of a poorly or not thermally conductive material.

By using a thermally conductive steel bushing instead a core made of non-thermally conductive material is in the surface zone of the recess or bore of the gray cast part an increased cooling rate of the cast iron and thus a greater hardness of the surface is achieved without that a significant distortion of the recess occurs, so that the desired sliding bearing surface by a simple mechanical Treatment of the surface, such as grinding, can be made. In particular by bringing about a ledeborite Microstructure with each. after setting the cooling rate, a higher or lower proportion of non-disintegrated Carbide and thus greater or lesser hardness become both sufficient hardness and satisfactory running properties having achieved surface. By using the method according to the invention, for example to create a sliding bearing surface in the bearing eye of a rocker arm for an internal combustion engine, are compared to the previously common Process entxveder the operations for. turning out the bearing eye and the insertion of the bushing as well as the bushing itself or the operations for a metallurgical treatment such as hardening, nitriding or the like, saved. Another advantage of the method according to the invention should be mentioned that by appropriate adjustment of the depth of the surface zone having a special structure both machining tolerances and the expected bearing load on the plain bearing can be taken into account.

In the drawing is a according to the inventive method manufactured rocker arm for an internal combustion engine shown in longitudinal section.

The rocker arm 1 is made of gray cast iron and essentially consists of a first lever arm 2 , together with the camshaft, and a second lever arm 2, with the

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tilschaft cooperating lever arm 3 and a bearing bore 4. On the cooperating with the camshaft 5 or the valve stem areas of the lever arms 2 and 5 are provided in the usual manner by inserting appropriate molds in the mold each having a hard microstructure having surface zones 5 and β. For the casting process xtf, a surface zone approximately 1 to 2 mm deep with a Ledeboritic microstructure 7 is created along the sliding bearing surface 4 'of the bearing bore K, via which the rocker arm 1 is pivotably mounted on the rocker arm shaft. In the drawing, the otahlbuchse 8 used to produce the ledeboritic microstructure 7 and inserted into the casting mold is shown. As a result of their "

Thermal conductivity causes the steel sleeve 8 a higher cooling rate of the cast iron in the surface zone along the sliding bearing surface 4 ″ of the bearing bore 4 and releases thereby the formation of a ledeboritic microstructure. After the rocker arm 1 has been removed from the mold, the steel bushing removed from the bearing bore 4 by turning and the sliding bearing surface 4 'ground to fit. No further follow-up treatment is required.

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© AD ORIGINAL

Claims (5)

192Β602 property rights claims 1. Process for the production of gray cast iron parts with internal sliding bearing surfaces, in particular of rocker arms for internal combustion engines, which have a bearing bore which is formed by a core inserted into the casting mold, characterized in that that the core is formed by a thin-walled steel bushing (6) which is inserted into the mold and after Removal of the casting (1) from the bore (4) and finally at least the plain bearing surface (V) forming section of the hole is ground to fit. 2. The method according to claim 1, characterized in that that the 3tahlbuch.se (8) can be screwed out or pressed out is removed from the hole. 3. The method according to claim 1, characterized in that that the steel bushing (8) vor.Beginn the casting process one Heat treatment, either heating or cooling, is subjected. 4. The method according to claim 1 to j5, characterized in that that the steel bushing (8) is dimensioned or pretreated is that the initial cooling rate of the cast iron is about 500 C / min, 5. The method according to claim 1 to 4, characterized net that at least during the pouring and solidification of the melt a cooling section eist rom through the steel bushing (8) b will. 6, method according to claim 1, characterized in that cIi. '.; fJfcahlbuf. '. hst) (Ö) mib frLnein your sleeves LfcfUhirj'keit ver. ^r iiadoi'iid; ui 'Ί -i- ^ ug voi'soh-ui u.ü, 8A0 ORIGINAL - Ϊ ■ - 0 0 9 8 5 1/1 0 5 3 - 7 - ο 50 7. The method according to claim 1 to 6, characterized in that that with simultaneous production of several castings with through holes or recesses in one For'n instead of individual otahlbuchsen (8) a continuous Steel pipe is used. 00 9 85 1 / i "053 8AOORlGtNAL Blank page