1. Field of the Invention
The present invention relates to a method and a device for the production of a piston pin having a hard peripheral area.
2. The Prior Art
It is known from the state of the art to manufacture piston pins having a peripheral area that has sufficiently great hardness that the use of bearing shells may be eliminated. Offenlegungsschrift DE 197 04 224 describes a cylindrical piston pin whose mantle surface has a layer of amorphous carbon. This piston pin is directly mounted in the eye of the connecting rod and in the pin boss of the piston, avoiding slide bearing shells.
From U.S. Pat. No. 1,742,015, it is known to encase a steel tube in order to produce a piston pin, after which the casting material is hardened by means of rapid cooling, using a cooling mantle that is supplied with a coolant.
The methods for the production of piston pins having a hardened outside surface known from the state of the art have the disadvantage that they are very complicated and costly.
It is an object of the present invention to provide a method for producing a piston pin that has a hard surface, which can be carried out simply and therefore inexpensively.
These and other problems are solved by a chill casting method and device according to the invention. In one aspect, a chill form having a mold cavity for at least one piston pin is embedded in a casting mold. Cast iron is poured into the mold cavity of the chill form. The peripheral area of the piston pin or pins that results from this process is chilled and forms a hard, ledeburite structure.
In another aspect, a device is provided for implementing the method according to the invention in which the casting mold is a sand mold. Practical further developments are discussed below.
Other objects and features of the present invention will become apparent from the following detailed description considered in connection with the accompanying drawings. It should be understood, however., that the drawings are designed for the purpose of illustration only and not as a definition of the limits of the invention.
In the drawings,
Turning now in detail to the drawings,
Sand mold 1 is shown with a completed, cast piston pin 2 after solidification, whereby the peripheral area 4 of piston pin 2 solidifies in a white color, because of the rapid cooling effected by chill form 3, and its inner region 5, which cools more slowly than peripheral area 4, assumes a dark color. Subsequent to the casting process, after the casting has been removed from chill form 3, its mantle surface is finished in conventional manner, i.e. it is ground and polished.
A ledeburite structure having a marked carbide texture forms in peripheral area 4, within the scope of the casting process, because of the high cooling speed, giving this region great hardness and wear resistance. Inner region 5 of piston pin 2 does not assume the hardness achieved by peripheral area 4. Because of the lower cooling speed, a pearlite structure is formed at inner region 5, in which the carbon is at least partially present as graphite. This graphite gives the inner region its dark color.
In this connection, cast iron with spheroidal graphite is used, i.e. an iron/carbon casting material whose carbon content, which is present as graphite, is present almost entirely in essentially spheroid, i.e. in spherolitic form.
Such cast parts have a hard, wear-resistant surface and improved ductility in the core and, therefore, can absorb shock and impact stress to a higher degree.
Examples of such chemical compositions of the cast iron are:
Material Example a):
Micrograph 13 clearly shows the graphite which is formed in a globular or spheroid shape as a result of the slow cooling speed.
Although only a few embodiments of the present invention have been shown and described, it is to be understood that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention as defined in the appended claims.