EP0504605B1 - Internal combustion cylinder, method and device - Google Patents

Description

The invention relates to a method for producing a cylinder of an internal combustion engine and an apparatus for performing this method.

The further development of internal combustion engines towards ever higher specific outputs has meant that the cylinder liner, particularly in its upper region, is exposed to ever higher stresses due to pressure and temperature. This results in the requirement to manufacture the cylinder liner from very high-strength steel. At the same time, there is also the requirement not to deteriorate the running behavior of the piston rings on the cylinder liner surface compared to the running properties achievable with gray cast iron. This double requirement has so far been met in that a gray cast iron running layer is spun onto the inner surface of the cylinder liner. The disadvantage of this method is that a very long cooling time is required after spinning to ensure the necessary quality of the composite cast cylinder liners. In addition, this process, in which a liquid and a material which is in the solidification phase is combined with one another, results in large quality fluctuations which significantly increase the reject rate.

The lining of a metal cylinder with an iron-based alloy by means of strolling is described in DE-B-1812766.

The invention has for its object to find a method and an apparatus for manufacturing a cylinder that avoid the disadvantage of long cooling time and can precisely represent the connection between steel and cast iron with little effort.

This object is achieved by a method with the features of claim 1 and by a device with the features of claim 9.

Advantageous developments of the invention are the subject of dependent claims.

Further features and advantages of the invention result from the description of an embodiment with reference to the single figure.

The single figure shows a schematic sectional illustration of a molding box 1 and therein an outer mold 2 made for vertical casting from mineral molding material. An associated core 3 is fastened centrally in the interior of the outer mold 2. The space between the core 3 and the outer mold 2, which is a casting mold 4, is dimensioned such that a steel ring 5 to be provided on its inner surface with a gray cast iron running layer and an induction coil 6 surrounding the steel ring 5 can be arranged concentrically with the core 3 to be introduced later. The induction coil 6 is fixed in the outer mold 2 with refractory concrete in such a way that a cavity 7 remains between the inner surface of the steel ring 5 and the outer surface of the core 3, which serves as a lower section of the mold 4 for receiving the iron forming the gray cast iron layer. A cavity 8 lying above the steel ring 5 forms the upper portion of the casting mold 4, the remaining cylindrical sleeve outer shape. The mold 4 is filled with protective gas, for example with argon. For the purpose of cooling water supply, tubular electrical feed lines 9 of the induction coil 6 as well as the induction coil 6, which is also made from tube cross sections, run in the molded material of the outer mold 2. The surface section of the core 3 opposite the steel ring 5 is provided with fireclay plates 10 for protection against the heat radiation.

The steel ring 5 is heated in the mold 4 by means of the induction coil 6 to white heat. Immediately afterwards, the casting mold 4 is filled with liquid gray cast iron via pouring channels 11, the latter entering into a fusion welded connection with the incandescent steel ring 5. After the composite blank has cooled, it is removed from the casting mold 4, destroying it, and fed to further processing.

In deviation from the exemplary embodiment described above, the preheating of the steel ring 5 can also be carried out in another way, for example by introducing a flame gas behind the steel ring 5 or according to the principle of resistance heating. Furthermore, the steel ring 5 can be provided on the inner surface with a protective layer of nickel, tin or other suitable materials before it is introduced into the casting mold 4 in order to ensure additional protection against oxidation.

• Das Vorheizen des Stahlrings verhindert, daß zwischen dem flüssigen Eisen und dem Stahlring nur eine örtlich begrenzte und damit ungenügende Verschmelzung erfolgt;
• das Vorheizen des Stahlrings verhindert, daß es wegen unterschiedlicher Temperaturen zu unterschiedlichen Schwindungsbeträgen und damit zur Bildung eines Schwindungsspalts zwischen den beiden zu verbindenden Materialien kommt;
• das Vorheizen des Stahlrings bewirkt im Gegenteil, daß es aufgrund des etwas stärkeren Schrumpfens des Stahls im Verhältnis zu dem des Graugusses zu einer kombinierten Schmelz- und Schrumpfverbindung kommt;
• das Einleiten eines Schutzgases in die Gußform 7 vor Beginn des Vorheizens des Stahlrings verhindert die Bildung einer Zunderschicht auf der Oberfläche des Stahlrings, die sonst einer sicheren Verschmelzung der beiden Materialien entgegenstehen würde;
• die nahezu unüberwindbaren Schwierigkeiten eines Verfahrens, bei dem das zunderfreie Vorheizen des Stahlrings, sein Einbringen in eine Gußform, das Schließen der Gußform und das anschließende Ausgießen mit flüssigem Eisen nacheinander erfolgen würden, entfallen durch das Vorheizen des Stahlrings in der gießfertigen Gußform unter Schutzgas;
• die reproduzierbar präzise Lage und Ausbildung der Verbindungszone zwischen Stahl und Grauguß ist ein wesentlicher Qualitätsvorteil und senkt in erheblichem Maße die Ausschußkosten gegenüber dem Schleuderverfahren.

The method for producing a cylinder liner described above by its steps has the following main advantages:

• The preheating of the steel ring prevents that there is only a localized and therefore insufficient fusion between the liquid iron and the steel ring;
• the preheating of the steel ring prevents different amounts of shrinkage due to different temperatures and thus the formation of a shrinkage gap between the two materials to be joined;
• on the contrary, the preheating of the steel ring results in a combined fusion and shrink connection due to the somewhat greater shrinkage of the steel in relation to that of the gray cast iron;
• introducing a protective gas into the mold 7 before the preheating of the steel ring begins prevents the formation of a Layer of scale on the surface of the steel ring, which would otherwise prevent a secure fusion of the two materials;
• The almost insurmountable difficulties of a process in which the scale-free preheating of the steel ring, its introduction into a casting mold, the closing of the casting mold and the subsequent pouring out with liquid iron would take place one after the other by the preheating of the steel ring in the ready-to-cast mold under protective gas;
• The reproducibly precise location and formation of the connection zone between steel and gray cast iron is a significant quality advantage and considerably reduces the reject costs compared to the centrifugal process.

Claims (9)

1. Process for the production of a cylinder of an internal combustion engine by means of a mould (4), comprising an outer mould (2) and a core (3) of mineral moulding material with the steps:

   - applying a heat source (6) acting in the mould (4) to heat a steel ring (5) to be introduced into the mould (4) and to be bonded with grey cast iron;

   - introducing into the mould (4) the steel ring (5) to be bonded with grey cast iron;

   - introducing the core (3) into the outer mould (2);

   - closing the mould (4);

   - filling the mould (4) with protective gas;

   - heating the steel ring (5) in the closed mould (4) to white heat;

   - casting the liquid grey cast iron, thus forming a grey cast iron bushing, and

   - cooling the steel ring (5) fused to the grey cast iron bushing.
2. Process according to claim 1, characterised in that heating of the steel ring (5) is effected by means of an induction coil (6).
3. Process according to claim 1, characterised in that heating of the steel ring (5) is effected by means of a gas flame.
4. Process according to claim 1, characterised in that heating of the steel ring (5) is effected in accordance with the principle of resistance heating.
5. Process according to one of claims 1 to 4, characterised in that the inner surface of the steel ring (5) is provided with an oxidation-resistant layer before being introduced into the mould (4).
6. Process according to claim 5, characterised in that a nickel layer is applied as the oxidation-resistant layer.
7. Process according to claim 5, characterised in that a tin layer is applied as the oxidation layer.
8. Process according to one of claims 1 to 7, characterised in that argon is used as the protective gas.
9. Device for carrying out the process according to claim 1, having a mould (4) which is formed from an outer mould (2) and a core (3) of mineral moulding material, wherein a heat source (6) is fitted in the mould (4), a steel ring (5) to be bonded with grey cast iron is introduced and can be heated by means of the heat source (6) to white heat, and the mould (4) is filled with protective gas so that it can be heated before casting without damage.

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