Patent Application
20160008877
The invention relates to a process for producing a composite cast part containing an insert part and casting material, wherein the insert part is integrally bonded to the casting material.
The production of composite cast parts makes it possible to combine the preferred properties of the materials at the appropriate points. Thus, components can be assembled optimally according to their requirements and fields of use on account of the material combination. However, this requires an integral or metallurgical bond between the materials. When casting steel parts into cast iron or aluminium alloys, there is often the problem of an inadequate bond between the steel part cast in and the surrounding or cast-in material. The early solidification of the molten mass on account of the contact with the insert part at room temperature hinders a metallurgical or integral bond between the casting material and the steel part, as a result of which gaps can form between the composite partners.
DE 10 2006 041 901 A1 discloses a process for producing metallic composite parts made of steel and/or cast iron. In this process, the part to be cast in, which is produced from steel or cast iron, is coated by means of flux. The aim of the coating is to reduce the oxide skin of the cast-in part, that is to say that the oxide skin of the cast-in part is dissolved and washed away during the casting-in process, as a result of which the casting material can enter into a metallurgical bond.
DE 10 2011 053 858 B3 discloses a process for the use of a component which can be cast in a lost casting mould, wherein a coating agent is applied to a surface of the component to be cast in. The coating agent forms an actively separating surface which prevents the adhesion of the material on the component and also corrosion before encapsulation with casting material.
DE 100 43 105 B4 discloses a process for forming a strong, tough, resilient and/or at least substantially flawless bond between an insert and a casting metal material having a melting point below that of the insert material. The insert is coated with a thin layer of a metallic material which is selected from the group consisting of silver, antimony, bismuth, chromium, gold, lead, magnesium, silicon, tin, titanium and zinc. Thereafter, the casting material is cast against the coated surface of the insert. The coefficient of thermal expansion of the coating is greater than that of the insert and less than that of the casting material. The coated insert is moreover held at a temperature of at least 100° C. for a period of time of at least 5 minutes. As a result of this process, part of the coating should dissolve and be sacrificed to the casting metal material, while part of this coating remains as a diffusion barrier between the insert and the casting material, which should achieve a highly tough bond between the insert and the casting material.
It is an object of the present invention to provide a process and a corresponding composite cast part which, compared to the prior art, achieves an improved bond between an insert part and casting material and also ensures economical production.
According to the invention, this object is achieved by virtue of the fact that the encapsulation or embedding of the insert part is formed by an exothermic material which ignites through the contact with the inflowing casting material or as a result of the ignition temperature being reached. In the process, energy is released and discharged to the surroundings, as a result of which there is a reduced temperature gradient between the solidifying molten mass and the insert part.
The process according to the invention comprises the following steps:
In addition to being used for welding (thermite welding mixtures), exothermic materials are also used in exothermic feeders for foundry purposes. The contact between the molten mass and the exothermic mass triggers a combustion reaction, this ensuring in the feeder that the molten mass solidifying last is located there and therefore it is possible to compensate for the varying volume during the solidification in the cast part. Materials of this type are known from the prior art; EP 1 050 354 A1, EP 0 888 199 B1 and DE 196 42 838 A1 disclose such materials.
In the present invention, such a known material which causes an exothermic reaction is used as an encapsulation or embedding for the insert part to be cast in. The material is ignited through the contact between the exothermic material and the liquid casting material or as a result of the ignition temperature of the exothermic mass being reached. As a result, the insert part is heated up from both sides; this prevents rapid solidification of the casting material in the boundary region to the insert part, since the insert part loses its quenching action for the casting material. The temperature gradient between the casting material and the insert part is minimized. This in turn promotes the carbon diffusion between the casting material and the insert part, as a result of which it is possible to produce an integral or metallurgical bond.
The insert part is preferably produced from steel, copper, bronze, brass, aluminium or an aluminium alloy. The process or the composite cast part can be used in a versatile manner owing to the broad material selection.
The exothermic material preferably comprises a readily oxidizable metal, in particular aluminium and/or magnesium.
Moreover, it is advantageous that the exothermic material comprises an oxidant for the readily oxidizable metal, in particular iron(III) oxide.
The back-fill material used is preferably an oxide, in particular SiO2. The back-fill material serves as filler material, which is mixed with the further substances such as aluminium and/or magnesium and also an oxidant.
The exothermic material preferably comprises a binder, which serves for the cohesion of the exothermic material. An alkali silicate is used as a preferred binder.
A preferred configuration consists in the fact that a cast iron, preferably GJS, GJL and/or GJV, is used as the casting material. By virtue of the insert part which has been cast in, it is possible to achieve a high strength and elongation at break at locations intended for this purpose in the cast component, or it is possible to provide the composite cast component with additional, positive properties for subsequent further treatment.
In the case of composite cast parts which have been produced by processes known from the prior art, the bonds between the casting material and the insert part are usually inadequate. Composite cast parts which have been produced by the process according to the invention have an improved integral bond between the materials.
The use of composite cast parts produced in this way affords a good alternative for substituting cast steel or welded steel structures with the advantage of the known cast iron alloys and the production processes therefor.
As a preferred embodiment, the casting material used is an aluminium alloy; as a result, it is possible, for example, to combine aluminium components with various metallic materials, as a result of which it is possible to utilize the advantage of the weight reduction owing to the lightweight aluminium.
It is preferable that the process according to the invention is employed with lost casting moulds.
This process makes it possible to use an insert part which has a sufficient thickness or wall thickness for making it possible to subject the insert part also to a heat treatment process or welding process after the casting process. Processes which are known from the prior art only make it possible to cast in a steel part which has very thin walls, in order to counter somewhat the rapid solidification and the hindered carbon diffusion owing to the contact between the steel part at room temperature and the casting material.
It is preferable that a hollow body is used as the insert part. The cavity is filled with the casting material and bonds integrally to the insert part. The outer surface of the insert part is encapsulated with the exothermic material or is embedded in the material. Owing to the exothermic reaction of the mass following contact with the molten mass, the mass also emits heat to the insert part, as a result of which there is a harmonized temperature gradient between the solidifying molten mass and the insert part. The insert part can also be bonded to the exothermic material on one side, or in the case of a hollow design from the inside. After the casting operation and removal from the mould, the exothermic material can readily be removed and the outer surface or the inner face of the insert part emerges. Reworking is subsequently possible, but in many cases is also not necessary since the dimensional accuracy and the surface condition are already of good quality. The process according to the invention is also of great interest from an economical point of view owing to the possible reduction of further machining steps. Furthermore, these processes give rise to extended possibilities for post-treating the cast component, e.g. welding or heat treating (also only partially on the insert part).
Composite cast parts of this type produced by the process according to the invention are suitable in particular for general mechanical engineering, for construction machines and for vehicle construction. It is thereby possible for different materials to be economically bonded to one another even in the case of high quantities and for the preferred properties of the individual materials to be combined with one another without the problem concerning an inadequate bond between the materials resulting from early solidification of the casting material arising.
Exemplary embodiments of the invention will be described with reference to the figures, the invention not being limited merely to the exemplary embodiments. In the drawing:
A further exemplary embodiment is shown in
The insert part 3 used is a cylindrical steel pipe made of a high-carbon steel having wall thicknesses of 5 mm which is formed in exothermic material 4 with a defined wall thickness. This steel pipe 3 with the surrounding exothermic material 4 is inserted into the mould 5 to be cast, as can be seen from
