Metal founding – Process – Shaping liquid metal against a forming surface
Patent
1991-05-08
1993-03-16
Batten, Jr., J. Reed
Metal founding
Process
Shaping liquid metal against a forming surface
164114, B22D 1302, B22D 1310
Patent
active
051936046
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a process for centrifugal casting copper, copper alloys, or other alloys, wherein, in order to reduce or, respectively, avoid the oxide layer that forms on the inner surface of the casting at least one additive is introduced into the mold. In addition, the present invention relates to an apparatus for centrifugal casting copper or copper alloys with a rotatable mold a pouring tube and a delivery means for additives, that, in addition to the pouring tube, leads or can be led into the mold, particularly into the interior of the casting.
The use of borax as a flux is generally known. Further, the addition of borax is known from the US-PS 2,265,740 for centrifugal casting of iron to tubes of cast iron; in this case borax is blown onto the inner surface of the molded tubes. The DE-OS 2,422,339 describes the addition of fluxes, for example common salt, cryolite, fluorite, sodium silicate, in the centrifugal casting of iron and non ferrous metals. Further, DE-AS 1,296,750 relates to the addition of liquid borax-lime-soda-window glass-mixtures when centrifugal casting iron, wherein, these mixtures have been heated to a temperature above the temperature of the iron melt. An apparatus similar to initially mentioned kind is usual for the delivery of additives, and is known from FR-A 2,481,624 or, JP-A 56-131,157. When producing centrifugal castings of copper or copper alloys, an oxidation layer forms on the inner surface of the castings as a result of oxidation, which layer must be turned out. The thickness of this oxidation layer depends in particular, on the wall thickness of the casting and from the amount of oxygen that is absorbed during the casting process and during cooling. A disturbing oxidation layer of considerable thickness is formed even at relatively thin wall thicknesses of approximately 15 to 20 mm, and this increases in proportion to the wall thickness. In the case of thicker castings, the thickness of this layer, which has to be turned off, can amount to up 15% of the wall thickness. The thickness of this oxidation layer is, in particular, affected by the cooling speed of the melt and the length of time during which the melt on the inner surface of the casting retains higher temperature since atmospheric oxygen has an unfavourable effect and affects the thickness of the oxide layer that forms on the inside surface.
DESCRIPTION OF THE INVENTION
According to the invention a process of the kind initially mentioned, by which process these disadvantages can be avoided, is characterized in that powdered borax is applied as an additive immediately after pouring the melt into the mold onto the particularly still liquid inner surface of the casting, if desired in conjunction with finely divided mixtures of metals that have an affinity for oxygen and/or powders of graphite and/or fire-clay and/or charcoal, with a layer thickness of 0.5 to 4 mm. After introducing the additive forming the layer, the mold with the casting is further rotated and is cooled with water. The introduction of borax after the melt has been poured substantially prevents the formation of an undesired layer of oxidation and reduces the transfer of heat, thus maintaining the flowability of the metal on the inner surface and enhancing the so-called post-drawing effect (subsequent flow of the still flowable metal during solidifying) during the hardening process. It has been shown that a considerable reduction of the previously required internal addition of approximately 1/4 overmeasure could be achieved. Thereby, in most instances, the castings that are produced do not require preliminary turning and, also in the case of thicker wall thicknesses, it is provided a possibility of being able to produce castings of this kind at a pre-machining quality. This results in considerable savings in labour, materials and weight which are accompanied by a considerable reduction of the costs.
With regard to the statements on page 10, fourth paragraph of the DE-OS 2 422 339, the additives are to be di
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patent: 4095643 (1978-06-01), Farlow et al.
patent: 4632172 (1986-12-01), Etienne et al.
Abstract of Japanese Patent Publication 56-151157 published Nov. 24, 1981.
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