JPH0520184B2 - - Google Patents

Abstract

1. Process for centrifugal casting of tubes in which liquid cast iron is introduced into a rotating metallic mould, wherein an additive material in powder form is also introduced into this, characterized in that there is introduced, as additive material, a nickel alloy in powder form on to the inner surface of the rotating mould before the introduction of the liquid cast iron, in order that an alloyed peripheral layer is formed at the outer surface of the tube.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a method for injecting molten cast iron into a rotating metal ingot mold, and charging a filler into the mold before or during pouring of the molten cast iron. The present invention relates to a method for centrifugal casting of tubes, comprising the steps of:

BACKGROUND OF THE INVENTION Methods for manufacturing tubes by centrifugal casting have been known for many years. In this method, a predetermined amount of molten metal passes through a runner and is injected into a rotating ingot mold to form a casting. The casting operation must be performed within a predetermined time to achieve the desired properties. It is widely known to cast molten cast iron for centrifugal casting of tubes, and the molten cast iron can be spheroidal graphite cast iron or layered graphite cast iron.

Problems to be Solved by the Invention Tubes manufactured by centrifugal casting methods have many possible uses. A particularly important field of use is the transport of all types of liquids. Pipelines manufactured for this purpose are buried underground, as a result of which the pipes are in direct contact with the soil. As a result of this contact, a chemical or electrochemical reaction can occur between the tube and the soil surrounding the tube, leading to failure of the tube.

The occurrence of chemical and/or electrochemical reactions in the above-mentioned pipes buried underground can be prevented by adopting various measures. However, the known procedures require further processing of the finished tube and, accordingly, corresponding equipment. These treatments involve applying tar to the tubes, which are then immersed in a tar bath.
Other known procedures include wrapping flexible plastic foil around the tube or coating the tube with polyethylene paint by spraying or extruding it. The application of glass fiber reinforced additive coatings is also known. Despite the considerable expenditure involved in applying protective coatings, complete and reliable protection cannot be ensured because the aforementioned protective coatings are damaged, especially during storage, transport and burial. However, even if the protective coating is not damaged before the pipe is buried, soil movement may occur subsequently, e.g. after burying the excavation pit in which the pipe was buried, due to traffic loads and consequent soil subsidence. Damage to the protective coating inevitably occurs as a result of this.

It has been found that they are particularly dangerous if the above-mentioned protective coatings are damaged at points. Corrosion is concentrated at the damaged point and then spreads rapidly from this point. Corrosion begins on the outer circumferential surface of the tube and spreads from the outside to the inside of the tube.

The problem of the present invention is a method for centrifugal casting of tubes as described above, which retains protection similar to that described above against chemical and/or electrochemical reactions between the tube and its surroundings, and which reliably prevents damage to said protection. to develop.

Means for Solving the Problem According to the invention, this problem is solved by forming a corrosion-resistant layer of an alloy with the tube on the outer surface of the tube into which the filler is centrifugally cast. Ta. Thus, the present invention involves injecting molten cast iron into a rotating metal ingot mold and having a higher specific gravity than the molten cast iron;
A filler made of a nickel alloy having a nickel content of 80% or more is charged in the form of a powder into the mold before or during pouring of the molten cast iron to coat the outer surface of the tube to be centrifugally cast with the nickel alloy. A method for centrifugal casting of a tube having a corrosion-resistant layer on its outer surface, characterized in that it produces a cast iron tube with a corrosion-resistant layer made of an alloy with the tube.

It is generally known to use fillers when pouring molten metal into a rotating ingot mold or during centrifugal casting of tubes. The mold is charged during pouring. These fillers include, for example, a fluxing agent (DE 3105145), which is used to form a sealing slug on the inner surface of the tube and which also absorbs impurities introduced into the molten metal. do.

Fillers can also be mixed in, for example, in order to retard the cooling of the molten metal in the ingot mold and thereby improve the texture and thus the quality of the tube (DE 2460510).

In connection with the centrifugal casting of tubes containing two metals, it is known to sequentially inject different molten charge materials to form different layers in a rotating ingot mold. (West German Patent Publication no.
No. 2852030). In this method, the next layer is only injected when the first layer reaches a temperature below the solidification temperature. The inner layer can be a plated layer containing nickel as an alloying component.

In contrast to the use of the above-mentioned known fillers during centrifugal casting of tubes, the present invention provides a solution to the aforementioned problems without forming an additional protective layer on the outer surface, and in which an alternative protective layer is applied to the metal tube wall. The idea is that this can only be achieved if the tube is formed as a part of the tube and the structure of the tube is changed correspondingly. The formation of the above-mentioned protective layer can be achieved in a relatively simple manner during pouring of the molten metal if a suitable filler is introduced into the ingot mold before or during the pouring of the molten metal into the mold. I recently discovered something surprisingly possible. Nickel alloys with a nickel content of 80% or more have proven particularly suitable. Other alloying elements can be boron, silicon, chromium and copper. The alloy is known and commercially available as a corrosion-resistant and heat-resistant material. This alloy is poured into a centrifugal casting mold in powder form with a particle size of about 0.1 to 1 mm. The specific gravity of the alloy is considerably greater than that of molten cast iron, approximately 7.8 g/cm ² .

The melting point of the nickel alloy should be below 1300°C, thus lower than the casting temperature of molten cast iron of 1350-1380°C. Particularly favorable conditions are obtained when the melting point of the nickel alloy is below the liquid phase (solidification) temperature of molten cast iron, ie below about 1150°C.

[Example] The present invention will be further explained by giving examples (simply described as examples unless otherwise specified) below. The following example illustrates an embodiment of a tube manufactured by centrifugal casting from spheroidal graphite cast iron using the method described above.

Example 1 A rotating steel ingot mold of a centrifugal casting machine was injected with a metal powder called Hastelloy D and having the following chemical analysis: 85% Ni;
Si10% and Cu3%. This material was injected in powder form through a runner simultaneously with the molten cast iron. The metal powder has a melting point of 1120° C. and a specific gravity of 7.8 g/cm ² .

In the outer wall area of the tube in which the metal powder and the injected cast iron are centrifugally cast, a sufficient amount is added so that the alloy outer wall area with a thickness of 0.1 to 1 mm, preferably 0.4 mm, consists of austenitic nodular cast iron (21 to 24% Ni). metal powder must be injected.

Example 2 A rotating steel ingot mold of a centrifugal casting machine has a chemical composition of 94% Ni, 3% B, and 3% Si, and the temperature is 1050℃.
A metal powder with a melting point of . The injection was carried out evenly over the entire mold, for example using a screen. The amount of metal powder was measured in a similar manner to Example 1.

After injecting the metal powder, in a second operation molten iron was injected into the mold. An alloy pipe outer skin made of austenitic nodular cast iron was again formed.

The method described above is not limited to the centrifugal casting of tubes using layered graphite cast iron or spheroidal graphite cast iron, but can in fact be used equally well for other molten metal charges. The metal powder used must have a lower melting point and higher specific gravity than the raw material.

Claims (1)

[Claims] 1. Molten cast iron is poured into a rotating metal ingot mold, and a filler made of a nickel alloy having a higher specific gravity than the molten cast iron and having a nickel content of 80% or more is added in the form of a powder. to produce a cast iron tube having a corrosion-resistant layer made of an alloy of the nickel alloy and the tube on the outer surface of the tube to be centrifugally cast by charging the molten cast iron into the mold before or during pouring. A method for centrifugal casting of tubes having a corrosion-resistant layer on the outer surface, characterized by: 2. Claim 1 in which the other alloying element is selected from the group consisting of boron, silicon, chromium and copper.
The method described in section. 3. The method according to claim 1, wherein the filler has a melting point of 1300°C or lower. 4 As the melting point of the filler, the liquidus temperature of molten cast iron,
A method according to claim 3, in which a temperature of 1150° C. or less is selected.