DE2740716C2 - Process for the continuous production of spheroidal graphite cast iron - Google Patents

Description

25th

The invention relates to a method / ur continuous production of spheroidal graphite cast iron, in which a ferrous Insert with a carbon content of not less than 2 wt .-%, an introduction of cast iron in solid State in the primary melt filling the furnace chamber to -Vi until the furnace chamber is filled and a the secondary melt is subsequently heated in the furnace up to the tapping temperature.

From the magazine "Gießereitechnik", 4th volume, issue 5. 1958. Page 118 is a method of production of cast iron with spheroidal graphite known, in which a master alloy is directly in the pan is placed under the iron beam. This master alloy is made in the acidic crucible from an amount of 6% metallic Mg. 30% ferrosilicon (75% Si), 50% ferrosilicon (45% Si) and 14% soft steel fragments produced, wherein the burn-up is 10%. The utilization of the Mg obtained in the master alloy is about 40 to 65%, whereby the pan must be heated to red heat before the magnesium treatment.

From DE-AS 13 02 000 a briquette for introducing magnesium into metallic melts is known, which is produced from a mixture of comminuted substances by cold pressing, is used to introduce comminuted pure magnesium into metallic melts, a binder-free mixture of 7 to 25 % crushed magnesium, the remainder crushed iron, is cold-pressed ^{under a pressure of at least 1 t / cm 2.} The aim of these briquettes is to ensure that the magnesium is only released after a considerable time and without the risk of an explosive generation of magnesium vapor without introducing undesired substances into the melt to be treated.

From DE-OS 14 33 565 is a multi-stage process for the production of cast iron using known from improved pig iron, which is characterized in that started from an iron ö5 whose casting would contain essentially type C AFS graphite with a stem-like cooking foam and that said molten iron contains a first effective amount of a spheroidal graphite-leading agent is added, then poured and cooled and that this pig iron, which is at least partly contains spheroidal graphite or nodular graphite and no cooking foam, added to an oven batch, then this batch melted and then with a second addition of nodular graphite and finally cast into cast iron with spheroidal graphite or nodular graphite the second addition can be kept lower than if the starting iron (with C AFS graphite) would not have been treated with spheroidal graphite-producing agent.

This process is based on a special iron, the casting of which is essentially CAFS-type graphite with stem-like cooking foam would contain, and this will melt a spheroidal graphite former is added and the solid cast iron obtained is added to a furnace charge, whereupon this batch melted and formed with a second addition of a spheroidal or nodular graphite Is offset by means. If this means, as known per se from the specialist literature (K. J. Wastschenko and LSofroni "Magnesium-treated cast iron" VEB German publishing house for basic industry, Leipzig 1960, Pages 195 to 198) is magnesium, there are twice the environmental pollution that comes with magnesium additions liquid iron melts can be observed, also for the repeated melting of the entire Batches require an enormous amount of energy.

The invention is based on the object of a process for the continuous production of nodular graphite castings with such a way of working and such surcharges to indicate to the liquid metal, that made the technological process simpler and reduced the working conditions for the personnel Environmental pollution can be improved.

In a method of the type mentioned at the outset, this is achieved according to the invention in that the added cast iron in the solid state at least one spheroidal graphite former in a 4 to 10 fold the content of normal nodular cast iron on the element in question contains and it alone or together with ductile iron return material with a normal content of spheroidal graphite former is added.

Magnesium and / or cerium are advantageously used as spheroidal graphite former.

The inventive method makes it possible to melt the cast iron by adding spheroidal graphite formers, like magnesium and / or cerium below the liquid metal level in the furnace and at a lower level To treat temperature at which, in contrast to the treatment of the melt in the pans, there is no Burn-off of the spheroidal graphite former results and thus also not the one with the formation of magnesium or Cereal vapors that cause environmental pollution when it dissolves in an explosive manner.

In the method according to the invention, the melting of the melt is also compatible added cast iron in the solid state with the excess content of the transferred into the melt Spheroidal graphite former with heating up to the tapping temperature. So the metal doesn't need any Heating up to higher temperatures and thus a corresponding energy saving is achieved.

As the treatment of molten cast iron

goes with the spheroidal graphite former in the method according to the invention in the furnace, are omitted the conventional processes necessary auxiliary equipment for the foundries, namely the vessels in which otherwise the spheroidal graphite formers are introduced.

In the method according to the invention, the air in the foundry and thus the working conditions for the operators are better to such an extent that they can do without powerful ventilation systems and the process can be continuous.

The addition of nodular cast iron fragments as return material means that the Casting waste from Kugeigraphitbildnern is now not lost, but for the spheroidization of the Graphite can be exploited. is

The method according to the invention is explained below with the aid of implementation examples.

example 1

In a neutrally lined induction furnace with a capacity of JO kg, 20 kg of normal foundry iron was melted, the melt filling ^{the furnace for 2} hours. The furnace was then refilled by adding solid cast iron with a magnesium content of 0.2 to 0.5% by weight (ie up to 10 times as much as in normal nodular cast iron) of the same chemical composition in blocks to the melt. After the cast iron had melted and the secondary melt had been heated to a tapping temperature of 1380 to 1400 "C, one third (10 kg) of the melt was tapped into a pan for casting in molds and 10 kg of solid cast iron at 0.3 Up to 0.5% by weight of magnesium was added again. The subsequent charging of the furnace with cast iron in the solid state, the melting of the insert and the heating of the secondary melt in the furnace proceed without pyro-effect and smoke development. The process proceeds as smoothly as in the Normal remelting of cast iron. The continuity of the process was maintained within 5 hours. During the entire melting process, the residual magnesium content (0.08 to 0.12% by weight) remained unchanged and graphite in spherical form was retained in the castings. The mechanical Properties of the cast iron such as tensile strength and the elongation A were included after a brief annealing

Oh = 65 kp / mm ² and ό = 7 to 8%.
Example 2

Cn

^{To accelerate the start of the melting process, a primary cast iron melt filling the furnace space to 2} U was formed in an induction furnace with a capacity of 60 kg, which was treated in a conventional manner by adding cerium. The melt in the induction furnace was then added to cast iron blocks with 0.2 to 0.5% by weight of cerium and normal nodular cast iron as return material (riser, sprues) in an amount making up the remaining 30% of the furnace's capacity. The result of continuous metal melting was similar to that of Example 1.

Example 3

28 kg of starting material from normal foundry iron was melted down in a 50 kg induction furnace. Solid cast iron with 0.2% by weight of cerium and magnesium of the same chemical composition was then introduced in blocks into the melt. After the cast iron with the increased cerium and magnesium content had become liquid and the furnace chamber had been filled with the melt, it was heated to 1340 ° C., whereupon it was cast under low pressure in molds to form castings with walls 2 to 20 mm thick. Then cast iron blocks with 0.2% by weight of magnesium and cerium and 25% by weight of normal nodular cast iron were placed in the furnace as return material, the addition taking place below the liquid metal level. The process was stable, and testing of the samples showed mechanical properties as in Example 1. Yttrium can also be used as a spheroidal graphite former.

For castings at higher temperatures (1450 ^° C.), solid cast iron with 0.8% by weight of magnesium was melted in an induction furnace. In this case, the graphite spheres that formed were smaller and the plastic properties of the cast iron (Λ = 10 to 12%) were better.

The tests confirm the advantages that the method according to the invention has over the known ones Procedure has. For example, it was found that the treatment of the primary cast iron melt through Adding solid cast iron with an increased content of spherigraphite formers to the furnace below of the liquid metal level at a relatively low temperature of the melt a smaller one Electricity consumption and minor losses of Kugeigraphitbildnern brings with it.

Moreover, the spheroidal graphite cast iron melting process goes on continuously, proceeds steadily, without Pyro effect and thus creates pollutants due to the lower amount of air in the foundry Smoke gases, but also the elimination of auxiliary equipment better working conditions for the operators.

Claims (2)

Patent claims: 1. Process for the continuous production of spheroidal graphite cast iron, in which an iron-containing insert with a carbon content of not less than 2% by weight is melted down, and solid cast iron is introduced into the ^{primary melt, which fills the furnace chamber to 2} A, until it is filled of the furnace chamber and a subsequent heating of the secondary melt in the furnace up to the tapping temperature takes place, characterized in that the added cast iron in the solid state contains at least one spheroidal graphite former in an amount that exceeds the content of normal nodular cast iron on the element in question and it is added alone or together with ductile iron return material with a normal content of spheroidal graphite former. 2. The method according to claim 1, characterized in that the spheroidal graphite former is magnesium and / or cerium can be used.