JPS61229462A - Production of nodular graphite cast iron - Google Patents

Abstract

PURPOSE:To produce a nodular graphite cast iron which does not contain metallic oxides and non-metallic inclusions and has defectless quality by treating the molten cast iron with a graphite spheroidizing agent then passing the molten metal into a porous ceramic body having open cells. CONSTITUTION:Two split casting molds consisting of a cope and rag are superposed to form a casting mold 12 provided with a casting cavity 24, a runner 14 and a sprue 20. A reaction chamber 16 is provided in the mid-way of a runner 14 of such casting mold and a graphite spheroidizing agent 18 of an Mg alloy is preliminarily put therein. The porous body 10 consisting of the three-dimensional network skeletal structure having the open cells made of ceramics such as cordierite, alumina or silicon carbide is rested on the down stream thereof. The molten cast iron poured from a sprue 20 reacts with the graphite spheroidizing agent 18 in the chamber 16 and changes the graphite shape of the cast iron from the flake to spheroidal or nodular shape. The cast iron passes through the porous body 10 made of the ceramics in succession thereto so that the sand grains, oxides such as dross and non-metallic inclusions contained n the molten modular graphite cast iron are captured and the nodular graphite cast iron having the defectless quality is cast into the cavity 24.

Description

Detailed Description of the Invention (Technical Field) The present invention relates to a method for manufacturing spheroidal graphite cast iron, and in particular, to a process for spheroidizing molten metal in the process of manufacturing spheroidal graphite cast iron. At the same time as getting
This invention relates to an instant spheroidization process that also serves to remove metal oxides, nonmetallic inclusions, etc. from the molten metal flowing into the casting cavity of the mold.

(Prior art and its problems) In general, when producing spheroidal graphite cast iron, the spheroidizing treatment of the molten metal is performed by adding metals such as magnesium, cerium, calcium, lanthanum, strontium, and lithium to Fe, Si, etc.
It is used as a ferroalloy such as, and is brought into contact with a predetermined molten metal. Therefore, in many cases, considering economic efficiency, etc.
Mg alloy is used for this spheroidizing agent, and Mg is contained in the molten cast iron at a ratio of about 0.030 to 0.040% or more to obtain the desired spheroidal graphite structure. There is.

By the way, Mg used as this spheroidizing agent is
Easily boils in the temperature range of molten cast iron. Generally, the vapor pressure of Mg at normal processing temperatures is more than 10 times the atmospheric pressure, and when it comes into contact with molten metal, it easily burns. Under such conditions, it can be said that it is a very difficult task to incorporate a small amount of Mg into the molten metal with an accurate yield.

Conventionally, in order to obtain a healthy spheroidal graphite structure, safety and
Various studies have been made, and various processing methods have been selected and implemented, taking into account economic efficiency, yield, quality reproducibility, etc.

Here, the methods can be roughly divided into methods in which the treatment is performed outside the mold and methods in which the treatment is performed within the mold. Of the former treatment outside the mold, the most common method is the first method. This is the sandwich method as shown in the figure.

In this sandwich method, the ratio of the inner diameter of the ladle 2: D to the height of the ladle 2: H is determined by considering the reaction time of the Mg alloy.
H is designed according to the processing weight of the molten metal 4, the Mg alloy 6 is placed on the bottom of the ladle 2, the molten metal 4 is poured on top of it, and Mg is contained in the molten metal 4, and there are other methods. This method is basically similar to the sandwich method because it is processed in a fixed container.

However, even in this most common method, Mg
There are problems with the yield of alloys, safety during reactions, etc., and the biggest problem is the disappearance phenomenon in which the Mg content decreases in proportion to the time after the spheroidization process and the effect disappears. , so-called "fading".

This phenomenon of disappearance of the spheroidization effect is due to oxidation or bonding of Mg.
The number of graphite particles decreases and the shape of graphite deteriorates, starting immediately after the spheroidization treatment and continuing to progress until pseudo-flake graphite appears.

Therefore, pouring healthy molten metal into the mold is subject to significant time constraints.

On the other hand, there is an in-mold method for spheroidizing treatment in a mold, in which a spheroidizing agent is charged into a reaction chamber that is part of the sprue system, and spheroidizing is performed at the same time as injection. be.

Therefore, this in-mold method has advantages such as a very high Mg yield and low risk of environmental and air pollution, and also because it does not cause the loss of spheroidization effect.
It can be said that it is an effective treatment method in terms of economic efficiency, workability, and obtaining a healthy spheroidal graphite structure.

In this way, in contrast to the sand-inch method, which is currently the most commonly used method, the in-mold method does not lose the spheroidizing effect, prevents smoke generation, and has a high yield of added Mg.
Although this method has many advantages, at the current stage it has problems such as non-metallic inclusions being mixed into the cast product.

That is, as mentioned above, the vapor pressure of Mg at normal processing temperatures is generally more than 10 times that of the atmosphere, and the boiling point of Mg is relatively low (approximately 100°C), so an extremely violent reaction occurs. This energy significantly damages the mold wall that forms the reaction chamber, causes sand grains to simultaneously enter the product (casting) cavity of the mold, and immediately after the reaction, the molten metal flows into the product cavity, causing a reaction. As MgO-based dross, which is sometimes generated, is guided into the product cavity and mixed in without being removed, even if a stable spheroidized structure is obtained, the product has a poor appearance due to sand grains, dross, etc. This causes major problems such as defects and quality deterioration.

(Solution Means) The present invention was made to solve the above-mentioned problems, and it is possible to carry out the spheroidal graphitization treatment safely in a mold, and to obtain a healthy molten metal according to the instant spheroidization treatment method. , in the manufacturing method of spheroidal graphite cast iron.

The gist of this is that a ceramic porous body with a three-dimensional network skeleton structure having continuous pores is installed in the molten metal passage leading to the casting cavity of the mold so as to partition the passage, and A spheroidizing treatment agent for converting graphite into a spheroid or nodular shape is arranged so that the graphite is located in the molten metal passage on the upstream side,
After the graphite in the poured predetermined molten metal is converted into a spheroid or nodular shape by the spheroidizing treatment agent, the treated molten metal is guided into the casting cavity of the mold through the ceramic porous body. This is a method for producing spheroidal graphite cast iron, characterized in that:

More specifically, the spheroidized cores as shown in FIGS. 2(a) to (C1) are made into spheroidized cores as shown in FIGS.
Place it in the mold as shown in figures (a) and (b),
The desired spheroidization process can be carried out by pouring the molten metal.

That is, in FIGS. 3A and 3B, the rectangular block-shaped ceramic foam (porous body) 10 shown in FIGS. A ceramic foam 1 is set on the path 14 to partition it, and this set ceramic foam 1
An intermediate chamber (reaction chamber) 16 is provided in the runner 14 portion on the upstream side of the runner 0, and a predetermined spherical and other agent 18 is accommodated therein.

Therefore, the predetermined molten cast iron poured from the sprue 20 of the runner 14 of the mold 12 is first poured into the spheroidizing agent 18 in the intermediate chamber 16.
The molten metal subjected to the spheroidization process is then guided through the porous weave of the ceramic foam 10 to a casting cavity 24 provided with a predetermined core 22 (if necessary). That will happen. When passing through this ceramic foam 10, metal oxides and non-metallic particles such as sand grains and dross that are present or mixed in the spheroidizing molten metal are removed. ``M'' is captured in the porous mesh-like weave of the ceramic foam 10 and does not flow into the casting cavity 24, so that a healthy, high-quality spheroidal graphite cast iron product can be obtained.

In addition, the ceramic foam 1 shown in FIG. 2 (C1)
0 has a substantially conical protrusion 26 formed on the surface located on the downstream side of the molten metal flow, unlike the one illustrated in FIG. By widening the flow, inclusions such as dross can be effectively captured within the ceramic foam 10.

Further, in another embodiment of the present invention shown in FIGS.
Ceramic foam 30 is set inside to partition it. The ceramic foam 30 is provided with a recess 32 on its upstream surface, and a predetermined spheroidizing agent 18 is accommodated in the recess 32, so that the poured molten metal becomes spherical. curing agent 1
After undergoing spheroidization treatment in step 8, ceramic foam 3
0 through the porous knitted structure into the casting cavity 24.

The spheroidizing agent 18 accommodated and held in the recess 32 of the ceramic foam 30 is preferably in a particulate form in order to enhance the effect of contact with the molten metal.
There is no problem even if it is formed into a shape such as a ring shape or a block shape. Under supported conditions,
It is also possible to contact the molten metal flowing through the runner 14.

The spheroidized core <to, 30) has a high porosity (for example, about 80 to 90%) and has a three-dimensional network skeleton structure of continuous pores, which is mainly composed of cordierite alumina, SiC, etc. A spheroidizing agent (Fe-3i-Ml?, li') made according to the material of spheroidal graphite cast iron or CV cast iron is added to the ceramic foam having
A material having a space in which it can be loaded or loaded with (e-3i-Ca-RE-Mg, Ni-Mg) is preferably used.

Therefore, when manufacturing a product with a casting weight of 30 kg per mold, the sand inch method moderates the reaction of Mg during processing, eliminates the generation of white smoke, and improves the working environment and safety. However, in the method of the present invention,
It is possible to use a ferroalloy with a relatively high Mg content. For example, when the Mg% in the molten metal after spheroidization treatment is set to 0.04%, the Mg alloy containing 8% Mg is 0.5%. Therefore, for a casting weight of 30 kg, the Mg alloy as a spheroidizing agent only needs to be added in a small amount of 150 g. Since it is a system filter, there is no restriction on the shape of the loading part of the spheroidizing agent, and it is possible to use either lumps or granules. The cleaning effect on the molten metal is that it passes through complex three-dimensional continuous pores and reaches the product cavity, which minimizes the amount of non-metallic inclusions, and at the same time, the rectification when the molten metal is injected into the product cavity. This is a highly effective and sound method for spheroidizing spheroidal graphite cast iron.

(Function/Effect) The spheroidization process currently implemented in foundries is economical both inside and outside the mold.

They have been adopted with consideration given to productivity, quality, and safety, but each has its advantages and disadvantages.

The most common spheroidizing method, the sand inch method, is an easy spheroidizing method, but due to the disappearance of the spheroidizing effect, the pouring ratio is subject to time constraints after the spheroidizing process. In addition, this method leaves problems in the automatic pouring system for spheroidized molten metal, and cannot be said to be a desirable processing method in the direction of unmanned and automated casting processes in the future.

On the other hand, the in-mold method as a spherical ratio treatment method in the mold is
There is no disappearance of the spheroidization effect, and there are many advantages such as improved yield of Mg alloy and improved working environment, but due to the contamination of non-metallic inclusions such as dross into the product cavity,
The idea is excellent, economical, safe, easy to work with, and there is no loss of spheroidizing effect, making it possible to create an automatic pouring system for molten metal. Although it has many advantages, the current situation is that it is not suitable for actual adoption.

It can be said that the present invention solves the deficiencies of the above-mentioned in-mold spheroidizing method.

First of all, the most important effect of the in-mold spheroidization treatment method is that there is no disappearance of the spheroidization effect, and there are many advantages such as improved yield of Mg alloy 2 less reaction smoke, stability of quality, and economy. It can have many effects, such as improving the work environment and safety.

Second, because the spheroidized core is a ceramic foam cast iron filter with a three-dimensional network skeleton structure of continuous pores with high porosity, the energy generated by the intense reaction when molten metal comes into contact with the Mg alloy is also absorbed into the spheroidal shape. The processed core absorbs
There was little damage to the mold wall, and nonmetallic inclusions such as slag that flowed in with the molten metal, sand grains from the sprue system through which the molten metal flowed, and MgO-based dross when the Mg alloy reacted with the molten metal were removed. In all cases, this spheroidized core acts as a filter and filters them, and only clean molten metal is injected into the product cavity, making it possible to produce sound castings and eliminating the need for conventional mold processing methods. This will greatly improve the defects.

Third, by selecting the type and amount of the spheroidizing agent to be filled into the spheroidizing core or the intermediate chamber, a range of materials for the spheroidal graphite cast iron can be selected using the same molten metal. This means that there are multiple molding lines within the foundry.
Conventionally, when each material was made of different materials, a separate spheroidization process was required each time, but according to the present invention, this is no longer necessary, which means that multi-material, small-volume production is easily possible. do.

In addition, conventionally, the introduction of an unmanned automatic pouring system for spheroidizing molten metal requires consideration of the phenomenon of loss of spheroidizing effect, and the flow of molten metal during pouring pulsates, making it difficult to pour quietly. However, the spheroidized core according to the present invention has the effect of filtering the molten metal and rectifying the flow of the molten metal, and has the effect of unmanned automation, which has been a problem in the past. It is believed that this will greatly contribute to the introduction of hot water pouring systems.

Therefore, the present invention has great significance as a mold meat treatment using the spheroidization process, and represents a new attempt for the future of the casting industry.

This spheroidizing method can also be fully adopted as a method for treating a small amount of spheroidizing material in C■ cast iron, so it can be said to be a multi-purpose spheroidizing method.

(Example) Next, in order to clarify the present invention more specifically, a comparative experiment was conducted between the sand inch method, the in-mold method, and the instant spheroidization treatment method according to the present invention, which have been widely adopted in the past. Here is an example of what was done.

The experiment was conducted using the method of pouring the metal into a mold after spheroidization using the sand inch method as shown in Figure 1, the conventional in-mold method that does not use ceramic foam, and the spheroidization process shown in Figure 4. The material was FCD50. The chemical compositions of the flake graphite cast iron and spheroidizing agent used are shown in Table 1 below.

Table 1: A sand mold was used as the mold, and the other experimental conditions were horizontal casting.The product was a mechanical part, and the product mold weighed 114 kg.

The casting weight was 20 kg, and the spheroidizing agent was 0.7% in the Sanderuch method and 0.4% in the in-mold method and the instant spheroidizing method according to the present invention.

During this experiment, the violent reaction during the spheroidization process before pouring in the Sand Inch method was not observed at all during pouring in the other two methods. The actual test piece taken from the product used in this experiment had a tensile strength of 51 to 52.5 kg/
mm", elongation rate: 16 to 19%, and it was confirmed that the mechanical strength of the product according to the present invention was the same as that of other methods.

In addition, by examining the microstructure photographs, we were able to confirm an excellent nozzier structure, and the product appearance also showed
There are no defects such as dross or sand eating like in the in-mold method, and the casting surface is excellent, and the yield of smoke and added Mg is 2.
It was possible to confirm the effects of the present invention in terms of workability, product appearance, etc.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram for explaining the conventional spheroidizing method using the sand inch method, FIG. 2(a) is a perspective view showing an example of the ceramic foam used in the present invention, and FIG. is a cross-sectional view of the ceramic foam in FIG. 2(a), FIG. 2(C1 is a diagram corresponding to FIG. 2(b) showing another example of a different ceramic foam, and FIG. FIG. 3 (b) is an enlarged view of part A in FIG. 3 (a), and FIG. FIG. 4(b) is an enlarged view of part B in FIG. 4(a), which is an explanatory diagram of a mold cross section showing an example.

Claims (3)

[Claims] (1) A ceramic porous body with a three-dimensional network skeleton structure having continuous pores is installed in the molten metal passage leading to the casting cavity of the mold so as to partition the passage, and a molten metal passage on the upstream side of the ceramic porous body A spheroidizing agent for converting graphite into spheroidal or nodular shapes is placed inside the spheroidizing agent, and the graphite in the poured molten metal is converted into spheroidal or nodular shapes by the spheroidizing agent. A method for producing spheroidal graphite cast iron, characterized in that the treated molten metal is introduced into a casting cavity of the mold through the ceramic porous body. (2) the spheroidizing agent is housed in an intermediate chamber provided in the mold so as to communicate with the molten metal passage of the mold;
The manufacturing method according to claim 1, wherein the poured molten metal is allowed to pass through the ceramic porous body after being subjected to a spheroidizing treatment using a spheroidizing agent in the intermediate chamber. Method. (3) The spheroidizing agent is supported or held by the ceramic porous body, and the poured molten metal is passed through the ceramic porous body immediately after being spheroidized by the spheroidizing agent. The manufacturing method according to claim 1, characterized in that the method is characterized in that: