DE3200104A1 - METHOD AND DEVICE FOR CASTING AN ALLOY - Google Patents

Description

Applicant: Abex Corporation,

530 Fifth Avenue, New York

Method and apparatus for casting a

alloy

The invention relates to casting metals that are alloyed with significant amounts of rapidly oxidizing elements such as aluminum, titanium, zirconium and others. Adding such elements in appreciable amounts can prevent the Significantly improve the properties of castings, especially the heat-resistant properties. He can also decrease the content of such critical elements as chromium in stainless steels or heat-resistant alloys. However, if the percentage is approximately more than 1% (weight percent), it is necessary in many cases to be in a vacuum pour to exclude an oxidizing atmosphere.

In the presence of oxygen, the easily oxidizing element impairs castability; it forms slag and non-metallic Inclusions in the surface and within the casting, which reduce the quality of the finished article and actually makes it unacceptable as a casting that is likely to fail in service.

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Vacuum casting is expensive and has a casting size limit. When the vacuum casting is not performed can be or an appropriate device is not available, the advantage of the higher amount of the oxidizable Element cannot be achieved in terms of a number of properties of the alloy.

If even fractions of a percent of such elements, e.g. Ti or Cr, are added, the proportion is of the alloy additive normally recovered in the casting, 70 to 40% of the amount added and sometimes even less, so that excessive amounts must usually be added to make up the desired balance to obtain. With the assuming cost of these materials, there is an adverse cost impact. Additionally difficulties are encountered in achieving the optimum proportion of these elements in the alloys, and according to the uncertainty in the determination or origin of the losses. Furthermore, the remainder of these elements is common given in the form of macroscopic oxide inclusions, in which form the element in question is not the desired one Provides improvement in properties.

An object of the invention is to enable significant amounts of a rapidly oxidizable element

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tes are introduced into a casting or alloyed with it can, wherein the casting is poured at ambient temperature and usual foundry conditions, while the impairing oxidation atmosphere at the contact with the metal pouring stream and the metal within the mold cavity effective is prevented.

Another object of the invention is to enable levels of 1/2% aluminum upwards in steel castings or highly heat-resistant castings can be introduced without resorting to vacuum melting processes must in order to produce a flawless and acceptable casting. Another job is to get a high To achieve recovery percentage of the added elements in the finished cast product.

The solution to these objects is given in the claims.

The invention is explained in more detail below in connection with the accompanying drawings, for example. Show it:

Figure 1 shows a section through a pouring device according to the invention at the first moment of pouring a Base alloy from a ladle,

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FIG. 2 shows a section like FIG. 1, in which the state the pouring device is shown after pouring out of the pan,

Figure 3 shows a section as in Figures 1 and 2, in which the device during the filling of the

The mold cavity is shown,

FIG. 4 shows a section through a simplified casting device in which a protective atmosphere is only available for the mold cavity is provided, Figure 5 is a schematic representation of a multiple casting arrangement using features according to the invention.

According to Figure 1, a casting device 5 closes an alloy chamber 10 used in this casting process.

The mixing of a base metal with a rapidly oxidizable alloy element takes place in the alloy chamber 10 (Figure 1). The space of the alloy chamber is against the atmosphere protected by using a lid 23 made of steel or ceramic. A sealing collar 25 is located between the top of the chamber and the lid 23 to create a seal against the atmosphere. A pouring cup 22 or a pouring ring is arranged above a pouring opening 26 in the cover 23. A non-oxidizing atmosphere becomes

is supplied to the alloy chamber at a pressure which is greater than the ambient pressure of a source 20. The displaced air leaves the alloy chamber through the opening 26 and through ventilation ducts 24.
5

A separable plate 12 is attached to the bottom of the chamber, and the chamber has a bottom pouring opening 14 extending through a fusible stopper 15 is closed. A separable gasket layer 13 is between the top a mold 16 (sand mold) and the steel plate 12 are provided. The alloy chamber and steel plate are on the Form clamped by an anchor bolt or bracket engaging the side of the sand mold box F, the type and Way from Figure 1 can be seen.

The plug 15 is fusible at the casting temperature of the molten metal M. A protective atmosphere (non-oxidizing or neutral) is supplied to the mold cavity with a pressure, which is greater than the ambient pressure of the source 20 connected to the inlet of a supply line 17 in a wall of the mold is connected, and the displaced air is via ventilation ducts 18, which are formed in the mold walls, from the Mold cavity pushed out. After an oxidizable metal 19 has been deposited on the bottom of the alloy chamber and after the protective atmosphere in the mold cavity and in

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Once the alloy chamber has been introduced, the pouring device is ready for pouring the molten metal M to be alloyed with the rapidly oxidizable metal (FIG. 1).
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When the base metal has been poured from the ladle 21 through the pouring ring 22 into the alloy chamber 10 is, it melts the oxidizable metal, which then alloy with the metal M, thereby forming the alloy M +.

Turbulence, melting of the oxidizable alloy element and rapid penetration of the atoms of the alloy element into the molten base metal, which is at a relatively high temperature, ensure a homogeneous distribution and an alloy of the oxidizing element in the base alloy. The expanding protective gas leaves the alloy chamber through the ventilation ducts 24. During this time, the plug 15 has kept the melt in the alloy chamber for a while (FIG. 2). Any incidental or accidental oxidation that can occur in the few minutes of mixing the solid additional element with the molten metal M will float as slag S (Figure 2) on top of the molten bath in the alloy chamber and will understandably be the last to flow out of the chamber in the worst case as slag or the like in the pouring channel , in the distributor channel and / or in the riser.

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find which parts will be separated from the casting. With the Time the plug 15 melts (Figure 3). When the first part of the molten metal due to gravity through the Mold opening flows through into the mold cavity and the temperature inside the mold cavity increases rapidly, the expanding protective atmosphere is quickly displaced through the ventilation ducts 18. This process is carried out by the inflowing molten metal accelerates further, which may block the ventilation ducts shown in FIG.

Thus, there is no contact between the interior of the mold cavity and the ambient atmosphere in the foundry until the last portions of the melt M + have left the alloy chamber. Air can only enter the mold cavity after which the molten metal completely from the alloy kairaner has flowed out and has filled the mold cavity, which is harmless with regard to the quality of the casting.

The castings produced as described above with aluminum as the oxidizable element have a uniform Distribution of aluminum in itself. The castings also have an exceptionally good surface appearance, which is characterized by a surface that is free of defect-causing oxides compared to castings the same alloy, but with only 2 to 3% aluminum,

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Cast in the usual way in which the foundry specialist expects or expects unclean or slagged surfaces. must assume that many oxidic surface precipitations or contain other oxide-related defects or impairments.

example

Using the method and apparatus described, a cast heat treatment tray was made a heat-resistant alloy prepared as follows.

49.8 kg of a base alloy A from a composition according to Table I were produced in an induction melting furnace, using conventional foundry methods. Next, an oil-bonded silica sand mold was replaced by conventional Mold making method prepared, but provided with ventilation ducts according to the new features.

The device described above was fitted with a fusible steel disc plug (1020 steel = unalloyed steel with 0.2% carbon), which had a thickness of 6.9 mm and a diameter of 82.6 mm. 2.72 kg of an aluminum alloy 356 from a composition according to Table I was melted separately and poured into the alloy chamber. This melt

then froze above the steel stopper. As can be seen, the weight of the aluminum alloy is about 5.2% the overall detail to be poured into the mold cavity, and the aluminum contained represents a value of approximately 4.8%.

As already mentioned, the alloy chamber was covered and the device was flushed with an amount of argon gas (approx 10 times the volume of the mold cavity) to the ambient air from both the alloy chamber and the mold cavity.

After flushing the alloy chamber and mold cavity, 49.8 kg of base alloy A was placed in a snout ladle entered and then at a temperature of 1593 ° C through the upper pouring opening of the alloy chamber With the help of the casting ring 22 poured into the alloy chamber.

Seven seconds after the end of this pouring process, the steel stopper and the new one, containing aluminum, melted Composition flowed through the bottom pour opening of the alloy chamber into the oxygen-free mold cavity.

The now formed casting solidified, and after cooling it was released from the sand mold and cleaned after the

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conventional foundry methods. Subsequent analysis revealed that the casting was 4.8% aluminum contained, so essentially a 100% recovery or preservation of the added aluminum. Contrary to expectations of those familiar with the effect aluminum has on cast quality has been the surface the cast shelf with 4.8% aluminum is completely free of slag or oxide-related roughness or defects and was judged to be actually superior to a conventional casting, the latter being free of aluminum apart from traces of the same, which are usually used for deoxidation.

Tabe lle I
Basic compositions of the alloys in the example

C% Cr% Ni% Fe% Al% Si% Mg% alloy A: 0.40 10.0 20.0 remainder alloy 356: - 92 (min) 7.0 0.3

For the person skilled in the art it is clear that the proposed subject is not limited to the exemplary embodiments described. E.g. the base alloys with quickly oxidizable metal, not ferrous metals be limited, provided that the oxidizable

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Component can be applied at a melting point appropriate to the process.

In the same way, the fusible stopper can be replaced by a mechanically removable, non-melting stopper made of metal, Refractory ceramic, graphite or another material corresponding to the characteristics of the process will.

The protective atmosphere can consist of nitrogen gas or another non-oxidizing gas. The oxidizable element, such as aluminum, can be placed on the bottom of the alloy chamber be laid in the form of an even layer of small, solid pieces (Figure 1). Alternatively, the aluminum separately melted and then poured onto the bottom of the alloy chamber, after which it solidifies there. Elements, such as titanium, which themselves have a fairly high melting point, can spread on the bottom of the alloy chamber are like prepared alloys selected for a high content of the aforementioned element with a melting temperature that is significantly lower than the melting temperature of the base alloy. Unlimited Alloy combinations of the rapidly oxidizable element can be achieved by using special or powder metal compacts prepared on the bottom of the alloy

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chamber to be distributed.

Examples of useful alloys for achieving degradation of the melting point of titanium are e.g. the eutectic alloys 72% Ti - 28% Ni and 68% Ti - 32% Fe with a melting point of 943 ° C and 1086 ° C, respectively; So far below the liquidus temperature of e.g. an iron alloy with 25% Cr, 20% Ni and 0.40% C, which is to be alloyed with titanium, i.e. at a temperature of about 1400 ° C. 10

The oil-bonded silica sand mold can be replaced by molds made by a large number of conventional mold-making

processes and materials are produced, as well as through sufficiently ventilated permanent molds. The proposed subject can also be used in the same way for the production of centrifugally cast objects, for which permanent molds are used will.

When the additional amount of an oxidizable element is not high enough or when the amount or scope of non-metallic Inclusions in a casting are not critical in terms of subsequent casting stress, in some cases Successful results can also be achieved without the use of a protective atmosphere in the alloy chamber. A corresponding change to the pouring device is

shown in FIG.

When filling multiple molds from a single ladle using conventional foundry methods, the oxidizable element is placed in the ladle and the concentration of the oxidizable element decreases casting to casting and excessive slagging causes serious problems.

Although the castings made according to the proposal contain rapidly oxidizable elements, this contains molten metal brought into the ladle and held in it, apart from any rapidly oxidizable elements of very small amounts used for the usual deoxidation. Hence, many forms can come from one single pouring or holding pan can be poured (Figure 5) without the risk of rapidly oxidizing elements are lost in the ladle slag during the time required for the multiple shapes.

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Claims (9)

Patent attorneys * "," ... * *., ",!. * .. *,! -. Q O Π Γ) 1 D- ..> ugo Wilcken O ZUU \ Dipi. Irin, Thomas Wilcken Musterbshn 1 · 2400 Lübeck 1 Applicant: "Abex Corporation, 530 Fifth Avenue, New York Claims 1. Method of casting an alloy containing one or more contains rapidly oxidizable elements, whereby atmospheric oxygen is excluded during casting and wherein the alloying of the base alloy or the base metal with the oxidizable element or elements in one Alloy chamber takes place shortly before casting, characterized by the following process steps: a) that a casting mold is made, the casting space with ventilation means for the escape of those located in the space Air is provided and which communicates with a supply passage through which a non-oxidizing gas to can be fed into the room, b) that an alloy chamber is positioned adjacent to the casting space, the casting chamber having a bottom Has casting opening which communicates with the casting space, wherein the alloy chamber by means of a removable Lid is isolated from the atmosphere and the lid has vents for the escape of air and a pouring opening has at its top, c) that the bottom pouring opening of the alloy chamber with a Stopper is closed to the casting chamber or alloy chamber to separate from the casting space or mold cavity, • w Q β a 32001OA a quantity of the oxidizable element being placed in the casting chamber, d) that non-oxidizing gas is supplied to the casting space and the casting chamber in an amount to displace the air contained therein and that, after the air has been displaced, molten metal is poured on top of the oxidizable element in the alloy chamber whereby the casting alloy is produced in the alloy chamber,
e) and that the plug is removed shortly after the oxidizable element has been alloyed with the molten metal in the alloy skammer to allow the alloyed metal to flow into the casting space, thereby displacing the protective atmosphere through the venting means, while at the same time the ingress of air into the casting room is avoided. 2. The method according to claim 1, characterized in that the plug is meltable by the molten metal. 3. The method according to claims 1 and 2, characterized in that the rapidly oxidizable metal is melted first and is poured into the alloy chamber above the stopper and solidified there before the molten metal is poured in will. - 3 - 4. Casting device for introducing at least one rapidly oxidizable element into a molten metal to alloying it with this, characterized by the following features: a) a mold is provided, the walls of which enclose a casting space and which are provided with a supply passage and at least one ventilation passage is provided, both passages communicating with the casting room, b) an alloy chamber is provided which is removable and is mounted adjacent to and communicating with the casting space for molten material through an upper pouring opening Pick up metal, which reaches the rapidly oxidizable element in the alloy chamber, this chamber has a bottom pouring opening that creates a connection to the pouring room, c) that the alloy chamber by means of a removable cover with an upper pouring opening against the atmosphere is insulated and wherein the alloy chamber has a gas supply duct and vent ducts, d) that means are provided which are a source of non-oxidizing Provide gas, the source being connected to the supply ducts, so that by supplying non-oxidizing Gas to the casting room and to the alloy chamber, the air located therein is displaced to the casting room and loading the alloy chamber of atmospheric oxygen free, e) that a removable plug in the bottom pour opening is provided to the alloy kairaner from the casting room to separate, f) and that sealing means between the bottom of the alloy chamber and the upper region of the casting chamber are provided to the surrounding, oxygen-containing atmosphere exclude or withhold .. 5. Apparatus according to claim 4, characterized in that the plug is a metal plug which is inserted through the Alloy chamber cast, molten metal is fusible. 6. Apparatus according to claim 4 or 5, characterized in that the mold consists of a sand mold and that the alloy chamber is a metal support lined with a refractory material. . 7. Apparatus according to claim 4, characterized in that the mold consists of a centrifugal mold for the production of centrifugally cast objects consists. 8. Apparatus according to claim 4 or 5, characterized in that the alloy chamber is open at the top and no protective contains atmosphere. 9. A method of casting multiple molds with an alloy containing rapidly oxidizable elements, in which the in Metal located in a holding pan or pouring ladle does not contain any rapidly oxidizable elements, characterized in that that the method according to claim 1 is used for pouring into any mold.