JP2000042706A - Premelting flux for centrifugal casting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a molten slag-formation and feeder head and heat insulation effect of flux used for a centrifugal casting. SOLUTION: This flux is composed of powder obtd. by heating and melting the powder mixture containing each compound of silica, alumina, calcium carbonate, magnesium carbonate and calcium fluoride and executing the pulverizing treatment of this cooled solidified material. Desirably, this flux has the composition (by wt.%) composed of 25-30% SiO2, 2.5-3.5% Al2O3, 35-45% CaO, 4.5-5.5% MgO, 8-15% CaF2, 2-9% LiO2 and the balance FeO and MnO and 1.2-1.5 basicity [(CaO)/(SiO2+Al2O3)]. The grain size of this flux is adjusted to 20-200 mesh and the transportation property is secured without damaging good feeder head and heat insulation effect and the automation of charging the powder into the molten metal is easily achieved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved flux for coating and protecting the surface of a molten metal in a mold in centrifugal casting.

[0002]

2. Description of the Related Art In centrifugal casting, molten metal (molten metal) injected into a mold is pressed in layers along the inner peripheral surface of the mold by the action of centrifugal force, and cooled and solidified while maintaining that state. A hollow cylindrical casting (tube) is formed. Flux is used for the purpose of improving and stabilizing the casting quality. The flux applied to the molten metal in the mold becomes molten slag due to the retained heat of the molten metal, coats the surface of the molten metal, shuts off contact with the atmosphere to prevent oxidation of the molten metal, and keeps and cleans the hot water for the molten metal. (E.g., absorption and removal of non-metallic inclusions), thereby improving casting quality. Silica sand (Si
O ₂ ), alumina (Al ₂ O ₃ ), calcium carbonate (C
ACO _3), magnesium carbonate (MgCO _3), calcium fluoride (CaF _2), a powder of other compounds, the powder mixture were mixed in the amounts ratio based on the setting basicity (particle size:
About 100-300 mesh) is used.

[0003]

In order to make the flux more effective in covering the molten metal, it is necessary to dissolve the applied flux quickly and uniformly coat the surface of the molten metal in a good fluidized state. It is. However, the conventional flux does not have a sufficiently high melting rate, and takes about 100 seconds (the surface temperature of the molten metal:
About 1500-1600 ° C). 10 as flux powder
Fine particles having a fine particle size of 0 to 300 mesh are used, but the melting rate cannot be sufficiently increased only by making the particles finer. In the case of a fine powder having a size exceeding 200 mesh, the particles tend to aggregate and float on the surface of the molten metal. Further, such fine powder has poor powder transportability, and it is difficult to automate the flux administration operation. The present invention provides an improved flux for overcoming the above problems associated with centrifugal casting.

[0004]

The flux for centrifugal casting according to the present invention is prepared by mixing silica,
A powder obtained by heating and melting a powder mixture containing each compound of alumina, calcium carbonate, magnesium carbonate, and calcium fluoride, and pulverizing the cooled solidified product.

[0005] The conventional flux for centrifugal casting is a raw material powder.
(Silica, alumina, calcium carbonate, magnesium carbonate
Mu, CaF_TwoIs a simple mixture of compound powders
In contrast, the flux of the present invention heats the powder mixture.
Manufactured via a melting process, which is referred to herein as
It is called pre-melt flux. Mixing of raw material powder
Calcium carbonate (CaCO)_Three) 、 Carbonated
Gnesium (MgCO_Three), Etc. are heated and melted
Then, the following thermal decomposition reaction occurs to generate CO_TwoIs separated. Subordinate
Therefore, the premelt flux of the present invention contains CaCO
_Three, MgCO_ThreeAre not present. CaCO_Three→ CaO + CO_Two↑ MgCO_Three→ MgO + CO_Two↑

A conventional flux containing a carbonate (CaCO ₃ , MgCO _3, etc.) is applied to the molten metal and causes a decomposition reaction (endothermic reaction) of the carbonate by the retained heat of the molten metal. Therefore, the formation of molten slag is delayed, and the generated CO ₂ gas serves as an oxygen supply source for the molten metal. On the other hand, the flux of the present invention does not have such a thermal decomposition reaction, shortens the time required for forming the molten slag, and eliminates the concern of oxidative contamination of the molten metal by CO ₂ gas.

In the conventional flux (mixture of plural kinds of compound powders), the melting point (SiO ₂ : about
2230 ℃, Al ₂ O ₃ : about 2020 ℃, CaO: about 2572 ℃, CaF: about 13
60 ° C) and specific gravity (SiO ₂ : about 2.3, Al ₂ O ₃ : about 3.99, Ca
O: about 3.4, CaF: about 3.2), etc., and the difference in physical properties between the components is a factor that hinders rapid and uniform melting of the flux. The premelt flux of the present invention eliminates such inconveniences as a result of the fusion and integration of a plurality of types of compounds. The effect of the flux of the present invention obtained via the pre-melt process to improve the slag forming property is remarkable, and the conventional flux (the slag forming time: about 1
00 seconds), the molten slag can be achieved in only a few seconds (4 to 6 seconds) (all at a temperature of the melt of 1500 to 1600 ° C.). Protect the coating.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The premelt flux of the present invention is prepared from silica, alumina, calcium carbonate, magnesium carbonate, calcium fluoride, and other compounds (iron oxide, manganese oxide, etc.) as in the conventional flux. It is manufactured using the selected compound powder as a raw material. These compounds are blended at an appropriate ratio based on the set basicity to obtain a raw material powder mixture. Note that carbonates such as calcium carbonate are subjected to a roasting process (about 700 to 800 ° C.) in advance, converted into powders such as CaO and MgO by a thermal decomposition reaction, and then mixed with other compound powders. It may be.

The raw material powder mixture is heated and melted by a heating device such as an electric furnace. The processing temperature is from 1200 to 1300 ° C., and the melt processing is achieved by heating and maintaining for an appropriate time (for example, 0.5 to 1 Hr) in a set temperature range. Cooling of the resulting melt may be furnace cooling or air cooling.
The cooled solidified product is pulverized to an appropriate particle size by a ball mill or other pulverizing means and classified to obtain a desired pre-melt.
Get flux.

The preferred components of the premelt flux of the present invention include the following. All component ratios are by weight. _{SiO 2: 25~30%, Al 2} O 3: 2.5~3.5
%, CaO: 35 to 45%, MgO: 4.5 to 5.5
%, CaF ₂ : 8 to 15%, Li ₂ O: 2 to 9%, balance: FeO and MnO, basicity = CaO / (SiO ₂ +
Al ₂ O _3): 1.2~1.5.

[0011] CaO and SiO ₂ are basic components of the flux. SiO ₂ enhances the homogeneity of the molten flux, and CaO has the effect of cutting the SiO ₂ network to increase the fluidity of the flux. Al ₂ O ₃ is
MgO enhances the wettability with the molten metal by promoting vitrification of the flux, and MgO improves the metallurgical wettability of the flux on the surface of the molten metal. CaF ₂ lowers the melting point of the flux and enhances the fluidity and the effect of absorbing and removing nonmetallic inclusions. Li ₂ O also lowers the viscosity of the flux and improves the fluidity. Furthermore, by adjusting the basicity to the range of 1.2 to 1.5, a low melting point of the flux is ensured, and the fluidity of the flux and the action of purifying the molten metal can be maintained well. Later, the peeling of the solidified flux remaining on the surface of the casting is facilitated.
FeO, MnO, and the like have an effect of improving the releasability of the solidified flux.

The powder particle size of the premelt flux of the present invention is the same as that of a conventional flux (particle size: 100 to 300 mesh).
, A relatively coarse particle size configuration of 20 to 200 mesh can be obtained, and even with such a relatively coarse particle size, good meltability can be ensured. In addition, in the particle size configuration, unlike the conventional fine powder, the powder has a good powder fluidity, so that the flux administration operation can be automated. For example, as shown in FIG. 1, the molten metal (M) is cast into the casting mold through the casting hopper (3) from the casting opening of the casting mold (2) horizontally mounted on the rotary drive roller (1), while the other end is formed. The flux (F) is administered to the molten metal (M) in the mold by the flux administration hopper (4) arranged at the casting port. Since the flux (F) has good powder transportability, it falls down in the hopper by its own weight and is automatically supplied to the molten metal in the mold, and the supply amount is optionally adjusted by a valve (such as a solenoid valve) (5). . The timing of the administration of the flux to the molten metal, the dosage, and the like may be set according to a conventional method of conventional centrifugal casting.

The pre-melt flux of the present invention has good releasability after solidification accompanying cooling and solidification of a casting. That is, since the solidified flux generated on the surface of the casting gradually peels off during the cooling process of the casting, there is almost no adhesion residue on the inner surface of the casting, and even if the adhesion remains, gently wipe it with a rag or the like. Thus, it can be easily removed. The inner surface of the casting using the conventional flux requires a grinding allowance of about 2 mm for finishing, but the inner casting surface of the casting obtained using the flux of the present invention is extremely smooth and beautiful. Therefore, there is almost no need for machining, and even when it is necessary, the grinding allowance is very small.

[0014]

EXAMPLES (1) Production of Test Flux Powders of silica, alumina, calcium carbonate, magnesium carbonate, calcium fluoride, iron oxide and manganese oxide are mixed. The mixed powder is charged into an electric furnace and heated and melted (1300
° C x 0.5Hr). After the melt is allowed to cool naturally in the air, the solid is pulverized (ball mill) and classified to obtain test fluxes A and B. As comparative examples, test fluxes a and b (mixture of raw material powders, without a pre-melt step) corresponding to conventional materials were separately prepared. The particle size of fluxes A and B (Premelt) is 20-200 mesh, fluxes a and b
The particle size of the (raw material powder mixture) is 100 to 300 mesh. Table 1 shows the composition of each test flux. The compositions of fluxes a and b (both mixed powders) are shown in terms of values after administration to molten metal (carbonate pyrolysis).

(2) Casting test Cast steel material: stainless cast steel (JIS G 5121 SCS 1 equivalent material) Molten casting temperature: 1640 ° C Cast pipe size: inner diameter 750, length 5000, wall thickness 110 (mm) Flux dose: The flux was applied to the molten metal in the 20 kg mold via a hopper arranged on the side of the centrifugal casting mold.

For each of the test fluxes, the melt slag time, the releasability of the solidified flux after casting, the casting surface properties (smoothness) of the inner surface of the casting tube, and the mechanical grinding allowance of the inner surface were compared and evaluated. The results shown were obtained. The molten slag time was determined by measuring the temperature of the molten metal surface coated with the flux immediately after the start of casting with a radiation thermometer. The peelability after casting was evaluated based on the amount of residual flux solidification observed on the inner surface of the cast tube cooled to room temperature and the strength of the adhesion. (...
Good, Δ: somewhat poor, ×: poor).

[0017]

[Table 1]

[0018]

[Table 2]

As shown in Table 2, the fluxes A and B of the invention example were molten in a very short time compared to the fluxes a and b of the comparative example. Further, the fluxes A and B have little adhesion of the solidified flux after casting, and have better releasability than the fluxes a and b of the comparative example. Further, the inner surface of the cast pipe using the fluxes a and b of the comparative example has a rough casting surface and requires a grinding allowance of 1.5 to 2 mm for finishing, whereas the fluxes A and B of the inventive example were used. The casting tube has a smooth and beautiful casting surface that does not require machining. This shows the excellent heating effect of the hot water by the flux, and the difference from the comparative example is obvious.

[0020]

The flux for centrifugal casting according to the present invention is quickly melted, exhibits an excellent heat retention effect, and has good releasability after casting. Due to the improved feeder heat retention effect of the flux of the present invention, the inner surface of the casting tube has a remarkably smooth and beautiful casting surface, and the finish grinding allowance can be greatly reduced, thereby reducing machining costs and improving product yield. Is obtained. This effect of improving the casting quality sufficiently compensates for the disadvantage of the additional cost required for heating and melting (premelt) the raw material powder mixture. Further, by adjusting the particle size of the flux powder, it is possible to automate the dosing of the molten metal, thereby enabling the efficiency of the centrifugal casting operation to be improved.

[Brief description of the drawings]

FIG. 1 is a front explanatory view showing an example of a supply mode of a flux in centrifugal casting.

[Explanation of symbols]

 1: Rotary drive roller 2: Mold 3: Melt casting hopper 4: Flux dosing hopper 5: Valve F: Flux M: Molten metal

Claims (3)

[Claims] 1. A powder mixture containing each compound of silica, alumina, calcium carbonate, magnesium carbonate and calcium fluoride, which is blended based on a set basicity, is heated and melted, and a cooled solidified product is obtained by pulverizing. Premelt flux for centrifugal casting made of powder. 2. SiO ₂ : 25 to 30% by weight, A
_{l 2 O 3: 2.5~3.5%,} CaO: 35~45%,
_{MgO: 4.5~5.5%, CaF 2:} 8~15%, L
i ₂ O: 2 to 9%, the balance being FeO and MnO;
Basicity [(CaO) / (SiO ₂ + Al ₂ O ₃ )]:
The pre-melt flux for centrifugal casting according to claim 1, wherein the flux is 1.2 to 1.5. 3. The premelt for centrifugal casting according to claim 1, which has a particle size of 20 to 200 mesh.
flux.