JPH0433761A - Casting method with pressurization - Google Patents

Abstract

PURPOSE:To restrain the development of casting defect of porosity corresponding to each material by casting in a pressure vessel and pressurizing with pressure given by the inequality while linking with progress of solidification in the casting. CONSTITUTION:Casting is executed in the pressure vessel and the pressurization is executed with the following pressure with linking with the progress of solidification in the casting. Pa>=0.5*a2*L<2>+Pg Wherein, Pa: pressurizing force a2=beta*fg*mu*fL/k beta: solidified shrinkage ratio, fg: variation or solidified ratio per unit time, mu: coefficient of viscosity, fL: liquid phase ratio, K: transitivity L: distance from the center of the casting to the top part of feeder head, Pg: equilibrium H2 gas pressure in liquid phase at the casting center. By this method, the development of the above casting defect corresponding to various used materials, is restrained and high quality casting can be manufactured with high accuracy and high efficiency.

Description

[Detailed description of the invention]

[Industrial Application U1] The present invention mainly relates to a casting method for casting metals such as aluminum alloys, magnesium alloys, titanium alloys, etc. under pressure in air or an inert atmosphere. [Prior art] In recent years, various methods of manufacturing highly reliable aluminum alloys (hereinafter referred to as aluminum alloys) with high durability have been developed and are becoming more widely used, and the materials for important safety parts of automobile parts are also changing from steel to aluminum alloy castings. Instead, weight reduction is being attempted. For this reason,
Conventionally, even relatively large products have been cast using a low-pressure casting method that enables efficient production with good dimensional accuracy. Special Note Publication No. 48225, 4522B2 This is a casting device that can be separated into upper and lower parts.The molten metal is held in a tundish with a stopper on the upper part, and the stopper is opened and the metal is poured into the mold on the lower part, and the inside of the container is heated to above atmospheric pressure. Pressure casting method. Patent Publication No. 1-309776: After pouring the molten metal into the mold, at least from the start of solidification to the completion of solidification, 2 to IO
While applying a pressure of kgf/c-2, and at 0.8℃7
A method for producing an aluminum alloy casting, which comprises cooling and solidifying a molten metal at a cooling rate of sec or more to make the grain size of microcrystals finer than 70μ decoy. [1L to be solved by the invention] In casting using the above-mentioned low-pressure casting method, it is difficult to completely prevent casting defects when producing thin-walled or edge-to-edge castings with complex shapes, or when using difficult-to-cast materials. n
It is. In order to improve these problems, there is no coagulation control method to prevent the occurrence of pinholes and microshrinkage defects, depending on the type of material used. In the present invention, as the injected molten metal solidifies in the mold, pressure is applied appropriately according to the shape and weight of the product, so that the molten metal is properly filled in the space during solidification and contraction. By not leaving the gas in the molten metal in the casting after solidification, the above-mentioned problems with the conventional low-pressure casting method can be solved, and the occurrence of the above-mentioned casting defects can be reduced in response to the various materials used. It is an object of the present invention to provide a casting method that can produce castings of inferior quality with high efficiency and suppressing the amount of metal. Measures to solve ctxu] Since metal contracts during solidification, in order to prevent pinholes and cavities (hereinafter referred to as porosity), the molten metal must be bonded as explained in Figure 1. . Porosity generation is suppressed by liquid phase replenishment in the Suzuka area where solidification has not progressed much, and by interdendritic flow IN in areas where solidification has progressed considerably. Porosity occurs when hydrogen gas vesicles are nucleated at the base of the dendrite trees, which separate from the dendrite as solidification progresses, and at the final stage of solidification, are located between the grains between the dendrites, and due to solidification contraction, the shape becomes large. become. Porosity nucleates and grows at the uni C (shaded area in Figure 1) where the melting pressure (P) in the ls material becomes lower than the hydrogen gas pressure (Pc). Here, by pressurizing with an inert gas during solidification, the inclined wall in the shaded area is eliminated and porosity is no longer generated.The present invention aims at this effect. The liquid phase hydrogen gas pressure Pa in the casting is expressed as follows. PG: [[Hslha(1-fL)Kso+fuKt
e)] 2(+) However, [)lal: Initial hydrogen gas concentration in the molten metal (to) fL: Liquid phase ratio Kin: Coefficient (0', 06cc/+00g @
at11"') KLH: Coefficient (0,6cc/100
ge gtm"2) Table 1 shows the relationship between the hydrogen gas pressure in the residual liquid phase, the initial hydrogen gas pressure, the initial hydrogen gas degree, and the liquid phase ratio. The change in pressure is shown in Figure 2. Hydrogen gas pressure increases rapidly as the liquid phase rate decreases. Table 1 Relationship between hydrogen gas pressure in the residual liquid phase, initial hydrogen gas pressure, initial hydrogen gas concentration, and liquid phase rate [Example 1] A silk product with a riser attached to the center of a +OOx+OOx30I1m flat plate specimen as shown in Figure 3 was cast. (f
L), pressure (P), velocity of liquid phase flow between dendrites (
U) is shown in FIG. L is the height of the riser. U is represented by the following formula. β is the amount of contraction accompanying coagulation, and in the case of ACIB, it is 0.059. If equation (2) is integrated and set to u:o(x:0), the following equation is obtained. u: a + book x
(3) Furthermore, the liquid phase flow velocity and melting pressure of dendrite a are as follows [1ar
The formula for cy holds true. However, k: Transmittance μ: Viscosity coefficient of liquid phase (4.59 in the case of ACIB)
010-"kg-s/c■2) From equations (3) and (4), the following equation is obtained. However, a 2 knee a + 寥a f
L/k (5) formula, P = Pa (x = O),
Integrating as P=Pa (x=shi), the following equation is obtained. P , = 0.5 zero a 2L 2+ P ,
(6) Equation (6) is
This is the formula for the pressing force Pa required to prevent porosity from occurring. In order to calculate Pa, fL is determined in advance by experiment or computer simulation. The transmittance k is calculated using the following formula. However, d: 7.5 zero 10-4Δ θ, @
, 2G Δθl: Partial solidification time at the position of L/2 fL: The pressurizing force necessary to suppress the liquid phase ratio porosity generation at the position of L/2 is shown in Table 2, in the case of an initial hydrogen gas concentration of 0.2 cc/100 g. Figure 5 shows the relationship between the liquid phase ratio and the pressurizing force at an initial hydrogen gas concentration of 0.6cc/
The case of +00g is shown in FIG. In the case of this experiment, the generation of porosity is suppressed if the residual liquid phase is 0.2 and the pressurizing force is 4 kgf/ci2 or more. Table 3 shows the relationship between the tensile properties and the applied force.
When 12 was added, the mechanical properties were significantly improved. Table 2 Pressure force required to suppress porosity generation Table 3 Relationship between tensile properties and pressure force

【Effect of the invention】

As described above, according to the present invention, it is possible to suppress the occurrence of porosity casting defects in accordance with each material without being limited to the materials used. It has excellent quality and
In addition, it is possible to efficiently manufacture products with high accuracy. Note that the present invention is not limited to aluminum alloys, but also magnesium alloys,
Effects similar to those described above can also be achieved when used for casting titanium alloys and the like.

[Brief explanation of the drawing]

Figure 11 Explanation of porosity generation in castings Zukka 2WA Change in hydrogen gas pressure during solidification Figure 3 Casting shape Figure 4 Flow rate and pressure of liquid phase between dendrites in casting 0 Liquid phase ratio No. 51g Initial hydrogen gas concentration 0 .2cc/10(Ig
Relationship between liquid phase ratio and pressurizing force in case of Fig. 6 Relationship between liquid phase ratio and pressurizing force in case of initial hydrogen gas concentration 0.6cc/+OOK Fig. 1 Fig. 6 Fig. 2 Fig. fL 4th 3rd Figure u, p, tL

Claims (1)

[Claims] A melting furnace or holding furnace and a mold are provided in a pressure vessel,
A pressurized additional casting method, characterized in that casting is performed in the pressure vessel, and pressurization is performed at the following pressure in conjunction with the progress of solidification of the casting. P_a≧0.5*a_2*L^2+P_Q However, P_a: Pressure force a_2=β*■_s*μ*f_L/k β: Solidification shrinkage rate ■_s: Change in solidification rate per unit time μ: Viscosity coefficient f_L : Liquid phase ratio k: Transmittance L: Distance from the center of the casting to the top of the feeder P_Q: Equilibrium H_2 gas pressure in the liquid phase at the center of the casting