RU2052316C1 - Casting method with successively directed crystallization - Google Patents

Abstract

FIELD: casting production. SUBSTANCE: method comprise steps of casting an alloy to a chill mold from a batch furnace along a metal duct into a pouring cup, from which along through a cavity of a feeder the alloy is being fed to a cavity of a mold. At time moment, when the alloy covers a bottom of the cavity of the mold and closes a cavity of the feeder, a mechanism for lifting a casting plate ans system for cooling the chill mold are being simultaneously turned on. The casting plate, being moved upwards, cuts off feeders from the casting being still in a liquid state. Using of a cooling member, whose part is arranged in a bottom of the cavity of the mold and contacts with the alloy, provides intensive heat sink uniformly along the whole bottom area. EFFECT: enhanced quality of casting structure. 2 cl, 4 dwg

Description

 The invention relates to foundry, in particular to permanent mold casting, and can be widely used in the manufacture of any castings, especially large ones, in which a flat crystallization front can be created and the largest of which can be used for power supply. The invention can be applied in the manufacture of castings from aluminum alloys.

 A known method of casting (Foundry technology. Color casting. Handbook. M. Engineering, 1989, S. 415-417), in which the mold, heated above the liquidus temperature of the alloy, is placed on a cooled tray crystallizer and filled with superheated alloy. When pouring, the mold is inside the heating device (inductor). After a short technological exposure, the mold is lowered down from the heating zone at a certain speed together with the mold pan. During the solidification process, a directional structure of the casting is formed. However, cast ingots are obtained by this method, and it is not possible to obtain castings of machine parts. The method is suitable only for individual production.

 The closest technical solution is a method of sequentially directed crystallization. The essence of this method is that the liquid alloy enters the lower part of the mold by a metal tube. The shape relative to the end of the tube slowly moves downward, i.e. new portions of the alloy arrive at the partially hardened part of the alloy in the mold, which ensures a sequentially directed crystallization of the casting.

 However, the known method has the following disadvantages: the method is suitable only for individual casting, as it requires a large preparation of the mold. This makes the method inefficient; yield is low, since there are costs of liquid metal on the gating system; gating system remains.

 The purpose of the invention is to increase productivity through the use of the proposed method on rotary multi-position chill machines using multi-seat chill tooling, increase yield (90% and higher) due to the lack of a gate system, which is cut off by a movable gate plate even in the liquid state of the alloy. The absence of the gate system makes it possible to completely eliminate very labor-intensive operations such as chipping and debris of the gate system.

 In FIG. 1 shows a diagram for implementing the method; in FIG. 2, section AA in FIG. 1; in FIG. 3 section BB in FIG. 1; in FIG. 4 lower part of the movable sprue plate.

 The scheme for implementing the method consists of the back half 1 of the chill mold, the front half 2 of the chill mold, the central stationary part 3 of the chill mold, in which the movable sprue plate 4 is installed, consisting of the upper part 5 of the plate 4, the lower part 6 of the plate 4 and the insulating layer 7. In the upper parts 5 of the plate 4 have a cavity 8 of the riser, a cavity 9 of the feeder and the sprue channel 10. In the rear half 1 of the chill mold and the front half 2 of the chill mold there is a cavity 11 of profit and a cavity 12 of the form, into the bottom of which radiators of refrigerators 13 are connected with the cooling channel 14, Happy Birthday from the other side abutting against the pressure plate 15 through the gasket 16. The mechanism for raising and lowering (not shown) the plate 4 includes a switching device 17 and a rod 18. A window 20 is made in the sprue bowl 19.

 The alloy is poured into the chill mold from the metering furnace through a metal wire (not shown) to the gating bowl 19, from which through the window 20 it enters the riser cavity 8, and then through the gating channel 10 to the feeder cavity 9 and then to the mold cavity 12. The lower part of the riser is made so that the kinetic energy of the alloy stream is extinguished and the alloy calmly, laminarly enters the cavity 12 of the form. At the moment when the alloy fills the bottom of the cavity 12 of the mold and overlaps the cavity 9 of the feeder, at the same time, a mechanism (not shown) for raising and lowering the plate 4 and cooling the chill mold are turned on. Plate 4 rises up and at the same time cuts off the feeders from the casting even in a liquid state. The cooling medium circulates through the cooling channel 14, washing away the radiators of the coolers 13 in contact with the alloy. Refrigerator radiators 13 are made of a material with high thermal conductivity, which makes it possible to quickly cool the cast alloy, creating a flat crystallization front.

 Upon completion of pouring, the plate 4 is returned to its original position by means of a mechanism (not shown) for raising and lowering. The parameters of the plate 4 are selected by calculation, depending on the cross section of the casting and the casting rate of crystallization of the casting. As the plate 4 rises, the alloy fills the overlying layers, as it were, by layers, feeding the underlying layers, providing sequentially directed crystallization of the casting, while simultaneously displacing sequentially generated gases (for example, from sand rods at the time the mold is filled with hot alloy).

где V_n скорость подъема литниковой плиты, м/с;
μ- коэффициент расхода (зависит от сечения питателя);
S_пит площадь поперечного сечения питателя, м²;
n число питателей;
g ускорение свободного падения, м²/с;
Н_о высота отливки, м;
S_ф площадь поперечного сечения отливки, м².The rate of rise of the sprue plate is determined from the condition of continuity of the flow of liquid metal;
v _p =

where V _{n the} speed of the gating plate, m / s;
μ - flow coefficient (depending on the cross section of the feeder);
S _pit the cross-sectional area of the feeder, m ² ;
n number of feeders;
g acceleration of gravity, m ² / s;
N _{about the} height of the casting, m;
S _f the cross-sectional area of the casting, m ² .

k где V_м линейная скорость истечения металла из питателя, м/с;
S_пит=

S_ф где τ_в- время заполнения формы сплавом, с;
Учитывая, что H_o= k

, то S_пит=

где k коэффициент затвердевания, м/с^1/2.The dimensions of the cross section of the feeder are determined from the condition of material balance in the solidification zone:
S _pit • v _m • n S

k where V _{m the} linear velocity of the flow of metal from the feeder, m / s;
S _pit =

S _f where τ _in is the time of filling the form with the alloy, s;
Given that H _o = k

, then S _pit =

where k is the coefficient of solidification, m / s ^1/2 .

≥ -ω_л

где Т_ж градиент температуры в жидкой фазе, ^оС/м;
V_в скорость затвердевания, м/с;
ω_л тангенс угла наклона линии ликвидус сплава;
С_т относительная концентрация второго компонента сплава в твердой фазе;
k_p коэффициент распределения компонента, равный
k_p=

, где С_ж относительная концентрация второго компонента в жидкой фазе;
Д_ж коэффициент диффузии второго компонента в жидкой фазе;
Максимальная скорость затвердевания из условия теплового баланса на фронте затвердевания в предположении Т_ж _→ 0 равна
v_макс=

где λ_т коэффициент теплопроводности твердого металла, Вт/м ^оС;
Т_т градиент температуры в твердой фазе, ^оС/м;
ρ_т плотность твердой фазы, кг/м³;
L удельная теплота кристаллизации, кДж/кг.It should be noted that the flat crystallization front is stable in the absence of concentration supercooling, which is determined by the condition:

≥ -ω _l

where T _{W the} temperature gradient in the liquid phase, ^about C / m;
V _{in the} speed of solidification, m / s;
ω _{l the} tangent of the slope of the liquidus line of the alloy;
C _{t is the} relative concentration of the second alloy component in the solid phase;
k _p component distribution coefficient equal to
k _p =

where C _{w the} relative concentration of the second component in the liquid phase;
_Well diffusion coefficient D of the second component in liquid phase;
The maximum rate of solidification from the condition of the heat balance at the solidification front under the assumption T _W _ → 0 is
v _max =

where λ _{t the} coefficient of thermal conductivity of the solid metal, W / m ^about ;
T _{t the} temperature gradient in the solid phase, ^about C / m;
ρ _{t the} density of the solid phase, kg / m ³ ;
L is the specific heat of crystallization, kJ / kg.

Using the proposed method with sequentially directed crystallization of castings in comparison with existing methods has the following advantages:
several times increase in productivity due to its use on existing high-performance equipment (for example, on rotary multi-position chill machines with multi-seat chill molds);
increase in yield (up to 90% or more) due to the lack of a sprue system;
the possibility of obtaining olives from composite alloys by creating a crystallization front.

Claims (2)

 1. METHOD FOR CASTING WITH SEQUENTIALLY DIRECTED CRYSTALLIZATION, comprising layer-by-layer pouring of the melt into the mold through the gate system, which from the beginning of pouring begins to move relative to the mold, and cooling from its bottom during crystallization, characterized in that the gate system having feeders They are carried out in a movable gate plate, from the beginning of pouring the melt, they begin to move it upward, cutting off the feeders from the casting in a liquid state.  2. The method according to claim 1, characterized in that the cooling is carried out using one or more cooling elements evenly placed with the upper end flush with the bottom of the working cavity of the mold and in contact with the melt for more intense heat removal from the bottom of the mold.

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