RU2125498C1 - Method of casting large-sized cylindrical shells - Google Patents

Abstract

FIELD: foundry. SUBSTANCE: mold is filled with liquid metal. After hardening in upper part of mold of metal layer of preset thickness of shell wall, metal is drained through draining hole. Draining is executed for the time equals to difference of duration of shell wall hardening at its upper and lower end faces. EFFECT: higher quality of shells and reduced labor input in manufacture of parts. 2 cl, 1 dwg

Description

 The invention relates to foundry, in particular to the production of large cylindrical shells.

 A known method of casting cylindrical shells [1], based on the so-called method of "freeze casting", in which the cylindrical surface of the shell is formed when the metal solidifies in a movable, vertical direction, mold. The disadvantage of this method is the complexity of its implementation, because strict adherence to the ratio of the rate of entry of liquid metal to the solidification front and the mold speed is required. In addition, the use of complex, expensive equipment (mixer, movement mechanism, control equipment, etc.) is required.

 A known method of casting large cylindrical shells [2], adopted as a prototype, comprising supplying liquid metal to a mold, hardening a metal layer to a predetermined shell wall thickness and draining unhardened metal through a drain hole to form the inner surface of the shell.

 The disadvantage of this method is a significant amount of allowance, which determines the appropriate amount of machining. In addition, the formation of defects in the form of shells, leaks, redistribution of alloying additives, etc., is possible in the thickness of the shell.

 The technical problem solved by the present invention is to improve the quality of cast shells and reduce the complexity of manufacturing large-sized parts from them.

 The problem is achieved in that in the method of casting large-sized cylindrical shells, including feeding liquid metal into a mold, hardening the metal layer to a predetermined shell wall thickness and draining unhardened metal through a drain hole to form the inner surface of the shell, the metal is drained immediately after solidification in the upper part of the shape of the metal layer of a given thickness and for a period of time equal to the difference in the duration of the solidification of the wall of the shell at its lower and upper end faces.

Устройство для отливки крупногабаритных цилиндрических обечаек показано на чертеже, где изображено 1 - форма для заливки металла; 2 - дно формы; 3 - сливное отверстие; 4 - стопорный механизм; 5 - литниковая сифонная система.When draining unhardened metal, the ratio of the areas of the drain hole (f) and the liquid metal mirror (F) is provided within

A device for casting large-sized cylindrical shells is shown in the drawing, which shows 1 - mold for pouring metal; 2 - bottom of the form; 3 - drain hole; 4 - locking mechanism; 5 - gating siphon system.

The method is as follows: the mold (1), in the form of a glass, preferably metal, mounted vertically and having a reverse slope of the inner wall, is filled with liquid metal. It is held until a layer of hardened metal of the required thickness is formed in the upper part of the casting (Δ _top ) and the liquid metal is drained through the drain hole (3) at such a rate that the drainage time is equal to the difference in the solidification times of the thickest shell wall at its lower end (Δ _lower ) and the thinnest - at the upper end (Δ _upper ).
The ratio of the areas of the drain hole and the liquid metal mirror is maintained within the range of 0.001 ... 0.006. This ratio is selected from the following provisions.

где
F - площадь зеркала жидкости;
f - площадь сливного отверстия;
H - высота жидкости.The time of emptying the vessel from the provisions of hydrodynamics is

Where
F is the area of the liquid mirror;
f is the area of the drain hole;
H is the height of the liquid.

где δ_н и δ_в - толщина стенки отливки у нижнего и верхнего торца;
k - коэффициент затвердевания металла в металлической форме = 3 мм/с^0,5.At the same time, in order to obtain a cylindrical inner surface of the casting in the mold, having a wall slope of (1.5 ... 2)%, the drain time is required equal to the difference in the solidification times of the casting wall at the lower and upper ends, i.e.:

where δ _n and δ _in - the wall thickness of the casting at the lower and upper end;
k is the coefficient of solidification of the metal in metal form = 3 mm / s ^0.5 .

или

Наиболее используемые высоты отливок H = (500....2000) мм, и толщины стенок (15...100) мм, с учетом уклонов (1,5...2)% дают соотношение

Если

то внутренняя поверхность отливки во всех случаях приобретает форму конуса с расширением кверху.For mold casting
τ ₂ = 11 (δ $\genfrac{}{}{0ex}{}{\text{2}}{\text{n}}$ -δ $\genfrac{}{}{0ex}{}{\text{2}}{\text{in}}$ ),
since τ ₁ = τ ₂ , then

or

The most used casting heights H = (500 ... 2000) mm, and wall thicknesses (15 ... 100) mm, taking into account slopes (1.5 ... 2)%, give the ratio

If

then the inner surface of the casting in all cases takes the form of a cone with an extension upward.

форму конуса с расширением книзу.If

cone shape with extension downward.

 This ratio is regulated by selecting the diameter of the sleeve in the drain hole or by adjusting the area of the metal mirror by introducing a central rod of refractory material.

тонкой

а их разница составляет 151 с. Следовательно, для получения цилиндрической внутренней поверхности диаметром 200 мм продолжительность слива должна составлять 151 с.An example implementation of the method:
The casing is cast from high-chromium cast iron with an outer diameter of 260 mm, an inner diameter of 200 mm, a length of 1000 mm in a painted mold with a reverse slope of 1.75% and a lined bottom with a drain hole. The coefficient of solidification k = 3 mm / s ^0.5 . The wall thickness of the casting at the top is 30 mm, at the bottom - 47.5 mm. Thickness Hardening Duration

fine

and their difference is 151 s. Therefore, to obtain a cylindrical inner surface with a diameter of 200 mm, the discharge time should be 151 s.

 With a drain metal mass of 226 kg (cylinder mass with a diameter of 200 mm and a height of 1000 mm), a mass discharge rate of 1.5 kg / s is required.

 To ensure such a drain rate under the considered casting conditions, a drain hole of 16 mm diameter is necessary.

 High-chromium cast iron was poured into the mold, with the parameters described above, with a closed drain hole to a height of 1100 mm. After exposure for 110 s (an increase in exposure compared to the calculated 10 s is associated with the removal of overheating) and the formation of a hardened layer 30 mm thick at the upper end of the casting, this drain hole was opened and the remaining liquid metal was drained. The shell obtained by this method did not have shrinkage defects, and the allowance for machining in height varied from 4 to 6.5 mm, which ensured the requirements for the part both in quality and in the complexity of machining.

 The invention can be industrially applicable in metallurgy, in the foundry of large-sized hollow ingots, for example, in the manufacture of bandages for rolling rolls made of hard-to-process materials.

Sources of information:
1. Copyright certificate N 103018, cl. B 22 D 23/02 - analogue.

 2. French patent N 804647, cl. B 22 D 7/04 - prototype.

Claims (2)

 1. A method of casting large cylindrical shells, including feeding liquid metal into a mold, solidifying a metal layer to a predetermined shell wall thickness and draining unhardened metal through a drain hole to form an inner surface of the shell, characterized in that the metal is drained after solidification in the upper part of the mold a metal layer of a given thickness and for a period of time equal to the difference in the duration of the solidification of the wall of the shell at its lower and upper ends.  2. The method according to p. 1, characterized in that when draining the liquid metal, the ratio of the areas of the drain hole f and the mirror of the liquid metal F is provided within f / F = 0.001 - 0.006.