RU2307003C1 - Method for producing cast pieces - Google Patents

Abstract

FIELD: foundry.

SUBSTANCE: method comprises steps of filling casting mold under gas counter-pressure with melt fed from vessel arranged under casting mold; soaking melt till freezing predetermined wall thickness of casting; increasing gas pressure higher than gas pressure acting upon melt. At producing castings having cavity closed downwards liquid residue is drained till level of bottom part of casting and performing soaking till solidification of melt.

EFFECT: lowered labor consumption of process.

2 cl, 6 dwg, 1 ex

Description

The invention relates to the field of engineering and can be used in foundry in the manufacture of thin-walled sealed containers, mainly for the storage of liquids and gases, including in fire extinguishers, cylinders for liquefied gas, etc.

A known method for producing sealed preforms by low pressure backpressure casting, including filling the mold with a melt under gas backpressure, lower in magnitude of the pressure on the melt in the casting tank located under the mold, holding time for the casting to solidify, depressurizing the mold and tank and removing the finished castings from the mold (G. Malinichev. The phenomenon of backpressure. Journal of "Engineering and Science", 1983, No. 4, p. 19).

According to this method, due to gas backpressure, the castings are non-porous and can be used in critical products, for example, in the cases of cylinders for compressed gases, etc.

To design cavities in such castings, it is necessary to use single rods, which is associated with an increase in the complexity of manufacturing the casting, an increase in its cost.

The aim of the present invention is to eliminate the noted disadvantages, i.e. reducing the complexity and cost of manufacturing castings.

This goal is achieved by the fact that in the method of manufacturing castings, comprising filling the mold with a melt under gas backpressure, lower in magnitude of the pressure on the melt in the casting tank located under the mold, holding time for the casting to solidify, depressurizing the mold and capacity and removing the finished casting from the mold after exposure for solidification casting, gas pressure in the form is raised above the gas pressure on the melt in the vessel and the liquid residue is drained (or gas pressure in the vessel is reduced _EMK P <P _).

Upon receipt of castings with a cavity closed from below, the liquid residue is drained to the level of the bottom point of the casting and soaked until it hardens.

The introduction of these methods allows for a given wall thickness of the casting to quickly drain the liquid residue from its cavity and to obtain a thin-walled shell with a smooth inner surface with a minimum difference within the tolerance.

The resulting hermetic casting does not have axial porosity, which is usually present in castings obtained using rods.

Example.

A cylinder for storing liquefied gas, operating under a pressure of 16 atmospheres, is made on a low pressure casting installation with back pressure from an aluminum alloy as follows.

Figure 1 shows a working casting scheme, including a sealed container 1 with a melt 2, a permanent casting mold 3, equipped with a hollow pin 4, having a porous foam-ceramic filter 5 at the end, an open composition. Form 3 is connected with the filling tank 1 with the melt 2 by a metal wire 6. The gas pressure P ₁ equal to 4 atm is supplied to the filling tank 1 and the casting mold 3.

Figure 2 shows the moment of filling form 3 with melt 2 at P ₂ <P ₁

Figure 3 - the moment of completion of filling the form 3 with the melt 2 and exposure to freeze the wall 7 of the casting at P ₂ <P ₁ .

Figure 4 - the moment of discharge of the liquid residue from the cavity of the casting 7 when P ₃ > P _1.

Figure 5 - the moment of discharge of the liquid residue to the level of the bottom of the casting at P ₄ = P ₁ -γh and exposure to harden it (P1 = P ₄ + γh).

Figure 6 - the moment before removing the finished casting 7 from form 3, P = P _ATM , where:

P ₁ - gas pressure above the molten metal in the furnace, kg / cm ² .

P ₂ (figure 2) is the gas pressure above the molten metal in the mold (when filling), kg / cm ² .

P ₃ - gas pressure in the mold when draining the liquid residue, kg / cm ² .

P ₄ is the pressure of the gas in the mold at the time of holding the melt to freeze the bottom of the casting.

γ is the specific gravity of the melt, kg / cm ² .

h is the height of the melt in the metal wire and the mold from the level of the melt in the furnace to the upper wall of the bottom of the casting, in cm

The casting process is as follows:

In the mold 3 and the filling tank 1 serves gas under a pressure of 4 ATM (figure 1). Then the gas pressure in the mold 3 is reduced, and the melt 2 is displaced through the metal wire 6 under gas back pressure (FIG. 2), and after the mold 3 is completely filled, an exposure is performed to freeze the casting 7 with a given wall thickness. After the casting 7 is formed, the gas pressure in the form 3 is increased to P ₃ > P ₁ (Fig. 4) and the liquid melt precipitate is quickly drained into the tank 1.

Upon receipt of the casting with a cavity closed from below, the liquid residue is drained to its bottom (to the level h above the melt mirror, Fig. 5) and soak until it solidifies.

Before removing the finished casting from mold 3, the pressure in the casting tank 1 and in the mold 3 is released to atmospheric.

The finished cast is removed from the mold, and the process is repeated.

The resulting casting has no pores, is airtight, has a smooth inner surface due to gas back pressure and is obtained without the use of rods.

The use of the invention allows to reduce labor costs when casting sealed containers, including for storing liquids and gas, and to reduce their cost.

Claims (2)

1. A method of manufacturing castings, including filling the mold with a melt under gas backpressure, lower in magnitude of the pressure on the melt in the casting tank located under the mold, holding time for solidification of the casting, depressurizing the mold and tank, removing the finished cast from the mold, characterized in that exposure is performed before freezing the given wall thickness of the casting, and then in the form they raise the gas pressure above the gas pressure on the melt in the container and drain the liquid residue. 2. A method of manufacturing castings according to claim 1, characterized in that upon receipt of the castings with a cavity closed at the bottom, the liquid residue is drained to the level of the bottom of the casting and soaked until it solidifies.

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