RU2123908C1 - Method of producing castings with oriented crystallization - Google Patents

Abstract

FIELD: foundry; may be used in producing of castings based on copper in metal mold. SUBSTANCE: melt is cast with uniform filling of mold over the entire surface of poured melt. To remove heat, use is made of additionally heat accumulating low-melting alloy located under metal mold base and cooled with circulating water at temperature of 50-60 C. Melting point of low-melting alloy is below the working temperature of mold by 20-30 C. EFFECT: higher quality of casting due to reduced number of micropores, fissures and other defects. 1 tbl

Description

 The invention relates to the field of foundry, in particular to a method for producing copper-based castings in a chill mold.

The closest to the proposed technical essence and the achieved result is a method for producing castings, including heating the chill mold, pouring the alloy through the gate system in the form of a funnel with a riser to the copper crystallizer, which is the base, and subsequent cooling of the alloy by heat removal from the mold using circulating refrigerant, for example, water at t = 8-14 ^o C.

However, this method does not allow to obtain blanks of volumetric castings without micro-slots, tears and other casting defects, because:
- the gating system used does not provide a smooth and uniform filling of the chill mold with liquid alloy over the entire mirror of the cast surface:
- the mold does not create a uniform temperature field along the working surface, which can lead to the formation of multi-storey "bridges" of dendrites and, as a result, the formation of microrough zones;
- the water circulating in the mold at t = 8-14 ^° C does not exclude the occurrence and growth of a columnar crystallization zone in the center of the bottom of the mold due to the relatively low thermal conductivity of water.

 The technical result that can be achieved by using this technical solution is to improve the quality of alloy castings, mainly on a copper basis, by reducing microflow, eliminating cracks and other defects.

The specified technical result is achieved due to the fact that in the method of producing castings with directional crystallization, including heating the chill mold, pouring the alloy into it through the gating system and then cooling the chill mold with casting by removing heat from the chill mold using circulating refrigerant, the casting is carried out with the possibility of uniform filling a chill mold over the entire mirror of the alloy being poured, to remove heat from the bottom, an additional heat storage element is used, for example, a low-melting alloy with temperatures nd melting exceeding 20-30 ^o C at the heating temperature of the mold, and the cooling water lead having a temperature of 50-60 ^o C.

 Obtaining castings with directed crystallization is as follows.

 The chill mold is mounted on a copper mold, which serves as the mold for the mold, in which two chambers are arranged successively one below the other to ensure a uniform crystallization front of the casting, the upper of which is filled with a heat-accumulating low-melting alloy, and the lower one is used for water circulation.

To obtain castings from copper-based alloys, the melting temperature of the heat-accumulating alloy should be in the range of 490-550 ^o C, since when using a low-melting alloy with a melting temperature below 490 ^o C, its volume increases and, as a result, an increase in production costs, and when the use of fusible alloy with a melting point above 550 ^o C reduces the effect of creating a uniform crystallization front.

The chill mold and the mold are heated to a temperature of 20-30 ^o C below the melting temperature of the heat-accumulating fusible alloy. Otherwise, heat absorption by the low-melting heat-accumulating alloy is not fully realized, since the greatest heat absorption occurs when the heat-accumulating low-melting alloy is melted.

After heating the chill mold, a copper-based liquid alloy is poured into it through a moving riser with a funnel, which at the end has a nozzle that ensures uniform and quiet (without splashing) alloy filling over the entire area of the liquid metal in the chill mold. At the same time, from the moment the alloy is poured, water is supplied to the mold, which has a temperature of 50-60 ^° С, since at this temperature the water has the highest thermal conductivity, which allows providing the most intense heat removal from the bottom of the chill mold in combination with a melting low-melting alloy. Due to this, the crystallization of the liquid alloy from the bottom part occurs at a faster rate than from the side walls of the chill mold, thus forming a uniform sequential growth of crystals from both the bottom part and the side walls of the chill mold, which eliminates the appearance of “bridges” from columnar dendrites and , thereby, the possibility of micro-slots and other casting defects in castings.

Concrete example
To obtain castings with dimensions d = 140 mm and l = 150 mm, tin-lead bronze Br010С2Н3 with high density requirements was used, and a low-melting alloy with a melting point of 490 ^o C and a volumetric energy consumption of 805-840 cal / was used as a heat storage element. cm ^{3 of the} following composition, wt.%:
copper - 15 - 30
zinc - 20 - 25
silicon - 5 - 12
nickel - - 2
iron - 0.03 - 1.5
aluminum - the rest
The chill mold and mold, pre-painted in the cold state with colloidal graphite, were heated to a temperature of 460 ^o C. before pouring.

After heating the chill mold, water with a temperature of 55 ^o C was supplied to the mold and at the same time pouring liquid bronze into the chill mold at a temperature of 1170 ^o C through a heated moving riser with a funnel ending in a ceramic "rain" nozzle covered in fiberglass, ensuring uniform filling of the chill volume throughout alloy mirror.

 The crystallized cast was extracted from the chill mold, cooled and subjected to a complete metallurgical study.

 The study showed that the casting throughout the volume has a dense structure without the presence of casting defects and meets the technical requirements of the drawing.

 The data obtained indicate (see the comparative table) that the claimed technical solution provides high-quality casting while observing the limits of the technological process.

 A comparative analysis of the results of the study of bronze castings (Br010C2H3), cast by known and proposed methods, showed that the proposed method provides high quality in density of volume castings by eliminating zones with microroughs and other casting defects in the thickness of the casting.

Claims (1)

A method of producing castings with directional crystallization, including heating the chill mold, pouring the alloy into it through the gate system and then cooling the casting by removing heat from the bottom of the chill mold with circulating refrigerant, characterized in that the alloy is cast when the chill mold is uniformly filled throughout the mirror of the cast alloy and carry out additional heat removal from the bottom of the chill mold with a heat-accumulating low-melting alloy with a melting temperature exceeding the heating temperature of the chill mold by 20 - 30 ^o C, while t the temperature of the circulating refrigerant is 50 - 60 ^o C.

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