SU780944A1 - Mixture for producing coating layer of moulds at aluminium alloy casting - Google Patents

Description

The invention relates to foundry production, namely, to the compositions of facing mixtures for the manufacture of molds for the production of aluminum; CASTING. . The highest values of the mechanical properties of castings from aluminum alloys are provided by casting them into metal molds (metal molds). At the same time, the properties of samples cut from castings are close in their values to the properties of separately cast samples or even superior to nxfll. However, in metal forms, it is possible to produce suitable castings only from alloys of the eutectic type, i.e. solidifying simultaneously in the whole volume and having a narrow crystallization range. In such castings, no internal stresses occur during the casting in the metal mold, resulting in the formation of hot cracks. When casting in metallic forms aluminum alloys having a wide crystallization range, for example, Al119 alloys, VAL-10 alloys, etc., the production of suitable castings is difficult due to the large internal stresses arising from the shrinkage of the castings, which leads to almost 100% Nomu marriage castings on cracks. It is economically feasible to use chill casting only in the case of the manufacture of a large number of castings. Therefore, despite the increase in the use of special casting methods (die-casting, etc.) that provide higher-strength castings, sand casting finds wide application even before sl-hr, in particular, in casting Al119 and Val-10 alloys. In this case, difficulties arise in obtaining suitable castings, in particular, because of the slower rate of crystallization in the castings, shrinkage porosity is formed, as a result of which their mechanical properties are sharply reduced and hot treating is possible. To combat shrinkage porosity, metal coolers made of cast iron, steel or aluminum are used. . However, the use of refrigerators causes a sharp temperature difference across the casting zones and often leads to the formation of hot cracks under or between the refrigerators.

780944 A more effective is the choice of molding facing sorbet for creating accelerated and uniform cooling of the liquid metal. The closest yarn is in the mixture for making the facing layer of the mold during casting and; , water and fuel oil (Y | --- "- - - --Active cooling effect of electrocorundum when used in the form in a full body mixture is explained by the high thermal conductivity, close to the thermal conductivity of the metal. However, the formula The present mixture is an improvement in the mechanical properties of the metal of the casting, "reducing the tendency to crack formation and ensuring the high quality of the casting. - To achieve this goal, the mixture for the manufacture of facing layer forms when casting aluminum alloys, including quartz sand, bold, electrocorundum and water, it additionally contains fluorocirconate in the following ratio ingredients, wt.%: Electrocorundum 30-eO. Water4-5 Potassium Fluorozirconate 0.5-3.0 Quartz sand, semi-., GreasyOther Fluorozirconate potassium interacts with the molten metal, zirconium reduced from the salt diffuses and the surface layer of the molten Metal grinds the grain and causes iverheating microalloying. Cracks in castings, as a rule, begin to develop from the surface of the casting, therefore grinding the structure of the surface layer of the casting drastically reduces the tendency to cracking. The interaction of potassium zirconium fluoride with aluminum proceeds according to the following reaction period, + 6KF + 3Zr. The content of potassium fluorocirconate in the formulation at the lower limit is due to the fact that when the amount is below 0.5%, its effect becomes ineffective, and its content above the upper limit of GB causes a violent interaction, accompanied by a strong gas release, which can lead to the formation of gas holes in the casting. . When the content of electrocorundum is below the lower limit, the required level of the mechanical properties of the casting is not achieved, and when its amount is above the upper limit, it becomes more difficult to work with the mixture because of its large specific weight and increased crumbling of the cladding layer. It is known that in the process of cooling only a layer of molding sand with a thickness of no more than 20-30 mm interacts with the casting metal, therefore the proposed molding sand is used only as a facing, and then the mold is filled with a mixture of a usual composition. In tab. 1 shows the composition of the proposed (1-3) and known (No. 4) facing mixtures. Table 1

Table 2 shows the mechanical properties of aluminum

alloy Val-10 T5, depending on the material of the facing layer form

table 2

42.8-43.8 8.5-9.8 36.2-38.75.7-7.5 44.0-44.3 9.9-10.15

44.9-46.6 10.0-12.5 38.0-41.76.0-9.8

40.6-42.7 7.0-8.5 33.0-35.74.8-6.5

From the data table. 2 that the proposed facing mixture provides for obtaining higher mechanical properties of the metal of the casting when testing both the separately cast specimens and specimens cut directly from the casting.

The tendency to crack formation and the quality of castings were assessed by casting the VAL-10 alloy with Bracket details.

Upon receipt of a series of these parts in forms with a known facing mixture in castings, the presence of liquation-type microcracks and gas pockets is noted, while in producing similar parts in forms with the proposed facing mixture, castings are free from the indicated defects.

Thus, the proposed facing molding mixture provides conditions for the directional and accelerated crystallization of the casting, contributes to obtaining high quality casting, without porosity, hot cracks, micro-tears and contributes to improving the mechanical properties of the metal casting of aluminum alloys.

Claims (2)

1. Kolobnev I. F., Krymov V. V. Melnikov A. V. Reference caster. Non-ferrous light alloy casting M, / Mash., 1974, p.41. 2. USSR author's certificate 366913, cl. In 22 C 1/00, 1973.