SU582906A1 - Metal surface protecting mixture - Google Patents

Description

(54) METHOD FOR GETTING CASTINGS

The invention relates to foundry and can be used in the preparation of sand castings.

There is a known method in which the casting after cooling is removed from the mold and transferred to heat treatment to improve the microstructure, improve the mechanical properties and relieve internal stresses. . ;; 1 and the decarburization of CASTINGS 111 o

The closest in technical cyu to the invention is the method of manufacture. COLD, it is envisaged to create a directional gas flow in the mold when it is filled with metal by connecting the mold to the vacuum system and supplying air or inert gas to the mold cavity under pressure. The method is intended to prevent the formation of gas holes in the castings. When the suction pump is turned on and the gas medium is pressurized, a directed air flow arises from the mold cavity through the walls of the mold B to the vacuum chamber. In the process of filling the mold cavity with metal, the vapors and gases formed upon contact of the metal with the surface of the mold are entrained by the AIR flow and removed by 21.

The disadvantage of the PM method is the low-CIRCLE DURAL EXTENSION due to the berry structure. To obtain a fine-grained structure and an effective strength, it is necessary to conduct heat treatment in special furnaces or devices.

The aim of the invention is to increase the strength of the CASTING During its cooling in the mold.

For this, a method is proposed in which the gas medium is supplied when the metal reaches the temperature of the ESO-ZOO C, while the flow rate of the gas medium is 4-6 l / sec per unit, the specific surface of the casting

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Claims (2)

The creation of this gas stream provides an increase in the cooling rate to 15-30 ° C / min during the passage of the critical points by the metal. The method is intended to produce normal and high quality castings from carbon and low alloy steel and cast iron in sand molds. The drawing shows the scheme of casting. During the pouring and crystallization of the metal, the bottom 1 and top 2 semi-pans are connected to the source 3 of the vacuum. Vacuum is created through hollow trunnions 4.5 and vacuum filters 6.7. When the casting 8 is cooled to a temperature of 900-8SQ ° C, the lower mold half is disconnected from the vacuum source by the crane 9 and at the same time through the trunnion 4 and the vacuum filter 6, which, under the action of overpressure, rises into the upper mold and through the filter 7, the trunnion 5, the valve 10 and the vacuum pump escapes into the atmosphere. After 5-10 minutes, the direction of the gas flow is changed to achieve uniform cooling of the casting. I connect the lower half-form - to the vacuum source with a crane 9, the upper one - to the cooling gas medium by a crane 10. The gas medium from the upper half-form is lowered into the lower one and inside the vacuum filter 6, the journal 4 and the vacuum pump goes to the atmosphere. The lower and upper vacuum filters operate alternately, as they pressurize and suck. The implementation of the method is illustrated by the example of the production of a batch of castings of blast drum tracks from steel 45l, weighing 5.5 kg. Liquid steel at a temperature of 1550-1570 is poured into a sand mold, which is under a vacuum of 350-400 mm Hg. After the casting in the mold is cooled to 900HP, a cooling gas medium (for example, compressed air, argon, nitrogen and other neutral gases under a pressure of 4-5 atm) is fed into the mold at a rate of 4-6 l / sec per unit surface area of the casting. This flow rate provides a cooling rate of 15-30s / min. If the gaseous medium is fed into the mold before it reaches the temperature of the casting, and below, a heterogeneous structure is formed, causing lower strength. If the gaseous medium is shut off before the temperature is cast, the casting is characterized by low toughness. Switching off the gaseous medium below does not affect the increase in strength properties | X characteristics and, therefore, is inexpedient due to lengthening of the technological cycle. An increase in the gas flow rate of more than 6; l / s per unit specific surface of the castings leads to the appearance of internal stresses — resins and porosity. Reducing the flow rate of the gas medium of less than 4 liters / sec causes: an insufficient cooling rate of the casting, the formation of a coarse-grained structure and low strength of the castings. According to the existing technology, the cycle of casting with subsequent heat treatment (normalization) takes 12-15 hours (including heat treatment 10-1; g hour). The proposed method allows to obtain a fine-grained structure and increase the strength of castings by 25-30% during their cooling in the form without additional heat treatment. The technological cycle of casting is reduced by 11-14 hours, the quality of castings is improved. The method of producing castings, which includes creating a vacuum in sandy form, feeding the gaseous medium under pressure, melting the molten metal and then cooling it, which is different in that, in order to increase the strength of the castings, gaseous medium is supplied when metal temperature 900ZOO C, while its consumption is 4-6 l / s unit of the specific surface of the casting. Sources of information {emation, taken into account during the examination: 1. Author's certificate dcCP 428008, cl. C 21 D 1/74, 08/05/1970, 1974. 2. The patent of Great Britain No. 932006, KL.83 (1) G, 1963.