SU925514A1 - Method of protecting steel casting surface from flaws - Google Patents

Description

(54) METHOD OF PROTECTION OF THE SURFACE OF STEEL MOLDINGS FROM DEFECTS

1i

The invention relates to foundry and is intended to prevent the occurrence of surface defects on castings when casting on melted models.

When casting on the produced models, both in and without the support filler, oxidation, decarburization of the surface of steel castings, as well as the occurrence of defects (protrusions above the surface of the castings of metal drops) are observed.

When casting without a support filler, oxidation, decarburization, "cutting through" and a new defect, the "p bin" (spherical depressions on the surface of the castings), develop more strongly.

In addition, when casting without a support filler, the calcined molds are cooled more rapidly over the period of time between unloading them from the tempering furnace and pouring. Lowering the temperature below 600 ° C before the start of pouring can lead to cracking of the mold and, accordingly, casting.

Decarburization significantly impairs the physical and mechanical properties of castings.

The oxidation of metal with the formation of scale reduces the accuracy of castings, increases the roughness of their surface.

In addition, the oxidation of the metal

5 high temperatures leads to the interaction of its oxides with the material of the form with the formation of an unrecoverable defect - “b.

Defect "perforation depends on speed

10 chilled deny poured metal. When the mold is cast with molten metal, its walls are heated to its temperature due to the heat of the cast metal. If the cooling rate of the poured metal

15 is small, sintering of ceramics occurs with the formation of pores within the time interval from the moment of the end of the pouring until the moment when the metal has not yet crystallized, i.e. it is in a liquid state

20 research institutes. Under these conditions:

1) the presence of pores formed after; sintering of ceramics;

2) the metal is in a liquid state;

25 metal penetrates the pores of the form with obrg

defects "nrosechka.

Known way to protect the surface

steel castings against defects at ;;

on melted models without support; 30 filler (particularly oxidized

decarburization) by adding thermosetting resins to the ceramic shell, which include materials that decompose to form gases that do not support oxidation, for example, 1 CO; .

The disadvantage of this method is that such forms, as a rule, have three zones (facing, neutral and cortical), which complicates the technology for the manufacture of forms. In addition, this method does not prevent the occurrence of a defect "perforation, since there is no possibility to accelerate the cooling of metal-filled forms.

There is also known a method for eliminating surface defects (mainly oxidation and decarburization) by blowing with natural or other hydrocarbon gases a supporting filler, in which the molded shell forms 2 are molded,

The gas entering the flask washes the shell forms in the metal filler in the support filler and decomposes to form pyrocarbon, which prevents the decarburization of the metal.

This method does not eliminate the "perforation" defect, since it does not affect the cooling rate. In addition, it is necessary to suck off the decomposition products of the gas that have not reacted with the form, which requires additional capital expenditures.

Closest to the proposed method for elimination of surface defects (oxidation, decougolol: wilting and reducing the physicochemical interaction of the metal being poured with the mold material), which is used to blow the molds with a mixture of hydrocarbon gas and air in a ratio of 1: 7.

This method does not eliminate the defect “perforation, since it does not affect the cooling rate of the cast forms, i.e., castings.

The aim of the invention is to improve the quality of the surface of the castings.

The goal is achieved in order to protect the surface of steel strips from defects produced in molds by produced models using a method of blowing a mold with a mixture of hydrocarbon gas and air immediately after casting the mold is blown with a neutral-reducing flame formed by burning a mixture of hydrocarbon gas with air taken in a ratio of 1: 1-5.

The drawing shows a diagram of the blowing unit without the reference filler gas flame.

When the flask 1 is unloaded from the prokalochny furnace with the block 3 fixed by means of rack 2, a burner 4 is put on it 4. A mixture of 1 part of hydrocarbon gas with 9-10 parts of air is fed through the mixer 5,

which ignites from the heat of the blocks and maintains their temperature. Before starting to fill the block off the flow of the mixture, the flame goes out. After the blocks have been poured, a mixture of a part of hydrocarbon gas and part I-5 of air is fed through mixer 5. In this case, due to the lack of air supplied to the burner, the air in the flask burns very quickly (in a few seconds) and the flame becomes neutral-reducing. It washes the flooded block, thereby protecting the metal from oxidation and its interaction with the form, i.e., preventing the occurrence of surface defects of the type “bin.

The composition of the atmosphere was experimentally established: 1 minute after the flame was turned on, CO2 was contained in the atmosphere - 2.8% -; O2 -5.8%; CO-- 1.8%; after 2 min - COA-5,4%; Oj-1,2%; CO-2.0%; through cereal-CO2 -5.2%; Og - no; СО-1.8%; after 4, 5, 6 min - a constant amount of CO2 and CO, equal to 3.2% and 1.8%, respectively; Oxygen is absent.

Since the heat capacity of a gas, and therefore of a neutral-reducing flame (flame temperature is 300 ° C), is twice the heat capacity of air, when blowing a flooded unit, its cooling rate increases, especially at high temperatures. This contributes to the rapid formation of a hardened metal crust, thereby preventing the occurrence of a notch.

Neutral reducing atmosphere eliminates the oxidation conditions of the cast metal, the occurrence of an alloy. Plum | I turn off no earlier than 7 minutes after pouring the blocks.

Castings have no surface defects, the surface roughness decreases from 6.3 to 3.2. The method, which is easily implemented in production, makes it possible to develop a technological process to precisely cast chemical and polymer equipment parts into fireclay ceramic molds on melted models without supporting filler.

The method has great potential for automating the process of calcining, pouring and cooling castings. For example, these operations can be combined in a single unit, i.e., a burner can also be used for calcining.

On the basis of this method, it is possible to modernize the NIIavtoprom model A-765 unit, in particular the pouring carousel. On this unit, the calcined formulas are molded before being poured into the support filler. In this operation, a large percentage of the forms are destroyed due to the temperature difference between the mold and the sand. Instead of molding on the casting carousel, you can install the burners and use this method with all its advantages.

The implementation of the invention will improve the surface quality of steel castings and eliminate surface defects, which will provide an economic effect of 400 rubles. for 1 ton of good to pour.

Claims (3)

Invention Formula The method of protecting the surface of steel castings from defects produced in molds by melted models, including blowing the molds with a mixture of hydrocarbon gas with air, characterized in that, in order to improve the quality of the surface of the castings, the mold blows immediately after casting with a neutral-reducing flame, the combustion of a mixture of hydrocarbon gas with air, taken in a volume ratio of 1: 1 - 5. Sources of information taken into account in the examination: 1. USSR Author's Certificate No. 113038, cl. B 22 C 3/00, 1958. 2. USSR Author's Certificate No. 505493, cl. B 22 C 3/00, 1976. 3. US patent number 3683996. cl. 164-14, pub. 1972. Wolda grriHOCi e / jbi