RU2312732C2 - Sand for making casting molds and cores - Google Patents

Abstract

FIELD: foundry.

SUBSTANCE: sand contains, mass %: refractory filler in the form of powder of electrical-engineering periclase under-melted at producing it, 40.0 - 50.0; binder in the form of melt glass, 5.0 - 12.0; powder of scrap of used casting molds of under-melted material, 45.0 - 48.0. Fraction size of powder of under-melted electrical-engineering periclase production and powder of scrap of used casting molds of under-melted material is in range 0.05 -2.50 mm. Relation of fractions consists, mass %: 2.50 - 1.60 mm, 43.0 - 50.0; 1.60 - 0.315 mm, 45.0 - 50.0; 0,315 - 0.05 mm, 5.0 - 7.0.

EFFECT: improved gas permeability, lowered collapsibility of casting molds and cores.

2 tbl, 1 ex

Description

The invention relates to foundry, in particular to compositions of molding mixtures for the manufacture of foundry molds and cores used in the casting of chemically active metals (titanium, aluminum, magnesium) and alloys based on them.

A known mixture for the manufacture of molds and cores, cured by carbon dioxide, containing wt.%: Moistened magnesite (periclase) powder 90-92 and liquid glass 8-10 (1).

A disadvantage of the known mixture is the high shedding of molds and rods made from it, which negatively affects the quality of the castings. Another disadvantage of the known mixture is the use as a base of scarce and expensive periclase powder.

A known mixture for the manufacture of foundry molds and cores, cured by carbon dioxide, containing wt.%: Filler material based on periclase in the form of scrap used casting molds and cores 50-80, liquid glass 10.5-13, periclase powder rest (1) .

Known (RF patent No. 1789319, publ. 23.01.93, bull. No. 3) the closest in technical essence and the achieved effect mixture for the manufacture of molds and cores, cured by carbon dioxide, containing in wt.%:

Under-production electrotechnical periclase 90-93 Liquid glass 7-10.

A disadvantage of the known mixture is that it gives increased flakeability and low gas permeability to the mold and cores. This leads to increased rejects of titanium shaped castings in gas sinks and in geometric parameters during high-temperature calcination and pouring of liquid metal.

The technical result of the invention is to reduce flaking and increase the gas permeability of the mold.

The technical result is achieved due to the fact that the mixture for the manufacture of foundry molds and cores, curable with carbon dioxide, containing a filler in the form of a sub-alloy of electrotechnical periclase and a binder in the form of liquid glass, according to the invention additionally contains a powder of scrap of used casting forms of an under-alloy, and as a binder a high-modulus sodium liquid glass with a silicate module of 2.0-3.2 and a density of 1.15-1.5 g / cm ^{3 was} taken in the following ratio of components, wt.%:

Underflooding Powder electrotechnical periclase 40.0-50.0 Used scrap powder under-casting molds 45.0-48.0 High Modulus Sodium silicate water glass 2.0-3.2 and a density of 1.15-1.5 g / cm ³ 5.0-12.0

while the size of fractions of the powder of the underfill of the production of electrical periclase and the powder of the scrap of used foundry molds from the underfuse should be within the following limits, and the ratio between the fractions should correspond to the following values, wt.%:

2.50-1.60 mm 43.0-50.0 1.60-0.315 mm 45.0-50.0 0.315-0.05 mm 5.0-7.0

The use of scrap powder of used casting molds from underfusion allows reuse of scarce and expensive periclase, which reduces the cost of casting molds and cores without affecting the quality of the latter.

It was experimentally established that in order to obtain casting molds and cores with optimal gas permeability and technological strength after calcination, it is necessary that the size fractions of the powder of underfusion of the production of electrotechnical periclase and the scrap powder of used casting molds from underfusion be within the following limits, and the ratio between fractions should correspond to the following values, wt.%:

2.50-1.60 mm 43.0-50.0 1.60-0.315 mm 45.0-50.0 0.315-0.05 mm 5.0-7.0

Coarse fractions (2.50-1.60) mm of sub-alloy powder for the production of electrotechnical periclase and scrap powder of used foundry molds from under-alloy in the amount of 43-50 wt.% Are necessary for the formation of the supporting frame of the mold and core, which in combination with medium and small fractions in the indicated ratios provide gas permeability and strength of casting molds and cores.

The average fractions (1.60-0.315) mm of sub-alloy powder for the production of electrotechnical periclase and scrap powder of used foundry molds from under-alloy in the amount of 45-50 wt.% Are fillers for creating a dense but gas-permeable package, providing technological strength both in the wet state and and after calcining it.

An increase in the amount of powder of medium fractions (1.60-0.315) mm of underfusion of the production of electrical periclase and scrap powder of used casting molds from underfusion of more than 50 wt.% And fine fraction (0.315-0.05) mm of more than 7.0 wt.% Leads to weakening of the mold or core frame.

A decrease in the amount of powder of the middle fraction of less than 45 wt.% And the fine fraction of less than 5 wt.% Leads to loosening and shedding of the mold and core during calcination and subsequent pouring of metal.

The use of high-modulus sodium liquid glass with a silicate module of 2.0-3.2 and a density of 1.15-1.5 g / cm ³ , which has increased fluidity, allows to provide wet strength in the manufacture of molds and cores, and most importantly to reduce crumbling and increase gas permeability .

An example of a specific implementation: for the preparation of the mixture for foundry molds and cores, mixing runners were used, in which the powder of underfusion of the production of electrical periclase of the following quantitative and qualitative composition was loaded, wt.%: MgO - 94.3, SiO ₂ - 3.32, Fe ₂ O ₃ - 0.28, CaO - 2.1 in the amount (wt.%): 40.0; 45.0; 50.0 of the weight of the batch and the scrap powder of the used casting molds from the subfusion of the following quantitative and qualitative composition, wt.%: MgO - 91.6, CaO - 2.12, SiO ₂ - 6.00, Fe ₂ O ₃ - 0 , 28, in the amount (wt.%): 45.0; 47.0 and 48.0 of the weight of the batch

with fractions of 2.50-1.60 mm in quantity (wt.%): 43.0; 45.0 and 50.0 of each powder;

with a size of fractions of 1.60-0.315 mm in an amount (wt.%): 50.0; 49.0 and 45.0 of each powder;

with a size of fractions of 0.315-0.05 mm in an amount (wt.%): 7.0; 6.0 and 5.0 of each powder.

After that, the runners were turned on and the mixture was thoroughly mixed to average the compositions for 5 minutes. Then sodium liquid glass with a silicate module of 2.0 and 3.2, diluted to a density of 1.15; 1.30 and 1.50 g / cm ³ in an amount (wt.%): 12.0; 8.0 and 5.0 and stirring continued for the next 5 minutes.

Next, the mixture was loaded into a metal container and the resulting mass was used to make a mold and cores, as well as samples to determine the crumbling and gas permeability of the molds.

Cylindrical samples with a diameter and height equal to 50 mm and molds weighing up to 200 kg were made from the obtained mixtures by manual packing, which were cured by blowing with carbon dioxide and then calcined in an electric furnace at a temperature of 1000 ° C.

On the manufactured samples, the crumbling value of the casting molds and gas permeability were determined.

Determination of crumbling was carried out on a device 056 complete with a device for shaking 022. For the indirect characterization of crumbling, the depth of crack propagation in calcined forms was visually determined using a measuring ruler according to GOST 427-75.

To determine the quality of castings, the molten titanium of the Т grade grade was poured into the calcined forms under high vacuum. The depth of the layer of increased hardness formed on the castings was measured using a PT-3M device, and the surface cleanliness of the castings was measured using a profilometer according to GOST 19300-86.

The gas permeability of the mold was carried out in the cured and calcined state according to GOST 29234.11-91.

The composition of the mixture for the manufacture of molds and cores is shown in table No. 1, the test results of samples of the mold in table No. 2.

Table 1
The composition of the mixture for the manufacture of molds and cores. Mixture composition Conventional composition number Liquid glass Electrotechnical periclase underfusion powder Scrap Powder Used Molds Content% Content% Fractions Content% Fractions Size mm Content% Size mm Content% Proposed one 5,0 50,0 2,50-1,60 43.0 45.0 2,50-1,60 43.0 1,60-0,315 50,0 1,60-0,315 50,0 0.315-0.05 7.0 0.315-0.05 7.0 2 8.0 45.0 2,50-1,60 45.0 47.0 2,50-1,60 45.0 1,60-0,315 49.0 1,60-0,315 49.0 0.315-0.05 6.0 0.315-0.05 6.0 3 12.0 40,0 2,50-1,60 50,0 48.0 2,50-1,60 50,0 1,60-0,315 45.0 1,60-0,315 45.0 0.315-0.05 5,0 0.315-0.05 5,0 Famous four 10.0 90.0 - - - - -

Table number 2
Test results of mold samples made from the proposed and known mixtures Mixture composition Conventional composition number Tailability of samples,% Crack propagation depth, mm The limit of compressive strength, N / mm ² Depth of the layer of increased hardness at a thickness of 20 mm, mm The surface finish of the castings, microns Gas permeability After purging with CO ₂ After firing at 1000 ° C Proposed one 0.0034 24 23 46 0.09 thirty 88 2 0.0021 twenty 25 51 0,07 21 one hundred 3 0.0018 thirty 45 61 0.09 32 73 Famous four 0.0095 40-60 47 92 0.10 34 - Note:
1. Tailability of the samples was determined after firing them at a temperature of 1000 ° C.
2. The table shows the averaged data after testing three samples per point.

Technical and economic efficiency from the use of the molding mixture according to the invention is expressed in improving the quality of castings from chemically active metals, as well as in reducing the cost of manufacturing molds and cores for producing these castings.

References

1. The journal "Refractories" No. 1 for 1987, pp. 34-37.

Claims (1)

A mixture for the manufacture of carbon dioxide curable foundry molds and cores, containing a filler in the form of a sub-alloy powder of the production of electrotechnical periclase and a binder, characterized in that it additionally contains scrap powder of the used non-alloy foundry molds and, as a binder, contains high-modulus sodium silicate glass with silicate a module of 2.0-3.2 and a density of 1.15-1.5 g / cm ³ in the following ratio of components, wt.%: Underflooding Powder electrotechnical periclase 40.0-50.0 Used scrap powder underfloor molds 45.0-48.0 High Modulus Sodium silicate water glass module 2.0-3.2 and a density of 1.15-1.5 g // cm ³ 5.0-12.0, the size of the fractions of the powder of the sub-alloy of the production of electrical periclase and the powder of the scrap of the used foundry molds from the sub-alloy is from 0.05 to 2.50 mm, and the ratio of the fractions is wt.%: 2.50-1.60 mm 43.0-50.0 1.60-0.315 mm 45.0-50.0 0.315-0.05 mm 5.0-7.0