RU2017564C1 - Method for fabricating of casting molds and cores of molten glass compound - Google Patents

Abstract

FIELD: foundry. SUBSTANCE: compacting is performed through the combustion energy of methane - air mixture. The following solidification of the glass compound is accomplished by means of bottom vacuumizing the mold (core) concurrently with compacting. EFFECT: higher productivity, reduced power consumption.

Description

 The invention relates to foundry, and in particular to methods of manufacturing foundry molds and cores from liquid glass mixtures, and can be used to obtain them on gas-pulse molding machines.

 A widely known method of manufacturing liquid glass molds and cores, in which the mixture is densified by vibration (Safronov V.Ya. Handbook of foundry equipment. M: Engineering, 1985, 320s.). However, this method has a number of significant drawbacks: underconsolidation of the upper layers of the mold, high noise level, low productivity — the average form compaction time is 30-40 s.

 Closest to the proposed technical essence and the achieved result is a method of manufacturing liquid glass foundry molds and cores, in which the compaction is carried out by the energy of combustion of a methane-air mixture, i.e. gas pulse method. The gas-pulse compaction method allows to obtain molds and rods of high quality and almost any size, in addition, it is one of the cheapest and most productive methods of compaction of molding and core mixtures.

However, in the manufacture of molds and cores from liquid-glass mixtures, this time advantage is almost completely leveled due to their low wet strength, which does not allow molds and cores to be freed from model equipment immediately after compaction and requires very long subsequent hardening (curing). So, the curing time of the liquid glass form in air is 1.5-2 hours, thermal drying takes 5-10 minutes, curing by blowing CO ₂ requires 30-40 s (Zhukovsky S.S. Mold strength, M .: Mashinostroenie, 1989, 288s .).

 In addition, one of the serious issues that have to be addressed in gas-pulse compaction is the removal of combustion products of the gas-air mixture.

 The purpose of the invention is to reduce the length of the cycle for the manufacture of foundry molds and cores from liquid glass mixtures and to ensure their high quality, as well as solving the issue of the disposal of combustion products of methane-air mixture.

This goal is achieved by the fact that in the manufacture of casting molds and cores from liquid glass mixtures by a method including compaction, carried out by the energy of combustion of a methane-air mixture, and subsequent curing of the liquid-glass mixture, simultaneously with the sealing process, lower evacuation of the mold (core) is performed, which ensures removal internal pore air and purging the mold (rod) with a high-temperature mixture of exhaust gases (CO ₂ , N ₂ , CO, etc.), formed during the combustion of methane-air mixture, which in turn, it leads to rapid dehydration and curing of the liquid-glass mixture directly at the sealing position. Thus, the application of the proposed method allows to combine the curing and gas-pulse compaction of foundry molds and cores from liquid glass mixtures, which significantly reduces the total time of their manufacture - already 10-12 seconds after the explosion, the half-mold or core gain sufficient strength for the release operations from model equipment and assembling the form for filling. In addition, it is advisable to resolve the issue of waste gas disposal. Passing through a layer of liquid-glass mixture, they give off carbon dioxide (CO ₂ ), which is used to cure the liquid-glass binder, take away a significant amount of water vapor and free moisture contained in the mixture, and thus actively cure the form, and then are removed through an air ventilation system .

 Figure 1 is a diagram of the installation for implementing the proposed method; figure 2 - graphs of the distribution of density along the height of the form.

 To carry out gas-pulse compaction of a liquid-glass mixture, an experimental setup assembled at the Moscow Automobile Institute was used.

 The method is as follows.

Vacuum submodel plate 2 with model 3 and flask 4 with filling frame 5 are fixed on table 1 of the gas-pulse installation. Then the flask and filling frame are filled with the molding mixture and a pulse head is installed above them 6. The table is pneumatically clamped with the assembled molding chamber to the pulse head and fixed the whole system with screeds 7. After that, oxygen and natural gas are successively supplied to the pulse head (dosing is carried out by changing the pressure in the combustion chamber (pressure gauge 10 )). The enrichment of the methane-air mixture with oxygen increases the stability of the gas-pulse process. The combustible gas mixture is thoroughly mixed by the fan 8. Then the ignition is turned on and the valve 13 opens, connecting the hollow submodel plate with a capacity 12, in which a vacuum is previously created. An electric spark causes an explosion in a combustible gas mixture - instantaneous combustion of a metal with high heat generation (CH ₄ + 2O ₂ - CO ₂ + 2H ₂ O + 892 kJ), which leads to an abrupt increase in pressure (up to 1.00-1.20 MPa) and pulse compaction of the mixture in the molding chamber. The pressure rise time in the conducted experiments was 0.025-0.030 s, and the maximum pressure over the mixture was 0.42-0.45 MPa. The increase in pressure over the mixture causes a sharp pressure drop over the height of the mold, which in turn causes intense filtering of the exhaust gases through the thickness of the liquid-glass mixture. The stream of filtered gases finally completes the mold and actively cures the mixture. When the pressure in the system of the molding chamber - the pulse head becomes less than atmospheric, the check valve 11 is activated, and the system is filled with air. Removing exhaust gases through a model plate has another advantage, namely, it prevents loosening of the upper layers of the mixture by compressed gases that escape into the atmosphere when the pulse head is pressed.

 The entire process described above lasts 1.5-2 s, and the compaction is completed after 0.06-0.09 s after ignition of the mixture, after 1.2-1.5 s the purge of the mixture with exhaust gases practically ends, and after 10-12 s after the explosion, the liquid-glass form (rod) gains strength equal to 0.45-0.50 MPa.

 To carry out the explosion in experiments, a combustible methane-air mixture was used, consisting of 80% oxygen-enriched air (up to 50% oxygen) and 20% methane. The pressure in the molding chamber before the explosion was set in the range 0.16-0.18 MPa. Fan speed 1000-1050 rpm in 1 min.

In the experiments we used a flask with dimensions 365x300x240 mm, a filling frame 200 mm high and a step model with steps of 80 and 160 mm. The volume of the gas pulse head of the experimental setup 2.2 of the total volume of the flask and the filling frame was 0.1 m ³ . During the experiments, the liquid-glass mixture of the following composition was compacted,%: 96-97 quartz sand 2KO2; 3.0-3.5 water glass (M = 2.7; γ = 1.47 g / cm ³ ).

 The quality of the forms obtained by the proposed method was evaluated by the uniformity of the density distribution along the height (Fig. 2) and the strength on the fret of the mold 10-12 s after compaction of the mixture (Table 1).

 A mixture compacted by the proposed method is characterized by a higher uniformity of compaction along the height of the mold (FIG. 2, curve 1) as compared to a mold compacted without evacuation (curve 2), in addition, it can be seen from the graphs that the mold compacted with using dilution, it has a much denser counterlad than the non-vacuum form.

 The experiments showed that each form, depending on the height, has an optimal rarefaction interval that provides the necessary hardening of the mixture. For molds sealed by the gas-pulse method, heights that are in the range of 200-400 mm are considered most acceptable. Assessment of the rarefaction value for these forms revealed a rational range of its values - 0.15-0.35 kPa (Table 1).

 From the experimental data given in Table 1, it follows that rarefactions smaller than the optimal level do not allow reaching the required mold strength. This is explained by the fact that not the entire volume of the mold is covered by hardening processes, since the filtration of gases at such rarefaction levels is local (zonal) in nature. The creation of a deeper vacuum leads to a sharp increase in the intensity of filtration of exhaust gases and, accordingly, a significant reduction in the time of their contact with the mixture. As a result, the exhaust gases do not have time to ensure the occurrence of gelation (curing) processes throughout the volume of the mixture and, as a result, the mold strength does not reach the required level.

For a comparative assessment of the proposed method, experiments were carried out to seal the liquid-glass mixture with a gas-pulse method without lower vacuum form. Since the liquid-glass form in air cures 1.5-2 hours, thermal drying was used to intensify the process (gas burners were used for heating) and curing by the CO ₂ process. The comparison results are summarized in table 2.

 Thus, the proposed method provides high-quality molds and cores from liquid-glass mixtures by the gas-pulse method, while simultaneously solving the problems of their compaction and curing, which in turn opens up great opportunities for creating automatic molding lines for molding in liquid-glass forms, in addition, it allows you to effectively solve the problem utilization of exhaust gases, directing them to the curing of the liquid-glass mixture.

Claims (2)

 1. METHOD FOR PRODUCING CASTING FORMS AND RODS FROM LIQUID-GLASS MIXTURES, comprising a seal provided by the combustion energy of a methane-air mixture, and subsequent curing of the liquid-glass mixture, characterized in that, in order to improve the quality of the molds and cores obtained, combining the processes of compaction and curing of the mixture and reducing the total duration of the cycle of manufacturing foundry molds and cores, as well as the disposal of combustion products, simultaneously with the compaction process, lower vacuum Contents shape (rod), blowing and curing is carried out the combustion products of methane-air mixtures by simultaneous compaction process with lower vacuum mold (rod).  2. The method according to p. 1, characterized in that the evacuation is carried out at a vacuum of 15 to 35 kPa, depending on the height of the mold or rod.

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