JPH0413438A - Method and system for regenerating used sand at foundry - Google Patents

Abstract

PURPOSE: To make it possible to obtain high-quality molding sand by heat treating used sand at a specific temp. and subjecting the used sand to classifying and mechanical treatment of sand grain surfaces in plural cycles at a specific sand grain moving speed. CONSTITUTION: The used casting sand is magnetically separated by a magnetic separating machine 4 and is disintegrated. The sand is then sieved by a sieve 5 and the surfaces of the sand grains are mechanically treated. The casting sand is heat-treated, classified and cooled at a device 26. The heat treatment is, thereupon, executed at 310 to 900 deg.C. The classification and the mechanical treatment of the sand grain surfaces are executed in the plural cycles at the sand grain moving speed of 5 to 50 m/sec at the time of the mechanical treatment. At least one of the cycles is executed at the sand grain moving speed of 5 to 7 m/sec in an aq. medium. As a result, the consumption of the fresh sand, bentonite and coal may be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD OF THE INVENTION The present invention relates to foundry practice and can be used to regenerate and prepare sand in the manufacture of foundries.

[Conventional technology]

The conventional method currently used to regenerate sand is to heat the used sand at temperatures between 540 and 820°C in an oxidizing atmosphere;
Including classification and cooling [1. B. Zaigelov, “Reclamation of spent sand in foundry braktis”
, Mashgiz, 1961, p. 49 (USSR)].

This method is disadvantageous as it is unsuitable for handling sands of different chemical nature (based on organic and inorganic binders).

In addition, particles of used mold material are magnetically separated, crushed, sieved, oxidized and heated to a temperature of 800°C, cooled, and polished.
Thermomechanical reclamation of sand from used sand-clay molding material and core sand based on organic binders, which consists of classification, is commonly used (“Recycling Sand from Spent Foundry Material”). "Apparatus for Polishing", Instructions RD 37.002.0446-85, KTIAM, Cheierabinsuf, 1986, pp. 4-5), and polishing can be carried out by air cleaning (A, A, Vector and V,N.

Skolniakov, “Apparatus and method for reclaiming spent sand in large batch/mass production foundries”, NIIMA
SH, Moscow, 1982, pp. 37-39). The essential drawback of this method is that the activated clay on the quartz grains
Glock at temperatures higher than the range of 00-490° C. considerably complicates grain cleaning methods and makes it impossible to prepare recycled sand that can be used in cores made, for example, in “hot boxes”. In addition, spent bentonite and resin sand containing liquid glass mixture, quartz grains will melt with soda and other liquid glass components at temperatures of 700-800 °C, further hindering the reclamation and negatively affecting the quality of reclaimed sand. Extends.

In addition, a three-stage regeneration method consisting of air treatment, heat treatment, and air treatment again on the sand grain surface is technically common (A
, A. Švector, V., S. Palestin and V. N. Skolniakov, "Sand Reclamation from Spent Mold Material", Foundry Braktis, NC.
L5. 1987, pp. 26-30). This method is suitable for processing complex multicomponent mixtures containing liquid glass, bentonite and synthetic resins. However, recovery of clay components by air treatment is complicated due to the high water content of used green sand. In this case the proportion of good sand is significantly reduced. However, the main drawback of this method is that the part of the activated clay remaining in the sand after the first cleaning step becomes glock during subsequent high-temperature calcination, and that post-calcination air treatment completely removes traces of the clay binder. It is a failure to remove. As a result, the quality of recycled material is inferior to that of green sand;
And recycled sand can only be used on a limited scale in core sand, for example in hot boxes.

Hydraulic reclamation of sand from mixed waste piles of automobile plants is further known in the art (A, A.

Schweter and V. N. Skolniakov,
[See Apparatus and Method for Recycling Spent Sand in Large-Batch/Mass-Production Foundries J, NIIMASH, Moscow, 1982, pp. 14-19).

However, this method cannot be used to produce high quality recycled sand. The reason is that only active bentonite is removed from the mixture, while bentonite in the form of glock and residues of coal and resin remain on the quartz grains. In addition to the poor properties of sand, which negatively affects the strength of cores produced in hot boxes, the destruction and sublimation of resin and coal residues during heating of core boxes has a considerable ecological impact in the core field. This can cause material contamination and interfere with the normal progress of the core manufacturing process.

The best results have so far been obtained by using regeneration methods in which the spent sand is subjected to magnetic separation, sieving, hydraulic polishing, classification, dewatering, oxidative calcination and cooling (A, A,
Schwechter and V.N.

Skolniakov, “Apparatus and method for reclaiming spent sand in large batch/mass production foundries”, NIIMA
S) I, Moscow, 1982, pp. 2600-28).

This method is suitable for regenerating sand for use in limited quantities (up to 3096) in core sands based on synthetic resins due to the poor quality of the regenerated sand. The basic reason behind this is that when the mold is filled with metal, a layer of glock-like bentonite film forms on the quartz grains which are heated to a temperature higher than the range of 400-490°C. The force applied to the treated sand grains during hydropolishing is insufficient to remove Glock film. The reason is that the high resistance of the aqueous medium prevents the considerable impact forces that must be applied to the grains. Adding recycled sand containing glock-like bentonite films instead of high-quality quartz sand to synthetic resin-based core sand increases the strength properties of the sand by 1.3
~3.0 times decrease. As a result, the scale of application of recycled sand is
reduced.

A device for removing the casting with the core from the mold flask, a vibrating grate connected to it by a conveyor device for removing the core from the casting, and a device for demolding the foundry sand from the mold flask, then continuous line for preparing sand and bentonite materials, including magnetic separators, sieves, coolers, sand mixers and automatic molding machines, and also continuously preparing foundry sand, including sand mixers and core molding machines. The system for preparing foundry manufacturing river sand, which includes lines for the production of foundries, is currently the most popular ["Experience of the Porzisky Motor Plant, Cast Iron Production", N11TAVTOPROM
, Moscow, 1971, pp. 127-131 (USSR)] In prior art systems, rejected cores consisting of pieces of different sizes are collected in a store for rejected cores and transported to a lift. The garbage is loaded into a dump truck and transported to a garbage dump. The core sand demolded from the castings on the vibrating grate and the used sand separated in the space under the sieve are
It is conveyed to a hydraulic slurry separation mixing tank, mixed with water, and pumped to a slurry settling tank, from which it is periodically transported to a waste dump. This system does not provide for processing and does not allow foundry and core sand waste to be reused. As a result, a significant amount of sand, bentonite and coal are constantly discharged from the sand preparation system and therefore, by introducing new additives, a constant supply of fresh sand, bentonite and coal to the mixer in the sand preparation line is required. should be supplemented.

[Object and structure of the invention]

The aim of the present invention is to improve the quality of recycled sand and reduce the power requirements and increase the utilization of recycled sand in core sand based on synthetic resins, while providing a system for preparing sand. must reduce the loss of fresh sand, bentonite and coal, save natural resources, protect the environment and reduce transportation costs.

The purpose is to use heat treatment to regenerate sand from used foundry molding material by magnetic separation, crushing, sieving, mechanically treating the surface of the sand grains, heat treating, classifying and cooling. carried out at a temperature of 310-900 °C, classification and mechanical treatment of the sand grain surface in several cycles (sand grains move at a speed of 5-50 m/s during mechanical treatment), at least one of the cycles This is achieved in a process for the reclamation of sand from used foundry mold material, which is characterized in that it is carried out at a sand grain velocity of 5-7 m/s in the medium. When carried out, the method involves curing in cold and hot molds and obtains high quality foundry sand and core sand that can be used in various molding materials containing resinous liquid glass and other binders. enable.

The purpose is to process used sand with a high proportion of activated clay and admixtures of coal and liquid glass mixtures so that the reclaimed sand can be used in foundry sand-bentonite, thermosetting core and shell mixtures. This is achieved by carrying out a heat treatment of the sand grain surface within a temperature range of 310-490°C followed by a mechanical treatment in an aqueous medium. At the same time, in the case of centered regeneration composites, it is possible, for example, to combine the method of hydraulic dressing of sand and the method of hydraulic regeneration with the method of preparing foundry fillers of the desired composition.

Regenerating used foundry bentonite mixtures with high @ amount of active and grog bentonite and high proportion of organic components (resin and coal) requiring large amounts of recycled sand to be used in core mixtures based on synthetic resins For this purpose, the heat treatment of the sand grain surface is preferably carried out at
The mechanical treatment is carried out before and after the heat treatment; furthermore, the mechanical treatment before the heat treatment is carried out in an aqueous medium, and the mechanical treatment after the heat treatment is carried out in an air medium at a grain speed of 30. ~50m/sec. The sequential treatment of residual binders and impurities reduces the costs of mining, beneficiation, transportation and burial of the most popular foundry fillers, producing a perfect replacement for fresh sand and without changing the composition of the mixture. allow it to be reduced to a minimum. To achieve said objective, a system for preparing and regenerating sand in foundry production has been developed. The system comprises a device for removing the casting with the core from the mold, a vibrating grate connected to the device by a conveyor device for extracting the core from the casting, and a device for demolding the sand from the mold. , then a sink line for preparing foundry sand, which successively comprises a magnetic separator, a sieve, a cooler, a foundry sand mixer and an automatic molding machine, and also a medium which successively includes a core sand mixer and a core molding machine. Includes a line for preparing child sand. According to the invention, the system consists of a feeder, a crusher for destroying rejected cores, a conveyor with a magnetic separator, a backflow sieve, for products under a grate connected to a foundry sand mixer by a conveyor device. A device for separating impurities from the surface of the sand grains is connected to the foundry sand mixer and the core sand mixer by means of a hopper, a fine crusher, a control sieve, and a conveyor device. A line for processing waste foundry sand and core sand is provided, including a sieve in the line for processing and a vibrating grate for removing the core from the casting.

Depending on the composition of the used sand, it is preferable to manufacture the device for separating impurities from the surface of the sand grains in two ways. In a first aspect, the apparatus includes a cooler;
It consists of a furnace for oxidation and calcination of used sand, which is successively arranged a hydraulic polisher, a two-product hydraulic classifier, a dehydrator and a dryer. In a second embodiment, to remove impurities from the surface of the sand grains such that all organic and mineral impurities, including films of grog-like bentonite that are difficult to separate, are completely removed from the surface of the sand grains. The equipment consists of a hydraulic polisher with a dry polisher with a cooler and a suction system, in which a hydraulic classifier, a dehydrator and a furnace for calcining the used sand are arranged in succession. Preferably, a segmented air regenerator is used as the dry polisher.

The system is suitable for implementing sand reclamation methods and produces economic benefits by reducing the consumption of fresh sand, bentonite and coal and cutting the volume of waste trucked to the dump. .

Studies have shown that each ton of waste helps save 570 kg of sand, 20 kg of bentonite and 0 kg of coal.

Besides, the system helps to economize natural resources and protect the environment against industrial waste. Certain embodiments of the invention will now be described with reference to the drawings, which illustrate a system for carrying out the sand reclamation method according to the invention.

[Detailed description of the invention]

The system for carrying out the sand production method according to the invention (see drawing) includes a line for preparing a foundry sand-bentonite mixture, a line for preparing core sand, and a line for disposing of waste cores and foundry mixtures. It consists of a line for processing (Figure 1).

The line for preparing molding sand consists of a device 1 for removing the core from the mold, a vibrating grate 2 for taking out the core from the mold, and a device 3 for releasing the molding sand from the mold. , then magnetic separator 4, sieve 5, cooler 6
, a recirculating foundry sand river hopper 7, a foundry sand mixer 8 and an automatic molding mann 9.

The line for preparing core sand comprises a core sand mixer 10 in which a core making machine 11, a ready core storage device 12 and a rejected core storage device 13 are arranged in series.

The system includes a fresh foundry sand hopper 14 connected to a foundry sand mixer 8, a fresh core sand hopper 15 connected to a core sand mixer 10, and connected to the hoppers 14 and 15 by a conveyor device, e.g. a belt conveyor. A fresh dry sand storage device 16 is included.

The line for processing waste cores and foundry mixtures comprises a feeder 17 and a coarse crusher 18 for successively destroying rejected cores, a belt conveyor 19 containing a magnetic separator 20, a backflow device. sieve 21 with 22
, e.g. belt conveyor with tripper, product hopper 23 under the grate, fine crusher 24
, a control sieve 25 and a device 26 for removing impurities from the surface of the quartz particles. The device 26 is connected to the hoppers 14 and 1 by means of a belt conveyor device 38.
5 and mixers 8 and 10.

The product hopper 23 under the grate is connected by a belt conveyor 37 to the recirculating foundry sand hopper 7 and the mixer 8, and the vibrating grate 2 and the sieve 5 are connected to the conveyor 19 by a belt conveyor 39. .

The device 26 for removing organic and mineral impurities from the surface of sand grains has two aspects.

- In an embodiment (FIG. 2), the impurity removal device comprises a used sand hopper 27, a feeder 28, successively a calciner 34, a cooler 35, a hydraulic polisher 29, a hydraulic classifier 30 and a dewatering device. machine 31, dryer 32, and hopper 33
is located. In a second embodiment (FIG. 3), the impurity removal device includes a used hopper 27 with a feeder 28, a hydraulic polisher 29, a hydraulic classifier 30, and a dehydrator 31.
, a calciner 34, a cooler 35, a drying grinder 36 and a hopper 33 (all arranged in series and interconnected by a conhairing device 42).

The system works as follows.

Foundry sand is prepared in mixer 8 by mixing recycled sand, fresh sand, bentonite, coal and water.

The prepared sand is fed to an automatic molding machine 9. Make a half-split, install the core from the storage device 12,
After assembling the mold and pouring the metal, the mold with the casting is advanced to a device 1 for removing the casting and then fed to a vibrating grate 2 for the core to be removed, while the mold is
Transfer from the mold flask to the device 3 for molding sand to be demolded.

The used foundry sand deformed by the device is supplied to a magnetic separator 4 and then to a sieve 5. The sieved material flows into a cooler 6 and then into a used foundry sand hopper 7 from which it is fed little by little to a foundry sand mixer 8.

Fresh sand is delivered from the storage device 16 to the hopper 14;
From this hopper 14, it is supplied little by little to the mixer 8, and also supplied to the hopper 15, from which it flows into the mixer 10. The prepared core sand is transferred to core molding machine 1.
Supply to 1. The prepared cores are transferred to a storage device 12 and then to a mold assembly station. Rejected cores are collected in a mold flask and transferred to a storage device 13 by a lift truck. The lift truck fills the feeder 17 with rejected cores and supplies these rejected cores to the coarse crusher 18. After rough crushing, rejected cores are transferred onto a belt conveyor 19 having a magnetic separator 20. At the same time, the belt conveyor 19 is fed with product from above the grate of the sieve 5 and also from below the vibrating grate 2.

In this vibrating grate 2, the core is removed from the casting.

Material free of metal impurities flows to sieve 21.

The product from under the grate of sieve 21, actually recycled foundry sand, is
It is collected by a backflow device 22 in a hopper 23, from which it is directed by a system of belt conveyors and lifted into a recirculating foundry sand hopper 7, where it is fed in portions to a mixer 8. The product from above the grate of the sieve 21 is fed to a fine crusher 24 . At the same time, the crusher can be fed with product from below the grate of the sieve 21 through a backflow device 22. This is required when recirculating foundry sand hopper 7 and hopper 23 are completely filled with material.

After the fine crusher 24, the material flows to a control sieve 25. The product from above the grate of the control sieve 25 is transferred to a waste dump, while the product from below the grate is delivered by a system of belt conveyors to a device 26 for removing impurities from the surface of the sand grains. The reclaimed sand is transferred by a pneumatic conveyance system, a belt conveyor, and lifted into hoppers 14 and 15. At the same time, fresh sand is stored in storage device 1
5 is delivered by a system of belt conveyors and lifted into hoppers 14 and 15. From the hopper 15, the mixture of fresh sand and polished material is fed in portions to the core sand mixer 10. From the hopper 14, the mixture of fresh sand and reclaimed sand is fed in portions to the foundry sand mixer 8.

Sand can be recycled in two different ways:

When the spent mixture contains significant proportions of activated clay and coal, and also impurities of liquid glass mixture, together with small amounts of grog-like bentonite, the impurities are removed from quartz by sequential treatment in the calciner 34 and in the hydraulic polisher 29. Preferably, a device 26 is used to remove the particles from the surface (FIG. 2). In this case, the product from under the grate of the control sieve 25 flows into a used sand hopper 27 with a feeder 28 from which it is fed in portions to the calciner 34 . The material is heated to a temperature of 310-490°C in an oxidizing atmosphere in a furnace. High volatiles burn from resin and coal films. The heated material flows into the cooler 35 and then into the hydraulic sander 29 where it mixes with water and separates from the bentonite film at a grain movement speed of 5-7 m/sec. Next, the material is
It is pumped to a hydraulic classifier 30 where it is separated into wet polishing sand and drain water. The polishing wet sand is supplied to a dehydrator 31, then to a dryer 32, and then to a hopper 33. The abrasive dry sand is transferred from hopper 33 to hoppers 14 and 15, from which it is fed in portions to mixers 8 and 10.

If the used sand contains a significant proportion of grog-like and activated bentonite and some organic impurities, an apparatus for separating the impurities from the surface of the quartz grains by sequential hydraulic treatment, heat treatment and mechanical treatment 2
5 is preferably used (Figure 3). In this case, the product from below the grate of the control sieve 25 is transferred to the feeder 2
8 and from this feeder 28 is fed together with water to a base polisher 29 where the bentonite film is substantially removed at a particle movement speed of 5 to 7 m/s and then to a hydraulic classifier 30. The material is then separated into abrasive wet sand and drain water. The abrasive wet sand is fed to a dehydrator 31 where the moisture content of the abraded material is first reduced from 20-25% to 6-8%, and then the dehydrated material is fed in portions to a furnace 34. The material is heated to a temperature of 700-900°C in an oxidizing atmosphere in a furnace. The organic film burns out as a result. The heated material
Transfer to cooler 35 and cool to room temperature.

The cooled material is fed to a dry polisher 36 where it is separated from the grain movement rate 30-5ρ, /j,'゛-films and dust, drawn into a ventilation system 41 and passed through a hopper 33.
from this hopper 33 to hoppers 14 and 1.
5 and then to mixers 8 and 10. The used mixture used in the production of castings in green sand-bentonite molds with cores based on synthetic resins consists essentially of quartz grains (approximately 90%) coated with films of organic and inorganic origin. (the quartz grains include resin and coal, and the film includes bentonite).

It is common knowledge that bentonite is composed of montmorillonite mineral. The montmorillonite structure consists of two sheets of silica tetrahedra separated in the center by an octahedral alumina sheet. Water molecules entering the spaces between the layers cause swelling of the lattice. Exchange cations should be found between the silicate layers. Heating to 100-200°C results in loss of bentonite film contained on the spent sand grains and loss of shrinkage and void water. Further heating of the material results in a bentonite film that loses its ability to reswell. The exact temperature at which swelling capacity is completely lost depends on the nature of the cations adsorbed by the bentonite. In the case of calcium bentonite, its temperature is
It is within the range of 310 to 400°C, and in the case of sodium bentonite, it is within the range of 400 to 490°C. When heating to temperatures above 400°C in the case of spent sand based on calcium bentonite and above 490°C in the case of sodium bentonite,
The hydroxyl water begins to decrease and the swelling ability is completely lost, resulting in calcination of the bentonite (grog formation) and chemical reaction with the quartz grains. Hydroxyl water is completely lost at 700°C, and the structure is reduced to 1/3 of the oxygen in the octahedral part.
It changes by removing . The extent of bentonite calcination on quartz increases with increasing temperature, heating duration and decreasing grain size. The conversion of bentonite on the quartz grains is completed within a temperature range of 700-900°C, depending on the heating time.

Bentonite heated to 310-490°C is active and loosely bound to the quartz grains and can be reused in bentonite foundry sand. Bentonite heated to temperatures above the range of 310-490°C becomes inert and tightly bound to the quartz grains and therefore cannot be used in bentonite foundry sands. The presence of active or inactive bentonite on the quartz grains drastically reduces the strength of the resin-based sand and requires the bentonite film to be removed from the spent sand grains.

In contrast, films of organic origin (resins and coal)
It begins to decompose when heated at 100-200°C in an oxidizing atmosphere. The decomposition process is accelerated with increasing temperature and treatment duration and is generally completed within the range of 700-800<0>C.

When regenerating sand from a spent sand-bentonite mixture and core sand based on resin and having a high proportion of active clay and a low proportion of inert clay (aspect 1), the first step of the regeneration method according to the invention consists of heating the mixture to 310-490°C in an oxidizing atmosphere. In the case of used mixtures containing calcium bentonite,
The heating temperature should not exceed the range 310-400<0>C; in the case of spent mixtures with sodium bentonite, this range is 400-490<0>C. This prevents the active bentonite from turning into glock on the quartz grains and helps remove the portion of organic impurities that decompose at these temperatures. The second step of the regeneration method according to the invention consists in removing the film of uncake activated bentonite by hydraulic techniques at a speed of sand grain movement in a water stream of 5 to 7 m/s. Activated bentonite has low agglomeration to quartz and therefore green bentonite is most completely removed. If, in addition to bentonite, the spent mixture also contains liquid glass, soluble sodium silicate is removed from the mixture in a second step. This process, which concludes with hydraulic classification and drying of the material, yields recycled sand that is a useful replacement for quartz sand in foundry bentonite and liquid glass mixtures and in shell core mixtures and can also be used in hot box core mixtures. Considering that the heating temperature of the hot box during the production of the core generally does not exceed 250 °C and the calcination temperature during the regeneration process is at least 310 °C, the gas is liberated from the organic matter remaining on the regenerated sand grains. probably won't.

When regenerating sand from a sand-bentonite spent mixture and a resin-based core mixture with a high proportion of inert and active clays (aspect 2), the first step according to the invention comprises It consists in separating the film by hydraulic techniques at a speed of sand grain movement in a water stream of 5-7 m/s. In this case, the green film has low agglomeration to the quartz and the activated clay particles are most completely separated. After hydraulic polishing and subsequent hydraulic classification,
The material is used in a second processing step.

After heat treatment at a temperature of 700-900°C and cooling, the material is completely separated from organic impurities.

In the final processing step, the grains must be subjected to maximum impact and abrasive forces that can separate the glock-like bentonite. This means, for example, that the sand grain movement speed is 30 to 50 m/
This is achieved by subjecting the air to air cleaning (seconds followed by classified dust removal) and repeated air treatment cycles (preferably 4 to 8).

The choice of a maximum speed of 50 m/s is explained by the fact that speeds above 50 m/s result in disintegration of the quartz grains themselves, and the yield of good sand is drastically reduced. The minimum speed of 30 m/s and the number of treatment cycles were determined experimentally. Clean quartz grains are obtained as a result of such treatment. In order to obtain high quality recycled sand, the material is subjected to treatment by dry classification in the final step to recover a useful fraction of 0.1 to 2.51.

〔Example〕

Below are examples illustrating certain aspects of the sand reclamation process carried out in the apparatus of the present invention for used sand-bentonite foundry mixtures and resin-based hot box/shell core mixtures.

Example 1 A used sand-bentonite foundry mixture and a core mixture based on thermosetting resin are subjected to the treatment according to the invention in the following sequence: crushing in a rotary crusher 24, on a sieve 25 with mesh size 10, Omm. sieving, oxidative heating in a shaft furnace 34, cooling in a fluidized bed cooler 35, polishing in a hydraulic polisher 29 at a grain movement speed of 6.0 m/sec, classification in a spiral classifier 30, and thermal drying in a fluidized bed dryer 32.

To carry out the oxidative heating step, the material containing calcium bentonite was fed into a furnace at a temperature of 310°C, where it was heated at a rate of 3°C/min.

The obtained recycled sand is used as a filler in an amount of up to 100%.
It was used to make molds from bentonite mixtures, synthetic resin-based hot box cores, and shell cores.

The shell mixture tested had the following composition (parts by weight): 100 filler, 4.5 CF-015 resin, 0.2 kerosene (based on resin), 33% of urotropin.
Solution 1.5, and calcium stearate 0.12°Curing temperature is 275°C, curing time is 60 seconds,
The sample thickness was 10+am.

Test results for shell mixtures prepared from recycled sand and fresh reinforced sand are given in Table 1. Table 1 demonstrates the possibility of completely replacing fresh sand with recycled sand.

Table 1 Properties of the shell mixture Processing conditions Name °C m/s Hot cooling (Example 1) A practical application of the method of the invention in one of the operating plants is the use of shells based on phenolic resin for making molds from bentonite mixtures. Reinforced sand 200.00 annually (by using recycled sand for the production of cores (by the cloning method) and partially for the production of hot-melt cores based on furan resin (by the hot-box method) This makes it possible to save time.

Example 2 A used casting/core mixture based on synthetic resin and free of magnetic metal inclusions was fed into a vibration@25 with a mesh size of 10 mm. The product from below the screen was stored in a hopper 27 from which it was transferred by a feeder 28 to a hydraulic polisher 29. This hydraulic polisher 29 is
The sand particles were moved at 6.0 m/sec. The spent mixture was separated from the green bentonite film in a hydraulic sander.

The wet material was transferred from the hydraulic sander to a hydraulic classifier 30 where the abrasive film and particulates were washed from the material by a stream of water. Direct the cleaned material to the dewatering station;
Therefore, dehydration was performed using a band vacuum filter 31. The dewatered sand was transferred to a countercurrent drum furnace 34 where it was heated to a temperature of 800° C. in an oxidizing atmosphere. The calcined material was simultaneously cooled to 35° C. in a fluidized bed cooler 35 and dedusted.

The cooled reclaimed sand was pneumatically purified by entering an air regenerator 36 consisting of several successive sections. Each of the sections consists of a casing having a nozzle, tube and barrier extending vertically upward in succession. Compressed air under a pressure of 0.03 MPa was supplied to the nozzle, at the outlet of which the compressed air trapped the sand particles, accelerated them to a speed of 30 m/s and caused them to impinge against a fixed barrier. Dust-like particles were drawn into the suction system by an exhaust fan while the sand was advanced to further sections for processing. After passing through the 8 sections of the air regenerator, the material is classified to separate particles larger than 2.5
．． Particles smaller than 1 mm were separated. Hopper 33
The recycled sand accumulated in f$(iii) was fed to the station where the foundry/core mixture was prepared.

The properties of the used starting mixture and of reclaimed sand and standard fresh reinforced sand from the Brtsevo deposit are shown in Table 2.

Reclaimed sand was used in amounts up to 100% as filler to make molds from sand-hentonite mixtures, hot box cores and shell cores.

Table 2 Material properties according to the content of impurities % Content, % Used 9.8 5.0 3.0 Mixture (Example 2) The foundry mixture on hot lagging had the following composition (parts by weight): Filler 100: Ferric oxide 0.5; 2
: A mixture of furan resin and phenolic resin in a ratio of 1:2
,0; Catalyst (copper nitrate) 0.5°Curing temperature was 210°C.

Test results for core mixtures prepared from recycled sand and reinforced sand are shown in Table 3.

From the data given in the table, the nature prepares a high-quality material that can be used in core mixtures (up to 100%) based on synthetic resins without any limitations and can completely replace reinforced quartz sand. It is clear that it is suitable for

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of a system for performing the sand manufacturing method according to the present invention, Fig. 2 is a schematic diagram of an embodiment of an apparatus for removing impurities from the surface of sand grains, and Fig. 3 is a schematic diagram of an embodiment of a device for removing impurities from the surface of sand grains. 3 is a schematic diagram of another embodiment of an apparatus for removal; FIG. 1... A device for taking out the casting having a core from the mold flask, 2... A grate, 3... A device for releasing the molding sand from the mold flask, 4... A magnetic separator, 5...
Sieve, 6... Cooler, 8... Foundry sand mixer, 9.
... Molding machine, 10 ... Core sand mixer 11 ... Core molding machine, 17 ... Feeder, 18.
...Rough crusher, 19...Conveyor, 20...
・Magnetic separator, 21... Sieve, 22... Backflow device, 2
3...Hopper, 24...Fine crusher, 25.
... Control sieve, 26... Device for separating impurities from the surface of sand grains, 29... Hydraulic polisher, 30... Hydraulic classifier, 31... Dehydrator, 32... Dryer , 34・
...Furnace, 35...Cooler, 36...Dry polishing machine,
37... Conveyor device, 38... Conveyor device,
39... Conveyor device, 40... Conveyor device,

Claims (1)

[Claims] 1. Heat treatment in regenerating used sand in foundries by magnetic separation, disintegration, sieving, mechanical treatment of the surface of sand grains, heat treatment, classification, and cooling. is carried out at a temperature of 310-900 °C, the classification and mechanical treatment of the sand grain surface is carried out in several cycles with a sand grain movement speed of 5-50 m/s during the mechanical treatment, at least one of the cycles is carried out in an aqueous medium. A method for recycling used sand in a foundry, characterized in that the method is carried out at a sand grain movement speed of 5 to 7 m/sec. 2. The method according to claim 1, wherein the heat treatment of the sand grain surface is carried out at a temperature of 310 to 490°C, and the mechanical treatment of the sand grain surface is carried out in an aqueous medium after the sand grain surface heat treatment. 3. Heat treatment of the sand grain surface is carried out at a temperature of 700 to 900 ° C, mechanical treatment of the sand grain surface is carried out before and after heat treatment, mechanical treatment of the sand grain surface is carried out in an aqueous medium before heat treatment, and heat treatment is carried out. 1 . The subsequent mechanical treatment of the sand grain surface is carried out in an air medium at a grain movement speed of 20 to 50 m/s.
The method described in. 4. a device (1) for removing the casting with the core from the mold flask; a vibrating grate (2) connected to the device (1) by a conveyor device (40) for removing the core from the casting; and A device for demolding the foundry sand from the mold flask (3), followed by a magnetic separator (4) and a sieve (5).
), a line for preparing foundry sand comprising a cooler (6), a foundry sand mixer (8) and an automatic molding machine (9), and also in series a core making machine (1
1) A system for carrying out the method according to claim 1, comprising a line for preparing core sand comprising a core sand mixer (10) with a feeder (17).
, coarse crusher (18) for crushing rejected cores
, a hopper for the product under the grate connected to the foundry sand mixer (8) by a conveyor (19) with a magnetic separator (20), a sieve (21) with a backflow device (22) and a conveyor device (37) (23), a fine crusher (24), a control sieve (25), and a conveyor device (
A device (26) for separating impurities from the surface of the sand grains is connected to the foundry sand mixer (8) and the core sand mixer (10) by a conveyor device (38). A line for processing waste foundry sand and core sand, which is connected to a sieve (5) of the line for preparing a bentonite mixture and a vibrating grate (2) for removing the core from the casting. A system characterized by the following. 5. A device for separating impurities from the surface of the sand grains includes a cooler (35) and continuously operates a hydraulic polisher (29).
), a hydraulic classifier (30), a dehydrator (31) and a dryer (32) are arranged.
).The system of claim 4. 6. The device for separating impurities from the surface of the sand grains includes a dry grinder (36) with a cooler (35) and a suction system (41), and in succession a hydraulic classifier (30
), dehydrator (31), furnace for calcining used sand (
5. The system according to claim 4, comprising a hydraulic polisher (29) in which a polisher (34) is arranged. 7. System according to claim 4, characterized in that the device for separating impurities from the surface of the sand grains as a dry sander (36) comprises a segmented air regenerator.