MX2012007889A

MX2012007889A - Treatment process for surplus sand from casting for use in core making and molding.

Info

Publication number: MX2012007889A
Application number: MX2012007889A
Authority: MX
Inventors: Wilson Luiz Guesser; Elaine Carina Carlini; Isaias Masiero; Marcos Antonio Moreira; Gilberto Fabris
Original assignee: Tupy S A
Priority date: 2010-01-11
Filing date: 2011-01-07
Publication date: 2012-10-05
Also published as: BRPI1000043B1; WO2011082464A1; MX353518B; BRPI1000043A2

Abstract

Treatment process for surplus sand from casting for use in core making and molding,wherein said process comprises the following steps: a) feeding of the surplus sand from casting into a silo (1 ); b) initial screening; c) processing the mixture in a first hydrocylone (4); d) processing in an attritor (6); e) second wet screening step; f) processing of the mixture in a second hydrocyclone (10); g) grading step; h) mixture processing with a third hydrocyclone (15); i) processing washed sand in a collecting gutter (16); j) drying in a dryer (17); and k) processing in a refrigerator (18).

Description

PROCESS OF TREATMENT OF EXCESSIVE SAND OF FOUNDRY FOR USE IN MACHARIA AND MOLDING The present Patent of Invention proposes a process of regeneration treatment of surplus casting sand, foreseeing its use in macharía and móldeos, a wet regeneration process, which has as objective the economic and technical equation for the problem of the sludge generated in the cleaning from sand to wet from conventional processes.

As is known to professionals in the foundry area, the green sand casting process basically uses two types of sand, which are: a) a molding sand, used to make the mold, which will shape the external parts of the sand the cast piece. This sand, usually silica, is agglomerated with bentonite and water, still having as additives the coal dust and eventually corn starch and wood dust; and b) a sand of macharía, used to make the males, whose parts of sand that are going to form the cavities or internal parts of the cast piece. This sand, silica or other refractory aggregate, is agglomerated with a chemical bond, which can be an organic (usually a resin) or inorganic (usually a silicate), and may even contain additives such as iron oxide, chromite, mulita, zirconia , wood dust, among others. In some foundry processes, this sand with chemical bond is also used for molding.

With the process of metal leakage, solidification, cold of the piece and demolding, it is normal and desirable that the male's ligament suffer thermal unbundling, so that in the demolding the sand of the male is mixed with the sand of the mold (in the molding sand the action of heat produces partial deactivation of the bentonite, transforming it into inert argilla, and also thermal deactivation of the coal dust, producing gases and coke).

This mixture of sands is then directed to the regeneration of the sand for use in molding, and consists of the steps of metal removal, desterroamiento, cold and repreparation, where in this last stage occurs the replacement of bentonite, water and additives The sand thus regenerated is sent to the mold making stage, and the process is repeated. i However, due to the incorporation of the core sand in the molding sand, this system undergoes mass increase, so that part of the molding sand must be removed from the system. This part of sand, known as surplus sand foundry, is used for other industrial purposes (cement, civil construction) or directed for landslides.

The preparation of the cores requires the use of new sand, since the presence of residues from the molding sand (bentonite, argilla burned, coal dust, coke) prevents the proper functioning of the resin bond film. In this way, in each casting cycle, a quantity of new sand corresponding to the weight of the cores is used, and which, depending on the type of piece produced, can be equivalent to the weight of the castings.

Some processes were proposed to regenerate the surplus sand from the smelter, so that it could be gradually added to the macharía. These processes envisage extracting, as much as possible, the bentonite, the inert argile, and the coal and coke dust that accompany the surplus foundry sand, leaving it as close as possible to the initial base sand.

A group of processes of regeneration of excess sand foundry are mechanical processes, where the surplus sand of cast iron is rubbed, removing the particles adhered to the grains of sand, and then subjected to a depletion, where these fine particles are separated.

The results obtained by these processes are not always satisfactory, since the degree of cleanliness obtained is not very great. Some smelting bu scan removes rlaa surplus casting in some special place in the demolding, removing not a middle fraction, but a fraction richer in sand of males, with less inorganic fines, which allows better results to these types of processes mechanics The rub can be achieved by impact between the grains of sand, impact against metal sheets, or even by the action of abrasive wheels.

Another group of processes of regeneration of surplus cast iron sand are the thermal ones, where the surplus sand is subjected to a heating stage with temperature between 500-800 ° C, in order to remove the hydroxyl of the bentonite and burn all the components organic (coal dust, coke, resins, wood dust), subtracting only inert argila together with grains of sand.

With the association to a mechanical process, this inert argila is separated from the grains of sand and removed by exhaustion. Eventually the process is done mechanical in two stages, one before and one after the thermal process. This type of processing provides a good quality of reclaimed sand, which can be used again in the production of cores, being, however, a process that involves high costs, mainly investment and energy (thermal and mechanical).

Another option is the wet processing of surplus sand, where the sand is rubbed to wet, in order to remove the particles adhered to the grains of sand, being that the fine particles can be removed by different processes, such as centrifugation or rub. Processes very similar to those used by processors of base sand are used, which remove sand deposits contaminated with argils and organic materials from nature, and purify them using wet processes.

Table 1 presents a comparison between results obtained by the different regeneration processes. It can be observed that the process of wet regeneration results in adequate values of male resistance.

Table 1 - Characterization of the sand regenerated by various processes.

One of the difficulties of this type of process is the cost of the water used, and its cleaning (removal of the fine particles taken from the surplus sand foundry), and the large quantities of mud generated. The high deposition cost of these fine particles removed from the sand is also important. Another important point of the cost refers to the drying of the sand, processed to wet. The regenerated sand can be used in macharía and molding, with chemical leagues, although it still contains appreciable amounts of organic materials.

There are also some processes that allow the recovery of sand used in the foundry, where the water coming from the washing is treated and reused by the system and the waste separated from the water generates a mud that has application in other industrial segments, such as in the manufacture of bricks, handles, tiles, ac ue rd o with the descriptions in documents PI9002540 and MU7100137. In addition, such processes require the use of new sand for the production of new males, thus raising both the cost of manufacturing males and damage to the environment.

Within this context, the present process of treating excess sand from smelting for regeneration is envisaged with a glimpse of its use in macharía and molding, a process that is a process of wet regeneration, and that brings an economic and technical equation for the problem of sludge generated in the cleaning of the sand to wet.

The present invention patent will be described according to figure 1, which is an organization chart of the process described herein.

In accordance with the illustrative I to figure 1 described above, and the process of treating excess sand from smelting for regeneration envisaging its use in hammering and molding consists of a set of stages, which can be thus discriminated: a) feeding the surplus sand of smelting in a silo (1); b) initial sieve, which can be made dry or even wet in a first sieve (2); c) processing the mixture in a first hydrocyclone (4), mixing that coming from the first screen (2) is previously directed to a first tank (3) (from where it is discarded, being that in the hydrocyclone (4) the first removal of fines from the sand occurs and from where the fine water is conducted to the first pond (5); d) processing in the wiper (6), where the mechanical agitation to humid occurs for separation of the particles of the grains; e) second stage of sieve to wet, which occurs in the second sieve (8), being that the mixture coming from the swab (6) is previously routed to the second tank (7); f) processing the mixture in a second hydrocyclone (10), where the second separation of fines from the sand occurs. The water with fines is conducted to the second pond (11). The mixture subjected to the second hydrocyclone (10) is previously routed to the third tank (9); g) classification step, d inde in a classifier (12), the separation of silica fines occurs. The water with fines is conducted for the first pond 5; h) processing of the mixture in a third hydrocyclone (15), when the third separation of fines from the sand occurs. The mixture before being admitted to the third hydrocyclone (15) is previously conducted to a fourth tank (14), the water being routed to a third pond (13); i) processing of the washed sand in drainage channel (16), which can include filter press, drain table, belt assisted by vacuum, gravity or centrifugation, another option is even the stacking of the mixture in the open. The water extracted in the drainage channel (16) is led to the third tank (13); j) drying in dryer (17), where the final removal of the water from the reclaimed sand occurs, a step that can be done in a rotary kiln or even in a fluid bed oven; k) processing in a cooler (18), where the sand has its reduced temperature for next to the environment. This can be done with a fluid bed or with pipelines with water circulation, or a combination of the two techniques.

Optionally, the processing of the mixture in the hydrocyclones (4, 10 and 15) of the steps "c", "f" and "h", can be carried out by classifier or sedimentation pond with siphoning. In the same way the processing of the mixture in the wiper (6) of the stage "d" can be carried out by pond with ultrasound.

The separated waters in the tanks (11), (13) can recirculate in the system, being able to return to the sieve executed in the second sieve (8), in the sieve (6) and in the classifier (12). The pond water (5) contains a large amount of solids and would be then, in a classical processing, subjected to a particle removal process, with the addition of polymers or chemical compounds, following a process of physical separation (decantation or centrifugation).

The present invention gives an economic destination to this sludge, leading it to the foundry to be used in the recovery of the molding sand, adding it in the cold and / or in the repreparation.

This sludge must be suitably treated so that when it is reintroduced into the sand system it does not damage the properties of the mold. This treatment constitutes an innovation, since this mud contains polyelectrolyte that damages the properties of the sand.

The treatment with sodium carbonate, in quantities of 0.013 to 0.52% (by weight) neutralizes the negative effect of polyelectrolyte. This way, the entire fraction of active components present in this sludge, such as bentonite and coal dust, is recovered, as well as replacing the water normally used in the cold and in the repreparation of the molding sand, which represents an important economic advantage for This process. Thus, the addition of sludge enables the reduction of 5.0% to 20% of the consumption of bentonite and 6.0% to 17% of the consumption of coal dust, which represents an important economy.

The treatment process of treated sand allows the production of males where 100% of this sand is used, showing the technical viability of the process. The parts are cast and shipped for m e c a n i z a l and assembly of various components, such as those for automotive use.

With this process it is technically and economically feasible to regenerate surplus cast iron sand, allowing about 80% of the new sand needs to be supplied in this way. This represents an important measure for the reduction of the consumption of natural resources, without the addition of water consumption, since all water used in regeneration or recirculation in the process itself or replaces the water in the cold and in the repreparation of the molding sand in the foundry.

Claims

1. - Process of treatment of surplus sand of cast iron for use in macharía and molding, being the aforementioned process characterized by the fact of foreseeing a sequence of stages, which include: a) feeding the surplus cast iron sand in a silo (1); b) initial sieve made in a first sieve (2); c) processing the mixture with fines in a first hydrocyclone (4), mixing that coming from the first ced azo (2) is previously directed to a first tank (3), being that in the hydrocyclone (4) the first removal of fines from the sand and from where the guide with fines is conducted for the first pond (5); d) processing in the wiper (6), where the mechanical to wet agitation occurs for separation of the particles of the grains; e) second stage of sieve to wet, which occurs in the second sieve (8), being that the mixture with fines from the swab (6) is previously routed to the second tank (7); f) processing of the mixture with fines in a second hydrocyclone (10), where the second separation of fines from the sand occurs, since the water with fines starting from the second hydrocyclone (10) is conducted to the second tank (11). ); the mixture subjected to the second hydrocyclone (10) is previously routed to the third tank (9); g) classification stage, where in a classifier (12), the separation of silica fines occurs, being that water with fines is conducted for the first pond (5); h) processing the mixture with fines in a third hydrocyclone (15), where the third separation of fines from the sand occurs; said mixture before being admitted to the third hydrocyclone (15) is previously conducted to a fourth tank (14), the water being routed to a third pond (13); i) processing of the washed sand in dewatering trough (16), the water extracted in the dewatering trough (16) is conducted to the third pond (13); j) drying in dryer (17), where the final removal of the water from the reclaimed sand occurs; Y k) processing of the regenerated sand in a cooler (18).

2. - Processing process of surplus sand of cast iron for use in macharía and molding, according to claim 1, characterized in that the volumes of water separated in ponds (11), (13) can recirculate in the system, being able to return in the sieve executed in the second sieve (8), in the sieve (6) and in the sorter (12).

3. - Process for treating excess sand of cast iron for use in macharía and molding, according to claim 1, characterized in that the sludge from the first hydrocyclone (4) is treated with sodium carbonate in the amount of 0.013 to 0 , 52% (by weight).

4. - Process of treatment of surplus casting sand for use in macharía and molding, according to claim 17, characterized in that the gas coming from the first hydrocyclone (4) treated with sodium carbonate is used in the repreparation of sand molding

5. - Process of treatment of surplus sand of cast iron for use in macharía and molding, according to claim 1, characterized by the fact that the sludge water treatment, from the first hydrocyclone (4) and introduced in the recovery of the molding sand, replaces part of the bentonite and conventionally used coal dust.

6. - Processing process of excess sand of cast iron for use in macharía and molding, according to claim 1, characterized in that the processing of the mixture in the hydrocyclones (4, 10 and 15) of the steps "c" , "f" and "h" can be made by classifier or sedimentation pond with siphoning.

7. - Processing process of surplus sand of cast iron for use in macharía and molding, according to claim 1, characterized in that the processing of the mixture in the rotator (6) of the stage "d" can be performed per pond with ultrasound.

8. - Processing process of surplus sand of cast iron for use in hammer and molding, according to claim 1, characterized by the fact that the initial sieve that is made in the first sieve (2) can be made dry.

9. - Process of treatment of surplus sand of cast iron for use in hammer and molding, according to claim 1, characterized by the fact that the initial sieve that is made in the first sieve (2) can be made wet.

10. - Process of treatment of surplus sand of cast iron for use in macharía and molding, according to claim 1, characterized in that the processing of the sand in the field of the stage "i" and using drainage channel (16) ) can include a filter press.

11. - Process of treatment of surplus sand of cast iron for use in macharía and molding, according to claim 1, characterized in that the processing of the sand in the field of the stage "i" and using drainage channel (16) ) can include a vacuum-assisted belt.

12. - Process of treatment of surplus sand of cast iron for use in macharía and molding, according to claim 1, characterized in that the processing of the sand in the field of the stage "i" and using drainage channel (16) ) may include the action of gravity.

13. - Process of treatment of surplus sand of cast iron for use in macharía and molding, according to claim 1, characterized in that the processing of the sand in the field of the stage "i" and using drainage channel (16) ) can include the centrifugation action.

14. - Process of treatment of surplus sand of cast iron for use in macharía and molding, according to claim 1, characterized in that the drying in dryer (17) performed in the field of stage "j" can be done in rotary oven.

15. - Process of treatment of surplus sand of cast iron for use in macharía and molding, according to claim 1, characterized in that the drying in dryer (17) performed in the field of stage "j" can be done in fluid bed oven.

16. - Process of treating excess sand of casting for use in hammering and molding, according to claim 1, characterized in that the cold stage carried out in the field of step "k" can be cast using the fluid bed technique.

17. - Process of treatment of surplus casting sand for use in hammering and molding, according to claim 1, characterized in that the cold stage carried out in the field of stage "k" can be hired by employment of the technique of pipes with water circulation.

18. - Processing process of surplus casting sand for use in macharía and molding, according to any of claims 1, 16 and 17, characterized by the fact that the cold stage carried out in the field of the stage "k" It is executed through the use of the combination of fluid bed techniques and pipes with water circulation.