JPH02218446A - Recycling of chromite sand for casting use - Google Patents

Abstract

PURPOSE:To restore the fire resistance of chromite sand by bringing the recovered sand into contact with a grindstone rotating at a high speed. CONSTITUTION:Chromite sand is introduced from an entrance opening 38 of a hopper 40 onto the bottom part 10a of a casing thereof. A motor 34 is energized to rotate a rotary grindstone 18 in the direction B at a high speed and a rotary drum 14 in the direction A at a lower speed, whereby the chromite sand collected on the casing bottom 10a is picked up by lifting blades 24 of the rotary drum 14 and delivered into each space S thereof through slits 22 and whereby the chromite sand C is dropped onto the grindstone 18 rotating at a high speed. This improves the fire resistance of the chromite sand.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a method for regenerating chromite sand for molds, and more specifically, for a mold using silica sand and chromite sand as foundry sand, after pouring and casting is completed. The present invention relates to a method for suitably recovering chromite sand whose fire resistance has been regenerated to the state of new sand from foundry sand whose mold has collapsed.

The molding sand that makes up the conventional mold has good moldability and appropriate strength, has appropriate air permeability and an appropriate particle size distribution, and has fire resistance that corresponds to the temperature of the metal being poured. It is required that various characteristics such as availability and economic availability be met. Among these properties, the fire resistance is particularly important because it is related to the permeability of the high-temperature metal being cast into the mold and the degree to which it is baked onto the casting surface.

Therefore, as foundry sand for molds, chromite sand, which has superior fire resistance (seizing resistance and penetration resistance) compared to silica sand, olivine sand, and zircon sand, is often used. However, chromite sand relies exclusively on imports from overseas, which increases the cost.1 For example, the amount of chromite sand used can be reduced by making it into pocket sand and molding it by binding it with an organic binder such as furan resin. It is common for there to be.

In a mold using silica sand or chromite sand as the foundry sand, when pouring is completed, the mold is separated after waiting for the molten metal to solidify and cool. ), the mold is self-collapsed or burst-collapsed by the dissolving frame, silica sand, chromite sand.

A mixture of iron powder, scale, and other organic binders attached to the surface of the foundry sand is obtained. From this mixture, silica sand and chromite sand are separated.

The silica sand is intended to be reused as foundry sand.

That is, the mixture of the foundry sand and the like is subjected to soft scrubbing in which the foundry sands collide with each other using centrifugal force, thereby removing the organic binder from the sand surface. Since chromite sand is made from chromite, it has some magnetism, so it can be separated from non-magnetic silicon by passing it through a strong magnetic field. When the scrubbed mixture of silica sand and chromite sand is supplied to a rotor type or ball element type and passed through a magnetic field of 25,000 to 27,000 Gauss, the chromite sand is magnetically attracted and separated from the silicon. It will be done. It is better to perform this magnetic sorting in two stages, in which ferromagnetic substances such as iron powder and scale are removed from the mixture in the first stage, and then the silica sand and chromite sand are separated from each other in the second stage. Common.

Problems to be Solved by the Invention As mentioned above, silica sand and chromite sand are sorted and separated from the foundry sand that has collapsed the mold after pouring, and the silica sand is used again as foundry sand. However, the reuse of the separated chromite sand has been extremely limited because its fire resistance has decreased due to the following reasons. Namely.

Giyang mineral (3Mg0.2SiO*.2H20) contained in chromite, which is the raw ore of chromite sand.
Intergranular substances mainly composed of silica (S i O,) mixed in from the silica sand during the molding process are formed and adhered to the surface layer of the separated chromite sand, and this is used as foundry sand. Deteriorates the fire resistance of

In addition, iron oxide (Fe
d) is diffused and reduced to the surface layer of the chromite sand due to the high heat during pouring, forming iron beads. These iron beads also deteriorate the refractory properties of the 5-separated chromite sand as foundry sand, and cause burning defects in the castings.

In this way, the fire resistance of chromite sand after separation from the collapsed foundry sand is reduced.

When reusing this, for example, it is limited to the use of molds for small, thin-walled products that are less prone to baking defects, or new chromite sand is added (20% or more). However, no matter what form of reuse is taken,
Basically, as long as chromite sand with reduced fire resistance is used as foundry sand.

There is always an inherent fear of causing seizing defects in castings.

Therefore, chromite sand after separation is generally not used for important casting products, and in view of the fact that the fire resistance has deteriorated, the chromite sand after one separation should be completely discarded and only silica sand should be reused. In this case, chromite sand, which is imported and expensive, would be discarded after just one use for the mold, and there was a need to reconsider from the standpoint of effective resource utilization. .

Purpose of the Invention This invention has been made in view of the problem that the chromite sand separated from the foundry sand that collapsed the mold after pouring the metal is not effectively reused due to its reduced fire resistance. The purpose of this proposal is to provide a method for recycling chromite sand for molds, which restores fire resistance to chromite sand after one separation and allows it to be used again as foundry sand. .

Means for Solving the Problems In order to overcome the above-mentioned problems and achieve the intended purpose, the present invention involves collapsing a mold made of foundry sand of silica sand and chromite sand after pouring, and disintegrating the molding sand from this collapsed molding sand. When regenerating the chromite sand for molds that has been separated and collected by magnetic separation, the collected chromite sand is brought into contact with a high-hardness grindstone rotating at high speed to remove intergranular substances containing silica as a main component from the surface of the chromite sand. The iron beads, which are reducing components of iron oxide, are removed by polishing, and the intergranular substances are discharged out of the system along with the air flow during polishing with a grindstone. The feature is that by separating and discharging the sand out of the system, the intergranular substances and iron beads are removed and the chromite sand whose fire resistance has been restored is regenerated.

EXAMPLES Next, the method for regenerating chromite sand for molds according to the present invention will be described below by giving preferred examples and referring to the accompanying drawings. As explained earlier, the chromite sand to be recycled in this example is produced by collapsing a mold made of silica sand and chromite sand after pouring, and then magnetically sorting chromite sand from the resulting foundry sand. means.

As mentioned above, after magnetic separation, chromite sand has intergranular substances mainly composed of silica (S i O) and iron beads, which are reducing components of iron oxide, formed on the surface of the chromite sand, resulting in the formation of foundry sand. As a result, the fire resistance is deteriorated. Therefore, the main content of the method of the present invention is to remove the intergranular substances and iron beads from the surface of the chromite sand and restore the once-lost refractoriness to the same level as new sand.

In order to remove this intergranular material and iron beads, it is preferable to bring the chromite sand into contact with a grindstone that is rotating at high speed and has a sufficiently high surface hardness, thereby polishing the intergranular material and iron beads from the sand surface. be done.

FIGS. 1 and 2 show an embodiment of an apparatus for removing intergranular substances from chromite sand using a single-rotation grindstone. As shown, a semi-cylindrical casing 10 is supported at the bottom by upright struts 12.

A large-diameter hollow rotating drum 14 is installed horizontally in the semi-cylindrical bottom portion 10a of the casing 10.
It is possible to rotate against. That is, the rotating drum 14
As shown in FIG. 2, it is constructed as a waterwheel-shaped member in which two ring-shaped disks 16, 16 arranged opposite to each other are connected by a plurality of defining plates 19 arranged radially at a required central angle. ,
A rotary grindstone 18, which will be described later, is rotatably inserted into a hollow hole 14a of a required diameter opened at the center of the drum 14.

A connecting plate 20 of a required width is provided on the outer periphery of the rotating drum 14 and connects to the end of each of the aforementioned dividing plates 19.
0 has a slit 22 formed between adjacent connecting plates 20 for introducing separated chromite sand into the drum as described later. Further, from the connecting plate 20, the rotary drum 1
A scraping blade 24 is formed to extend outwardly, and is bent in a direction facing the rotation direction of 4 (direction of arrow A).

Note that the scraping blade 24 has its tip and the casing bottom 10a.
It is set so that it can move forward and backward so that the distance between it and the front can be variably adjusted. Furthermore, inside the rotating drum 14.

A required space S is defined by each connecting plate 20, the defining plate 19, and the adjacent defining plate 19, and this space S is open at the slit 22 and the hollow hole 14a.

Note that the rotary drum 14 has bosses 26.26 that share the same axis with the hollow hole 14a and extend on both sides of the casing 10, and as shown in FIG. It is rotatably extrapolated onto a common shaft 28 . Further, a roller 3o driven by an external drive source is disposed on the pillar 12, and this roller 30 is driven by the boss 2.
6.26, the one-rotation drum 14 is driven to rotate independently of the rotary grindstone 18. The direction of rotation is between the one-rotation drum 14 (in the direction of the arrow) and the rotating grindstone 18.
(direction of arrow B).

Next, a cylindrical grindstone 18 is rotatably supported in the hollow hole 14a of the rotating drum 14.
is constructed by mounting a plurality of ring-shaped grindstones L8a of a required thickness on a common shaft 28, and this shaft 28 is horizontally supported by bearings 32, 32 provided on the pillar 12 so as to be able to freely rotate once.

In this case, the plurality of ring-shaped grindstones 18a are tightened and fixed to a common shaft 28 at both ends thereof by a balance adjusting plate 21 having a weight that also serves as a fastening screw. The cylindrical grindstone 18 may be made of materials that are sufficiently harder than the intergranular substances or iron beads, such as carborundum, alumina, ceramic, borazone, etc.
A whetstone made of tungsten carbide or the like, with a high abrasive grain density and numerous irregularities on its surface is selected and used.

The common shaft 28 of the cylindrical grindstone 18 is connected via a belt 36 to the output shaft of a motor 34 with a speed reducer provided at the bottom of the support column 12, and the grindstone 18 is rotated at high speed by driving the motor 34. Further, it is preferable that the driving force of the roller 30 for rotating the rotary drum 14 is provided by branching the output from the motor 34.

As shown in FIGS. 1 and 2, an input port 38 for supplying separated chromite sand is provided on the side surface of the casing 10 that intersects with the rotational axis of the grindstone 18 and at a position diagonally above the rotating drum 14. A hopper 40 is connected to the input port 38. Further, in the upper part of the casing 10, a dust separation chamber 4 defining an enlarged sealed space is provided.
2 are installed upright in communication, and the top of this separation chamber 42 communicates with a cyclone type dust collector 46 via a dust collection conduit 44. Further, the semi-cylindrical bottom portion 10a of the casing 10
An outlet 48 is provided for collecting chromite sand after the regeneration process described below.

This outlet 48 is opened and closed by a shutter 52 driven by a pneumatic cylinder 50.

A process of polishing the intergranular substances and iron beads from separated chromite sand using the apparatus configured as described above will be described. The chromite sand is supplied to the hopper 40 and thrown into the casing bottom 10a from the inlet 38. The motor 34 is also started to rotate the rotary grindstone 18 at high speed in the direction of arrow B as shown in FIG.
~14 r, p, m,), whereby the chromite sand deposited on the casing bottom 10a is scraped up by the scraping blades 24 of the one-rotation drum 14, and the chromite sand is scraped up into the slit 2.
2 into each space S of the rotating drum 14.

As shown in FIG. 3, the chromite sand C falls and collides with the rotating grindstone 18 that is rotating at high speed, contacts the grindstone surface and is rotated, and then falls and accumulates on the casing bottom 10a again. As mentioned above, the one-turn grindstone 18 has a hardness sufficiently greater than that of the intergranular substances and iron beads, has a high abrasive grain density, and has numerous irregularities on its surface. Therefore, due to contact with this rotating grindstone 18, chromite sand C
is polished, and intergranular substances mainly composed of silica and iron beads and iron beads, which are reducing components of iron oxide, are removed from the sand surface. Note that the chromite sand deposited on the casing bottom 10a is repeatedly scraped up by the blades 24 of the rotating drum 14, and the contact polishing with the rotating grindstone 18 is repeated. The time required for this polishing and the rotational speed of the grindstone 18 are appropriately adjusted depending on the degree of adhesion of intergranular substances and iron beads in the separated chromite sand, the amount of sand to be processed, and the like.

In this way, by removing intergranular substances and iron beads, which are the culprits of deteriorating the fire resistance required for foundry sand, the chromite sand is regenerated and restored to the same fire resistance as new sand. In addition, as the surface of the recycled chromite sand is polished, it becomes rounded and has a small specific surface area, so when used as foundry sand, it also has the advantage of requiring only a small amount of binder.

By contacting this rotary grindstone 18, the chromite sand C
Among the substances removed by polishing, intergranular substances mainly composed of silica have a low specific gravity.

During grindstone polishing, the dust is scattered into the dust separation chamber 42 in the upper part of the casing, and is discharged out of the system along with the airflow by the dust collector 46 via the dust collection conduit 44. However, since iron beads are a reducing component of iron oxide, they have a high specific gravity, and after being polished away by the grindstone 18, most of them fall to the casing bottom 10a, and the chromite sand deposited there (after and during regeneration) ).

Even if chromite sand is recycled, it cannot be reused as foundry sand if it contains iron beads that reduce its refractoriness.

Therefore, after completing the grindstone polishing for the required time, the shutter 52 is driven by the pneumatic cylinder 50 marked #, and the outlet 48 is closed.
is opened and the regenerated chromite sand containing the removed iron beads is recovered. Since this iron bead is a reduced component of iron oxide, it has fairly strong magnetism. Therefore, as shown in FIG. 5, the recycled chromite sand after recovery is made to contact and pass through the magnetic rotors 56, 56 of a counter-electrode type magnetic separator 54, for example. As mentioned earlier, chromite sand also has magnetism, but its magnetism is quite low.Therefore, iron beads magnetically attract the magnetic force of the magnet rotor 56°56, but chromite sand does not. .

3000 Gauss), the iron beads are adsorbed to the rotor 56 and separated from the chromite sand. The separated iron beads are removed from the rotor 56 and discharged outside the system, yielding recycled chromite sand.

Nu1ju2 The fire resistance of recycled chromite sand (recycled sand) was compared with new chromite sand (new sand) and chromite sand recovered from collapsed foundry sand (recovered sand), and the results are shown in Table 1 below. Obtained.

Table 1 % It can be seen that the recovered sand contains a large amount of silica (S i O,) and has a high degree of inoculation of the intergranular substances. It was also found that although the fire resistance of the recycled sand had clearly deteriorated, the fire resistance of the recycled sand had recovered to the same level as the new sand. That is, the effect of removing one intergranular substance and iron beads from the chromite sand after recovery and separation was clearly recognized.

Cores were prepared using Fu1 Goshu new sand, recovered sand, and recycled sand, and their seizing resistance was compared.

That is, as shown in FIG. 4, the cavity 6 of the mold 58
0 is formed into a rectangular tube shape with a height of 5005 m and a length and width of 2501 cm,
A cylindrical core 62 (height: 40 cm, diameter: 25 cm) was placed in the cavity 60. The cores 62 were prepared for each of new sand, recovered sand, and recycled sand: (1) a type in which 1.3% of water-soluble phenol resin was added as a binder, and (2) a type in which 1% of furan resin was added as a binder. Also for the core 62.

One coat of zircon based alcohol mold was applied.

A molten metal made of SC5SC514A (19cr-1ONi-2) is placed in the mold 58 at a temperature of 1500 to 15
The core 62 was cast at 20° C., and the volume of the core 62 before and after pouring was compared to determine the burning rate (%).

In other words, the burning rate (%) is.

It was determined by 100 - (core volume after pouring/core volume before pouring), and the results were as shown in Table 2 below.

Table 2 As is clear from the table, regardless of whether the core was added with water-soluble phenolic resin or furan resin.

Recovered sand has an extremely high scorching rate, making it difficult to reuse it as foundry sand. In contrast, recycled sand has a low burning rate, indicating that it can be fully reused as foundry sand. In particular, it is noteworthy that the type to which water-soluble phenolic resin is added has a burning rate that exceeds that of fresh sand.

In addition, recycled sand and new sand were tested for resistance pressure when molded into molds. As a binder.

1.3% of water-soluble phenolic resin was added. At this time,
Whereas the particle size of new sand is AFS No. 44.

The particle size of the recycled sand was 46, as a result of the specific surface area being reduced by grinding with a grindstone.

A pressure of kgf/- was applied to each mold, and the mold was allowed to stand for a required period of time to determine its counterpressure. The result is the 6th
Regarding the anti-pressure, graphically shown in fig.

The recycled sand was found to be superior and improved over the new sand. This is presumed to be because the specific surface area of each sand grain of the recycled sand has been reduced by polishing with a whetstone, and the sand grains have been rounded as a whole, making the bonds between the sand grains strong and strong.

As described in detail, the method for regenerating chromite sand for molds according to the present invention involves bringing chromite sand, which has been magnetically sorted from foundry sand after pouring and disintegrating it, into contact with a high-hardness grindstone rotating at high speed. The main content of this process is to polish and remove intergranular substances mainly composed of silica and iron beads, which are reducing components of iron oxide, from the surface of the chromite sand.

In this way, by removing the intergranular substances and iron beads that cause the deterioration of the refractory properties of foundry sand, the refractory properties of the recycled chromite sand are restored, and along with this, the seizing resistance and The mold resistance pressure is also restored or improved.

For this reason, the separated chromite sand, which had previously been mixed with a considerable amount of new sand for reuse or completely discarded due to concerns about casting failure due to burning, can now be recycled and mixed with new sand. It can be reused as foundry sand as is. Therefore, the chromite sand that is imported from overseas can be effectively reused, which has the beneficial advantage of reducing running costs.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of an apparatus that can suitably carry out the method for regenerating chromite sand for molds according to the present invention. Figure 2 is a vertical cross-sectional side view of the device shown in Figure 1, and Figure 3 is a chromite sand drop collided with a rotating grindstone rotating at high speed to remove intergranular matter and iron beads from the sand surface. Fig. 4 is a schematic explanatory drawing of a mold and core for comparing the seizing resistance of cores using fresh sand 1 recovered sand and recycled sand, and Fig. 5 is an explanatory enlarged view showing the state in which An explanatory diagram showing the schematic configuration of a magnetic separator that magnetically separates iron beads from recycled chromite sand after recovery. Figure 6 is a graph showing the counter pressure when pressure is applied to each mold and the mold is left for the required time. be. 10...Casing 14...Rotating drum 18.
...Rotary grindstone 24...Scraping blade FIo, 5 5L 10...Casing 14...Rotating drum 18...Rotary grindstone 24...Scraping blade FIG, 3 18...Rotating grindstone FIG , 4 Ding FIG, 6 Nukyoki tpa (h ``)

Claims (1)

[Scope of Claims] When collapsing a mold made of foundry sand of silica sand and chromite sand after pouring, and regenerating chromite sand for molds separated and collected from the collapsed foundry sand by magnetic separation, The chromite sand is brought into contact with a high-hardness grindstone rotating at high speed, and intergranular substances mainly composed of silica and iron beads, which are reducing components of iron oxide, are polished off from the surface of the chromite sand, and the intergranular substances are During grindstone polishing, the iron beads are discharged from the system along with the air flow, and the iron beads, which are magnetic substances, are magnetically separated and discharged from the system after polishing the chromite sand, thereby separating the intergranular substances and iron beads. 1. A method for regenerating chromite sand for molds, which comprises regenerating chromite sand whose fire resistance has been restored by removing the chromite sand.