CN1323779C

CN1323779C - Renovation and reclamation process for silicate-bonded sand

Info

Publication number: CN1323779C
Application number: CNB02135538XA
Authority: CN
Inventors: 李明星
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-09-13
Filing date: 2002-09-13
Publication date: 2007-07-04
Anticipated expiration: 2022-09-13
Also published as: CN1481950A

Abstract

The present invention relates to a technique of high-collapsibility casting water glass sand capable of being regenerated and recycled, which has the technical scheme that when regenerated used water glass sand containing a certain quantity of harmful residues is recycled, an additive method for controlling or eliminating the adverse effect of the residues is used by using the chemical regeneration principle of water glass sand so as to achieve the goal of recycling used sand in large proportion. The present invention easily solves the problem that used water glass sand is difficult to regenerate and recycle for a long time. When the technique of the present invention is used, all the used water glass sand can be recycled except for part of the sand lost in the regeneration process, and the recycle rate reaches more than 90%. The technique of the present invention not only can enhance the regeneration and recycle rate, but also improves the collapsibility and the moisture-resistant storage performance of the water glass sand, and comprehensively treats the water glass sand.

Description

Regeneration and reuse method of sodium silicate sand

The technical field is as follows:

sodium silicate sand is a molding (core) sand process which takes sodium silicate as a binder and is widely applied in casting production. The invention relates to a high-collapsibility casting sodium silicate sand process capable of being completely recycled, which belongs to the technical field of casting molding materials and treatment thereof, and is characterized by using an additive with a special function and a binder.

(II) background technology:

the water glass is non-toxic, odorless and low in cost, and the water glass sand process using water glass as binder can adopt heating hardening and CO process to make mould (core)₂The different technological methods of air-blowing hardening (cold hard sand), ester hardening (self-hardening sand) and the like are convenient to use, less smoke pollution is caused during casting, particularly the unique and excellent high-temperature toughness can effectively prevent the hot cracking defect of the casting, and therefore, the method is widely applied to casting production, particularly cast steel production. However, the process has poor collapsibility, difficult sand removal of castings, particularly difficult regeneration of used sand, and extremely low recycling rate, and the waste of a large amount of the high-alkalinity sodium silicate used sand wastes precious raw sand resources and causes serious environmental pollution, so the sodium silicate used sand must be regenerated and recycled.

At present, the regeneration treatment method of the used sodium silicate sand mainly comprises a wet method and a dry method:

the wet regeneration mainly utilizes that a part of residues of the used sodium silicate sand is active and soluble in water, and when the used sand cleaned by water is used for mixing molding (core) sand, the normal temperature performance of the used sand is the same as that of new sand, so that the service life is not influenced. However, the wet-process reclaimed sand still contains partial insoluble or hardly soluble residues (about 30-50%), and the accumulation of the residues deteriorates the high-temperature performance of the core sand (during casting)Na in the residue under the action of high temperature₂SiO of O and quartz sand₂Sintered into a vitreous body, sand grains are corroded, the refractoriness is reduced, and the residual strength is increased), so the recycling proportion of the wet-process reclaimed sand is limited, the wet-process reclaimed sand can not be used in large quantity, generally not more than 50 percent, in addition, the wet-process reclamation not only consumes a large amount of precious water resources, but also easily causes secondary water pollution, the treatment of the sewage is more complicated, the occupied area is large, the equipment investment is more, and the cost is higher. Therefore, the wet regeneration can not completely regenerate and recycle the used sand, the cost is high, secondary pollution is easy to cause, and the application of the method is greatly limited.

The dry regeneration is to use the used sodium silicate sand directly after mechanical crushing, rubbing regeneration and powder sieving dust removal treatment. The dry regeneration process is simple, low in cost and free of secondary pollution. The reclaimed sand still contains more than 50 percent of residues, and like the reclaimed sand by a wet method, the residues can also deteriorate the high-temperature performance of the core sand during recycling, and in addition, active parts in the residues can also react with a water glass binder, so that the dry strength of the core sand is greatly reduced, and the service life is even lost. Therefore, the recycling rate of the dry reclaimed sand is low.

In order to solve the problem, a chemical regeneration method is proposed in the article of 'chemical regeneration of used sodium silicate sand' (hot working process 1998, No. 2), which is to add NaOH solution when the used dry-method sand is recycled, to recover part of active residues in the used dry-method sand into a binder system, to control the premature reaction of the residues, and to adopt a low modulus sodium silicate binder. This method allows effective control of the usable time of the molding (core) sand prepared from the dry reclaimed sand to some extent. However, this method is not easy to control the proper amount of NaOH due to the unstable content of the residue in the reclaimed sand, and NaOH is added and a low modulus water glass (Na) is used₂High content of O), increases Na in the sodium silicate-bonded sand system₂The content of O further deteriorates the high temperature performance (Na) of the core sand₂O with SiO in sand at high temperature₂Formation of Na₂O-SiO₂Low-melting-point glass body erodes sand grains, so that the reusability of a molding sand system is poor, the residual strength is increased, and the sand cleaning is difficult). Therefore, it is difficult to significantly increase the reuse rate of the regenerated used sand.

(III) the invention content:

the invention aims to provide a method capable of greatly improving the regeneration and reuse rate of used sodium silicate-bonded sand. So as to reduce the waste amount of used sand, thereby reducing the waste of raw sand resources and the environmental pollution caused by the waste of the used sand.

The conception of the invention is as follows: according to the principle of the chemical regeneration method, namely, the characteristic that a part of residues in the water glass reclaimed sand can be converted into a binder under certain conditions, a dissolving-assistant additive capable of promoting the dissolution of reclaimed sand residues is used in sand mixing to control the workability of the reclaimed sand-containing core sand without excessively increasing harmful Na₂The content of O, thereby the reclaimed sand can be recycled in large proportion on the premise of ensuring the normal temperature and high temperature performance.

The basic method of the invention is that ① used sodium silicate sand is regenerated, ② treated regenerated sand (a proper amount of new sand can be added) is added with sodium silicate and additive to mix into molding sand, which is characterized in that ③ the additive is hydrolytic starch solution (commonly called maltose).

The hydrolyzed starch solution (commonly called maltose) has good instant dissolution effect on residues in the reclaimed sand during sand mixing, so that part of the residues are converted into one part of the binder, the early reaction of a molding sand system is inhibited, the service life of the molding sand system is prolonged, and the side effect of the residues can be effectively eliminated. Meanwhile, the hydrolyzed starch solution (commonly called maltose) has a dissolving effect on grown colloidal particles in aged water glass, can eliminate the aging of the water glass, improves the bonding strength of the water glass and reduces the adding amount of the water glass. And due to the addition of the hydrolyzed starch solution (commonly called maltose), the bonding film in the used sand after casting becomes brittle, thereby not only improving the collapsibility of the sodium silicate sand and being beneficial to cleaning of shakeout, but also facilitating the mechanical regeneration treatment of the used sand and having high regeneration and demoulding rate. Therefore, the sodium silicate sand can be recycled in a large proportion, and the waste amount of used sand is reduced, so that the waste of raw sand resources and the environmental pollution caused by the waste of the used sand are reduced.

In practical application, the addition amount of the hydrolyzed starch solution (commonly called maltose) (the general concentration is 70-85%) generally accounts for 0.2-1.5% of the weight of the sand. Too little has no obvious effect, and too much not only increases the cost, but also reduces the hardening speed of the molding sand and increases the moisture absorption of the sand mold.

In order to further improve the usable time and strength of the molding sand, a phosphate, preferably trisodium phosphate or sodium tripolyphosphate solution, may be added on the basis of the above. The optimal addition amount is 0.01-0.10% of the weight of the sand. Since the phosphate has a surface-active action on the water glass, premature reaction of the old adhesive film residue with the newly added water glass can be suppressed.

On the basis of the above, if carbonate is addedSuch as calcium carbonate and lithium carbonate, not only can make the molding sand have good moisture-resistant storage property, but also can raise the high-temperature sintering-resistant capacity of the molding sand. The carbonate is generally added in an amount of 0.2 to 2.5% by weight based on the sand. The carbonate has moisture absorption resistance, can improve the moisture storage resistance of the molding sand, and when the carbonate is decomposed under the action of high casting temperature, the continuity of the old adhesive film is damaged, the collapsibility of the sodium silicate sand is improved, and meanwhile, the GaO decomposed when the calcium carbonate is adopted can improve Na in a molding sand system₂O-SiO₂High temperature performance of the system, especially with P in phosphate₂O₅Formation of GaO-P₂O₅High melting point phase, further improves the high temperature performance of the molding sand, and reduces Na₂The corrosion of O to sand grains at high temperature improves the reusability of the molding sand, and meanwhile, the GaO also enables Na₂O-SiO₂Is Na or Na₂O-P₂O₅-SiO₂The residue becomes brittle, and the collapsibility is improved, and the residue is easy to mechanically remove, so that the reproducibility of the used sand is improved.

When the continuous sand mixer is used for mixing sand, the additives can be uniformly mixed with the water glass to form the composite binder for use, and the composite binder is also used.

The essence of the invention lies in that the chemical regeneration principle of the water glass sand is utilized, when the regenerated water glass used sand containing a certain amount of harmful residues is recycled, a method of using an additive capable of controlling or eliminating the harmful effect of the residues is adopted, and the purpose of recycling the used sand in a high proportion is achieved. The problem that the used sodium silicate sand is difficult to regenerate and reuse for a long time is easily solved. By adopting the method, the used sodium silicate sand can be completely recycled except for part of sand lost in the regeneration process, and the recycling rate can reach more than 90 percent. The method improves the regeneration and reuse rate, improves the collapsibility and the moisture-resistant storage property of the sodium silicate sand, and comprehensively treats the sodium silicate sand.

(IV) description of the drawings: (without attached figure)

(V) specific embodiment:

example 1.

Example 2.

In examples 1 to 2, the water glass modulus was 2.2 to 2.4 and the density was 1.50 to 1.56, and the mixture was ground with a roller mill, CO₂And (5) air blowing hardening process. The recycling rate of the used sand can reach 80-90%.

Example 3.

① composite binder is prepared from water glass 100%, water 20%, maltose 20%, trisodium phosphate 1%, and calcium carbonate 20% by stirring;

② reclaimed used sand 90% + new sand 10% + ester curing agent 0.2% + ① 4% → sand (single sand) or:

②' regenerated used sand 50% + new sand 50% + ester curing agent 0.2% + ① 4% → sand (top sand);

②' regenerated used sand 100% + ester curing agent 0.2% + ① 2.5.5% → sand (back sand).

In example 3, the water glass modulus is 2.2 to 2.4, the density is 1.50 to 1.56, and a sand mixing and ester hardening process of a continuous sand mixer is adopted. The recycling rate of the used sand can reach 85-95%.

Claims

1. A regeneration and reuse method of sodium silicate sand comprises ① regenerating used sodium silicate sand, ② adding sodium silicate and additive into the treated regenerated sand to prepare molding (core) sand, and is characterized in that ③ the additive is hydrolyzed starch solution, and the addition amount of the starch solution accounts for 0.2-1.5% of the sand weight.

2. The method of claim 1 wherein ④ said additive further comprises a phosphate salt.

3. The method of claim 2, wherein: the phosphate is trisodium phosphate or sodium tripolyphosphate solution.

4. The method of claim 3, wherein: the addition amount of the trisodium phosphate or the sodium tripolyphosphate accounts for 0.01-0.10% of the weight of the sand.

5. The method of claim 1 or 2 or 3 or 4 wherein ⑤ the additive further comprises a carbonate.

6. The method of claim 5, wherein: the carbonate is calcium carbonate or lithium carbonate.

7. The method of claim 5, wherein: the addition amount of the carbonate accounts for 0.2-2.5% of the weight of the sand.

8. The method of claim 1 or 2 or 3 or 4, wherein: the additive and water glass are mixed uniformly to form a composite binder for reuse.

9. The method of claim 5, wherein: the additive and water glass are mixed uniformly to form a composite binder for reuse.

10. The method of claim 6, further comprising: the additive and water glass are mixed uniformly to form a composite binder for reuse.

11. The method of claim 7, further comprising: the additive and water glass are mixed uniformly to form a composite binder for reuse.