JPS60244444A - Regeneration of foundry sand - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the reclamation of mold bonded particulate material, typically sand, after casting an article of molten metal in a mold. The present invention is particularly valuable for regenerating particulate materials when the binder for the particulate materials is sodium silicate. Sodium silicate is a widely used binder because it is readily available, relatively inexpensive, non-toxic, and non-contaminating. Sodium silicate binds very effectively with all types of sand and the thus bound sand is rapidly hardened in situ by passing CO2 gas or by adding hardening agents such as organic esters to this sand mixture. Self-hardening by this. The molds and cores thus obtained have precision, rigidity, and stability, making it possible to obtain castings of extremely satisfactory quality. However, when using sodium silicate bonded molds, a considerable amount of fresh sand must be consumed. The economics of using fresh sand can be overcome to some extent by lowering the sand-to-metal ratio in the casting, but in general, 3 to 5 ml of fresh sand per metric ton of steel casting produced. It's a metric ton, which is a significant amount.

Over recent years, as the price of new silica has increased, so has the cost of disposing of used sand that cannot be reused. Furthermore, disposal sites are becoming scarce, and new laws are likely to further limit the types of materials that can be disposed of. - Sand bound with organic resin binders is currently being recycled by dry methods, and this recycled sand gives satisfactory casting performance with high levels of reuse, e.g. above 80%. Although this dry reclamation process can be used to regenerate the sodium silicate bond layer, the reuse level of the regenerated sand typically remains at 50%. The known methods of wet regeneration of the sodium silicate bonding layer do not require high product quality or complex equipment, high investment costs, high maintenance costs, and the additional and expensive treatment of industrial wastewater. This leads to drainage treatment problems that require additional equipment. Government agencies are becoming increasingly strict in defining the types of waste they are willing to dispose of.

Used sodium silicate bonding layers include:

9. After milling, unreacted sodium silicate (hydrogel-silica bonding layer) consists of dehydrated sodium carbonate and sodium bicarbonate organic materials, such as sugar and its decomposition products (unreacted sodium silicate) silica gel bond. layers) consisting of dehydrated unreacted esters alcohols and acids (sodium salts) organic substances and their decomposition products Many of these residues are readily soluble in water or exposed to sand at moderate temperatures, above about 600°C. When heated to , the bonding layer melts into a stable insoluble decomposition product that adheres strongly to the sand particles. When the sand is heated to a high temperature (close to the metal-mold interface temperature), the sodium silicate bond layer melts, causing erosion of the silica sand particles and promoting their transformation into tridymite and cristobalite.

Therefore, regeneration in a complete sense is more difficult with sodium silicate than with other types of binders used in foundries. However, the reality is that regeneration is desirable, and various techniques are being tried to perform this regeneration, whether dry or wet. To the best of the inventors' knowledge, no technology has been completely successful in terms of economic advantages, combined with the need to produce wastewater that can be discharged into main drains, sewers, or rivers without creating pollution or other hazards. There isn't.

The purpose of the present invention is to regenerate chemically bonded granular materials,
The objective is to provide a method for obtaining reusable granular materials and relatively safe by-products. As used herein, reusable granular material refers to material, typically sand, that has been recycled to be approximately equivalent to new material in terms of clean grain size and absence of fines. Achieving perfect purity is very difficult, expensive, and practically unnecessary. Recycled material has a medium (1
It is sufficient to perform dilution (0 to 20%), and this level of regeneration is sufficient. The term relatively safe by-product refers to water that can be discharged directly into municipal water systems in accordance with specific local legal requirements. -The shell contains solids suspended in water with a pH of 7
lower than 500 mg/l measured at p)((
M must be in the range 5-10.

According to a first feature of the invention, there is provided a method for recycling silicate-bonded particulate material in contact with molten metal (e.g., used to make molds) for pre-use, the method comprising: A method comprising: (a) crushing the material to particle size, mixing the material with water, and stirring the mixture to wash the water-soluble derivatives from the particles, comprising: (b) stirring this mixture; (c) stopping the stirring and allowing the solids to precipitate onto the porous membrane to remove the particulate matter present on the membrane; (d) draw water from the container through this bed, and P1. It is possible to obtain a method characterized in that leaving a fine particulate material on the membrane and (e) separating this fine particulate material from the sand.

Because the water is removed from the container through a layer of particulate matter and fine particles, the solids suspended in the water is less than about 500 mg/liter.

According to another feature of the invention, there is provided a method for treating a used silicate-bound particulate material containing a water-soluble derivative to be removed to obtain a reusable particulate material and water that can be discharged into a municipal wastewater system. The alkalinity of the water added to the particulate material is adjusted to facilitate the removal of derivatives and to a pH suitable for disposal, preferably by addition of acid until the pH of the water is below 10. It is possible to obtain a method characterized in that:

Because it adjusts the acidity of the water, the removal of the derivatives being removed, typically sodium derivatives, becomes more effective, improving the cleanliness rate, and reducing the acidity of the extracted water before it is discharged into the municipal wastewater system. -・It becomes suitable for the layer.

According to a more particular aspect of the invention, the above method comprises: (+) adding water and particulate material to a container in a weight ratio of l:l to about 3=1 and adjusting the pH of the water to a value below 10; (ii)'; stirring the mixture of C for a sufficient period of time to elute the water-soluble derivative from the particulate material, then stopping the stirring and allowing the particulate material to settle as a bed on the porous membrane bed; ji) Extraction of water containing water-soluble binder products from the particulate material through a porous membrane bed under vacuum drawn through the bed and/or air pressure applied thereto, either alone or mixed with clean water; (iv) adding clean water to the particulate material in a weight ratio of approximately 1:1;
agitating the mixture for a sufficient period of time to liberate any remaining water-soluble binder product from the particulate material; (V) drawing water containing any remaining water-soluble binder product from the particulate material; Used in cleaning process.

(v i) Drying and cooling the treated granular material, and removing very fine granular material by elutriation.

According to a more preferred feature, heating elements are present in the container above the membrane, these heating elements being located within the layer of deposited particulate material, and when the material is washed and the water is withdrawn, the heating elements are is energized and a vacuum is applied to dry the material. After removing the vacuum, the material is fluidized to remove very fine particles, resulting in a thoroughly dried and classified material ready for mixing with virgin particulate material.

The particulate material can be any sand or similar material that is chemically bonded, ie, silicate bonded, to form a template. The mold can be used to cast articles of molten metal, such as steel, aluminum, iron.

Preferably, a flocculant is included in the particulate material/water mixture. The type of flocculant and its concentration will depend to a wide extent on the nature of the particulate material, ie the sand being treated. For silica sand it is advantageous to have about 1 or 2 mg/g of polymeric non-ionic flocculant and for zircon sand about 30 mg/l of low-molecular cationic flocculant.
I found it to be appropriate. The presence of a flocculant facilitates the agglomeration of ultrafine particles to form a porous structure in the surface layer present on the bends of settled sand. Flocculants also retain ultrafine particles and help increase water extraction.

The porous membrane is preferably made of a material with a pore size of less than 75 μm. Suitable materials include porous plastics, ceramics, sintered metals, woven metals, and fabrics.

Most preferably, the porous membrane is a suspended bed or baffle wall or weir that supports water and particulate matter.

Water is first filled into a container and acidified with an acidifying agent to maintain solution alkalinity below pH 10.

Water and particulate matter are preferably mixed in the water, with a material ratio of 2:l depending on their nature.

The particulate material can be present in a variety of forms ranging from crushed to granular. More preferably, the material is reduced to particle size before being added to the container. This can be done by pressure jet action, mechanical grinding (either dry or wet) or any other pulverizing action. The material is typically sodium silicate bound sand, but other materials may be present, such as decomposers.

Necessary agitation can be achieved by mechanical agitation, tampling, or the like. More preferred features include approximately 2 to 3041 b/i
Stirring is carried out using compressed air applied at a pressure of n2 (0.14 to 2.0.7 par). This stirring is done for about 5 to 2 minutes.
It is best to do this for 0 minutes.

At the end of stirring, water is drawn through the porous membrane. This is preferably done using vacuum or compressed air or both.

We have determined that a vacuum on the order of 15 inches (381 mm) Hg is sufficient to extract most of the water and may be maintained for, for example, 3 to 30 minutes. The extracted water contains suspended solids, and these suspended solids are at a level and have the required pH to be acceptable for discharge into the F water system. Some or all of the extracted water may be used for processing the next batch of spent particulate material, or it may be discharged as wastewater. Fine particulate matter (minus 63 pLm particles) is retained within the bed of particulate material and does not contaminate the extraction water.

Our measurements have shown that several factors influence the amount of suspended solids in the p-liquid. Due to stirring number i2, the solids are suspended in the water. If there is a time between the cessation of agitation F and the extraction of water, the amount of suspended solids increases and tends to fall into the settled particulate matter. For this reason, it is important to associate the start of water extraction with the cessation of agitation depending on the desired level of suspended solids in the p-liquid. The depth of the settled particulate material bed assists in determining the amount of fine particulate material that is retained within the bed and not extracted with the water. If it is necessary to keep the suspended solids content in the wastewater fairly low, the depth of the bed must be increased, for example by using a suitably shaped container.

A particulate material and water undergo two or more stirring and extraction steps,
Water-soluble derivatives, typically sodium salts, may be extracted. The inventors have found that although the same water can be used more than once, it is advantageous to use fresh water, especially in the secondary washing step.

In the foregoing description, the pinta was sodium silicate, but the invention is also applicable to other water-soluble pinta, such as sand bound with potassium silicate.

The present invention includes particulate material recycled by this method, mixtures of this recycled material and virgin material, and articles made therefrom.

In order to provide a better understanding of the invention, the invention will now be described with reference to the accompanying drawings. In the attached drawings,
It should be understood that the same reference numerals are used to describe different specific examples.

The container of FIG. 1 is a steel container V having a filling chamber C at its bottom. The filling chamber C is made of a porous membrane, for example.

It has a ceiling in the form of a suspended floor F made of stainless steel mesh. The plenum chamber has an inlet l and an outlet 2. The container has a lid with four inlets 3.4.5.6. Each of these channels 1-6 has a valve 7.

In use, the used sodium silicate bound sand is reduced to a particle size (g r
Crush until ai siz e). This sand is then fed into the container through one of the inlets in the ML. Water to which acid has been added is applied to the sand through a separate inlet. The water weight ratio is approximately 1:2.

A flocculant is also added through a separate inlet. In the case of silica sand,
A polymeric nonionic flocculant at a concentration of about 2 mg/kg is preferred.

It is then blown upward through the bed F via inlet l to agitate the sand and water mixture, scrubbing the sand particles and removing soluble sodium derivatives. This is the state shown in FIG. After a period of time (minutes), the air supply is turned off and the solids are allowed to settle onto bed F. Relatively dense sand particles settle first to form a bed of sand S, followed by finer particulate matter. These precipitated substances form an agglomerated layer A with a thickness of about 2-3 mm due to the presence of the agglomerating agent.

Water W is above it. A vacuum is then applied to the container and the water is extracted through the chamber C. This is the state shown in FIG. As the water is extracted through the sand, fine particles are left behind and the suspended solids content of the extracted water is 500 m
lower than g/l.

Add fresh water to the container. Stirring is repeated and water is extracted under vacuum. Then the sand is taken out, dried, cooled and
Can be classified.

According to our measurements, there is a relationship between the depth of the sand bed S, the level of suspended solids in the extracted water, and the time it takes to extract water from the container V through the sand bed. . FIG. 3 illustrates this relationship for the regeneration of carbon dioxide-cured silicate-bonded silica sand. This graph shows that as the sand bed depth increases beyond about 6 inches (15 cm), the water extraction time increases, but the level of suspended solids in the extraction water decreases. Figure 4.5 shows the benefits of adding flocculant to water. In the case of Figure 4, a polymeric non-ionic flocculant was added to a mixture of water and silicate sand particles. This silicate sand is hardened and bonded using an ester/silicate system. As the graph in FIG. 4 shows, when the flocculant is present at a concentration of about 2 mg/l, the content of suspended solids is low. The extraction time was approximately 3 minutes. There was no point in increasing the proportion of flocculant. When regenerating ester-hardened silicate-bonded zircon sand, as the addition rate of low-molecular-weight cation flocculant increases, the extraction time and the acid content of suspended solids in the extracted water become optimal values, as shown in Figure 5. There was a trend and then an increase was observed. Approximately 30
At a flocculant moisture content of mg/liter, the extraction time is reduced to about 5 minutes;
The suspended solid content in the extracted water was approximately 20 mg/liter.

In the embodiment of FIG. 6, the vessel contains rows of heating elements spaced on two sides of bed F. During use, sand, acidified water and flocculant are introduced into the container. The mixture is stirred and the water is extracted. energizing the heating element F and applying a vacuum;
Let the sand dry. After stopping the vacuum action, air is supplied to fluidize the sand, and the air passing through the sand blows out the fine particles. The sand is then cooled, blown into a storage hopper, and mixed with virgin sand.

, the invention is illustrated by the following examples. Measurements were made of the water-soluble sodium oxide content of the sand, the pH value and the suspended solids content of the extracted water. The measurements were performed as follows.

The water-soluble sodium oxide content of sand is rAFSInte
rnational Ca5t Metals Jou
rchemistry by K. Sri nagesh, rnalJ March 1979 issue, pp. 50-63.
of Sodiumas a Binder J. The method is as follows.

Modification 0, IN Hydrochloric Acid 1 Chemical balance with sensitivity up to 10 mg 125 m Conical beaker 50 m Grass cylinder 25 m Billet Electric hot plate or Bunsen burner Electromagnetic stirrer and stirring rod pH meter Distilled water 50 m In the standing room Dry sand10. Boil oog for 5 minutes.

Add the cooled solution to 0.1N, paying attention to the volume of acid required.
Titrate to pH 4 using HC. Next, water-soluble Na20=0
．． 1N HCI (1) 0.031XmJ1. Before use, the pH meter must be calibrated according to the manufacturer's instructions.

The pH value of the extracted water was measured as follows.

Stir the extracted water in a beaker, eg, 250 m, with a magnetic stirrer and a stir bar pH meter for at least 5 minutes and measure the pH value at short intervals until constant. Before use, the pH meter must be calibrated according to the manufacturer's instructions.

The suspended solids content of the extracted water was determined by Yorkshire e.
W a t e r A u t h Or j t
y(7) Test procedure Measured by a method according to YWA method 190-01.

5N nitric acid ■ Chemical balance sensitive to 0.2 mg Drying oven (105°C) Beaker, e.g. 250 m Bunjin dropper 100 m J2 Graduated cylinder with stomper Magnetic stirrer and stirring rod pH meter Glass m-fiber filter paper, Whatman GF/C grade, 5.
A two-piece Buchner funnel filter flask suction pump with a 5 cm diameter sintered glass stem was used.Following the above procedure for measuring pH, the pH value is 7.0.
Add acid solution through a dropper until ±0.2.

Insert the glass fiber filter paper into the funnel assembly and add 100 m of distilled water.
Lightly suction and clean with water. Place the filter paper on a large diameter paper and dry at 105°C for 1 hour. Cool the filter paper in a desiccator for 5 minutes and then record its weight (Ws, g).

Place the p paper back into the funnel and moisten it with strawberry distilled water.

Shake the extraction water vigorously and immediately fill it with a graduated cylinder (volume Vmu
) into a funnel (usually V = 100 ml).

By suction, the solids remaining in the graduated cylinder are transferred to the funnel with distilled water. Wash out the residue three times with 10 m of distilled water. Place the filter paper on a large diameter paper and dry at 105°C for 1 hour. Allow the paper to cool in a desiccator for 5 minutes and record the weight of paper plus solids (w2g).

Therefore, It is.

The effectiveness of the present invention was investigated by treating various types of sand using various methods. Materials, conditions and results are shown in Table 1.

The material in Test 1 is C02 process sand dried and regenerated at a local foundry. The materials for tests 2-5 are demolded sand from silicate bonded molds cured in a C02 process. This molded sand is crushed and then passed through a sieve with a mesh opening of about 1.0 mm, followed by specified treatment. Water-soluble soda content was measured as described above.

The wash water was acidified using the indicated acidifying agent.

One particulate material was then treated as specified and the treated sand and wash water tested as specified. For Test 2, the wash water was reused, and for the other tests, fresh wash water was used. What is the weight ratio of water to sand?

In tests 1 to 4, the ratio was 2:1, and in test 5, it was 1:1.

The results show that by using the specified wash water, the water-soluble sodium oxide content was dramatically reduced.

T! s1 Table Washing Water Reuse Generally, after washing twice with clean washing water, the content will be reduced to about 80%. The cleaned sand can be used in combination with a low proportion of virgin sand. Wastewater can be discharged into drains. Generally, suspended solids measured at pH 7 are well below 500 mg/l, reducing alkalinity to pH 7.
This is because it can be easily controlled to less than H10.

Support The sand recycled using the method described above was bound with sodium silicate and hardened using carbon dioxide gas.

The results are shown in Table 2.

As can be seen from these results, the degassing properties of unwashed joints and dried reclaimed sand are significantly affected by
strength) was poor. Sand reclaimed according to the method of the invention showed results that were slightly lower than those of virgin sand, but still usable. No attempt was made to remove fines in these tests. The presence of fines can adversely affect the compressive strength obtained in the last three results of Table 2.

Table 2 Strength properties of sand recombined with 3% TI sodium silicate (gas release rate: 5 min/min) Sand Compressive strength kN/m') Chelmford 50 (new) 625 2990 3
440 5215 Crushed spent CO, sand (unwashed),
tss 1320 -- 2560 dry regeneration 101
790 1180 3985 Dry regeneration, cleaning (Test 1)
300 2560 2850 4445 Crushed used sand, cleaning (Test 2) 550 2655 3305 4
585 Crushed used sand, cleaning (Test 3) 485 24
30 2850 5130

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view of a vessel in which a sand-water mixture is being stirred. FIG. 2 is a similar diagram showing a later stage of FIG. Figure 3.4.5 is a graph showing the relationship between various parameters in the case of silica acid and zircon sand treatment. FIG. 6 is a view similar to FIG. 2, showing another container. In the drawing, ■...Container, Cφ...Charm chamber, F#
It 11 hanging floor, l, 2 a a writing exit, 3.4.
5.6-- Entrance, L... Lid, 7... Patent agent Akira Kono's drawing (no changes in d) FIG, 1゜FIG, 2゜9'/-be' 27℃ 5v (in size n$'<,
# il #, fy=y (n71) None, possible, first name 1
1985 Patent Application No. 18'! 69 No. 2, Title of the invention: Recycling of molding sand 3, Relationship with amendment (!1) Name of patent applicant: Steel Castings Rereach Antdraid Associative 3-4, Agent Address: 107

Claims (11)

[Claims] (1) A method for regenerating for reuse silicate-bonded particulate material that has come into contact with molten metal (e.g., used to make molds). A process comprising: (a) crushing used material into particles; mixing this material with water; and agitating the mixture to wash the water-soluble derivatives from the particles; (b) stir this mixture; (c) stop stirring and allow the solids to settle on the porous membrane; , forming a pend consisting of the denser particles of the particulate material on the membrane and the finer particles at L of these dense particles; (d) drawing water from the container through this bed and forming the bed - Leaving fine particulate matter of 1, (e
) A method characterized by the separation of this fine granular material from the sand. (2) In the method described in claim 1, 1
A method characterized in that the alkalinity of the water added to the granular material is adjusted by adding acid until its pH is below 10. (3) In the method according to claim 1 or t52, (i) water and particulate matter are added to a container in a weight ratio of 1:1 to about 3=1, and the pH of the water is increased from 10 to 10. (ii) stirring the mixture for a sufficient period of time;
to elute the water-soluble derivatives from the particulate matter, then after stopping the agitation, the particulate matter is allowed to settle as a bed on the porous membrane bed E; Extract the water containing the water-soluble binder products from the particulate material through a bed using air pressure or both applied to Released for disposal. (iv) adding clean water to the particulate material in a weight ratio of about 1:1;
The mixture is stirred for a sufficient period of time to liberate any remaining water-soluble binder product from the particulate material. (v) drawing water containing residual water-soluble binder products from the particulate material and using that water in a primary cleaning process; (vi) drying and cooling the treated particulate material and elutriating very fine particulate material; A method characterized in that the method comprises: (4) Any one of Claims 1.2.3
In the method described in paragraph 1, heating elements are present in the container on the L side of the porous membrane, these heating elements being within the layer of deposited particulate material, washing the particulate material and draining the water. When the heating elements are energized, a vacuum is simultaneously applied to dry the particulate material, and then the vacuum is removed.
A method characterized in that the granular material is fluidized to remove very fine particles and to obtain a completely dry and classified material ready for mixing with virgin granular material. (5) A method according to any one of claims 1.2.3 and 4, characterized in that a flocculant is added to the mixture of particulate material and water. (6) In the method according to claim 5,
A method characterized in that the spent particulate material is silica and contains about 1 or 2 mg/l of a polymeric nonionic flocculant. (7) The method according to claim 5XJ, characterized in that the used granular material is zircon sand and contains about 30 mg/l of a low molecular weight cationic flocculant. (8) In the method according to any one of claims 1 to 7, the porous membrane has 75p
A method characterized in that the pore size is less than m. (9) A method according to any one of claims 1 to 8, wherein the stirring step comprises about 5
Approximately 2-301b/in2 over a period of ~20 minutes (
A method characterized in that it is carried out using compressed air applied at a pressure of 0.14 to 2.07 par). (10) In the method of any one of claims 1 through 9, the porous material is A method characterized by drawing water through a membrane. (11) Used granular material, typically silica sand or zircon sand, which can be reused by the method described in any one of claims 1 to 10. Particulate matter characterized by being treated as follows. (12. An apparatus used for carrying out the method described in any one of claims 1 to 11, comprising a porous membrane having pores of less than 75 pm. comprising a suspended bed, an inlet 1 for introducing spent particulate matter and water, a container with a plenum below the suspended bed, means for supplying stirring air under pressure and means for evacuating the container. A device characterized by: