A method for regenerating foundry clay waste sand

Abstract

The present invention belongs to the field of industrial solid waste resource recycling, and specifically relates to a method for regenerating foundry clay waste sand. The method for regenerating foundry clay waste sand of the present invention includes drying, magnetic separation, I-level mechanical regeneration and II-level mechanical regeneration steps of the clay waste sand. The regeneration process of the present invention has the advantages of low operating cost, simple process flow, good quality of regenerated sand, and can realize industrial production; the method of the present invention fully utilizes the available materials in solid waste, complies with the policy of energy conservation and emission reduction; and solves the bottleneck problem of high cost and complex process of clay waste sand regeneration.

Description

Technical Field

[0001] The invention belongs to the field of industrial solid waste resource recycling, and specifically relates to a method for regenerating foundry clay waste sand. Background Art

[0002] According to statistics from relevant departments, my country's foundry industry emits 30 million tons of waste sand each year, of which clay sand accounts for 30%, or about 10 million tons. One part is landfilled and the other part is recycled. However, the current process for recycling clay waste sand is complicated and consumes a lot of natural gas and electricity, which is costly. The cost of the regeneration process exceeds 300 yuan / ton, resulting in reduced added value of resource recycling.

[0003] Although the prior art has conducted relevant research on the regeneration of clay waste sand (hereinafter referred to as waste sand), it is difficult to apply it in industrialization due to various constraints. The invention "A method for regenerating and reusing mixed waste sand for casting" (CN102133616A) discloses the classification, screening, drying and dehumidification of waste sand and dry regeneration, and then wet regeneration and dehydration of regenerated sand suitable for wet regeneration, and thermal regeneration of regenerated sand suitable for thermal regeneration, and then the two parts of regenerated sand are mixed again according to a certain proportion, and the heat of thermal regenerated sand is used to heat and dry the wet regenerated sand, and finally the regenerated sand is obtained by humidity and temperature adjustment. This method organically combines the advantages of wet regeneration process and thermal regeneration process, and synchronously regenerates mixed waste sand. However, the method is complex in process, the production cost of regeneration is high, and the wet regeneration used therein has the problem of sewage discharge, especially when it is applied in industrialization, a large amount of sewage will be generated.

[0004] The utility model patent "Used clay sand regeneration equipment" (CN201168766Y) discloses a used clay sand regeneration equipment, including the following devices connected in the order of the direction of the clay sand: a magnetic separation and conveying device, a primary lifting device, a disc feeding device, a drying device, a dust and sand separation device, a secondary lifting device and a clay sand regeneration device; the clay sand regeneration equipment also includes a dust collector connected to the dust and sand separation device and the clay sand regeneration device. The complete set of equipment completes the regeneration of the old clay sand in a one-time flow operation, so the production efficiency is high and the regeneration cost is low. In this scheme, the clay sand is wet, and the impurity particles therein cannot be effectively magnetically separated, and the effective components in the clay sand cannot be reused, resulting in a waste of resources. Summary of the invention

[0005] In order to solve the problems in the prior art of difficulty in regenerating waste clay sand, complex process, high energy consumption and poor regeneration effect, the present application provides a method for regenerating waste foundry clay sand.

[0006] This application found that there are several technical difficulties in the regeneration of waste clay sand:

[0007] During the production process, the molten metal is generally cast at a high temperature of 1350-1500℃. Due to the presence of fluxing agents sodium oxide and aluminum oxide in bentonite, the silica sand close to the molten metal will undergo vitrification on its surface in the temperature range of 700-850℃, thereby losing its basic physical and chemical properties, resulting in a decrease in its refractoriness, brittleness, and reduced hardness.

[0008] The main impurity components of the waste clay sand obtained after the production are shown in Table 1. The surface of the waste clay sand is not only covered with the vitrified layer as described above, but also has some bentonite (Na2O with binder properties) and coal powder that have not lost their activity. At the same time, Al2O3 and Fe2O3 have high melting points, and the melting point of Al2O3 is even higher than that of SiO2. Therefore, the conventional thermal process can only remove moisture and coal powder, and it is difficult to remove Al2O3 and Fe2O3 with high melting points.

[0009] Table 1 Main chemical components of clay waste sand

[0010] chemical composition Mass fraction % source <![CDATA[SiO2]]> 80～ Silica sand itself <![CDATA[Al2O3]]> 10～ Bentonite <![CDATA[Fe2O3]]> 2～ Iron adsorbed by silica sand in contact with molten metal <![CDATA[Na2O]]> 3～ Bentonite Moisture content 4～ The moisture added during modeling keeps the clay sand cohesive Coal powder 2～ Coal powder is added as an additive to molding materials

[0011] How to effectively remove the impurity components (bentonite) and the vitrified layer on the surface of the waste foundry sand to obtain regenerated sand with high SiO2 purity is the purpose of the present invention.

[0012] According to a specific embodiment of the present invention, a method for regenerating foundry clay waste sand comprises the following steps:

[0013] (1) Drying the clay waste sand to remove moisture;

[0014] (2) The dried waste clay sand is subjected to magnetic separation to remove metal objects;

[0015] (3) Level I mechanical regeneration: The clay waste sand after magnetic separation is sprayed into a closed device by high-pressure air, and the clay waste sand is made to collide with a wear-resistant baffle to remove coal powder and bentonite on the surface of the clay waste sand, wherein the clay waste sand enters the closed device at a flow rate of 20-40 kg / min, and the wear-resistant baffle is arranged vertically;

[0016] (4) Level II mechanical regeneration: The clay waste sand treated in step (3) is subjected to friction and collision under the drive of a high-speed rotor to obtain regenerated sand, wherein the rotation speed of the high-speed rotor is 1000-2000 rpm.

[0017] The present invention specifically designs the above regeneration method according to the main chemical components contained in the waste clay sand, thereby effectively removing the impurity components in the waste clay sand and obtaining regenerated sand with higher SiO2 purity.

[0018] According to the method for regenerating foundry clay waste sand in a specific embodiment of the present invention, in step (1), the moisture content of the clay waste sand after drying is ≤0.5%.

[0019] Since the active bentonite on the surface of clay waste sand has a certain bonding activity, when the water content of clay waste sand is high, it can be extruded into shape, but magnetic separation and mechanical regeneration cannot be carried out in this state; when the water content of clay waste sand is ≤0.5%, the active bentonite on the surface of clay waste sand basically loses its bonding property, and the sand particles exist as single particles, so that magnetic separation and mechanical regeneration can be carried out in subsequent steps.

[0020] According to the method for regenerating foundry clay waste sand in a specific embodiment of the present invention, in step (1), the clay waste sand is dried at 100-130° C. The drying temperature should not be too high, which will increase energy consumption; if the drying temperature is too low, it will lead to insufficient water removal and slow drying efficiency, affecting the subsequent magnetic separation and mechanical regeneration steps.

[0021] According to the method for regenerating foundry clay waste sand in a specific embodiment of the present invention, in step (2), the clay waste sand is subjected to magnetic separation in a magnetic field of 8000-15000 Gauss. The dispersed clay waste sand after drying contains metal objects such as iron balls and iron beans. If they are not removed, the quality of the regenerated sand will be affected. If they are removed after the mechanical regeneration step, the subsequent mechanical regeneration device will be damaged and the service life of the device will be shortened.

[0022] According to the method for regenerating foundry clay waste sand in a specific embodiment of the present invention, in step (3), the separated coal powder and bentonite leave the closed device under the action of negative pressure; and the clay waste sand that hits the wear-resistant baffle settles at the bottom of the closed device.

[0023] The method of the present invention adopts a mechanical regeneration method to treat clay waste sand, wherein the first-level mechanical regeneration performs mild mechanical friction on the dried clay waste sand, with the purpose of collecting active coal powder and bentonite on the surface of the waste sand, which can continue to be used as raw materials in molding sand for casting production; and the vitrified layer tightly adhered to the sand surface is removed by strong second-level mechanical regeneration.

[0024] Among them, the principle of level I mechanical regeneration is: inject waste sand and high-pressure air into a closed container at the same time, with a flow rate of 20-40kg / min. If the flow rate is too high, the impact effect will be poor, and the flow rate will be low and the efficiency will be slow; the waste sand will hit the wear-resistant baffle at high speed, and the active bentonite and coal powder will fall off under the high-speed impact of the sand particles. Under the influence of continuous high-pressure air, positive pressure is generated in the container, which is discharged from the top of the container and can be collected.

[0025] Principle of Level II Mechanical Regeneration: After Level I mechanical regeneration, the waste sand will be deposited at the bottom of the container, and then the high-speed rotor will be started at 1000-2000 rpm to drive the sands to rub against each other and remove the vitrified material adhering to the surface of the regenerated sand. At this time, the inside of the closed device (no high-pressure air injection) is at normal pressure, and the fine dust produced will not escape at the top, so high-purity coal powder and bentonite can be obtained.

[0026] At the same time, wear-resistant ribs are arranged at the bottom and sides of the closed device to prevent the clay waste sand from wearing the container wall and to prevent the clay waste sand from moving centrifugally with the rotor, thereby losing the friction effect.

[0027] According to the method for regenerating foundry clay waste sand in a specific embodiment of the present invention, the method also includes the step of screening the regenerated sand, screening according to a particle size specification of 50, 100, 70 or 140, and removing glassy fine powder mixed in the regenerated sand.

[0028] Beneficial effects of the present invention:

[0029] The present invention specifically designs the regeneration steps of the waste clay sand according to the impurity components contained in the waste clay sand, and mainly adopts the mechanical regeneration method to achieve the regeneration purpose. Among them, the drying and magnetic separation steps provide sufficient conditions for the subsequent mechanical regeneration, which not only makes the waste clay sand in a dispersed and non-bonded state, but also avoids the damage of the metal objects therein to the mechanical device. At the same time, a two-step mechanical regeneration method, i.e., level I mechanical regeneration and level II mechanical regeneration, is adopted to remove the coal powder and bentonite on the surface of the waste clay sand, and the vitrified layer tightly adhered to the sand surface in steps, so as to realize the regeneration of the waste clay sand.

[0030] The present invention also has the following advantages:

[0031] 1) Low operating cost, simple process flow, good quality of regenerated sand, and industrial production can be realized;

[0032] 2) Make full use of the recyclable materials in solid waste in accordance with the policy of energy conservation and emission reduction;

[0033] 3) Solve the bottleneck problem of high cost and complex process of waste clay sand regeneration. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0035] Figure 1 is a schematic diagram of the structure of a mechanical regeneration device for mechanical regeneration;

[0036] Figure 2 The process flow of regenerating waste clay sand of the present invention is shown;

[0037] Figure 3 These are photos of the appearance of regenerated sand, where a is clay waste sand; b is the sand morphology after level I mechanical regeneration; and c is the sand morphology after level II mechanical regeneration.

[0038] In the figure, 1 is a sealing device; 2 is a wear-resistant baffle; 3 is a high-speed rotor; and 4 is a wear-resistant rib. DETAILED DESCRIPTION

[0039] To make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0040] In the description of the present invention, it is necessary to understand that the terms "upper", "lower", "inside", "outside", "top", "bottom", etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application.

[0041] In the present invention, unless otherwise clearly defined and specified, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected, or indirectly connected through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0042] The method for regenerating waste clay sand of the present invention uses a related device, and a brief description is given of the device.

[0043] Embodiment 1 Mechanical regeneration equipment of the present invention

[0044] The mechanical regeneration step of the waste clay sand of the present invention is completed in a mechanical regeneration device, such as Figure 1As shown, the mechanical regeneration device includes a closed device 1, which can maintain an airtight state. An inlet is arranged on the side of the closed device 1 for injecting clay waste sand and high-pressure air into the closed device 1.

[0045] A wear-resistant baffle 2 is arranged inside the closed device 1. The wear-resistant baffle 2 is arranged vertically, and the center line of the inlet coincides with the center line of the wear-resistant baffle. The size of the wear-resistant baffle is larger than the maximum area formed by the clay waste sand colliding with the wear-resistant baffle and ejected.

[0046] The top of the closed device is provided with an opening, and the opening is provided just above the wear-resistant baffle. Affected by the high-pressure air continuously sprayed into the closed device, a positive pressure is formed inside the closed device, so that the coal powder and bentonite generated by the impact are discharged from the opening at the top of the closed device.

[0047] A high-speed rotor 3 is arranged on the bottom surface of the sealed device 1, and the high-speed rotor 3 is driven by a motor. At the same time, a plurality of wear-resistant ribs 4 are arranged on the side surface of the sealed device, and the plurality of wear-resistant ribs are evenly distributed along the inside of the sealed device; a plurality of wear-resistant ribs are also arranged on the bottom surface of the sealed device 1.

[0048] After completing the first-level mechanical regeneration, the clay waste sand continues to settle to the bottom of the closed device. The closed device is at normal pressure, and then the high-speed rotor is started at 1000-2000 rpm to drive the sand to rub against each other and remove the vitrified material adhering to the surface of the regenerated sand. At this time, the inside of the container is at normal pressure, and the fine dust produced will not escape at the top. Wear-resistant ribs 4 are set at the bottom and sides to prevent the sand from wearing the container wall and to prevent the sand and the rotor from doing centrifugal motion together, thereby losing the friction effect.

[0049] This embodiment describes the mechanical regeneration device that can be implemented. It should be noted that the mechanical regeneration device is not limited to the structure in this embodiment. For example, in this embodiment, both the level I mechanical regeneration and the level II mechanical regeneration are completed in the same closed device. In another embodiment, the level I mechanical regeneration can be completed in one closed device, and the level II mechanical regeneration can be performed in another device, which can be closed or not.

[0050] Therefore, any device that can complete mechanical regeneration according to the process flow of the present invention is within the protection scope of the present invention, and those skilled in the art can design relevant devices according to actual needs without having to engage in creative work.

[0051] The process flow of the method for regenerating waste clay sand of the present invention is as follows: Figure 2As shown, the method for regenerating waste clay sand of the present invention is to dry it first and then carry out subsequent processes. According to the existence form and characteristics of the surface material of silica sand, it is divided into two-stage mechanical regeneration, I and II, with a high impurity removal rate, and active bentonite and coal powder are reused.

[0052] The specific process steps are described below through Examples 2-4.

[0053] Example 2

[0054] The method for regenerating foundry clay waste sand of the present invention comprises the following steps:

[0055] (1) drying the waste clay sand at 100° C., wherein the moisture content of the waste clay sand after drying is ≤0.5%;

[0056] (2) Magnetic separation of clay waste sand under a magnetic field of 8000 gauss to remove metal objects;

[0057] (3) Level I mechanical regeneration: The clay waste sand after magnetic separation is sprayed into a closed device by high-pressure air, and the clay waste sand is made to hit the wear-resistant baffle to remove the coal powder and bentonite on the surface of the clay waste sand, wherein the clay waste sand enters the closed device at a flow rate of 20 kg / min, and the wear-resistant baffle is arranged vertically; the separated coal powder and bentonite leave the closed device through the outlet under pressure; the clay waste sand after hitting the wear-resistant baffle settles to the bottom of the closed device;

[0058] (4) Level II mechanical regeneration: The clay waste sand treated in step (3) is subjected to friction and collision under the drive of a high-speed rotor, the speed of which is 1000 rpm, to obtain regenerated sand;

[0059] (5) Screening the regenerated sand according to the particle size specification of 50, 100, 70 or 140; and removing the glassy fine powder mixed in the regenerated sand.

[0060] like Figure 3 shown.

[0061] Example 3

[0062] The method for regenerating foundry clay waste sand of the present invention comprises the following steps:

[0063] (1) drying the waste clay sand at 115° C., wherein the moisture content of the waste clay sand after drying is ≤0.5%;

[0064] (2) magnetic separation of clay waste sand under a magnetic field of 10,000 gauss to remove metal objects;

[0065] (3) Level I mechanical regeneration: The clay waste sand after magnetic separation is sprayed into a closed device by high-pressure air, and the clay waste sand is made to collide with a wear-resistant baffle to remove the coal powder and bentonite on the surface of the clay waste sand, wherein the clay waste sand enters the closed device at a flow rate of 30 kg / min, and the wear-resistant baffle is arranged vertically; the separated coal powder and bentonite leave the closed device through the outlet under pressure; the clay waste sand after hitting the wear-resistant baffle settles to the bottom of the closed device;

[0066] (4) Level II mechanical regeneration: The clay waste sand treated in step (3) is subjected to friction and collision under the drive of a high-speed rotor, the speed of which is 1500 rpm, to obtain regenerated sand;

[0067] (5) Screening the regenerated sand according to the particle size specification of 50, 100, 70 or 140; and removing the glassy fine powder mixed in the regenerated sand.

[0068] Example 4

[0069] The method for regenerating foundry clay waste sand of the present invention comprises the following steps:

[0070] (1) drying the waste clay sand at 130° C., wherein the moisture content of the waste clay sand after drying is ≤0.5%;

[0071] (2) Magnetic separation of clay waste sand under a magnetic field of 15,000 gauss to remove metals;

[0072] (3) Level I mechanical regeneration: The clay waste sand after magnetic separation is sprayed into a closed device by high-pressure air, and the clay waste sand is made to hit the wear-resistant baffle to remove the coal powder and bentonite on the surface of the clay waste sand, wherein the clay waste sand enters the closed device at a flow rate of 40 kg / min, and the wear-resistant baffle is arranged vertically; the separated coal powder and bentonite leave the closed device through the outlet under pressure; the clay waste sand after hitting the wear-resistant baffle settles to the bottom of the closed device;

[0073] (4) Level II mechanical regeneration: The clay waste sand treated in step (3) is subjected to friction and collision under the drive of a high-speed rotor, the speed of which is 2000 rpm, to obtain regenerated sand;

[0074] (5) Screening the regenerated sand according to the particle size specification of 50, 100, 70 or 140; and removing the glassy fine powder mixed in the regenerated sand.

[0075] The quality of the regenerated sand obtained in Examples 2-4 of the present invention is compared with the original sand from Inner Mongolia and (CN102133616A A method for regenerating and reusing mixed waste sand for casting).

[0076] Reference standards: "GBT 7143-2010 Chemical analysis method of silica sand for foundry", "GBT 26659-2011 Recycled silicon for foundry".

[0077] Table 2 Comparison of regenerated sand quality

[0078]

[0079] With the increase of drying temperature, the water content of regenerated sand tends to decrease. During the trial use of regenerated sand with high water content, castings are prone to pore defects.

[0080] The acid consumption value refers to the content of residual alkaline inorganic salts (Na2O, Fe2O3) on the surface of regenerated sand; the higher the acid consumption value, the faster the curing when phenolic resin is added, which affects the early curing during subsequent core making.

[0081] High mud content and high mud content on the surface of regenerated sand are directly related to the removal rate of bentonite, which will reduce the core-making strength of the regenerated sand.

[0082] As the rotor speed increases, the mud content and acid consumption of the regenerated sand tend to decrease, but the cost also increases.

[0083] The loss on ignition indicates the removal rate of coal powder. The lower the coal powder content, the lower the loss on ignition. A high coal powder content will reduce the refractoriness of the regenerated sand. As the flow rate increases from 20 to 40 kg / min, the loss on ignition gradually increases.

[0084] The present invention also calculates the cost. Based on the production of 1 ton of regenerated sand (1 ton of clay waste sand is processed per hour), the energy consumption is as follows:

[0085] Process Electricity natural gas Low temperature drying 8Kwh <![CDATA[2-5m 3 ]]> magnetic separation 6Kwh Level I Mechanical Regeneration 11Kwh Level II Mechanical Regeneration 30Kwh Particle size screening 5Kwh total 60Kwh <![CDATA[2-5m 3 ]]>

[0086] Note: 1) The industrial electricity price is 0.7 yuan / kmh, and the natural gas price is 4 yuan / m 3

[0087] a) Electricity fee = 60kw × 0.7 yuan / km = 42 yuan / ton;

[0088] b) Natural gas is calculated based on the highest consumption = 5 × 4 = 20 yuan / ton;

[0089] c) The investment for the whole set of equipment is about RMB 1 million. Based on 10-year depreciation and the annual waste sand output of a medium-sized foundry of 20,000 tons, the equipment depreciation cost for recycled sand is RMB 5 per ton.

[0090] The total cost of regenerated sand is 67 yuan / ton, and the cost of conventional technology is the lowest 300 yuan / ton, which saves 233 yuan per ton of sand, and can save 4.66 million yuan per year (calculated at 20,000 tons).

[0091] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for regenerating foundry clay waste sand, characterized in that: The method comprises the following steps: (1) Drying the clay waste sand to remove moisture; (2) Magnetic separation is performed on the dried clay waste sand to remove metal objects; (3) Level I mechanical regeneration: The clay waste sand after magnetic separation is sprayed into a closed device by high-pressure air, and the clay waste sand is made to collide with a wear-resistant baffle to remove coal powder and bentonite on the surface of the clay waste sand, wherein the clay waste sand enters the closed device at a flow rate of 20-40 kg / min, and the wear-resistant baffle is arranged vertically; (4) Level II mechanical regeneration: The clay waste sand treated in step (3) is subjected to friction and collision under the drive of a high-speed rotor to obtain regenerated sand, wherein the speed of the high-speed rotor is 1000-2000 rpm; In step (1), the moisture content of the dried waste clay sand is ≤0.5%; In step (3), the separated coal powder and bentonite leave the closed device under the action of negative pressure; the clay waste sand settles at the bottom of the closed device after hitting the wear-resistant baffle.

2. The method for regenerating foundry clay waste sand according to claim 1, characterized in that: In step (1), the waste clay sand is dried at 100-130°C.

3. The method for regenerating foundry clay waste sand according to claim 1, characterized in that: In step (2), the clay waste sand is magnetically separated in a magnetic field of 8000-15000 Gauss.

4. The method for regenerating foundry clay waste sand according to claim 1, characterized in that: The method further comprises the step of screening the regenerated sand.

5. The method for regenerating foundry clay waste sand according to claim 4, characterized in that: When screening the regenerated sand, it is screened according to the particle size specifications of 50, 100, 70 or 140.

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