A composite blowing hardening water glass sand additive and method of use thereof

Abstract

The present application belongs to the technical field of foundry molding sand additive, and particularly relates to a kind of composite blowing hardening sodium silicate sand additive and its using method, which is characterized by being composed of the following raw materials: polyvinyl alcohol aqueous solution, isopropyl alcohol, glucose, glucoside and silicon dioxide powder.Compared with the prior art, the present application has the following beneficial effects: 1) the instant tensile strength of the present application is ≥0.5MPa, the room temperature tensile strength is ≥1.8MPa, the fluidity is ≥2.5g, the collapsibility (high temperature residual tensile strength) is ≤0.01MPa, and the sand core has high strength, good fluidity and collapsibility under a lower binder addition amount.2) It is suitable for carbon dioxide and compressed air hardening sand core under a certain blowing pressure, which can effectively prevent the CO2 "overblowing" phenomenon.At the same time, the compressed air can also cause the dehydration of sodium silicate sand, promote the gelation of sodium silicate, and improve the hardening speed of sodium silicate sand.

Description

Technical Field

[0001] The invention belongs to the technical field of casting molding sand additives, and particularly relates to an additive for composite air-blowing hardening water glass sand and a use method thereof. Technical Background

[0002] The foundry industry has high expectations for inorganic binder core manufacturing technology. Inorganic binders offer low gas emissions, are non-toxic, and are environmentally friendly, making them a promising technology for foundry applications. Waterglass, a traditional inorganic binder used for molding and core making, was introduced into foundry production in the 1950s and boasts a history of over 50 years. Waterglass sand offers superior performance and flexibility, suitable for both molding and core making. The earliest CO2 gas-hardened cold-box process is believed to be the waterglass-CO2 method.

[0003] The main problems encountered in the current inorganic binder core manufacturing technology are: 1) The viscosity of water glass sand is high, and the mixed molding sand has poor fluidity. It is difficult to form a dense molding end of the complex structure sand core, which is very likely to cause casting defects such as bulges, sand inclusions and sand sticking. 2) The core strength prepared by the carbon dioxide gas hardening water glass sand process is relatively low, and the amount of binder needs to be increased to improve the strength, but it will cause trouble in the subsequent cleaning of the molding sand, resulting in difficult to clean the castings. The biggest problem with CO2 hardened water glass sand is its poor collapsibility after pouring, which makes it difficult to clean the casting sand and recycle the old sand, which seriously hinders its promotion and application.

[0004] Chinese invention patent application number 201110307628.2 discloses a method for preparing water glass sand for foundry use. The method includes two steps: preparing modified water glass and preparing molding sand. The modified water glass is prepared using a composite modifier consisting of talc, starch, polypropylene alcohol, and nano-alumina powder. The total amount of the composite modifier is 35-50% talc, 6-12% starch, 14-18% polypropylene alcohol, and 25-35% nano-alumina powder. This method improves strength and collapsibility, but does not address how to enhance the fluidity and later strength of the sand core, failing to meet the development needs of the foundry industry.

[0005] Purpose of the Invention

[0006] The purpose of the present invention is to provide an additive for composite air-hardened water glass sand and a method for using the same, so as to overcome the shortcomings of the prior art, optimize the additive components, and improve the fluidity and strength of the sand core, so that the sand core still has high strength, good fluidity and collapsibility at a lower binder addition amount, thereby meeting the demand of the foundry industry for high-end sand core products.

[0007] To achieve the above objectives, the present invention adopts the following technical solutions:

[0008] A kind of composite blowing hardening water glass sand additive, it is characterized by being made of the following raw materials by weight percentage, polyvinyl alcohol aqueous solution 10-35%, isopropanol 15-35%, glucose 0-10%, glucoside 0-10%, silicon dioxide powder 30-50%.

[0009] The silicon dioxide powder has surface Si-OH activity, which can be obtained by dry, wet, gas phase surface activity modification.

[0010] The polyvinyl alcohol aqueous solution concentration is 2-10%, the average molecular weight of polyvinyl alcohol is 16000-200000, the polymerization degree is 1700-2400, and the alcoholysis degree is 88-99%.

[0011] The isopropanol is replaced by n-propanol.

[0012] The glucose is replaced by any one or any two or more combinations of allose, fructose, sorbose, allose, altrose, mannose, alpha-D-furanose and beta-D-furanose.

[0013] The additive is used to prepare water glass sand core, and the formula ratio is as follows: raw sand, water glass binder is 2.0-3.0% of the mass of raw sand, and the additive is 0.3-1% of the mass of raw sand. First, the raw sand is premixed with the additive for 5-10s, then the water glass binder is added to the premix, and mixed uniformly to be used for making sand core.

[0014] In the process of making sand core, the ambient temperature is kept at 25-30 DEG C, the sand mixing time is set to 60-120s, and the hardening process is as follows: first blowing CO2 for 1-120s, blowing pressure 0.2-0.3MPa, gas temperature ≤25 DEG C, then blowing compressed air for ≥45s, blowing pressure ≥0.3MPa, gas temperature ≤25 DEG C.

[0015] The raw sand is replaced by any one of zircon sand, chromite sand and corundum sand; the water glass binder is replaced by resin or clay.

[0016] In the formula, the components synergize. The purity of the silicon dioxide powder is ≥90%, which mainly improves the fluidity of the molding sand by using its large specific surface area, and the active Si-OH on the surface reacts with the Si-OH in the water glass binder to enhance the strength of the core. The chemical formula of polyvinyl alcohol is [C2H4O] n, the appearance is white flake, flocculent or powdery solid, odorless. The chemical formula of isopropyl alcohol is C3H8O, which is an isomer of n-propyl alcohol and is a colorless transparent liquid. Glucoside is synthesized from natural fatty alcohols and glucose. It is a nonionic surfactant that has the characteristics of ordinary nonionic and anionic surfactants, with high surface activity, good ecological safety and compatibility. The molecular formula of glucose is C6H 12 O6.

[0017] The concentration of the polyvinyl alcohol aqueous solution is 2%-10%. The polyvinyl alcohol can be selected from an average molecular weight of 16,000-200,000, a degree of polymerization of 1,700-2,400, and a degree of alcoholysis of 88-99%. It has excellent film-forming properties and can effectively improve the toughness of the core while enhancing the bonding strength of the water glass sand core, thereby improving the overall strength of the water glass core.

[0018] Isopropyl alcohol has strong water retention properties, which can ensure low solubility of carbon dioxide in the binder when too much carbon dioxide is blown in, thereby preventing the strength of the water glass sand core from decreasing during later storage.

[0019] The mechanism of action of glucose is that after it is mixed with the water glass binder, due to the alkalinity of the water glass, an alkalinization reaction will slowly occur during the sand core molding and subsequent dehydration and hardening process. The aldehyde group or ketone group in the glucose can spontaneously and rapidly undergo a reversible reaction with the hydroxyl group on another carbon atom on the same molecule to generate hemiacetal, thereby forming a ring structure. The hydroxyl group on the first carbon atom is called the hemiacetal hydroxyl group, which has very active chemical properties and will react with the Si-OH in the water glass to improve the bonding performance of the water glass, thereby increasing the core strength.

[0020] Glucoside has low surface tension, strong wetting power, is non-toxic, harmless, quickly and thoroughly biodegrades, and is highly alkali-resistant. Adding it to strongly alkaline water glass molding sand can reduce the binder's surface tension, improve the binder's wetting and coating properties on the sand surface, and thus increase the sand's fluidity.

[0021] Compared with the prior art, the present invention has the following advantages: 1) It has an instantaneous tensile strength ≥ 0.5 MPa, a room temperature tensile strength ≥ 1.8 MPa, a fluidity ≥ 2.5 g, and a collapsibility (i.e., high-temperature residual tensile strength) ≤ 0.01 MPa. The sand core exhibits high strength, good fluidity, and collapsibility at relatively low binder levels. 2) It is suitable for hardening sand cores using carbon dioxide and compressed air at a certain blowing pressure, effectively preventing CO2 "overblowing." Furthermore, compressed air can dehydrate the water glass sand, thereby promoting its gelation and increasing its hardening rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1Schematic diagram of the mechanism of action of silica powder with Si-OH surface activity and a binder in an embodiment of the present invention. Specific embodiments

[0023] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with specific embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0024] Therefore, the following detailed description of the embodiments of the present invention provided in the examples is not intended to limit the scope of the invention as claimed, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0025] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the embodiments required for use in the specific embodiments or the description of the prior art. Obviously, the embodiments described below are some embodiments of the present invention. For those of ordinary skill in the art, other embodiments can be obtained based on these embodiments without inventive work. Therefore, the following detailed description of the embodiments of the present invention provided in the examples is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention.

[0026] In the following examples, an "8"-shaped core is prepared by mixing the molding sand and the mold (or using a core shooter). The prepared core is first introduced with carbon dioxide gas, then with compressed air, and finally the sand core is taken out and the corresponding performance parameters are measured according to relevant standards. The ambient temperature is 25°C and the humidity is 30% RH. The sand mixing time is set to 120s, and the hardening process is to first blow CO2 for 25s and then blow compressed air for 45s. The blowing pressure of CO2 is 0.2MPa and that of compressed air is 0.5MPa. In addition, in actual production, the gas flow rate and blowing time can be adjusted according to the thickness and complexity of the sand core and the structural design of the core box mold. The blowing sequence can be interchanged or the blowing can be cross-changed. This is a prior art and will not be described in detail.

[0027] Among the components, silica powder has surface Si-OH activity and can be modified through dry, wet, or vapor-phase methods. Isopropyl alcohol can be replaced by n-propyl alcohol in equal proportions. The raw sand can be any of zircon sand, chromite sand, and corundum sand; the water glass binder can be replaced by resin or clay. Glucose can be replaced by any of psicose, fructose, sorbose, allose, altrose, mannose, α-D-furanose, and β-D-furanose, or a combination of two or more. The concentration of the polyvinyl alcohol aqueous solution is 2%-10%, the average molecular weight of the polyvinyl alcohol is 16,000-200,000, the degree of polymerization is 1,700-2,400, and the degree of alcoholysis is 88-99%.

[0028] Example 1

[0029] Weigh each additive component separately: 45g of Si-OH surface-active silica powder, 15g of a 5% aqueous solution of polyvinyl alcohol, 30g of isopropyl alcohol, 5g of glucose, and 5g of glucoside. Mix thoroughly and set aside. Weigh 0.8g of the additive and premix with 100g of raw sand for 5 seconds. Then, add 2.8g of waterglass binder and mix the sand to make cores.

[0030] The sand core is tested according to the GB / T2684-2009 testing standard. The immediate tensile strength of the hardened sand core is 0.53MPa, the 24h tensile strength is 1.96MPa, the high temperature residual strength is 0MPa, and the molding sand fluidity is 3.14g.

[0031] Example 2

[0032] Weigh each component of the additives: 40g of Si-OH surface active silica powder, 23g of 5% polyvinyl alcohol aqueous solution, 23g of isopropyl alcohol, 7g of glucose, and 2g of glucoside, mix them evenly and set aside. The sand mixing and core making process is the same as in Example 1.

[0033] The sand core was tested according to the GB / T2684-2009 testing standard. After hardening, the instant tensile strength of the sand core was measured to be 0.58MPa, the 24h tensile strength was 1.89MPa, the high temperature residual strength was 0MPa, and the molding sand fluidity was 3.36g.

[0034] Example 3

[0035] Weigh each component of the additives, 50g of Si-OH surface active silica powder, 25g of 5% polyvinyl alcohol aqueous solution, 20g of n-propanol, 2g of glucose, and 3g of glucoside, mix them evenly and set aside. The sand mixing and core making process is the same as in Example 1.

[0036] The sand core was tested according to the GB / T2684-2009 testing standard. After hardening, the instant tensile strength of the sand core was measured to be 0.61MPa, the 24h tensile strength was 1.92MPa, the high temperature residual strength was 0MPa, and the molding sand fluidity was 2.68g.

[0037] Example 4

[0038] Weigh each component of the additives: 40g of Si-OH surface active silica powder, 30g of 5% polyvinyl alcohol aqueous solution, 20g of isopropyl alcohol, 7g of sorbitol, and 3g of glucoside, mix them evenly and set aside. The sand mixing and core making process is the same as in Example 1.

[0039] The sand core was tested according to the GB / T2684-2009 testing standard. After hardening, the instant tensile strength of the sand core was measured to be 0.55MPa, the 24h tensile strength was 2.06MPa, the high temperature residual strength was 0MPa, and the molding sand fluidity was 3.45g.

[0040] Example 5

[0041] Weigh each component of the additives, 40g of Si-OH surface active silica powder, 30g of 5% polyvinyl alcohol aqueous solution, 25g of isopropyl alcohol, 4g of glucose, and 1g of glucoside, mix them evenly and set aside. The sand mixing and core making process is the same as in Example 1.

[0042] The sand core was tested according to the GB / T2684-2009 testing standard. After hardening, the instant tensile strength of the sand core was measured to be 0.52MPa, the 24h tensile strength was 1.97MPa, the high temperature residual strength was 0MPa, and the molding sand fluidity was 3.35g.

[0043] Comparative example (sand core without additives)

[0044] Weigh 100g of raw sand, add 2.0g of water glass binder, mix the sand and make cores.

[0045] The sand core is tested according to the GB / T2684-2009 testing standard. After air hardening, the instant tensile strength of the sand core is measured to be 0.12MPa, the 24h tensile strength is 0.18MPa, the high temperature residual strength is 0.05MPa, and the molding sand fluidity is 1.45g.

[0046] Conclusion: The tensile strength of the present invention is greater than or equal to 1.8 MPa, which is equivalent to a dry compressive strength of approximately 7 MPa or greater, significantly higher than the 3.6 MPa in the referenced documents. The high-temperature residual strength of the present invention is ≤ 0.01 MPa, and the fluidity is ≥ 2.5 g. Compared with the referenced documents, the present invention has significant technical advantages and can be widely applied to sand molds for various high-precision, ultra-thin, and other high-end special-shaped castings.

Claims

1. An additive for composite air-blowing hardening water glass sand, characterized in that: The product is prepared from the following raw materials by weight: 10% to 35% polyvinyl alcohol aqueous solution, 15% to 35% isopropyl alcohol, 0% to 10% glucose, 0% to 10% glucoside, and 30% to 50% silicon dioxide powder; The silicon dioxide powder has surface Si-OH activity and is obtained by surface activity modification by dry method, wet method or gas phase method; The concentration of the polyvinyl alcohol aqueous solution is 2%-10%, the average molecular weight of the polyvinyl alcohol is 16000-200000, the degree of polymerization is 1700-2400, and the alcoholysis degree is 88-99%.

2. The additive for composite air-blowing hardening water glass sand according to claim 1, characterized in that: The isopropyl alcohol was replaced by n-propyl alcohol.

3. The additive for composite air-blowing hardening water glass sand according to claim 1, characterized in that: The glucose is any one of psicose, fructose, sorbose, allose, altrose, mannose, α-D-glucopyranose, and β-D-glucopyranose, or a combination of any two or more thereof.

4. The method for using the additive for composite air-blowing hardening water glass sand according to claim 1, characterized in that: The additive is used to prepare water glass sand cores, and the formula ratio thereof is as follows by weight percentage: raw sand, water glass binder accounts for 2.0%-3.0% of the mass of the raw sand, and the additive accounts for 0.3%-1% of the mass of the raw sand. The raw sand and the additive are premixed for 5-10 seconds, and then the water glass binder is added to the premix. After mixing evenly, the mixture can be used to make sand cores.

5. The method for using the additive for composite air-blowing hardening water glass sand according to claim 4, characterized in that: During the sand core making process, the ambient temperature is maintained at 25°C-30°C, the sand mixing time is set to 60-120s, and the hardening process is: first blow CO2 for 1s-120s, the blowing pressure is 0.2-0.3MPa, and the gas temperature is ≤25°C, then change to blowing compressed air for ≥45s, the blowing pressure is ≥0.3MPa, and the gas temperature is ≤25°C.

6. The method for using the additive for composite air-blowing hardening water glass sand according to claim 4, characterized in that: The raw sand is any one of zircon sand, chromite sand and corundum sand; and the water glass binder is resin or clay.

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