Environment-friendly sodium silicate foundry binder with anti-aging function

Abstract

This invention belongs to the field of casting binder technology, and particularly relates to an environmentally friendly water glass casting binder with anti-aging function. The raw material composition of this invention includes: sodium water glass, lithium water glass, polymethyl methacrylate, and lithium carbonate, which enables: 1. Polymethyl methacrylate combined with lithium carbonate to provide more hydrogen bonds to the water glass binder system, changing the surface potential energy and solvation ability of the water glass, improving the stability of the water glass, and thus obtaining better "anti-aging" ability; 2. Lithium carbonate itself has the effect of a dispersant, and combined with water glass at a specific modulus, it can further improve the dispersibility of the sand mold; 3. Polymethyl methacrylate itself has basic bonding strength, and by limiting the modulus of the water glass, it can also appropriately improve the bonding strength of the entire binder; 4. The amount of organic polymethyl methacrylate added to this binder is sufficiently small, ensuring that the binder has sufficient safety and environmental protection advantages.

Description

Technical Field

[0001] This invention belongs to the field of casting binder technology, and particularly relates to an environmentally friendly water glass casting binder with anti-aging function. Background Technology

[0002] Casting binders are binding agents used in sand casting operations to solidify sand. Common casting binders are mainly divided into two types: organic and inorganic. Resin binders are representative of the former, while water glass binders are representative of the latter.

[0003] Resin adhesives have the advantage of high bonding strength, but their disadvantages are also obvious: they easily emit harmful gases during use, resulting in an overall less healthy and environmentally friendly effect. Water glass adhesives, on the other hand, are safe, environmentally friendly, and low-cost.

[0004] However, there are still many aspects of existing common water glass binders that can be improved, such as: 1. How to enable the sand mold to quickly reach sufficient strength; 2. How to maintain the bonding strength of the sand mold for a relatively long period of time, that is, to alleviate the "aging" phenomenon of water glass binders; 3. How to make the sand mold have sufficient collapsibility after casting, so that the sand can be quickly and completely removed from the casting.

[0005] Chinese invention patent with publication number CN108672648A and publication date of October 19, 2018, discloses a binder for casting sand molds. The raw material components are as follows by weight percentage: sodium silicate 1-90%, potassium silicate 1-90%, lithium silicate 1%, dextrin 0.5%, sodium carboxymethyl cellulose 0.5%, sodium alginate 0.5%, carbon dioxide-cured phenolic resin 0.5%, and water 3%.

[0006] The binder in this invention patent combines inorganic binders with organic binders, and the final performance is as follows: under carbon dioxide hardening, the strength at room temperature can reach more than 1MPa after 24 hours, while the strength of the sand mold after high-temperature casting is about 0.6MPa, improving the collapsibility of the sand mold.

[0007] However, when this binder is used in actual sand casting operations, it still has at least two shortcomings, which are the technical problems that this invention aims to solve.

[0008] First, the adhesive lacks sufficient "anti-aging" ability and cannot significantly slow down the rate of decline in the bonding strength of water glass.

[0009] Secondly, the strength of the sand mold after casting is still maintained at around 0.6 MPa, which is insufficient. At this point, it is still relatively difficult and laborious to remove the sand mold from the casting.

[0010] Therefore, in summary, there is an urgent need for a new type of water glass binder that has both significant anti-aging properties and sufficient disintegration performance, for use in sand casting operations. Summary of the Invention

[0011] This invention provides an environmentally friendly water glass casting binder with anti-aging properties, the raw material composition of which includes: sodium silicate, lithium silicate, polymethyl methacrylate, and lithium carbonate, such that:

[0012] 1. Polymethyl methacrylate combined with lithium carbonate can provide more hydrogen bonds to the water glass binder system, change the surface potential energy and solvation ability of water glass, improve the stability of water glass, and thus obtain better "anti-aging" ability.

[0013] 2. Lithium carbonate itself acts as a collapsing agent, and when combined with water glass at a specific modulus, it can further improve the collapsing performance of sand molds;

[0014] 3. Polymethyl methacrylate itself has basic bonding strength. Similarly, by limiting the modulus of water glass, the bonding strength of the entire adhesive can be appropriately improved.

[0015] 4. The amount of organic polymethacrylic acid added to this adhesive is sufficiently small, ensuring that the adhesive has sufficient safety and environmental protection advantages.

[0016] The technical solution adopted by the present invention to solve the above problems is: an environmentally friendly water glass casting binder with anti-aging function, the raw material composition including: sodium water glass, lithium water glass, polymethyl methacrylate, and lithium carbonate, wherein the modulus of the sodium water glass is 2.6-2.8, the modulus of the lithium water glass is 4.0-4.5, the added weight of the polymethyl methacrylate is 1.2-1.4% of the total added weight of the sodium water glass and lithium water glass, and the added weight of the lithium carbonate is 7.5-8.0% of the total added weight of the sodium water glass and lithium water glass.

[0017] In this invention, the method of combining sodium silicate with lithium silicate has more stable bonding performance compared to a single type of silicate.

[0018] In addition, the main function of polymethacrylic acid is to provide and accept hydrogen bonds, and the main function of lithium carbonate is to act as a dispersant. However, there are multiple synergistic effects between these two and sodium silicate and lithium silicate, specifically including the following two points.

[0019] First, although lithium carbonate itself lacks hydrogen bond-providing ability, it still has outstanding hydrogen bond-accepting performance. Therefore, the addition of lithium carbonate can increase the number of hydrogen bonds in this water glass binder system. Hydrogen bonds are key to the "anti-aging" ability of water glass. Hydrogen bonds can adsorb polymethyl methacrylate onto the surface of water glass molecules, changing their surface potential energy and solvation ability, improving the stability of water glass, and thus slowing down its "aging" rate.

[0020] Secondly, both the dispersant properties of lithium carbonate and the adhesive properties of polymethyl methacrylate can achieve relatively greater performance when using a combination of sodium silicate modulus of 2.6-2.8 and lithium silicate modulus of 4.0-4.5, which is very important.

[0021] Finally, polymethyl methacrylate not only has very low toxicity, but also requires a relatively small amount to be added, so this water glass casting binder has the advantages of being environmentally friendly and safe.

[0022] A further preferred technical solution is that the molecular weight of the polymethacrylic acid is ≥80000.

[0023] In this invention, if the molecular weight of polymethacrylic acid is less than 8000, the test results show that its ability to form hydrogen bonds is relatively poor, and its improvement effect on the "anti-aging" properties of water glass is at least not significant.

[0024] A further preferred technical solution is that the purity of the lithium carbonate is 99.6-99.9%.

[0025] A further preferred technical solution is that the D50 of the lithium carbonate is 50-95μm.

[0026] In this invention, D50 refers to the median particle size. For example, when D50 is 60 μm, it means that in this batch of lithium carbonate, the material with a particle size larger than 60 μm and the material with a particle size smaller than 60 μm each account for half.

[0027] Furthermore, if the D50 of the lithium carbonate is less than 50 μm, it will significantly increase its cost, while if it is greater than 90 μm, its collapsibility is not comprehensive enough, and it cannot guarantee that the sand mold can be quickly and thoroughly removed from the casting after casting. The harmful manifestation is that many sand blocks that need to be manually broken off remain on the casting.

[0028] A further preferred technical solution is that the raw material composition includes the following components by weight: 32-36% sodium silicate and 55-58% lithium silicate.

[0029] A further preferred technical solution is that the raw material composition also includes: cyclodextrin, silane coupling agent, and sodium tripolyphosphate.

[0030] In this invention, the main component of cyclodextrin, namely starch, not only has a certain binding strength, but also has a certain sand-like disintegration effect, similar to lithium carbonate.

[0031] In addition, common silane coupling agents include KH550, KH560, KH570, and KH792, which couple cyclodextrin and polymethacrylic acid, resulting in greater overall strength of the binder. Sodium tripolyphosphate, on the other hand, is used as a general chelating agent.

[0032] A further preferred technical solution is that the adhesive is prepared by stirring at a temperature of 45-50°C.

[0033] A further preferred technical solution is that: after the adhesive is prepared, a heat preservation operation is performed, with the heat preservation temperature being 40-60℃ and the heat preservation time being 1.5-2.0h.

[0034] In this invention, the above-mentioned heat preservation operation can further fully leverage the synergistic hydrogen bond formation effect of polymethacrylic acid and lithium carbonate.

[0035] A further preferred technical solution is that the binder is used for pure quartz sand, or for a quartz sand mixture with a replacement amount of ≤5%, wherein the sand used for replacement is any one or a mixture of two of olivine sand and zircon sand.

[0036] A further preferred technical solution is that the amount of the binder added to the pure quartz sand, or the quartz sand mixture, is ≤2wt%.

[0037] In existing technologies, the amount of adhesive used is generally 4-5 wt%. The reason for this is that the adhesive itself has relatively low bonding strength and a fast "aging" rate, so a larger amount has to be added.

[0038] However, this results in the sand mold's collapse resistance being far from sufficient. For example, the strength of the sand mold after casting is between 0.7 and 0.8 MPa. At this point, it becomes quite troublesome to completely remove the sand mold from the casting, requiring repeated hammering of the sand mold, which seriously affects the quality of the casting.

[0039] Therefore, the binder in this invention, after being limited by specific material composition and preparation process, can have its addition amount controlled to below 2wt%. At this point, the strength before sand casting is sufficient, and the strength after sand casting can quickly drop to a small value. The former ensures the stability of the casting operation, and the latter ensures high casting quality. Detailed Implementation

[0040] The following description is only a preferred embodiment of the present invention and is not intended to limit the scope of the present invention.

[0041] Example 1

[0042] An environmentally friendly water glass casting binder with anti-aging properties, comprising the following components by weight:

[0043] Sodium silicate 34%, lithium silicate 55%, polymethyl methacrylate 1.2%, lithium carbonate 7%, cyclodextrin 1.5%, silane coupling agent 0.7%, sodium tripolyphosphate 0.6%.

[0044] The sodium silicate has a modulus of 2.8, and the lithium silicate has a modulus of 4.2.

[0045] Polymethacrylic acid has a molecular weight ≥80,000, lithium carbonate has a purity of 99.8%, and its D50 is 62μm.

[0046] Furthermore, the preparation method of this adhesive includes the following steps in sequence:

[0047] S1. Using a vacuum pump, sodium silicate, lithium silicate, polymethyl methacrylate and lithium carbonate are all drawn into the mixing tank. Then the mixing tank is turned on, the temperature inside the tank is set to 45℃, and the mixture is stirred for 30 minutes to obtain the precursor material.

[0048] S2. Add cyclodextrin, silane coupling agent and sodium tripolyphosphate to the precursor material, keep the stirring temperature constant, and stir for another 10 minutes to obtain the intermediate material.

[0049] S3. Raise the internal temperature of the mixing tank to 50℃, keep it at that temperature for 1.5 hours, and finally use a metering pump to discharge and fill the product to obtain the final adhesive product.

[0050] The binder in this embodiment is used in pure quartz sand, or in a quartz sand mixture with a substitution amount of ≤5%, wherein the sand used for substitution is any one or a mixture of two of olivine sand and zircon sand. Furthermore, the amount of binder added to the pure quartz sand, or the quartz sand mixture, is 1.8 wt%.

[0051] Example 2

[0052] An environmentally friendly water glass casting binder with anti-aging properties, comprising the following components by weight:

[0053] Sodium silicate 34%, lithium silicate 56%, polymethyl methacrylate 1.1%, lithium carbonate 7.1%, cyclodextrin 0.5%, silane coupling agent 0.4%, sodium tripolyphosphate 0.9%.

[0054] The sodium silicate has a modulus of 2.6, and the lithium silicate has a modulus of 4.5.

[0055] Polymethacrylic acid has a molecular weight ≥80,000, lithium carbonate has a purity of 99.9%, and its D50 is 78μm.

[0056] Furthermore, the preparation method of this adhesive includes the following steps in sequence:

[0057] S1. Using a vacuum pump, sodium silicate, lithium silicate, polymethyl methacrylate and lithium carbonate are all drawn into the mixing tank. Then the mixing tank is turned on, the temperature inside the tank is set to 50℃, and the mixture is stirred for 30 minutes to obtain the precursor material.

[0058] S2. Add cyclodextrin, silane coupling agent and sodium tripolyphosphate to the precursor material, keep the stirring temperature constant, and stir for another 10 minutes to obtain the intermediate material.

[0059] S3. Raise the internal temperature of the mixing tank to 55℃ and keep it at that temperature for 2.0 hours. Finally, use a metering pump to discharge and fill the product to obtain the final adhesive product.

[0060] The binder in this embodiment is used in pure quartz sand, or in a quartz sand mixture with a substitution amount of ≤5%, wherein the sand used for substitution is any one or a mixture of two of olivine sand and zircon sand. Furthermore, the amount of the binder added to the pure quartz sand, or the quartz sand mixture, is 1.9 wt%.

[0061] Example 3

[0062] An environmentally friendly water glass casting binder with anti-aging properties, comprising the following components by weight:

[0063] Sodium silicate 36%, lithium silicate 55%, polymethyl methacrylate 1.1%, lithium carbonate 6.9%, cyclodextrin 0.2%, silane coupling agent 0.4%, sodium tripolyphosphate 0.4%.

[0064] The sodium silicate has a modulus of 2.6, and the lithium silicate has a modulus of 4.4.

[0065] Polymethacrylic acid has a molecular weight ≥80,000, lithium carbonate has a purity of 99.9%, and its D50 is 75μm.

[0066] Furthermore, the preparation method of this adhesive includes the following steps in sequence:

[0067] S1. Using a vacuum pump, sodium silicate, lithium silicate, polymethyl methacrylate and lithium carbonate are all drawn into the mixing tank. Then the mixing tank is turned on, the temperature inside the tank is set to 50℃, and the mixture is stirred for 30 minutes to obtain the precursor material.

[0068] S2. Add cyclodextrin, silane coupling agent and sodium tripolyphosphate to the precursor material, keep the stirring temperature constant, and stir for another 10 minutes to obtain the intermediate material.

[0069] S3. Raise the internal temperature of the mixing vessel to 60℃, keep it at that temperature for 2.0h, and finally use a metering pump to discharge and fill the product to obtain the final adhesive product.

[0070] The binder in this embodiment is used in pure quartz sand, or in a quartz sand mixture with a substitution amount of ≤5%, wherein the sand used for substitution is any one or a mixture of two of olivine sand and zircon sand. Furthermore, the amount of the binder added to the pure quartz sand, or the quartz sand mixture, is 2.0 wt%.

[0071] Comparative Example 1

[0072] The binder in this comparative example differs from that in Example 1 in only one aspect, namely:

[0073] Replace 1.2% polymethacrylic acid with 1.2% sodium silicate.

[0074] Comparative Example 2

[0075] The binder in this comparative example differs from that in Example 1 in only one aspect, namely:

[0076] Replace 7% lithium carbonate with 7% sodium silicate.

[0077] Comparative Example 3

[0078] The binder in this comparative example differs from that in Example 1 in only one aspect, namely:

[0079] Replace 1.2% polymethacrylic acid and 7% lithium carbonate with 8.2% sodium silicate.

[0080] Comparative Example 4

[0081] The binder in this comparative example differs from that in Example 1 in only one aspect, namely:

[0082] Replace 1.5% cyclodextrin, 0.7% silane coupling agent, and 0.6% sodium tripolyphosphate with 2.8% sodium silicate.

[0083] Comparative Example 5

[0084] The binder in this comparative example differs from that in Example 1 in only two aspects: its material composition, preparation method, and application method.

[0085] 1. Use sodium silicate with a modulus of 3.2;

[0086] 2. Select lithium-ion glass with a module of 5.5.

[0087] Performance testing

[0088] The above-mentioned 8 groups of adhesive products, 5 sand samples containing their respective adhesive products were taken from each group, and cubic blocks with a side length of 2cm and a single central diameter of 1cm were made according to common methods of existing technology. Finally, a total of 40 cubic blocks were tested for the 4 performance items in Table 1 below, and the average results are shown in Table 1 below.

[0089] Table 1

[0090]

[0091] Results Analysis

[0092] The perforated cubic "sand mold" in the first and third embodiments has the combined advantages of relatively high initial strength, extremely high compressive strength at peak performance after 1 hour, relatively insignificant strength decay after 48 hours, large strength decrease after casting, and convenient sand mold removal.

[0093] In the second and third embodiments, by relying on the combination of polymethyl methacrylate and lithium carbonate, as well as the overall improvement of material formulation, preparation and usage methods, the cubic sand mold has the unexpected effect of high initial strength and high overall strength, but the strength decreases most significantly and the decrease is the largest after casting. This is very important in sand casting operations and has great promotional value.

[0094] Third, the binder consists of polymethyl methacrylate and lithium carbonate. If either of them is missing, the structural strength before casting will be greatly reduced. However, on the contrary, the decrease in strength after casting is not obvious, which leads to the problem of inconvenient sand mold removal after casting.

[0095] Fourth, the addition of cyclodextrin, silane coupling agent and sodium tripolyphosphate can improve the overall strength properties of cubic sand molds, but the improvement effect is not significant.

[0096] Fifth, the modulus limitations for sodium silicate and lithium silicate do not significantly improve the strength of cubic sand molds compared to the fourth point mentioned above.

[0097] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various modifications can be made without departing from the spirit of the present invention. These are all non-inventive modifications, and are protected by patent law as long as they fall within the scope of the claims of the present invention.

Claims

1. An environmentally friendly water glass foundry binder with anti-aging function, characterized in that The raw material composition includes: sodium silicate, lithium silicate, polymethyl methacrylate, and lithium carbonate. The modulus of the sodium silicate is 2.6-2.8, the modulus of the lithium silicate is 4.0-4.5, the added weight of the polymethyl methacrylate is 1.2-1.4% of the total added weight of the sodium silicate and lithium silicate, and the added weight of the lithium carbonate is 7.5-8.0% of the total added weight of the sodium silicate and lithium silicate. The molecular weight of the polymethacrylic acid is ≥80,000; The purity of the lithium carbonate is 99.6-99.9%; The D50 of the lithium carbonate is 50-95 μm; The raw material composition includes the following components by weight: 32-36% sodium silicate and 55-58% lithium silicate; The raw material composition also includes: cyclodextrin, silane coupling agent, and sodium tripolyphosphate; The adhesive was prepared by a stirring method at a stirring temperature of 45-50℃. After the adhesive is prepared, it is then subjected to a heat preservation operation at a temperature of 40-60℃ for 1.5-2.0 hours.

2. The environment-friendly sodium silicate foundry binder with anti-aging function according to claim 1, characterized in that: The binder is used for pure quartz sand, or for quartz sand mixtures with a replacement amount of ≤5%, wherein the sand used for replacement is any one or a mixture of two of olivine sand and zircon sand.

3. The environment-friendly sodium silicate foundry binder with anti-aging function according to claim 2, characterized in that: The amount of the binder added to the pure quartz sand or the quartz sand mixture is ≤2wt%.

Images