Lost foam composite coating

Abstract

The invention relates to the technical field of lost foam casting, in particular to a lost foam composite coating, the lost foam composite coating takes a refractory material of an investment casting regenerated shell membrane as a refractory aggregate, the refractory aggregate comprises mullite and a mixture containing an inorganic preservative A and a sintering stripping material B, and one or more of quartz powder and graphite are selected. In the invention, an efficient anti-corrosion additive with sintering stripping is researched and developed as a refractory material auxiliary additive, and meanwhile, low-price refractory materials such as regenerated mullite and recycled quartz powder are utilized to form the lost foam coating aggregate, so that the selection of traditional refractory aggregate is broken through, and the reutilization of waste resources is realized; the environment pollution is reduced while the raw material cost is reduced, meanwhile, the aggregate performance is optimized by adding the raw materials such as calcium oxide and iron oxide red, and the comprehensive performance such as air permeability, suspension stability, high-temperature strength and toughness of the coating is remarkably improved through reasonable matching of the composite binder.

Description

Technical Field

[0001] The present invention relates to the technical field of lost foam casting, and particularly relates to a lost foam composite coating. Background Art

[0002] The lost foam casting process is a process that has developed rapidly in recent years and belongs to the scope of green casting. Its greatest feature is that the sand mold for molding does not require a binder. It uses a vacuum negative pressure method to compact the molding sand. At the same time, the mold used is made of EPS plastic, which has a certain strength and a relatively low gas evolution rate. When casting molten steel, the plastic mold gasifies, and the molten steel fills the mold cavity. After cooling, a casting blank is obtained. The accuracy is much higher than that of traditional sand mold casting, and the cleaning process is simple. Most of the coating layer can be automatically peeled off, and a casting with a smooth surface can be obtained through simple shot blasting treatment. It is very suitable for small-batch castings with quick delivery, as well as large-scale production by enterprises with their own foam foaming machines.

[0003] On the other hand, the casting industry is highly competitive, and everyone is trying to reduce costs. Among them, the lost foam coating market is highly competitive. For cast iron coatings, the market price ranges from 1,800 yuan / t to 3,000 yuan / t. Generally, enterprises purchase Guilin No. 5 binder by themselves and prepare coatings with refractory aggregates such as bauxite, refined quartz powder, and kyanite. The costs are relatively high. The prices of coatings for cast steel, even alloy steel and stainless steel, are even higher. The main costs come from (1) the binder, represented by Guilin No. 5, with a cost accounting for more than 600 yuan / t in each ton of coating, and (2) refractory aggregates, mainly bauxite, graphite, quartz powder, etc., with a general cost of more than 1,500 yuan per ton. Since lost foam coatings are generally dip-coated and large parts are flow-coated, the consumption of coatings is generally larger than that of alcohol-based coatings for sand molds. Generally, the lost foam coating accounts for 2-5% of the casting. For high-demand thick and large parts with more than three layers of coating, the coating ratio even reaches 8%. Objectively, this increases the cost of castings. At the same time, this is also the reason why the production and sales volume of domestic lost foam coating enterprises is much higher than that of alcohol-based and water-based coatings for sand molds.

[0004] Another reason is that a large amount of expanded starch is used in the binder of lost foam coatings. When it encounters water or is exposed to moisture, it is extremely easy to ferment. Especially in the Yangtze River Basin and the areas south of it, this binder is prone to ferment and deteriorate, and even produce a foul smell, greatly reducing the strength of the coating and making it unusable. Even if some preservatives are added, due to its being an organic substance and easy to volatilize, the anti-corrosion time is not long, and it is difficult to exceed 2 months. Using vacuum packaging also increases the cost of the coating.

[0005] In summary, the lost foam casting, as a rapidly developing green casting process in recent years, features fast molding. The mold is made of foam, which has a shorter production cycle and lower cost compared to metal molds and plastic molds. Moreover, the sand can be reused repeatedly without the use of sand binders for molding. The casting has high dimensional accuracy and is particularly suitable for cast iron products and low-carbon steel products. However, since most of the binders in the coatings used contain expanded starch materials, even with the addition of commonly used preservatives on the market, the effect is still not ideal, and they are basically organic substances. On the one hand, it increases the cost, and on the other hand, it increases the gas evolution of the coating. And the commonly used refractory aggregates such as bauxite, graphite, and quartz powder in lost foam coatings do not have natural anti-corrosion properties. Once the additives of the binder ferment, the coating performance drops sharply, the strength decreases, and it cannot resist the erosion of high-temperature molten steel during casting, resulting in large-area sand sticking on the casting. Developing a lost foam composite coating is still a key problem urgently to be solved in the field of lost foam casting technology. Summary of the Invention

[0006] Aiming at the problems existing in the prior art, the purpose of the present invention is to provide regenerated mullite and its preparation method.

[0007] To achieve the above purpose, the present invention provides the following technical solutions:

[0008] A lost foam composite coating, which uses the refractory material of the regenerated shell film of investment casting as the refractory aggregate. The refractory aggregate includes mullite and a mixture containing inorganic preservative A and sintering peeling material B, and one or more of quartz powder and graphite are selected. The particle size of the mixture is 150 - 250 mesh. Mullite is the main component in the refractory aggregate, and its composition contains 36 - 50% of alumina, 0 - 5% of zirconia, 0.5 - 1.5% of iron oxide, and 50 - 60% of silica.

[0009] The present invention is further configured as: mixing the refractory aggregate and the lost foam binder according to the ratio of composite aggregate: binder: water = 10:1:4 - 6 for more than 2 hours to obtain the lost foam composite coating.

[0010] The present invention is further configured as: the main component of the inorganic preservative A in the mixture is calcium oxide, and the inorganic preservative A accounts for 0.1 - 0.3% in the refractory aggregate. Its particle size is below 200 mesh, and the pH is greater than 13.5.

[0011] The present invention is further configured as: the main component of the sintering peeling aid B in the mixture is iron oxide red, with a particle size below 200 mesh, and the content of ferric oxide in the sintering peeling aid B is 50 - 65%. The sintering peeling aid B accounts for 3 - 5% in the refractory aggregate.

[0012] The present invention is further configured as: the pH of the refractory aggregate is 8.5 - 10.

[0013] Beneficial effects

[0014] Adopting the technical solution provided by the present invention, compared with the known public technology, it has the following

[0015] Beneficial effects:

[0016] (1) In the present invention, the waste shell film of investment casting is recycled to produce refractory aggregates mainly composed of mullite, and inorganic substances with high-efficiency preservatives and materials with sintering and peeling characteristics are added to form a lost foam dry powder coating, breaking through the traditional selection of refractory aggregates, realizing the reuse of waste resources, reducing raw material costs while reducing environmental pollution. At the same time, the recycled raw materials are inexpensive, the preparation process is simple, the production cost is effectively reduced, the market competitiveness of products is improved, and the green economy development of the casting industry is promoted;

[0017] (2) In the present invention, the coating with investment casting recycled shell film refractory material as the aggregate, relying on its unique composition and structure, has good air permeability, can effectively discharge the gas generated by the gasification of the foam plastic pattern, reduce the gas holes in the casting, ensure the dimensional accuracy and surface quality of the casting. At the same time, by adding raw materials such as calcium oxide and iron oxide red to optimize the aggregate performance and the reasonable combination of composite binders, and their synergistic effects, the deficiencies of single components are made up, and the comprehensive performance such as air permeability, suspension stability, high-temperature strength and toughness of the coating is significantly improved. Specific embodiments

[0018] To make the objectives, 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. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0019] The present invention will be further described below in conjunction with embodiments.

[0020] Embodiment 1: This embodiment provides a lost foam composite coating, a coating solution for cast iron lost foam, with the material being HT200 or QT400, and the products being flat plates and elbows. According to the refractory aggregate 90% (70 - 95% investment casting recycled mullite, 5 - 30% quartz powder, 1 - 3% graphite), 10% of the commercially available Guilin No. 5 binder, and additionally adding 0.1 - 0.3% of inorganic preservative A (calcium oxide) and 3% of sintering and peeling aid B (iron oxide red);

[0021] When mixing and preparing the lost foam composite coating, the following steps are included:

[0022] Step 1: Pretreatment of refractory aggregates: Crush the refractory materials of the investment casting recycled shell mold, and then mix the crushed shell mold raw materials with quartz powder or graphite (or a mixture of both), inorganic preservative A, and sintering release material B evenly in proportion. Mullite is used as the main component, and its particle size and purity need to meet the requirements of the coating performance. High-temperature calcination, pickling and other pretreatments can be carried out according to specific conditions to improve its refractory performance and purity;

[0023] Step 2: Dry mixing: Add the treated refractory aggregates (mullite, mixture, quartz powder or graphite) and binder into a mixer, and carry out dry mixing first. Control the mixing speed at a relatively low level, such as 200 - 500 r / min, and the mixing time is 10 - 30 min to preliminarily mix all components evenly;

[0024] Wet mixing: Add an appropriate amount of water and binder for wet mixing. The mixing speed can be appropriately increased during wet mixing, such as 500 - 1000 r / min, and the mixing time is 1 - 2.5 h. During the mixing process, the addition amounts of water and binder can be adjusted timely according to the performance requirements such as the viscosity and fluidity of the coating. The binder needs to be pre-dissolved or diluted and should be subjected to corresponding treatments before being added to the mixer;

[0025] Step 3: Grinding or ball milling: In order to further refine the refractory aggregate particles and improve the uniformity and performance of the coating, the wet-mixed coating can be put into a grinding machine or ball mill for grinding or ball milling. The grinding or ball milling time depends on the specific requirements of the coating, generally ranging from several hours to dozens of hours. After grinding or ball milling, the particle size in the coating is finer and more evenly distributed, which helps to improve the coating performance and refractory performance;

[0026] Step 4: High-speed stirring or homogenization treatment: Put the coating after grinding or ball milling into a mixer again for high-speed stirring or homogenization treatment. The stirring speed can reach above 1000 r / min, and the stirring time is 10 - 20 min. This step can make all components in the coating more evenly dispersed in water, and also helps to improve the rheology and thixotropy of the coating;

[0027] Step 5: Performance adjustment and testing: Adjust the performance of the coating according to the specific requirements of lost foam casting, and test the performance of the prepared lost foam composite coating, including testing indexes such as refractoriness, suspension stability, air permeability, strength, viscosity, thixotropy, etc. If it is found that the performance of the coating does not meet the requirements, the reasons should be analyzed and corresponding adjustments should be made until the expected performance indexes are achieved.

[0028] Step 6: Packaging and storage: Put the qualified paint into a suitable packaging container. The packaging should be well sealed to prevent the paint from being affected by the external environment during storage and deteriorating or performance degradation. Store the packaged paint in a cool, dry, ventilated warehouse, avoid direct sunlight and high temperature environment. At the same time, pay attention to prevent the paint from mechanical collision and extrusion, so as not to affect its performance and packaging integrity. During storage, check the paint regularly. If precipitation, agglomeration, deterioration, etc. are found, they should be handled in time;

[0029] In this embodiment, dry mixing is first performed for 15 to 30 minutes to prepare a dry powder coating. When used, the dry powder coating is wet mixed with water in a ratio of 10:5 for more than 2 hours. The Baume degree is tested. The Baume degree of the first layer is 68 to 72, the Baume degree of the second layer is 78 to 82, the pH value is above 8, and the mold drying temperature is 45 to 55°C. After drying, the coating has high strength and has a high-hardness ceramic sound when knocked. There is no powder loss but only scratches at the scratches of nails. The cast casting has a smooth appearance, and most of the coatings are automatically peeled off during the cooling process. The coating cost per ton is less than 1,300 yuan, which is much lower than the cost of 2,000 to 2,200 yuan / t of general cast iron coatings.

[0030] Example 2: This example provides a lost foam composite coating, which is used to prepare a lost foam cast steel coating. The material is low carbon steel, and the refractory aggregate component accounts for 89.5% (85-95% mullite recycled from investment casting waste shell membrane + 5% quartz powder), and the Guilin No. 5 binder purchased from the market accounts for 10.5%. In addition, according to 100 parts of refractory aggregate + binder, 0.1-0.3% of inorganic preservative A and 5% of sintering stripping material B (red iron oxide) are added. The mixing method is the same as that of Example 1. Since the casting temperature of the cast steel part is high, the refractoriness and coating strength need to be improved accordingly, and for the sake of sintering stripping properties, the proportion of red iron oxide added is appropriately increased. The coating detection method is the same as that of Example 1.

[0031] Embodiment 3: This embodiment provides a lost foam composite coating, which is a coating composed of different refractory materials. According to the material requirements of the casting, the first layer of the cast iron and cast steel lost foam coating can be the coating layer of Embodiment 1 or Embodiment 2. The second layer mainly serves as a reinforcement, while taking into account improving the air permeability. Refractory materials mainly composed of quartz sand can be used, and the particle size can be increased accordingly. Waste clay quartz sand or water glass sand can also be selected. If the casting requires a third layer of coating, Embodiment 3 can also be adopted. It is particularly suitable for castings with thick walls and three or more layers of coating, such as counterweight parts. In this way, the comprehensive cost of the coating is lower. It is estimated that the coating cost per ton can be less than 1,000 yuan, and it does not affect the quality of the casting.

[0032] Example 4: This example provides a lost foam composite coating, which uses the circulating water of a foaming machine as the carrier liquid. Some enterprises have the ability to manufacture foam molds by themselves. Although the circulating water has been cooled and enters the pool, its temperature is often higher than room temperature, and in severe cases, it is even above 45°C. Since there is residual coating in the coating pool and it is rarely cleaned up in time on the same day, the starch in the coating ferments quickly, resulting in the rapid deterioration of the newly added coating the next day. If a bactericide similar to formaldehyde is added, it is extremely harmful to the health of workers. All the preservatives purchased on the market are organic substances, which volatilize quickly when heated. After the coating has been in the pool for more than 8 hours, it begins to deteriorate, and the sour smell at the site is relatively obvious. Even if the thickness of the coating is increased, the desired effect of the coating cannot be achieved. Adding calcium oxide in proportion to the residual coating directly in the pool can effectively eliminate this hidden danger.

[0033] Test experiment: The lost foam composite coatings prepared in Examples 1 to 3 are denoted as Example Groups 1 to 3. To comprehensively evaluate the performance of the lost foam composite coatings prepared in the above examples, key indicators such as air permeability, suspension stability, high-temperature strength and toughness, and environmental protection performance are focused on. Using industry-standard test methods and procedures, the performance tests of the lost foam composite coatings in Example Groups 1 to 3 are carried out respectively, and the relevant data are recorded in Table 1;

[0034] Among them, the vacuum decompression method is used to conduct the air permeability test according to the relevant standards of "Test Method for Air Permeability of Lost Foam Casting Coatings"; the suspension stability is evaluated by observing the sedimentation of the coating within a certain period of time, and the suspension stability test is carried out with reference to "Determination Method for Suspension Stability of Coatings"; the high-temperature strength and toughness tests are carried out by combining the high-temperature flexural strength test and the thermal shock test. The high-temperature flexural strength is based on "Test Method for Flexural Strength of Refractory Materials", and the thermal shock test refers to "Test Method for Thermal Shock Stability of Refractory Materials"; according to the relevant standards of "Limits of Hazardous Substances in Coatings", the content of heavy metals (lead, cadmium, chromium, mercury) and the content of volatile organic compounds (VOC) in the coating are detected for environmental protection performance.

[0035] Table 1: Test Data Record Table

[0036]

[0037]

[0038] National standards stipulate that the lead content ≤ 90 mg / kg, the cadmium content ≤ 75 mg / kg, the chromium content ≤ 60 mg / kg, the mercury content ≤ 60 mg / kg, and the VOC content ≤ 120 g / L;

[0039] As can be seen from Table 1, through comprehensive performance testing of the lost foam composite coating prepared in Example Groups 1 to 3, it can be seen that the coating has excellent performance in terms of air permeability, suspension stability, high temperature strength and toughness, and environmental protection performance. Good air permeability is conducive to gas discharge and reduces the pores of the casting. High suspension stability ensures uniform use of the coating. High high temperature strength and toughness can resist the erosion of molten metal. The coatings of the three embodiments all meet environmental protection standards and are environmentally friendly. These properties indicate that the coating can be effectively used in lost foam casting production to improve casting quality and production efficiency, and has good application prospects.

[0040] In the present invention, by utilizing refractory aggregates mainly composed of mullite recycled from waste shell membranes of investment casting, adding inorganic substances with high-efficiency preservatives and materials with sintering and peeling properties, lost foam dry powder coating is formed. The dry mixed material of the lost foam coating made of the aggregate has a validity period of more than one year, and the wet mixed material has a validity period of more than half a year. The traditional refractory aggregate selection is broken through, and the refractory material of the recycled shell membrane of investment casting is used as the main refractory aggregate, so as to realize the recycling of waste resources, reduce the cost of raw materials and reduce environmental pollution, and open up a new way for the raw materials of lost foam coating; at the same time, the cost of recycled raw materials is low, the preparation process is simple, and no special equipment is required, which effectively reduces the production cost, improves the market competitiveness of products, promotes the development of green economy in the foundry industry, and achieves the purpose of significantly reducing the cost of coatings;

[0041] In addition, the coating with investment casting recycled shell film refractory material as aggregate has good air permeability due to its unique composition and structure. It can effectively discharge the gas generated by the vaporization of foam plastic pattern and reduce the pores of castings. The excellent suspension stability ensures that the coating is uniform during storage and use. The high high-temperature strength and toughness enable it to resist the erosion of molten metal and ensure the dimensional accuracy and surface quality of castings. The refractory aggregate components are precisely formulated, and the aggregate performance is optimized by adding raw materials such as calcium oxide and red iron oxide. The reasonable combination of composite binders and their synergistic effects make up for the deficiencies of single components and significantly improve the comprehensive performance of the coating such as air permeability, suspension stability, high-temperature strength and toughness.

[0042] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0043] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments described. Obviously, many modifications and variations can be made according to the content of this specification. These embodiments are selected and specifically described in this specification to better explain the principles and practical applications of the present invention, so that those skilled in the art can well understand and utilize the present invention. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. A lost foam composite coating, characterized in that, The lost foam composite coating uses the refractory material of the recycled shell film in investment casting as the refractory aggregate. The refractory aggregate includes mullite and a mixture containing inorganic preservative A and sintering stripping material B, and one or more of quartz powder and graphite are selected. The particle size of the mixture is 150-250 mesh. Mullite is the main component in the refractory aggregate, and its composition contains 36-50% alumina, 0-5% zirconia, 0.5-1.5% iron oxide, and 50-60% silica.

2. The lost foam composite coating according to claim 1, wherein The refractory aggregate and the lost foam binder are mixed in the ratio of composite aggregate: binder: water = 10:1:4-6 for more than 2 hours to obtain the lost foam composite coating.

3. The lost foam composite coating according to claim 1, characterized in that, The main component of the inorganic preservative A in the mixture is calcium oxide, and the inorganic preservative A accounts for 0.1-0.3% in the refractory aggregate. Its particle size is below 200 mesh, and the pH is greater than 13.

5.

4. The lost foam composite coating according to claim 1, wherein The main component of the sintering stripping aid B in the mixture is iron oxide red, and the particle size is below 200 mesh. The content of ferric oxide in the sintering stripping aid B is 50-65%, and the sintering stripping aid B accounts for 3-5% in the refractory aggregate.

5. The lost foam composite coating according to claim 1, wherein The pH of the refractory aggregate is 8.5-10.

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