Low-expansion, anti-veining, baked modified sand and method of making same

Abstract

The application relates to the technical field of foundry sand preparation, and discloses low-expansion anti-veining roasting modified sand and a preparation method thereof. The preparation method comprises the following steps: raw sand pretreatment, high-temperature roasting, hot-state homogenization, split-flow precooling, back-and-forth mixing, reset cooling, final cooling, impurity removal through screening and packaging. The first part of sand flow is first lowered to the low-temperature side of the quartz phase change, and then the second part of sand flow is used to provide heat, so that the mixed material is raised to the phase change sensitive area and kept, so as to adjust the phase change stress state in the cooling process of the roasting sand. The method does not depend on additional anti-veining agents or heterogeneous sand compounding, is favorable for reducing the generation of fine powder and expansion mutation of the sand particles when the sand particles are heated again, and improves the anti-veining stability of the roasting modified sand when the roasting modified sand is used as sand core sand or precoated sand base material.

Description

Technical Field

[0001] This invention relates to the field of casting sand preparation technology, and in particular to a low-expansion, anti-veining calcined modified sand and its preparation method. Background Technology

[0002] Silica sand for casting has a stable source, good refractoriness, and low cost, and is a commonly used raw sand in sand casting and sand core preparation. Its main component is quartz, which undergoes thermal expansion and crystal transformation under the action of molten metal at high temperature. When the expansion stress on the surface of the sand mold or sand core cannot be released in time, cracks, gap expansion or local protrusions are easily generated, and veins are formed on the surface of the casting. Iveta Vaskova et al. pointed out in "Examination of Behavior from Selected Foundry Sands with Alkali Silicate-Based Inorganic Binders" published in Metals that the main drawback of silica sand is the thermal expansion caused by the phase transformation of quartz.

[0003] Regarding vein defects, existing technologies have various treatment approaches. For example, Chinese patent CN101036932A discloses a raw sand additive to prevent vein defects in castings. This additive reacts with silica to alleviate grain boundary stress and absorb the volume expansion of quartz sand during phase transformation. Chinese patent CN114367628A discloses an anti-vein coating sand for turbine housings and its preparation method. This sand uses Inner Mongolia roasted sand, olivine sand, chromite sand, and an anti-vein agent combined with a phenolic resin system to reduce the expansion rate and improve vein defects. Chinese patent CN108275987A discloses a surface-modified quartz sand and its preparation method. This sand reduces the coefficient of thermal expansion through a coating layer containing alumina, silica, and other components.

[0004] The above-mentioned solutions mainly improve the anti-veining performance by replacing sand types, adding anti-veining components, or coating the surface of sand particles. However, for the process of preparing roasted sand using silica sand as raw material, the sand particles will also pass through the quartz phase transition temperature zone during the process of cooling from the high temperature exiting the kiln to the room temperature. Existing processes usually only focus on conventional indicators such as roasting outlet temperature, final discharge temperature, loss on ignition, gas generation, acid consumption value, and mud content, while the temperature path control of the quartz phase transition temperature zone during the cooling return process is insufficient.

[0005] In production practice, it has been found that when silica sand calcined sand is cooled from high temperature to room temperature, the shrinkage response of the surface and interior of the sand particles is not completely consistent. If only natural cooling or ordinary drum cooling is used after exiting the kiln, residual stress concentration or weakened areas are easily formed in the vicinity of the quartz phase transition temperature zone. These weakened areas may not show abnormalities in conventional quality indicators, but when the temperature is raised again during subsequent casting, they may become the starting point for crack propagation and local expansion, making it impossible for the low expansion characteristics of the calcined sand to be stably transformed into anti-vein properties. Summary of the Invention

[0006] The technical problem to be solved by this invention is: to address the problem of insufficient control of the cooling return temperature path in the existing silica sand roasting process, to provide a low-expansion anti-veining roasted modified sand and its preparation method, which suppresses the generation of fine powder and abrupt expansion of the phase transition zone when reheated.

[0007] To achieve the above objectives, this application adopts the following technical solution: a method for preparing low-expansion anti-veining calcined modified sand, comprising the following steps: S1: calcining silica sand raw material to obtain calcined sand with a kiln exit temperature of 870-930℃; S2: subjecting the calcined sand to hot homogenization treatment, and dividing the calcined sand after hot homogenization treatment into a first sand stream and a second sand stream; S3: cooling the first sand stream to 540-560℃, and maintaining the second sand stream at 610-640℃; S4: mixing the first sand stream and the second sand stream, raising the temperature of the mixture to 570-590℃, and maintaining the mixture in the range of 570-590℃ for 4-12 minutes; S5: cooling the mixture to 500-520℃, and then finally cooling it to 45-55℃ to obtain low-expansion anti-veining calcined modified sand.

[0008] Preferably, the silica sand raw material is subjected to impurity removal, mud removal, particle size separation, and particle size inspection before roasting.

[0009] Preferably, the particle size of the silica sand raw material is 40 / 70 mesh, 50 / 100 mesh, or 70 / 140 mesh.

[0010] Preferably, the material temperature during the hot homogenization process is maintained within the range of 780-850℃, and the homogenization time is 3-10 minutes.

[0011] Preferably, the first part of the sand flow is cooled to 540-560℃ using an insulated pre-cooling chamber, natural wind cooling, or low-volume dry air cooling.

[0012] Preferably, after the second part of the sand flow enters the insulation chamber, the insulation state or discharge speed of the insulation chamber is adjusted to keep the second part of the sand flow at 610-640℃.

[0013] Preferably, the mass ratio of the first part of the sand flow to the second part of the sand flow is 1:0.5-0.8.

[0014] Preferably, the mixing of the first part of the sand flow and the second part of the sand flow is carried out by one of the following methods: material turning mixing, rotary mixing, insulated hopper deflection mixing, or insulated buffer cylinder mixing.

[0015] Preferably, when the mixture is cooled to 500-520℃, a heat preservation and slow cooling method, low-volume dry air cooling or rotary buffer cooling method is adopted, and the average cooling rate is controlled at 3-8℃ / min.

[0016] A low-expansion, anti-veining calcined modified sand, wherein the low-expansion, anti-veining calcined modified sand is prepared by the above-described preparation method.

[0017] The technical effects and advantages of this invention are as follows:

[0018] In this invention, the roasted sand exiting the kiln undergoes hot homogenization, diversion, pre-cooling, recirculation mixing, and holding treatment. During the cooling return process, the silica sand is divided into a first sand stream and a second sand stream. The first sand stream is first cooled to the low-temperature side of the quartz phase transformation temperature, and then the homogeneous heat of the second sand stream is used to raise the mixture to 570-590℃ and maintain it. This allows the sand particles to undergo a controlled pre-cooling, recirculation, and holding process. Compared with ordinary natural cooling, unidirectional slow cooling, or ordinary hot sand remixing, this invention repositions and controls the phase transformation-sensitive stage during the cooling return process, which helps to suppress the formation of a weakening zone due to residual stress on the surface of the sand particles. Experimental results show that the roasted modified sand prepared by this invention produces less fine powder after thermal cycling, maintains good particle size retention after repeated thermal shock in the phase transformation zone, and exhibits low expansion abruptness upon reheating. When used as core sand, it can reduce veins, burrs, or local protrusion defects on the surface of castings. Attached Figure Description

[0019] The disclosure of this invention is illustrated with reference to the accompanying drawings. It should be understood that the drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention. In the drawings, the same reference numerals are used to refer to the same parts:

[0020] Figure 1 Bar charts showing the target particle size distribution of each group of sand samples;

[0021] Figure 2 This is a bar chart showing the relative range between groups of conventional quality indicators.

[0022] Figure 3 Add a bar chart of fine powder content for thermal cycling of each group of sand samples;

[0023] Figure 4 A bar chart showing the decrease in target particle size after repeated thermal shock in the phase transition zone of each sand sample group;

[0024] Figure 5 A bar chart showing the increase in the amount of material passing through a 100-mesh sieve after repeated thermal shock in the phase transition zone of each sand sample group;

[0025] Figure 6 Bar chart showing the abrupt expansion in the phase transition zone of each sand sample group;

[0026] Figure 7 This is a graph showing the linear expansion of some sand samples during the heating process.

[0027] Figure 8 A bar chart showing the percentage of vein defect area in the castings corresponding to each group of sand samples;

[0028] Figure 9 This is a bar chart showing the maximum vein height of the castings corresponding to each group of sand samples. Detailed Implementation

[0029] It is readily understood that, based on the technical solution of this invention, those skilled in the art can propose various interchangeable structural methods and implementations without altering the essential spirit of the invention. Therefore, the following detailed embodiments and accompanying drawings are merely illustrative examples of the technical solution of this invention and should not be considered as the entirety of the invention or as limitations or restrictions on the technical solution of this invention.

[0030] Without departing from the technical concept of this invention, those skilled in the art can make adaptive adjustments to the corresponding process parameters based on the original sand particle size, the type of calcining kiln, the capacity of the cooling equipment, and the product specification requirements.

[0031] This invention provides a method for preparing low-expansion, vein-resistant calcined modified sand, specifically including the following steps:

[0032] S1: The silica sand raw material is subjected to impurity removal, mud removal, particle separation and particle size inspection to obtain silica sand that meets the particle size requirements of foundry sand. The silica sand is sent into a roasting kiln for high-temperature roasting, and the temperature of the roasted sand exiting the kiln is controlled at 870-930℃.

[0033] S2: The calcined sand after exiting the kiln is subjected to hot homogenization treatment, and then the hot homogenized calcined sand is divided into the first sand stream and the second sand stream.

[0034] S3: Pre-cool the first part of the sand flow to reduce its temperature to 540-560℃; maintain the temperature of the second part of the sand flow within the range of 610-640℃;

[0035] S4: Mix the first part of the sand flow with the second part of the sand flow to raise the temperature of the mixture to 570-590℃ and maintain it within the range of 570-590℃ for 4-12 minutes; wherein, the mass ratio of the first part of the sand flow to the second part of the sand flow is adjusted according to their actual temperatures to keep the temperature of the mixture within the range of 570-590℃, and the mass ratio is 1:0.5-0.8;

[0036] S5: Cool the mixture to 500-520℃, then cool it to 45-55℃, and after screening to remove impurities, package it to obtain low-expansion anti-veining calcined modified sand.

[0037] Specifically, in S1, the particle size of the silica sand raw material can be 40 / 70 mesh, 50 / 100 mesh, 70 / 140 mesh, or other particle size specifications determined according to the requirements of casting sand. Among them, 40 / 70 mesh means that the sand particles are mainly distributed between a 40 mesh sieve and a 70 mesh sieve, 50 / 100 mesh means that the sand particles are mainly distributed between a 50 mesh sieve and a 100 mesh sieve, and 70 / 140 mesh means that the sand particles are mainly distributed between a 70 mesh sieve and a 140 mesh sieve.

[0038] In S2, the temperature of the hot homogenization process is maintained in the range of 780-850℃, and the homogenization time is 3-10 minutes. During the hot homogenization process, low-speed turning, material flow reversal, or buffer stacking are used to reduce the local temperature difference of the material.

[0039] In S3, the first part of the sand flow is pre-cooled to 540-560℃ using an insulated pre-cooling chamber, natural wind slow cooling, and low-volume dry air cooling. During the pre-cooling process, the first part of the sand flow is reduced from a high temperature state to below the quartz phase transition temperature.

[0040] The second part of the sand flow is maintained in a temperature range of 610-640℃, which is used to raise the temperature of the first part of the sand flow to 570-590℃ in the subsequent mixing process. The temperature of the first part of the sand flow and the second part of the sand flow can be controlled by temperature measurement at the discharge end of the silo, continuous temperature measurement or sampling temperature measurement.

[0041] In S4, the mixing method of the first part of the sand flow and the second part of the sand flow can be low drop turning, low speed rotation mixing, heat-insulated hopper baffle mixing or heat-insulated buffer cylinder mixing. The mixture is kept in the range of 570-590℃ for 4-12 minutes, so that the first part of the sand flow forms a short-range temperature rise under the heat action of the second part of the sand flow, and the internal temperature state of the mixture tends to be uniform.

[0042] In S5, the mixture is first cooled to 500-520℃ at a rate of 3-8℃ / min using methods such as heat preservation and slow cooling, low air volume dry air cooling, or rotary buffer cooling. Then, it is transferred to cooling drum, belt conveyor cooling equipment, cooling hopper, or other final cooling equipment to reduce the material temperature to 45-55℃.

[0043] The present invention also provides low-expansion anti-veining calcined modified sand prepared by the above method, wherein the calcined modified sand is 40 / 70 mesh, 50 / 100 mesh, 70 / 140 mesh or other casting sand particle size specifications, and can be used as coated sand base material, resin sand base material or sand core sand.

[0044] The present invention will be described in detail below with reference to specific embodiments. It should be noted that these embodiments are only used to explain the present invention and do not constitute any limitation on the scope of protection of the present invention. Those skilled in the art can make adaptive adjustments to the embodiments based on their understanding of the technical solutions of the present invention, and these adjustments still fall within the scope of protection of the present invention.

[0045] Example 1

[0046] This embodiment provides a method for preparing low-expansion, vein-resistant calcined modified sand, using 50 / 100 mesh silica sand as the raw sand, specifically including the following steps:

[0047] S1: The silica sand is subjected to impurity removal, mud removal and particle size testing in sequence. After removing stones, fine mud powder and other impurities, it is sent to the roasting kiln for high-temperature roasting. The material temperature at the discharge end of the roasting kiln is controlled at 890±10℃.

[0048] S2: The roasted sand from the kiln is fed into a hot homogenizing hopper with an insulation layer for short-term homogenization. The material is kept at 800±20℃ for 5 minutes. During the homogenization process, a low-drop turning method is used to make the material flow slowly in order to reduce the local temperature difference of the material exiting the kiln.

[0049] S3: The calcined sand after hot homogenization is divided into a first sand stream and a second sand stream. The first sand stream is sent to an insulated pre-cooling chamber and slowly cooled by low-volume dry air to reduce the temperature of the first sand stream to 550±5℃. The second sand stream is sent to another insulated chamber and the temperature of the second sand stream is maintained at 625±10℃ by adjusting the insulation status of the chamber and the discharge speed.

[0050] S4: The first and second sand streams are fed into the heat-insulated rotary mixing drum and mixed at a mass ratio of 1:0.65. The mixing drum is operated at a low speed to allow the materials to complete contact heat exchange under low impact conditions. After mixing, the material temperature rises to 580±5℃.

[0051] S5: The mixed material is placed in the heat-insulated rotary mixing drum and kept at 575-585℃ for 8 minutes. Then the material is cooled to 510±10℃ with low-volume dry air and then sent to the cooling drum for final cooling, so that the material temperature drops to 50±5℃. After final cooling, the material is screened, impurities are removed and packaged to obtain low-expansion anti-veining calcined modified sand.

[0052] Example 2

[0053] This embodiment provides a method for preparing low-expansion anti-veining roasted modified sand. The difference from Embodiment 1 is that a relatively low process window is used, specifically: the material temperature at the discharge end of the roasting kiln is controlled at 880±10℃.

[0054] After hot homogenization, the first part of the sand flow is pre-cooled to 542±2℃, and the temperature of the second part of the sand flow is controlled at 612±2℃. The first part of the sand flow and the second part of the sand flow are mixed at a mass ratio of 1:0.75.

[0055] After mixing, the material temperature rises to 572±2℃, and then is maintained in the range of 570-574℃ for 5 minutes. After the maintenance period, the material is gently cooled to 505±5℃, and then enters the cooling drum for final cooling to 50±5℃. After screening, impurity removal and packaging, low-expansion anti-veining calcined modified sand is obtained.

[0056] Example 3

[0057] This embodiment provides a method for preparing low-expansion anti-veining roasted modified sand. The difference from Embodiment 1 is that a relatively high process window is used, specifically: the material temperature at the discharge end of the roasting kiln is controlled at 900±10℃.

[0058] After hot homogenization, the first part of the sand flow is pre-cooled to 558±2℃, and the temperature of the second part of the sand flow is controlled at 638±2℃. The first part of the sand flow and the second part of the sand flow are mixed at a mass ratio of 1:0.60.

[0059] After mixing, the material temperature rises to 588±2℃, and is then maintained in the range of 586-590℃ for 12 minutes. After the maintenance period, the material is gently cooled to 515±5℃ and then cooled to 50±5℃ in a cooling drum. After screening, impurity removal and packaging, low-expansion anti-veining calcined modified sand is obtained.

[0060] Comparative Example 1

[0061] This comparative example provides a method for preparing calcined sand, which differs from Example 1 in that the calcined sand exiting the kiln is directly cooled naturally and then enters a cooling drum for final cooling to 50±5℃.

[0062] Comparative Example 2

[0063] This comparative example provides a method for preparing calcined sand. The difference from Example 1 is that after the calcined sand exiting the kiln is homogenized in a hot state, it is not subjected to diversion and mixing treatment, but is directly and slowly cooled to 580±5℃ and held for 8 minutes. After holding, the material is gently cooled to 510±10℃ and then enters the cooling drum for final cooling to 50±5℃.

[0064] Comparative Example 3

[0065] This comparative example provides a method for preparing calcined sand, which differs from Example 1 in that the calcined sand after hot homogenization is divided into a first sand stream and a second sand stream. The temperature of the first sand stream is controlled at 650±5℃, and the temperature of the second sand stream is controlled at 520±5℃. The first sand stream and the second sand stream are then mixed at a mass ratio of 1:1.15, and the temperature of the mixed material is controlled at 580±5℃. The mixed material is kept in the range of 575-585℃ for 8 minutes, then gently cooled to 510±10℃, and finally cooled to 50±5℃.

[0066] Comparative Example 4

[0067] This comparative example provides a method for preparing calcined sand. The difference from Example 1 is that after the calcined sand exiting the kiln is homogenized in a hot state, it is not subjected to diversion and mixing treatment. Instead, the material is pre-cooled to 550±5℃ and kept in the range of 550±5℃ for 8 minutes. After the holding period, the material is further cooled to 510±10℃ and then finally cooled to 50±5℃.

[0068] Comparative Example 5

[0069] This comparative example provides a method for preparing calcined sand. The difference from Example 1 is that after the first part of the sand stream and the second part of the sand stream are mixed, when the temperature of the mixture rises to 580±5℃, it is not kept in the range of 575-585℃ for 8 minutes, but the material is directly cooled to 510±10℃ and then finally cooled to 50±5℃.

[0070] Comparative Example 6

[0071] This comparative example provides a method for preparing calcined sand. The difference from Example 1 is that after the first part of the sand stream is pre-cooled to 550±5℃, the second part of the sand stream is not used for mixing. Instead, homogeneous calcined sand at a temperature of 25±5℃ is mixed with the first part of the sand stream at a mass ratio of 1:0.65. After mixing, the material does not rise back to 570-590℃, but continues to cool down, and then is finally cooled to 50±5℃.

[0072] Comparative Example 7

[0073] This comparative example provides a method for preparing calcined sand, which differs from Example 1 in that, after the first part of the sand stream is pre-cooled to 550±5℃, the temperature of the second part of the sand stream is controlled at 660±5℃, and the first part of the sand stream and the second part of the sand stream are mixed at a mass ratio of 1:1, so that the temperature of the mixed material is controlled at 605±5℃, and then maintained in the range of 600-610℃ for 8 minutes. After the maintenance is completed, the temperature is gently reduced to 510±10℃, and then finally cooled to 50±5℃.

[0074] To further verify the effect of the preparation method of the present invention on the thermal stability and anti-vein properties of calcined modified sand, the applicant used the sand samples obtained in the above examples and comparative examples as experimental objects for testing. Except for the different processing technology, the original sand particle size, final cooling temperature and screening and packaging conditions were kept consistent for each group of sand samples.

[0075] Experimental Example 1

[0076] This experimental example aims to confirm that the sand samples obtained from the examples and comparative examples are comparable in terms of particle size composition and conventional quality indicators, so as to eliminate the influence of basic quality differences on the subsequent thermal cycling stability and anti-veining verification results.

[0077] Sand samples obtained from Examples 1-3 and Comparative Examples 1-7 were used as experimental subjects. Each group of sand samples was sampled after final cooling, sieving, impurity removal and packaging. When sampling, five initial spot samples were first drawn from different packaging positions of the same group of sand samples, combined and thoroughly mixed, and then the quartering method was used to reduce the mass to the required mass for testing. Three parallel samples were set for each group of sand samples.

[0078] Particle size distribution was determined using a standard sieve array consisting of 40 mesh, 50 mesh, 70 mesh, 100 mesh, 140 mesh, and a sieve tray. Before testing, the sand sample was dried to constant weight at 105±5℃ and cooled to room temperature. 500.00 g of the sample was then weighed as the sieve sample. The sieve array was stacked in descending order of mesh size and sieved for 10 minutes on a mechanical vibrating sieve. The mass of the material retained in each sieve layer and the material passing through the sieve tray were weighed. For 50 / 100 mesh sand samples, the portion passing through the 50 mesh sieve and retained on the 100 mesh sieve was taken as the target particle size. The target particle size content was calculated, and the mass percentages of the material passing through the 50 mesh sieve and passing through the 100 mesh sieve were recorded. The results are shown in Table 1 and [Table data missing]. Figure 1 As shown.

[0079] Table 1. Detection results of particle size distribution of sand samples in each group

[0080]

[0081] From Table 1 and Figure 1It can be seen that the target particle size content of the sand samples obtained in Examples 1-3 and Comparative Examples 1-7 is 94.21%-94.70%, the content of material over 50 mesh sieve is 2.28%-2.58%, and the content of material under 100 mesh sieve is 3.01%-3.21%. The sand samples in each group are mainly composed of 50 / 100 mesh particles. The difference between the groups of target particle size content is small, and the standard deviation of parallel samples is also at a low level, indicating that the sand samples in each group are comparable in terms of particle size composition.

[0082] When testing the loss on ignition, take 10.000g of sand sample dried to constant weight at 105±5℃, place it in a porcelain crucible, and ignite it in a muffle furnace at 950±10℃ for 2 hours. After removing it, place it in a desiccator to cool to room temperature and weigh it. Calculate the loss on ignition based on the mass difference before and after ignition. When testing the gas emission, weigh 10.00g of dried sand sample, place it in the quartz boat of the gas emission test device, heat it at 850±10℃, record the gas volume collected within 180s, and convert it to mL / g based on the gas volume per unit mass of sand sample.

[0083] When testing the acid consumption value, weigh 50.00 g of dried sand sample, add 50.00 mL of 0.1000 mol / L hydrochloric acid standard solution, shake for 5 min, let stand for 30 min, and filter; take 25.00 mL of filtrate, titrate with 0.1000 mol / L sodium hydroxide standard solution to pH 7.00, and simultaneously perform a blank test. The difference in volume of sodium hydroxide standard solution consumed by the blank test and the sample filtrate is converted into the number of milliliters of hydrochloric acid consumed by 50.00 g of sand sample, which is taken as the acid consumption value.

[0084] When testing the mud content, 50.00 g of dried sand sample was weighed, 500 mL of water was added and stirred for 5 min. After standing for 2 min, the suspension was decanted. The supernatant was washed repeatedly until there was no obvious turbidity. The washed sand sample was then dried to constant weight at 105±5℃. The mud content was calculated based on the mass difference before and after washing. When testing the moisture content, 100.00 g of packaged sand sample was weighed and dried to constant weight at 105±5℃. The moisture content was calculated based on the mass difference before and after drying. The results are shown in Table 2.

[0085] Table 2 Results of routine quality index tests for sand samples in each group

[0086]

[0087] As shown in Table 2, the loss on ignition of each group of sand samples was 0.143%-0.156%, the gas generation was 1.50-1.58 mL / g, the acid consumption was 2.46-2.55 mL, the mud content was 0.155%-0.170%, and the moisture content was 0.073%-0.083%.

[0088] To further observe the fluctuation range of each routine quality indicator among different groups, the relative range between groups was calculated based on the data in Table 2. The results are shown below. Figure 2 As shown, the relative range is calculated by subtracting the minimum value from the maximum value and then dividing by the average value. It is used to reflect whether different treatment methods lead to differentiation in conventional quality indicators.

[0089] Combine Table 2 and Figure 2 It can be seen that Examples 1-3 and Comparative Examples 1-7 are at similar levels in terms of particle size distribution, loss on ignition, gas generation, acid consumption, mud content, and moisture content. This indicates that the differences in subsequent verification are not related to conventional quality indicators and should be evaluated in conjunction with the differences in the cooling return treatment methods of each group of sand samples.

[0090] Experiment Example 2

[0091] This experimental example aims to evaluate the formation of fine powder from the sand samples obtained in the examples and comparative examples after being reheated at high temperatures.

[0092] Sand samples obtained from Examples 1-3 and Comparative Examples 1-7 were used as experimental subjects. Each group of sand samples was sampled after final cooling, sieving, impurity removal and packaging. When sampling, five initial spot samples were first drawn from different packaging positions of the same group of sand samples, combined and thoroughly mixed, and then the quartering method was used to reduce the mass to the required mass for testing. Three parallel samples were set for each group of sand samples.

[0093] Before testing, each group of sand samples was dried to constant weight at 105±5℃ and cooled to room temperature. 500.00g of the samples were weighed as test samples. The test samples were placed on a 200-mesh standard sieve and sieved for 10 minutes on a mechanical vibrating sieve. The mass of the material passing through the 200-mesh sieve was collected and weighed as the mass of fine powder before thermal cycling. The sand sample retained on the 200-mesh sieve was then taken as the object of thermal cycling and spread evenly in a pre-weighed heat-resistant ceramic boat. The thickness of the sand layer was controlled at 10-15mm to reduce the impact of the difference in the thickness of the pile on the uniformity of heating.

[0094] The porcelain boat containing the sand sample was placed in a muffle furnace heated to 850±10℃ and kept warm for 10 minutes. After the warming was completed, the porcelain boat was removed and placed on a heat-resistant pad. It was then allowed to cool naturally to 25±5℃ at room temperature. The cooled sand sample was then placed on a 200-mesh standard sieve and sieved for 10 minutes under the same conditions as the initial sieve. The amount of material passing through the 200-mesh sieve after the thermal cycle was collected and weighed.

[0095] In this experimental example, the percentage of the material passing through the 200-mesh sieve before thermal cycling relative to the mass of a 500.00g sample was used as the content of the material passing through the 200-mesh sieve before thermal cycling; the percentage of the newly added material passing through the 200-mesh sieve after thermal cycling relative to the mass of a 500.00g sample was used as the newly added fine powder content after thermal cycling; the sum of the two was used as the cumulative fine powder content after thermal cycling. The test results are expressed as the average and standard deviation of three parallel samples, and the results are shown in Table 3 and [Table data missing]. Figure 3 As shown.

[0096] Table 3 Results of fine powder increase in each group of sand samples after thermal cycling

[0097]

[0098] From Table 3 and Figure 3 It can be seen that the content of the material under the 200-mesh sieve before thermal cycling of each group of sand samples is 0.181%-0.210%, with little difference. This indicates that the initial fine powder content of each group of samples before thermal cycling is at a similar level. This result is consistent with the conclusion in Experiment 1 that the particle size composition of each group of sand samples is relatively close, indicating that the difference in the newly added fine powder content after thermal cycling is not related to the difference in the initial fine powder content.

[0099] The newly added fine powder content during thermal cycling in the examples was 0.28%, 0.34%, and 0.26%, respectively, all lower than that of the comparative examples. To further illustrate the differences between Example 1 and the comparative examples, the reduction in the newly added fine powder content of Example 1 relative to the comparative examples was calculated based on the newly added fine powder content during thermal cycling in Table 3. The results are shown in Table 4. This reduction was calculated by subtracting the newly added fine powder content during thermal cycling of Example 1 from the newly added fine powder content during thermal cycling of the corresponding comparative examples, and then dividing by the newly added fine powder content during thermal cycling of the corresponding comparative examples.

[0100] Table 4 Comparison of the newly added fine powder content due to thermal cycling in Example 1 and various comparative examples

[0101]

[0102] As shown in Table 4, the content of fine powder generated by thermal cycling in Example 1 was reduced by 62.2%, 50.0%, and 54.8% compared to Comparative Examples 1, 2, and 3, respectively, indicating that the present invention can suppress the generation of fine powder after sand particles are reheated.

[0103] The newly added fine powder content of Comparative Example 4 was 0.53% after thermal cycling, which was higher than that of Example 1. This indicates that pre-cooling to below the quartz phase transition temperature alone cannot achieve the same fine powder control effect as Example 1. The newly added fine powder content of Comparative Example 5 was 0.49% after thermal cycling, which was still higher than that of Example 1. This indicates that maintaining the mixture in the range of 570-590℃ for a certain period of time is beneficial to reducing the generation of fine powder during thermal cycling.

[0104] Comparative Example 6 shows that the newly added fine powder content from thermal cycling is 0.78%, which is relatively high among all comparative examples. This indicates that the remixing of homogeneous sand at room temperature cannot replace the thermal effect of the sand flow in the second part of this invention. Comparative Example 7 shows that the newly added fine powder content from thermal cycling is 0.66%, which is higher than that of Example 1. This indicates that when the temperature of the mixed material deviates from the range of 570-590℃, the inhibitory effect on the generation of fine powder from thermal cycling weakens.

[0105] Experimental Example 3

[0106] This experimental example aims to evaluate the particle size retention of sand samples obtained from the examples and comparative examples after repeated passage through the quartz phase transition temperature range.

[0107] Sand samples obtained from Examples 1-3 and Comparative Examples 1-7 were used as experimental subjects. Each group of sand samples was sampled after final cooling, sieving, impurity removal and packaging. When sampling, five initial spot samples were first drawn from different packaging positions of the same group of sand samples, combined and thoroughly mixed, and then the quartering method was used to reduce the mass to the required mass for testing. Three parallel samples were set for each group of sand samples.

[0108] Before testing, each group of sand samples was dried to constant weight at 105±5℃ and cooled to room temperature. 500.00g of each sample was weighed as the test sample. The test sample was initially sieved using a standard sieve group consisting of 40 mesh, 50 mesh, 70 mesh, 100 mesh, 140 mesh and a base plate. The sieve time was 10min. The content of the target particle size of 50 / 100 mesh and the content of the 100 mesh sieve undersize were recorded before the thermal shock. After the initial sieve was completed, all the material retained in each sieve layer and the material undersize in the base plate were recovered and remixed. The mixture was then spread evenly in a heat-resistant ceramic boat with the sand layer thickness controlled at 10-15mm.

[0109] Prepare two box-type resistance furnaces. Set the temperature of one furnace to 620±10℃ and the temperature of the other furnace to 520±10℃. Place the ceramic boat containing the sand sample in the 620±10℃ resistance furnace for 5 minutes, then transfer it to the 520±10℃ resistance furnace for 5 minutes. This constitutes one phase change zone thermal shock cycle. Repeat this cycle 5 times. After the 5th cycle, remove the ceramic boat and place it on a heat-resistant pad. Allow it to cool naturally to 25±5℃ at room temperature.

[0110] After cooling, the sand samples were sieved again using the same sieve group and sieve time as the initial sieve. The content of the 50 / 100 mesh target particle size after thermal shock was recorded. The decrease in target particle size was calculated as the difference between the target particle size content before and after thermal shock. Three parallel samples from each group were independently sieved, subjected to repeated thermal shock, and sieved after thermal shock. The results are shown in Table 5. Figure 4 As shown.

[0111] Table 5. Changes in target particle size in the phase transition zone of sand samples before and after repeated thermal shock.

[0112]

[0113] Simultaneously, the content of material passing through the 100-mesh sieve was recorded. The increase in the content of material passing through the 100-mesh sieve was calculated as the difference between the content of material passing through the 100-mesh sieve after thermal shock and the content of material passing through the 100-mesh sieve before thermal shock. Three parallel samples from each group independently completed the initial sieving, repeated thermal shock, and post-thermal shock sieving. The results are shown in Table 6 and... Figure 5 As shown.

[0114] Table 6. Changes in the material content under 100 mesh sieve before and after repeated thermal shock in the phase transition zone of sand samples in each group.

[0115]

[0116] Combine Tables 5 and 6 Figure 4 and Figure 5 It can be seen that the target particle size reduction in Example 1 is 0.52%, indicating that the sand sample obtained in Example 1 can still maintain a main particle size of 50 / 100 mesh after repeatedly passing through the phase transition zone.

[0117] Comparative Example 4 showed a target particle size reduction of 0.96% and an increase in the amount of material passing through the 100-mesh sieve of 0.82%. Although Comparative Example 5 showed a recovery process, it did not maintain the temperature within the range of 570-590℃. Its target particle size reduction was 0.86% and the increase in the amount of material passing through the 100-mesh sieve of 0.74%. This indicates that when pre-cooling or recovery is performed without maintenance, the particle size retention ability of the sand sample after repeated thermal shock in the phase change zone is still weaker than that of Example 1.

[0118] Comparative Example 6 used room temperature homogeneous sand remixing, and its target particle size reduction was 1.40%, and the increase in 100-mesh sieve undersize was 1.24%; Comparative Example 7 had a target particle size reduction of 1.22% and an increase in 100-mesh sieve undersize of 1.06%, indicating that it is difficult to obtain the same phase change zone repeated thermal shock stability as the examples when remixing at room temperature or deviating from the swing temperature range.

[0119] The examples showed a lower decrease in target particle size and a lower increase in 100-mesh sieve material after repeated thermal shock in the phase change zone. Combined with the results of the thermal cycling fine powder increase detection in Experiment 2, it can be further shown that the treatment method of the present invention is beneficial to suppress the generation of fine powder by sand particles under repeated thermal cycling and phase change zone impact conditions.

[0120] Experiment Example 4

[0121] This experimental example aims to evaluate the abrupt expansion of sand samples obtained from the examples and comparative examples when they are reheated and pass through the phase transition zone.

[0122] Sand samples obtained from Examples 1-3 and Comparative Examples 1-7 were used as experimental subjects. Each group of sand samples was sampled after final cooling, sieving, impurity removal and packaging. When sampling, five initial spot samples were first drawn from different packaging positions of the same group of sand samples, combined and thoroughly mixed, and then the quartering method was used to reduce the mass to the required mass for testing. Three parallel samples were set for each group of sand samples.

[0123] Before testing, each group of sand samples was dried to constant weight at 105±5℃ and cooled to room temperature for later use. 5.00g of dried sand sample was weighed for each parallel sample and placed into a high-temperature alumina sample tube with an inner diameter of 12mm. The sample was gently shaken for 30s to ensure that the sand sample was stacked in a consistent manner. Then, the surface of the sand layer was gently pressed with a flat pressing plate to keep the height of the sample column within the range of 30±1mm before testing. The sample tube after loading was placed on the sample stage of the thermal expansion instrument, and the measuring push rod was adjusted to contact the surface of the sand sample. The load on the push rod was controlled at 20±2g.

[0124] During testing, the sample column height at room temperature was used as the reference height. The temperature was increased from room temperature to 850℃ in air at a rate of 5℃ / min. The instrument continuously recorded the change in sample column height, and the linear expansion rates corresponding to 540℃, 610℃, and 850℃ were read. The expansion change within the 540-610℃ range was considered the abrupt change in expansion in the phase transition region. The linear expansion rate was calculated by converting the measured height change with the reference height. The abrupt change in expansion in the phase transition region was obtained by subtracting the linear expansion rate at 540℃ from the linear expansion rate at 610℃. Three parallel samples from each group were independently prepared and tested. The results are expressed as mean and standard deviation. The test results are shown in Table 7 and [Table data missing]. Figure 6 As shown.

[0125] Table 7 Detection results of abrupt expansion in the phase transition zone of sand samples in each group.

[0126]

[0127] Combined with Table 7 and Figure 6 It can be seen that the expansion mutation amount in the phase transition region of Comparative Example 1 is 0.78%, Comparative Example 2 is 0.59%, and Comparative Example 3 is 0.65%, all of which are higher than the 0.32% of Example 1. This indicates that the sand samples obtained by ordinary roasting and cooling, unidirectional slow cooling, and ordinary hot sand remixing treatment still have a large expansion mutation when heated again through the 540-610℃ range.

[0128] The abrupt change in phase change zone expansion in Comparative Example 4 was 0.55%, and in Comparative Example 5 it was 0.50%, both higher than in Example 1. This indicates that simply pre-cooling the material to 550±5℃, or not maintaining it after raising it back to 580±5℃, cannot achieve the same effect as in Example 1 in controlling the abrupt change in phase change zone expansion. The abrupt change in phase change zone expansion in Comparative Example 6 was 0.82%, and in Comparative Example 7 it was 0.70%, indicating that when the homogeneous sand is remixed at room temperature and when the swing temperature deviates, the expansion change of the sand sample when it is heated again and passes through the phase change zone is still quite obvious.

[0129] To further illustrate the differences in the amount of expansion abruptly in the phase transition region between Example 1 and the comparative examples, the reduction in the amount of expansion abruptly in Example 1 relative to the comparative examples was calculated based on the data in Table 7. The results are shown in Table 8 and... Figure 7 As shown, where, Figure 7 The shaded area is in the range of 540-610℃, used to show the expansion changes of each group of sand samples near the quartz phase transition temperature.

[0130] Table 8 Comparison of abrupt expansion in the phase transition region between Example 1 and each comparative example.

[0131]

[0132] From Table 8 and Figure 7 It can be seen that the expansion abrupt change in the phase transition zone of Example 1 was reduced by 36.0%-61.0% compared with Comparative Examples 1-7. In the range of 540-610℃, the temperature rise expansion curve of Example 1 changed relatively gently, while the curves of Comparative Examples 1, 3 and 7 had larger slopes in this temperature range. This result is consistent with the results of Experimental Examples 2 and 3, indicating that when the sand sample obtained from the examples passes through the phase transition zone again, not only is less fine powder generated, but the expansion abrupt change is also lower.

[0133] This indicates that, under conditions where the conventional quality indicators of the sand samples in each group are similar, the amount of abrupt expansion in the phase transition zone of the sand samples obtained in Examples 1-3 is lower than that in each comparative example, which shows that the present invention is beneficial to reducing the abrupt expansion of sand particles when they are heated again and pass through the phase transition zone.

[0134] Experimental Example 5

[0135] This experimental example aims to evaluate the anti-veining performance of the sand samples obtained from the examples and comparative examples when used as core sand.

[0136] Sand samples obtained from Examples 1-3 and Comparative Examples 1-7 were used as experimental subjects. Each group of sand samples was sampled after final cooling, sieving, impurity removal and packaging. When sampling, five initial samples were first drawn from different packaging positions of the same group of sand samples, combined and thoroughly mixed, and then the fractions were reduced to the mass required for core making using the quartering method.

[0137] When preparing sand cores, all sand samples in each group used the same resin sand formula and the same core-making conditions. Based on 100 parts by weight of sand sample, 1.20 parts by weight of furan resin and 0.36 parts by weight of sulfonic acid curing agent were added. When mixing the sand, the sand sample was first added to the sand mixer and stirred at low speed for 30 seconds, then the curing agent was added and stirred for 45 seconds, followed by the addition of furan resin and stirring for another 90 seconds. The mixed resin sand was immediately loaded into a metal core box with a core box cavity size of 25mm×25mm×120mm. Strip sand cores were prepared using the same amount of sand added and the same compaction time. Six sand cores were prepared for each group. The sand cores were cured at 25±3℃ for 24 hours, demolded, dried at 105±5℃ for 30 minutes, and cooled to room temperature for later use.

[0138] The casting simulation was completed using the same test sand mold and the same casting conditions. Each group of sand cores was placed in the corresponding position in the test sand mold, so that the sand cores could be in contact with the molten metal. The casting material was gray cast iron melt, the casting temperature was controlled at 1420±20℃, the mass of molten metal poured in a single pour was 3.0±0.2kg, and the pouring time was controlled at 6-10s. After the casting was completed, the sand mold was cooled at room temperature for 2 hours before being opened. Floating sand and adhering substances on the surface of the casting were cleaned, and the inner surface of the casting formed in contact with the sand core was observed and measured.

[0139] When determining vein defects, the appearance of raised ridges, linear protrusions, or vein-like burrs extending along the sand core direction on the casting surface is considered a vein defect. For each casting, the presence of visible veins, the total vein length, the maximum vein height, and the percentage of the vein defect area are recorded. The total vein length is measured segment by segment along the vein direction using vernier calipers and then summed. The maximum vein height is measured using a depth gauge with an accuracy of 0.02 mm. The percentage of the vein defect area is calculated by taking images of the casting's inspection surface and then comparing the projected area of ​​the vein region with the area of ​​the inspection surface. The inspection results for each group of samples are shown in Table 9. Figure 8 and Figure 9 As shown.

[0140] Table 9. Simulation verification results of anti-veining sand cores for each group of sand samples

[0141]

[0142] From Table 9, Figure 8 and Figure 9 It can be seen that the sand cores prepared from the sand samples obtained in the examples have lower numbers of visible veins, total vein lengths, maximum vein heights, and vein defect area ratios on the surface of the corresponding castings under the same casting conditions than the comparative examples. This indicates that the present invention can improve the anti-vein performance of the sand used for sand cores under casting conditions by controlling the cooling return temperature path of the silica sand roasting sand.

[0143] The technical scope of this invention is not limited to the content described above. Those skilled in the art can make various modifications and variations to the above embodiments without departing from the technical concept of this invention, and all such modifications and variations should fall within the protection scope of this invention.

Claims

1. A method of producing a low-expansion, vein-resistant, baked modified sand, characterized by, Includes the following steps: S1: Calcine the silica sand raw material to obtain calcined sand with a kiln exit temperature of 870-930℃; S2: The calcined sand is subjected to hot homogenization treatment, and the calcined sand after hot homogenization treatment is divided into a first sand stream and a second sand stream. S3: Cool the first part of the sand flow to 540-560℃, and keep the second part of the sand flow at 610-640℃; S4: Mix the first part of the sand flow with the second part of the sand flow, raise the temperature of the mixture to 570-590℃, and keep the mixture in the range of 570-590℃ for 4-12 minutes. S5: Cool the mixture to 500-520℃, then cool it to 45-55℃ to obtain low-expansion, vein-resistant calcined modified sand.

2. The method of making a low expansion, vein resistant, baked modified sand of claim 1, wherein: The silica sand raw material is subjected to impurity removal, mud removal, particle size separation, and particle size inspection before roasting.

3. The method of claim 2, wherein the low expansion, anti-veining, fired modified sand is prepared by: The particle size of the silica sand raw material is 40 / 70 mesh, 50 / 100 mesh, or 70 / 140 mesh.

4. The method for preparing low-expansion, anti-veining calcined modified sand according to claim 1, characterized in that: The material temperature during the hot homogenization process is maintained within the range of 780-850℃, and the homogenization time is 3-10 minutes.

5. The method for preparing low-expansion, anti-veining calcined modified sand according to claim 1, characterized in that: The first part of the sand flow is cooled to 540-560℃ using an insulated pre-cooling chamber, natural wind slow cooling, or low-volume dry air cooling.

6. The method for preparing low-expansion, anti-veining calcined modified sand according to claim 1, characterized in that: After the second part of the sand flow enters the insulation chamber, the insulation status or discharge speed of the insulation chamber is adjusted to keep the second part of the sand flow at 610-640℃.

7. The method for preparing low-expansion, anti-veining calcined modified sand according to claim 1, characterized in that: The mass ratio of the first part of the sand flow to the second part of the sand flow is 1:0.5-0.

8.

8. The method for preparing low-expansion, anti-veining calcined modified sand according to claim 1, characterized in that: The mixing of the first part of the sand flow and the second part of the sand flow is carried out by one of the following methods: material turning mixing, rotary mixing, heat-insulated hopper deflection mixing, or heat-insulated buffer cylinder mixing.

9. The method for preparing low-expansion, anti-veining calcined modified sand according to claim 1, characterized in that: When the mixture is cooled to 500-520℃, heat preservation and slow cooling, low-volume dry air cooling or rotary buffer cooling are adopted, and the average cooling rate is controlled at 3-8℃ / min.

10. A low-expansion, vein-resistant calcined modified sand, characterized in that: The low-expansion, anti-veining calcined modified sand is prepared by the preparation method described in any one of claims 1-9.

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