Dynamic control method for water content in silica sol coating for precision casting

Abstract

The invention relates to the technical field of high-temperature alloy precision casting, in particular to a method for dynamically controlling the water content in silica sol coating for precision casting, which comprises the following steps: firstly, measuring the standard water content of the prepared silica sol coating which is put in a shell making chamber and is not consumed and applied; then dynamically measuring the water content in real time before the silica sol coating in consumption application is gelatinized; and according to comparison between the real-time water content measured each time and the reference water content, supplementing water with the corresponding mass into the current residual silica sol coating, and stirring to prepare the silica sol coating meeting the allowable range value of the reference water content. According to the method, the standard water content of the silica sol coating before consumption application is measured, the real-time water content is dynamically measured in the consumption application before gelatinization, water replenishing is guided according to the change of the real-time water content relative to the standard water content, and it is ensured that the water content of the silica sol coating in the consumption application period is kept stable; and the service life period is effectively prolonged.

Description

Technical Field

[0001] The invention relates to the technical field of high-temperature alloy precision casting, in particular to a method for dynamically controlling the water content in a silica sol coating used for high-temperature alloy precision casting. Background Art

[0002] High-temperature alloy parts are usually made by precision casting, which relies on ceramic mold shells as mold shells. It can be seen that the production and molding quality of ceramic mold shells are one of the key technical factors for obtaining high-quality high-temperature alloy parts.

[0003] Silica sol coating is a water-based coating, which is composed of binder silica sol, ceramic powder, wetting agent and defoaming agent. It has the technical characteristics of easy manufacturing, simple use, non-flammable, long storage period, high shell sintering strength and strong resistance to thermal deformation. It has been widely used in the shell making process of precision casting and is a common material for making ceramic mold shells.

[0004] In the shell making application, the water content of silica sol coating will continue to decrease due to the continuous evaporation of water, while the SiO2 content in the binder will increase accordingly. When the SiO2 concentration in the binder reaches a certain value, the coating will tend to gel or gel, and the coating performance will change greatly at this time, and the shell will not be made or the structural layer in the shell making process or the mold shell in the subsequent drying process will crack or peel. In severe cases, the binder will fail and the shell strength will be significantly reduced. In the later dewaxing, roasting, pouring and other processes, a large amount of high-temperature alloy waste will be generated. Therefore, in the consumption and application process of silica sol coating, how to ensure that the water content in the coating remains stable to balance the SiO2 content in the binder is the technical key to extending the service life cycle of silica sol coating.

[0005] Based on the particularity of the above silica sol coating, during the consumption and application process of the silica sol coating, water must be replenished in time to ensure that the water content in the coating remains stable.

[0006] Since the powder in the silica sol coating will absorb a certain amount of water, and the silica sol coating will be continuously consumed during use, its quality is constantly changing; in addition, the water in the silica sol coating will evaporate every moment. As a result, in the actual production process, the total mass and composition ratio of the silica sol coating are constantly changing, and it is impossible to simply and directly replenish water accurately. It is necessary to measure the performance of the silica sol coating that is constantly consumed in the application, so as to control its water content by targeted water replenishment.

[0007] Currently, there are two commonly used methods for measuring the performance of silica sol coatings and guiding water replenishment operations.

[0008] One is the viscosity method. The viscosity method is to test the viscosity of the silica sol coating in the consumption application to determine its viscosity change. When the viscosity of the silica sol coating increases significantly, the viscosity is adjusted within a certain range of values ​​by adding water. However, the water replenishment under this method is relatively passive, and it is impossible to relatively objectively and reliably guarantee the accuracy of the water content of the coating after water replenishment. This is because: when the viscosity of the silica sol coating is detected to increase, it indicates that the silica sol coating has a gelation trend. Under this premise, water replenishment is irreversible for the gelation trend that has occurred in the silica sol coating, and it only temporarily stops the further deterioration of the gelation trend. As for the effectiveness and timeliness of this suspension, it depends on the subjective experience of the operator. In addition, according to the current industry research on the gelation process of silica sol coatings, it is found that during the gelation process, the space network formed between the agglomerated particles will wrap some free water, which will result in the actual amount of free water contained in the silica sol coating after water replenishment being greater than the allowable free water content designed when the silica sol coating was formulated, which in turn leads to a significant decrease in the performance of the silica sol coating after water replenishment (such as coating thickness, density, etc.), and the ceramic shells prepared subsequently are prone to various defects. It can be seen that the objectivity, reliability and accuracy of the dynamic control of the water content in the silica sol coating guided by the viscosity method are obviously insufficient, which is not conducive to improving the long-term effectiveness of the service life cycle of the silica sol coating.

[0009] The second is the SiO2 content method. The SiO2 content method is to sample the silica sol coating in the consumption application, first use centrifugal equipment to separate the sample to obtain the silica sol clear liquid (that is, the powder in the silica sol coating and the silica sol are separated by high-speed centrifugation), and then use thermogravimetric analysis to measure the SiO2 content in the silica sol, and then calculate the water replenishment amount based on the SiO2 content. However, in the high-speed separation process, it is impossible to guarantee that all the water and silica sol particles are centrifuged into the silica sol clear liquid, nor that all the powder particles are separated from the silica sol clear liquid, resulting in a large operational error in the water content obtained, and this method is relatively rarely used in the industry. Summary of the invention

[0010] The technical purpose of the present invention is to provide a dynamic water content control method that can objectively, reliably and accurately guide the water replenishment of the silica sol coating, keep the water content in the silica sol coating stable, and effectively extend the service life cycle of the silica sol coating, in view of the particularity of the application of the above-mentioned silica sol coating in the high-temperature alloy precision casting process and the shortcomings of the existing technology.

[0011] In order to achieve the above technical purpose, the technical solution adopted by the present invention is a method for dynamically controlling the water content in a silica sol coating for precision casting, wherein the method for dynamically controlling the water content in the silica sol coating is:

[0012] First, the base water content of the prepared silica sol coating that has been placed in the shell making room and has not been consumed is measured;

[0013] Then, the real-time moisture content of the silica sol coating in the consumption application is dynamically measured before the gelation state occurs;

[0014] Then, according to the comparison between the real-time moisture content measured each time and the reference moisture content, a corresponding mass of water is added to the currently remaining silica sol coating, and the silica sol coating is stirred to form a silica sol coating that meets the allowable range of the reference moisture content.

[0015] More specifically, the method for dynamically controlling the water content in the silica sol coating comprises the following process steps:

[0016] Step 1. Determine the base water content of the prepared silica sol coating that is placed in the shell making room and not consumed, and record the initial mass of the silica sol coating and the initial liquid level height in the coating bucket;

[0017] Step 2. In the application of silica sol coating consumption before the gel state occurs, the real-time moisture content of the silica sol coating in the coating bucket is measured, and the real-time drop in the liquid level height in the coating bucket when the real-time moisture content is measured is recorded;

[0018] The real-time drop in the liquid level in the paint bucket is based on the initial liquid level in the paint bucket in step 1;

[0019] Step 3. Compare the real-time moisture content measured in step 2 with the reference moisture content in step 1, and use the allowable range of the measured real-time moisture content deviation from the reference moisture content as a reference to determine whether the remaining silica sol coating needs to be replenished;

[0020] If it is determined that the current remaining silica sol coating does not need to be replenished with water, then steps 2 and 3 are dynamically repeated to perform real-time moisture content measurement and judgment until it is determined that the current remaining silica sol coating needs to be replenished with water;

[0021] If it is determined that the remaining silica sol coating needs to be refilled with water, the shell making operation is suspended, and the following steps 4 to 9 are performed to complete the refilling operation in two steps;

[0022] Step 4. Take the real-time moisture content measured in step 2 as the first real-time moisture content, and calculate in combination with the real-time drop in the liquid level in the paint bucket in step 2 and the initial mass of the silica sol paint in step 1, the initial liquid level in the paint bucket and the reference moisture content to obtain the estimated mass of supplementary water in the silica sol paint when the first real-time moisture content is measured;

[0023] Step 5. Add water with a mass less than the estimated supplementary mass obtained in step 4 into the current remaining silica sol coating and stir it thoroughly;

[0024] Record the actual water replenishment quality for the first time;

[0025] Complete initial water replenishment operations;

[0026] Step 6. Conducting a second real-time moisture content measurement on the silica sol coating obtained in step 5;

[0027] Step 7. The mass of the first actual water replenishment is calculated in combination with the second real-time moisture content determined in step 6 and the first real-time moisture content determined in step 2 to obtain the mass of the remaining silica sol coating before the first actual water replenishment;

[0028] Step 8. The mass of the remaining silica sol coating before the first actual water replenishment is calculated in combination with the reference moisture content determined in step 1 and the second real-time moisture content determined in step 6 to obtain the mass of water that should be replenished for the second time on the basis of the first actual water replenishment;

[0029] Step 9. According to the mass of water to be replenished for the second time obtained in step 8, add the corresponding mass of water into the silica sol coating in step 5 and stir it thoroughly;

[0030] Complete precise water replenishment operations;

[0031] The silica sol coating with precise water filling is used for shell making;

[0032] During the continuous consumption and application of the silica sol coating, steps 2 to 9 are dynamically repeated to ensure that the silica sol coating in the coating bucket does not gel and that the water content is within the allowable range of the benchmark water content.

[0033] Furthermore, in step 4, the mass of the estimated supplementary water in the silica sol coating during the first real-time moisture content measurement is calculated to satisfy the following relationship:

[0034] M 估补 =M0×(H0-H1) / H0×(Sa);

[0035] Where M 估补 The estimated mass of supplementary water in the silica sol coating at the time of the first real-time moisture content measurement;

[0036] M0 is the initial mass of silica sol coating;

[0037] H0 is the initial liquid level height of silica sol paint in the paint bucket;

[0038] H1 is the height of the liquid level drop of the silica sol paint in the paint bucket when the real-time moisture content is measured for the first time;

[0039] S is the base moisture content;

[0040] a is the real-time moisture content measured for the first time.

[0041] Furthermore, in step 7, the mass of the remaining silica sol coating before the first actual water replenishment is calculated to satisfy the following relationship:

[0042] N=M 实补 ×(1-b) / (ba);

[0043] Where N is the mass of the remaining silica sol coating before the first actual water replenishment;

[0044] M 实补 is the mass of the first actual water replenishment; wherein, preferably M 实补 =M 估补 (50~98%);

[0045] a is the real-time moisture content measured for the first time;

[0046] b is the real-time moisture content measured for the second time.

[0047] Furthermore, in step 8, the mass of water to be replenished for the second time is calculated to satisfy the following relationship:

[0048] m = N (Sb) / (1-S);

[0049] In the formula, m is the mass of water to be replenished for the second time;

[0050] N is the mass of the remaining silica sol coating before the first actual water replenishment;

[0051] S is the base moisture content;

[0052] b is the real-time moisture content measured for the second time.

[0053] Furthermore, in step 5, after replenishing water, the stirring rate of the silica sol coating is 30 to 80 rpm, and the stirring time is at least 0.5 hour.

[0054] Furthermore, in step 9, after replenishing water, the stirring rate of the silica sol coating is 30 to 80 rpm, and the stirring time is at least 0.5 hour.

[0055] Furthermore, the allowable range of the reference moisture content satisfies the following relationship:

[0056] Y = S (1-K) ~ S;

[0057] Where, Y is the allowable range of the base moisture content;

[0058] S is the base moisture content;

[0059] K is the fluctuation value of the base moisture content, K≤5%.

[0060] Furthermore, the moisture content is determined by thermogravimetric analysis;

[0061] Thermogravimetric analysis is used to determine the water content in silica sol coatings, including the following process steps:

[0062] S1. Weigh the initial mass of the crucible itself using a weighing balance;

[0063] S2. Add a sample of silica sol coating into a crucible and weigh the mass of the crucible with sample before heating using a weighing balance;

[0064] S3. The crucible is heated at a temperature of 120 to 150 ° C and a heating time of 0.3 to 0.5 hours;

[0065] S4. Weigh the mass of the crucible with sample after heating using a weighing balance;

[0066] S5. Calculate the water content in the current silica sol coating sample using the following relationship:

[0067] Moisture content = (m2-m3) / (m2-m1)×100%;

[0068] m2 is the mass of the crucible with sample before heating;

[0069] m3 is the mass of the crucible with sample after heating;

[0070] m1 is the initial mass of the crucible itself;

[0071] The precision of the weighing balance is ≥0.001g.

[0072] Furthermore, the ambient temperature in the shell making room is 21-23°C and the ambient humidity is 57-60%;

[0073] The determination of the base moisture content is completed within 12 hours after the preparation of the unconsumed silica sol coating.

[0074] In determining whether the silica sol coating needs to be replenished with water, the real-time moisture content is measured at least twice a day.

[0075] The beneficial technical effect of the present invention is: the above technical measures are aimed at the particularity of the application of the above silica sol coating in the high-temperature alloy precision casting process. By measuring the baseline moisture content of the silica sol coating before consumption and application, and actively performing real-time moisture content dynamic measurement during the consumption and application process before gelation occurs, the water replenishment operation is guided by the change of the real-time moisture content compared with the baseline moisture content, and the gelation trend does not wait for the occurrence of the water content of the silica sol coating to ensure that the moisture content of the silica sol coating remains stable (or constant, and the constant is based on the allowable range value of the baseline moisture content as a reference standard) during the entire consumption and application cycle, thereby effectively extending the service life cycle of the silica sol coating.

[0076] Specifically, in the above technical measures, the water replenishment operation is triggered as the moisture content of the silica sol coating changes in the consumption application; the water replenishment operation is divided into two steps: the early estimated water replenishment and the later precise water replenishment. The mass of the remaining silica sol coating before water replenishment is calculated based on the real-time moisture content change after the early estimated water replenishment, so as to effectively grasp the mass of the remaining silica sol coating that cannot be accurately known in the consumption application and is constantly changing. Then, the accurate amount of water replenishment is calculated based on the accurately grasped mass of the remaining silica sol coating, combined with the benchmark moisture content of the silica sol coating when the finished product is prepared. In this way, the water replenishment operation is guided to be carried out relatively objectively, reliably and accurately, with strong operability, and the interference factors of operation errors or manual experience on the water replenishment operation are reduced as much as possible, or even avoided, so that the water replenishment operation can be carried out as accurately as possible, and the moisture content of the silica sol coating can be reliably guaranteed to remain stable throughout the consumption application cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0077] Figure 1 Schematic diagram of the change in liquid level height of silica sol paint in a paint bucket during consumption application.

[0078] Figure 2 This is a linear graph of the stability of silica sol coating, water evaporation and time. DETAILED DESCRIPTION

[0079] The present invention relates to the technical field of high-temperature alloy precision casting, and in particular to a method for dynamically controlling the water content in a silica sol coating for high-temperature alloy precision casting. Figure 1 indicate; Figure 1 The diagram shows the silica sol paint in the paint bucket. Under the condition that the diameter Φ of the paint bucket remains unchanged, the liquid level height changes with the consumption and application process. H0 is the initial liquid level height of the silica sol paint in the paint bucket, and H1 is the height of the liquid level drop of the silica sol paint in the paint bucket at a certain moment in the continuous consumption and application process (based on the liquid surface at the initial liquid level height).

[0080] It should be noted that the drawings of the present invention are schematic, and unnecessary details have been simplified to clarify the technical purpose of the present invention, so as to avoid blurring the technical solution of the present invention that contributes to the prior art. In addition, the expressions "approximately", "substantially" and the like regarding quantity or matching relationship in the following text mean that reasonable assembly errors and processing errors in the industry are allowed to exist, and do not literally express absolute quantities or matching relationships.

[0081] The present invention aims at the particularity of water loss when silica sol coating is used in high-temperature alloy precision casting process, and the technical demand of maintaining stable water content in the consumption application of silica sol coating. The quality of silica sol coating in the coating bucket is constantly changing during the consumption application process. Therefore, the following method of dynamic control of water content in silica sol coating based on water content detection is formed. The core technical measures of the control method are:

[0082] First, the base water content of the prepared silica sol coating that has been placed in the shell making room and has not been consumed is measured;

[0083] Then, the real-time moisture content of the silica sol coating in the consumption application is dynamically measured before the gelation state occurs;

[0084] Then, according to the comparison between the real-time moisture content measured each time and the reference moisture content, a corresponding mass of water is added to the currently remaining silica sol coating, and the silica sol coating is stirred to form a silica sol coating that meets the allowable range of the reference moisture content.

[0085] Specifically, the control method includes the following specific process steps:

[0086] Step 1. Prepare silica sol coating using a publicly available silica sol coating formula;

[0087] Usually, the formula of silica sol coating contains two key components, namely high-purity corundum powder and silica sol; the Al2O3 content in the corundum powder is above 99%, and the mesh number of the corundum powder is about 325 mesh; the average particle size of the silica sol is about 8-14nm, the pH value is 8.5-10.5, the SiO2 content is about 30-35wt.%, and the Na2O content is ≤0.5wt.%; the powder-liquid mass ratio of corundum powder to silica sol is 3.0-3.5:1;

[0088] The prepared silica sol coating A is placed in the shell making room, and the ambient temperature range in the shell making room is usually controlled at 21-23°C, and the ambient humidity range is usually controlled at 57-60%;

[0089] The prepared silica sol coating A is in the state of being used before consumption, especially within 12 hours (the sooner the better) after the preparation is completed (including sufficient stirring, generally sufficient stirring in the preparation means continuous stirring for 12 to 24 hours; the preparation completion mentioned below refers to the coating after sufficient stirring), the water content in the silica sol coating is determined by thermogravimetric analysis, and the water content is used as the reference water content S;

[0090] The mass of the prepared silica sol coating A in the unconsumed application state can be accurately known, and the liquid level height in the coating bucket can also be accurately known. Therefore, the initial mass M0 of the prepared silica sol coating A in the unconsumed application state and the initial liquid level height H0 in the coating bucket should be recorded;

[0091] Step 2. To ensure that the water content of the silica sol coating placed in the shell making room remains stable and to slow down or even prevent the gelling trend, the real-time water content of the silica sol coating should be dynamically measured every day after the completion of the benchmark water content measurement. The frequency of dynamic measurement of the real-time water content is at least twice a day, preferably once every 4 hours;

[0092] That is, in the application of silica sol paint consumption before the gel state occurs, the moisture content of the silica sol paint in the paint bucket is measured in real time at a set frequency;

[0093] Each time the real-time moisture content is measured, the real-time drop in the liquid level height H1 in the paint bucket at that time should be recorded; the real-time drop in the liquid level height H1 in the paint bucket is based on the liquid surface of the initial liquid level height H0 in the paint bucket in step 1;

[0094] Step 3. Compare the real-time moisture content measured in step 2 with the reference moisture content S in step 1, and use the allowable range value Y of the measured real-time moisture content deviating from the reference moisture content S as a reference to determine whether the current remaining silica sol coating B needs to be replenished;

[0095] Among them, the allowable range value Y of the reference moisture content S satisfies the following relationship:

[0096] Y = S (1-K) ~ S;

[0097] Where, Y is the allowable range of the base moisture content;

[0098] S is the base moisture content;

[0099] K is the fluctuation value of the base moisture content;

[0100] K is taken as the value of the set fluctuation range, that is, on the basis of the reference moisture content S, negative fluctuation of K is allowed; of course, this fluctuation value is set according to the requirements for moisture content control in silica sol coatings. The smaller the value, the higher the accuracy of moisture content control, but the requirement for water replenishment frequency increases. On the contrary, the accuracy requirement and water replenishment frequency decrease, but the timeliness of grasping the change of gelation trend is easily ignored. Generally, it should not exceed 5% (for example, 5% of the reference moisture content S, 3% of the reference moisture content S or 1% of the reference moisture content S, etc.);

[0101] According to the above comparison and judgment method, if the measured real-time moisture content is within the allowable range value Y of the reference moisture content S (i.e., lower than the reference moisture content S, but within the lower limit of the allowable range value Y), it indicates that the water loss in the current remaining silica sol coating B is within the allowable range and no water replenishment is required, that is, it is determined that the current remaining silica sol coating B does not need water replenishment, and then dynamically repeat steps 2 and 3 to perform real-time moisture content measurement and judgment until it is determined that the current remaining silica sol coating needs to be replenished;

[0102] According to the above comparison and judgment method, if the measured real-time moisture content exceeds the allowable range value Y of the reference moisture content S (that is, it is lower than the lower limit range of the allowable range value Y of the reference moisture content S, and whether the lower limit value itself is included is determined according to the setting requirements of the working environment), it indicates that the water loss in the current remaining silica sol coating B exceeds the allowable range and needs to be replenished, that is, it is determined that the current remaining silica sol coating B needs to be replenished. At this time, the shell making operation is suspended, and the silica sol coating in the coating bucket is in a non-consumable static state. The following steps 4 to 9 are executed to complete the water replenishment operation in two times;

[0103] Step 4. Take the real-time water content that triggers the water replenishment operation condition measured in step 2 as the first real-time water content a, and calculate the estimated replenishment water mass M in the remaining silica sol coating B at the time of the first real-time water content a by combining the real-time drop in the coating bucket height H1 in step 2 and the initial mass M0 of the silica sol coating in step 1, the initial liquid level height H0 in the coating bucket and the reference water content S. 估补 ;

[0104] Among them, the estimated mass M of the supplementary water in the remaining silica sol coating B when the first real-time moisture content a is measured 估补 The calculation satisfies the following relationship:

[0105] M 估补 =M0×(H0-H1) / H0×(Sa);

[0106] Where M 估补 The estimated mass of supplementary water in the silica sol coating at the time of the first real-time moisture content measurement;

[0107] M0 is the initial mass of silica sol coating;

[0108] H0 is the initial liquid level height of silica sol paint in the paint bucket;

[0109] H1 is the height of the liquid level drop of the silica sol paint in the paint bucket when the real-time moisture content is measured for the first time;

[0110] S is the base moisture content;

[0111] a is the real-time moisture content measured for the first time;

[0112] Step 5. Use the estimated make-up water M calculated in step 4 估补 As a reference standard, the mass is less than M 估补 of water (i.e., the mass of the actual supplemented water) is added to the currently remaining silica sol coating B; stirring is continued for at least 0.5 hour (e.g., 0.5 hour, 1 hour, or 2 hours) at a stirring rate of about 30 to 80 rpm (e.g., 30 rpm, 50 rpm, or 80 rpm, etc.) to fully mix the silica sol coating after replenishment, thereby obtaining a silica sol coating C;

[0113] Record the mass M of the first actual water replenishment 实补 ;

[0114] Complete initial water replenishment operations;

[0115] The reason why the water quality M is not supplemented according to the estimated 估补 The actual water replenishment is carried out because the actual mass of the remaining silica sol coating B cannot be accurately known. The estimated mass of replenished water M is calculated. 估补 It is too theoretical and may have actual calculation errors. According to the actual water replenishment, the water content measured after water replenishment may exceed the upper limit of the allowable range of the benchmark water content (i.e., the benchmark water content S), resulting in the water content in the silica sol coating being excessive and irreversible. Therefore, the mass of the supplementary water M is estimated. 估补 The mass of the first actual replenished water M 实补 The upper limit reference standard for the first actual replenishment water quality M 实补 Provide guidance, the quality of water actually replenished for the first time M 实补 The value is usually the estimated quality of the make-up water M 估补 50-98% of M 实补 =(50~98%)M 估补 , for example, M 实补 =50%M 估补 、M 实补 =70%M 估补 or M 实补 =98%M 估补 wait;

[0116] Step 6. Perform a second measurement of the real-time moisture content b of the silica sol coating C obtained in step 5 by thermogravimetric analysis;

[0117] Step 7. Use the actual water quality M for the first replenishment. 实补 , combined with the second real-time moisture content b measured in step 6 and the first real-time moisture content a measured in step 2, the mass N of the remaining silica sol coating B before the first actual water replenishment is obtained;

[0118] The calculation of the mass N of the remaining silica sol coating B before the first actual water replenishment satisfies the following relationship:

[0119] N=M 实补 ×(1-b) / (ba);

[0120] Where N is the mass of the remaining silica sol coating before the first actual water replenishment;

[0121] M 实补 The quality of the first actual water replenishment;

[0122] a is the real-time moisture content measured for the first time;

[0123] b is the real-time moisture content measured for the second time;

[0124] It can be seen that the mass M of the first actual water replenishment determined in steps 4 and 5 above is 实补 In fact, it is a prerequisite for converting the mass of the remaining silica sol coating B before the first actual water replenishment, so as to accurately know the mass N of the remaining silica sol coating B that has been consumed and needs to be replenished but has not yet been replenished;

[0125] Step 8. The mass N of the remaining silica sol coating B before the first actual water replenishment is combined with the reference moisture content S measured in step 1 and the second real-time moisture content b measured in step 6 to calculate the mass m of water that should be replenished for the second time on the basis of the first actual water replenishment;

[0126] The calculation of the mass m of water to be replenished for the second time satisfies the following relationship:

[0127] m = N (Sb) / (1-S);

[0128] In the formula, m is the mass of water to be replenished for the second time;

[0129] N is the mass of the remaining silica sol coating before the first actual water replenishment;

[0130] S is the base moisture content;

[0131] b is the real-time moisture content measured for the second time;

[0132] Step 9. Based on the mass m of water to be supplemented calculated in step 8, add the corresponding mass of water to the silica sol coating C in step 5; stir continuously for at least 0.5 hour (e.g., 0.5 hour, 1 hour, or 2 hours) at a stirring rate of about 30 to 80 rpm (e.g., 30 rpm, 50 rpm, or 80 rpm, etc.) to fully mix the silica sol coating after water supplementation to obtain silica sol coating D;

[0133] Complete precise water replenishment operations;

[0134] The silica sol coating D with precise water replenishment is used for shell making;

[0135] It can be seen that the above method uses the mass N of the remaining silica sol coating B as a benchmark, combined with the benchmark moisture content S to determine the precise mass of water to be supplemented, so as to ensure that the moisture content of the silica sol coating after supplementation meets the allowable range value of the benchmark moisture content, and is relatively objective, reliable and accurate.

[0136] Since the silica sol paint in the paint bucket is continuously consumed before it is completely consumed, during the continuous consumption and application of the silica sol paint, steps 2 to 9 are dynamically repeated according to the set detection frequency and trigger water replenishment conditions to ensure that the silica sol paint in the paint bucket does not gel and the water content is within the allowable range of the benchmark water content.

[0137] In the above control method, the water content is determined by thermogravimetric analysis. The water content in the silica sol coating is determined by thermogravimetric analysis, including the following specific process steps:

[0138] S1. Weigh the initial mass of the crucible itself using a weighing balance;

[0139] S2. Add a sample of silica sol coating into a crucible and weigh the mass of the crucible with sample before heating using a weighing balance;

[0140] S3. The crucible is heated at a temperature ranging from 120 to 150 ° C (eg, 120 ° C, 130 ° C, 140 ° C or 150 ° C, etc.), and a heating time ranging from 0.3 to 0.5 hours (eg, 0.3 hours, 0.4 hours or 0.5 hours, etc.);

[0141] S4. Weigh the mass of the crucible with sample after heating using a weighing balance;

[0142] S5. Calculate the water content in the current silica sol coating sample using the following relationship:

[0143] Moisture content = (m2-m3) / (m2-m1)×100%;

[0144] m2 is the mass of the crucible with sample before heating;

[0145] m3 is the mass of the crucible with sample after heating;

[0146] m1 is the initial mass of the crucible itself.

[0147] The accuracy of the above weighing balance is ≥ 0.001g.

[0148] To summarize the technical logic of the present invention, under stable process conditions, the evaporation area of ​​water in the silica sol coating, ambient temperature, ambient humidity, wind speed and coating stirring speed are basically unchanged, the coating composition is stable and the amount of water evaporation is linearly related to time. Figure 2 As shown. The water content in the initial coating is measured by thermogravimetric analysis as the standard value. At any time during the use of the coating, the total amount of remaining coating can be calculated by using the parameter method (adding a certain amount of parameter water) and the water content values ​​in the coating before and after adding water. The required amount of water is calculated based on the standard water content and the water is added to the standard water content to ensure that the control of the water content in the coating is objective, reliable and accurate, and then the silica sol gelation process in the coating is controlled to ensure that the coating has qualified performance.

[0149] The above control method of the present invention has been implemented through application tests.

[0150] Several embodiments are selected as follows to further illustrate the technical solution of the present invention.

[0151] Example 1

[0152] The silica sol coating A was prepared by conventional process, with a weight of 21.2 kg.

[0153] Silica sol coating A is prepared by mixing high-purity corundum powder and silica sol. The Al2O3 content in the corundum powder is greater than 99.5%, and the mesh size of the corundum powder is 325 mesh; the average particle size of the silica sol is 10nm, the pH value is 8.9, the SiO2 content is 30wt.%, the Na2O content is ≤0.05wt.%, and the powder-liquid mass ratio is 3.2:1.

[0154] Two hours after the coating was stirred and prepared, the water content in the coating was measured by thermogravimetric analysis. The precision of the weighing balance was 0.001g. The specific measurement method was as follows:

[0155] Weigh the original mass m1 of the alumina crucible to be 24.134 g;

[0156] After adding the slurry, the mass m2 is 28.384 g;

[0157] The heating temperature is 130°C and the heating time is 0.5 hours;

[0158] Then weigh the mass of the crucible and slurry m3 to be 27.676g;

[0159] The moisture content calculated by the relationship (m2-m3) / (m2-m1)×100% is 16.66%, and this value is used as the reference moisture content S.

[0160] The allowable fluctuation value of the reference moisture content S is set to 5% of S, that is, the allowable range value of the reference moisture content (retain two decimal places) is 15.83% to 16.66%.

[0161] Silica sol coating consumption application. After 7 days, the water content a in the coating was measured by thermogravimetric analysis and was 13.2%. The real-time water content has deviated from the allowable range of the benchmark water content, and water replenishment is required.

[0162] After calculation, the remaining silica sol coating B needs to be replenished with water M 估补 =M0×(H0-H1) / H0×(Sa)=514g. Add water M 实补 The amount of water added was 500 g (about 97% of the estimated water replenishment mass). After stirring for 0.5 hours, the water content b in the silica sol coating C was measured to be 15.9%.

[0163] According to the parameter water M 实补 It is calculated that the total mass of the remaining silica sol coating B at this time is N=M(1-b) / (ba)=500(1-15.9%) / (15.9%-13.2%)=15574g.

[0164] After calculation, the amount of water to be added subsequently is m=N(Sb) / (1-S)=15574(16.66%-15.9%) / (1-16.66%)=142.0g.

[0165] The water to be supplemented later was added to the silica sol coating C and stirred for 0.5 hours. The actual water content in the silica sol coating D was verified by thermogravimetric analysis to be 16.61%, which was within the allowable range of the benchmark water content of 15.83% to 16.66%, and the amount of water supplemented in the coating was accurately controlled.

[0166] Example 2

[0167] Silica sol coating A was prepared in an amount of 25 kg using conventional technology.

[0168] Silica sol coating A is prepared by mixing high-purity corundum powder and silica sol. The Al2O3 content in the corundum powder is greater than 99.5%, and the mesh size of the corundum powder is 325 mesh; the average particle size of the silica sol is 10nm, the pH value is 8.9, the SiO2 content is 30wt.%, the Na2O content is ≤0.5wt.%, and the powder-liquid mass ratio is 3.0:1.

[0169] 0.1 hour after the paint is stirred, the water content in the paint is measured by thermogravimetric analysis. The precision of the weighing balance is 0.001g. The specific measurement method is:

[0170] Weigh the original mass m1 of the alumina crucible to be 23.365 g;

[0171] After adding the slurry, the mass m2 is 25.384 g;

[0172] The heating temperature is 150°C and the heating time is 0.3 hours;

[0173] Then weigh the mass of the crucible and slurry m3 to be 25.031g;

[0174] The moisture content calculated by the relationship (m2-m3) / (m2-m1)×100% is 17.48%, and this value is used as the reference moisture content S.

[0175] The allowable fluctuation value of the reference moisture content S is set to 3% of S, that is, the allowable range value of the reference moisture content (retain two decimal places) is 16.96% to 17.48%.

[0176] Consumption and application of silica sol coating. After 5 days, the water content a in the coating was measured by thermogravimetric analysis and was 15.4%. The real-time water content has deviated from the allowable range of the benchmark water content and water replenishment is required.

[0177] After calculation, the remaining silica sol coating B needs to be replenished with water M 估补 =M0×(H0-H1) / H0×(Sa)=495g. Add water M 实补 The amount of water added was 400 g (approximately 81% of the estimated water replenishment mass). After stirring for 2 hours, the water content b in the silica sol coating C was measured to be 16.8%.

[0178] According to the parameter water M 实补 It is calculated that the total mass of the remaining silica sol coating B at this time is N=M(1-b) / (ba)=400(1-16.8%) / (16.8%-15.4%)=23771g.

[0179] After calculation, the amount of water to be added subsequently is m=N(Sb) / (1-S)=23771(17.48%-16.8%) / (1-17.48%)=195.9g.

[0180] The water to be supplemented later was added to the silica sol coating C and stirred for 2 hours. The actual water content in the silica sol coating D was verified by thermogravimetric analysis to be 17.40%, which was within the allowable range of the base water content of 16.96% to 17.48%, and the amount of water supplemented in the coating was accurately controlled.

[0181] Example 3

[0182] Silica sol coating A was prepared in an amount of 25 kg using conventional technology.

[0183] Silica sol coating A is prepared by mixing high-purity corundum powder and silica sol. The Al2O3 content in the corundum powder is greater than 99.5%, and the mesh size of the corundum powder is 325 mesh; the average particle size of the silica sol is 10nm, the pH value is 8.9, the SiO2 content is 30wt.%, the Na2O content is ≤0.5wt.%, and the powder-liquid mass ratio is 3.0:1.

[0184] 12 hours after the paint was stirred, the water content in the paint was measured by thermogravimetric analysis. The precision of the weighing balance was 0.001g. The specific measurement method was:

[0185] Weigh the original mass m1 of the alumina crucible to be 24.658 g;

[0186] After adding the slurry, the mass m2 is 26.986 g;

[0187] The heating temperature is 120°C and the heating time is 0.5 hours;

[0188] Then weigh the crucible and slurry mass m3 to be 26.578g;

[0189] The moisture content calculated by the relationship (m2-m3) / (m2-m1)×100% is 17.50%, and this value is used as the reference moisture content S.

[0190] The allowable fluctuation value of the reference moisture content S is set to 3% of S, that is, the allowable range value of the reference moisture content (retain two decimal places) is 16.96% to 17.50%.

[0191] Consumption and application of silica sol coating. After 14 days, the moisture content a in the coating was measured by thermogravimetric analysis and was 12.4%. The real-time moisture content has deviated from the allowable range of the benchmark moisture content and water replenishment is required.

[0192] After calculation, the remaining silica sol coating B needs to be replenished with water M 估补 =M0×(H0-H1) / H0×(Sa)=1035g. Add water M 实补 The amount of water added was 1000 g (approximately 97% of the estimated water replenishment mass). After stirring for 2 hours, the water content b in the silica sol coating C was measured to be 16.5%.

[0193] According to the parameter water M 实补 It is calculated that the total mass of the remaining silica sol coating B at this time is N=M(1-b) / (ba)=1000(1-16.5%) / (16.5%-12.4%)=20365.9g.

[0194] After calculation, the amount of water to be added subsequently is m=N(Sb) / (1-S)=20365.9(17.50%-16.5%) / (1-17.50%)=246.9g.

[0195] The water to be supplemented later was added to the silica sol coating C and stirred for 2 hours. The actual water content in the silica sol coating D was verified by thermogravimetric analysis to be 17.49%, which was within the allowable range of the benchmark water content of 16.96% to 17.48%, and the amount of water supplemented in the coating was accurately controlled.

[0196] Example 4

[0197] The silica sol coating A was prepared by conventional process, with a weight of 21.2 kg.

[0198] Silica sol coating A is prepared by mixing high-purity corundum powder and silica sol. The Al2O3 content in the corundum powder is greater than 99.5%, and the mesh size of the corundum powder is 325 mesh; the average particle size of the silica sol is 10nm, the pH value is 8.9, the SiO2 content is 30wt.%, the Na2O content is ≤0.05wt.%, and the powder-liquid mass ratio is 3.2:1.

[0199] 5 hours after the paint was stirred, the water content in the paint was measured by thermogravimetric analysis. The precision of the weighing balance was 0.001g. The specific measurement method was:

[0200] Weigh the original mass m1 of the alumina crucible to be 24.535 g;

[0201] After adding the slurry, the mass m2 is 28.781 g;

[0202] The heating temperature is 130°C and the heating time is 0.5 hours;

[0203] Then weigh the mass of the crucible and slurry m3 to be 28.074g;

[0204] The moisture content calculated by the relationship (m2-m3) / (m2-m1)×100% is 16.65%, and this value is used as the reference moisture content S.

[0205] The allowable fluctuation value of the reference moisture content S is set to 5% of S, that is, the allowable range value of the reference moisture content (retain two decimal places) is 15.82% to 16.65%.

[0206] Silica sol coating consumption application. After 24 days, the moisture content a in the coating was measured by thermogravimetric analysis and was 14.76%. The real-time moisture content has deviated from the allowable range of the benchmark moisture content, and water replenishment is required.

[0207] After calculation, the remaining silica sol coating B needs to be replenished with water M 估补=M0×(H0-H1) / H0×(Sa)=182g. Add water M 实补 The water content b of the silica sol coating C was 100.4 g (about 55% of the estimated water replenishment mass). After stirring for 0.5 hours, the water content b in the silica sol coating C was measured to be 15.57%.

[0208] According to the parameter water M 实补 It is calculated that the total mass of the remaining silica sol coating B at this time is N=M(1-b) / (ba)=100.4(1-15.57%) / (15.57%-14.76%)=10465.2g.

[0209] After calculation, the amount of water to be added subsequently is m=N(Sb) / (1-S)=10465.2(16.66%-15.57%) / (1-16.66%)=136.9g.

[0210] The water to be supplemented later was added to the silica sol coating C and stirred for 0.5 hours. The actual water content in the silica sol coating D was verified by thermogravimetric analysis to be 16.65%, which was within the allowable range of the benchmark water content of 15.83% to 16.66%, and the amount of water supplemented in the coating was accurately controlled.

[0211] The above embodiments are only used to illustrate the present invention, but not to limit it.

[0212] Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the above embodiments or make equivalent substitutions for some of the technical features therein; and these modifications or substitutions do not deviate the essence of the corresponding technical solutions from the spirit and scope of the present invention.

Claims

1. A method for dynamically controlling the water content in a silica sol coating for precision casting, characterized in that: The dynamic control method of the water content in the silica sol coating is: First, the base water content of the prepared silica sol coating that has been placed in the shell making room and has not been consumed is measured; Then, the real-time moisture content of the silica sol coating in the consumption application is dynamically measured before the gelation state occurs; Then, according to the comparison between the real-time moisture content measured each time and the reference moisture content, a corresponding mass of water is added to the currently remaining silica sol coating, and the silica sol coating is stirred to form a silica sol coating that meets the allowable range of the reference moisture content.

2. The method for dynamically controlling the water content in the silica sol coating for precision casting according to claim 1, characterized in that: The method for dynamically controlling the water content in the silica sol coating specifically comprises the following process steps: Step 1. Determine the base water content of the prepared silica sol coating that is placed in the shell making room and not consumed, and record the initial mass of the silica sol coating and the initial liquid level height in the coating bucket; Step 2. In the application of silica sol coating consumption before the gel state occurs, the real-time moisture content of the silica sol coating in the coating bucket is measured, and the real-time drop in the liquid level height in the coating bucket when the real-time moisture content is measured is recorded; The real-time drop in the liquid level in the paint bucket is based on the initial liquid level in the paint bucket in step 1; Step 3. Compare the real-time moisture content measured in step 2 with the reference moisture content in step 1, and use the allowable range of the measured real-time moisture content deviation from the reference moisture content as a reference to determine whether the remaining silica sol coating needs to be replenished; If it is determined that the current remaining silica sol coating does not need to be replenished with water, then steps 2 and 3 are dynamically repeated to perform real-time moisture content measurement and judgment until it is determined that the current remaining silica sol coating needs to be replenished with water; If it is determined that the remaining silica sol coating needs to be refilled with water, the shell making operation is suspended, and the following steps 4 to 9 are performed to complete the refilling operation in two steps; Step 4. Take the real-time moisture content measured in step 2 as the first real-time moisture content, and calculate in combination with the real-time drop in the liquid level in the paint bucket in step 2 and the initial mass of the silica sol paint in step 1, the initial liquid level in the paint bucket and the reference moisture content to obtain the estimated mass of supplementary water in the silica sol paint when the first real-time moisture content is measured; Step 5. Add water with a mass less than the estimated supplementary mass obtained in step 4 into the current remaining silica sol coating and stir it thoroughly; Record the actual water replenishment quality for the first time; Complete initial water replenishment operations; Step 6. Conducting a second real-time moisture content measurement on the silica sol coating obtained in step 5; Step 7. The mass of the first actual water replenishment is calculated in combination with the second real-time moisture content determined in step 6 and the first real-time moisture content determined in step 2 to obtain the mass of the remaining silica sol coating before the first actual water replenishment; Step 8. The mass of the remaining silica sol coating before the first actual water replenishment is calculated in combination with the reference moisture content determined in step 1 and the second real-time moisture content determined in step 6 to obtain the mass of water that should be replenished for the second time on the basis of the first actual water replenishment; Step 9. According to the mass of water to be replenished for the second time obtained in step 8, add the corresponding mass of water into the silica sol coating in step 5 and stir it thoroughly; Complete precise water replenishment operations; The silica sol coating with precise water filling is used for shell making; During the continuous consumption and application of the silica sol coating, steps 2 to 9 are dynamically repeated to ensure that the silica sol coating in the coating bucket does not gel and that the water content is within the allowable range of the benchmark water content.

3. The method for dynamically controlling the water content in the silica sol coating for precision casting according to claim 2, characterized in that: In step 4, the mass of the estimated supplementary water in the silica sol coating during the first real-time moisture content measurement is calculated to satisfy the following relationship: M 估补 =M0×(H0-H1) / H0×(Sa); Where M 估补 The estimated mass of supplementary water in the silica sol coating at the time of the first real-time moisture content measurement; M0 is the initial mass of silica sol coating; H0 is the initial liquid level height of silica sol paint in the paint bucket; H1 is the height of the liquid level drop of the silica sol paint in the paint bucket when the real-time moisture content is measured for the first time; S is the base moisture content; a is the real-time moisture content measured for the first time.

4. The method for dynamically controlling the water content in the silica sol coating for precision casting according to claim 2, characterized in that: In step 7, the mass of the remaining silica sol coating before the first actual water replenishment is calculated to satisfy the following relationship: N=M 实补 ×(1-b) / (b-a); Where N is the mass of the remaining silica sol coating before the first actual water replenishment; M 实补 The quality of the first actual water replenishment; a is the real-time moisture content measured for the first time; b is the real-time moisture content measured for the second time.

5. The method for dynamically controlling the water content in the silica sol coating for precision casting according to claim 2, characterized in that: In step 8, the mass calculation of the water to be replenished for the second time satisfies the following relationship: m = N (Sb) / (1-S); In the formula, m is the mass of water to be replenished for the second time; N is the mass of the remaining silica sol coating before the first actual water replenishment; S is the base moisture content; b is the real-time moisture content measured for the second time.

6. The method for dynamically controlling the water content in the silica sol coating for precision casting according to claim 2, characterized in that: In step 5, after replenishing water, the stirring rate of the silica sol coating is 30 to 80 rpm, and the stirring time is at least 0.5 hour.

7. The method for dynamically controlling the water content in the silica sol coating for precision casting according to claim 2, characterized in that: In step 9, after replenishing water, the stirring rate of the silica sol coating is 30 to 80 rpm, and the stirring time is at least 0.5 hour.

8. The method for dynamically controlling the water content in the silica sol coating for precision casting according to claim 1 or 2, characterized in that: The allowable range of the reference moisture content satisfies the following relationship: Y = S (1-K) ~ S; Where, Y is the allowable range of the base moisture content; S is the base moisture content; K is the fluctuation value of the base moisture content, K≤5%.

9. The method for dynamically controlling the water content in the silica sol coating for precision casting according to claim 1 or 2, characterized in that: The moisture content is determined by thermogravimetric analysis. Thermogravimetric analysis is used to determine the water content in silica sol coatings, including the following process steps: S1. Weigh the initial mass of the crucible itself using a weighing balance; S2. Add a sample of silica sol coating into a crucible and weigh the mass of the crucible with sample before heating using a weighing balance; S3. The crucible is heated at a temperature of 120 to 150 ° C and a heating time of 0.3 to 0.5 hours; S4. Weigh the mass of the crucible with sample after heating using a weighing balance; S5. Calculate the water content in the current silica sol coating sample using the following relationship: Moisture content = (m2-m3) / (m2-m1)×100%; m2 is the mass of the crucible with sample before heating; m3 is the mass of the crucible with sample after heating; m1 is the initial mass of the crucible itself; The precision of the weighing balance is ≥0.001g.

10. The method for dynamically controlling the water content in the silica sol coating for precision casting according to claim 1 or 2, characterized in that: The ambient temperature in the shell making room is 21-23°C and the ambient humidity is 57-60%; The determination of the base moisture content is completed within 12 hours after the preparation of the unconsumed silica sol coating. In determining whether the silica sol coating needs to be replenished with water, the real-time moisture content is measured at least twice a day.

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