A method for testing the shrinkage of ceramic cores during secondary sintering at high temperature

Abstract

The present invention relates to a method for testing the shrinkage rate of secondary sintering of a ceramic core at high temperature, and belongs to the technical field of shrinkage rate testing. The method for testing the shrinkage rate of secondary sintering of a ceramic core at high temperature comprises the following steps: (1) preparing a standard sample of a core; (2) preparing a wax mold sample; (3) preparing a measuring module; (4) preparing a measuring module; (5) measuring the inner cavity size of a casting; (6) calculating the shrinkage rate A of the secondary sintering of a core at high temperature: bringing the above four length dimensions into the following calculation formula: A=T3 / T2-T4 / T1-C. For each of the multiple wax mold samples in the measuring module, the secondary sintering shrinkage rate A is calculated and the average value is obtained as the secondary sintering shrinkage rate of the core under the corresponding casting conditions. Beneficial effects: The principle is simple, the operation is easy, and it does not rely on professional high-precision measuring equipment. It can effectively convert high-temperature measurement into low-temperature measurement, and solves the problem that the high-temperature secondary sintering shrinkage of the core cannot be accurately reflected by simply relying on the thermal expansion coefficient.

Description

Technical Field

[0001] The invention belongs to the technical field of shrinkage testing, and in particular relates to a method for testing the shrinkage of a ceramic core subjected to secondary sintering at high temperature. Background Art

[0002] In investment casting, ceramic cores are used to shape the inner cavity of the casting. The state of the core directly affects the state of the inner cavity of the casting, including the inner cavity size, surface roughness, etc. Among them, the inner cavity size is the most important. If the inner cavity size does not conform to the part design drawing, the part will be scrapped directly. Among the many performance requirements for the core, the high-temperature dimensional stability is closely related to the inner cavity size of the casting. The high-temperature dimensional stability of the core consists of two parts: one is the high-temperature deformation of the core, and the other is the high-temperature secondary sintering shrinkage of the core. The so-called secondary sintering shrinkage means that when the core operating temperature exceeds the core sintering temperature, the core will undergo secondary sintering. The secondary sintering will bring about changes in the core size, and in most cases it will shrink.

[0003] In the prior art, there are clear methods for measuring and evaluating the high-temperature deformation in the high-temperature dimensional stability of the core, but there is no clear test method for the high-temperature secondary sintering shrinkage rate. The reasons for this are, firstly, practitioners of investment casting are accustomed to using experience to directly determine the dimensional change rate after pouring, and secondly, the dimensional monitoring requirements under high-temperature conditions are too high, which is difficult to achieve with current testing equipment. In the case that the current secondary sintering shrinkage rate of the core cannot be measured, there are major problems with investment castings, mainly manifested in that there is no accurate basis for the normal temperature dimensional requirements of the core, and all rely on experience; the actual performance of the core cannot be monitored and evaluated, and when the secondary sintering shrinkage of the core fluctuates, a large number of parts with unqualified inner cavity dimensions are likely to appear, resulting in a huge waste of resources. Therefore, it is very necessary to invent a test method for the high-temperature secondary sintering shrinkage rate of ceramic cores. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a method for testing the shrinkage rate of ceramic cores after secondary sintering at high temperature. The method has a simple principle, is easy to operate, does not rely on professional high-precision measuring equipment, and can effectively convert high-temperature measurements into low-temperature measurements, thus solving the problem that relying solely on the thermal expansion coefficient cannot accurately reflect the shrinkage of the core after secondary sintering at high temperature.

[0005] The present invention solves the above technical problems with the following technical solutions: A method for testing the shrinkage of a ceramic core after secondary sintering at high temperature, comprising the following steps:

[0006] (1) Preparation of standard core specimens:

[0007] A core standard specimen is pressed using core slurry. A core head is provided along the length direction of the effective outer dimension of the core standard specimen. After the pressing is completed, the core standard specimen is fired through a firing process, and the length dimension T1 of the core specimen is measured.

[0008] (2) Preparation of wax mold specimens:

[0009] Wrap wax paper around the core head of the core standard sample obtained in step (1), place it in a wax mold sample mold and press it. After pressing is completed and cooled, a wax mold sample is obtained, and the length dimension T2 of the wax mold sample is measured;

[0010] (3) Preparation of measurement module:

[0011] The wax mold samples obtained in step (2) are formed into an equiaxed crystal mold group or an oriented crystal mold group, and multiple wax mold samples are evenly distributed around the circumference of each mold group, and a measurement shell is obtained by coating, dewaxing and baking;

[0012] (4) Preparation of measurement module:

[0013] After preheating the measurement shell obtained in step (3), casting is performed. After the metal is completely solidified and cooled, the residual shell on the surface is removed, and the casting sample is taken out from the measurement shell, and the length dimension T3 of the casting sample is measured;

[0014] (5) Measurement of casting inner cavity dimensions:

[0015] After de-coring the casting sample obtained in step (4), the casting sample is cut open along the length direction from the inner cavity position, and the inner cavity length dimension T4 of the casting sample is measured;

[0016] (6) Calculation of core high temperature secondary sintering shrinkage A:

[0017] Substitute the above four length dimensions into the following calculation formula:

[0018] A=T3 / T2-T4 / T1,-C; C is the correction coefficient, which is a constant. The correction coefficient is different for different system shells;

[0019] The secondary sintering shrinkage A of multiple wax mold samples in the measurement module is calculated respectively, and then the average value is calculated as the secondary sintering shrinkage of the core under the corresponding casting conditions.

[0020] Beneficial effects:

[0021] The principle is simple, the operation is easy, and it does not rely on professional high-precision measuring equipment. It can effectively convert high-temperature measurement into low-temperature measurement, solving the problem that relying solely on the thermal expansion coefficient cannot accurately reflect the core's high-temperature secondary sintering shrinkage.

[0022] On the basis of the above technical solution, the present invention can also be improved as follows.

[0023] Preferably, the effective dimensions of the core standard sample in step (1) are 20 mm in length × 5 mm in width × 100 mm in height.

[0024] Preferably, the effective size of the core head in step (1) is 10 mm in length × 5 mm in width × 10 mm in height.

[0025] Preferably, the effective size of the wax mold sample in step (2) is 30 mm × 20 mm × 110 mm in length × width × height.

[0026] Preferably, the thickness of the wax paper in step (2) is 0.3-0.5 mm.

[0027] Preferably, the material of the measuring shell in step (3) is a SiO2-AL2O3 system ceramic shell material, and the number of shell layers is 5-7.

[0028] Preferably, the mass of methyltrimethoxysilane in step (3) is 1-10 times the mass of cellulose.

[0029] Preferably, the chemical vapor deposition time in step (3) is 20-720 min.

[0030] Preferably, in step (4), the preheating temperature for the equiaxed crystal mold group is 1100° C.-1250° C., and for the oriented crystal mold group, the preheating temperature is 1400° C.-1550° C.; the crystal pulling speed is 3 mm-8 mm / min.

[0031] Preferably, in step (5), after the casting sample is cut along the length direction from the inner cavity position, the burrs on the cut surface need to be removed before measuring the inner cavity length dimension T4 of the casting sample. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0033] Figure 1 It is a schematic diagram of the core standard specimen;

[0034] Figure 2 Schematic diagram of a wax mold specimen containing a core standard specimen;

[0035] Figure 3 Schematic diagram of the dissection of the casting sample after pouring. DETAILED DESCRIPTION

[0036] The principles and features of the present invention are described below. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0037] Example 1:

[0038] Standard core specimens were pressed using a core ceramic slurry prepared for casting equiaxed crystal parts. During the pressing process, the slurry temperature was 90°C, the injection pressure was 40 bar, and the injection time was 5 seconds. After pressing, the wet core specimens were embedded in calcined alumina powder and sintered at a heating rate of 3°C per minute to 1200°C for 2 hours. After sintering, the core specimens were cooled to room temperature in the furnace. The core specimens were removed and cleaned of any alumina deposits. The length dimension, T1, of the core specimens was measured with a vernier caliper and is listed in Table 1. The core specimens were then soaked in silica sol and then in epoxy resin solution, allowed to dry, and then set aside.

[0039] Take a completely dry standard core sample, wrap the ends of the core with 0.3 mm thick wax paper, and place the core sample into the wax mold to press the wax sample. During the pressing process, the wax temperature is 65°C, the injection pressure is 8 bar, and the injection time is 8 seconds. After the wax sample cools, use a vernier caliper to measure the wax pattern length dimension T2, which is listed in Table 1.

[0040] Six wax mold specimens were evenly distributed around the circumference of the mold using an equiaxed crystal mold assembly. After assembly, the mold was dipped in a SiO2-Al2O3 ceramic shell material and then sanded six times. After complete drying, the mold was dewaxed and fired at 900°C to obtain the sample mold.

[0041] The prepared mold was preheated at 1100°C for 4 hours. A K465 nickel-based superalloy melt at 1500°C was poured into the mold. After the melt completely solidified and cooled to room temperature, the mold was removed. Castings converted from the wax pattern were cut from the mold and their length, T3, was measured with a vernier caliper. The length dimension, T3, is listed in Table 1.

[0042] After the cut casting sample was de-cored by chemical method, it was cut open from the inner cavity of the casting sample along the length direction using wire cutting equipment. After the burrs on the cut surface were removed with a diamond file, the inner cavity length dimension T4 of the casting sample was measured with a vernier caliper, which is listed in Table 1.

[0043] Substitute the above length dimensions into the formula A=T3 / T2-T4 / T1, -C, where C is the correction coefficient. For the SiO2-AL2O3 system ceramic shell, C is taken as 0.8%. Calculate the core high-temperature secondary sintering shrinkage rate A. After calculating the average value of A for 6 samples respectively, the results are listed in Table 1.

[0044] Example 2:

[0045] Standard core specimens were pressed using a core ceramic slurry prepared for casting directional grained parts. During the pressing process, the slurry temperature was 95°C, the injection pressure was 50 bar, and the injection time was 8 seconds. After pressing, the wet core specimens were embedded in calcined alumina powder and sintered at a heating rate of 3°C per minute to 1225°C for 2 hours. After sintering, the core specimens were cooled to room temperature in the furnace. The core specimens were removed and cleaned of any alumina deposits. The length dimension, T1, of the core specimens was measured with a vernier caliper and is listed in Table 1. The core specimens were then soaked in silica sol and then in epoxy resin solution, allowed to dry, and then set aside.

[0046] Take a completely dry standard core sample, wrap the ends of the core with 0.5 mm thick wax paper, and place the core sample into the wax mold to press the wax sample. During the pressing process, the wax temperature is 65°C, the injection pressure is 8 bar, and the injection time is 8 seconds. After the wax sample cools, use a vernier caliper to measure the wax pattern length dimension T2, which is listed in Table 1.

[0047] Six wax mold specimens were evenly distributed around the circumference of the mold using a directional crystallization mold assembly. After assembly, the mold was dipped in a SiO2-Al2O3 ceramic shell material and then sanded seven times. After complete drying, the mold was dewaxed and fired at 900°C to obtain the sample mold.

[0048] The prepared mold was preheated to 1540°C for 30 minutes. A 1540°C DZ40M nickel-based superalloy melt was poured into the mold. After a 2-minute standstill, crystal pulling began at a speed of 3 mm / min. After the crystal pulling was complete and the molten metal completely solidified and cooled to room temperature, the mold was removed. Castings converted from wax molds were cut from the mold and the length, T3, of the castings was measured with a vernier caliper. The length dimension, T3, is listed in Table 1.

[0049] After the cut casting sample was de-cored by chemical method, it was cut open from the inner cavity of the casting sample along the length direction using wire cutting equipment. After the burrs on the cut surface were removed with a diamond file, the inner cavity length dimension T4 of the casting sample was measured with a vernier caliper, which is listed in Table 1.

[0050] Substitute the above length dimensions into the formula A=T3 / T2-T4 / T1-C, where C is the correction coefficient. For the SiO2-AL2O3 system ceramic shell, C is taken as 0.8%. Calculate the core high-temperature secondary sintering shrinkage rate A. After calculating the average value of A for 6 samples, the results are listed in Table 1.

[0051] Table 1

[0052] T1 / mm T2 / mm T3 / mm T4 / mm A / ％ Implementation Example 1 98.87 111.50 110.00 96.48 0.28 Implementation Example 2 98.62 109.65 108.42 96.32 0.41

[0053] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for testing the shrinkage of a ceramic core after secondary sintering at high temperature, characterized in that: The following steps are involved: (1) Preparation of standard core specimens: A core standard specimen is pressed using core slurry. A core head is provided along the length direction of the effective outer dimension of the core standard specimen. After the pressing is completed, the core standard specimen is fired through a firing process, and the length dimension T1 of the core specimen is measured. (2) Preparation of wax mold specimens: Wrap wax paper around the core head of the core standard sample obtained in step (1), place it in a wax mold sample mold and press it. After pressing is completed and cooled, a wax mold sample is obtained, and the length dimension T2 of the wax mold sample is measured; (3) Preparation of measurement module: The wax mold samples obtained in step (2) are formed into an equiaxed crystal mold group or an oriented crystal mold group, and multiple wax mold samples are evenly distributed around the circumference of each mold group, and a measurement shell is obtained by coating, dewaxing and baking; (4) Preparation of measurement module: After preheating the measurement shell obtained in step (3), casting is performed. After the metal is completely solidified and cooled, the residual shell on the surface is removed, and the casting sample is taken out from the measurement shell, and the length dimension T3 of the casting sample is measured; (5) Measurement of casting inner cavity dimensions: After de-coring the casting sample obtained in step (4), the casting sample is cut open along the length direction from the inner cavity position, and the inner cavity length dimension T4 of the casting sample is measured; (6) Calculation of core high temperature secondary sintering shrinkage A: Substitute the above four length dimensions into the following calculation formula: A=T3 / T2-T4 / T1-C, C is the trimming coefficient; The secondary sintering shrinkage A of multiple wax mold samples in the measurement module is calculated respectively, and then the average value is calculated as the secondary sintering shrinkage of the core under the corresponding casting conditions.

2. The method for testing the shrinkage rate of the ceramic core after secondary sintering at high temperature according to claim 1, characterized in that: The effective dimensions of the core standard sample in step (1) are 20 mm in length × 5 mm in width × 100 mm in height.

3. The method for testing the shrinkage rate of the ceramic core after secondary sintering at high temperature according to claim 1, characterized in that: The effective dimensions of the core head in step (1) are 10 mm in length × 5 mm in width × 10 mm in height.

4. The method for testing the shrinkage rate of the ceramic core after secondary sintering at high temperature according to claim 1, characterized in that: The effective dimensions of the wax mold sample in step (2) are 30 mm in length × 20 mm in width × 110 mm in height.

5. The method for testing the shrinkage rate of the ceramic core after secondary sintering at high temperature according to claim 1, characterized in that: The thickness of the wax paper in step (2) is 0.3-0.5 mm.

6. The method for testing the shrinkage rate of the ceramic core after secondary sintering at high temperature according to claim 1, characterized in that: The material of the measuring shell in step (3) is SiO2-AL2O3 system ceramic shell material, and the number of shell layers is 5-7.

7. The method for testing the shrinkage rate of the ceramic core after secondary sintering at high temperature according to claim 1, characterized in that: In the step (4), the preheating temperature for the equiaxed crystal mold group is 1100° C.-1250° C., and for the oriented crystal mold group, the preheating temperature is 1400° C.-1550° C.; the crystal pulling speed is 3 mm-8 mm / min.

8. The method for testing the shrinkage rate of the ceramic core after secondary sintering at high temperature according to claim 1, characterized in that: In the step (5), after the casting sample is cut along the length direction from the inner cavity position, the burrs on the cut surface need to be removed before measuring the inner cavity length dimension T4 of the casting sample.

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