CN103048255A - Device and method for testing air permeability of investment precision casting shells - Google Patents

Abstract

An investment casting investment casting shell air permeability test device and its test method, it includes a test branch circuit and a test trunk circuit, they all include a number of gas circuit control elements, to control and measure the gas pressure and flow, the test method is : 1) According to the manufacturing method of the investment casting test sample and the manufacturing process of the shell, a number of shells to be tested are prepared and installed in the test device; 2) At the same time, the air storage tank is inflated by the air compressor to obtain 3) Control the high-temperature electric furnace to the required test temperature T through the temperature controller; 4) Control the pressure of the gas circuit system through the switch valve and the pressure reducing valve, and control the pressure of the gas system through the regulating valves of each test branch. Adjust the test pressure P of the test branch; 5) Read the flow Q / t of the test branch through the flowmeter; 6) Calculate the air permeability K of the investment casting shell under the temperature T condition according to the formula; The invention can not only be used for the air permeability test of multiple shells at the same time, but also has simple and convenient operation.

Description

A test device and test method for air permeability of investment casting mold shell

technical field

The invention relates to a test device and a test method for the gas permeability of an investment casting mold shell.

Background technique

Investment casting is a near-net shape technology for metal parts, which can be used for precision casting of various metal materials. Investment casting can produce parts with complex shapes. It is not only suitable for the trial production of small batches of single pieces, but also for the production of large batches of parts. It is widely used in the production of engine core parts by aviation companies, especially in recent years. Most of them are used in the manufacture of superalloy parts. The formula and manufacturing process of the mold shell are one of the most important components of investment casting, which directly affects the casting process, determines the quality of the final metal parts (dimensional accuracy, surface roughness, etc.), and even affects the mechanical properties of the parts. At present, silica sol, ethyl silicate and water glass are widely used in the manufacture of molded shells. Among them, silica sol is a binder with excellent performance. The environmental pollution is small, and the formed parts have good dimensional accuracy and surface roughness, which makes the silica sol shell more and more widely used in the aviation manufacturing industry. The shell made of ethyl silicate has high dimensional accuracy, low surface roughness, high shell strength, rapid drying during the manufacturing process, and ammonia gas can be used to further speed up the drying of the shell, making its production efficiency relatively high. High, very suitable for manufacturing precision parts for aviation, but this type of shell has a greater impact on the environment. However, the water glass shell has poor wettability to the investment mold and low high temperature strength, resulting in low surface quality and dimensional accuracy of the casting. Currently, it is mainly used to manufacture some parts with lower requirements.

The formula and manufacturing process of the investment casting shell will directly affect its air permeability, and the air permeability of the shell directly determines the filling of the molten metal and ultimately affects the quality of the casting. The shell has defects such as insufficient pouring and pores. At present, most of the research focuses on the impact of the shell formula and shell making process on the strength and dimensional accuracy of the shell. Due to the lack of test equipment for the air permeability of the shell, especially the air permeability at high temperatures, the research on the air permeability of the shell It is less, which makes it difficult to fully evaluate the performance of the shell; at present, there is a lack of related equipment and methods for the air permeability test of the shell.

Contents of the invention

The object of the present invention is to provide a test device for the air permeability of investment casting shell and its testing method, which has the advantages of convenient testing shell data and improving the molding quality of precision casting.

The present invention is achieved in this way, a test device for the air permeability of investment casting shells, which includes an air compressor, an air storage tank, a filter, an on-off valve, a pressure reducing valve, a pressure gauge I, a metal pipeline, a regulator Valve, stop valve, flow meter, pressure gauge II, temperature controller, quartz tube and high-temperature electric furnace, characterized in that the air compressor, gas storage tank, filter, switch valve, pressure reducing valve and pressure gauge I are connected in series to form a test Trunk, the end of the test trunk is connected to several test branches, each test branch is composed of a regulating valve, a shut-off valve, a flow meter and a pressure gauge II connected in series on the metal pipeline, the end of each test branch Both are connected to one end of the quartz tube, and the other end of the quartz tube is located in a high-temperature electric furnace, and a temperature controller is connected to the high-temperature electric furnace; the test method includes the following steps: 1) According to the manufacturing method and shell of the investment casting test sample Manufacturing process, prepare a number of shells to be tested and install them in the test device; 2) Inflate the gas storage tank through the air compressor at the same time to obtain the pressure gas for testing; 3) Control the high-temperature electric furnace to the The required test temperature T ; 4) Control the pressure of the gas circuit system through the switch valve and the pressure reducing valve, and adjust the test pressure P of the test branch through the regulating valve of each test branch; 5) Read the pressure P through the flow meter The flow rate Q / t of the test branch; 6) According to the formula (1), the air permeability K of the investment casting shell under the condition of temperature T is obtained,

 （1）

(1)

Where: K — air permeability of type shell, m ⁴ /(N·min);

Q / t — gas flow through the shell, m ³ /min;

d - the average wall thickness of the sample, m;

P —air pressure, Pa (N/m ² );

A — inner surface area of the sample, m ² ;

The gas permeability of the shell at a specific temperature T is determined by four parameters: the gas flow Q / t passing through the shell, the average wall thickness d of the sample, the air pressure P , and the inner surface area A of the sample.

The technical effect of the present invention is: the present invention can not only be used to measure the air permeability of the shell at various temperatures, evaluate the influence of the formula of the shell, the manufacturing process, etc. on the air permeability of the shell, but also complete multiple shells at the same time. The test is simple and convenient; it improves the shell quality and filling performance of investment casting, and then improves the molding quality of investment casting.

Description of drawings

Fig. 1 is a structural schematic diagram of an investment casting shell air permeability testing device.

Fig. 2 is a schematic block diagram of the method for testing the air permeability of investment casting shells.

Fig. 3 is a schematic structural diagram of a test sample for air permeability testing.

In the figure, 1. Air compressor 2. Air storage tank 3. Filter 4. On-off valve 5. Pressure reducing valve 6. Pressure gauge Ⅰ 7. Metal pipeline 8. Regulating valve 9. Globe valve 10. Flow meter 11 , pressure gauge Ⅱ 12, temperature controller 13, quartz tube 14, high temperature electric furnace 15, test trunk 16, test branch 17, shell 18, wax type.

Detailed ways

Below in conjunction with accompanying drawing and example the specific mode of work of the present invention is set forth in further detail, from the manufacture of investment casting mold shell test sample, investment mold precision casting mold shell test device and investment mold precision casting mold shell gas permeability test method 3 aspects are explained in detail.

(1) Manufacture of investment casting test samples

FIG. 3 is a schematic structural view of the investment casting mold shell, which mainly includes a mold shell 17 , a wax pattern 18 and a quartz tube 13 . Wherein the wax type 2 is spherical, manufactured by a pressing mold, or directly adopts a table tennis ball instead of the wax type as a model, and then performs shell making according to the required shell making process to obtain the molded shell 17. During the shell making process, the quartz tube 13 and Shell making is carried out after pattern (wax-type or table tennis ball) is assembled, and quartz tube 13 is mainly used for introducing the gas with pressure.

(2) Investment casting shell test device

The investment casting shell test device is shown in Figure 1. The device uses the air compressor 1 as the gas source, the air compressor 1, the gas storage tank 2, the filter 3, the switch valve 4, the pressure reducing valve 5 and the pressure gauge I 6 are sequentially connected in series to form a test trunk 15, and the high-pressure gas is supplied by the air compressor. The machine 1 is transported to the air storage tank 2 through the pipeline. In order to avoid the impact of impurities in the air on the air permeability of the shell, the pressure gas is filtered by the filter 3 before entering the gas system pipeline. The pressure valve 5 adjusts the pressure air to the value required for the experiment, and the pressure gauge I6 displays and records it. In order to test the air permeability of a plurality of shells at the same time, the end of the test trunk 15 is connected with several test branches 16, and each test branch 16 is composed of a regulating valve 8, a shut-off valve 9, The flow meter 10 and the pressure gauge II 11 are composed of the end of each test branch 16 connected with one end of the quartz tube 13, and the other end of the quartz tube 13 is located in the high-temperature electric furnace 14, and the high-temperature electric furnace 14 is connected with a temperature controller 12. A regulating valve 8 and a cut-off valve 9 are installed on each test branch circuit 16, the regulating valve 8 is used to adjust the test pressure of each test branch circuit 16, the stop valve 9 is used to prevent the backflow of high temperature gas, and each test branch circuit 16 Can be controlled and tested separately. In order to obtain the two key parameters of the gas flow rate and pressure passing through the shell 17 to be tested, each test branch 16 is equipped with a flow meter 10 and a pressure gauge II1. Finally, the end of each test branch 16 is connected to the quartz tube 13, and the other end of the quartz tube 13 is connected to the shell 17 to be tested, and the shell 17 to be tested is placed in the high-temperature electric furnace 14 and fixed, and the high-temperature electric furnace The temperature of 14 is controlled by the temperature controller 12 to adjust the required temperature for the test.

(3) Test method for air permeability of investment casting shell

As shown in Figure 2, the gas permeability test process of the investment casting shell is as follows:

1) According to the manufacturing method of the investment casting test sample and the shell manufacturing process, a number of shells 17 to be tested are prepared and installed in the test device;

2) At the same time, the gas storage tank 2 is inflated through the air compressor 1 to obtain the pressure gas for testing;

3) Control the high-temperature electric furnace 14 to the required test temperature T by the temperature controller 12;

4) Control the pressure of the gas circuit system through the switch valve 4 and the pressure reducing valve 5, and adjust the test pressure P of the test branch 16 through the regulating valve 8 of each test branch 16;

5) Read the flow Q / t of the test branch through the flowmeter 10;

6) According to the formula (1), the air permeability K of the investment casting shell under the condition of temperature T is obtained;

 （1）

(1)

Where: K — air permeability of type shell, m ⁴ /(N·min);

Q / t — gas flow through the shell, m ³ /min;

d - the average wall thickness of the sample, m;

P —air pressure, Pa (N/m ² );

A — inner surface area of the sample, m ² ;

The gas permeability of the shell at a specific temperature T is determined by four parameters: the gas flow Q / t passing through the shell, the average wall thickness d of the sample, the air pressure P , and the inner surface area A of the sample.

The air permeability K of the mold shell is one of the important parameters to characterize the performance of the mold shell, and has a significant impact on the process of metal casting and filling. The shell-making cycle of the shell is long, and there are many shell-making process parameters and types of shells, and the shell-making formula and process parameters determine the air permeability of the shell, which in turn affects the quality of the casting. This test device can realize the air permeability performance test of the investment casting shell, mainly including the test of the air permeability of the investment casting shell at a specific temperature, the experiment of the influence of temperature on the air permeability of the investment casting shell and the investment casting mold The shell manufacturing process (including the shell material and process) affects the air permeability experiment. The specific test process is described as follows:

1. Gas permeability test of investment casting mold shell at a specific temperature: Prepare 3 same test samples and install them in the high-temperature electric furnace 14, heat the high-temperature electric furnace 14 to the test temperature T , turn on the air compressor 1, the switch valve 4 and the pressure reducing valve 5, adjust the test pressure P of each test branch 16 through the regulating valve 8, and read the gas flow Q / t through the investment casting shell from the flow meter 10. After the experiment is completed, measure the sample to obtain its inner surface area A and the average value d . Then, calculate the air permeability of the three samples at a specific temperature T by formula (1), and take the average value as the air permeability of the investment casting mold shell at a specific temperature T ;

2. Experiment on the influence of temperature on the air permeability of the investment casting mold shell: prepare 3 same test samples and install them in the high-temperature electric furnace 14, heat the high-temperature electric furnace 14 to the test temperature T1 , turn on the air compressor 1 and the switch valve 4 And the pressure reducing valve 5, adjust the test pressure P of each test branch 16 through the regulating valve 8, and read the gas flow Q / t through the investment casting mold shell from the flow meter 10; then adjust the high temperature electric furnace 14 temperature to T2 , and use the same steps as before to test the air permeability of the investment casting shell at T2 temperature, and repeat this, test the air permeability at multiple temperatures T1 , T2 , T3 ... Tn , etc., and obtain the temperature effect on investment casting The influence law of shell air permeability.

3. Experiments on the influence of investment casting shell manufacturing process (including shell material and process) on gas permeability: Prepare the shells to be tested according to the shell materials and processes, and prepare 3 identical test samples for each shell and test them. Installed in the high-temperature electric furnace 14, the high-temperature electric furnace 14 is heated to the test temperature T , the air compressor 1, the switch valve 4 and the pressure reducing valve 5 are opened, and the test pressure P of each test branch 16 is adjusted through the regulating valve 8, and from The flow meter 10 reads the gas flow Q / t passing through the investment casting shell; after the experiment is completed, measure the sample to obtain its inner surface area A and the average value d . Then, the air permeability of each sample is calculated by the formula (1), so as to study the influence of the shell manufacturing process on the air permeability.

Claims (2)

1. precision investment casting mould case ventilation property test device, it comprises air compressor machine, gas-holder, filtrator, switch valve, reduction valve, the tensimeter I, metal tubes, variable valve, stop valve, flowmeter, the tensimeter II, temperature controller, quartz ampoule and high-temperature electric resistance furnace, it is characterized in that air compressor machine, gas-holder, filtrator, switch valve, reduction valve and tensimeter I are composed in series the test main line successively, the end on test main line connects several test branch roads, each test branch road is by the variable valve that is connected on successively on the metal tubes, stop valve, flowmeter and tensimeter II form, the terminal of each test branch road all links to each other with an end of quartz ampoule, the other end of quartz ampoule is positioned at high-temperature electric resistance furnace, is connected with temperature controller on the high-temperature electric resistance furnace.

2. the method for testing of a kind of precision investment casting mould case ventilation property test device as claimed in claim 1 is characterized in that said method comprising the steps of:

1) according to manufacture method and the shell manufacturing process of investment pattern precision casting test sample, it is some to produce shell to be tested, and is mounted in the proving installation;

2) by air compressor machine gas-holder is inflated simultaneously, obtained the pressed gas of test usefulness;

3) control high-temperature electric resistance furnace to required probe temperature by temperature controller T

4) control the pressure of air-channel system by switch valve and reduction valve, and regulate respectively the test pressure of test branch road by the variable valve of each bar test branch road P

5) read the flow of this test branch road by flowmeter Q/ t

6) calculate this temperature of acquisition according to formula (1) TThe gas penetration potential of precision investment casting mould case under the condition K,

（1）

In the formula: K-shell gas penetration potential, m ⁴/ (Nmin);

Q/ t-gas flow by shell, m ³/ min;

d-sample mean wall thickness, m;

P-air pressure, Pa(N/m ²);

A-sample internal surface area, m ²

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