method for reducing shell cracking in investment casting processTechnical Field
The invention belongs to the technical field of investment casting, and particularly relates to a method for reducing shell cracking in an investment casting process.
Background
The investment casting technology is very convenient and fast for small castings with complex structures, but in actual production, technicians find that shells formed after wax molds are melted by heating are easy to crack or split, because the wax mold core generates a large amount of gas during combustion, and the gas can burst the shells after gathering. Referring to fig. 1, when cracks or shells are serious, the size of a casting is not standard, corners and burrs are excessive, and a subsequent removal process is complex; during casting, even the phenomenon of fire running can occur, so that more defective products exist in finished castings, the casting with high requirement on product precision is high in processing difficulty, and the processing cost is increased due to more defective products.
the traditional method for reducing shell cracks or shell cracks is characterized in that a shell material with higher cost is replaced or the burning time of a wax mould is prolonged, the processing time is long, the cost is high, the method is only suitable for casting single or small-batch castings, and the large-scale production of large-batch castings is difficult to realize.
disclosure of Invention
Aiming at the problems that the shell is easy to crack or is cracked in the wax mold heating and melting process, so that the production cost of the product is high, the yield is low and the product precision is low, the invention provides a method for reducing shell cracking in the investment casting process, wherein an exhaust rod is arranged on a channel through which gas is exhausted or liquid flows, so that the gas generated by melting the wax mold is exhausted in time. The method for processing the shell mold has short time and low cost, is suitable for large-scale production, and has the following specific technical scheme:
a method of reducing shell cracking during investment casting comprising the steps of:
1) making wax patterns
Manufacturing a wax mould core by using resin, and covering a common wax mould layer on the wax mould core by using wax to form a wax mould after the wax mould core is shaped;
2) arrange exhaust stick
Installing an exhaust rod on the common wax mould layer of the wax mould in the step 1);
3) Making a mould shell
a. Keeping the temperature of the operation room at 20-26 ℃ and the relative humidity of 40-60%, and coating on the wax mold with the exhaust rod installed in the step 2) to manufacture a shell blank;
b. After the coating process in the step a is finished, removing the exhaust rod, heating the shell blank for 15-30 minutes, controlling the heating temperature to be 80-200 ℃, and completely melting the common wax pattern layer on the wax pattern in the shell blank;
c. and c, after the common wax mold layer on the wax mold in the step b is completely melted, roasting the shell blank body for 3-5 hours at 400-600 ℃, and melting off the wax mold core body of the wax mold.
further limiting, the thickness of the common wax pattern layer of the wax pattern in the step 1) is 0.08-0.2 mm.
Further, the wax mold core of the wax mold in the step 1) is manufactured by a 3D printing technology.
further limiting, the 3D printing technology requires further processing after being manufactured, and the further processing includes removing the 3D printing support and the leftover bits on the wax pattern core.
Further limiting, at least one exhaust rod in the step 2), when the outer surface area of the wax mold is 600-800 mm2, 1-2 exhaust rods should be installed, when the outer surface area of the wax mold is 1500-1800 mm2, when the outer surface area of the wax mold is 800-1500 mm2, 2-4 exhaust rods should be installed, and 4-6 exhaust rods should be installed.
further, the diameter of the exhaust rod (2) ranges from 3 mm to 5 mm, and the length of the exhaust rod ranges from 8 mm to 10 mm.
further, the material used in the coating process in the step 3) a is zircon powder slurry, and the material used in the material supplementing process in the step 3) e is the same as that used in the coating process in the step a.
Further, the step 3) b is carried out by a high temperature spray gun.
further, the cleaning liquid used in the cleaning process in the step 3) d is alcohol.
Compared with the prior art, the invention has the following advantages:
1. the wax mould comprises a wax mould core body and a common wax mould layer covered on the outer side of the wax mould core body, wherein an exhaust rod is arranged on the common wax mould layer, when the wax mould is melted, the exhaust rod is removed, the common wax mould layer is melted firstly, and then the wax mould core body is melted, so that gas generated when the wax mould core body is melted is collected in the melted common wax mould layer space and then is exhausted from a hole for installing the exhaust rod, and the expansion and cracking of a shell caused by the sudden rise of the air pressure in the shell are avoided, so that the cracking or cracking of the shell is avoided; and after dewaxing, roasting the shell blank at 400-600 ℃ for 3-5 hours to melt the wax mold core of the wax mold, and roasting the shell blank to reduce slag inclusion of a cast. The method for manufacturing the shell does not need to prolong the burning time of the wax mould and replace materials with higher cost, thereby saving the time cost and the capital cost.
2. the wax mould core body is manufactured by a 3D printing technology, so that the process of manually casting a model is reduced, mass rapid production can be realized, and the production efficiency is improved.
Drawings
FIG. 1 is a shell made using a prior art method;
FIG. 2 is a shell made by the method of example 1;
FIG. 3 is a schematic view of the configuration of the wax pattern and the air bar;
Wherein, 1-wax pattern and 2-exhaust bar.
Detailed Description
the method according to the invention is further explained below with reference to the figures and examples, but the invention is not limited to the embodiments explained below.
The method of reducing shell cracking during investment casting according to the present invention will be described in detail below by taking stainless steel castings as an example.
Example 1
The method for reducing shell cracking in the investment casting process of the embodiment specifically comprises the following steps:
1) Manufacture of wax mold 1
Manufacturing a wax mould core by using nylon and a 3D printing technology, after the wax mould core is shaped, removing a 3D printing support part and leftover bits on the wax mould core, and covering a common wax mould layer with the thickness of 0.1 mm on the wax mould core by using paraffin to form a wax mould 1;
2) Arranging exhaust rods 2
Referring to fig. 3, in the step 1), the area of the outer surface of the wax mould 1 is 1600mm2, and 4 exhaust rods 2 with the diameter of 5 mm and the length of 9 mm are arranged on the common wax mould layer;
3) Making a mould shell
a. keeping the temperature of the operating room at 20 ℃ and the relative humidity at 40%, and coating the wax mold 1 provided with the exhaust rod 2 in the step 2) with zirconium sound powder slurry and sand to manufacture a shell blank;
b. After the coating process in the step a is finished, removing the exhaust rod 2, heating the shell blank body by using a high-temperature spray gun for 30 minutes, controlling the heating temperature to be 80 ℃, and completely melting the common wax pattern layer on the wax pattern 1 in the shell blank body;
c. B, after the common wax pattern layer on the wax pattern 1 is completely melted in the step b, roasting the shell blank body for 5 hours at 400 ℃, and melting off the wax pattern core body of the wax pattern 1;
d. Cleaning the shell blank with alcohol, and cleaning the residual nylon or paraffin on the inner wall of the shell blank;
e. And (3) supplementing and polishing the part of the shell blank body, which is provided with the exhaust rod 2, with zirconium sound powder slurry and sand, and then roasting at 1050 ℃ to manufacture a complete shell, wherein the shell structure is shown in figure 2.
Example 2
The method for reducing shell cracking in the investment casting process of the embodiment specifically comprises the following steps:
1) manufacture of wax mold 1
the method comprises the steps of manufacturing a wax mould core body by using PS powder (polystyrene powder) and adopting a 3D printing technology, removing 3D printing support parts and leftover bits and pieces on the wax mould core body after the wax mould core body is shaped, and covering a common wax mould layer with the thickness of 0.08 mm on the wax mould core body by using white wax to form a wax mould 1;
2) Arranging exhaust rods 2
in the step 1), the external surface area of the wax mould 1 is 800mm2, and 2 exhaust rods 2 with the diameter of 3 mm and the length of 8 mm are arranged on the common wax mould layer;
3) Making a mould shell
a. keeping the temperature of the operating room at 26 ℃ and the relative humidity at 60%, and coating the wax mold 1 provided with the exhaust rod 2 in the step 2) with zirconium sound powder slurry and sand to manufacture a shell blank;
b. after the coating process in the step a is finished, removing the exhaust rod 2, heating the shell blank body by using a high-temperature spray gun for 24 minutes, controlling the heating temperature to be 100 ℃, and completely melting the common wax pattern layer on the wax pattern 1 in the shell blank body;
c. b, after the common wax pattern layer on the wax pattern 1 is completely melted in the step b, roasting the shell blank body for 3 hours at 600 ℃, and melting off the wax pattern core body of the wax pattern 1;
d. Cleaning the shell blank with alcohol, and cleaning the PS powder or white wax remained on the inner wall of the shell blank;
e. and (3) supplementing and polishing the part of the shell blank body, which is provided with the exhaust rod 2, by using zirconium sound powder slurry and sand materials, and roasting at 1060 ℃ to manufacture a complete shell.
Example 3
The method for reducing shell cracking in the investment casting process of the embodiment specifically comprises the following steps:
1) Manufacture of wax mold 1
Manufacturing a wax mould core by using nylon and a 3D printing technology, after the wax mould core is shaped, removing a 3D printing support part and leftover bits on the wax mould core, and covering a common wax mould layer with the thickness of 0.2 mm on the wax mould core by using paraffin to form a wax mould 1;
2) Arranging exhaust rods 2
Referring to fig. 3, in the step 1), the area of the outer surface of the wax mold 1 is 1800mm2, and 6 exhaust rods 2 with the diameter of 5 mm and the length of 10 mm are arranged on the common wax mold layer;
3) Making a mould shell
a. Keeping the temperature of the operating room at 26 ℃ and the relative humidity at 60%, and coating the wax mold 1 provided with the exhaust rod 2 in the step 2) with zirconium sound powder slurry and sand to manufacture a shell blank;
b. after the coating process in the step a is finished, removing the exhaust rod 2, heating the shell blank body by using a high-temperature spray gun for 15 minutes, controlling the heating temperature to be 200 ℃, and completely melting the common wax pattern layer on the wax pattern 1 in the shell blank body;
c. B, after the common wax pattern layer on the wax pattern 1 is completely melted in the step b, roasting the shell blank body for 5 hours at 600 ℃, and melting off the wax pattern core body of the wax pattern 1;
d. Cleaning the shell blank with alcohol, and cleaning the residual nylon or paraffin on the inner wall of the shell blank;
e. and (3) supplementing and polishing the part of the shell blank body, which is provided with the exhaust rod 2, with zirconium sound powder slurry and sand, and roasting at 1060 ℃ to manufacture a complete shell.
Example 4
the method for reducing shell cracking in the investment casting process of the embodiment specifically comprises the following steps:
1) manufacture of wax mold 1
manufacturing a wax mould core by using nylon and a 3D printing technology, after the wax mould core is shaped, removing a 3D printing support part and leftover bits on the wax mould core, and covering a common wax mould layer with the thickness of 0.1 mm on the wax mould core by using paraffin to form a wax mould 1;
2) arranging exhaust rods 2
Referring to fig. 3, in the step 1), the area of the outer surface of the wax mold 1 is 1500mm2, and 4 exhaust rods 2 with the diameter of 5 mm and the length of 10 mm are arranged on the common wax mold layer;
3) Making a mould shell
a. Keeping the temperature of the operating room at 24 ℃ and the relative humidity at 45%, and coating the wax mold 1 provided with the exhaust rod 2 in the step 2) with zirconium sound powder slurry and sand to manufacture a shell blank;
b. After the coating process in the step a is finished, removing the exhaust rod 2, heating the shell blank body by using a high-temperature spray gun for 18 minutes, controlling the heating temperature to be 180 ℃, and completely melting the common wax pattern layer on the wax pattern 1 in the shell blank body;
c. B, after the common wax pattern layer on the wax pattern 1 is completely melted in the step b, roasting the shell blank body for 5 hours at 600 ℃, and melting off the wax pattern core body of the wax pattern 1;
d. Cleaning the shell blank with alcohol, and cleaning the residual nylon or paraffin on the inner wall of the shell blank;
e. And (3) supplementing the part, provided with the exhaust rod 2, of the shell blank by using zirconium sound powder slurry and sand, polishing, and roasting at 1050 ℃ to manufacture a complete shell.
Example 5
the method for reducing shell cracking in the investment casting process of the embodiment specifically comprises the following steps:
1) Manufacture of wax mold 1
manufacturing a wax mould core by using nylon and a 3D printing technology, after the wax mould core is shaped, removing a 3D printing support part and leftover bits on the wax mould core, and covering a common wax mould layer with the thickness of 0.09 mm on the wax mould core to form a wax mould 1;
2) arranging exhaust rods 2
Referring to fig. 3, in the step 1), the area of the outer surface of the wax mold 1 is 600mm2, and 1 exhaust rod 2 with the diameter of 3 mm and the length of 8 mm is arranged on the common wax mold layer;
3) Making a mould shell
a. keeping the temperature of the operating room at 25 ℃ and the relative humidity at 55%, and coating the wax mold 1 provided with the exhaust rod 2 in the step 2) with zirconium sound powder slurry and sand to manufacture a shell blank;
b. After the coating process in the step a is finished, removing the exhaust rod 2, heating the shell blank body by using a high-temperature spray gun for 20 minutes, controlling the heating temperature to be 120 ℃, and completely melting the common wax pattern layer on the wax pattern 1 in the shell blank body;
c. b, after the common wax pattern layer on the wax pattern 1 is completely melted in the step b, roasting the shell blank body for 4 hours at 500 ℃, and melting off the wax pattern core body of the wax pattern 1;
d. Cleaning the shell blank with alcohol, and cleaning the residual nylon or paraffin on the inner wall of the shell blank;
e. And (3) supplementing the part, provided with the exhaust rod 2, of the shell blank by using zirconium sound powder slurry and sand, polishing, and roasting at 1050 ℃ to manufacture a complete shell.
The shell prepared in example 1 was subjected to subsequent liquid metal casting to prepare a cast article, which was compared with a shell to which the exhaust rod 2 was not added and a shell cast article which was not fired after dewaxing. The results are shown in the following table:
the same operations as in the above-described tests were performed on the shells produced in examples 2 to 5. The results are the same as the test results, the shell without the exhaust rod 2 is subjected to expansion cracking after dewaxing, so that pouring can not be carried out, the exhaust rod 2 is added, and if roasting and shell washing are not carried out after dewaxing, although expansion cracking does not occur, the casting has a phenomenon of slight slag inclusion; if the roasting and shell washing are carried out after dewaxing, the phenomena of expansion crack and slag inclusion are not generated.
the processes not specifically described in the above examples are conventional processes.