Silica sol type shell profiled connection nut and preparation method of large castings based on the profiled connection nut

Abstract

The present application belongs to the technical field of silica sol shell, and relates to a special-shaped connecting nut for silica sol shell and a preparation method of large castings based on the special-shaped connecting nut. The special-shaped connecting nut can be embedded in a wax mold module. A mechanical hand grabbing rod is rigidly connected with a screw rod framework through the special-shaped connecting nut. The weight of the module supported by the mechanical hand grabbing rod is directly transmitted to the screw rod framework through the special-shaped connecting nut, thereby avoiding the generation of micro-cracks in the shell due to micro-vibration in the automatic shell-making process of the mechanical hand, avoiding the deformation of the module caused by long-time suspension and standing for drying, and effectively improving the strength of the module during coating and long-time drying and standing. The preparation method of the large castings is simple to operate, reduces the manual auxiliary reinforcement link, reduces the uncertainty caused by human intervention, has high shell manufacturing efficiency, and achieves the purpose of reducing cost and increasing efficiency.

Description

Technical Field

[0001] This invention belongs to the field of silica sol shell technology, and relates to a special-shaped connecting nut for silica sol shell and a method for preparing large castings based on the special-shaped connecting nut. Background Technology

[0002] With the rapid development of my country's aviation, aerospace, and weaponry sectors, large and complex alloy components have been widely used in national defense equipment. However, these alloy components face numerous challenges, including complex structures, high machining costs, long processing cycles, and limited processing shapes. Their dimensional accuracy and internal quality directly affect the reliable operation of weapons and equipment. To address this, investment casting technology has been adopted for one-time production, which not only improves the overall structural performance and reliability of equipment and reduces structural weight, but also replaces some forgings, machined assemblies, and sheet metal forming parts, reducing manufacturing costs and shortening the manufacturing cycle.

[0003] Industry experts know that investment casting is a special casting method with minimal or no machining. Castings produced using this method have high dimensional accuracy and smooth surfaces, saving significant machining time and equipment, thus improving the utilization rate of metal materials. However, with the increasing emphasis on environmental protection, investment casting commonly uses silica sol as a shell binder. Silica sol shells are a mainstream shell-making method in investment casting, employing physical drying and hardening without the need for chemical hardening, making the shell-making method environmentally friendly and efficient.

[0004] With the gradual introduction of automated shell-making lines using robotic arms, robots complete shell-making actions such as slurry application, slurry control, sand application, and transfer. The modules are dynamically dried using a catenary suspension system on the shell-making line. For small and medium-sized castings, this significantly improves the efficiency and quality of silica sol shell production. However, for large castings, on the one hand, the shapes are often irregular, and on the other hand, to ensure the metallurgical quality of large castings, a multi-dimensional gating system combining ingates, runners, and sprues must be used. The modules are heavy, and due to the automated coating process using robotic arms, the axial and radial shear forces can easily damage the modules. The silica sol shell hardening method is physical drying hardening, which has a long drying time. The modules are suspended for extended periods, and under the influence of gravity, the coating is prone to cracking and the modules to deform, ultimately leading to the casting being scrapped due to inclusions and deformation. The traditional solution involves pre-embedding a screw frame during the fabrication of the main runner and connecting it to the robotic gripper via wire. While this method strengthens the module, the non-rigid connection between the robotic gripper and the module leaves the coating susceptible to cracking and deformation. Furthermore, the pressing operation is cumbersome, and removal after demolding is difficult. This process also easily generates inclusions in the mold cavity, affecting the casting yield. Therefore, this invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a special-shaped connecting nut for silica sol shell and a method for preparing large castings based on the special-shaped connecting nut. It can be used for coating shells of all large casting modules, and has high versatility and good stability.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] On one hand, the present invention provides a special-shaped connecting nut for silica sol shells, which is pre-embedded in a wax mold module. The special-shaped connecting nut includes a nut body, an axial screw skeleton screw-in hole is opened at the center of the nut body, and a robotic gripper is installed at the bottom of the nut body. Wax contact reinforcement holes are evenly distributed around the axial screw skeleton screw-in hole, and the wax contact reinforcement holes are arranged in a direction parallel to the axial direction of the nut body. The nut body is also provided with a plurality of evenly distributed radial screw skeleton screw-in holes, which are connected to the axial screw skeleton screw-in holes.

[0008] Furthermore, the material of the irregular-shaped connecting nut is selected from quenched and tempered 45# steel.

[0009] Furthermore, the radial screw skeleton has 4 to 8 screw-on holes.

[0010] On the other hand, the present invention also provides a method for preparing a large casting based on some or all of the above-described silica sol-molded shell irregular connecting nuts, specifically including the following steps:

[0011] Step 1) Design the casting gating system according to the structure of the part to be cast;

[0012] Step 2) Determine the number and angle of the screw mounting holes for the irregular connecting nut and bolt skeleton based on the number and angle of the horizontal runners in the casting gating system;

[0013] Step 3) Pre-screw the screw skeleton into the special-shaped connecting nut, press the horizontal runner and the vertical runner, and make the screw skeleton extend 20-30mm beyond the corresponding runner;

[0014] Step 4) Connect the sprue cup with the robotic gripper to the horizontal runner and vertical runner with the irregular connecting nut and screw skeleton;

[0015] Step 5) Assemble the wax mold modules and use a robotic automated shell-making line to produce the mold shell;

[0016] Step 6) Dewax and bake the shell. After dewaxing, remove the screw skeleton one by one by twisting. Then, pull out the irregular connecting nut from the direction of the pouring cup. Wrap the process hole left after the screw skeleton is removed with aluminum foil. Finally, seal it with silica sol, sand and powder.

[0017] Step 7) Cast the shell obtained in step 6) using anti-gravity casting;

[0018] Step 8) Clean the mold shell around the casting and gating system from Step 7), remove the gating system, and clean and grind the surface of the casting.

[0019] Step 9) Heat treat the casting from step 8) to complete the preparation of the structure to be cast.

[0020] Furthermore, in step 4), the sprue cup with the robotic gripper is connected to the horizontal and vertical runners by adding spring washers and using a torque wrench.

[0021] Furthermore, the above preparation method also includes the following steps:

[0022] Step 10) Perform X-ray radiography and fluorescence penetrant testing on the casting structure from Step 9) to determine whether the casting structure has inclusion defects.

[0023] Furthermore, the above preparation method also includes the following steps:

[0024] Step 11) Perform blue light scanning dimensional inspection and fitter scribing inspection on the casting structure in Step 9) to determine whether the casting structure is deformed.

[0025] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0026] 1. A special-shaped connecting nut is pre-embedded in the wax mold module. The robotic arm gripper is rigidly connected to the screw frame through the special-shaped connecting nut. The weight of the module borne by the robotic arm gripper is directly transferred to the screw frame through the special-shaped connecting nut. This avoids the generation of micro-cracks in the mold shell caused by micro-vibration during the automated shell making process of the robotic arm, and avoids deformation caused by the module being suspended and dried for a long time. This effectively improves the strength of the module during coating and long-term drying and standing.

[0027] 2. The preparation method of this large casting is simple to operate, reduces the manual reinforcement process, reduces the uncertainty caused by human intervention, and has high shell production efficiency, thus achieving the goal of cost reduction and efficiency improvement.

[0028] 3. The preparation method of this large casting can be used for coating and shell making of all large casting modules, with high versatility and good stability. Attached Figure Description

[0029] The accompanying drawings are incorporated in and form part of this specification, and together with the description serve to explain the principles of the invention.

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a structural diagram of the irregular-shaped connecting nut for silica sol-type shells provided by the present invention;

[0032] Figure 2 This is a top view of the irregularly shaped connecting nut for a silica sol-type shell provided in Embodiment 1 of the present invention;

[0033] Figure 3 This is a top view of the irregularly shaped connecting nut for a silica sol-type shell provided in Embodiment 2 of the present invention;

[0034] Figure 4 This is a top view of the irregularly shaped connecting nut for the silica sol shell provided in Embodiment 3 of the present invention.

[0035] Among them: 1. Radial screw skeleton screw mounting hole; 2. Screw mounting hole for robotic arm gripping rod; 3. Axial screw skeleton screw mounting hole; 4. Wax material contact reinforcement hole. Detailed Implementation

[0036] Exemplary embodiments will be described in detail below. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of methods consistent with some aspects of the present invention as detailed in the appended claims.

[0037] Combination Figure 1 As shown, the present invention provides a special-shaped connecting nut for a silica sol shell, which is pre-embedded in a wax mold module. The special-shaped connecting nut includes a nut body, an axial screw skeleton screw-on hole 3 is provided in the center of the nut body, and a robotic gripper is installed at the bottom of the nut body (the robotic gripper screws 2 are installed at the bottom of the nut body). Wax contact reinforcement holes 4 are evenly distributed around the axial screw skeleton screw-on hole 3, and the wax contact reinforcement holes 4 are arranged in a direction parallel to the axial direction of the nut body. The nut body is also provided with a plurality of evenly distributed radial screw skeleton screw-on holes 1, which are connected to the axial screw skeleton screw-on holes 3.

[0038] Furthermore, the material of the irregular-shaped connecting nut is selected as 45# steel after quenching and tempering.

[0039] Furthermore, the radial screw skeleton has 4 to 8 screw-on holes.

[0040] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0041] Example 1

[0042] Taking the shell of a certain type of helicopter winch for aviation as an example, its corresponding casting outline dimensions are 673×694×476mm. The structure is barrel-shaped + large tail flange + complex side pipe casting. The complex and thick side pipes on the casting are prone to deformation of the barrel-shaped part of the casting, resulting in insufficient roundness. The specific steps to achieve this are as follows:

[0043] Step 1) Design the casting gating system based on the structure of the winch shell casting, using a combination of horizontal and vertical runners;

[0044] Step 2) Determine the number of radial screw skeleton screw mounting holes 1 for the irregular connecting nut to be 4 (i.e., 2 through holes) based on the number and angle of the horizontal runner, with a radial angle of 78°, and 1 axial screw skeleton screw mounting hole 3. Produce the drawing (see partial sectional view). Figure 2 Machining and forming;

[0045] Step 3) Pre-screw the screw skeleton onto the special-shaped connecting nut. The radial screw skeleton corresponds to the horizontal runner, and the axial screw skeleton corresponds to the vertical runner. The screw skeleton extends 20-30mm beyond the end face of the corresponding runner and presses the horizontal runner and vertical runner.

[0046] Step 4) Connect the sprue cup with the robotic gripper to the horizontal and vertical runners with the irregular connecting nut and screw skeleton by adding spring washers and using a torque wrench;

[0047] Step 5) Assemble the wax mold modules and use a robotic automated shell-making line to produce the mold shell;

[0048] Step 6) Dewax and bake the shell. After dewaxing, remove the screw skeleton one by one by twisting. Then, pull out the irregular connecting nut from the direction of the pouring cup. Wrap the process hole left after the screw skeleton is removed with aluminum foil. Finally, seal it with silica sol, sand and powder.

[0049] Step 7) Cast the shell obtained in step 6) using anti-gravity casting;

[0050] Step 8) Clean the mold shell around the casting and gating system from Step 7), remove the gating system, and clean and grind the surface of the casting;

[0051] Step 9) Perform heat treatment on the casting from step 8);

[0052] Step 10) Perform X-ray radiography and fluorescence penetrant testing on the castings from Step 9);

[0053] Step 11) Perform blue light scanning dimensional inspection and fitter scribing inspection on the castings from Step 9).

[0054] The castings prepared by the above method, produced by the automated shell-making line using a robotic arm, showed no micro-cracks or peeling of the shell surface. After X-ray and fluorescence penetrant testing, over 96.7% of the winch shell castings showed no inclusion defects. The castings underwent blue light scanning dimensional inspection and machinist scribing inspection, achieving a 100% dimensional inspection pass rate with no deformation issues. The overall first-pass yield was over 96%.

[0055] Example 2

[0056] Taking a load-bearing mounting bracket casting for a certain type of military fighter jet as an example, the casting has an outline size of 1308×965×204mm and a kite-shaped, thin-walled structure. The casting requires high flatness, and traditional coating and shell-making methods are prone to module deformation. The specific steps to achieve this are as follows:

[0057] Step 1) Design the casting gating system based on the structure of the load-bearing bracket casting, using a combination of horizontal and vertical runners;

[0058] Step 2) Determine the number of radial screw skeleton screw-in holes for the irregular connecting nut based on the number and angle of the horizontal runner. The radial angle of each hole is 72°. Also determine the number of axial screw skeleton screw-in holes (3). Produce the drawing (see partial sectional view). Figure 3 Machining and forming;

[0059] Step 3) Pre-screw the screw skeleton onto the special-shaped connecting nut. The radial screw skeleton corresponds to the horizontal runner, and the axial screw skeleton corresponds to the vertical runner. The screw skeleton extends 20-30mm beyond the end face of the corresponding runner and presses the horizontal runner and vertical runner.

[0060] Step 4) Connect the sprue cup with the robotic gripper to the horizontal and vertical runners with the irregular connecting nut and screw skeleton by adding spring washers and using a torque wrench;

[0061] Step 5) Assemble the wax mold modules and use a robotic automated shell-making line to produce the mold shell;

[0062] Step 6) Dewax and bake the shell. After dewaxing, remove the screw skeleton one by one by twisting. Then, pull out the irregular connecting nut from the direction of the pouring cup. Wrap the process hole left after the screw skeleton is removed with aluminum foil. Finally, seal it with silica sol, sand and powder.

[0063] Step 7) Cast the shell obtained in step 6) using anti-gravity casting;

[0064] Step 8) Clean the mold shell around the casting and gating system from Step 7), remove the gating system, and clean and grind the surface of the casting;

[0065] Step 9) Perform heat treatment on the casting from step 8);

[0066] Step 10) Perform X-ray radiography and fluorescence penetrant testing on the castings from Step 9);

[0067] Step 11) Perform blue light scanning dimensional inspection and fitter scribing inspection on the castings from Step 9).

[0068] The castings prepared by the above method are produced by automated shell-making lines with robotic arms, and the mold shells are free of micro-cracks and shell surface peeling. After X-ray and fluorescence penetrant testing, more than 98% of the load-bearing mounting bracket castings are free of inclusion defects. After blue light scanning dimensional inspection and fitter scribing inspection, the casting deformation problem is effectively controlled, the dimensional inspection pass rate is over 94%, and the overall first-pass inspection pass rate is over 95%.

[0069] Example 3

[0070] Taking a certain type of artillery shell launching base casting as an example, the casting outline dimensions are φ708×560mm. It features a barrel-shaped structure with complex internal threading channels, resulting in a large casting assembly system and heavy modules. Even after coating, the module weight reaches 85Kg. Traditional coating and shell-making methods are prone to issues such as shell cracking at the module's pouring cup area and module breakage. The specific steps to achieve this are as follows:

[0071] Step 1) Design the casting gating system based on the structure of the shell launching base casting, using a horizontal sprue as the main method;

[0072] Step 2) Based on the number and angle of the horizontal runner, determine the number of radial screw skeleton screw mounting holes for the irregular connecting nut as 6 (i.e., 3 through holes), with a radial angle of 60°, and one axial screw skeleton screw mounting hole as 3 (see partial sectional view). Figure 4 ), produce drawings, and machine into shape;

[0073] Step 3) Pre-screw the screw skeleton onto the special-shaped connecting nut. The radial screw skeleton corresponds to the horizontal runner, and the axial screw skeleton corresponds to the vertical runner. The screw skeleton extends 20-30mm beyond the end face of the corresponding runner and presses the horizontal runner and vertical runner.

[0074] Step 4) Connect the sprue cup with the robotic gripper to the horizontal and vertical runners with the irregular connecting nut and screw skeleton by adding spring washers and using a torque wrench;

[0075] Step 5) Assemble the wax mold modules and use a robotic automated shell-making line to produce the mold shell;

[0076] Step 6) Dewax and bake the shell. After dewaxing, remove the screw skeleton one by one by twisting. Then, pull out the irregular connecting nut from the direction of the pouring cup. Wrap the process hole left after the screw skeleton is removed with aluminum foil. Finally, seal it with silica sol, sand and powder.

[0077] Step 7) Cast the shell obtained in step 6) using anti-gravity casting;

[0078] Step 8) Clean the mold shell around the casting and gating system from Step 7), remove the gating system, and clean and grind the surface of the casting;

[0079] Step 9) Perform heat treatment on the casting from step 8);

[0080] Step 10) Perform X-ray radiography and fluorescence penetrant testing on the castings from Step 9);

[0081] Step 11) Perform blue light scanning dimensional inspection and fitter scribing inspection on the castings from Step 9).

[0082] The castings prepared by the above method are free from shell cracking and module breakage in the automated shell-making line produced by the robotic arm; after X-ray and fluorescence penetrant testing, more than 99% of the shell launcher base castings were free of inclusion defects; after blue light scanning dimensional inspection and fitter scribing inspection, the casting dimensional inspection pass rate was 100%, and the overall first-pass pass rate was over 99%.

[0083] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention.

[0084] It should be understood that the present invention is not limited to the content already described above, and various modifications and changes can be made without departing from its scope. The scope of the present invention is limited only by the appended claims.

Claims

1. A method for preparing a large casting using a silica sol-molded shell-type special-shaped connecting nut, characterized in that, Specifically, the following steps are included: Step 1) Design the casting gating system according to the structure of the part to be cast; Step 2) Determine the number and angle of the screw mounting holes for the irregular connecting nut and bolt skeleton based on the number and angle of the horizontal runners in the casting gating system; Step 3) Pre-screw the screw skeleton into the irregular connecting nut, press the horizontal runner and vertical runner, and make the screw skeleton extend 20~30mm beyond the corresponding runner; Step 4) Connect the sprue cup with the robotic gripper to the horizontal runner and vertical runner with the irregular connecting nut and screw skeleton; Step 5) Assemble the wax mold modules and use a robotic automated shell-making line to produce the mold shell; Step 6) Dewax and bake the shell. After dewaxing, remove the screw skeleton one by one by twisting. Then, pull out the irregular connecting nut from the direction of the pouring cup. Wrap the process hole left after the screw skeleton is removed with aluminum foil. Finally, seal it with silica sol, sand and powder. Step 7) Cast the shell obtained in step 6) using anti-gravity casting; Step 8) Clean the mold shell around the casting and gating system from Step 7), remove the gating system, and clean and grind the surface of the casting; Step 9) Heat treat the casting from step 8) to complete the preparation of the structure to be cast; The aforementioned shaped connecting nut for the silica sol shell is pre-embedded in the wax mold module. The shaped connecting nut includes a nut body, an axial screw skeleton screw-on hole (3) is provided in the center of the nut body, and a robotic gripper is installed at the bottom of the nut body. Wax contact reinforcement holes (4) are evenly distributed around the axial screw skeleton screw-on hole (3), and the wax contact reinforcement holes (4) are arranged in a direction parallel to the axial direction of the nut body. The nut body is also provided with a plurality of evenly distributed radial screw skeleton screw-on holes (1), and the radial screw skeleton screw-on holes (1) are connected to the axial screw skeleton screw-on holes (3).

2. The method for preparing a large casting using a silica sol-molded shell with a special-shaped connecting nut according to claim 1, characterized in that, The special-shaped connecting nut is made of quenched and tempered 45# steel.

3. The method for preparing a large casting using a silica sol-molded shell with a special-shaped connecting nut according to claim 1, characterized in that, The number of radial screw skeleton screw mounting holes (1) is 4 to 8.

4. The method for preparing a large casting using a silica sol-molded shell with a special-shaped connecting nut according to claim 1, characterized in that, In step 4), the sprue cup with the robotic gripper is connected to the horizontal and vertical runners by adding spring washers and using a torque wrench.

5. The method for preparing a large casting using a silica sol-molded shell with a special-shaped connecting nut according to claim 1, characterized in that, It also includes the following steps: Step 10) Perform X-ray radiography and fluorescence penetrant testing on the casting structure from Step 9) to determine whether the casting structure has inclusion defects.

6. The method for preparing a large casting using a silica sol-molded shell with a special-shaped connecting nut according to claim 5, characterized in that, It also includes the following steps: Step 11) Perform blue light scanning dimensional inspection and fitter scribing inspection on the casting structure in Step 10) to determine whether the casting structure is deformed.

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