Method for preparing electric contact material based on vacuum magnetic suspension smelting technology

Abstract

The invention relates to the technical field of electric contact material preparation, in particular to a method for preparing an electric contact material based on a vacuum magnetic suspension smelting technology. The vacuum magnetic suspension smelting technology and the centrifugal casting technology are adopted in the field of electric contact materials for the first time, then after a casting is turned and machined through a lathe, a 1100 t extruding machine is adopted to conduct extrusion, drawing and wire machining on a cast ingot, internal oxidation is conducted on a machined wire section, the extruding machine is adopted to conduct extrusion on an oxidized spindle, and the electric contact material is obtained. And completing the preparation of the electric contact material. A molten material and the crucible wall are kept in a dynamic contact or non-contact state by means of electromagnetic force, a traditional crucible material is replaced, the alloy purity is high, and the crucible can be repeatedly used for thousands of times; and then the liquid metal is injected into a casting mold rotating at a high speed, cooling forming is conducted under a centrifugal force field, the process yield is increased, the casting is high in density, few in defects such as air holes and slag inclusion and high in mechanical property, and the material machining performance can be effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of electric contact material preparation, and in particular to a method for preparing electric contact material based on vacuum magnetic levitation melting technology. Background Art

[0002] The current preparation processes for electrical contact materials mainly include alloy internal oxidation method, powder mixing method, atomization method and other processes. In the alloy internal oxidation method, the metal raw materials (silver and other metals) need to be melted to form alloy liquid, which is then injected into a mold to form an alloy ingot, and then internally oxidized. Among them, the alloy smelting process is crucial. The purity and smelting temperature of the alloy have a great influence on the material forming. The existing equipment is mainly induction melting. The material is melted in a crucible. The process easily introduces Si and other impurities. The purity of the alloy is highly dependent on the cleanliness of the crucible and other stirring equipment.

[0003] Vacuum induction levitation melting (ISM) is a high-quality alloy melting technology that has developed rapidly in recent years. Its applications span the foundry industry, including aerospace, naval vessels and automobiles, nuclear power hydrogen storage, medical and sports, and additive manufacturing. Daido Steel Co., Ltd. pioneered the development of a large-scale cold crucible semi-levitation melting (ISM) bottom pouring device, which has been used to shorten the process flow for preparing profiles of materials such as titanium alloys, vanadium alloys, molybdenum, niobium, and tantalum. This significantly shortens the process route, achieving energy conservation, emission reduction, and cost reduction. The device features a 240L cold crucible volume, a 2400kW power supply, and an 800Hz frequency, capable of melting 500k titanium. Summary of the Invention

[0004] The purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art and to provide a method for preparing electrical contact materials based on vacuum magnetic levitation melting technology.

[0005] The technical solution adopted by the present invention is as follows: a method for preparing an electrical contact material based on vacuum magnetic levitation melting technology, the method comprising the following steps:

[0006] (1) Vacuum magnetic levitation melting: The raw materials are loaded into the furnace with electrical contact, vacuum is drawn, and the vacuum magnetic levitation melting process is started. The current passes through the induction coil to generate eddy current in the alloy to heat the alloy until the smelting material is completely melted into an alloy melt. Under the action of electromagnetic force, the surface of the alloy melt tends to be spherical and levitates on the surface of the crucible;

[0007] (2) Centrifugal casting: The liquid metal after vacuum magnetic levitation melting in step (1) is poured into a high-speed rotating mold to form a casting;

[0008] (3) Cooling: taking out the casting from the mold in step (2), cooling it so that convection no longer occurs on the surface of the casting and the casting gradually solidifies until the melt is completely solidified to form a casting;

[0009] (4) Post-processing process: The casting formed in step (3) is turned using a lathe, heated, extruded into an ingot, internally oxidized, and extruded into a material to obtain an electrical contact material.

[0010] In step (1), the crucible is cleaned before loading into the furnace.

[0011] In step (1), the smelting chamber pressure is reduced to 10 -3 to 10 -5 Pa, after vacuuming, introduce inert gas to 50-100 mm Hg.

[0012] In step (1), the smelting process includes an electromagnetic heating process, which, after being started, causes the metal raw material to be lifted by the magnetic field.

[0013] The electromagnetic heating procedure includes a preheating stage and a full melting stage which are carried out successively. The preheating stage is used to soften the metal surface, and the full melting stage is used to completely liquefy the metal.

[0014] The preheating stage is to apply a current of 10-20 kHz to the induction coil; the full melting stage is to apply a current of 20-50 kHz to the induction coil.

[0015] In step (2), the starting speed of the mold is 800-1000 r / min. After the liquid metal is injected into the high-speed rotating mold, the liquid metal gradually cools and forms under the action of the centrifugal field. During this stage, the rotation speed of the mold is controlled to be 50-1000 r / min, and the time is 3-8 hours.

[0016] In step (3), the casting is controlled to be cooled in stages at a rate of 2-6 kW / min.

[0017] In step (4), the turning is to turn 1-3 mm on the surface of the casting.

[0018] The beneficial effects of the present invention are as follows:

[0019] 1. This invention is the first to use vacuum magnetic levitation melting technology in the field of electrical contact materials. Relying on electromagnetic force, the melted material maintains dynamic contact or non-contact with the crucible wall, replacing traditional crucible materials. The alloy is pure and high in purity, and the crucible can be reused thousands of times.

[0020] 2. The present invention adopts centrifugal casting technology to inject liquid metal melted by vacuum magnetic levitation melting technology into a high-speed rotating mold, and cools and forms it under a centrifugal field. There is almost no metal consumption in the pouring system and riser system, which improves the process yield. The casting has high density, few defects such as pores and slag inclusions, and high mechanical properties, which can effectively improve the material processing performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, without paying any creative work, other drawings obtained based on these drawings still fall within the scope of the present invention.

[0022] Figure 1 The following are process flow charts of some specific embodiments of the present invention. DETAILED DESCRIPTION

[0023] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention will be described in further detail below with reference to the accompanying drawings.

[0024] The present invention provides a method for preparing an electrical contact material based on vacuum magnetic levitation melting technology, the method comprising the following steps:

[0025] (1) Vacuum magnetic levitation melting: The metal raw materials are loaded into the furnace with electrical contact, vacuum is drawn, and the vacuum magnetic levitation melting process is started. The current passes through the induction coil to generate eddy current in the alloy to heat the alloy until the molten metal material is completely melted into an alloy melt. Under the action of electromagnetic force, the surface of the alloy melt tends to be spherical and suspends on the surface of the crucible; through vacuum magnetic levitation melting

[0026] (2) Centrifugal casting: The liquid metal after vacuum magnetic levitation melting in step (1) is poured into a high-speed rotating mold to form a casting;

[0027] (3) Cooling: taking out the casting from the mold in step (2), cooling it so that convection no longer occurs on the surface of the casting and the casting gradually solidifies until the melt is completely solidified to form a casting;

[0028] (4) Post-processing process: The casting formed in step (3) is turned using a lathe, heated, extruded into an ingot, internally oxidized, and extruded into a material to obtain an electrical contact material.

[0029] The present invention is applicable to materials such as AgSnO2, AgZnO, AgCuO, and AgCdO that can be subjected to an internal oxidation process. The present invention employs vacuum magnetic levitation melting technology for the first time to prepare electrical contact materials. A high-frequency current is passed through the induction coil, and the alternating electromagnetic field generates high-frequency eddy currents on the surface of the metal material. The high-frequency eddy currents interact with the external magnetic field to generate a Lorentz force. By changing the power of the high-frequency power supply, the electromagnetic force can be made equal to the force of gravity, achieving electromagnetic levitation. Simultaneously, the eddy currents on the metal generate Joule heat, causing the metal body to melt, thereby achieving the purpose of smelting. By relying on electromagnetic force to maintain dynamic contact or non-contact between the molten material and the crucible wall, traditional crucible materials are replaced, resulting in a pure alloy with high purity. The crucible can be reused thousands of times. Furthermore, centrifugal casting technology is employed to cool and shape the alloy liquid under a centrifugal field. Metal consumption in the pouring system and riser system is virtually eliminated, thereby improving the process yield rate. The castings have high density, few defects such as pores and slag inclusions, and high mechanical properties, effectively improving the material's processing performance.

[0030] In some embodiments of the present invention, in step (1), the crucible is cleaned before loading into the furnace to prevent the residual material of the previously smelted material from doping the current smelting.

[0031] In some embodiments of the present invention, in step (1), the evacuation is performed to reduce the pressure of the smelting chamber to 10-3 to 10 -5 Pa, after evacuation, introduce inert gas to 50-100 mm Hg. The inert gas may be nitrogen, argon, etc.

[0032] In some embodiments of the present invention, in step (1), the smelting program includes an electromagnetic heating program, which, after startup, causes the metal raw material to be lifted by the magnetic field. The frequency of the magnetic field controlled by the electromagnetic heating program is 10-50KHZ. Specifically, the electromagnetic heating program includes a preheating stage and a full melting stage, which are carried out successively. The preheating stage is used to soften the metal surface to avoid sudden cracking due to heat, and the full melting stage is used to completely liquefy the metal. The preheating stage is to apply a current of 10-20KHZ to the induction coil; the full melting stage is to apply a current of 20-50KHZ to the induction coil. At the same time, the liquid metal maintains a rotating state under the action of the magnetic field to promote the homogenization of the composition.

[0033] In some embodiments of the present invention, in step (2), the starting speed of the casting is 800-1000 r / min, so that the liquid metal is evenly distributed in the centrifugal field. After the liquid metal is injected into the high-speed rotating casting, the liquid metal is gradually cooled and formed under the action of the centrifugal field. During this stage, the rotation speed of the casting is controlled to 50-1000 r / min and the time is 3-8 hours to ensure the quality of the casting.

[0034] In step (3), the cooling method of the casting can be selected according to the desired material properties, such as natural air cooling, or controlled staged cooling by external temperature control in the furnace. In some embodiments of the present invention, the casting is cooled in stages at a rate of 2-6 kW / min to control the solidification rate to obtain a specific crystal structure.

[0035] In some embodiments of the present invention, in step (4), the turning is to turn 1-3 mm on the surface of the casting to remove surface pores and impurities.

[0036] In some embodiments of the present invention, in step (4), the first extrusion forms material segments with a length of 2-20 mm and a diameter of 80-150 mm to facilitate internal oxidation, and the second extrusion forms sheets, strips, or wires as needed.

[0037] The following are some specific embodiments of the present invention.

[0038] Example 1:

[0039] A method for preparing electrical contact materials based on vacuum magnetic levitation melting technology, the specific steps are as follows:

[0040] Step (1), vacuum magnetic suspension melting: Before the test, the rotating drum is shot peened. After the shot peening is completed, the Ag plate and Sn plate additives are loaded into the furnace. Start the pump group to exhaust the air and reduce the pressure of the melting chamber to 10 -3 Pa, after vacuuming, the protective gas is nitrogen, argon or other inert gas 50mm Hg column to remove waste gas and volatile impurities in the alloy.

[0041] Start the electromagnetic suspension system with a magnetic field starting frequency of 10 kHz. The metal raw material is lifted by the magnetic field. The current passes through the induction coil to generate eddy current in the alloy to heat the alloy. Increase the coil power to 30 kHz. The liquid metal maintains a rotating state under the action of the magnetic field, promoting the homogenization of the composition. The alloy is completely melted into a molten pool and the surface tends to be spherical and suspended on the crucible surface under the action of the electromagnetic force. The smelting duration is 20 minutes.

[0042] Step (2), centrifugal casting: liquid metal is poured into a high-speed rotating mold at a speed of 800 r / min, so that the molten metal undergoes centrifugal motion to fill the mold and form a casting. After gradually cooling, the centrifuge speed is gradually reduced to 50 r / min-0 r / min. After cooling for 5 hours, the casting is taken out and the casting quality is observed.

[0043] Step (3), cooling: the power is reduced to 0 (at a rate of 3 kW / min) in stages to cool the melt. Convection no longer occurs on the melt surface and the melt gradually solidifies. When the melt is completely solidified, it is continued to cool in a vacuum furnace with cooling water.

[0044] Step (4), turning and alloy ingot extrusion: After the casting is turned and heated using a lathe, the ingot is extruded using an 1100t extruder at an extrusion pressure of 150 MPa.

[0045] Step (5), internal oxidation of the material segment: internal oxidation of the processed silk material segment, oxygen pressure: 0.5 MPa, oxidation time: 50 h, oxidation temperature: 700°C.

[0046] Step (6), AgSnO2 extrusion: the oxidized ingot is extruded using an extruder, the extrusion pressure is 180 MPa, and the extrusion method is forward extrusion.

[0047] Example 2:

[0048] A method for preparing electrical contact materials based on vacuum magnetic levitation melting technology, the specific steps are as follows:

[0049] Step (1), vacuum magnetic suspension melting: Before the test, the rotating drum is shot peened. After the shot peening is completed, the Ag plate and Cd plate additives are loaded into the furnace. Start the pump group to exhaust the air and reduce the pressure of the melting chamber to 10 - 4Pa, after vacuuming, the protective gas is nitrogen, argon or other inert gas 60mm Hg column to remove waste gas and volatile impurities in the alloy.

[0050] Start the electromagnetic suspension system with a magnetic field starting frequency of 20 kHz. The metal raw material is lifted by the magnetic field. The current passes through the induction coil to generate eddy current in the alloy to heat the alloy. Increase the coil power to 40 kHz. The liquid metal maintains a rotating state under the action of the magnetic field, promoting the homogenization of the composition. The alloy is completely melted into a molten pool and the surface tends to be spherical and suspended on the crucible surface under the action of the electromagnetic force. The smelting duration is 30 minutes.

[0051] Step (2), centrifugal casting: liquid metal is poured into a high-speed rotating mold at a speed of 1000 r / min, so that the molten metal undergoes centrifugal motion to fill the mold and form a casting. After gradually cooling, the centrifuge speed is gradually reduced to 80 r / min-0 r / min. After cooling for 5 hours, the casting is taken out and the casting quality is observed.

[0052] Step (3), cooling: the power is reduced to 0 (5 kW / min rate) in stages to cool the melt. The melt surface no longer generates convection and gradually solidifies. The melt is completely solidified and continues to cool in a vacuum furnace with cooling water.

[0053] Step (4), turning and alloy ingot extrusion: After the casting is turned and heated using a lathe, the ingot is extruded using an 1100t extruder at an extrusion pressure of 180 MPa.

[0054] Step (5), internal oxidation of the material segment: internal oxidation of the processed silk material segment, oxygen pressure: 0.8 MPa, oxidation time: 60 h, oxidation temperature: 750°C.

[0055] Step (6), AgCdO extrusion: using an extruder to extrude the oxidized ingot, the extrusion pressure is 200 MPa, and the extrusion method is forward extrusion.

[0056] The above disclosure is merely a preferred embodiment of the present invention and certainly cannot be used to limit the scope of the present invention. Therefore, equivalent changes made according to the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for preparing electrical contact materials based on vacuum magnetic levitation melting technology, characterized in that: The method comprises the following steps: (1) Vacuum magnetic levitation melting: The metal raw materials are loaded into the furnace, vacuum is drawn, and the vacuum magnetic levitation melting process is started. The current passes through the induction coil to generate eddy current in the alloy to heat the alloy until the molten metal material is completely melted into an alloy melt. Under the action of electromagnetic force, the surface of the alloy melt tends to be spherical and levitates on the surface of the crucible; (2) Centrifugal casting: The liquid metal after vacuum magnetic levitation melting in step (1) is poured into a high-speed rotating mold to form a casting; (3) Cooling: taking out the casting from the mold in step (2), cooling it so that convection no longer occurs on the surface of the casting and the casting gradually solidifies until the melt is completely solidified to form a casting; (4) Post-processing process: The casting formed in step (3) is turned using a lathe, heated, extruded into an ingot, internally oxidized, and extruded into a material to obtain an electrical contact material.

2. The method for preparing electrical contact materials based on vacuum magnetic levitation melting technology according to claim 1, characterized in that: In step (1), the crucible is cleaned before loading into the furnace.

3. The method for preparing electrical contact materials based on vacuum magnetic levitation melting technology according to claim 1, characterized in that: In step (1), the smelting chamber pressure is reduced to 10 -3 to 10 -5 Pa, after vacuuming, introduce inert gas to 50-100 mm Hg.

4. The method for preparing electrical contact materials based on vacuum magnetic levitation melting technology according to claim 1, characterized in that: In step (1), the smelting process includes an electromagnetic heating process, which causes the metal raw material to be lifted by the magnetic field after being started.

5. The method for preparing electrical contact materials based on vacuum magnetic levitation melting technology according to claim 4, characterized in that: The electromagnetic heating procedure includes a preheating stage and a full melting stage which are carried out successively. The preheating stage is used to soften the metal surface, and the full melting stage is used to completely liquefy the metal.

6. The method for preparing electrical contact materials based on vacuum magnetic levitation melting technology according to claim 5, characterized in that: The preheating stage is to apply a current of 10-20 kHz to the induction coil; the full melting stage is to apply a current of 20-50 kHz to the induction coil.

7. The method for preparing electrical contact materials based on vacuum magnetic levitation melting technology according to claim 1, characterized in that: In step (2), the starting speed of the mold is 800-1000 r / min. After the liquid metal is injected into the high-speed rotating mold, the liquid metal gradually cools and forms under the action of the centrifugal field. During this stage, the rotation speed of the mold is controlled to be 50-1000 r / min, and the time is 3-8 hours.

8. The method for preparing electrical contact materials based on vacuum magnetic levitation melting technology according to claim 1, characterized in that: In step (3), the casting is controlled to be cooled in stages at a rate of 2-6 kW / min.

9. The method for preparing electrical contact materials based on vacuum magnetic levitation melting technology according to claim 1, characterized in that: In step (4), the turning is to turn 1-3 mm on the surface of the casting.

Images