Mould pressing manufacturing process for hard graphite polar plate

Abstract

The invention relates to a mould pressing manufacturing process for a hard graphite polar plate. The mould pressing manufacturing process specifically comprises the following steps: crushing raw materials, purifying the raw materials, pulping, mixing, drying, prefabricating a blank plate, heating and drying the blank plate, carrying out compression molding, carrying out precision detection and air tightness detection, carrying out hole sealing treatment, carrying out surface treatment, carrying out performance testing, cementing a single polar plate, bonding a bipolar plate and curing the bipolar plate. According to the method, the hard graphite polar plate is processed by adopting a brand new processing technology, so that the problems of low processing efficiency, high processing cost, large material waste, poor processing environment and low yield in the traditional processing technology are solved; and the purity of the raw material before the blank plate is pre-pressed is improved.

Description

Technical Field

[0001] This invention relates to the field of new energy technology, and in particular to a molding process for manufacturing hard graphite electrode plates. Background Technology

[0002] Graphite plates are widely used in new energy products such as fuel cells, flow batteries, and PEM electrolyzers. They require strict consistency in quality and performance, and their wide application has significant commercial value. Currently, the production process for hard graphite plates involves conventional organic processing and engraving, which suffers from low efficiency, high cost, significant material waste, poor processing environment, low yield, and defects such as easy powder shedding from the processed surface.

[0003] For example, Chinese patent CN115786958A discloses a method for preparing a graphite electrode plate, a graphite electrode plate, and an alkaline electrolytic cell. The method for preparing the graphite electrode plate includes: pre-pressing the graphite electrode plate raw material to obtain a dense blank; sequentially molding and demolding the dense blank to obtain a shaped blank; and coating the shaped blank to obtain a graphite electrode plate.

[0004] As can be seen from the above-mentioned technologies, there are currently impurities in the raw materials for graphite plates. The current method is to directly pre-press the raw materials to obtain the blanks, which can easily lead to low purity in the processed graphite plates.

[0005] To address the aforementioned problems, this invention develops a new manufacturing process to meet the needs of large-scale industrial manufacturing. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a molding process for hard graphite electrode plates.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A molding process for manufacturing hard graphite electrode plates includes the following steps:

[0009] Raw material crushing, raw material purification, pulping, mixing, drying, prefabrication of blank plates, heating of blank plates, pressing and molding, precision testing and airtightness testing, sealing treatment, surface treatment, performance testing, single-plate gluing process or bipolar plate bonding process and bipolar plate curing process.

[0010] Among them, the raw material crushing process adopts ball milling and sieving to crush the graphite raw material into powder with a uniform particle size of 25-45μm.

[0011] The raw material purification process uses alkaline high-temperature melting and acid hydrolysis to remove impurities from the raw materials, and then washes and dries the raw materials with clean water.

[0012] The pulping process uses N-methylpyrrolidone (NMP) as a solvent and polyvinylidene fluoride (PVDF) as a binder;

[0013] The average molecular weight of the binder is 200,000 to 500,000, the mass percentage of the binder to the solvent is 5% to 10%, the mixing time is 1 to 4 hours, and the viscosity of the slurry at room temperature after uniform mixing is no greater than 5 Pa·s.

[0014] Furthermore, the steps of the mixing process are as follows:

[0015] First, mix carbon fiber and graphite powder in a certain proportion until they are evenly mixed. Then, add the mixed powder to the slurry and stir for 30 to 240 minutes to ensure that the materials are fully mixed.

[0016] The mass ratio of carbon fiber to graphite powder in the mixed powder is 1:20 to 1:1, and the mass ratio of mixed powder to slurry is 2:1 to 1:2.

[0017] Furthermore, the drying process employs low-temperature stirring, with a drying temperature of 50-80℃ and a drying time of 60-240 minutes.

[0018] Furthermore, the precast blank plate process involves accurately weighing, leveling, and pre-pressing the powder, pressing the mixture in a press mold, and bonding the powder into a blank plate with a certain strength under a certain pressure pre-pressing.

[0019] Furthermore, the heating process of the blank plate is carried out in a heating furnace under PID control. The heating furnace can be an electric furnace, electromagnetic induction heating, microwave heating or radiation heating, with a heating temperature of 115℃-215℃ and a heating and holding time of 5-60 minutes.

[0020] Furthermore, the pressing process involves placing the heated high-temperature blank plate into a mold for vacuum pressing. The vacuum level inside the mold reaches 1-10 kPa, the blank plate temperature is 150-215℃, the pressure is 50-100 MPa, the pressure is held for 10-60 seconds, and the blank plate is cooled to 50-80℃ inside the mold before being removed and air-cooled.

[0021] Furthermore, the specific steps of the precision testing process and the airtightness testing process are as follows:

[0022] For precision testing of molded products, laser thickness gauges or photoelectric detection devices are used to detect the thickness, parallelism tolerance, and various dimensional and surface precision of the sealing groove and flow field of the graphite electrode.

[0023] For air tightness testing, an online full inspection mode is adopted, and the air tightness of the graphite plate is tested using the pressure drop method, pressure difference method, flow rate method or helium detection method.

[0024] When the airtightness test fails, the graphite plate is subjected to a sealing process, which includes impregnation, cleaning, heat curing, and drying.

[0025] Furthermore, the surface treatment process involves repairing burrs and rough edges, removing adhesive residue, clearing blockages, and removing dust from the graphite monopolar plates after airtightness testing and after sealing.

[0026] The performance testing process involves testing the strength and conductivity data of graphite plates.

[0027] Furthermore, the specific steps of the single-plate bonding process are as follows:

[0028] First, a single-electrode plate is glued to its sealing surface. The glued plate is produced by injection molding or bonding sealing strips to create a split assembly single-electrode plate. The glued single-electrode plate and another corresponding single-electrode plate form anode and cathode plates, which are then paired and assembled into bipolar plates.

[0029] When bonding anode and cathode plates into bipolar plates, a bipolar plate bonding process and a bipolar plate curing process are required. For bonded bipolar plates, first apply glue or screen print it onto the bonding surface of a set monopolar plate, then align and attach the monopolar plates that are paired with its anode and cathode plates, apply pressure, and place it in a curing oven for heating and curing to obtain a graphite bipolar plate.

[0030] The beneficial effects of this invention are as follows: This invention uses a brand-new processing technology to process hard graphite plates, which overcomes the problems of low processing efficiency, high processing cost, large material waste, poor processing environment and low yield in traditional processing technology.

[0031] Meanwhile, the present invention processes raw materials into uniform and pure granules through raw material crushing and purification, and simultaneously weighs, mixes and stirs solvents and binders to make slurry, adds carbon fiber to the above graphite powder and mixes it evenly, and then mixes and stirs the mixed powder and slurry evenly, and then dries it, thereby improving the purity of the raw materials before the pre-pressing of the blank plate. Attached Figure Description

[0032] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0033] like Figure 1 As shown, a manufacturing process for hard graphite electrode plates by molding includes the following steps: raw material crushing, raw material purification, pulping, mixing, drying, preforming blank plates, heating and drying of blank plates, pressing and molding, precision testing and airtightness testing, sealing treatment, surface treatment, performance testing, single electrode plate gluing, bipolar plate bonding and bipolar plate curing.

[0034] When the incoming material is natural flake graphite, it is first crushed using a ball mill and then sorted using an air sieve to pulverize it into uniform powder with a particle size of 25-45μm. After pulverizing, the graphite is soaked in high-temperature molten NaOH and acidified with HCl, then washed with clean water to remove impurities and improve the graphite purity to over 99%. The incoming material can also be pre-pulverized and purified finished graphite.

[0035] The pulping process involves using N-methylpyrrolidone (NMP) as a solvent and polyvinylidene fluoride (PVDF) with an average molecular weight of 200,000 to 500,000 as a binder to prepare a mixture with a mass percentage of 5% to 10% of binder and solvent. The stirring time is 1 to 4 hours, and the viscosity of the pulp at room temperature after uniform mixing is no greater than 5 Pa·s.

[0036] The mixing process specifically involves selecting short-cut carbon fibers and mixing them evenly with the slurry, then adding pulverized and purified graphite powder to the mixture. The carbon fibers and graphite powder are added in a specific ratio, and the mixing time is 30–240 minutes to ensure thorough mixing. The mass ratio of carbon fibers to graphite powder in the mixed powder is 1:20–1:1, and the mass ratio of the mixed powder to the slurry is 2:1–1:2.

[0037] The drying process involves using a low-temperature mixing tank and drying at 50-80℃ for 60-240 minutes to achieve a powder dryness of 90%-97%.

[0038] The precast blank slab process specifically involves weighing, leveling, and pre-pressing the mixture in the mold of a press to form a blank slab with a certain strength.

[0039] The blank plate is heated in a heating furnace under PID control. The heating furnace can be an electric furnace, electromagnetic induction heating, microwave heating, or radiation heating. The heating temperature is 115℃-215℃, and the heating and holding time is 5-60 minutes.

[0040] The process allows the remaining solvent in the preform plate to fully evaporate. After the solvent evaporates, open micropores are formed on the surface of the graphite monopolar plate, which facilitates the discharge of the closed gas inside the graphite monopolar plate, dries the inside of the preform plate, and facilitates the vacuum removal of the gas inside the graphite monopolar plate. It also allows the binder inside the preform plate to partially melt and form adhesion.

[0041] The pressing process involves placing a heated high-temperature preform into a molding die. The die is then evacuated to remove gas from the graphite monopolar plate at high temperature, reaching a vacuum level of 1-10 kPa. When the graphite monopolar plate temperature reaches 150-215℃, pressure is applied to the die at 50-100 MPa and held for 10-60 seconds to produce a graphite monopolar plate of a specific thickness. This process eliminates internal and surface voids in the graphite monopolar plate, improving its sealing performance. Simultaneously, the graphite monopolar plate is cooled within the die to 50-80℃ to fully solidify the binder before being removed and air-cooled, ensuring the quality and precision of the graphite monopolar plate.

[0042] The precision testing and airtightness testing processes specifically involve precision testing of the molded products. Precision testing can be conducted online (full inspection) or offline (sampling inspection). Laser thickness gauges or photoelectric detection devices can be used to test the thickness, parallelism tolerance, and dimensional accuracy and surface finish of the sealing grooves and flow fields. Airtightness testing employs an online full inspection mode and can use pressure drop, differential pressure, flow rate, or helium gas detection methods to test the airtightness of graphite molded parts.

[0043] The sealing process involves sealing the graphite monopolar plate when it fails the airtightness test, eliminating blind holes and through holes. The sealing process includes impregnation, cleaning, heat curing, and drying to seal the micropores of the graphite monopolar plate and improve its airtightness.

[0044] The surface treatment process specifically involves repairing burrs and rough edges, removing adhesive residue, clearing blockages, and removing dust from graphite monopolar plates that have passed airtightness testing and after sealing treatment, without damaging the graphite monopolar plates themselves during the repair process.

[0045] The performance testing process involves testing the strength and conductivity of the produced graphite monopolar plates under conditions such as changing raw materials and modifying process parameters. The testing methods can be online testing or offline batch sampling.

[0046] The specific process of graphite monopolar plate gluing is as follows: in the production of assembled bipolar plates, a set monopolar plate sealing surface is first glued, and the gluing production is carried out by injection molding or adhesive sealing strips to produce a split assembled monopolar plate. The glued monopolar plate and another corresponding monopolar plate form anode and cathode plates, which are then paired and assembled into a bipolar plate.

[0047] The bipolar plate bonding process and bipolar plate curing process are as follows: In the production of bonded bipolar plates, adhesive is first applied or screen-printed on the bonding surface of a set monopolar plate, and then the monopolar plates that are matched with its anode and cathode are aligned, bonded, and placed in a curing oven for heating and curing to obtain a graphite bipolar plate. The graphite bipolar plate is an integral bonded bipolar plate, and it does not need to be assembled separately during bipolar plate assembly.

[0048] In summary, this invention processes raw materials into uniform and pure granules through crushing and purification. Simultaneously, solvents and binders are weighed, mixed, and stirred to form a slurry. Carbon fibers are added to the graphite powder and mixed evenly. The mixed powder and slurry are then mixed and stirred evenly, and dried to a certain degree of dryness. Subsequently, a preform plate is produced under quantitative and pressure conditions. The preform plate is placed in a heating furnace and heated, then vacuum-pressed to form the final shape. The formed graphite monopolar plates undergo thickness and airtightness testing. Graphite monopolar plates that do not meet airtightness requirements are sealed. Graphite monopolar plates that pass airtightness testing and are sealed undergo surface treatment and performance testing, and are then classified and stored. Alternatively, according to production requirements, the qualified monopolar plates can be online into a bonding process to produce bonded, modular monopolar plates; or a bipolar plate bonding and curing process can be directly performed to produce an integrally bonded bipolar plate.

[0049] This invention employs a novel processing technique to process hard graphite plates, overcoming the problems of low processing efficiency, high processing cost, significant material waste, poor processing environment, and low yield in traditional processing techniques.

[0050] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention. The scope of protection claimed by the appended claims and their equivalents is defined.

Claims

1. A molding process for manufacturing hard graphite electrode plates, characterized in that, Includes the following steps: Raw material crushing, raw material purification, pulping, mixing, drying, prefabrication of blank plates, heating of blank plates, pressing and molding, precision testing and airtightness testing, sealing treatment, surface treatment, performance testing, single-plate gluing process or bipolar plate bonding process and bipolar plate curing process. The raw material crushing process employs ball milling and sieving to crush the graphite raw material into uniform powder with an average particle size of 25-45μm. The raw material purification process uses alkaline high-temperature melting and acid hydrolysis to remove impurities from the raw materials, and then washes and dries the raw materials with clean water. The pulping process uses N-methylpyrrolidone (NMP) as a solvent and polyvinylidene fluoride (PVDF) as a binder. The binder has an average molecular weight of 200,000 to 500,000, the mass percentage of binder to solvent is 5% to 10%, the mixing time is 1 to 4 hours, and the viscosity of the slurry at room temperature after uniform mixing is not greater than 5 Pa·s.

2. The die-forming process for hard graphite electrode plates according to claim 1, characterized in that, The steps of the mixing process are as follows: First, mix carbon fiber and graphite powder in a certain proportion until they are evenly mixed. Then, add the mixed powder to the slurry and stir for 30 to 240 minutes to ensure that the materials are fully mixed. The mass ratio of carbon fiber to graphite powder in the mixed powder is 1:20 to 1:1, and the mass ratio of the mixed powder to the slurry is 2:1 to 1:

2.

3. The die molding manufacturing process for hard graphite electrode plates according to claim 1 or 2, characterized in that, The drying process employs low-temperature stirring, with a drying temperature of 50-80℃ and a drying time of 60-240 minutes.

4. The die-forming process for hard graphite electrode plates according to claim 3, characterized in that, The precast blank plate process involves accurately weighing, leveling, and pre-pressing the powder, pressing the mixture in a press mold, and bonding the powder into a blank plate with a certain strength under a certain pressure pre-pressing.

5. The die molding manufacturing process for hard graphite electrode plates according to claim 3, characterized in that, The heating process of the blank plate is carried out in a heating furnace under PID control. The heating furnace can be an electric furnace, electromagnetic induction heating, microwave heating or radiation heating. The heating temperature is 115℃-215℃ and the heating and holding time is 5-60min.

6. The die molding manufacturing process for hard graphite electrode plates according to claim 3, characterized in that, The pressing process involves placing a heated high-temperature blank into a mold for vacuum pressing. The vacuum level inside the mold reaches 1-10 kPa, the blank temperature is 150-215℃, the pressure is 50-100 MPa, the pressure is held for 10-60 seconds, and the blank is removed and air-cooled after cooling to 50-80℃ inside the mold.

7. The die molding manufacturing process for hard graphite electrode plates according to claim 3, characterized in that, The specific steps of the accuracy testing process and the airtightness testing process are as follows: For precision testing of molded products, laser thickness gauges or photoelectric detection devices are used to detect the thickness, parallelism tolerance, and various dimensional and surface precision of the sealing groove and flow field of the graphite electrode. For air tightness testing, an online full inspection mode is adopted, and the air tightness of the graphite plate is tested using the pressure drop method, pressure difference method, flow rate method or helium detection method. When the airtightness test fails, the graphite electrode plate is subjected to the sealing process, which includes impregnation, cleaning, heating and curing, and drying.

8. The die-forming process for manufacturing hard graphite electrode plates according to claim 3, characterized in that, The surface treatment process involves repairing burrs and rough edges, removing adhesive residue, clearing blockages, and removing dust from graphite monopolar plates after airtightness testing and after sealing. The performance testing process involves testing the strength and conductivity data of the graphite electrode.

9. The die molding manufacturing process for hard graphite electrode plates according to claim 3, characterized in that, The specific steps of the single-plate bonding process are as follows: First, a single-electrode plate is glued to its sealing surface. The glued plate is produced by injection molding or bonding sealing strips to create a split assembly single-electrode plate. The glued single-electrode plate and another corresponding single-electrode plate form anode and cathode plates, which are then paired and assembled into bipolar plates. When it is necessary to bond anode and cathode plates into bipolar plates, the aforementioned bipolar plate bonding process and bipolar plate curing process must be adopted. For bonded bipolar plates, first apply glue or screen print on the bonding surface of a set monopolar plate, then align and bond the monopolar plates that are paired with its anode and cathode plates, apply pressure, and place it in a curing oven for heating and curing to obtain a graphite bipolar plate.

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