Graphite-filled phenolic plastic for high-performance mechanical seals and method for producing same

Abstract

The application provides a kind of high-performance mechanical seal graphite filled phenolic plastic and its preparation method, the plastic includes the following components by weight parts: phenolic resin 50-80 parts, graphite 20-35 parts, petroleum coke 10-15 parts, compound lubricant 5-15 parts, coupling agent 1-3 parts, curing agent 8-15 parts, curing accelerator 1-3 parts, toughening agent 10-20 parts, calcium metasilicate 2-7 parts and ethylene bis-stearamide 1-3 parts.The application uses compound lubricant composed of zinc stearate, calcium laurate and ethylene bis-stearamide, which cooperates with graphite to form continuous and stable lubricating film on the friction interface.Zinc stearate and calcium laurate provide initial and medium temperature lubrication, and ethylene bis-stearamide migrates to the surface at high temperature to make up the defect of high temperature failure of single graphite lubricating film.Meanwhile, petroleum coke supports the lubricating layer as rigid skeleton to avoid the lubricant being squeezed out too fast.

Description

Technical Field

[0001] This invention relates to the field of phenolic plastics technology, and particularly to a high-performance graphite-filled phenolic plastic for mechanical seals and its preparation method. Background Technology

[0002] Mechanical seals are widely used in rotating shaft seals of pumps, reactors, compressors, etc. Their key performance requirements include a low coefficient of friction, high wear resistance, good heat resistance, and a certain level of mechanical strength. Phenolic plastics are widely used as the matrix for sealing materials due to their low cost, good molding process, and excellent heat resistance. However, pure phenolic resin is brittle after curing and lacks sufficient self-lubricating properties, making it difficult to meet the sealing requirements under high-speed and high-pressure conditions.

[0003] To improve self-lubrication, existing technologies typically add solid lubricants such as graphite to phenolic resins. However, simple binary or ternary mixtures often suffer from uneven filler dispersion and poor interfacial bonding with the resin. When the amount of graphite added is high, although lubrication is improved, the material's density and mechanical strength (such as flexural and compressive strength) decrease significantly, leading to easy wear or brittle fracture of the seals during use. Furthermore, under high temperature or dry friction conditions, pure graphite lubrication is prone to lubricant film failure, resulting in an increased coefficient of friction. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a graphite-filled phenolic plastic for mechanical seals that has excellent self-lubricating properties, high mechanical strength and good heat resistance.

[0005] A high-performance mechanical seal using graphite-filled phenolic plastic comprises the following components by weight: 50-80 parts phenolic resin, 20-35 parts graphite, 10-15 parts petroleum coke, 5-15 parts compound lubricant, 1-3 parts coupling agent, 8-15 parts curing agent, 1-3 parts curing accelerator, and 10-20 parts toughening agent. The compound lubricant comprises 2-5 parts zinc stearate, 2-7 parts calcium silicate, and 1-3 parts ethylene bis-stearamide.

[0006] Graphite and petroleum coke form a coarse-fine gradation system. Graphite sheets form a continuous, low-shear-strength lubricating film on the friction surface, while petroleum coke particles fill the gaps between the graphite sheets and the micropores of the resin matrix. This not only improves the bulk density and compactness of the material, but also acts as a rigid skeleton to withstand compressive stress and prevent the graphite sheets from being crushed or extruded.

[0007] Preferably, the curing agent is hexamethylenetetramine; the curing accelerator is one or a combination of magnesium oxide, lime, iron oxide and zinc oxide.

[0008] Preferably, the toughening agent is carboxyl-terminated nitrile butadiene rubber or liquid nitrile butadiene rubber.

[0009] The carboxyl groups in carboxyl-terminated nitrile butadiene rubber can react chemically with the hydroxymethyl groups in phenolic resin to form chemical bonds, enhancing interfacial adhesion and preventing direct detachment of rubber particles.

[0010] Preferably, the graphite is flake graphite with a particle size of 50-300 mesh; the petroleum coke is calcined petroleum coke with a particle size of 200-500 mesh.

[0011] Flake graphite, being in the form of flakes, has a large particle size that easily aligns along the shear direction during friction, forming a continuous, low-shear-strength lubricating film. Petroleum coke, being hard calcined particles with an even finer particle size, can fill the gaps between graphite flakes and the micropores of the resin matrix, serving as both a "skeletal support" and a "pore-sealing" agent.

[0012] A method for preparing graphite-filled phenolic plastic for high-performance mechanical seals includes the following steps: Graphite and petroleum coke are dried and then mixed with a coupling agent to obtain a modified carbon material mixture. Phenolic resin was ball-milled with a compounded lubricant and a curing accelerator to obtain a resin-lubricant premix. The modified carbon material mixture, resin-lubricant premix, toughening agent and curing agent are kneaded in a kneader to obtain a lump material; The lumpy material is cooled to room temperature, crushed, and sieved to obtain molding powder. The molding powder is then molded to obtain the graphite-filled phenolic plastic for high-performance mechanical seals.

[0013] Coupling agent pretreatment forms an organic coating layer on the filler surface, improving wettability with the resin. Ball milling premixing ensures that the lubricant and curing accelerator are uniformly coated on the resin powder surface, preventing agglomeration. The curing agent is added during the kneading stage, stepwise with the accelerator (see below), to inhibit pre-curing. Compression molding densifies the material and completes cross-linking and curing.

[0014] Preferably, graphite and petroleum coke are dried at 105–120°C for 2–4 hours, and then mixed with a coupling agent in a mixer for 10–20 minutes to obtain a modified carbon material mixture.

[0015] Preferably, the phenolic resin, compound lubricant, and curing accelerator are ball-milled in a ball mill at a speed of 200-300 rpm for 1-2 hours to obtain a resin-lubricant premix.

[0016] Preferably, the mixture is kneaded at 70–90°C for 30–60 minutes to obtain a lumpy material.

[0017] Preferably, after drying and before premixing with the coupling agent, the method further includes the step of surface oxidation treatment of graphite and petroleum coke with an oxidizing agent.

[0018] Graphite and petroleum coke surfaces are inherently inert with very few oxygen-containing functional groups, making it difficult to form strong chemical bonds with coupling agents. Oxidation treatments (such as dilute nitric acid or hydrogen peroxide) can introduce oxygen-containing active groups such as hydroxyl (-OH) and carboxyl (-COOH) groups onto the carbon material surface. These groups become chemical anchors for coupling agents (such as KH-550). The silanol groups after hydrolysis of silane coupling agents can condense with hydroxyl groups to form Si-OC covalent bonds, thereby achieving a strong chemical grafting.

[0019] Preferably, the surface oxidation treatment step includes: adding dried flake graphite and petroleum coke to a dilute nitric acid solution with a mass concentration of 10-25%, stirring in a water bath at 60-80°C for 1-3 hours; washing with deionized water until the pH is 6.5-7.0, filtering, and drying at 105-120°C for 2-4 hours.

[0020] The present invention has the following beneficial effects: This invention employs a compound lubricant composed of zinc stearate, calcium laurate, and ethylene bis-stearamide, which works synergistically with graphite to form a continuous and stable lubricating film at the friction interface. Zinc stearate and calcium laurate provide initial and mid-temperature lubrication, while ethylene bis-stearamide melts and migrates to the surface at high temperatures, compensating for the high-temperature failure defects of a single graphite lubricating film. Simultaneously, petroleum coke acts as a rigid framework to support the lubricating layer, preventing the lubricant from being extruded too quickly. The resulting material exhibits an extremely low coefficient of friction under dry friction conditions and remains stable over a wide temperature range.

[0021] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description and the accompanying drawings.

[0022] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0023] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 A schematic flowchart illustrating the preparation method of graphite-filled phenolic plastic for high-performance mechanical seals provided by the present invention. Detailed Implementation

[0024] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0025] This invention provides a high-performance mechanical seal using graphite-filled phenolic plastic, comprising the following components by weight: 50-80 parts phenolic resin, 20-35 parts graphite, 10-15 parts petroleum coke, 5-15 parts compound lubricant, 1-3 parts coupling agent, 8-15 parts curing agent, 1-3 parts curing accelerator, and 10-20 parts toughening agent. The compound lubricant comprises 2-5 parts zinc stearate, 2-7 parts calcium silicate, and 1-3 parts ethylene bis-stearamide.

[0026] The polar groups of zinc stearate and calcium laurate can adsorb onto the carbonaceous surfaces of graphite and petroleum coke, reducing the interfacial tension between the filler and phenolic resin and promoting the uniform dispersion of graphite flakes and petroleum coke particles in the molten resin state. Ethylene bis-stearamide partially softens at the kneading temperature, acting as an external lubricant to prevent material adhesion to the kneading equipment. The combined effect of these three components ensures that coarse-diameter graphite and fine-diameter petroleum coke are stacked in an orderly manner according to the gradation design, avoiding filler agglomeration or stratification. Furthermore, zinc stearate significantly reduces the demolding force during compression molding, and calcium laurate, being weakly alkaline, neutralizes acidic byproducts such as formic acid and acetic acid released during the curing process of phenolic resin, acting as an acid absorbent and heat stabilizer.

[0027] Coupling agents modify the surface of graphite and petroleum coke, introducing active groups that can react with phenolic resins onto the filler surface, forming a chemically bonded interface. Simultaneously, the carboxyl groups in the toughening agent (carboxyl-terminated nitrile rubber or liquid nitrile rubber) can react not only with the hydroxymethyl groups of the phenolic resin but also with the amino or epoxy groups of the coupling agent, thereby establishing cross-interfacial chemical connections between the filler, coupling agent, toughening agent, and resin.

[0028] like Figure 1 As shown, the present invention also provides a method for preparing graphite-filled phenolic plastic for high-performance mechanical seals, comprising the following steps: Graphite and petroleum coke are dried and then mixed with a coupling agent to obtain a modified carbon material mixture. Phenolic resin was ball-milled with a compounded lubricant and a curing accelerator to obtain a resin-lubricant premix. The modified carbon material mixture, resin-lubricant premix, toughening agent and curing agent are kneaded in a kneader to obtain a lump material; The lumpy material is cooled to room temperature, crushed, and sieved to obtain molding powder. The molding powder is then molded to obtain the graphite-filled phenolic plastic for high-performance mechanical seals.

[0029] Coupling agent pretreatment forms an organic coating layer on the filler surface, improving wettability with the resin. Ball milling premixing ensures that the lubricant and curing accelerator are uniformly coated on the resin powder surface, preventing agglomeration. The curing agent is added during the kneading stage, stepwise with the accelerator (see below), to inhibit pre-curing. Compression molding densifies the material and completes cross-linking and curing.

[0030] The present invention will be further described below with reference to embodiments.

[0031] All raw materials used in the following examples and comparative examples were commercially available industrial products. The phenolic resin was a thermosetting phenolic resin (softening point 85-95℃); graphite (particle size 50-300 mesh, carbon content ≥98%); petroleum coke (particle size 200-500 mesh); zinc stearate, calcium laurate, and ethylene bis-stearamide (EBS) were all industrial grade; KH-550 was used as the coupling agent; hexamethylenetetramine was the curing agent; magnesium oxide was the curing accelerator; and carboxyl-terminated acrylonitrile butadiene rubber (acrylonitrile content 26%, carboxyl value 0.3 mmol / g) was the toughening agent.

[0032] Example 1

[0033] By weight: 50 parts phenolic resin, 20 parts flake graphite, 10 parts petroleum coke, 5 parts compound lubricant (including 2 parts zinc stearate, 2 parts calcium laurate, and 1 part ethylene bis-stearamide), 1 part coupling agent, 8 parts curing agent, 1 part curing accelerator, and 10 parts toughening agent.

[0034] Preparation method: (1) Graphite and petroleum coke were dried at 105°C for 2 hours. After drying, they were mixed with coupling agent in a high-speed mixer for 10 minutes to obtain modified carbon material.

[0035] (2) Phenolic resin, compound lubricant and curing accelerator are ball-milled in a ball mill at 200 rpm for 1 hour (ball-to-material ratio 2:1) to obtain resin-lubricant premix.

[0036] (3) The modified carbon material, resin-lubricant premix, toughening agent and curing agent are kneaded in a kneader at 70°C for 30 minutes to obtain a lump material.

[0037] (4) After the lumpy material is cooled, it is crushed and passed through an 80-mesh sieve to obtain molding powder.

[0038] (5) Compression molding: mold temperature 100℃, pre-compression pressure 5 MPa, venting twice, pre-compression for 5 minutes; then heat up to 160℃ at 2℃ / min, pressure up to 15 MPa, hold pressure and cure for 30 minutes. After demolding, cure at 180℃ for 4 hours.

[0039] Example 2

[0040] By weight: 65 parts phenolic resin, 27.5 parts flake graphite, 12.5 parts petroleum coke, 10 parts compound lubricant (3.5 parts zinc stearate, 4.5 parts calcium laurate, 2 parts EBS), 2 parts coupling agent, 11.5 parts curing agent, 2 parts curing accelerator, and 15 parts toughening agent.

[0041] Preparation method parameters: Drying at 110℃ for 3 hours; ball milling at 250 rpm for 1.5 hours; kneading at 80℃ for 45 minutes; passing through a 100-mesh sieve; molding: pre-pressing at 105℃ for 6.5 MPa, heating rate at 3.5℃ / min to 168℃, pressure at 20 MPa, holding pressure for 45 minutes; post-curing at 190℃ for 6 hours.

[0042] Example 3

[0043] By weight: 80 parts phenolic resin, 35 parts flake graphite, 15 parts petroleum coke, 15 parts compound lubricant (5 parts zinc stearate, 7 parts calcium laurate, 3 parts EBS), 3 parts coupling agent, 15 parts curing agent, 3 parts curing accelerator, and 20 parts toughening agent.

[0044] Preparation method parameters: Drying at 120℃ for 4 hours; mixing for 20 minutes; ball milling at 300 rpm for 2 hours; kneading at 90℃ for 60 minutes; passing through a 120-mesh sieve; molding: pre-pressing at 110℃ for 8 MPa, heating rate at 5℃ / min to 175℃, pressure at 25 MPa, holding pressure for 60 minutes; post-curing at 200℃ for 8 hours.

[0045] Example 4

[0046] The components are the same as in Example 2.

[0047] The process parameters in the preparation method are as follows: drying at 105℃ for 2 hours; mixing with coupling agent for 10 minutes; ball milling at 200 rpm for 1 hour; kneading at 70℃ for 30 minutes; passing through an 80-mesh sieve; molding: pre-pressing at 100℃ for 5 MPa, heating up to 160℃ at 2℃ / min, holding at 15 MPa for 30 minutes; post-curing at 180℃ for 4 hours.

[0048] Example 5

[0049] The components are the same as in Example 2.

[0050] The process parameters in the preparation method are as follows: drying at 120℃ for 4 hours; mixing with coupling agent for 20 minutes; ball milling at 300 rpm for 2 hours; kneading at 90℃ for 60 minutes; passing through a 120-mesh sieve; molding: pre-pressing at 110℃ for 8 MPa, heating up to 175℃ at 5℃ / min, holding at 25 MPa for 60 minutes; post-curing at 200℃ for 8 hours.

[0051] Example 6

[0052] The components are the same as in Example 2.

[0053] The preparation method is the same as in Example 2, except that an oxidant treatment is added.

[0054] Oxidizing agent treatment: Add 10% dilute nitric acid solution, stir in a 60°C water bath for 1 hour, wash until pH 6.5, and dry at 105°C for 2 hours.

[0055] Example 7

[0056] The components are the same as in Example 2.

[0057] The preparation method is the same as in Example 2, except that an oxidant treatment is added.

[0058] Oxidizing agent treatment: Add 25% dilute nitric acid solution, stir in an 80°C water bath for 3 hours, wash until pH 7.0, and dry at 120°C for 4 hours.

[0059] Comparative Example 1 By weight: 65 parts phenolic resin, 27.5 parts flake graphite, 3.5 parts zinc stearate, 2 parts coupling agent, 11.5 parts curing agent, 2 parts curing accelerator, and 15 parts toughening agent.

[0060] Comparative Example 2 A sample was prepared using a commercially available brand of graphite-filled phenolic molding compound, following the manufacturer's recommended molding process.

[0061] Tests: The coefficient of friction was tested according to GB / T 3960-2016, the bending strength was tested according to GB / T 9341-2008, and the heat distortion temperature was tested according to GB / T 1634.2-2019. The results are shown in Table 1.

[0062] Table 1

[0063] As can be seen from Examples 1-3, with the increase of the content of each component (especially graphite, compound lubricant, and toughening agent), the coefficient of friction of the material gradually decreases, while the bending strength and heat distortion temperature both show an upward trend, indicating that the performance within the formulation range of the present invention is controllable and excellent. Examples 4 and 5 use intermediate components but change the process parameters. The results show that Example 5 is beneficial for further improving the density and crosslinking degree, resulting in better mechanical properties and heat resistance. Examples 6 and 7 use an oxidation process, which further improves the mechanical properties and heat resistance.

[0064] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A graphite-filled phenolic plastic for a high-performance mechanical seal, characterized in that, The product comprises the following components by weight: 50-80 parts phenolic resin, 20-35 parts graphite, 10-15 parts petroleum coke, 5-15 parts compound lubricant, 1-3 parts coupling agent, 8-15 parts curing agent, 1-3 parts curing accelerator, and 10-20 parts toughening agent, wherein the compound lubricant comprises 2-5 parts zinc stearate, 2-7 parts calcium silicate, and 1-3 parts ethylene bis-stearamide.

2. The graphite-filled phenolic plastic for high-performance mechanical seals according to claim 1, characterized in that, The curing agent is hexamethylenetetramine; the curing accelerator is one or a combination of magnesium oxide, lime, iron oxide and zinc oxide.

3. The graphite-filled phenolic plastic for high-performance mechanical seals according to claim 1, characterized in that, The toughening agent is carboxyl-terminated nitrile butadiene rubber or liquid nitrile butadiene rubber.

4. The graphite-filled phenolic plastic for high-performance mechanical seals according to claim 1, characterized in that, The graphite used is flake graphite with a particle size of 50-300 mesh; the petroleum coke used is calcined petroleum coke with a particle size of 200-500 mesh.

5. A method for preparing graphite-filled phenolic plastic for high-performance mechanical seals according to any one of claims 1 to 4, characterized in that, Includes the following steps: Graphite and petroleum coke are dried and then mixed with a coupling agent to obtain a modified carbon material mixture. Phenolic resin was ball-milled with a compounded lubricant and a curing accelerator to obtain a resin-lubricant premix. The modified carbon material mixture, resin-lubricant premix, toughening agent and curing agent are kneaded in a kneader to obtain a lump material; The lumpy material is cooled to room temperature, crushed, and sieved to obtain molding powder. The molding powder is then molded to obtain the graphite-filled phenolic plastic for high-performance mechanical seals.

6. The preparation method according to claim 5, characterized in that, Graphite and petroleum coke are dried at 105–120°C for 2–4 hours, and then mixed with a coupling agent in a mixer for 10–20 minutes to obtain a modified carbon material mixture.

7. The preparation method according to claim 5, characterized in that, Phenolic resin, compounded lubricant, and curing accelerator are ball-milled in a ball mill at 200–300 rpm for 1–2 hours to obtain a resin-lubricant premix.

8. The preparation method according to claim 5, characterized in that, Knead at 70–90°C for 30–60 minutes to obtain a lump-like material.

9. The preparation method according to claim 5, characterized in that, After drying and before premixing with the coupling agent, the following steps are also included: surface oxidation treatment of graphite and petroleum coke with an oxidant.

10. The preparation method according to claim 9, characterized in that, The surface oxidation treatment steps include: adding dried flake graphite and petroleum coke to a dilute nitric acid solution with a mass concentration of 10-25%, stirring in a water bath at 60-80℃ for 1-3 hours; washing with deionized water until the pH is 6.5-7.0, filtering, and drying at 105-120℃ for 2-4 hours.

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