Method for producing sliding bearing bush, sliding bearing bush and use of carbon-filled polymer material

Abstract

The invention relates to a method for producing a sliding bearing bush (10) for a pump, to a sliding bearing bush, to a pump having a sliding bearing bush, and to the use of a material for forming a sliding bearing bush, the sliding bearing bush being made of a carbon-filled polymer material, the material having a thermoplastic polymer. The thermoplastic polymer is meltable and has a melting point < = 230 DEG C. The material has a thermoplastic polymer content gt by volume; 20% to 65% by volume and a carbon content gt by volume; 35% to 80% by volume, the material being free of perfluoroor polyfluoroalkyl compounds (PFAS), the sliding bearing bush being formed by an injection molding process.

Description

Technical Field

[0001] The invention relates to a method for producing a plain bearing bushing, a plain bearing bushing for a pump and a pump for a dishwasher or the like, the plain bearing bushing being made of a carbon-filled polymer material comprising a thermoplastic polymer. Background Art

[0002] Sliding bearing bushings are well known in the prior art and are often used to mount pump shafts, for example in circulation pumps in heating circuits or dishwashers. In particular, the pump gear in such pumps is rotatably mounted in a pump housing. The sliding bearings in the pump and / or the pump housing are surrounded by or in contact with the pumped medium and / or the associated liquid. In order to ensure a long service life of the pump, special requirements are placed on the sliding pairing of pump shaft and sliding bearing. For example, the shaft can be made of corrosion-resistant steel, ceramic material or composite materials. In pumps for heating circuits or dishwashers, the pumped water contains dirt or corrosive substances. In particular, dishwasher water is heavily contaminated with dirt, which mainly consists of food residues. This water also has a high salt content, alkaline detergents and polishing additives. As a result, the material of the sliding bearing is subject to corresponding wear, which can affect the service life and noise emissions of the pump.

[0003] Such plain bearing bushings for pumps are known to be made of graphite-filled polytetrafluoroethylene (PTFE). This composite material is produced by mixing polytetrafluoroethylene with graphite in a wet mixing process and subsequently drying. Forming is achieved, for example, by dry pressing the material and sintering at about 300° C. A post-treatment is also required to achieve the required tolerances. This manufacturing method allows the polytetrafluoroethylene to be filled with up to 25% by volume of graphite. The good sliding properties, chemical resistance, adaptability to hard dirt particles and high temperature tolerance of polytetrafluoroethylene enable the production of durable and low-noise plain bearing bushings. However, the production of such plain bearing bushings is relatively complex and therefore costly.

[0004] Furthermore, polytetrafluoroethylene is a per- and polyfluoroalkyl substance (PFAS), which are widely used, in particular in textiles, electronic devices, food contact materials and medical products. These are generally persistent substances, hardly degradable in the environment and can be detected in increasing concentrations in living organisms and the environment. Furthermore, they are considered to be at least partially harmful to health and the environment. Therefore, the European Union (EU) has already restricted the use of some of these substances. There are reasons to suspect that the use of these substances may be further restricted in the future. It is therefore desirable to find a suitable material that does not involve the above-mentioned problems. Summary of the invention

[0005] The object of the present invention is therefore to propose a method for producing a plain bearing bushing, a plain bearing bushing, a pump and a use which allow cost-effective production and use which do not cause concerns with regard to the environment and health.

[0006] This object is achieved by a method having the features of claim 1 , a plain bearing bushing having the features of claim 12 , a pump having the features of claim 13 and the use of a material having the features of claim 18 .

[0007] In the method for manufacturing a sliding bearing bushing for a pump (especially a circulating pump, etc.) according to the present invention, the sliding bearing bushing is made of a carbon-filled polymer material, the material has a thermoplastic polymer, the thermoplastic polymer is meltable and has a melting point of ≤230°C, the material has a thermoplastic polymer content by volume >20% to 65% by volume, a carbon content by volume >35% to 80% by volume, the material does not contain perfluorinated or polyfluoroalkyl compounds (PFAS), and the sliding bearing bushing is formed by an injection molding method.

[0008] Therefore, the sliding bearing bushing is first manufactured by mixing carbon and thermoplastic polymers in a specified content to form a material and / or a molding material, and then injecting the material into a mold by an injection molding method. This is achieved in particular by using a thermoplastic polymer that can be melted at a specified melting temperature. Compared with non-meltable polytetrafluoroethylene, the injection molding method is thus possible, thereby saving many processing steps. In particular, the wet mixing process, drying, sintering and post-treatment can be omitted. It is also possible to significantly increase the carbon content in the material and reduce the thermoplastic polymer content, which can also save costs. Other achievable advantages include less shrinkage during the injection molding process, thus having better dimensional accuracy, and a lower thermal expansion coefficient and higher thermal conductivity of the sliding bearing bushing. In addition, any unqualified sliding bearing bushing can be reused as recycled material by the injection molding method. In addition, the relatively low melting temperature requires relatively little energy, which can save costs. In addition, by filling the above-mentioned content of carbon in the polymer material, the sliding performance and wear resistance of the sliding bearing bushing can be improved, and the high achievable filling content brings additional cost savings. Finally, the use of materials free of perfluorinated and polyfluorinated alkyl compounds allows the manufacture of plain bearing bushings without raising any environmental and health concerns. Overall, the method according to the invention makes the manufacture of plain bearing bushings simpler and therefore more cost-effective and also without raising any environmental and health concerns.

[0009] The material can advantageously have a thermoplastic polymer content of 20% by volume to <50% by volume and a carbon content of >50% by volume to 80% by volume. It has been shown that the method can be carried out particularly efficiently with these thermoplastic polymers and carbon contents.

[0010] The material can consist only of carbon and a meltable thermoplastic polymer. However, in principle it is also possible to add other polymers or other additives to the material and these materials can be processed using the injection molding method.

[0011] In particular, the material may be free of fluoropolymers, in particular polytetrafluoroethylene (PTFE) or ethylenetetrafluoroethylene (ETFE), which belong to the group of per- and polyfluoroalkyl compounds.

[0012] Advantageously, the material can be free of polyethylene (PE). This enables the design of a plain bearing bushing with a relatively high temperature resistance.

[0013] Advantageously, a portion of MoS2 (molybdenum (IV) sulfide or molybdenum disulfide) can be added to the material. This additive can further improve the sliding properties of the plain bearing bushing.

[0014] Advantageously, the melting point of the thermoplastic polymer may be ≥ 170° C. In alternative embodiments of the method, the melting point may be ≥ 180° C., ≥ 190° C. or ≥ 200° C.

[0015] Advantageously, the water absorption of the thermoplastic polymer can be ≥0.05% and ≤3%, preferably ≥0.1% and ≤2%. The plain bearing bushing can then also be advantageously used in places where it comes into contact with liquids, in particular water. The water absorption of the thermoplastic polymer can also be ≥0.5% and ≤3% or ≥1% and ≤2%.

[0016] Advantageously, the density of the thermoplastic polymer may be ≥ 1.0 g / cm 3 And ≤1.5g / cm 3 .

[0017] Furthermore, the thermoplastic polymer may have a dimensional stability temperature of ≥ 110°C and ≤ 160°C at 0.45 MPa.

[0018] Advantageously, the elastic modulus and / or tensile modulus of the thermoplastic polymer may be ≥1000 MPa and ≤3500 MPa. The elastic modulus and / or tensile modulus of the thermoplastic polymer may also be ≥1500 MPa and ≤3500 MPa.

[0019] Advantageously, the thermoplastic polymer may have chemical resistance. In particular, the thermoplastic polymer has good chemical resistance to fats, oils, solvents, fuels, alkalis and salt solutions.

[0020] The carbon used can be graphite, a solid substance containing mainly carbon, petroleum coke or a mixture of these substances. The material can then initially be in powder form, which significantly facilitates its mixing with the thermoplastic polymer. In particular, a relatively high carbon content in the material enables the formation of particularly chemically resistant and temperature-stable plain bearing bushings. In addition, a high carbon content means that particularly favorable friction coefficients of plain bearing bushings can be achieved.

[0021] As part of the method, a molding material of the material can be formed by melting a thermoplastic polymer and mixing with carbon, and the molding material can be placed in an injection mold by an injection molding machine. For example, uniform mixing with carbon can be simply carried out in an extruder and / or a mixer. The use of an injection molding machine can also form a relatively long plain bearing bushing and / or a plain bearing sleeve with a relatively high aspect ratio of almost any geometry. In contrast, when formed by dry pressing, it is not easy to manufacture a long plain bearing bushing and / or a plain bearing bushing with a high aspect ratio, because the wall friction effect prevents uniform compaction, resulting in uneven material properties over the length of the plain bearing bushing.

[0022] The material can be compounded and / or processed in a screw extruder, preferably a twin-screw extruder. This also allows rejects to be fed back into the material flow.

[0023] Furthermore, provision can be made to machine the plain bearing bushing at least on the bearing surface. Although particularly dimensionally accurate plain bearing bushings can already be obtained by using the injection molding method, a more precise adaptation to the shaft or axle of the pump gear can be achieved by machining. In addition, the plain bearing bushing can also be machined after injection molding, for example by vibration finishing. One surface of the plain bearing bushing can then advantageously be designed as a sliding surface.

[0024] The plain bearing bushings can be plasticized or granulated and / or shredded, and the resulting material can be used to manufacture new plain bearing bushings using the method according to the invention. For example, plain bearing bushings manufactured using the method according to the invention can be classified as defective due to dimensional deviations or other manufacturing errors. These plain bearing bushings can then be plasticized or granulated and / or shredded, subsequently plasticized, and the material can then be processed as regrind in an injection molding method. This can save a lot of material.

[0025] The sliding bearing bushing for a pump (in particular a circulation pump, etc.) according to the present invention is made of a carbon-filled polymer material, which contains a thermoplastic polymer, which is meltable and has a melting point of ≤230°C, the material has a thermoplastic polymer content of >20% by volume to 65% by volume and a carbon content of >35% by volume to 80% by volume, the material does not contain perfluorinated or polyfluoroalkyl compounds (PFAS), and the sliding bearing bushing is formed by an injection molding method. Regarding the advantages of the sliding bearing bushing according to the present invention, please refer to the description of the advantages of the method according to the present invention. In particular, the use of an injection molding method to manufacture the sliding bearing bushing does not lead to any density differences as may occur during dry pressing and sintering of the material. Other advantageous embodiments of the sliding bearing bushing are derived from the characterizing description of the dependent claims referring to claim 1.

[0026] A pump for a dishwasher or the like according to the invention has an electric motor for driving a pump gear of the pump, the electric motor being made up of a stator, a rotor and a shaft, the rotor and the pump gear being attached to the shaft, the shaft being mounted on at least one sliding bearing of the pump so as to be rotatable and being located between the rotor and the pump gear, the sliding bearing having a sliding bearing bushing according to the invention.

[0027] The plain bearing bushing can be arranged on the shaft such that the plain bearing bushing is in contact with the liquid that can be conveyed by the pump. For example, the plain bearing bushing can be mounted in the pump housing such that the liquid inevitably comes into contact with the plain bearing bushing and / or flows around it. In this case, provision can be made for the pump gear of the pump to be arranged directly adjacent to the plain bearing bushing on the shaft.

[0028] It is further provided that only the pump has a plain bearing bushing. In principle, the shaft can be fitted with two or more plain bearing bushings. However, in order to save installation space, only one relatively long plain bearing bushing and / or one having a relatively high aspect ratio can be provided. This means that the length of the plain bearing bushing can be set so that tilting of the shaft is avoided and the shaft can be mounted sufficiently securely.

[0029] Advantageously, the electric motor can be designed as a canned motor. This makes it possible to completely seal the rotor from the liquid to be conveyed, thereby allowing the liquid to flow around the rotor.

[0030] The rotor can be made of permanent magnets or squirrel cage windings, and the spacer disk of the pump is attached to the shaft, abutting the axial side surface of the plain bearing bushing. The spacer disk then allows the axial mounting of the rotor and can absorb the axial forces of the pump gear if necessary. The spacer disk can be attached to the shaft, or the shaft can form the spacer disk. Preferably, the spacer disk can be made of the material of the shaft or of a different material.

[0031] Further advantageous embodiments of the pump emerge from the characterizing features of the dependent claims which refer back to claim 1 .

[0032] According to the invention, a carbon-filled polymer material having a melting point ≤ 230° C., having a thermoplastic polymer content of >20% by volume to 65% by volume and a carbon content of >35% by volume to 80% by volume is used for forming a plain bearing bushing for a pump by an injection molding process, the material being free of per- or polyfluoroalkyl substances (PFAS). Further advantageous embodiments of the use of the material result from the characterizing description of the dependent claims referring to claim 1 and claim 12. DETAILED DESCRIPTION

[0033] Embodiments of the present invention are described in more detail below with reference to the accompanying drawings.

[0034] The drawing shows a side view of a plain bearing bushing 10. The plain bearing bushing 10 is rotationally symmetrical and has a through opening 11 for accommodating the shaft of the pump. In addition, a raised ring 13 is formed at one end 12 of the plain bearing bushing 10. The inner surface 14 of the through opening 11 forms a radial sliding surface 15, and the side surface 16 of the raised ring 13 forms an axial sliding surface 17 for the shaft (not shown here) and / or a spacer disk located on the shaft. The plain bearing bushing 10 can be pressed into a bearing seat of a pump housing (not shown here) of the pump through the outer surface 18. In particular, a ratio of the length L to the diameter D of the plain bearing bushing 10 is selected to be ≥2:1. This is achieved by forming the plain bearing bushing 10 using an injection molding method.

[0035] When manufacturing the sliding bearing bushing 10, a carbon-filled polymer material is used, which has a meltable thermoplastic polymer and does not contain perfluorinated and polyfluoroalkyl compounds. First, a uniform molding material having a thermoplastic polymer content of >20% by volume to 65% by volume and a carbon content of >35% by volume to 80% by volume is formed using, for example, an extruder. Using an injection molding machine, the molding material having a melting point of ≤230°C is placed in an injection mold, thereby forming the sliding bearing bushing 10 shown.

Claims

1. A method for manufacturing a plain bearing bushing (10) for a pump, in particular a circulating pump or the like, the plain bearing bushing being made of a carbon-filled polymer material, the material having a thermoplastic polymer, characterized in that: The thermoplastic polymer is meltable and has a melting point of ≤230°C, the material has a thermoplastic polymer content of >20% by volume to 65% by volume, a carbon content of >35% by volume to 80% by volume, the material does not contain perfluorinated or polyfluoroalkyl compounds (PFAS), and the sliding bearing bushing is formed by an injection molding method.

2. The method according to claim 1, characterized in that The material does not contain fluoropolymers, in particular polytetrafluoroethylene (PTFE) or ethylene tetrafluoroethylene (ETFE).

3. The method according to claim 1 or 2, characterized in that: The material does not contain polyethylene (PE).

4. The method according to any one of the preceding claims, characterized in that A portion of MoS2 (molybdenum(IV) sulfide) is added to the material.

5. The method according to any one of the preceding claims, characterized in that The melting point of thermoplastic polymers is ≥170°C.

6. The method according to any one of the preceding claims, characterized in that The water absorption of the thermoplastic polymer is ≥0.05% and ≤3%, preferably ≥0.1% and ≤2%.

7. The method according to any one of the preceding claims, characterized in that Density of thermoplastic polymer ≥1.0g / cm 3 And ≤1.5g / cm 3 .

8. The method according to any one of the preceding claims, characterized in that Thermoplastic polymers are chemically resistant.

9. The method according to any one of the preceding claims, characterized in that The carbon used is graphite, a solid substance mainly containing carbon, petroleum coke or a mixture of these substances.

10. The method according to any one of the preceding claims, characterized in that The molding material is formed by melting a thermoplastic polymer and mixing it with carbon, and then placing the molding material in an injection mold by an injection molding machine.

11. The method according to claim 10, characterized in that The materials are mixed in a screw extruder, which is preferably a twin-screw extruder.

12. A plain bearing bushing (10) for a pump, in particular a circulation pump or the like, the plain bearing bushing being made of a carbon-filled polymer material, the material comprising a thermoplastic polymer, characterized in that: The thermoplastic polymer is meltable and has a melting point of ≤230°C, the material has a thermoplastic polymer content of >20% by volume to 65% by volume, a carbon content of >35% by volume to 80% by volume, the material does not contain perfluorinated or polyfluoroalkyl compounds (PFAS), and the sliding bearing bushing is formed by an injection molding method.

13. A pump for a dishwasher or the like, having an electric motor for driving a pump gear of the pump, the electric motor being made up of a stator, a rotor and a shaft, the rotor and the pump gear being attached to the shaft, the shaft being mounted on at least one sliding bearing of the pump so as to be rotatable and being located between the rotor and the pump gear, the sliding bearing having a sliding bearing bushing (10) according to claim 12.

14. The pump according to claim 13, characterized in that The plain bearing bushing (10) is arranged on the shaft such that the plain bearing bushing is in contact with the liquid that can be delivered by the pump.

15. A pump according to claim 13 or 14, characterized in that Only the pump has a plain bearing bushing (10).

16. A pump according to any one of claims 13 to 15, characterized in that The motor is designed as a canned motor.

17. A pump according to any one of claims 13 to 16, characterized in that The rotor is made of permanent magnet or squirrel cage windings and the spacer discs of the pump are attached to the shaft, abutting the axial side surface (17) of the sliding bearing bushing (10).

18. A use of a carbon-filled polymer material, wherein the melting point of the carbon-filled polymer material is ≤230°C, and the content of the thermoplastic polymer is >20% by volume to 65% by volume, the carbon content is >35% by volume to 80% by volume, the material does not contain perfluorinated or polyfluoroalkyl compounds (PFAS), and the sliding bearing bushing for a pump is formed by an injection molding method.

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