Process for producing a plain bearing bush, plain bearing bush and use of a carbon-filled polymeric material

Abstract

The invention relates to a process for producing a plain bearing bush (10) for a pump, to a plain bearing bush, to a pump having a plain bearing bush and to the use of a material for the formation of a plain bearing bush, wherein the plain bearing bush is formed from a carbon-filled polymeric material, wherein the material includes a thermoplastic polymer, wherein the thermoplastic polymer is meltable and has a melting point of ≤ 230°C, wherein the material has a proportion of the thermoplastic polymer of >20% by volume to 65% by volume and a proportion of the carbon of > 35% by volume to 80% by volume, wherein the material is free of per- and polyfluorinated alkyl compounds (PFASs), and wherein the plain bearing bush is formed by means of an injection moulding process.

Description

[0001] Method for producing a plain bearing bush, plain bearing bush and use of a carbon-filled polymer material

[0002] The invention relates to a method for producing a plain bearing bush, a plain bearing bush for a pump and a pump for a dishwasher, in particular a dishwasher or the like, wherein the plain bearing bush is formed from a carbon-filled, polymeric material, wherein the material comprises a thermoplastic polymer.

[0003] Plain bearing bushings are well known in the art and are regularly used to support pump shafts, for example in circulation pumps in heating circuits or dishwashers. In particular, in such pumps, a pump impeller is rotatably mounted within a pump housing. The plain bearings in the pump or pump housing are surrounded by the medium or liquid to be pumped or come into contact with it. To ensure a long service life of the pump, special requirements are placed on the sliding pairing of a pump shaft and the plain bearings. The shaft can be made of, for example, a corrosion-resistant steel, a ceramic material, or a composite material. In pumps for heating circuits or dishwashers, the water to be pumped contains dirt or corrosive substances.Dishwasher water, in particular, is heavily contaminated with dirt, primarily composed of food scraps. This water also contains high salt content, alkaline detergents, and polishing additives. The material of the plain bearing is therefore subject to corresponding wear, which can affect the pump's service life and noise emissions.

[0004] For example, it is known to manufacture such plain bearing bushings for pumps from graphite-filled polytetrafluoroethylene (PTFE). This type of composite material is produced by blending polytetrafluoroethylene with graphite in a wet mixing process followed by drying. Shaping is achieved, for example, by dry pressing the material and sintering at approximately 300°C. Post-processing to achieve the desired tolerances is also required. This manufacturing process enables the polytetrafluoroethylene to be filled with up to 25 vol.% graphite. The good sliding properties of polytetrafluoroethylene, its resistance to chemicals, its flexibility towards hard dirt particles, and its high temperature resistance enable the creation of long-lasting and quiet plain bearing bushings. However, the production of such a plain bearing bush is relatively complex and therefore cost-intensive.

[0005] Polytetrafluoroethylene is also one of the per- and polyfluorinated alkyl compounds (PFAS), which are widespread and used particularly in textiles, electronic devices, food contact materials, and medical devices. These are generally persistent substances that are hardly degradable in the environment and can be detected in organisms and the environment as concentrations increase. Furthermore, they are considered, at least in part, harmful to health and the environment. For this reason, the European Union (EU) has already restricted the use of some of these substances. There is concern that the use of these substances could be subject to further restrictions in the future. It is therefore desirable to find a suitable material that does not exhibit the aforementioned problems.

[0006] The present invention is therefore based on the object of proposing a method for producing a plain bearing bush, a plain bearing bush, a pump and a use which enables cost-effective production and use which is unproblematic with regard to environmental and health aspects.

[0007] This object is achieved by a method having the features of claim 1, a plain bearing bush having the features of claim 12, a pump having the features of claim 13 and a use of a material having the features of claim 18.

[0008] In the method according to the invention for producing a plain bearing bush for a pump, in particular a circulation pump or the like, the plain bearing bush is formed from a carbon-filled polymeric material, wherein the material comprises a thermoplastic polymer, wherein the thermoplastic polymer is meltable and has a melting point of < 230 °C, wherein the material has a proportion of the thermoplastic polymer of > 20 vol.% to 65 vol.% and a proportion of the carbon of > 35 vol.% to 80 vol.%, wherein the material is free of per- and polyfluorinated alkyl compounds (PFAS), wherein the plain bearing bush is formed by means of an injection molding process.

[0009] Accordingly, the material or molding compound is first formed from a mixture of carbon and the thermoplastic polymer in the specified proportions, and then the plain bearing bush is manufactured using the injection molding process by injecting the material into a mold. This is made possible in particular by using a meltable thermoplastic polymer with the specified melting temperature. In contrast to polytetrafluoroethylene, which is not meltable, this makes it possible to use the injection molding process, which can eliminate a number of work steps. In particular, the wet mixing process, drying, sintering, and post-processing can be dispensed with. It is also possible to significantly increase the proportion of carbon in the material and reduce the proportion of thermoplastic polymer, which can also save costs.Further achievable advantages include reduced shrinkage during injection molding, resulting in better dimensional accuracy, as well as a lower thermal expansion coefficient and higher thermal conductivity of the plain bearing bush. Furthermore, potentially defectively manufactured plain bearing bushes can be reused as recycled material using the injection molding process. Furthermore, the comparatively low melting temperature requires comparatively low energy consumption, thus resulting in cost savings. Furthermore, filling the polymer material with carbon in the aforementioned proportions can improve the sliding properties and wear resistance of the plain bearing bush, with the high achievable filler content leading to additional cost savings.Ultimately, the use of the material, which is free of per- and polyfluorinated alkyl compounds, allows for the production of the plain bearing bushing without any problems in terms of environmental and health aspects. Overall, the plain bearing bushing is significantly simpler and thus more cost-effective to manufacture thanks to the process according to the invention, and is also unproblematic in terms of environmental and health aspects.

[0010] The material can advantageously have a thermoplastic polymer content of 20 vol.% to < 50 vol.% and a carbon content of > 50 vol.% to 80 vol.%. It has been found that the process can be carried out particularly efficiently with these proportions of thermoplastic polymer and carbon.

[0011] The material can consist exclusively of carbon and the meltable thermoplastic polymer. In principle, however, it is also possible to add additional polymers or other additives to the material, which can be processed using an injection molding process.

[0012] In particular, the material may be free of fluoropolymers belonging to the per- and polyfluorinated alkyl compounds, in particular polytetrafluoroethylene (PTFE) or ethylene-tetrafluoroethylene copolymer (ETFE).

[0013] Advantageously, the material can be free of polyethylene (PE). This makes it possible to design the plain bearing bush with comparatively high temperature resistance.

[0014] Advantageously, a proportion 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 bush.

[0015] Advantageously, the thermoplastic polymer may have a melting point of > 170 °C. In alternative embodiments of the process, the melting point may be > 180 °C, > 190 °C, or > 200 °C.

[0016] Advantageously, the thermoplastic polymer can have a water absorption of > 0.05% and < 3%, preferably > 0.1% and < 2%. The plain bearing bush can then also be advantageously used where it comes into contact with a liquid, in particular with water. The thermoplastic polymer can also have a water absorption of > 0.5% and < 3% or > 1% and < 2%. Advantageously, the thermoplastic polymer can have a density of > 1.0 g / cm 3 and < 1.5 g / cm 3 have.

[0017] Furthermore, the thermoplastic polymer can have a heat distortion temperature of > 110 °C and < 160 °C at 0.45 MPa.

[0018] Advantageously, the thermoplastic polymer can have a modulus of elasticity or tensile strength of > 1000 MPa and < 3500 MPa. The thermoplastic polymer can also have a modulus of elasticity or tensile strength of > 1500 MPa and < 3500 MPa.

[0019] Advantageously, the thermoplastic polymer can be chemically resistant. In particular, the thermoplastic polymer can exhibit good chemical resistance to fats, oils, solvents, fuels, alkalis, and saline solutions.

[0020] Graphite, a predominantly carbon-containing solid, petroleum coke, or a mixture of these substances can be used as carbon. The material in question can then initially be in powder form, which makes mixing with the thermoplastic polymer much easier. In particular, the comparatively high carbon content of the material allows for the formation of a particularly chemically resistant and temperature-stable plain bearing bush. Furthermore, the high carbon content allows for a particularly favorable coefficient of friction for the plain bearing bush.

[0021] Within the scope of the process, a molding compound of the material can first be formed by melting the thermoplastic polymer and mixing it with carbon, whereby the molding compound can then be introduced into an injection mold using an injection molding machine. For example, homogeneous mixing with carbon can be easily carried out in an extruder or compounder. The use of an injection molding machine also makes it possible to produce comparatively long plain bearing bushes or plain bearing bushes with a comparatively high aspect ratio and with almost any geometry. In contrast, with forming by dry pressing, the production of a long plain bearing bush or a plain bearing bush with a high aspect ratio is not easily possible because wall friction effects prevent uniform compaction and thus lead to inhomogeneous material properties over the length of the plain bearing bush.

[0022] Compounding or processing of the material can be carried out in a screw extruder, preferably a twin-screw extruder. This also allows, among other things, the recycling of reject parts into the material flow.

[0023] Furthermore, it can be provided that the plain bearing bushing is machined at least on the bearing surfaces. While the injection molding process can already produce a particularly dimensionally accurate plain bearing bushing, machining can also achieve an even more precise adaptation to a shaft or axle of a pump impeller. Among other things, it is also possible to machine the plain bearing bushing after injection molding, for example, by tumbling. One surface of the plain bearing bushing can then advantageously be designed as a sliding surface.

[0024] The plain bearing bushing can be plasticized, granulated, or crushed, and the material thus produced can be used to manufacture a new plain bearing bushing using the method according to the invention. For example, plain bearing bushings produced using the method according to the invention can be classified as scrap due to dimensional deviations or other manufacturing defects. These plain bearing bushings can then be plasticized, granulated, or crushed and subsequently plasticized. This material can then be processed as recyclate in the injection molding process. This allows for significant savings in material.The plain bearing bushing according to the invention for a pump, in particular a circulation pump or the like, is made of a carbon-filled, polymeric material, wherein the material comprises a thermoplastic polymer, wherein the thermoplastic polymer is meltable and has a melting point of <230°C, wherein the material has a thermoplastic polymer content of >20 vol.% to 65 vol.% and a carbon content of >35 vol.% to 80 vol.%, wherein the material is free of per- and polyfluorinated alkyl compounds (PFAS), wherein the plain bearing bushing is formed by means of an injection molding process. For the advantages of the plain bearing bushing according to the invention, reference is made to the description of the advantages of the method according to the invention. In particular, the production of the plain bearing bushing by the injection molding process does not result in density differences such as can occur during dry pressing and sintering of materials.Further advantageous embodiments of a plain bearing bush emerge from the descriptions of the features of the subclaims referring back to claim 1.

[0025] The pump according to the invention for a dishwasher, in particular a dishwasher or the like, is designed with an electric motor for driving an impeller of the pump, wherein the electric motor is formed from a stator, a rotor and a shaft, wherein the rotor and the impeller are attached to the shaft, wherein the shaft is rotatably mounted between the rotor and the impeller on at least one plain bearing of the pump, wherein the plain bearing is designed with a plain bearing bush according to the invention.

[0026] The plain bearing bushing can be arranged on the shaft in such a way that it can come into contact with a fluid pumped by the pump. For example, the plain bearing bushing can be installed in a pump housing in such a way that the fluid inevitably comes into contact with the plain bearing bushing or flows around it. In this case, the pump impeller can be arranged directly adjacent to the plain bearing bushing on the shaft.

[0027] Furthermore, the pump can be provided with a single plain bearing bushing. In principle, the shaft can be supported with two or more plain bearing bushings. However, to save space, only a single plain bearing bushing can be provided, which is comparatively long or has a comparatively high aspect ratio. This means that the length of the plain bearing bushing can be dimensioned such that tilting of the shaft is prevented and sufficiently secure support of the shaft is possible.

[0028] The electric motor can advantageously be designed as a canned motor. This allows the rotor to be completely sealed against the fluid being pumped, allowing the fluid to flush around the rotor.

[0029] The rotor can be formed from a permanent magnet or a squirrel-cage winding, whereby a pump thrust washer attached to the shaft can rest against an axial side surface of the plain bearing bush. The thrust washer then allows axial support of the rotor and can, if necessary, absorb axial forces from the pump impeller. The thrust washer can be mounted on the shaft, or the shaft can form the thrust washer. The thrust washer can preferably be made of the same material as the shaft or a different material.

[0030] Further advantageous embodiments of a pump emerge from the descriptions of the features of the subclaims which refer back to claim 1.

[0031] According to the invention, a carbon-filled, polymeric material with a melting point of <230 °C and a thermoplastic polymer content of >20 vol.% to 65 vol.% and a carbon content of >35 vol.% to 80 vol.%, wherein the material is free of per- and polyfluorinated alkyl compounds (PFAS), is used to form a plain bearing bush for a pump in an injection molding process. Further advantageous embodiments of a use of this material emerge from the feature descriptions of the subclaims referring back to claim 1 and claim 12.

[0032] An embodiment of the invention is explained below with reference to the figure.

[0033] The figure 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 receiving a pump shaft. Furthermore, a collar 13 is formed at one end 12 of the plain bearing bushing 10. An inner surface 14 of the through-opening 11 forms a radial sliding surface 15 and a side surface 16 of the collar 13 forms an axial sliding surface 17 for the shaft (not shown here) or a thrust washer located on the shaft. The plain bearing bushing 10 can be pressed into a bearing seat of a pump housing (not shown here) of a pump via an outer surface 18. In particular, a ratio of a length L to a diameter D of the plain bearing bushing 10 > 2:1 is selected. This is made possible by the fact that the plain bearing bushing 10 is formed using an injection molding process.

[0034] In the production of the plain bearing bushing 10, a carbon-filled, polymeric material is used. The material comprises a meltable thermoplastic polymer and is free of per- and polyfluorinated alkyl compounds. First, a homogeneous molding compound with a thermoplastic polymer content of > 20 vol.% to 65 vol.% and a carbon content of > 35 vol.% to 80 vol.% is formed using, for example, an extruder. Using an injection molding machine, the molding compound, which has a melting point of < 230°C, is introduced into an injection mold, thus forming the illustrated plain bearing bushing 10.

Claims

Patent claims Method for producing a plain bearing bush (10) for a pump, in particular a circulation pump or the like, wherein the plain bearing bush is formed from a carbon-filled, polymeric material, wherein the material comprises a thermoplastic polymer, characterized in that the thermoplastic polymer is meltable and has a melting point of < 230 °C, wherein the material has a proportion of the thermoplastic polymer of > 20 vol.% to 65 vol.% and a proportion of the carbon of > 35 vol.% to 80 vol.%, wherein the material is free of per- and polyfluorinated alkyl compounds (PFAS), wherein the plain bearing bush is formed by means of an injection molding process. Method according to claim 1, characterized in that the material is free of fluoropolymers, in particular polytetrafluoroethylene (PTFE) or ethylene-tetrafluoroethylene copolymer (ETFE). Process according to claim 1 or 2, characterized in that the material is free of polyethylene (PE). Process according to one of the preceding claims, characterized in that a proportion of M0S2 (molybdenum(IV) sulfide) is added to the material. Process according to one of the preceding claims, characterized in that the thermoplastic polymer has a melting point of > 170 °C. Process according to one of the preceding claims, characterized in that the thermoplastic polymer has a water absorption of > 0.05% and < 3%, preferably of > 0.1% and < 2%. Process according to one of the preceding claims, characterized in that the thermoplastic polymer has a density of > 1.0 g / cm 3 and < 1.5 g / cm 3Process according to one of the preceding claims, characterized in that the thermoplastic polymer is chemically resistant. Process according to one of the preceding claims, characterized in that the carbon, graphite, a predominantly carbon-containing Solid, petroleum coke or a mixture of these substances is used.

10. Method according to one of the preceding claims, characterized in that a molding compound of the material is formed by melting the thermoplastic polymer and mixing it with carbon, the molding compound being subsequently introduced into an injection mold by means of an injection molding machine.

11. Process according to claim 10, characterized in that the material is compounded in a screw extruder, preferably a twin-screw extruder.

12. A plain bearing bush (10) for a pump, in particular a circulation pump or the like, wherein the plain bearing bush is formed from a carbon-filled, polymeric material, wherein the material comprises a thermoplastic polymer, characterized in that the thermoplastic polymer is meltable and has a melting point of < 230 °C, wherein the material has a proportion of the thermoplastic polymer of > 20 vol.% to 65 vol.% and a proportion of the carbon of > 35 vol.% to 80 vol.%, wherein the material is free of per- and polyfluorinated alkyl compounds (PFAS), wherein the plain bearing bush is formed by means of an injection molding process.

13. Pump for a dishwasher, in particular a dishwasher or the like, with an electric motor for driving a pump wheel of the pump, wherein the electric motor is formed from a stator, a rotor and a shaft, wherein the rotor and the pumppenrad are attached to the shaft, wherein the shaft is rotatably mounted between the rotor and the pump wheel on at least one plain bearing of the pump, wherein the plain bearing is designed with a plain bearing bush (10) according to claim 12. Pump according to claim 13, characterized in that the plain bearing bush (10) is arranged on the shaft in such a way that the plain bearing bush comes into contact with a liquid that can be pumped by the pump. Pump according to claim 13 or 14, characterized in that the pump alone has a plain bearing bush (10). Pump according to one of claims 13 to 15, characterized in that the electric motor is designed as a canned motor.Pump according to one of claims 13 to 16, characterized in that the rotor is formed from a permanent magnet or a squirrel-cage winding, wherein a pump thrust washer attached to the shaft bears against an axial side surface (17) of the plain bearing bush (10). Use of a carbon-filled, polymeric material with a melting point of < 230 °C and with a thermoplastic polymer content of > 20 vol.% to 65 vol.% and a carbon content of > 35 vol.% to 80 vol.%, wherein the material is free from per- and polyfluorinated alkyl compounds. fertilizers (PFAS) is used to form a plain bearing bush (10) for a pump in an injection molding process.

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