Method for preparing flexible thrust bearings
A room-temperature crosslinking process for flexible thrust bearings using a liquid polysiloxane composition addresses the high-temperature vulcanization challenges, reducing costs and complexity while maintaining mechanical performance.
Patent Information
- Application Number
- FR2022013925
- Authority / Receiving Office
- FR · FR
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2022-12-20
- Publication Date
- 2024-12-13
- Estimated Expiration
- 2042-12-20
AI Technical Summary
Existing flexible thrust bearings for propellers require high-temperature vulcanization, leading to increased energy consumption, material costs, and operational complexity, while existing low-temperature polysiloxane processes do not meet mechanical performance requirements.
A method using a liquid polysiloxane composition crosslinked at room temperature, comprising a polydimethylsiloxane base and catalyst, with specific ratios and additives, to form flexible stops with equivalent mechanical performance to high-temperature vulcanized materials.
Reduces manufacturing costs and energy consumption, simplifies the process, and maintains mechanical performance, enabling flexible stops to operate over a wider temperature range.
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Abstract
Description
Title of the invention: Method for preparing flexible stops for thrusters Technical field of the invention
[0001] The invention relates to the production of flexible stops commonly used in the field of propulsion to form joints connecting a nozzle to the body of a propellant. State of the art
[0002] It is common to articulate a nozzle of a propellant or rocket engine by means of a flexible stop comprising a laminated structure consisting of alternating layers of elastomer and rigid reinforcements made of metallic material or of composite material having a frustum of a sphere shape. The flexible stop thus forms a flexible connection between the nozzle and the body of the propellant so that the nozzle can be oriented by means of a jack arranged between the body of the propellant and the divergent part.
[0003] In order to allow relative movement between the nozzle and the body of the propellant, the flexible stop must resist mechanical stresses due to internal pressure while remaining watertight and without opposing excessive resistance torque.
[0004] To date, flexible thruster stops are mainly made from rubber materials. These materials provide robustness and reproducibility to flexible stops, and meet user needs in terms of final mechanical performance.
[0005] However, these solid materials have disadvantages in terms of implementation times and costs because they need to be vulcanized at high temperatures (~140°C, and up to ~200°C), and consequently require heavy and expensive human and material resources, such as heating presses and molds, which consume a lot of electrical energy.
[0006] The invention aims to simplify the manufacture of flexible stops by using a specific liquid polysiloxane composition capable of crosslinking at room temperature, while having a level of mechanical performance equivalent to that of flexible stops obtained by hot vulcanization.
[0007] The use of polysiloxane to manufacture flexible stops is known from the prior art, but not at low temperatures. Application EP 3 059 082 A1, for example, describes a method for manufacturing flexible stops from polysiloxane materials requiring vulcanization at temperatures close to 170°C.
[0008] Thus, the main advantages of the invention are: - an overall simplification of the manufacturing process for flexible stops and its implementation, - a reduction in manufacturing costs: reduction in energy costs (electricity consumption) due to implementation at room temperature, and a reduction in the costs of raw materials and tools (molds, press, mixer, etc.) (50% reduction in the cost of molds, for example), - a gain in productivity (significant reduction in operating times), the process of the invention requiring few human and material resources (no need for an injection press, for example, since the composition used is liquid) and low maintenance costs for the process, - maintaining the mechanical performance of the flexible stops obtained by the method of the invention, and - an ability to operate in a wider temperature range from -50°C to +70°C, as existing compositions are not mechanically resistant to negative temperatures. Summary of the invention
[0009] The present invention aims to overcome the drawbacks of the prior art by proposing a method for manufacturing flexible stops for thrusters that is simplified and consumes little electrical power, and is therefore much more economical than existing methods, while maintaining a level of mechanical performance of the flexible stops equivalent to that of existing flexible stops.
[0010] The inventors have demonstrated the fact that it is possible to crosslink at room temperature a liquid polysiloxane composition comprising a base and a polydimethylsiloxane catalyst with a specific polydimethylsiloxane oil.
[0011] Thus, according to a first aspect, the invention relates to a method for manufacturing a flexible stop for a propellant comprising a step of preparing a specific polysiloxane composition by liquid means, then injecting it into a mold and crosslinking it at room temperature.
[0012] According to a second aspect, the invention relates to a flexible stop for a propellant obtained according to the method of the invention, comprising a cured polysiloxane composition.
[0013] Finally, according to a last aspect, the invention relates to a propellant comprising a body extended by a nozzle, comprising a flexible stop according to the invention, said flexible stop forming an articulated connection between the nozzle and the body of the propellant. Brief description of the drawings
[0014] [Fig.l] illustrates the mechanical performance of flexible stops manufactured according to the method of the invention, and more particularly their characterization in traction on H2 type test specimen, compared to comparative and reference flexible stops. Description of the invention
[0015] According to a first aspect, the invention relates to a method of manufacturing a flexible stop for a thruster comprising the following steps: i. preparation of a liquid polysiloxane composition by mixing:
[0016] (1) a polydimethylsiloxane base A having a vinyl group and a -SiH group in chain end, and a polydimethylsiloxane oil of formula Si(CH3)3-[O-Si(CH3)2]n -OSi(CH3)3 in which n varies from 2 to 2,000, with
[0017] (2) a polydimethylsiloxane catalyst B having vinyl groups at the end of chain and a platinum catalyst,
[0018] the polydimethylsiloxane base A, the polydimethylsiloxane oil, and the polydimethylsiloxane catalyst B being different polydimethylsiloxane materials, i. injecting the liquid polysiloxane composition obtained at the end of step (i) into a flexible stop mold, and ii. crosslinking at room temperature of the liquid polysiloxane composition injected during step (ii).
[0019] Part (1) of the liquid polysiloxane composition prepared in step (i) constitutes a premix. This premix is preferably obtained by mixing the components of part (1) in a planetary mixer. Advantageously, the step of mixing the premix is carried out for a period of time ranging from 5 to 30 minutes, and more advantageously for approximately 15 minutes. The premix of part (1) is then mixed with the catalyst of part (2), preferably in a static mixer.
[0020] In certain embodiments, the polydimethylsiloxane base A has a molecular weight ranging from 15,000 to 30,000 g.mol ', preferably from 17,000 to 28,000 g.mol *, and more preferably from 20,000 to 25,000 g.mol *.
[0021] In certain embodiments, the polydimethylsiloxane catalyst B has a molecular weight ranging from 10,000 to 30,000 g.mol *, preferably from 15,000 to 25,000 g.mol1 , and more preferably from 18,000 to 22,000 g.mol *.
[0022] The polydimethylsiloxane oil advantageously corresponds to a formula Si(CH3)3 -[O-Si(CH3)2]n-OSi(CH3)3 in which n varies from 10 to 500, and preferably from 50 to 200.
[0023] In certain embodiments, the polydimethylsiloxane oil of formula Si(CH3)3 -[O-Si(CH3)2]n-Si(CH3)3 has a molecular weight ranging from 1,000 to 20,000 g.mol *, preferably from 3,000 to 12,000 g.mol *, and more preferably from 6,000 to 9,000 g.mol i
[0024] The weight ratio between the polydimethylsiloxane base A and the polydimethyl- catalyst siloxane B preferably varies from 5 / 1 to 15 / 1, more preferably from 8 / 1 to 12 / 1, and even more preferably is 10 / 1.
[0025] In certain embodiments, the polydimethylsiloxane base A represents from 50 to 95% by weight, preferably from 60 to 85% by weight, and more preferably from 65 to 80% by weight, relative to the total weight of the liquid polysiloxane composition prepared during step (i).
[0026] In certain embodiments, the polydimethylsiloxane catalyst B represents from 5 to 10% by weight, preferably from 6 to 10% by weight, and more preferably from 7 to 9% by weight, relative to the total weight of the liquid polysiloxane composition prepared during step (i).
[0027] In certain embodiments, the polydimethylsiloxane oil represents from 1 to 50% by weight, preferably from 10 to 40% by weight, and more preferably from 20 to 30% by weight, relative to the total weight of the liquid polysiloxane composition prepared during step (i).
[0028] In certain embodiments, the polydimethylsiloxane oil of formula Si(CH3)3 -[O-Si(CH3)2]n-OSi(CH3)3 used during step (i) has a kinematic viscosity ranging from 10 to 100 mm2, s', and preferably from 30 to 70 mm2, s', at 25°C.
[0029] The liquid polysiloxane composition prepared during step (i) advantageously has a viscosity ranging from 5 to 18 Pa.s, and even more advantageously ranging from 8 to 15 Pa.s, measured at room temperature.
[0030] In certain embodiments, the liquid polysiloxane composition used during step (i) comprises in its part (1) a retarding agent, also called a kinetics retarding agent or setting retarding agent.
[0031] In certain embodiments, the retarding agent is chosen from acetylenic alcohols of formula RR'C(OH)-C=CH in which R is chosen from a linear or branched C1-C20 alkyl radical, or a phenyl radical; R' is chosen from a hydrogen atom, a linear or branched C1-C20 alkyl radical, or a phenyl radical; the radicals R and R' may optionally form a ring between them. Preferably, the retarding agent is chosen from ethynyl-1-cyclohexanol, 3-methylbutyn-1-ol, methyl-3-dodecyne-1-ol, trimethyl-3,7,11-dodecyne-1-ol, diphenyl-1,1-propyne-2-ol, ethyl-3-ethyl-6-nonyne-1-ol, methyl-3-pentadecyne-1-ol, and mixtures thereof. In a preferred embodiment, the retarding agent is ethynyl-1-cyclohexan-1-ol.
[0032] The retarding agent advantageously represents from 0.1 to 5% by weight, preferably from 0.2 to 3% by weight, and more preferably from 0.5 to 1% by weight, relative to the total weight of the liquid polysiloxane composition prepared during step (i).
[0033] In certain embodiments, the composition used during step (i) comprises in its part (1) an opacifying agent, and preferably carbon black.
[0034] The opacifying agent advantageously represents from 0.05 to 3% by weight, preferably from 0.1 to 2% by weight, and more preferably from 0.2 to 1% by weight, relative to the total weight of the liquid polysiloxane composition prepared during step (i).
[0035] Crosslinking step (iii) is carried out at room temperature. For the purposes of the invention, room temperature means a temperature between 17 and 23°C, and more precisely a temperature of approximately 20°C. In certain embodiments, crosslinking step (iii) lasts from 24 hours to 14 days, preferably from 3 to 10 days, and more preferably 7 days.
[0036] According to another aspect, the invention relates to a flexible stop for a propellant obtained according to the method of the invention, said flexible stop comprising a cured polysiloxane composition comprising crosslinked polysiloxane chains of a polydimethylsiloxane base A having a vinyl group and a -SiH group at the chain end, and of a polydimethylsiloxane catalyst B having vinyl groups at the chain end.
[0037] In certain embodiments, the flexible stop for a thruster according to the invention has an annular shape.
[0038] According to a final aspect, the invention relates to a propellant comprising a body extended by a nozzle comprising a flexible stop according to the invention, said flexible stop forming an articulated connection between the nozzle and the body of the propellant.
[0039] In addition to the preceding provisions, the invention also comprises other provisions which will emerge from the additional description which follows, which relates to examples of implementation of the method for manufacturing a flexible stop according to the invention, and comparative and reference examples. Examples
[0040] Different flexible stops were prepared from the compositions shown in Table 1 in which the ratio of polydimethylsiloxane base A / polydimethylsiloxane catalyst B is equal to 10 (the values indicated correspond to the % by weight relative to the total weight of the polysiloxane composition):
[0041]
[0042]
[0043] [Tables 1] Raw materials Functions Composition 1 according to the invention Composition 2 according to the invention Comparative composition BLUESIL™ RTV 3131 A (Elkem Silicones) Polydimethylsiloxane base A 76.10 66.05 89.77 BLUESIL™ RTRD PA 40 (BLUESTAR SILICONES) Retarding agent 0.68 0.59 0.81 Carbon black PRINTEX® XE2B (STOBEC) Opacifying agent 0.38 0.33 0.45 RHODORSIL ® OILS 47 V50 (BLUESTAR SILICONES) Polydimethylsiloxane oil with a molecular weight of 7,000 - 8,000 g.mol1 (viscosity: 10 Pa.s at 23°C) 15.22 26.42 BLUESIL™ RTV 3131 B (Elkem Silicones) Polydimethylsiloxane catalyst B 7.61 6.61 8.98 In a first step (i), BLUESIL™ RTV 3131 A (Elkem Silicones), BLUESIL™ RTRD PA 40 (5% ethynyl-l-cyclohexan-l-ol) (BLUESTAR SILICONES), PRINTEX® XE2B carbon black, and optionally RHODORSIL® HUILES 47 V 50 (BLUESTAR SILICONES) were introduced into a planetary mixer under vacuum, then mixed for 1 minute at 1,000 rpm without vacuum, then for 4 minutes at 1,000 rpm under vacuum, and finally for 1 minute at 1,000 rpm without vacuum, to obtain a premix. The previously degassed BLUESIL™ RTV 3131 B catalyst (Elkem Silicones) is then added to the premix (1) in a static mixer. In a second step (ii), the liquid polysiloxane composition obtained at the end from step (i) was injected into a flexible stop mold (watertight mold made of metal reinforcements).
[0044] The viscosity measured at room temperature (20°C) of compositions 1 and 2 of the invention was 7 Pas.s. This viscosity was measured using a Texas Instrument Discovery hybrid rheometer, under a shear frequency of 1 Hz, and with a 40 mm diameter plane / plane mobile. Measured under the same conditions, the viscosity of the comparative composition was 20 Pa.s, and was therefore much less manipulable.
[0045] The pot life measured at room temperature (20°C) for compositions 1 and 2 of the invention was 5 hours. This pot life corresponds to the time beyond which the composition hardens and is no longer manipulable / injectable. The pot life of the comparative composition was also 5 hours.
[0046] In a third step (iii), the polysiloxane composition was allowed to crosslink in the flexible stop mold for 7 days at room temperature (20°C + / - 3°C).
[0047] After crosslinking, the flexible stop was demolded.
[0048] A reference flexible stop was also prepared from a vulcanizable natural rubber composition shown in Table 2 (the values indicated correspond to the % by weight relative to the total weight of the composition):
[0049] [Tables2] Raw Materials Reference Composition Natural Rubber SVR CV60 (SONG HOANG DAT CO., LTD.) 66.9 Hydrocarbon Oil 20.2 Activator 4.8 Fillers 3.4 Vulcanizing Agent 1.0 Accelerator 2.2 Retarder 1.5
[0050] In a first step, a mixture was prepared from the natural rubber, hydrocarbon oil, activator, fillers, accelerator and retarder, then homogenized in an internal mixer, before transfer to an open mixer.
[0051] The mixture thus prepared was then calendered between two rollers. In parallel, a flexible stop mold (heating mold made of metal reinforcements) was heated to reach a temperature T~200°C.
[0052] The viscosity of the mixture measured using a Monsanto MDR 2000™ moving die rheometer at a temperature T~200°C was 250 Pa.s.
[0053] The mixture was then injected by vacuum compression into the flexible stop mold at T~200°C mounted on a press, then vulcanized by adding the vulcanizing agent.
[0054] The flexible stop was then demolded.
[0055] The performances of the different flexible stops thus prepared were evaluated, by tensile characterization according to the following test (according to standard NF ISO 37:2005):
[0056] H2 test pieces in the shape of dumbbells of standard dimensions (length 110 mm, thickness: 2 mm) were placed between the two jaws of an Instron 5565 tensile-compression tester meeting the following specifications:
[0057] - Cell: Instron 2kN - 415-0322
[0058] - Extensometer: 70-840-126, L0 = 20 mm
[0059] - Touch probe: FR174906036
[0060] - Crosshead speed: 50 mm / min
[0061] - Processing software: BlueHill3
[0062] The conditions for carrying out the test are as follows:
[0063] - Load speed: 50 mm.min 1
[0064] - Stress temperature: 20°C
[0065] - Evaluated section: 4 x 2 mm over a length of 25 mm
[0066] The extensometers made it possible to monitor the dimension of the specimen throughout the test until failure.
[0067] The results of the tensile test obtained for each of the flexible stops are presented in Table 3 below:
[0068] [Tables3] Reference composition Composition 1 according to the invention Composition 2 according to the invention Comparative composition Elongation (%) 656 531 487 518 C100 (MPa) 0.48 0.39 0.33 0.72 C200 (MPa) 0.78 0.76 0.59 1.28
[0069] C100 corresponds to the stress at 100% elongation (C100).
[0070] C200 corresponds to the stress at 200% elongation (C200).
[0071] The results obtained are shown in [Fig.l]. It is observed that the flexible stop compositions of the invention make it possible to achieve me canics close to the reference flexible stop composition based on natural rubber, in particular around the 200% elongation stress (C200). Thus, the method of the invention makes it possible to obtain flexible stops having satisfactory mechanical properties, according to a much simpler manufacturing process, and this without having to heat the liquid polysiloxane composition to allow its crosslinking, the flexible stops being manufactured at room temperature.
Claims
Claims
1. A method of manufacturing a flexible stop for a thruster comprising the following steps: i. preparing a liquid polysiloxane composition by mixing: (1) a polydimethylsiloxane base A having a vinyl group and a -SiH group at the chain end, and a polydimethylsiloxane oil of formula Si(CH3)3-[O-Si(CH3)2]nO-Si(CH3)3 in which n varies from 2 to 2000, with (2) a polydimethylsiloxane catalyst B having vinyl groups at the chain end and a platinum catalyst, the polydimethylsiloxane base A, the polydimethylsiloxane oil, and the polydimethylsiloxane catalyst B being different polydimethylsiloxane materials, i. injecting the liquid polysiloxane composition obtained at the end of step (i) into a flexible stop mold, and ii. crosslinking at room temperature of the liquid polysiloxane composition injected during step (ii).
2. Method according to claim 1, characterized in that the polydimethylsiloxane base A has a molecular weight ranging from 15,000 to 30,000 g.mol *, preferably from 17,000 to 28,000 g.mol *, and more preferably from 20,000 to 25,000 g.mol *.
3. Process according to claim 1 or claim 2, characterized in that the polydimethylsiloxane catalyst B has a molecular weight ranging from 10,000 to 30,000 g.mol *, preferably from 15,000 to 25,000 g.mol *, and more preferably from 18,000 to 22,000 g.mol *.
4. Method according to one of claims 1 to 3, characterized in that the polydimethylsiloxane oil has a formula Si(CH3)3-[O-Si(CH3)2]n -O-Si(CH3)3 in which n varies from 10 to 500, and preferably from 50 to 200.
5. Method according to one of claims 1 to 4, characterized in that the polydimethylsiloxane oil of formula Si(CH3)3-[O-Si(CH3)2]n -O-Si(CH3)3 has a molecular weight ranging from 1,000 to 20,000 g.mol *, preferably from 3,000 to 12,000 g.mol *, and more preferably from 6,000 at 9,000 g.mol *.
6. Method according to one of claims 1 to 5, characterized in that the weight ratio between the polydimethylsiloxane base A and the polydimethylsiloxane catalyst B varies from 5 / 1 to 15 / 1, preferably from 8 / 1 to 12 / 1, and more preferably is 10 / 1.
7. Process according to one of claims 1 to 6, characterized in that the polydimethylsiloxane base A represents from 50 to 95% by weight, preferably from 60 to 85% by weight, and more preferably from 65 to 80% by weight, relative to the total weight of the liquid polysiloxane composition prepared during step (i).
8. Process according to one of claims 1 to 7, characterized in that the polydimethylsiloxane catalyst B represents from 5 to 10% by weight, preferably from 6 to 10% by weight, and more preferably from 7 to 9% by weight, relative to the total weight of the liquid polysiloxane composition prepared during step (i).
9. Process according to one of claims 1 to 8, characterized in that the polydimethylsiloxane oil represents from 1 to 50% by weight, preferably from 10 to 40% by weight, and more preferably from 20 to 30% by weight, relative to the total weight of the liquid polysiloxane composition prepared during step (i).
10. Method according to one of claims 1 to 9, characterized in that the liquid polysiloxane composition prepared during step (i) has a viscosity ranging from 5 to 18 Pa.s, and preferably from 8 to 15 Pa.s, measured at room temperature.
11. Method according to one of claims 1 to 10, characterized in that the liquid polysiloxane composition used during step (i) comprises in its part (1) a retarding agent; preferably chosen from acetylenic alcohols of formula RR'C(OH)-C=CH in which R is chosen from a linear or branched C1-C20 alkyl radical, or a phenyl radical; R' is chosen from a hydrogen atom, a linear or branched C1-C20 alkyl radical, or a phenyl radical; the radicals R and R' can optionally form a cycle between them; and more preferably chosen from ethynyl-1-cyclohexanol, 3-methylbutyn-1-ol, methyl-3-dodecyne-1-ol, trimethyl-3,7,11-dodecyne-1-ol, diphenyl-1,1-propyne-2-ol, ethyl-3-ethyl-6-nonyne-1-ol, methyl-3-pentadecyne-1-ol, and mixtures thereof; ethynyl-1-cyclohexan-1-ol being the preferred retarding agent.
12. Process according to claim 11, characterized in that the retarding agent represents from 0.1 to 5% by weight, preferably from 0.2 to 3% by weight, and more preferably from 0.5 to 1% by weight, relative to the total weight of the liquid polysiloxane composition prepared during step (i)
13. Method according to one of claims 1 to 12, characterized in that the composition used during step (i) comprises in its part (1) an opacifying agent, and preferably carbon black.
14. Method according to claim 13, characterized in that the opacifying agent represents from 0.05 to 3% by weight, preferably from 0.1 to 2% by weight, and more preferably from 0.2 to 1% by weight, relative to the total weight of the liquid polysiloxane composition prepared during step (i).
15. Method according to one of claims 1 to 14, characterized in that step (iii) of crosslinking at room temperature lasts from 24 hours to 14 days, preferably from 3 to 10 days, and more preferably 7 days.
16. Flexible stop for a propellant obtained according to the method of claims 1 to 15, characterized in that it comprises a cured polysiloxane composition comprising crosslinked polysiloxane chains of a polydimethylsiloxane base A having a vinyl group and a -SiH group at the chain end, and of a polydimethylsiloxane catalyst B having vinyl groups at the chain end.
17. Propellant comprising a body extended by a nozzle, characterized in that it comprises a flexible stop according to claim 16, said flexible stop forming an articulated connection between the nozzle and the body of the propellant.