Polyurethane pipe material for hydraulic cylinder fire-retardant bumper and forming process thereof

Abstract

The present application relates to a kind of hydraulic cylinder flame-retardant buffer polyurethane pipe material and its forming process, belong to polyurethane pipe material technical field, according to weight parts, the preparation raw material of the polyurethane sizing material includes 65-80 parts polyurethane particle, 3-6 parts trimethylolpropane, 1-3 parts pentaerythritol, 5-8 parts peroxide carbonate, 10-15 parts white carbon black, 5-6 parts antioxidant, 2-5 parts zinc stearate.Polyurethane pipe material is prepared by using multiple components to obtain flame-retardant particles, which can effectively play a flame-retardant role when polyurethane pipe material is used, wherein, lignin and oleanolic acid cooperate to produce synergistic effect, realize efficient flame-retardant effect, so that polyurethane pipe material has excellent self-extinguishing performance away from fire, polyurethane pipe material can be used in some locations with higher temperature or closer to the source of fire, increase the use range of polyurethane pipe material.

Description

Technical Field

[0001] This invention belongs to the field of polyurethane pipe processing technology, specifically relating to a polyurethane pipe for a flame-retardant damper of a hydraulic cylinder and its molding process. Background Technology

[0002] Polyurethane, short for polyurethane, is a high-molecular-weight material with excellent mechanical properties formed by the condensation reaction of polyols and polyisocyanates. It is extremely ductile and can be used in some flame-retardant shock absorbers for hydraulic cylinders.

[0003] However, in flame-retardant dampers for hydraulic cylinders, traditional polyurethane tubing is subjected to harsh conditions of high pressure and high temperature for extended periods. The high-pressure environment subjects it to continuous and significant mechanical stress, while the high temperature accelerates the thermo-oxidative aging process of the material. Under the combined effect of these two factors, the molecular structure of the polyurethane tubing is easily damaged, leading to reduced elasticity, increased hardness, embrittlement, and even cracking. This accelerated aging severely affects the damper's sealing performance and cushioning effect, thereby shortening its service life and potentially causing hydraulic system failures. Summary of the Invention

[0004] The purpose of this invention is to provide a polyurethane tubing for a flame-retardant damper in a hydraulic cylinder and its molding process in order to solve the above-mentioned problems.

[0005] The present invention achieves the above objectives through the following technical solutions:

[0006] This invention provides a polyurethane tubing for a flame-retardant damper in a hydraulic cylinder. The polyurethane tubing is obtained by coating an inner core material with a polyurethane protective layer. The polyurethane protective layer is made of polyurethane adhesive, and the inner core material is made of polyurethane adhesive mixed with flame-retardant microparticles.

[0007] The raw materials for preparing the polyurethane adhesive, by weight, include: 65-80 parts polyurethane particles, 3-6 parts trimethylolpropane, 1-3 parts pentaerythritol, 5-8 parts peroxide carbonate, 10-15 parts silica, 5-6 parts antioxidant, and 2-5 parts zinc stearate.

[0008] As a further optimization of the present invention, the raw materials for preparing the flame-retardant microparticles, by weight, include 35-55 parts of polydodecyl lactam particles, 30-45 parts of magnesium hydroxide, 2-4 parts of potassium carbonate, 5-10 parts of lignin, 8-16 parts of oleanolic acid and 15-23 parts of zinc borate.

[0009] As a further optimization of the present invention, the preparation process of flame-retardant microparticles is as follows:

[0010] S1. Place magnesium hydroxide, potassium carbonate, lignin, oleanolic acid and zinc borate into a drying oven and dry at 60-80℃ for 3-5 hours for later use.

[0011] S2, magnesium hydroxide, potassium carbonate, lignin, oleanolic acid and zinc borate were pulverized using a ball mill and set aside for later use;

[0012] S3, add polydodecyl lactam particles, magnesium hydroxide, potassium carbonate, lignin, oleanolic acid and zinc borate into a mixer and stir at 65 r / min for 20-30 min to obtain the preform;

[0013] S4. Add the pre-made material to the internal mixer, heat it to 175-195℃, and mix for 8 minutes to obtain the composite material.

[0014] S5. The obtained composite material is cooled and solidified, then pulverized and passed through a 150-mesh sieve to obtain flame-retardant microparticles.

[0015] As a further optimization of the present invention, the ball mill uses zirconia grinding balls of two sizes, Φ5mm and Φ6mm, with a mass ratio of large to small balls of 1:1; the ball-to-material ratio is 12:1.

[0016] As a further optimization of the present invention, the antioxidant is 4,4'-bis(α,α-dimethylbenzyl)diphenylamine or 2,2,4-trimethyl-1,2-dihydroquinoline.

[0017] This invention also provides a method for preparing polyurethane tubing for flame-retardant dampers in hydraulic cylinders, comprising the following steps:

[0018] S1, pre-pass polyurethane granules on a two-roll mill for 15-20 minutes, put silica into a drying oven and dry at 60-80℃ for 3-5 hours to obtain a billet;

[0019] S2, put the billet into an internal mixer at 100-135℃, add zinc stearate and antioxidant, and mix for 3-5 minutes;

[0020] S3, heat the silica to 55℃ and add it, mix for 4 minutes, then add trimethylolpropane and pentaerythritol and mix for 10-15 minutes.

[0021] S4, add peroxide carbonate heated to 30°C, mix for 8 minutes to obtain polyurethane compound;

[0022] S5, mix the polyurethane adhesive with flame-retardant microparticles and knead for 5 minutes to obtain the inner core material;

[0023] S6. The polyurethane adhesive is wrapped around the outside of the inner core material and filled into the mold cavity preheated to 160°C. A pressure of 10-20MPa is applied, and the material is kept at the same temperature and pressure for 5-15 minutes. After demolding and cooling, the polyurethane tube material is obtained.

[0024] As a further optimization of the present invention, the rolling temperature of the open mill is 60-85℃ and the rolling gap is 2mm.

[0025] As a further optimization of the present invention, the mass ratio of polyurethane adhesive to flame-retardant microparticles is 1:0.2; the mass ratio of the inner core material to the polyurethane protective layer is 1:1.2.

[0026] The beneficial effects of this invention are as follows: the polyurethane pipe material prepared by the method of this invention is made of multiple components to obtain flame-retardant microparticles, which can effectively play a flame-retardant role when the polyurethane pipe material is used. Among them, lignin and oleanolic acid work together to produce a synergistic effect, achieving a highly efficient flame-retardant effect, giving the polyurethane pipe material excellent self-extinguishing performance after being removed from the flame, and allowing the polyurethane pipe material to be used in some locations with high temperature or close to the fire source, thus increasing the application range of polyurethane pipes. Detailed Implementation

[0027] The present application will now be described in further detail. It should be noted that the following specific embodiments are only used to further illustrate the present application and should not be construed as limiting the scope of protection of the present application. Those skilled in the art can make some non-essential improvements and adjustments to the present application based on the above application content.

[0028] Unless otherwise specified, all methods used in this invention are conventional methods known to those skilled in the art, and all reagents and materials used are commercially available products.

[0029] Example 1

[0030] The preparation process of flame-retardant microparticles is as follows:

[0031] S1, magnesium hydroxide, potassium carbonate, lignin, oleanolic acid and zinc borate were placed in a drying oven and dried at 60℃ for 3 hours for later use;

[0032] S2, magnesium hydroxide, potassium carbonate, lignin, oleanolic acid and zinc borate are pulverized separately using a ball mill and set aside for later use (the ball mill uses zirconia grinding balls of two sizes, Φ5mm and Φ6mm, with a mass ratio of large to small balls of 1:1; the ball-to-material ratio is 12:1).

[0033] S3, add 35 parts of polydodecyl lactam granules, 30 parts of magnesium hydroxide, 2 parts of potassium carbonate, 5 parts of lignin, 8 parts of oleanolic acid and 15 parts of zinc borate into a mixer and stir at 65 r / min for 20 min to obtain the preform.

[0034] S4. Add the pre-made material to the internal mixer, heat it to 175°C, and mix for 8 minutes to obtain the composite material.

[0035] S5. The obtained composite material is cooled and solidified, then pulverized and passed through a 150-mesh sieve to obtain flame-retardant microparticles.

[0036] The preparation process of polyurethane pipe material is as follows:

[0037] S1, 65 parts of polyurethane granules were pre-passed on a two-roll mill for 15 minutes (the roller temperature of the two-roll mill was 60℃ and the roller gap was 2mm), and 10 parts of silica were placed in a drying oven and dried at 60℃ for 3 hours to obtain the billet.

[0038] S2, at 100℃, the billet is put into an internal mixer, 2 parts of zinc stearate and 5 parts of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine are added, and the mixture is mixed for 3 minutes;

[0039] S3, add 10 parts of silica heated to 55°C, mix for 4 minutes, add 3 parts of trimethylolpropane and 1 part of pentaerythritol and mix for 10 minutes.

[0040] S4, add 6 parts of peroxide carbonate heated to 30°C, mix for 8 minutes to obtain polyurethane compound;

[0041] S5, mix the polyurethane compound with flame-retardant microparticles (the mass ratio of polyurethane compound to flame-retardant microparticles is 1:0.2), and knead for 5 minutes to obtain the inner core material.

[0042] S6. Coat the outside of the inner core material with polyurethane adhesive (the mass ratio of the inner core material to the polyurethane protective layer is 1:1.2), fill it into the mold cavity preheated to 160°C, apply a pressure of 10 MPa, keep it warm and pressurized for 5 minutes, demold and cool to obtain polyurethane tube material.

[0043] Example 2

[0044] The preparation process of flame-retardant microparticles is as follows:

[0045] S1, magnesium hydroxide, potassium carbonate, lignin, oleanolic acid and zinc borate were placed in a drying oven and dried at 70℃ for 4 hours for later use;

[0046] S2, magnesium hydroxide, potassium carbonate, lignin, oleanolic acid and zinc borate are pulverized separately using a ball mill and set aside for later use (the ball mill uses zirconia grinding balls of two sizes, Φ5mm and Φ6mm, with a mass ratio of large to small balls of 1:1; the ball-to-material ratio is 12:1).

[0047] S3, add 45 parts of polydodecyl lactam granules, 35 parts of magnesium hydroxide, 3 parts of potassium carbonate, 8 parts of lignin, 12 parts of oleanolic acid and 20 parts of zinc borate into a mixer and stir at 65 r / min for 25 min to obtain the preform.

[0048] S4. Add the pre-made material to the internal mixer, heat it to 185°C, and mix for 8 minutes to obtain the composite material.

[0049] S5. The obtained composite material is cooled and solidified, then pulverized and passed through a 150-mesh sieve to obtain flame-retardant microparticles.

[0050] The preparation process of polyurethane pipe material is as follows:

[0051] S1, 75 parts of polyurethane granules were pre-passed on a two-roll mill for 18 minutes (the roller temperature of the two-roll mill was 70℃ and the roller gap was 2mm), and 12 parts of silica were placed in a drying oven and dried at 70℃ for 4 hours to obtain the billet.

[0052] S2, the billet is put into an internal mixer at 120℃, 3 parts of zinc stearate and 5 parts of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine are added, and the mixture is mixed for 4 min;

[0053] S3, add 12 parts of silica heated to 55°C, mix for 4 minutes, add 4 parts of trimethylolpropane and 2 parts of pentaerythritol and mix for 12 minutes.

[0054] S4, add 6 parts of peroxide carbonate heated to 30°C, mix for 8 minutes to obtain polyurethane compound;

[0055] S5, mix the polyurethane compound with flame-retardant microparticles (the mass ratio of polyurethane compound to flame-retardant microparticles is 1:0.2), and knead for 5 minutes to obtain the inner core material.

[0056] S6. The polyurethane adhesive is wrapped around the outside of the inner core material (the mass ratio of the inner core material to the polyurethane protective layer is 1:1.2), filled into the mold cavity preheated to 160°C, a pressure of 15 MPa is applied, and the temperature and pressure are maintained for 10 minutes. After demolding and cooling, the polyurethane tube material is obtained.

[0057] Example 3

[0058] The preparation process of flame-retardant microparticles is as follows:

[0059] S1, magnesium hydroxide, potassium carbonate, lignin, oleanolic acid and zinc borate were placed in a drying oven and dried at 70℃ for 4 hours for later use;

[0060] S2, magnesium hydroxide, potassium carbonate, lignin, oleanolic acid and zinc borate are pulverized separately using a ball mill and set aside for later use (the ball mill uses zirconia grinding balls of two sizes, Φ5mm and Φ6mm, with a mass ratio of large to small balls of 1:1; the ball-to-material ratio is 12:1).

[0061] S3, add 45 parts of polydodecyl lactam granules, 35 parts of magnesium hydroxide, 3 parts of potassium carbonate, 8 parts of lignin, 12 parts of oleanolic acid and 20 parts of zinc borate into a mixer and stir at 65 r / min for 25 min to obtain the preform.

[0062] S4. Add the pre-made material to the internal mixer, heat it to 190°C, and mix for 8 minutes to obtain the composite material.

[0063] S5. The obtained composite material is cooled and solidified, then pulverized and passed through a 150-mesh sieve to obtain flame-retardant microparticles.

[0064] The preparation process of polyurethane pipe material is as follows:

[0065] S1, 75 parts of polyurethane granules were pre-passed on a two-roll mill for 18 minutes (the roller temperature of the two-roll mill was 70℃ and the roller gap was 2mm), and 12 parts of silica were placed in a drying oven and dried at 70℃ for 4 hours to obtain the billet.

[0066] S2, at 135℃, the billet is put into an internal mixer, 3 parts of zinc stearate and 5 parts of 2,2,4-trimethyl-1,2-dihydroquinoline are added, and the mixture is mixed for 4 minutes.

[0067] S3, add 12 parts of silica heated to 55°C, mix for 4 minutes, add 4 parts of trimethylolpropane and 2 parts of pentaerythritol and mix for 12 minutes.

[0068] S4, add 6 parts of peroxide carbonate heated to 30°C, mix for 8 minutes to obtain polyurethane compound;

[0069] S5, mix the polyurethane compound with flame-retardant microparticles (the mass ratio of polyurethane compound to flame-retardant microparticles is 1:0.2), and knead for 5 minutes to obtain the inner core material.

[0070] S6. The polyurethane adhesive is wrapped around the outside of the inner core material (the mass ratio of the inner core material to the polyurethane protective layer is 1:1.2), filled into the mold cavity preheated to 160°C, a pressure of 15 MPa is applied, and the temperature and pressure are maintained for 10 minutes. After demolding and cooling, the polyurethane tube material is obtained.

[0071] Comparative Example 1

[0072] The preparation process of flame-retardant microparticles is as follows:

[0073] S1. Place magnesium hydroxide, potassium carbonate, oleanolic acid and zinc borate into a drying oven and dry at 70℃ for 4 hours for later use.

[0074] S2, magnesium hydroxide, potassium carbonate, oleanolic acid and zinc borate are pulverized separately using a ball mill and set aside for later use (the ball mill uses zirconia grinding balls of two sizes, Φ5mm and Φ6mm, with a mass ratio of large to small balls of 1:1; the ball-to-material ratio is 12:1).

[0075] S3, add 45 parts of polydodecyl lactam granules, 35 parts of magnesium hydroxide, 3 parts of potassium carbonate, 20 parts of oleanolic acid and 20 parts of zinc borate into a mixer and stir at 65 r / min for 25 min to obtain the preform.

[0076] S4. Add the pre-made material to the internal mixer, heat it to 185°C, and mix for 8 minutes to obtain the composite material.

[0077] S5. The obtained composite material is cooled and solidified, then pulverized and passed through a 150-mesh sieve to obtain flame-retardant microparticles.

[0078] The preparation process of polyurethane pipe material is as follows:

[0079] S1, 75 parts of polyurethane granules were pre-passed on a two-roll mill for 18 minutes (the roller temperature of the two-roll mill was 70℃ and the roller gap was 2mm), and 12 parts of silica were placed in a drying oven and dried at 70℃ for 4 hours to obtain the billet.

[0080] S2, the billet is put into an internal mixer at 120℃, 3 parts of zinc stearate and 5 parts of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine are added, and the mixture is mixed for 4 min;

[0081] S3, add 12 parts of silica heated to 55°C, mix for 4 minutes, add 4 parts of trimethylolpropane and 2 parts of pentaerythritol and mix for 12 minutes.

[0082] S4, add 6 parts of peroxide carbonate heated to 30°C, mix for 8 minutes to obtain polyurethane compound;

[0083] S5, mix the polyurethane compound with flame-retardant microparticles (the mass ratio of polyurethane compound to flame-retardant microparticles is 1:0.2), and knead for 5 minutes to obtain the inner core material.

[0084] S6. The polyurethane adhesive is wrapped around the outside of the inner core material (the mass ratio of the inner core material to the polyurethane protective layer is 1:1.2), filled into the mold cavity preheated to 160°C, a pressure of 15 MPa is applied, and the temperature and pressure are maintained for 10 minutes. After demolding and cooling, the polyurethane tube material is obtained.

[0085] Comparative Example 2

[0086] The preparation process of flame-retardant microparticles is as follows:

[0087] S1, magnesium hydroxide, potassium carbonate, lignin and zinc borate were placed in a drying oven and dried at 70℃ for 4 hours, and then set aside for later use;

[0088] S2, magnesium hydroxide, potassium carbonate, lignin and zinc borate are pulverized separately using a ball mill and set aside (the ball mill uses zirconia grinding balls of two sizes, Φ5mm and Φ6mm, with a mass ratio of large to small balls of 1:1; the ball-to-material ratio is 12:1).

[0089] S3, add 45 parts of polydodecyl lactam granules, 35 parts of magnesium hydroxide, 3 parts of potassium carbonate, 20 parts of lignin and 20 parts of zinc borate into a mixer and stir at 65 r / min for 25 min to obtain the preform.

[0090] S4. Add the pre-made material to the internal mixer, heat it to 185°C, and mix for 8 minutes to obtain the composite material.

[0091] S5. The obtained composite material is cooled and solidified, then pulverized and passed through a 150-mesh sieve to obtain flame-retardant microparticles.

[0092] The preparation process of polyurethane pipe material is as follows:

[0093] S1, 75 parts of polyurethane granules were pre-passed on a two-roll mill for 18 minutes (the roller temperature of the two-roll mill was 70℃ and the roller gap was 2mm), and 12 parts of silica were placed in a drying oven and dried at 70℃ for 4 hours to obtain the billet.

[0094] S2, the billet is put into an internal mixer at 120℃, 3 parts of zinc stearate and 5 parts of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine are added, and the mixture is mixed for 4 min;

[0095] S3, add 12 parts of silica heated to 55°C, mix for 4 minutes, add 4 parts of trimethylolpropane and 2 parts of pentaerythritol and mix for 12 minutes.

[0096] S4, add 6 parts of peroxide carbonate heated to 30°C, mix for 8 minutes to obtain polyurethane compound;

[0097] S5, mix the polyurethane compound with flame-retardant microparticles (the mass ratio of polyurethane compound to flame-retardant microparticles is 1:0.2), and knead for 5 minutes to obtain the inner core material.

[0098] S6. The polyurethane adhesive is wrapped around the outside of the inner core material (the mass ratio of the inner core material to the polyurethane protective layer is 1:1.2), filled into the mold cavity preheated to 160°C, a pressure of 15 MPa is applied, and the temperature and pressure are maintained for 10 minutes. After demolding and cooling, the polyurethane tube material is obtained.

[0099] Comparative Example 3

[0100] The preparation process of polyurethane pipe material is as follows:

[0101] S1, 75 parts of polyurethane granules were pre-passed on a two-roll mill for 18 minutes (the roller temperature of the two-roll mill was 70℃ and the roller gap was 2mm), and 12 parts of silica were placed in a drying oven and dried at 70℃ for 4 hours to obtain the billet.

[0102] S2, the billet is put into an internal mixer at 120℃, 3 parts of zinc stearate and 5 parts of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine are added, and the mixture is mixed for 4 min;

[0103] S3, add 12 parts of silica heated to 55°C, mix for 4 minutes, add 4 parts of trimethylolpropane and 2 parts of pentaerythritol and mix for 12 minutes.

[0104] S4, add 6 parts of peroxide carbonate heated to 30°C, mix for 8 minutes to obtain polyurethane compound;

[0105] S5, mix polyurethane adhesive with magnesium hydroxide (mass ratio of polyurethane adhesive to magnesium hydroxide is 1:0.2), mix for 5 minutes to obtain the inner core material;

[0106] S6. The polyurethane adhesive is wrapped around the outside of the inner core material (the mass ratio of the inner core material to the polyurethane protective layer is 1:1.2), filled into the mold cavity preheated to 160°C, a pressure of 15 MPa is applied, and the temperature and pressure are maintained for 10 minutes. After demolding and cooling, the polyurethane tube material is obtained.

[0107] Performance testing

[0108] The following test methods were used to perform performance tests on polyurethane pipe samples.

[0109] ①The tensile strength and elongation at break of the polyurethane tube samples prepared by the methods of Examples 1-3 and Comparative Examples 1-3 were tested in accordance with GB / T 528-2009 "Determination of tensile stress-strain properties of vulcanized rubber or thermoplastic rubber".

[0110] ②The low-temperature brittleness of the polyurethane pipe samples prepared by the methods of Examples 1-3 and Comparative Examples 1-3 was tested in accordance with GB / T 7758-2020 "Determination of Low-Temperature Properties of Vulcanized Rubber".

[0111] The results are shown in Table 1:

[0112] Table 1

[0113] project Tensile strength / MPa Elongation at break / % Low-temperature brittleness temperature / ℃ Example 1 18 460 -60 Example 2 19 460 -62 Example 3 17 458 -60 Comparative Example 1 15 453 -57 Comparative Example 2 15 452 -58 Comparative Example 3 14 448 -55

[0114] As can be seen from the table above, the polyurethane pipe samples prepared by the methods of Examples 1-3 have better tensile strength, elongation at break and low temperature resistance than the polyurethane pipe samples prepared by Examples 1, 3 and Comparative Examples 1-3. Comparing Example 2 with Comparative Examples 1-2 in turn, it can be seen that the synergistic effect of lignin and oleanolic acid in Example 2 is better than that of adding either lignin or oleanolic acid alone to Comparative Examples 1 and 2.

[0115] ③The compression set of the polyurethane pipe samples prepared by the methods of Example 2 and Comparative Example 3 was tested according to GB / T 3512-2014 "Accelerated aging and heat resistance test of vulcanized rubber or thermoplastic rubber in hot air".

[0116] ④ The polyurethane pipe samples prepared by the methods of Example 2 and Comparative Example 3 were tested for hot air aging rate according to GB / T 7759.1-2015 "Determination of compression set of vulcanized rubber or thermoplastic rubber - Part 1: Under normal and high temperature conditions". (Test conditions: aging at 85°C for 72 hours).

[0117] ⑤ The combustion performance of the polyurethane pipe samples prepared by the methods of Example 2 and Comparative Example 3 was tested according to GB 8624-2012 "Classification of Combustion Performance of Building Materials and Products" (A (A1, A2), B1 (Flame-retardant), B2 (Combustible), B3 (Flammable)).

[0118] ⑥ In accordance with GB / T 20284-2006 "Single Combustion Test of Building Materials or Products", the polyurethane pipe samples prepared by the methods of Example 2 and Comparative Example 3 were tested for SMOGRA (Smoke Generation Rate Index) and 600s Total Smoke Production (TSP). 600 s) is used for testing.

[0119] The results are shown in Table 2:

[0120] Table 2

[0121] project Compression permanent deformation / % Hot air aging / % Combustion performance Flue gas formation rate index Total smoke production in 600 seconds Example 2 22 16 B1 95 m² / s² 185 m² Comparative Example 3 26 19 B2 89 m² / s² 182 m²

[0122] As can be seen from the table above, when comparing the polyurethane pipe sample prepared by the method of Example 2 with the polyurethane pipe sample prepared by the method of Comparative Example 3, it is obvious that Comparative Example 3, which only uses magnesium hydroxide as flame retardant microparticles, is significantly inferior to Example 2 in terms of compression set and hot air aging performance. It can be seen that the polyurethane pipe sample prepared by the method of Example 2 has better performance.

[0123] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A polyurethane tubing material for a flame-retardant damper in a hydraulic cylinder, characterized in that, The polyurethane tube is obtained by coating the inner core material with a polyurethane protective layer. The polyurethane protective layer is made of polyurethane adhesive, and the inner core material is made of polyurethane adhesive mixed with flame-retardant microparticles. The raw materials for preparing the polyurethane compound, by weight, include: 65-80 parts polyurethane particles, 3-6 parts trimethylolpropane, 1-3 parts pentaerythritol, 5-8 parts peroxide carbonate, 10-15 parts silica, 5-6 parts antioxidant, and 2-5 parts zinc stearate. The raw materials for preparing the flame-retardant microparticles, by weight, include 35-55 parts of polydodecanoic acid particles, 30-45 parts of magnesium hydroxide, 2-4 parts of potassium carbonate, 5-10 parts of lignin, 8-16 parts of oleanolic acid and 15-23 parts of zinc borate. The preparation process of the flame-retardant microparticles is as follows: S1. Place magnesium hydroxide, potassium carbonate, lignin, oleanolic acid and zinc borate into a drying oven and dry at 60-80℃ for 3-5 hours for later use. S2, magnesium hydroxide, potassium carbonate, lignin, oleanolic acid and zinc borate were pulverized using a ball mill and set aside for later use; S3, add polydodecyl lactam particles, magnesium hydroxide, potassium carbonate, lignin, oleanolic acid and zinc borate into a mixer and stir at 65 r / min for 20-30 min to obtain the preform; S4. Add the pre-made material to the internal mixer, heat it to 175-195℃, and mix for 8 minutes to obtain the composite material. S5. The obtained composite material is cooled and solidified, then pulverized and passed through a 150-mesh sieve to obtain flame-retardant microparticles.

2. The polyurethane tubing for a flame-retardant damper in a hydraulic cylinder according to claim 1, characterized in that, The ball mill uses zirconia grinding balls of two sizes, Φ5mm and Φ6mm, with a mass ratio of 1:1 between the large and small balls. Its ball-to-material ratio is 12:

1.

3. The polyurethane tubing for a flame-retardant damper in a hydraulic cylinder according to claim 1, characterized in that, The antioxidant is 4,4'-bis(α,α-dimethylbenzyl)diphenylamine or 2,2,4-trimethyl-1,2-dihydroquinoline.

4. A method for preparing polyurethane tubing for a flame-retardant damper of a hydraulic cylinder as described in any one of claims 1-3, characterized in that, Includes the following steps: S1, pre-pass polyurethane granules on a two-roll mill for 15-20 minutes, put silica into a drying oven and dry at 60-80℃ for 3-5 hours to obtain a billet; S2, put the billet into an internal mixer at 100-135℃, add zinc stearate and antioxidant, and mix for 3-5 minutes; S3, heat the silica to 55℃ and add it, mix for 4 minutes, then add trimethylolpropane and pentaerythritol and mix for 10-15 minutes. S4, add peroxide carbonate heated to 30°C, mix for 8 minutes to obtain polyurethane compound; S5, mix the polyurethane adhesive with flame-retardant microparticles and knead for 5 minutes to obtain the inner core material; S6. The polyurethane adhesive is wrapped around the outside of the inner core material and filled into the mold cavity preheated to 160°C. A pressure of 10-20 MPa is applied, and the material is kept at the same temperature and pressure for 5-15 minutes. After demolding and cooling, the polyurethane tube material is obtained.

5. The method for preparing polyurethane tubing for a flame-retardant damper of a hydraulic cylinder according to claim 4, characterized in that, The open mill has a roll temperature of 60-85℃ and a roll gap of 2mm.

6. The method for preparing polyurethane tubing for a flame-retardant damper of a hydraulic cylinder according to claim 4, characterized in that, The mass ratio of the polyurethane adhesive to the flame-retardant microparticles is 1:0.2; the mass ratio of the inner core material to the polyurethane protective layer is 1:1.2.