CN111705683A - Dehumidification and corrosion prevention method for main cable of large suspension bridge - Google Patents
Dehumidification and corrosion prevention method for main cable of large suspension bridge Download PDFInfo
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- E—FIXED CONSTRUCTIONS
- E01—CONSTRUCTION OF ROADS, RAILWAYS, OR BRIDGES
- E01D—CONSTRUCTION OF BRIDGES, ELEVATED ROADWAYS OR VIADUCTS; ASSEMBLY OF BRIDGES
- E01D22/00—Methods or apparatus for repairing or strengthening existing bridges ; Methods or apparatus for dismantling bridges
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- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
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- D01F6/88—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from mixtures of polycondensation products as major constituent with other polymers or low-molecular-weight compounds
- D01F6/94—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from mixtures of polycondensation products as major constituent with other polymers or low-molecular-weight compounds of other polycondensation products
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- E01—CONSTRUCTION OF ROADS, RAILWAYS, OR BRIDGES
- E01D—CONSTRUCTION OF BRIDGES, ELEVATED ROADWAYS OR VIADUCTS; ASSEMBLY OF BRIDGES
- E01D11/00—Suspension or cable-stayed bridges
- E01D11/02—Suspension bridges
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- E01D19/00—Structural or constructional details of bridges
- E01D19/16—Suspension cables; Cable clamps for suspension cables ; Pre- or post-stressed cables
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
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- C08J2379/00—Characterised by the use of macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing nitrogen with or without oxygen, or carbon only, not provided for in groups C08J2361/00 - C08J2377/00
- C08J2379/04—Polycondensates having nitrogen-containing heterocyclic rings in the main chain; Polyhydrazides; Polyamide acids or similar polyimide precursors
- C08J2379/08—Polyimides; Polyester-imides; Polyamide-imides; Polyamide acids or similar polyimide precursors
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Abstract
The invention discloses a dehumidification and corrosion prevention method for a main cable of a large suspension bridge, which mainly comprises the following steps: winding a layer of steel wire on the peripheral surface of the main cable; spirally winding a layer of polyimide film containing a spongy pore structure on the peripheral surface of the steel wire; winding two layers of polyimide fibers with nanopores on the peripheral surface of the polyimide film; covering a layer of pipeline-shaped sealing sheath layer made of high-density polyethylene with carbon black uniformly distributed on the peripheral surface of the polyimide fiber; and conveying dry air to the inside of the sealed main cable. The method for sealing the main cable and conveying the dry air to the interior of the main cable greatly enhances the corrosion resistance of the main cable system of the suspension bridge and prolongs the service life of the main cable.
Description
Technical Field
The invention relates to the technical field of dehumidification and corrosion prevention of a main cable of a suspension bridge. More particularly, the invention relates to a dehumidification and corrosion prevention method for a main cable of a large suspension bridge.
Background
The main cable is one of the most important stressed members of the suspension bridge, called "lifelines", which is exposed to the atmospheric environment for a long time and is subject to corrosion from various adverse environments, and at the same time, since the main cable is an irreplaceable member, the life of the main cable directly determines the service life of the suspension bridge. Traditional main push-towing rope protection is through carrying out sealed parcel (main push-towing rope putty + kinking + coating application) to the main push-towing rope skin and preventing that moisture from invading inside in order to reach the anticorrosion purpose, but the main push-towing rope will experience longer construction period, can cause inside ponding, and the main push-towing rope inoxidizing coating can have local damage or fracture when long-term the use, leads to the protective effect not ideal. The existing emerging technology adopts a main cable dehumidification anticorrosion system, namely, dry air is supplied to the inside of a sealed main cable to take away water in the gaps of steel wires in the main cable and maintain a dry environment, so that the corrosion of the steel wires of the main cable is avoided, and the durability of the main cable structure is improved. But the main cable dehumidification corrosion prevention system still has the following defects: the existing sealing sheath layer is of a metal thin-wall cylinder type structure, is easy to deform and damage during installation and use, causes the risk of air leakage of a dehumidification system and corrosion of a main cable, and has the problem of self corrosion prevention and protection; in addition, the large-scale suspension bridge has large span and the main cable has long length, so that the air supply length is long, the required air supply pressure is high, the air leakage of the dehumidification system is increased along with the increase of the air supply pressure, and the efficiency of drying the main cable is reduced. Therefore, a dehumidification and corrosion prevention method for a main cable of a large suspension bridge is urgently needed to solve the problems.
Disclosure of Invention
An object of the present invention is to solve at least the above problems and to provide at least the advantages described later.
The invention also aims to provide a dehumidification and corrosion prevention method for the main cable of the large suspension bridge, which increases the pressure resistance by winding the polyimide film and the polyimide fiber, obviously improves the sealing effect of the main cable, and achieves the purpose of dehumidification and corrosion prevention for the main cable.
To achieve these objects and other advantages in accordance with the purpose of the invention, a dehumidification corrosion prevention method for a main cable of a large suspension bridge is provided, which mainly comprises the steps of:
winding a layer of steel wire on the peripheral surface of a main cable;
spirally winding a layer of belt-shaped polyimide film containing a spongy hole structure on the peripheral surface of the steel wire, wherein the rear ring of the polyimide film covers one half of the front ring;
obliquely winding a layer of polyimide fiber with nano holes on the peripheral surface of the polyimide film, and symmetrically obliquely winding a second layer of polyimide fiber with nano holes on the first layer of polyimide fiber;
covering a layer of pipeline-shaped sealing sheath layer made of high-density polyethylene uniformly distributed with carbon black on the peripheral surface of the second layer of polyimide fiber, wherein a plurality of exhaust ports with valves are formed in the sealing sheath layer and are arranged at equal intervals;
and fifthly, sealing and coating air inlet covers at the end parts of the two ends of the main cable, wherein the air inlet covers are provided with air inlets connected with air inlet pipelines, and dry air is conveyed into the main cable through the air inlet pipelines.
Preferably, the preparation method of the polyimide film in the second step comprises: using NaNO3As a template, polyamic acid and NaNO3Dissolving in dimethyl formamide, mixing, stirring and clarifying to obtain a coating solution with the concentration of 15 wt%, wherein the polyamic acid and NaNO are3The mass ratio of the substances is 2:1, the coating liquid is coated on a glass plate to form a film, the film is placed for 24 hours at the temperature of 0 ℃ after being coated, then the film is placed into water for solvent exchange for 5 days at the temperature of 5 ℃, the film is frozen and dried, and the film is immersed into acetic anhydride and triethyl acetateAnd (3) adding the mixed solution of amine with the volume ratio of 4:1, and heating at 100 ℃ for 36 hours to obtain the polyimide film.
Preferably, the polyimide film has an average pore diameter of 5 to 20 μm and a thickness of 10 to 30 mm.
Preferably, the preparation method of the polyimide fiber in the third step comprises the following steps: dissolving polyamic acid in dimethylformamide to prepare a raw material spinning solution with the concentration of 12 wt%, and adding TiO into the raw material spinning solution2Nanoparticles of said TiO2The adding amount of the nano particles is 0.3-0.5% of the amount of the polyamic acid substance, the nano particles are uniformly mixed and then stand for 24h, a wet spinning method is adopted to prepare fibers, the fibers are placed in a coagulating bath for solvent exchange for 5d, the temperature of the coagulating bath is 5 ℃, the coagulating bath is water and ethanol in a mass ratio of 6:4, then natural drying is carried out, the fibers are immersed in a mixed solution of acetic anhydride and triethylamine in a volume ratio of 4:1, and heating is carried out at 100 ℃ for 36 h, so that the polyimide fibers are obtained.
Preferably, the average pore diameter of the two layers of polyimide fibers is 10 to 50 nm.
Preferably, the winding directions of the two layers of polyimide fibers and the axial direction of the main cable are respectively 45 degrees and 135 degrees.
Preferably, the content of the carbon black in the fourth step is 2-2.5% of the mass of the high-density polyethylene.
Preferably, the thickness of the sealing sheath layer is 40-60 mm.
Preferably, a pressure detector is installed at the exhaust port.
The invention at least comprises the following beneficial effects:
firstly, a steel wire is wound outside a main cable, a polyimide film with a spongy pore structure is wound outside a steel wire layer in a spiral mode, the spongy pore structure can well disperse air supply pressure and has high pressure resistance, meanwhile, the polyimide film is in a belt shape, and the rear ring covers one half of the front ring, so that air leakage at a winding gap caused by high air supply pressure when dry air is conveyed into the main cable is prevented;
secondly, two layers of polyimide fibers are wound on the periphery of the polyimide film, the polyimide has hydrophobicity, and meanwhile, a nano-pore structure is fully distributed in the polyimide fibers, so that when air molecules are in pores smaller than 70nm, the air molecules lose the free flowing capacity, external water vapor is effectively prevented from entering the inside of the main cable, the inclination angles of the two layers of fibers are symmetrical, and the air molecules are prevented from flowing in a fiber gap;
thirdly, the sealing sheath layer is a pipeline made of high-density polyethylene with carbon black uniformly distributed, has excellent aging resistance and cannot be damaged by ultraviolet radiation;
fourthly, when carrying dry air to main cable inside through the admission line at first, all open the valve of a plurality of gas vents department, accelerate the circulation of air in the main cable, discharge original moist air as early as possible in the main cable, when treating that the gas vent goes out the air and becomes dry, the valve of gas vent department that will be located the main cable intermediate position is opened, the valve of all the other gas vents department is closed, reduce air feed pressure, guarantee the state of the inside pressure-fired of main cable, the pressure value that monitoring gas vent goes out pressure detector shows, whether the differentiation has the gas leakage phenomenon.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention.
Drawings
FIG. 1 is a graph showing the distribution of pore diameters of polyimide membranes prepared in examples 2 to 4 of the present invention;
fig. 2 is a pore size distribution diagram of the polyimide membrane prepared in comparative example 3.
Detailed Description
The present invention is further described in detail below with reference to examples and the accompanying drawings so that those skilled in the art can implement the invention by referring to the description.
It will be understood that terms such as "having," "including," and "comprising," as used herein, do not preclude the presence or addition of one or more other elements or groups thereof.
It is to be noted that the experimental methods described in the following embodiments are all conventional methods unless otherwise specified, and the reagents and materials are commercially available unless otherwise specified.
< example 1>
The dehumidification and corrosion prevention method for the main cable of the large suspension bridge mainly comprises the following steps:
winding a layer of steel wire on the peripheral surface of a main cable;
spirally winding a layer of belt-shaped polyimide film containing a spongy hole structure on the peripheral surface of the steel wire, wherein the rear ring of the polyimide film covers one half of the front ring;
obliquely winding a layer of polyimide fiber with nano holes on the peripheral surface of the polyimide film, and symmetrically obliquely winding a second layer of polyimide fiber with nano holes on the first layer of polyimide fiber;
covering a layer of pipeline-shaped sealing sheath layer made of high-density polyethylene uniformly distributed with carbon black on the peripheral surface of the second layer of polyimide fiber, wherein a plurality of exhaust ports with valves are formed in the sealing sheath layer and are arranged at equal intervals;
and fifthly, sealing and coating air inlet covers at the end parts of the two ends of the main cable, wherein the air inlet covers are provided with air inlets connected with air inlet pipelines, and dry air is conveyed into the main cable through the air inlet pipelines.
Among them, a band-shaped polyimide film having a spongy porous structure and a polyimide fiber having a nanopore are commercially available.
< example 2>
The dehumidification and corrosion prevention method for the main cable of the large suspension bridge mainly comprises the following steps:
winding a layer of steel wire on the peripheral surface of a main cable;
spirally winding a layer of belt-shaped polyimide film containing a spongy hole structure on the peripheral surface of the steel wire, wherein the rear ring of the polyimide film covers one half of the front ring;
obliquely winding a layer of polyimide fiber with nano holes on the peripheral surface of the polyimide film, and symmetrically obliquely winding a second layer of polyimide fiber with nano holes on the first layer of polyimide fiber;
covering a layer of pipeline-shaped sealing sheath layer made of high-density polyethylene uniformly distributed with carbon black on the peripheral surface of the second layer of polyimide fiber, wherein a plurality of exhaust ports with valves are formed in the sealing sheath layer and are arranged at equal intervals;
and fifthly, sealing and coating air inlet covers at the end parts of the two ends of the main cable, wherein the air inlet covers are provided with air inlets connected with air inlet pipelines, and dry air is conveyed into the main cable through the air inlet pipelines.
The preparation method of the polyimide film with the spongy pore structure comprises the following steps: using NaNO3As a template, polyamic acid and NaNO3Dissolving in dimethyl formamide, mixing, stirring and clarifying to obtain a coating solution with the concentration of 15 wt%, wherein the polyamic acid and NaNO are3The mass ratio of the substances is 2:1, the film coating liquid is blade-coated on a glass plate to form a film, the thickness of the film is 15mm, the film is placed for 24 hours at 0 ℃ after being coated, then the film is placed in water for solvent exchange for 5 days at 5 ℃, the film is frozen and dried, the film is immersed in a mixed solution of acetic anhydride and triethylamine, the volume ratio of the acetic anhydride to the triethylamine is 4:1, and the mixed solution is heated for 36 hours at 100 ℃, so that the polyimide film with the thickness of 10mm is prepared.
The preparation method of the polyimide fiber with the nano-pore structure comprises the following steps: dissolving polyamic acid in dimethylformamide to prepare a raw material spinning solution with the concentration of 12 wt%, and adding TiO into the raw material spinning solution2Nanoparticles of said TiO2The adding amount of the nano particles is 0.5 percent of the amount of the polyamic acid substance, the nano particles are uniformly mixed and then stand for 24 hours, a wet spinning method is adopted to prepare the fiber, the fiber is placed in a coagulating bath for solvent exchange for 5 days, the temperature of the coagulating bath is 5 ℃, the coagulating bath is water and ethanol with the mass ratio of 6:4, then natural drying is carried out, the fiber is immersed in a mixed solution of acetic anhydride and triethylamine with the volume ratio of 4:1, and the mixture is heated for 36 hours at 100 ℃, so that the polyimide fiber is obtained.
< example 3>
The other steps are the same as example 2, except that the specific method for preparing the polyimide film with the spongy porous structure is as follows:
using NaNO3As a template, polyamic acid and NaNO3Dissolving in dimethyl formamide, mixing, stirring and clarifying to obtain a coating solution with the concentration of 15 wt%, wherein the polyamic acid and NaNO are3The mass ratio of the substances is 2:1, the film coating liquid is blade-coated on a glass plate to form a film, the thickness of the film is 30mm, the film is placed at 0 ℃ for 24h after being coated, then the film is placed in water for solvent exchange at 5 ℃ for 5d, the film is frozen and dried, the film is immersed in a mixed solution of acetic anhydride and triethylamine, the volume ratio of the acetic anhydride to the triethylamine is 4:1, and the mixed solution is heated at 100 ℃ for 36 hours, so that the polyimide film with the thickness of 18mm is prepared.
The specific method for preparing the polyimide fiber with the nano-pore structure comprises the following steps: dissolving polyamic acid in dimethylformamide to prepare a raw material spinning solution with the concentration of 12 wt%, and adding TiO into the raw material spinning solution2Nanoparticles of said TiO2The adding amount of the nano particles is 0.3 percent of the amount of the polyamic acid substance, the nano particles are uniformly mixed and then stand for 24 hours, a wet spinning method is adopted to prepare the fiber, the fiber is placed in a coagulating bath for solvent exchange for 5 days, the temperature of the coagulating bath is 5 ℃, the coagulating bath is water and ethanol with the mass ratio of 6:4, then natural drying is carried out, the fiber is immersed in a mixed solution of acetic anhydride and triethylamine with the volume ratio of 4:1, and the mixture is heated for 36 hours at 100 ℃, so that the polyimide fiber is obtained.
< example 4>
The other steps are the same as example 2, except that the specific method for preparing the polyimide film with the spongy porous structure is as follows:
using NaNO3As a template, polyamic acid and NaNO3Dissolving in dimethyl formamide, mixing, stirring and clarifying to obtain a coating solution with the concentration of 15 wt%, wherein the polyamic acid and NaNO are3The mass ratio of the substances is 2:1, the film coating liquid is blade-coated on a glass plate to form a film, the thickness of the film is 45mm, the film is placed for 24 hours at 0 ℃ after being coated, then the film is placed in water for solvent exchange for 5 days at 5 ℃, the film is frozen and dried, the film is immersed in a mixed solution of acetic anhydride and triethylamine with the volume ratio of 4:1, and the mixed solution is heated for 36 hours at 100 ℃ to prepare the film with the thickness of 4:1A polyimide film having a thickness of 30 mm.
The specific method for preparing the polyimide fiber with the nano-pore structure comprises the following steps: dissolving polyamic acid in dimethylformamide to prepare a raw material spinning solution with the concentration of 12 wt%, and adding TiO into the raw material spinning solution2Nanoparticles of said TiO2The adding amount of the nano particles is 0.4 percent of the amount of the polyamic acid substance, the nano particles are uniformly mixed and then stand for 24 hours, a wet spinning method is adopted to prepare the fiber, the fiber is placed in a coagulating bath for solvent exchange for 5 days, the temperature of the coagulating bath is 5 ℃, the coagulating bath is water and ethanol with the mass ratio of 6:4, then natural drying is carried out, the fiber is immersed in a mixed solution of acetic anhydride and triethylamine with the volume ratio of 4:1, and the mixture is heated for 36 hours at 100 ℃, so that the polyimide fiber is obtained.
< comparative example 1>
The dehumidification and corrosion prevention method for the main cable of the large suspension bridge mainly comprises the following steps:
winding a layer of steel wire on the peripheral surface of a main cable;
covering a layer of pipeline-shaped sealing sheath layer made of high-density polyethylene uniformly distributed with carbon black on the peripheral surface of the steel wire, wherein a plurality of exhaust ports with valves are formed in the sealing sheath layer and are arranged at equal intervals;
and step three, hermetically coating air inlet covers at the end parts of the two ends of the main cable, wherein the air inlet covers are provided with air inlets connected with air inlet pipelines, and conveying dry air to the interior of the main cable through the air inlet pipelines.
< comparative example 2>
The dehumidification and corrosion prevention method for the main cable of the large suspension bridge mainly comprises the following steps:
winding a layer of steel wire on the peripheral surface of a main cable;
spirally winding a layer of belt-shaped polyimide film containing a spongy pore structure on the outer peripheral surface of the steel wire;
winding a layer of polyimide fiber with nano holes on the peripheral surface of the polyimide film;
covering a layer of pipeline-shaped sealing sheath layer made of high-density polyethylene uniformly distributed with carbon black on the peripheral surface of the polyimide fiber, wherein a plurality of exhaust ports with valves are formed in the sealing sheath layer and are arranged at equal intervals;
and fifthly, sealing and coating air inlet covers at the end parts of the two ends of the main cable, wherein the air inlet covers are provided with air inlets connected with air inlet pipelines, and dry air is conveyed into the main cable through the air inlet pipelines.
Wherein the polyimide film and the polyimide fiber were prepared in the same manner as in example 1.
< comparative example 3>
The dehumidification and corrosion prevention method for the main cable of the large suspension bridge mainly comprises the following steps:
winding a layer of steel wire on the peripheral surface of a main cable;
spirally winding a layer of strip-shaped polyimide film on the peripheral surface of the steel wire, wherein the rear ring of the polyimide film covers one half of the front ring;
obliquely winding a layer of polyimide fibers on the peripheral surface of the polyimide film, and symmetrically and obliquely winding a second layer of polyimide fibers on the first layer of polyimide fibers;
covering a layer of pipeline-shaped sealing sheath layer made of high-density polyethylene uniformly distributed with carbon black on the peripheral surface of the second layer of polyimide fiber, wherein a plurality of exhaust ports with valves are formed in the sealing sheath layer and are arranged at equal intervals;
and fifthly, sealing and coating air inlet covers at the end parts of the two ends of the main cable, wherein the air inlet covers are provided with air inlets connected with air inlet pipelines, and dry air is conveyed into the main cable through the air inlet pipelines.
The specific method for preparing the polyimide film comprises the following steps: dissolving polyamic acid in dimethylformamide to prepare a coating solution with the concentration of 15 wt%, carrying out blade coating on the coating solution on a glass plate to form a film, wherein the thickness of the film is 15mm, immediately putting the film into water for solvent exchange at 25 ℃ for 5d after coating, naturally drying, immersing the film into a mixed solution of acetic anhydride and triethylamine with the volume ratio of 4:1, and heating at 100 ℃ for 36 hours to prepare the polyimide film with the thickness of 10 mm.
The preparation method of the polyimide fiber with the nano-pore structure comprises the following steps: dissolving polyamide acid in dimethylformamide to prepare a raw material spinning solution with the concentration of 12 wt%, preparing fibers by a wet spinning method, placing the fibers in a coagulating bath for solvent exchange for 5d, wherein the temperature of the coagulating bath is 25 ℃, the coagulating bath is water and ethanol with the mass ratio of 6:4, then naturally drying, immersing the fibers in a mixed solution of acetic anhydride and triethylamine with the volume ratio of 4:1, and heating at 100 ℃ for 36 hours to obtain the polyimide fibers.
In examples 1-4, by using the dehumidification and corrosion prevention method for the main cable of the large suspension bridge, a steel wire is wound outside the main cable, and then a polyimide film with a spongy pore structure is spirally wound outside a steel wire layer, the spongy pore structure can well disperse air supply pressure and has strong pressure resistance, meanwhile, the polyimide film is in a belt shape, and a rear ring of the polyimide film covers one half of a front ring, so that air leakage at a winding gap caused by high air supply pressure is prevented when dry air is conveyed into the main cable; two-layer polyimide fiber of winding in polyimide film periphery, the polyimide has the hydrophobicity, polyimide fiber inside is covered with nanometer form pore structure simultaneously, when air molecule is when being less than 70 nm's gas pocket, will lose the ability of free flow, inside effectively having prevented outside vapor entering main push-towing rope, two-layer fibrous inclination symmetry, prevent that air molecule from flowing in the fibre clearance, even sealed restrictive coating produces gas leakage, also can be at a period internal resistance water proof steam and pass through, time guarantee is provided for repairing sealed restrictive coating.
In comparative example 1, a steel wire was wound only around the outer circumference of the main rope, and a pipe-shaped sealing sheath layer made of high density polyethylene, in which carbon black was uniformly distributed, was coated on the outer circumferential surface of the steel wire. When letting in dry air in to the main push-towing rope, air feed pressure directly uses sealed restrictive coating, in case sealed restrictive coating produces the gas leakage, will lead to vapor to lead to the rust of main push-towing rope by steel wire clearance department and main push-towing rope contact.
In comparative example 2, a steel wire was wound around a main cable, a band-shaped polyimide film having a spongy porous structure was simply wound around the steel wire, a layer of polyimide fiber having nano-pores was wound around the outer circumferential surface of the polyimide film, and a pipe-shaped sealing sheath layer made of high-density polyethylene having carbon black uniformly distributed around the outer circumferential surface of the polyimide fiber was coated. When letting in dry air in to the main push-towing rope, air feed pressure obtains the dispersion through the polyimide film of spongy pore structure, but the winding clearance department of polyimide film produces gas leakage easily, causes clearance department pressure concentration to lead to sealed system to suffer destruction easily, in case sealed restrictive coating produces gas leakage, will lead to vapor to be contacted with the main push-towing rope by polyimide fibrous clearance and steel wire clearance department, lead to the main push-towing rope to rust.
< Membrane pore size distribution test >
The polyimide membranes prepared in examples 2 to 4 and comparative example 3 were subjected to pore size distribution measurement tests, and the results are shown in fig. 1 and 2. The results show that the pores in the polyimide films prepared in examples 1-3 are all nano-scale, and the polyimide films have uniform pore structures, are sponge-like structures and have good pressure resistance; the polyimide film prepared in comparative example 3 has both nano-scale and micro-scale pore structures as measured by conventional methods, since the surface of the film has nano-scale pores and the inside of the film has typical micro-scale finger pore structures.
< test of pressure resistance of film >
The polyimide films used in examples 1 to 4 and comparative example 3 were subjected to a pressure resistance test to measure the maximum pressure that they can withstand, and the test results are shown in table 1:
TABLE 1 comparison of the pressure resistance of the films
| Example 1 | Example 2 | Example 3 | Example 4 | Comparative example 3 | |
| Pressure resistance (KPa) | 183 | 273 | 266 | 289 | 55 |
The test results showed that the commercially available polyimide film used in example 1, which also had a spongy pore structure, had excellent pressure resistance; examples 2 to 4 use NaNO3The polyimide film is prepared by taking the polyimide film as a template agent, polyamide acid is placed at 0 ℃ for 24 hours after being subjected to blade coating to form a film, the polyamide acid sol is converted into gel at low temperature, a three-dimensional network structure is formed in the system, a dimethylformamide solvent is filled in the network, solvent exchange is carried out at low temperature, the dimethylformamide solvent and water are slowly replaced, then freeze drying is carried out, the network structure is kept as far as possible, and the finally prepared polyimide film forms a uniform spongy pore structure through chemical imidization, so that the polyimide film prepared in examples 2-4 has better pressure resistance. The polyimide film prepared by the traditional method in the comparative example 3 has a typical finger-shaped hole structure, the pressure resistance of the finger-shaped hole structure is poor, when dry air is introduced into the main cable, air supply pressure acts on the polyimide film, the polyimide fibers and the sealing sheath layer, when the air supply pressure is high, the polyimide film is easy to generate holes, the local pressure is too high, the risk of damage of the sealing sheath layer is increased, air leakage is generated, and the main cable is subjected to the risk of possible damage.
< pore diameter measurement test >
The average pore diameters of the polyimide fibers used in examples 1 to 4 and comparative example 3 were measured, and the results are shown in Table 2:
TABLE 2 comparison of mean pore diameters
The results show that the average pore diameter of the polyimide fibers used in examples 1-4 is less than 70nm, and air molecules lose the free flow capacity in pores, so that external water vapor can be effectively prevented from entering the main cable; comparative example 3 the polyimide fiber prepared by the conventional method has a large average pore size, and once the sealing system outside the main cable is damaged, the large pore size polyimide fiber does not well prevent the flow of water vapor, thereby increasing the risk of corrosion of the main cable.
The number of apparatuses and the scale of the process described herein are intended to simplify the description of the present invention. Applications, modifications and variations of the present invention will be apparent to those skilled in the art.
While embodiments of the invention have been described above, it is not limited to the applications set forth in the description and the embodiments, which are fully applicable to various fields of endeavor for which the invention may be embodied with additional modifications as would be readily apparent to those skilled in the art, and the invention is therefore not limited to the details given herein and to the examples shown and described without departing from the generic concept as defined by the claims and their equivalents.
Claims (9)
1. A dehumidification and corrosion prevention method for a main cable of a large suspension bridge is characterized by mainly comprising the following steps:
winding a layer of steel wire on the peripheral surface of a main cable;
spirally winding a layer of belt-shaped polyimide film containing a spongy hole structure on the peripheral surface of the steel wire, wherein the rear ring of the polyimide film covers one half of the front ring;
obliquely winding a layer of polyimide fiber with nano holes on the peripheral surface of the polyimide film, and symmetrically obliquely winding a second layer of polyimide fiber with nano holes on the first layer of polyimide fiber;
covering a layer of pipeline-shaped sealing sheath layer made of high-density polyethylene uniformly distributed with carbon black on the peripheral surface of the second layer of polyimide fiber, wherein a plurality of exhaust ports with valves are formed in the sealing sheath layer and are arranged at equal intervals;
and fifthly, sealing and coating air inlet covers at the end parts of the two ends of the main cable, wherein the air inlet covers are provided with air inlets connected with air inlet pipelines, and dry air is conveyed into the main cable through the air inlet pipelines.
2. The dehumidification and corrosion prevention method for the main cable of the large suspension bridge according to claim 1, wherein the preparation method of the polyimide film in the second step comprises the following steps: using NaNO3As a template, polyamic acid and NaNO3Dissolving in dimethyl formamide, mixing, stirring and clarifying to obtain a coating solution with the concentration of 15 wt%, wherein the polyamic acid and NaNO are3The mass ratio of the substances is 2:1, the film coating liquid is blade-coated on a glass plate to form a film, the film is placed for 24 hours at the temperature of 0 ℃ after being coated, then the film is placed into water for solvent exchange for 5 days at the temperature of 5 ℃, the film is frozen and dried, the film is immersed into a mixed solution of acetic anhydride and triethylamine with the volume ratio of 4:1, and the mixed solution is heated for 36 hours at the temperature of 100 ℃, so that the polyimide film is prepared.
3. The dehumidification and corrosion prevention method for the main cable of the large suspension bridge according to claim 1, wherein the polyimide film has an average pore size of 5 to 20 μm and a thickness of 10 to 30 mm.
4. The dehumidification and corrosion prevention method for the main cable of the large suspension bridge according to claim 1, wherein the preparation method of the polyimide fiber in the third step comprises the following steps: dissolving polyamic acid in dimethylformamide to prepare a raw material spinning solution with the concentration of 12 wt%, and adding TiO into the raw material spinning solution2Nanoparticles of said TiO2NanoparticlesThe additive amount of the polyamide acid is 0.3-0.5% of the amount of the polyamide acid substance, the polyamide acid substance and the polyamide acid substance are uniformly mixed and then are kept stand for 24h, the fiber is prepared by a wet spinning method, the fiber is placed in a coagulating bath for solvent exchange for 5d, the temperature of the coagulating bath is 5 ℃, the coagulating bath is water and ethanol in a mass ratio of 6:4, then natural drying is carried out, the fiber is immersed in a mixed solution of acetic anhydride and triethylamine in a volume ratio of 4:1, and the mixture is heated at 100 ℃ for 36 h, so that the polyimide fiber is obtained.
5. The dehumidification and corrosion prevention method for the main cable of the large suspension bridge according to claim 1, wherein the average pore diameter of the two layers of polyimide fibers is 10-50 nm.
6. The dehumidification and corrosion prevention method for the main cable of the large suspension bridge according to claim 1, wherein the winding directions of the two layers of polyimide fibers and the axial direction of the main cable are respectively 45 ° and 135 °.
7. The dehumidification and corrosion prevention method for the main cable of the large suspension bridge according to claim 1, wherein the content of the carbon black in the fourth step is 2-2.5% of the mass of the high density polyethylene.
8. The dehumidification and corrosion prevention method for the main cable of the large suspension bridge according to claim 1, wherein the thickness of the sealing sheath layer is 40-60 mm.
9. The dehumidification corrosion prevention method for a main cable of a large suspension bridge according to claim 1, wherein a pressure detector is installed at the air outlet.
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| CN114232478A (en) * | 2021-09-06 | 2022-03-25 | 郑州大学 | Efficient dehumidification method for main cable of suspension bridge |
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