RU2807418C1 - Fibre optic tunneling - Google Patents

Abstract

FIELD: fibre optic technology.

SUBSTANCE: invention relates namely to pass-through devices for hermetically sealed input of optical fibres through a partition, and can be used to introduce optical fibres between areas with different pressures. A fibre-optic penetration containing a housing with optical fibres passing through it from the high pressure side to the low pressure side; hermetic blocks are introduced into the housing, which form cavities, at least two of which are filled with an epoxy sealing compound, while the hermetic blocks are made individually for each optical fibre through holes filled with a sealing compound. At least one body cavity between the hermetic blocks is filled with viscous liquid material. The inner surface of the housing in the specified housing cavity is equipped with transverse annular grooves. Each hole in the hermetic blocks delimiting the specified body cavity has a dumbbell shape.

EFFECT: increase in the operational reliability of tunnelling under conditions of explosive experiments in underground protective structures while increasing its service life.

1 cl, 2 dwg

Description

The invention relates to fiber optic technology, namely to pass-through devices for hermetically sealed input of optical fibers through a partition, and can be used to introduce optical fibers between areas with different pressures.

A unit for longitudinal sealing of optical cables is known from the field of technology [RF patent No. 2091828, IPC G02B 6/24, 6/44, pub. 09.27.1997], containing a housing (shell), the internal cavity of which is filled with a sealing material with optical fibers (cables) placed in it. The sealing material and the housing, which are a single unit, are made of the same compound. On the outside of the housing there are diametrical grooves for sealing rings. The presence of rubber rings allows you to repeatedly install and demonstrate elements of fiber-optic transmission lines without violating the tightness of the assembly.

The advantage of this unit is the simplicity of the design and the absence of dissimilar materials in the composition, which minimizes the occurrence and accumulation of internal stresses, prevents a decrease in strength and increases service life.

However, the known device has the following disadvantages: low reliability of sealing, due to the presence of a single sealed cavity, as well as due to the body being made of a compound, which is a fragile material for impact or explosive effects, as well as a material of low strength and wear resistance, which contributes to damage or complete destruction of the housing during operation of the unit. Also, a disadvantage of the known unit is the possibility of optical fibers coming into contact with each other and the formation of voids and other inhomogeneities when pouring the compound (due to uncontrolled movement of the fibers while placing them in the sealing material), which reduces the strength of the housing and increases the likelihood of loss of tightness. The formation of grooves for sealing rings is carried out when pouring the compound, which reduces the quality of the surface of the grooves, and subsequent mechanical processing of the defects that appear is difficult or impossible due to glued optical fibers.

A fiber optic sealed junction is also known [RF patent No. 2685083, IPC G02B 6/24, pub. 04/16/2019], containing a housing with optical fibers passing through it from the high pressure side to the low pressure side, hermetic blocks (separators) are introduced into the housing, which form cavities, at least two of which are filled with an epoxy sealing compound, while the hermetic blocks are made with individual through holes filled with sealing compound for each optical fiber. The housing in this device is hermetically installed in the passage opening of the sealed device. At least one cavity between the separators forms an air gap. To reduce internal thermal stresses caused by dissimilar materials, the holes in the separators are located evenly over the entire surface of the separators. Moreover, the holes in the pair of separators delimiting each cavity are made of different diameters. In one pair of separators, the diameter of the holes is equal to the diameter of the optical fibers passing through the holes, and in the other pair of separators, the diameter of the holes exceeds the diameter of the optical fibers passing through them, providing a given gap to create conditions for high-quality continuous filling and controlled release of excess sealing material. This device is accepted as a prototype.

The disadvantage of the prototype is its relatively low operational reliability under conditions of explosive experiments in underground protective structures, which requires a long service life and long-term operation. In the prototype, in the cavities between the separators there is a large volume of sealing material (EL-20 glue), which polymerizes over time (after two years from the date of manufacture), resulting in its shrinkage. Microcracks form, glue peels off from the inner surface of the housing and optical fibers, which, when operated under conditions of excess pressure, will lead to leakage of explosion products, reducing the operational reliability of the junction. These processes occur simultaneously in both cavities limited by the separators. In addition, the description of the prototype indicates that the holes in the separators for sealing the optical fiber have diameters that provide clearance with the fibers passing through them. The diameter of these holes, based on the conditions for minimizing the adhesive seam between the internal surfaces of each hole and the optical fiber, should ensure free passage of EL-20 glue. This minimum diameter is usually determined by the capabilities of the manufacturing technology. For example, when making holes using cutting technology for the passage of flowable glue with an optical fiber diameter of 0.125 mm in diameter, the hole diameter can be 0.3...0.4 mm. In this case, when sealing the separators, excess glue is squeezed out through the gaps and creates adhesive drips around the fibers. During explosive experiments, where shock linear accelerations reach 4000 g, excess glue, adhesively connected to the optical fibers and not mechanically connected to the separator body, moves, mechanically affecting the optical fiber. These phenomena can lead to both distortion of the light signal and loss of tightness, negatively affecting the operational reliability of the junction. Technologically, with the dimensions of the adhesive seam shown above, it is extremely difficult to ensure reliable sealing of optical fibers with minimal excess of squeezed out glue.

The technical result to which the claimed invention is aimed is to increase the operational reliability of tunneling under conditions of explosive experiments in underground protective structures while increasing its service life.

The technical result is achieved by the fact that a fiber-optic penetration containing a housing with optical fibers passing through it from the high pressure side to the low pressure side; hermetic blocks are introduced into the housing, which form cavities, at least two of which are filled with an epoxy sealing compound, while the hermetic blocks made with individual through holes filled with a sealing composition for each optical fiber, according to the invention, at least one housing cavity between the HDAs is filled with a viscous liquid material, while the inner surface of the housing in the specified housing cavity is equipped with transverse annular grooves, and each hole in the HDAs limiting the specified the body cavity has a dumbbell shape.

Filling at least one housing cavity between the HDAs with a viscous liquid material, while the inner surface of the housing in said housing cavity is equipped with transverse annular grooves, makes it possible to organize “traps” for fine aerosols (active gas), which will accumulate inside the housing in the form of a “bubble” » due to the viscosity of the liquid material. The size of the “bubble” will be determined by the presence of air dissolved in the viscous liquid and possibly appearing when the liquid is poured into the housing. It should be noted that evacuation of the liquid eliminates the presence of air only partially. Thus, the gas "bubble" will increase until the pressure inside the housing is balanced by the high external pressure. As is known, when operating in an underground structure, the position of the penetration is close to horizontal. Based on this, the gas “bubble” will rise upward, accumulate inside the housing and move along the upper generatrix of the housing cavity towards the low-pressure hermetic block, including to the points where optical fibers enter. The presence of “traps” creates additional resistance to the movement of active gas, excluding its movement from the high pressure side to the low pressure side, thereby localizing a possible gas breakthrough through the adhesive sealing of optical fibers on the low pressure side, thereby increasing the operational reliability of the penetration. During long-term operation of the penetration (increasing service life) under conditions of explosive experiments in underground protective structures, there is a possibility of depressurization of the pressurized units for reasons inherent to the prototype. However, in the claimed solution, when active gas molecules continuously leak into the micropores of the adhesive joint of the HDA from the high pressure side in the area “adhesive (epoxy sealing composition) - optical fiber - housing", due to the difference in the sizes of the molecules of the viscous liquid and the sizes of the microgaps, the molecules liquids will not penetrate into the gaps. Active gas molecules will diffuse into the gaps due to the difference in pressure - high outside the housing, initially normal inside the housing.

Making each hole in the hermetic blocks delimiting the specified hull cavity shaped like a dumbbell increases operational reliability under conditions of explosive experiments in underground protective structures. The dumbbell-shaped shape of each hole, in which the narrow (middle) part is the main element of sealing, ensuring minimization of the scale factor of the adhesive seam, and the outer parts (larger diameter) are necessary for supplying glue and controlling the quality of the fill. The adhesive composition is fed under pressure into the indicated holes through a common cavity inside the HDA, and at the point where the glue enters the middle part of each hole, the filling speed increases, ensuring high-quality, cavity-free filling of optical fibers. In the prototype, when filling holes in hermetic blocks with an epoxy sealing composition, the quality of the filling is judged by the release of glue from the indicated holes, while excess (sagging) glue is formed outside, which, under shock acceleration in conditions of explosive experiments, can move sharply, picking up the fiber, which can lead to distortion of the optical signal and depressurization of the connection. It is important to exclude the presence of excess glue that is not mechanically connected to the HDA body outside the holes; this allows the implementation of dumbbell-shaped holes in the claimed technical solution. In dumbbell-shaped holes, excess glue is placed in the “socket” (the outermost parts of the larger diameter of the hole) without the glue coming out. By the level of glue release from the narrow (middle) part of the holes, one can judge the presence of glue and the quality of the fill in the holes being filled. The significant volume of the “socket” of the dumbbell-shaped hole, which can be filled completely or partially with a sealing adhesive composition, allows this to be achieved technologically. In this case, the adhesive volume of the created adhesive “plug” is mechanically connected to the inner surface of the hole, which prevents its movement under shock loads, while the impact on the optical fiber is minimized. In addition, the dumbbell-shaped shape of the hole indicates that the diameter of its narrow part is commensurate with the diameter of the optical fiber passing through it, and the length of the narrow part exceeds the diameter of the narrow part of the hole, which also has a positive effect on ensuring the tightness of the penetration, ensuring operational reliability under operating conditions in explosive experiments. This is due to the increase in the interface surface of each optical fiber with the metal surface of the narrow part of each dumbbell-shaped hole. The diameter of the hole for the optical fiber is minimized, its size is minimized by the existing manufacturing technology. The mating surfaces are filled with glue, and the reliability of the connection depends on the length of the adhesive seam. Due to the shrinkage of the glue, possible depressurization is local in nature, creating the so-called “tunnel” effect, when the tightness is maintained due to the preservation of possible bridges in the adhesive seam. The quality of the sealing adhesive inlet is affected by the volume of glue (thickness of the adhesive seam) enveloping the optical fiber. The smaller the thickness of the adhesive seam, the less shrinkage and the higher the reliability of the connection, and accordingly the longer the service life.

Thus, the combination of these distinctive features of the proposed device ensures an increase in the operational reliability of tunneling under conditions of explosive experiments in underground protective structures while increasing its service life.

The presence in the claimed invention of features that distinguish it from the prototype allows us to consider it to meet the “novelty” condition.

New features contained in the distinctive part of the claims have not been identified in technical solutions for a similar purpose. On this basis, we can conclude that the claimed invention complies with the “inventive step” condition.

The invention is illustrated by drawings, where in FIGS. 1 shows an axial section of the proposed fiber optic penetration, and FIG. Figure 2 shows a dumbbell-shaped hole in the HDA.

In fig. 1-2 the following notations are adopted:

1 - body;

2 - hermetic block on the high pressure side;

3 - plug on the high pressure side;

4 - hermetic block on the low pressure side;

5 - plug on the low pressure side;

6 - optical fiber;

7 - rubber sealing ring;

8 - nut;

9 - plug;

10 - rubber seal;

11 - cavity between the HDA and the plug on the high pressure side, filled with epoxy adhesive;

12 - cavity between the HDA and the plug on the low pressure side, filled with epoxy adhesive;

13 - body cavity filled with viscous liquid material;

14 - annular groove in the body cavity;

15 - dumbbell-shaped hole;

16 - hole for optical fiber in the plug;

17 - bushing;

18 - Kevlar protective tube on optical fiber;

19 - viscous liquid material.

The device is designed as follows.

The fiber optic penetration (Fig. 1-2) contains a housing 1, made in the form of a steel hollow cylinder with optical fibers 6 (up to 48 pcs.) passing through it from the high pressure side to the low pressure side. To install penetrations into the wall, for example, a sealed device (not shown), on the outer surface of the housing 1 there are annular grooves for installing rubber sealing rings 7. Hermetic blocks 2, 4 with plugs 3, 5 are inserted into the housing 1, which form the cavities. At least two cavities 11, 12 are filled with an epoxy sealing compound, and one body cavity 13 is filled with a viscous liquid material 19 (for example, oil), which is held in the body 1 by plugs 9. Hermetic blocks 2, 4 with plugs 3, 5 are made with individual ones for each optical fiber 6 through holes 15, 16 filled with epoxy sealant, respectively. The hermetic blocks 2, 4 are installed in the housing 1 by means of rubber seals 10. The plugs 3, 5 are fixed in the housing 1 on the high and low pressure side with nuts 8. The inner surface of the housing 1 in the housing cavity 13 is equipped with transverse annular grooves 14. Each hole 15 in the hermetic blocks 2 , 4, limiting the cavity 13, has a dumbbell shape. The narrow part of each hole 15 has a diameter commensurate with the diameter of the optical fiber 6 passing through it and a length significantly greater than the diameter of the narrow part of the hole 15.

The penetration is assembled as follows.

First, the optical fibers 6 are threaded into the corresponding passage holes 15 of the HDA 2 and holes 16 in the plug 3. The assembly is oriented vertically and under pressure through the holes 16 in the plug 3, which is subsequently plugged by the sleeve 17, the cavity 11 between the HDA 2 and the plug 3 is filled with an adhesive composition. while sealing the optical fibers 6 in the dumbbell-shaped holes 15. During the sealing process, the amount of glue required for sealing is controlled without it coming out of the holes 15.

After polymerization of the glue, the HDA 2 with plug 3 is installed into the housing 1 through rubber seals 10 and secured with a nut 8. Next, the optical fibers 6 are threaded through the cavity 13 into the corresponding holes 15, 16 of the HDA 4 and plug 5, placing them in the housing 1. The plug 5 is fixed nut 8. The sealing of optical fibers 6 in the HDA 4 with plug 5 is carried out in the same way as the sealing of HDA 2 with plug 3. Since the designs of HDA 2, 4 and plugs 3, 5 are the same, to fill HDA 4 with plug 5, a certain amount of adhesive composition is used when sealing hermetic block 2 with plug 3.

After polymerization of the glue in the hermetic block 4 with a plug 5, the body 1 is oriented vertically with the hermetic block 4 up and the cavity 13 is filled with viscous liquid material 19 through the holes, which are subsequently closed with plugs 9. On the outer surface of the body 1, rubber sealing rings 7 are installed in the annular grooves. optical fibers 6 are put on Kevlar protective tubes 18, which are fixed with glue in the corresponding holes 16 in plugs 3, 5.

The penetration is checked for leaks by applying excess gas pressure (freon, helium) to the end of housing 1 (from the high pressure side) with external control in the areas where protective tubes 16 of optical fibers 6 exit from housing 1 (from the low pressure side). After checking the penetration for leaks, based on the absence of gas molecules from the high pressure side, the suitability of the penetration for operation is judged.

A significant factor influencing the reliability of the adhesive joint is the selection of the epoxy sealing adhesive composition and the quality of the filling of optical fibers 6 in the holes 15. Almost all adhesive compositions have an extended period of complete polymerization, the time of which depends on the operating temperature: it accelerates at positive temperatures and slows down at negative temperatures . Polymerization of the adhesive composition is accompanied by a decrease in its volume, which, during long-term operation of the penetration, leads to the appearance of microgaps along the cladding of each optical fiber 6 and the microleak itself - the diffusion of superfluid dangerous aerosols into the internal cavity of the housing 1. To minimize the amount of microleakage over the period of the overall operation of the penetration, a sealing adhesive composition is used selected from conditions of increased fluidity and delayed polymerization. Since the service life of the penetration in an underground structure is characterized by long-term operation (15 years or more) at subzero temperatures - minus 5°C, then under these conditions the ongoing polymerization, which accompanies shrinkage of the adhesive volume, is significantly slowed down and extended during operation. At the same time, production time, storage in a warehouse and transportation to the place of use at positive temperatures are limited.

The passage works as follows.

When conducting explosive experiments in underground structures, several scenarios for using the proposed technical solution are possible:

- carrying out a direct explosive experiment and further long-term operation of the penetration, corresponding to the total service life (ensuring tightness at constant excess pressure);

- operation of the penetration for 2...3 years or more, then conducting an explosive experiment and further operation of the penetration during the total service life (ensuring tightness at constant excess pressure).

The second scenario is the most critical for ensuring reliable operation. In this scenario, the adhesive compositions of the sealing joints are already subject to polymerization before the experiment, then an explosive experiment is carried out, as a result of which an impact load is applied to the joint, and high pressure is applied to the protective shells on the optical fibers. During subsequent operation, further polymerization of the adhesive compositions occurs with inevitable shrinkage of the sealing volumes. In this scenario, in the event of depressurization of the pressurized unit 2 from the high pressure side and the appearance of a micro-leak in the adhesive joint, superfluid aerosols through the pressurized unit 2 will begin to penetrate into the internal volume of the housing cavity 13 of the penetration, filled with viscous liquid material 19. Gas bubbles will accumulate at the point where the optical fiber exits hermetic block 2, unite with each other into a common “bubble”, the size of which will increase until the external pressures are balanced and the pressure created in the viscous liquid material 19, due to the presence of air inclusions. In this case, due to its increased viscosity, the liquid material 19 will not be squeezed out through possible microgaps in the sealed connection. With a relatively horizontal location of the penetration, the “bubble” can move, overcoming the resistance of the viscous medium 19, towards the pressurized unit 4 from the low pressure side, where the qualitative state of the adhesive joints is similar to the pressurized unit 2. The gas “bubble” will rise to the upper region of the internal volume of the housing cavity 13 and captured in it by annular grooves 14. When the pressure equilibrium described above is achieved, the volume and position of the gas “bubble” will be stabilized. Gas inclusions will be fixed in the annular grooves 14 of the body cavity 13, without reaching the hermetic block 4. Thus, possible depressurization of the adhesive joints will be localized by the viscous liquid material 19. The tightness and operational reliability of the penetration based on the proposed technical solution will be maintained.

Currently, design documentation has been developed, and prototypes of fiber-optic penetrations made in accordance with the claimed invention are being manufactured. The performance of the proposed penetration is confirmed by calculations.

The information presented indicates that the following set of conditions are met when using the claimed invention:

- the claimed penetration relates to fiber-optic technology, namely, feed-through devices for hermetically sealed input of optical fibers through a partition, and can be used to introduce optical fibers between areas with different pressures;

- the claimed penetration, when used, is capable of increasing the operational reliability of the penetration under conditions of explosive experiments in underground protective structures while increasing its service life;

- for the claimed device in the form in which it is characterized in the claims, the possibility of its implementation has been confirmed using the means and methods described in the application and known before the priority date.

Consequently, the declared fiber-optic penetration meets the condition of “industrial applicability”.

Claims (1)

A fiber-optic penetration containing a housing with optical fibers passing through it from the high pressure side to the low pressure side; hermetic blocks are introduced into the housing, which form cavities, at least two of which are filled with an epoxy sealing compound, while the hermetic blocks are made individually for each optical fiber with through holes filled with a sealing compound, characterized in that at least one body cavity between the HDAs is filled with a viscous liquid material, while the inner surface of the body in said body cavity is equipped with transverse annular grooves, and each hole in the HDAs delimiting said body cavity is dumbbell-shaped.

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