Elastic stress tube and preparation method thereof

Abstract

The invention discloses an elastic stress pipe and a preparation method thereof, and relates to the technical field of cable accessories. The elastic stress tube is prepared from the following raw materials in parts by weight: 70 to 100 parts of silicon rubber, 5 to 15 parts of carbon black, 20 to 40 parts of active high dielectric filler, 5 to 10 parts of active magnesium oxide, 30 to 60 parts of fumed silica, 3 to 6 parts of diphenyl silanediol, 0.5 to 1 part of antioxidant, 1 to 5 parts of lubricant, 0.5 to 1 part of sensitization cross-linking agent and 1 to 5 parts of organic peroxide. The elastic stress pipe with high and low temperature resistance (-50 DEG C to + 200 DEG C), high elasticity and high tear resistance can be obtained, and the elastic stress pipe can tightly wrap a cable, does not generate permanent deformation, is waterproof, avoids partial discharge, is long in service life, maximally evacuates electric field stress, and homogenizes an electric field near a cable shielding layer. The preparation method is simple, high in practicability and beneficial to industrial large-scale production.

Description

Technical Field

[0001] This invention relates to the field of cable accessories technology, and more specifically, to an elastic stress tube and its manufacturing method. Background Technology

[0002] One of the most important functions of medium-voltage cable terminations and intermediate accessories is to homogenize the extremely strong non-uniform electric field at the point of cable shield interruption, preventing partial discharge caused by the non-uniform electric field. Due to the extremely strong electric field, any tiny voids or gaps in these areas can cause partial discharge due to the voltage difference between the two ends of the gap, creating a potential risk to the long-term safe operation of the cable. Currently, heat-shrinkable cable accessories both domestically and internationally generally use fully heat-shrinkable components, but because the functions of each component are different, the material formulations also vary considerably. When installing cable accessories by heating, a high external temperature needs to be applied, and significant temperature differences will also occur when the cable is operating under different loads. Therefore, after shrinking, the different components will produce gaps of varying degrees due to differences in thermal expansion and contraction, leading to partial discharge, which is one of the main drawbacks of heat-shrinkable cable accessories. The application of elastic stress tubes can eliminate or greatly reduce these gaps, significantly reducing partial discharge during testing and ensuring the long-term stable operation of the cable accessories.

[0003] Heat-shrinkable stress sleeves are commonly used in medium and high voltage power cable accessories, installed at the junction of the main insulation and semi-conductive layer of the cable. They serve to mitigate / disperse the electric field stress concentration at the cable shield end. The conventional manufacturing process for heat-shrinkable stress sleeves mainly includes: blending and modifying various polymer materials to form masterbatch—extrusion molding—radiation crosslinking—expansion—tube cutting and packaging. Currently, the materials and processes used for heat-shrinkable stress sleeves in China are prone to problems such as moisture absorption, poor processing performance, and unstable dielectric constant and volume resistivity. For cable accessory applications, the product's clamping force is crucial. Besides the selection of formulation materials, increasing the degree of crosslinking is a key way to improve clamping force. However, heat-shrinkable sleeves are limited by the expansion process; a high degree of crosslinking can easily lead to expansion cracking. These problems can easily lead to partial discharge in cable accessories, causing cable accessory breakdown accidents during long-term cable operation.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide an elastic stress tube and its preparation method. The process is simple, requiring only the blending and modification of various polymer materials to form a compound, open milling and vulcanization, and compression molding. Crosslinking and molding are integrated, eliminating the need for expansion. Products of different specifications, lengths, and thicknesses can be designed according to cable dimensions. In application, it is manually slipped onto the cable splice using a flexible nylon braided mesh to replace the stress tube. The operation is simple and the installation time is shortened. In medium and high voltage cables, it plays a role in dispersing the electric field stress concentration at the cable shield end, reducing the partial discharge level, thereby ensuring the long-term reliability and service life of the cable.

[0006] This invention is implemented as follows: In a first aspect, the present invention provides an elastic stress tube, the raw materials of which, by weight, include: 70-100 parts of silicone rubber, 5-15 parts of carbon black, 20-40 parts of active high dielectric filler, 5-10 parts of active magnesium oxide, 30-60 parts of fumed silica, 3-6 parts of diphenylsilanediol, 0.5-1 part of antioxidant, 1-5 parts of lubricant, 0.5-1 part of sensitizing crosslinking agent, and 1-5 parts of organic peroxide.

[0007] In an optional embodiment, the mass ratio of the carbon black, the fumed silica, and the diphenylsilanediol is 1:3-6:0.4-0.5.

[0008] In an optional embodiment, the organic peroxide is liquid or paste-like 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane. Paste-like 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane refers to 35-50% of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane dispersed in silica gel.

[0009] In an optional embodiment, the silicone rubber is methyl vinyl silicone rubber or a blend of methyl vinyl silicone rubber and methyl phenyl vinyl silicone rubber in a ratio of (3-4):(0.5-1.5).

[0010] In an optional embodiment, the active high-dielectric filler is a blend of one or more of nickel salts, strontium salts, or barium salts after surface coupling treatment with a surface treatment agent, and the active magnesium oxide is magnesium oxide after surface activation treatment with a surface treatment agent, wherein the filler mesh size of the active magnesium oxide is ≥3000 mesh; wherein the surface treatment agent is a silane coupling agent, titanate coupling agent, or aluminate coupling agent.

[0011] In an optional embodiment, the lubricant is a blend of one or both of stearic acid and polyethylene wax.

[0012] In an optional embodiment, the sensitizing crosslinking agent is trimethylolpropane triacrylate or triallyl isocyanurate.

[0013] Secondly, the present invention provides a method for preparing an elastic stress tube, comprising: first, uniformly mixing the raw materials of the elastic stress tube as described in any of the foregoing embodiments to obtain a compound, and then molding the compound into a tube.

[0014] In an optional embodiment, mixing the raw materials uniformly includes: (1) First, add the silicone rubber, carbon black, active high dielectric filler, active magnesium oxide, fumed silica, diphenylsilanediol, antioxidant, lubricant and sensitizing crosslinking agent to a conical mixer according to the ratio, mechanically premix for 10-15 min, and then use an internal mixer to mix at 100-150℃ for 20-40 min, and use open milling to sheet out to obtain a compound rubber sheet for elastic stress tube with a thickness of 1.5-2.5 mm; (2) The elastic stress tube compounding film is mixed at 100~150℃ for 10-20min using an open mill, and then the organic peroxide is added according to the formula and mixed for 10-20min. The thickness is adjusted to 1.5-2.5mm before sheeting.

[0015] In an optional embodiment, the compound is molded using a flat vulcanizing machine equipped with a template; Preferably, the molding temperature is 170-180℃, the pressure is 10-20 MPa, and the time is 5-15 min.

[0016] The present invention has the following beneficial effects: The elastic stress tube provided by this invention, through the selection and compounding of raw materials, can achieve high and low temperature resistance (-50℃~+200℃), high elasticity, and high tear resistance. Furthermore, this elastic stress tube can tightly wrap the cable without permanent deformation, and is waterproof, prevents partial discharge, has a long service life, and maximizes the dissipation of electric field stress, thus homogenizing the electric field near the cable shielding layer. Its preparation method is simple, requiring only mixing and molding to produce the elastic stress tube, without the need for irradiation or other operations. It is highly practical and conducive to large-scale industrial production. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0018] This invention provides an elastic stress tube, the raw materials of which, by weight, include: 70-100 parts silicone rubber, 5-15 parts carbon black, 20-40 parts active high dielectric filler, 5-10 parts active magnesium oxide, 30-60 parts fumed silica, 3-6 parts diphenylsilanediol, 0.5-1 part antioxidant, 1-5 parts lubricant, 0.5-1 part sensitizing crosslinking agent, and 1-5 parts organic peroxide.

[0019] The elastic stress tube of this invention has excellent high and low temperature resistance: -50℃~+200℃. In addition to high elasticity and high tear resistance, it breathes with the cable body, can tightly wrap the cable, and will not produce permanent deformation. It is waterproof, prevents partial discharge, has a long service life, and disperses electric field stress to the greatest extent, so as to homogenize the electric field near the cable shielding layer.

[0020] The mass ratio of carbon black, fumed silica and diphenylsilanediol is 1:3-6:0.4-0.5.

[0021] In this invention, a composite system of carbon black and silica is employed. Carbon black provides basic strength and abrasion resistance, and through physical adsorption, it entangles with rubber molecular chains to form a "filler network," significantly improving tensile strength, tear strength, and abrasion resistance. Silica fills the gaps in the rubber, increasing its density, and also enhances elasticity and dynamic properties while reducing rolling resistance, achieving a balance of performance.

[0022] Furthermore, by using diphenylsilanediol (DPSD) as an organosilicon additive in this invention, the surface properties and dispersion state of silica can be controlled, thereby optimizing the processing performance and mechanical properties of the elastomer material.

[0023] Silica (fumed silica) has a large number of hydroxyl groups (-OH) on its surface. These hydroxyl groups interact strongly through intermolecular hydrogen bonds, causing silica particles to easily form hard agglomerates. Diphenylsilanediol, with its two hydroxyl groups (-Si-OH) in its molecular structure, can undergo a dehydration condensation reaction with the hydroxyl groups on the silica surface (generating -Si-O-Si- covalent bonds), replacing some of the active hydroxyl groups, reducing the hydrogen bonding between silica particles, thereby breaking up agglomerates and significantly improving its dispersion uniformity in rubber matrices. Silica has extremely high surface energy (approximately 300-400 mJ / m²). 2Directly mixing silica into rubber can cause a sharp increase in the Mooney viscosity of the compound, increasing mixing difficulty and energy consumption, and even leading to scorching due to excessive frictional heat. Diphenylsilanediol reduces the surface energy of silica through surface modification, reducing its frictional resistance with rubber molecular chains, lowering Mooney viscosity, shortening mixing time, and improving processing stability. The phenyl groups (larger in size) of diphenylsilanediol inhibit excessive cross-linking of the silica network through steric hindrance (avoiding the formation of an overly rigid three-dimensional structure), allowing the vulcanized rubber to maintain high resilience while reducing compression set, which is crucial for the dimensional stability of elastic stress tubes under long-term pressure. Improved aging and media resistance: The phenyl groups have excellent UV and oxidation resistance, which can synergistically work with the hydroxyl groups of silica to reduce the oxidative breakage of rubber molecular chains; at the same time, the surface-modified silica has a tighter bond with the rubber interface, reducing the penetration rate of media such as oil and water, and improving the media resistance life of the stress tube.

[0024] In this invention, by controlling the mass ratio of carbon black, fumed silica, and diphenylsilanediol within the range of 1:3-6:0.4-0.5, a synergistic effect can be achieved. In the mixed system of carbon black and fumed silica, diphenylsilanediol mainly functions by modifying fumed silica, while also indirectly synergizing with carbon black. Diphenylsilanediol improves the dispersibility of fumed silica, preventing fumed silica agglomerates from adsorbing carbon black and forming larger defects, thus forming composite agglomerates. The phenyl groups of diphenylsilanediol can simultaneously improve the compatibility between fumed silica (polar) and carbon black (non-polar), reducing interfacial repulsion between the two fillers and improving the tensile strength of the mixed system.

[0025] Furthermore, in this invention, the organic peroxide is liquid or paste-like 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane. Paste-like 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane refers to 35-50% of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane dispersed in silica gel. 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (DBPH) acts as an organic peroxide crosslinking agent, initiating a crosslinking reaction of the elastomer molecular chains to impart necessary mechanical properties, thermal stability, and media resistance to the material. Under heating conditions, the peroxy bonds (-OO-) in the organic peroxide molecules break, generating active free radicals (tert-butoxy radicals). These free radicals abstract hydrogen atoms from the elastomer molecular chains, causing the molecular chains to form active free radicals, which then combine to form CC or COC crosslinking bonds, transforming the linear molecular chains into a three-dimensional network structure. The paste-like 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane is safer and easier to disperse. The free radical activity of DBPH is less affected by fillers, and it can meet the filling requirements of 5-15 parts of carbon black and 30-60 parts of fumed silica in this application while still maintaining the degree of crosslinking.

[0026] Furthermore, the silicone rubber in this invention is a blend of methyl vinyl silicone rubber and methyl phenyl vinyl silicone rubber in a ratio of (3-4):(0.5-1.5). Methyl vinyl silicone rubber exhibits an excellent temperature range, allowing for long-term use at -60℃ to 200℃, and also possesses good processability. Methyl phenyl vinyl silicone rubber exhibits excellent low-temperature performance, maintaining elasticity below -80℃, and also demonstrates radiation resistance, flame retardancy, and relatively excellent high-temperature stability.

[0027] The active high dielectric filler is a blend of one or more of nickel salts, strontium salts, or barium salts after surface coupling treatment with a surface treatment agent. The active magnesium oxide is magnesium oxide after surface activation treatment with a surface treatment agent. The filler mesh size of the active magnesium oxide is ≥3000 mesh. The surface treatment agent is a silane coupling agent, titanate coupling agent, or aluminate coupling agent.

[0028] In this invention, a compound of highly active dielectric filler and active magnesium oxide is used. The highly active dielectric filler can regulate dielectric properties and optimize electric field distribution. The active magnesium oxide with a mesh size of 3000 corresponds to a particle size of ≤5μm (often reaching submicron level) and a large specific surface area (≥50m²). 2 Magnesium oxide (MgO) exhibits enhanced hydroxyl (-OH) activity after surface treatment, resulting in higher reactivity with the matrix and coupling agents. Simultaneously, it acts as a sulfidation activator, promoting the generation of peroxide free radicals and shortening the sulfidation time. Furthermore, magnesium oxide possesses properties such as heat resistance and aging resistance.

[0029] The lubricant is a blend of one or both of stearic acid and polyethylene wax. The lubricant improves the processing fluidity of materials, reduces interfacial friction, ensures the stability of processes such as mixing, extrusion, and vulcanization, and indirectly optimizes the surface quality and mechanical properties of the finished product.

[0030] The sensitizing crosslinking agent is trimethylolpropane triacrylate or triallyl isocyanurate. Through synergy with organic peroxides, the sensitizing crosslinking agent enhances the crosslinking efficiency of the elastomer, optimizes the crosslinking network structure, and ultimately strengthens the material's mechanical properties, heat resistance, and creep resistance.

[0031] In addition, the present invention provides a method for preparing an elastic stress tube, which includes: first, mixing the raw materials of the above-mentioned elastic stress tube evenly to obtain a compound, and then molding the compound into a tube.

[0032] Specifically, it includes the following steps: (1) First, add silicone rubber, carbon black, active high dielectric filler, active magnesium oxide, fumed silica, diphenylsilanediol, antioxidant, lubricant and sensitizing crosslinking agent into a conical mixer according to the ratio, mechanically premix for 10~15min, then use an internal mixer to mix at 100~150℃ for 20-40min, and use open milling to sheet out to obtain a compound rubber sheet for elastic stress tube with a thickness of 1.5-2.5mm.

[0033] In this invention, by first mixing the raw materials other than organic peroxides, it is possible to ensure that the silicone rubber matrix is ​​uniformly mixed with fillers (carbon black, high dielectric fillers, etc.) and additives (lubricants, sensitizing crosslinking agents, etc.) through the synergy of mechanical force and temperature, thereby improving the dispersion of fillers and achieving preliminary plasticization of the rubber compound. Since no organic peroxides are added, high-temperature mixing only results in physical dispersion and no chemical crosslinking.

[0034] (2) Mix the elastic stress tube compound film at 100~150℃ for 10-20 minutes using an open mill, then add organic peroxide according to the ratio and mix for 10-20 minutes. Adjust the thickness to 1.5-2.5mm before sheeting.

[0035] At a relatively low temperature (100-150℃, below the decomposition temperature threshold of organic peroxides), the peroxides are uniformly mixed into the rubber compound, and the peroxides are only physically dispersed without initiating crosslinking. The two-roll mill secondary mixing uses double-roll shearing to uniformly disperse the peroxides into the base rubber compound, ensuring that the peroxide concentration deviation in each gram of rubber compound is small, avoiding "scorching" caused by excessive peroxides in some areas or insufficient crosslinking caused by insufficient peroxides during subsequent vulcanization.

[0036] (3) Use a flat vulcanizing machine equipped with a template to mold the compound rubber; preferably, the molding temperature is 170-180℃, the pressure is 10~20Mpa, and the time is 5~15min.

[0037] Temperature (170-180℃) triggers the decomposition of peroxides, which rapidly generate free radicals. This initiates a copolymerization reaction between the vinyl groups of silicone rubber and the double bonds of the sensitized crosslinking agent, forming a three-dimensional network of rubber molecular chains. Simultaneously, pressure ensures the shape and dimensional accuracy of the product, preventing defects such as bubbles and insufficient adhesive. Furthermore, it promotes tighter molecular chain alignment and improves the regularity of the crosslinking network. Under high pressure, the rubber compound adheres tightly to the template, resulting in a smooth product surface (roughness Ra < 0.8μm), eliminating the need for subsequent polishing.

[0038] In this invention, by delaying the addition of peroxides to the second step, premature decomposition during the high-temperature mixing stage is avoided, thus resolving the contradiction between "high-temperature dispersion requirements for high-filler systems" and "limited thermal stability of peroxides." A gradual temperature gradient is formed from premixing (room temperature) → mixing (100-150℃) → peroxide mixing (100-150℃) → vulcanization (170-180℃), ensuring both dispersion efficiency and precise control of crosslinking timing. For difficult-to-disperse components such as high-dielectric fillers and nano-silica in the formulation, a three-stage dispersion process—conical premixing + mixing shearing + open mill homogenization—ensures their functions (such as dielectric regulation and reinforcement) are fully utilized.

[0039] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0040] Example 1 This embodiment provides an elastic stress tube, the raw materials of which include, by weight, 100 parts of methyl vinyl silicone rubber, 20 parts of silane coupling agent modified barium salt, surface-activated magnesium oxide, 30 parts of fumed silica, 5 parts of organic peroxide, 10 parts of carbon black, 5 parts of diphenylsilanediol, 0.8 parts of antioxidant, 3 parts of lubricant, and 0.6 parts of sensitizing crosslinking agent, totaling 174.4 parts.

[0041] Its preparation methods include: (1) First, add silicone rubber, carbon black, active high dielectric filler, active magnesium oxide, fumed silica, diphenylsilanediol, antioxidant, lubricant and sensitizing crosslinking agent into a cone mixer according to the ratio, mechanically premix for 12 min, then use an internal mixer to mix at 125℃ for 30 min, and use open milling to sheet out to obtain a 2 mm thick compounded rubber sheet for elastic stress tubes; (2) Mix the elastic stress tube compound film at 125°C for 15 minutes using an open mill, then add organic peroxide according to the ratio and mix for 15 minutes. Adjust the thickness to 2 mm before sheeting.

[0042] (3) Use a flat vulcanizing machine equipped with a template to mold the compound rubber; the molding temperature is 175℃, the pressure is 15Mpa, and the time is 10min.

[0043] Example 2 This embodiment provides an elastic stress tube, the raw materials of which include, by weight, 100 parts of methyl vinyl silicone rubber, 40 parts of silane coupling agent modified barium salt, 5 parts of surface-activated magnesium oxide, 30 parts of fumed silica, 5 parts of organic peroxide, 10 parts of carbon black, 5 parts of diphenylsilanediol, 0.8 parts of antioxidant, 3 parts of lubricant, and 0.6 parts of sensitizing crosslinking agent, totaling 199.4 parts.

[0044] Its preparation methods include: (1) First, add silicone rubber, carbon black, active high dielectric filler, active magnesium oxide, fumed silica, diphenylsilanediol, antioxidant, lubricant and sensitizing crosslinking agent into a cone mixer according to the ratio, mechanically premix for 10 min, then use an internal mixer to mix at 100℃ for 40 min, and use open milling to sheet out to obtain a 1.5 mm thick compounded rubber sheet for elastic stress tubes; (2) Mix the elastic stress tube compound film at 100°C for 20 minutes using an open mill, then add organic peroxide according to the ratio and mix for 20 minutes. Adjust the thickness to 1.5 mm before sheeting.

[0045] (3) Use a flat vulcanizing machine equipped with a template to mold the compound rubber; the molding temperature is 170℃, the pressure is 10Mpa, and the time is 15min.

[0046] Example 3 This embodiment provides an elastic stress tube, the raw materials of which include, by weight, 100 parts of methyl vinyl silicone rubber, 20 parts of silane coupling agent modified barium salt, 5 parts of surface-activated magnesium oxide, 60 parts of fumed silica, 5 parts of organic peroxide, 10 parts of carbon black, 5 parts of diphenylsilanediol, 0.8 parts of antioxidant, 3 parts of lubricant, and 0.6 parts of sensitizing crosslinking agent, totaling 209.4 parts.

[0047] Its preparation methods include: (1) First, add silicone rubber, carbon black, active high dielectric filler, active magnesium oxide, fumed silica, diphenylsilanediol, antioxidant, lubricant and sensitizing crosslinking agent into a conical mixer according to the ratio, mechanically premix for 15 min, then use an internal mixer to mix at 150°C for 20 min, and use open milling to sheet out to obtain a 2.5 mm thick compounded rubber sheet for elastic stress tubes; (2) Mix the elastic stress tube compound film at 150°C for 10 minutes using an open mill, then add organic peroxide according to the ratio and mix for 10 minutes. Adjust the thickness to 2.5 mm before sheeting.

[0048] (3) Use a flat vulcanizing machine equipped with a template to mold the compound rubber; the molding temperature is 180℃, the pressure is 20Mpa, and the time is 5min.

[0049] Example 4 This embodiment provides an elastic stress tube, the raw materials of which include, by weight, 100 parts of methyl vinyl silicone rubber, 20 parts of silane coupling agent modified barium salt, 5 parts of surface-activated magnesium oxide, 45 parts of fumed silica, 5 parts of organic peroxide, 10 parts of carbon black, 5 parts of diphenylsilanediol, 0.8 parts of antioxidant, 3 parts of lubricant, and 0.6 parts of sensitizing crosslinking agent, totaling 194.4 parts.

[0050] The preparation method is consistent with that in Example 1.

[0051] Example 5 This embodiment provides an elastic stress tube, the raw materials of which include, by weight, the following: 90 parts of methyl vinyl silicone rubber, 10 parts of methyl phenyl vinyl silicone rubber, 20 parts of silane coupling agent modified barium salt, 5 parts of surface-activated magnesium oxide, 30 parts of fumed silica, 5 parts of organic peroxide, 10 parts of carbon black, 5 parts of diphenylsilanediol, 0.8 parts of antioxidant, 3 parts of lubricant, and 0.6 parts of sensitizing crosslinking agent, totaling 179.4 parts.

[0052] The preparation method is consistent with that in Example 1.

[0053] Example 6 This embodiment provides an elastic stress tube, the raw materials of which include, by weight, the following: 60 parts of methyl vinyl silicone rubber, 20 parts of methyl phenyl vinyl silicone rubber, 30 parts of silane coupling agent modified barium salt, 8 parts of surface-activated magnesium oxide, 30 parts of fumed silica, 1 part of organic peroxide, 5 parts of carbon black, 3 parts of diphenylsilanediol, 0.5 parts of antioxidant, 1 part of lubricant, and 0.5 parts of sensitizing crosslinking agent, totaling 159 parts.

[0054] The preparation method is consistent with that in Example 1.

[0055] Example 7 This embodiment provides an elastic stress tube, the raw materials of which include, by weight, 90 parts of methyl vinyl silicone rubber, 10 parts of methyl phenyl vinyl silicone rubber, 30 parts of silane coupling agent modified barium salt, 10 parts of surface-activated magnesium oxide, 30 parts of fumed silica, 3 parts of organic peroxide, 15 parts of carbon black, 6 parts of diphenylsilanediol, 1 part of antioxidant, 5 parts of lubricant, and 0.1 parts of sensitizing crosslinking agent, totaling 200.1 parts.

[0056] The preparation method is consistent with that in Example 1.

[0057] Comparative Example 1 This comparative example provides a radiation crosslinking stress tube HSC-100.

[0058] Comparative Example 2 This comparative example provides a radiation crosslinking stress tube HSC-360.

[0059] Comparative Example 3 This comparative example is basically the same as Example 1, except that in this comparative example, neither the barium salt nor the magnesium oxide has been modified or activated by a silane coupling agent.

[0060] Comparative Example 4 This comparative example is basically the same as Example 1, except that diphenylsilanediol is omitted in this comparative example.

[0061] Comparative Example 5 This comparative example is basically the same as Example 1, except that the organic peroxide 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane is replaced with bis(2,4-dichlorobenzoyl peroxide).

[0062] Comparative Example 6 This comparative example is basically the same as Example 1, except that in this comparative example, fumed silica is replaced with precipitated silica.

[0063] Experimental Example The elastic stress tubes prepared in Examples 1-7 and Comparative Examples 1-6 were tested. The test items, technical requirements, test standards and test results are shown in the table below.

[0064]

[0065] As can be seen from the table above, Examples 1-7 of this application all meet the technical requirements and have good overall performance. However, the commercially available radiation-crosslinked stress tubes provided in Comparative Examples 1 and 2 show significantly lower elongation at break than those of the embodiments of this application, and do not meet the technical requirements. Furthermore, their Shore hardness is significantly higher than that of the embodiments of this application, also failing to meet the technical requirements. The dielectric constants of different models of radiation-crosslinked stress tubes also show significant differences; for example, the dielectric constant of the model in Comparative Example 2 is 42, significantly higher than that of Comparative Example 1, and does not meet the technical requirements. In Comparative Example 3, neither the barium salt nor the magnesium oxide was modified or activated by the silane coupling agent. In this case, the reactivity of the barium salt and magnesium oxide with the matrix and coupling agent is reduced, resulting in significantly lower tensile strength, elongation at break, and tear strength than in Example 1, and a rough surface, failing to meet the technical requirements. In Comparative Example 4, diphenylsilanediol was omitted. Diphenylsilanediol, as a structure control agent, is used to inhibit the tendency of fumed silica compounds to undergo structural changes (such as thickening and hardening) during storage or processing. Therefore, Comparative Example 4 shows fluctuations in hardness, tensile strength, elongation at break, and tear strength during compound storage. In Comparative Example 5, bis(2,4-dichlorobenzoyl) peroxide was replaced with an organic peroxide. Its vulcanization temperature is higher, its process adaptability is poorer, its vulcanization speed is slower, and its production efficiency is reduced. Comparative Example 5 shows a decrease in tensile strength, elongation at break, and tear strength. In Comparative Example 6, precipitated silica was used. Its reinforcing effect decreased, tensile strength and elongation at break decreased, tear strength decreased, processing performance deteriorated, and it was prone to agglomeration. Due to uneven dispersion, the surface of the product was prone to particle formation and pitting.

[0066] In summary, the elastic stress tube provided by this invention, through the selection and compounding of raw materials, can achieve high and low temperature resistance (-50℃ to +200℃), high elasticity, and high tear resistance. Furthermore, this elastic stress tube can tightly wrap the cable without permanent deformation, is waterproof, prevents partial discharge, has a long service life, and maximizes the dissipation of electric field stress, thus homogenizing the electric field near the cable shielding layer. Its preparation method is simple, requiring only mixing and molding to produce the elastic stress tube, without the need for irradiation or other operations. It is highly practical and conducive to large-scale industrial production.

[0067] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An elastic stress tube, characterized in that, The raw materials, by weight, include: 70-100 parts silicone rubber, 5-15 parts carbon black, 20-40 parts active high dielectric filler, 5-10 parts active magnesium oxide, 30-60 parts fumed silica, 3-6 parts diphenylsilanediol, 0.5-1 part antioxidant, 1-5 parts lubricant, 0.5-1 part sensitizing crosslinking agent, and 1-5 parts organic peroxide.

2. The elastic stress tube according to claim 1, characterized in that, The mass ratio of the carbon black, the fumed silica, and the diphenylsilanediol is 1:3-6:0.4-0.

5.

3. The elastic stress tube according to claim 1, characterized in that, The organic peroxide is liquid or paste-like 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane. Paste-like 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane refers to 35-50% of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane dispersed in silica gel.

4. The elastic stress tube according to claim 1, characterized in that, The silicone rubber is a blend of methyl vinyl silicone rubber and methyl phenyl vinyl silicone rubber in a ratio of (3-4):(0.5-1.5).

5. The elastic stress tube according to claim 1, characterized in that, The active high dielectric filler is a blend of one or more of nickel salts, strontium salts, or barium salts after surface coupling treatment with a surface treatment agent; the active magnesium oxide is magnesium oxide after surface activation treatment with a surface treatment agent; and the filler mesh size of the active magnesium oxide is ≥3000 mesh. The surface treatment agent is a silane coupling agent, a titanate coupling agent, or an aluminate coupling agent.

6. The elastic stress tube according to claim 1, characterized in that, The lubricant is a blend of one or two of stearic acid and polyethylene wax.

7. The elastic stress tube according to claim 1, characterized in that, The sensitizing crosslinking agent is trimethylolpropane triacrylate or triallyl isocyanurate.

8. A method for preparing an elastic stress tube, characterized in that, It includes: First, the raw materials for the elastic stress tube as described in any one of claims 1-7 are mixed evenly to obtain a compound, and then the compound is molded into a tube.

9. The method for preparing the elastic stress tube according to claim 8, characterized in that, Mixing the raw materials evenly includes: (1) First, add the silicone rubber, carbon black, active high dielectric filler, active magnesium oxide, fumed silica, diphenylsilanediol, antioxidant, lubricant and sensitizing crosslinking agent to a conical mixer according to the ratio, mechanically premix for 10-15 min, and then use an internal mixer to mix at 100-150℃ for 20-40 min, and use open milling to sheet out to obtain a compound rubber sheet for elastic stress tube with a thickness of 1.5-2.5 mm; (2) The elastic stress tube compounding film is mixed at 100~150℃ for 10-20min using an open mill, and then the organic peroxide is added according to the formula and mixed for 10-20min. The thickness is adjusted to 1.5-2.5mm before sheeting.

10. The method for preparing the elastic stress tube according to claim 8, characterized in that, The compound is molded using a flat vulcanizing machine equipped with a template; Preferably, the molding temperature is 170-180℃, the pressure is 10-20 MPa, and the time is 5-15 min.

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