A small-pitch high-efficiency transmission instrument cable and a processing method thereof

Abstract

The application discloses a kind of small pitch high-efficiency transmission instrument cable and processing method thereof, belong to the technical field of instrument cable, the cable is prepared using secondary ladder twisting process, by once large pitch pre-twisting stress release, secondary small pitch fine twisting electrical performance is promoted, while composite shielding layer, double-layer insulation structure and elastic flame-retardant filling body are innovatively designed, solve the industry problem that traditional rubber instrument cable once small pitch twisting is easy to slip, pitch is uneven, insulation damage.The instrument cable prepared by the application has a pitch of less than 40 mm, a magnetic field interference attenuation of greater than or equal to 45 dB, a bending radius of less than or equal to 8D, a 4-20mA analog signal transmission distance of more than 500m, and excellent anti-interference, transmission stability and flexible durability, suitable for harsh environments such as industrial site strong electromagnetic, frequency conversion and frequent bending of drag chain.

Description

Technical Field

[0001] This invention relates to the field of instrument cable technology, and in particular to a small-pitch, high-efficiency transmission instrument cable and its processing method. Background Technology

[0002] Instrumentation cables are key components in industrial automation control systems used to transmit 4-20mA analog signals, digital pulse signals, and weak voltage signals. Their signal transmission quality directly affects the accuracy and reliability of the control system. With the continuous improvement of industrial automation, the electromagnetic environment in industrial settings is becoming increasingly complex. Strong electromagnetic interference generated by frequency converters, power lines, and other sources places higher demands on the anti-interference performance of instrumentation cables.

[0003] Pitch design is one of the core technologies of instrument cables. The smaller the pitch, the tighter the twisting of the wire pairs, the stronger the ability to cancel external magnetic and electric field interference, and the lower the signal crosstalk and attenuation. According to relevant standards and specifications, when the conductor cross-section is ≤1.5mm², the pitch of the instrument cable should be ≤100mm; in strong interference scenarios, the pitch needs to be ≤40mm to achieve the optimal magnetic field interference suppression effect.

[0004] However, for rubber-insulated instrument cables, due to the high elasticity and friction coefficient of the rubber insulation layer, it is difficult to consistently achieve a small pitch of ≤40mm using conventional single-stranding processes. Direct single-stranding with a small pitch can easily lead to problems such as core displacement, uneven pitch, insulation wear, and even cracking, severely affecting the cable's electrical performance and service life. Furthermore, the traditional single-shield structure has limited shielding effectiveness in environments with strong electromagnetic interference, making it difficult to meet the requirements of high-precision instrument signal transmission. Simultaneously, excessively reducing the pitch to pursue anti-interference performance results in stiff cables with high internal stress and poor bending performance, making them unsuitable for scenarios involving cable chains and frequent bending.

[0005] Therefore, there is an urgent need to develop a small-pitch rubber instrument cable and its processing method that can take into account anti-interference performance, transmission stability and flexibility and durability, so as to solve the above-mentioned problems in the existing technology. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a small-pitch, high-efficiency transmission instrument cable and its processing method. By using a secondary stepped stranding process to break through the small-pitch bottleneck of rubber cables, and by innovatively designing a composite shielding layer, a double-layer insulation structure, and an elastic flame-retardant filler, the invention achieves a comprehensive improvement in the cable's anti-interference performance, transmission efficiency, and mechanical properties.

[0007] The technical solution adopted by this invention to solve its technical problem is: a small-pitch high-efficiency transmission instrument cable, comprising a cable core, an inner wrapping layer, a composite shielding layer, an outer wrapping layer, and a sheath layer arranged sequentially from the inside to the outside; the cable core is formed by two insulated wire cores twisted together in a two-step manner, and the insulated wire core includes a conductor and a double-layer insulation layer covering the outside of the conductor; the twisting pitch of the cable core is <40mm, and the pitch-to-diameter ratio is 5-8.

[0008] Furthermore, the double-layer insulation layer comprises an inner ethylene propylene rubber insulation layer and an outer flame-retardant rubber insulation layer, wherein the thickness of the inner ethylene propylene rubber insulation layer is 0.2-0.4 mm and the thickness of the outer flame-retardant rubber insulation layer is 0.3-0.5 mm.

[0009] Furthermore, the composite shielding layer includes a copper strip wrapped shielding layer and a tinned copper wire braided shielding layer arranged sequentially from the inside out; the wrapping overlap rate of the copper strip wrapped shielding layer is 25%-30%, and the braiding density of the tinned copper wire braided shielding layer is ≥90%.

[0010] Furthermore, the space between the cable core and the inner cladding is filled with an elastic flame-retardant filler, which is a low-smoke halogen-free polyolefin elastomer with a Shore hardness of 60-70A.

[0011] Furthermore, both the inner and outer wrapping layers are polyester tape wrapping layers with a wrapping overlap rate of 15%-20%; the sheath layer is an oil-resistant rubber sheath layer with a thickness of 1.0-1.5mm.

[0012] A method for processing the above-mentioned small-pitch high-efficiency transmission instrument cable includes the following steps: S1 conductor preparation: The conductor is prepared by stranding multiple strands of fine copper wire, with a stranding diameter ratio of 12-15; S2 insulation extrusion: An inner ethylene propylene rubber insulation layer and an outer flame-retardant rubber insulation layer are extruded sequentially on the outside of the conductor to form an insulated wire core; S3 First Pre-Twisting: Two insulated wire cores are fed into a cable cage stranding machine for pre-twisting, with a pitch ratio of 25-30 and a pitch of 90-110mm. At the same time, the first untwisting process is carried out, with an untwisting rate of 80%-90%. S4 Secondary Fine Stranding: The pre-stretched cable core is fed into a stranding machine for secondary fine stranding. The pitch ratio is 5-8 and the pitch is <40mm. At the same time, a second reverse untwisting process is performed, with an untwisting rate of 95%-100%. S5 cable wrapping: After secondary fine stranding, the cable core is wrapped with an inner wrapping layer, a composite shielding layer, an outer wrapping layer, and a sheath layer in sequence to obtain the finished cable.

[0013] Further, in step S3, the stranding tension of the cable cage stranding machine is controlled at 15-20N, and the stranding speed is 30-50m / min; in step S4, the stranding tension of the cable stranding machine is controlled at 8-12N, and the stranding speed is 15-25m / min.

[0014] Furthermore, in step S4, during the secondary fine stranding process, an online laser diameter gauge is used to detect the outer diameter of the cable core in real time. When the outer diameter deviation exceeds ±0.1mm, the stranding tension and pitch are automatically adjusted.

[0015] Further, in step S5, the coating process of the composite shielding layer is as follows: first, a copper strip wrapping machine is used to wrap the copper strip to wrap the shielding layer with a wrapping tension of 5-8N, and then a braiding machine is used to braid the tin-plated copper wire to braid the shielding layer with a braiding tension of 3-5N.

[0016] Furthermore, after step S5 is completed, step S6, performance testing, is included: the finished cable undergoes electrical performance, mechanical performance, and environmental resistance testing. Electrical performance testing includes DC resistance, distributed capacitance, capacitance imbalance, and shielding attenuation; mechanical performance testing includes bending radius and number of bends; and environmental resistance testing includes high and low temperature cycling and oil resistance.

[0017] The beneficial effects of this invention are: by employing a two-stage stepped stranding process that combines large-pitch pre-stretching with small-pitch fine stranding, it solves the problems of core displacement, uneven pitch, and insulation layer damage that easily occur with small pitch during the primary stranding of rubber-insulated cables, achieving a 40 While maintaining a small pitch of less than mm, the cable's flexibility and structural stability are ensured. The composite shielding layer consists of a copper tape wrapping shielding layer and a tinned copper wire braided shielding layer. The copper tape wrapping layer provides effective shielding against electric field interference, while the tinned copper wire braided layer provides complementary suppression against magnetic field interference. Together, they improve the signal transmission quality of the cable in high-intensity electromagnetic interference environments. The double-layer insulation structure uses an inner ethylene propylene rubber insulation layer and an outer flame-retardant rubber insulation layer. The inner layer has excellent electrical properties to reduce dielectric loss and signal attenuation, while the outer layer provides mechanical strength and environmental resistance to protect the inner layer structure. Low-smoke halogen-free polyolefin elastomer is used as a filler to fill the gaps between the cable cores. Its elastic properties make the cable core structure more rounded, while improving the cable's flexibility and impact resistance. An online laser diameter gauge detects the outer diameter of the cable core in real time and automatically adjusts the stranding tension and pitch, improving stranding accuracy and product consistency, and ensuring the stable and reliable electrical performance of the cable. Attached Figure Description

[0018] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0019] Figure 1 This is a schematic diagram of the structure of the present invention.

[0020] Figure 2This is a flowchart of the method of the present invention.

[0021] In the diagram: 1. Cable core, 11. Insulated core, 111. Conductor, 112. Double insulation layer, 1121. Inner EPDM rubber insulation layer, 1122. Outer flame-retardant rubber insulation layer, 2. Inner wrapping layer, 3. Composite shielding layer, 31. Copper tape wrapping shielding layer, 32. Tinned copper wire braided shielding layer, 4. Outer wrapping layer, 5. Sheath layer, 6. Elastic flame-retardant filler. Detailed Implementation

[0022] The present invention will now be described in further detail with reference to the accompanying drawings. These drawings are simplified schematic diagrams, illustrating only the basic structure of the invention, and therefore only show the components relevant to the invention.

[0023] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0024] Figure 1 and Figure 2 The present invention illustrates a small-pitch, high-efficiency transmission instrument cable, comprising, from the inside out, a cable core 1, an inner sheath 2, a composite shielding layer 3, an outer sheath 4, and a sheath layer 5. The cable core 1 is formed by two insulated cores 11 twisted together in a double-step manner. Each insulated core 11 includes a conductor 111 and a double-layer insulation layer 112 covering the outside of the conductor 111. The twist pitch of the cable core 1 is <40mm, and the pitch-to-diameter ratio is 5-8.

[0025] The double-layer insulation layer 112 comprises an inner ethylene propylene rubber insulation layer 1121 and an outer flame-retardant rubber insulation layer 1122. The inner ethylene propylene rubber insulation layer 1121 has a thickness of 0.2-0.4 mm and possesses excellent electrical insulation properties, effectively reducing dielectric loss and signal attenuation. The outer flame-retardant rubber insulation layer 1122 has a thickness of 0.3-0.5 mm and possesses good elasticity, abrasion resistance, and oil resistance, protecting the inner insulation layer from mechanical damage and chemical corrosion.

[0026] The composite shielding layer 3 comprises a copper tape wrapped shielding layer 31 and a tinned copper wire braided shielding layer 32 arranged sequentially from the inside out. The copper tape wrapped shielding layer 31 has a wrapping overlap rate of 25%-30%, providing excellent shielding against electric field interference. The tinned copper wire braided shielding layer 32 has a braiding density of ≥90%, providing good suppression against magnetic field interference and improving the tensile strength of the cable.

[0027] An elastic flame-retardant filler 6 is used to fill the gap between the cable core 1 and the inner cladding 2. The elastic flame-retardant filler 6 is a low-smoke halogen-free polyolefin elastomer with a Shore hardness of 60-70A. It has good elasticity, flame retardancy and aging resistance, and can fill the gap between the cable cores, making the cable core structure more rounded, while improving the flexibility and impact resistance of the cable.

[0028] Both the inner wrapping layer 2 and the outer wrapping layer 4 are polyester tape wrapping layers with an overlap rate of 15%-20%, which can play a role in insulation, isolation and protection. The sheath layer 5 is an oil-resistant rubber sheath layer with a thickness of 1.0-1.5mm. It has excellent oil resistance, wear resistance, weather resistance and tear resistance, and can adapt to various harsh industrial environments.

[0029] The processing method for the small-pitch high-efficiency transmission instrument cable of the present invention includes the following steps: S1 conductor preparation: Conductor 111 is prepared by stranding multiple strands of fine copper wire with a diameter of 0.15-0.2mm. The stranding pitch ratio is 12-15, which gives the conductor good flexibility and conductivity.

[0030] S2 Insulation Extrusion: A double-layer co-extrusion process is adopted, in which an inner ethylene propylene rubber insulation layer 1121 and an outer flame-retardant rubber insulation layer 1122 are extruded sequentially on the outside of the conductor 111 to form the insulated wire core 11. The extrusion temperature is controlled at 70-100℃ to ensure that the insulation layer is tightly bonded to the conductor, without bubbles or pinholes, and the vulcanization temperature is controlled at 180-200℃.

[0031] S3 First Pre-Twisting: Two insulated cores 11 are fed into the cable cage stranding machine for pre-twisting, with a pitch ratio of 25-30 and a pitch of 90-110mm. Simultaneously, a first un-twist treatment is performed, with an un-twist rate of 80%-90%, to release the initial torsional stress of the rubber-insulated cores and prevent stress concentration during the second small-pitch stranding, which could lead to insulation cracking and core rebound. The stranding tension of the cable cage stranding machine is controlled at 15-20N, and the stranding speed is 30-50m / min, ensuring a regular cable core structure after pre-twisting, with no core crossing or displacement.

[0032] S4 Secondary Fine Stranding: The pre-stretched cable core is fed into a stranding machine for secondary fine stranding, with a pitch ratio of 5-8 and a pitch <40mm. Simultaneously, a second reverse untwisting process is performed, with an untwisting rate of 95%-100%, further offsetting residual torque, ensuring the cable is free from rotation and twisting, resulting in a more stable structure. The stranding tension of the stranding machine is controlled at 8-12N, and the stranding speed is 15-25m / min. During the secondary fine stranding process, an online laser diameter gauge is used to monitor the outer diameter of cable core 1 in real time. When the outer diameter deviation exceeds ±0.1mm, the stranding tension and pitch are automatically adjusted to ensure a uniform outer diameter of the cable core.

[0033] S5 Cable Coating: After secondary fine stranding, the cable core 1 is sequentially wrapped with an inner wrapping layer 2, a composite shielding layer 3, an outer wrapping layer 4, and a sheath layer 5. The specific process is as follows: First, a polyester tape wrapping machine is used to wrap the inner wrapping layer 2, with a wrapping overlap rate of 15%-20%; then, a copper tape wrapping machine is used to wrap the copper tape shielding layer 31, with a wrapping overlap rate of 25%-30% and a wrapping tension of 5-8N; next, a braiding machine is used to braid the tinned copper wire shielding layer 32, with a braiding density ≥90% and a braiding tension of 3-5N; then, a polyester tape wrapping machine is used to wrap the outer wrapping layer 4, with a wrapping overlap rate of 15%-20%; finally, an extruder is used to extrude the sheath layer 5, with the extrusion temperature controlled at 65-95℃ and the vulcanization temperature controlled at 180-200℃, resulting in the finished cable.

[0034] S6 Performance Testing: Finished cables undergo electrical, mechanical, and environmental performance testing. Electrical performance testing includes 20℃ DC resistance, distributed capacitance, capacitance imbalance, and shielding attenuation; mechanical performance testing includes bending radius and number of bends; environmental performance testing includes high and low temperature cycling from -40℃ to 85℃ and oil resistance. Only products that pass these tests are allowed to leave the factory.

[0035] Example 1: This example provides a small-pitch, high-efficiency transmission instrument cable with a conductor cross-section of 1.0 mm². The specific structure and parameters are as follows: Conductor 111: It is made of 7 strands of fine copper wire with a diameter of 0.43 mm, with a stranding diameter ratio of 14; Double insulation layer 112: The inner ethylene propylene rubber insulation layer 1121 has a thickness of 0.3 mm, and the outer flame-retardant rubber insulation layer 1122 has a thickness of 0.4 mm; Cable core 1: It is formed by two insulated wire cores 11 through two steps of twisting. The first pre-twisting has a pitch ratio of 28 and a pitch of 100mm; the second fine twisting has a pitch ratio of 6 and a pitch of 35mm. Elastic flame-retardant filler 6: Low smoke halogen-free polyolefin elastomer with a Shore hardness of 65A; Inner wrapping layer 2 and outer wrapping layer 4: polyester tape, 0.05 mm thick, with a wrapping overlap rate of 18%; Composite shielding layer 3: Copper strip wrapped shielding layer 31 has a thickness of 0.05mm and a wrapping overlap rate of 28%; tin-plated copper wire braided shielding layer 32 has a braiding density of 92%. Sheath layer 5: Oil-resistant rubber sheath layer, with a thickness of 1.2mm.

[0036] The instrument cable prepared in this embodiment has the following performance characteristics after testing: DC resistance deviation at 20℃: 0.3%; distributed capacitance fluctuation: ±1.5%; capacitance imbalance: 0.8pF / m; magnetic field interference attenuation: 48dB; bending radius: 7D; number of bends: 12 million without breakage; 4-20mA analog signal transmission distance: 550m.

[0037] Example 2: This example provides a small-pitch, high-efficiency transmission instrument cable with a conductor cross-section of 1.5 mm². The specific structure and parameters are as follows: Conductor 111: It is made of 7 strands of fine copper wire with a diameter of 0.52mm, with a stranding diameter ratio of 13; Double insulation layer 112: The inner ethylene propylene rubber insulation layer 1121 has a thickness of 0.35mm, and the outer flame-retardant rubber insulation layer 1122 has a thickness of 0.45mm; Cable core 1: It is formed by two insulated wire cores 11 through two steps of twisting. The first pre-twisting has a pitch ratio of 26 and a pitch of 95mm; the second fine twisting has a pitch ratio of 7 and a pitch of 38mm. Elastic flame-retardant filler 6: Low smoke halogen-free polyolefin elastomer with a Shore hardness of 68A; Inner wrapping layer 2 and outer wrapping layer 4: polyester tape, 0.05 mm thick, with a wrapping overlap rate of 20%; Composite shielding layer 3: Copper strip wrapped shielding layer 31 has a thickness of 0.06mm and a wrapping overlap rate of 30%; tin-plated copper wire braided shielding layer 32 has a braiding density of 95%. Sheath layer 5: Oil-resistant rubber sheath layer, with a thickness of 1.4mm.

[0038] The instrument cable prepared in this embodiment has the following performance characteristics after testing: DC resistance deviation at 20℃: 0.4%; distributed capacitance fluctuation: ±1.8%; capacitance imbalance: 0.7pF / m; magnetic field interference attenuation: 50dB; bending radius: 7.5D; number of bends: 11 million without breakage; 4-20mA analog signal transmission distance: 520m.

[0039] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for processing a small-pitch, high-efficiency transmission instrument cable, characterized in that, Includes the following steps: S1 conductor preparation: The conductor (111) is prepared by stranding multiple strands of fine copper wire, with a stranding diameter ratio of 12-15; S2 insulation extrusion: An inner ethylene propylene rubber insulation layer (1121) and an outer flame-retardant rubber insulation layer (1122) are extruded sequentially on the outside of the conductor (111) to form an insulated wire core (11); S3 First pre-twisting: Two insulated wire cores (11) are fed into the cable cage winding machine for pre-twisting. The pitch ratio is 25-30 and the pitch is 90-110mm. At the same time, the first untwisting treatment is carried out, with an untwisting rate of 80%-90%. S4 Secondary Fine Stranding: The pre-stretched cable core is fed into a stranding machine for secondary fine stranding. The pitch ratio is 5-8 and the pitch is <40mm. At the same time, a second reverse untwisting process is performed, with an untwisting rate of 95%-100%. S5 Cable Coating: The inner wrapping layer (2), composite shielding layer (3), outer wrapping layer (4) and sheath layer (5) are sequentially wrapped around the outside of the cable core (1) after secondary fine stranding to obtain the finished cable; The insulated core (11) includes a conductor (111) and a double-layer insulation layer (112) covering the outside of the conductor (111); the stranding pitch of the cable core (1) is <40mm and the pitch-to-diameter ratio is 5-8.

2. The processing method of a small-pitch high-efficiency transmission instrument cable according to claim 1, characterized in that, The double-layer insulation layer (112) includes an inner ethylene propylene rubber insulation layer (1121) and an outer flame-retardant rubber insulation layer (1122). The thickness of the inner ethylene propylene rubber insulation layer (1121) is 0.2-0.4 mm, and the thickness of the outer flame-retardant rubber insulation layer (1122) is 0.3-0.5 mm.

3. The processing method of a small-pitch high-efficiency transmission instrument cable according to claim 1, characterized in that, The composite shielding layer (3) includes a copper strip wrapped shielding layer (31) and a tin-plated copper wire braided shielding layer (32) arranged sequentially from the inside to the outside; the wrapping overlap rate of the copper strip wrapped shielding layer (31) is 25%-30%, and the braiding density of the tin-plated copper wire braided shielding layer (32) is ≥90%.

4. The processing method of a small-pitch high-efficiency transmission instrument cable according to claim 1, characterized in that, The cable core (1) and the inner cladding (2) are filled with an elastic flame-retardant filler (6), which is a low-smoke halogen-free polyolefin elastomer with a Shore hardness of 60-70A.

5. The processing method of a small-pitch high-efficiency transmission instrument cable according to claim 1, characterized in that, The inner wrapping layer (2) and the outer wrapping layer (4) are both polyester tape wrapping layers with a wrapping overlap rate of 15%-20%; the sheath layer (5) is an oil-resistant rubber sheath layer with a thickness of 1.0-1.5mm.

6. The processing method of a small-pitch high-efficiency transmission instrument cable according to claim 1, characterized in that, In step S3, the stranding tension of the cable cage stranding machine is controlled at 15-20N, and the stranding speed is 30-50m / min; in step S4, the stranding tension of the cable stranding machine is controlled at 8-12N, and the stranding speed is 15-25m / min.

7. The processing method of a small-pitch high-efficiency transmission instrument cable according to claim 1, characterized in that, In step S4, during the secondary fine stranding process, an online laser diameter gauge is used to detect the outer diameter of the cable core (1) in real time. When the outer diameter deviation exceeds ±0.1mm, the stranding tension and pitch are automatically adjusted.

8. The processing method of a small-pitch high-efficiency transmission instrument cable according to claim 1, characterized in that, In step S5, the coating process of the composite shielding layer (3) is as follows: first, a copper strip wrapping machine is used to wrap the copper strip to wrap the shielding layer (31) with a wrapping tension of 5-8N, and then a braiding machine is used to braid the tin-plated copper wire to braid the shielding layer (32) with a braiding tension of 3-5N.

9. The processing method of a small-pitch high-efficiency transmission instrument cable according to claim 1, characterized in that, After step S5 is completed, step S6, performance testing, is also included: electrical performance, mechanical performance and environmental resistance performance testing of the finished cable. The electrical performance includes DC resistance, distributed capacitance, capacitance imbalance and shielding attenuation; the mechanical performance includes bending radius and number of bends; and the environmental resistance performance includes high and low temperature cycling and oil resistance.

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