For the structural characteristics and performance requirements of Cat. 6 and Cat.7 LAN cables, companies should work hard on production process to meet the requirements of standards for LAN cable performance indicators.
(1) Insulation process
The elongation rate of copper wire should be stably controlled within ±2%. The fluctuation range of conductor diameter is ±0.002mm. The fluctuation range of insulation outer diameter is ±0.01mm. Concentricity is greater than 96%. Coaxial capacitance is limited to ±1.5pF/m. The conductor preheating temperature should be stable and appropriate to ensure good bonding between the copper wire and the insulation layer. Cat.7 LAN cable foaming materials must be extruded evenly, the change of air injection pressure, the screw revolution, and the tension of the retracting and unwinding wires must be as small as possible. The foam of the foaming layer must be uniform and dense, so that the equivalent dielectric constant of the insulation on the entire single wire remains uniform.
The adhesion between the copper wire and the insulation is one of the main factors affecting return loss. The preheating temperature should be controlled well. The wire should be bright and clean before extrusion, without water, oil and other dirt. After extrusion, it must be cooled in sections to ensure that the adhesion is controlled within the range specified by the process.
The material quality and addition ratio of color masterbatch should be strictly controlled. Inferior color masterbatch will not only cause an increase in single wire breakdown points, but also make the insulation layer low in strength, not wear-resistant, and easily damaged; adding too much color masterbatch will affects the return loss value of the LAN cable. Therefore, high-quality masterbatch should be selected, and the color of the single wire after addition should be distinguishable and identifiable, and should not be too dark, to reduce the adverse effects of color masterbatch.
Use high-quality insulating materials and reasonable process parameters to ensure that the surface of the single wire is smooth and round, and prevent the single wire from being worn by the guide wheel, inverted rod, dies, etc. in subsequent processes due to high friction on the surface of the single wire.
(2) Twisting process
The twisted pair pitch of Cat.6 LAN cable is 8~16mm, and the twisted pair pitch of Cat.7 LAN cable is 20~40mm. When designing the pitch of pairs, the pitch difference between adjacent pairs should be as large as possible, and the pitch of adjacent and similar pairs should not be in a low integer multiple relationship.
The twisting process mainly controls the tension of the pay-off and take-up and the bending radius of the single pairs. The tension of the single wires and the tension of the pairs should be uniform to prevent one wire from being slightly wound around another wire. Preventing periodic crushing and severe deformation of insulated single wires at twisted point. The bending radius of a single pairs must be greater than 50mm to prevent the single pairs from being structurally unstable.
The twisting machine must have baktwist function to improve the impact of the eccentricity and unevenness of the insulation layer on the electrical performance. Currently, there are two main types of pair twisting machine with backtwist: non backtwist pair twisting machines and partial backtwist pair twisting machines. The non backtwist pair twisting machines only twists and rotates the two wires when twisting the wires, but the single wire itself does not rotate. Therefore, the single wire is not damaged and basically does not affect the return loss value of the LAN cable. The partial backtwist pair twisting machines means that the single wire is pre-twisted in the opposite direction before twisting. After twisting, it is equivalent to partial backtwist. Since the single wire is twisted twice in the forward and reverse directions, the single wire will be damaged to varying degrees. Therefore, the back-twist rate is generally controlled at about 30%, and the maximum should not exceed 50%.
The twisted pair pitch tolerance is limited to ±0.5mm. The symmetry properties and axial distance difference between the two wires must be maintained during production to prevent twisted asymmetry. When Cat.7 LAN cables are twisted and shielded, the tension change range of the shielding tape during the process should be less than ±10%. All twisted pairs must be shielded with an equal amount of compression.
(3) Cabling process
The cabling should use an active pay-off device with tension feedback control to ensure consistent tension of the twisted pairs throughout the cable length. And ensure that the reverse tension of the four pairs is constant to ensure good geometric performance of the LAN cable and keep its pitch stable.
When cabling, it is necessary to ensure that the cable core is symmetrical and the alignment position is relatively fixed. The cable pitch is generally 100~150mm. Cabling has a greater impact on crosstalk. If the pitch is too large, the return loss and characteristic impedance will be affected after the cable is bent and stressed; if the pitch is too small, the cable capacitance and attenuation will easily increase.
The purpose of cabling with backtwist is to prevent the core wires from being twisted, which will change the structure of the twisted pairs and affect the performance indicators, so that the pair pitch and shielding will not change when the twisted pairs are cabled. Therefore, cabling with backtwist is an effective means to improve cable transmission performance. During the entire cabling process, the extension tension of the twisted pairs should be kept within ±10%, and the bending radius of the twisted pairs should be greater than 75mm to maintain the stability of the cable core structure and prevent performance degradation.
When Cat.7 LAN cables are shielded with aluminum foil, the tension of the shielding tape during the process must prevent periodic fluctuations and should be kept constant, and its variation range should be less than ±10%. During the shielding process, it is necessary to design a reasonable mold size so that the coating tightness of the aluminum foil is appropriate, to ensure the stability of the cable transmission performance. Because if the coating of aluminum foil is not tight, gaps are prone to appear in the shielding layer when the cable is bent, affecting the transfer impedance and shielding performance of the LAN cable; the aluminum foil coating is too tight, which will affect the capacitance and insertion loss values of the LAN cable. When using braided copper wire shielding, the tension and braiding density of the braided copper wire should be effectively controlled. The bending radius of the cable core should be greater than 150mm.
(4) Sheathing process
The die must be reasonably configured to ensure that the sheath is appropriately tight and the outer diameter of the sheath is uniform. The sheath of Cat.6 LAN cables cannot be too tight, because if the sheath too tight will cause the pairs insulation layer to be compressed and deformed, affecting the transmission performance; The outer sheath of Cat.7 LAN cables should be close to the shielding layer to prevent the cable from deforming when subjected to external force, causing the relative position of the cable core to change, and its transmission performance will inevitably be affected. The tension adjustment of the sheath pay-off and take-up is very critical. If the take-up tension is too tight, the cable will be easily squashed and the cable core will be deformed. The characteristic impedance, return loss and other properties of the finished product will be affected to varying degrees.