Fire Retardant Cable

Explore the longest 330kV cable laying site in China

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Dancing a 700 meter long ultra-high voltage AAAC Cable that is thick at the mouth of the bowl and runs 3 kilometers underground, what are you doing? How many people will that take? How fierce is that? How hard is it to control?
On May 27, with a series of questions, the author came to the venue area of the 14th National Games in the northeast of Xi’an, Shaanxi Province, walked into the cable construction site of 330kV Jingxuan line I and II project of Shaanxi power transmission and Transformation Engineering Co., Ltd., and explored how to lay the longest 330kV UHV cable in China.
700 meter long cable “Jiaolong”


The 14th National Games is located in the northeast of Xi’an, and the ancient city ushers in the National Games for the first time. The relocation and landing of 330kV overhead transmission line in the northeast of Xi’an provides reliable power guarantee for the main stadium and surrounding area of Xi’an Olympic Sports Center. At the same time, by optimizing the 330kV line design and replacing the overhead line with the ground ABC Cable, the 330kV overhead line will be eliminated in the key areas of the National Games, creating a new sky landscape and showing the new style and features of the Millennium “charming ancient city” New weather.
The relocation and landing project of 330kV overhead transmission line in Northeast Xi’an involves 7 relocation and 2 new lines, 2 21km cable pipe corridors, 2 cable terminal stations and 100 km 330kV EHV cable lines, with a total investment of 8.274 billion yuan. After the completion of the project, it will be the largest 330kV and above UHV cable project in China.
The cable part of 330kV Jingxuan I and II line project is the longest and largest 330kV cable line in China. The first stage laying construction task is along the cable pipe gallery of Xingwei Road, with a total length of 6.3 km for single phase and 37 km for all cables. It is divided into nine sections, each section is 700 meters long, and each section contains six 700 meters long cables.
Green concept behind
There are 30 air vents in the underground high-voltage pipe gallery of Xingwei section, and 8 shafts for high-voltage cable laying. According to the conventional operation, each section of cable can enter the pipe gallery from the ground by selecting the nearest shaft, so as to minimize the cable transmission path. However, the actual construction scheme did not follow the conventional operation. Only two shafts were selected to enter the 9 sections of cables, and 6 of them need the whole cable to enter the pipe gallery and continue to transmit underground. After entering from shaft 24, the section with the longest transmission distance still needs to travel 3 kilometers underground, and it takes 6 hours to be in place.
Why choose this unconventional scheme of underground transmission?


“Mainly to make way for greening.” Wang Hailong, manager of Shaanxi power transmission and transformation construction project, said. High pressure pipe gallery in Xingwei section is mainly constructed by large-scale excavation except for shield construction in some sections. After the backfill treatment of the pipe gallery construction, the ground surface is planned as urban road and green belt according to the unified planning of the venue area of the 14th National Games“ Road construction, green belt planting, all need time, we occupy the site, we have to drag green back. At present, most of the greening of Xingwei road has been in good order.
Behind the posture is strength
Dancing “Jiaolong”
Following Wang Hailong into the underground high-voltage pipe gallery, he saw the sparse construction workers along the cable line, and was puzzled: “can such a few people dance the 700 meter cable?”
“Let’s call four or two thousand catties.” Wang Hailong squatted down, pointed to the roller under the cable and said, “this is the frequency conversion guide wheel, the main power of underground horizontal transmission of the cable.” A total of 900 electric frequency conversion rollers are arranged along the laying line, with a spacing of 5 meters, and a non powered roller support is arranged between the two. 900 variable frequency rollers are controlled by intelligent control box to start and stop synchronously. Although each variable-frequency roller intelligently generates a torque of 70kg, if 900 wheels rotate at the same time, the 700m “dragon” will move steadily along the passage at the speed of 6m per minute. In addition to the need for two people at the front end of the cable to lift the cable end to the next roller, the remaining 30 workers just need to watch the roller run well.
What should we do if there is any abnormality? There’s no cell phone in the tunnel. Moreover, the channel is too long and there are many turns, so the transmission distance of walkie talkie is greatly reduced.
“We have two call systems.” Wang Hailong said. They are equipped with 30 walkie talkies with coaxial cable signal relay. Another 50 walkie talkies are equipped with wireless chain relay. The two systems operate independently, which can realize the information synchronization of the whole cable laying line without delay, and ensure that the system can be shut down at the first time in case of abnormality.
“The pipe gallery is a limited space. In order to prevent accidents, we have gas masks every other section.” They did what they should have thought under special conditions.
“At the most spectacular time, there were three 700 meter long pipes running underground. The pipe gallery could not see the end at a glance, and the scene of more than 40 people dancing the 700 meter” dragon “could not be fully seen.” Wang Hailong added. Behind the grand scene is the courage, responsibility and courage of Shaanxi power transmission and transformation to seize the new challenges, explore new fields, start new engines, stimulate new power, help the new development of Shaanxi power grid, and serve the economic take-off of Shaanxi.

How to solve these problems in PVC

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1、 Troubleshooting of common faults in injection molding of ACSR Cables
Under note
Fault analysis and Troubleshooting:
(1) The temperature of the melt is too low. The forming temperature should be increased properly.
(2) Forming cycle is too short. It should be extended appropriately.
(3) Insufficient injection pressure. It should be improved appropriately.
(4) The injection rate is too slow. It should be accelerated appropriately.
(5) Insufficient supply. The supply shall be increased.
(6) The temperature of the die is too low, so it should be properly raised. In particular, the cooling circuit of the mold should be set reasonably to keep the temperature of the mold uniform.


(7) The shape and structure of plastic parts are not designed reasonably or the wall is too thin. Adjustments should be made in the event of possible changes.
(8) The structure size of the pouring system is small. Gate and runner sections shall be enlarged appropriately.
(9) The exhaust of the mold is poor. The exhaust hole should be added to improve the exhaust performance of the AAAC Cables.
(10) The strength of the die is not enough. The rigidity should be improved as much as possible.
· shrinkage marks
Fault analysis and Troubleshooting:
(1) The barrel temperature is too high. The barrel temperature shall be properly reduced.
(2) Insufficient injection pressure. It should be improved appropriately.
(3) The holding time is too short. It should be extended appropriately.
(4) The cooling time is too short. The cooling efficiency shall be improved or the cooling time shall be prolonged.
(5) Insufficient supply. The supply shall be increased.
(6) The temperature of the die is not uniform. The cooling system of the mould should be adjusted and the cooling circuit should be set reasonably.
(7) The shape structure design of plastic parts is unreasonable or the wall of plastic parts is too thick. Adjustments should be made where possible.
(8) Gate cross section is too small. It should be increased appropriately.
· weld marks
Fault analysis and Troubleshooting:
(1) The temperature of the melt is too low. The forming temperature should be increased properly.
(2) Insufficient injection pressure. It should be improved appropriately.
(3) The injection rate is too slow. It should be accelerated appropriately.
(4) The temperature of the die is too low, so it should be properly raised.
(5) The gate section is too small. It should be increased appropriately.
(6) Poor exhaust of mould. The exhaust hole should be added to improve the exhaust performance of the die.
(7) The structure size of cold material hole is too small or the position is not correct. It should be adjusted reasonably.
(8) Impurities are mixed in the raw materials. Foreign matters and impurities shall be removed thoroughly or new materials shall be used.
(9) The dosage of release agent is too much. The amount of the product should be minimized.
(10) The insert is not set up reasonably. It should be adjusted appropriately.
(11) The raw material is not uniformly colored. The colorant with good dispersibility and the mixing time should be prolonged to make the raw material coloring even.
Flow marks
Fault analysis and Troubleshooting:
(1) The temperature of the melt is too low. The forming temperature should be increased properly.
(2) Insufficient injection pressure. It should be improved appropriately.
(3) The holding time is too short. It should be extended appropriately.
(4) The temperature of the die is too low, so it should be properly raised.
(5) The temperature of the die is not uniform. The cooling system of the mould should be adjusted and the cooling circuit should be set reasonably.
(6) Gate cross section is too small. It should be increased appropriately.
(7) The structure size of cold material hole is too small or the position is not correct. It should be adjusted reasonably.
(8) The raw material is not uniformly colored. The color additive with good dispersibility should be selected, and the mixing time should be prolonged.


Poor gloss
Fault analysis and Troubleshooting:
(1) The temperature of the melt is too low. The forming temperature should be increased properly.
(2) The molding cycle is too long. It should be shortened appropriately.
(3) Screw back pressure is too low. It should be improved appropriately.
(4) The temperature of the die is too low, so it should be properly raised.
(5) The structure size of the pouring system is small. Gate and runner sections shall be enlarged appropriately.
(6) Poor exhaust of mould. The exhaust hole should be added to improve the exhaust performance of the die.
(7) Impurities are mixed in the raw materials. Foreign matters and impurities shall be removed thoroughly or new materials shall be used.
(8) The dosage of release agent is too much. The amount of the product should be minimized.
(9) Raw materials are not fully dried. The drying temperature and time should be increased appropriately.
· bubbles
Fault analysis and Troubleshooting:
(1) The barrel temperature is too high. The barrel temperature shall be properly reduced.
(2) The molding cycle is too long. It should be shortened appropriately.
(3) Insufficient injection pressure. It should be improved appropriately.
(4) The injection speed is too fast. It should be slowed down appropriately.
(5) The holding time is too short. It should be extended appropriately.
(6) The temperature of the die is not uniform. The cooling system of the mould should be adjusted and the cooling circuit should be set reasonably.
(7) The shape structure design of plastic parts is unreasonable or the wall of plastic parts is too thick. Adjustments should be made where possible.
(8) Gate cross section is too small. It should be increased appropriately.
(9) The exhaust of the mold is poor. The exhaust hole should be added to improve the exhaust performance of the die.
(10) Raw materials are not fully dried. The drying temperature and time should be increased appropriately.
? uneven color
Fault analysis and Troubleshooting:
(1) The barrel temperature is too high. The barrel temperature shall be properly reduced.
(2) The molding cycle is too long. It should be shortened appropriately.
(3) The raw material is not uniformly colored. The color additive with good dispersibility should be selected, and the mixing time should be prolonged.
Burnt and black
Fault analysis and Troubleshooting:
(1) The barrel temperature is too high. The barrel temperature shall be properly reduced.
(2) The molding cycle is too long. It should be shortened appropriately.
(3) The injection pressure is too high. It should be reduced appropriately.
(4) The injection rate is too fast. It should be slowed down appropriately.
(5) Screw back pressure is too high. It should be reduced appropriately.
(6) Gate cross section is too small. It should be increased appropriately.
(7) The exhaust of the mold is poor. The exhaust hole should be added to improve the exhaust performance of the die.
(8) The dosage of release agent is too much. The amount of the product should be minimized.
(9) Raw materials are not fully dried. The drying temperature and time should be increased appropriately.
· overfill edge


Fault analysis and Troubleshooting:
(1) The temperature of the melt is too high. The temperature of the barrel and the nozzle shall be properly reduced.
(2) The injection pressure is too high. It should be reduced appropriately.
(3) The injection rate is too fast. It should be slowed down appropriately.
(4) The holding time is too long. It should be shortened appropriately.
(5) There is too much supply. It should be reduced appropriately.
(6) The closing force is insufficient. It should be improved appropriately.
(7) The mold temperature is too high. It should be reduced appropriately.
(8) The shape structure design of plastic parts is unreasonable, and should be adjusted appropriately in case of possible changes.
(9) The strength of the die is not enough. We should try to increase its rigidity.
(10) The insert is not set up reasonably. According to the shape of plastic parts and the structure of the mold, proper adjustment shall be made.
Warping and deformation
Fault analysis and Troubleshooting:
(1) The barrel temperature is too low. It should be improved appropriately.
(2) Forming cycle is too short. It should be extended appropriately.
(3) The injection pressure is too high. It should be reduced appropriately.
(4) The injection speed is too fast. It should be slowed down appropriately.
(5) The holding time is too long. It should be shortened appropriately.
(6) The mold temperature is too high. It should be reduced appropriately.
(7) The cooling system of the mould is not reasonable, and the cooling circuit should be set reasonably according to the cooling requirements of the plastic structure.
(8) Gate cross section is too small. It should be increased appropriately.
(9) The setting of ejector is unreasonable. The area of jacking out and the point of jacking shall be increased as much as possible.
(10) The strength of the die is not enough. We should try to increase its rigidity.
· delamination
Fault analysis and Troubleshooting:
(1) If the melt temperature is too low, the temperature of the barrel and nozzle should be increased properly.
(2) The injection rate is too fast. It should be slowed down appropriately.
(3) The mold temperature is too low. It should be improved appropriately.
(4) Impurities are mixed in the raw materials. Foreign matters and impurities shall be removed thoroughly or new materials shall be used.
? discoloration of the surface
Fault analysis and Troubleshooting:
(1) The barrel temperature is too high. It should be reduced appropriately.
(2) The molding cycle is too long. It should be shortened appropriately.
(3) The injection rate is too fast. It should be slowed down appropriately.
(4) Screw back pressure is too high. It should be reduced appropriately.
(5) The gate section is too small. It should be increased appropriately.
(6) Poor exhaust of mould. The exhaust hole should be added to improve the exhaust performance of the die.
(7) Impurities are mixed in the raw materials. Foreign matters and impurities shall be removed thoroughly or new materials shall be used.
2、 Troubleshooting of common faults in injection molding of soft PVC
Poor gloss on the surface of the product
Fault analysis and Troubleshooting:
(1) The processing temperature is too low, and the material is not plasticized. The processing temperature should be improved properly to improve the plasticizing effect.
(2) The mold temperature is too low. The mold temperature should be increased appropriately.
(3) The material fluidity is too bad, the raw material should be replaced or the raw material formula should be adjusted.
(4) The surface finish of mold cavity is too poor. The surface finish of mold cavity should be improved properly.
(5) During the forming process, the auxiliary agent precipitates, and forms scaling on the surface of the mold. The mold surface scale should be removed in time. If it is serious, the formula should be adjusted.
(6) Too much recycled material. The amount of recycled material shall be reduced appropriately.
(7) The material temperature is too high, and the resin is decomposed. The injection temperature should be reduced and the thermal stability system should be improved.
? shrinkage deformation
Fault analysis and Troubleshooting:
(1) The holding time is too short. The time of pressure preservation should be prolonged, especially when shrinkage occurs near the gate, the method of prolonging the pressure holding time can be used to solve.
(2) The pressure holding pressure is too low. The pressure holding time should be improved properly.
(3) Injection pressure is too low. Injection time should be improved appropriately.
(4) The molding temperature is too high. The forming temperature shall be reduced appropriately.
(5) The amount of feed is insufficient. The amount of feed shall be increased appropriately.
(6) The mold temperature is too high or the heating is uneven. The cooling efficiency of the mould should be improved.
(7) The mold is opened too early and the product cooling is insufficient. The cooling time of the product in the mold shall be extended.
(8) The thickness difference of the products is too big, and the parts of the thickness of the products in process are prone to sag shrinkage due to the insufficient pressure. The design of the product shall be modified.
(9) Gate cross section is too small. It should be increased appropriately.
Under injection, lack of material
Fault analysis and Troubleshooting:
(1) Injection pressure or pressure retaining pressure is too low. Injection pressure or pressure retaining pressure should be increased appropriately.
(2) The holding time is too short. The holding time shall be extended appropriately.
(3) The processing temperature is too low. The processing temperature should be raised appropriately.
(4) The injection rate is too slow. The injection speed should be increased appropriately.
(5) The temperature of the mold or nozzle is too low. The temperature of the mold or nozzle shall be increased appropriately.
(6) Impurities or decomposition are blocked at the nozzle. The injection molding machine nozzles shall be cleaned.
(7) The gate section is too small. It should be increased appropriately.
(8) The exhaust hole of the mold is blocked. The plug in the die vent should be removed.
(9) Injection rate of injection molding machine is too small. The injection volume should be increased appropriately.
Coking decomposition
Fault analysis and Troubleshooting:
(1) The injection temperature is too high, the material is coking and decomposed, and the focus of the product is formed with the injection mold of the molten material. The injection temperature should be properly reduced to remove foreign matters from the dead angle of the barrel and the runner.
(2) Injection speed is too high. The injection rate should be reduced properly.
(3) Impurities or decomposition are blocked at the nozzle. The injection nozzle shall be cleaned.
(4) The thermal stability of raw materials is too poor. The material should be replaced or the formula adjusted to improve the thermal stability system.
(5) The lubricant is not used enough. The lubricant dosage should be increased appropriately.
(6) Poor exhaust of mould. The die exhaust system should be improved.
(7) The gate section of the mold is too small. The gate section of the mold shall be expanded appropriately.

Requirements for fire protection certification of cables

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In order to solve the long-standing problem of the lack of flame retardant classification standards in the AAC Cable industry and the imperfection of the evaluation index dimension in the original flame retardant standard system, the former Sichuan Fire Protection Research Institute of the Ministry of public security organized relevant units to take the lead in formulating the national mandatory standard GB 31247-2014 “classification of burning performance of cables and optical cables”, which was issued on December 5, 2014 and officially implemented from September 1, 2015. On the basis of full investigation and verification test, combined with the relevant requirements of EN 13501-6:2014 and the actual grading assessment needs of domestic cables and optical cables, GB 31247-2014 finally forms four grades A, B1, B2 and B3. The assessment dimensions include the main grading indexes such as combustion calorific value, flame spread, heat release, smoke production characteristics and smoke density, and the main grading indexes such as combustion droplet / particle, smoke emission and so on The toxicity and corrosivity of flue gas are three additional classification indexes. Generally speaking, these assessment indexes can more truly reflect the combustion characteristics of cables under actual fire conditions, and the evaluation of cable combustion performance grade will be more scientific, reasonable and practical.


In order to promote the flame retardant cable classification standard and link up the related testing and certification work, China Quality Certification Center and National Center for quality supervision and inspection of fire resistant building materials (nftc) have cooperated closely since the standard drafting stage to develop cqc17-463416-2015 “implementation rules for classification certification of burning performance of cables for construction Engineering”, Since 2015, we have held publicity and implementation meetings on standards and certification in Nanjing, Yixing, Guangzhou, Jinan, Chengdu and other places, actively promoting the application and acceptance of standards to relevant architectural design units and architectural design specifications, and achieved good promotion results. This work also lays a foundation for the domestic flame retardant cable export to meet the relevant technical requirements of the European Union CPR building product regulations.
Considering the identification and type selection requirements of cables with different flame retardant grades, the new version of the implementation rules (cqc17-463416-2020) in 2020 adds the model naming provisions of cables with flame retardant grades, and adds some products with flame retardant grades B1 and B2, such as wdzb1-yjy, zb2-bv, etc., and provides the new products to Jiangsu Shangshang, Wuxi Jiangnan, Wuxi Jiangnan, etc Some excellent cable enterprises such as Jiangsu Zhongmei and Sichuan Xinshiji have issued the first batch of new CQC fire prevention certificates.


The new version of CQC fire prevention Certification Implementation Rules includes power cable, wiring, control cable, computer cable, flexible cable, communication cable, optical cable and other construction cable products. The CQC fire prevention certification mark shown in Figure 1 can be applied to the certified products to prove that the products meet the relevant requirements of each flame retardant grade. After the implementation and promotion of flame retardant classification standards and certification, many laboratories including the National Center for quality supervision and inspection of fire resistant building materials, the National Center for quality supervision and inspection of wire and cable products (Yixing) and Shanghai ABC Cable wisdom Testing Technology Co., Ltd. (istcw) have obtained the relevant recognition of the flame retardant classification certification.
3、 Some misunderstandings and development prospects of flame retardant graded cables
In recent years, with the popularization and application of GB / T 19666 “general rules for flame retardant and fire resistant wires, cables or optical cables” and the flame retardant categories of ZA, ZB, ZC and ZD, due to the common sense tendency to code a-b-c-d level arrangement and the non-metallic content from high to low in the test, there are a large number of manufacturers, users and technical institutions in the industry that bundle flame retardant ZA, ZB, ZC and ZD are flame retardant levels, It is also understood that flame retardant class A is superior to (covering) class B, class C, and then to class D.
However, the standard analysis shows that the main difference of bunched flame retardant (ZA, ZB, ZC, ZD) categories lies in the different application and evaluation occasions, and the grade relationship or classification concept is not mentioned in the relevant standards. In particular, in the article “understanding and suggestions on the requirements of Flame Retardancy for wiring bundles” recently received in the Journal of quality and certification, verification tests were carried out on five groups of samples of typical wiring products from different manufacturers: za-bv 450 / 750V 2.5 and wdza-byj 450 / 750V 2.5, and the above ten groups of samples were tested in accordance with GB / T 18380 series standards Class C and class D combustion tests. By analyzing the carbonization height of the samples before and behind the steel ladder after the combustion test, the results show that the carbonization height of most of the bundles of this kind of wire products is higher than that of class A, and even some of the samples have passed the flame retardant class a test, and the flame retardant class D is unqualified. The bundle combustion verification test of this cloth and wire product also proves that the traditional bundle flame retardant ZA, ZB, ZC and ZD do not belong to the classification of flame retardant performance, and there is no relationship between high and low levels.


In contrast, GB 31247-2014 “classification of burning performance of cables and optical cables” scientifically and systematically classifies the burning performance of cables used in construction projects through multi-dimensional index assessment and evaluation, which is close to the requirements of actual building fire safety scenarios, and gives a clear description of the performance grade in the standard, for example, the burning performance B1 is flame retardant 1 cable (optical cable), The combustion performance of grade B2 is flame retardant grade 2 cable (optical cable), etc（ This also lays a solid foundation for the reference and acceptance of GB 31247-2014 flame retardant classification in GB 51348 standard for electrical design of civil buildings.
It is believed that with the promulgation and heavy implementation of GB 51348 “standard for electrical design of civil buildings” and subsequent relevant design specifications, a more unified and clear understanding and application of the classification of combustion performance of cables and optical cables will be formed from user units, design units, supervision units, testing and certification Institutions to manufacturers and other relevant policies, The flame retardant cables and optical cables used in domestic construction projects will also usher in a brighter development prospect.

For more information about wires and cables, please click Joy ’cable Blog

Discussion on cable production process: extrusion process

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Extrusion process is an indispensable part in cable manufactor, which includes insulation and sheath production process. Insulation production methods include coating, winding, extruding and their combination. Now the main insulation production is coating (winding wire, no longer in the scope of production license management) and extrusion (wire and cable).
1、 Plastic extrusion equipment and mould
1. Plastic extrusion equipment: extruder
1.1 working principle of the extruder: the screw of specific shape is used to rotate in the heated barrel, and the plastic sent from the hopper is pressed forward to make the plastic plasticize evenly. The plastic is extruded into products of various shapes through the head and molds of different shapes.
1.2 basic structure of extruder: the extruder is composed of extrusion system, transmission system and heating system (cooling).
1.2.1 extrusion system (including screw, barrel, hopper, head and die)
① Screw: screw is an important part of the extruder. It is made of high strength, heat-resistant and corrosion-resistant alloy steel. Its function is to push the plastic forward, produce pressure, stir, and produce friction heat with the plastic when rotating, so as to melt the plastic and continuously send the melt into the extruder. It is directly related to the application scope and productivity of the extruder.


② The barrel is a metal barrel, which is generally made of alloy steel or composite steel lined with alloy steel with high strength of heat resistance and pressure resistance, strong wear resistance and corrosion resistance. It and screw constitute the basic structure of the extrusion system for plastic plasticization and conveying. The length of the barrel is generally 15 ~ 30 times of its straight diameter, so as to make the material fully heated and plasticized. The barrel should have enough thickness, rigidity and smooth inner wall. A resistance or induction heater measuring device and a cooling system are installed outside the barrel.
③ The hopper is usually a conical container with a capacity of at least 1 hour. The bottom of the hopper is equipped with a device for cutting off the material flow. The side of the hopper is equipped with a sight hole for calibration and measurement.
④ The head is the forming part of the extruder. The head is mainly composed of filter device (perforated plate and screen), connecting pipe, diverter, mold core seat, mold, etc.
1.2.2 transmission system
Its function is to ensure that the screw rotates at a constant speed with the required torque and speed. Generally, Weidong system includes three necessary links: the prime mover, the transmission and the reducer. It is required that the rotation speed of screw should be stable and not change with its load, so as to ensure the uniform quality of products. But in different occasions, the screw is required to be able to change speed to meet the requirements of extruding products of different specifications with one equipment. For this reason, drive motor generally uses rectifier motor, DC motor, etc.
1.2.3 heating and cooling system
Function: through the heating or cooling of the barrel, to ensure that the plastic is always extruded within its process temperature range.
① Heating method of the extruder: when the screw speed of the extruder is kept constant, the main factor affecting the stability of the rubber output is the body temperature of the extruder.
There are usually two heating methods for cross-linking extruder, which are carrier heating (such as adding hot water) and resistor heating. The carrier heating is characterized by uniform heating and not easy to produce local overheating, but the carrier heating temperature has high requirements on the sealing performance of the system and high cost. Therefore, it can be used in the extruder with higher temperature control requirements.
② Cooling of plastic machine: in the extrusion process, the temperature of the plastic in the barrel is often too high and the heat is too much. If too much heat is not discharged in time, it is easy to cause “pre crosslinking” of the material; The extruder is generally cooled in two parts: barrel cooling and head cooling.
a. Barrel cooling (there are two methods of barrel cooling, air cooling and water cooling)
From the cooling effect, the air cooling is relatively soft, the cooling speed is slow, and the water cooling speed is fast, but it is relatively fierce, and it is easy to cause strong “thermal vibration”. The design of the water cooling system is relatively complex. In addition to its good cooling effect, it should also have good sealing to prevent leakage, so that when cooling is not needed, the water cooling system can be used for cooling, It is better to make all the water in the cooling system escape, so as to avoid the blockage of the cooling system due to the scale generated by the water storage. The structure should also be conducive to maintenance. Most of the current water cooling systems turn out the spiral groove on the outer surface of the barrel, and then coil the cooling pipe.


b. Screw cooling
The main purpose of the cooling screw is to prevent the plastic from overheating. In addition, the feeding section of the cooling screw is also conducive to the conveying of materials to the machine head. The cooling medium into the screw is usually water, and the water temperature can maintain a certain value according to the requirements. Even the cooling length of the screw can be adjusted, sometimes the whole length of the screw can be cooled, sometimes only part of the screw can be cooled, and the screw temperature of the latest designed extruder can be adjusted by zones.
1.2.4 screw parameters of extruder
The main parameters of screw are diameter length diameter ratio, compression ratio, pitch, groove width, helix angle, clearance between screw and barrel, etc.
① Screw diameter D: the size of the extruder is usually expressed by the screw diameter. The larger the diameter is, the larger the amount of glue will be. The extrusion amount is approximately proportional to its square. Therefore, a small increase in the screw diameter will cause a significant increase in the extrusion amount.
② Length diameter ratio L / D: the ratio of length L and diameter D of screw working part. When the screw diameter is fixed, increasing the length to diameter ratio means increasing the length of the screw. The larger the length to diameter ratio is, it is conducive to the full plasticization of the material. At the same time, it can produce greater pressure to ensure that the product is more dense and improve the quality. However, too large ratio of length to diameter is not enough, resulting in over plasticization of cross-linked materials, leading to early cross-linking of materials. For extruders of cross-linking units, the ratio of length to diameter is generally between 20 and 25 times.
③ The compression ratio is the ratio of the volume of the first slot in the feeding section to the volume of the last screw slot in the homogenizing section. The selection of compression ratio should not be determined according to the raw materials. The properties of plastics are different, and the compression ratio is also different. The particles are large and the compression ratio is small; The compression ratio of LDPE is 2 ~ 3 times.
④ Groove depth h: the difference between the outer radius and the root radius of the thread. According to the compression requirements, the groove depth of the feeding section is greater than that of the melting section, and the melting section is greater than that of the homogenizing section. The large groove depth of the feeding section is conducive to improving its conveying capacity. The grooves of the melting section and homogenizing section are shallow, and the screw can produce a higher shear speed for the material, It is beneficial to the heat transfer from the cylinder wall to the material and the mixing and plasticizing of the material.
2. Die of extruder
2.1 the die of extruder is divided into extrusion type, semi extrusion type and extrusion type（ (see figure below)

2.2 characteristics of various molds:
2.2.1. Advantages of extrusion type
1) The structure of extruded plastic layer is compact and firm.
2) The insulation is closely connected with the conductor without gap, and the insulation strength of the extruded layer is reliable.
3) The outer surface is flat and smooth.
2.2.2. Disadvantages of extrusion type
1) It is not easy to adjust the eccentric core.
2) The accuracy of die matching is high, and the product quality is highly dependent on the die.
3) The bending of extrusion line is not good.
2.2.3 advantages of tube extrusion
1) The extrusion speed is fast.
2) The operation is simple and the core adjustment is easy.
3) Large clearance, small wear and long service life.
4) It is convenient to match the mold.
5) The extrusion strength of plastics increases with the directional drawing of plastics.
6) The sheath thickness is easy to control.
2.2.4 disadvantages of tube extrusion type
1) The density is poor.
2) The combination of plastic and wire core is poor.
2.2.5 semi extruded pipe: it absorbs the advantages of extruded pipe and extruded pipe.
2、 Crosslinking methods of cross-linked polyethylene materials are divided into chemical and physical methods
1. Chemical crosslinking: peroxide crosslinking (1) steam crosslinking (SCP); 2. Infrared crosslinking (RCP) and dry crosslinking; 3. Mdcv crosslinking; 4. Pressurized lava salt crosslinking (PLCV) process; 5. Silicone oil crosslinking (fzcv) process.) And silane graft crosslinking (one-step, two-step, copolymerization).
2. Physical crosslinking: high energy radiation crosslinking.

The load that the indoor common wire can bear

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Wire load is a concern before we buy wires. At present, the wire specifications commonly used in our life include 1 square wire, 1.5 square wire, 2.5 square wire, 4 square wire, 6 square wire, etc., so how many watts can these wires load? Let’s look at the number of watts the 1, 1.5, 2.5, 4, 6 square wires can load.

1、 How many watts can a square wire load

An “empirical formula” commonly used by electricians: as long as it is copper core wire, the cross-section area of each square millimeter can pass through the rated current of 4-5a safely; In the single-phase circuit of 220V, the current is about 4.5a for every 1kW power; In 380V three-phase balance circuit, the current is about 2a for every 1kW power. The above values are very close to the results calculated by physical calculation formulas. Therefore, in order to remember the “cumbersome” calculation formulas, electricians can remember these in the work. Then according to this algorithm, we know that: if the copper core wire is used in 220V single-phase circuit, it can safely carry the current passing through 1kW load; If used in three-phase balanced load (such as motor) circuit, the current passing through 2.5kW load can be safely carried.

2、 1.5 how many watts can the square wire load

If the power supply line is copper core wire, the first is that the maximum allowable working current for open wire installation is 20a, namely 4400 watts; The second is the concealed steel pipe, with current of 16a and power of 3520 watts; Third, PVC pipe is concealed, current is 14a, then the power is 3000 watts.

3、 2.5 how many watts can the square wire load

The power supply of 2.5 square wires is about 5500 watts, and the aluminum core wires are 2.5 square millimeter, 13a-20a, 4400 watts of 220VAC voltage, which is no more than 15A for a long time, and the maximum standard of 10A is not more than 15A.

4、 How many watts can the 4 square wires load

The 1kW of single-phase power supply is about 4.5a and 8kw is about 36a. The current carrying capacity of 4 square wires (single plastic copper wire) is about 30A. Smaller ones, change 6 square wires (single running power supply). Your watch and gate must be changed. Don’t use such a high power, minimum 4kw, also can. How much kilowatt power is the power supply of 4 square wires depends on whether you use 220V in your home or 380V in the factory. If the 4 square wires of 220 can load 6 to 8 kilowatts.

5、 How many watts can 6 square wires load

The power line diameter of the 6 square wire can load is not directly related to the power delivered. Generally speaking, 6 square wires are more than enough for air conditioning wires. The maintenance power supply on the construction site is generally 10X6 + 1×4 cable. As for the current intensity, according to my experience in construction, this kind of cable is generally controlled by 63A air switch. 6 square aluminum wire can load 6 kW, 6 square copper wire can load 10 kW.

Up 80%! Some people “cover” copper not sold

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“Do you have a copper machine tool? We can make a home valuation! ” Lao Zhao is a recycling business of scrap metals. Recently, he is circulating recycling advertisements by friends.
After the Spring Festival, copper prices have set a high, recycling manufacturers are looking for scrap copper. Zhao also took the opportunity to make a profit in this wave of market. He said that before the Spring Festival, the price of copper acsr cable was about 40000 yuan per ton, and now it has risen to more than 70000 yuan a ton, or nearly 80 percent.


With the continuous increase of copper price, the raw material cost pressure of downstream metallurgical and processing enterprises is becoming increasingly prominent. In this context, relatively low-cost and environmental protection of waste copper has become “fragrant bun”.
Industry insiders said that the rising copper price and the increase of copper cost are the main reasons for the popularity of recycled copper resources. In the future, the depletion and supply reduction of copper resources abroad will be the trend of the whole world. The market of urban mines and recycled copper resources will have unlimited potential.

01
Downstream telephone burst, waste copper recycling station “cover not sell”

Near a scrap metal recycling station in the suburb of Tanggu, Tianjin, the abandoned copper wires were piled on the roadside, and the sun was golden. Once, this is the “urban waste” that nobody asks for. Nowadays, they are precious renewable resources that enterprises plunder.
In the warehouse built up by color steel plate, Shanghai Securities News reporter saw that the door was a black and abandoned cable, which was randomly collected by several sacks. Walk down the wall, and the white sack behind it is filled with yellow copper cables. The staff said that these are copper wires picked up from the cable at the door. Once, these copper wires were not worth a few money, and now they are worth a lot.

“We have been operating this recycling station for more than ten years, and this year’s good market has hardly seen.” Lao Qin, the head of the recycling station, said that the scrap copper sold only 40000 per ton a ton a ton a year ago, but there was not much downstream goods, and the warehouse was filled with goods that could not be sold. After the Spring Festival, copper and brass cables suddenly became “fragrant bun”, which has exceeded 80000 yuan per ton.
In the past, recyclers were “unreasonable” about copper waste resources, waiting for customers to ask for the recovery price. Now they are starting to drive to factories around the country to find copper scrap valuations.
The copper recovered by Laozhao in Shanghai comes from the abandoned machine tools, cables, copper pots, and parts removed from various old appliances. He took his recycling company for example, in the past, after he recycled and processed it every month, copper sold at most 12000 yuan, and now it can reach more than 100000 yuan per month“ Taking advantage of the high copper prices in recent months, I have shipped all the hoards that I couldn’t sell in the past, making a lot of money net. ”

However, more copper recyclers have a “business experience” and do not rush to sell the accumulated copper to intermediate agents or downstream copper refineries.
“Copper is now priced one day, and the cable copper, which was once slow to sell after the Spring Festival, is almost double.” Old Meng, boss of the scrap metal recycling base from Foshan, said.
Old mengning can backlog some scrap copper, and sell them together when prices are higher. The recyclers around him also sniffed business opportunities. Although agents and middlemen called to order goods every day, they still covered the scrap copper in their hands.
Such “business” also sinks to the basic environmental sanitation workers. According to a big data service provider for waste products in Chengdu, at present, many environmental sanitation workers in Chengdu will consciously look for copper containing cans and electronic components, “the items were sold for a maximum of 1200 yuan a day before, and now they can sell threeorfour yuan or more.”
Although the price of scrap copper has risen greatly, the sales profit of different recycling stations is quite different. Shanghai Securities News reporter understands that compared with the previous year, the most of them have reached several times or even ten times, while the few are only 30%. According to zz91 regeneration network data, as of the 12th, the average price of main copper scrap in Jiangsu, Zhejiang and Shanghai was about 65000 yuan / ton, up 32% from the beginning of the year.
In response, Wu Xinyong, an analyst in the copper industry of Shanghai Nonferrous network, said the main factors determining the profit of scrap copper recovery are the recovery cost when recycling and the price difference before the delivery price at the time of sale. If the scrap copper is recovered at the low point of copper price before the year ago and sold at the current copper price high, the intermediate profit will be considerable.

02
“Price difference between refined waste” and the economy of waste copper are highlighted

As for the phenomenon of copper scrap is tight since this year, Wang siran, director of Ping An Futures Research Institute, told Shanghai Securities News that in practice, many products of copper processing enterprises can take refined copper as raw materials and scrap copper as raw materials. There is a price difference between scrap copper and refined copper, and the price of scrap copper is not as fast as that of refined copper.
Wei Lai, director of all color research of Tianfeng futures research, told Shanghai Securities News that since this year, downstream enterprises have been in stable demand for copper, especially in emerging fields such as new energy vehicles, electronics, home appliances and other industries, with higher demand for copper. With the continuous increase of international copper price, the economy of waste copper has been highlighted. Because of the excessive cost of using refined copper, processing and smelting enterprises tend to increase the consumption of waste copper.
“The supply of copper concentrate abroad is relatively tight this year, and there are epidemic and strike in the main production areas of copper concentrate such as Chile.” Wei Lai said.
In March, copper production in Chile has fallen for 10 consecutive months, according to data. According to the National Bureau of statistics, Chile’s copper production in the first quarter of 2021 was 1.4 million tons. The year-on-year decrease was 2.2%.
The decline in copper production has shifted some demand to scrap copper, which also promotes domestic imports of scrap copper. My non-ferrous network data show that, due to steady growth of downstream demand, the import of recycled copper has increased significantly since this year. In the first quarter of 2021, the import of recycled copper was 363700 tons, an increase of 73.39% year-on-year.
“The use of scrap copper is no longer new. The industry has mature technology to convert waste copper into refined copper. From the perspective of environmental protection and carbon neutralization, it is also in line with the trend to increase the use of waste copper. ” Wei Lai said.

Development of high flexible fireproof cable

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With the development of society, the scale of the city has been expanding, high-rise buildings have been emerging, and the number of important buildings has been increasing. The fire caused by the electric line, especially the huge fire accident, endangers the safety of life and property, and some fatal and huge fire, often causes a series of social problems and accountability. Once the fire happens, rescue is very important, fire pump, fire smoke exhaust, emergency lighting, fire elevator and other rescue equipment become the protection of people's escape, and these protection "lifeline" is the fire-proof cable. Due to the frequent occurrence and serious consequences of fire, more and more attention has been paid to the performance and testing of fire-resistant cables. Table 1 gives examples of the structure and standard test conditions of fire-resistant cables in some countries and regions, from Table 1, we can see the different requirements of GB, IEC, BS, AS for the test performance of fire-proof cable. China fire-resistant cables mainly implement the national standards, fire resistance requirements through BS 6387 or BS8491 fire-resistant + vibration + spray fire test.

At present, the fire-proof cables on the market are mainly divided into two categories from insulating materials, namely, magnesium oxide insulated fire-proof cables and mica-mineral compound insulated fire-proof cables, the common custom is respectively called the rigid fireproof cable and the flexible fireproof cable. Because of the difference of structure design and material technology, the two kinds of cables have their own characteristics and need to be improved. As a rigid fireproof cable, it has many advantages, such as high temperature resistance, radiation resistance, long life and good earthing, etc. . The other category is flexible fireproof cable with twisted conductor + mineral composite insulation + Metal Sheath or fireproof mud composite sheath, theoretically speaking, tubular metal or metal sheathed fireproof cable after mechanical deformation through rolling, the flexibility is mainly relative to solid conductors, and the flexibility of fireproof cables with fireproof mud insulation is limited by the hardness of the fireproof mud. Compared with conventional cables, these fireproof cables need special accessories and technology in connection, and it is more difficult to realize pre-branching. Their branch joints are often connected by branch boxes, except for complicated installation, construction strength, fire performance, joint performance and sealing moisture performance is also uneven.

We study the structure and material of the fireproof cable deeply, and take the flexibility, fireproof safety and construction convenience as the research direction, develop a kind of flexible fireproof cable, it has passed GB, IEC, BS and AS tests, and is a kind of truly flexible fireproof cable. On this basis, we developed the prefabricated branch type environmental protection fireproof cable. This prefabricated branch type fireproof cable has low manufacturing cost and not only retains the advantages of the traditional fireproof cable, the utility model also overcomes the problems of moisture absorption of the fire-proof layer of the general fire-proof cable and the poor flexibility of the cable, and is convenient to install and lay.

Explore Future Trends of Fire Retardant Cable Market

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In our lives, electrical fire accidents caused by short circuits and spontaneous combustion caused by the aging of cables frequently occur, and the losses caused are countless. With the continuous acceleration of domestic economic construction and the heating of urbanization speed, the number of various large-scale industrial facilities, high-rise commercial buildings, underground buildings and residential houses has suddenly increased. At the same time, it has also driven the large-scale cable use. This inevitably leads to another problem: the safety of the cable.

The fire-retardant and flame-retardant cable market continues to ferment. What is its future trend?
The use of high-performance, efficient and safe special power cable products has become the common voice of the entire society. This also makes people deeply aware that in addition to enhancing awareness of fire safety in daily life, strict standards for related types should also be formulated to vigorously promote various flame-retardant cable products.

Standardized products will gradually move towards standardization
Industry standards are an important cornerstone for the development of industries and enterprises, and product technical standards are an effective guarantee for determining product quality. With the development and maturity of China’s cabling industry, the national competent authority is also vigorously promoting the standardization process of the cabling industry. At present, the formulation of technical standards for fire-retardant and flame-retardant cable products has been included in the work plan for the next stage. We believe that with the joint efforts of the government, industry and enterprises, the production and quality assurance of fire-retardant and flame-retardant cable products will be standardized, and the technology and application of fire-retardant and flame-retardant cables will be more reliable and professional. The field of chemistry is advancing rapidly.

Up-and-coming leaders will occupy the mainstream market
After decades of development, China’s integrated wiring industry has formed a certain scale. Driven by global economic integration, leading companies among different products in the industry will inevitably emerge, and industry concentration will continue to rise. Only in this way can the entire industry form a common development concept and avoid low-quality and low-end unfair competition. At present, the domestic leader in the fire and flame retardant industry has begun to take shape. The domestic fire and flame retardant cable market has formed a number of mainstream companies. These companies have continued to extend their products and channels through continuous improvement in corporate management and team building. , Whether in terms of brand influence, overall improvement of product quality, and service standards, it has been increasingly accepted and affirmed by the industry and users. Therefore, the trend of leading companies to occupy the mainstream market will be unstoppable.

Pay attention to service and enhance the safety awareness of the whole people
Cable products bear important data, images and other information transmission tasks in buildings and engineering safety systems. Because users or engineering companies do not pay enough attention to the purchase of cable products, especially fire-resistant and flame-retardant cable products, problems often endanger life and property safety. These painful lessons have made more and more users and engineering companies pay attention to the selection and correct use of cable types, and gradually changed the idea that the price dominates the purchase of wiring and cable products in engineering use. The important role of fire-retardant and flame-retardant cables in engineering use is becoming more and more recognized by everyone. In the future, the fire-retardant and flame-retardant cable manufacturing enterprises will not only provide products in a simple sense at this stage, but will also strengthen the service concept while continuously extending the product chain, providing users with a full line of compatible products, and ensuring that the products are correct. Reasonable use provides a full range of technical support and services, which will surely become the market development trend of the fire-retardant cable wiring industry.

Go abroad to build an international brand
“Being the world’s cable manufacturer and building an international national brand in China’s cabling industry” has become the development goal and corporate mission of outstanding companies in the industry. Under the guidance of this belief, China’s cable products have been widely penetrated into multiple fields in various industries. Fire-retardant and flame-retardant cables have also been increasing with everyone’s attention to safety and the demand for international trends. International cooperation between enterprises and enterprises in advanced developed countries has been carried out in all directions. At present, several of the strongest domestic cable companies have also followed the international trend of market development and extensively promoted special cables such as fireproof and flame retardant. And invested a large amount of funds for independent research and development. A few years ago, it has begun to formulate and launch a global development strategy. Through extensive cooperation and exchanges in technology, capital, management, etc., the introduction of advanced technology and management concepts from foreign companies has made the company Strength has been rapidly improved and developed. And actively go abroad, seek international markets, increase product exports, and now a large number of fire-retardant cable products are exported to all parts of the world.

With the rapid development of China’s wire and cable industry, people’s safety requirements have increased, and awareness of fire and flame retardant has continued to increase, which has greatly improved the overall technical level of the flame retardant cable industry. Many wiring companies and governments continue to promote and promote fire-retardant cables, which have contributed to our further understanding of the application and technology of flame-retardant cables. The problem of cable fire-retardant and flame retardant will undoubtedly receive more and more attention. Flame-retardant cables will also get more applications in actual projects, bringing opportunities for information security and personal safety in data centers. The cable selection of the majority of users when wiring is related to the fast, convenient and safe future data transmission, and it also provides a strong guarantee for the safety of life and property.

At the same time, only high quality can be recognized by customers to a higher degree. High quality and good reputation are the true value of the brand and the foundation for the survival of brand enterprises. The rise of fire-resistant and flame-retardant cables in China is not an unrealistic fantasy, but the call of the integrated wiring market.